CN109768259B

CN109768259B - Iron-doped germanium dioxide with hierarchical structure

Info

Publication number: CN109768259B
Application number: CN201910062463.3A
Authority: CN
Inventors: 魏明灯; 武俊秀
Original assignee: Fuzhou University
Current assignee: Fuzhou University
Priority date: 2019-01-23
Filing date: 2019-01-23
Publication date: 2021-04-27
Anticipated expiration: 2039-01-23
Also published as: CN109768259A

Abstract

The invention discloses iron-doped germanium dioxide with a hierarchical structure, which is prepared by mixing GeO₂And FeCl₃·6H₂And adding a mixed solution consisting of ethanolamine and ethanol in proportion, adjusting the pH value by using 2-methylpiperazine, performing simple solvothermal reaction, drying and annealing to obtain the iron-doped germanium dioxide with the hierarchical structure. The obtained material has good electrochemical stability and higher specific capacity, and can be used for preparing lithium ion batteries.

Description

Iron-doped germanium dioxide with hierarchical structure

Technical Field

The invention belongs to the technical field of lithium ion battery materials, and particularly relates to iron-doped germanium dioxide with a hierarchical structure.

Background

Germanium-based materials have received much attention because of their higher theoretical capacity and higher conductivity than silicon of the same main group. However, the material has large volume expansion in the process of lithium intercalation and deintercalation, so that the active material is easy to fall off seriously on a pole piece, the cycle stability is reduced sharply, and the application of the material is also limited greatly. Germanium dioxide, as a transition type germanium-based negative electrode material, has been widely noted because of its high theoretical capacity, but since its transition reaction with lithium ions is considered irreversible, the rate of capacity fade is significantly accelerated. According to the invention, the electrochemical performance of germanium dioxide can be greatly improved by doping iron, but a method for synthesizing germanium dioxide with a hierarchical structure by adopting a doping method is not available at present, and the germanium dioxide has excellent lithium storage performance when being applied to a lithium ion battery, so that the preparation of the iron-doped germanium dioxide has important research significance.

Disclosure of Invention

In order to improve the phenomenon, the invention provides iron-doped germanium dioxide with a hierarchical structure for the first time, the in-situ doping of transition metal iron in a germanium dioxide matrix is realized by a simple solvothermal method, and the iron salt is used as a structure guiding agent to enable the germanium dioxide to be self-assembled into the hierarchical structure after being dissolved, so that the germanium dioxide has good electrochemical stability and higher specific capacity, and is suitable for preparing a lithium ion battery.

In order to achieve the purpose, the invention adopts the following technical scheme:

the preparation method of the iron-doped germanium dioxide with the hierarchical structure comprises the following steps:

1) adding GeO₂And FeCl₃·6H₂Adding O into a mixed solution of ethanolamine and ethanol (the volume ratio of the ethanolamine to the ethanol is 1: 2) according to a molar ratio of 10:1, and adding 2-methylpiperazine to adjust the pH value of the solution>7；

2) Placing the mixture obtained in the step 1) in a polytetrafluoroethylene reaction lining, reacting for 24 hours in an oven at 180 ℃, and then cooling to room temperature;

3) washing the obtained product with deionized water for several times, and drying in an oven at 70 ℃ for 12 hours to obtain Fe-GeO₂The yellow powder of (4);

4) and annealing the obtained yellow powder for 1 hour at the temperature of 550-650 ℃ in an argon environment to obtain the iron-doped hierarchical structure germanium dioxide.

The obtained iron-doped germanium dioxide with the hierarchical structure can be used for preparing a lithium ion battery.

The invention has the following remarkable advantages:

according to the invention, the properties of the germanium-based material are improved by doping iron for the first time, wherein iron salt is used as a structure directing agent, so that a germanium dioxide main body becomes a graded nano sheet and self-assembles into a micro-flower structure to improve the electrochemical stability of the material and buffer the volume expansion of the germanium dioxide in a graded manner, and iron atoms can be simultaneously used as a doping agent after calcination and doped with GeO₂The lattice is distorted inside the lattice, so that lattice defects are caused, more lithium insertion sites are added, and the specific capacity of the material is improved. And 2-methylpiperazine can also introduce many active sites while increasing conductivity, so as to increase lithium insertion sites and further improve the specific capacity of the material.

Electrochemical research results show that the capacity of the lithium ion battery prepared by adopting the iron-doped germanium dioxide with the hierarchical structure can still reach 1114.1 mAh/g after three hundred circles of charge-discharge circulation under the current density of 0.5A/g.

Drawings

Figure 1 shows XRD patterns of doped and undoped germanium dioxide.

FIG. 2 is a scanning electron micrograph of iron-doped germanium dioxide popcorn.

Fig. 3 is a graph of the electrochemical performance of iron-doped germanium dioxide popcorn.

Detailed Description

In order to make the present invention more comprehensible, the technical solutions of the present invention are further described below with reference to specific embodiments, but the present invention is not limited thereto.

Examples

1) 1 mmol of GeO₂And 0.1 mmol FeCl₃·6H₂Adding O into a mixed solution of 5-10 ml ethanolamine and 10-20 ml ethanol (the volume ratio of the two is 1: 2), and adding 2-methylpiperazine to adjust the pH value of the solution>7；

The XRD patterns of doped and undoped germanium dioxide are shown in figure 1. As can be seen from fig. 1, both lines belong to pure-phase germanium dioxide, no other impurity peak exists, and it can be seen from the enlarged picture that the peak of the doped germanium dioxide is obviously shifted toward a small angle, which proves the successful synthesis of the iron-doped germanium dioxide.

A scanning electron micrograph of iron-doped germanium dioxide popcorn is shown in FIG. 2. As can be seen from fig. 2, it is a micro-flower of self-assembled nano-sheets, with a size of about 2 μm.

Assembling the lithium battery:

preparing iron-doped germanium dioxide with a hierarchical structure, polyvinylidene fluoride and acetylene black according to a mass ratio of 7: 2: 1 after mixing and grinding, uniformly coating on a copper net to be used as a negative electrode, wherein the reference electrode and the counter electrode are bothLithium metal, electrolyte made of 1M LiPF₆EC + DMC + EMC (EC/DMC/EMC =1/1/1 v/v) solution. All assembly was performed in a glove box.

The results of the electrochemical performance test are shown in FIG. 3. As can be seen from FIG. 3, after three hundred cycles of charge and discharge, the capacity of the obtained lithium battery can still reach 1114.1 mAh/g, and the lithium battery still has high specific capacity of 511 mAh/g under the current density of 10 Ah/g, and shows excellent rate capability.

The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.

Claims

1. An iron-doped germanium dioxide with a hierarchical structure, which is characterized in that: the preparation method comprises the following steps:

1) adding GeO₂And FeCl₃·6H₂Adding O into mixed solution of ethanolamine and ethanol, and adding 2-methylpiperazine to adjust the pH of the solution>7；

3) washing the obtained product with deionized water, and drying at 70 ℃ for 12 hours to obtain Fe-GeO₂The yellow powder of (4);

2. The iron-doped graded structure germanium dioxide of claim 1, wherein: GeO used₂And FeCl₃·6H₂The molar ratio of O is 10: 1.

3. The iron-doped graded structure germanium dioxide of claim 1, wherein: in the mixed solution composed of the ethanolamine and the ethanol, the volume ratio of the ethanolamine to the ethanol is 1: 2.

4. Use of the iron-doped graded germanium dioxide of claim 1 in the preparation of a lithium ion battery.