Low-temperature electrolyte applied to lithium-manganese dioxide battery and preparation method thereof

Abstract

The application relates to a low-temperature electrolyte applied to a lithium-manganese dioxide battery and a preparation method, wherein firstly, lithium bisfluorosulfonylimide (LiFSI) solutions are prepared by taking diethyl ether and methyl formate as solvents respectively, then the diethyl ether solution of lithium bisfluorosulfonylimide (LiFSI) and the methyl formate solution of lithium bisfluorosulfonylimide (LiFSI) are mixed in proportion to obtain the low-temperature electrolyte. The low-temperature electrolyte has a low melting point, can avoid phase change under low-temperature conditions, and can also maintain good fluidity under low-temperature conditions; after being injected into a lithium-manganese dioxide battery, the battery has higher discharge specific energy, lower interface impedance and charge transfer impedance in a low-temperature environment; the low-temperature electrolyte can improve the low-temperature performance of the lithium-manganese dioxide battery; and the low-temperature electrolyte preparation method is simple, the preparation conditions are easy to meet, and the method is easy for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of lithium primary battery technology, and in particular relates to a low-temperature electrolyte for use in lithium manganese dioxide batteries and its preparation method. Background Technology

[0002] Lithium-manganese dioxide batteries have become a widely used battery system in lithium primary battery systems due to their advantages of high specific energy and low cost. However, due to their poor electronic conductivity and the reaction type of conversion reaction, their reaction kinetics are poor, and they will suffer from severe voltage hysteresis and capacity decay under low temperature conditions.

[0003] For lithium-manganese dioxide batteries, reaction kinetics mainly include ion transport, electron transport, and the breaking and reforming of chemical bonds. Current low-temperature electrolyte designs generally improve the bulk transport rate during ion transport by increasing ionic conductivity. However, higher ionic conductivity often corresponds to a higher desolvation energy barrier, making the desolvation process difficult. At low temperatures, the desolvation energy barrier dominates the ion transport process, resulting in current low-temperature electrolytes having a limited effect on improving the low-temperature performance of lithium-manganese dioxide batteries. However, by introducing diethyl ether and methyl formate, which have low dielectric constants and small molecular structures, into the electrolyte system, the desolvation energy barrier can be effectively reduced while maintaining appropriate bulk conductivity, thereby significantly improving the low-temperature performance of lithium-manganese dioxide batteries. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a low-temperature electrolyte for lithium manganese dioxide batteries and its preparation method.

[0005] The technical solution adopted in this invention is: a method for preparing a low-temperature electrolyte for lithium manganese dioxide batteries, wherein lithium bis(fluorosulfonyl)imide is dissolved in a mixed solvent of diethyl ether and methyl formate to form a low-temperature electrolyte.

[0006] Preferably, the specific preparation method is as follows:

[0007] Step 1: Dissolve lithium bis(fluorosulfonyl)imide (LiFSI) in diethyl ether (Me2O). The concentration range of LiFSI is 2-3.5M. After complete dissolution, solution 1 is obtained.

[0008] Lithium bis(fluorosulfonyl)imide (LiFSI) was dissolved in methyl formate (MF) at a concentration of 1-2.5 M. After complete dissolution, solution two was obtained.

[0009] Step 2: Mix solution 1 and solution 2 and stir thoroughly to obtain a low-temperature electrolyte.

[0010] Preferably, the volume ratio of solution one to solution two is 6-1:1.

[0011] Preferably, when preparing solution one, a magnetic stirrer is used to stir at a speed of 300-500 r / min for 0.6-1.2 h; when preparing solution two, a magnetic stirrer is used to stir at a speed of 500-700 r / min for 0.5-1 h; when mixing solution one and solution two, the magnetic stirrer speed is 300-500 r / min and the stirring time is 0.3-1 h.

[0012] Preferably, the preparation process is carried out in a glove box, where both the oxygen concentration and water concentration are less than 0.01 ppm.

[0013] The low-temperature electrolyte was prepared by a method for preparing low-temperature electrolytes for lithium manganese dioxide batteries.

[0014] A lithium manganese dioxide battery, comprising a low-temperature electrolyte.

[0015] The advantages and positive effects of this invention are: the low-temperature electrolyte has a low melting point, which can avoid phase change under low-temperature conditions and maintain good fluidity under low-temperature conditions; after being injected into a lithium-manganese dioxide battery, the battery has a higher discharge specific energy and lower interfacial impedance and charge transfer impedance in a low-temperature environment; the low-temperature electrolyte can improve the low-temperature performance of lithium-manganese dioxide batteries; and the preparation method of the low-temperature electrolyte is simple, the preparation conditions are easy to meet, and it is easy to industrially produce. Attached Figure Description

[0016] Figure 1 The electrolyte prepared in Example 1 was in the following states at 55°C and -55°C.

[0017] Figure 2 Discharge curve of lithium manganese dioxide battery at 35℃;

[0018] Figure 3 Discharge curve of lithium manganese dioxide battery at -55℃;

[0019] Figure 4 EIS curve of lithium manganese dioxide battery;

[0020] Figure 5 DRT curve of lithium manganese dioxide battery;

[0021] Figure 6 A schematic diagram of the ion transport mechanism in low-temperature electrolytes. Detailed Implementation

[0022] The embodiments of the present invention will now be described with reference to the accompanying drawings.

[0023] This invention relates to a low-temperature electrolyte for lithium-manganese dioxide batteries and its preparation method. By introducing diethyl ether and methyl formate, which have low dielectric constants and small molecular structures, into the electrolyte, the desolvation energy barrier of lithium ions is lowered, thereby improving the low-temperature performance of the lithium-manganese dioxide battery. In the preparation process, firstly, lithium bis(fluorosulfonyl)imide (LiFSI) solutions are prepared using diethyl ether and methyl formate as solvents, respectively. Then, the diethyl ether solution and the methyl formate solution of lithium bis(fluorosulfonyl)imide (LiFSI) are mixed in a specific ratio to obtain the low-temperature electrolyte. The ion transport mechanism of the low-temperature electrolyte is between solvent diffusion transport and structure transport, exhibiting a low desolvation energy barrier. The ion transport mechanism is as follows: Figure 6 As shown, the positively charged sphere in the figure is Li. + The negatively charged spheres are anions, the other small spheres inside the white circle are solvent molecules in the first solvation sheath, and the small spheres outside the white circle are solvent molecules in the second solvation sheath. The interaction between the solvent molecules in the second solvation sheath and lithium ions can promote the dissociation of lithium ions from the solvent molecules and anions in the first solvation sheath, thereby promoting the bulk transport of lithium ions.

[0024] The specific preparation method of the low-temperature electrolyte is as follows:

[0025] Step 1: Dissolve lithium bis(fluorosulfonyl)imide (LiFSI) in diethyl ether (Me2O). The concentration of LiFSI should be in the range of 2-3.5M. Stir thoroughly to ensure complete dissolution. You can use a magnetic stirrer to stir at a speed of 300-500 r / min for 0.6-1.2 h until the lithium salt is completely dissolved and the solution is clear and transparent to obtain Solution 1.

[0026] Lithium bis(fluorosulfonyl)imide (LiFSI) is dissolved in methyl formate (MF) with a concentration range of 1-2.5M. The mixture is stirred thoroughly, using a magnetic stirrer at a speed of 500-700 r / min for 0.5-1 h, until the solution becomes clear and transparent, thus obtaining solution two.

[0027] Step 2: Mix solution 1 and solution 2 and stir thoroughly. The volume ratio of solution 1 to solution 2 is 6:1 to 1:1. A magnetic stirrer can be used for stirring at a speed of 300-500 r / min for 0.3-1 h until the solution is clear and transparent without any layering. The final product is a low-temperature electrolyte.

[0028] The above preparation process needs to be carried out in a glove box, with both oxygen and water concentrations less than 0.01 ppm. The resulting low-temperature electrolyte exhibits high bulk conductivity and a low desolvation energy barrier under low-temperature conditions.

[0029] By selecting diethyl ether and methyl formate, which have low dielectric constants and small molecular structures, as the main solvents of the electrolyte, a low melting point is ensured, thus avoiding phase transitions at low temperatures. Simultaneously, the high lithium salt concentration ensures a relatively stable solvation structure for lithium ions over a wide temperature range. The small molecular structure of the solvent allows solvent molecules in the second solvation sheath to exert an inductive effect on lithium ions, thereby lowering the desolvation energy barrier and consequently reducing the energy barrier during bulk transport, ultimately improving the bulk conductivity of lithium ions over a wide temperature range. The low desolvation energy barrier also facilitates lithium ion transport at the solid-liquid interface, significantly improving the battery's low-temperature performance. The selected lithium salt, LiFSI, has a high degree of dissociation, thus maintaining high conductivity even in solvents with low dielectric constants. Furthermore, the high lithium salt concentration further increases the concentration of anions in the solvation sheath, thereby enhancing the inorganic component content in the interfacial layer during chemical film formation, improving interfacial stability and reducing interfacial impedance.

[0030] The present invention will now be described with reference to the accompanying drawings. Experimental methods not specifically described in terms of operation steps are performed in accordance with the corresponding product manuals. Unless otherwise specified, the instruments, reagents, and consumables used in the embodiments can be purchased from commercial companies.

[0031] Comparative Example

[0032] LiCLO4 was dissolved in a mixed solvent of PC, DOL and DME in a volume ratio of 2:5:4, and the concentration of LiCLO4 in the mixed solvent was 0.75M to prepare an electrolyte.

[0033] Example 1

[0034] Lithium difluorosulfonylimide (LiFSI) was dissolved in diethyl ether (Me₂O) at a concentration of 3.5 M. The solution was stirred with a magnetic stirrer at 300 rpm for 1.2 h to ensure complete dissolution and prepare solution one. Lithium difluorosulfonylimide (LiFSI) was dissolved in methyl formate (MF) at a concentration of 2.5 M. The solution was stirred with a magnetic stirrer at 500 rpm for 1 h until the solution became clear and transparent to prepare solution two. Solutions one and two were mixed at a volume ratio of 1:1 and stirred with a magnetic stirrer at 500 rpm for 0.3 h until the solution became clear and transparent to obtain the low-temperature electrolyte. The low-temperature electrolyte remained liquid at both 55 °C and -55 °C and exhibited good fluidity. Figure 1 As shown, this illustrates that it has a wide operating temperature range.

[0035] The electrolytes prepared in Example 1 and the comparative example were injected into lithium manganese dioxide batteries, and the battery performance was tested. The discharge specific energy was tested at 35°C, and the results are as follows: Figure 2 As shown, the battery injected with the electrolyte prepared in Example 1 has a discharge specific energy that is almost identical to that of the comparative example. The electrolyte prepared in Example 1 has a lower desolvation energy barrier, which can reduce the polarization effect during discharge, thereby increasing the discharge voltage and discharge specific energy of the battery.

[0036] The discharge specific energy was tested again at -55℃, and the results are as follows: Figure 3 As shown, the electrolyte prepared in Example 1, when injected into a lithium manganese dioxide battery, exhibits a higher discharge specific energy at -55°C, demonstrating a significant improvement in battery performance. This is mainly due to the synergistic effect of several factors. Firstly, the low melting points and dielectric constants of diethyl ether and methyl formate ensure that the electrolyte remains liquid and has low viscosity at low temperatures. Secondly, the high lithium salt concentration in the electrolyte ensures that the lithium-ion solvation structure remains relatively stable at low temperatures, without significant changes. Simultaneously, the small molecular structure of diethyl ether and methyl formate allows the solvent molecules in the second solvation sheath to lower the desolvation barrier of lithium ions through an inductive effect, thereby increasing the bulk conductivity of lithium ions and reducing their charge transfer impedance. Furthermore, the high lithium salt concentration increases the concentration of anions in the electrolyte, thereby increasing the content of inorganic components in the chemical film formation process and reducing interfacial transport impedance.

[0037] EIS impedance analysis and DRT impedance analysis were performed on the lithium manganese dioxide batteries prepared in Example 1 and the comparative example, respectively. The results are as follows: Figure 4 and Figure 5 As shown, the lithium-manganese dioxide battery injected with the electrolyte prepared in Example 1 has lower interfacial impedance and charge transfer impedance, mainly due to the lower interfacial transport impedance and lower desolvation energy barrier of the electrolyte prepared in Example 1.

[0038] Example 2

[0039] Lithium bis(fluorosulfonyl)imide (LiFSI) was dissolved in diethyl ether (Me₂O) at a concentration of 2M. The solution was stirred with a magnetic stirrer at 500 rpm for 0.6 h to ensure complete dissolution, yielding solution one. Lithium bis(fluorosulfonyl)imide (LiFSI) was then dissolved in methyl formate (MF) at a concentration of 1M. The solution was stirred with a magnetic stirrer at 700 rpm for 0.5 h until the solution became clear and transparent, yielding solution two. Solutions one and two were mixed at a volume ratio of 6:1 and stirred thoroughly with a magnetic stirrer at 300 rpm for 1 h until the solution became clear and transparent, yielding the low-temperature electrolyte.

[0040] Example 3

[0041] Lithium bis(fluorosulfonyl)imide (LiFSI) was dissolved in diethyl ether (Me₂O) at a concentration of 3 M. The solution was stirred with a magnetic stirrer at 400 rpm for 0.8 h to ensure complete dissolution, yielding solution one. Lithium bis(fluorosulfonyl)imide (LiFSI) was then dissolved in methyl formate (MF) at a concentration of 1.5 M. The solution was stirred with a magnetic stirrer at 600 rpm for 1 h until the solution became clear and transparent, yielding solution two. Solutions one and two were mixed at a product ratio of 4:1 and stirred thoroughly with a magnetic stirrer at 400 rpm for 0.5 h until the solution became clear and transparent, yielding the low-temperature electrolyte.

[0042] The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A method for preparing a low-temperature electrolyte for use in lithium manganese dioxide batteries, characterized in that: Difluorosulfonylimide lithium is dissolved in a mixed solvent of diethyl ether and methyl formate to form a low-temperature electrolyte.

2. The method for preparing a low temperature electrolyte for use in lithium-manganese dioxide batteries according to claim 1, characterized in that: The specific preparation method is as follows: Step one: Difluorosulfonylimide lithium is dissolved in diethyl ether, and the concentration of difluorosulfonylimide lithium ranges from 2 to 3.5 M. After sufficient dissolution, solution one is obtained; Difluorosulfonylimide lithium is dissolved in methyl formate, and the concentration of difluorosulfonylimide lithium ranges from 1 to 2.5 M. After sufficient dissolution, solution two is obtained; Step two: Solution one and solution two are mixed and fully stirred to obtain a low-temperature electrolyte.

3. The method for preparing a low temperature electrolyte for use in lithium-manganese dioxide batteries according to claim 2, characterized in that: The volume ratio of solution one to solution two is 6-1:

1.

4. The method for preparing a low temperature electrolyte for use in lithium-manganese dioxide batteries according to claim 2, characterized in that: When preparing solution one, a magnetic stirrer is used to stir at a speed of 300-500 r / min for 0.6-1.2 h; when preparing solution two, a magnetic stirrer is used to stir at a speed of 500-700 r / min for 0.5-1 h; when mixing solution one and solution two, a magnetic stirrer is used to stir at a speed of 300-500 r / min for 0.3-1 h.

5. The method for preparing a low temperature electrolyte for lithium-manganese dioxide batteries according to any one of claims 1 to 4, characterized in that: The preparation process is carried out in a glove box, and the oxygen concentration and water concentration are both less than 0.01 ppm.

6. The low-temperature electrolyte prepared by the preparation method of the low-temperature electrolyte for lithium-manganese dioxide batteries according to any one of claims 1-5.

7. A lithium-manganese dioxide battery characterized by: The low-temperature electrolyte according to claim 6.

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