1. A compound having an aromatized nitric free radical, characterized by:

the structure of the effective component is an aromatized nitric acid free radical structure.

2. The compound having an aromatized nitric radical according to claim 1,

the compound is one of compounds shown in formulas 1-8:

3. the method for preparing a lithium metal negative electrode modified with the compound according to claim 2, comprising the steps of:

dissolving a compound containing an aromatic nitric acid free radical in an organic solvent to obtain a compound solution containing the aromatic nitric acid free radical;

then, under the protection of inert gas, uniformly dripping a compound solution containing aromatic free radical of nitric acid on the surface of lithium metal, and reacting the aromatic free radical of nitric acid with the lithium metal to form an SEI film to be covered on the surface of the lithium metal; standing to obtain the lithium metal cathode modified by the aromatized nitric acid free radicals.

4. A method for preparing a lithium metal negative electrode modified with the compound of claim 3, wherein:

the mass fraction of the compound solution containing the aromatized nitric acid free radical is 0.1-5%.

5. The method of preparing a lithium metal negative electrode modified with the compound of claim 4, wherein:

the organic solvent is one or more of acetone, tetrahydrofuran, N-dimethylformamide, N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone and methyl salicylate.

6. The method of preparing a lithium metal negative electrode modified with the compound of claim 4, wherein:

the inert gas is one or more of helium, neon and argon.

7. The method of preparing a lithium metal negative electrode modified with the compound of claim 6, wherein:

the thickness of the SEI film is 100 nm-3 mu m.

8. A method for preparing a lithium metal negative electrode modified with the compound of claim 7, wherein:

the standing temperature is 20-100 ℃; the standing time is 1-24 h.

9. An aromatized nitric acid radical modified lithium metal negative electrode, which is characterized by being obtained by the preparation method of any one of claims 3 to 8.

10. The application of the lithium metal cathode modified by the aromatized nitric acid free radicals in assembling a lithium metal battery; the lithium metal battery includes: the positive electrode, the lithium metal negative electrode modified by aromatized nitric acid free radicals, a diaphragm and electrolyte;

the material of the positive electrode is S or LiCoO₂；

The diaphragm is a polyethylene film;

the electrolyte is an ether electrolyte or an ester electrolyte.

Background

Since the commercialization of lithium ion batteries, the existing electrochemical systems have gradually approached the bottleneck through many years of development.

With the arrival of the late lithium ion battery age represented by the long-cruise electric vehicle, the large capacity of the battery has become one of the most important performance indexes, and the traditional lithium ion battery is difficult to be used as a high-energy electrochemical energy storage device.

In many electrochemical energy storage systems, lithium metal based batteries are lightweight (relative atomic mass 6.941g mol)^-1And a density of 0.534g cm^-3) High theoretical specific capacity (3860mAh g^-1) And a lower chemical potential (-3.04V, relative to a standard hydrogen electrode), and thus a higher energy density.

In particular, based on lithium-free positive electrodes (S, air or O)₂) And lithium metal negative electrodes have extremely high theoretical specific capacity and energy density. However, a major problem with lithium metal anodes is the growth of lithium dendrites.

During cycling, sites of lithium ion deposition will exhibit a lower overpotential, and subsequent lithium ions will gradually deposit onto these sites, forming lithium dendrites. And the lithium dendrites continue to grow along with the circulation process, and once the lithium dendrites penetrate through the diaphragm and are directly contacted with the positive electrode, the battery is short-circuited, so that safety accidents are caused.

Meanwhile, the volume expansion in the lithium metal circulation process can cause the breakage of an unstable SEI film, which can cause the side reaction of the lithium metal and the electrolyte, lead to the loss of the lithium metal and the electrolyte, reduce the coulombic efficiency of the battery and improve the interface impedance of the battery.

Both lithium dendrite growth and its low coulombic efficiency have severely affected the commercial application of lithium metal negative electrodes. Therefore, the key to realize the breakthrough of the energy density of the lithium battery is to construct a high-efficiency, stable and safe lithium metal cathode.

Because of this, much work has been done by researchers to ameliorate this type of problem. For example, researchers have developed a layer of Li with high mechanical strength and high ion conductivity on the surface of lithium metal by etching a silicon wafer into a Si film of about 26 μm in KOH solution and pressing it onto a lithium foil_xA Si alloy film. Surface alloyed lithium metal negative electrodes up to 25mA cm^-2Current density of (1) and 100mAh cm^-2Can realize the deposition and the stripping of Li without dendrite (adv. energy mater.2020,10,1902343). Researchers convert Cu₃The Li is constructed by blending N nano particles and styrene butadiene rubber and reacting with metallic lithium₃N/styrene-butadiene rubber composite protective film, wherein Li₃The N component provides excellent ionic conductivity and mechanical strength, and the styrene-butadiene rubber with good flexibility helps to maintain the integrity of the protective film and prevent the stress from generating cracks, so that the current intensity of the lithium metal battery in the ester electrolyte is 1mA cm^-2The cycle can be cycled for 100 circles, and the coulombic efficiency can be stabilized at 97.4% (Advanced Materials,2017,29, 1605531.).

Although the above studies have achieved some success in the protection of lithium metal anodes and provide a completely new concept. However, the preparation method is complicated, and the large-scale application is difficult in the existing stage.

Disclosure of Invention

The invention provides preparation and application of a lithium metal cathode modified based on an aromatized nitric acid free radical, aiming at the problems of potential safety hazard caused by lithium dendrite growth and low coulomb efficiency of the lithium metal cathode.

The invention is realized by the following technical scheme:

a compound with aromatized nitric acid free radical has an effective component structure of aromatized nitric acid free radical structure;

the compound is one of compounds shown in formulas 1-8:

the preparation method of the lithium metal negative electrode modified by the compound comprises the following steps:

dissolving a compound containing an aromatic nitric acid free radical in an organic solvent to obtain a compound solution containing the aromatic nitric acid free radical;

then, under the protection of inert gas, uniformly dripping a compound solution containing aromatic free radical of nitric acid on the surface of lithium metal, and reacting the aromatic free radical of nitric acid with the lithium metal to form an SEI film to be covered on the surface of the lithium metal; standing to obtain the lithium metal cathode modified by the aromatized nitric acid free radicals.

The mass fraction of the compound solution containing the aromatized nitric acid free radical is 0.1-5%.

The organic solvent is one or more of acetone, tetrahydrofuran, N-dimethylformamide, N-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone and methyl salicylate.

The inert gas is one or more of helium, neon and argon.

The thickness of the SEI film is 100 nm-3 mu m.

The standing temperature is 20-100 ℃; the standing time is 1-24 h.

The lithium metal cathode modified by the aromatized nitric acid free radical is obtained by the preparation method.

The application of the lithium metal cathode modified by the aromatized nitric acid free radicals in assembling a lithium metal battery; the lithium metal battery includes: the positive electrode, the lithium metal negative electrode modified by aromatized nitric acid free radicals, a diaphragm and electrolyte;

the material of the positive electrode is S or LiCoO₂(ii) a The diaphragm is a Polyethylene (PE) film; the electrolyte is ether electrolyte or ester electrolyte.

The invention adopts a simple and effective lithium metal surface modification method, and forms an SEI film with uniform structure, strong mechanical strength and high ionic conductivity by the strong electron obtaining capability of aromatized nitric acid free radicals and the reaction with lithium metal. The SEI film benefits from a conjugated twisted structure, so that the SEI film with uniform structure, strong mechanical strength and high ionic conductivity can be formed only by a simple dropping method. The SEI film can promote the rapid transmission of lithium ions to reduce concentration polarization and induce the uniform deposition of the lithium ions, thereby inhibiting the growth of lithium dendrites. Meanwhile, the direct contact between lithium metal and electrolyte can be effectively reduced, the generation of side reaction is reduced, and the coulomb efficiency is effectively improved.

Compared with the prior art, the technical scheme of the invention has the beneficial technical effects that:

(1) the SEI film formed by the simple dropping method has the advantages of uniform structure, strong mechanical strength, high ionic conductivity and other excellent physicochemical properties. The uniform structure, high ionic conductivity and strong mechanical strength are beneficial to the uniform deposition of lithium ions, and the generation and growth of lithium dendrites are effectively inhibited. This effectively improves the safety problem of the lithium metal negative electrode. Meanwhile, the formation of the SEI film effectively isolates lithium metal from electrolyte, reduces the generation of side reactions and obviously improves the coulombic efficiency of the lithium metal cathode. The lithium-sulfur battery with the matched positive electrode shows more excellent cycle performance and electrochemical performance.

(2) The lithium metal surface modification process is completed by only one-step dripping and coating method, and the technical means is simple and easy to implement.

(3) The lithium metal cathode modified by the aromatized nitric acid free radical has the advantages of simple process operation, cheap raw materials, environmental friendliness, easiness in enlarged production, matching with a high-capacity cathode material, capability of meeting the use requirement of a novel high-energy-density power battery and wide application prospect.

Drawings

FIG. 1 is an SEM image of a lithium metal cathode modified with an aromatized nitric acid radical in example 1.

FIG. 2 shows the negative electrode of lithium metal modified with aromatized nitric acid radicals in example 1 at a current density of 5mA/cm²The deposition capacity is 5mAh/cm²SEM images after 100h cycling.

FIG. 3 is a diagram of a Li | Li symmetric battery assembled by the lithium metal cathode modified with aromatized nitric acid radicals and the untreated lithium metal cathode in example 1, wherein the current density of the Li symmetric battery is 5mA/cm²The deposition capacity is 5mAh/cm²SEM image of lithium metal negative electrode after 100h of lower cycle.

FIG. 4 is a schematic diagram of a Li | Cu symmetric battery assembled by the lithium metal cathode modified with the aromatized nitric acid radicals and the untreated lithium metal cathode and copper foil in example 2, wherein the current density of the Li | Cu symmetric battery is 1mA/cm²The deposition capacity is 1mAh/cm²Coulomb efficiency graph below.

Fig. 5 is a cycle performance diagram of a full cell assembled by the lithium metal negative electrode modified by the aromatized nitric acid radical and the untreated lithium metal negative electrode and the S positive electrode in example 2 at a current density of 0.5C.

FIG. 6 is a schematic diagram of a Li | Li symmetric battery assembled by the lithium metal cathode modified with the aromatized nitric acid radical and the untreated lithium metal cathode in example 3, at a current density of 10mA/cm²The deposition capacity is 10mAh/cm²The following charge-discharge curve diagram.

Fig. 7 is a cycle performance diagram of a full cell assembled by the lithium metal cathode modified by the aromatized nitric acid radical and the S cathode in example 4 at a current density of 0.2C.

FIG. 8 is a diagram of a Li | Li symmetric battery assembled by the lithium metal cathode modified by the aromatized nitric acid radicals in example 5, wherein the current density of the battery is 1mA/cm²The deposition capacity is 1mAh/cm²The following charge-discharge curve diagram.

Fig. 9 is a cycle performance diagram of a full cell assembled by the lithium metal cathode modified by the aromatized nitric acid radical and the S-cathode in the embodiment 6 under a large current density of 2C.

FIG. 10 is a diagram of a Li | Li symmetric battery assembled by the lithium metal cathode modified by the aromatized nitric acid radicals in example 7, wherein the current density of the battery is 1mA/cm²The large deposition capacity is 20mAh/cm²The following charge-discharge curve diagram.

FIG. 11 shows the modification of lithium metal negative electrode and LiCoO by aromatized nitric acid radicals in example 8₂And assembling the positive electrode into a cycle performance diagram of the full cell at the current density of 0.5C.

Detailed Description

The present invention will be described in further detail with reference to specific examples.

The experimental procedures in the examples are conventional unless otherwise specified.

Example 1:

under the protection of argon gas, dissolving a compound (1) containing an aromatic nitric acid free radical in dimethyl sulfoxide (DMSO) to prepare a solution with the mass fraction of 0.1%, taking 50 mu L of the solution by using a liquid transfer gun, vertically dropping the solution on the surface of a lithium metal cathode, uniformly coating the solution, standing at room temperature for 12h to obtain the lithium metal cathode modified by the aromatic nitric acid free radical, wherein the thickness of a protective layer is about 100 nm.

The surface of the lithium metal negative electrode modified by the aromatized nitric acid free radicals is flat (see figure 1). The prepared lithium metal cathode takes a mixed solution of 1M lithium bistrifluoromethanesulfonylimide (LiTFSI) dissolved in 1, 3-Dioxolane (DOL)/ethylene glycol dimethyl ether (DME) (volume ratio is 1: 1) as an electrolyte and 2 wt% of LiNO₃As additive, PE is a diaphragm to assemble the Li symmetrical battery with the current density of 5mA/cm²The deposition capacity is 5mAh/cm²Under the condition, the charge-discharge curve is stable, the cycle time can reach 1000h, and the hysteresis voltage is also obviously improved to be about 120mV (see figure 2). By observing the lithium metal negative electrode after 100h of cycle, it can be seen that the surface of the modified lithium metal negative electrode is flat, and many lithium dendrites are generated on the surface of the unmodified lithium metal negative electrode (see fig. 3). The lithium ion battery and an S positive electrode are assembled into a full battery, the specific discharge capacity of the lithium ion battery is still as high as 662mAh/g after 100 cycles under the current density of 1C (1C: 1675mAh/g), and the lithium ion battery shows extremely excellent rate stability.

Example 2:

under the protection of argon gas, dissolving a compound (1) containing an aromatic nitric acid free radical in Tetrahydrofuran (THF) to prepare a solution with the mass fraction of 0.5%, taking 50 mu L of the solution by using a liquid transfer gun, vertically dropping the solution on the surface of a lithium metal cathode, uniformly coating the solution, standing at room temperature for 12 hours to obtain the lithium metal cathode modified by the aromatic nitric acid free radical, wherein the thickness of a protective layer is about 450 nm.

The lithium metal negative electrode prepared by the method uses a mixed solution of 1M LiTFSI dissolved in DOL/DME (volume ratio of 1: 1) as an electrolyte and 2 wt% LiNO₃As an additive, PE is a diaphragm, and the PE and the copper foil are assembled into a Li [ II ] Cu battery, and tests show that the current density is 1mA/cm²The deposition capacity is 1mAh/cm²Under these conditions, the coulombic efficiency remained 94% after 120 cycles (see FIG. 4). The lithium iron phosphate/lithium iron.

Example 3:

under the protection of argon gas, dissolving a compound (1) containing an aromatized nitric acid free radical in N, N-Dimethylformamide (DMF) to prepare a solution with the mass fraction of 1.0%, taking 50 mu L of the solution by using a liquid transfer gun, vertically dropping the solution on the surface of the lithium metal cathode, uniformly coating the solution, standing at room temperature for 12 hours to obtain the lithium metal cathode modified by the aromatized nitric acid free radical, wherein the thickness of a protective layer is about 900 nm.

The lithium metal negative electrode prepared by the method is assembled into a symmetrical battery with the current density of 10mA/cm²The deposition capacity is 10mAh/cm²Under the condition, the charge-discharge curve is stable, the cycle time can reach 600h, and the hysteresis voltage is also greatly improved (see figure 6). The method shows that the lithium metal cathode modified by the aromatized nitric acid free radicals can effectively inhibit the growth of lithium dendrites, and shows excellent electrochemical stability.

Example 4:

under the protection of argon gas, dissolving a compound (1) containing an aromatic nitric acid free radical in N, N-Dimethylacetamide (DMAC) to prepare a solution with the mass fraction of 5.0%, taking 50 mu L of the solution by using a liquid transfer gun, vertically dropping the solution on the surface of a lithium metal cathode, uniformly coating the solution, and standing at 80 ℃ for 3 hours to obtain the lithium metal cathode modified by the aromatic nitric acid free radical, wherein the thickness of a protective layer is 3 mu m.

The lithium metal cathode prepared by the method is matched with an S anode material to be assembled into a full battery, and tests show that after the lithium metal cathode is cycled for 500 circles at 0.2C current density, the discharge specific capacity still reaches 500mAh/g, and the capacity retention rate reaches 62.5% (see figure 7).

Example 5:

under the protection of argon gas, dissolving a compound (1) containing an aromatized nitric acid free radical in NMP, preparing a solution with the mass fraction of 2%, taking 50 mu L of the solution by using a liquid transfer gun, vertically dropping the solution on the surface of the metal lithium cathode, uniformly coating the solution, and standing at 40 ℃ for 10 hours to obtain the lithium metal cathode modified by the aromatized nitric acid free radical, wherein the thickness of a protective layer is 1.5 mu m.

The lithium metal negative electrode prepared by the method uses a mixed solution of 1M LiTFSI dissolved in DOL/DME (volume ratio of 1: 1) as an electrolyte and 2 wt% LiNO₃As an additive, PE is a diaphragm, and the PE and the copper foil are assembled into a Li [ II ] Cu battery, and tests show that the current density is 2mA/cm²The deposition capacity is 2mAh/cm²Under the condition, the coulomb efficiency of the product is still 80 percent after 50 cycles. The lithium metal negative electrode prepared by the method is assembled into a Li symmetrical battery with the current density of 1mA/cm²The deposition capacity is 1mAh/cm²Under the condition, the charging and discharging curve is stable, the cycle time can reach 2000h, the hysteresis voltage is also obviously improved, about 40mV shows excellent stability (see figure 8).

Example 6:

under the protection of neon gas, dissolving a compound (1) containing aromatic nitric acid free radicals in DMF to prepare a solution with the mass fraction of 0.25%, taking 50 mu L of the solution by using a liquid transfer gun, vertically dropping the solution on the surface of the lithium metal cathode, uniformly coating the solution, and standing at 60 ℃ for 6 hours to obtain the self-healing polymer modified lithium metal cathode, wherein the thickness of a protective layer is 200 nm.

The lithium metal cathode prepared by the method is matched with an S cathode material to be assembled into a full battery, and tests show that after the lithium metal cathode is cycled for 100 circles under 2C high current density, the discharge specific capacity of the lithium metal cathode still has 450mAh/g, and the capacity retention rate is 83.3% (see figure 9).

Example 7:

under the protection of argon gas, dissolving a compound (2) containing an aromatized nitric acid free radical in DMSO to prepare a solution with the mass fraction of 0.2%, taking 50 mu L of the solution by using a pipette, vertically dropping the solution on the surface of the lithium metal cathode, uniformly coating the solution, and standing at room temperature for 12 hours to obtain the lithium metal cathode modified by the aromatized nitric acid free radical, wherein the thickness of a protective layer is about 200 nm.

The prepared lithium metal cathode takes a mixed solution of 1M LiTFSI dissolved in DOL/DME (volume ratio of 1: 1) as an electrolyte and 2 wt% LiNO₃As additive, PE is a diaphragm to assemble the Li symmetrical battery with the current density of 1mA/cm²The large deposition capacity is 20mAh/cm²Under the condition, the charge-discharge curve is stable, the cycle time can reach 450h, the hysteresis voltage is also obviously improved, and the excellent cycle performance is shown (see figure 10).

Example 8:

under the protection of helium gas, dissolving a compound (2) containing an aromatized nitric acid free radical in THF to prepare a solution with the mass fraction of 0.5%, taking 50 mu L of the solution by using a liquid-transferring gun, vertically dropping the solution on the surface of the lithium metal cathode, uniformly coating the solution, and standing at room temperature for 12 hours to obtain the lithium metal cathode modified by the aromatized nitric acid free radical, wherein the thickness of a protective layer is about 500 nm.

The obtained lithium metal negative electrode was treated with 1M lithium hexafluorophosphate (LiPF)₆) Dissolved in Ethylene Carbonate (EC)/diethyl carbonate (DEC) (volume ratio 1: 1) the mixed solution of (A) and (B) is an electrolyte, PE is a diaphragm, and LiCoO with high surface capacity₂Cathode material (19 mg/cm)²) Matched to assemble a full cell, and tested to find stable cycling at 1C current density for 60 cycles (see fig. 11).

As described above, the present invention can be preferably realized.

The SEI film formed on the surface of the lithium metal is very uniform, so that the side reaction between the electrolyte and the lithium metal interface is obviously reduced; meanwhile, the SEI film has high ionic conductivity and mechanical strength, so that the growth of lithium dendrites can be effectively inhibited, and the lithium metal negative electrode has safe and stable long-cycle performance. The preparation method is simple, is suitable for large-scale production, is matched with a high-capacity anode material, can meet the use requirement of a novel high-energy-density power battery, and has wide application prospect.

The embodiments of the present invention are not limited to the above-described embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and they are included in the scope of the present invention.