A solid-state sodium / lithium ion battery ionic gel electrolyte, a preparation method and application thereof

Abstract

The application belongs to the field of sodium / lithium ion batteries, and relates to a solid-state sodium / lithium ion battery ion gel electrolyte and a preparation method and application thereof, to solve the problem that the solid-state polymer electrolyte in the current sodium / lithium ion battery is difficult to simultaneously realize high ion conductivity and sodium ion transference number at normal temperature, and it is more difficult to form a good interface layer on the electrode surface, thereby affecting the rate and cycle performance of the solid-state battery at normal temperature. The electrolyte comprises a basic ion gel composed of an inorganic salt, a polymer base and an ionic liquid, and an organic additive, wherein the organic additive is R is H or an alkoxy group with 1-2 carbon atoms, and the addition amount is 0.6-5wt% of the total mass of the organic additive, the ionic liquid and the polymer base. The organic additive widens the electrochemical stability window of the ion gel electrolyte, improves the normal temperature ion conductivity and sodium ion transference number of the ion gel, and has good ion transmission kinetics and rate performance when applied to a sodium / lithium battery.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of sodium / lithium ion batteries, and relates to a solid-state sodium / lithium ion battery ion gel electrolyte as well as a preparation method and application thereof. BACKGROUND

[0002] Sodium / lithium ion batteries have made great progress in current large-scale energy storage, especially in the field of electric vehicles today, and have made great achievements, but their safety problems are still of concern. In the sodium / lithium ion battery system, the electrolyte is an indispensable medium for the transmission of Na + / Li + ions, and has been deeply studied by many scholars. The traditional organic electrolyte still has great hidden dangers in safety, and as a countermeasure, the emergence of solid-state polymer electrolyte brings a glimmer of hope for safe sodium ion batteries, and it is studied by many people because of its safety advantage of no electrolyte leakage.

[0003] However, the low ion conductivity (<10 -3 Scm -1 ), low ion transference number and poor electrode / electrolyte interface of the solid-state polymer electrolyte at room temperature make its application more difficult. Without the use of additional organic liquid electrolyte, the ion conductivity and ion transference number are difficult to be greatly improved. In addition, compared with the organic liquid electrolyte, the interaction between the substances in the solid-state polymer electrolyte is more complex, and the poor electrolyte electrochemical performance and the degradation mechanism of the battery performance are still difficult to be analyzed by the current mainstream analysis instruments. Therefore, although there are many reports on solid-state polymer electrolytes, some solid-state polymer electrolytes such as NaFSI / C3mPyrFSI / PVDF-HFP, NaFSI / Pyr 13 FSI / PVDF-HFP, LiFSI / EmimFSI / PVDF-HFP, LiTFSI / PEO, etc. Although these quasi-solid-state electrolytes have good ion conductivity, their ion transference number is not very high, and they still face the problem that the actual effective ion conductivity is not high, which leads to the difficulty in significantly improving the performance of the battery.

[0004] One of the methods to solve the above problems is to use additives to improve the performance of the solid-state polymer electrolyte. Hashmi et al. introduced diglycol dimethyl ether (DGM) into the PVDF-HFP / NaFSI system to achieve an ion conductivity of 1.12×10 -3 Scm -1 at room temperature and a moderate sodium ion transference number of 0.58, and the electrochemical stability window is as high as 5.2V. The assembled Na / Na 0.7 CoO2battery shows 34.4mAhg -1reversible capacity. Rajendra et al. introduced a large amount of ionic liquid Bmim-MS as a plasticizer in the PEO / NaMS system to reduce the crystallinity of the PEO system, optimize ion transport, and have a 1.05 x 10 -4 Scm -1 ion conductivity and moderate sodium ion transference number: 0.46. However, the above quasi-solid polymer electrolyte has a low ion transference number, resulting in a low actual effective sodium ion conductivity. Therefore, the rapid transmission of metal ions in the entire battery system is hindered, which further affects the rate performance and cycle performance of the battery. SUMMARY

[0005] In view of the technical problems that the solid-state polymer electrolyte in the current sodium / lithium ion battery is difficult to simultaneously achieve high ion conductivity and sodium / lithium ion transference number at room temperature, the solid-state polymer electrolyte is difficult to form a better interface layer (CEI) on the electrode surface, and further, the poor ion transmission kinetics and the poor CEI will further affect the rate performance and cycle performance of the solid-state battery at room temperature, the present application provides a solid-state sodium / lithium ion battery ionic gel electrolyte and a preparation method and application thereof. A small amount of organic additives added to the electrolyte can improve the transmission kinetics of ions in the electrolyte body phase, and effectively passivate the decomposition of sodium / lithium salt and ionic liquid in the electrolyte, optimize the composition and formation of CEI on the electrode surface, help to form a thinner and more uniform CEI layer, and help to improve the rate performance and cycle performance of the solid-state sodium / lithium ion battery.

[0006] In order to achieve the above purpose, the technical scheme of the present application is as follows:

[0007] A solid-state sodium / lithium ion battery ionic gel electrolyte, comprising a basic ionic gel composed of an inorganic salt, a polymer substrate and an ionic liquid, and an organic additive, wherein the organic additive is a naphthyl derivative.

[0008] Further, the naphthyl derivative has the structural formula wherein R is H or an alkoxy group with 1-2 carbon atoms.

[0009] Further, the functional group with 0 carbon atoms is -H, and the alkoxy group with 1-2 carbon atoms is any one of -OCH3, -OCH2CH3 or -OCH2COOH.

[0010] Further, the specific structural formula of the naphthyl derivative is as follows:

[0011] Furthermore, the inorganic salt is either sodium bis(trifluoromethanesulfonyl)imide or lithium bis(trifluoromethanesulfonyl)imide; the polymer substrate is polyvinylidene fluoride-hexafluoropropylene; and the ionic liquid is 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide salt.

[0012] Furthermore, the mass ratio of the polymer substrate (containing additives) to the ionic liquid and inorganic salt is 0.5:0.6:(0.117~0.5), wherein the concentration of the inorganic salt in the basic ionic gel is 1~4 mol / L; the amount of the organic additive added is 0.6~5 wt% of the total mass of the additives, ionic liquid and polymer substrate.

[0013] The preparation method of the above-mentioned solid sodium / lithium-ion battery ion gel electrolyte includes the following steps:

[0014] (1) Dissolve the polymer substrate in acetone to obtain a polymer precursor solution;

[0015] (2) Add organic additives to the polymer precursor solution obtained in step (1) to obtain a mixed precursor solution;

[0016] (3) Add the ionic liquid and inorganic salt to the mixed precursor solution obtained in step (2), and after dispersing evenly, obtain the sodium / lithium ion battery ion gel precursor solution.

[0017] (4) Pour the sodium / lithium ion battery ion gel precursor solution obtained in step (3) onto a smooth glass plate and scrape it with a scraper to form a thin film ion gel electrolyte. After drying, a solid sodium / lithium ion battery ion gel electrolyte is obtained.

[0018] Furthermore, in step (4), the scraping height of the scraper is 400 μm; the drying is done in a vacuum oven for 24 hours.

[0019] A sodium / lithium-ion battery includes a positive electrode, a negative electrode, and the aforementioned solid sodium / lithium-ion battery ion gel electrolyte, wherein the solid sodium / lithium-ion battery ion gel electrolyte is disposed between the positive electrode and the negative electrode.

[0020] Furthermore, the positive electrode includes a positive current collector and a positive electrode membrane disposed on the positive current collector. The positive electrode membrane includes a positive active material, a positive conductive agent, and a binder. The negative electrode includes a negative current collector and a negative electrode membrane disposed on the negative current collector. The negative electrode membrane includes a negative active material and a negative conductive agent. Both the positive and negative conductive agents can be any one of acetylene black, Super P Li, or carbon nanotubes, and the binder is polyvinylidene fluoride (PVDF) or carboxymethyl cellulose (CMC), etc.

[0021] The positive electrode includes a positive electrode active material; the negative electrode includes a negative electrode current collector and a negative electrode film disposed on the negative electrode current collector, the negative electrode film including a negative electrode active material, a negative electrode conductive agent and a binder.

[0022] Furthermore, the positive electrode active material of the sodium-ion battery includes any one or more of sodium vanadium fluorophosphate, sodium vanadium phosphate, sodium iron sulfate, or sodium iron pyrophosphate in the polyanionic compound, and the negative electrode active material is sodium titanium phosphate or metallic sodium; the positive electrode active material of the lithium-ion battery is lithium iron phosphate, and the negative electrode active material is metallic lithium.

[0023] The present invention has the following beneficial effects:

[0024] The quasi-solid-state ion gel electrolyte of this invention contains a naphthyl derivative organic molecular additive. On the one hand, the functional groups on the organic molecular additive can synergistically decompose sodium / lithium salts and ionic liquids, participate in interface formation, balance the decomposition ratio of sodium / lithium salts and ionic liquids, and form a thin and uniform CEI on the surface of the sodium vanadium phosphate electrode, inhibiting excessive film formation of ionic liquids and sodium salts and reducing the impedance of the positive electrode interface. On the other hand, some electron-donating functional groups in the organic molecular additive can enhance the adsorption of naphthalene rings, attract sodium salts and promote the dissociation of sodium salts, improving the uniformity of sodium dispersion in the ion gel electrolyte, and having a higher adsorption strength for cations in ionic liquids, thus limiting the removal of Na+. + Migration of external cations. Taking 2-naphthyl methyl ether of formula I as an example, it increases the migration of Na+. + The transport number (0.79, only 0.37 without 2-naphthyl methyl ether) and ionic conductivity (1.37 × 10⁻⁶) were significantly higher. -3 S cm -1 The fraction without 2-naphthyl methyl ether was only 0.79 × 10⁻⁶. -3 S cm -1 Furthermore, the voltage window increased from 4.27V to 4.47V. The ionic conductivity of the lithium-ion battery is 1.65 × 10⁻⁶. -3 S cm -1 (The fraction without 2-naphthyl methyl ether is only 0.93 × 10⁻⁶) -3 S cm -1 This improved the overall ion transport kinetics of sodium / lithium-ion batteries, increasing the electrochemical window from 4.05V to 4.17V. Sodium / lithium-ion batteries with added organic molecular additives maintained a capacity retention of over 97% after 100 cycles at 0.5C, while those without organic additives maintained a capacity retention of less than 94% or experienced overcharge and short circuits. This demonstrates that organic molecular additives play a crucial role in the ion transport kinetics and cycle stability of sodium / lithium-ion batteries. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art 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.

[0026] Figure 1 The diagrams show the ionic conductivity of the ion gel electrolyte prepared in Comparative Example 1 and the ion gel electrolyte prepared in Examples 1-4, the sodium ion transport number of the ion gel electrolyte prepared in Comparative Example 1 and the ion gel electrolyte prepared in Example 1, and the ionic conductivity of the ion gel electrolyte prepared in Comparative Example 2 and the ion gel electrolyte prepared in Examples 5-8.

[0027] Figure 2 The graphs show the cycle performance test curves of the sodium-ion battery prepared in Example 1 and the sodium-ion battery prepared in Comparative Example 1 of this invention.

[0028] Figure 3 The diagram shows the cycle performance test curves of the sodium-ion batteries prepared in Examples 2-4 and Comparative Example 1.

[0029] Figure 4 The graphs show the cycle performance test curves of the lithium-ion battery prepared in Example 5 and the lithium-ion battery prepared in Comparative Example 2 of this invention.

[0030] Figure 5 This is a comparison chart of the charge-discharge curves of the sodium-ion batteries prepared in Examples 2-4 of this invention and the sodium-ion battery prepared in Comparative Example 1 during the fifth week.

[0031] Figure 6 This is a comparison of the charge-discharge curves of the lithium-ion batteries prepared in Examples 6-8 of this invention during the fifth week.

[0032] Figure 7 The images show a cryo-transmission electron microscope (cryo-TEM) comparison of the CEI thickness and uniformity of the sodium vanadium phosphate cathode prepared in Example 1 and the sodium vanadium phosphate cathode prepared in Comparative Example 1 after the first charge to 3.8V; the inset is a partial magnified view of the cryo-TEM.

[0033] Figure 8 The graphs show the rate performance test curves of the sodium-ion battery prepared in Example 1 and the sodium-ion battery prepared in Comparative Example 1 of this invention. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0035] All raw materials used in the embodiments of the present invention are commercially available products.

[0036] Example 1

[0037] This embodiment describes a method for preparing a quasi-solid-state ion gel electrolyte for sodium-ion batteries using 2-naphthyl methyl ether (II-2) as an organic additive. The steps are as follows:

[0038] (1) Preparation of quasi-solid-state ion gel electrolyte containing 2-naphthyl methyl ether organic additive for sodium-ion batteries

[0039] 0.45 g of PVDF-HFP was dissolved in acetone to form a polymer precursor solution. 0.05 g of 2-naphthyl methyl ether organic additive (4.5 wt% of the total mass of the polymer matrix, ionic liquid, and additive) was added, along with 0.6 g of EmimFSI ionic liquid and 0.125 g of NaTFSI sodium salt, to obtain a modified electrolyte precursor solution. The concentration of NaTFSI was 1 mol / L (volume conversion based on ionic liquid density and mass). The modified electrolyte precursor solution was coated onto a smooth glass plate using a doctor blade to a height of 400 μm. After film formation, it was dried in a vacuum drying oven and cut into quasi-solid electrolyte membranes with a diameter of 19 mm (thickness ~85 μm). These membranes were then stored in an argon-filled glove box for later use.

[0040] (2) Assembly of sodium-ion batteries

[0041] Sodium-ion batteries were assembled using the modified quasi-solid-state ion gel electrolyte described above, with metallic sodium as the negative electrode, sodium vanadium phosphate as the positive electrode, PDVF as the binder, and Super P Li as the conductive agent, and CR2025 coin cells were assembled.

[0042] Example 2

[0043] This embodiment describes a method for preparing a quasi-solid-state ion gel electrolyte for sodium-ion batteries using naphthalene(II-1) as an organic molecular additive. The steps are as follows:

[0044] (1) Preparation of quasi-solid-state ion gel electrolyte containing naphthalene organic additive for sodium-ion batteries

[0045] 0.45 g of PVDF-HFP was dissolved in acetone to form a polymer precursor solution. 0.05 g of naphthalene organic additive (4.5 wt% of the total mass of the polymer matrix, ionic liquid, and additive) was added, along with 0.6 g of EmimFSI ionic liquid and 0.125 g of NaTFSI sodium salt, to obtain a modified electrolyte precursor solution. The concentration of NaTFSI was 1 mol / L (volume conversion based on ionic liquid density and mass). The modified electrolyte precursor solution was coated onto a smooth glass plate using a doctor blade to a height of 400 μm. After film formation, it was dried in a vacuum drying oven and cut into quasi-solid electrolyte membranes with a diameter of 19 mm (thickness ~85 μm). These membranes were then stored in an argon-filled glove box for later use.

[0046] (2) Assembly of sodium-ion batteries

[0047] Sodium-ion batteries were assembled using the modified quasi-solid-state ion gel electrolyte described above, with metallic sodium as the negative electrode, sodium vanadium phosphate as the positive electrode, PDVF as the binder, and Super P Li as the conductive agent, and CR2025 coin cells were assembled.

[0048] Example 3

[0049] This embodiment describes a method for preparing a quasi-solid-state ion gel electrolyte for sodium-ion batteries using 2-naphthylethyl ether (II-3) as an organic molecular additive. The steps are as follows:

[0050] (1) Preparation of quasi-solid-state ion gel electrolyte containing 2-naphthyl ether organic additive for sodium-ion batteries

[0051] 0.45 g of PVDF-HFP was dissolved in acetone to form a polymer precursor solution. 0.05 g of 2-naphthyl ethyl ether organic additive (4.5 wt% of the total mass of the polymer matrix, ionic liquid, and additive) was added, along with 0.6 g of EmimFSI ionic liquid and 0.125 g of NaTFSI sodium salt, to obtain a modified electrolyte precursor solution. The concentration of NaTFSI was 1 mol / L (volume conversion based on ionic liquid density and mass). The modified electrolyte precursor solution was coated onto a smooth glass plate using a doctor blade to a height of 400 μm. After film formation, it was dried in a vacuum drying oven and cut into quasi-solid electrolyte membranes with a diameter of 19 mm (thickness ~85 μm). These membranes were then stored in an argon-filled glove box for later use.

[0052] (2) Assembly of sodium-ion batteries

[0053] Sodium-ion batteries were assembled using the modified quasi-solid-state ion gel electrolyte described above, with metallic sodium as the negative electrode, sodium vanadium phosphate as the positive electrode, PDVF as the binder, and Super P Li as the conductive agent, and CR2025 coin cells were assembled.

[0054] Example 4

[0055] This embodiment describes a method for preparing a quasi-solid-state ion gel electrolyte for sodium-ion batteries using 2-naphthoxyacetic acid (II-4) as an organic molecular additive. The steps are as follows:

[0056] (1) Preparation of quasi-solid-state ion gel electrolyte containing 2-naphthoxyacetic acid organic additive for sodium-ion batteries

[0057] 0.45 g of PVDF-HFP was dissolved in acetone to form a polymer precursor solution. 0.05 g of 2-naphthoxyacetic acid organic additive (4.5 wt% of the total mass of the polymer matrix, ionic liquid, and additive) was added, along with 0.6 g of EmimFSI ionic liquid and 0.125 g of NaTFSI sodium salt, to obtain a modified electrolyte precursor solution. The concentration of NaTFSI was 1 mol / L (volume conversion based on ionic liquid density and mass). The modified electrolyte precursor solution was coated onto a smooth glass plate using a doctor blade to a height of 400 μm. After film formation, it was dried in a vacuum drying oven and cut into quasi-solid electrolyte membranes with a diameter of 19 mm (thickness ~85 μm). These membranes were then stored in an argon-filled glove box for later use.

[0058] (2) Assembly of sodium-ion batteries

[0059] Sodium-ion batteries were assembled using the modified quasi-solid-state ion gel electrolyte described above, with metallic sodium as the negative electrode, sodium vanadium phosphate as the positive electrode, PDVF as the binder, and Super P Li as the conductive agent, and CR2025 coin cells were assembled.

[0060] Example 5

[0061] This embodiment describes a method for preparing a quasi-solid-state ion gel electrolyte for lithium-ion batteries using 2-naphthyl methyl ether (II-2) as an organic molecular additive. The steps are as follows:

[0062] (1) Preparation of quasi-solid-state ion gel electrolyte containing 2-naphthyl methyl ether organic additive for lithium-ion batteries

[0063] 0.45 g of PVDF-HFP was dissolved in acetone to form a polymer precursor solution. 0.05 g of 2-naphthyl methyl ether organic additive (4.5 wt% of the total mass of the polymer matrix, ionic liquid, and additive) was added, along with 0.6 g of EmimFSI ionic liquid and 0.117 g of LiTFSI lithium salt, to obtain a modified electrolyte precursor solution. The concentration of LiTFSI was 1 mol / L (volume conversion based on ionic liquid density and mass). The modified electrolyte precursor solution was coated onto a smooth glass plate using a doctor blade to a height of 400 μm. After film formation, it was dried in a vacuum drying oven and cut into quasi-solid electrolyte membranes with a diameter of 19 mm (thickness ~80 μm). These membranes were then stored in an argon-filled glove box for later use.

[0064] (2) Assembly of lithium-ion batteries

[0065] The modified quasi-solid-state ion gel electrolyte described above was used to assemble a lithium-ion battery, with lithium metal as the negative electrode, lithium iron phosphate as the positive electrode, PDVF as the binder, and Super P Li as the conductive agent, and CR2025 coin cells were assembled.

[0066] Example 6

[0067] This embodiment describes a method for preparing a quasi-solid-state ion gel electrolyte for lithium-ion batteries using naphthalene(II-1) as an organic molecular additive. The steps are as follows:

[0068] (1) Preparation of quasi-solid-state ion gel electrolyte containing naphthalene organic additives for lithium-ion batteries

[0069] 0.45 g of PVDF-HFP was dissolved in acetone to form a polymer precursor solution. 0.05 g of naphthalene organic additive (4.5 wt% of the total mass of the polymer matrix, ionic liquid, and additive) was added, along with 0.6 g of EmimFSI ionic liquid and 0.117 g of LiTFSI lithium salt, to obtain a modified electrolyte precursor solution. The concentration of LiTFSI was 1 mol / L (volume conversion based on ionic liquid density and mass). The modified electrolyte precursor solution was coated onto a smooth glass plate using a doctor blade to a height of 400 μm. After film formation, it was dried in a vacuum drying oven and cut into quasi-solid electrolyte membranes with a diameter of 19 mm (thickness ~80 μm). These membranes were then stored in an argon-filled glove box for later use.

[0070] (2) Assembly of lithium-ion batteries

[0071] The modified quasi-solid-state ion gel electrolyte described above was used to assemble a lithium-ion battery, with lithium metal as the negative electrode, lithium iron phosphate as the positive electrode, PDVF as the binder, and Super P Li as the conductive agent, and CR2025 coin cells were assembled.

[0072] Example 7

[0073] This embodiment describes a method for preparing a quasi-solid-state ion gel electrolyte for lithium-ion batteries using 2-naphthylethyl ether (II-3) as an organic molecular additive. The steps are as follows:

[0074] (1) Preparation of quasi-solid-state ion gel electrolyte containing 2-naphthyl ether organic additive for lithium-ion batteries

[0075] 0.45 g of PVDF-HFP was dissolved in acetone to form a polymer precursor solution. 0.05 g of 2-naphthyl ethyl ether organic additive (4.5 wt% of the total mass of the polymer matrix, ionic liquid, and additive) was added, along with 0.6 g of EmimFSI ionic liquid and 0.117 g of LiTFSI lithium salt, to obtain a modified electrolyte precursor solution. The concentration of LiTFSI was 1 mol / L (volume conversion based on ionic liquid density and mass). The modified electrolyte precursor solution was coated onto a smooth glass plate using a doctor blade to a height of 400 μm. After film formation, it was dried in a vacuum drying oven and cut into quasi-solid electrolyte membranes with a diameter of 19 mm (thickness ~80 μm). These membranes were then stored in an argon-filled glove box for later use.

[0076] (2) Assembly of lithium-ion batteries

[0077] The modified quasi-solid-state ion gel electrolyte described above was used to assemble a lithium-ion battery, with lithium metal as the negative electrode, lithium iron phosphate as the positive electrode, PDVF as the binder, and Super P Li as the conductive agent, and CR2025 coin cells were assembled.

[0078] Example 8

[0079] This embodiment describes a method for preparing a quasi-solid-state ion gel electrolyte for lithium-ion batteries using 2-naphthoxyacetic acid (II-4) as an organic molecular additive. The steps are as follows:

[0080] (1) Preparation of quasi-solid-state ion gel electrolyte containing 2-naphthoxyacetic acid organic additive for lithium-ion batteries

[0081] 0.45 g of PVDF-HFP was dissolved in acetone to form a polymer precursor solution. 0.05 g of 2-naphthoxyacetic acid organic additive (4.5 wt% of the total mass of the polymer matrix, ionic liquid, and additive) was added, along with 0.6 g of EmimFSI ionic liquid and 0.117 g of LiTFSI lithium salt, to obtain a modified electrolyte precursor solution. The concentration of LiTFSI was 1 mol / L (volume conversion based on ionic liquid density and mass). The modified electrolyte precursor solution was coated onto a smooth glass plate using a doctor blade to a height of 400 μm. After film formation, it was dried in a vacuum drying oven and cut into quasi-solid electrolyte membranes with a diameter of 19 mm (thickness ~80 μm). These membranes were then stored in an argon-filled glove box for later use.

[0082] (2) Assembly of lithium-ion batteries

[0083] The modified quasi-solid-state ion gel electrolyte described above was used to assemble a lithium-ion battery, with lithium metal as the negative electrode, lithium iron phosphate as the positive electrode, PDVF as the binder, and Super P Li as the conductive agent, and CR2025 coin cells were assembled.

[0084] Example 9

[0085] This embodiment describes a method for preparing a quasi-solid-state ion gel electrolyte for sodium-ion batteries using 2-naphthyl methyl ether (II-2) as an organic additive. The steps are as follows:

[0086] (1) Preparation of quasi-solid-state ion gel electrolyte containing 2-naphthyl methyl ether organic additive for sodium-ion batteries

[0087] 0.467 g of PVDF-HFP was dissolved in acetone to form a polymer precursor solution. 0.033 g of 2-naphthyl methyl ether organic additive (3.0 wt% of the total mass of the polymer matrix, ionic liquid, and additive) was added, along with 0.6 g of EmimFSI ionic liquid and 0.25 g of NaTFSI sodium salt, to obtain a modified electrolyte precursor solution. The concentration of NaTFSI was 2 mol / L (volume conversion based on ionic liquid density and mass). The modified electrolyte precursor solution was coated onto a smooth glass plate using a doctor blade to a height of 400 μm. After film formation, it was dried in a vacuum drying oven and cut into quasi-solid electrolyte membranes with a diameter of 19 mm (thickness ~85 μm). These membranes were then stored in an argon-filled glove box for later use.

[0088] (2) Assembly of sodium-ion batteries

[0089] Sodium-ion batteries were assembled using the modified quasi-solid-state ion gel electrolyte described above, with metallic sodium as the negative electrode, sodium vanadium fluorophosphate as the positive electrode, PDVF as the binder, and Super P Li as the conductive agent, and CR2025 coin cells were assembled.

[0090] Example 10

[0091] This embodiment describes a method for preparing a quasi-solid-state ion gel electrolyte for sodium-ion batteries using 2-naphthyl methyl ether (II-2) as an organic additive. The steps are as follows:

[0092] (1) Preparation of quasi-solid-state ion gel electrolyte containing 2-naphthyl methyl ether organic additive for sodium-ion batteries

[0093] 0.489 g of PVDF-HFP was dissolved in acetone to form a polymer precursor solution. 0.011 g of 2-naphthyl methyl ether organic additive (1.0 wt% of the total mass of the polymer matrix, ionic liquid, and additive) was added, along with 0.6 g of EmimFSI ionic liquid and 0.5 g of NaTFSI sodium salt, to obtain a modified electrolyte precursor solution. The concentration of NaTFSI was 4 mol / L (volume conversion based on ionic liquid density and mass). The modified electrolyte precursor solution was coated onto a smooth glass plate using a doctor blade to a height of 400 μm. After film formation, it was dried in a vacuum drying oven and cut into quasi-solid electrolyte membranes with a diameter of 19 mm (thickness ~85 μm). These membranes were then stored in an argon-filled glove box for later use.

[0094] (2) Assembly of sodium-ion batteries

[0095] Sodium-ion batteries were assembled using the modified quasi-solid-state ion gel electrolyte described above, with metallic sodium as the negative electrode, sodium iron phosphate as the positive electrode, PDVF as the binder, and Super P Li as the conductive agent, and CR2025 coin cells were assembled.

[0096] Comparative Example 1

[0097] This comparative example demonstrates the preparation method of a quasi-solid-state ion gel for sodium-ion batteries without organic additives. The steps are as follows:

[0098] (1) Preparation of quasi-solid-state ion gels for sodium-ion batteries

[0099] 0.5 g of PVDF-HFP was dissolved in acetone to form a polymer precursor solution. Then, 0.6 g of EmimFSI ionic liquid and 0.125 g of NaTFSI sodium salt were added to obtain the electrolyte precursor solution. The concentration of NaTFSI was 1 mol / L (volume conversion based on ionic liquid density and mass). The electrolyte precursor solution was coated onto a smooth glass plate using a doctor blade to a height of 400 μm. After film formation, it was dried in a vacuum drying oven and cut into quasi-solid electrolyte membranes with a diameter of 19 mm (thickness ~85 μm). These membranes were then stored in an argon-filled glove box for later use.

[0100] (2) Assembly of sodium-ion batteries

[0101] Sodium-ion batteries were assembled using the aforementioned quasi-solid-state ion gel electrolyte, with metallic sodium as the negative electrode, sodium vanadium phosphate as the positive electrode, and PDVF as the binder, and CR2025 coin cells were assembled.

[0102] Comparative Example 2

[0103] This comparative example demonstrates a method for preparing a quasi-solid-state ion gel for lithium-ion batteries without organic additives. The steps are as follows:

[0104] (1) Preparation of quasi-solid-state ion gels for lithium-ion batteries

[0105] 0.5 g of PVDF-HFP was dissolved in acetone to form a polymer precursor solution. Then, 0.6 g of EmimFSI ionic liquid and 0.117 g of LiTFSI lithium salt were added to obtain the electrolyte precursor solution. The concentration of LiTFSI was 1 mol / L (volume conversion based on ionic liquid density and mass). The electrolyte precursor solution was coated onto a smooth glass plate using a doctor blade to a height of 400 μm. After film formation, it was dried in a vacuum drying oven and cut into quasi-solid electrolyte membranes with a diameter of 19 mm (thickness ~80 μm). These membranes were then stored in an argon-filled glove box for later use.

[0106] (2) Assembly of lithium-ion batteries

[0107] Sodium-ion batteries were assembled using the aforementioned quasi-solid-state ion gel electrolyte, with lithium metal as the negative electrode, lithium iron phosphate as the positive electrode, and PDVF as the binder, and CR2025 coin cells were assembled.

[0108] Effect Analysis

[0109] The performance test conditions are as follows:

[0110] 1. The sodium-ion batteries prepared in Example 1 and Comparative Example 1 were tested under a 0.5C charge-discharge rate mode. The discharge cutoff voltage was 2.5V and the charging cutoff voltage was 3.8V.

[0111] 2. The sodium-ion batteries prepared in Examples 2-4 and Comparative Example 1 were tested under a 0.5C charge-discharge rate mode. The discharge cutoff voltage was 2.5V and the charging cutoff voltage was 3.8V.

[0112] 3. The lithium-ion batteries prepared in Example 5 and Comparative Example 2 were tested under a 0.5C charge / discharge rate. The discharge cutoff voltage was 2.8V and the charging cutoff voltage was 4.0V.

[0113] Figure 1The diagrams show the ionic conductivity of the ionogel electrolyte prepared in Comparative Example 1 and Comparative Examples 1-4, the sodium ion transport number of the ionogel electrolyte prepared in Comparative Example 1 and Example 1, and the ionic conductivity of the ionogel electrolyte prepared in Comparative Example 2 and Examples 5-8. Figure 1 It can be seen that the organic additive 2-naphthyl methyl ether (II-2) used in Examples 1 and 5 has the most significant effect on improving ionic conductivity, which is 1.37 × 10⁻⁶ in sodium / lithium batteries. -3 S cm -1 and 1.65×10 -3 S cm -1 The second most effective result was achieved by the organic additive 2-naphthyl ethyl ether (II-3) used in Examples 3 and 7. Furthermore, in sodium-ion batteries, the sodium ion transport number of the ion gel electrolyte prepared in Example 1 was 0.79, significantly higher than the 0.37 of the ion gel electrolyte prepared in Comparative Example 1.

[0114] Figure 2 The graphs show the cycle performance test curves of the sodium-ion battery prepared in Example 1 and the sodium-ion battery prepared in Comparative Example 1 of this invention. Figure 2 It is evident that the organic additive 2-naphthyl methyl ether (II-2) used in Example 1 can improve the cycle stability of the battery, with almost no capacity fluctuation during 50 cycles, a capacity retention rate >99%, and the ability to maintain 112.4 mAh g⁻¹. -1 The reversible specific capacity.

[0115] Figure 3 The graphs show the cycle performance test curves of the sodium-ion batteries prepared in Examples 2-4 and Comparative Example 1, respectively. Figure 3 It is evident that the organic additives naphthalene (II-1) and 2-naphthyl ethyl ether (II-3) used in Examples 2 and 3 can improve the cycle stability of the battery, with a capacity retention rate exceeding 99.6% (even higher than the initial capacity) and a coulombic efficiency maintained above 99%.

[0116] Figure 4 The graphs show the cycle performance test curves of the lithium-ion battery prepared in Example 5 and the lithium-ion battery prepared in Comparative Example 2 of this invention. Figure 4 It is evident that the organic additive 2-naphthyl methyl ether (II-2) used in Example 5 can prevent overcharging of the battery and improve the cycle reversibility of the battery.

[0117] Figure 5 This is a comparison of the charge-discharge curves of the sodium-ion batteries prepared in Examples 2-4 of this invention and the sodium-ion battery prepared in Comparative Example 1 during the fifth week. Figure 5It is known that the organic additives naphthalene (II-1) and 2-naphthyl ethyl ether (II-3) used in Examples 2 and 3 can improve the ion transport kinetics performance in sodium-ion batteries, while the organic additive 2-naphthoxyacetic acid (II-4) used in Example 4 has a certain adverse effect.

[0118] Figure 6 This is a comparison of the charge-discharge curves of the lithium-ion batteries prepared in Examples 6-8 of this invention during the fifth week. Figure 6 It can be seen that the polarization of the lithium-ion batteries prepared in Examples 6 and 7 is better than that of the lithium-ion battery prepared in Example 8, showing that the electrode material LiFePO4 has a good lithium deintercalation / intercalation platform, indicating that the optimization effect of naphthalene (II-1) and 2-naphthyl ethyl ether (II-3) on ion gel is significantly better than that of 2-naphthoxyacetic acid (II-4).

[0119] Figure 7 Cryo-transmission electron microscopy (CTEM) comparison images of the CEI thickness and uniformity of the sodium vanadium phosphate cathode prepared in Example 1 and Comparative Example 1 after initial charging to 3.8V. Figure 7 It can be seen that Example 1, compared to Comparative Example 1, can form a thinner and more uniform CEI, which facilitates the rapid transport of sodium ions. The inset is a partial enlarged view.

[0120] Figure 8 The graphs show the rate performance test curves of the sodium-ion battery prepared in Example 1 and the sodium-ion battery prepared in Comparative Example 1 of this invention. Figure 8 It can be seen that the organic additive 2-naphthyl methyl ether (II-2) used in Example 1 can improve the ion transport performance of the battery, and the capacity decreases less with changes in current, maintaining a good level. At 3C rate, the sodium-ion battery in Example 1 still maintains 87.6 mAh g⁻¹. -1 The capacity of [specific capacity] is [specific capacity], while the comparative example 1 has only 43.6 mAh g. -1 This indicates that the introduction of the organic additive 2-naphthyl methyl ether (II-2) helps the battery quickly reach a stable state and fully utilize the performance of the electrode materials.

[0121] In summary, on the one hand, the functional groups on the organic molecular additives in this invention can synergistically decompose sodium / lithium salts and ionic liquids, participate in interface formation, balance the decomposition ratio of sodium / lithium salts and ionic liquids, and form a thin and uniform CEI on the surface of the sodium vanadium phosphate electrode, inhibiting excessive film formation of ionic liquids and sodium salts and reducing the impedance of the positive electrode interface. On the other hand, some electron-donating functional groups in the organic molecular additives can enhance the adsorption of naphthalene rings, attract sodium salts and promote the dissociation of sodium salts, improving the uniformity of sodium dispersion in the ionic gel electrolyte, and having a higher adsorption strength for cations in ionic liquids, thus limiting the removal of Na+. + Migration of cations outside the body.

[0122] This invention relates to the Na+ of sodium-ion batteries. + The transport number and ionic conductivity of Na+ were determined. Taking 2-naphthyl methyl ether of Formula I as an example, the method of this invention improved the Na+ ion conductivity. + The transport number (0.79, only 0.37 without 2-naphthyl methyl ether) and ionic conductivity (1.37 × 10⁻⁶) were significantly higher. -3 S cm -1 The fraction without 2-naphthyl methyl ether was only 0.79 × 10⁻⁶. -3 S cm -1 Furthermore, the voltage window was increased from 4.27V to 4.47V. Simultaneously, this invention measured the ionic conductivity of lithium-ion batteries, and the study found that, taking 2-naphthyl methyl ether of Formula I as an example, the ionic conductivity in lithium-ion batteries is 1.65 × 10⁻⁶. -3 S cm -1 (The fraction without 2-naphthyl methyl ether is only 0.93 × 10⁻⁶) -3 Scm -1 This improved the overall ion transport kinetics of sodium / lithium-ion batteries, increasing the electrochemical window from 4.05V to 4.17V.

[0123] Therefore, the above experiments show that sodium / lithium-ion batteries with added organic molecular additives all retain more than 97% of their capacity after 100 cycles at 0.5C, while sodium / lithium-ion batteries without organic additives all retain less than 94% of their capacity or are overcharged and short-circuited. This proves that organic molecular additives play an important role in the ion transport kinetics, cycle stability, and rate performance of sodium / lithium-ion batteries.

[0124] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A solid sodium / lithium-ion battery ion gel electrolyte, characterized in that: The basic ionic gel comprises an inorganic salt, a polymer substrate, and an ionic liquid, along with an organic additive, wherein the organic additive is a naphthyl derivative, and the structural formula of the naphthyl derivative is as follows: R is -OCH3 or -OCH2CH3; the amount of the organic additive added is 0.6 to 5 wt% of the total mass of the organic additive, ionic liquid and polymer substrate, and the ionic liquid is 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide salt.

2. The solid sodium / lithium-ion battery ion gel electrolyte according to claim 1, characterized in that: The inorganic salt is either sodium bis(trifluoromethanesulfonyl)imide or lithium bis(trifluoromethanesulfonyl)imide; the polymer substrate is polyvinylidene fluoride-hexafluoropropylene.

3. The solid sodium / lithium-ion battery ion gel electrolyte according to claim 1, characterized in that: The mass ratio of the polymer substrate, additives, ionic liquid, and inorganic salt is 0.5:0.6:(0.117~0.5), wherein the concentration of inorganic salt in the basic ionic gel is 1~4 mol / L.

4. The method for preparing the solid sodium / lithium-ion battery ion gel electrolyte according to any one of claims 1-3, characterized in that, The steps are as follows: (1) Dissolve the polymer substrate in acetone to obtain a polymer precursor solution; (2) Add organic additives to the polymer precursor solution obtained in step (1) to obtain a mixed precursor solution; (3) Add the ionic liquid and inorganic salt to the mixed precursor solution obtained in step (2), and after dispersing evenly, obtain the sodium / lithium ion battery ion gel precursor solution. (4) The sodium / lithium ion battery ion gel precursor liquid obtained in step (3) is coated on glass to form a thin film ion gel electrolyte. After drying, a solid sodium / lithium ion battery ion gel electrolyte is obtained.

5. The method for preparing solid sodium / lithium-ion battery ion gel electrolyte according to claim 4, characterized in that: In step (4), the coating height is 400 μm.

6. A sodium / lithium-ion battery, characterized in that: It includes a positive electrode, a negative electrode, and a solid sodium / lithium-ion battery ion gel electrolyte as described in any one of claims 1-3.

7. The sodium / lithium-ion battery according to claim 6, characterized in that: The positive electrode includes a positive current collector and a positive electrode membrane disposed on the positive current collector. The positive electrode membrane includes a positive active material, a positive conductive agent, and a binder. The negative electrode includes a negative current collector and a negative electrode membrane disposed on the negative current collector. The negative electrode membrane includes a negative active material, a negative conductive agent, and a binder.

8. The sodium / lithium-ion battery according to claim 7, characterized in that: The positive electrode active material of the sodium-ion battery includes any one or more of sodium vanadium fluorophosphate, sodium vanadium phosphate, sodium iron sulfate, or sodium iron pyrophosphate in the polyanionic compound, and the negative electrode active material is sodium titanium phosphate or metallic sodium; the positive electrode active material of the lithium-ion battery is lithium iron phosphate, and the negative electrode active material is metallic lithium.

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