CN114784383A

CN114784383A - Free solvent molecule-free electrolyte system and manufacturing method and application thereof

Info

Publication number: CN114784383A
Application number: CN202210346107.6A
Authority: CN
Inventors: 易先辉; 鲁兵安; 许志
Original assignee: Xifeng 2d Fujian Material Technology Co ltd
Current assignee: Xifeng 2d Fujian Material Technology Co ltd
Priority date: 2022-03-31
Filing date: 2022-03-31
Publication date: 2022-07-22
Also published as: WO2023185944A1

Abstract

The invention relates to an electrolyte system without free solvent molecules, which comprises a metal salt electrolyte and a metal organic framework compound; the metal organic framework compound is internally provided with an angstrom-level solid ion trap structure. The invention aims to provide an electrolyte system without free solvent molecules and a manufacturing method and application thereof, and solves the problems of battery safety risk and poor electrochemical performance caused by the existence of the free solvent molecules in the electrolyte system.

Description

Electrolyte system without free solvent molecules and preparation method and application thereof

Technical Field

The invention relates to an electrolyte system without free solvent molecules and a manufacturing method and application thereof.

Background

The great development of power sources for consumer electronics, electric vehicles and power grid energy storage is a necessity of the development of economic society. Although Lithium Ion Batteries (LIBs) are one of the most energy-storing devices in today's society, the limited lithium resources limit their further applications in mass-produced electric vehicles and plug-in hybrid vehicles. Among the next generation batteries, Potassium Ion Batteries (PIBs) are receiving attention and research because of their low cost, rich in potassium resources and high in energy density, and thus are considered as suitable substitutes for LIBs. However, current PIBs are generally based on liquid electrolytes (ether and carbonate solvents) that contain free organic solvent molecules. Free organic solvent molecules in the electrolyte are inflammable, volatile and easy to oxidize, and have serious safety problems in the aspects of overheating, fire and the like. In addition, there is also a need for an electrolyte that is resistant to irreversible reactions and dendrite growth during long term charge/discharge cycles in the electrode aspect, especially in potassium cathodes.

It is well known that in conventional liquid (e.g., organic solvent and water) electrolyte systems, free liquid solvent molecules provide a transport medium, thereby providing the electrolyte with high ionic conductivity. However, the free solvent molecules in the liquid electrolyte are the root cause of safety risks and poor electrochemical performance, for example, they readily dissolve the active material. Therefore, the development of an electrolyte free of free solvent molecules is an effective way to realize a high-safety and high-performance metal ion battery.

Disclosure of Invention

The invention aims to provide an electrolyte system without free solvent molecules and a manufacturing method and application thereof, and solves the problems of battery safety risk and poor electrochemical performance caused by the presence of the free solvent molecules in the electrolyte system.

The purpose of the invention is realized by the following technical scheme:

an electrolyte system without free solvent molecules comprises a metal salt electrolyte and a metal organic framework compound; the metal organic framework compound is internally provided with an angstrom-level solid ion trap structure.

A method for preparing a free solvent-free molecular electrolyte system comprises the following steps,

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

step B, preparing a metal salt liquid electrolyte;

step C, immersing the metal organic framework compound film into a metal salt liquid electrolyte;

and D, drying to remove the residual solvent.

The application of the free solvent-free molecular electrolyte system is used as an electrolyte of a metal ion battery.

Compared with the prior art, the invention has the advantages that:

(1) the electrolyte system without free solvent molecules has the advantages of low cost, high ionic conductivity, dendritic crystal growth inhibition, shuttle effect inhibition, electrode dissolution resistance, high oxidation stability (the electrolyte (NOSMS) based on the free organic solvent molecules exceeds 5.9V), high reduction stability (the electrolyte (NWMS) based on the free water molecules is lower than-1V, and a graphite electrode can be used) and wide applicability.

(2) The metal ion battery based on the electrolyte system without free solvent molecules has excellent electrochemical performance and safety. The concrete expression is as follows: graphite (cathode) | | PTCDI (anode) potassium ion battery based on NOSMS electrolyte at 50mA g^-1After 1000 times of the next cycle, the average capacity fading rate of each cycle was only 0.036%, and 243.9Wh kg was exhibited^-1The energy density of (2).

(3) The electrolyte system (NOSMS/NWMS) without free solvent molecules provided by the invention is not flammable in nature, has good thermal stability and cuttability, and the metal ion battery prepared by the system has high safety.

Drawings

FIG. 1 is a schematic diagram of an electrolyte system without free solvent molecules according to the present invention.

FIG. 2 is a K | | | K cell at 0.1mA cm K based on the NOSMS of example 1 and the conventional KFSI electrolyte system of comparative example 1^-2Constant current cycling at current density and corresponding voltage hysteresis curves.

FIG. 3 is a K | | | K battery at 0.1mA cm based on the NWMS of example 2^-2Constant current cycling at current density and corresponding voltage hysteresis curves.

Fig. 4 is a plot of coulombic efficiency and charge and discharge for K | | | Cu cells based on the conventional KFSI electrolyte system of example 1NOSMS and comparative example 1.

Fig. 5 is a graphite K cell based on the NWMS of example 2 to provide a battery cell100mA g^-1Current density of (a).

FIG. 6 is a graphite | | | K battery based on example 2NWMS at 100mA g^-1The current density of (a).

FIG. 7 is a graphite | | | K cell based on the conventional KFSI electrolyte system of example 1NOSMS and comparative example 1 at 100mA g^-1The cycle performance at current density of (a).

FIG. 8 is a voltammogram scanned at a scan rate of 0.005V/s based on example 1NOSMS, example 2NWMS, example 3NWMS-1, and comparative example 1KFSI electrolyte, comparative example 2KCl electrolyte, and comparative example 3KFSI electrolyte, respectively.

Fig. 9 is a constant current charge distribution plot for a KVPF (positive) K half-cell based on the comparative example 1 conventional KFSI electrolyte system.

FIG. 10 shows KVPF (Positive electrode) | | K half-cell at 50mA g based on NOSMS in example 1^-1Current density and charge-discharge curve at cut-off voltage of 2-4.6V.

FIG. 11 shows KVPF (Positive electrode) | | K half-cell at 50mA g K based on NOSMS in example 1^-1Current density and long-term cycling performance curves at 2-4.6V cutoff.

Fig. 12 is a schematic illustration of the inhibition of PTCDI positive electrode dissolution for a battery based on the free solvent molecule free electrolyte system of the present invention and a conventional electrolyte system.

Fig. 13 is a charge and discharge curve for a PTCDI (positive electrode) | | K half-cell based on the example 1NOSMS and comparative example 1 conventional KFSI electrolyte system.

Fig. 14 is a charge and discharge curve of a PTCDI (positive electrode) | | K half-cell based on example 2 NWMS.

FIG. 15 is a PTCDI (Positive electrode) | | K half-cell at 50mA g/g based on NOSMS in example 1^-1Long-term cycling performance plot at current density.

FIG. 16 is a PTCDI (Positive electrode) | | K half cell at 50mA g based on example 2NWMS^-1Long-term cycling performance plot at current density.

FIGS. 17-19 are schematic diagrams of the "shuttle effect" suppression of a battery based on an electrolyte system without free solvent molecules according to the present invention; FIG. 17 is a schematic view of suppressing the positive "shuttling effect" at KI; FIG. 18 is a3 rd charge-discharge curve for a K | | | KI cell based on the conventional KFSI electrolyte system of example 1NOSMS and comparative example 1; fig. 19 is a graph of cycle performance for K | | | KI batteries.

Fig. 20-22 are performance plots for potassium ion full cells based on PTCDI (positive electrode) | nosmi | graphite (negative electrode) of example 1 nosmi; FIG. 20 is a typical constant current charge and discharge curve; fig. 21 is a charge and discharge curve of the full cell; FIG. 22 is a plot of full cell voltage versus time after full charge based on the NOSMS of example 1 and the conventional KFSI electrolyte system of comparative example 1.

FIG. 23 shows potassium ion full cell at 50mA g of PTCDI (positive electrode) | NOSMS | graphite (negative electrode) based on NOSMS of example 1^-1The current density of (a).

Detailed Description

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

The metal salt electrolyte comprises a metal salt electrolyte and a solvent; the metal electrolyte is one of alkali metal salt electrolyte, aluminum-based salt electrolyte, zinc-based salt electrolyte, magnesium-based salt electrolyte, calcium-based salt electrolyte and iron-based salt electrolyte; the solvent is an organic solvent or an aqueous 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 potassium bis (fluorosulfonyl) imide salt, potassium chloride or potassium hexafluorophosphate.

The metal organic framework compound is zeolite imidazole ester framework (ZIF-7), 2-methylimidazolium zinc salt MAF-4(ZIF-8), Cu-MOF-74 and poly [ Zn ]₂(BIM)₄]Zr-based-UiO-67 or Cu-BTC (C)₁₈H₆Cu₃O₁₂，Tricopper；benzene-1,3,5-tricarboxylate)。

step B, preparing a metal salt liquid electrolyte;

and D, drying to remove the residual solvent.

The specific method of the step A is that,

a1, fully stirring and mixing the metal organic framework compound and the binder to prepare metal organic framework compound slurry;

step a2, coating the metal organic framework compound slurry on a substrate, and then drying;

a3, soaking the base material coated with the metal organic framework compound in an organic solvent to peel the metal organic framework compound from the base material so as to prepare a flexible metal organic framework compound film;

step a4, the flexible metal organic framework compound film is punched into a desired shape, followed by activation.

The weight ratio of the metal organic framework compound to 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 step a2 comprises the specific steps of coating the metal organic framework compound slurry on a flat base material, and drying the base material in vacuum for 3 to 5 hours at the temperature of between 60 and 80 ℃; the substrate is a metal foil or a high polymer material film. The metal organic framework compound slurry can be coated on a substrate by adopting a knife coating (such as a doctor blade coating), a roller coating, a spraying mode and the like. The polymer film is preferably a polymer film that does not react with an alcohol or ketone organic solvent.

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

The step a4 is specifically carried out by punching the flexible metal organic framework compound film into a required shape and then reactivating the film for 12 to 18 hours under vacuum at the temperature of 180 ℃ and 220 ℃.

And C, immersing the metal organic framework compound film prepared in the step A into the metal salt electrolyte prepared in the step B, and treating at 70-80 ℃ for 40-50h to ensure that metal salt electrolyte molecules and solvent molecules are fully immersed into a solid ion trap of the metal organic framework compound, wherein anions and solvent molecules are fixed by the solid ion trap, and cations can move freely.

And D, removing the metal salt electrolyte on the surface of the metal organic framework compound film prepared in the step C, and then further removing the residual solvent when the film is dried in vacuum at the temperature of 80-100 ℃ for 20-24 hours to prepare an electrolyte system without free solvent molecules. The metal salt electrolyte on the surface can be removed by wiping or blowing and the like.

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 a potassium ion battery.

Detailed description of the preferred embodiments

The specific embodiment provides an electrolyte system without free solvent molecules, which comprises potassium salt electrolyte molecules, solvent molecules and metal organic framework compound Materials (MOFs); the metal organic framework compound composite material mainly comprises a zeolite imidazole ester framework (ZIF-7) and a binder, and the zeolite imidazole ester framework (ZIF-7) is internally provided with

The solid ion trap structure of (1); the solid ion trap structure can effectively capture free solvent molecules [ such as Ethylene Carbonate (EC), diethyl carbonate (DEC), water and the like]And anions (e.g. FSI)^-Ions, Cl^-Etc.) and locks it, realizing an electrolyte system in which only potassium ions can freely move.

The preparation method of the electrolyte system without free solvent molecules comprises the following steps:

first, a ZIF-7 film with an ion trap was prepared: mixing a ZIF-7 material and polyvinylidene fluoride (PVDF) according to a weight ratio of 9: 1, fully stirring and mixing to obtain ZIF-7 slurry; uniformly coating the obtained ZIF-7 slurry on an aluminum foil by using a scraper, and drying the aluminum foil for 3 hours at the temperature of 60-80 ℃ in vacuum, wherein the thickness of a dried ZIF-7 film is 2-50 microns; then, the obtained aluminum foil and ZIF-7 film are immersed in ethanol for 0.5h to ensure that the MOFs film is peeled off from the aluminum foil to obtain a flexible ZIF-7 film; the ZIF-7 film was then punched into the desired shape of the cell and reactivated under vacuum at 200 ℃ for 12 h.

Secondly, preparing a traditional sylvite liquid electrolyte; wherein the conventional potassium salt liquid electrolyte comprises a potassium salt electrolyte and a solvent; the solvent is one of an organic solvent or a water solvent. The potassium salt electrolyte is potassium bis (fluorosulfonyl) imide salt (KFSI), potassium chloride (KCl) or potassium hexafluorophosphate (KPF)₆) One kind of (1).

Thirdly, putting the ZIF-7 film into a sylvite liquid electrolyte to enable solvent molecules and electrolyte ions to be immersed into the ion trap: namely, the reactivated ZIF-7 film is immersed in a conventional potassium salt liquid electrolyte and treated at 60-80 ℃ for 48 hours, so that electrolyte molecules and solvent molecules are fully immersed in the ion trap of ZIF-7.

Finally, vacuum drying treatment removes residual solvent: taking the treated ZIF-7 film out, wiping the surface solvent with a paper towel, and vacuum drying at 80-100 ℃ for 20h to further remove the residual solvent to obtain an electrolyte system without free solvent molecules.

The invention also provides a potassium ion battery, which comprises a positive electrode, a negative electrode and electrolyte, wherein the electrolyte used by the potassium ion battery is the electrolyte system without free solvent molecules.

Example 1

Organic solvent based electrolyte system NOSMS free of free organic solvent molecules

First, a ZIF-7 film with an ion trap was prepared: mixing a ZIF-7 material and polyvinylidene fluoride (PVDF) according to a weight ratio of 9: 1, fully stirring and mixing to obtain ZIF-7 slurry; uniformly coating the obtained ZIF-7 slurry on an aluminum foil by using a scraper, and performing vacuum drying at 80 ℃ for 3 hours; then, the obtained aluminum foil and ZIF-7 film is immersed in ethanol for 0.5h to ensure that the MOFs film is peeled off from the aluminum foil to obtain a flexible ZIF-7 film; the ZIF-7 film was then punched into the desired shape of the cell and reactivated under vacuum at 200 ℃ for 12 h.

Secondly, preparing 1mol/L KFSI electrolyte; that is, 5ml of hot EC and 5ml of DEC were rapidly mixed, and then 10mmol of KFSI powder was added to the mixed solvent with constant stirring to obtain 1mol/L KFSI electrolyte based on the organic solvent EC/DEC (1/1, v/v).

Thirdly, putting the ZIF-7 film into KFSI electrolyte to ensure that solvent molecules and electrolyte ions are immersed into the ion trap: namely, the reactivated ZIF-7 film is immersed in KFSI electrolyte and treated at 80 ℃ for 48h, so that electrolyte molecules and solvent molecules are fully immersed in an ion trap of the ZIF-7, and FSI is performed^-The ions and organic solvent molecules are held by the ion trap, and K⁺Can move freely.

Finally, vacuum drying treatment removes residual solvent: taking out the treated ZIF-7 film, wiping the surface solvent with a paper towel, and vacuum drying at 80 ℃ for 20h to further remove the residual solvent to obtain an electrolyte system NOSMS free of free organic solvent molecules and anions.

Example 2

Electrolyte system NWMS based on water solvent and free water solvent molecules

First, a ZIF-7 thin film having an ion trap was prepared in the same manner as in example 1.

Secondly, preparing 1mol/L KCl electrolyte, namely adding 10mmol KCl powder into 10ml water solvent, and fully mixing to obtain 1mol/L KCl electrolyte based on the water solution.

Thirdly, putting the ZIF-7 film into a KCl electrolyte to enable solvent molecules and electrolyte ions to be immersed into the ion trap: namely, the reactivated ZIF-7 film is immersed in KCl electrolyte and treated at 90 ℃ for 48 hours, so that electrolyte molecules and solvent molecules are fully immersed in an ion trap of the ZIF-7, and Cl^-The ion and water solvent molecules are immobilized by the ion trap, and K⁺Can move freely.

Finally, vacuum drying treatment removes residual solvent: the procedure is as in example 1, and finally, an electrolyte system NWMS free of free water solvent molecules and anions is obtained.

Example 3

Electrolyte system NWMS-1 based on water solvent and free water solvent molecules

Secondly, preparing 1mol/L KFSI electrolyte, namely adding 10mmol KFSI powder into 10ml of water solvent, and fully mixing to obtain 1mol/L KFSI electrolyte based on the water solution.

Thirdly, putting the ZIF-7 film into KFSI electrolyte to ensure that solvent molecules and electrolyte ions are immersed into the ion trap: namely, the reactivated ZIF-7 film is immersed in KFSIl electrolyte and treated at 90 ℃ for 48 hours to fully immerse electrolyte molecules and solvent molecules in the ion trap of ZIF-7, with Cl^-The ion and water solvent molecules are immobilized by the ion trap, and K⁺Can move freely.

Finally, vacuum drying treatment removes residual solvent: the procedure is as in example 1, and finally, NWMS-1, an electrolyte system free of 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 an aqueous solution.

NOSMS of example 1 and NWMS performance and suitability evaluation of example 2:

1) evaluation of NOSMS dendrite formation inhibition performance of K | | K battery

As shown in fig. 2 to 3, in order to prove that NOSMS can effectively suppress dendrite formation, the results of the plating/electrolysis test of the KFSI electrolyte of comparative example 1 and the NOSMS of example 1 against potassium versus battery (K | | K battery) were used, respectively. K | | | K battery at 0.2mAh cm^-2Surface capacity of (2) and 0.1mA cm^-2The current density of (c) is run. The results show that the K | | | K cell based on the comparative example 1KFSI electrolyte, the polarization of the cell increased and undergone drastic and irregular changes in the first hundred hours, after which the polarization continued to increase and finally the K dendrites pierced the separator over 160 hours (see inset in fig. 2) and the cell 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 because uneven K deposition and dendrite growth resulted in an accumulated thick passivation film, and a sudden drop in voltage hysteresis after 160 hours indicated the presence of short circuits caused by dendrite growth. On the other hand, based on the K | | | K battery of the NOSMS in the embodiment 1, the polarization in the circulation process is gradually reduced and continuously kept at about 0.06V, and the circulation service life is prolonged>4,000 hours. The NOSMS provided by the invention can well inhibit the growth of K dendrites and effectively prolong the cycle life of the potassium battery. As shown in fig. 3, the same effect was achieved for the battery based on the NWMS of comparative example 2>A cycle life of 3,500 hours, which may be the first time that K metal is operating stably in an electrolyte system involving water molecules.

2) Evaluation of NOSMS-based coulombic efficiency performance for K | | Cu batteries

As shown in fig. 4, the coulombic efficiency of K metal plating/electrolysis during charge and discharge was investigated using K | | Cu cells. The initial coulombic efficiency of the conventional electrolyte system cell based on comparative example 1 was 53.5%, followed by a slow increase, eventually reaching around 90%, which can be attributed to potassium dendrite growth and continuous breakdown/re-establishment of Cu surface passivation film. Whereas the initial coulombic efficiency of the cell based on the NOSMS of example 1 reached 72.9%, the average coulombic efficiency was close to 100%, indicating a significant plating/electrolysis efficiency, which also indicates that a stable passivation film was formed on the electrode surface and that K could be allowed⁺High speed reversible transmission. Even if electroplatingTriple increase in the amount of electrolytic K (0.1mA cm)^-2，0.3mAh cm^-2) The NOSMS-based K | | | Cu battery can still exhibit high coulombic efficiency; the coulombic efficiency of the K | | | Cu battery based on the conventional electrolyte system of comparative example 1 sharply decreases after 80 cycles, and the battery completely fails. These results all show that the NOSMS provided by the present invention are superior to conventional electrolyte systems in all respects.

3) Evaluation of matching conditions of NWMS (negative electrode) | | K half-cell and NOSMS (negative electrode of graphite) with graphite negative electrode

Graphite is one of the most promising negative electrodes of PIBs, and whether graphite can stably store potassium is a breakthrough point in the industrialization of PIBs, especially in the aspect of water-based batteries which are more in line with practical industrialization and high safety requirements. As shown in FIGS. 5 and 6, commercial graphite negative electrodes based on NWMS were operated at 100mA g^-1The current density of the graphite I K half-cell shows that the graphite I K half-cell has the weight of 220mAh g^-1The specific capacity of the lithium ion battery is hardly reduced after 300 times of circulation, and the coulombic efficiency is close to 100%, so that the feasibility of the graphite cathode in an NWMS electrolyte system is verified, and a new good method is provided for the low-cost potassium graphite battery. As shown in fig. 7, comparing the long-term cycle performance of the graphite | K half-cell based on the conventional KFSI electrolyte of comparative example 1 and the NOSMS of example 1, the results show that the capacity of the graphite | K half-cell based on the conventional electrolyte of comparative example 1 decreases very rapidly, whereas 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 matching between NWMS and NOSMS with the positive electrode of KVPF

The high voltage window is of great significance to the electrolyte because it determines whether the electrolyte system can be used universally, and on the other hand, increasing the working voltage can significantly increase the energy density of the battery. However, the electrochemical window of imide salt (KFSI) liquid electrolytes does not exceed 4V. The test was performed using Linear Sweep Voltammetry (LSV). As shown in fig. 8, the electrochemical window of NOSMS is significantly enlarged to 5.9V (vs. K/K +), which is much higher than the conventional electrolyte system, and provides a basis for the research of high voltage positive electrodes. Again, the NWMS voltammogram of comparative example 2 was compared with the KCl aqueous electrolyte of example 2. The results show that the reduction stability and oxidation stability of the NWMS-based potassium battery are greatly improved, which further proves the feasibility of the NWMS-based graphite | | | K battery and provides a foundation for the operation of a high-voltage electrode. In addition, the voltammograms of the aqueous KFSI 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 NWMS-1 based potassium battery are also improved respectively, again demonstrating the unique structure and function of the solid ion trap of the free solvent molecule-free electrolyte system provided by the present invention to capture and lock the solvent molecules and anions.

As shown in fig. 9 and 10, a KVPF (positive electrode) | | | K half-cell based on the KFSI conventional electrolyte of comparative example 1 and the NOSMS of example 1 was compared to perform a test at a current density of 50mA g-1 and a cut-off voltage of 2 to 4.6V. The results show that the conventional electrolyte based KVPF (positive electrode) | | K half-cell was charged to around 4V, and the voltage did not rise any more, indicating that the aluminum current collector was corroded and other side reactions occurred. Whereas the NOSMS-based KVPF (positive) K half-cell can be charged to 4.6V. Specifically, fig. 10 and 11 show that average output voltages as high as 3.92V can be obtained, along with significant cycling stability (cycling over 1,000 cycles) and low capacity fade rate (about 0.1% per cycle).

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

It is well known that there should be a great deal of development in PIBs of organic anodes with potentially low cost and sustainability. However, a long-standing challenge in the practical application of organic anodes (such as PTCDI) is that the active material is easily dissolved by the electrolyte, leading to poor cycle life (as shown in fig. 12). The electrochemical performance of PTCDI (positive electrode) | | K half-cells based on the conventional KFSI electrolyte of comparative example 1 and the NOSMS of example 1 were compared. As shown in FIG. 5, PTCDI (Positive electrode) | | K half-cell based on conventional KFSI electrolyte has a large capacity fade due to dissolution in the first 20 cycles, i.e., at 50mA g^-1Providing about 122mAh g at current density^-1The first discharge capacity of (4); however, after 20 charge-discharge cycles, the corresponding capacity was reduced to 70mAh g^-1The capacity retention was only 57% (as shown in fig. 15). In contrast, there were no liquid solvent molecules to dissolve PTCDI (as shown in figure 12) since the solvent molecules in NOSMS were trapped and locked to form crystals. Therefore, the NOSMS-based PTCDI (positive electrode) | K half-cell operated stably for 2000 cycles (over 11 months) with reduced capacity fade and coulombic efficiency over 99%, indicating that the cycle life of the PTCDI positive electrode was greatly extended. This excellent performance fully represents the unique advantage of NOSMS in organic electrodes (including in organic cathodes). More importantly, as shown in fig. 14 and 16, the PTCDI (positive) K half-cell based on NWMS of example 2 still provides 101mAh g for 300 cycles^-1And a coulombic efficiency of over 99%. This shows that the NWMS provided by the present invention can be used as an electrolyte system for stabilizing the positive electrode, and provides a new paradigm for ultra-inexpensive electrolyte systems.

6) KI (anode) | | K half-cell evaluation NWMS and NOSMS match with KI anode

Another promising positive electrode material (e.g. iodine I)₂) Once the shuttle effect of the lithium battery is solved, the lithium battery becomes a high-performance potassium positive electrode. Potassium iodide (KI) with high marine storage capacity and low cost is selected as a positive electrode to study the inhibition effect of NOSMS on the shuttle effect. As shown in fig. 17, the very small pore of 2.9 angstroms in NOSMS of example 1 made KI and its reactants difficult to pass through, thus avoiding its "shuttling effect". As shown in fig. 18 to 19, the KI (positive electrode) | | K half-cell based on the conventional electrolyte of comparative example 1 could not be recharged after two cycles, indicating that the "shuttle effect" present severely hampered the development of the electrode. Under the same conditions, the half-cell was operated at 100mA g/g in KI (positive electrode) | | K based on NOSMS of example 1^-1Providing 121mAh g at current density^-1And after 50 cycles, there was little drop in capacity, indicating that NOSMS effectively suppressed the "shuttle effect".

7) PTCDI (positive electrode) | NOSMS | graphite (negative electrode) -based potassium ion battery

PTCDI as positive electrode, graphite as negative electrode, and NOSMS of example 1 as electrolyte system. The mass loading of PTCDI reaches 25mg cm^-2To obtain 2.89mAh cm^-22.18Ah pouch cells (nine-layer double-sided stack) were assembled by simple stacking integration. Typical charge and discharge curves of PTCDI | K cells, graphite | K cells, and PTCDI | NOSMS | graphite full cells are shown in fig. 20. The PTCDI nosm graphite battery has high safety, and even if cut twice, can still work as usual and light up the light emitting diode screen, proving that the safety is high. The discharge curve in fig. 21 shows that no change in capacity was observed after 72 hours of interruption of the discharge process, indicating excellent ion storage capacity, and that the battery can provide sufficient power to drive a small helicopter. Figure 22 shows the voltage change over time after full charge (charging to 3.2V) for two batteries based on NOSMS of example 1 and the conventional KFSI electrolyte of comparative example 1. After the batteries are stored for more than 180 hours, the open-circuit voltages of the two batteries are sharply reduced within the first 2 hours of standing, and then tend to be stable within the next 50 hours; thereafter, the voltage of the PTCDI | KFSI | graphite full cell based on the conventional KFSI electrolyte system of comparative example 1 continued to decrease due to self-discharge and dissolution of the organic positive electrode, and the voltage of the PTCDI | nosm | graphite full cell based on nosm of example 1 remained stable, with the difference gradually increasing. As shown in FIG. 23, the PTCDI NOSMS graphite all cell was at 50mA g^-1Can provide 123mAh g at the current density of^-1The coulombic efficiency was over 99% based on the mass of the positive electrode. In addition, the average capacity fading rate per cycle in 1000 cycles was 0.036%, while 243.9Wh kg was exhibited^-1High energy density. In addition, the full cell can save practical space and increase voltage through simple stacking integration.

In summary, the electrolyte system without free solvent molecules provided by the present invention is specifically designed to be constructed by the solid ion trap and the conductive substrate so as to capture anions and solvent molecules simultaneously and lock them through the preset fixed ion trap, thereby realizing an electrolyte system in which only alkali metal ions can move freely. Compared with the traditional electrolyte system, the electrolyte system without free solvent molecules has the advantages of low cost, high ionic conductivity, dendritic crystal growth inhibition, shuttle effect inhibition and electrode dissolution inhibition, high oxidation stability (the electrolyte (NOSM) based on the free organic solvent molecules exceeds 5.9V), high reduction stability (the electrolyte (NWM) based on the free water molecules is lower than-1V, and graphite electrodes can be used) and wide applicability. The metal ion battery based on the electrolyte system without free solvent molecules has excellent electrochemical performance and safety.

The above description is intended to be illustrative of the preferred embodiment of the present invention and should not be taken as limiting the invention, but rather, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Claims

1. An electrolyte system free of free solvent molecules, characterized in that: it comprises metal salt electrolyte and metal organic framework compound; the metal organic framework compound is internally provided with an angstrom-level solid ion trap structure.

2. The free solvent molecule-free electrolyte system of claim 1, wherein: the metal salt electrolyte is an alkali metal salt electrolyte, an aluminum base salt electrolyte, a zinc base salt electrolyte, a magnesium base salt electrolyte, a calcium base salt electrolyte or an iron base salt electrolyte.

3. The free solvent molecule-free electrolyte system of claim 2, wherein: the metal salt electrolyte comprises 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; the solvent is an organic solvent or an aqueous solvent.

4. The free solvent molecule-free electrolyte system of claim 3, wherein: the alkali metal salt electrolyte is a lithium salt electrolyte, a sodium salt electrolyte or a potassium salt electrolyte; the potassium salt electrolyte is potassium bis (fluorosulfonyl) imide salt, potassium chloride or potassium hexafluorophosphate.

5. The free solvent molecule-free electrolyte system of any of claims 1-4, wherein: the metal organic framework compound is a zeolite imidazole ester framework, 2-methylimidazole zinc salt MAF-4, Cu-MOF-74, Cu-BTC, Zr-group-UiO-67 or poly [ Zn ]₂(BIM)₄]。

6. A method of preparing the free solvent-free molecular electrolyte system of any of claims 1 to 5, wherein: which comprises the following steps of,

step B, preparing a metal salt liquid electrolyte;

and D, drying to remove the residual solvent.

7. The method of claim 6, wherein the free solvent-free molecular electrolyte system comprises: the specific method of the step A is that,

8. The method of claim 7, wherein the free solvent-free molecular electrolyte system comprises: the weight ratio of the metal organic framework compound to the binder is 1: (0.1-0.5), and the binder is polyvinylidene fluoride, styrene-butadiene rubber, carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile or polyacrylate.

9. The method of claim 7, wherein the free solvent-free molecular electrolyte system comprises: the step a2 is specifically characterized in that the metal organic framework compound slurry is coated on a flat substrate and is dried in vacuum for 3-5h at the temperature of 60-80 ℃; the substrate is a metal foil or a high polymer material film.

10. The method of claim 7, wherein the free solvent-free molecular electrolyte system comprises: the step a3 is specifically that the substrate coated with the metal organic framework compound is soaked in an organic solvent for 0.5-1h, so that the metal organic framework compound is peeled off from the substrate, and the flexible metal organic framework compound film is prepared.

11. The method of claim 7, wherein the free solvent-free molecular electrolyte system comprises: the step a4 is specifically carried out by punching the flexible metal organic framework compound film into the required shape, and then reactivating for 12-18h under vacuum at 180-220 ℃.

12. The method of claim 6, wherein the free solvent-free molecular electrolyte system comprises: and C, immersing the metal organic framework compound film prepared in the step A into the metal salt electrolyte prepared in the step B, and treating at 70-80 ℃ for 40-50h to ensure that metal salt electrolyte molecules and solvent molecules are fully immersed into a solid ion trap of the metal organic framework compound, wherein anions and solvent molecules are fixed by the solid ion trap, and cations can move freely.

13. The method of claim 6, wherein the free solvent-free molecular electrolyte system comprises: and D, removing the metal salt electrolyte on the surface of the metal organic framework compound film prepared in the step C, and then further removing the residual solvent when the film is dried in vacuum at 80-100 ℃ for 20-24h to prepare an electrolyte system without free solvent molecules.

14. Use of a free solvent-free molecular electrolyte system according to any one of claims 1 to 13, wherein: the free solvent-free molecular electrolyte system is applied as an electrolyte of a metal ion battery.

15. Use of a free solvent-free molecular electrolyte system according to claim 14, wherein: 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 a potassium ion battery.