Electrode, Method for Producing an Electrode and Energy Store having an Electrode

Abstract

A method for producing an electrode having an electrically conductive base element on which there is arranged an active material comprising a silicon nanostructure includes introducing a precursor mixture comprising a silicon-containing material and a base matrix into a spinning unit, arranging an electrically conductive base body at a defined distance from a delivery device of the spinning unit, and delivering at least part of the precursor mixture from the delivery device to the base body. The method further includes applying an electrical voltage between at least part of the spinning unit and the base body so as to spin a silicon-containing nanostructure onto the base body, heat-treating the silicon-containing nanostructure, removing the heat-treated nanostructure from the base body, processing the removed nanostructure to a slurry, and applying the slurry to the base element to produce the electrode.

Claims

1. A method for producing an electrode having an electrically conductive base element on which there is arranged an active material comprising a silicon nanostructure, the method comprising: introducing a precursor mixture comprising a silicon-containing material and a base matrix into a spinning unit; arranging an electrically conductive base body at a defined distance from a delivery device of the spinning unit; delivering at least part of the precursor mixture from the delivery device to the base body; applying an electrical voltage between at least part of the spinning unit and the base body so as to spin a silicon-containing nanostructure onto the base body; heat-treating the silicon-containing nanostructure; removing the heat-treated nanostructure from the base body; processing the removed nanostructure to a slurry; and applying the slurry to the base element to produce the electrode.

2. The method as claimed in claim 1, wherein the heat-treating is one or more of carried out in the absence of oxygen, carried out at a temperature in the range from 800 to 1000 C., and carried out for a period of 1 to 7 hours.

3. The method as claimed in claim 1, wherein the base body is formed of one or more of copper and aluminum.

4. The method as claimed in claim 1, wherein the applied voltage generates an electrical field of a magnitude in a range from 100 kV/m to 500 kV/m.

5. The method as claimed in claim 1, wherein spinning the silicon-containing nanostructure includes producing a wirelike silicon nanostructure having a length of >200 m.

6. The method as claimed in claim 1, wherein the base matrix is a polyolefin.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Further advantages and advantageous embodiments of the subject matter of the disclosure will be illustrated by the drawings and elucidated in the description below. It should be borne in mind here that the drawings have only a descriptive character, and are not intended to restrict the disclosure in any form. In the drawings,

[0029] FIG. 1 shows a schematic representation of a spinning unit for implementing the method of the disclosure; and

[0030] FIG. 2 shows a schematic representation showing the heat-treating step of the method of the disclosure.

DETAILED DESCRIPTION

[0031] FIG. 1 shows a schematic representation of a spinning unit 1 for implementing the method of the disclosure. In accordance with the disclosure it is possible in particular to produce an electrode having an electrically conductive base body 2, disposed on which there is an active material comprising a silicon nanostructure 3. An electrode of this kind may find use in particular in a lithium-based energy storage device, such as a lithium ion battery, a lithium polymer battery, or a thin-film lithium battery, for example.

[0032] In accordance with the disclosure a precursor mixture 4 is first introduced into the spinning unit 1. For this purpose, the spinning unit 1 may have, for example, a container 5 for the precursor mixture 4. This precursor mixture 4 comprises a silicon-containing material and a base matrix. This silicon-containing material may be selected from alkylsilanes, arylsilanes, or silicon nanoparticles. The base matrix may comprise a polymer, which more particularly may be selected from the group consisting of polyethylene, polypropylene, and polystyrene, polycaprolactone. Furthermore, the precursor mixture 4 may further comprise a solvent, which may be selected in respect of the polymer. Suitable solvents may be aromatics, alcohols, or ketones, for example.

[0033] The spinning unit 1, in particular on the container 5 or on its underside, additionally has a delivery means 6, such as a nozzle, for example. The base body 2 is disposed at a defined distance from the delivery means 6 of the spinning unit 1. The base body 2 may be formed of copper and/or aluminum, for example, or may consist of this or these materials. At least part of the precursor mixture 4 may then be delivered from the delivery means 6 or from the container 5. Additionally, between at least part of the spinning unit 1 and the base body 2, a voltage may be applied. A voltage may be used, for example, that generates an electrical field that is situated within a range from 100 kV/m to 500 kv/m. Furthermore, the voltage may be applied, for instance, between the base body 2 and the delivery means 6. The application of the voltage allows the electrospinning process itself to be carried out, in which a silicon-containing nanostructure 8, embedded in the base matrix, is spun onto the base body 2, in the way in which the flow 7 of the precursor mixture 4 is intended to show.

[0034] The silicon-containing nanostructure 8 that has been generated can subsequently be heat-treated, in order to produce a silicon nanostructure 3. The heat treatment may be carried out for instance in the absence of oxygen. Other advantageous conditions for the heat treatment include temperatures in a range from 800 to 1000 C. and/or periods in a range from 1 to 7 hours.

[0035] The heat treatment produces a silicon nanostructure, in which silicon may be encased, for example, in a further material, such as carbon, for instance, when a polymer is used as base matrix. Depending on the conditions employed, the silicon nanostructure may comprise particles, a fiber, or a mesh. This is shown in FIG. 2. In accordance with FIG. 2, a matrix 10, which is more particularly the base matrix, comprises a multiplicity of elements 9, more particularly of finely divided elements 9, of the silicon-containing material. As a result of different reaction conditions a), b), and c), particularly in the case of a heat-treating step or else of the actual electrospinning process, it is then possible to set the precise formation, such as the spatial arrangement, for instance, of the silicon nanostructure.

[0036] FIG. 2 describes in a nonrestricting manner a reaction of a precursor mixture 4 comprising a polymer. In principle it is possible here for a silicon nanostructure to be formed, with the silicon encased in carbon. This is indicated by the carbon shell C. In the case of the reaction a), for example, a silicon wire or a silicon fiber may be formed, which may have a length, for example, of >200 m and/or may be amenable to further processing to a weave structure, for example. This fiber may therefore be disposed in any of a very wide variety of configurations. In the case of the reaction conditions of reaction b), a substantially unordered mesh is obtained in which short silicon fibers are encased in a carbon shell C. In accordance with reaction c), individual silicon particles are produced, which are independent of one another and which are, again, encased in a carbon shell C obtained by carbonization of the polymer matrix. These particles may have a diameter in the range from 1 nm to 1000 nm, as for example 10 nm to 100 nm. To the skilled person it is understandable here that the aforesaid structures are intended to be only by way of example and without restriction.

[0037] In a further embodiment, the base element 2 may be an element of the kind that is able to serve only temporarily as a substrate for the application or generation of the silicon nanostructure, but does not serve as a constituent of an electrode. Instead, after the heat treatment, the nanostructure produced can be removed from the base body 2 and processed to a slurry with a solvent, such as N-methyl-2-pyrrolidone (NMP), acetone, tetrahydrofuran (THF), or methyl ethyl ketone (MEK), for example, or dispersed in the solvent. The slurry may then be applied to a base element for an electrode, for example in accordance with the so-called Bellcore technology, or by printing or knifecoating. The slurry or the dispersion here may further comprise, for example, a binder and/or conductive carbon. This embodiment may be suitable in particular for silicon nanoparticles as the silicon nanostructure. In this embodiment, it is possible to increase the density of silicon on the surface of the base element in the electrode, and hence to increase the capacity. In this embodiment, accordingly, the method of the disclosure encompasses the further steps of detaching the silicon nanostructure, more particularly comprising silicon nanoparticles, from the base element 2, dispersing the silicon nanostructure in a solvent, and applying the dispersion, more particularly by knifecoating or printing, to a base element of an electrode. The applied material may subsequently be dried.