An electrolyte for a lithium / carbon fluoride battery and its application

Abstract

The present invention discloses an electrolyte for a lithium / carbon fluoride battery and its application, belonging to the technical field of electrolyte preparation. The electrolyte includes a lithium salt, an ester solvent, an ether solvent, a sulfone solvent and a boron-containing additive. In the lithium / carbon fluoride battery electrolyte prepared by the present invention, three solvents are simultaneously used and a boron-containing additive is introduced. This additive can react with the discharge product lithium fluoride, keeping the active material carbon fluoride in contact with the electrolyte, enabling the carbon fluoride to fully react, that is, increasing the room temperature discharge specific capacity of the carbon fluoride, and further increasing the specific energy of the lithium / carbon fluoride battery. In addition, as the lithium / carbon fluoride battery discharges, the discharge product lithium fluoride generated on the surface of the carbon fluoride is promptly reacted by the boron-containing additive, making the discharge reaction of the carbon fluoride easier to proceed, thus effectively alleviating the heat generation problem of the lithium / carbon fluoride battery. Finally, simultaneously using three solvents in the electrolyte and introducing a boron-containing additive can also improve the low-temperature performance of the lithium / carbon fluoride battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrolyte preparation, and particularly relates to an electrolyte for lithium / carbon fluoride batteries and its application. Background Art

[0002] With the technological progress in fields such as mobile communication, aerospace, transportation, and military equipment, the development of various high specific energy power batteries has become an urgent need for the development of the national economy. Due to the characteristics of light mass and negative electrode potential of metallic lithium, the development of primary lithium batteries with lithium as the negative electrode has received great attention. Primary lithium batteries mainly include lithium-manganese dioxide (Li / MnO2), lithium-sulfur dioxide (Li / SO2), lithium-thionyl chloride (Li / SOCl2), and lithium-carbon fluoride (Li / CF x ) and other battery systems. Compared with other primary batteries, the Li / CFx battery has the highest theoretical specific energy value (2180 Wh / kg). At the same time, the Li / CF x battery also has advantages such as high safety, stable discharge voltage, and environmental friendliness, and is particularly suitable as the power source for instrument equipment used in unmanned or enclosed environments. Such as cardiac pacemakers, missile ignition systems, radio transmitters, underwater electronic detectors, etc., especially as the communication power source for military long-range reconnaissance and carried by soldiers, it has great application potential.

[0003] Although the Li / CFx battery has a high theoretical specific energy (about 2180 Wh / kg), its actual specific energy is 300 - 700 Wh / kg, far lower than its theoretical value; in addition, as is well known, the Li / CFx battery has a serious heat generation problem during the discharge process. From the perspective of safety, the heat generation of Li / CFx needs to be reduced. Summary of the Invention

[0004] In view of the above-mentioned problems in the prior art, the present invention designs and provides a high specific energy lithium-carbon fluoride battery by improving the electrolyte. This battery has a large discharge specific capacity and a relatively high specific energy; at the same time, the heat generation problem of this battery is significantly improved; and the low-temperature performance of the battery is significantly improved.

[0005] The present invention is mainly achieved by optimizing the solvent ratio in the electrolyte for carbon fluoride batteries and the content of boron-containing additives.

[0006] The technical solution of the present invention is as follows:

[0007] The present invention provides an electrolyte for lithium / carbon fluoride batteries, which includes a lithium salt, an ester solvent, an ether solvent, a sulfone solvent, and a boron-containing additive;

[0008] The boron-containing additive includes one or more of tridecyl borate, tris(pentafluorophenyl)borane, tri(tetradecyl) borate, trihexyl borate, triphenyl borate, trimethyl borate, tri-n-octyl borate, tri(2-cyanoethyl) borate, tri(hexafluoroisopropyl) borate, tributyl borate, tri(2,2,2-trifluoroethyl) borate, tri-n-octyl borate, triethyl borate, tri-o-tolyl borate, triisopropanolamine borate, tri(hexafluoroisopropyl) borate;

[0009] The volume ratio of the ester solvent, ether solvent, and sulfone solvent is (65 - 90):(5 - 15):(5 - 20).

[0010] Furthermore, the boron-containing additive is 1 wt% - 10 wt% of the sum of the masses of the lithium salt, ester solvent, ether solvent, and sulfone solvent.

[0011] Preferably, the boron-containing additive is 1 wt% - 5 wt% of the sum of the masses of the lithium salt, ester solvent, ether solvent, and sulfone solvent.

[0012] Preferably, the lithium salt includes one or more of lithium perchlorate and lithium tetrafluoroborate, and the molar concentration of the lithium salt in the electrolyte is 1 - 1.5 M.

[0013] Preferably, the ester solvent includes one or more of dimethyl carbonate, ethyl methyl carbonate, ethyl acetate, propylene carbonate, 1,4-butyrolactone, and diethyl carbonate.

[0014] Preferably, the ether solvent includes one or more of diethylene glycol dimethyl ether, tetrahydrofuran, and 1,3-dioxolane.

[0015] Preferably, the sulfone solvent includes one or more of dimethyl sulfoxide, bisphenol S, and sulfolane.

[0016] The present invention also provides an application of the above electrolyte in a lithium / carbon fluoride electrolytic cell.

[0017] Furthermore, it is used for battery operation at low temperatures of -40°C to 30°C.

[0018] Beneficial Effects

[0019] 1. By optimizing the types, ratios of solvents, and the content of the boron-containing additive in the electrolyte, under the optimized types and ratios of solvents, the boron-containing additive can react with the discharge product (lithium fluoride) of the lithium / carbon fluoride battery, enabling the carbon fluoride to always be in contact with the electrolyte and allowing the carbon fluoride to react fully, that is, increasing the room-temperature discharge specific capacity of the carbon fluoride and thus increasing the specific energy of the lithium / carbon fluoride battery.

[0020] 2. As the discharge progresses, the lithium fluoride formed as a discharge product on the surface of carbon fluoride is promptly reacted with the boron-containing additive, making the discharge reaction of carbon fluoride easier to proceed, thereby effectively alleviating the heat generation problem of lithium / carbon fluoride batteries.

[0021] 3. Simultaneously using three solvents and introducing a boron-containing additive in the electrolyte can improve the low-temperature performance of lithium / carbon fluoride batteries. Specific embodiments

[0022] The present application will be described in detail below with reference to the embodiments, but the present application is not limited to these embodiments. Unless otherwise specified, the raw materials in the embodiments of the present application are all purchased through commercial channels. The electrochemical performance of the lithium / carbon fluoride battery is tested using a LAND-CT2001A charge-discharge tester.

[0023] Example 1:

[0024] Prepare the electrolyte: In a glove box filled with nitrogen, using propylene carbonate, diethyl carbonate, tetrahydrofuran, and bisphenol S as solvents, lithium perchlorate is dissolved in the above solvents at a molar concentration of 1 mol / L, where the volume ratio of the solvents propylene carbonate, diethyl carbonate, tetrahydrofuran, and bisphenol S is: 35:30:15:20. Then add a boron-containing additive, the boron-containing additive is trihexyl borate and triphenyl borate (the volume ratio of the two is 1:1), and the boron-containing additive accounts for 10 wt% of the total mass of the electrolyte. The total mass of the electrolyte refers to the total mass of the lithium salt lithium perchlorate and each solvent.

[0025] Using carbon fluoride (CF 0.85 ) as the positive electrode material and lithium metal (Li) as the negative electrode material to assemble a soft-pack lithium / carbon fluoride battery, where the electrode area is 5 cm * 7.7 cm, and the above-prepared electrolyte is used as the electrolyte of the battery. The following tests are performed on the above battery: First, perform a pre-discharge at a rate of 0.1C for 5 min; after the pre-discharge ends, take 2 lithium / carbon fluoride batteries and discharge them to 1V at a rate of 0.1C at room temperature of 25°C and low temperature of -40°C respectively, and simultaneously monitor the temperature change of the battery discharged at room temperature (25°C) (evaluating the heat generation of the battery by the temperature rise during discharge). The test data under each condition are shown in Table 1.

[0026] Example 2:

[0027] Preparation of electrolyte: In a glove box filled with nitrogen, using propylene carbonate, ethyl acetate, dimethyl carbonate, ethyl methyl carbonate, tetrahydrofuran, and sulfolane as solvents, lithium perchlorate is dissolved in the above solvents at a molar concentration of 1 mol / L. The volume ratio of the solvents propylene carbonate, ethyl acetate, dimethyl carbonate, ethyl methyl carbonate, tetrahydrofuran, and sulfolane is: 25:20:30:15:5:5. Then, a boron-containing additive is added. The boron-containing additive is trimethyl borate, and the boron-containing additive accounts for 1 wt% of the total mass of the electrolyte. The total mass of the electrolyte refers to the total mass of the lithium salt lithium perchlorate and each solvent.

[0028] The electrodes, batteries, and other conditions are the same as those in Example 1.

[0029] Example 3:

[0030] Preparation of electrolyte: In a glove box filled with nitrogen, using propylene carbonate, diethyl carbonate, 1,3-dioxolane, and sulfolane as solvents, lithium perchlorate is dissolved in the above solvents at a molar concentration of 1 mol / L. The volume ratio of the solvents propylene carbonate, diethyl carbonate, 1,3-dioxolane, and sulfolane is: 45:35:10:10. Then, a boron-containing additive is added. The boron-containing additives are triethyl borate and tri-o-tolyl borate (the volume ratio of the two is 2:1), and the boron-containing additive accounts for 5 wt% of the total mass of the electrolyte. The total mass of the electrolyte refers to the total mass of the lithium salt lithium perchlorate and each solvent.

[0031] The electrodes, batteries, and other conditions are the same as those in Example 1.

[0032] Example 4:

[0033] Preparation of electrolyte: In a glove box filled with nitrogen, using propylene carbonate, ethyl acetate, tetrahydrofuran, and sulfolane as solvents, lithium perchlorate is dissolved in the above solvents at a molar concentration of 1 mol / L. The volume ratio of the solvents propylene carbonate, ethyl acetate, tetrahydrofuran, and sulfolane is: 40:35:10:15. Then, a boron-containing additive is added. The boron-containing additives are trimethyl borate and tri-n-octyl borate (the volume ratio of the two is 3:1), and the boron-containing additive accounts for 3 wt% of the total mass of the electrolyte. The total mass of the electrolyte refers to the total mass of the lithium salt lithium perchlorate and each solvent.

[0034] The electrodes, batteries, and other conditions are the same as those in Example 1.

[0035] Comparative Example 1:

[0036] (Same as Example 4, except that the amount of the boron-containing additive is not within the scope of the present invention)

[0037] Prepare the electrolyte: In a glove box filled with nitrogen, using propylene carbonate, ethyl acetate, tetrahydrofuran, and sulfolane as solvents, dissolve lithium perchlorate at a molar concentration of 1 mol / L in the above solvents. The volume ratio of the solvents propylene carbonate, ethyl acetate, tetrahydrofuran, and sulfolane is: 40:35:10:15. Then add a boron-containing additive. The boron-containing additive is trimethyl borate and tri-n-octyl borate (the volume ratio of the two is 3:1), and the boron-containing additive accounts for 0.5 wt% of the total mass of the electrolyte. The total mass of the electrolyte refers to the total mass of the lithium salt lithium perchlorate and each solvent.

[0038] The electrodes, batteries, and other conditions are the same as in Example 1.

[0039] Comparative Example 2:

[0040] (Same as Example 4, except that the amount of the boron-containing additive is not within the scope of the present invention)

[0041] Prepare the electrolyte: In a glove box filled with nitrogen, using propylene carbonate, ethyl acetate, tetrahydrofuran, and sulfolane as solvents, dissolve lithium perchlorate at a molar concentration of 1 mol / L in the above solvents. The volume ratio of the solvents propylene carbonate, ethyl acetate, tetrahydrofuran, and sulfolane is: 40:35:10:15. Then add a boron-containing additive. The boron-containing additive is trimethyl borate and tri-n-octyl borate (the volume ratio of the two is 3:1), and the boron-containing additive accounts for 11 wt% of the total mass of the electrolyte. The total mass of the electrolyte refers to the total mass of the lithium salt lithium perchlorate and each solvent.

[0042] The electrodes, batteries, and other conditions are the same as in Example 1.

[0043] Comparative Example 3:

[0044] Use commercial electrolyte 1, where the solvents are propylene carbonate and diethyl carbonate (the volume ratio of the two is 70:30), the lithium salt is lithium perchlorate, and the concentration is 1 mol / L. The boron-containing additive is trimethyl borate and tri-n-octyl borate (the volume ratio of the two is 3:1), and the boron-containing additive accounts for 3 wt% of the total mass of the electrolyte. The total mass of the electrolyte refers to the total mass of the lithium salt lithium perchlorate and each solvent.

[0045] Other conditions are the same as in Example 1.

[0046] Comparative Example 4:

[0047] Use commercial electrolyte 2, where the solvents are propylene carbonate, 1,3-dioxolane, and tetrahydrofuran (the volume ratio is 50:20:30), the lithium salt is lithium perchlorate, and the concentration is 1 mol / L. The boron-containing additive is trimethyl borate, and the boron-containing additive accounts for 2 wt% of the total mass of the electrolyte. The total mass of the electrolyte refers to the total mass of the lithium salt lithium perchlorate and each solvent.

[0048] Other conditions are the same as those in Example 1.

[0049] Comparative Example 5:

[0050] A commercial electrolyte 3 is used, where the solvents are propylene carbonate, ethylene glycol dimethyl ether, 1,3-dioxolane, and fluorinated ether (with a volume ratio of 40:20:30:10), the lithium salt is lithium tetrafluoroborate with a concentration of 1 mol / L. The boron-containing additive is trimethyl borate, and the boron-containing additive accounts for 1 wt% of the total mass of the electrolyte. The total mass of the electrolyte refers to the total mass of the lithium salt lithium perchlorate and each solvent.

[0051] Other conditions are the same as those in Example 1.

[0052] Comparative Example 6:

[0053] A commercial electrolyte 4 is used, where the solvents are propylene carbonate, dimethyl carbonate, ethyl acetate, and sulfolane (with a volume ratio of 40:20:20:20), the lithium salt is lithium tetrafluoroborate with a concentration of 1 mol / L. The boron-containing additive is trimethyl borate, and the boron-containing additive accounts for 10 wt% of the total mass of the electrolyte. The total mass of the electrolyte refers to the total mass of the lithium salt lithium perchlorate and each solvent.

[0054] Other conditions are the same as those in Example 1.

[0055] Comparative Example 7: (Solvent ratio not within the range)

[0056] A commercial electrolyte 5 is used, where the solvents are propylene carbonate, dimethyl carbonate, ethyl acetate, tetrahydrofuran, and sulfolane (with a volume ratio of 40:35:20:2.5:2.5), the lithium salt is lithium perchlorate with a concentration of 1 mol / L. The boron-containing additive is trimethyl borate, and the boron-containing additive accounts for 5 wt% of the total mass of the electrolyte. The total mass of the electrolyte refers to the total mass of the lithium salt lithium perchlorate and each solvent.

[0057] Other conditions are the same as those in Example 1.

[0058] Comparative Example 8: (Solvent ratio not within the range)

[0059] A commercial electrolyte 6 is used, where the solvents are propylene carbonate, ethyl acetate, tetrahydrofuran, and sulfolane (with a volume ratio of 30:25:20:25), the lithium salt is lithium perchlorate with a concentration of 1 mol / L. The boron-containing additive is trimethyl borate, and the boron-containing additive accounts for 3 wt% of the total mass of the electrolyte. The total mass of the electrolyte refers to the total mass of the lithium salt lithium perchlorate and each solvent.

[0060] Other conditions are the same as those in Example 1.

[0061] Comparative Example 9:

[0062] (Without boron-containing additive)

[0063] In a glove box filled with nitrogen, using propylene carbonate, diethyl carbonate, tetrahydrofuran, and bisphenol S as solvents, lithium perchlorate was dissolved in the above solvents at a molar concentration of 1 mol / L, where the volume ratio of the solvents propylene carbonate, diethyl carbonate, tetrahydrofuran, and bisphenol S was: 35:30:15:20.

[0064] Other conditions were the same as in Example 1.

[0065] Comparative Example 10:

[0066] (Boron-containing additive outside the present invention)

[0067] In a glove box filled with nitrogen, using propylene carbonate, diethyl carbonate, tetrahydrofuran, and bisphenol S as solvents, lithium perchlorate was dissolved in the above solvents at a molar concentration of 1 mol / L, where the volume ratio of the solvents propylene carbonate, diethyl carbonate, tetrahydrofuran, and bisphenol S was: 35:30:15:20. The boron-containing additive was lithium bis(oxalato)borate (LiB(C2O4)2), and the boron-containing additive accounted for 3 wt% of the total mass of the electrolyte. The total mass of the electrolyte refers to the total mass of the lithium salt lithium perchlorate and each solvent.

[0068] Other conditions were the same as in Example 1.

[0069] Analysis of test results: In the present invention, by improving the electrolyte, optimizing the volume ratio of each solvent in the electrolyte, and introducing a boron-containing additive and optimizing its content (such as in Examples 1-4 and Comparative Examples 1-2). The test results show (as shown in Table 1): Under the optimized solvent components and ratios in the present invention (ester solvent: ether solvent: sulfone solvent = (65-90):(5-15):(5-20)), after introducing an appropriate content of the boron-containing additive, the room temperature discharge specific capacity of the lithium / carbon fluoride battery using the above electrolyte is significantly improved, up to 791.2 mAh / g at most (such as in Example 4). At the same time, the low-temperature performance of the lithium / carbon fluoride battery is also significantly improved. At a low temperature of -40 °C, the discharge specific capacity is up to 223.7 mAh / g at most (such as in Example 4). In addition, the heat generation during the discharge of the lithium / carbon fluoride battery (the maximum temperature rise is only 71 °C) is also effectively suppressed. When the electrolyte for the lithium / carbon fluoride battery adopts the optimized solvent components and ratios in the present invention but does not introduce the boron-containing additive in the present invention (Comparative Example 9) or introduces other inorganic boron-containing additives (Comparative Example 10), the room temperature performance and low-temperature performance are not ideal, and the heat generation during the discharge process is significantly higher than that in the examples of the present invention. When the electrolyte for the lithium / carbon fluoride battery introduces the boron-containing additive in the present invention but does not adopt the optimized solvent components or ratios in the present invention (Comparative Examples 3-8), the room temperature performance and low-temperature performance are also not ideal, and the heat generation during the discharge process is also significantly higher than that in the examples of the present invention. In summary, the present invention provides an electrolyte for a lithium / carbon fluoride battery, which needs to include a lithium salt, three solvents and a boron-containing additive at the same time, and when each component is within a suitable range, the lithium / carbon fluoride battery can achieve the expected technical effects. Under the optimized solvent components and ratios in the present invention, the boron-containing additive introduced into the electrolyte can react with the discharge product (lithium fluoride) of the lithium / carbon fluoride battery, keeping the active material carbon fluoride in contact with the electrolyte, enabling the active material carbon fluoride to react fully, that is, improving the room temperature discharge specific capacity of carbon fluoride, and further improving the specific energy of the lithium / carbon fluoride battery; in addition, as the lithium / carbon fluoride battery discharges, a part of the discharge product lithium fluoride generated on the surface of the carbon fluoride is consumed by the boron-containing additive, making the discharge reaction of the carbon fluoride easier to proceed, thus effectively alleviating the heat generation problem of the lithium / carbon fluoride battery and at the same time improving the low-temperature performance of the lithium / carbon fluoride battery.

[0070] Table 1 Discharge performance of lithium / carbon fluoride batteries using different electrolytes at 25 °C and -40 °C

[0071]

[0072]

Claims

1. An electrolyte for a lithium / carbon fluoride battery, characterized in that, It includes a lithium salt, an ester solvent, an ether solvent, a sulfone solvent and a boron-containing additive; The boron-containing additive includes: one or more of tridecyl borate, tris(pentafluorophenyl)borane, tris(tetradecyl) borate, trihexyl borate, triphenyl borate, trimethyl borate, tri-n-octyl borate, tris(2-cyanoethyl) borate, tris(hexafluoroisopropyl) borate, tributyl borate, tris(2,2,2-trifluoroethyl) borate, tri-n-octyl borate, triethyl borate, tri-o-tolyl borate, triisopropanolamine borate, tris(hexafluoroisopropyl) borate; The volume ratio of the ester solvent, the ether solvent and the sulfone solvent is (65-90):(5-15):(5-20).

2. The electrolyte for a lithium / carbon fluoride battery according to claim 1, wherein, The boron-containing additive is 1 wt%-10 wt% of the sum of the masses of the lithium salt, the ester solvent, the ether solvent and the sulfone solvent.

3. The electrolyte for a lithium / carbon fluoride battery according to claim 2, wherein The boron-containing additive is 1-5 wt% of the sum of the masses of the lithium salt, the ester solvent, the ether solvent and the sulfone solvent.

4. The electrolyte for a lithium / carbon fluoride battery according to claim 1, characterized in that, The lithium salt includes one or more of lithium perchlorate and lithium tetrafluoroborate, and the molar concentration of the lithium salt in the electrolyte is 1-1.5 M.

5. The electrolyte for a lithium / carbon fluoride battery according to claim 1, characterized in that, The ester solvent includes: one or more of dimethyl carbonate, ethyl methyl carbonate, ethyl acetate, propylene carbonate, 1,4-butyrolactone, diethyl carbonate.

6. The electrolyte for a lithium / carbon fluoride battery according to claim 1, characterized in that, The ether solvent includes: one or more of diethylene glycol dimethyl ether, tetrahydrofuran, 1,3-dioxolane.

7. The electrolyte for a lithium / carbon fluoride battery according to claim 1, wherein The sulfone solvent includes: one or more of dimethyl sulfoxide, bisphenol S, sulfolane.

8. Application of the electrolyte according to any one of claims 1-7 in a lithium / fluorinated carbon battery.

9. The application according to claim 8, wherein It is used for battery operation at low temperatures of -40°C to 30°C.

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