Ether local super-concentrated electrolyte containing disubstituted aromatic diluent and lithium metal battery based on ether local super-concentrated electrolyte

Abstract

The invention discloses an ether local super-concentrated electrolyte containing a disubstituted aromatic diluent and a lithium metal battery based on the ether local super-concentrated electrolyte. The electrolyte is prepared from fluorine-containing lithium salt, an ether solvent and the disubstituted aromatic diluent. Compared with the existing electrolyte, the ether electrolyte provided by the invention uses the aromatic diluent with disubstituted functional groups, shows relatively good reduction stability and oxidation stability, can effectively inhibit the growth of lithium dendrites and realize highly reversible lithium metal deposition / stripping, and meanwhile, ensures the stable circulation of a high-voltage lithium metal battery; the problem of low stability of a positive-negative electrode interface of the lithium metal battery is solved, and the application prospect is wide.

Description

Technical Field

[0001] This invention belongs to the field of lithium metal battery technology, specifically relating to an electrolyte containing a dual-substituted aromatic diluent and a lithium metal battery based thereon. Background Technology

[0002] Currently, traditional lithium-ion batteries using graphite as the negative electrode are widely used in portable electronic devices and electric vehicles, but their energy density is gradually approaching its theoretical limit, making it difficult to meet the ever-increasing demand for high-specific-energy storage. In contrast, lithium metal anodes have an ultra-high theoretical specific capacity of 3860 mAh / g and a minimum electrochemical potential of -3.04 V (vs. SHE). When matched with high-voltage layered transition metal oxide cathodes, they can achieve high energy densities of over 500 Wh / kg, making them a technological route with great industrialization potential for next-generation high-specific-energy storage batteries.

[0003] However, the commercial application of lithium metal batteries still faces key technological bottlenecks: traditional carbonate electrolytes have a wide electrochemical window, but poor compatibility with lithium metal anodes, easily forming unstable solid electrolyte interphase (SEI), resulting in low lithium deposition / stripping coulombic efficiency and uncontrolled lithium dendrite growth, thus limiting battery cycle life and safety performance. Ether electrolytes have excellent compatibility with lithium metal anodes, but their own oxidation stability is insufficient, easily forming unstable cathode electrolyte interphase (CEI) at the high-voltage cathode interface, which cannot support long-term stable cycling of high-voltage cathode materials.

[0004] To improve the high-voltage compatibility of ether-based electrolytes, existing technologies propose a locally ultra-concentrated electrolyte approach: first, a high-concentration lithium salt-ether solvent system is constructed to enhance the electrolyte's oxidation stability; then, an inert diluent is introduced to reduce the system's viscosity and optimize ionic conductivity, thereby balancing the electrochemical stability of the positive and negative electrode interfaces. Aromatic compounds, due to their low viscosity and density and low raw material cost, have become the preferred category of diluents for lithium metal batteries. However, current conventional aromatic diluents (such as fluorobenzene and difluorobenzene) suffer from insufficient cycle stability under high voltage / high rate conditions, and some varieties exhibit potential biotoxicity, making it difficult to simultaneously meet the dual technical requirements of >4.3 V high-voltage positive electrode compatibility and high coulombic efficiency of the lithium metal negative electrode.

[0005] Therefore, a dual-substituted aromatic diluent-based ether electrolyte system with controllable R&D costs, readily available raw materials, and the ability to synergistically match the stability of high-voltage cathodes with the efficient deposition / stripping of lithium metal anodes is of great practical significance for breaking through the technological bottlenecks in the industrialization of high-energy-density lithium metal batteries and promoting their engineering applications. Summary of the Invention

[0006] To overcome the shortcomings of existing ether-based electrolytes, such as insufficient high-voltage oxidation stability, poor high-rate cycling stability of conventional aromatic diluents in 4.3 V lithium metal batteries, and poor compatibility with lithium anodes, this invention provides a locally ultra-concentrated ether-based electrolyte suitable for high-voltage lithium metal batteries. By screening specific compound systems of fluorinated lithium salts, ether solvents, and disubstituted aromatic diluents, long-term stable cycling of lithium metal batteries at a working voltage of 4.3 V is achieved.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: This invention provides an ether-based locally ultra-concentrated electrolyte containing a disubstituted aromatic diluent, which is composed of a fluorinated lithium salt, an ether solvent, and a disubstituted aromatic diluent.

[0008] Further: the fluorinated lithium salt is selected from one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium hexafluorophosphate; the ether solvent is selected from one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; the disubstituted aromatic diluent is selected from one or more of 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 2-fluorotrifluorotoluene, and 2-fluorotrifluoromethoxybenzene.

[0009] As a preferred technical solution: the fluorinated lithium salt contains at least lithium bis(fluorosulfonyl)imide. The ether solvent contains at least ethylene glycol dimethyl ether. The disubstituted aromatic diluent is selected from one or more of 1,2-difluorobenzene, 2-fluorotrifluorotoluene, and 2-fluorotrifluoromethoxybenzene.

[0010] As a preferred technical solution, the concentration of fluorinated lithium salt in the electrolyte is 0.4 M to 2.5 M.

[0011] As a preferred technical solution, based on the total volume of ether solvent and disubstituted aromatic diluent, the volume fraction of ether solvent is 20-35% and the volume fraction of disubstituted aromatic diluent is 65-80%.

[0012] The preparation method of the ether-based locally ultra-concentrated electrolyte of the present invention is as follows: In an argon-protected glove box, a fluorinated lithium salt is added to an ether solvent and stirred until the fluorinated lithium salt is completely dissolved to form a homogeneous and transparent base solution; then, a disubstituted aromatic diluent is added to the base solution and stirred thoroughly until the system is clear, transparent and uniformly mixed to obtain the ether-based locally ultra-concentrated electrolyte containing the disubstituted aromatic diluent.

[0013] The present invention also provides a lithium metal battery, comprising a lithium metal negative electrode, a transition metal layered oxide positive electrode, a separator, and an electrolyte, wherein the electrolyte is the above-mentioned locally ultra-concentrated ether electrolyte containing a disubstituted aromatic diluent.

[0014] Compared with existing technologies, the beneficial effects of this invention are reflected in: 1. This invention utilizes a dual-substituted aromatic diluent to construct an ether-based locally ultra-concentrated electrolyte, which significantly improves the high-voltage oxidation stability of the electrolyte and gives it excellent interfacial compatibility with the high-nickel ternary cathode, enabling long-term stable cycling of lithium metal batteries at a high voltage of 4.3 V. At the same time, this type of diluent has excellent matching with the lithium metal anode, forming a dense and stable SEI film, effectively improving the lithium deposition / stripping coulombic efficiency and ensuring the overall electrochemical performance of the battery.

[0015] 2. The fluorinated lithium salt, ether solvent and disubstituted aromatic diluent selected in this invention are all industrially mass-produced chemicals. The raw materials are widely available and inexpensive. The electrolyte preparation process is simple and the system dosage is controllable. It has cost and process advantages for large-scale industrial application.

[0016] 3. The ether-based locally ultra-concentrated electrolyte of the present invention effectively improves the problems of high viscosity and poor membrane wettability of traditional carbonate electrolytes while synergistically taking into account the dual interface stability of the positive electrode CEI and negative electrode SEI. It optimizes the internal ion transport dynamics of the battery and further enhances the cycle stability and reliability of lithium metal batteries.

[0017] 4. The high-voltage adaptable ether electrolyte system developed in this invention breaks through the technical bottlenecks of high-voltage instability of conventional ether electrolytes and insufficient compatibility of traditional aromatic diluents with the negative electrode. It provides an efficient and feasible electrolyte solution for the industrialization of high-energy-density lithium metal batteries and has important technical promotion and application value. Attached Figure Description

[0018] Figure 1 The long-cycle performance and coulombic efficiency of the 450μm Li||NMC811 full cells assembled using the electrolytes in Examples 1, 2 and Comparative Example 1 were measured at room temperature after activation at 0.1C for 3 cycles, followed by charging at 0.5C, discharging at 1C, and testing within a voltage window of 2.8~4.3V. Figure 2 The long-cycle performance and coulombic efficiency of the 50μm Li||NMC811 full cells assembled using the electrolytes in Examples 1, 2 and Comparative Example 1 were measured at room temperature after activation at 0.1C for 3 cycles, followed by charging at 0.5C, discharging at 1C, and testing within a voltage window of 2.8~4.3V. Figure 3 The image shows the lithium metal anode deposition / stripping coulombic efficiency obtained by Aurbach testing for Li||Cu half-cells assembled using the electrolytes in Examples 1, 2, and Comparative Example 1. Figure 4 To use the electrolyte from Example 1, at 0.5 mA cm⁻¹ -2Current density, 1.0 mAh cm⁻¹ -2 SEM images of lithium metal deposition morphology obtained at the deposition capacity; Figure 5 To use the electrolyte of Example 2, at 0.5 mA cm⁻¹ -2 Current density, 1.0 mAh cm⁻¹ -2 SEM images of lithium metal deposition morphology obtained at the deposition capacity; Figure 6 To use the electrolyte of Comparative Example 1, at 0.5 mA cm⁻¹ -2 Current density, 1.0 mAh cm⁻¹ -2 SEM images of lithium metal deposition morphology obtained at the deposition capacity. Detailed Implementation

[0019] To further understand the present invention, preferred embodiments are described below with reference to examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims. The scope of protection of the present invention is not limited to the following embodiments.

[0020] Example 1 This embodiment provides a locally concentrated ether electrolyte containing a disubstituted aromatic diluent, specifically as follows: lithium bis(fluorosulfonyl)imide is used as the lithium salt, ethylene glycol dimethyl ether as the solvent, and 2-fluorotrifluoromethoxybenzene as the diluent. The preparation method is as follows: In an argon-protected glove box, 187 mg (1.0 mmol) of lithium bis(fluorosulfonyl)imide is weighed and added to 108 mg (1.2 mmol, 125 μL, volume fraction 23.5%) of ethylene glycol dimethyl ether. The mixture is stirred until the fluorinated lithium salt is completely dissolved, forming a homogeneous and transparent base solution. Subsequently, 540 mg (3.0 mmol, 408 μL, volume fraction 76.5%) of 2-fluorotrifluoromethoxybenzene is added to the base solution, and the mixture is stirred thoroughly until the system is clear, transparent, and uniformly mixed, thus obtaining the locally concentrated ether electrolyte containing a disubstituted aromatic diluent. The molar ratio of lithium salt to ether solvent is 1:1.2, and the molar ratio of ether solvent to diluent is 1.2:3.

[0021] Example 2 This embodiment provides a locally concentrated ether electrolyte containing a disubstituted aromatic diluent, specifically as follows: lithium bis(fluorosulfonyl)imide is used as the lithium salt, ethylene glycol dimethyl ether as the solvent, and 2-fluorotrifluorotoluene as the diluent. The preparation method is as follows: In an argon-protected glove box, 187 mg (1.0 mmol) of lithium bis(fluorosulfonyl)imide is weighed and added to 108 mg (1.2 mmol, 125 μL, volume fraction 24.7%) of ethylene glycol dimethyl ether. The mixture is stirred until the fluorinated lithium salt is completely dissolved, forming a homogeneous and transparent base solution. Subsequently, 492 mg (3.0 mmol, 381 μL, volume fraction 75.3%) of 2-fluorotrifluoromethoxybenzene is added to the base solution, and the mixture is stirred thoroughly until the system is clear, transparent, and uniformly mixed, thus obtaining the locally concentrated ether electrolyte containing a disubstituted aromatic diluent. The molar ratio of lithium salt to ether solvent is 1:1.2, and the molar ratio of ether solvent to diluent is 1.2:3.

[0022] Comparative Example 1 This comparative example provides an ether-based locally ultra-concentrated electrolyte containing a monosubstituted aromatic diluent, specifically as follows: lithium bis(fluorosulfonyl)imide is used as the lithium salt, ethylene glycol dimethyl ether as the solvent, and fluorobenzene as the diluent. The preparation method is as follows: In an argon-protected glove box, 187 mg (1.0 mmol) of lithium bis(fluorosulfonyl)imide is weighed and added to 108 mg (1.2 mmol, 125 μL, volume fraction 29.7%) of ethylene glycol dimethyl ether. The mixture is stirred until the fluorinated lithium salt is completely dissolved, forming a homogeneous and transparent base solution. Subsequently, 342 mg (3.0 mmol, 282 μL, volume fraction 70.3%) of fluorobenzene is added to the base solution, and the mixture is stirred thoroughly until the system is clear, transparent, and uniformly mixed, thus obtaining the ether-based locally ultra-concentrated electrolyte containing a monosubstituted aromatic diluent. The molar ratio of lithium salt to ether solvent is 1:1.2, and the molar ratio of ether solvent to diluent is 1.2:3.

[0023] This invention also provides a lithium metal full battery, which comprises a lithium metal anode, an NMC811 cathode, an electrolyte, and a Celgard2325 separator. The lithium metal anode, NMC811 cathode, and Celgard2325 separator are all conventional commercial materials in the relevant technical field or can be conventionally prepared by those skilled in the art. The electrolyte is an ether-based locally ultra-concentrated electrolyte prepared using the above technical solution.

[0024] To verify the technical effectiveness of the electrolyte of the present invention, the electrochemical performance and morphology characterization tests were conducted on the ether electrolytes prepared in Examples 1, 2 and Comparative Example 1. The specific test steps, conditions and results are as follows: Step 1: Long-term cycle performance test of 450 μm Li||NMC811 full cell Using the electrolytes of Example 1, Example 2, and Comparative Example 1, 450 μm lithium metal anode || NMC811 cathode full cells were assembled. The test environment was room temperature. The cells were first activated by cycling at a 0.1C charge-discharge rate for 3 cycles, and then charged at a 0.5C rate and discharged at a 1C rate. The charge-discharge voltage window was set to 2.8~4.3V for long-cycle performance testing.

[0025] Figure 1 The graphs show the long-cycle performance and coulombic efficiency of the 450 μm Li||NMC811 full cells assembled in the above embodiments and comparative examples under the above test conditions. Test results show that: Comparative Example 1 achieved a maximum discharge specific capacity of 212.59 mAh / g at 0.1C, 188.69 mAh / g in the first cycle at 1C, and decreased to 155.24 mAh / g after 31 cycles, maintaining a discharge specific capacity retention of 82.27% and an average coulombic efficiency of 98.5%; Example 2 achieved a maximum discharge specific capacity of 210.50 mAh / g at 0.1C, 183.52 mAh / g in the first cycle at 1C, and decreased to 147.48 mAh / g after 56 cycles, maintaining a discharge specific capacity retention of 80% and an average coulombic efficiency of 99.3%; Example 1 achieved a maximum discharge specific capacity of 213.29 mAh / g at 0.1C, 185.57 mAh / g in the first cycle at 1C, and still maintained a discharge specific capacity of 181.27 mAh / g after 200 cycles. It has a capacity of mAh / g, a discharge specific capacity retention rate of up to 97.68%, and an average coulombic efficiency of 99.8%.

[0026] The test results clearly show that, compared with Example 2 and Comparative Example 1, the electrolyte of Example 1 can significantly improve the high-voltage long-cycle stability and coulombic efficiency of lithium metal batteries, and has outstanding electrochemical performance advantages.

[0027] Step 2: Long-term cycle performance testing of 50 μm Li||NMC811 full cells Using the electrolytes of Example 1, Example 2, and Comparative Example 1, 50 μm lithium metal anode || NMC811 cathode full cells were assembled. The test environment, activation conditions, charge / discharge rate, and voltage window were consistent with those in step one. Long-cycle performance tests were conducted to simulate the actual application scenario of thin lithium anodes.

[0028] Figure 2The graphs show the long-cycle performance and coulombic efficiency of the 50 μm Li||NMC811 full cells assembled in the above embodiments and comparative examples under the above test conditions. Test results show that: Comparative Example 1 achieved a maximum discharge specific capacity of 210.97 mAh / g at 0.1C, 190.30 mAh / g in the first cycle at 1C, and decreased to 143.98 mAh / g after 22 cycles, maintaining a discharge specific capacity retention rate of 77.28% and an average coulombic efficiency of 97.7%; Example 2 achieved a maximum discharge specific capacity of 209.60 mAh / g at 0.1C, 184.72 mAh / g in the first cycle at 1C, and decreased to 148.02 mAh / g after 47 cycles, maintaining a discharge specific capacity retention rate of 80.1% and an average coulombic efficiency of 99.1%; Example 1 achieved a maximum discharge specific capacity of 210.89 mAh / g at 0.1C, 183.61 mAh / g in the first cycle at 1C, and still maintained a discharge specific capacity of 181.27 mAh / g after 100 cycles. It has a capacity of mAh / g, a discharge specific capacity retention rate of up to 98.63%, and an average coulombic efficiency of 99.7%.

[0029] The test results further confirm that the electrolyte of Example 1 can significantly improve the cycle stability of lithium metal batteries even in thin lithium anode systems, making it suitable for practical application requirements. Its performance advantages are significantly better than those of Example 2 and Comparative Example 1.

[0030] Step 3: Aurbach test of Li||Cu half-cell (evaluation of lithium deposition / stripping coulombic efficiency) Li||Cu half-cells were assembled using the electrolytes of Example 1, Example 2, and Comparative Example 1, respectively. The test environment was room temperature, and the Aurbach test method was used to evaluate the deposition / stripping coulombic efficiency of the lithium metal anode in the electrolyte, which directly reflects the compatibility between the electrolyte and the lithium metal anode.

[0031] Figure 3 The figures show the Aurbachelor test results for the Li||Cu half-cells assembled in the above embodiments and comparative examples. The test results show that the coulombic efficiency of the Li||Cu half-cell in Comparative Example 1 is 99.55%, the coulombic efficiency of the Li||Cu half-cell in Example 2 is 96.19%, while the coulombic efficiency of the Li||Cu half-cell in Example 1 is as high as 99.58%, slightly better than Comparative Example 1 and significantly better than Example 2. This demonstrates that the electrolyte of Example 1 has better compatibility with the lithium metal anode, enabling efficient and reversible lithium deposition / stripping processes.

[0032] Step 4: SEM characterization of lithium metal deposition morphology Li||Cu half-cells were assembled using the electrolytes from Examples 1, 2, and Comparative Example 1, respectively. Each half-cell employed a 450 μm thick lithium metal electrode as the negative electrode, a 25 μm thick copper foil as the positive electrode, and a Celgard 2325 membrane. The electrolyte was measured at 0.5 mA cm⁻¹. -2 Current density, 1 mAh cm -2 Constant current deposition tests were conducted under capacity density conditions. After the test, the battery was quickly transferred into a glove box for disassembly, and the morphology of the lithium metal anode deposition surface was characterized by scanning electron microscopy (SEM).

[0033] Figure 4 , Figure 5 , Figure 6 The images show the SEM morphology of lithium metal after deposition in the electrolyte systems of Examples 1, 2, and Comparative Example 1, respectively. Characterization results show that the lithium metal deposited in the electrolyte of Comparative Example 1 has a loose and porous structure with obvious lithium dendrite growth, which easily leads to the risk of battery short circuits. The lithium metal deposited in the electrolyte of Example 2 also exhibits a severe lithium dendrite growth trend, and the interface structure is unstable. In contrast, the lithium metal deposited in the electrolyte of Example 1 exhibits a uniform and dense morphology with no obvious lithium dendrite formation, further confirming that the electrolyte of Example 1 can effectively regulate lithium deposition behavior, suppress lithium dendrite growth, and has excellent compatibility with the lithium metal anode, providing a guarantee for long-term stable battery cycling.

[0034] The specific embodiments of the present invention have been described in detail above, but they are merely examples, and the present invention is not limited to the specific embodiments described above. For those skilled in the art, any equivalent modifications and substitutions to the present invention are also within the scope of the present invention. Therefore, all equivalent transformations and modifications made without departing from the spirit and scope of the present invention should be covered within the scope of the present invention.

Claims

1. A locally concentrated electrolyte containing a disubstituted aromatic diluent, characterized in that, The electrolyte is composed of fluorinated lithium salt, ether solvent and disubstituted aromatic diluent.

2. The ether-based locally concentrated electrolyte according to claim 1, characterized in that, The fluorinated lithium salt is selected from one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium hexafluorophosphate.

3. The ether-based locally concentrated electrolyte according to claim 1, characterized in that, The ether solvent is selected from one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

4. The ether-based locally concentrated electrolyte according to claim 1, characterized in that, The disubstituted aromatic diluent is selected from one or more of 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 2-fluorotrifluorotoluene, and 2-fluorotrifluoromethoxybenzene.

5. The ether-based locally concentrated electrolyte according to claim 1, characterized in that, The concentration of fluorinated lithium salt in the electrolyte is 0.4 M to 2.5 M.

6. The ether-based locally concentrated electrolyte according to claim 1 or 5, characterized in that, Based on the total volume of ether solvents and disubstituted aromatic diluents, the volume fraction of ether solvents is 20-35%, and the volume fraction of disubstituted aromatic diluents is 65-80%.

7. The method for preparing the ether-based locally ultra-concentrated electrolyte according to any one of claims 1 to 6, characterized in that: In an argon-protected glove box, fluorinated lithium salt is added to an ether solvent and stirred until the fluorinated lithium salt is completely dissolved to form a homogeneous and transparent base solution. Then, a disubstituted aromatic diluent is added to the base solution and stirred thoroughly until the system is clear, transparent and uniformly mixed, thus obtaining a locally ultra-concentrated ether electrolyte containing a disubstituted aromatic diluent.

8. A lithium metal battery, comprising a lithium metal anode, a transition metal layered oxide cathode, a separator, and an electrolyte, characterized in that: The electrolyte is the ether-based locally ultra-concentrated electrolyte as described in any one of claims 1 to 6.

Images