WO2016019901A1 - A sulfur-pan composite, a method for preparing said composite, and an electrode and a lithium-sulfur battery comprising said composite - Google Patents

A sulfur-pan composite, a method for preparing said composite, and an electrode and a lithium-sulfur battery comprising said composite Download PDF

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Publication number
WO2016019901A1
WO2016019901A1 PCT/CN2015/086370 CN2015086370W WO2016019901A1 WO 2016019901 A1 WO2016019901 A1 WO 2016019901A1 CN 2015086370 W CN2015086370 W CN 2015086370W WO 2016019901 A1 WO2016019901 A1 WO 2016019901A1
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sulfur
polyacrylonitrile
composite
carbon
cnt
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PCT/CN2015/086370
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French (fr)
Inventor
Nahong ZHAO
Joerg Thielen
Bernd Schumann
Yunhua Chen
Chuanling LI
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Robert Bosch Gmbh
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Priority to CN201580042528.8A priority Critical patent/CN106661149A/en
Priority to DE112015003654.7T priority patent/DE112015003654T5/en
Publication of WO2016019901A1 publication Critical patent/WO2016019901A1/en

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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/02—Elements
    • C08K3/06—Sulfur
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/02—Elements
    • C08K3/04—Carbon
    • C08K3/041—Carbon nanotubes
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L33/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides or nitriles thereof; Compositions of derivatives of such polymers
    • C08L33/18—Homopolymers or copolymers of nitriles
    • C08L33/20—Homopolymers or copolymers of acrylonitrile
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a sulfur-polyacrylonitrile composite, which comprises polyacrylonitrile particles, sulfur and one or more carbon conductive additives.
  • the present invention further relates to a method for preparing said sulfur-polyacrylonitrile composite, and an electrode and a lithium-sulfur battery comprising said sulfur-polyacrylonitrile composite.
  • Li-Sulfur (Li-S) batteries have attracted considerable attention for their high energy density and low cost.
  • the theoretical energy density of 2600 Wh/kg cannot be reached because of sulfur’s insulating nature.
  • conductive additives have to be added and consequently the theoretical value is reduced to a realistic 600 Wh/kg.
  • elemental sulfur forms polysulfides, S x 2- , during reduction, which is soluble in the electrolyte. Therefore, several concepts have been elaborated upon that focus on retaining sulfur in the cathode matrix.
  • One of the most promising concepts is to embed sulfur into a conductive matrix of pyrolized polyacrylonitrile (PAN) .
  • PAN pyrolized polyacrylonitrile
  • the present invention provides a sulfur-polyacrylonitrile (SPAN) composite, which provides a high sulfur content and a favorable electrical conductivity. It is promising to deliver a high cathode capacity and a good rate capability when discharging under a large current density.
  • SPAN sulfur-polyacrylonitrile
  • a sulfur-polyacrylonitrile composite which comprises polyacrylonitrile particles, sulfur and one or more carbon conductive additives, and said one or more carbon conductive additives are adopted and/or embedded in the polyacrylonitrile particles.
  • a method for preparing a sulfur-polyacrylonitrile composite including the following steps:
  • step 1) one or more carbon conductive additives are additionally applied to the polyacrylonitrile particles in the course of the preparation of polyacrylonitrile particles.
  • the present invention relates an electrode, which comprises the sulfur-polyacrylonitrile composite according to the present invention.
  • the present invention relates a lithium-sulfur battery, which comprises the electrode according to the present invention.
  • FIG. 1a is a schematic diagram of the sulfur-polyacrylonitrile (SPAN) composite in a form of particles with SuperP carbon black;
  • SPAN sulfur-polyacrylonitrile
  • FIG. 1b is a schematic diagram of the sulfur-polyacrylonitrile (SPAN) composite in a form of particles without SuperP carbon black; and
  • Figure 2 is a transmission electron microscope (TEM) image of SuperP carbon black.
  • the present invention relates to a sulfur-polyacrylonitrile composite, which comprises polyacrylonitrile particles, sulfur and one or more carbon conductive additives, and said one or more carbon conductive additives are adopted and/or embedded in the polyacrylonitrile particles.
  • said sulfur-polyacrylonitrile composite can be formed in such a way that said polyacrylonitrile particles are dehydrogenated and cyclized in the presence of sulfur and bonded with sulfur or polysulfide.
  • the diameter of said polyacrylonitrile particles can be between 100 nm and 10 ⁇ m, preferably between 100 nm and 2 ⁇ m, for example about 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 ⁇ m, 1.5 ⁇ m, 5 ⁇ m, or 8 ⁇ m.
  • said one or more carbon conductive additives can bridge from one polyacrylonitrile particle to another polyacrylonitrile particle, so as to bridge the electron conductive network in-between the the particles.
  • one end of the carbon conductive additive can be embedded in one polyacrylonitrile particle and the other end of the same carbon conductive additive can be embedded in another polyacrylonitrile particle.
  • said one or more carbon conductive additives can be selected from carbon nanotube (CNT) , graphite, and carbon nanoparticle, such as acetylene black, SuperP carbon black (Fig. 2) or ketjen black.
  • the carbon nanotube (CNT) which can be used in the sulfur-polyacrylonitrile composite according to the present invention preferably has a diameter of 1 –100 nm, for example about 2 nm, 3 nm, 5 nm, 10 nm, 30 nm, 40 nm, 60 nm, or 80 nm.
  • the length of the carbon nanotube (CNT) used here is not particularly limited, for example less than 5 ⁇ m, 5 –15 ⁇ m, or more than 15 ⁇ m.
  • a preferable length of the CNT can be 0.3 –6 times the PAN particle diameter.
  • CNT carbon nanotube
  • SWNT Single-walled carbon nanotube
  • DWNT double-walled carbon nanotube
  • MWNT multi-walled carbon nanotube
  • said carbon nanotube (CNT) can be open-ended, and the inner voids of the carbon nanotube (CNT) can be filled with 1 –30 wt. %, preferably 10 –20 wt. %of sulfur to form a sulfur-carbon nanotube composite (S/CNT) , based on the weight of the sulfur-carbon nanotube composite (S/CNT) .
  • the content of said one or more carbon conductive additives is less than or equal to 15 wt. %, preferably less than or equal to 10 wt. %, more preferably less than or equal to 8 wt. %, most preferably less than or equal to 5 wt. %, in each case based on the total weight of the polyacrylonitrile particles and the carbon conductive additives.
  • the sulfur load amount of said sulfur-polyacrylonitrile composite can be 20 –55 wt. %, preferably 30 –50 wt. %, in each case based on the total weight of the sulfur-polyacrylonitrile composite.
  • the present invention relates to a method for preparing a sulfur-polyacrylonitrile composite, said method including the following steps:
  • step 1) heating the product prepared from step 1) together with sulfur, characterized in that during step 1) , one or more carbon conductive additives are additionally applied to the polyacrylonitrile particles in the course of the preparation of polyacrylonitrile particles.
  • Polyacrylonitrile particles can be prepared by electrospraying or spray drying from a polyacrylonitrile solution or dispersion.
  • concentration of polyacrylonitrile in said solution or dispersion is not particularly limited, for example 3 –20 wt. %, preferably 5 –15 wt.%, more preferably 6 –10 wt. %, and can be determined according to the desired diameter of polyacrylonitrile particles.
  • one or more carbon conductive additives can be additionally applied to the polyacrylonitrile particles in the course of the preparation of polyacrylonitrile particles, so that said one or more carbon conductive additives can be adopted and/or embedded in the polyacrylonitrile particles.
  • the content of said one or more carbon conductive additives is less than or equal to 15 wt. %, preferably less than or equal to 10 wt. %, more preferably less than or equal to 8 wt.%, most preferably less than or equal to 5 wt. %, in each case based on the total weight of the polyacrylonitrile particles and the carbon conductive additives.
  • said polyacrylonitrile solution or dispersion can additionally contain one or more carbon conductive additives, so that polyacrylonitrile particles with carbon conductive additives adopted and/or embedded therein can be prepared at the same time by electrospraying or spray drying.
  • a solution or dispersion of one or more carbon conductive additives can be sprayed at the same time through a nozzle close to the nozzle for said electrospraying or spray drying, so that said one or more carbon conductive additives can be preferably adopted and/or embedded in the polyacrylonitrile particles, and said one or more carbon conductive additives can bridge from one polyacrylonitrile particle to another polyacrylonitrile particle, so as to bridge the electron conductive network in-between the the particles.
  • one end of the carbon conductive additive can be embedded in one polyacrylonitrile particle and the other end of the same carbon conductive additive can be embedded in another polyacrylonitrile particle.
  • said one or more carbon conductive additives can be selected from carbon nanotube (CNT) , graphite, and carbon nanoparticle, such as acetylene black, SuperP carbon black (Fig. 2) or ketjen black.
  • the carbon nanotube (CNT) which can be used in the polyacrylonitrile solution or dispersion additionally containing carbon conductive additives or in the solution or dispersion of carbon conductive additives preferably has a diameter of 1 –100 nm, for example about 2 nm, 3 nm, 5 nm, 10 nm, 30 nm, 40 nm, 60 nm, or 80 nm.
  • the length of the carbon nanotube (CNT) used here is not particularly limited, for example less than 5 ⁇ m, 5 –15 ⁇ m, or more than 15 ⁇ m.
  • a preferable length of the CNT can be 0.3 –6 times the PAN particle diameter.
  • CNT carbon nanotube
  • SWNT Single-walled carbon nanotube
  • DWNT double-walled carbon nanotube
  • MWNT multi-walled carbon nanotube
  • said carbon nanotube (CNT) can be open-ended, and before the carbon nanotube (CNT) is used in the polyacrylonitrile solution or dispersion additionally containing carbon conductive additives or in the solution or dispersion of carbon conductive additives, it can be calcined together with sulfur in vacuo at 550 –700°C, preferably at about 600°C, for about 48 hours, so that the inner voids or cavities of the carbon nanotube (CNT) can be filled with 1 –30 wt. %, preferably 10 –20 wt. %of sulfur to form a sulfur-carbon nanotube composite (S/CNT) , in each case based on the weight of the sulfur-carbon nanotube composite (S/CNT) .
  • step 2) the product prepared from step 1) together with sulfur can be heated at a temperature of 280 –460 °C, preferably 390 –460 °C, for 0.5 –6 hours, preferably 0.5 –4 hours, more preferably 0.5 –3 hours, in a protective atmosphere, such as argon, so that the polyacrylonitrile can be dehydrogenated and cyclized in the presence of sulfur and bonded with sulfur or polysulfide.
  • a protective atmosphere such as argon
  • the SPAN nanoparticle can be mixed with carbon black and poly- (vinyl difluoride) (PVDF) and pasted on an Al foil.
  • PVDF poly- (vinyl difluoride)
  • Lithium foil can be used as the counter electrode, and assembled with a separator and carbonate electrolyte consisted of LiPF 6 salt and ethylene carbonate solvent.
  • the present invention relates to an electrode, which comprises the sulfur-polyacrylonitrile composite according to the present invention.
  • the present invention relates to a lithium-sulfur battery, which comprises the electrode according to the present invention.
  • the SPAN obtained according to the present invention has a higher electronic conductivity compared to the SPAN synthesized from the conventional PAN and sulfur only. CNTs on the outer surface of the PAN still remain on the outer surface of the SPAN, providing a conductive coating.
  • This SPAN composite electrode thus shows a high cathode capacity, a low resistance, an excellent cycling stability, and a favorable rate performance.
  • the inventors have investigated the chemical process of the dehydrogenation of polyacrylonitrile in the presence of sulfur, and revealed the chemical structure of the polyacrylonitrile-derived cyclized backbone. It has been found that a higher synthesis temperature results in a higher degree of graphitization of the polymer backbone and eventually in a higher C-rate capability and a higher cycling stability. However, the composite degrades when prepared at a higher temperature which results in a lower sulfur content and eventually in a lower cathode capacity. At the same time, the SPAN composite prepared at a higher temperature displays a larger specific surface area, which also supports the higher C-rate performance. Despite of this trade off in between the capacity and the high C-rate capability, an optimum synthesis temperature can be selected from 390 to 460°C.
  • Potential applications of the composite according to the present invention include high-energy-density lithium ion batteries with acceptable high power density for energy storage applications, such as power tools, photovoltaic cells and electric vehicles.

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Abstract

The present invention relates to a sulfur-polyacrylonitrile composite, which comprises polyacrylonitrile particles, sulfur and one or more carbon conductive additives. The present invention further relates to a method for preparing said sulfur-polyacrylonitrile composite, and an electrode and a lithium-sulfur battery comprising said sulfur-polyacrylonitrile composite.

Description

A SULFUR-PAN COMPOSITE, A METHOD FOR PREPARING SAID COMPOSITE, AND AN ELECTRODE AND A LITHIUM-SULFUR BATTERY COMPRISING SAID COMPOSITE Technical Field
The present invention relates to a sulfur-polyacrylonitrile composite, which comprises polyacrylonitrile particles, sulfur and one or more carbon conductive additives. The present invention further relates to a method for preparing said sulfur-polyacrylonitrile composite, and an electrode and a lithium-sulfur battery comprising said sulfur-polyacrylonitrile composite.
Background Art
Lithium-Sulfur (Li-S) batteries have attracted considerable attention for their high energy density and low cost. However, the theoretical energy density of 2600 Wh/kg cannot be reached because of sulfur’s insulating nature. Thus, conductive additives have to be added and consequently the theoretical value is reduced to a realistic 600 Wh/kg. Additionally, elemental sulfur forms polysulfides, Sx 2-, during reduction, which is soluble in the electrolyte. Therefore, several concepts have been elaborated upon that focus on retaining sulfur in the cathode matrix. One of the most promising concepts is to embed sulfur into a conductive matrix of pyrolized polyacrylonitrile (PAN) . This appealing sulfur-polyacrylonitrile (SPAN) composite has been used as an active cathode material showing a high specific capacity, a good efficiency, a low self-discharge, an excellent cycling stability and an improved rate performance. In view of the status quo in high energy density battery applications, the energy density of this Li-sulfur system has to be improved essentially. To do so, many researches have been conducted to improve the material capacity of SPAN composite.
Summary of Invention
The present invention provides a sulfur-polyacrylonitrile (SPAN) composite, which provides a high sulfur content and a favorable electrical conductivity. It is promising to deliver a high cathode capacity and a good rate capability when discharging under a large current density.
According to one aspect of the present invention, a sulfur-polyacrylonitrile composite is provided, which comprises polyacrylonitrile particles, sulfur and one or more carbon conductive additives, and said one or more carbon conductive additives are adopted and/or embedded in the polyacrylonitrile particles.
According to another aspect of the present invention, a method for preparing a sulfur-polyacrylonitrile composite is provided, said method including the following steps:
1) preparation of polyacrylonitrile particles by electrospraying or spray drying from a polyacrylonitrile solution or dispersion；
2) heating the product prepared from step 1) together with sulfur,
characterized in that during step 1) , one or more carbon conductive additives are additionally applied to the polyacrylonitrile particles in the course of the preparation of polyacrylonitrile particles.
According to another aspect, the present invention relates an electrode, which comprises the sulfur-polyacrylonitrile composite according to the present invention.
According to a further aspect, the present invention relates a lithium-sulfur battery, which comprises the electrode according to the present invention.
Brief Description of Drawings
Each aspect of the present invention will be illustrated in more detail in conjunction with the accompanying drawings, wherein :
Figure 1a is a schematic diagram of the sulfur-polyacrylonitrile (SPAN) composite in a form of particles with SuperP carbon black；
Figure 1b is a schematic diagram of the sulfur-polyacrylonitrile (SPAN) composite in a form of particles without SuperP carbon black； and
Figure 2 is a transmission electron microscope (TEM) image of SuperP carbon black.
Detailed Description of Preferred Embodiments
All publications, patent applications, patents and other references mentioned herein, if not otherwise indicated, are explicitly incorporated by reference herein in their entirety for all purposes as if fully set forth.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions, will control.
When an amount, concentration, or other value or parameter is given as either a range, preferred range or a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether ranges are separately disclosed. Where a range of numerical values is recited herein, unless otherwise stated, the range is intended to include the endpoints thereof, and all integers and fractions within the range.
The present invention, according to one aspect, relates to a sulfur-polyacrylonitrile composite, which comprises polyacrylonitrile particles, sulfur and one or more carbon conductive additives, and said one or more carbon conductive additives are adopted and/or embedded in the polyacrylonitrile particles.
In accordance with an embodiment of the sulfur-polyacrylonitrile composite according to the present invention, said sulfur-polyacrylonitrile composite can be formed in such a way that said polyacrylonitrile particles are dehydrogenated and cyclized in the presence of sulfur and bonded with sulfur or polysulfide.
In accordance with another embodiment of the sulfur-polyacrylonitrile composite according to the present invention, the diameter of said polyacrylonitrile particles can be between 100 nm and 10 μm, preferably between 100 nm and 2 μm, for example about 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 μm, 1.5 μm, 5 μm, or 8 μm.
In accordance with another embodiment of the sulfur-polyacrylonitrile composite according to the present invention, said one or more carbon conductive additives can bridge from one polyacrylonitrile particle to another polyacrylonitrile particle, so as to bridge the electron conductive network in-between the the particles. In particular, one end of the carbon conductive additive can be embedded in one polyacrylonitrile particle and the other end of the same carbon conductive additive can be embedded in another polyacrylonitrile particle.
In accordance with another embodiment of the sulfur-polyacrylonitrile composite according to the present invention, said one or more carbon conductive additives can be selected from carbon nanotube (CNT) , graphite, and carbon nanoparticle, such as acetylene black, SuperP carbon black (Fig. 2) or ketjen black.
The carbon nanotube (CNT) which can be used in the sulfur-polyacrylonitrile composite according to the present invention preferably has a diameter of 1 –100 nm, for example about 2 nm, 3 nm, 5 nm, 10 nm, 30 nm, 40 nm, 60 nm, or 80 nm. The length of the carbon nanotube (CNT) used here is not particularly limited, for example less than 5 μm, 5 –15 μm, or more than 15 μm. A preferable length of the CNT can be 0.3 –6 times the PAN particle diameter.
There is no limit to the specific form of the carbon nanotube (CNT) used here. Single-walled carbon nanotube (SWNT) , double-walled carbon nanotube (DWNT) and multi-walled carbon nanotube (MWNT) can be used.
In accordance with another embodiment of the sulfur-polyacrylonitrile composite according to the present invention, said carbon nanotube (CNT) can be open-ended, and the inner voids of the carbon nanotube (CNT) can be filled with 1 –30 wt. ％, preferably 10 –20 wt. ％of sulfur to form a sulfur-carbon nanotube composite (S/CNT) , based on the weight of the sulfur-carbon nanotube composite (S/CNT) .
In accordance with another embodiment of the sulfur-polyacrylonitrile composite according to the present invention, the content of said one or more carbon conductive additives is less than or equal to 15 wt. ％, preferably less than or equal to 10 wt. ％, more preferably less than or equal to 8 wt. ％, most preferably less than or equal to 5 wt. ％, in each case based on the total weight of the polyacrylonitrile particles and the carbon conductive additives.
In accordance with another embodiment of the sulfur-polyacrylonitrile composite according to the present invention, the sulfur load amount of said sulfur-polyacrylonitrile composite can be 20 –55 wt. ％, preferably 30 –50 wt. ％, in each case based on the total weight of the sulfur-polyacrylonitrile composite.
The present invention, according to another aspect, relates to a method for preparing a sulfur-polyacrylonitrile composite, said method including the following steps:
1) preparation of polyacrylonitrile particles by electrospraying or spray drying from a polyacrylonitrile solution or dispersion；
2) heating the product prepared from step 1) together with sulfur, characterized in that during step 1) , one or more carbon conductive additives are additionally applied to the polyacrylonitrile particles in the course of the preparation of polyacrylonitrile particles.
1) Preparation of polyacrylonitrile particles comprising carbon conductive additives Polyacrylonitrile particles can be prepared by electrospraying or spray drying from a polyacrylonitrile solution or dispersion. The concentration of polyacrylonitrile in said solution or dispersion is not particularly limited, for example 3 –20 wt. ％, preferably 5 –15 wt.％, more preferably 6 –10 wt. ％, and can be determined according to the desired diameter of polyacrylonitrile particles.
During step 1) , one or more carbon conductive additives can be additionally applied to the polyacrylonitrile particles in the course of the preparation of polyacrylonitrile particles, so that said one or more carbon conductive additives can be adopted and/or embedded in the polyacrylonitrile particles.
Preferably the content of said one or more carbon conductive additives is less than or equal to 15 wt. ％, preferably less than or equal to 10 wt. ％, more preferably less than or equal to 8 wt.％, most preferably less than or equal to 5 wt. ％, in each case based on the total weight of the polyacrylonitrile particles and the carbon conductive additives.
In accordance with another embodiment of the method according to the present invention, said polyacrylonitrile solution or dispersion can additionally contain one or more carbon conductive additives, so that polyacrylonitrile particles with carbon conductive additives adopted and/or embedded therein can be prepared at the same time by electrospraying or spray drying.
In accordance with another embodiment of the method according to the present invention, a solution or dispersion of one or more carbon conductive additives can be sprayed at the same time through a nozzle close to the nozzle for said electrospraying or spray drying, so that said one or more carbon conductive additives can be preferably adopted and/or embedded in the polyacrylonitrile particles, and said one or more carbon conductive additives can bridge from one polyacrylonitrile particle to another polyacrylonitrile particle, so as to bridge the electron conductive network in-between the the particles. In particular, one end of the carbon conductive additive can be embedded in one polyacrylonitrile particle and the other end of the same carbon conductive additive can be embedded in another polyacrylonitrile particle.
In accordance with another embodiment of the method according to the present invention, said one or more carbon conductive additives can be selected from carbon nanotube (CNT) , graphite, and carbon nanoparticle, such as acetylene black, SuperP carbon black (Fig. 2) or ketjen black.
The carbon nanotube (CNT) which can be used in the polyacrylonitrile solution or dispersion additionally containing carbon conductive additives or in the solution or  dispersion of carbon conductive additives preferably has a diameter of 1 –100 nm, for example about 2 nm, 3 nm, 5 nm, 10 nm, 30 nm, 40 nm, 60 nm, or 80 nm. The length of the carbon nanotube (CNT) used here is not particularly limited, for example less than 5 μm, 5 –15 μm, or more than 15 μm. A preferable length of the CNT can be 0.3 –6 times the PAN particle diameter.
There is no limit to the specific form of the carbon nanotube (CNT) used here. Single-walled carbon nanotube (SWNT) , double-walled carbon nanotube (DWNT) and multi-walled carbon nanotube (MWNT) can be used.
In accordance with another embodiment of the method according to the present invention, said carbon nanotube (CNT) can be open-ended, and before the carbon nanotube (CNT) is used in the polyacrylonitrile solution or dispersion additionally containing carbon conductive additives or in the solution or dispersion of carbon conductive additives, it can be calcined together with sulfur in vacuo at 550 –700℃, preferably at about 600℃, for about 48 hours, so that the inner voids or cavities of the carbon nanotube (CNT) can be filled with 1 –30 wt. ％, preferably 10 –20 wt. ％of sulfur to form a sulfur-carbon nanotube composite (S/CNT) , in each case based on the weight of the sulfur-carbon nanotube composite (S/CNT) .
2) Heating the product prepared from step 1) together with sulfur
In accordance with another embodiment of the method according to the present invention, during step 2) , the product prepared from step 1) together with sulfur can be heated at a temperature of 280 –460 ℃, preferably 390 –460 ℃, for 0.5 –6 hours, preferably 0.5 –4 hours, more preferably 0.5 –3 hours, in a protective atmosphere, such as argon, so that the polyacrylonitrile can be dehydrogenated and cyclized in the presence of sulfur and bonded with sulfur or polysulfide.
In accordance with another embodiment of the method according to the present invention, the sulfur load amount of said sulfur-polyacrylonitrile composite can be 20 –55 wt. ％, preferably 30 –50 wt. ％, in each case based on the total weight of the sulfur-polyacrylonitrile composite.
Preparation of working electrode
The SPAN nanoparticle can be mixed with carbon black and poly- (vinyl difluoride) (PVDF) and pasted on an Al foil. Lithium foil can be used as the counter electrode, and assembled with a separator and carbonate electrolyte consisted of LiPF6 salt and ethylene carbonate solvent.
The present invention, according to another aspect, relates to an electrode, which comprises the sulfur-polyacrylonitrile composite according to the present invention.
The present invention, according to another aspect, relates to a lithium-sulfur battery, which comprises the electrode according to the present invention.
Due to the high surface area of the PAN according to the present invention which provides a huge reaction interphase to sulfur, a higher sulfur content can be achieved compared to the conventional synthesis procedure starting with conventional crude PAN. At the same time, the SPAN obtained according to the present invention has a higher electronic conductivity compared to the SPAN synthesized from the conventional PAN and sulfur only. CNTs on the outer surface of the PAN still remain on the outer surface of the SPAN, providing a conductive coating. This SPAN composite electrode thus shows a high cathode capacity, a low resistance, an excellent cycling stability, and a favorable rate performance.
The inventors have investigated the chemical process of the dehydrogenation of polyacrylonitrile in the presence of sulfur, and revealed the chemical structure of the polyacrylonitrile-derived cyclized backbone. It has been found that a higher synthesis temperature results in a higher degree of graphitization of the polymer backbone and eventually in a higher C-rate capability and a higher cycling stability. However, the composite degrades when prepared at a higher temperature which results in a lower sulfur content and eventually in a lower cathode capacity. At the same time, the SPAN composite prepared at a higher temperature displays a larger specific surface area, which also supports the higher C-rate performance. Despite of this trade off in between the capacity and the high C-rate capability, an optimum synthesis temperature can be selected from 390 to 460℃.
Potential applications of the composite according to the present invention include high-energy-density lithium ion batteries with acceptable high power density for energy storage applications, such as power tools, photovoltaic cells and electric vehicles.

Claims (17)

  1. A sulfur-polyacrylonitrile composite, characterized in that said sulfur-polyacrylonitrile composite comprises polyacrylonitrile particles, sulfur and one or more carbon conductive additives, and said one or more carbon conductive additives are adopted and/or embedded in the polyacrylonitrile particles.
  2. The sulfur-polyacrylonitrile composite of claim 1, characterized in that polyacrylonitrile is dehydrogenated and cyclized in the presence of sulfur and bonded with sulfur or polysulfide.
  3. The sulfur-polyacrylonitrile composite of claim 1 or 2, characterized in that said polyacrylonitrile particles have a diameter of between 100 nm and 10 μm, preferably between 100 nm and 2 μm.
  4. The sulfur-polyacrylonitrile composite of any one of claims 1 to 3, characterized in that said one or more carbon conductive additives bridge from one polyacrylonitrile particle to another polyacrylonitrile particle.
  5. The sulfur-polyacrylonitrile composite of any one of claims 1 to 4, characterized in that said one or more carbon conductive additives are selected from carbon nanotube (CNT) , carbon nanoparticle and graphite.
  6. The sulfur-polyacrylonitrile composite of claim 5, characterized in that the carbon nanotube (CNT) is open-ended, and the inner voids of the carbon nanotube (CNT) are filled with 1–30 wt.％, preferably 10–20 wt.％ of sulfur to form a sulfur-carbon nanotube composite (S/CNT) , based on the weight of the sulfur-carbon nanotube composite (S/CNT) .
  7. The sulfur-polyacrylonitrile composite of any one of claims 1 to 6, characterized in that the content of said one or more carbon conductive additives is less than or equal to 15 wt.％ based on the total weight of the polyacrylonitrile particles and the carbon conductive additives.
  8. The sulfur-polyacrylonitrile composite of any one of claims 1 to 7, characterized in that said sulfur-polyacrylonitrile composite has a sulfur load amount of 20–55 wt.％, preferably 30–50 wt.％, in each case based on the total weight of the sulfur-polyacrylonitrile composite.
  9. A method for preparing a sulfur-polyacrylonitrile composite, said method including the following steps:
    1) preparation of polyacrylonitrile particles by electrospraying or spray drying from a polyacrylonitrile solution or dispersion；
    2) heating the product prepared from step 1) together with sulfur,
    characterized in that during step 1) , one or more carbon conductive additives are additionally applied to the polyacrylonitrile particles in the course of the preparation of polyacrylonitrile particles.
  10. The method of claim 9, characterized in that the polyacrylonitrile solution or dispersion additionally contains one or more carbon conductive additives.
  11. The method of claim 9, characterized in that a solution or dispersion of one or more carbon conductive additives is sprayed at the same time through a nozzle close to the nozzle for said electrospraying or spray drying.
  12. The method of any one of claims 9 to 11, characterized in that said one or more carbon conductive additives are selected from carbon nanotube (CNT) , carbon nanoparticle and graphite.
  13. The method of claim 12, characterized in that the carbon nanotube (CNT) is open-ended, and the inner voids of the carbon nanotube (CNT) are filled with 1–30 wt.％, preferably 10–20 wt.％ of sulfur to form a sulfur-carbon nanotube composite (S/CNT) , based on the weight of the sulfur-carbon nanotube composite (S/CNT) .
  14. The method of any one of claims 9 to 13, characterized in that during step 2) , the product prepared from step 1) together with sulfur is heated at a temperature of 280–460 ℃, preferably 390–460 ℃, for 0.5–6 hours, preferably 0.5–4 hours, more preferably 0.5–3 hours, in a protective atmosphere.
  15. The method of any one of claims 9 to 14, characterized in that said sulfur-polyacrylonitrile composite has a sulfur load amount of 20–55 wt.％, preferably 30–50 wt.％, in each case based on the total weight of the sulfur-polyacrylonitrile composite.
  16. An electrode, characterized in that the electrode comprises the sulfur-polyacrylonitrile composite of any one of claims 1 to 8 or the sulfur-polyacrylonitrile composite prepared by the method of any one of claims 9 to 15.
  17. A lithium-sulfur battery, characterized in that the lithium-sulfur battery comprises the electrode of claim 16.
PCT/CN2015/086370 2014-08-07 2015-08-07 A sulfur-pan composite, a method for preparing said composite, and an electrode and a lithium-sulfur battery comprising said composite WO2016019901A1 (en)

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