A high-stability electrolyte for lithium metal batteries and the lithium metal battery itself.

Abstract

This invention discloses a highly stable electrolyte suitable for lithium metal batteries and a lithium metal battery. The electrolyte comprises a lithium salt and a mixed solvent system consisting of a specific three-dimensional network coordination ether, a linear ether, and a third solvent. The electrolyte of this invention effectively suppresses lithium dendrite growth and side reactions by forming a robust and stable interfacial film on the surface of the lithium metal anode. It also exhibits high oxidation stability, can be matched with high-voltage cathodes, and the three-dimensional network coordination ether weakens lithium-ion-solvent coordination, improving the rate performance of the electrolyte and significantly enhancing the cycle life, coulombic efficiency, rate performance, and safety performance of the lithium metal battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, specifically relating to a highly stable electrolyte for lithium metal batteries and a lithium metal battery. Background Technology

[0002] Lithium metal possesses extremely high theoretical specific capacity (3860 mAh / g) and extremely negative electrochemical potential (-3.04 V vs. standard hydrogen electrode), making it an ideal anode material for next-generation high-energy-density batteries. However, the commercialization of lithium metal batteries faces severe challenges, mainly including: 1) Violent side reactions between lithium metal and the electrolyte continuously consume active lithium and electrolyte, leading to low coulombic efficiency and rapid capacity decay; 2) Uneven growth of lithium dendrites may puncture the separator, causing internal short circuits and posing serious safety hazards.

[0003] Electrolytes, as the "blood" of batteries, directly affect the properties of the electrode / electrolyte interface and are key to solving the aforementioned problems. Traditional carbonate-based electrolytes cannot form a stable and dense solid electrolyte interphase (SEI) film on the highly active lithium metal surface, making it difficult to suppress lithium dendrite growth and side reactions.

[0004] Ether electrolytes, especially chain ethers (such as diethylene glycol dimethyl ether and diethylene glycol dimethyl ether), have attracted attention due to their high compatibility with lithium metal and certain film-forming ability. However, single ether solvents suffer from poor oxidation stability (typically <4.0 V vs. Li / Li+), high volatility, and low flash point, making them unsuitable for high-voltage cathodes (such as nickel-cobalt-manganese ternary materials and lithium cobalt oxide), thus limiting their application in high-energy-density full batteries.

[0005] Therefore, developing a novel electrolyte system that is highly compatible with lithium metal anodes, can withstand high-voltage cathode oxidation, and possesses both high safety and long cycle life is crucial for promoting the practical application of lithium metal batteries. Summary of the Invention

[0006] To address the above-mentioned improvement needs of existing technologies, this invention provides a highly stable electrolyte for lithium metal batteries and a lithium metal battery in general. This electrolyte, through the synergistic effect of specific three-dimensional network coordination ethers, linear ethers, and other solvents, can form a robust, inorganic-rich SEI film on the surface of the lithium metal anode, effectively suppressing lithium dendrites and side reactions. Simultaneously, this system exhibits high oxidation stability, can be matched with high-voltage cathode materials, and the three-dimensional network coordination ethers weaken the lithium-ion-solvent coordination effect, improving the rate performance of the electrolyte, thereby achieving efficient, long-cycle, and safe operation of the lithium metal battery.

[0007] To achieve the above objectives, according to one aspect of this application, a highly stable electrolyte for lithium metal batteries is provided, comprising a lithium salt, a non-aqueous organic solvent, and optional additives; wherein the non-aqueous organic solvent is composed of a first solvent, a second solvent, and a third solvent;

[0008] The first solvent is one or more three-dimensional network coordination ethers, with the following general structural formula:

[0009]

[0010] Wherein, R1, R2, R3, and R4 are the same or different C1-C5 alkyl groups;

[0011] The second solvent is one or more linear ethers, with the following general structural formula:

[0012]

[0013] Wherein, R5 and R6 are the same or different C1-C4 alkyl groups, and n is an integer from 1 to 4;

[0014] The third solvent is one or more high dielectric constant solvents and / or fluorinated solvents;

[0015] The mass ratio of the first solvent, the second solvent, and the third solvent is (1-5): (1-5): (0.5-3).

[0016] The present invention also provides a lithium metal battery, comprising a positive electrode, a negative electrode, a separator, and the above-mentioned highly stable electrolyte.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. Three-dimensional network coordination ethers synergistically form films to stabilize lithium anodes: Compared to linear chelate ethers, three-dimensional network coordination ethers (such as trimethyl orthoformate) have relatively weaker coordination ability with lithium ions. This characteristic significantly increases the concentration of aggregates (AGG) and contact ion pairs (CIP) in the electrolyte, allowing more anions to participate in the primary solvation sheath structure. These anions are preferentially reduced at the lithium metal anode interface, participating in the construction of a dense, high-mechanical-strength, and stable SEI film rich in inorganic substances such as LiF and Li3N, thereby fundamentally inhibiting the growth of lithium dendrites and the continuous decomposition of the electrolyte.

[0019] 2. Enhanced lithium salt dissociation and improved ion transport: Linear ethers (such as diethylene glycol dimethyl ether) have good Li+ solvation ability. They work synergistically with solvents with high dielectric constant to promote the dissociation of lithium salts and optimize the primary solvation sheath structure of Li+, which promotes the rapid transport of Li+ in the electrolytic liquid phase and at the interface, and helps to achieve uniform lithium deposition / stripping.

[0020] 3. Expanding the electrochemical window: By introducing high dielectric constant solvents and / or fluorinated solvents as the third component, the antioxidant capacity of the electrolyte system is effectively improved, and its oxidation stability is improved beyond 4.2 V (vs. Li / Li+), even reaching above 4.5 V. This enables it to match high-voltage cathode materials and improve the working voltage and energy density of the full battery.

[0021] 4. Safety and environmental protection: The selected ether solvents have low toxicity, and through the reasonable ratio of each component, the flash point and thermal stability of the electrolyte are improved compared with the single ether system, thus enhancing the safety of the battery. Attached Figure Description

[0022] Figure 1 The graph shows the coulomb efficiency and linearity of the circulation loop for Example 1 and Comparative Example 1. Detailed Implementation

[0023] The embodiments of this application are described in detail below, and examples of these embodiments are shown in the accompanying drawings and tables.

[0024] Those skilled in the art will understand that, unless otherwise stated, the singular forms “a,” “an,” “the,” and “the” used herein may also include the plural forms. It should be further understood that the word “comprising” as used in the specification of this application means the presence of the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. It should be understood that the measures “and / or” used herein include all or any units and all combinations of one or more associated listed items.

[0025] First, a highly stable electrolyte for lithium metal batteries according to the first aspect of the present invention will be described.

[0026] According to a first aspect of the present invention, a highly stable electrolyte for lithium metal batteries comprises a lithium salt, a non-aqueous organic solvent, and optional additives; wherein the non-aqueous organic solvent is composed of a first solvent, a second solvent, and a third solvent.

[0027] The first solvent is one or more three-dimensional network coordination ethers, with the following general structural formula:

[0028]

[0029] Wherein, R1, R2, R3, and R4 are the same or different C1-C5 alkyl groups;

[0030] The second solvent is one or more linear ethers, with the following general structural formula:

[0031]

[0032] Wherein, R5 and R6 are the same or different C1-C4 alkyl groups, and n is an integer from 1 to 4;

[0033] The third solvent is one or more high dielectric constant solvents and / or fluorinated solvents;

[0034] The mass ratio of the first solvent, the second solvent, and the third solvent is (1-5): (1-5): (0.5-3).

[0035] In a highly stable electrolyte for lithium metal batteries according to a first aspect of the present invention, the three-dimensional network coordination ether is selected from one or more of trimethyl orthoformate, trimethyl orthoacetate, trimethyl orthopropionate, trimethyl orthobutyrate, triethyl orthoformate, triethyl orthoacetate, triethyl orthopropionate, triethyl orthobutyrate, and tripropyl orthoformate.

[0036] In a high-stability electrolyte for lithium metal batteries according to a first aspect of the present invention, the linear ether is selected from one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0037] In a high-stability electrolyte for lithium metal batteries according to a first aspect of the present invention, the high dielectric constant solvent is selected from one or more of ethylene carbonate, propylene carbonate, vinylene carbonate, fluoroethylene carbonate, dimethyl sulfite, and diethyl sulfite.

[0038] In a high-stability electrolyte for lithium metal batteries according to a first aspect of the present invention, the fluorinated solvent is selected from one or more of trifluoroethyl methyl carbonate, bis(2,2,2-trifluoroethyl) ether, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0039] In a highly stable electrolyte for lithium metal batteries according to a first aspect of the present invention, the concentration of the lithium salt is from 0.5 M to 3.0 M; the lithium salt is selected from one or more of lithium dioxalatoborate, lithium difluorooxalatoborate, lithium difluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium tetrafluorooxalatophosphate, lithium dioxalatodifluorophosphate, and lithium hexafluorophosphate.

[0040] In a high-stability electrolyte for lithium metal batteries according to a first aspect of the present invention, the additives include one or more of lithium nitrate, lithium difluorophosphate, ethylene sulfate, fluoroethylene carbonate, and lithium difluorobis(oxalato)phosphate, and the total mass of the additives accounts for 0.1% to 5.0% of the total mass of the electrolyte.

[0041] Next, a lithium metal battery according to a second aspect of the present invention will be described.

[0042] According to a second aspect of the present invention, a lithium metal battery includes a positive electrode, a negative electrode, a separator, and the aforementioned highly stable electrolyte.

[0043] In a lithium metal battery according to a second aspect of the present invention, the negative electrode is a lithium metal foil or a composite negative electrode containing lithium metal.

[0044] In a lithium metal battery according to a second aspect of the present invention, the cathode is one of lithium cobalt oxide, nickel-cobalt-manganese ternary material, nickel-cobalt-aluminum ternary material, lithium-rich manganese-based material, lithium manganese oxide, lithium iron phosphate, or sulfur composite cathode.

[0045] The following describes comparative examples and embodiments of a highly stable electrolyte for lithium metal batteries according to the present invention.

[0046] Example 1

[0047] Lithium difluorosulfonylimide and lithium difluorooxalate borate were mixed at a total concentration of 1 mol L⁻¹ and a molar ratio of 3:1 and dissolved in an electrolyte solvent containing trimethyl orthoformate, diethylene glycol dimethyl ether, and ethyl fluorophosphate in a mass ratio of 3:3:1. 0.1% lithium difluorophosphate was then added to obtain a stable and homogeneous electrolyte, LMB01. A lithium-copper-lithium metal deposition half-cell was assembled using copper foil, a separator, and lithium sheets in an argon-protected glove box, and the above electrolyte was added dropwise.

[0048] Experimental results: The coulombic efficiency of the assembled coin cell was tested, and the amount of deposited lithium metal was 1 mAh, with a current density of 1 mA cm⁻¹. -2 The lithium copper half-cell assembled with LMB01 electrolyte can cycle for 150 cycles, and after 200 cycles, the average coulombic efficiency is still over 99.0%.

[0049] Example 2

[0050] Based on Example 1, the electrolyte solvent was changed to a mixture of trimethyl orthoacetate, ethylene glycol dimethyl ether, and fluoroethylene carbonate in a mass ratio of 3:4:1, and the additive was changed to 5.0% fluoroethylene carbonate, while the other conditions remained the same.

[0051] Experimental results: The coulombic efficiency of the assembled battery was tested, with a deposited lithium metal amount of 1 mAh and a current density of 0.5 mA cm⁻¹. -2 The lithium copper half-cell assembled with LMB02 electrolyte can cycle for 180 cycles, with an average coulombic efficiency of 98.8% after 180 cycles.

[0052] Example 3

[0053] Based on Example 1, the electrolyte lithium salt was changed to lithium bis(fluorosulfonyl)imide and lithium difluorooxalate borate mixed in a molar ratio of 4:1, the additive was changed to 2.0% ethylene sulfate, and the other conditions remained the same.

[0054] Experimental results: The coulombic efficiency of the assembled battery was tested, with a deposited lithium metal amount of 1 mAh and a current density of 0.5 mA cm⁻¹. -2 The lithium copper half-cell assembled with LMB03 electrolyte can cycle for 80 cycles, and the average coulombic efficiency is 99.2% after 80 cycles.

[0055] Example 4

[0056] Based on Example 1, the lithium salt in the electrolyte was changed to a lithium salt of lithium bis(fluorosulfonyl)imide and lithium difluorooxalate borate mixed in a molar ratio of 4:1, the electrolyte solvent was changed to a solvent of trimethyl orthobutyrate, ethylene glycol diethyl ether, and fluoroethylene carbonate mixed in a body weight ratio of 5:4:1, and the additive was changed to 2.0% ethylene sulfate. All other conditions remained the same.

[0057] Experimental results: The coulombic efficiency of the assembled battery was tested, with a deposited lithium metal amount of 1 mAh and a current density of 0.5 mA cm⁻¹. -2 The lithium copper half-cell assembled with LMB04 electrolyte can cycle for 100 cycles, with an average coulombic efficiency of 98.5% after 100 cycles.

[0058] Example 5

[0059] Based on Example 1, the lithium salt in the electrolyte was replaced with lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate mixed in a molar ratio of 4:1. The electrolyte solvent was replaced with trimethyl propionate, diethylene glycol diethyl ether, and fluoroethylene carbonate mixed in a mass ratio of 5:4:1. The additive was replaced with 1.0% ethylene sulfate. All other conditions remained the same.

[0060] Experimental results: The assembled battery was tested for coulombic efficiency. The amount of deposited lithium metal was 1 mAh, and the current density was 0.5 mA cm⁻¹. -2 The lithium copper half-cell assembled with LMB05 electrolyte can cycle for 250 cycles, with an average coulombic efficiency of 99.3% after 250 cycles.

[0061] Comparative Example 1

[0062] Based on Example 1, the lithium salt in the electrolyte was replaced with lithium hexafluorophosphate, the electrolyte solvent was replaced with ethylene carbonate, and the solvent of dimethyl carbonate mixed at a mass ratio of 1:1 remained the same as other conditions.

[0063] Experimental results: The assembled battery was tested for coulombic efficiency. The amount of deposited lithium metal was 1 mAh, and the current density was 0.5 mA cm⁻¹.-2 The lithium copper half-cell assembled with BLANK1 electrolyte achieved an average coulombic efficiency of 40.5% after 80 cycles.

[0064] Based on the coulombic efficiency test results and the average coulombic efficiency after cycling of Examples 1-5 and Comparative Example 1, this indicates that the five electrolytes LMB01 to LMB05 have good compatibility with lithium metal, can achieve reversible lithium metal deposition, and can achieve stable long-term cycling of lithium metal batteries.

[0065] The experimental results of Examples 1-5 and Comparative Example 1 are shown in Table 1:

[0066] Example 6

[0067] Based on Example 1, a full cell was assembled using LiCo2 cathode material, NCM811 cathode material, separator, and lithium sheet in an argon-protected glove box, and LMB01 was added. The assembled coin cell was then subjected to cycle testing within a voltage range of 3-4.3V.

[0068] Experimental results: The LiCo2 full cell assembled with LMB01 electrolyte retained 95.1% of its capacity after 200 cycles; the NCM811 full cell assembled with LMB01 electrolyte retained 90.3% of its capacity after 200 cycles.

[0069] Example 7

[0070] Based on Example 2, a full cell was assembled using LiCo2 cathode material, NCM811 cathode material, separator, and lithium sheet in an argon-protected glove box, and LMB02 was added. The assembled coin cell was then subjected to cycle testing within a voltage range of 3-4.3V.

[0071] Experimental results: The LiCo2 full cell assembled with LMB02 electrolyte retained 93.4% of its capacity after 300 cycles; the NCM811 full cell assembled with LMB02 electrolyte retained 89.2% of its capacity after 150 cycles.

[0072] Example 8

[0073] Based on Example 3, a full cell was assembled using LiCo2 cathode material, NCM811 cathode material, separator, and lithium sheet in an argon-protected glove box, and LMB03 was added. The assembled coin cell was then subjected to cycle testing within a voltage range of 3-4.3V.

[0074] Experimental results: The LiCo2 full cell assembled with LMB03 electrolyte retained 95.8% of its capacity after 400 cycles; the NCM811 full cell assembled with LMB03 electrolyte retained 91.7% of its capacity after 200 cycles.

[0075] Example 9

[0076] Based on Example 4, a full cell was assembled using LiCo2 cathode material, NCM811 cathode material, separator, and lithium sheet in an argon-protected glove box, and LMB04 was added. The assembled coin cell was then subjected to cycle testing within a voltage range of 3-4.3V.

[0077] Experimental results: The LiCo2 full cell assembled with LMB04 electrolyte retained 94.5% of its capacity after 350 cycles; the NCM811 full cell assembled with LMB04 electrolyte retained 92.3% of its capacity after 200 cycles.

[0078] Example 10

[0079] Based on Example 5, a full cell was assembled using LiCo2 cathode material, NCM811 cathode material, separator, and lithium sheet in an argon-protected glove box, and LMB05 was added. The assembled coin cell was then subjected to cycle testing within a voltage range of 3-4.3V.

[0080] Experimental results: The LiCo2 full cell assembled with LMB05 electrolyte retained 96.1% of its capacity after 200 cycles; the NCM811 full cell assembled with LMB05 electrolyte retained 93.5% of its capacity after 200 cycles.

[0081] Comparative Example 2

[0082] Based on Example 6, the electrolyte solvent was changed to ethylene glycol dimethyl ether, while all other conditions remained the same. The assembled battery was subjected to library cycle testing within a voltage range of 3-4.3V.

[0083] Experimental results: The lithium cobalt oxide full cell assembled with BLANK2 electrolyte retained 41.6% of its capacity after 200 cycles; the lithium cobalt oxide full cell assembled with BLANK2 electrolyte retained 36.2% of its capacity after 200 cycles.

[0084] Based on the capacity retention test results of Examples 6-10 and Comparative Example 2, this indicates that the five electrolytes LMB01 to LMB05 have good compatibility with lithium metal, can achieve reversible lithium metal deposition, have high oxidation potential, and have excellent compatibility with high-voltage cathode materials, enabling stable long-cycle operation of high-energy-density lithium metal batteries.

[0085] The experimental results of Examples 6-10 and Comparative Example 2 are shown in Table 2:

[0086]

[0087] Taking Example 1 and Comparative Example 1 as examples, when recording the coulombic efficiency and cycle number of Example 1 and Comparative Example 1 using experimental instruments, the following results can be obtained: Figure 1 The linear results are shown in the graph.

[0088] The above description is only a partial embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A highly stable electrolyte for lithium metal batteries, characterized in that: It includes lithium salts, non-aqueous organic solvents, and optional additives; the non-aqueous organic solvents consist of a first solvent, a second solvent, and a third solvent; The first solvent is one or more three-dimensional network coordination ethers, with the following general structural formula: Wherein, R1, R2, R3, and R4 are the same or different C1-C5 alkyl groups; The second solvent is one or more linear ethers, with the following general structural formula: Wherein, R5 and R6 are the same or different C1-C4 alkyl groups, and n is an integer from 1 to 4; The third solvent is one or more high dielectric constant solvents and / or fluorinated solvents; The mass ratio of the first solvent, the second solvent, and the third solvent is (1-5):(1-5):(0.5-3).

2. The high-stability electrolyte for lithium metal batteries as described in claim 1, characterized in that: The three-dimensional network coordination ether is selected from one or more of trimethyl orthoformate, trimethyl orthoacetate, trimethyl orthopropionate, trimethyl orthobutyrate, triethyl orthoformate, triethyl orthoacetate, triethyl orthopropionate, triethyl orthobutyrate, and tripropyl orthoformate.

3. The high-stability electrolyte for lithium metal batteries as described in claim 1, characterized in that: The linear ether is selected from one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

4. The high-stability electrolyte for lithium metal batteries as described in claim 1, characterized in that: The high dielectric constant solvent is selected from one or more of ethylene carbonate, propylene carbonate, vinylene carbonate, fluoroethylene carbonate, dimethyl sulfite, and diethyl sulfite.

5. The high-stability electrolyte for lithium metal batteries as described in claim 1, characterized in that: The fluorinated solvent is selected from one or more of trifluoroethyl methyl carbonate, bis(2,2,2-trifluoroethyl) ether, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

6. The high-stability electrolyte for lithium metal batteries as described in claim 1, characterized in that: The concentration of the lithium salt is from 0.5 M to 3.0 M; The lithium salt is selected from one or more of lithium dioxaborate, lithium difluorooxaborate, lithium difluorophosphate, lithium difluorosulfonylimide, lithium bis(trifluoromethylsulfonylimide), lithium tetrafluorooxaborate phosphate, lithium dioxaborate difluorophosphate, and lithium hexafluorophosphate.

7. The high-stability electrolyte for lithium metal batteries as described in claim 1, characterized in that: The additives include one or more of lithium nitrate, lithium difluorophosphate, vinyl sulfate, fluoroethylene carbonate, and lithium difluorobis(oxalato)phosphate, and the total mass of the additives accounts for 0.1% to 5% of the total mass of the electrolyte.

8. A lithium metal battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that: The electrolyte is the electrolyte according to any one of claims 1 to 7.

9. A lithium metal battery as described in claim 8, characterized in that: The negative electrode is a lithium metal foil or a composite negative electrode containing lithium metal; the positive electrode material is selected from one of lithium cobalt oxide, nickel-cobalt-manganese ternary materials, nickel-cobalt-aluminum ternary materials, lithium-rich manganese-based materials, lithium manganese oxide, lithium iron phosphate, or sulfur composite positive electrode.

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