A high-rate lithium / carbon monofluoride primary battery electrolyte and its application

Abstract

The present invention belongs to the technical field of lithium batteries, and particularly relates to a high-rate lithium / carbon monofluoride primary battery electrolyte and its application. By using sodium salts and / or potassium salts, the present invention changes the discharge mechanism of Li / CF x batteries, playing a dual role in the ion intercalation reaction mechanism and the nucleation and growth of discharge products. Compared with solvated Li + , the desolvation energy of solvated Na + with the same structure is about 30% lower, which transforms the original desolvation and intercalation mechanism involving lithium salts throughout the process into an early reaction between sodium ions and fluoride ions, reducing the reaction energy barrier of the early electrochemical reaction. At the same time, in various solvents, the Stokes radius of K + is smaller than that of Li + , which means that the diffusion rate of K + is faster, which can not only reduce polarization but also increase the ion intercalation rate, achieving good rate performance. Finally, the present invention realizes an increase in the discharge specific capacity and specific power of the battery, without sacrificing the specific capacity and specific power due to the increase in the mass of non-active substances.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and particularly relates to a high-rate lithium / carbon monofluoride primary battery electrolyte and its application. Background Art

[0002] Lithium primary batteries are primary chemical power sources with high specific energy using lithium metal anodes. Currently, the lithium primary batteries that have been studied more include: lithium-manganese dioxide batteries (Li / MnO 2 ), lithium-thionyl chloride batteries (Li / SOCl 2 ), lithium-sulfur dioxide batteries (Li / SO 2 ), lithium-carbon monofluoride batteries (Li / CF x ), etc. Compared with traditional zinc-manganese and silver-zinc chemical power sources, lithium primary batteries have many advantages such as high working voltage, high specific energy, and wide working temperature range, and are widely used in many fields such as cardiac pacemakers, missile ignition systems, communication devices, and wearable devices.

[0003] Li / CF x batteries have the advantages of stable discharge, low self-discharge rate, and good safety performance, and have the highest theoretical specific energy (2180 Wh / kg) among existing lithium primary batteries with solid cathodes, and have great commercial value. However, the polarization phenomenon of Li / CF x batteries is relatively serious, the discharge specific capacity is low at high rates, and even cannot discharge, which limits its application range. Aiming at the difficulty of poor rate performance of the battery mainly caused by the poor electronic conductivity of the carbon monofluoride material itself (the conductivity decreases with the increase of the fluorine content in the carbon monofluoride material), researchers have adopted various methods to improve the rate performance of Li / CF x batteries. These methods include preparing composite electrodes such as MnO 2 / CF x , selecting carbon source precursors with better conductivity (such as carbon nanotubes, graphene, etc.), adding conductive agents with better conductivity such as multi-walled carbon nanotubes, and using low-fluorination-degree carbon monofluoride active materials with slightly lower specific capacity or discharge voltage but better rate performance. However, these methods not only bring process difficulties and cost increases, but also often achieve high-rate discharge of Li / CF x batteries at the expense of part of the capacity. As an important component of the battery, the electrolyte plays an important role in improving the rate performance of the battery. Therefore, the rate performance of Li / CF x batteries can be improved by improving the electrolyte.

[0004] Li / CF x The common formulations of battery electrolytes are: (1) lithium perchlorate (LiClO 4 ), lithium tetrafluoroborate (LiBF 4(1) As the lithium salt, propylene carbonate (PC) and ethylene glycol dimethyl ether (DME) are used as organic solvents; (2) Lithium hexafluorophosphate (LiPF 6 ) is used as the lithium salt, and ethylene carbonate (EC) and dimethyl carbonate (DMC) are used as organic solvents; (3) Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is used as the lithium salt, and 1,3-dioxolane (DOL) and DME are used as organic solvents. However, there are still many problems in the Li / CF x batteries based on the above electrolyte systems in practical applications, such as poor battery discharge rate performance, obvious voltage hysteresis, and relatively serious polarization phenomenon of the battery. Therefore, it is necessary to develop a primary battery electrolyte with high rate performance and high power Li / CF x . SUMMARY OF THE INVENTION

[0005] Aiming at the above problems or deficiencies, to solve the problems of poor rate performance and serious polarization phenomenon of the existing Li / CF x batteries, the present invention provides a high rate lithium / carbon fluoride (Li / CF x ) primary battery electrolyte and its application.

[0006] A high rate Li / CF x primary battery electrolyte, which includes sodium salt and / or potassium salt, organic solvent, and the electrolyte concentration is 0.3 - 2.0 mol / L.

[0007] The sodium salt includes sodium hexafluorophosphate (NaPF 6 ), sodium tetrafluoroborate (NaBF 4 ), sodium perchlorate (NaClO 4 ), sodium bis(oxalato)borate (NaBOB), sodium difluoro(oxalato)borate (NaDFOB), sodium trifluoromethanesulfonate (NaCF 3 SO 3 ), sodium bis(fluorosulfonyl)imide (NaFSI) and / or sodium bis(trifluoromethanesulfonyl)imide (NaTFSI).

[0008] The potassium salt includes potassium hexafluorophosphate (KPF 6 ), potassium tetrafluoroborate (KBF 4 ), potassium perchlorate (KClO 4 ), potassium bis(oxalato)borate (KBOB), potassium difluoro(oxalato)borate (KDFOB), potassium trifluoromethanesulfonate (KCF 3 SO 3 ), potassium bis(fluorosulfonyl)imide (KFSI) and / or potassium bis(trifluoromethanesulfonyl)imide (KTFSI).

[0009] The organic solvent is carbonate, ether, carboxylic acid ester, nitrile, sulfate ester and / or fluorinated solvent.

[0010] Further, the carbonates are: ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), vinylene carbonate (VC).

[0011] Further, the ethers are: tetrahydrofuran (THF), 1,3-dioxolane (DOL), 2-methyltetrahydrofuran (2-MeTHF), ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (TriEGDME), tetraethylene glycol dimethyl ether (TeEGDME).

[0012] Further, the carboxylic acid esters are: γ-butyrolactone (BL), methyl acetate (MA), ethyl acetate (EA).

[0013] Further, the nitriles are: acetonitrile (AN).

[0014] Further, the sulfates are: dimethyl sulfite (DMS), ethylene sulfite (ES).

[0015] Further, the fluorinated solvents are: fluoroethylene carbonate (FEC), bis(2,2,2-trifluoroethyl) ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE).

[0016] Further, for the high-rate Li / CF x Only potassium salts are selected in the primary battery electrolyte so that the Li / CF has better rate performance during application. x The primary battery has better rate performance.

[0017] In a glove box filled with argon, sodium salts and / or potassium salts are dissolved in an organic solvent. After the electrolyte salts are fully dissolved, an electrolyte solution with a concentration of 0.3 - 2.0 mol / L is prepared. For the Li / CF x The primary battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte; the positive electrode is prepared from active material CF x powder (0.5 < x < 1.3), the negative electrode is a commercial lithium sheet, and the separator is a glass fiber filter paper or a polymer separator.

[0018] Due to the presence of a large number of C-F covalent bonds in the CF x material, the electronic conductivity of the material itself is poor. In the Li / CF xDuring the discharge process of the primary battery, insoluble lithium fluoride (LiF) is generated, which is an insulating product. The crystallization rate of LiF increases with the increase of the discharge rate, damaging the conductive network structure of the electrode material, increasing the internal resistance of the battery, increasing the heat generation during battery discharge, hindering the subsequent discharge of the battery, and thus reducing the actual discharge capacity of the battery and the efficiency of converting the chemical energy of the battery into electrical energy. To improve the above-mentioned disadvantage of poor rate performance in the Li / CF x primary battery. In the electrolyte of the present invention, the use of sodium salts and / or potassium salts changes the discharge mechanism of the Li / CF x battery and plays a dual role in the ion intercalation reaction mechanism and the nucleation and growth of discharge products. Compared with solvated Li + , the desolvation energy of solvated Na + with the same structure is about 30% lower, which changes the desolvation and intercalation mechanism involving the original lithium salt throughout the process into the early reaction between sodium ions and fluoride ions, reducing the reaction energy barrier of the early electrochemical reaction. At the same time, in various solvents, the Stokes radius of K + is smaller than that of Li + , which means that the diffusion rate of K + is faster, and it also brings faster reaction kinetics, which can reduce polarization while increasing the ion intercalation rate, achieving good rate performance. In addition, the solubility of sodium fluoride (NaF) and potassium fluoride (KF) in common organic solvents is lower than that of LiF, and the crystal precipitation barrier is smaller. The high concentration of Na + and K + at the electrode-electrolyte interface is more likely to nucleate with F - , thus helping to promote the diffusion of F - , making the charge transfer impedance smaller. The precipitation of KF and NaF changes the nucleation and growth paths of the subsequent products of LiF, making a large number of metal fluoride products outside the carbon layer instead of between the carbon layers, and will not cause the positive electrode to swell severely due to the large amount of LiF precipitating between the carbon layers at high current and separating from the current collector, resulting in a sharp increase in impedance. The initially formed KF particles can not only provide more sites for the nucleation and growth of subsequent crystals, but also maintain the layered structure of CF x better, providing better openings for Li + with a smaller radius, increasing the ion diffusion coefficient, and achieving good rate performance.

[0019] In summary, the present invention improves the rate performance of the Li / CF x battery from the perspective of improving the electrolyte. Since the mass ratio of the electrolyte in the battery remains basically unchanged, the improvement effect of the present invention on the rate performance of the Li / CF x battery is directly reflected in the increase of the high-current discharge specific capacity and specific power of the battery, and will not sacrifice the specific capacity and specific power due to the increase of the mass of non-active substances. Description of the Drawings

[0020] Figure 1 Schematic diagram of the performance of the primary battery equipped with the electrolyte prepared in Example 1 at different rates;

[0021] Figure 2 Schematic diagram of the performance of the primary battery equipped with the electrolyte prepared in Example 2 at different rates;

[0022] Figure 3 Schematic diagram of the performance of the primary battery equipped with the electrolyte prepared in Control Group 1 at different rates;

[0023] Figure 4 Schematic diagram of the performance of the primary battery equipped with the electrolyte prepared in Control Group 2 at different rates;

[0024] Figure 5 Schematic diagram of the electrochemical impedance spectroscopy of the primary battery equipped with the electrolyte prepared in Example 1. Detailed Description of the Invention

[0025] The present invention will be further described in detail below with reference to the drawings and examples.

[0026] Preparation of the electrode: The mass ratio of the solid materials of the battery positive electrode is as follows: active material: Super P: carbon nanotubes (CNTs): polyvinylidene fluoride (PVDF) = 8:0.7:0.3:1. The preparation process is as follows: Weigh PVDF and dissolve it in N-methylpyrrolidone (NMP) at a solid content of 3.5% to obtain a transparent solution. Mix the active material, conductive carbon black, and carbon nanotubes in the mass ratio and grind them evenly, and then add the above-prepared transparent solution thereto and stir and grind to obtain a slurry. Use a 100-μm doctor blade to evenly coat the slurry on the carbon-coated aluminum foil, transfer it to an 80°C oven and dry for 4 h, punch it into a 14-mm-diameter round piece, transfer it to a vacuum drying oven at 100°C and dry for 6 h, then weigh it, and finally place it in a vacuum drying oven at 100°C and dry for 10 h, and then transfer it to a glove box for standby.

[0027] Preparation of the electrolyte: In a glove box filled with argon (H 2 O≤0.1 ppm, O 2 ≤0.1 ppm), use type molecular sieve to first purify and remove impurities and water from the organic solvent to obtain a pure solvent.

[0028] Example 1

[0029] In a glove box filled with argon, take the pure solvent ethylene glycol dimethyl ether (DME), and then add sodium hexafluorophosphate (NaPF 6) After mixing evenly and standing for 24 hours, a sodium salt electrolyte solution with a concentration of 1.0 mol / L is obtained.

[0030] Example 2

[0031] In a glove box filled with argon, pure solvent ethylene glycol dimethyl ether (DME) is taken, and then potassium hexafluorophosphate (KPF 6 ) is added to the solvent. After mixing evenly and standing for 24 hours, a potassium salt electrolyte solution with a concentration of 1.0 mol / L is obtained.

[0032] Example 3

[0033] In a glove box filled with argon, ethylene glycol dimethyl ether (DME) with a volume fraction of 80% and propylene carbonate (PC) with a volume fraction of 20% are mixed evenly. Then, sodium hexafluorophosphate (NaPF 6 ) is added to the mixed solvent. After mixing evenly and standing for 24 hours, a sodium salt electrolyte solution with a concentration of 0.4 mol / L is obtained.

[0034] Example 4

[0035] In a glove box filled with argon, ethylene glycol dimethyl ether (DME) with a volume fraction of 80% and propylene carbonate (PC) with a volume fraction of 20% are mixed evenly. Then, potassium hexafluorophosphate (KPF 6 ) is added to the mixed solvent. After mixing evenly and standing for 24 hours, a potassium salt electrolyte solution with a concentration of 0.4 mol / L is obtained.

[0036] Example 5

[0037] In a glove box filled with argon, ethylene glycol dimethyl ether (DME) with a volume fraction of 60%, γ-butyrolactone (BL) with a volume fraction of 20%, and acetonitrile (AN) with a volume fraction of 20% are mixed evenly. Then, potassium hexafluorophosphate (KPF 6 ) is added to the mixed solvent. After mixing evenly and standing for 24 hours, a potassium salt electrolyte solution with a concentration of 0.5 mol / L is obtained.

[0038] Example 6

[0039] In a glove box filled with argon, ethylene glycol dimethyl ether (DME) with a volume fraction of 80% and propylene carbonate (PC) with a volume fraction of 20% are mixed evenly. Then, a double salt of sodium hexafluorophosphate (NaPF 6 ) and potassium hexafluorophosphate (KPF 6 ) with a molar ratio of 1:1 is added. After mixing evenly and standing for 24 hours, an electrolyte solution with a concentration of 0.5 mol / L is obtained.

[0040] Control Group 1

[0041] In a glove box filled with argon, pure solvent propylene carbonate (PC) was taken, and then sodium hexafluorophosphate (NaPF 6 ) was added to the solvent. After mixing evenly and standing for 24 hours, a sodium salt electrolyte solution with a concentration of 1.0 mol / L was obtained.

[0042] Control group 2

[0043] In a glove box filled with argon, ethylene carbonate (EC) with a volume fraction of 50% and diethyl carbonate (DEC) with a volume fraction of 50% were mixed evenly. Then, sodium hexafluorophosphate (NaPF 6 ) was added to the mixed solvent. After mixing evenly and standing for 24 hours, a sodium salt electrolyte solution with a concentration of 1.0 mol / L was obtained.

[0044] Control group 3

[0045] In a glove box filled with argon, ethylene glycol dimethyl ether (DME) with a volume fraction of 50% and propylene carbonate (PC) with a volume fraction of 50% were mixed evenly. Then, lithium hexafluorophosphate (LiPF 6 ) was added to the mixed solvent. After mixing evenly and standing for 24 hours, a lithium salt electrolyte solution with a concentration of 1.0 mol / L was obtained.

[0046] Control group 4

[0047] In a glove box filled with argon, pure solvent ethylene glycol dimethyl ether (DME) was taken, and then lithium tetrafluoroborate (LiBF 4 ) was added to the solvent. After mixing evenly and standing for 24 hours, a lithium salt electrolyte solution with a concentration of 1.0 mol / L was obtained.

[0048] Assembly and testing of the battery:

[0049] The prepared positive electrode sheet was placed in the positive electrode case, 20 μL of the electrolyte was added dropwise, the separator was placed, and then another 20 μL of the electrolyte was added dropwise. After that, a lithium metal sheet, a gasket, a spring sheet, and a negative electrode case were placed in sequence, and a CR2025 button cell was encapsulated with a battery encapsulation machine. After standing for 12 h, the constant current discharge was carried out at different rates to the cut-off voltage of 1.5 V in a constant temperature test chamber at 25°C. Figure 1 Schematic diagram of the performance of the primary battery equipped with the electrolyte prepared in Example 1 at different rates; Figure 2 Schematic diagram of the performance of the primary battery equipped with the electrolyte prepared in Example 2 at different rates; Figure 3 Schematic diagram of the performance of the primary battery equipped with the electrolyte prepared in Control group 1 at different rates; Figure 4 Schematic diagram of the performance of the primary battery equipped with the electrolyte prepared in Control group 2 at different rates; Figure 5Schematic diagram of the electrochemical impedance spectrum of the primary battery equipped with the electrolyte prepared in Example 1.

[0050] The experimental data of the above examples and the control group are recorded in Table 1. It can be seen from the discharge capacity that, regardless of the current density, the discharge capacity of the examples is higher than that of the control group. This shows that the electrolyte of the present invention can well improve the discharge capacity and rate performance of the CF x battery.

[0051] Table 1

[0052]

Claims

1. A high-rate lithium / carbon monofluoride primary battery, characterized in that: the electrolyte of the primary battery comprises a sodium salt, a potassium salt and an organic solvent, and the concentration of the sodium salt and the potassium salt in the electrolyte is 0.3 - 2.0 mol / L; The sodium salt includes sodium hexafluorophosphate (NaPF 6 ), sodium tetrafluoroborate (NaBF 4 ), sodium perchlorate (NaClO 4 ), sodium bis(oxalato)borate (NaBOB), sodium difluoro(oxalato)borate (NaDFOB), sodium trifluoromethanesulfonate (NaCF 3 SO 3 ), sodium bis(fluorosulfonyl)imide (NaFSI) and / or sodium bis(trifluoromethanesulfonyl)imide (NaTFSI); The potassium salts include potassium hexafluorophosphate (KPF 6 ), potassium tetrafluoroborate (KBF 4 ), potassium perchlorate (KClO 4 ), potassium bis(oxalato)borate (KBOB), potassium difluoro(oxalato)borate (KDFOB), potassium trifluoromethanesulfonate (KCF 3 SO 3 ), potassium bis(fluorosulfonyl)imide (KFSI) and / or potassium bis(trifluoromethanesulfonyl)imide (KTFSI); the organic solvent is at least one of carbonate esters, ethers, carboxylic acid esters, nitriles, sulfate esters and fluorinated solvents.

2. The high-rate lithium / carbon monofluoride primary battery according to claim 1, characterized in that the carbonate esters are: ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), vinylene carbonate (VC).

3. The high-rate lithium / carbon monofluoride primary battery according to claim 1, characterized in that the ethers are: tetrahydrofuran (THF), 1,3-dioxolane (DOL), 2-methyltetrahydrofuran (2-MeTHF), ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (TriEGDME), tetraethylene glycol dimethyl ether (TeEGDME).

4. The high-rate lithium / carbon monofluoride primary battery according to claim 1, characterized in that the carboxylic acid esters are: γ-butyrolactone (BL), methyl acetate (MA), ethyl acetate (EA).

5. The high-rate lithium / carbon monofluoride primary battery according to claim 1, characterized in that the nitriles are: acetonitrile (AN).

6. The high-rate lithium / carbon monofluoride primary battery according to claim 1, characterized in that the sulfate esters are: dimethyl sulfite (DMS), vinylene sulfite (ES).

7. The high-rate lithium / carbon monofluoride primary battery according to claim 1, characterized in that the fluorinated solvents are: fluoroethylene carbonate (FEC), bis(2,2,2-trifluoroethyl) ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE).

8. The high-rate lithium / carbon monofluoride primary battery according to any one of claims 1 - 7, characterized in that: The high-rate Li / CF x Only potassium salts are selected in the primary battery electrolyte to make the Li / CF x primary battery have better rate performance.

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