DE102016011895A1 - Coated solid electrolyte for solid battery cell - Google Patents

Abstract

The invention relates to a solid electrolyte (1) for a solid state battery cell (3), the side of the solid electrolyte (1) facing the solid state battery cell (3) in an installed state of the anode (4) and the solid state battery cell (3) facing the cathode (5) Side of the solid electrolyte (1) has a coating (2, 2 ') made of aluminum oxide or an ion-conducting glass. The invention further relates to a method for producing the solid electrolyte (1) and a solid-state battery cell (3) with the solid electrolyte (1).

Description

The invention relates to a coated solid electrolyte for a solid state battery cell. Furthermore, the invention relates to a method for producing such a coated solid electrolyte and a solid-state battery cell with the coated solid electrolyte.

Due to dwindling fossil raw materials and thus the expected medium and long-term rising prices for fuels based on such raw materials and anthropogenic carbon dioxide emissions and the associated climate changes in recent years, the topics of electric mobility and energy supply by means of so-called. renewable energy sources has become a focus of interest.

In the field of electromobility, there are various approaches, ranging from purely battery electric powered vehicles, over electrically powered vehicles (plug-in hybrid vehicles and serial hybrid vehicles) to vehicles with a fuel cell as the main energy source. In purely battery-powered vehicles - as the term implies - exclusively rechargeable batteries (traction batteries) are used as energy sources. In electrically powered vehicles as powerful as possible rechargeable batteries serve that their internal combustion engines must be used as little as possible, as well as a cache for energy recovered by recuperation. And also in fuel cell vehicles is regularly a secondary battery for times of high power demand and as a buffer for energy recovered by recuperation provided.

The availability of regenerative energy sources, such as sunlight and wind, is known to be subject to large fluctuations (daytime, seasonal, regional, etc.), requiring a stable energy supply based on regenerative energy sources, such as the storage of excess, already in electrical Energy converted regenerative energy at low-consumption times or times of a high supply of renewable energy. One way of doing this is to store electrical energy in rechargeable batteries. For the sake of simplicity, rechargeable batteries, secondary batteries, traction batteries, etc. are often referred to simply as "batteries."

At the time of this application dominate in the field of traction batteries for at least electrically powered vehicles as well as (intermediate) storage medium for regenerative energies quite clearly lithium-ion batteries. In conventional lithium ion batteries, lithium transition metal oxides (eg LiCoO ₂ ) or lithium transition metal phosphates (eg LiFePO ₄ ) are often used as cathode materials and a carbon material (such as graphite) as the anode material. During the discharge process, lithium ions intercalate into the cathode and deintercalate out of the cathode during the charging process; a corresponding opposite process takes place at the anode. Arranged between the cathode and anode are often a liquid electrolyte and a separator through which the lithium ions move. A liquid electrolyte for lithium-ion battery regularly contains one or more aprotic organic compounds (solvents) and one or more conductive salts.

Other types of batteries that are currently predominantly still in the research stage, in which alternative metal ions are used for lithium ions (for example, sodium ions, aluminum ions, magnesium ions, etc.) often have a similar structure on.

In the case of liquid electrolytes, there is a risk of their leakage from the battery cell and its ignition in the event of overheating of the battery cell. Moreover, many currently known liquid electrolytes are certainly toxic to mammals, including humans.

Against this background efforts have been and are being made to replace liquid or even gel electrolyte for solid electrolyte. In a solid electrolyte, at least one type of ion is mobile so that an electric current carried by this type of ion can flow. Solid electrolytes are thus electrically conductive, in contrast to metals but no or only a small electronic conductivity. There are known organic solid electrolytes, which are based predominantly on polymers, as well as crystalline and amorphous solid electrolytes.

Solid electrolytes exhibit increased resistance to ion transport compared to liquid electrolytes (with the same layer thickness and more comparable temperature), resulting in a reduced power density compared to conventional batteries. This disadvantage is attempted to be counteracted by the smallest possible thickness of the solid electrolyte.

Another problem of solid electrolytes arises in relation to the transition between the solid electrolyte and the likewise fixed electrodes. While a liquid electrolyte itself "Seamlessly" adapted to the surface of the fixed electrodes and possibly even penetrate into the pores of the electrodes, this is not possible for the solid electrolyte. This results in the disadvantage of an increased contact resistance between the electrodes and the solid electrolyte compared to liquid electrolytes. This disadvantage is tried to be counteracted by the most intimate possible "pressing" of anode, solid electrolyte and cathode.

However, the layers of a solid state battery cell have different material compositions and different thermal expansion coefficients. Due to the changing temperatures during operation of a solid-state battery cell, different extents of the individual layers thus occur. The associated mechanical stress leads in currently known solid state battery cells to rapid aging due to cracking at the contact surfaces between the solid electrolyte and the respective electrode and the consequent decreasing electrical and ionic conductivity.

In the field of lithium-ion batteries include solid electrolytes based on LATP (Li _{1 + x} Al _x Ti _2-x (PO ₄ ) ₃ ) and LAGP (Li _{1 + x} Al _x Ge ₂ Ti _2-x (PO ₄ ) ₃ ) known. For example, the LATP and LAGP solid electrolytes may be prepared by melting an appropriate mixture of starting materials, pouring the resulting melt onto an iron plate, and quenching the melt. The glass-ceramic melt, which has been broken into pieces, can then be ground to a powder, pressed into platelets, and the pellets sintered (see, for example: Yuantao Cui, C. Ziebert, M. Rohde: Solid electrolytes for high-temperature lithium-ion batteries; Production and characterization of solid electrolytes and cells based thereon; in: Impulses for the Future of Energy, Doctoral Symposium, June 13, 2013; KIT Scientific Publishing; ISBN 978-3-7315-0097-1; Pp. 33-38 ).

However, such solid electrolytes often show a high brittleness, so that they can be processed only badly as larger areas. And even if it is possible to produce and process such solid electrolytes over a large area, cracking in the solid electrolyte is increasingly to be expected in solid-state battery cells equipped with vibrations such as occur, for example, in vehicles.

From the field of metal batteries (such as lithium batteries) and metal ion batteries, it is also known to provide the anode with a glassy or amorphous protective layer, such as the formation of dendrites and "mossy" metal deposits at the anode to prevent or minimize, and / or to avoid direct contact between the anode and the liquid electrolyte (see US 6,025,094 ; WO 01/39303 A1 and WO 2005/083829 A2 ).

It is an object of the present invention to provide a solid electrolyte improved in comparison with the prior art and a solid state battery cell equipped therewith. This object is achieved by the solid electrolyte according to claim 1, the method for producing a solid electrolyte according to claim 4 and the solid state battery cell according to claim 6. Advantageous developments and refinements of the present invention are the subject of the dependent claims and can be taken from the following description, the figures and the description of the figures become.

According to the invention, a solid electrolyte for a solid-state battery cell is proposed, which is characterized in that in an installed state of the anode of the solid state battery cell facing side of the solid electrolyte and the cathode of the solid state battery cell facing side of the solid electrolyte having a coating of aluminum oxide or an ion-conducting glass.

By coating a solid electrolyte with alumina or an ion-conducting glass having a surface which has only a very low roughness, a sliding of the existing and pressed in a solid state battery cell electrodes (anode, cathode) is possible. As a result, a mechanical aging is avoided by the different temperatures at different temperatures expansions of the three layers of the solid state battery cell (solid electrolyte, anode, cathode) and it significantly reduces the cyclical aging of the cell layers. The electrical contact does not change, whereby the internal resistance remains constant.

The layer thickness of the aluminum oxide or glass layer is not particularly limited, but is advantageously in the range of 0.8 .mu.m to 7 .mu.m.

Also, advantageously, the solid electrolyte according to the present invention is a ceramic or composite solid electrolyte.

• – Bereitstellen eines flächigen Feststoffelektrolyts, bevorzugt eines flächigen keramischen oder flächigen Komposit-Feststoffelektrolyts,
• – Aufbringen einer Beschichtung aus Aluminiumoxid oder einem ionenleitenden Glas auf der in einem Einbauzustand der Anode der Feststoffbatteriezelle zugewandten Seite des Feststoffelektrolyts und der der Kathode der Feststoffbatteriezelle zugewandten Seite des Feststoffelektrolyts, wobei die Beschichtung bevorzugt eine Dicke im Bereich von 0,8 μm bis 7 μm aufweist; und
• – Sintern des beschichteten Feststoffelektrolyts.

Also encompassed by the present invention is a process for producing a solid electrolyte according to the invention or one of its advantageous developments and refinements, comprising the steps:

• Providing a flat solid electrolyte, preferably a flat ceramic or sheet-like composite solid electrolyte,
• Applying a coating of aluminum oxide or an ion-conducting glass on the side of the solid electrolyte facing the anode of the solid state battery cell and the side facing the cathode of the solid electrolyte cell side of the solid electrolyte, wherein the coating preferably has a thickness in the range of 0.8 .mu.m to 7 .mu.m having; and
• - sintering of the coated solid electrolyte.

In the process, the coating can be applied in any suitable manner, but advantageously using a laser transfer or gas deposition process.

Also included in the present invention is a solid state battery cell having an anode, cathode and a solid electrolyte disposed between anode and cathode, which is characterized in that the solid electrolyte is one prepared according to the present invention or one according to the present invention.

The solid-state battery cell according to the present invention may be, for example, a prismatic or round cell.

Further advantages, features and details of the invention will become apparent from the following description of a preferred embodiment and from the drawing. The features and feature combinations mentioned above in the description as well as the features and feature combinations mentioned below in the description of the figures and / or in the figures alone can be used not only in the respectively specified combination but also in other combinations or in isolation, without the scope of To leave invention.

Showing:

1 A schematic, not to scale example of a solid electrolyte according to the present invention;

2 a schematic, not to scale example of a solid state battery cell according to the present invention.

In the figures, the same elements and functionally identical elements are provided with the same reference numerals.

As in the 1 and 2 is shown schematically and not to scale, the solid electrolyte 1 according to the present invention both in the state of installation of the anode 4 a solid-state battery cell 3 facing side as well as in the installed state of the cathode 5 a solid-state battery cell 3 facing side a coating 2 . 2 ' of alumina or an ion-conductive glass.

Of course, the solid electrolyte 1 according to the present invention also be provided on all its surfaces with a coating of aluminum oxide or an ion-conducting glass.

The solid electrolyte 1 is not particularly limited, but it is the solid electrolyte 1 advantageously a ceramic or a composite solid electrolyte 1 , preferably a ceramic solid electrolyte 1 , A variety of ceramic and composite solid electrolytes are known to those skilled in the art.

To have the smoothest possible surface of the coating 2 . 2 ' and at the same time a very good conductive connection between the solid electrolyte 1 and the coating 2 . 2 ' It is advantageous if in a first step on the provided solid electrolyte 1 the coating 2 . 2 ' the two sides, for example by means of a laser transfer or gas deposition process ("pulsed laser deposition", chemical vapor deposition, etc.) takes place and then the coated solid electrolyte 1 subjected to a sintering process.

Unless provided in the present application of a provided sheet solid electrolyte 1 is spoken of, including a precursor of a finished solid electrolyte 1 to understand. As mentioned above, solid electrolytes 1 For example, be prepared by a sintering process of compacts of a suitable material. It is therefore encompassed by the present invention if such or a similar precursor of a solid electrolyte 1 is provided in flat form, this precursor then at least on the two, in an installed state of each electrode 4 . 5 facing sides with a coating 2 . 2 ' is provided from aluminum oxide or an ion-conducting glass and from this thus coated precursor by a subsequent sintering process, the finished coated solid electrolyte 1 will be produced.

The conditions for the sintering process can usually be based on the parameters for the sintering process, which also for the production of the non-coated solid electrolyte 1 would come to the application. There is great flexibility in terms of the temperatures used, the temperature profile, the duration, etc. Suitable or optimized parameters are known to a person skilled in the art or he can determine these by a few experiments.

By the inventively provided coating 2 . 2 ' may also be solid state battery cells with a solid electrolyte 1 can be produced without this coating 2 . 2 ' would not be suitable for the respective battery type, for example. Because of the solid electrolyte 1 react with the anode material or would be destroyed by the anode material.

For the purposes of the present invention, it is necessary that the coating 2 . 2 ' in any case, for the metal ion of the active material (in the case of a lithium or lithium-ion battery, that is to say for the lithium ion), it is ionically conductive. In addition, however, it is advantageous if the coating 2 . 2 ' is also ionic for other metal ions, such as, for example, for the almost always present sodium or magnesium ions. If such "additional" ionic conductivity is not present, there is a risk that the ionic conductivity as a whole by a "clogging" of the coating 2 . 2 ' by these "foreign ions" decreases rapidly. As the inventor has found, such "clogging" can be achieved by a sufficiently thin coating 2 . 2 ' , Which by means of a sintering process a highly inflated structure with the solid electrolyte 1 (Fixed ion conductor) trains to be bypassed.

A person skilled in the art knows a large number of glass types which have the required ion conductivity (s). Against this background, a person skilled in the art can select a suitable type of glass for the particular type of solid-state battery cell or determine and / or produce a suitable type of glass by a few experiments. In that regard, reference is expressly made to the cited prior art and the glasses mentioned therein, of which an ionic conductivity is known.

Since, as the inventor has found out, for the purposes of the present invention thinnest coatings 2 . 2 ' are sufficient with a thickness in the range of about 0.8 microns to 7.0 microns, is provided by the inventively provided coating 2 . 2 ' the volumetric energy density of a solid state battery cell practically not adversely affected. Due to the smooth surface of the coatings 2 . 2 ' However, sliding the layers of the solid state battery cell (anode, cathode, coated solid electrolyte) against each other allows (ie no cracking due to different expansion coefficients), which significantly reduces the cyclical aging of the cell layers.

The alumina or glass layer usually has a coefficient of thermal expansion, that of the solid electrolyte 1 very similar or with that of the solid electrolyte 1 is identical. Because of this circumstance and the thinness of the coating 2 . 2 ' There are also no problems with respect to the expansion of the solid electrolyte in the various temperatures occurring during operation of a solid-state battery cell 1 on the one hand and the coating 2 . 2 ' on the other hand.

The solid battery cell 3 According to the present invention, there is no particular limitation, and all the battery technologies that are suitable for a solid-state battery cell may be provided 3 suitable. In the solid battery cell 3 Thus, it may be about a metal battery, a metal-ion battery, a metal-sulfur battery, etc. As active metals for a solid state battery cell 3 For example, lithium, sodium, aluminum, magnesium, etc. may be provided. Suitable anodes 4 and cathodes 5 These are known to a person skilled in the art.

The solid battery cell 3 According to the present invention, for example, can be prepared by technically conventional pressing (calendering under heat) of the coated solid electrolyte 1 with the two electrodes 4 . 5 ,

The geometric shape of the solid-state battery cell 3 There is also no particular restriction and this may be a prismatic or a round cell. A solid-state battery often consists of a plurality of solid-state battery cells 3 which are suitably connected in parallel and / or in series with each other.

LIST OF REFERENCE NUMBERS

1

Solid electrolyte

2, 2 '

coating

3

Solid battery cell

4

anode

5

cathode

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 6025094 [0014]
• WO 01/39303 A1 [0014]
• WO 2005/083829 A2 [0014]

Cited non-patent literature

• Yuantao Cui, C. Ziebert, M. Rohde: Solid electrolytes for high-temperature lithium-ion batteries; Production and characterization of solid electrolytes and cells based thereon; in: Impulses for the Future of Energy, Doctoral Symposium, June 13, 2013; KIT Scientific Publishing; ISBN 978-3-7315-0097-1; Pp. 33-38 [0012]

Claims (7)

Solid electrolyte ( 1 ) for a solid state battery cell ( 3 ), characterized in that in an installed state of the anode ( 4 ) of the solid state battery cell ( 3 ) facing side of the solid electrolyte ( 1 ) and the cathode ( 5 ) of the solid state battery cell ( 3 ) facing side of the solid electrolyte ( 1 ) a coating ( 2 . 2 ' ) of alumina or an ion-conductive glass. Solid electrolyte ( 1 ) according to claim 1, characterized in that the coating ( 2 . 2 ' ) has a thickness in the range of 0.8 microns to 7 microns. Solid electrolyte ( 1 ) according to one of claims 1 or 2, characterized in that the solid electrolyte ( 1 ) is a ceramic or composite solid electrolyte. A process for producing a solid electrolyte according to any one of claims 1 to 3, comprising the steps of: Providing a flat solid electrolyte, preferably a flat ceramic or sheet-like composite solid electrolyte, Applying a coating of aluminum oxide or an ion-conducting glass on the side of the solid electrolyte facing the anode of the solid state battery cell and the side facing the cathode of the solid electrolyte cell side of the solid electrolyte, wherein the coating preferably has a thickness of in the range of 0.8 .mu.m to 7 has μm; and - sintering of the coated solid electrolyte. The method of claim 4, wherein the coating is applied using a laser transfer or gas deposition process. Solid state battery cell ( 3 ) with an anode ( 4 ), Cathode ( 5 ) and one between anode ( 4 ) and cathode ( 5 ) arranged solid electrolyte ( 1 ), characterized in that the solid electrolyte ( 1 ) one according to one of claims 1 to 3 or one produced according to one of claims 4 or 5. Solid state battery cell ( 3 ) according to claim 6, characterized in that it comprises a prismatic or round cell ( 3 ).

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