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

Abstract

The invention relates to a low-temperature electrolyte applied to a lithium manganese dioxide battery and a preparation method of the low-temperature electrolyte, firstly, diethyl ether and methyl formate are respectively used as solvents to prepare a lithium bis (fluorosulfonyl) imide (LiFSI) solution, and then the diethyl ether solution of the lithium bis (fluorosulfonyl) imide (LiFSI) and the methyl formate solution of the lithium bis (fluorosulfonyl) imide (LiFSI) are mixed in proportion to obtain the low-temperature electrolyte. The low-temperature electrolyte has a relatively low melting point, can avoid phase change under a low-temperature condition, and also can keep good fluidity under the low-temperature condition; after the material is injected into a lithium-manganese dioxide battery, the battery has higher discharge specific energy and 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; moreover, the preparation method of the low-temperature electrolyte is simple, preparation conditions are easy to meet, and industrial production is easy.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium primary batteries, and in particular relates to a low-temperature electrolyte used in lithium manganese dioxide batteries and a preparation method thereof. Background Art

[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 own poor electronic conductivity and the reaction type of conversion reaction, their reaction kinetics are poor, and there will be serious voltage hysteresis and capacity decay under low temperature conditions.

[0003] For lithium-manganese dioxide batteries, the reaction kinetics mainly include ion transfer process, electron transfer process and chemical bond breakage and recombination process. The current low-temperature electrolyte design generally adopts the method of improving ion conductivity to improve the bulk transfer rate in the ion transfer process. However, higher ion conductivity often corresponds to a high desolvation energy barrier, which makes the desolvation process of ions difficult. Under low temperature conditions, the desolvation energy barrier of ions plays a dominant role in the ion transfer process, which makes the current low-temperature electrolyte poor in improving the low-temperature performance of lithium-manganese dioxide batteries. By introducing ether and methyl formate with lower dielectric constant and small molecular structure into the electrolyte system, the desolvation energy barrier of the electrolyte can be effectively reduced on the basis of ensuring the appropriate bulk conductivity of the electrolyte, thereby significantly improving the low-temperature performance of lithium-manganese dioxide batteries. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a low-temperature electrolyte for lithium manganese dioxide battery and a preparation method thereof.

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

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

[0007] Step 1: dissolving lithium bis(fluorosulfonyl)imide (LiFSI) in diethyl ether (Me2O), wherein the concentration of LiFSI is in the range of 2-3.5 M, and obtaining solution 1 after full dissolution;

[0008] Dissolving lithium bis(fluorosulfonyl)imide (LiFSI) in methyl formate (MF), wherein the concentration of LiFSI is in the range of 1-2.5 M, and obtaining solution 2 after full dissolution;

[0009] Step 2: Mix solution 1 and solution 2 and stir them 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 at a speed of 300-500 r / min for 0.6-1.2 h; when preparing solution two, a magnetic stirrer is used at a speed of 500-700 r / min for 0.5-1 h; when mixing solution one and solution two, the speed of the magnetic stirrer 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, and the oxygen concentration and water concentration are both less than 0.01 ppm.

[0013] The low-temperature electrolyte is prepared by a preparation method of a low-temperature electrolyte applied to lithium manganese dioxide batteries.

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

[0015] The advantages and positive effects of the present invention are: the low-temperature electrolyte has a lower melting point, can avoid phase change under low-temperature conditions, and can maintain good fluidity under low-temperature conditions; after injecting it into a lithium-manganese dioxide battery, in a low-temperature environment, the battery has a higher discharge specific energy, lower interface impedance and charge transfer impedance; the low-temperature electrolyte can improve the low-temperature performance of the lithium-manganese dioxide battery; 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The electrolyte prepared in Example 1 is in the state 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 Mechanistic diagram of ion transport in low-temperature electrolytes. DETAILED DESCRIPTION

[0022] The embodiments of the present invention are described below with reference to the accompanying drawings.

[0023] The present invention relates to a low-temperature electrolyte for lithium manganese dioxide batteries and a preparation method thereof. The desolvation energy barrier of lithium ions is reduced by introducing diethyl ether and methyl formate with a relatively low dielectric constant and a small molecular structure into the electrolyte, thereby improving the low-temperature performance of the lithium-manganese dioxide battery. During the preparation, firstly, diethyl ether and methyl formate are used as solvents to prepare a lithium bis(fluorosulfonyl)imide (LiFSI) solution, and then the diethyl ether solution of lithium bis(fluorosulfonyl)imide (LiFSI) and the methyl formate solution of lithium bis(fluorosulfonyl)imide (LiFSI) are mixed in proportion to obtain a low-temperature electrolyte. The ion transport mode of the low-temperature electrolyte is between solvent diffusion transport and structural transport, and has a relatively low desolvation energy barrier. The mechanism of ion transport 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 in 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 the 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: dissolving lithium bis(fluorosulfonyl)imide (LiFSI) in diethyl ether (Me2O), wherein the concentration of LiFSI is in the range of 2-3.5 M, and stirring the mixture sufficiently to dissolve the mixture. A magnetic stirrer may be used to stir the mixture 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, thereby obtaining solution 1.

[0026] Dissolve lithium bis(fluorosulfonyl)imide (LiFSI) in methyl formate (MF), wherein the concentration of LiFSI is 1-2.5 M, stir thoroughly, and use a magnetic stirrer at a speed of 500-700 r / min for 0.5-1 h until the solution becomes clear and transparent, to obtain solution 2;

[0027] Step 2: Mix solution 1 and solution 2 and stir them fully, the volume ratio is 6:1-1:1, and a magnetic bar can be used for stirring, the speed of the magnetic bar is 300-500r / min, and the stirring time is 0.3-1h, until the solution has no stratification phenomenon and is clear and transparent; finally, a low-temperature electrolyte is obtained;

[0028] The above preparation process needs to be carried out in a glove box, and the oxygen concentration and water concentration are both less than 0.01 ppm. The prepared low-temperature electrolyte has a higher bulk conductivity and a lower desolvation energy barrier under low temperature conditions.

[0029] By selecting ether and methyl formate with low dielectric constant and small molecular structure as the main solvent of the electrolyte, the electrolyte is ensured to have a low melting point, thereby avoiding phase change under low temperature conditions; at the same time, the high lithium salt concentration ensures a relatively stable solvation structure of lithium ions under wide temperature conditions, and the small molecular structure of the solvent enables the solvent molecules in the second solvation sheath to have an inductive effect on lithium ions, thereby reducing the desolvation energy barrier of lithium ions, thereby reducing the energy barrier in the bulk phase transmission process, and finally improving the bulk conductivity of lithium ions under wide temperature conditions; at the same time, the low desolvation energy barrier is also conducive to the transmission of lithium ions at the solid-liquid interface, thereby significantly improving the low-temperature performance of the battery. The selected lithium salt LiFSI has a high degree of dissociation, so it can still maintain a high conductivity in a solvent with a low dielectric constant. At the same time, the high lithium salt concentration further increases the concentration of anions in the solvation sheath, thereby enhancing the content of inorganic components in the interface layer in chemical film formation, thereby improving the stability of the interface and reducing the interface impedance.

[0030] The scheme of the present invention is described below in conjunction with the accompanying drawings, wherein the experimental methods without specific operating steps are all carried out in accordance with the corresponding product instructions, and the instruments, reagents, and consumables used in the examples can all be purchased from commercial companies unless otherwise specified.

[0031] Comparative Example

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

[0033] Example 1

[0034] Dissolve lithium bis(fluorosulfonyl)imide (LiFSI) in diethyl ether (Me2O) with a LiFSI concentration of 3.5M. Stir with a magnetic particle at a speed of 300r / min for 1.2h and stir thoroughly to fully dissolve it to prepare solution 1. Dissolve lithium bis(fluorosulfonyl)imide (LiFSI) in methyl formate (MF) with a LiFSI concentration of 2.5M. Stir with a magnetic particle at a speed of 500r / min and a stirring time of 1h until the solution becomes clear and transparent to prepare solution 2. Mix solution 1 and solution 2 in a volume ratio of 1:1 and stir thoroughly with a magnetic particle at a speed of 500r / min and a stirring time of 0.3h until the solution becomes clear and transparent to obtain a low-temperature electrolyte. The low-temperature electrolyte is liquid at 55°C and -55°C and has good fluidity, such as Figure 1 As shown, it has a wide application 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. The results are as follows: Figure 2 As shown, the discharge specific energy of the battery injected with the electrolyte prepared in Example 1 is almost the same as that of the comparative example. The electrolyte prepared in Example 1 has a lower desolvation energy barrier, so it can reduce the polarization effect during the discharge process, thereby increasing the discharge voltage and discharge specific energy of the battery.

[0036] Then test the discharge specific energy under -55℃ condition, the result is as follows Figure 3 As shown, it can be seen that the electrolyte prepared in Example 1 has a higher discharge specific energy after being injected into the lithium manganese dioxide battery and discharged at -55°C, which shows that its battery performance has been significantly improved. This is mainly due to the synergistic effect of several aspects. First, the lower melting point and dielectric constant of ether and methyl formate ensure that the electrolyte is still liquid and has a lower viscosity under low temperature conditions; secondly, the high lithium salt concentration electrolyte makes the lithium ion solvation structure in the electrolyte relatively stable under low temperature conditions and will not change significantly; at the same time, the small molecular structure of ether and methyl formate allows the solvent molecules in the second solvation sheath to reduce the desolvation energy barrier of lithium ions through the induction effect, thereby improving the bulk conductivity of lithium ions and reducing the charge transfer impedance of lithium ions. The high lithium salt concentration increases the concentration of anions in the electrolyte, thereby increasing the content of inorganic components in the mold component in the chemical film formation, thereby reducing the interface transmission impedance.

[0037] The lithium manganese dioxide batteries prepared in Example 1 and the comparative example were subjected to EIS impedance analysis and DRT impedance analysis, respectively. The results are as follows: Figure 4 and Figure 5 It can be seen that the lithium-manganese dioxide battery injected with the electrolyte prepared in Example 1 has lower interface impedance and charge transfer impedance, which is mainly due to the fact that the electrolyte prepared in Example 1 has smaller interface transmission impedance and smaller desolvation energy barrier.

[0038] Example 2

[0039] Dissolve lithium bis(fluorosulfonyl)imide (LiFSI) in ether (Me2O), the concentration of LiFSI is 2M, stir with a magnetic particle at a speed of 500r / min for 0.6h and stir thoroughly to fully dissolve it to obtain solution 1. Dissolve lithium bis(fluorosulfonyl)imide (LiFSI) in methyl formate (MF), the concentration of LiFSI is 1M, the speed of the magnetic particle is 700r / min, the stirring time is 0.5h, until the solution is clear and transparent to obtain solution 2. Mix solution 1 and solution 2 in a volume ratio of 6:1, and stir thoroughly with a magnetic particle at a speed of 300r / min for 1h until the solution becomes clear and transparent to obtain a low-temperature electrolyte.

[0040] Example 3

[0041] Dissolve lithium bis(fluorosulfonyl)imide (LiFSI) in ether (Me2O), the concentration of LiFSI is 3M, stir with a magnetic particle at a speed of 400r / min for 0.8h and stir thoroughly to fully dissolve it to obtain solution 1. Dissolve lithium bis(fluorosulfonyl)imide (LiFSI) in methyl formate (MF), the concentration of LiFSI is 1.5M, the speed of the magnetic particle is 600r / min, the stirring time is 1h, until the solution is clear and transparent to obtain solution 2. Mix solution 1 and solution 2 in a volume ratio of 4:1, and stir thoroughly with a magnetic particle at a speed of 400r / min for 0.5h until the solution becomes clear and transparent to obtain a low-temperature electrolyte.

[0042] The embodiments of the present invention are described in detail above, but the contents described are only preferred embodiments of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A method for preparing a low-temperature electrolyte for lithium manganese dioxide batteries, characterized in that: Lithium bis(fluorosulfonyl)imide is dissolved in a mixed solvent of ether and methyl formate to form a low-temperature electrolyte.

2. The method for preparing a low-temperature electrolyte for lithium manganese dioxide battery according to claim 1, characterized in that: The specific preparation method is as follows: Step 1: dissolving lithium bis(fluorosulfonyl)imide in ether, wherein the concentration of lithium bis(fluorosulfonyl)imide is in the range of 2-3.5 M, and obtaining solution 1 after sufficient dissolution; Dissolving lithium bis(fluorosulfonyl)imide in methyl formate, wherein the concentration of lithium bis(fluorosulfonyl)imide is in the range of 1-2.5 M, and obtaining solution 2 after the lithium bis(fluorosulfonyl)imide is fully dissolved; Step 2: Mix solution 1 and solution 2 and stir them thoroughly to obtain a low-temperature electrolyte.

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

1.

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

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

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

7. A lithium manganese dioxide battery, characterized in that: Including the low-temperature electrolyte as described in claim 6.

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