Double-salt system lithium battery polymer solid electrolyte as well as preparation method and application thereof

Abstract

The invention discloses a double-salt system lithium battery polymer solid electrolyte, and relates to the technical field of energy, the double-salt system lithium battery polymer solid electrolyte comprises an electrolyte salt and a polymer matrix, the main salt of the electrolyte salt is LiX, the auxiliary salt is MX, and the polymer matrix is a polyethylene oxide (PEO) electrolyte; the invention also discloses a preparation method of the double-salt system lithium battery polymer solid electrolyte. The invention also discloses application of the double-salt lithium battery solid electrolyte in a lithium battery. According to the PEO-based composite solid electrolyte and the preparation method thereof disclosed by the invention, relatively cheap monovalent or high-valence metal salt is used and has extremely high compatibility with a PEO system, an additive is customized for the PEO-based composite solid electrolyte, the ionic conductivity of the PEO-based composite solid electrolyte and the interface chemistry of lithium metal can be improved at the same time, so that lithium ions are in a high-dissociation and weak-coordination state, the conductivity of the lithium ions is improved, and the service life of the PEO-based composite solid electrolyte is prolonged. The introduced metal ions can form an electrostatic shielding effect on the surface of the lithium metal negative electrode by regulating and controlling the concentration of the metal ions, so that the growth of lithium dendrites is inhibited.

Description

Technical Field

[0001] This invention relates to the field of energy technology, specifically to a dual-salt system lithium battery polymer solid electrolyte, its preparation method, and its application. Background Technology

[0002] All-solid-state batteries, when used in conjunction with non-flammable solid-state electrolytes, can achieve both safety and energy density. Ethylene oxide (PEO)-based composite polymer solid-state electrolytes possess high flexibility, low interfacial resistance, and lithium metal chemical compatibility; however, their low lithium-ion conductivity at room temperature, poor electrochemical stability at high voltages, and low critical current density (CCD) hinder their commercial viability. Common modification methods include adding a second filler (MOF, LLZO, Al2O3) or organic fillers. However, due to their weak interaction with PEO, these fillers tend to aggregate significantly, failing to form continuous lithium-ion conductive channels within the PEO and even disrupting existing lithium-ion transfer pathways. Furthermore, the high cost and complex preparation processes of organic materials or novel lithium salts further complicate commercial applications. Summary of the Invention

[0003] The purpose of this invention is to provide a dual-salt system lithium battery polymer solid electrolyte, its preparation method and application, in order to solve the problems mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a dual-salt system lithium battery polymer solid electrolyte, comprising an electrolyte salt and a polymer matrix, wherein the main salt of the electrolyte salt is LiX, the auxiliary salt is MX, the polymer matrix is ​​a polyethylene oxide electrolyte, and the selected solvent is anhydrous acetonitrile.

[0005] In a further embodiment, X is an OTF. - TFSI - FSI - DFOP - ClO4 - .

[0006] In a further embodiment, M is an alkali metal, an alkaline earth metal, or a trivalent metal.

[0007] Preferably, a method for preparing a dual-salt system lithium battery polymer solid electrolyte, used to prepare the dual-salt system lithium battery polymer solid electrolyte, includes: A1. Mix anhydrous lithium salt with polyethylene oxide and anhydrous acetonitrile, and stir at 50-60℃ for 24 hours. After stirring, add auxiliary salt and continue stirring at the above temperature for 24 hours. A2. After stirring, transfer the container out of the glove box and sonicate it three times, 10 minutes each time, with a 10-minute interval between each time. A3. After ultrasonic defoaming, place the container in a 60℃ oven overnight to remove water. A4. The membrane is then transferred to a glove box for casting. The thickness of the membrane is controlled according to the mold specifications and the amount of polymer added. After the membrane is formed, it can be further hot-pressed to obtain an ultra-thin solid electrolyte membrane.

[0008] Preferably, the dual-salt lithium battery solid electrolyte is used in lithium batteries, employing the dual-salt system lithium battery polymer solid electrolyte, characterized in that: the dual-salt system lithium battery solid electrolyte has a better electrochemical window, lithium-ion conductivity, cycle capacity, and stability than existing single-salt system lithium battery solid electrolytes.

[0009] Compared with the prior art, the beneficial effects of the present invention are: This invention uses relatively inexpensive monovalent or high-priced metal salts that have extremely high compatibility with the PEO system. It is a customized additive for PEO-based composite solid electrolytes, which can simultaneously improve their ionic conductivity and lithium metal interfacial chemistry. The cations in the introduced metal salts compete with lithium ions in the intrinsic lithium salts through cation competitive coordination effects, competing for anions and functional groups such as ether oxygen bonds in the PEO electrolyte. This keeps lithium ions in a highly dissociated and weakly coordinated state, improving lithium ion conductivity. In addition, by controlling the concentration of the introduced metal ions, they can form an electrostatic shielding effect on the lithium metal anode surface, inhibiting the growth of lithium dendrites. Attached Figure Description

[0010] Figure 1 This is the electrochemical window spectrum of the solid electrolyte of the LiTFSI-Mg(TFSI)2-PEO system in Example 1; Figure 2 These are the electrochemical impedance spectroscopy spectra of the solid electrolyte membrane of the LiTFSI-Mg(TFSI)2-PEO system in Example 1 and the solid electrolyte membrane of the PEO-LiTFSI system in the comparative example; Figure 3 This is a cycle diagram of lithium batteries assembled from the LiTFSI-Mg(TFSI)2-PEO solid electrolyte system in Example 1 and the LiTFSI-PEO solid electrolyte system in the comparative example; Figure 4 These are the electrochemical impedance spectroscopy (EIC) spectra of the solid electrolyte membranes of the LiTFSI-Ca(TFSI)2-PEO system in Example 2 and the solid electrolyte membranes of the PEO-LiTFSI system in the comparative example.

[0011] Figure 5 This is a cycle diagram of the lithium battery assembled from the LiTFSI-Ca(TFSI)2-PEO solid electrolyte system in Example 2 and the comparative LiTFSI-PEO solid electrolyte system. Detailed Implementation

[0012] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0013] This embodiment provides a dual-salt system lithium battery polymer solid electrolyte, comprising an electrolyte salt and a polymer matrix, wherein the electrolyte salt is mainly composed of LiX. n X is OTF - TFSI - FSI - DFOP - ClO4 - The co-salt is MX n M represents alkali metals, alkaline earth metals, and trivalent metals.

[0014] The electrolyte solvent is an ether electrolyte, preferably polyethylene oxide or polyethylene glycol dimethyl ether.

[0015] Where n is selected from any integer from 1 to 3.

[0016] The organic solvent may include anhydrous acetonitrile, tetrahydrofuran, or other organic solvents.

[0017] Preferably, the molar ratio of the auxiliary salt to the lithium salt is 1:(1~40). For example, a typical solid electrolyte membrane composition may be PEO-LiTFSI-Mg(TFSI)2.

[0018] Another aspect of the present invention provides a method for preparing the dual-salt system lithium battery solid electrolyte, comprising: Anhydrous lithium salt LiX was mixed with the polymer and organic solvent and stirred at 50-60°C for 24 hours. After the mixture was homogeneous, the auxiliary salt MX was added. n Continue stirring at the above temperature for 24 hours until the auxiliary salt is evenly dispersed. Transfer the container outside the glove box for ultrasonic treatment, performing three intermittent ultrasonic treatments, each lasting 10 minutes with a 10-minute interval. After ultrasonic degassing, transfer the container back into the glove box and pour it into a custom-made PTFE mold. Electrolyte films of varying thicknesses are obtained based on the amount of electrolyte added to the container and the mold specifications. Furthermore, the electrolyte film thickness can be reduced by using a hot press at 80°C. LiX-MX is thus prepared. n -PEO dual-salt system lithium battery solid electrolyte.

[0019] In some more specific embodiments, the preparation method may include: weighing a certain amount of anhydrous lithium salt and polymer and adding them to a certain amount of organic solvent, stirring at 50-60°C for 24 hours, adding a certain amount of auxiliary salt after stirring evenly, and continuing to stir at the above temperature for 24 hours, so that the concentration ratio of auxiliary salt to lithium salt is controlled in the range of 1:(1~40). The dual-salt system lithium battery solid electrolyte is then prepared by ultrasonic defoaming, casting, and hot pressing.

[0020] Another aspect of this embodiment provides the use of the dual-salt system lithium battery solid electrolyte in lithium batteries.

[0021] Furthermore, the lithium battery includes a primary lithium battery, a secondary lithium battery, or a lithium-ion battery, preferably a lithium metal battery.

[0022] Furthermore, the negative electrode in the lithium-ion battery can be elemental lithium metal or a material that has undergone lithium ion intercalation / deintercalation.

[0023] The dual-salt system lithium battery solid electrolyte provided by this invention is a type of highly ion-conductive active electrolyte with excellent lithium-ion conductivity and can be applied to rechargeable lithium batteries, while also exhibiting excellent electrical performance.

[0024] Comparative Example: Preparation of Solid Electrolytes in PEO-LiTFSI System (Single Salt System - Comparative Example) 0.6 g of polyethylene oxide and 0.196 g of lithium bis(trifluoromethanesulfonyl)imide were first added to 15 ml of anhydrous acetonitrile solvent and stirred at 60 °C for 24 hours. The container was then transferred outside a glove box for ultrasonic treatment. Subsequently, it was kept in a 60 °C oven for a period of time before being transferred inside the glove box for casting. PEO-LiTFSI was obtained.

[0025] Example 1: Preparation of solid electrolyte in PEO-LiTFSI-Mg(TFSI)2 system: 0.6 g of polyethylene oxide and 0.196 g of lithium bis(trifluoromethanesulfonyl)imide were first added to 15 ml of anhydrous acetonitrile solvent and stirred at 60°C for 24 hours. Then, 0.19 g of magnesium bis(trifluoromethanesulfonyl)imide was added, and the mixture was heated and stirred for another 24 hours. The container was then transferred to a glove box for ultrasonic treatment. Afterward, it was kept in a 60°C oven for a period of time before being transferred back into the glove box for casting. PEO-LiTFSI-Mg(TFSI)2 was obtained.

[0026] See Figure 1 As shown, the electrochemical window of the electrolyte in this embodiment is 4.5 V (vs. Li). + / Li). See also Figure 2 The ionic conductivity of this electrolyte membrane is more than three times higher than that of the comparative sample, reaching 1.13 × 10⁻⁶.-3 S cm -1 See also Figure 3 The lithium battery assembled with this electrolyte exhibits improved cycle specific capacity and capacity retention.

[0027] Example 2: Preparation of solid electrolyte in PEO-LiTFSI-Ca(TFSI)2 system: 0.6 g of polyethylene oxide and 0.196 g of lithium bis(trifluoromethanesulfonyl)imide were first added to 15 ml of anhydrous acetonitrile solvent and stirred at 60°C for 24 hours. Then, 0.19 g of calcium bis(trifluoromethanesulfonyl)imide was added, and the mixture was heated and stirred for another 24 hours. The container was then transferred to a glove box for ultrasonic treatment. Afterward, it was kept in a 60°C oven for a period of time before being transferred back into the glove box for casting. PEO-LiTFSI-Ca(TFSI)2 was obtained.

[0028] See Figure 4 In this embodiment, the ionic conductivity of the electrolyte membrane is 5.53 × 10⁻⁶. -4 Scm -1 The ionic conductivity of the PEO-LiTFSI electrolyte membrane was improved compared to the comparative example. (See reference...) Figure 5 In this embodiment, the lithium battery assembled with the electrolyte membrane exhibits significantly improved cycle specific capacity and capacity retention. The lithium battery assembled with the electrolyte membrane in this embodiment retains 91% of its capacity after 300 cycles.

[0029] In summary, this invention utilizes relatively inexpensive monovalent or high-valent metal salts, exhibiting high compatibility with the PEO system. It provides a customized additive for PEO-based composite solid electrolytes, simultaneously improving both ionic conductivity and lithium metal interfacial chemistry. The introduced metal salt cations compete with lithium ions in the intrinsic lithium salt through a cation-competitive coordination effect, vying for anions and functional groups such as ether-oxygen bonds in the PEO electrolyte. This results in lithium ions being in a highly dissociated, weakly coordinated state, thus improving lithium ion conductivity. Furthermore, by controlling the concentration of the introduced metal ions, an electrostatic shielding effect can be formed on the lithium metal anode surface, inhibiting lithium dendrite growth.

[0030] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A dual-salt system lithium battery polymer solid electrolyte, characterized in that, include: The electrolyte salt and the polymer matrix are provided, wherein the main salt of the electrolyte salt is LiX and the auxiliary salt is MX, and the polymer matrix is ​​a polyethylene oxide electrolyte.

2. The dual-salt system lithium battery polymer solid electrolyte according to claim 1, characterized in that: X is an OTF - TFSI - FSI - DFOP - ClO4 - .

3. The dual-salt system lithium battery polymer solid electrolyte according to claim 1, characterized in that: M represents alkali metals, alkaline earth metals, and trivalent metals.

4. A method for preparing a dual-salt system lithium battery polymer solid electrolyte, used to prepare the dual-salt system lithium battery polymer solid electrolyte according to any one of claims 1-3, characterized in that: include: A1. Mix anhydrous lithium salt with polyethylene oxide and anhydrous acetonitrile, and stir at 50-60℃ for 24 hours. After stirring, add auxiliary salt and continue stirring at the above temperature for 24 hours. A2. After stirring, transfer the container out of the glove box and sonicate it three times, 10 minutes each time, with a 10-minute interval between each time. A3. After ultrasonic defoaming, place the container in a 60℃ oven overnight to remove water. A4. The membrane is then transferred to a glove box for casting. The thickness of the membrane is controlled according to the mold specifications and the amount of polymer added. After the membrane is formed, it can be further hot-pressed to obtain an ultra-thin solid electrolyte membrane.

5. The use of the dual-salt lithium battery solid electrolyte in lithium batteries, employing the dual-salt system lithium battery polymer solid electrolyte according to any one of claims 1-3, characterized in that: The dual-salt system lithium battery solid electrolyte has better electrochemical window, lithium-ion conductivity, cycle capacity and stability than the existing single-salt system lithium battery solid electrolyte.

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