An electrolyte matching high voltage lithium metal battery and preparation method thereof

Abstract

The present invention discloses an electrolyte matching a high-voltage lithium metal battery and a preparation method thereof, comprising a lithium salt: lithium hexafluorophosphate (LiPF 6 ), the mass of which accounts for 14.0% of the mass of the electrolyte; non-aqueous organic solvents: fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC) and 2,2,2-trifluoroethyl methyl carbonate (FEMC), mixed according to the mass ratio; additives: 4-propargylthiomorpholine-1,1-dioxide (PTD, CAS No.: 10442-03-2) and 1,4-diethynyl-2,5-difluorobenzene (DDF, CAS No.: 156016-23-8); the mass ratio of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC) and 2,2,2-trifluoroethyl methyl carbonate (FEMC) of the non-aqueous organic solvent is 1:1:8; the electrolyte matching the high-voltage lithium metal battery can improve the lithium plating of the lithium metal negative electrode, and enable the lithium metal battery to still have a long cycle life and good high temperature performance when used at a charging cut-off voltage of up to 4.65V.

Description

Technical Field

[0001] The present invention relates to the technical field of battery electrolytes, and in particular to an electrolyte matching a high-voltage lithium metal battery and a preparation method thereof. Background Art

[0002] With the rapid development of portable electronic devices and electric vehicles, the market demand for the energy density of electrochemical energy storage systems is increasing. High-energy-density lithium metal batteries based on metal lithium anodes and high-voltage cathodes have great application prospects and have become a research hotspot. However, the key issues that limit the practical application of high-voltage lithium metal batteries are: on the one hand, the high-voltage cathode side is characterized by instability of the cathode electrolyte interface (CEI) and destruction of the cathode structure; on the other hand, the highly active lithium metal anode tends to induce rapid depletion of the electrolyte, random deposition of lithium dendrites and unstable solid electrolyte interface (SEI), and the dissolution of transition metals from the cathode and shuttle to the anode exacerbates the degradation of the metal lithium anode.

[0003] Electrolyte is an important component of the battery and is particularly important for the electrochemical performance of the battery. In the prior art, many studies have attempted to optimize the performance of lithium metal batteries by changing the composition of the electrolyte, introducing additives, etc. However, most of the research focuses on improving the energy density or safety of the battery. For lithium metal batteries in high voltage environments, how to simultaneously solve the problems of positive electrode CEI stability, negative electrode SEI stability, and long cycle life at high temperatures is still a technical problem that needs to be solved urgently. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the existing defects and provide an electrolyte matching a high-voltage lithium metal battery and a preparation method thereof, which can improve the lithium plating of the lithium metal negative electrode and enable the lithium metal battery to still have a long cycle life and good high-temperature performance when used at a charging cut-off voltage of up to 4.65V, and can effectively solve the problems in the background technology.

[0005] To achieve the above object, the present invention provides the following technical solutions: an electrolyte matching a high voltage lithium metal battery and a preparation method thereof, the electrolyte comprising a lithium salt, a non-aqueous organic solvent and an additive; the lithium salt: lithium hexafluorophosphate (LiPF 6 ), the mass accounts for 14.0% of the mass of the electrolyte; non-aqueous organic solvent: fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC) and 2,2,2-trifluoroethyl methyl carbonate (FEMC), mixed according to the mass ratio; additives: 4-propargylthiomorpholine-1,1-dioxide (PTD, CAS No.: 10442-03-2) and 1,4-diethynyl-2,5-difluorobenzene (DDF, CAS No.: 156016-23-8).

[0006] Furthermore, the mass ratio of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC) and 2,2,2-trifluoroethyl methyl carbonate (FEMC) of the non-aqueous organic solvent is 1:1:8.

[0007] Furthermore, the mass of 4-propargylthiomorpholine-1,1-dioxide (PTD, CAS No.: 10442-03-2) accounts for 0.3%-2.0% of the mass of the electrolyte.

[0008] Furthermore, the mass of 1,4-diethynyl-2,5-difluorobenzene (DDF, CAS No.: 156016-23-8) accounts for 0.5%-4.0% of the mass of the electrolyte.

[0009] Furthermore, a method for preparing an electrolyte matching a high-voltage lithium metal battery comprises the following specific steps: mixing fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC) and 2,2,2-trifluoroethyl methyl carbonate (FEMC) in a mass ratio of 1:1:8; adding 0.3%-2.0% of 4-propargylthiomorpholine-1,1-dioxide (PTD) and 0.5%-4.0% of 1,4-diethynyl-2,5-difluorobenzene (DDF) based on the total mass of the electrolyte to the mixed solvent in sequence; and then slowly adding lithium hexafluorophosphate (LiPF6), which accounts for 14.0% of the total mass of the electrolyte, and stirring until completely dissolved to obtain the electrolyte.

[0010] Further, the prepared electrolyte is injected into the positive electrode LiCoO 2 Materials, in the soft-pack battery with lithium metal as the negative electrode, the battery is packaged, stored at 45°C, high-temperature formed, secondary packaged, and capacity divided to obtain a high-voltage lithium metal battery.

[0011] Furthermore, the preparation process was carried out in an argon-protected glove box, and the moisture and oxygen contents were respectively less than 1 ppm.

[0012] The role of PTD (4-propargylthiomorpholine-1,1-dioxide) in the positive electrode:

[0013] PTD preferentially forms a stable cathode electrolyte interface (CEI) on the cathode surface through a chemical ring-opening reaction; 2 The group combines with the transition metal and lattice oxygen through a double bond, causing the double site to be inactivated, thereby helping to passivate the positive electrode surface; in this way, PTD not only improves the stability of the positive electrode, but also effectively reduces the dissolution of transition metal ions and the occurrence of side reactions, especially under high voltage; at the same time, the -C≡C group makes full use of the high activity and strong polymerization ability of the unsaturated bond to form a highly stable CEI film layer, further improving the cycle stability under high voltage, reducing the internal resistance of the battery, and inhibiting the dissolution of transition metal ions.

[0014] In addition, the -N group in PTD can effectively capture water, phosphorus pentafluoride (PF 5 ) and corrosive acids such as hydrofluoric acid. With the introduction of a strongly electronegative -C≡C group at the terminal, the carbon-carbon triple bond (sp hybridization) forms a conjugated effect with other atoms; this effect helps to induce by-products such as phosphorus pentafluoride to form a bond with the -N group with a lone pair of electrons, thereby inhibiting the decomposition of lithium salts and significantly improving the high temperature performance of the battery.

[0015] The role of DDF (1,4-diethynyl-2,5-difluorobenzene) in the negative electrode:

[0016] DDF molecules preferentially react with the surface of lithium metal negative electrode, and combine with lithium ions through coordination to form a solid electrolyte interface (SEI) rich in lithium fluoride; this SEI film layer can significantly reduce the diffusion energy barrier of lithium ions in SEI, which helps the uniform deposition of lithium ions and thus inhibits the formation of lithium dendrites; the introduction of DDF also reduces the chemical hardness, and molecules with lower hardness are more stable in the reduced state, which enables the SEI film to be formed in a more controllable manner and remain stable during the reduction process.

[0017] The synergistic effect between DDF and PTD can also form a fluorine-nitrogen cross-linked SEI film on the surface of metallic lithium; this special structure helps to improve the stability of the battery, reduce the interfacial impedance, and make the SEI film adaptive, so that it can cope with the interfacial changes that may occur on the surface of metallic lithium during the cycle, maintain the structure and properties of the SEI, and further improve the cycle stability of the battery.

[0018] Functions of FEC, DFEC and FEMC:

[0019] The electrolyte of the present invention uses a perfluorinated solvent mixed with FEC, DFEC and FEMC. 6 ⁻The synergistic reaction generates a SEI rich in lithium fluoride and lithium oxide. This SEI can ensure the uniform deposition of lithium metal and effectively inhibit the growth of lithium dendrites; in addition, FEC, DFEC and FEMC all show excellent antioxidant ability and can build a stable and strong positive electrode electrolyte interface (CEI) at high voltage, significantly improving the high voltage performance and stability of the battery.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The synergistic effect of PTD and DDF enhances the stability of the electrolyte interface on the positive and negative electrode surfaces; the CEI formed by PTD at the positive electrode not only improves the cycle performance of the battery, but also effectively reduces the occurrence of side reactions; and the SEI formed by DDF at the negative electrode optimizes the deposition of lithium metal and inhibits the growth of lithium dendrites; the synergistic effect of the two not only improves the safety of the battery, but also significantly improves its performance under high temperature and high voltage, so that the electrolyte of the present invention can adapt to more harsh working environments and extend the service life of the battery.

[0022] 2. Through the synergistic effect of various components, the electrolyte can reduce the formation of lithium dendrites in LiCoO2 positive electrode materials and lithium metal negative electrode lithium-ion batteries at high voltage, while having good cycle performance and high temperature performance.

[0023] 3. By rationally designing the composition of the electrolyte, the dissolution of transition metals can be effectively inhibited, side reactions can be reduced, and the overall performance of the battery can be improved; the electrolyte can still maintain low internal resistance and high stability under high temperature and high voltage environments, ensuring the reliability and safety of the battery under extreme conditions, providing strong support for the practical application of high-voltage lithium metal batteries, and has broad application prospects. DETAILED DESCRIPTION

[0024] The present invention is further described below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Example 1

[0025] In a glove box filled with argon, with water content less than 1ppm and oxygen content less than 1ppm, fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC) and 2,2,2-trifluoroethyl methyl carbonate (FEMC) were mixed in a mass ratio of 1:1:8, 0.3% of 4-propargylthiomorpholine-1,1-dioxide (PTD, CAS No.: 10442-03-2) and 2.0% of 1,4-diethynyl-2,5-difluorobenzene (DDF, CAS No.: 156016-23-8) based on the total mass of the electrolyte were added to the mixed solvent, and then 14.0% of lithium hexafluorophosphate (LiPF60) based on the total mass of the electrolyte was slowly added to the mixed solution. 6 ), and stirred until it is completely dissolved to obtain the lithium ion battery electrolyte of Example 1.

[0026] Inject the prepared electrolyte into the positive electrode LiCoO 2 Materials, in the soft-pack battery with lithium metal as the negative electrode, the battery is packaged, stored at 45°C, high-temperature formed, secondary packaged, and capacity divided to obtain a high-voltage lithium metal battery.

[0027] As shown in Table 1, in Examples 2-5 and Comparative Examples 1-2, except that the components and proportions of the electrolyte are added as shown in Table 1, everything else is the same as Example 1.

[0028]

[0029] Performance test of lithium metal battery:

[0030] The lithium ion batteries prepared in the above Examples 1-5 and Comparative Examples 1-2 were subjected to the following related experiments:

[0031] (1) Room temperature cycle performance test: At 25°C, the divided battery is charged to 4.65V with a constant current and constant voltage of 0.5C, and the cut-off current is 0.01C, and then discharged to 3.0V with a constant current of 0.5C; after 250 cycles of charge and discharge, the retention rate of the capacity at the 250th cycle is calculated; the calculation formula is as follows:

[0032] The 250th cycle capacity retention rate (%) = (250th cycle discharge capacity / 1st cycle discharge capacity) × 100%.

[0033] (2) High temperature storage performance: The divided battery is charged to 4.65V at 0.5C constant current and constant voltage at 25℃, with a cut-off current of 0.01C, and then discharged to 3.0V at 0.5C constant current, and the discharge capacity is recorded. This discharge capacity is the initial capacity of the battery before storage; then the battery is charged to 4.65V at constant current and constant voltage, with a cut-off current of 0.01C, that is, fully charged; then the battery is placed in an 85℃ oven for 10 hours. After the storage is completed, the battery is taken out and cooled to 25℃, and then discharged to 3.0V at 0.5C to measure the discharge capacity of the battery, which is the battery retention capacity; the calculation formula is as follows:

[0034] Battery capacity retention rate (%) = retained capacity / initial capacity × 100%.

[0035] (3) Observation of the surface of the metallic lithium negative electrode: At 25°C, the divided battery was charged to 4.65V at 0.5C constant current and constant voltage, with a cut-off current of 0.01C, and then discharged to 3.0V at 0.5C constant current. After 100 cycles of charge and discharge, the battery was fully charged and placed in a glove box for battery disassembly. The surface of the metallic lithium negative electrode was observed under an optical microscope to see whether lithium dendrites were generated.

[0036] The results of the above electrochemical performance tests are shown in Table 2.

[0037]

[0038] It can be seen from the test results of Example 1, Example 2, Example 3 and Comparative Example 1 in Table 2 that adding PTD to the electrolyte significantly improves the performance of LiCoO2 The high-temperature storage performance of the battery at high voltage and the lithium dendrite situation are also improved; this is because PTD is closely related to the lithium metal anode and LiCoO 2 The cathode has excellent compatibility, and PTD can be used in LiCoO 2 A strong CEI with an inorganic inner layer and an organic outer layer, as well as an inorganic-rich SEI, are formed on the surface of the material. These inorganic substances enhance the interface stability and pave the way for lithium ion transport, while sulfur-containing organics improve the interface flexibility to alleviate stress accumulation, making the CEI and SEI formed by PTD have rapid lithium ion transport characteristics and excellent thermal stability.

[0039] From the test results of Example 2, Example 4, Example 5 and Comparative Example 2 in Table 2, it can be seen that adding DDF to the electrolyte significantly improves the LiCoO 2 The battery has good cycle stability under high voltage and effectively inhibits the formation of lithium dendrites. The reason is that DDF forms a fluorine-nitrogen-rich low-impedance SEI film on the surface of the negative electrode metal lithium, and the SEI formed by triple bond polymerization is more conducive to the deposition of metal lithium and reduces the formation of lithium dendrites.

[0040] In summary, the electrolyte provided by the present invention can make LiCoO 2 Positive electrode materials and lithium metal anode lithium-ion batteries can reduce lithium dendrite formation at high voltages while having good cycle performance and high temperature performance.

[0041] The basic principles, main features and advantages of the present invention are shown and described above. Without departing from the spirit and scope of the present invention, the present invention may also be subject to various changes and improvements, which all fall within the scope of the present invention to be protected.

Claims

1. An electrolyte matching a high voltage lithium metal battery, characterized in that: The electrolyte includes the following components: Lithium salt: lithium hexafluorophosphate (LiPF6), accounting for 14.0% of the electrolyte mass; Non-aqueous organic solvent: fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC) and 2,2,2-trifluoroethyl methyl carbonate (FEMC), mixed in a mass ratio; Additives: 4-propargylthiomorpholine-1,1-dioxide (PTD) and 1,4-diethynyl-2,5-difluorobenzene (DDF).

2. The electrolyte matching a high voltage lithium metal battery according to claim 1, characterized in that: The mass ratio of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC) and 2,2,2-trifluoroethyl methyl carbonate (FEMC) in the non-aqueous organic solvent is 1:1:

8.

3. The electrolyte matching a high voltage lithium metal battery according to claim 1, characterized in that: The mass of 4-propargylthiomorpholine-1,1-dioxide (PTD) accounts for 0.3%-2.0% of the mass of the electrolyte.

4. The electrolyte matching a high voltage lithium metal battery according to claim 1, characterized in that: The mass of 1,4-diethynyl-2,5-difluorobenzene (DDF) accounts for 0.5%-4.0% of the mass of the electrolyte.

5. A method for preparing an electrolyte matching a high-voltage lithium metal battery according to any one of claims 1 to 4, characterized in that: The specific steps are as follows: fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC) and 2,2,2-trifluoroethyl methyl carbonate (FEMC) are mixed in a mass ratio of 1:1:8; 0.3%-2.0% of 4-propargylthiomorpholine-1,1-dioxide (PTD) and 0.5%-4.0% of 1,4-diethynyl-2,5-difluorobenzene (DDF) based on the total mass of the electrolyte are added to the mixed solvent in sequence; then lithium hexafluorophosphate (LiPF6) is slowly added, wherein the lithium hexafluorophosphate (LiPF6) accounts for 14.0% of the total mass of the electrolyte; and the mixture is stirred until completely dissolved to obtain the electrolyte.

6. The method for preparing an electrolyte matching a high voltage lithium metal battery according to claim 5, characterized in that: The preparation process was carried out in an argon-protected glove box, and the moisture and oxygen contents were less than 1 ppm, respectively.

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