Ultralow-temperature lithium primary battery electrolyte and obtained product

Abstract

The invention relates to the technical field of electrochemical batteries, in particular to an ultralow-temperature lithium primary battery electrolyte and an obtained product. The electrolyte comprises a lithium salt, a composite solvent and an additive, and the composite solvent is formed by mixing 2-methyltetrahydrofuran, 3-fluorotetrahydrofuran and 1, 3-dioxolane. In the composite solvent, the mass ratio of 2-methyltetrahydrofuran to 3-fluorotetrahydrofuran to 1, 3-dioxolane is 2: 1: 1 to 4: 1: 1. The viscosity of the cyclic ether solvents is far lower than that of carbonic ester solvents, the three cyclic ether solvents are used as composite solvents of the electrolyte, and through molecular structure complementation and characteristic synergy, the problems that a traditional electrolyte is solidified at low temperature, ion transmission is blocked and the like are fundamentally solved. The discharge capacity retention rate of the obtained lithium primary battery at the low temperature of-60 DEG C is greater than or equal to 55%, and the application requirements of the lithium primary battery in an ultralow-temperature environment can be effectively met.

Description

Technical Field

[0001] This invention relates to the field of electrochemical battery technology, and in particular to an ultra-low temperature lithium primary battery electrolyte and the resulting product. Background Technology

[0002] Lithium-ion primary batteries, due to their characteristics such as no need for charging, high energy density, and long storage life, have irreplaceable application value in extreme scenarios such as polar scientific expeditions, military applications, and emergency power supply in high-altitude and frigid regions. These scenarios often face ultra-low temperature environments below -50°C, and the performance of lithium-ion primary batteries is extremely sensitive to temperature. The degradation of electrolyte function at low temperatures directly restricts the practical application of lithium-ion primary batteries in extreme low-temperature scenarios.

[0003] Traditional lithium-ion primary battery electrolytes often use carbonate-based mixed solvents, such as ethylene carbonate and propylene carbonate combined with lithium salts like lithium perchlorate and lithium hexafluorophosphate. These solutions exhibit several fatal flaws in ultra-low temperature environments. Carbonate solvents have high freezing points and are prone to solidification or a sharp increase in viscosity at low temperatures, leading to loss of electrolyte fluidity, obstruction of ion migration channels, a sharp drop in conductivity, a dramatic increase in battery internal resistance, and a significant decrease in discharge capacity, even resulting in a "zero voltage" phenomenon. Traditional lithium-ion primary batteries have a discharge capacity of less than 33% of that at room temperature at -40°C, and cannot even discharge stably at -60°C, completely failing to meet the power supply requirements of extreme low-temperature scenarios.

[0004] Chinese patent CN109449485A discloses an ultra-low temperature resistant lithium battery electrolyte, comprising: an organic solvent; a lithium salt electrolyte; and additives, wherein the additives are selected from one or more groups of potassium bromide, sodium bis(trifluoromethanesulfonyl)imide, potassium bis(trifluoromethanesulfonyl)imide, and zinc di[bis(trifluoromethanesulfonyl)imide], with a mass content of 0.05%-0.15%. Since the freezing point of ethylene glycol dimethyl ether is greater than -60℃, a low temperature of -60℃ will lead to a decrease in the electrolyte ion migration rate, further deteriorating the battery's rate performance at low temperatures, failing to meet the battery's electrical performance requirements in ultra-low temperature scenarios. Potassium bromide and sodium bis(trifluoromethanesulfonyl)imide easily corrode aluminum current collectors, potassium bis(trifluoromethanesulfonyl)imide increases the electrolyte viscosity to a certain extent, and zinc di[bis(trifluoromethanesulfonyl)imide] accelerates electrode corrosion and electrolyte consumption, shortening battery life. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a solution to the problem of electrolyte solidification or high viscosity at low temperatures, and provides an ultra-low temperature lithium primary battery electrolyte.

[0006] To solve the above-mentioned technical problems, the technical solution provided by the present invention is: an ultra-low temperature lithium primary battery electrolyte, comprising lithium salt, composite solvent and additives, wherein the composite solvent is composed of a mixture of 2-methyltetrahydrofuran, 3-fluorotetrahydrofuran and 1,3-dioxolane.

[0007] Further: In the above-mentioned ultra-low temperature lithium primary battery electrolyte, the lithium salt content accounts for 8-12 wt% of the total mass of the lithium primary battery electrolyte, the composite solvent content accounts for 80-90 wt% of the total mass of the lithium primary battery electrolyte, and the additive content accounts for 1-2 wt% of the total mass of the lithium primary battery electrolyte, with the sum of the mass percentages of each substance being 100%.

[0008] In the composite solvent, the mass ratio of 2-methyltetrahydrofuran, 3-fluorotetrahydrofuran, and 1,3-dioxolane is 2:1:1 to 4:1:1. The viscosity of the cyclic ether solvent itself is much lower than that of carbonate solvents. 2-methyltetrahydrofuran has a freezing point of approximately -136℃, 3-fluorotetrahydrofuran has a freezing point below -80℃, and 1,3-dioxolane has a freezing point of approximately -95℃; all three cyclic ether solvents have extremely low freezing points. A solvent mass ratio of 2:1:1 to 4:1:1 uses 2 to 4 parts of 2-methyltetrahydrofuran as the "low-temperature skeleton solvent" of the system, which dominates the low freezing point of the mixed solvent and reduces the overall viscosity. Even at extreme low temperatures of -60℃ or even -80℃, there will be no solidification of the electrolyte or a sudden increase in viscosity, ensuring unobstructed migration pathways. Secondly, 1 part of 3-fluorotetrahydrofuran serves as an auxiliary solvent, exhibiting low viscosity and compensating for the conductivity deficiency of 2-methyltetrahydrofuran while aiding in lithium salt dissociation. 1 part of 1,3-dioxolane also enhances electrolyte conductivity and assists in lithium salt dissociation. Within a given mass ratio, a higher proportion of 2-methyltetrahydrofuran results in better low-temperature fluidity, making it suitable for lower-temperature applications; conversely, a lower proportion of 2-methyltetrahydrofuran leads to superior conductivity, necessitating a balance between the three solvent ratios.

[0009] The lithium salt is a composite system of lithium bis(trifluoromethanesulfonyl)imide and lithium perchlorate. In the lithium salt, the mass ratio of lithium bis(trifluoromethanesulfonyl)imide to lithium perchlorate is 4:1 to 5:1. 4-5 parts of lithium bis(trifluoromethanesulfonyl)imide have high conductivity and high solubility in organic solvents, and are not easily precipitated at low temperatures. As the main component of the lithium salt, its combination with the aforementioned low-temperature cyclic ether composite solvent makes it more suitable for ultra-low temperature environments. Lithium perchlorate has high conductivity and can assist ion transport at extremely low temperatures, but its safety is poor. To maintain battery safety performance, its proportion in the lithium salt is relatively small.

[0010] The additive is a mixture of lithium difluorooxalate borate and lithium difluorophosphate. In the additive, the mass ratio of lithium difluorooxalate borate to lithium difluorophosphate is 1:4 to 3:1. Both lithium difluorooxalate borate and lithium difluorophosphate exhibit good low-temperature solubility and conductivity, and their mass ratio of 1:4 to 3:1 is better suited to the aforementioned lithium salt and solvent.

[0011] The ultra-low temperature lithium primary battery electrolyte of the present invention is obtained by mixing lithium salt, solvent and additives under an inert gas protective atmosphere and then stirring uniformly.

[0012] The present invention also provides lithium primary batteries made from the electrolyte of the aforementioned invention, which are any one of lithium-carbon fluoride batteries, lithium-iron disulfide batteries and lithium-manganese dioxide batteries.

[0013] Compared with existing technologies, the above-mentioned ultra-low temperature lithium primary battery electrolyte includes lithium salt, composite solvent, and additives. The composite solvent is a mixture of 2-methyltetrahydrofuran, 3-fluorotetrahydrofuran, and 1,3-dioxolane. The cyclic ether solvent itself has a much lower viscosity than carbonate solvents. 2-methyltetrahydrofuran acts as the "low-temperature skeleton solvent" of the system, dominating the low freezing point and high conductivity characteristics of the mixed solvent and reducing the overall viscosity. 3-fluorotetrahydrofuran and 1,3-dioxolane help prevent viscosity increases caused by agglomeration. The synergistic effect of the three cyclic ether solvents is far superior to that of a single solvent or a binary mixture system, ultimately achieving the core low-temperature performance of low freezing point, low viscosity, and high conductivity. This invention uses three cyclic ether solvents as the composite solvent of the electrolyte, fundamentally solving the problems of solidification and ion transport obstruction at low temperatures in traditional electrolytes through complementary molecular structures and synergistic properties. In addition, lithium difluorophosphate and lithium difluorooxalate phosphate, which have good low-temperature performance, are also added to the electrolyte as additives. The electrolyte designed using this composite low-temperature cyclic ether solvent and low-temperature additive system exhibits high conductivity, low viscosity, and a low freezing point, resulting in a freezing point as low as -70°C. The resulting lithium primary battery retains ≥55% of its discharge capacity at -60°C, effectively meeting the application requirements of lithium primary batteries in ultra-low temperature environments. In other words, the lithium battery of this invention possesses excellent discharge performance at ultra-low temperatures. Detailed Implementation

[0014] The main objective of this invention is to leverage the excellent conductivity and electrochemical stability of the lithium salt combination of lithium bis(trifluoromethanesulfonyl)imide and lithium perchlorate in the electrolyte, and to improve the ultra-low temperature discharge performance of lithium primary batteries by adding various cyclic ether solvents to the electrolyte, specifically a composite solvent of 2-methyltetrahydrofuran, 3-fluorotetrahydrofuran, and 1,3-dioxolane. The invention is further detailed below with reference to specific examples. The content mentioned in these examples is not intended to limit the invention, and the selection of raw materials can be tailored to local conditions without substantially affecting the results.

[0015] Example 1 Preparation of lithium primary battery electrolyte: Under an inert gas protective atmosphere, lithium salt, solvent, and additives are mixed and stirred uniformly to prepare the lithium primary battery electrolyte. The electrolyte contains 8 wt% lithium bis(trifluoromethanesulfonyl)imide, 2 wt% lithium perchlorate, 53 wt% 2-methyltetrahydrofuran, 18 wt% 3-fluorotetrahydrofuran, 18 wt% 1,3-dioxolane, 0.3 wt% lithium difluorooxalateborate, and 0.7 wt% lithium difluorophosphate.

[0016] Preparation of lithium-manganese dioxide soft-pack battery: Vacuum-dried manganese dioxide positive electrode sheet, separator, and lithium metal negative electrode sheet are aligned and wound into bare cells in sequence. The top and sides of the bare cells are sealed with an aluminum-plastic film shell after being perforated. After partial encapsulation, electrolyte is injected and vacuum pre-sealed. After the first pre-discharge, the battery is aged and the edges are cut. The assembly of CF332544 lithium-manganese dioxide soft-pack battery is completed by a second pre-discharge.

[0017] Example 2 Preparation of lithium primary battery electrolyte: Under an inert gas protective atmosphere, lithium salt, solvent, and additives are mixed and stirred uniformly to prepare the lithium primary battery electrolyte. The electrolyte contains 8 wt% lithium bis(trifluoromethanesulfonyl)imide, 2 wt% lithium perchlorate, 53 wt% 2-methyltetrahydrofuran, 18 wt% 3-fluorotetrahydrofuran, 18 wt% 1,3-dioxolane, 0.5 wt% lithium difluorooxalateborate, and 0.5 wt% lithium difluorophosphate.

[0018] The CF332544 type lithium-manganese dioxide soft-pack battery was prepared according to the method described in Example 1.

[0019] Example 3 Preparation of lithium primary battery electrolyte: Under an inert gas protective atmosphere, lithium salt, solvent, and additives are mixed and stirred uniformly to prepare the lithium primary battery electrolyte. The electrolyte contains 8 wt% lithium bis(trifluoromethanesulfonyl)imide, 2 wt% lithium perchlorate, 53 wt% 2-methyltetrahydrofuran, 18 wt% 3-fluorotetrahydrofuran, 18 wt% 1,3-dioxolane, 0.7 wt% lithium difluorooxalateborate, and 0.3 wt% lithium difluorophosphate.

[0020] The CF332544 type lithium-manganese dioxide soft-pack battery was prepared according to the method described in Example 1.

[0021] Example 4 Preparation of lithium primary battery electrolyte: Under an inert gas protective atmosphere, lithium salt, solvent, and additives are mixed and stirred uniformly to prepare the lithium primary battery electrolyte. The electrolyte contains 8 wt% lithium bis(trifluoromethanesulfonyl)imide, 2 wt% lithium perchlorate, 49 wt% 2-methyltetrahydrofuran, 20 wt% 3-fluorotetrahydrofuran, 20 wt% 1,3-dioxolane, 0.3 wt% lithium difluorooxalateborate, and 0.7 wt% lithium difluorophosphate.

[0022] The CF332544 type lithium-manganese dioxide soft-pack battery was prepared according to the method described in Example 1.

[0023] Example 5 Preparation of lithium primary battery electrolyte: Under an inert gas protective atmosphere, lithium salt, solvent, and additives are mixed and stirred uniformly to prepare the lithium primary battery electrolyte. The electrolyte contains 8 wt% lithium bis(trifluoromethanesulfonyl)imide, 2 wt% lithium perchlorate, 49 wt% 2-methyltetrahydrofuran, 20 wt% 3-fluorotetrahydrofuran, 20 wt% 1,3-dioxolane, 0.5 wt% lithium difluorooxalateborate, and 0.5 wt% lithium difluorophosphate.

[0024] The CF332544 type lithium-manganese dioxide soft-pack battery was prepared according to the method described in Example 1.

[0025] Example 6 Preparation of lithium primary battery electrolyte: Under an inert gas protective atmosphere, lithium salt, solvent, and additives are mixed and stirred uniformly to prepare the lithium primary battery electrolyte. The electrolyte contains 8 wt% lithium bis(trifluoromethanesulfonyl)imide, 2 wt% lithium perchlorate, 49 wt% 2-methyltetrahydrofuran, 20 wt% 3-fluorotetrahydrofuran, 20 wt% 1,3-dioxolane, 0.7 wt% lithium difluorooxalateborate, and 0.3 wt% lithium difluorophosphate.

[0026] The CF332544 type lithium-manganese dioxide soft-pack battery was prepared according to the method described in Example 1.

[0027] Example 7 Preparation of lithium primary battery electrolyte: Under an inert gas protective atmosphere, lithium salt, solvent, and additives are mixed and stirred uniformly to prepare the lithium primary battery electrolyte. The electrolyte contains 8 wt% lithium bis(trifluoromethanesulfonyl)imide, 2 wt% lithium perchlorate, 43 wt% 2-methyltetrahydrofuran, 23 wt% 3-fluorotetrahydrofuran, 23 wt% 1,3-dioxolane, 0.3 wt% lithium difluorooxalateborate, and 0.7 wt% lithium difluorophosphate.

[0028] The CF332544 type lithium-manganese dioxide soft-pack battery was prepared according to the method described in Example 1.

[0029] Example 8 Preparation of lithium primary battery electrolyte: Under an inert gas protective atmosphere, lithium salt, solvent, and additives are mixed and stirred uniformly to prepare the lithium primary battery electrolyte. The electrolyte contains 8 wt% lithium bis(trifluoromethanesulfonyl)imide, 2 wt% lithium perchlorate, 43 wt% 2-methyltetrahydrofuran, 23 wt% 3-fluorotetrahydrofuran, 23 wt% 1,3-dioxolane, 0.5 wt% lithium difluorooxalateborate, and 0.5 wt% lithium difluorophosphate.

[0030] The CF332544 type lithium-manganese dioxide soft-pack battery was prepared according to the method described in Example 1.

[0031] Example 9 Preparation of lithium primary battery electrolyte: Under an inert gas protective atmosphere, lithium salt, solvent, and additives are mixed and stirred uniformly to prepare the lithium primary battery electrolyte. The electrolyte contains 8 wt% lithium bis(trifluoromethanesulfonyl)imide, 2 wt% lithium perchlorate, 43 wt% 2-methyltetrahydrofuran, 23 wt% 3-fluorotetrahydrofuran, 23 wt% 1,3-dioxolane, 0.7 wt% lithium difluorooxalateborate, and 0.3 wt% lithium difluorophosphate.

[0032] The CF332544 type lithium-manganese dioxide soft-pack battery was prepared according to the method described in Example 1.

[0033] Example 10: Preparation of lithium primary battery electrolyte: Under an inert gas protective atmosphere, lithium salt, solvent, and additives are mixed and stirred uniformly to prepare the lithium primary battery electrolyte. The electrolyte contains: lithium bis(trifluoromethanesulfonyl)imide at 10 wt%, lithium perchlorate at 2 wt%, 2-methyltetrahydrofuran at 49 wt%, 3-fluorotetrahydrofuran at 19 wt%, 1,3-dioxolane at 19 wt%, lithium difluorooxalateborate at 0.7 wt%, and lithium difluorophosphate at 0.3 wt%.

[0034] The CF332544 type lithium-manganese dioxide soft-pack battery was prepared according to the method described in Example 1.

[0035] Example 11 Preparation of lithium primary battery electrolyte: Under an inert gas protective atmosphere, lithium salt, solvent, and additives are mixed and stirred uniformly to prepare the lithium primary battery electrolyte. The electrolyte contains 10 wt% lithium bis(trifluoromethanesulfonyl)imide, 2 wt% lithium perchlorate, 43 wt% 2-methyltetrahydrofuran, 22 wt% 3-fluorotetrahydrofuran, 22 wt% 1,3-dioxolane, 0.7 wt% lithium difluorooxalateborate, and 0.3 wt% lithium difluorophosphate.

[0036] The CF332544 type lithium-manganese dioxide soft-pack battery was prepared according to the method described in Example 1.

[0037] Comparative Example 1 Preparation of lithium primary battery electrolyte: Under an inert gas protective atmosphere, lithium salt, solvent, and additives are mixed and stirred uniformly to prepare the lithium primary battery electrolyte. The electrolyte contains 8 wt% lithium bis(trifluoromethanesulfonyl)imide, 2 wt% lithium perchlorate, 89 wt% 2-methyltetrahydrofuran, 0.5 wt% lithium difluorooxalateborate, and 0.5 wt% lithium difluorophosphate.

[0038] The CF332544 type lithium-manganese dioxide soft-pack battery was prepared according to the method described in Example 1.

[0039] Comparative Example 2 Preparation of lithium primary battery electrolyte: Under an inert gas protective atmosphere, lithium salt, solvent, and additives are mixed and stirred uniformly to prepare the lithium primary battery electrolyte. The electrolyte contains 8 wt% lithium bis(trifluoromethanesulfonyl)imide, 2 wt% lithium perchlorate, 89 wt% 3-fluorotetrahydrofuran, 0.5 wt% lithium difluorooxalateborate, and 0.5 wt% lithium difluorophosphate.

[0040] The CF332544 type lithium-manganese dioxide soft-pack battery was prepared according to the method described in Example 1.

[0041] Comparative Example 3 Preparation of lithium primary battery electrolyte: Under an inert gas protective atmosphere, lithium salt, solvent, and additives are mixed and stirred uniformly to prepare the lithium primary battery electrolyte. The electrolyte contains 8 wt% lithium bis(trifluoromethanesulfonyl)imide, 2 wt% lithium perchlorate, 89 wt% 1,3-dioxolane, 0.5 wt% lithium difluorooxalateborate, and 0.5 wt% lithium difluorophosphate.

[0042] The CF332544 type lithium-manganese dioxide soft-pack battery was prepared according to the method described in Example 1.

[0043] The difference between Comparative Examples 1-3 and Examples 1-11 is that the electrolyte of Comparative Example 1 does not contain 3-fluorotetrahydrofuran and 1,3-dioxolane; the electrolyte of Comparative Example 2 does not contain 2-methyltetrahydrofuran and 1,3-dioxolane; and the electrolyte of Comparative Example 3 does not contain 2-methyltetrahydrofuran and 3-fluorotetrahydrofuran.

[0044] The discharge performance of batteries prepared with different electrolytes in Examples 1-11 and Comparative Examples 1-3 was tested, and the test results are shown in Table 1: Table 1: Comparison of constant current discharge capacity of CF332544 lithium-manganese dioxide soft-pack battery at different temperatures

[0045] By comparing the constant current discharge performance at different temperatures of Examples 1-11 and Comparative Examples 1-3 in Table 1, it was found that the ultra-low temperature discharge performance of the lithium-manganese dioxide soft-pack battery using the electrolyte of the present invention was enhanced, indicating that the electrolyte of this embodiment can effectively improve the ultra-low temperature discharge performance of the lithium-manganese dioxide soft-pack battery.

[0046] The embodiments described above are merely preferred implementations of the present invention and are not intended to limit the scope of the present invention. Any obvious modifications and substitutions made without departing from the concept of the present invention are within the protection scope of the present invention.

Claims

1. An ultra-low temperature lithium primary battery electrolyte, comprising lithium salt, composite solvent and additives, characterized in that: The composite solvent is composed of a mixture of 2-methyltetrahydrofuran, 3-fluorotetrahydrofuran and 1,3-dioxolane.

2. The ultra-low temperature lithium primary battery electrolyte according to claim 1, characterized in that: The lithium salt content accounts for 8-12 wt% of the total mass of the lithium primary battery electrolyte, the composite solvent content accounts for 80-90 wt% of the total mass of the lithium primary battery electrolyte, and the additive content accounts for 1-2 wt% of the total mass of the lithium primary battery electrolyte. The sum of the mass percentages of all substances is 100%.

3. The ultra-low temperature lithium primary battery electrolyte according to claim 2, characterized in that: In the composite solvent, the mass ratio of 2-methyltetrahydrofuran, 3-fluorotetrahydrofuran, and 1,3-dioxolane is 2:1:1 to 4:1:

1.

4. The ultra-low temperature lithium primary battery electrolyte according to claim 3, characterized in that: The lithium salt is a compound system of lithium bis(trifluoromethanesulfonylimide) and lithium perchlorate.

5. The ultra-low temperature lithium primary battery electrolyte according to claim 4, characterized in that: In lithium salts, the mass ratio of lithium bis(trifluoromethanesulfonyl)imide to lithium perchlorate is 4:1 to 5:

1.

6. The ultra-low temperature lithium primary battery electrolyte according to claim 5, characterized in that: The additive is a mixture of lithium difluorooxalate borate and lithium difluorophosphate.

7. The ultra-low temperature lithium primary battery electrolyte according to claim 6, characterized in that: In the additive, the mass ratio of lithium difluorooxalate borate to lithium difluorophosphate is 1:4 to 3:

1.

8. The ultra-low temperature lithium primary battery electrolyte according to any one of claims 1-7, characterized in that: It is obtained by mixing lithium salt, solvent and additives under an inert gas protective atmosphere and then stirring evenly.

9. A primary lithium battery, characterized in that: It includes the lithium primary battery electrolyte as described in claim 8.

10. The lithium primary battery according to claim 9, characterized in that: The primary lithium battery is any one of lithium-carbon fluoride battery, lithium-iron disulfide battery, and lithium-manganese dioxide battery.

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