CN108321432B - A carbon-nitrogen polymer benchmark solid-state electrolyte for inhibiting lithium dendrite growth and its preparation method and application - Google Patents

Abstract

The invention relates to a carbon-nitrogen polymer benchmark solid-state electrolyte for inhibiting the growth of lithium dendrites and its preparation method and application. The quasi-solid-state electrolyte includes an electrolyte and an electrolyte filler, and the electrolyte filler is a lightweight carbon nitrogen polymer. The invention uses light carbon-nitrogen polymers as electrolyte filling agents to prepare a quasi-solid electrolyte capable of effectively inhibiting the growth of lithium dendrites in lithium metal batteries. Among them, the lightweight carbon-nitrogen polymer has a surprising layered structure, which is conducive to the absorption of electrolyte, thereby forming a mud-like quasi-solid electrolyte, which can be used to suppress the growth of lithium anode dendrites in lithium metal batteries.

Description

A carbon-nitrogen polymer benchmark solid-state electrolyte for inhibiting lithium dendrite growth and its Preparation method and application

technical field

The invention belongs to the technical field of new energy, and in particular relates to a light carbon-nitrogen polymer benchmark solid-state electrolyte for inhibiting the growth of lithium dendrites, a preparation method and application thereof.

Background technique

Lithium metal batteries represented by Li-S and Li- _O2 have attracted extensive attention due to their higher energy density than Li-ion batteries. Due to its low voltage and high theoretical specific capacity (3860mAh/g), the negative metal lithium is the best candidate for this type of high-capacity conversion reaction battery system. However, during the electrochemical cycle, lithium metal is deposited/stripped unevenly on the surface of the negative electrode, leading to the growth of lithium dendrites and the deterioration of the electrochemical performance of the battery, and the lithium dendrites can even penetrate the separator and cause a short circuit of the battery. . In recent years, various strategies have been attempted to improve the Li deposition process and suppress Li dendrite growth. For example, metal lithium is melted and infiltrated into a conductive framework matrix with a lithium-friendly surface to construct a flexible metal lithium negative electrode with small volume change, which can eliminate lithium dendrites. By constructing a current collector with a three-dimensional nanostructure to replace a two-dimensional Li-loading plane, the deposition behavior of Li metal can be improved, thereby avoiding the growth of Li dendrites. Changing the intrinsic properties and concentration of the electrolyte or introducing electrolyte additives is also an important strategy. For example, based on ionic liquids or high-concentration fluorosulfonimide ions (FSI ^- ), it can effectively ensure high rate and stable lithium metal batteries. During the deposition process, FSI ^- can be reduced on the surface of lithium metal (mainly generating LiF), forming a solid solid electrolyte interfacial layer (SEI) in situ, thereby ensuring that lithium dendrites will not be generated during lithium metal deposition. For the Li-S battery system, the simultaneous addition of lithium polysulfides and lithium nitrate can produce a synergistic effect to strengthen the SEI, thereby protecting the lithium anode from corrosion. The modification of the separator (such as introducing polar functional groups on the surface of the separator fiber) can also effectively ensure the uniform deposition of lithium metal on the negative electrode.

Compared with additive-enhanced electrolytes, solid or quasi-solid electrolytes have better mechanical strength and are expected to have a better inhibitory effect on lithium dendrites. However, the conductivity of all-solid electrolytes is usually not enough, and the problem of poor interfacial contact is also difficult to solve. Quasi-solid electrolytes have similar conductivity to electrolytes and good interfacial wetting ability, and are considered to be one of the best candidates for new electrolytes for lithium metal batteries. Quasi-solid electrolytes are often solidified by adding non-aqueous electrolyte or lithium salt to a polymer skeleton (such as polyethylene oxide) or inorganic nanoparticles (such as nano-silicon dioxide) filler. The quasi-solidification of the electrolyte not only does not lead to a significant decrease in conductivity, but in some cases, it may increase its conductivity due to the space charge effect. However, the traditional polyethylene oxide-based polymer film has weak mechanical strength and cannot effectively suppress lithium dendrites, and often needs to be improved by adding hard inorganic nanoparticles.

Contents of the invention

In view of the above problems, the object of the present invention is to provide a novel polymer base solid electrolyte with high mechanical strength and its preparation method and application.

On the one hand, the present invention provides a kind of light-weight carbon-nitrogen polymer benchmark solid electrolyte (for the carbon-nitrogen polymer benchmark solid-state electrolyte that is used to restrain lithium dendrite growth) for suppressing lithium dendrite growth, comprising electrolytic solution, and electrolytic Liquid filler, the electrolyte filler is light carbon nitrogen polymer.

The invention uses light carbon-nitrogen polymers as electrolyte filling agents to prepare a quasi-solid electrolyte capable of effectively inhibiting the growth of lithium dendrites in lithium metal batteries. Among them, the lightweight carbon-nitrogen polymer has a surprising layered structure, which is conducive to the absorption of electrolyte, thereby forming a mud-like quasi-solid electrolyte, which can be used to suppress the growth of lithium anode dendrites in lithium metal batteries. The polymer gC ₃ N ₄ itself has high mechanical strength, and the close packing of the layered structure further enhances the mechanical strength. Therefore, as an electrolyte filler, gC ₃ N ₄ can effectively inhibit the growth of lithium dendrites. When the light-weight carbon-nitrogen polymer benchmark solid-state electrolyte is in contact with a lithium metal negative electrode, the quasi-solid-state electrolyte also has an interface impedance of the same order of magnitude as that of a conventional electrolyte, and good interface adhesion. Moreover, during the long cycle of lithium metal symmetric batteries, the quasi-solid electrolyte can greatly slow down the increase in voltage polarization during lithium metal deposition/stripping, and enhance the cycle stability of the battery.

Preferably, the lightweight carbon-nitrogen polymer includes self-assembled three-dimensional mesoporous spherical gC ₃ N ₄ , two-dimensional nano-thin layer gC ₃ N ₄ , oxygen-doped exfoliated few-layer OgC ₃ N ₄ , S-doped At least one of SgC ₃ N ₄ .

The mass percentage of the light carbon nitrogen polymer in the light carbon nitrogen polymer benchmark solid state electrolyte is 20-25 wt%.

Preferably, the electrolyte solution includes a solute and a solvent, and the solute is at least one of lithium bistrifluoromethanesulfonimide LiTFSI, lithium hexafluorophosphate LiPF ₆ , lithium perchlorate LiClO ₄ , and lithium bisfluorosulfonimide LiFSI A kind; The solvent is diglyme DGM, triethylene glycol dimethyl ether TEGDME, ionic liquid 1-ethyl-3 methyl bistrifluoromethanesulfonimide EmimTFSI, ethylene carbonate EC and two At least one of methyl carbonate DMC; the concentration of the solute in the electrolyte is 0.5-1.5 mol/L.

Also, preferably, the electrolyte is a diglyme DGM solution in which the solute is lithium bistrifluoromethanesulfonimide LiTFSI, a triethylene glycol dimethyl ether TEGDME solution in which the solute is LiTFSI, or a solute of Lithium hexafluorophosphate LiPF ₆ is a solution of ethylene carbonate EC and dimethyl carbonate DMC with a volume ratio of 1:1; the concentration of solute in the electrolyte is 0.5-1.5 mol/L.

On the other hand, the present invention provides a method for preparing a light carbon-nitrogen polymer benchmark solid electrolyte. The light carbon-nitrogen polymer is fully mixed with an electrolyte to obtain the light carbon-nitrogen polymer benchmark solid electrolyte.

Preferably, the particle size distribution of the light carbon nitrogen polymer is 3.5-8 μm. When the light carbon-nitrogen polymer has a nanometer structure, it is very easy to mix with the electrolyte to form a slurry, which ensures the simple molding process of the quasi-solid electrolyte.

In a third aspect, the present invention also provides a lithium metal symmetric battery system based on a light carbon-nitrogen polymer benchmark solid electrolyte, the lithium metal symmetric battery system includes a light carbon nitrogen polymer benchmark solid electrolyte, and a lightweight Lithium flakes flanked by carbonitride polymer benchmark solid-state electrolytes.

When the lightweight carbon-nitrogen polymer benchmark solid electrolyte is used in a lithium metal symmetric battery, it has good interface stability and low interface impedance, which reduces the voltage polarization difference in the metal lithium deposition/stripping process, and enhances The cycle stability of the symmetrical battery is ensured, and the surface of metallic lithium after a long cycle of the symmetrical battery is still smooth and dense.

In a fourth aspect, the present invention also provides a lithium metal battery comprising a positive electrode, a negative electrode, and a light carbon-nitrogen polymer base solid electrolyte between the positive electrode and the negative electrode, the negative electrode is a metal lithium sheet, and the The positive electrode is at least one of FeS ₂ , carbon-sulfur compound, LiFePO ₄ , LiMn ₂ O ₄ , LiCoO ₂ , nickel-rich ternary system and lithium-rich manganese-based solid solution.

Preferably, the positive electrode is preferably FeS ₂ . When the lightweight carbon-nitrogen polymer benchmark solid-state electrolyte is used in Li _- FeS lithium metal batteries, it improves the morphology of the lithium negative electrode, weakens the shuttle effect of polysulfides, and ensures a long battery life of more than 400 cycles. life.

The present invention has the following positive and progressive effects.

(1) The present invention uses light carbon-nitrogen polymers as electrolyte fillers for quasi-solid electrolytes, which proves its superiority as electrolyte fillers. For example, in the synthesis process of spherical gC ₃ N ₄ , a large number of thin-layer nanosheets self-assemble into uniform mesoporous spheres. This fine layered structure is conducive to the absorption of electrolyte, and at the same time, the nanostructured powder is very easy to mix with The electrolyte is mixed into mud, which ensures the simple molding process of this quasi-solid electrolyte.

(2) In the present invention, spherical gC ₃ N ₄ can be effectively attached to the surface of metal lithium or electrode material by the uniform mud mixed with the electrolyte, and the interface impedance of the quasi-solid electrolyte and the metal lithium negative electrode is higher than that of the pure electrolyte system. Impedance is easier to achieve stability, the transmission impedance of the former at the interface can be as low as 115Ωcm ² , and the diffusion activation energy at the interface in the temperature range of 30 to 70°C is 0.45eV.

(3) When the quasi-solid electrolyte in the present invention is used in a lithium metal symmetric battery, the polarization potential difference during the reversible deposition/stripping process of metal lithium is significantly reduced, and the cycle stability of the symmetric battery is enhanced. The stable deposition/stripping of lithium metal symmetric batteries based on quasi-solid electrolytes is benefited from the inhibition of lithium dendrite growth by the electrolytes.

(4) When the lightweight carbon-nitrogen polymer benchmark solid electrolyte in the present invention is used in Li-FeS ₂ lithium metal batteries, since the lithium dendrites are suppressed, the morphology of the lithium negative electrode is significantly improved, and the quasi-solid electrolyte can also weaken more The shuttling effect of sulfides thus ensures the long lifetime of the Li- _FeS2 battery >400 cycles.

The method of the invention has a simple and convenient production process, is suitable for large-scale application, and is of great significance to the development of lithium metal batteries.

Description of drawings

Figure 1 is the XRD pattern of gC ₃ N ₄ composed of three-dimensional mesoporous spherical particles;

Figure 2 is the SEM image of gC ₃ N ₄ composed of three-dimensional mesoporous spherical particles;

Figure 3 is the time-evolving interface AC impedance spectrum of a metallic lithium symmetric battery based on gC ₃ N ₄ quasi-solid electrolyte, insert figure: the change of interface impedance value with time;

Figure 4 is the variable temperature AC impedance spectrum of a metal lithium symmetric battery based on gC ₃ N ₄ quasi-solid electrolyte;

Fig. 5 is the Arrhenius point diagram of the impedance value derivation at different temperatures of the metallic lithium symmetric battery based on the gC ₃ N ₄ quasi-solid electrolyte;

Figure 6 is a plot of potential curves of lithium metal deposition/stripping cycles at 0.5mA/ ^cm2 for lithium metal symmetric cells based _{on gC3N4} quasi-solid electrolyte or pure electrolyte, insert: enlarged potential at a specific number of cycles curve comparison;

Figure 7 is a graph of potential curves of lithium metal deposition/stripping cycles at 2mA/ ^cm2 for lithium metal symmetric batteries based on gC ₃ N ₄ quasi-solid electrolyte or pure electrolyte, insert: enlarged potential curve at a specific number of cycles Compare;

Fig. 8 is a SEM surface morphology image of lithium metal symmetric battery based on gC ₃ N ₄ quasi-solid electrolyte at 2mA/cm ² after 120 cycles of lithium metal deposition/stripping;

Fig. 9 is the charge-discharge curve diagram of the first ₂₀₀ cycles of the Li-FeS battery based on gC ₃ N ₄ quasi-solid electrolyte;

Figure 10 is the time-evolving interface AC impedance spectrum of a metal lithium symmetric battery based on OgC ₃ N ₄ quasi-solid electrolyte, insert figure: the change of interface impedance value with time;

Fig. 11 is a potential curve diagram of the lithium metal deposition/stripping cycle of the lithium metal symmetric battery based on the OgC ₃ N ₄ quasi-solid electrolyte at 0.5 and 2 mA/cm ² .

Detailed ways

The present invention will be further described below through the following embodiments. It should be understood that the following embodiments are only used to illustrate the present invention, not to limit the present invention.

In the invention, a nanostructure polymer filler with high mechanical strength is added to the electrolyte to solidify the electrolyte and construct a quasi-solid electrolyte to achieve the purpose of inhibiting the growth of lithium negative electrode dendrites in lithium metal batteries. Specifically, lightweight carbon-nitrogen polymers are used as electrolyte fillers and uniformly mixed with the electrolyte to form a mud-like quasi-solid electrolyte, which can be used to inhibit the growth of lithium anode dendrites in lithium metal batteries. The weight percentage of the light carbon nitrogen polymer in the light carbon nitrogen polymer standard solid state electrolyte can be 20-25 wt%. If the content is too high or too low, it will be difficult to form a good slimy electrolyte.

The upper light carbon nitrogen polymer can be selected as self-assembled three-dimensional mesoporous spherical gC ₃ N ₄ (brown yellow), two-dimensional nano-thin layer gC ₃ N ₄ (bright yellow), oxygen-doped exfoliated few-layer OgC ₃ N ₄ (white), S-doped SgC ₃ N ₄ (taupe).

The lightweight carbon-nitrogen polymer benchmark solid-state electrolyte of the present invention is formed by uniformly mixing carbon-nitrogen polymers and electrolytes, wherein the electrolytes include solutes and solvents. The solute may be at least one of lithium bistrifluoromethanesulfonimide LiTFSI, lithium hexafluorophosphate LiPF ₆ , lithium perchlorate LiClO ₄ , and lithium bisfluorosulfonimide LiFSI. The solvent can be diglyme DGM, triethylene glycol dimethyl ether TEGDME, ionic liquid 1-ethyl-3 methyl bistrifluoromethanesulfonimide EmimTFSI, ethylene carbonate EC and dimethyl At least one of carbonate DMC. The concentration of the solute in the electrolyte may be 0.5-1.5 mol/L. The electrolytic solution can be preferably: a solute is a diglyme (DGM) solution of bistrifluoromethanesulfonimide lithium (LiTFSI), a solute is a triethylene glycol dimethyl ether (TEGDME) solution of LiTFSI, The solute is a solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) with a volume ratio of lithium hexafluorophosphate (LiPF ₆ ) of 1:1, and the concentration of the electrolyte is 0.5-1.5mol/L.

The preparation method of the light carbon-nitrogen polymer benchmark solid electrolyte provided by the present invention is exemplarily described below.

The light carbon nitrogen polymer is fully mixed with the electrolyte to obtain the light carbon nitrogen polymer benchmark solid state electrolyte. The particle size distribution of the light carbon nitrogen polymer may be 3.5-8 μm. As an example, take 50-150 mg of gC ₃ N ₄ powder sample in an agate mortar, then add 250-350 μl of electrolyte solution, and grind thoroughly to obtain a light carbon-nitrogen polymer benchmark solid electrolyte. The thickness of the lightweight carbon-nitrogen polymer reference solid electrolyte can be adjusted according to needs, and its thickness can generally be 80-120 microns.

The lithium metal symmetric battery system provided by the present invention refers to a battery in which both sides of the quasi-solid electrolyte are metallic lithium sheets. The current density of the lithium deposition and stripping cycle test of the lithium metal symmetric battery system can be 0.5-2 mA/cm ² , and the deposition or stripping time in each cycle can be 1-3 hours.

In the lithium metal battery provided by the present invention, the metal lithium sheet is used for the negative electrode, and the positive electrode can be FeS ₂ , carbon-sulfur compound, LiFePO ₄ , LiMn ₂ O ₄ , LiCoO ₂ , nickel-rich ternary system, and lithium-rich manganese-based solid solution. At least one, no separator is required, and a quasi-solid electrolyte is placed between the positive and negative electrodes. Due to dendrite suppression, the carbon-nitrogen polymer-based Li- _FeS2 quasi-solid-state battery has a long lifetime greater than 400 cycles.

The invention uses light carbon-nitrogen polymer as electrolyte filling agent to obtain mud-like quasi-solid electrolyte, and effectively inhibits the growth of lithium dendrites in lithium metal batteries. The quasi-solid electrolyte has an interface impedance similar to that of the electrolyte; when used in lithium metal symmetric batteries, it has good interface stability and low interface impedance, which greatly reduces the voltage polarization during lithium metal deposition/stripping Poor, the cycle stability of the symmetrical battery is enhanced, the morphology of the deposited lithium metal is improved, and the metal lithium surface of the symmetrical battery is still smooth and dense after a long cycle. When used in Li- _FeS2 batteries, it weakens the shuttle effect of polysulfides, significantly slows down the decay of battery capacity, and ensures the long life of the battery greater than 400 cycles.

Examples are given below to describe the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention, and should not be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art according to the above contents of the present invention all belong to the present invention scope of protection. The specific process parameters and the like in the following examples are only examples of suitable ranges, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not limited to the specific values exemplified below.

Example 1

1) Preparation of mesoporous spherical gC ₃ N ₄

Weigh 1.9977g of melamine and dissolve it in 80mL of dimethyl sulfoxide (DMSO); dissolve cyanuric acid (2.0446g) with an equal number of moles in 40mL of dimethyl sulfoxide. The two solutions were each stirred at 60° C., and after being uniformly dissolved, they were mixed with each other, kept stirring at 60° C. for 10 minutes, and then left to stand at room temperature. After the mixture was centrifuged, washed with ethanol for 5 times, and dried in a vacuum oven at 50° C., a white powder was obtained. Put the white powder into a ceramic crucible, place it in a tube furnace, raise the temperature to 550°C at a rate of 2.3°C/min in an atmosphere of high-purity argon, and sinter it for 4 hours to obtain a brown-yellow sample powder. Its XRD is shown in Figure 1, and the diffraction peaks correspond to the pure phase of gC ₃ N ₄ with nanostructures. The SEM of gC ₃ N ₄ is shown in Figure 2. It can be seen that gC ₃ N ₄ is composed of spherical particles with a size of about 5 microns, and each particle is self-assembled and aggregated by a large number of thin-layer nanosheets, so it is porous shape.

2) Preparation of electrolyte

The preparation of electrolyte is carried out in an argon glove box with water value and oxygen value less than 0.1ppm. 1.4354 g (5 mmol) of lithium bistrifluoromethanesulfonimide (LiTFSI) was dissolved in 5 mL of diglyme (DGM), then the solution was placed on a magnetic stirrer and stirred for 24 hours to obtain 1 mol/ L LiTFSI/DGM electrolyte.

3) Preparation of quasi-solid electrolyte

The gC ₃ N ₄ powder sample obtained in 1) was vacuum-dried in a vacuum oven at 120° C. for 24 hours, and then transferred to an argon glove box. Take 100 mg of gC ₃ N ₄ powder sample in an agate mortar, then add 300 μl of LiTFSI/DGM electrolyte, and grind it thoroughly to obtain a quasi-solid electrolyte with mesoporous spherical gC ₃ N ₄ as polymer filler. The mass percentage of the light carbon nitrogen polymer in the light carbon nitrogen polymer benchmark solid state electrolyte is 20wt%.

4) Assembly and testing of lithium metal symmetric batteries

The assembly of 2032 button cells was carried out in an argon glove box with water value and oxygen value less than 0.1ppm. Specifically, take a metal lithium sheet with a diameter of 12 mm, uniformly coat a layer of quasi-solid electrolyte described in 3) of about 0.1 mm on the surface, and then spread a metal lithium sheet with a diameter of 10 mm on the surface of the quasi-solid electrolyte. pieces, assembled into button cells. As a comparison, using Celgard as the diaphragm and adding 70 μl of LiTFFSI/DGM electrolyte, a symmetrical battery is similarly assembled. At room temperature, carry out the AC impedance test of the symmetrical battery, set the bias voltage as 100mV, and the frequency range as 10 ^-2 -10 ⁶ Hz. In order to test the evolution of the interface impedance of metal lithium and quasi-solid electrolyte (or Celgard load electrolyte) over time, a test was performed every 24 hours until the impedance value did not fluctuate significantly. Figure 3 shows the interfacial impedance between metallic lithium and the quasi-solid electrolyte over time. It can be seen that the interfacial impedance stabilizes at around ^115Ωcm after 48 hours. Then, the variable temperature AC impedance test was carried out on the symmetrical battery after the room temperature was stabilized. The temperature range was 30-70°C, and the test was performed every 10°C. Each temperature node was kept warm for 1 hour to ensure the stability of the battery system. Figure 4 shows the AC impedance spectrum of a symmetric battery based on a quasi-solid electrolyte at a temperature range of 30-70°C. According to the AC impedance values at different temperatures, the diffusion activation energy at the interface can be calculated as 0.45eV according to the Arrhenius equation. , Figure 5 is the corresponding Arrhenius point.

The assembled 2032 button-type symmetrical battery was charged and discharged on the LAND electrochemical workstation. At a current density of 0.5mA/ ^cm2 , it was charged at a constant current for 3 hours, and then discharged at a constant current for 3 hours to detect the deposition of lithium metal. The voltage polarization of the /stripping process is poor, and the cycle is unrolled at this step. Figure 6 and Figure 7 are cycle curves of lithium metal deposition/stripping processes based on mesoporous spherical gC ₃ N ₄ quasi-solid electrolyte and pure electrolyte at different current densities. It can be seen from the figure that the quasi-solid electrolyte significantly The polarization potential difference during metal Li deposition/stripping process is significantly reduced, and the cycle stability of the symmetric battery is enhanced. At a current density of 0.5mA/cm ² , after 50 cycles, the polarization voltage difference is maintained at about 50mV, while the pure electrolyte system symmetric battery has a polarization voltage difference as high as 400mV after 50 cycles. At a current density as high as 2mA/cm ² , the deposition/stripping time remains unchanged (3 hours), and the polarization voltage difference of the quasi-solid-state system can still be maintained at a low level of about 100mV. After the symmetrical battery cycled for a certain number of times, the battery was disassembled in a glove box filled with argon gas, and the metal lithium sheet was taken out, washed several times in the electrolyte solvent DGM, dried naturally, and placed in a scanning electron microscope under the protection of argon gas. Microscope device for morphology observation. Figure 8 shows the morphology of the metal lithium surface of the quasi-solid electrolyte symmetric battery after 120 cycles at a current density of 2mA/ ^cm2 . It can be seen from the figure that the lithium metal surface is still smooth and dense after a high current density cycle, confirming the Li dendrite growth was effectively suppressed.

5) Assembly and testing of Li- _FeS2 batteries based on quasi-solid electrolytes

a) Preparation of _FeS2 cathode material

Weigh 35 mg of commercial FeS ₂ powder sample and 10 mg of Super P, put them into a mortar and grind for 30 minutes, then add 100 μl of NMP solution with a PVDF concentration of 20 mg/μl, and grind for 10-15 minutes. Spread the black slurry evenly on an aluminum foil with an area of 50 mm ² and dry it in a vacuum oven at 80°C for 12 hours. The aluminum foil loaded with active substance after vacuum drying is weighed again, and packed into a glove box;

b) Assembly and testing of batteries

The assembly of 2032 button cells was carried out in an argon glove box with water value and oxygen value less than 0.1ppm. The specific process is to uniformly coat a layer of the above-mentioned quasi-solid electrolyte on a lithium sheet with a diameter of 10mm, and then place the positive electrode sheet loaded with active materials on the electrolyte to assemble a Li- _FeS2 lithium metal battery. The assembled battery is charged and discharged on the LAND electrochemical workstation, the voltage range is 1-3V, and the current rate is 0.1C (1C corresponds to the 4-electron conversion reaction of FeS ₂ or the theoretical specific capacity of 892mAh/g is completed in 1 hour required current density). Figure 9 is a typical charge-discharge curve of a Li- _FeS2 battery in the first 200 cycles. Due to the inhibition of lithium dendrites, the morphology of the lithium negative electrode is significantly improved, and the polarity of the quasi-solid electrolyte is also conducive to weakening the polysulfides. Shuttle effect, thus ensuring a long life of the battery greater than 400 cycles.

Example 2

1) Preparation of monolayer flake OgC ₃ N ₄

4g of melamine was placed in a muffle furnace, the muffle furnace was connected to the air, and the temperature was raised to 550°C at a rate of 2°C/min, and kept at this temperature for 4 hours to obtain a bright yellow bulky loose solid sample. After the sample was fully ground into powder, it was placed in a combustion boat, and the temperature was raised to 550°C at a rate of 5°C/min and kept for 1 hour to obtain a light yellow solid powder. Then the powder was heated up to 550° C. at a rate of 2° C./min and held for 1 hour to obtain a white final sample. All the above-mentioned heating processes are carried out in the air atmosphere;

2) Electrolyte configuration

The preparation of electrolyte is carried out in an argon glove box with water value and oxygen value less than 0.1ppm. 1.4354 g (5 mmol) of lithium bistrifluoromethanesulfonimide (LiTFSI) was dissolved in 5 mL of diglyme (DGM), then the solution was placed on a magnetic stirrer and stirred for 24 hours to obtain 1 mol/ L LiTFSI/DGM electrolyte;

3) Preparation of quasi-solid electrolyte

The lamellar OgC ₃ N ₄ powder sample obtained in 1) was vacuum-dried in a vacuum oven at 120° C. for 24 hours, and then transferred to an argon glove box. Take 120 mg of OgC ₃ N ₄ powder sample in an agate mortar, add 300 μl of LiTFSI/DGM electrolyte, and grind thoroughly to obtain a quasi-solid electrolyte with oxygen-doped lamellar OgC ₃ N ₄ as polymer filler. The mass percentage of light carbon nitrogen polymer in the light carbon nitrogen polymer benchmark solid state electrolyte is 25wt%;

4) Assembly and testing of lithium metal symmetric batteries

The assembly of 2032 button cells was carried out in an argon glove box with water value and oxygen value less than 0.1ppm. Specifically, take a metal lithium sheet with a diameter of 12 mm, uniformly coat the surface with the quasi-solid electrolyte described in 3) of about 0.1 mm, and then spread a metal lithium sheet with a diameter of 10 mm on the quasi-solid electrolyte. Lithium sheets, assembled into button cells. As a comparison, Celgard was used as a separator, loaded with 70 μl of LiTFSI/DGM electrolyte, and a symmetrical battery was also assembled. The interface AC impedance test (including the stability of the interface impedance over time and the temperature-varying AC impedance) was carried out on the above-mentioned symmetrical battery, and the charge-discharge test of lithium metal deposition/stripping under different current densities. Figure 10 shows the change of interface impedance over time between metal lithium and OgC ₃ N ₄ reference solid electrolyte. It can be seen that the interface impedance value stabilizes at about 550Ωcm ² after 168 hours. Figure 11 shows the cycle curves of lithium metal deposition/stripping process of a symmetric battery based on OgC ₃ N ₄ quasi-solid electrolyte at current densities of 0.5 mA/cm ² and 2 mA/cm ² , it can be seen from the figure that low current density can Maintain better cycle stability, and the potential polarization after 80 cycles is still maintained at about 100mV.

Finally, it is necessary to explain here that: the above examples are only used to further describe the technical solutions of the present invention in detail, and cannot be interpreted as limiting the protection scope of the present invention. Non-essential improvements and adjustments all belong to the protection scope of the present invention.

Claims (7)

1. A light-weight carbon-nitrogen polymer benchmark solid-state electrolyte for suppressing lithium dendrite growth, characterized in that, the light-weight carbon-nitrogen polymer benchmark solid-state electrolyte is a mud-like quasi-solid electrolyte, including electrolyte, and electrolytic Liquid filler, the electrolyte filler is a light carbon-nitrogen polymer, and the mass percentage of the light carbon-nitrogen polymer in the light carbon-nitrogen polymer benchmark solid state electrolyte is 20 to 25wt%; The electrolyte includes a solute and a solvent, and the solute is at least one of lithium bistrifluoromethanesulfonimide LiTFSI, lithium hexafluorophosphate LiPF ₆ , lithium perchlorate LiClO ₄ , and lithium bisfluorosulfonyl imide LiFSI; The solvents are diglyme DGM, triethylene glycol dimethyl ether TEGDME, ionic liquid 1-ethyl-3 methyl bistrifluoromethanesulfonimide EmimTFSI, ethylene carbonate EC and dimethyl carbonate At least one of DMC; the solute concentration in the electrolyte is 0.5-1.5 mol/L. 2. The lightweight carbon-nitrogen polymer benchmark solid electrolyte according to claim 1, characterized in that the lightweight carbon-nitrogen polymer comprises self-assembled three-dimensional mesoporous spheres gC ₃ N ₄ , two-dimensional nano-thin layers gC At least one of ₃ N ₄ , oxygen-doped exfoliated few-layer OgC ₃ N ₄ , S-doped SgC ₃ N ₄ . 3. according to claim 1 and 2 described lightweight carbon-nitrogen polymer benchmark solid state electrolytes, it is characterized in that, described electrolytic solution is the diglyme DGM that solute is two trifluoromethanesulfonimide lithium LiTFSI solution, the solute is the triethylene glycol dimethyl ether TEGDME solution of LiTFSI, or the ethylene carbonate EC and dimethyl carbonate DMC solution that the volume ratio of the lithium hexafluorophosphate LiPF ₆ is 1:1; the solute in the electrolyte The concentration is 0.5-1.5 mol/L. 4. a preparation method of light carbon-nitrogen polymer benchmark solid state electrolyte as described in any one in claim 1-3, it is characterized in that, light carbon-nitrogen polymer is fully mixed with electrolytic solution, obtains described Lightweight carbon-nitrogen polymer benchmark solid-state electrolyte. 5. The preparation method according to claim 4, characterized in that the particle size distribution of the light carbon nitrogen polymer is 3.5-8 μm. 6. A lithium metal symmetric battery system based on a light carbon-nitrogen polymer benchmark solid electrolyte, characterized in that the lithium metal symmetric battery system comprises the light carbon-nitrogen polymer described in any one of claims 1-3 solid-state electrolyte, and metal lithium sheets on both sides of the light-weight carbon-nitrogen polymer-based solid-state electrolyte. 7. A lithium metal battery based on a lightweight carbon-nitrogen polymer benchmark solid-state electrolyte, characterized in that, the lithium metal battery comprises a positive pole, a negative pole, and any of claims 1-3 between the positive pole and the negative pole. One of the lightweight carbon-nitrogen polymer benchmark solid electrolytes, the negative electrode is lithium metal sheet, the positive electrode is FeS ₂ , carbon-sulfur compound, LiFePO ₄ , LiMn ₂ O ₄ , LiCoO ₂ , nickel-rich ternary system and at least one of lithium-rich manganese-based solid solution.