Water-charged potassium-magnesium mixed ionic electrolyte, preparation method and application thereof

Abstract

The application provides a kind of water-based potassium-magnesium mixed ionic electrolyte and its preparation method and application, and relates to the technical field of electrochemical energy storage.A kind of water-based potassium-magnesium mixed ionic electrolyte preparation method, the specific steps are as follows: potassium acetate and magnesium triflate are added to water to obtain a water-based potassium-magnesium mixed electrolyte;In the water-based potassium-magnesium mixed electrolyte, the molar concentration of potassium acetate is 1.0-4.0 mol / L, and the molar concentration of magnesium triflate is 1.0-4.0 mol / L;The molar concentration ratio of potassium acetate to magnesium triflate is 1:3.A water-based potassium-magnesium mixed ionic battery prepared by the application has high operating voltage, high energy density and good cycle stability;And the preparation method is simple, low in cost and easy to implement, and under the background of high performance and high reliability requirements for large deep-sea energy storage systems, this water-based potassium-magnesium mixed ionic battery with high energy density, fast kinetics and durability shows wide application potential.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrochemical energy storage, in particular to a rechargeable aqueous potassium-magnesium hybrid ionic electrolyte and a preparation method and application thereof. BACKGROUND

[0002] China has a large number of marine islands, and power supply is particularly critical, but the stability of power supply on remote islands has been a problem for maritime and communication work. Because these islands are far from the coast, traditional diesel generators are often used to ensure energy supply. In order to make full use of the abundant but unstable clean energy on the South China Sea islands, building a coupling utilization system of various new clean energy will be an important method to solve the problem of energy supply on the islands. Among many electrochemical energy storage technologies, aqueous potassium ion batteries have advantages such as long life and high voltage, and aqueous magnesium ion batteries have advantages such as low cost and high energy density. Aqueous potassium-magnesium hybrid ion battery is a strong choice for distributed energy storage system, and is also one of the most promising directions in marine electrochemical energy storage technology.

[0003] The basic mechanism of aqueous ion battery is similar to that of commercial rechargeable ion battery system based on organic electrolyte, which transmits electrons through an external circuit between two electrodes and transmits metal ions through electrolyte. In addition, the intercalation / deintercalation (or deposition / dissolution) in the electrode material is accompanied by the occurrence of redox reaction, and the charge transfer occurs at the interface between the electrode material and the electrolyte. At present, aqueous ion battery uses non-toxic electrode materials and water-based electrolyte system, which not only significantly reduces material cost and environmental impact, but also has advantages of high safety and power density. The low self-discharge characteristic of aqueous ion battery also greatly reduces the dependence on battery management system, showing unique potential for intermittent renewable energy storage. Aqueous ion battery has strong adaptability to application environment with long charging and discharging time, and is particularly suitable for large marine energy storage battery applications with high safety and reliability requirements, frequent charging and discharging, and high operation and maintenance costs.

[0004] At present, the research on aqueous ion battery mainly focuses on electrolyte research, but most of them are high-concentration electrolyte and single-ion electrolyte. High-concentration electrolyte can expand the electrochemical window of aqueous electrolyte and inhibit negative electrode dendrites, etc. However, high-concentration salt has high production cost and certain safety hazards, and high-concentration salt electrolyte has low conductivity and high viscosity, which is difficult to apply to actual production. Single-ion electrolyte is limited by the limitations of the added ions, such as low energy density of monovalent ions and large coulomb repulsion of multivalent ions, etc. It lacks multifunctionality, which limits the applicability of electrolyte in diversified electrochemical systems. Mixed-ion electrolyte can combine the advantages of single and multivalent ions, utilize the synergistic effect of multivalent and monovalent ions, and improve the cycle life and energy density of the battery. SUMMARY

[0005] In view of this, the application provides a water-based potassium-magnesium mixed ionic electrolyte, a preparation method and application thereof.

[0006] The technical scheme of the application is as follows:

[0007] A preparation method of the water-based potassium-magnesium mixed ionic electrolyte comprises the following steps: adding potassium acetate and magnesium triflate into water to obtain a water-based potassium-magnesium mixed electrolyte.

[0008] In the water-based potassium-magnesium mixed electrolyte, the molar concentration of potassium acetate is 1.0-4.0 mol / L, and the molar concentration of magnesium triflate is 1.0-4.0 mol / L.

[0009] Further, the molar concentration ratio of potassium acetate to magnesium triflate is 1:3.

[0010] The application further provides a water-based potassium-magnesium mixed ionic electrolyte prepared by any one of the preparation methods.

[0011] The application further provides application of the water-based potassium-magnesium mixed ionic electrolyte in preparation of a water-based potassium-magnesium mixed ionic battery.

[0012] Further, the water-based potassium-magnesium mixed ionic battery is composed of a positive electrode sheet, a negative electrode sheet, a diaphragm and the water-based potassium-magnesium mixed ionic electrolyte.

[0013] Further, the diaphragm is a glass fiber membrane.

[0014] Further, the positive electrode sheet and the negative electrode sheet each contain a binder, a conductive agent and a current collector, and the surface of the current collector is attached with a film containing an active material.

[0015] Further, the mass ratio of the binder, the conductive agent and the active material in the positive electrode sheet is 1:1-2:7-8, and the mass ratio of the binder, the conductive agent and the active material in the negative electrode sheet is 1:1-2:7-8.

[0016] Further, the active material in the positive electrode sheet is Prussian blue, the binder is polytetrafluoroethylene, and the conductive agent is Ketjen black; and the active material in the negative electrode sheet is any one of vanadium dioxide, vanadium pentoxide or iron vanadium oxide, the binder is polytetrafluoroethylene, and the conductive agent is Ketjen black.

[0017] Further, the preparation method of the positive electrode sheet and the negative electrode sheet is as follows: the active material, the binder and the conductive agent are rolled into a plastic film, and the film is attached to the current collector after drying.

[0018] Compared with the prior art, the application has the following beneficial effects:

[0019] 1.The present application selects specific potassium acetate and magnesium triflate to prepare a water-based potassium-magnesium mixed ionic electrolyte, and a rechargeable water-based potassium-magnesium mixed ionic battery is prepared, which has high working voltage, high energy density and good cycle stability, and has good electrochemical performance; and the preparation method is simple, low in cost and easy to implement, and under the background of excellent performance and high reliability requirements for large deep-sea energy storage systems, this rechargeable water-based potassium-magnesium mixed ionic battery with high energy density, fast kinetic characteristics and durability shows wide application potential.

[0020] 2.The specific concentration ratio of potassium-magnesium mixed ionic electrolyte of the present application, the rechargeable water-based potassium-magnesium mixed ionic battery assembled by the present application utilizes the synergistic effect of multivalent ions and monovalent ions, the high thermodynamic priority and strong diffusion dynamics of potassium ions, the first embedding of materials, the opening of ion transmission channels, and the second embedding of magnesium ions, which improves the working voltage and energy density of the battery; magnesium ions are multivalent ions, which hydrolyze to produce protons during embedding materials, and utilize the advantages of fast ion transmission dynamics and cycle reversibility of protons to improve the high-rate performance and cycle stability of the battery.

[0021] 3.Compared with traditional single-ion batteries, the rechargeable water-based potassium-magnesium mixed ionic battery of the present application has a wider electrode material adaptation surface, a faster ion diffusion rate, a higher working voltage, a higher energy density and a higher cycle stability, which opens up a road for the practical application of water-based mixed ionic batteries. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The cycle stability performance chart of the rechargeable water-based ionic battery of Examples 1-4;

[0023] Among them, Example 1 is 1MKAC+3MMg(OTf)2, Example 2 is 1MKAC+1MMg(OTf)2, Example 3 is 1MKAC+2MMg(OTf)2, and Example 4 is 1MKAC+4MMg(OTf)2.

[0024] Figure 2 The cycle stability performance chart of the rechargeable water-based ionic battery of Examples 1, Comparative Examples 1-2;

[0025] Among them, Example 1 is 1MKAC+3MMg(OTf)2, Comparative Example 1 is 1MK(AC)2+3MMg(OTf)2, and Comparative Example 2 is 1MKAC+3MKOTf.

[0026] Figure 3 The rate performance chart of the rechargeable water-based ionic battery of Examples 1, Comparative Examples 1-2;

[0027] Among them, Example 1 is 1MKAC+3MMg(OTf)2, Comparative Example 1 is 1MK(AC)2+3MMg(OTf)2, and Comparative Example 2 is 1MKAC+3MKOTf.

[0028] Figure 4 Impedance performance diagrams of rechargeable aqueous ion batteries for Example 1 and Comparative Examples 1-2;

[0029] Among them, Example 1 is 1MKAC+3MMg(OTf)2, Comparative Example 1 is 1MK(AC)2+3MMg(OTf)2, and Comparative Example 2 is 1MKAC+3MKOTf.

[0030] Figure 5 The cyclic voltammogram of the rechargeable aqueous potassium-magnesium hybrid ion battery of Example 1 is shown.

[0031] Example 1 is 1MKAC+3MMg(OTf)2.

[0032] Figure 6 The cyclic voltammetry diagram is for the rechargeable aqueous magnesium-ion battery of Comparative Example 1.

[0033] Among them, Comparative Example 1 is 1MK(AC)2+3MMg(OTf)2.

[0034] Figure 7 The cyclic voltammetry diagram is for the rechargeable aqueous potassium-ion battery of Comparative Example 2.

[0035] Comparative Example 2 is 1MKAC+3MKOTf.

[0036] Figure 8 The cycling stability performance diagram of the rechargeable aqueous ion battery in Example 1 and Comparative Example 3 is shown.

[0037] In Example 1, the solution was 1M KAC + 3M Mg(OTf)2, and in Comparative Example 3, the solution was 1M NaCit + 3M Mg(OTf)2. Detailed Implementation

[0038] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention.

[0039] Unless otherwise specified, the experimental methods used in the embodiments of this invention are all conventional methods.

[0040] Unless otherwise specified, all materials and reagents used in the embodiments of this invention are commercially available.

[0041] Example 1

[0042] A method for preparing an aqueous potassium-magnesium mixed ion electrolyte, comprising the following steps:

[0043] Take 14.5 g of magnesium triflate powder with a purity of 98% and 1.47 g of potassium acetate powder with a purity of 99.98%, add 30 mL of capacity bottle, add 15 mL of deionized water, place on a heating stirring table, stir at a temperature of 60°C for 10 min, then place the capacity bottle in an ultrasonic shaker, 4 kHz, 500 rpm, ultrasonic for 20 min, repeat the above heating, ultrasonic steps 1 time, get the potassium-magnesium mixed electrolyte, the concentration ratio of potassium acetate and magnesium triflate is 1:3.

[0044] A rechargeable water-based potassium-magnesium mixed ion battery, the specific preparation steps are:

[0045] (1) Take the positive active material Prussian blue, the conductive agent Ketjen black and the binder PTFE with a mass ratio of 7:2:1, transfer to a mortar, roll into a film with a thickness of 5 mg / cm 3 after grinding, place the film in a vacuum drying oven at 70°C and dry for 18 h;

[0046] (2) Take the negative active material vanadium dioxide, the conductive agent Ketjen black and the binder PTFE with a mass ratio of 7:2:1, transfer to a mortar, roll into a film with a thickness of 5 mg / cm 3 after grinding, place the film in a vacuum drying oven at 70°C and dry for 18 h;

[0047] (3) Cut the titanium mesh as a current collector, rinse with deionized water and ethanol three times respectively, then place it in anhydrous ethanol for ultrasonic treatment for 30 s, after removing the ethanol, dry it in a 60°C oven for 10 min, weigh two portions of the dried films of step (1) and step (2), and press them on the titanium mesh under a pressure of 10 MPa, namely the negative electrode sheet and the positive electrode sheet;

[0048] (4) Place the negative electrode sheet, the separator and the positive electrode sheet in a CR2032 button cell in the order of negative electrode sheet, separator and positive electrode sheet, add 150 μL of the prepared mixed ion electrolyte, then seal the button cell, and get a rechargeable water-based potassium-magnesium mixed ion battery.

[0049] Example 2

[0050] The difference between Example 1 and Example 2 is that the concentration of potassium acetate is kept unchanged, and the concentration of magnesium triflate is changed, so that the concentration ratio of potassium acetate and magnesium triflate in the final potassium-magnesium mixed electrolyte is 1:1, and the others are consistent with Example 1.

[0051] Example 3

[0052] The difference between the example 1 is that the concentration of potassium acetate is kept unchanged, the concentration of magnesium triflate is changed, the concentration ratio of potassium acetate and magnesium triflate in the final potassium-magnesium mixed electrolyte is 1:2, and the others are consistent with example 1.

[0053] Example 4

[0054] The difference between the example 1 is that the concentration of potassium acetate is kept unchanged, the concentration of magnesium triflate is changed, the concentration ratio of potassium acetate and magnesium triflate in the final potassium-magnesium mixed electrolyte is 1:4, and the others are consistent with example 1.

[0055] Test example 1

[0056] The potassium-magnesium mixed ion battery prepared in examples 1-4 is subjected to electrochemical performance detection, Figure 1 The cycle stability performance of each battery is compared.

[0057] From Figure 1 It can be seen that when the concentration ratio of potassium acetate and magnesium triflate in example 1 is 1:3, the cycle stability and specific capacity of the rechargeable aqueous potassium-magnesium mixed ion battery are the best, and under the current density of 100mA·g -1 The initial capacity of example 1 can reach 93mAh·g -1 , the capacity is 73mAh·g -1 after 100 cycles, and the capacity retention rate is 78%, indicating that the rechargeable aqueous potassium-magnesium mixed ion battery prepared in example 1 has excellent cycle stability and energy density.

[0058] Comparative example 1

[0059] The difference between the example 1 is that the potassium acetate is replaced by magnesium acetate, that is, a single magnesium ion electrolyte is prepared, and the others are consistent with example 1.

[0060] Comparative example 2

[0061] The difference between the example 1 is that the magnesium triflate is replaced by potassium triflate, that is, a single potassium ion electrolyte is prepared, and the others are consistent with example 1.

[0062] Test example 2

[0063] The potassium-magnesium mixed ion battery prepared in examples 1, comparative examples 1-2 is subjected to electrochemical performance detection.

[0064] From Figure 2 The cycle stability performance of the rechargeable aqueous ion battery can be seen from the figure, the potassium ion and magnesium ion in example 1 are embedded / extracted from the material together, play a synergistic effect, and improve the cycle stability and energy density of the rechargeable aqueous ion battery. 500mA·g-1 The initial capacity of the rechargeable aqueous ion battery of Example 1 is 80 mAh g -1 After 250 cycles, the capacity is 63 mAh g -1 The capacity retention rate is 80%. Compared with Example 1, the initial capacity of the single magnesium ion battery of Comparative Example 1 is 82 mAh g -1 After 250 cycles, the capacity is 55 mAh g -1 The capacity retention rate is 67%. Although the capacity of the single magnesium ion battery of Comparative Example 1 is high, this is mainly because the magnesium ion is a divalent ion with a large charge density, but the large size of the hydrated ion of the magnesium ion will damage the structure of the material for a long time, reducing the cycle stability of the battery. The initial capacity of the single potassium ion battery of Comparative Example 2 is 65 mAh g -1 After 250 cycles, the capacity is 16 mAh g -1 The capacity retention rate is 25%, because the potassium ion in the single potassium ion battery of Comparative Example 2 has the largest ionic radius, and repeated deintercalation will cause serious impact on the crystal structure of vanadium dioxide, leading to irreversible damage and collapse, thereby causing rapid decay of the battery capacity.

[0065] From the rate performance graph of the rechargeable aqueous ion battery of Figure 3 It can be seen that Example 1 of the present application exhibits excellent rate performance, and the specific capacity at a current density of 3 A g -1 can reach 46 mAh g -1 When the current density returns to 0.5 A g -1 , the specific capacity has almost no decay, because when the potassium ion is inserted and extracted from the positive electrode Prussian blue material, the potassium ion has the smallest Stokes radius and the strongest desolvation energy, and has a fast ion deintercalation ability; and when the magnesium ion is deintercalated from the negative electrode vanadium dioxide, protons are produced by hydrolysis, and the protons have the smallest size and mass and have a super-high ion mobility, so the battery has good rate performance. The specific capacity of the single magnesium ion battery of Comparative Example 1 at a current density of 3 A g -1 decreased to 36 mAh g -1 When the current density returns to 0.5 A g -1 , the specific capacity has decayed, because the magnesium ion has a large coulomb repulsion and a low migration rate, resulting in poor battery rate performance. The specific capacity of the single potassium ion battery of Comparative Example 2 at a current density of 3 A g -1 decreased to 17 mAh g -1 When the current density returns to 0.5 A g -1The specific capacity of the battery decreases significantly over time, because the single potassium ion battery cannot quickly deintercalate the vanadium dioxide material due to the large ion radius and the large resistance received by the intercalation and deintercalation crystal, resulting in poor rate performance of the battery.

[0066] From Figure 4 As can be seen from the impedance performance graph of the rechargeable aqueous ion battery of Example 1, Comparative Example 1 and Comparative Example 2, the charge transfer rate of the batteries of Comparative Example 2, Example 1 and Comparative Example 1 gradually decreases, which is consistent with the characteristics of the migration rates of potassium ions and magnesium ions.

[0067] Figures 5-7 As can be seen from the cyclic voltammograms of the rechargeable aqueous ion batteries of Example 1, Comparative Example 1 and Comparative Example 2, the average operating voltage of the potassium-magnesium mixed ion battery of Example 1 is higher than that of the single potassium ion battery and the single magnesium ion battery, which is consistent with the foregoing analysis and will not be described here.

[0068] Comparative Example 3

[0069] The difference between Example 1 and Comparative Example 3 is that potassium acetate is replaced by sodium citrate, and the other aspects are consistent with Example 1.

[0070] Test Example 3

[0071] The rechargeable aqueous ion batteries prepared in Example 1 and Comparative Example 3 were subjected to electrochemical performance testing, Figure 8 The comparison chart of the cycle stability performance of the batteries. As can be seen from the chart, the performance of the ion battery with sodium citrate and magnesium triflate is far inferior to that of the battery with potassium acetate and magnesium triflate in Example 1.

[0072] In addition, through a large number of experiments, it has been verified that when the molar concentration ratio of potassium acetate to magnesium triflate in the potassium-magnesium mixed ion electrolyte is 1:3, the performance of the battery prepared by replacing it with the molar concentration ratio of potassium triflate to magnesium acetate 1:3 will also decrease.

[0073] As can be seen, only the specific single and multiple valence ion type and concentration mixture of the present application will have a positive effect on the performance improvement of the aqueous battery.

[0074] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing a water-fillable potassium-magnesium mixed ion electrolyte, characterized in that, The preparation method comprises the following steps: adding potassium acetate and magnesium triflate into water to obtain a water-based potassium-magnesium mixed electrolyte. In the water-based potassium-magnesium mixed electrolyte, the molar concentration of potassium acetate is 1.0-4.0 mol / L, and the molar concentration of magnesium triflate is 1.0-4.0 mol / L. The molar concentration ratio of potassium acetate to magnesium triflate is 1:

3.

2. A water-chargeable potassium-magnesium mixed ionic electrolyte, characterized by comprising: The preparation method is prepared by the preparation method in claim 1.

3. The application of the water-based potassium-magnesium mixed ionic electrolyte in claim 2 in the preparation of a water-based potassium-magnesium mixed ionic battery.

4. Use according to claim 3, wherein the compound is ###0002### The water-based potassium-magnesium mixed ionic battery is composed of a positive electrode sheet, a negative electrode sheet, a diaphragm and the water-based potassium-magnesium mixed ionic electrolyte in claim 2.

5. The use according to claim 4, wherein the compound is ###0002### The diaphragm is a glass fiber membrane.

6. The use according to claim 4, wherein the compound is ###0002### Both the positive electrode sheet and the negative electrode sheet contain a binder, a conductive agent and a current collector, and the surface of the current collector is attached with a film containing an active material.

7. Use according to claim 6, wherein The mass ratio of the binder, the conductive agent and the active material in the positive electrode sheet is 1:1-2:7-8, and the mass ratio of the binder, the conductive agent and the active material in the negative electrode sheet is 1:1-2:7-8.

8. Use according to claim 7, wherein the compound is ###0002### The active material in the positive electrode sheet is Prussian blue, the binder is polytetrafluoroethylene, and the conductive agent is Ketjen black; the active material in the negative electrode sheet is any one of vanadium dioxide, vanadium pentoxide or iron vanadium oxide, the binder is polytetrafluoroethylene, and the conductive agent is Ketjen black.

9. The use according to claim 6, wherein The preparation method of the positive electrode sheet and the negative electrode sheet is as follows: rolling the active material, the binder and the conductive agent into a plastic film, and then attaching the film on the current collector after drying.

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