CN102185127A - Lithium sulphur battery anode piece added with absorbent and lithium sulphur battery - Google Patents

Abstract

The invention relates to a lithium-sulfur battery positive pole piece added with an adsorbent and the lithium-sulfur battery. In the present invention, the material with high specific surface area and strong adsorption performance is used as an adsorbent, which is added to the positive electrode sheet in the lithium-sulfur battery, and the amount of the adsorbent added is more than 5% of the mass of the positive electrode sheet. The addition of the adsorbent can adsorb the polysulfides formed in the lithium-sulfur battery during charging and discharging, avoiding its adsorption on the surface of the sulfur-based composite material and reducing the conductivity of the active material, and at the same time inhibiting the diffusion of polysulfides to the surface of the negative electrode and corrosion of lithium reaction, leading to irreversible capacity loss of the battery. Therefore, the addition of this adsorbent can improve the performance of lithium-sulfur batteries.

Description

Lithium-sulfur battery positive electrode sheet and lithium-sulfur battery with adsorbent added

technical field

The invention relates to the technical field of lithium-sulfur batteries, in particular to a lithium-sulfur battery positive pole piece and a lithium-sulfur battery added with an adsorbent.

technical background

Cathode materials have always been the bottleneck restricting the development of lithium batteries. The current commercial lithium battery active materials are mainly LiCoO ₂ , LiMnO ₄ and so on. Compared with the negative electrode, the specific capacity of commercial positive electrode materials is too low, the specific capacity of LiCoO ₂ is 130-140mAh/g, and the specific capacity of LiMnO ₄ is 110-130mAh/g, and they are expensive. Therefore, it is particularly critical and urgent to develop new green energy storage cathode materials with high energy density, low cost and long cycle life.

As a cathode material, elemental sulfur has the advantages of high specific capacity, low price, and low toxicity. The theoretical specific capacity of elemental sulfur is 1675mAh/g, and the theoretical specific energy is 2600Wh/Kg, which is the highest specific capacity among the positive electrode materials known so far, far larger than the secondary batteries that have been commercialized at this stage. Not only that, the operating voltage of lithium-sulfur batteries is around 2.1V, which can meet the application requirements of various occasions, and the price of elemental sulfur is cheap and abundant. Therefore, the research and development of lithium-sulfur batteries and their key materials has attracted much attention. Although the use of elemental sulfur as the positive electrode material in lithium-sulfur batteries has many advantages such as high specific capacity and low cost, there are also problems such as poor conductivity, fast capacity decay and short cycle life. The "shuttle phenomenon" caused by the dissolution in the medium.

Studies have shown that the main reason for the capacity fading of lithium-sulfur batteries is the destruction of the electrode structure and morphology. During the discharge process, the elemental sulfur is first reduced to form soluble polysulfides, and the intermediate polysulfides in the discharge process are easily dissolved in the electrolyte, resulting in a decrease in the coulombic efficiency of battery charge and discharge, and it will diffuse with the electrolyte to The surface of the negative electrode corrodes and reacts with lithium, resulting in irreversible capacity loss. As the discharge process progressed, the soluble polysulfides were finally reduced to Li ₂ S and Li ₂ S ₂ . The final products of discharge in the cathode material, Li ₂ S and Li ₂ S _{2 ,} have extremely poor conductivity, and they will cover the surface of the cathode active material in the form of a solid film, thereby hindering the electrochemical reaction between the electrolyte and the electrode active material. Therefore, how to solve the problem of dissolution of intermediate products in the charging and discharging process and improve the cycle performance of the battery is one of the focuses of research on sulfur-based cathode materials.

In order to improve the cycle performance of the lithium-sulfur battery, the present invention adds an adsorbent to the existing positive electrode material to absorb the polysulfides produced during the charging and discharging process of the lithium-sulfur battery and suppress the generation of the "shuttle phenomenon", so as to Improving the performance and lifetime of lithium-sulfur batteries.

Contents of the invention

The object of the present invention is to provide a lithium-sulfur battery positive pole piece added with an adsorbent and a lithium-sulfur battery containing the positive pole piece of the present invention.

Traditional lithium-sulfur battery cathode sheets are mainly composed of cathode active materials, binders and conductive agents. In order to improve the problem that polysulfides, the intermediate products of lithium-sulfur batteries, are easy to dissolve in the electrolyte and diffuse to the negative electrode with the electrolyte, resulting in battery capacity attenuation and cycle performance reduction, etc., the present invention adds an adsorbent to the positive electrode sheet of the lithium-sulfur battery. The additive amount of the additive is more than 5% of the mass of the positive pole piece.

The mass percent of the positive electrode sheet of the present invention is composed of: 50%-75% of positive electrode active material, 10%-20% of conductive agent, 10%-20% of binder, and 5%-15% of adsorbent.

The adsorbent described in the present invention is uniformly dispersed in the material of the positive pole sheet.

In the positive electrode sheet of the present invention, the adsorbent is mainly selected from materials with high specific surface area, porous structure and good adsorption performance, such as activated carbon, carbon microspheres, mesoporous carbon, carbon molecular sieve, carbide derived carbon (pore size distribution 0.5～ 5nm) and adsorption resin, etc. The adsorption of adsorbate molecules by adsorbent materials mainly depends on the physical and chemical structure of the surface. The adsorption of adsorbate by adsorbent materials is also divided into physical adsorption and chemical adsorption. Physical adsorption is caused by van der Waals force, while chemical adsorption is caused by the chemical binding force between the surface of the adsorbent and the adsorbate. Most adsorption processes are physical adsorption.

The adsorption material with porous structure and high surface area will form a strong adsorption field on the surface of the material due to van der Waals force. When the adsorbate is adsorbed into the pore structure of the adsorbent material, the capillary adsorption force of the pore size will enhance the adsorption of the adsorbate by the material. .

The positive electrode active materials used in lithium-sulfur batteries are usually carbon-sulfur composite materials or metal sulfide materials. The carbon in the carbon-sulfur composite materials is carbon nanotubes, mesoporous carbon, activated carbon and carbide-derived carbon, etc., and the metal sulfide materials are MoS ₂ , FeS ₂ , V ₂ S ₂ or NiS. During the charge and discharge process of the battery, the positive electrode active material will produce polysulfides as transition products. Polysulfides are easily soluble in the electrolyte, and migrate to the negative electrode with the electrolyte, react with the negative electrode and corrode the negative electrode, resulting in a decrease in the performance of the battery. Therefore, adding adsorption materials to lithium-sulfur batteries can not only effectively adsorb polysulfides dissolved in the electrolyte, prevent their migration in lithium-sulfur batteries, but also prevent the discharge end products Li ₂ S ₂ and Li ₂ S from covering the positive active material surface, thereby improving the performance and cycle life of lithium-sulfur batteries.

The present invention adds activated carbon, carbon microspheres, mesoporous carbon, carbide-derived carbon or adsorption resin and other adsorption materials to the positive electrode material of the battery when preparing the positive electrode sheet of the battery to improve the performance of the lithium-sulfur battery. The positive pole piece prepared by the present invention is assembled into a lithium-sulfur battery, and its electrochemical performance is tested. The specific preparation process is as follows:

1. Preparation of positive electrode material: Weigh various materials required for preparing the positive electrode sheet, including: positive electrode active material, conductive agent, binder and adsorbent, in terms of mass percentage, 50% to 75% of the positive electrode active material, The conductive agent is 10%-20%, the binder is 10%-20%, and the adsorbent is 5%-15%. The positive electrode active material is a carbon-sulfur composite material or a metal sulfide material. Carbon-sulfur composite materials are activated carbon and sulfur composite materials, carbon nanotubes and composite materials, mesoporous carbon and sulfur composite materials, and carbide-derived carbon and sulfur composite materials; metal sulfide materials are MoS ₂ , FeS ₂ , V ₂ S ₂ or NiS. The binder is 15wt% polyvinylidene fluoride solution, and the solvent in the solution is N-methylpyrrolidone. The conductive agent is acetylene black or superconducting carbon black. Fully disperse and grind each positive electrode component material with absolute ethanol to obtain a positive electrode slurry, coat the prepared positive electrode slurry on nickel foam to make a sheet, and dry to obtain a positive electrode sheet.

2. Battery preparation: Assemble the lithium-sulfur battery with the prepared positive electrode sheet, negative electrode and separator. The positive electrode uses an aluminum sheet as a current collector, and the negative electrode uses a copper sheet as a current collector. Metal lithium sheets or lithium alloys are selected as the negative electrode, and the lithium alloys are Li and Si alloys, Li and Sn alloys, or Li and C alloys. The diaphragm is made of polypropylene, polyethylene, polyvinylidene fluoride or polypropylene and polyethylene double-layer film. The electrolyte is liquid, solid or gel electrolyte. The liquid electrolyte mainly uses some linear ether or carbonate solvents, such as ethylene methyl carbonate, propylene carbonate, dimethyl carbonate, dioxolane, tetraethylene glycol Dimethyl ether or tetrahydrofuran, etc., commonly used are two or more mixed organic solvents, such as ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate mixed solvent, oxolane and tetraethylene glycol dimethyl ether mixed solvent. The supporting solute is lithium hexafluorophosphate, lithium perchlorate or lithium trifluoromethanesulfonate, etc.

The test lithium-sulfur battery is unified as a CR2025 button battery. The battery charge and discharge test conditions are: at room temperature, the charge and discharge test is carried out under the conditions of a limited voltage of 1.2-3.0V and a charge-discharge current density of 0.15mA/cm ² .

Description of drawings

Figure 1 is a schematic diagram of the positive electrode of lithium-sulfur battery without adding adsorbent.

Fig. 2 is a schematic diagram of a positive electrode of a lithium-sulfur battery in which an adsorbent is dispersed and added to the positive electrode sheet.

Fig. 3 is the cycle performance comparison curve of the lithium-sulfur battery with adsorbent added and the lithium-sulfur battery without adsorbent obtained in Example 1 and Comparative Example 1.

In the figure: 1-current collector, 2-diaphragm, 3-binder, 4-conductive agent, 5-active material, 6-adsorbent.

Detailed ways

The following examples further illustrate the preparation of the lithium-sulfur battery positive electrode sheet of the present invention and the lithium-sulfur battery containing the positive electrode sheet of the present invention.

The mass percent composition of the lithium-sulfur battery positive pole piece of the present invention is: 50%-75% of the positive electrode active material, 10%-20% of the conductive agent, 10%-20% of the binder, and 5%-15% of the adsorbent.

Example 1

Activated carbon with a specific surface area of 1000m ² /g is selected as the adsorbent, the mass percentage of the adsorbent in the positive electrode material is 15%, the positive electrode active material is a carbon nanotube and sulfur composite material, acetylene black is used as a conductive agent, and 5wt% of PVDF (Polyvinylidene fluoride) solution (solvent is NMP, N-methylpyrrolidone) is used as binder to prepare positive electrode slurry; then the slurry is coated on foamed nickel to prepare positive electrode sheet, and dried to obtain the required The positive pole piece, the thickness of the positive pole piece is 45 ~ 55um. Select Celgard2400 film as the battery diaphragm to assemble the battery, the electrolyte is 1mol/L LiPF6/EC:DMC:EMC (1:1:1 volume ratio, EC: ethylene carbonate, DMC: dimethyl carbonate, EMC: carbonic acid methyl ethyl ester), and the entire battery assembly process was completed in a glove box.

The constant current charge and discharge test results show that the first discharge specific capacity of the battery reaches 945.8mAh/g, and after 50 charge and discharge cycles, it remains at 549.2mAh/g. The results are shown in Figure 3. Compared with the cells without the addition of adsorbents, the cells with added adsorbents showed good battery performance.

Example 2

Activated carbon and sulfur composite materials are selected as the positive electrode active material, and porous carbon microspheres are used as the adsorbent material to prepare the positive electrode sheet. The conductive agent is superconducting carbon black BP2000, and the mass ratio of the positive electrode active material, conductive agent, binder and adsorbent is It is 60%: 15%: 15%: 10%. Prepare the positive electrode sheet and assemble the battery by the same method as in Example 1. The battery charge and discharge test results show that the first charge and discharge specific capacity of the material is 867.4mAh/g, and the specific capacity after 50 cycles is also maintained at 535.6mAh/g. Good battery performance was shown.

Example 3

A composite material of carbide-derived carbon and sulfur (wherein the pore size distribution of carbide-derived carbon is 0.5-5nm) is selected as the positive electrode active material, and mesoporous carbon is used as the adsorbent material to prepare the positive electrode sheet, wherein the positive electrode active material, conductive agent, binder The mass ratio of agent and adsorbent is 75%:10%:10%:5%. The same method as in Example 1 was used to prepare the positive electrode sheet and assemble the battery. The charge-discharge test results show that the initial charge-discharge specific capacity of the material is 924.1mAh/g, and the specific capacity remains at 607.9mAh/g after 50 cycles, showing good battery performance.

Example 4

Mesoporous carbon and sulfur composite materials are selected as positive electrode active materials, and carbon molecular sieves are used as adsorbent materials to prepare positive electrode sheets, wherein the mass ratio of positive electrode active materials, conductive agents, binders and adsorbents is 60%: 15%: 15% : 10%. The same method as in Example 1 was used to prepare the positive electrode sheet and assemble the battery. The charge and discharge test results show that the first charge and discharge specific capacity of the material is mAh/g, and the specific capacity remains at mAh/g after 50 cycles, showing good battery performance.

Example 5

Mesoporous carbon and sulfur composite materials are selected as the positive electrode active material, and the macroporous adsorption resin Amberlite XAD-4 is used as the adsorbent material to prepare the positive electrode sheet, wherein the mass ratio of the positive electrode active material, conductive agent, binder and adsorbent is 60% : 15% : 15% : 10%. The same method as in Example 1 was used to prepare the positive electrode sheet and assemble the battery. The charge-discharge test results show that the first charge-discharge specific capacity of the material is 853.0mAh/g, and the specific capacity remains at 558.6mAh/g after 50 cycles, showing good battery performance.

Example 6

_FeS2 is selected as the positive electrode active material, and carbide-derived carbon (pore size distribution 0.5-5nm) is used as the adsorbent to prepare the positive electrode sheet, wherein the mass ratio of the positive electrode active material, the conductive agent, the binder and the adsorbent is 50%: 20 %: 20%: 10%. The electrolyte is 1mol/L LiCF ₃ SO ₃ /TGM:DOL (1:1 volume ratio, TGM: tetraethylene glycol dimethyl ether, DOL: dioxolane), positive electrode sheet preparation and battery assembly and examples 1 in the same way.

The charge and discharge test results show that the first charge and discharge specific capacity of the material is 752.6mAh/g, and the specific capacity remains at 566.9mAh/g after 50 cycles, showing good battery performance.

Example 7

Except that NiS was selected as the positive electrode active material, the positive electrode sheet was prepared and the battery was assembled by the same method as in Example 6. The charge and discharge test results show that the first charge and discharge specific capacity of the material is 641.2mAh/g, and the specific capacity remains at 493.7mAh/g after 50 cycles, showing good battery performance.

comparative example

Referring to Figure 1, the traditional positive pole piece is composed of positive active material, conductive agent and binder. During the battery preparation process, no adsorbent was added. The positive electrode active material is a carbon nanotube and sulfur composite material, and the mass ratio of the positive electrode active material, the conductive agent and the binding agent is 75%: 15%: 10%, and acetylene black is also selected as the conductive agent, and 5wt% of PVDF (polypropylene oxide) Vinyl fluoride) solution (solvent is NMP, N-methylpyrrolidone) as binder to prepare positive electrode slurry. Coating the slurry on the foamed nickel to prepare a positive pole piece, drying to obtain the required positive pole piece, the thickness of the positive pole piece is 45-55um. Select Celgard2400 film as the battery diaphragm to assemble the battery, and the electrolyte is 1mol/L LiPF ₆ /EC:DMC (1:1 volume ratio, EC: ethylene carbonate, DMC: dimethyl carbonate).

Table 1 shows the battery charge and discharge test results obtained in various examples and comparative examples.

Table 1

It can be seen from Table 1 that, compared with the comparative examples, the specific capacity and cycle performance of the battery have been significantly improved in the examples in which the adsorption material is added to the positive electrode material.

The lithium-sulfur battery added with the adsorbent of the present invention can absorb the polysulfides dissolved in the electrolytic solution through the adsorption of the adsorption material, thereby improving the service performance and cycle life of the lithium-sulfur battery.

Claims (10)

1. A lithium-sulfur battery positive pole piece, which includes a positive electrode active material, a conductive agent and a binding agent, is characterized in that an adsorbent is added in the positive pole piece, and the amount of the adsorbent added is 5% of the quality of the positive pole piece above. 2. The positive pole piece of lithium-sulfur battery according to claim 1, characterized in that, the mass percentage of the positive pole piece is composed of: 50% to 75% of positive electrode active material, 10% to 20% of conductive agent, viscose The binder is 10% to 20%, and the adsorbent is 5% to 15%. 3. The lithium-sulfur battery cathode sheet according to claim 1, wherein the adsorbent is uniformly dispersed in the cathode sheet material. 4. The lithium-sulfur battery cathode sheet according to claim 1, 2 or 3, wherein the adsorbent is a porous adsorption material with a high specific surface area: activated carbon, carbon microspheres, mesoporous carbon, carbon Molecular sieve, carbide-derived carbon or adsorption resin, the carbide-derived carbon pore size distribution is 0.5-5nm. 5. The lithium-sulfur battery positive electrode sheet according to claim 1, wherein the positive electrode active material is a carbon-sulfur composite material or a metal sulfide, wherein carbon in the carbon-sulfur composite material is activated carbon, carbon nanotubes, Mesoporous carbon or carbide derived carbon, the metal sulfide is FeS ₂ or NiS. 6. The lithium-sulfur battery cathode sheet according to claim 1, wherein the binder is a 15 wt% polyvinylidene fluoride solution, and the solvent of the solution is N-methylpyrrolidone. 7. The lithium-sulfur battery cathode sheet according to claim 1, wherein the conductive agent is acetylene black or superconducting carbon black. 8. A lithium-sulfur battery, characterized in that, the lithium-sulfur battery is assembled from the positive electrode sheet according to claim 1, the negative electrode and the diaphragm, the positive electrode uses an aluminum sheet as a current collector, and the negative electrode uses a copper sheet as a current collector. The negative electrode is made of metal lithium sheet, Li and Si alloy, Li and Sn alloy, or Li and C alloy. 9. The lithium-sulfur battery according to claim 8, wherein the separator is a porous polypropylene and polyethylene double-layer membrane. 10. The lithium-sulfur battery according to claim 8, wherein the electrolyte is a non-aqueous electrolyte, and the solvent is a mixed solvent of dimethyl carbonate and ethyl methyl carbonate, or oxolane and tetraethylene glycol diol Methyl ether mixed solvent, the solute is lithium hexafluorophosphate or lithium trifluoromethanesulfonate.

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