Electrolyte for improving the performance of lithium-carbon fluoride batteries and use thereof

Abstract

The application discloses electrolyte for improving performance of lithium-carbon fluoride batteries and application thereof, and belongs to the field of lithium-carbon fluoride primary batteries. The electrolyte comprises an organic electrolyte system, and the organic electrolyte system contains a boron trifluoride complex additive in addition to a basic additive. The additive in the application has a synergistic effect with the existing basic additive for electrolyte, and when used in lithium / carbon fluoride batteries, can simultaneously improve and enhance the rate performance and high-temperature storage stability of the batteries.

Description

Technical Field

[0001] This invention belongs to the field of lithium-fluorinated carbon primary battery technology, specifically relating to an electrolyte for improving the performance of lithium-fluorinated carbon batteries and its application. Background Technology

[0002] In recent years, lithium / carbon fluoride batteries have attracted widespread attention among primary lithium batteries due to their ultra-high theoretical specific energy (2180Wh / kg). However, lithium carbon fluoride batteries suffer from problems such as increased internal resistance, significant voltage drop, severe electrode polarization, and low discharge specific capacity during high-rate discharge. In addition, during high-temperature storage, side reactions occur between the electrolyte and electrode materials, leading to capacity decay in lithium carbon fluoride batteries during storage. This, to some extent, limits the widespread application of lithium carbon fluoride batteries.

[0003] Studies have shown that modifying and optimizing the electrolyte composition can effectively improve the above-mentioned problems. Regarding the poor rate performance of lithium fluorocarbon batteries, existing technologies report the introduction of sulfur-containing or boron-based compounds into the electrolyte. Although the rate performance of the corresponding lithium fluorocarbon batteries using the above electrolytes has been significantly improved, with the maximum discharge rate reaching 5C, it still cannot meet the practical application requirements of lithium fluorocarbon batteries. The rate performance of lithium fluorocarbon batteries needs to be further improved.

[0004] To address the capacity decay issue in lithium-carbon fluoride (LCF) batteries during high-temperature storage, existing technologies report the introduction of cyclic phosphate ester additives and fluorinated solvents into the electrolyte. This electrolyte can reduce the electrode / electrolyte reaction rate in lithium / LCF batteries, thereby significantly improving their high-temperature storage performance. While the aforementioned electrolyte technologies have improved the high-temperature storage performance of lithium-LCF batteries to some extent, they cannot simultaneously improve the rate performance of lithium / LCF batteries. Summary of the Invention

[0005] This invention addresses the aforementioned problems in the prior art by providing an electrolyte and its application for improving the performance of lithium-carbon fluoride batteries. This electrolyte has high conductivity, low viscosity, and good compatibility with electrode materials, thereby improving the rate performance and high-temperature storage (shelving) performance of lithium / carbon fluoride batteries.

[0006] The first aspect of this invention protects an electrolyte for improving the performance of lithium-carbon fluoride batteries, comprising an organic electrolyte system containing a boron trifluoride complex additive. The boron trifluoride complex additive includes one or more of boron trifluoride organic lipid solvent complexes, boron trifluoride organic ether solvent complexes, and boron trifluoride sulfone solvent complexes. The amount of the boron trifluoride complex additive added is 1-10 wt%, preferably 2-5 wt%, of the total mass of the electrolyte. The total mass of the electrolyte is the sum of the mass of the lithium salt and the mass of the organic solvent.

[0007] Furthermore, the boron trifluoride-organic lipid solvent complex includes one of the following: boron trifluoride ethyl acetate complex, boron trifluoride ethyl chloroacetate complex, boron trifluoride propylene carbonate complex, boron trifluoride methyl ethyl carbonate complex, boron trifluoride dimethyl carbonate complex, and their derivatives.

[0008] Furthermore, the boron trifluoride organic ether solvent complex includes one of the following: boron trifluoride diethyl ether complex, boron trifluoride butyl ether complex, boron trifluoride dimethyl ether complex, and boron trifluoride tetrahydrofuran complex.

[0009] Furthermore, the boron trifluoride sulfone solvent complex includes one of the following: boron trifluoride cyclobutane sulfone complex, boron trifluoride dimethyl sulfoxide complex, boron trifluoride phenylethyl sulfone complex, boron trifluoride diethyl sulfone complex, and boron trifluoride diphenyl sulfone complex.

[0010] Furthermore, the organic electrolyte system is prepared by dissolving lithium salts and basic additives in an organic solvent. The lithium salts include one or more of LiPF6, LiBF4, LiClO4, LiAsF6, LiBOB, LiODFB, LiFSI, and LiTFSI. The basic additives include one or more of vinyl sulfate (DTD), lithium difluorophosphate (LPF), and 1,3-propanesulfonic acid lactone (PS).

[0011] Furthermore, the concentration of the lithium salt in the organic electrolyte system is 0.6-1.2 mol / L.

[0012] Further, the organic solvent includes one or more of propylene carbonate, methyl ethyl carbonate, dimethyl carbonate, ethyl acetate, diethyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, ethyl propyl carbonate, ethyl isopropyl carbonate, ethylene glycol dimethyl ether, tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, and sulfolane.

[0013] Furthermore, the mass of the basic additive accounts for 0.5-5 wt% of the total mass of the electrolyte.

[0014] The second aspect of this invention protects the application of the electrolyte for improving the performance of lithium-carbon fluoride batteries in improving battery rate performance and high-temperature storage performance, wherein the electrolyte can be used in a temperature range of -40°C to 85°C.

[0015] Beneficial effects:

[0016] The electrolyte system of this invention introduces a boron trifluoride complex additive, wherein boron trifluoride can react with the discharge product LiF of a lithium-carbon fluoride battery to generate a lithium salt LiBF4. This lithium salt can be used as the lithium salt in the electrolyte for lithium-carbon fluoride batteries. Its generation is equivalent to supplementing the electrolyte with lithium ions, which is beneficial to high-rate discharge performance. In addition, the discharge product LiF is non-conductive, and its reaction with the additive is beneficial to the reaction of internal fluorinated carbon, thereby improving the rate performance of the battery. In this invention, boron trifluoride is introduced into the electrolyte in the form of a complex (solid), which makes it easy to control the amount added. In addition, the solvent complexed with it can be used as a solvent for the electrolyte. As boron trifluoride reacts with the battery discharge product, the solvent complexed with it enters the electrolyte and can dissolve the newly generated lithium salt LiBF4, thereby not changing the viscosity of the electrolyte and improving the rate performance of the battery.

[0017] The electrolyte system of this invention simultaneously incorporates boron trifluoride complex additives and basic additives. The latter is beneficial to the shelf stability of lithium-carbon fluoride batteries. In summary, the electrolyte of this invention simultaneously improves and enhances the rate performance and high-temperature shelf stability of the battery. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific examples. These specific embodiments are only used to explain the invention and are not intended to limit the invention.

[0019] Example 1

[0020] Fluorinated graphite material, polyvinylidene fluoride (PVDF), and acetylene black conductive agent were mixed in a mass ratio of 92:4:4. The mixture was homogenized with N-methylpyrrolidone (NMP) solvent and stirred for 10 hours to form a fluorinated graphite slurry. This slurry was then coated onto a composite aluminum foil current collector, with the fluorinated graphite loading controlled at ~10 mg / cm³. 2The modified fluorinated graphite positive electrode sheet was obtained by drying at 100℃. Finally, the electrode was vacuum dried at 85℃ for 24h and used as the positive electrode. A lithium / carbon fluoride battery was assembled with a lithium metal strip as the negative electrode. The separator was Celgard 2400 and the electrolyte was: the lithium salt was LiClO4 with a concentration of 1mol / L, the solvent was PC∶DMC∶EA=30vol%∶40vol%∶30vol%, the basic additives were 1wt% DTD and 1.5wt% LPF, and the boron trifluoride complex was 1wt% boron trifluoride ethyl acetate complex. The discharge performance of the battery at 0.1C, 1C and 20C rates was tested, and the corresponding discharge specific capacity was obtained. Three prepared lithium / carbon fluoride batteries were placed in an oven at 60°C for 30 days, and the discharge specific capacity of the batteries at 0.1C rate at room temperature was tested. In addition, the discharge performance of the corresponding batteries at 0.1C rate, low temperature -40°C and high temperature 85°C was also tested.

[0021] Example 2

[0022] The electrolyte, battery, battery assembly and testing methods in this embodiment are basically the same as in Example 1, except that the dosage of boron trifluoride ethyl acetate complex added is 5 wt%.

[0023] Example 3

[0024] The electrolyte, battery, battery assembly and testing methods in this embodiment are basically the same as in Example 1, except that the dosage of boron trifluoride ethyl acetate complex added is 2wt%.

[0025] Example 4

[0026] The electrolyte, battery, battery assembly and testing methods in this embodiment are basically the same as in Example 1, except that the dosage of boron trifluoride ethyl acetate complex added is 10 wt%.

[0027] Example 5

[0028] The electrolyte, battery, battery assembly and testing method in this embodiment are basically the same as in Embodiment 1. The difference is that the boron trifluoride complex additive in the electrolyte is boron trifluoride sulfolane complex, and the amount added is 2wt%.

[0029] Example 6

[0030] The electrolyte, battery, battery assembly and testing method in this embodiment are basically the same as in Embodiment 1. The difference is that the boron trifluoride complex additive in the electrolyte is boron trifluoride dimethyl ether complex, and the amount added is 2wt%.

[0031] Example 7

[0032] The electrolyte, battery, battery assembly and testing methods in this embodiment are basically the same as in Embodiment 1, except that the amount of basic additives added to the electrolyte is 0.5 wt%.

[0033] Example 8

[0034] The electrolyte, battery, battery assembly and testing methods in this embodiment are basically the same as in Embodiment 1, except that the amount of basic additives added to the electrolyte is 5 wt%.

[0035] Example 9

[0036] The electrolyte, battery, battery assembly and testing methods in this embodiment are basically the same as in Embodiment 1, except that the lithium salt concentration in the electrolyte is 0.6 mol / L.

[0037] Example 10

[0038] The electrolyte, battery, battery assembly and testing methods in this embodiment are basically the same as in Embodiment 1, except that the lithium salt concentration in the electrolyte is 1.2 mol / L.

[0039] Comparative Example 1

[0040] The electrolyte, battery, battery assembly and testing methods of this comparative example are basically the same as those in Example 1, except that the amount of boron trifluoride ethyl acetate complex added to the electrolyte is 11 wt%.

[0041] Comparative Example 2

[0042] The electrolyte, battery, battery assembly and testing methods in this comparative example are basically the same as in Example 1, except that the amount of boron trifluoride ethyl acetate complex added to the electrolyte is 0.5 wt%.

[0043] Comparative Example 3

[0044] The electrolyte, battery, battery assembly, and testing methods in this comparative example are basically the same as in Example 1, except that boron trifluoride complex additives were not added to the electrolyte.

[0045] Comparative Example 4

[0046] The electrolyte, battery, battery assembly and testing methods in this comparative example are basically the same as in Example 1, except that 10 wt% of a sulfate ester solvent—dimethyl sulfite—is added to the electrolyte.

[0047] Comparative Example 5

[0048] The electrolyte, battery, battery assembly, and testing methods in this comparative example are basically the same as in Example 1. The difference is that the boron trifluoride complex additive in the electrolyte is replaced with 5 wt% of perfluorinated triphenylborone (TPFPB) additive.

[0049] Comparative Example 6

[0050] The electrolyte, battery, battery assembly, and testing methods in this comparative example are basically the same as in Example 1. The difference is that the boron trifluoride complex additive in the electrolyte is replaced with 5 wt% of an additive containing fluorine, boron, and phosphorus (its structural formula is shown in the figure below).

[0051]

[0052] Comparative Example 7

[0053] The electrolyte, battery, battery assembly and testing methods in this comparative example are basically the same as in Example 1, except that the amount of basic additive added to the electrolyte is 0.2 wt%.

[0054] Comparative Example 8

[0055] The electrolyte, battery, battery assembly and testing methods in this comparative example are basically the same as in Example 1, except that the amount of basic additive added to the electrolyte is 6 wt%.

[0056] Comparative Example 9

[0057] The electrolyte, battery, battery assembly, and testing methods in this comparative example are basically the same as in Example 1, except that the lithium salt concentration in the electrolyte is 1.5 mol / L.

[0058] Comparative Example 10

[0059] The electrolyte, battery, battery assembly and testing methods in this comparative example are basically the same as in Example 1, except that the lithium salt concentration in the electrolyte is 0.5 mol / L.

[0060] Table 1

[0061]

[0062]

[0063]

[0064] The discharge performance of the lithium / carbon fluoride batteries of Examples 1-10 and Comparative Examples 1-10 is shown in Table 2:

[0065] Table 2 Discharge performance of lithium / carbon fluoride batteries

[0066]

[0067]

[0068] Note: The 20C / 0.1C capacity retention rate (%) in the appendix refers to the discharge specific capacity of a single battery cell at 20C rate / discharge specific capacity of a single battery cell at 0.1C rate * 100%; the capacity retention rate (%) after 30 days of storage at 60°C refers to the discharge specific capacity of a battery after 30 days of storage at 60°C and discharge at 0.1C rate, divided by the discharge specific capacity of an unstored battery at the same rate * 100%.

[0069] Test Results and Analysis: As shown in the attached table, the amount of boron trifluoride complex added to the electrolyte, the type of boron trifluoride complex, the amount of basic additives added to the electrolyte, and the lithium salt concentration of the electrolyte all affect the capacity performance (0.1C), rate performance (20C discharge specific capacity and 20C / 0.1C capacity retention rate), and shelf stability performance (capacity retention rate after 30 days of shelf life at 60℃) of lithium fluoride carbon batteries. When the amount of boron trifluoride complex added is in the range of 1-10 wt% (as in Examples 1-4 and Comparative Examples 1-2), the overall performance of the corresponding battery cells is better. Further preferred, when the amount of boron trifluoride complex added is in the range of 2-5 wt%, the overall battery performance is better. Better performance (as in Examples 2-3), i.e., higher specific capacity at 0.1C and 20C discharge rates, and a higher 20C / 0.1C capacity retention rate (%), indicating that the corresponding battery has excellent rate performance; in addition, the corresponding battery has almost no capacity loss after being stored at 60 degrees Celsius for 30 days, i.e., exhibiting a capacity retention rate of over 99%, indicating that the battery has excellent storage stability; the preferred boron trifluoride complex is a boron trifluoride ester complex (as in Examples 3, 5-6); when the amount of basic additives added to the electrolyte is in the range of 0.5-5wt%, the battery has good high-temperature storage performance (as in Examples 1, 7-8, and Comparative Examples 7 and 8). When the lithium salt concentration in the electrolyte is in the range of 0.6-1.2M, the battery exhibits good rate performance and high-temperature storage performance (e.g., Examples 1, 9-10, Comparative Examples 9, 10). When boron trifluoride complex additives are not added to the electrolyte, or when sulfur-containing solvents, boron-containing solvents, or fluorine, phosphorus, and boron-containing additives are added (e.g., Comparative Examples 3-6), the rate performance and high-temperature storage stability of the lithium fluoride carbon battery cannot achieve the same technical effects as the present invention. In addition, the electrolyte provided by the present invention can discharge at a low temperature of -40°C with a discharge capacity of more than 50% of that at room temperature, and can discharge normally at a high temperature of 85°C without the battery bloating.

[0070] In summary, compared with the prior art, the electrolyte system of the present invention introduces boron trifluoride complex additives, which have a synergistic effect with existing basic additives for electrolytes (such as Examples 1, 7-8, and Comparative Examples 7 and 8). When used in lithium / carbon fluoride batteries, it can simultaneously improve and enhance the rate performance and high-temperature storage stability of the battery.

[0071] The electrolyte system of this invention introduces a boron trifluoride complex additive, wherein boron trifluoride can react with the discharge product LiF of a lithium-carbon fluoride battery to generate a lithium salt LiBF4. This lithium salt can be used as the lithium salt in the electrolyte for lithium-carbon fluoride batteries. Its generation is equivalent to supplementing the electrolyte with lithium ions, which is beneficial to high-rate discharge performance. In addition, the discharge product LiF is non-conductive, and its reaction with the additive is beneficial to the reaction of internal fluorinated carbon, thereby improving the battery's capacity and rate performance. In this invention, boron trifluoride is introduced into the electrolyte in the form of a complex (solid), which makes it easy to control the amount added. Furthermore, the solvent complexed with it can be used as a solvent for the electrolyte. As boron trifluoride reacts with the battery discharge product, the solvent complexed with it enters the electrolyte and can dissolve the newly generated lithium salt LiBF4, thereby not changing the viscosity of the electrolyte and improving the battery's rate performance.

[0072] The electrolyte system of this invention simultaneously incorporates boron trifluoride complex additives and basic additives. The latter is beneficial to the shelf stability of lithium-carbon fluoride batteries. In summary, the electrolyte of this invention...

[0073] Simultaneously improve and enhance the battery's rate performance and high-temperature storage stability.

[0074] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. An electrolyte for improving the performance of lithium-carbon fluoride batteries, characterized in that, The system includes an organic electrolyte system containing a boron trifluoride complex additive. The boron trifluoride complex additive includes one or more of the following: boron trifluoride organic lipid solvent complex, boron trifluoride organic ether solvent complex, and boron trifluoride sulfone solvent complex. The amount of the boron trifluoride complex additive added accounts for 1-10 wt% of the total mass of the electrolyte, and the total mass of the electrolyte is the sum of the mass of the lithium salt and the mass of the organic solvent.

2. The electrolyte for improving the performance of lithium-carbon fluoride batteries according to claim 1, characterized in that, The amount of the boron trifluoride complex additive is 2-5 wt% of the total mass of the electrolyte.

3. The electrolyte for improving the performance of lithium-carbon fluoride batteries according to claim 1, characterized in that, The boron trifluoride organic lipid solvent complex includes one of the following: boron trifluoride ethyl acetate complex, boron trifluoride ethyl chloroacetate complex, boron trifluoride propylene carbonate complex, boron trifluoride methyl ethyl carbonate complex, boron trifluoride dimethyl carbonate complex, and their derivatives.

4. The electrolyte for improving the performance of lithium-carbon fluoride batteries according to claim 1, characterized in that, The boron trifluoride organic ether solvent complex includes one of the following: boron trifluoride diethyl ether complex, boron trifluoride butyl ether complex, boron trifluoride dimethyl ether complex, and boron trifluoride tetrahydrofuran complex.

5. The electrolyte for improving the performance of lithium-carbon fluoride batteries according to claim 1, characterized in that, The boron trifluoride sulfone solvent complex includes one of the following: boron trifluoride cyclobutane sulfone complex, boron trifluoride dimethyl sulfoxide complex, boron trifluoride phenylethyl sulfone complex, boron trifluoride diethyl sulfone complex, and boron trifluoride diphenyl sulfone complex.

6. The electrolyte for improving the performance of lithium-carbon fluoride batteries according to claim 1, characterized in that, The organic electrolyte system is made by dissolving lithium salts and basic additives in an organic solvent. The lithium salts include one or more of LiPF6, LiBF4, LiClO4, LiAsF6, LiBOB, LiODFB, LiFSI, and LiTFSI. The basic additives include one or more of vinyl sulfate, lithium difluorophosphate, and 1,3-propanesulfonic acid lactone.

7. The electrolyte for improving the performance of lithium-carbon fluoride batteries according to claim 6, characterized in that, The concentration of the lithium salt in the organic electrolyte system is 0.6~1.2 mol / L.

8. The electrolyte for improving the performance of lithium-carbon fluoride batteries according to claim 6, characterized in that, The organic solvent includes one or more of propylene carbonate, methyl ethyl carbonate, dimethyl carbonate, ethyl acetate, diethyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, ethyl propyl carbonate, ethyl isopropyl carbonate, ethylene glycol dimethyl ether, tetrahydrofuran, 1,3-dioxolane, and sulfolane.

9. The electrolyte for improving the performance of lithium-carbon fluoride batteries according to claim 6, characterized in that, The basic additive accounts for 0.5 to 5 wt% of the total mass of the electrolyte.

10. The application of the electrolyte for improving the performance of lithium-carbon fluoride batteries according to any one of claims 1 to 9 in improving battery rate performance and high-temperature storage performance, characterized in that, The electrolyte can be applied in a temperature range of -40℃ to 85℃.

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