CN103050667A - Composite anode of multi-layer structure for lithium-sulfur rechargeable battery and preparation method - Google Patents

Abstract

The invention discloses a multi-layer structure composite positive electrode for a lithium-sulfur secondary battery and a preparation method thereof. , spray a layer of conductive film on its surface. The surface film of the positive electrode plays two roles of conduction and sulfur interception in the cycle process, thereby effectively improving the initial capacity retention rate and cycle stability of the battery.

Description

A kind of multilayer structure composite cathode for lithium-sulfur secondary battery and preparation method thereof

technical field

The invention belongs to the field of preparation of positive electrodes of sulfur secondary batteries, and relates to a method for preparing composite sulfur positive electrodes with a multi-level structure.

Background technique

With the gradual depletion of natural resources such as coal and oil, the energy crisis has become one of the major issues that human beings must solve in the future. And rechargeable batteries that are safe, cheap, high energy density and long life have attracted more and more attention.

Lithium-sulfur rechargeable batteries have very broad application prospects and are one of the most promising candidates for future lithium batteries. The theoretical specific capacity of elemental sulfur is 1675mAh/g, and when assembled with lithium to form a battery, its theoretical specific energy reaches 2600Wh/kg, which meets the requirements of electric vehicles for batteries, and also meets the requirements of "light, thin and small" batteries for portable electronic products . In addition, because sulfur also has the advantages of wide sources, low cost, and environmental friendliness, it will be widely used in lithium secondary batteries.

Despite these advantages of lithium-sulfur batteries, there are still many challenges to be faced. On the one hand, the poor electrical conductivity of sulfur (~5×10 ^-30 S/cm, 25°C) makes the electrochemical reaction difficult to realize, and it is difficult to be directly used as a cathode material. In order to have high electrical conductivity and reversible electrochemical reaction under high current, sulfur must be in close contact with additional electrical conductors before it can be used as a cathode material. On the other hand, polysulfide intermediates formed during charge and discharge are dissolved in anionic organic solvents and penetrate through the separator to reach the anode, where electrically insulating precipitates (Li ₂ S ₂ and Li ₂ S), reducing the conductivity of the lithium negative electrode, resulting in poor reversibility of charge and discharge and a decrease in capacity. During the discharge process, the expansion and accumulation of solid precipitates on the surface of the cathode can also lead to irreversible electrochemical reactions, which in turn leads to mass loss of active materials and further causes capacity fading.

In response to the challenges of poor conductivity of the sulfur cathode and sulfide dissolution, researchers have recently made some progress in improving electrode materials, optimizing operation processes, and selecting suitable electrolytes, such as developing new electrolyte systems to reduce sulfide in electrolysis. Dissolution in liquid; use carbon with high conductivity and high specific surface area to combine with sulfur to form a carbon-sulfur composite material; use conductive polymer as a carrier to infiltrate or replace sulfur into the polymer to form a conductive polymer- Sulfur composite materials; polymer-coated modified sulfur-containing cathode materials, etc.

Contents of the invention

The technical problem to be solved by the present invention is to provide a multi-layered structure composite sulfur compound (for a single positive electrode structure, a layer is added to its surface) for lithium-sulfur secondary batteries that can improve the initial capacity retention and cycle stability. Positive electrode and preparation method.

In order to achieve the above object, the inventors of the present invention tried to improve the positive electrode sheet. First, the inventors tried to improve the positive electrode material by directly spraying a conductive film on the positive electrode material on the surface of the positive electrode sheet by means of chemical deposition, electrochemical deposition, and sputtering, and controlled the conductivity of the positive electrode material. This dense conductive film inhibits the dissolution and shuttling of sulfide in the electrolyte at the same time, but what the inventors cannot understand is whether the above attempts can effectively improve the initial capacity retention and cycle stability. In addition, the inventors do not yet know What conditions should be controlled so that the positive pole piece sprayed with conductive film can still have low impedance and good conductivity. Through further research and development, the inventors found that when the thickness of the conductive thin film in the present invention is 10-1000 nm, the lithium-sulfur secondary battery can have a higher initial capacity retention rate and cycle stability. If it is higher than 1000nm, the contact between the material and the electrolyte will be significantly affected, the interface contact resistance will increase significantly, the battery polarization will be obvious, and the electrochemical performance will deteriorate. Dissolution in the electrolyte, poor first efficiency and cycle performance.

Therefore, through the above-mentioned research and development, the inventor proposes the following technical scheme of the present invention, including steps:

Mix the positive electrode active material, conductive agent, and binder evenly, coat it on the current collector, and then spray a layer of conductive film on its surface by means of magnetron sputtering, chemical deposition or electrochemical deposition; the conductive film The thickness is 10-1000nm.

The active substance is one or more of sulfur powder, sulfur-carbon composite, inorganic sulfide, and organic sulfide; the conductive agent is one or more of conductive carbon black, acetylene black, and graphite powder; The binding agent is one or more of polyvinyl alcohol, polytetrafluoroethylene emulsion, sodium carboxymethyl cellulose, polyolefins, SBR rubber, fluorinated rubber, PVDF/NMP, polyurethane; The mass ratio of the substance, the conductive agent and the binder is 50-98:1-20:1-30.

The sulfur-carbon composite is one or more of porous carbon-sulfur composites, carbon nanotube-sulfur composites, carbon fiber-sulfur composites, graphene-sulfur composites, and hollow carbon sphere-sulfur composites. The mass percent content of sulfur in the sulfur-carbon composite is 10%-90%.

The current collector is one of aluminum foil, aluminum mesh, carbon mesh and carbon film.

The conductive film is composed of one or more of carbon, foil, gold, silver, copper, indium, indium oxide, indium tin oxide, ruthenium dioxide, polyaniline, and polypyrrole.

The surface film in the positive electrode structure designed by the present invention plays two roles of conduction and sulfur interception during the cycle of the battery, thereby improving the initial capacity retention rate and cycle stability of the battery.

The beneficial effects that the present invention has are:

The multi-layer structure composite sulfur positive electrode prepared by the method of the present invention has the following advantages: the conductive film is directly sprayed on the surface of the positive electrode sheet by means of chemical deposition, electrochemical deposition, and sputtering, and the sprayed film can have a smooth surface and a controllable thickness. , the characteristics of less raw materials required. The conductive film sprayed on the surface of the material is in close contact with the positive electrode material, and the technical solution of the present invention well controls the occurrence of excessive interfacial contact impedance while fully suppressing the dissolution and shuttling of sulfide in the electrolyte, which can make On the one hand, the present invention increases the conductivity of the electrode, and on the other hand, wraps the sulfur exposed on the surface, so that the generated lithium sulfide can be intercepted during the cycle, and the dissolution and shuttling of the sulfide in the electrolyte can be inhibited. The initial capacity retention rate and cycle performance of the sulfur cathode material with the structure of the present invention are obviously improved.

In summary, the present invention is an efficient method for preparing a multi-layer structure composite sulfur cathode with high conductivity and inhibited sulfide dissolution shuttling. This method can significantly improve the initial capacity retention rate and cycle stability of the lithium-sulfur battery.

Description of drawings

The accompanying drawing is a schematic structural view of the positive electrode sheet of the present invention.

Detailed ways

The present invention will be further described below in combination with specific embodiments. The following examples are intended to illustrate the present invention without further limiting the invention.

Example 1:

Using polyvinyl alcohol as binder, conductive carbon black as conductive agent, and carbon nanotube-sulfur composite materials with sulfur content of 10%, 25%, 50%, and 75% as active material, according to active material: conductive Agent: The binder is mixed in a mass ratio of 8:1:1, ground evenly, scraped on the aluminum foil current collector, dried in a vacuum oven at 60°C for 24 hours, and then placed in a magnetron sputtering machine. A layer of conductive carbon is sputtered on its surface (the sputtering time is 10min, and the target used is a conductive carbon target), and a multi-layer structure composite sulfur positive electrode can be obtained. The thickness of the carbon film is 10nm. The electrochemical cycle performance was tested in the voltage range of V. See Table 1 under the current density of 160mA/g(S).

Experimental conditions and results of table 1 example 1

Example 2:

Use PVDF as the binder (NMP as the solvent), acetylene black as the conductive agent, and sublimed sulfur powder as the active material, mix according to the mass ratio of active material: conductive agent: binder: 6:3:1, and grind evenly , scrape-coated on the carbon mesh current collector, dried in a vacuum oven at 60°C for 24 hours, used it as the cathode, and used the silver plate as the anode, and silver-plated the surface in a silver nitrate solution to obtain a multi-layer structure composite sulfur cathode , the thickness of the coating is 2, 100, 750, 2000nm respectively, and the electrochemical cycle performance of the assembled button battery is tested in the voltage range of 3.0-1.5V and the current density of 160mA/g(S). Its 1 ^st , 2 ^nd and 50 ^th discharge specific capacities are shown in Table 2.

Experimental condition and result of table 2 example 2

Example 3:

Sodium carboxymethyl cellulose is used as a binder, conductive carbon black is used as a conductive agent, and molybdenum disulfide is used as an active material, and the active material: conductive agent: binder is mixed according to the mass ratio of 5:3:2, and ground Evenly, scrape it on the aluminum mesh collector, dry it in a vacuum oven at 60°C for 24 hours, insert it into the solution containing aniline monomer after treatment, and add potassium persulfate solution drop by drop to make the polyaniline sticky. Attached to the surface of the pole piece and dried to obtain a multi-layer structure composite sulfur positive electrode, the thickness of the coating is 1000nm, and it is assembled into a button battery. Electrochemical cycle performance The electrochemical cycle performance was tested. Its 1 ^st , 2 ^nd and 50 ^th discharge specific capacities are 1051, 903, 843mAh/g, respectively.

Claims (6)

1. the preparation method of a kind of multilayered structure anode composite for lithium-sulfur rechargeable battery, it is characterised in that including following preparation process：Positive active material, conductive agent, binding agent are well mixed, on a current collector, then on its surface, the mode through magnetron sputtering, chemical deposition or electrochemical deposition sprays layer of conductive film for coating；The thickness of the conductive film is 10~1000nm.

2. it is according to claim 1 a kind of for multilayered structure anode composite of lithium-sulfur rechargeable battery and preparation method thereof, it is characterised in that：The active material is the one or more in sulphur powder, sulphur carbon complex, inorganic sulphide, organic sulfur compound；The conductive agent is the one or more in conductive carbon black, acetylene black, graphite powder；The binding agent is the one or more in polyvinyl alcohol, ptfe emulsion, sodium carboxymethylcellulose, TPO, SBR rubber, Viton, PVDF/NMP, Polyurethane；The active material, conductive agent, the mass ratio of binding agent are 50~98：1~20：1~30.

3. it is piece according to claim 2 a kind of for multilayered structure anode composite of lithium-sulfur rechargeable battery and preparation method thereof, it is characterised in that：The sulphur carbon complex is the one or more in porous carbon-sulfur compound, CNT-sulfur compound, carbon fiber-sulfur compound, graphene-sulfur compound, hollow carbon balls-sulfur compound；The weight/mass percentage composition of sulphur is 10%~90% in the sulphur carbon complex.

4. it is according to claim 1 a kind of for multilayered structure anode composite of lithium-sulfur rechargeable battery and preparation method thereof, it is characterised in that：The collector is one kind in aluminium foil, aluminium net, carbon net, carbon film.

5. it is according to claim 1 a kind of for multilayered structure anode composite of lithium-sulfur rechargeable battery and preparation method thereof, it is characterised in that：The composition of the conductive film is the one or more in carbon, platinum, gold, silver, copper, indium, indium oxide, indium tin oxide, ruthenic oxide, polyaniline, polypyrrole.

6. a kind of multilayered structure anode composite for lithium-sulfur rechargeable battery obtained by the method described in claim any one of 1-5.