CN109888193B

CN109888193B - Method for improving electrodeposition and dissolution reversibility of sodium metal negative electrode

Info

Publication number: CN109888193B
Application number: CN201910031215.2A
Authority: CN
Inventors: 毛秉伟; 唐帅; 颜佳伟; 董全峰; 郑明森
Original assignee: Xiamen University
Current assignee: Xiamen University
Priority date: 2019-01-14
Filing date: 2019-01-14
Publication date: 2021-02-19
Anticipated expiration: 2039-01-14
Also published as: CN109888193A

Abstract

The invention discloses a method for improving sodium metal negativeA method of electro-deposition and dissolution reversibility comprising the steps of: (1) loading nano particles or micro particles of metal M capable of generating alloy with sodium on the surface of a current collector made of metal N material not generating alloy with Na to prepare a pole piece; (2) the pole piece is taken as a working electrode, a Na piece is taken as a counter electrode and a reference electrode, the battery is assembled by matching with electrolyte and a diaphragm, the dissolution cut-off potential of Na is controlled to be lower than the dealloying initial potential of Na in Na-metal M alloy, and the dissolution cut-off potential is controlled to be 2mAcm^‑2The current density of (a) is subjected to electrochemical deposition and dissolution cycles. The invention can realize that the sodium metal is at 2mAcm by constructing a current collector capable of alloying with sodium^‑2Under the current of (1), the circulation is efficiently and stably performed for 1700-2000 circles, the average coulombic efficiency is 99.9%, the commercial application of the sodium metal battery can be promoted, and a cheap and high-capacity cathode is provided for energy storage systems of mobile electronic equipment, electric automobiles and the like.

Description

Method for improving electrodeposition and dissolution reversibility of sodium metal negative electrode

Technical Field

The invention belongs to the technical field of energy storage, and particularly relates to a method for improving electrodeposition and dissolution reversibility of a sodium metal cathode.

Background

The energy storage technology with high specific capacity and low cost has great significance for meeting the development of electric vehicles and smart power grids. The sodium metal cathode is an important choice in the design of the next generation of batteries due to the advantages of high theoretical capacity, abundant crustal storage, low price and the like. However, the reversibility of the cycle is poor due to dendritic growth of Na metal during deposition and high chemical reactivity of Na metal to the electrolyte, which severely hampers its application. Studies on room temperature sodium metal anodes have been relatively rare and have been concentrated in the last two or three years.

Methods for improving the electrodeposition and dissolution reversibility of the sodium metal negative electrode can be classified into the following aspects:

1) selection of electrolyte: when using 1M NaPF₆When the sodium metal is dissolved in an ether solvent as an electrolyte, the sodium metal can be efficiently deposited and dissolved out on the Cu foil; when high-concentration NaFSI is dissolved in DME as electrolyte, high-efficiency deposition and dissolution of Na metal on the Cu foil can be realized.

2) Improvement of solid electrolyte membrane: an ultrathin inert protective layer with good mechanical properties is formed on the surface of the sodium metal by a physical or chemical method to serve as an artificial SEI film, so that the cycling stability of the sodium metal cathode can be improved; additives such as Na₂S₆0.01M KTFSI was also reported to improve Na metal cycling stability.

3) Designing a current collector: such as porous aluminum, porous copper arrays, different types of carbon materials and the like, can reduce the real current density of Na deposition, provide partial space for Na deposition and reduce the generation of Na dendrites. In addition, elements such as N, S, O and the like are doped in the carbon material, so that sodium-philic sites can be provided, the nucleation barrier of Na deposition is reduced, and the uniformity of Na deposition is improved. The ultra-thin Au layer is sputtered on the Cu foil before the group of subjects, so that the sodium nucleation barrier can be reduced, and the sodium deposition and dissolution efficiency can be improved in a shorter time.

However, the methods in the prior art have relatively limited improvement on the reversibility of the sodium metal negative electrode, and can be circulated more efficiently in a short time under a small current.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a method for improving the electrodeposition and dissolution reversibility of a sodium metal negative electrode.

The specific principle of the invention is as follows:

na is on electrodes such as Sn and Sb, and a Na-M (Sn, Sb) alloy layer is formed through an alloying reaction before Na deposition occurs. The alloy layer has good sodium affinity, the alloy sodium affinity layer has larger binding force with sodium, the nucleation overpotential of sodium deposition can be reduced, the morphology of sodium deposition is further improved, the sodium deposition and dissolution efficiency is improved, and the Na-M alloy substrate becomes a sodium affinity substrate. Further research has found that a problem limiting the deposition and dissolution cycle life of sodium on such sodium-philic substrates is the repeated alloying and dealloying reactions during the cycle causing the alloy layer to powderize off the current collector. Therefore, by controlling the dissolution potential of sodium, the sodium-philic substrate is stabilized from the second cycle without undergoing alloying and dealloying processes, and the service life of the sodium-philic substrate can be significantly improved.

The technical scheme of the invention is as follows:

a method for improving the electro-deposition and dissolution reversibility of a sodium metal cathode comprises the following steps:

(1) loading nano particles or micro particles of metal M capable of generating alloy with sodium on the surface of a current collector made of metal N material not generating alloy with Na to prepare a pole piece;

(2) the pole piece is taken as a working electrode, a Na piece is taken as a counter electrode and a reference electrode, the battery is assembled by matching with electrolyte and a diaphragm, the dissolution cut-off potential of Na is controlled to be lower than the dealloying initial potential of Na in Na-metal M alloy, and the dissolution cut-off potential is controlled to be 2mAcm^-2The current density of the electrode plate is subjected to electrochemical deposition and dissolution circulation, in the process, before Na deposition, Na firstly forms a Na-metal M alloy layer through alloying reaction only in the first circulation, and the subsequent circulation does not generate alloying and dealloying processes, so that the electrode plate is stabilized, and finally the cycle life of Na deposition dissolution reaches 1700-2000 circles.

In a preferred embodiment of the present invention, the metal M includes Sn and Sb.

More preferably, the elution cut potential of Na is less than 0.15V.

In a preferred embodiment of the present invention, the metal N includes Cu, a1 and Ni.

In a preferred embodiment of the present invention, the metal M is supported on the surface of the current collector by a binder.

Further preferably, the mass ratio of the metal M to the binder is 90-100: 5-10.

Further preferably, the binder is sodium carboxymethyl cellulose.

In a preferred embodiment of the invention, the electrolyte is 1M NaOTf-diglyme-0.01M NaTFSI.

In a preferred embodiment of the invention, the separator is of the type Celgard 2400.

The invention has the beneficial effects that: the invention can realize that the sodium metal is at 2mAcm by constructing a current collector capable of alloying with sodium^-2Under the current of (1), the circulation is efficiently and stably performed for 1700-2000 circles, the average coulombic efficiency is 99.9%, the commercial application of the sodium metal battery can be promoted, and a cheap and high-capacity cathode is provided for energy storage systems of mobile electronic equipment, electric automobiles and the like.

Drawings

Fig. 1 is a photograph of a current collector fabricated in example 1 of the present invention: optical photographs of the physically sputtered Sn and Sb are a and b, respectively, and scanning electron micrographs are c and d, respectively; optical images of SnNPs and Sb MPs fixed to the Cu foil with a binder are e and f, respectively, and scanning electron micrographs are g and h, respectively.

FIG. 2: is a Cyclic Voltammogram (CV) of the current collector manufactured in example 1 of the present invention: the cyclic voltammograms of Sn and Sb are respectively as indicated by the symbols in the figure.

Fig. 3 is a graph of the cycle efficiency under the control of the method in example 1 of the present invention, where a is the cycle efficiency of Na deposition dissolution on the two current collectors of Sn film and Sn NPs that are physically sputtered, and b is the cycle efficiency of Na deposition dissolution on the two current collectors of Sb film and Sb MPs that are physically sputtered under the control of the method in example 1 of the present invention.

Detailed Description

The technical solution of the present invention will be further illustrated and described below with reference to the accompanying drawings by means of specific embodiments.

Example 1

Sn with the thickness of 50nm is sputtered on copper foil by a magnetron sputtering method to form a pole piece, as shown in figure 1, on an optical photo, the surface of the pole piece can be seen to be blue, and a thin layer can also be seen from a scanning electron microscope. The electrode plate is used as a working electrode, and a sodium plate is used as a counter electrode and a reference electrode to assemble the CR2032 type button cell. The electrolyte is 1MNaOTf-diglyme-0.01M NaTFSI, and the diaphragm is Celgard 2400 type.

When the button cell is used for cyclic voltammetry experiments, as seen from a cyclic voltammogram shown in fig. 2, Na not only has sodium deposition and dissolution reaction on Sn and Sb electrodes, but also has alloying and dealloying processes. The dealloying onset potentials of Na on Sn and Sb were 0.15 and 0.60V, respectively.

At a distance of 2mAcm^-2The electrochemical deposition and dissolution cycle are carried out, two dissolution cut-off potentials of 0.10 and 1.00V are set, and as can be seen from figure 3a, the stable cycle can be only carried out for 800 circles when the dissolution potential of sodium is controlled to 1.00V, and the stable cycle can be 600 circles when the dissolution potential is controlled to 0.10V. This is mainly because, when the stripping potential is set to 1.00V, not only the deposition and stripping reaction of sodium but also the sodium alloy and dealloying reaction occur per cycle, and the repeated alloying/dealloying process causes the Sn layer to fall off from the Cu foil surface; when the dissolution cut-off potential is set to be 0.10V, the potential is lower than the initial potential of 0.12V of sodium which is removed from Na-Sn, so that the alloying process is only generated in the first cycle, and the alloying and dealloying processes are not generated in the subsequent cycles, thereby stabilizing the pole piece.

Further, the physically sputtered Sn layer is replaced with Sn Nanoparticles (NPs), and the Sn NPs are fixed in the form of a binder. It was found that at a dissolution potential of 0.10V, the cycle life of sodium deposition dissolution could be further extended to 2000 cycles.

The electrode sheet is specifically prepared by mixing commercial Sn NPs or Sb (micro-meters, MPs) and carboxymethyl cellulose sodium (CMC) as binder at a mass ratio of 92: 8, stirring for 6h, coating the prepared slurry on the surface of copper foil (Cu), and vacuum drying at 120 deg.C for 12 h. The loading capacity of SnNPs or Sb MPs is 0.5mgcm^-2As shown in FIGS. 1e and g, the prepared pole piece has a uniform dark black layer on the surface of the copper foil when viewed on an optical photo, and obvious nanoparticles with the diameter of about 150am can be seen on a scanning electron microscope.

Similarly, the same comparison was made with inexpensive Sb. As shown in fig. 3b, it was found that Na could be deposited for 200 dissolution cycles at a 1.00V cut-off on sputtered Sb films; and when the cut-off potential is controlled to be 0.10V, Na can be stably deposited and dissolved for 800 circles. When commercial Sb Micro Particles (MPs) were used instead of physically sputtered Sb, Na was stable deposited at 0.10V cutoff voltage for 1700 cycles.

The above description is only a preferred embodiment of the present invention, and therefore should not be taken as limiting the scope of the invention, which is defined by the appended claims.

Claims

1. A method for improving the electro-deposition and dissolution reversibility of a sodium metal cathode is characterized by comprising the following steps:

(1) loading nano particles or micro particles of metal M capable of generating alloy with sodium on the surface of a current collector made of metal N material not generating alloy with Na to prepare a pole piece; the metal M is Sn or Sb, the metal N is Cu, Al or Ni, and the dissolution cut-off potential of Na is lower than 0.1V;

2. The method of claim 1, wherein: the metal M is loaded on the surface of the current collector through a binder.

3. The method of claim 2, wherein: the mass ratio of the metal M to the binder is 90-100: 5-10.

4. A method according to claim 2 or 3, characterized by: the binder is sodium carboxymethyl cellulose.

5. The method of claim 1, wherein: the electrolyte is 1M NaOTf-diglyme-0.01M NaTFSI.

6. The method of claim 1, wherein: the diaphragm is of the type Celgard 2400.