A lithium battery electrolyte containing nitrate ions

Abstract

This invention provides a lithium battery electrolyte containing nitrate ions, comprising an organic solvent, an electrolyte, and an additive. The organic solvent is an organic carbonate, and the electrolyte is a lithium salt. Based on the volume of the organic solvent, the concentration of the electrolyte is 0.5–5 mol / L. The additive is an ionic liquid, wherein the cation of the ionic liquid is one or more of pyrrolidine cations, pyridine cations, imidazole cations, and quaternary ammonium cations, and the anion of the ionic liquid is a nitrate anion. The mass content of the ionic liquid in the lithium battery electrolyte is 0.5–5%. Thus, the anion of the ionic liquid can preferentially reduce and decompose before the lithium salt to form a solution rich in LiN3 and LiN. x O y A stable, highly conductive solid electrolyte layer (SEI) for lithium oxide.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery electrolytes, and relates to a lithium battery electrolyte, specifically a lithium battery electrolyte containing nitrate ions. Background Technology

[0002] With the continuous upgrading of modern electric vehicles and portable electronic devices, the demand for high-energy-density batteries is becoming increasingly urgent. Among them, lithium batteries are widely used in daily life due to their higher energy density. However, when lithium metal comes into contact with an electrolyte, the electrolyte decomposes due to the low electrode potential of the lithium anode, forming a solid electrolyte layer (SEI) at the electrode / electrolyte interface. This SEI allows lithium ions to pass through but blocks electron transport. The SEI formed by electrolyte decomposition is an inhomogeneous structure composed of organic oligomers and inorganic substances, exhibiting poor ductility and thermodynamic instability. These shortcomings cause the SEI to be unable to adapt to the dynamic changes of the electrodes during battery charging and discharging, leading to continuous electrolyte decomposition and the formation of dendritic lithium dendrites, resulting in low coulombic efficiency (CE) and rapid capacity decay. Simultaneously, the unstable SEI exhibits poor Li... + Electrical conductivity, which hinders Li + Transport and desolvation processes in the SEI layer.

[0003] Lithium nitrate (LiNO3) is widely used as an inorganic additive in diethyl ether electrolytes. Compared to solvent molecules in the electrolyte, LiNO3, with its lowest unoccupied molecular orbitals (LUMO), is preferentially reduced at the anolyte to form lithium nitride-rich (Li3N) and LiN2-rich compounds. x O y A stable SEI layer of lithium oxide (Li₂O) is formed, which can suppress the continuous decomposition of the electrolyte and protect the lithium electrode; in addition, it has high Li₂O content. + The high electrical conductivity of Li3N and Li2O promotes the growth of Li in the SEI. + The diffusion kinetics of transport. However, with the narrow electrochemical window of ether electrolytes (<4V vs Li / Li), + In contrast, carbonate organic solvents (such as ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC)) can be matched with most high-voltage cathode materials and achieve high-energy-density LMBs (lithium metal batteries). However, LiNO3 has very low solubility in carbonate organic solvents.

[0004] In existing technologies, researchers have increased the solubility of LiNO3 in carbonate electrolytes by adding co-solvents. However, the introduced co-solvents can affect the cycle performance of the battery, causing a decrease in battery energy density and shortening the battery cycle time. Summary of the Invention

[0005] In order to solve the above-mentioned technical problems, the purpose of this invention is to provide a lithium battery electrolyte containing nitrate ions.

[0006] To achieve the above-mentioned technical objectives, this invention provides a lithium battery electrolyte containing nitrate ions, comprising an organic solvent, an electrolyte, and an additive. The organic solvent is an organic carbonate, and the electrolyte is a lithium salt. Based on the volume of the organic solvent, the concentration of the electrolyte is 0.5–5 mol / L. The additive is an ionic liquid, wherein the cation of the ionic liquid is one or more of pyrrolidine cations, pyridine cations, imidazole cations, and quaternary ammonium cations, and the anion of the ionic liquid is a nitrate anion. The mass content of the ionic liquid in the lithium battery electrolyte is 0.5–5%. The concentration of the electrolyte can be selected according to actual needs, but a commonly used concentration is 1 mol / L. Optimally, the amount of the ionic liquid added is 2%.

[0007] When the voltage is ≥4V (high voltage, i.e., the charging cutoff voltage of a lithium battery), the cation of the ionic liquid is or / and In the formula, R1 and R2 are independently alkyl chains. Preferably, R1 has 1 to 6 carbon atoms and R2 has 8 to 14 carbon atoms; more preferably, R1 has 1 to 3 carbon atoms and R2 has 10 to 12 carbon atoms.

[0008] When the voltage is ≤4V, the cation of the ionic liquid is selected from... One or more of the following, wherein R1, R2, R3, and R4 are independently alkyl chains. Preferably, R1 has 1-6 carbon atoms, and R2 has 8-14 carbon atoms; R 11 R 12 R 13 and R 14 The number of carbon atoms in each of them is independently 6-14; preferably, the number of carbon atoms in R1 is 1-3, and the number of carbon atoms in R2 is 10-12; the R 11 R 12 R 13 and R 14 The number of carbon atoms in each alkyl chain is independently 8-10. It is important to note that the alkyl chain should not be too short, as this makes the ionic liquid difficult to dissolve in the electrolyte; conversely, the alkyl chain should not be too long, as this makes the ionic liquid unstable under high pressure. To ensure the ionic liquid functions well in lithium-ion battery electrolytes, the number of carbon atoms in R1 of pyrrolidine, pyridine, and imidazole cations is 1-6, and the number of carbon atoms in R2 is 8-14; for quaternary ammonium salt cations, the number of carbon atoms in R2 is... 11 R12 R 13 R 14 The number of carbon atoms is 6-14; preferably, the number of carbon atoms of R1 in pyrrolidine, pyridine, and imidazole cations is 1-3, and the number of carbon atoms of R2 is 10-12; the number of carbon atoms of R in quaternary ammonium salt cations is 6-14. 11 R 12 R 13 R 14 It has 8-10 carbon atoms.

[0009] Optimally, the organic solvent is one or more selected from ethylene carbonate, propylene carbonate, methyl ethyl carbonate, dimethyl carbonate, and diethyl carbonate; preferably, the organic solvent is a mixture of ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate in a volume ratio of 1:1:1.

[0010] Preferably, the electrolyte is one or more of lithium hexafluorophosphate, lithium bis(oxalate-borate), lithium difluorooxalate-borate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethylsulfonyl)imide.

[0011] This invention relates to a lithium battery electrolyte containing nitrate ions. By mixing a specifically structured ionic liquid with an organic solvent and an electrolyte, without the need for additional solubilizers, the ionic liquid can dissolve in the organic solvent. This allows the anions of the ionic liquid to preferentially reduce and decompose before the lithium salt, forming a solution rich in LiN3 and LiN. x O y A stable, highly conductive solid electrolyte layer (SEI) for lithium oxide suppresses the continuous decomposition of the electrolyte and protects the lithium electrode; the highly conductive SEI layer is beneficial for Li... + The transport at the interface facilitates the insertion and extraction of lithium ions, forming a dense lithium deposition. This avoids the formation of dendritic lithium dendrites and the occurrence of battery short circuits, thereby effectively improving battery performance and extending battery life. Attached Figure Description

[0012] Figure 1 The electrolyte containing 2 wt% ionic liquid prepared in Example 1 of this invention;

[0013] Figure 2 This is a battery cycle diagram of a lithium battery based on the electrolyte of Example 1 of the present invention;

[0014] Figure 3 This is an electron microscope image of a lithium sheet after 600 cycles of a lithium battery based on the electrolyte of Example 1 of the present invention. Detailed Implementation

[0015] The preferred embodiments of the present invention will now be described in detail.

[0016] Example 1

[0017] This embodiment provides a lithium battery electrolyte containing nitrate ions, such as... Figure 1 As shown, it includes: organic solvents, electrolytes, and ionic liquid additives. Figure 1 The baseline is a commercial electrolyte (a 1M LiPF6 EC / DMC / EMC mixed solution);

[0018] The organic solvent is a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1, 20 ml; the electrolyte is lithium hexafluorophosphate, 0.02 mol (baseline of organic solvent and electrolyte composition);

[0019] The amount of ionic liquid added is 2 wt% (based on the electrolyte, i.e., the total mass of lithium battery electrolyte containing nitrate ions is 0.5 g).

[0020] The ionic liquid is 1-methyl-1-decylpyrrolidine nitrate ( The preparation method is as follows: 5g of 1-methylpyrrolidine (0.06mol) and 13.295g of 1-bromo-n-decane (0.06mmol) were dissolved in 15ml of acetonitrile, and the reaction was stirred to obtain the ionic liquid 1-methyl-1-decylpyrrolidine bromide; then 5g (16.4mmol) of 1-methyl-1-decylpyrrolidine bromide and 2.78g (16.4mmol) of silver nitrate were added to anhydrous methanol, and the mixture was stirred in the dark for 12h to obtain the aforementioned ionic liquid.

[0021] Example 2

[0022] This embodiment provides a lithium battery electrolyte containing nitrate ions, which is basically the same as that in Example 1, except that the amount of ionic liquid added is 1 wt%.

[0023] Example 3

[0024] This embodiment provides a lithium battery electrolyte containing nitrate ions, which is basically the same as that in Example 1, except that the amount of ionic liquid added is 0.5 wt%.

[0025] Example 4

[0026] This embodiment provides a lithium battery electrolyte containing nitrate ions, which is basically the same as that in Example 1, except that the amount of ionic liquid added is 5 wt%.

[0027] Example 5

[0028] This embodiment provides a lithium battery electrolyte containing nitrate ions, which is basically the same as that in Example 1, except that the ionic liquid is 1-decylpiperidine nitrate.

[0029] Example 6

[0030] This embodiment provides a lithium battery electrolyte containing nitrate ions, which is basically the same as that in Example 1, except that the ionic liquid is 1-methyl-3-decylimidazolium nitrate.

[0031] Example 7

[0032] This embodiment provides a lithium battery electrolyte containing nitrate ions, which is basically the same as that in Example 1, except that the ionic liquid is tetraoctylamine nitrate.

[0033] Comparative Example 1

[0034] This embodiment provides a lithium battery electrolyte containing nitrate ions, which is basically the same as that in Example 1, except that the amount of ionic liquid added is 0.2 wt%.

[0035] Comparative Example 2

[0036] This embodiment provides a lithium battery electrolyte containing nitrate ions, which is basically the same as that in Example 1, except that the amount of ionic liquid added is 8 wt%.

[0037] Comparative Example 3

[0038] This embodiment provides a lithium battery electrolyte that does not contain nitrate ions. It is basically the same as that in Example 1, except that silver nitrate is not used for ion exchange.

[0039] Comparative Example 4

[0040] This embodiment provides a lithium battery electrolyte that does not contain nitrate ions. It is basically the same as that in Example 1, except that the ionic liquid is 1-methyl-1-decylpyrrolidine borate.

[0041] The electrolytes from Examples 1-9 and Comparative Examples 1-5 were mixed with lithium foil and LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811) is used to assemble lithium batteries (active material loading is 1.5-1.7 mg / cm³). -2Using the lithium metal anode and NCM811 cathode obtained above, a coin cell (CR2025) was manufactured in a glove box filled with argon (H2O and O2 < 0.01 ppm) for performance testing, wherein the performance in Example 1 was as follows. Figure 2 and Figure 3 As shown, other test data are shown in Table 1.

[0042] Table 1. Battery test data based on the electrolytes used in Examples 1-7 and Comparative Examples 1-5.

[0043] Number of cycles Coulomb efficiency Capacity retention Example 1 200 >99％ 97.27％ Example 2 200 >99％ 85.48％ Example 3 200 >99％ 73.76％ Example 4 200 >99％ 58.73％ Example 5 200 >98％ 80.23％ Example 6 200 >98％ 76.47％ Example 7 200 >98％ 73.63％ Comparative Example 1 200 96％ 70.53％ Comparative Example 2 200 91％ 45.68％ Comparative Example 3 200 >99％ 67.49％ Comparative Example 4 200 >98％ 62.97％

[0044] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A lithium battery electrolyte containing nitrate ions, comprising an organic solvent, an electrolyte, and additives, wherein the organic solvent is an organic carbonate, and the electrolyte is a lithium salt; the concentration of the electrolyte is 0.5–5 mol / L based on the volume of the organic solvent, characterized in that: The additive is an ionic liquid, wherein the cation of the ionic liquid is one or more of pyrrolidine cations, pyridine cations, imidazole cations, and quaternary ammonium salt cations, and the anion of the ionic liquid is a nitrate anion, and the mass content of the ionic liquid in the lithium battery electrolyte is 0.5-5%. When the voltage is ≥4V, the cation of the ionic liquid is or / and In the formula, R1 and R2 are alkyl chains that are independent of each other; When the voltage is ≤4V, the cation of the ionic liquid is selected from... One or more of the following, wherein R1, R2, R3 and R4 are alkyl chains that are independent of each other; The organic solvent is one or more selected from ethylene carbonate, propylene carbonate, methyl ethyl carbonate, dimethyl carbonate, and diethyl carbonate; The electrolyte is one or more of lithium hexafluorophosphate, lithium bis(oxalato)borate, lithium difluorooxalato)borate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethyl)sulfonylimide.

2. The lithium battery electrolyte containing nitrate ions according to claim 1, characterized in that: The amount of the ionic liquid added is 2%.

3. The lithium battery electrolyte containing nitrate ions according to claim 1, characterized in that: The number of carbon atoms in R1 is 1 to 6, and the number of carbon atoms in R2 is 8 to 14.

4. The lithium battery electrolyte containing nitrate ions according to claim 1, characterized in that: The number of carbon atoms in R1 is 1 to 3, and the number of carbon atoms in R2 is 10 to 12.

5. The lithium battery electrolyte containing nitrate ions according to claim 1, characterized in that: The number of carbon atoms in R1 is 1-6, and the number of carbon atoms in R2 is 8-14; the R 11 R 12 R 13 and R 14 The number of carbon atoms in each carbon atom is 6-14, which are independent of each other.

6. The lithium battery electrolyte containing nitrate ions according to claim 5, characterized in that: The number of carbon atoms in R1 is 1-3, and the number of carbon atoms in R2 is 10-12; the R 11 R 12 R 13 and R 14 The number of carbon atoms in each carbon atom is 8-10 independently.

7. The lithium battery electrolyte containing nitrate ions according to claim 1, characterized in that: The organic solvent is a mixture of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate in a volume ratio of 1:1:1.

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