Electrolyte applied to lithium ferrous disulfide battery and preparation method thereof

Abstract

The application provides an electrolyte applied to a lithium ferrous disulfide battery and a preparation method, the preparation method comprises the following steps: S1, dissolving lithium nitrate and lithium iodide in dioxolane (DOL), fully stirring to make them fully dissolved, and obtaining a first solution; S2, adding ethylene glycol dimethyl ether (DME) into the first solution, fully stirring until clear and transparent, and obtaining a second solution; S3, adding dimethylacetamide (DMAC) into the second solution, fully stirring until clear and transparent, and obtaining a finished electrolyte. The solvent dimethylacetamide (DMAC) with a high DN value is added, dioxolane (DOL) is made to form a thinner interface film to ensure the diffusion efficiency of lithium ions, and the activation energy required by a reaction is reduced by weakening the ferrous-sulfur bond, so that the discharge voltage and the discharge capacity of the lithium ferrous disulfide battery in a wider temperature range, especially at low temperature, are ensured, and the rate performance of the battery is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium iron disulfide battery technology, and in particular to an electrolyte for use in lithium iron disulfide batteries and its preparation method. Background Technology

[0002] Lithium iron disulfide batteries have a theoretical specific capacity of up to 893 mAh / g based on a 4-electron transfer reaction. They also have good rate performance due to the formation of metallic iron in the discharge reaction products, and are therefore widely used in many fields. However, polysulfides are generated during the reaction process, and these polysulfides will exhibit a "shuttle effect" during cycling, leading to battery capacity decay.

[0003] Technicians in this field often use dioxolane (DOL) as one of the main solvents to formulate the electrolyte for lithium iron disulfide batteries, in order to achieve film formation on the positive electrode surface, thereby preventing the "shuttle effect" of polysulfides and thus preventing side reactions. However, an excessively thick interfacial film on the positive electrode surface can hinder the diffusion of lithium ions, thus affecting the rate performance of the battery. Furthermore, a problem with existing technology is that the strong bond energy between sulfide and ferrous bonds causes the actual discharge voltage of lithium iron disulfide batteries to be lower than the theoretical value, reducing the actual discharge capacity of lithium iron disulfide batteries. Summary of the Invention

[0004] The purpose of this invention is to provide an electrolyte and preparation method for lithium iron disulfide batteries. By introducing a high DN value solvent, dimethylacetamide (DMAC), into the electrolyte, the gelation film thickness of dioxane (DOL) can be controlled, thereby improving the rate performance of the battery. At the same time, the high DN value solvent is also beneficial to breaking the sulfide-ferrous bond, reducing the activation energy required for the reaction, which is conducive to improving the battery discharge voltage.

[0005] The technical solution adopted in this invention is: a method for preparing an electrolyte for lithium iron disulfide batteries, comprising the following steps:

[0006] S1. Dissolve lithium nitrate and lithium iodide in dioxolane (DOL) and stir thoroughly to ensure complete dissolution, thus obtaining the first solution;

[0007] S2. Add ethylene glycol dimethyl ether (DME) to the first solution and stir thoroughly until clear and transparent to obtain the second solution;

[0008] S3. Add dimethylacetamide (DMAC) to the second solution and stir thoroughly until clear and transparent to obtain the finished electrolyte.

[0009] Furthermore, in step S1, the concentration of lithium nitrate is 1.4M to 1.8M, and the concentration of lithium iodide is 0.6M to 0.8M.

[0010] Furthermore, the volume ratio of the ethylene glycol dimethyl ether (DME) to the dioxolane (DOL) is 7:10 to 4:5.

[0011] Furthermore, the volume ratio of dimethylacetamide (DMAC) to dioxolane (DOL) is 1:5 to 3:10.

[0012] Furthermore, in step S1, a magnetic stirrer is used to stir the mixture at a speed of 300-400 r / min for 0.8-1 h.

[0013] Furthermore, in step S2, a magnetic stirrer is used to stir the mixture at a speed of 600-800 r / min for 0.5-1 h.

[0014] Furthermore, in step S3, a magnetic stirrer is used to stir the mixture at a speed of 300-500 r / min for 0.6-1 h.

[0015] Furthermore, the lithium nitrate, lithium iodide, dioxolane (DOL), ethylene glycol dimethyl ether (DME), and dimethylacetamide (DMAC) are all ultra-dry grade.

[0016] An electrolyte for use in lithium iron disulfide batteries is prepared by the method for preparing an electrolyte for use in lithium iron disulfide batteries as described in any of the preceding claims.

[0017] The beneficial effects of this invention are:

[0018] (1) Adding dimethylacetamide (DMAC), a solvent with a high DN value, can reduce the polymerization of dioxane (DOL), resulting in a thinner interface layer on the positive electrode surface. This interface layer weakens the "shuttle effect" of polysulfides while ensuring the diffusion efficiency of lithium ions, thus ensuring the discharge voltage and discharge capacity of lithium iron disulfide batteries over a wide temperature range, especially at low temperatures, thereby improving the rate performance of the battery.

[0019] (2) Meanwhile, dimethylacetamide (DMAC), a solvent with a high DN value, can attract ferrous ions, weaken the thioferrous bond, reduce the activation energy required for the reaction, thereby increasing the Gibbs free energy of the reaction, which macroscopically manifests as an increase in the discharge voltage of the battery. Attached Figure Description

[0020] Figure 1 These are photographs of the electrolyte prepared according to an embodiment of the present invention at 55°C and -40°C;

[0021] Figure 2The discharge curves at 25°C are obtained by injecting the electrolyte prepared in one embodiment of the present invention and the 0.75M LiI-DOL / DME electrolyte into a lithium iron disulfide battery, respectively.

[0022] Figure 3 The discharge curves of the electrolyte prepared in one embodiment of the present invention and the 0.75M LiI-DOL / DME electrolyte after being injected into a lithium iron disulfide battery at -40°C are shown. Detailed Implementation

[0023] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0024] Reference Appendix Figure 1-3 This invention provides a method for preparing an electrolyte for lithium iron disulfide batteries, comprising the following steps:

[0025] S1. Dissolve lithium nitrate and lithium iodide in dioxolane (DOL) and stir thoroughly at a speed of 300-400 r / min for 0.8-1 h to ensure complete dissolution of lithium nitrate and lithium iodide, to obtain a first solution. The concentration of lithium nitrate in the first solution is 1.4 M-1.8 M and the concentration of lithium iodide is 0.6 M-0.8 M.

[0026] S2. Add ethylene glycol dimethyl ether (DME) to the first solution and stir thoroughly with a magnetic stirrer at a speed of 600-800 r / min for 0.5-1 h until clear and transparent to obtain the second solution. The volume ratio of ethylene glycol dimethyl ether (DME) to dioxolane (DOL) in the second solution is 7:10 to 4:5.

[0027] S3. Add dimethylacetamide (DMAC) to the second solution and stir thoroughly with a magnetic stirrer at a speed of 300-500 r / min for 0.6-1 h until clear and transparent to obtain the finished electrolyte. The volume ratio of dimethylacetamide (DMAC) to dioxolane (DOL) in the finished electrolyte is 1:5-3:10.

[0028] In step S1, dioxolane (DOL) is used as the main component of the electrolyte. Its ability to form a film on the surface of the positive electrode prevents the "shuttle effect" of polysulfides, thereby improving the battery's rate performance. In step S2, diethylene glycol dimethyl ether (DME) has a low viscosity, which effectively accelerates the entry of solvated lithium ions into the negative electrode, further improving the battery's rate performance. In step S3, dimethylacetamide (DMAC) has a high DN value, thus exhibiting a strong attraction to positive charges. On one hand, it acts on the Lewisite on the surface of ferrous disulfide. The s-acidic sites compete with dioxane (DOL), hindering the formation of a film of dioxane (DOL) on the surface of ferrous disulfide. This results in a thinner interfacial film formed by dioxane (DOL), ensuring the diffusion efficiency of lithium ions and guaranteeing the discharge voltage and discharge capacity of lithium ferrous disulfide batteries over a wider temperature range, especially at low temperatures, thus improving the rate performance of the battery. On the other hand, by attracting divalent iron ions, it reduces the bond energy of the sulfide-ferrous bond, making the sulfide-ferrous bond easier to break. That is, by lowering the activation energy of the reaction, it improves the low-temperature performance and discharge voltage of the battery.

[0029] It is worth noting that the lithium nitrate, lithium iodide, dioxolane (DOL), dimethyl ethylene glycol (DME), and dimethylacetamide (DMAC) used in the experiment were all ultra-dry grade. Ultra-dry grade means that the water content at the time of packaging is less than 50 ppm. With a low water content, it can act as a very high-purity organic solvent to react fully with lithium ions and prevent the metallic lithium at the negative electrode of the battery from reacting violently with water.

[0030] Preferably, steps S1, S2 and S3 are all performed in a glove box, where the oxygen and water concentrations are both less than 0.01 ppm, to avoid side reactions of some oxygen-sensitive or water-sensitive raw materials.

[0031] Example 1:

[0032] S1. Dissolve lithium nitrate and lithium iodide in dioxolane (DOL) and stir thoroughly at 300 r / min for 1 h using a magnetic stirrer to fully dissolve the lithium nitrate and lithium iodide to obtain the first solution. The first solution is clear and transparent, with a lithium nitrate concentration of 1.4 M and a lithium iodide concentration of 0.8 M.

[0033] S2. Add ethylene glycol dimethyl ether (DME) to the first solution and stir thoroughly at 800 r / min for 0.5 h until clear and transparent to obtain the second solution. The second solution is clear and transparent, and the volume ratio of ethylene glycol dimethyl ether (DME) to dioxolane (DOL) is 4:5.

[0034] S3. Add dimethylacetamide (DMAC) to the second solution and stir thoroughly at 300 r / min for 1 h until clear and transparent to obtain the finished electrolyte. The finished electrolyte is clear and transparent, and the volume ratio of dimethylacetamide (DMAC) to dioxolane (DOL) is 1:5.

[0035] The lithium iron disulfide battery was assembled and tested using commonly used lithium iron disulfide battery experimental battery devices.

[0036] Experimental results:

[0037] The electrolyte prepared in Example 1 has a wide operating temperature range, such as... Figure 1 As shown, the electrolyte prepared in Example 1 is liquid not only at 55°C but also at -40°C, indicating that it has a low melting point and therefore a wide range of application temperatures.

[0038] The electrolyte prepared in Example 1, when injected into a lithium iron disulfide battery and discharged at 25°C with a current density of 0.1 A / g, exhibited a higher discharge voltage than the 0.75 M LiI-DOL / DME electrolyte. Figure 2 As shown; this is mainly because the dimethylacetamide (DMAC) in the electrolyte prepared in Example 1 competes with dioxolane (DOL) for Lewis acidic sites on the surface of ferrous disulfide, allowing dioxolane (DOL) to form a thinner interface layer on the positive electrode surface, ensuring the diffusion efficiency of lithium ions and improving the discharge voltage of the battery; at the same time, dimethylacetamide (DMAC) attracts ferrous ions to reduce the bond energy of ferrous sulfide bonds, induces the breaking of ferrous sulfide bonds, reduces the activation energy required for the reaction, and thus increases the Gibbs free energy of the reaction, thereby increasing the discharge voltage of the battery.

[0039] The electrolyte prepared in Example 1, when injected into a lithium iron disulfide battery and discharged at -40°C with a current density of 0.1 A / g, exhibited a higher discharge capacity than the 0.75 M LiI-DOL / DME electrolyte. Figure 3 As shown, this indicates that dimethylacetamide (DMAC) enables dioxolane (DOL) to form a thinner interfacial layer, ensuring the diffusion efficiency of lithium ions. This not only improves the discharge voltage of the battery at room temperature but also effectively guarantees the discharge efficiency and capacity of the battery under low-temperature conditions. In addition, the high content of low-melting-point solvents dioxolane (DOL) and dimethyl ethylene glycol ether (DME) in the electrolyte significantly reduces the melting point of the electrolyte, which also plays a key role in the high conductivity of the electrolyte under lower temperature conditions.

[0040] Example 2:

[0041] S1. Dissolve lithium nitrate and lithium iodide in dioxolane (DOL) and stir thoroughly at 400 r / min for 0.8 h using a magnetic stirrer to fully dissolve the lithium nitrate and lithium iodide to obtain the first solution. The first solution is clear and transparent, with a lithium nitrate concentration of 1.8 M and a lithium iodide concentration of 0.6 M.

[0042] S2. Add ethylene glycol dimethyl ether (DME) to the first solution and stir thoroughly at 600 r / min for 1 h until clear and transparent to obtain the second solution. The second solution is clear and transparent, and the volume ratio of ethylene glycol dimethyl ether (DME) to dioxolane (DOL) is 7:10.

[0043] S3. Add dimethylacetamide (DMAC) to the second solution and stir thoroughly at 500 r / min for 0.6 h until clear and transparent to obtain the finished electrolyte. The finished electrolyte is clear and transparent, and the volume ratio of dimethylacetamide (DMAC) to dioxolane (DOL) is 3:10.

[0044] Example 3:

[0045] S1. Dissolve lithium nitrate and lithium iodide in dioxolane (DOL) and stir thoroughly at 350 r / min for 1 h using a magnetic stirrer to fully dissolve the lithium nitrate and lithium iodide to obtain the first solution. The first solution is clear and transparent, with a lithium nitrate concentration of 1.6 M and a lithium iodide concentration of 0.8 M.

[0046] S2. Add ethylene glycol dimethyl ether (DME) to the first solution and stir thoroughly at 700 r / min for 0.5 h until clear and transparent to obtain the second solution. The second solution is clear and transparent, and the volume ratio of ethylene glycol dimethyl ether (DME) to dioxolane (DOL) is 7:10.

[0047] S3. Add dimethylacetamide (DMAC) to the second solution and stir thoroughly at 400 r / min for 1 h until clear and transparent to obtain the finished electrolyte. The finished electrolyte is clear and transparent, and the volume ratio of dimethylacetamide (DMAC) to dioxolane (DOL) is 1:5.

[0048] The electrolytes prepared in Examples 2-3 are chemically identical to those prepared in Example 1, and their physical properties and electrochemical performance are basically the same.

[0049] The advantages and beneficial effects of this invention are as follows: Adding dimethylacetamide (DMAC), a solvent with a high DN value, can reduce the polymerization effect of dioxolane (DOL), resulting in a thinner interface layer on the positive electrode surface. This interface layer weakens the "shuttle effect" of polysulfides while ensuring the diffusion efficiency of lithium ions, thus guaranteeing the discharge voltage and discharge capacity of lithium iron disulfide batteries over a wide temperature range, especially at low temperatures, thereby improving the rate performance of the battery. At the same time, dimethylacetamide (DMAC), a solvent with a high DN value, can attract ferrous ions, weaken the sulfide-ferrous bond, and reduce the activation energy required for the reaction, thereby increasing the Gibbs free energy of the reaction, which macroscopically manifests as an increase in the discharge voltage of the battery.

[0050] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the claims, or equivalent forms of such scope and boundaries.

Claims

1. A method for preparing an electrolyte for lithium iron disulfide batteries, characterized in that, The electrolyte solvent is composed of dioxolane, ethylene glycol dimethyl ether, and dimethylacetamide, and the preparation method includes the following steps: S1. Dissolve lithium nitrate and lithium iodide in dioxolane (DOL) and stir thoroughly to ensure complete dissolution, thus obtaining the first solution; S2. Add ethylene glycol dimethyl ether (DME) to the first solution and stir thoroughly until clear and transparent to obtain the second solution; S3. Add dimethylacetamide (DMAC) to the second solution and stir thoroughly until clear and transparent to obtain the finished electrolyte; The volume ratio of the ethylene glycol dimethyl ether (DME) to the dioxolane (DOL) is 7:10 to 4:5; The volume ratio of dimethylacetamide (DMAC) to dioxolane (DOL) is 1:5 to 3:

10.

2. The method for preparing an electrolyte for a lithium iron disulfide battery according to claim 1, characterized in that, In step S1, the concentration of lithium nitrate is 1.4M~1.8M, and the concentration of lithium iodide is 0.6M~0.8M.

3. The method for preparing an electrolyte for a lithium iron disulfide battery according to claim 2, characterized in that, In step S1, a magnetic stirrer is used to stir the mixture at a speed of 300-400 r / min for 0.8-1 h.

4. The method for preparing an electrolyte for a lithium iron disulfide battery according to claim 3, characterized in that, In step S2, a magnetic stirrer is used to stir the mixture at a speed of 600-800 r / min for 0.5-1 h.

5. The method for preparing an electrolyte for a lithium iron disulfide battery according to claim 4, characterized in that, In step S3, a magnetic stirrer is used to stir the mixture at a speed of 300-500 r / min for 0.6-1 h.

6. The method for preparing an electrolyte for a lithium iron disulfide battery according to claim 5, characterized in that, The lithium nitrate, lithium iodide, dioxolane (DOL), ethylene glycol dimethyl ether (DME), and dimethylacetamide (DMAC) are all ultra-dry grade.

7. An electrolyte for use in lithium iron disulfide batteries, characterized in that, The electrolyte used in the lithium iron disulfide battery is prepared by the method for preparing the electrolyte for the lithium iron disulfide battery according to any one of claims 1-6.

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