WO2023185944A1

WO2023185944A1 - Electrolyte system free of free solvent molecules, preparation method therefor, and application thereof

Info

Publication number: WO2023185944A1
Application number: PCT/CN2023/084780
Authority: WO
Inventors: 易先辉; 鲁兵安; 许志
Original assignee: 福建新峰二维材料科技有限公司
Priority date: 2022-03-31
Filing date: 2023-03-29
Publication date: 2023-10-05
Also published as: CN114784383A

Abstract

The present invention relates to an electrolyte system free of free solvent molecules. The electrolyte system comprises a metal salt electrolyte and a metal organic framework compound; and the metal organic framework compound is internally provided with an Å solid ion trap structure. An objective of the present invention is to provide an electrolyte system free of free solvent molecules, a preparation method therefor, and an application thereof so as to avoid the problems of battery safety risks and poor electrochemical performance caused by the presence of free solvent molecules in the electrolyte system.

Description

An electrolyte system without free solvent molecules and its production method and application

Technical field

The invention relates to an electrolyte system without free solvent molecules and its preparation method and application.

Background technique

Vigorously developing power supplies for consumer electronics, electric vehicles and grid energy storage is an inevitable choice for economic and social development. Although lithium-ion batteries (LIBs) are one of the most abundant energy storage devices in today's society, limited lithium resources limit their further application in mass-produced electric vehicles and plug-in hybrid electric vehicles. Among the next generation batteries, potassium-ion batteries (PIBs) have attracted much attention and exploration due to their low cost, abundant potassium resources and high energy density, so they are considered to be a suitable substitute for LIBs. However, current PIBs are usually based on liquid electrolytes (ether and carbonate solvents), which contain free organic solvent molecules. The free organic solvent molecules in the electrolyte are flammable, volatile, and easily oxidized, which pose serious safety problems in terms of overheating and fire. In addition, in terms of electrodes, especially potassium anodes, there is also a need for an electrolyte that can resist irreversible reactions and dendrite growth during long-term charge/discharge cycles.

As we all know, in traditional liquid (such as organic solvents and water) electrolyte systems, free liquid solvent molecules provide the transmission medium, resulting in high ionic conductivity of the electrolyte. However, free solvent molecules in liquid electrolytes are the root cause of safety risks and poor electrochemical performance, such as their tendency to dissolve active materials. Therefore, developing electrolytes without free solvent molecules is an effective way to achieve highly safe and high-performance metal ion batteries.

Contents of the invention

The purpose of the present invention is to provide an electrolyte system without free solvent molecules and its production method and application, so as to avoid the problems of battery safety risks and poor electrochemical performance caused by the presence of free solvent molecules in the electrolyte system.

The object of the present invention is achieved through the following technical solutions:

An electrolyte system without free solvent molecules, which includes a metal salt electrolyte and a metal-organic framework compound; the metal-organic framework compound has an Angstrom-level solid ion trap structure.

A method for preparing a free solvent molecular electrolyte system, which includes the following steps:

Step A, preparing a metal-organic framework compound film with a solid ion trap structure;

Step B, prepare metal salt liquid electrolyte;

Step C, the metal organic framework compound film is immersed in the metal salt liquid electrolyte;

Step D, dry to remove residual solvent.

An application of the free solvent-free molecular electrolyte system as an electrolyte for a metal ion battery.

Compared with the prior art, the advantages of the present invention are:

(1) The electrolyte system without free solvent molecules has low cost, high ionic conductivity, the ability to inhibit dendrite growth, the "shuttle effect" and electrode dissolution, and high oxidation stability [based on electrolytes without free organic solvent molecules (NOSMS ) over 5.9V], high reduction stability [based on electrolytes without free water molecules (NWMS) below -1V, graphite electrodes can be used] and wide applicability.

(2) Metal ion batteries based on this electrolyte system without free solvent molecules have excellent electrochemical performance and safety. The specific performance is as follows: After 1000 cycles of a potassium-ion battery based on NOSMS electrolyte graphite (negative electrode)||PTCDI (positive electrode) at 50mA g ^-1 , the average capacity decay rate per cycle is only 0.036%, while exhibiting 243.9 Energy density of Wh kg ^-1 .

(3) The electrolyte system without free solvent molecules (NOSMS/NWMS) provided by the present invention is essentially non-flammable, has good thermal stability and cutability, and the metal ion battery made with this system has high safety.

Description of drawings

Figure 1 is a schematic structural diagram of an electrolyte system without free solvent molecules of the present invention.

Figure 2 is a galvanostatic cycle and corresponding voltage hysteresis curve of a K||K battery based on the NOSMS of Example 1 and the traditional KFSI electrolyte system of Comparative Example 1 at a current density of 0.1 mA cm ^-2 .

Figure 3 is a graph of the galvanostatic cycle and the corresponding voltage hysteresis curve of the K||K battery based on the NWMS of Example 2 at a current density of 0.1 mA cm ^-2 .

Figure 4 is a graph showing the Coulombic efficiency and charge and discharge curves of the K||Cu battery based on the NOSMS of Example 1 and the traditional KFSI electrolyte system of Comparative Example 1.

Figure 5 is the charge and discharge curve of the graphite ||K battery based on the NWMS of Example 2 at a current density of 100 mA g ^-1 .

Figure 6 is a cycle performance curve diagram of the graphite ||K battery based on the NWMS of Example 2 at a current density of 100 mA g ^-1 .

Figure 7 is a cycle performance curve diagram of a graphite ||K battery based on the NOSMS of Example 1 and the traditional KFSI electrolyte system of Comparative Example 1 at a current density of 100 mA g ^-1 .

Figure 8 is a voltammetry curve based on Example 1 NOSMS, Example 2 NWMS, Example 3 NWMS-1, and Comparative Example 1 KFSI electrolyte, Comparative Example 2 KCl electrolyte, and Comparative Example 3 KFSI electrolyte at a scan rate of 0.005 V/s.

Figure 9 is a galvanostatic charge distribution diagram of the KVPF (positive electrode)||K half cell based on the traditional KFSI electrolyte system of Comparative Example 1.

Figure 10 is the charge and discharge curve of the KVPF (positive electrode) ||K half cell based on the NOSMS of Example 1 at a current density of 50 mA g ^-1 and a cut-off voltage of 2-4.6V.

Figure 11 is the long-term cycle performance curve of the KVPF (positive electrode) ||K half cell based on the NOSMS of Example 1 at a current density of 50 mA g ^-1 and a cut-off voltage of 2-4.6V.

Figure 12 is a schematic diagram of batteries based on the electrolyte system without free solvent molecules of the present invention and the traditional electrolyte system to inhibit the dissolution of the PTCDI positive electrode.

Figure 13 is the charge and discharge curve of the PTCDI (positive electrode) ||K half-cell based on the NOSMS of Example 1 and the traditional KFSI electrolyte system of Comparative Example 1.

Figure 14 is the charge and discharge curve of the PTCDI (positive electrode) ||K half cell based on the NWMS of Example 2.

Figure 15 is a long-term cycle performance curve of the PTCDI (positive electrode) ||K half cell at a current density of 50 mA g ^-1 based on Example 1 NOSMS.

Figure 16 is a long-term cycle performance curve of the PTCDI (positive electrode) ||K half cell at a current density of 50 mA g ^-1 based on the NWMS of Example 2.

Figures 17 to 19 are schematic diagrams of the suppression of the "shuttle effect" of the battery based on an electrolyte system without free solvent molecules of the present invention; Figure 17 is a schematic diagram of suppression of the "shuttle effect" of the KI positive electrode; Figure 18 is a schematic diagram of the NOSMS based on Example 1 and Comparative Example 1 The third charge and discharge curve of the K||KI battery with the traditional KFSI electrolyte system; Figure 19 is the cycle performance curve of the K||KI battery.

Figures 20 to 22 are performance diagrams of potassium ion full batteries based on PTCDI (positive electrode) | NOSMS | graphite (negative electrode) of Example 1 NOSMS; Figure 20 is a typical galvanostatic charge and discharge curve; Figure 21 is a charge and discharge curve of the full battery ; Figure 22 is a voltage variation curve with time after the full battery is fully charged based on the NOSMS of Example 1 and the traditional KFSI electrolyte system of Comparative Example 1.

Figure 23 is a cycle performance curve of a potassium ion full battery based on PTCDI (positive electrode) | NOSMS | graphite (negative electrode) of Example 1 NOSMS at a current density of 50 mA g ^-1 .

Detailed ways

The metal salt electrolyte is an alkali metal salt electrolyte, an aluminum-based salt electrolyte, a zinc-based salt electrolyte, a magnesium-based salt electrolyte, a calcium-based salt electrolyte or an iron-based salt electrolyte.

The metal salt electrolyte includes a metal salt electrolyte and a solvent; the metal electrolyte is one of an alkali metal salt electrolyte, an aluminum-based salt electrolyte, a zinc-based salt electrolyte, a magnesium-based salt electrolyte, a calcium-based salt electrolyte, and an iron-based salt electrolyte. species; the solvent is an organic solvent or a water solvent.

The alkali metal salt electrolyte is a lithium salt electrolyte, a sodium salt electrolyte or a potassium salt electrolyte; the potassium salt electrolyte is a bisfluorosulfonimide potassium salt, potassium chloride or potassium hexafluorophosphate.

The metal organic framework compounds are zeolite imidazole ester framework (ZIF-7), 2-methylimidazole zinc salt MAF-4 (ZIF-8), Cu-MOF-74, poly[Zn ₂ (BIM) ₄ ], Zr Base-UiO-67 or Cu-BTC (C ₁₈ H ₆ Cu ₃ O ₁₂ , Tricopper; benzene-1,3,5-tricarboxylate).

Step B, prepare metal salt liquid electrolyte;

Step D, dry to remove residual solvent.

The specific method of step A is:

In step a1, the metal organic framework compound and the binder are thoroughly stirred and mixed to prepare a metal organic framework compound slurry;

Step a2, the metal organic framework compound slurry is coated on the substrate and then dried;

In step a3, the substrate coated with the metal organic framework compound is immersed in an organic solvent to peel off the metal organic framework compound from the substrate to prepare a flexible metal organic framework compound film;

In step a4, the flexible metal-organic framework compound film is punched into a desired shape and then activated.

The weight ratio of the metal organic framework compound and the binder is 1: (0.1-0.5), and the binder is polyvinylidene fluoride, styrene-butadiene rubber, carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile or Polyacrylate.

The specific method of step a2 is to coat the metal organic framework compound slurry on a flat substrate and vacuum drying at 60-80°C for 3-5 hours; the base material is metal foil or polymer material film. The metal organic framework compound slurry can be coated on the substrate by means of blade coating (such as blade coating), roller coating, spray coating, etc. The polymer material film is preferably a polymer material film that does not react with alcohol or ketone organic solvents.

The specific method of step a3 is that the substrate coated with the metal organic framework compound is immersed in an organic solvent for 0.5-1 h, so that the metal organic framework compound is peeled off from the substrate to prepare a flexible metal organic framework compound film; The organic solvent is an alcohol-based organic solvent or a ketone-based organic solvent.

The specific method of step a4 is to punch the flexible metal organic framework compound film into the required shape, and then reactivate it under vacuum at 180-220°C for 12-18 hours.

The specific method of step C is to immerse the metal organic framework compound film prepared in step A into the metal salt electrolyte prepared in step B, and treat it at 70-80°C for 40-50 hours, so that the metal salt electrolyte molecules and Solvent molecules are fully immersed in the solid ion trap of the metal-organic framework compound. Anions and solvent molecules are fixed by the solid ion trap, while cations can move freely.

The specific method of step D is to remove the metal salt electrolyte on the surface of the metal-organic framework compound film prepared in step C, and then vacuum dry it at 80-100°C for 20-24 hours to further remove the residual solvent to obtain a free film. Electrolyte system with free solvent molecules. The metal salt electrolyte on the surface can be removed by wiping or blowing.

The metal ion battery is an alkali metal ion battery, an aluminum-based ion battery, a zinc-based ion battery, a magnesium-based ion battery, a calcium-based ion battery or an iron-based ion battery; the alkali metal ion battery is a lithium-ion battery, a sodium-ion battery Or potassium-ion batteries.

Specific implementation cases

This specific embodiment provides an electrolyte system without free solvent molecules. The electrolyte system without free solvent molecules includes potassium salt electrolyte molecules, solvent molecules and metal organic framework compound materials (MOFs); the metal organic framework compound compound The material is mainly composed of zeolite imidazolate framework (ZIF-7) and binder, which contains The solid ion trap structure; the solid ion trap structure can effectively capture free solvent molecules [such as ethylene carbonate (EC), diethyl carbonate (DEC), water, etc.] and anions (such as FSI ^- ions, Cl ^- etc.) and lock it to achieve an electrolyte in which only potassium ions can move freely system.

The preparation method of the electrolyte system without free solvent molecules includes:

First, prepare a ZIF-7 film with an ion trap: fully stir and mix the ZIF-7 material and polyvinylidene fluoride (PVDF) at a weight ratio of 9:1 to obtain a ZIF-7 slurry; use a scraper to scrape the obtained ZIF-7 film. 7. The slurry is evenly coated on the aluminum foil and vacuum dried at 60-80°C for 3 hours. The thickness of the ZIF-7 film after drying is 2-50 microns; then the obtained aluminum foil + ZIF-7 film is immersed in ethanol. 0.5h, the MOFs film is peeled off from the aluminum foil to obtain a flexible ZIF-7 film; then the ZIF-7 film is punched into the shape required by the battery and reactivated under vacuum at 200°C for 12h.

Secondly, a traditional potassium salt liquid electrolyte is prepared; wherein the traditional potassium salt liquid electrolyte contains a potassium salt electrolyte and a solvent; the solvent is one of an organic solvent or a water solvent. The potassium salt electrolyte is one of potassium bisfluorosulfonimide (KFSI), potassium chloride (KCl), and potassium hexafluorophosphate (KPF ₆ ).

Again, the ZIF-7 film is placed in the potassium salt liquid electrolyte to immerse the solvent molecules and electrolyte ions into the ion trap: the reactivated ZIF-7 film is immersed in the traditional potassium salt liquid electrolyte and treated at 60-80°C for 48 hours, so that the electrolyte molecules and solvent molecules are fully immersed in the ion trap of ZIF-7.

Finally, the residual solvent is removed by vacuum drying: take out the treated ZIF-7 film and wipe the surface solvent with a paper towel, and vacuum dry it at 80-100°C for 20 hours to further remove the residual solvent, obtaining an electrolyte system without free solvent molecules.

The present invention also provides a potassium ion battery, which includes a positive electrode, a negative electrode, and an electrolyte. The electrolyte used in the potassium ion battery is the electrolyte system without free solvent molecules.

Example 1

Electrolyte system NOSMS based on organic solvents without free organic solvent molecules

First, prepare a ZIF-7 film with an ion trap: fully stir and mix the ZIF-7 material and polyvinylidene fluoride (PVDF) at a weight ratio of 9:1 to obtain a ZIF-7 slurry; use a scraper to scrape the obtained ZIF-7 film. 7 slurry is evenly coated on the aluminum foil and vacuum dried at 80°C for 3 hours; then the obtained aluminum foil + ZIF-7 film is immersed in ethanol for 0.5 hours to make the MOFs film peel off from the aluminum foil to obtain flexible ZIF-7 film; the ZIF-7 film was then punched into the desired shape of the battery and reactivated under vacuum at 200°C for 12h.

Secondly, prepare an electrolyte solution of 1mol/L KFSI; that is, quickly mix 5ml hot EC and 5ml DEC, and then add 10mmol KFSI powder to the mixed solvent under constant stirring to obtain a solution based on 1 mol/L KFSI electrolyte of organic solvent EC/DEC (1/1, v/v).

Third, the ZIF-7 film is placed in the KFSI electrolyte to immerse the solvent molecules and electrolyte ions into the ion trap: the reactivated ZIF-7 film is immersed in the KFSI electrolyte and treated at 80°C for 48 hours to fully absorb the electrolyte molecules and solvent molecules. Immersed in the ion trap of ZIF-7, FSI ^- ions and organic solvent molecules are immobilized by the ion trap, while K ⁺ is free to move.

Finally, the residual solvent is removed by vacuum drying: take out the treated ZIF-7 film and wipe the surface solvent with a paper towel, and vacuum dry it at 80°C for 20 hours to further remove the residual solvent, obtaining an electrolyte system NOSMS without free organic solvent molecules and anions. .

Example 2

Water solvent-based electrolyte system NWMS without free water solvent molecules

First, prepare a ZIF-7 film with an ion trap, and the steps are the same as in Example 1.

Secondly, prepare an electrolyte of 1mol/L KCl, that is, add 10mmol KCl powder to 10ml of water solvent, and mix thoroughly to obtain a 1mol/L KCl electrolyte based on the aqueous solution.

Again, the ZIF-7 film is placed in the KCl electrolyte to immerse the solvent molecules and electrolyte ions into the ion trap: the reactivated ZIF-7 film is immersed in the KCl electrolyte and treated at 90°C for 48 hours, so that the electrolyte molecules and solvent molecules Fully immersed in the ion trap of ZIF-7, Cl ^- ions and water solvent molecules are immobilized by the ion trap, while K ⁺ can move freely.

Finally, the residual solvent is removed by vacuum drying: the steps are the same as in Example 1. Finally, an electrolyte system NWMS without free water solvent molecules and anions is obtained.

Example 3

Water solvent-based electrolyte system NWMS-1 without free water solvent molecules

Secondly, prepare an electrolyte of 1mol/L KFSI, that is, add 10mmol KFSI powder to 10ml of water solvent, and mix thoroughly to obtain a 1mol/L KFSI electrolyte based on the aqueous solution.

Again, the ZIF-7 film is placed in the KFSI electrolyte to immerse the solvent molecules and electrolyte ions into the ion trap: the reactivated ZIF-7 film is immersed in the KFSI electrolyte and treated at 90°C for 48 hours to immerse the electrolyte molecules and solvent molecules Fully immersed in the ion trap of ZIF-7, Cl ^- ions and water solvent molecules are immobilized by the ion trap, while K ⁺ can move freely.

Finally, the residual solvent is removed by vacuum drying: the steps are the same as in Example 1. Finally, the electrolyte system NWMS-1 without free water solvent molecules and anions is obtained.

Comparative example 1

1mol/L KFSI electrolyte based on organic solvent EC/DEC (1/1, v/v).

Comparative example 2

1mol/L KCl electrolyte based on aqueous solution.

Comparative example 3

1mol/LKFSI electrolyte based on aqueous solution.

Performance and applicability evaluation of the NOSMS of Example 1 and the NWMS of Example 2:

1) K||K battery evaluates the performance of NOSMS in inhibiting dendrite formation

As shown in Figures 2 to 3, in order to prove that NOSMS can effectively inhibit dendrite formation, the KFSI electrolyte of Comparative Example 1 and the NOSMS of Example 1 were used to conduct electroplating/electrolysis tests on the potassium battery (K||K battery). result. K||K cells operate with an areal capacity of 0.2mAh cm ^-2 and a current density of 0.1mA cm ^-2 . The results show that for the K||K battery based on the KFSI electrolyte of Comparative Example 1, the polarization of the battery increases and changes drastically and irregularly within the first one hundred hours, and then the polarization continues to increase, and finally the K dendrites appear at 160 hours The above pierced the separator (see inset in Figure 2), and the battery completely failed; in addition, its voltage hysteresis curve increased significantly from about 0.11V at the initial cycle to 0.26V at 164 hours, mainly due to uneven K deposition and dendrites. The accumulated thick passivation film caused by crystal growth, and the sudden drop in voltage hysteresis after 160 hours indicate the presence of a short circuit caused by dendrite growth. For the K||K battery based on the NOSMS of Example 1, the polarization during the cycle gradually decreases and remains at about 0.06V, with a cycle life of >4,000 hours. It shows that the NOSMS provided by the present invention can well inhibit the growth of K dendrites and effectively extend the cycle life of potassium batteries. As shown in Figure 3, the counter battery based on the NWMS of Comparative Example 2 also achieved a cycle life of >3,500 hours. This may be the first time that K metal operates stably in an electrolyte system involving water molecules.

2) K||Cu battery evaluation of Coulombic efficiency performance based on NOSMS

As shown in Figure 4, a K||Cu battery was used to study the Coulombic efficiency of K metal electroplating/electrolysis during the charge and discharge process. The initial Coulombic efficiency of the traditional electrolyte system battery based on Comparative Example 1 was 53.5%, and then increased slowly, finally reaching about 90%, which can be attributed to the growth of potassium dendrites and the continuous breakdown/reconstruction of the Cu surface passivation film. The initial Coulombic efficiency of the battery based on the NOSMS of Example 1 reached 72.9%, with an average The Coulombic efficiency is close to 100%, indicating significant plating/electrolysis efficiency, which also indicates that a stable passivation film is formed on the electrode surface and can allow high-speed reversible transport of K ⁺ . Even if the amount of electroplated/electrolyzed K is increased to three times (0.1mA cm ^-2 , 0.3mAh cm ^-2 ), the NOSMS-based K||Cu battery can still exhibit high Coulombic efficiency; while the traditional electrolytic liquid based on Comparative Example 1 The Coulombic efficiency of the K||Cu battery dropped sharply after 80 cycles, and the battery completely failed. These results show that the NOSMS provided by the present invention is superior to the traditional electrolyte system in all aspects.

3) Graphite (negative electrode)||K half cell evaluation of NWMS and NOSMS matching with graphite negative electrode

Graphite is one of the most promising anodes for PIBs. Whether graphite can stably store potassium is a breakthrough point for the industrialization of PIBs, especially in water-based batteries that are more in line with actual industrialization and high safety requirements. As shown in Figures 5 and 6, the charge-discharge curves and electrochemical performance of the NWMS-based commercial graphite anode at a current density of 100mA g ^-1 show that the graphite ||K half-cell has a specific capacity of up to 220mAh g ^-1 , There is almost no decrease in capacity after 300 cycles, and the Coulombic efficiency is close to 100%, confirming the feasibility of the graphite anode in the NWMS electrolyte system and providing a new and good method for low-cost potassium graphite batteries. As shown in Figure 7, comparing the long-term cycle performance of the graphite ||K half-cell based on the traditional KFSI electrolyte of Comparative Example 1 and the NOSMS of Example 1, the results show that the graphite || The capacity of the battery decreases very quickly, while the graphite ||K half-cell based on the NOSMS of Example 1 can maintain stable operation for more than 500 cycles, with an average Coulombic efficiency of 99.8%.

4) KVPF (positive electrode)||K half cell evaluation of the matching of NWMS and NOSMS with KVPF positive electrode

The high voltage window is of great significance to the electrolyte because it determines whether the electrolyte system can be universal. On the other hand, increasing the operating voltage can significantly increase the battery energy density. However, the electrochemical window of imide salt (KFSI) liquid electrolyte does not exceed 4V. Linear sweep voltammetry (LSV) was used for testing. As shown in Figure 8, the electrochemical window of NOSMS is significantly expanded to 5.9V (vs. K/K+), which is much higher than the traditional electrolyte system, providing a basis for the research of high-voltage cathodes. Furthermore, compare the NWMS voltammetry curves of the KCl aqueous electrolyte of Comparative Example 2 and Example 2. The results show that the reduction stability and oxidation stability of the NWMS-based potassium battery are greatly improved, which further confirms the feasibility of the NWMS-based graphite ||K battery and provides a basis for the operation of high-voltage electrodes. In addition, the voltammetry curves of the KFSI aqueous electrolyte of Comparative Example 3 and the NWMS-1 of Example 3 were compared. The results show that the reduction stability and oxidation stability of the potassium battery based on NWMS-1 have also been improved respectively, which once again confirms that the solid ion trap of the electrolyte system without free solvent molecules provided by the present invention captures and locks solvent molecules and anions. Unique structure and functionality.

As shown in Figures 9 and 10, the current density of the KVPF (positive electrode) ||K half-cell at 50mA g-1 and the cut-off of 2-4.6V based on the KFSI traditional electrolyte of Comparative Example 1 and the NOSMS of Example 1 are compared. Test under voltage. The results show that when the KVPF (positive electrode)||K half-cell based on traditional electrolyte is charged to about 4V, the voltage no longer rises, indicating that the aluminum current collector is corroded and other side reactions occur. The NOSMS-based KVPF (positive pole)||K half cell can be charged to 4.6V. Precisely, Figures 10 and 11 show that average output voltages as high as 3.92V can be obtained, along with remarkable cycling stability (over 1,000 cycles) and low capacity fading rate (approximately 0.1% per cycle).

5) PTCDI (positive electrode)||K half-cell evaluation of the matching of NWMS and NOSMS with PTCDI positive electrode

It is known that organic cathodes with potential low cost and sustainability should be vigorously developed in PIBs. However, the long-term challenge faced by the practical application of organic cathodes (such as PTCDI) is that the active materials are easily dissolved by the electrolyte, which is the main reason for poor cycle life (as shown in Figure 12). The electrochemical performance of the PTCDI (positive electrode) ||K half-cell based on the conventional KFSI electrolyte of Comparative Example 1 and the NOSMS of Example 1 was compared. As shown in Figure 5, the PTCDI (positive electrode)||K half-cell based on the traditional KFSI electrolyte has a large capacity fading due to dissolution in the first 20 cycles, that is, it provides approximately 122mAh at a current density of 50mA g ^-1 The first discharge capacity is g ^-1 ; but after 20 charge and discharge cycles, the corresponding capacity is reduced to 70mAh g ^-1 , and the capacity retention rate is only 57% (as shown in Figure 15). In contrast, since the solvent molecules in NOSMS are trapped and locked to form crystals, there are no liquid solvent molecules to dissolve PTCDI (as shown in Figure 12). Therefore, the NOSMS-based PTCDI (positive electrode) ||K half-cell operates stably for 2000 cycles (more than 11 months) with small capacity fading and a Coulombic efficiency exceeding 99%, indicating that the cycle life of the PTCDI positive electrode has been greatly extended. This excellent performance fully reflects the unique advantages of NOSMS in organic electrodes (including organic negative electrodes). More importantly, as shown in Figures 14 and 16, the PTCDI (positive electrode) ||K half-cell based on the NWMS of Example 2 still provides a reversible capacity of 101 mAh g ^-1 after 300 cycles, and the Coulombic efficiency exceeds 99% . This shows that the NWMS provided by the present invention can be used as an electrolyte system to stabilize the positive electrode, providing a new paradigm for ultra-cheap electrolyte systems.

6) KI (positive electrode)||K half cell evaluation of NWMS and NOSMS matching with KI positive electrode

Another promising cathode material (such as iodine I ₂ ) will become a high-performance potassium cathode once its own "shuttle effect" is solved. Potassium iodide (KI), which has high reserves and low cost in the ocean, was chosen as the cathode to study the inhibitory effect of NOSMS on the "shuttle effect". As shown in Figure 17, the extremely small pore of 2.9 angstroms in the NOSMS of Example 1 makes it difficult for KI and its reactants to pass through, thereby avoiding its "shuttle effect". As shown in Figures 18 and 19, the KI (positive electrode) ||K half-cell based on the traditional electrolyte of Comparative Example 1 was cycled twice. It can no longer be charged, indicating that the existence of the "shuttle effect" seriously hinders the development of the electrode. Under the same conditions, the KI (positive electrode) ||K half-cell based on the NOSMS of Example 1 provided a high discharge capacity of 121 mAh g ^-1 at a current density of 100 mA g ^-1 , and after 50 cycles, the capacity was almost no decrease, indicating that NOSMS effectively suppresses the "shuttle effect".

7) Potassium ion battery based on PTCDI (positive electrode) | NOSMS | graphite (negative electrode)

A potassium ion battery with PTCDI as the positive electrode, graphite as the negative electrode, and NOSMS of Example 1 as the electrolyte system. The mass loading capacity of PTCDI reaches 25mg cm ^-2 , resulting in an area capacity of 2.89mAh cm ^-2 , and a 2.18Ah soft pack battery is assembled by simply stacking and integrating (nine-layer double-sided stacking). The typical charge and discharge curves of PTCDI||K battery, graphite||K battery and PTCDI|NOSMS| graphite full battery are shown in Figure 20. This PTCDI|NOSMS|graphite battery has high safety. Even if it is cut twice, it can still work as usual and light up the LED screen, proving its high safety. The discharge curve in Figure 21 shows that no capacity change was observed after the discharge process was interrupted for 72 hours, indicating that with excellent ion storage capacity, the battery can provide enough power to drive a small helicopter. Figure 22 shows the change in voltage over time after two batteries based on the NOSMS of Example 1 and the conventional KFSI electrolyte of Comparative Example 1 are fully charged (charged to 3.2V). After the batteries were stored for more than 180 hours, the open circuit voltages of both batteries dropped sharply within the first 2 hours of standing, and then stabilized over the next 50 hours; thereafter, due to self-discharge and dissolution of the organic cathode, based on the comparative example The voltage of the PTCDI|KFSI|graphite full cell based on the traditional KFSI electrolyte system of Example 1 continues to decrease, while the voltage of the PTCDI|NOSMS|graphite full cell based on the NOSMS of Example 1 remains stable, and the gap between the two gradually widens. As shown in Figure 23, the PTCDI|NOSMS|graphite full cell can provide a capacity of 123mAh g ^-1 (based on the mass of the positive electrode) at a current density of 50mA g ^-1 , and the Coulombic efficiency exceeds 99%. Furthermore, the average capacity fading rate per cycle over 1000 cycles is 0.036%, while exhibiting a high energy density of 243.9Wh kg ^-1 . Additionally, this full cell is integrated through a simple stack, saving physical space while increasing voltage.

In summary, the electrolyte system without free solvent molecules provided by the present invention is specifically designed to be constructed of a solid ion trap and a conductive matrix to simultaneously capture and lock anions and solvent molecules through a preset fixed ion trap, thereby achieving only alkali An electrolyte system in which metal ions can move freely. Compared with traditional electrolyte systems, the electrolyte system without free solvent molecules provided by the present invention has low cost, high ionic conductivity, the ability to inhibit dendrite growth, inhibit "shuttle effect" and electrode dissolution, and high oxidation stability [based on Electrolytes without free organic solvent molecules (NOSM) exceeding 5.9V], high reduction stability [based on electrolytes without free water molecules (NWM) below -1V, graphite electrodes can be used] and wide applicability. based on The metal ion battery with an electrolyte system without free solvent molecules has excellent electrochemical performance and safety.

The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention shall be included in the protection of the present invention. within the range.

Claims

An electrolyte system without free solvent molecules is characterized in that it includes a metal salt electrolyte and a metal-organic framework compound; the metal-organic framework compound has an Angstrom-level solid ion trap structure.
The electrolyte system without free solvent molecules according to claim 1, characterized in that: the metal salt electrolyte is an alkali metal salt electrolyte, an aluminum-based salt electrolyte, a zinc-based salt electrolyte, a magnesium-based salt electrolyte, Calcium-based salt electrolyte or iron-based salt electrolyte.
The electrolyte system without free solvent molecules according to claim 2, characterized in that: the metal salt electrolyte includes a metal salt electrolyte and a solvent; the metal electrolyte is an alkali metal salt electrolyte, an aluminum-based salt electrolyte, a zinc-based salt One of an electrolyte, a magnesium-based salt electrolyte, a calcium-based salt electrolyte, and an iron-based salt electrolyte; the solvent is an organic solvent or a water solvent.
The electrolyte system without free solvent molecules according to claim 3, characterized in that: the alkali metal salt electrolyte is a lithium salt electrolyte, a sodium salt electrolyte or a potassium salt electrolyte; the potassium salt electrolyte is bisfluorosulfonimide Potassium salt, potassium chloride or potassium hexafluorophosphate.
The electrolyte system without free solvent molecules according to any one of claims 1 to 4, characterized in that: the metal organic framework compound is a zeolite imidazole ester framework, 2-methylimidazole zinc salt MAF-4, Cu-MOF -74, Cu-BTC, Zr-based-UiO-67 or poly[Zn 2 (BIM) 4 ].
A method for preparing the free solvent-free molecular electrolyte system according to any one of claims 1 to 5, characterized in that: it includes the following steps:

Step A, preparing a metal-organic framework compound film with a solid ion trap structure;

Step B, prepare metal salt liquid electrolyte;

Step C, the metal organic framework compound film is immersed in the metal salt liquid electrolyte;

Step D, dry to remove residual solvent.
The preparation method of free solvent-free molecular electrolyte system according to claim 6, characterized in that: the specific method of step A is:

In step a1, the metal organic framework compound and the binder are thoroughly stirred and mixed to prepare a metal organic framework compound slurry;

Step a2, the metal organic framework compound slurry is coated on the substrate and then dried;

In step a3, the substrate coated with the metal organic framework compound is immersed in an organic solvent to peel off the metal organic framework compound from the substrate to prepare a flexible metal organic framework compound film;

In step a4, the flexible metal-organic framework compound film is punched into a desired shape and then activated.
The preparation method of a free solvent-free molecular electrolyte system according to claim 7, characterized in that: the weight ratio of the metal-organic framework compound and the binder is 1: (0.1-0.5), and the binder is polypropylene Vinyl difluoride, styrene-butadiene rubber, carboxymethylcellulose, polyacrylic acid, polyacrylonitrile or polyacrylate.
The preparation method of a free solvent-free molecular electrolyte system according to claim 7, characterized in that: the specific method of step a2 is to coat the metal organic framework compound slurry on a flat substrate, and coat it at 60- Vacuum dry at 80°C for 3-5 hours; the base material is metal foil or polymer material film.
The method for preparing a free solvent-free molecular electrolyte system according to claim 7, characterized in that: the specific method of step a3 is to immerse the substrate coated with the metal-organic framework compound into an organic solvent for 0.5-1 h, allowing the metal to The organic framework compound is exfoliated from the substrate to prepare a flexible metal-organic framework compound film.
The preparation method of a free solvent-free molecular electrolyte system according to claim 7, characterized in that: the specific method of step a4 is to punch the flexible metal organic framework compound film into the required shape, and then vacuum it at 180-220°C Reactivate for 12-18h.
The preparation method of a free solvent-free molecular electrolyte system according to claim 6, characterized in that: the specific method of step C is to immerse the metal organic framework compound film prepared in step A into the metal salt electrolysis prepared in step B. liquid and treated at 70-80°C for 40-50 hours, so that the metal salt electrolyte molecules and solvent molecules are fully immersed in the solid ion trap of the metal organic framework compound. The anions and solvent molecules are fixed by the solid ion trap, while the cations can move freely. .
The method for preparing a free solvent-free molecular electrolyte system according to claim 6, characterized in that: the specific method of step D is to remove the metal salt electrolyte on the surface of the metal organic framework compound film prepared in step C, and then Vacuum dry at 80-100°C for 20-24 hours to further remove the residual solvent to obtain an electrolyte system without free solvent molecules.
An application of the free solvent-free molecular electrolyte system according to any one of claims 1 to 13, characterized in that the free solvent-free molecular electrolyte system is used as an electrolyte for a metal ion battery.
The application of free solvent-free molecular electrolyte system according to claim 14, characterized in that: the metal ion battery is an alkali metal ion battery, an aluminum-based ion battery, a zinc-based ion battery, a magnesium-based ion battery, a calcium-based ion battery Or iron-based ion battery; the alkali metal ion battery is a lithium-ion battery, a sodium-ion battery or a potassium-ion battery.