Ether-based electrolyte for silicon-copper reversible battery and preparation method thereof, and silicon-copper reversible battery

Abstract

This invention relates to the field of lithium-ion battery technology, and more particularly to an ether-based electrolyte for a silicon-copper reversible battery, its preparation method, and the silicon-copper reversible battery itself. The ether-based electrolyte comprises: a lithium salt and a mixed organic solvent; the lithium salt includes lithium bis(trifluoromethanesulfonyl)imide; the mixed organic solvent includes tetrahydrofuran and N,N-dimethylformamide; the concentration of the lithium salt in the ether-based electrolyte is 2.5 mol / L. ‑1 Up to 6 mol L ‑1 The volume ratio of tetrahydrofuran to N,N-dimethylformamide is (6-9.5):(0.5-4). This invention utilizes the excellent lithium salt solubility of tetrahydrofuran and the high dielectric constant of N,N-dimethylformamide to achieve the dissolution of high-concentration lithium salts, providing sufficient active lithium ions for the silicon-copper battery system. The ether-based electrolyte can form a stable and dense solid electrolyte interface film on the surface of the silicon-based anode, effectively mitigating the volume expansion of the silicon anode during cycling.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to an ether-based electrolyte for silicon-copper reversible batteries, a method for preparing the same, and the silicon-copper reversible battery. Background Technology

[0002] Silicon anode materials have extremely high theoretical specific capacity (4200 mAh g). -1 Silicon, second only to lithium metal, boasts advantages such as a relatively low voltage plateau, no risk of lithium dendrite formation, abundant natural reserves, and low price. Crucially, silicon's intrinsic chemical reactivity is far lower than that of lithium metal, meaning there are relatively fewer side reactions between the silicon anode and the electrolyte, which is beneficial for improving coulombic efficiency. Theoretically, replacing the lithium metal anode in lithium-copper batteries with a silicon anode can fundamentally eliminate the corrosion problem of lithium metal caused by the copper ion shuttle effect, while also avoiding the safety hazards posed by lithium dendrites.

[0003] Despite the theoretical advantages of silicon-copper battery systems, in practical applications, the lithium source in the electrochemical system comes solely from lithium salts in the electrolyte. This necessitates the design of highly polar solvents to dissolve a sufficient concentration of lithium salts, providing ample active lithium ions for the battery. Silicon-based anodes undergo significant volume expansion (up to 300%) during lithium insertion / extraction. This expansion leads to cracking and pulverization of the anode material, causing the active material to detach from the current collector. Furthermore, the stress generated by the expansion affects electron transport paths and lithium-ion migration channels, resulting in rapid capacity decay.

[0004] Therefore, existing technologies still need further development and improvement. Summary of the Invention To address the aforementioned technical problems, this invention proposes an ether-based electrolyte for silicon-copper reversible batteries and its preparation method, aiming to solve the problem of volume expansion in silicon-based anodes during lithium insertion / extraction processes in existing technologies. Specifically: In a first aspect, an ether-based electrolyte for a silicon-copper reversible battery, comprising: a lithium salt and a mixed organic solvent; said lithium salt comprising lithium bis(trifluoromethanesulfonyl)imide; The mixed organic solvent comprises tetrahydrofuran and N,N-dimethylformamide; the concentration of the lithium salt in the ether-based electrolyte is 2.5 mol / L. -1 Up to 6 mol L -1 The volume ratio of the tetrahydrofuran to N,N-dimethylformamide is (6-9.5):(0.5-4).

[0005] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The purpose and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0006] As a preferred technical solution, the ether-based electrolyte further includes one or more of the following lithium salts: lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, or lithium chloride.

[0007] As a preferred technical solution, the ether-based electrolyte further includes at least one of the following in the mixed organic solvent: ethylene glycol dimethyl ether, fluoroethylene carbonate, vinylene carbonate, methyl ethyl carbonate, diethyl carbonate, ethylene carbonate, or dimethyl carbonate.

[0008] As a preferred technical solution, in the ether-based electrolyte, the concentration of the lithium salt in the electrolyte is 3 mol / L. -1 Up to 5 mol L -1 .

[0009] Secondly, a method for preparing the above-described ether-based electrolyte, comprising the following steps: The tetrahydrofuran and N,N-dimethylformamide were mixed in a volume ratio to obtain a preliminary mixed solvent; The lithium salt is dispersed in the initial mixed solvent to obtain the ether-based electrolyte.

[0010] Thirdly, a silicon-copper reversible battery, comprising: The positive electrode has metallic copper as its active material; The negative electrode includes silicon-based negative electrode materials; and the ether-based electrolyte as described above.

[0011] As a preferred technical solution, in the aforementioned silicon-copper reversible battery, the silicon-based negative electrode material is a silicon-carbon composite material; during the charge-discharge cycle, the copper crystal exhibits a preferred orientation growth with a (2 0 0) crystal plane.

[0012] As a preferred technical solution, the silicon-copper reversible battery further includes a separator, which is a glass fiber membrane or a composite membrane of polyionic liquid and polypropylene.

[0013] As a preferred technical solution, the silicon-copper reversible battery, wherein the silicon-copper reversible battery is at 2 mA cm⁻¹ -2 At current density, the cycle life is not less than 500 hours.

[0014] Fourthly, the application of the aforementioned silicon-copper reversible battery in energy storage devices, electric vehicles, or portable electronic devices.

[0015] Beneficial effects: Compared with existing technologies, this invention uses a solvent system of tetrahydrofuran and N,N-dimethylformamide mixed at a specific volume ratio. Utilizing the excellent lithium salt solubility of tetrahydrofuran and the high dielectric constant of N,N-dimethylformamide, it achieves effective dissolution of high-concentration lithium salts, providing sufficient active lithium ions for the silicon-copper battery system and ensuring optimal battery capacity. Simultaneously, the ether-based electrolyte can form a stable and dense solid electrolyte interface film on the silicon-based anode surface, effectively mitigating the volume expansion of the silicon anode during cycling, reducing the loss of active material, improving coulombic efficiency, and extending battery cycle life. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 The diagram shows the ESP calculation for each solvent in the embodiments of the present invention.

[0018] Figure 2 The diagram shows the HOMO and LUMO calculations for each solvent in the embodiments of the present invention.

[0019] Figure 3 The diagram shows the molecular dynamics simulation calculations of various electrolytes in the embodiments of the present invention.

[0020] Figure 4 Examples 2 and 3 of the present invention are based on 2 mA cm -2 and 0.1 mAh cm -2 and 2 mA cm -2 and 0.5 mAhcm -2 Cyclic performance curves and charge / discharge curves.

[0021] Figure 5 The images show the SEM images of the copper positive electrode and the silicon-based negative electrode before and after cycling in Example 2 of this invention.

[0022] Figure 6 The XRD patterns of the copper cathode before and after cycling in Embodiment 2 of the present invention are shown. Detailed Implementation

[0023] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0024] In embodiments of the present invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0025] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0026] To address the issues of high cost of lithium metal anodes in lithium-copper batteries and volume expansion of silicon anodes during cycling, this invention provides an ether-based electrolyte for silicon-copper reversible batteries. LiTFSI is selected as the lithium salt, THF (thorium fluoride) is used as the main solvent, and a certain volume percentage of DMF is added. THF has advantages such as strong dissolving power, strong decomposition and polymerization tendency, and the formation of an inorganic-rich SEI on the surface of the silicon-based anode. Furthermore, DMF has stronger polarity and can dissolve higher concentrations of lithium salts. Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is a commonly used lithium salt with high ionic conductivity and good thermal stability. Its anion TFSI... - With a large ionic radius and highly delocalized negative charge, it can effectively reduce the interaction between anions and lithium ions and increase the degree of dissociation of lithium salts.

[0027] Combination Figure 1 As shown, by calculating the ESP of the molecule, the oxygen atom in DMF has a more negative electrostatic potential, possibly closer to that of Li. +First, it is reduced to SEI. Generally speaking, the LUMO energy level represents electron accepting ability, and the HOMO energy level represents electron donating ability. The lower the LUMO energy level, the easier it is for the electrolyte components to gain electrons and undergo reducing decomposition at the anode; the higher the HOMO energy level, the easier it is for the electrolyte components to lose electrons and undergo oxidative decomposition at the cathode. Calculations show that DMF has a lower LUMO energy level. Therefore, during the first discharge of the battery, the DMF additive can preferentially decompose on the silicon-based anode surface to form an SEI film, thereby reducing solvent decomposition.

[0028] Molecular dynamics simulations show that the aforementioned mixed solvents possess extremely strong solvation structures, TFSI - Anions and Li + The contact between them is extremely strong and stable. N,N-dimethylformamide (DMF) is a polar aprotic solvent with a dielectric constant as high as 36.7, which can significantly enhance the solubility of lithium salts in the electrolyte. It is compatible with THF and TFSI. - Together, they form a very robust anion-involved inner solvation sheath. This strong solvation / anion coordination structure can provide an ideal structure for building a stable SEI film on silicon-based anodes, promote the formation of a robust LiF layer to cope with volume expansion, and at the same time promote anion participation in CEI film formation at the cathode, thereby building a more stable interface on the copper surface and making the deposition on the cathode side more uniform.

[0029] In one embodiment of the present invention, the lithium salt further includes one or more of lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, or lithium chloride. The mixed organic solvent further includes at least one of ethylene glycol dimethyl ether, fluoroethylene carbonate, vinylene carbonate, methyl ethyl carbonate, diethyl carbonate, ethylene carbonate, or dimethyl carbonate.

[0030] In one embodiment of the present invention, the concentration of the lithium salt in the electrolyte is 3 mol / L. -1 Up to 3.5 mol L -1 When the lithium salt concentration is within this range, the solvation structure of the electrolyte reaches an ideal state, enabling the formation of a stable and dense interfacial film on the electrode surface while maintaining good ion transport performance.

[0031] Based on the same inventive concept, the present invention also provides a method for preparing the above-mentioned ether-based electrolyte, comprising the following steps: The tetrahydrofuran and N,N-dimethylformamide were mixed in a volume ratio to obtain a preliminary mixed solvent; The lithium salt is dispersed in the initial mixed solvent to obtain the ether-based electrolyte.

[0032] In this embodiment, the synergistic effect of tetrahydrofuran and N,N-dimethylformamide effectively dissolves lithium salts, providing ample active lithium ions for the battery system and ensuring full utilization of battery capacity. Furthermore, this preparation method is simple and easy to operate, using common raw materials, resulting in controllable production costs and easy scalability.

[0033] Based on the same inventive concept, the present invention also provides a silicon-copper reversible battery, comprising: a positive electrode, the active material of which is metallic copper; a negative electrode, comprising a silicon-based negative electrode material; and the ether-based electrolyte described above.

[0034] In one embodiment of the present invention, the silicon-copper reversible battery further includes a separator, which is a glass fiber membrane or a composite membrane of polyionic liquid and polypropylene. The glass fiber membrane has high porosity (approximately 90%), good wettability to ether-based electrolytes, and a large liquid absorption capacity, enabling it to store sufficient electrolyte for recycling. Simultaneously, the glass fiber membrane exhibits excellent thermal stability, preventing shrinkage or melting even at high temperatures, ensuring battery safety. A composite membrane of polyionic liquid and polypropylene is used as the separator. This composite membrane combines the mechanical strength of polypropylene with the high ionic conductivity of polyionic liquid. The polyionic liquid layer promotes rapid lithium-ion transport and reduces interfacial impedance. Batteries assembled using this separator, under the same test conditions, show a reduction in overpotential of approximately 10 mV compared to those assembled with a glass fiber membrane, indicating reduced ion transport resistance.

[0035] In contrast, a conventional polypropylene (PP) single-layer separator was used. PP separators have low porosity (approximately 40%) and poor wettability to ether-based electrolytes. The assembled battery exhibited a high initial impedance at 2 mA cm⁻¹. -2 At the current density, the overpotential is about 25 mV higher than that of the glass fiber membrane. After 300 hours of cycling, due to insufficient electrolyte wetting, the internal resistance of the battery gradually increases, and the cycle stability decreases.

[0036] In this embodiment, DMF molecules in the electrolyte have a low LUMO energy level and preferentially decompose on the silicon anode surface during the first charge, forming a dense SEI film rich in LiF. This SEI film has high mechanical strength and good lithium-ion conductivity, effectively inhibiting the continuous decomposition of the electrolyte, alleviating the volume expansion of the silicon anode during cycling (volume change can reach 300%), preventing the shedding and pulverization of active materials, and significantly improving coulombic efficiency and cycle stability. A stable CEI film rich in TFSI is also constructed on the copper cathode surface by the electrolyte. -The decomposition products of anions can regulate the diffusion and nucleation process of copper ions, inducing copper crystals to grow with a preferred orientation on the (2 0 0) crystal plane. The (2 0 0) crystal plane is a crystal plane with low energy, dense structure and high stability. Its preferred growth guides copper ions to deposit in an orderly, dense and stable manner, forming a flat deposition layer, effectively suppressing the formation of copper dendrites and improving the safety and cycle stability of the battery.

[0037] At 2 mA cm -2 At the specified current density, the silicon-copper battery of this invention achieves a cycle life of 500 to 800 hours, while maintaining a coulombic efficiency of over 98.5%. The battery also exhibits good rate performance at 5 mA cm⁻¹. -2 The capacity retention rate remains above 60% even at high current densities. The battery exhibits stable performance under varying temperatures and application scenarios, making it suitable for multiple fields such as energy storage devices, electric vehicles, and portable electronic devices.

[0038] Silicon and copper are both abundant natural elements, and their prices are far lower than those of precious metals such as lithium and cobalt. The preparation method of the electrolyte is simple, requiring only a mixed solvent and dissolved lithium salt, without the need for complex synthesis processes, making it easy to industrialize and commercialize.

[0039] The following specific preparation examples will further explain the above-mentioned technical solutions provided by the present invention.

[0040] Example 1 1-1. At room temperature, 3 mol L -1 LiTFSI powder was added to 1.8 mL of THF and 0.2 mL of DMF to prepare an electrolyte. A battery was assembled using silicon-carbon material as the negative electrode and metallic copper as the positive electrode. The battery was tested at 1 mA cm⁻¹. -2 0.1 mAhcm -2 Under certain conditions, the cycle time can reach up to 900 hours.

[0041] 1-2. At room temperature, 3 mol L -1 LiTFSI powder was added to 1.8 mL of THF and 0.2 mL of DMF to prepare an electrolyte. A battery was assembled using silicon-carbon material as the negative electrode and metallic copper as the positive electrode. The battery was tested at 2 mAh cm⁻¹. -2 0.1 mAhcm -2 Under certain conditions, the cycle time can reach up to 1000 hours.

[0042] 1-3. At room temperature, 3 mol L -1LiTFSI powder was added to 1.8 mL of THF and 0.2 mL of DMF to prepare an electrolyte. A battery was assembled using silicon-carbon material as the negative electrode and metallic copper as the positive electrode. The battery was tested at 2 mAh cm⁻¹. -2 0.5 mAhcm -2 Under certain conditions, the cycle time can reach up to 500 hours.

[0043] Perform SEM scan (e.g.) Figure 5 As shown in the figure), comparing the morphological changes of the initial electrode and the copper positive electrode and silicon-based negative electrode after 200 cycles, it was found that after cycling, the surface of the copper positive electrode remained smooth without obvious dendrites, while the silicon-based negative electrode had a dense morphology without particle breakage or electrode pulverization. XRD tests were performed on the copper positive electrode after 200 cycles (e.g., ...). Figure 6 As shown in the figure, copper crystals exhibit a significant (2 0 0) crystal plane preferred orientation growth characteristic. The (2 0 0) crystal plane is one of the lowest energy, most dense, and most stable crystal planes in copper crystals. Its advantage is not to "promote" deposition, but to guide copper ions to deposit in a more ordered, dense, and stable manner, effectively suppressing the formation of harmful dendrites and obtaining a smooth and dense deposition layer.

[0044] 1-4. At room temperature, 3.5 mol L -1 LiTFSI powder was added to 1.8 mL of THF and 0.2 mL of DMF to prepare an electrolyte. A battery was assembled using silicon-carbon material as the negative electrode and metallic copper as the positive electrode. The battery was tested at 2 mAh cm⁻¹. -2 0.1mAh cm -2 Under certain conditions, the cycle time can reach up to 800 hours.

[0045] 1-5. At room temperature, 2.5 mol L -1 LiTFSI powder was added to 1.8 mL of THF and 0.2 mL of DMF to prepare an electrolyte. A battery was assembled using silicon-carbon material as the negative electrode and metallic copper as the positive electrode. The battery was tested at 2 mAh cm⁻¹. -2 0.1mAh cm -2 Under certain conditions, the cycle time can reach up to 700 hours.

[0046] 1-6. At room temperature, 4 mol L -1 LiTFSI powder was added to 1.8 mL of THF and 0.2 mL of DMF to prepare an electrolyte. A battery was assembled using silicon-carbon material as the negative electrode and metallic copper as the positive electrode. The battery was tested at 2 mAh cm⁻¹. -2 0.1 mAhcm -2 Under certain conditions, the cycle time can reach up to 650 hours.

[0047] 1-7. At room temperature, 3 mol L -1 LiTFSI powder was mixed thoroughly with 1.6 mL of THF and 0.4 mL of DMF to prepare the electrolyte. A battery was assembled using silicon-carbon material as the negative electrode and metallic copper as the positive electrode. The battery was tested at a 2 mAh / cm² temperature. -2 0.1 mAhcm -2 Under certain conditions, the cycle time can reach up to 780 hours.

[0048] 1-8. At room temperature, 3 mol L -1 LiTFSI powder was mixed thoroughly with 1.4 mL of THF and 0.6 mL of DMF to prepare the electrolyte. A battery was assembled using silicon-carbon material as the negative electrode and metallic copper as the positive electrode. The battery was tested at a 2 mAh / cm² temperature. -2 0.1 mAhcm -2 Under certain conditions, the cycle time can reach up to 640 hours.

[0049] 1-9. At room temperature, 3 mol L -1 LiFSI powder was mixed thoroughly with 1.8 mL of THF and 0.2 mL of DMF to prepare the electrolyte. A battery was assembled using silicon-carbon material as the negative electrode and metallic copper as the positive electrode. The battery was tested at a 2 mAh / cm² temperature. -2 0.1 mAhcm -2 Under certain conditions, the cycle time can reach up to 400 hours.

[0050] 1-10. At room temperature, 5 mol L -1 LiFSI powder was added to 1.4 mL of THF and 0.6 mL of DMF and mixed thoroughly to prepare an electrolyte. The ionic conductivity of this electrolyte was measured to be 6.5 mS / cm. -1 .

[0051] Example 2 2-1. At room temperature, mix tetrahydrofuran and N,N-dimethylformamide in a volume ratio of 6:0.5. Measure 6 mL of tetrahydrofuran and 0.5 mL of N,N-dimethylformamide, mix thoroughly, and then add an appropriate amount of LiTFSI to achieve a lithium salt concentration of 3 mol / L. -1 The electrolyte was obtained after stirring and dissolving. The ionic conductivity of the electrolyte was measured to be 7.2 mS / cm. -1 .

[0052] 2-2. At room temperature, mix tetrahydrofuran and N,N-dimethylformamide at a volume ratio of 8:2. Measure 8 mL of tetrahydrofuran and 2 mL of N,N-dimethylformamide, mix thoroughly, and then add an appropriate amount of LiTFSI to achieve a lithium salt concentration of 3 mol / L. -1The electrolyte was obtained after stirring and dissolving. The ionic conductivity of the electrolyte was measured to be 8.8 mS / cm. -1 .

[0053] 2-3. At room temperature, mix tetrahydrofuran and N,N-dimethylformamide at a volume ratio of 9:1. Measure 9 mL of tetrahydrofuran and 1 mL of N,N-dimethylformamide, mix thoroughly, and then add an appropriate amount of LiTFSI to achieve a lithium salt concentration of 3 mol / L. -1 The electrolyte was obtained after stirring and dissolving. The ionic conductivity of the electrolyte was measured to be 7.8 mS / cm. -1 .

[0054] 2-4. At room temperature, mix tetrahydrofuran and N,N-dimethylformamide in a volume ratio of 9.5:4. Measure 9.5 mL of tetrahydrofuran and 4 mL of N,N-dimethylformamide, mix thoroughly, and then add an appropriate amount of LiTFSI to achieve a lithium salt concentration of 3 mol / L. -1 The electrolyte was obtained after stirring and dissolving. The ionic conductivity of the electrolyte was measured to be 9.2 mS / cm. -1 .

[0055] Example 3 3-1. Mix tetrahydrofuran and N,N-dimethylformamide at a volume ratio of 7:3, and add 2.7 mol L. -1 LiTFSI and 0.3 mol L -1 Lithium bis(fluorosulfonyl)imide (LiFSI) with a total lithium salt concentration of 3 mol / L -1 LiFSI anionic FSI - It has a smaller size and higher ionic conductivity, but its thermal stability is not as good as TFSI. - By combining two lithium salts, the advantages of both can be combined. An electrolyte with an ionic conductivity of 9.8 mS / cm was prepared. -1 It is higher than that of pure LiTFSI electrolyte.

[0056] 3-2. Add 2.5 mol L of the mixed solvent at a volume ratio of 7:3. -1 LiTFSI and 0.5 mol L -1 Lithium hexafluorophosphate (LiPF6), total concentration 3 mol L -1 LiPF6 is the most commonly used lithium salt in commercial lithium-ion batteries, and its decomposition products can form a stable passivation film on the electrode surface. An electrolyte was prepared with an ionic conductivity of 8.3 mS / cm. -1 .

[0057] 3-3. Add 2.8 mol L of the mixed solvent at a volume ratio of 7:3. -1LiTFSI and 0.2 mol L -1 Lithium tetrafluoroborate (LiBF4), total concentration 3 mol L -1 LiBF4 is inexpensive and has good thermal stability. The resulting electrolyte has an ionic conductivity of 8.1 mS / cm. -1 .

[0058] 3-4. Add 2.7 mol L of the mixed solvent at a volume ratio of 7:3. -1 LiTFSI and 0.3 mol L -1 Lithium trifluoromethanesulfonate (LiOTf), total concentration 3 mol L -1 The OTf anion of LiOTf - With TFSI - Similar in structure but smaller in size. An electrolyte was prepared with an ionic conductivity of 9.1 mS / cm. -1 .

[0059] 3-5. Add 2.9 mol L of the mixed solvent at a volume ratio of 7:3. -1 LiTFSI and 0.1 mol L -1 Lithium chloride (LiCl), total concentration 3 mol L -1 Cl in LiCl - Ions can participate in the formation of the SEI film, which helps to improve interfacial stability. An electrolyte was prepared with an ionic conductivity of 8.6 mS / cm. -1 .

[0060] By adding other lithium salts to LiTFSI, the physicochemical properties and electrochemical performance of the electrolyte can be modulated. Composite lithium salt systems can combine the advantages of different lithium salts, further optimizing the composition and performance of the electrode interface film and improving the cycle stability of the battery.

[0061] Example 4 4-1. In a mixed solvent of tetrahydrofuran and N,N-dimethylformamide at a volume ratio of 7:3, add 5 vol% of ethylene glycol dimethyl ether (DME). DME is a linear ether solvent with good compatibility with THF, which can further improve the solubility of lithium salts. Add 3 mol L... -1 An electrolyte was prepared using LiTFSI. The specific procedure was as follows: 6.65 mL of THF, 2.85 mL of DMF, and 0.5 mL of DME were measured, mixed thoroughly, and then an appropriate amount of LiTFSI was added. The ionic conductivity of this electrolyte was 8.9 mS / cm. -1 .

[0062] 4-2. In a 7:3 volume ratio of THF and DMF mixed solvent, add 2 vol% of fluoroethylene carbonate (FEC). FEC is a fluorinated additive that preferentially reduces and decomposes on the negative electrode surface, forming a dense SEI film rich in LiF, effectively inhibiting the continuous decomposition of the electrolyte and the volume expansion of the silicon negative electrode. Measure 6.86 mL of THF, 2.94 mL of DMF, and 0.2 mL of FEC, mix them, and then add 3 mol L... -1 LiTFSI was used to obtain an electrolyte with an ionic conductivity of 8.4 mS / cm. -1 .

[0063] 4-3. Add 1 vol% vinylene carbonate (VC) to a 7:3 volume ratio of THF and DMF mixed solvent. VC can polymerize on the negative electrode surface to form a flexible polymer film, effectively buffering the volume change of the silicon negative electrode. Measure 6.93 mL of THF, 2.97 mL of DMF, and 0.1 mL of VC, mix them, and then add 3 mol L... -1 LiTFSI was used to obtain an electrolyte with an ionic conductivity of 8.3 mS / cm. -1 .

[0064] 4-4. Add 3 vol% ethyl methyl carbonate (EMC) to a 7:3 volume ratio of THF and DMF mixed solvent. EMC is a low-viscosity carbonate solvent that can reduce electrolyte viscosity and improve ionic conductivity. Measure 6.79 mL THF, 2.91 mL DMF, and 0.3 mL EMC, mix them, and then add 3 mol L... -1 LiTFSI was used to obtain an electrolyte with an ionic conductivity of 9.3 mS / cm. -1 .

[0065] 4-5. In a mixed solvent of THF and DMF with a volume ratio of 7:3, add the following composite additives: 1 vol% FEC, 1 vol% VC, and 2 vol% DME. Measure 6.72 mL THF, 2.88 mL DMF, 0.1 mL FEC, 0.1 mL VC, and 0.2 mL DME, mix them, and then add 3 mol L... -1 LiTFSI was used to obtain an electrolyte with an ionic conductivity of 8.7 mS / cm. -1 .

[0066] The overall performance of the electrolyte can be further optimized by adding functional solvent components. Ether solvents (such as DME) can enhance the dissolution capacity of lithium salts; film-forming additives (such as FEC and VC) can improve the quality of the electrode interface film; and low-viscosity solvents (such as EMC, DEC, and DMC) can improve the ion transport rate.

[0067] Example 5 In the fabrication of silicon-copper reversible batteries, a silicon-carbon composite material was selected as the negative electrode active material. This material is composed of nano-silicon particles and a carbon matrix, with the silicon particles having an average particle size of 50-100 nm and being uniformly dispersed in the carbon matrix. The silicon-carbon composite material contains 60% silicon and 40% carbon by mass.

[0068] The negative electrode slurry was prepared according to a mass ratio of 80:10:10, specifically consisting of 80% silicon-carbon composite material (active material), 10% acetylene black (conductive agent), and 10% polyvinylidene fluoride (PVDF, binder). These components were added to N-methylpyrrolidone (NMP) solvent, controlling the solid content to 35%. The mixture was then stirred using a planetary ball mill at 300 rpm for 3 hours to obtain a homogeneous negative electrode slurry. The slurry was black and viscous, with no obvious particle agglomeration.

[0069] The negative electrode slurry was coated onto a copper foil current collector (10 μm thick) using a doctor blade method, with the coating thickness controlled at 80 μm (after drying). After coating, the electrode was placed in a vacuum oven and pre-dried at 60°C for 2 hours to remove most of the solvent, followed by vacuum drying at 120°C for 12 hours to completely remove residual solvent. The dried electrode was then subjected to roll pressing to control the compaction density at 1.2 g / cm³. -3 The electrode was cut into circular electrode sheets with a diameter of 14 mm, and the active material loading was weighed and recorded as approximately 2.5 mg / cm³. -2 .

[0070] High-purity copper foil (purity ≥99.9%) was used as the positive electrode active material. The copper foil was 50 μm thick, and its surface underwent degreasing and acid pickling to remove the oxide layer and impurities. The specific treatment steps were as follows: first, the copper foil was immersed in acetone solution and ultrasonically cleaned for 10 minutes to remove oil stains; then, it was immersed in 5 wt% dilute sulfuric acid solution for 5 minutes to remove the surface oxide layer; subsequently, it was repeatedly rinsed with deionized water until neutral; finally, it was dried in a vacuum oven at 60°C for 2 hours. The treated copper foil was cut into circular electrode sheets with a diameter of 16 mm and used directly as the positive electrode.

[0071] Glass fiber membrane (Whatman GF / D) was used as the separator. The glass fiber membrane exhibits good electrolyte wettability, high porosity (approximately 90%), and excellent thermal stability, effectively preventing contact between the positive and negative electrodes while allowing free transport of lithium ions. The glass fiber membrane was cut into circular separator sheets with a diameter of 19 mm and dried in a vacuum oven at 120°C for 12 hours before use to remove adsorbed moisture.

[0072] Battery assembly was performed in an argon-atmospheric glove box (H2O < 0.1 ppm, O2 < 0.1 ppm). A CR2032 coin cell battery case was used for assembly. The assembly sequence was as follows: negative electrode (silicon-based negative electrode side up), separator, positive electrode (copper foil side down), stainless steel gasket, and spring sheet were placed sequentially in the negative electrode case. Then, 100 μL of the ether-based electrolyte prepared in the above example was added dropwise, ensuring the separator was fully wetted. The battery was allowed to stand for 10 minutes to allow the electrolyte to completely penetrate the electrode pores. The positive electrode case was then replaced, and the battery was sealed using a sealing machine at 0.8 MPa pressure. After sealing, the battery was allowed to stand at room temperature for 24 hours to allow the electrodes to fully contact the electrolyte and reach interface equilibrium.

[0073] Comparative Example 1 Pure tetrahydrofuran was used as the solvent, and the LiTFSI concentration was 1 mol / L. -1 The electrolyte. Due to the low lithium salt concentration, this electrolyte has a high ionic conductivity (12.5 mS / cm). -1 However, it cannot provide enough active lithium ions for the battery. The assembled silicon-copper battery has an initial discharge capacity of only 1.5 mAh cm⁻¹. -2 After 50 cycles, the capacity decayed to 0.8 mAh / cm³. -2 The capacity retention rate was only 53.3%.

[0074] Comparative Example 2 Pure N,N-dimethylformamide was used as the solvent, and the LiTFSI concentration was 3 mol / L. -1 The electrolyte. Although the high polarity of DMF is beneficial for dissolving lithium salts, pure DMF electrolyte has a high viscosity (14.2 mPa·s) and low ionic conductivity (4.2 mS·cm). -1 The assembled silicon-copper cells exhibited poor rate performance at 2 mA cm⁻¹. -2 At the current density, the discharge capacity is only 1.8 mAh cm⁻¹. -2 .

[0075] Comparative Example 3 A carbonate solvent system was used, specifically a 1:1 volume ratio mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC), with a LiTFSI concentration of 1 mol / L. -1 Carbonate solvents exhibit good stability at high voltages, but they tend to decompose continuously on the silicon anode surface, making it difficult to form a stable SEI film. The assembled silicon-copper battery achieved an initial coulombic efficiency of only 75.2%, and this efficiency remained below 95% throughout cycling, indicating severe side reactions. After 100 cycles, the capacity decayed to 45% of its initial value.

[0076] Comparative Example 4 A mixed solvent of tetrahydrofuran and DMF in a volume ratio of 5:5 (not within the scope of this invention) was used, with a LiTFSI concentration of 3 mol / L. -1 The DMF content in this formulation is too high, resulting in a high electrolyte viscosity (11.8 mPa·s) and a decrease in ionic conductivity to 5.8 mS·cm. -1 The assembled battery functions normally, but its rate performance is poor, specifically at 5 mA cm⁻¹. -2 At current density, the capacity retention is only 42%.

[0077] Comparative Example 5 A mixed solvent of tetrahydrofuran and DMF in a volume ratio of 9.8:0.2 (not within the scope of this invention) was used, with a LiTFSI concentration of 3 mol / L. -1 The DMF content in this formulation is too low, resulting in insufficient electrolyte polarity and poor SEI film stability during cycling. After 100 cycles, the battery's capacity retention is only 68%, lower than that of the embodiments of this invention.

[0078] Example 6 Silicon batteries are used in energy storage devices. A silicon-copper battery prepared using the electrolyte of Example 1-1 is used at 0.5 mAcm⁻¹. -2 Long-term cycling tests were conducted at low current densities to simulate the charge-discharge conditions of energy storage devices. After 1000 cycles, the battery retained 75% of its capacity and maintained a coulombic efficiency above 99%. No thermal runaway or safety issues occurred throughout the cycling process, demonstrating excellent safety. Considering the abundant and inexpensive resources of silicon and copper, this battery system has broad application prospects in large-scale energy storage.

[0079] Example 7 Silicon-copper batteries, prepared using the electrolytes of Examples 1-2, were used in portable electronic devices. During abuse tests, including nail penetration and overcharge, the batteries did not exhibit any fire or explosion. Furthermore, the silicon-copper batteries have a suitable operating voltage (approximately 1.5-2.5 V), which can be connected in series to meet the voltage requirements of different devices. In tests simulating mobile phone charge / discharge conditions (1C charging, 2C discharging), the batteries maintained 80% capacity retention after 300 cycles, meeting the requirements for use in portable electronic devices.

[0080] In summary, this invention provides an ether-based electrolyte for a silicon-copper reversible battery, a method for preparing the same, and the silicon-copper reversible battery. The ether-based electrolyte comprises a lithium salt and a mixed organic solvent; the lithium salt includes lithium bis(trifluoromethanesulfonyl)imide; the mixed organic solvent includes tetrahydrofuran and N,N-dimethylformamide; and the concentration of the lithium salt in the ether-based electrolyte is 2.5 mol / L. -1 Up to 6 mol L-1 The volume ratio of tetrahydrofuran to N,N-dimethylformamide is (6-9.5):(0.5-4). Through the synergistic effect of THF and DMF, the electrolyte of this invention can dissolve 2.5 to 6 mol / L of [a specific substance / component]. -1 The high concentration of lithium salts provides ample active lithium ions to the battery system, ensuring full utilization of the battery capacity. This is especially true in the 3 to 5 mol L⁻¹ concentration range. -1 Within the preferred concentration range, the electrolyte achieves an optimal balance between ionic conductivity and lithium source supply. DMF molecules in the electrolyte have a low LUMO energy level and preferentially decompose on the silicon anode surface during the first charge, forming a dense SEI film rich in LiF. This SEI film exhibits high mechanical strength and good lithium-ion conductivity, effectively suppressing the continuous decomposition of the electrolyte, mitigating the volume expansion of the silicon anode during cycling (volume change can reach 300%), preventing the shedding and pulverization of active materials, and significantly improving coulombic efficiency and cycle stability. A stable CEI film rich in TFSI is also constructed on the copper cathode surface by the electrolyte. - The decomposition products of anions can regulate the diffusion and nucleation process of copper ions, inducing copper crystals to grow with a preferred orientation on the (200) crystal plane. The (200) crystal plane is a low-energy, dense, and highly stable crystal plane. Its preferred growth guides copper ions to deposit in an ordered, dense, and stable manner, forming a smooth deposition layer. This effectively suppresses the formation of copper dendrites and improves the safety and cycle stability of the battery. (At 2 mA cm⁻¹) -2 At the specified current density, the silicon-copper battery of this invention achieves a cycle life of 500 to 800 hours, while maintaining a coulombic efficiency of over 98.5%. The battery also exhibits good rate performance at 5 mA cm⁻¹. -2 The battery maintains a capacity retention rate of over 60% even at high current densities. It exhibits stable performance under varying temperatures and application scenarios, making it suitable for multiple fields such as energy storage devices, electric vehicles, and portable electronic devices. Silicon and copper are both abundant natural elements, with prices far lower than precious metals like lithium and cobalt. The electrolyte preparation method is simple, requiring only a mixed solvent and dissolved lithium salt, eliminating the need for complex synthesis processes and facilitating industrial production and commercial application.

[0081] Finally, it should be noted that the above embodiments are only for illustrating the present invention and not for limiting the present invention. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that various combinations, modifications, or equivalent substitutions of the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention and should be covered within the scope of the claims of the present invention.

Claims

1. An ether-based electrolyte for use in silicon-copper reversible batteries, characterized in that, It comprises: a lithium salt and a mixed organic solvent; the lithium salt includes lithium bis(trifluoromethanesulfonyl)imide; The mixed organic solvent comprises tetrahydrofuran and N,N-dimethylformamide; the concentration of the lithium salt in the ether-based electrolyte is 2.5 mol / L. -1 Up to 6 mol L -1 The volume ratio of the tetrahydrofuran to N,N-dimethylformamide is (6-9.5):(0.5-4).

2. The ether-based electrolyte according to claim 1, characterized in that, The lithium salt further includes one or more of lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, or lithium chloride.

3. The ether-based electrolyte according to claim 1, characterized in that, The mixed organic solvent also includes at least one of the following: ethylene glycol dimethyl ether, fluoroethylene carbonate, vinylene carbonate, methyl ethyl carbonate, diethyl carbonate, ethylene carbonate, or dimethyl carbonate.

4. The ether-based electrolyte according to claim 1, characterized in that, The concentration of the lithium salt in the electrolyte is 3 mol / L. -1 Up to 3.5 mol L -1 .

5. A method for preparing the ether-based electrolyte according to claim 1, characterized in that, Includes the following steps: The tetrahydrofuran and N,N-dimethylformamide were mixed in a volume ratio to obtain a preliminary mixed solvent; The lithium salt is dispersed in the initial mixed solvent to obtain the ether-based electrolyte.

6. A silicon-copper reversible battery, characterized in that, include: The positive electrode has metallic copper as its active material; Negative electrode, including silicon-based negative electrode materials; And the ether-based electrolyte as described in any one of claims 1-4.

7. The silicon-copper reversible battery according to claim 6, characterized in that, The silicon-based anode material is a silicon-carbon composite material; during the charge-discharge cycle, the copper crystals of the cathode exhibit a preferred orientation growth of the (200) crystal plane.

8. The silicon-copper reversible battery according to claim 6, characterized in that, The silicon-copper reversible battery also includes a separator, which is a glass fiber membrane or a composite membrane of polyionic liquid and polypropylene.

9. The silicon-copper reversible battery according to claim 6, characterized in that, The silicon-copper reversible battery operates at 2 mA cm⁻¹ -2 At current density, the cycle life is not less than 500 hours.

10. The application of a silicon-copper reversible battery according to any one of claims 6-9 in an energy storage device, an electric vehicle, or a portable electronic device.

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