Lithium / carbon fluoride battery electrolyte based on aprotic polar solvent

Abstract

The invention discloses a lithium / carbon fluoride battery electrolyte based on an aprotic polar solvent, and belongs to the technical field of lithium / carbon fluoride battery preparation. Based on the discharge characteristic of the lithium / carbon fluoride battery, the electrolyte is designed as a starting point, and an organic solvent formed by mixing an aprotic polar solvent and an ether solvent, a lithium salt and a fluorine ion acceptor jointly form the electrolyte, so that the discharge reaction kinetics of the lithium / carbon fluoride battery is improved by utilizing the regulation and control effect of the aprotic polar solvent. The electrolyte provides a favorable environment for fluorocarbon bond breakage, reduces a discharge reaction energy barrier, can improve a discharge reaction platform, can reduce adverse effects caused by poor conductor lithium fluoride, reduces discharge polarization, and can effectively promote interfacial ion transmission and charge transfer. When the electrolyte is applied to the lithium / carbon fluoride battery, the energy density can be effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of lithium / carbon fluoride batteries, and particularly relates to an electrolyte for a lithium / carbon fluoride battery based on an aprotic polar solvent. Background Art

[0002] Lithium / carbon fluoride batteries have broad application prospects in multiple fields due to their advantages such as high energy density, long storage life, and wide temperature range window, including military equipment, aerospace, and other fields with high requirements for storage and energy density applications. Nevertheless, current lithium / carbon fluoride batteries still cannot meet the higher requirements of future applications. During the discharge reaction process, lithium / carbon fluoride batteries have problems such as severe internal polarization and low utilization rate of active material materials. These problems inevitably cause energy loss and limit the development and wider application of lithium / carbon fluoride.

[0003] The energy density of lithium / carbon fluoride batteries is closely related to electrochemistry reaction kinetics and thermodynamics. Based on the laws of thermodynamics, the discharge platform of lithium / carbon fluoride batteries should be close to the open-circuit voltage. However, not only is the open-circuit voltage of lithium / carbon fluoride batteries much lower than the theoretical value (4.57 V), but the actual discharge platform is also much lower than the open-circuit voltage, ultimately resulting in a great loss of energy density. The discharge reaction of lithium / carbon fluoride batteries follows a bimolecular nucleophilic substitution reaction, which has been discovered and discussed in early research. During the nucleophilic substitution reaction of halogenated hydrocarbons, the solvent is an important participant and affects both the reaction activity and rate. For the special reaction scenario of lithium / carbon fluoride batteries, the electrons transmitted therein can be regarded as nucleophiles, and the electrolyte is regarded as the reaction medium. In the bimolecular nucleophilic substitution reaction, the reaction proceeds in one step, that is, when the carbon fluoride positive electrode breaks the carbon-fluorine bond, lithium fluoride crystals are formed as products. Among them, the reaction media of non-polar solvents and aprotic polar solvents are conducive to the progress of the bimolecular nucleophilic substitution reaction. Summary of the Invention

[0004] The present invention aims to provide an electrolyte for a lithium / carbon fluoride battery based on an aprotic polar solvent, which regulates the electrode-electrolyte interface for the discharge reactant carbon fluoride and the discharge product lithium fluoride to synergistically improve the reaction kinetics of the battery, thereby achieving the improvement of the voltage platform and rate performance of the lithium / carbon fluoride battery.

[0005] To achieve the above object, the present invention adopts the following technical solutions: An electrolyte for a lithium / carbon fluoride battery based on an aprotic polar solvent, which includes an organic solvent, an additive, and a lithium salt; the organic solvent is composed of a mixture of an aprotic polar solvent and an ether solvent, and the additive includes a fluoride ion acceptor.

[0006] Furthermore, the aprotic polar solvent includes one or two of acetone of ketones; pyridine and acetonitrile of nitrogen-containing hydrocarbons; dimethyl sulfoxide of sulfoxides; and dimethylacetamide, dimethylformamide, N-methylpyrrolidone, 1,3-dimethyl-2-imidazolidinone, and hexamethylphosphoramide of amides.

[0007] Furthermore, the ether solvent includes one or two of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0008] Furthermore, the fluoride ion receptor is a Lewis acid metal salt and oxide system, which includes one or two of aluminum chloride, zinc chloride, ferric chloride, antimony trioxide, stannous chloride, tin tetrachloride, and boron trifluoride complex systems.

[0009] Furthermore, the boron trifluoride complex system includes boron trifluoride-ethyl ether complex, boron trifluoride-butyl ether complex, boron trifluoride-tetrahydrofuran complex, boron trifluoride-diethylene glycol dimethyl ether complex, benzylamine boron trifluoride complex, and boron trifluoride-dimethyl ether complex.

[0010] Furthermore, the lithium salt includes one or two of lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl imide), lithium bis(fluorosulfonyl imide), lithium difluorooxalatoborate, lithium nitrate and lithium perchlorate.

[0011] Furthermore, the aprotic solvent accounts for 20%-80% of the total volume of the organic solvent.

[0012] Furthermore, the concentration of the fluoride ion receptor in the electrolyte is 0.01-10 mol L -1 , preferably 0.01-2 mol L -1 .

[0013] Furthermore, the concentration of the lithium salt in the electrolyte is 0.1-10 mol L -1 .

[0014] The present invention introduces aprotic polar solvents, which can significantly improve the electrochemical performance of carbon fluoride batteries through the following multi-scale synergistic mechanism: (1) Molecular-scale reaction kinetics regulation. Aprotic polar solvents, with their unique electron cloud distribution characteristics, form a local electric field gradient during the discharge process. This electric field effect can significantly reduce the dissociation energy of the carbon-fluorine bond, causing the carbon-fluorine bond in the fluorinated carbon cathode material to break, generating highly active fluorine anion intermediates, which promote the discharge reaction.

[0015] (2) Solvation synergistic catalysis mechanism. Solvent molecules form a solvent sheath with alkali metal ions through strong nucleophilic interactions. This dynamic solvation structure can not only enhance ionic conductivity but also be more conducive to increasing the concentration of actual electrons transferred to the positive electrode side, that is, the nucleophile required for the bimolecular nucleophilic substitution reaction, providing an electrolyte environment favorable for the cleavage of carbon-fluorine bonds. At the same time, the solvated alkali metal ions generate an instantaneous positive electric field during migration. This electric field undergoes electrostatic attraction with the fluorine atoms on the surface of carbon fluoride, forming an "ion traction - bond cleavage" coupling mechanism, significantly promoting the homolytic reaction process. Therefore, the electrolyte based on aprotic polar solvents can effectively reduce the polarization during the battery discharge process and improve the discharge platform and the energy density of the battery.

[0016] (3) Interfacial phase reconstruction effect. Aprotic polar solvents will affect the formation of lithium fluoride as the discharge product. The discharge product lithium fluoride exhibits unique dissolution - recrystallization behavior in aprotic solvents, forming lithium fluoride with a small - size morphology, which is beneficial to charge transfer at the interface.

[0017] The beneficial effects of the present invention are as follows: (1) The present invention provides a novel electrolyte, which utilizes aprotic polar solvents to achieve the synergistic regulation of discharge reactants and discharge products at the interface between the electrolyte and the positive electrode, so as to achieve the purpose of improving the energy density of lithium / carbon fluoride batteries. In contrast, protic polar solvents (including ethylenediamine and triethylamine in amines, acetic acid and trifluoroacetic acid in carboxylic acids, ethanol, isopropanol, tert - butanol in alcohols, etc.) have strong electrophilicity and polarity, but are incompatible with the lithium metal negative electrode, so they are not applicable to lithium / carbon fluoride batteries; while aprotic non - polar solvents (including hexane and cyclohexane in saturated hydrocarbons, benzene, toluene, xylene in aromatic hydrocarbons, chloroform in halogenated hydrocarbons, etc.) can also promote the bimolecular nucleophilic substitution reaction, but due to the non - polarity or low polarity of the solvent, they cannot dissolve or dissociate lithium salts, resulting in extremely low ionic conductivity in the electrolyte and being not applicable to lithium / carbon fluoride batteries.

[0018] (2) The electrolyte of the present invention is easy to prepare, and the electrolyte components have the advantages of low cost and safety, and can be applied to actual production. Description of the Drawings

[0019] Figure 1 Discharge curves of the lithium / carbon fluoride button batteries prepared in Examples 1 - 5 under the conditions of 0.1 C rate and 1 C rate.

[0020] Figure 2 Discharge curves of the lithium / carbon fluoride button batteries prepared in Example 1 and Example 6 under the condition of 5 C rate.

[0021] Figure 3 Discharge curves of the lithium / carbon fluoride button batteries prepared in Example 6 (a) and the comparative example (b) under different rate conditions. Detailed implementation mode

[0022] A lithium / carbon fluoride battery electrolyte based on an aprotic polar solvent, which comprises an organic solvent, an additive and a lithium salt; the organic solvent is composed of a mixture of an aprotic polar solvent and an ether solvent, and the additive includes a fluoride ion acceptor.

[0023] Among them, the aprotic solvent accounts for 20%-80% of the total volume of the organic solvent. The concentration of the fluoride ion acceptor in the electrolyte is 0.01-10 mol L -1 . The concentration of the lithium salt in the electrolyte is 0.1-10 mol L -1 .

[0024] The aprotic polar solvent includes acetone of ketones; pyridine and acetonitrile of nitrogen-containing hydrocarbons; dimethyl sulfoxide of sulfoxides; one or two of dimethylacetamide, dimethylformamide, N-methylpyrrolidone, 1,3-dimethyl-2-imidazolidinone, and hexamethylphosphoramide of amides.

[0025] The ether solvent includes one or two of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0026] The fluoride ion acceptor is a Lewis acid metal salt and oxide system, which includes one or two of aluminum chloride, zinc chloride, iron chloride, antimony trioxide, stannous chloride, stannic chloride, and boron trifluoride complex system.

[0027] The boron trifluoride complex system includes boron trifluoride-ethyl ether complex, boron trifluoride-butyl ether complex, boron trifluoride-tetrahydrofuran complex, boron trifluoride-diethylene glycol dimethyl ether complex, benzylamine boron trifluoride complex, and boron trifluoride-dimethyl ether complex.

[0028] The lithium salt includes one or two of lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluoro(oxalato)borate, lithium nitrate, and lithium perchlorate.

[0029] In order to make the content of the present invention easier to understand, the technical solutions of the present invention will be further described below in conjunction with specific implementation modes, but the present invention is not limited thereto.

[0030] Example 1 1) Preparation of electrolyte: Under the atmosphere of high-purity argon, using 1,3-dimethyl-2-imidazolidinone, an aprotic polar solvent, as the single solvent of the electrolyte, lithium tetrafluoroborate was added to the solvent at a concentration of 1 mol L -1 , and stirred thoroughly to dissolve.

[0031] 2) Preparation of the positive electrode sheet: Graphite fluoride, conductive carbon black, and the binder polyvinylidene fluoride were thoroughly mixed at a mass ratio of 8:1:1 and uniformly dispersed in N-methylpyrrolidone. Subsequently, it was uniformly coated on an aluminum foil current collector and vacuum dried at 80 °C for 12 h to obtain the final positive electrode.

[0032] 3) Assembly of the battery: Under an atmosphere of high-purity argon, a button battery was assembled with a lithium metal sheet as the negative electrode and the positive electrode prepared in step 2).

[0033] Example 2 In step 1), N-methylpyrrolidone was used as the single solvent for the electrolyte, and the remaining steps were the same as those in Example 1.

[0034] Example 3 In step 1), dimethylacetamide was used as the single solvent for the electrolyte, and the remaining steps were the same as those in Example 1.

[0035] Example 4 In step 1), triethyl phosphate was used as the single solvent for the electrolyte, and the remaining steps were the same as those in Example 1.

[0036] Example 5 In step 1), dimethyl carbonate was used as the single solvent for the electrolyte, and the remaining steps were the same as those in Example 1.

[0037] Example 6 Under an atmosphere of high-purity argon, 1,3-dimethyl-2-imidazolidinone and ethylene glycol dimethyl ether at a volume ratio of 1:1 were used as solvents, and boron trifluoride-tetrahydrofuran complex was used as an additive. Boron trifluoride-tetrahydrofuran complex and lithium tetrafluoroborate were added to the solvent at concentrations of 0.015 mol L -1 , 1 mol L -1 respectively, and stirred thoroughly to dissolve. The remaining steps were the same as those in Example 1.

[0038] Comparative Example Under an atmosphere of high-purity argon, propylene carbonate and ethylene glycol dimethyl ether at a volume ratio of 1:1 were used as solvents, and boron trifluoride-tetrahydrofuran complex was used as an additive. Boron trifluoride-tetrahydrofuran complex and lithium tetrafluoroborate were added to the solvent at concentrations of 0.015mol L -1 , 1 mol L -1 respectively, and stirred thoroughly to dissolve. The remaining steps were the same as those in Example 1.

[0039] The button batteries assembled in the above examples and comparative examples were left to stand at 25 °C for 12 h to achieve full wetting inside the battery, and then were subjected to constant current discharge at rates of 0.1 C, 1 C, and 5 C at 25 °C respectively for electrochemical performance testing. The test voltage range was from the open circuit voltage to 1.5 V (vs. Li / Li+ ) to obtain the corresponding discharge curve.

[0040] Table 1 Discharge test results of lithium / carbon fluoride batteries prepared based on different aprotic polar solvents at different rates

[0041] From Figure 1 and the comparison of Examples 1 to 5 in Table 1, it can be seen that at the same rate, the electrolytes with stronger electron-donating ability and polarity exhibit the best electrochemical performance. Especially in Example 1, it shows the most excellent discharge performance at low rates of 0.1 C and 1 C. This fully demonstrates that aprotic polar solvents are beneficial to the cleavage of the carbon-fluorine bond of the carbon fluoride cathode in lithium / carbon fluoride batteries, reducing the energy barrier of the discharge reaction, and thus can significantly improve the problem that the actual voltage platform of lithium / carbon fluoride batteries is much lower than the ideal voltage platform. And Example 1 benefits from the regulation of the carbon-fluorine bond by 1,3-dimethyl-2-imidazolidinone, forming a reaction environment conducive to the cleavage of the carbon-fluorine bond, which can reduce the polarization during the discharge process and accelerate the interfacial reaction kinetics, so the voltage platform is the highest. With the decrease of electron-donating property and polarity, the discharge platform decreases correspondingly, and the discharge specific capacity also shows a certain degree of decrease.

[0042] And from Figure 2 and the comparison of Example 1 and Example 6 in Table 1, it can be seen that after introducing the ether co-solvent, the discharge performance of the battery at low rates of 0.1 C and 1 C is equivalent to that of the battery without introducing the ether co-solvent, while its performance at a high rate of 5 C is significantly improved. This is due to the introduction of the ether solvent, which reduces the viscosity of the electrolyte and greatly improves the ion-ion transport and the wettability inside the battery, so it can meet the higher demand for ion transport at high rates. At the same time, from Figure 3 and the comparison of Example 6 and the comparative example in Table 1, it can be seen that compared with the comparative example using a mixed solvent containing propylene carbonate as the electrolyte, the electrolyte in Example 6 benefits from the high ion transport performance obtained by mixing 1,3-dimethyl-2-imidazolidinone and the ether solvent, and the initial voltage lag is significantly improved, and a stable high discharge platform is maintained during the subsequent discharge process. Therefore, by combining specific aprotic polar solvents and ether solvents, lithium / carbon fluoride batteries can benefit in terms of voltage platform and rate performance, showing a high discharge platform and excellent rate performance, providing new ideas for the electrolyte design of high specific energy lithium / carbon fluoride batteries.

[0043] The above results are only the preferred embodiments of the present invention. However, the present invention is not limited to the above specific implementation manners. The above specific implementation manners are merely illustrative and not restrictive. Under the inspiration of the present invention, those of ordinary skill in the art can also make many forms without departing from the purpose of the present invention and the scope protected by the claims. All of these fall within the protection scope of the present invention.

Claims

1. A lithium / carbon fluoride battery electrolyte based on an aprotic polar solvent, characterized in that The electrolyte includes an organic solvent, an additive, and a lithium salt; the organic solvent is composed of a non-protic polar solvent and an ether solvent, and the additive includes a fluoride ion acceptor.

2. The electrolyte of a lithium / carbon fluoride battery based on an aprotic polar solvent according to claim 1, characterized in that: The non-protic polar solvent includes one or two of acetone of ketones; pyridine and acetonitrile of nitrogen-containing hydrocarbons; dimethyl sulfoxide of sulfoxides; dimethylacetamide, dimethylformamide, N-methylpyrrolidone, 1,3-dimethyl-2-imidazolidinone, and hexamethylphosphoramide of amides.

3. The electrolyte of a lithium / carbon fluoride battery based on an aprotic polar solvent according to claim 1, characterized in that: The ether solvent includes one or two of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

4. A non-aqueous polar solvent-based lithium / carbon fluoride battery electrolyte according to claim 1, wherein: The fluoride ion acceptor includes one or two of aluminum chloride, zinc chloride, iron chloride, antimony trioxide, stannous chloride, tin tetrachloride, and boron trifluoride complex system.

5. The electrolyte of a lithium / carbon fluoride battery based on an aprotic polar solvent according to claim 1, wherein: The lithium salt includes one or two of lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluoro(oxalato)borate, lithium nitrate, and lithium perchlorate.

6. The electrolyte of a lithium / carbon fluoride battery based on an aprotic polar solvent according to claim 1, characterized in that: The non-protic solvent accounts for 20%-80% of the total volume of the organic solvent.

7. The electrolyte of a lithium / carbon fluoride battery based on an aprotic polar solvent according to claim 1, characterized in that: The concentration of the fluoride ion receptor in the electrolyte is 0.01 - 10 mol L -1 .

8. The electrolyte of a lithium / carbon fluoride battery based on an aprotic polar solvent according to claim 1, characterized in that: The concentration of the lithium salt in the electrolyte is 0.1 - 10 mol L -1 .

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