CN109037626B - Alkali metal-based negative electrode and preparation method and application thereof - Google Patents

Abstract

The invention discloses an alkali metal-based negative electrode and a preparation method and application thereof. According to the invention, the carbon fluoride material is introduced into the alkali metal, the fluoride of the alkali metal can be formed in situ in the charging and discharging processes, the fluoride and the carbon material form a synergistic effect, and a uniform electric field is formed in the charging and discharging processes, so that the uniform deposition of the alkali metal is promoted, the formation of alkali metal dendrites and the interface reaction of the alkali metal and an electrolyte are effectively inhibited, and the safety performance and the cycling stability of the alkali metal battery are improved.

Description

A kind of alkali metal base negative electrode and its preparation method and application

technical field

The invention relates to the technical field of energy storage batteries, in particular to an alkali metal-based negative electrode and a preparation method and application thereof.

Background technique

Although lithium-ion batteries still occupy a dominant position in secondary batteries, as new energy vehicles require higher and higher energy density of lithium-ion batteries, the energy density of traditional lithium-ion batteries based on intercalation reactions has reached the limit, namely The energy density of lithium-ion batteries with graphite as the negative electrode is close to the bottleneck value, and it is imperative to develop lithium batteries (including lithium-sulfur batteries and lithium-air batteries) with metal lithium as the negative electrode. On the other hand, with the development of new energy vehicles, the consumption of lithium resources is rapid, but the reserves of lithium on the earth are very limited. In contrast, the reserves of sodium and potassium are relatively abundant, which can meet the large-scale use. Therefore, developing novel sodium- and potassium-based batteries has become a current research hotspot.

However, a fatal problem of batteries using alkali metals directly as negative electrodes is that alkali metals will form lithium dendrites during charge-discharge cycles, causing battery safety issues. In addition, the compatibility of alkali metals with liquid electrolytes and some solid electrolytes is poor, and long-term cycling will lead to corrosion of alkali metals or the formation of interface passivation layers, thereby reducing the cycle life of batteries. Therefore, in order to improve the safety and life of the alkali metal battery, the alkali metal must be protected.

Previous studies have focused on the protection of alkali metals by carbon materials and fluorides. For example, the Chinese patent document with publication number CN 108063218A discloses a method for preparing a thin-layer metal lithium-based negative electrode. The negative electrode has a copper foil current collector as the substrate. , using chemical vapor deposition method to synthesize a single-layer graphene film on the surface of the copper foil current collector, the graphene supported by this copper foil is used as the negative electrode, and the lithium-rich material or lithium salt is used as the positive electrode to form a lithium battery, and then a current is applied to make the lithium-rich battery Lithium in the material or lithium salt is deposited in the graphene supported by copper foil to obtain a metal lithium/graphene composite negative electrode. Although a relatively uniform composite negative electrode can be obtained by this method, it is suitable for relatively thin electrodes, but when the electrode is thicker It is easy to cause uneven distribution of lithium in graphene. In addition, although carbon materials have a good effect on inhibiting lithium dendrites, they have a weak effect on protecting the electrode and inhibiting the reaction with the electrolyte.

Another example is the Chinese patent document whose authorized publication number is CN 207441857U, which discloses a metal lithium/artificial inorganic salt composite electrode, which is obtained after depositing an inorganic substance on the metal lithium surface by a magnetron sputtering method, and the inorganic substance such as Lithium fluoride, lithium bromide, lithium chloride, etc. Although this method can obtain a relatively uniform surface coating, it is also only suitable for thin electrodes, and it is not easy to achieve large-scale preparation. In addition, due to the low conductivity of inorganic materials, The introduction of pure inorganic compounds will cause the decrease of electrode conductivity.

SUMMARY OF THE INVENTION

The invention discloses a novel alkali metal base negative electrode, which can effectively inhibit the formation of alkali metal dendrites and the interface reaction between the alkali metal and the electrolyte, and improve the safety performance and cycle stability of the alkali metal battery.

The specific technical solutions are as follows:

An alkali metal-based negative electrode includes alkali metal and carbon fluoride material uniformly distributed in the alkali metal.

In the present invention, the carbon fluoride material is introduced into the alkali metal for the first time, and the fluoride of the alkali metal can be formed in situ during the charging and discharging process. The formation of a synergistic effect between carbon materials and carbon materials can form a uniform electric field during the charging and discharging process, thereby promoting the uniform deposition of alkali metals, effectively suppressing the formation of alkali metal dendrites, and improving the safety of alkali metal batteries; on the other hand, the in-situ formation of Fluoride and carbon materials will effectively protect alkali metals, inhibit the reaction of alkali metals with organic electrolytes or solid electrolytes, and improve the interfacial stability of alkali metals and electrolytes, thereby improving the cycle life of batteries; The conductivity of the composite negative electrode, thereby reducing the polarization of the electrode.

The so-called polarization refers to the absolute value of the deviation from the origin when the electrode is charged or discharged.

It has been found through experiments that when the technical solution of directly adding fluoride and carbon material is adopted, it is difficult to achieve uniform dispersion of fluoride in the carbon material, and it is even more difficult to achieve the bonding effect of the two, so the synergistic effect of the two cannot be achieved to suppress. The formation and protection of alkali metal dendrites, local enrichment of fluorides with low conductivity will also lead to an increase in electrode polarization, resulting in high electrode polarization and short cycle life.

The alkali metal is selected from at least one of lithium, sodium and potassium;

The fluorinated carbon material is selected from at least one of fluorinated carbon nanotubes, fluorinated carbon fibers, fluorinated graphene, fluorinated hard carbon, fluorinated soft carbon, fluorinated fullerene, and fluorinated graphite.

Preferably, in the alkali metal-based negative electrode, the weight ratio of the carbon fluoride material to the alkali metal is 1-20:100. In the alkali metal-based negative electrode, reasonable content of alkali metal and carbon fluoride is beneficial to fully protect the alkali metal without affecting the capacity and reversibility of the alkali metal negative electrode. Further preferably, the weight ratio of the carbon fluoride material to the alkali metal is 2.5-10:100. In the alkali metal-based negative electrode, an excessively low fluorine content is not conducive to effective protection of the alkali metal. Due to the low conductivity of carbon fluoride, an excessively high fluorine content will reduce the conductivity of the composite negative electrode, thereby reducing the negative electrode's conductivity. Rate performance and capacity. Preferably, in the carbon fluoride material, the fluorine content is 5-65%. Based on the current commercialization of fluorocarbon materials, commercially available fluorocarbon materials with a fluorine content of 50% are directly selected. At this time, the fluorine content can also be adjusted by adjusting the proportion of fluorocarbon materials to the total weight of the raw materials.

Preferably, the carbon fluoride material is in powder form with a size of 10 nm˜50 μm. It is further preferably a nano-scale material with a size of 10 nm to 500 nm. The so-called nano-size, as long as the size of at least one direction in the three-dimensional direction is nano-scale; the particle size is too small and easy to agglomerate, and the particle size is too large. It is evenly dispersed in the medium, and the binding force with alkali metals becomes weak.

Preferably, the fluorinated carbon material is selected from fluorinated carbon nanotubes, fluorinated carbon fibers or fluorinated graphene.

Further preferred:

The fluorinated carbon material is selected from fluorinated carbon nanotubes;

The weight ratio of the fluorinated carbon material to the alkali metal is 2.5 to 5:100; the diameter of the fluorinated carbon nanotube is 30 to 60 nm, and the length is 500 nm to 2 μm. According to the weight ratio, the fluorine in the fluorinated carbon nanotube The content is 50%.

It has been found through experiments that the lowest polarization value of the battery assembled with the alkali metal-based negative electrode prepared from the above-mentioned further optimized raw materials is only 22 mV.

The invention also discloses a preparation method of the alkali metal-based negative electrode, which is prepared by using industrialized carbon fluoride material as a raw material by a simple mechanical mixing method, and the specific steps are as follows:

1) Under the protection of inert atmosphere, knead the alkali metal into flakes;

2) Evenly loading the carbon fluoride powder on the surface of the alkali metal, applying pressure to make it adhere to the alkali metal, and then repeatedly folding and kneading to obtain the alkali metal-based negative electrode.

In step 1), the inert atmosphere is argon, nitrogen or helium, preferably argon is the preparation atmosphere.

In step 2), the pressure applied is not particularly specified, so that the carbon fluoride powder adheres to the alkali metal and does not fall off.

In step 3), the number of times of repeated folding and kneading is not particularly specified, and it is advisable that the carbon fluoride powder is uniformly dispersed in the alkali metal. The so-called uniformity does not have a strict judgment standard. prevail.

The invention also discloses the application of the alkali metal base negative electrode in alkali metal batteries, alkali metal-sulfur batteries and alkali metal-air batteries.

Compared with the prior art, the present invention has the following advantages:

1. The alkali metal-based negative electrode of the present invention uses alkali metal and carbon fluoride material as raw materials, and introduces the carbon fluoride material into the alkali metal through a simple mechanical mixing method, and can form the alkali metal in situ during the charging and discharging process. Fluoride, the fluoride and the carbon material form a synergistic effect to form a uniform electric field during the charging and discharging process, thereby promoting the uniform deposition of alkali metal, effectively inhibiting the formation of alkali metal dendrites and the interface reaction between alkali metal and electrolyte, and improving alkali metal. The safety performance and cycling stability of metal batteries, meanwhile, the in-situ formed carbon materials can improve the electrical conductivity and reduce the polarization of the electrodes.

2. The preparation process of the alkali metal-based negative electrode in the present invention adopts cheap raw materials, the process is simple, the energy consumption is low, the cost is small, and the cycle is short, which is favorable for large-scale production.

Description of drawings

Fig. 1 is the X-ray diffraction (XRD) pattern of the lithium/fluorinated carbon nanotube composite negative electrode prepared in Example 1;

2 is a scanning electron microscope (SEM) photo of the lithium/fluorinated carbon nanotube composite negative electrode prepared in Example 1;

Fig. 3 is the charge-discharge curve of the symmetrical battery assembled with the lithium/fluorinated carbon nanotube composite negative electrode prepared in Example 1;

Fig. 4 is the F1s X-ray photoelectron spectroscopy (XPS) of the lithium/fluorinated carbon nanotube composite negative electrode prepared in Example 1 after charging and discharging;

FIG. 5 is a charge-discharge curve of a symmetrical battery assembled with the lithium negative electrode prepared in Comparative Example 1. FIG.

Detailed ways

The present invention will be described in further detail below with reference to the accompanying drawings and embodiments. It should be noted that the following embodiments are intended to facilitate the understanding of the present invention, but do not have any limiting effect on it.

Example 1

Under the protection of argon atmosphere, the metal lithium is kneaded into flakes; the fluorinated carbon nanotube powder is evenly loaded on the metal lithium surface, and pressure is applied to make the fluorinated carbon nanotube powder adhere to the metal lithium surface. The weight ratio of fluorinated carbon nanotubes to metal lithium is 2.5%, the fluorine content of fluorinated carbon nanotubes is 50wt%, the diameter of fluorinated carbon nanotubes is 30-60nm, and the length is 500nm-2μm; the surface is loaded with fluorinated nanotubes. Alkali metal folding and kneading of the carbon tube powder, and repeated folding and kneading to obtain a metal lithium/fluorinated carbon nanotube composite negative electrode.

Fig. 1 shows the XRD pattern of the composite negative electrode prepared in the present embodiment. It can be seen from the pattern that the diffraction peak is a lithium peak, and the fluorinated carbon nanotubes do not have a diffraction peak in the figure due to their low content and low crystallinity.

FIG. 2 is an SEM photograph of the composite negative electrode prepared in this example. From the photograph, it can be seen that the fluorinated carbon nanotubes are relatively uniformly dispersed in metal lithium.

3 is the charge-discharge curve of the symmetrical battery assembled with the composite negative electrode prepared in this example (using LiClO ₄ triethylene glycol dimethyl ether (TEGDME) solution as electrolyte, Celgard C480 membrane as separator). When the current density is 0.5mA/cm ² and the capacity is 1mAh/cm ² , it can be seen from the figure that after 200 hours, the polarization of the symmetrical battery is only 22 mV. When the current density is 5mA/cm ² , the capacity is 1mAh/cm ^2. After 200 hours, the polarization of the symmetrical cell is 99 mV, and after 400 hours, the polarization of the symmetrical cell is 188 mV.

FIG. 4 shows the F1s XPS spectrum of the composite negative electrode prepared in this example after charge and discharge. It can be seen from the spectrum that LiF is formed.

Comparative Example 1

The preparation of the electrode and the assembly of the battery are as in Example 1, except that no fluorinated carbon nanotubes are added to the metal lithium. The electrochemical test shows that under the same test conditions (current density 0.5mA/cm ² , capacity At 1mAh/ ^cm2 , after 200 hours), the polarization is 34mV, see Figure 5.

Comparative Example 2

The preparation of the electrode and the assembly of the battery are as in Example 1, the difference is that the ordinary carbon nanotubes of the same weight are added in the metallic lithium instead of the fluorinated carbon nanotubes. The electrochemical test shows that under the same test conditions ( When the current density is 0.5 mA/cm ² and the capacity is 1 mAh/cm ² , after 200 hours), the polarization is 28 mV.

Comparative Example 3

The preparation of the electrode and the assembly of the battery are as in Example 1, the difference is that lithium fluoride and carbon nanotubes are added to the lithium metal, and the molar amount of fluorine in the carbon nanotubes and lithium fluoride is the same as the fluorinated nanocarbon in the example. The molar amounts of carbon and fluorine in the tube are the same. Electrochemical tests showed that under the same test conditions (current density 0.5 mA/cm ² , capacity 1 mAh/cm ² over 200 hours), the polarization was 32 mV.

Example 2

The preparation of the electrode of the electrode and the assembly of the battery are as in Example 1, the difference is that the fluorinated carbon nanotubes are replaced with fluorinated graphite with the same addition amount and the same fluorine content. The electrochemical test shows that under the same test conditions down (200 hours elapsed at a current density of 0.5 mA/cm ² and a capacity of 1 mAh/cm ² ), the polarization was 30 mV.

Example 3

Under the protection of argon atmosphere, the metal sodium is kneaded into flakes; the fluorinated graphene powder is evenly loaded on the metal sodium surface, and pressure is applied to make the fluorinated graphene powder adhere to the metal sodium surface. The weight ratio of metal sodium is 5%, and the fluorine content of fluorinated graphene is 50 wt%; the metal sodium with fluorinated graphene powder loaded on the surface is folded and pressed, and then repeatedly folded and pressed to obtain metal sodium/fluoride Graphene composite anode. The product is characterized as metallic sodium by XRD, and the fluorinated graphene has no diffraction peaks in the figure due to its low content and low crystallinity. The product was characterized by SEM, and the fluorinated graphene was relatively uniformly dispersed in metal sodium. Electrochemical tests show that (at a current density of 0.5 mA/cm ² and a capacity of 1 mAh/cm ² , after 200 hours), the polarization of the symmetric cell with Na metal/graphene fluoride as electrodes is only 25 mV.

Example 4

Under the protection of argon atmosphere, the potassium metal is kneaded into flakes; the carbon fluoride fiber powder is evenly loaded on the surface of the metal potassium, and pressure is applied to make the carbon fluoride fiber powder adhere to the surface of the metal potassium, and the weight of the carbon fluoride fiber is equal to that of the metal potassium. The weight ratio is 10%, and the fluorine content of the carbon fluoride fiber is 50 wt%; the potassium metal with the carbon fluoride fiber powder loaded on the surface is folded and pressed, and then repeatedly folded and pressed to obtain the metal potassium/carbon fluoride fiber composite negative electrode. The product is characterized as potassium metal by XRD, and there is no diffraction peak in the figure due to the low content and low crystallinity of carbon fluoride fibers. The product was characterized by SEM, and the carbon fluoride fibers were relatively uniformly dispersed in potassium metal. Electrochemical tests show that (when the current density is 0.5 mA/cm ² and the capacity is 1 mAh/cm ² , after 200 hours, the polarization of the symmetrical battery with potassium metal/carbon fluoride fiber as the electrode is only 32 mV.

Claims (4)

1. an alkali metal base negative electrode for secondary battery, it is characterized in that, comprise alkali metal, and the carbon fluoride material that is evenly distributed in alkali metal; The fluorinated carbon material is a fluorinated carbon nanotube; The weight ratio of the fluorinated carbon material to the alkali metal is 2.5 to 5:100; the diameter of the fluorinated carbon nanotube is 30 to 60 nm, and the length is 500 nm to 2 μm. According to the weight ratio, the fluorine in the fluorinated carbon nanotube The content is 50%; The preparation method of described alkali metal base negative electrode, the steps are as follows: 1) Under the protection of inert atmosphere, knead the alkali metal into flakes; 2) The fluorinated carbon nanotube powder is evenly loaded on the surface of the alkali metal, and pressure is applied to make it adhere to the alkali metal, and then the alkali metal-based negative electrode is obtained after repeated folding and kneading. 2. alkali metal base negative electrode according to claim 1, is characterized in that: The alkali metal is selected from at least one of lithium, sodium and potassium. 3 . The alkali metal-based negative electrode according to claim 1 , wherein the inert atmosphere is selected from argon, nitrogen or helium. 4 . 4. An application of the alkali metal-based negative electrode according to claim 1 or 2 in an alkali metal battery, an alkali metal-sulfur battery, and an alkali metal-air battery.

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