WO2008059408A1

WO2008059408A1 - Electrochemical energy source and electronic device provided with such an electrochemical energy source

Info

Publication number: WO2008059408A1
Application number: PCT/IB2007/054540
Authority: WO
Inventors: Rogier A. H. Niessen; Petrus H. L. Notten
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2006-11-14
Filing date: 2007-11-08
Publication date: 2008-05-22

Abstract

Electrochemical energy sources based on solid-state electrolytes are known in the art. These (planar) energy sources, or 'solid-state batteries', efficiently convert chemical energy into electrical energy and can be used as the power sources for portable electronics. The invention relates to an improved electrochemical energy source. The invention also relates to an electronic device provided with such an electrochemical energy source.

Description

ELECTROCHEMICAL ENERGY SOURCE AND ELECTRONIC DEVICE PROVIDED WITH SUCH AN ELECTROCHEMICAL ENERGY SOURCE

FIELD OF THE INVENTION

The invention relates to an improved electrochemical energy source. The invention also relates to an electronic device provided with such an electrochemical energy source.

BACKGROUND OF THE INVENTION

Electrochemical energy sources based on solid-state electrolytes are known in the art. These (planar) energy sources, or 'solid-state batteries', efficiently convert chemical energy into electrical energy and can be used as the power sources for portable electronics. At small scale such batteries can be used to supply electrical energy to e.g. microelectronic modules, more particular to integrated circuits (ICs). An example hereof is disclosed in the international patent application WO 00/25378, where a solid-state thin-film micro battery is fabricated directly onto a specific substrate. During this fabrication process the first electrode, the intermediate solid-state electrolyte, and the second electrode are subsequently deposited as a stack onto the substrate. Presently, a wide range of solid electrolytes exist that can be utilized in the thin film battery design.

These include (among others) halide spinels (Li₂FeCl₄), halide rocksalts (LiI, LiBr), sulphides (Li₂S-P₂Ss), nitrides (Li₃N), Garnet-type structured (Li₅La₃Ta₂Oi₂), Li- silicates (Li₄SiO₄, Li₉SiAlOs), and Pervoskites (Li_2/3__3xLa_xTi0₃). However, many of these electrolytes are only stable within a restricted potential range. Li₃N for example is only stable within a potential range of between 0 and 0.44 V (in an electrochemical half cell measured versus Li/Li⁺), while Li_2/3-_3xLa_xTi0₃ is only stable within a potential range of between 1.5 and 4 V (in an electrochemical half cell measured versus LiZLi⁺). Outside these characteristic potential ranges the electrolytes are either electrochemically active (and thus unstable) at certain potentials and/or chemically unstable versus the used active electrode materials.

Electrochemical instability will lead to active reduction or oxidation of compounds, which results in a changed stoichiometry and hence to other material properties. Chemical incompatibility will lead to the formation of interfacial layers with undesired properties, or decomposing of one or both materials. It is an object of the invention to provide an improved electrochemical energy source having an increased stability window.

SUMMARY OF THE INVENTION This object can be achieved by providing an electrochemical energy source according to the invention, comprising: a substrate, and at least one cell deposited onto said substrate, the cell comprising: a first electrode, and a second electrode, wherein said first electrode and said second electrode being separated by a stack of electrolytic layers, said stack comprising at least one first electrolytic layer being stable within a first potential range, and at least one second electrolytic layer being stable within a second potential range deviating from the first potential range. By applying a stack of multiple electrolytic layers (instead of a traditionally applied single electrolytic layer), said electrolytic layers being stable within mutually deviating potential ranges, the overall stability of the electrochemical energy source can be improved significantly enabling the electrochemical energy source to be applied in high-power applications. In particular by intelligently matching two (or more) solid-state electrolytic layers, each electrolytic layer being stable within distinctive potential ranges respectively, a solid-state electrolytic laminate can be obtained with an overall stability range (i.e. the overall potential range in which the electrolytic laminate will operate in a stable manner) on the outer planes (in contact with the active electrode materials) that is large enough to be effectively applied in the electrochemical energy source according to the invention. Both chemical incompatibility and the electrochemical instability can be prevented, or at least counteract, by intelligent assembling the electrolytic stack. In this context it is noted that each of the adjacent solid electrolytes materials in the solid electrolyte laminate is preferably (electro)chemically stable versus each other to prevent chemical incompatibilities within the electrolytic stack.

Commonly, the first electrode comprises an anode, and the second electrode comprises a cathode. Preferably the electrolytic layer, being stable in the lowest potential range with respect to the potential range(s) of one or more other electrolytic layers is directed to the anode. In another preferred embodiment the electrolytic layer being stable in the highest potential range with respect to the potential range of at least one other electrolytic layer, is directed to the cathode. Applying the preferred orientations of the stack as mentioned in this paragraph will commonly optimise the overall stability of the electrolytic stack, and hence of the electrochemical energy source according to the invention. Preferably, at least one electrode of the energy source according to the invention is adapted for storage of active species of at least one of following elements: hydrogen (H), lithium (Li), beryllium (Be), magnesium (Mg), aluminium (Al), copper (Cu), silver (Ag), sodium (Na) and potassium (K), or any other suitable element which is assigned to group 1 or group 2 of the periodic table. So, the electrochemical energy source of the energy system according to the invention may be based on various intercalation mechanisms and is therefore suitable to form different kinds of (reserve-type) battery cells, e.g. Li- ion battery cells, NiMH battery cells, et cetera. In a preferred embodiment at least one electrode, more the battery anode, comprises at least one of the following materials: C, Sn, Ge, Pb, Zn, Bi, Sb, Li, and, preferably doped, Si. A combination of these materials may also be used to form the electrode(s). Preferably, n-type or p-type doped Si is used as electrode, or a doped Si-related compound, like SiGe or SiGeC. Also other suitable materials may be applied as anode, preferably any other suitable element which is assigned to one of groups 12-16 of the periodic table, provided that the material of the battery electrode is adapted for intercalation and storing of the abovementioned reactive species. The aforementioned materials are in particularly suitable to be applied in lithium ion based battery cells. In case a hydrogen based battery cell is applied, the anode preferably comprises a hydride forming material, such as AB5-type materials, in particular LaNi₅, and such as magnesium-based alloys, in particular Mg_xTii__x. The cathode for a lithium ion based cell preferably comprises at least one metal- oxide based material, e.g. LiCoO₂, LiNiO₂, LiMnO₂ or a combination of these such as. e.g. Li(NiCoMn)O₂. In case of a hydrogen based energy source, the cathode preferably comprises Ni(OH)₂ and/or NiM(OH)₂, wherein M is formed by one or more elements selected from the group of e.g. Cd, Co, or Bi.

In a preferred embodiment the stack comprises at least three electrolytic layers to achieve an improved overall stability of the electrolytic stack. Preferably, the electrolytic layers are ranged logically such that the electrolytic layers are stable in (gradually) increasing or decreasing potential ranges. In a particular preferred embodiment the electrolytic layer being stable in the lowest potential range with respect to the potential range the other electrolytic layers, is directed to the anode, and that the electrolytic layer being stable in the highest potential range with respect to the potential range of the other electrolytic layers, is directed to the cathode. In this manner the overall stability of the electrolytic stack can be commonly be maximised, and hence be optimised. In order to prevent electrochemical instability of one or more electrolytic layers of the stack, preferably layers are applied which are stable within partially overlapping potential ranges respectively. The presence of a commonly undesired range gap between the potential range of an electrolytic layer and another potential range of an adjacent electrolytic layer can be eliminated this way.

Preferably electrolytic layers are applied that exhibit a relatively high ionic conductivity. Utilization of multiple "narrow-stability" electrolytic layers with very high ionic conductivity to form the electrolytic stack, will lower the internal impedance of the electrochemical energy source according to the invention immensely, opening up the route towards power sources for high-drain applications. In a particular preferred embodiment the ionic conductivity of at least one, and more preferably all electrolytic layers is at least 10^~5 S/cm, preferably at least 10^~4 S/cm, more preferably at least 10^~3 S/cm, in particular at least 10^~2 S/cm. However, a combination of at least high ionic conductive layer (> 10^~5 S/cm) and at least low ionic conductive layer (<10^~5 S/cm) would also be conceivable for a person skilled in the art in certain situations.

In a preferred embodiment at least one electrode of the first electrode and the second electrode is patterned at least partially. By patterning or structuring one, and preferably both, electrodes of the electrochemical energy source according to the invention, a three-dimensional surface area, and hence an increased surface area per footprint of the electrode(s), and an increased contact surface per volume between the at least one electrode and the electrolytic stack is obtained. This increase of the contact surface(s) leads to an improved rate capacity of the energy source, and hence to an increased performance of the energy source according to the invention. In this way the power density in the energy source may be maximized and thus optimized. Due to this increased cell performance a small-scale energy source according to the invention will be adapted for powering a small-scale electronic device in a satisfying manner. Moreover, due to this increased performance, the freedom of choice of (small-scale) electronic components to be powered by the electrochemical energy source according to the invention will be increased substantially. The nature, shape, and dimensioning of the pattern may be various, as will be elucidated below. It is preferred that at least one surface of at least one electrode is substantially regularly patterned, and more preferably that the applied pattern is provided with one or more cavities, in particular pillars, trenches, slits, or holes, which particular cavities can be applied in a relatively accurate manner. In this manner the increased performance of the electrochemical energy source can also be predetermined in a relatively accurate manner. In this context it is noted that a surface of the substrate onto which the stack is deposited may be either substantially flat or may be patterned (by curving the substrate and/or providing the substrate with trenches, holes and/or pillars) to facilitate generating a three-dimensional oriented cell. Preferably, each electrode comprises a current collector. By means of the current collectors the cell can easily be connected to an electronic device. Preferably, the current collectors are made of at least one of the following materials: Al, Ni, Pt, Au, Ag, Cu, Ta, Ti, TaN, and TiN. Other kinds of current collectors, such as, preferably doped, semiconductor materials such as e.g. Si, GaAs, InP may also be applied to act as current collector.

The electrochemical energy source preferably comprises at least one barrier layer being deposited between the substrate and at least one electrode, which barrier layer is adapted to at least substantially preclude diffusion of active species of the cell into said substrate. In this manner the substrate and the electrochemical cell will be separated chemically, as a result of which the performance of the electrochemical cell can be maintained relatively long-lastingly. In case a lithium ion based cell is applied, the barrier layer is preferably made of at least one of the following materials: Ta, TaN, Ti, and TiN. It may be clear that also other suitable materials may be used to act as barrier layer. In a preferred embodiment preferably a substrate is applied, which is ideally suitable to be subjected to a surface treatment to pattern the substrate, which may facilitate patterning of the electrode(s). The substrate is more preferably made of at least one of the following materials: C, Si, Sn, Ti, Ge, Al, Cu, Ta, and Pb. A combination of these materials may also be used to form the substrate(s). Preferably, n-type or p-type doped Si or Ge is used as substrate, or a doped Si-related and/or Ge-related compound, like SiGe or SiGeC. Beside relatively rigid materials, also substantially flexible materials, such as e.g. foils like Kapton^® foil, may be used for the manufacturing of the substrate.

It may be clear that also other suitable materials may be used as a substrate material. The invention also relates to an electronic device provided with at least one electrochemical energy source according to the invention, and at least one electronic component connected to said electrochemical energy source. The at least one electronic component is preferably at least partially embedded in the substrate of the electrochemical energy source. In this manner a System in Package (Sip) may be realized. In a SiP one or multiple electronic components and/or devices, such as integrated circuits (ICs), actuators, sensors, receivers, transmitters, et cetera, are embeddded at least partially in the substrate of the electrochemical energy source according to the invention. The electrochemical energy source according to the invention is ideally suitable to provide power to relatively small high power electronic applications, such as (bio)implantantables, hearing aids, autonomous network devices, and nerve and muscle stimulation devices.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is illustrated by way of the following non- limitative examples, wherein:

Fig. Ia shows a schematic cross section of an electrochemical energy source according to the prior art,

Fig. Ib shows a schematic chart of the energy source according to figure Ia in an equilibrium state,

Fig. Ic shows a schematic chart of the energy source according to figure Ia during operation,

Fig. 2a shows a schematic cross section of an electrochemical energy source according to the invention, Fig. 2b shows a schematic chart of the energy source according to figure 2a in an equilibrium state, and

Fig. 2c shows a schematic chart of the energy source according to figure 2a during operation.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Figure Ia shows a schematic cross section of an electrochemical energy source 1 according to the prior art. The known electrochemical energy source 1 comprises a substrate 2 on top of which an electrochemical cell 3 is deposited. The cell 3 comprises a first electrode 4, an electrolyte 5, and a second electrode 6. In this example, the first electrode 4 consists of a first current collector 7, and an anode 8 deposited on top the first current collector 7, while the second electrode 6 consists of a cathode 9, and a second current collector 10 deposited on top of the cathode 9. In this example, the substrate 2 is made from silicon in which one or more electronic components 11 may be embedded, wherein the current collectors 7, 10 are commonly electrically connected to the electronic component(s) 11. Figure Ib shows a schematic chart of the energy source 1 according to figure Ia in an equilibrium state. In this example the situation is shown, wherein the electrochemical cell 3 is a lithium ion based cell 3. The anode 8 has a potential of about 0.3 V, whereas the cathode 9 has a potential of about 3.7 V. When a current is applied to this cell 3 during discharge (see figure Ib), electrochemical conversion takes place and the concentration of lithium changes both in the anode 8 and in the cathode 9, resulting in a potential distribution. This potential distribution is presently shown linearly. However, it is noted that this distribution will often be non- linearly in practice. Also, in the solid-state electrolyte 5 a concentration gradient of Li ions results in a potential change, and more particularly a linear drop. From figures Ib and Ic it is apparent that the single solid electrolyte 5 used needs to be stable against both the anode 8 and cathode 9, resulting in the fact that its electrochemical stability window should range from at least 0.3 - 3.6 V. Preferably this range should even be a bit higher (from 0 - 4 V) as overpotentials during charging conditions also need to be taken into account also. Unfortunately, only a very selected number of solid-state ionic conductors exhibit properties associated with this wide electrochemical stability range. Additionally, the solid electrolyte 5 employed needs to be chemically stable versus both active electrode materials. Unfortunately, the solid-state electrolytes which are deemed to be sufficiently stable are generally solid electrolytes with a non-ideal, medium-fast ionic conductivity of the order of 10^"6 S/cm. Examples hereof are the well-known LiPON and the Garnet-type Li₅La₃Ta₂Oi₂. The main drawback of using these materials is that the impedance of the electrolyte 5 in the operational cell 3 is rather large, resulting in a poor rate capability and making said batteries generally unsuitable for high-drain applications. Preferably one would like to incorporate and utilize solid electrolyte materials with a high ionic conductivity in the range of- 10^"3 S/cm. Examples hereof are Li₃N and Li_2/3-3_XLa_xTiθ₃ Perovskites. However, these only exhibit a sufficient stability in a relatively narrow potential range. Li₃N for example is merely stable between 0 and 0.44 V (in an electrochemical half cell measured versus Li/Li⁺), while Li_2/3- 3_XLa_xTi0₃ is merely stable between 1.5 and 4 V (in an electrochemical half cell measured versus Li/Li⁺).

Figure 2a shows a schematic cross section of an electrochemical energy source 12 according to the invention. The known electrochemical energy source 12 comprises a substrate 13 on top of which an electrochemical cell 14 is deposited. The cell 14 is a lithium ion based cell 14 and comprises a first electrode 15, an electrolyte 16, and a second electrode 17. The first electrode 15 consists of a first current collector 18, and an anode 19 deposited on top the first current collector 18, while the second electrode 17 consists of a cathode 20, and a second current collector 21 deposited on top of the cathode 20. Again, the substrate 13 is made from silicon in which one or more electronic components 22 may be embedded, wherein the current collectors 18, 21 are commonly electrically connected to the electronic component(s) 22. However, in the energy source 12 as shown in figure 2a the electrolyte 16 comprises a stack of multiple electrolytic layers 16a, 16b, wherein each electrolytic layer 16a, 16b is stable in a characteristic and distinctive potential range respectively. Both electrolytic layers 16a, 16b are made of different materials in this example. The application of a multilayered electrolyte 16 will improve the overall stability of the electrolyte 16 as will be elucidated further hereinafter. Figure 2b shows a schematic chart of the energy source according to figure 2a in an equilibrium state, wherein no current is flowing. When a current is applied to the cell 14 electrochemical conversion takes place, resulting in a potential distribution across the layers. This is shown in Figure Ib for discharging the battery cell 14. It should be obvious from Figure 2 that the potential range in which each individual solid electrolyte layer 16a, 16b is operational is much more restricted compared to the situation as shown in figures Ib and Ic. In this illustrative embodiment of the energy source 12 according to the invention, the electrolytic layer 16a directed to the anode 19 needs to be stable between roughly 0 - 2 V (in a lithium cell 14), whereas the electrolytic layer 16b directed to the cathode 20 needs to be stable between roughly 2 - 4 V (in a lithium cell 14). This implies that by intelligently matching two (or more) solid electrolyte layers 16a, 16b, wherein each layer 16a, 16b will be stable in a different potential range respectively, and wherein both layers 16a, 16b preferably are made of a material having high ionic conductivity (~ 10^"3 S/cm), an electrolyte 16 can be obtained with an increased overall stability on the outer planes in contact with the anode 19 and the cathode 20. In this example, the electrolytic layer 16a directed to the anode 19 is made of the Halide spinel Li₂FeCl₄, while the electrolytic layer 16b directed to the cathode 20 is made of the Perovskite Li₂/3-3χLa_xTiθ3. The mentioned the Halide spinel and the Perovskite have stability ranges of 0 - 3.3 V and 1.5 - 4 V, respectively. This combination can thus be successfully used in the battery cell 14 comprising a lithium metal anode 19 (average voltage plateau = 0 V) and a LiCoO₂ cathode 20 (average voltage plateau = 3.9 V). Although the electrochemical cell 14 of the energy source 12 shown in figure 2a is shown as planar stack, it will be clear the cell 14 could also be given a threedimensional orientation the improve the contact surface between the different layers 16a, 16b, 18, 19, 20, 21 of the cell 12.

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Claims

CLAIMS:

1. Electrochemical energy source, comprising: a substrate, and at least one cell deposited onto said substrate, the cell comprising: a first electrode, and - a second electrode, wherein said first electrode and said second electrode being separated by a stack of electrolytic layers, said stack comprising at least one first electrolytic layer being stable within a first potential range, and at least one second electrolytic layer being stable within a second potential range deviating from the first potential range.

2. Electrochemical energy source according to claim 1, characterized in that the first electrode comprises an anode, and/or that the second electrode comprises a cathode.

3. Electrochemical energy source according to claim 2, characterized in that the electrolytic layer, being stable in the lowest potential range with respect to the potential range of at least one other electrolytic layer, is directed to the anode.

4. Electrochemical energy source according to claim 2 or 3, characterized in that the electrolytic layer, being stable in the highest potential range with respect to the potential range of at least one other electrolytic layer, is directed to the cathode.

5. Electrochemical energy source according to one of claims 2-4, characterized in that both the anode and the cathode are adapted for storage of active species of at least one of following elements: H, Li, Be, Mg, Cu, Ag, Na and K.

6. Electrochemical energy source according to one of claims 2-5, characterized in that at least one of the anode and the cathode is made of at least one of the following materials: C, Sn, Ge, Pb, Zn, Bi, Li, Sb, and, preferably doped, Si.

7. Electrochemical energy source according to one of the foregoing claims, characterized in that the stack comprises at least three electrolytic layers.

8. Electrochemical energy source according to one of claims 2-6 and claim 7, characterized in that the electrolytic layer being stable in the lowest potential range with respect to the potential range the other electrolytic layers, is directed to the anode, and that the electrolytic layer being stable in the highest potential range with respect to the potential range of the other electrolytic layers, is directed to the cathode.

9. Electrochemical energy source according to one of the foregoing claims, characterized in that the potential ranges at least two adjacent electrolytic layers are respectively stable are partially overlapping potential ranges.

10. Electrochemical energy source according to one of the foregoing claims, characterized in that the ionic conductivity of at least one electrolytic layer is at least 10^~5

S/cm, preferably at least 10^"4 S/cm, more preferably at least 10^"3 S/cm, in particular at least 10^"2 S/cm.

11. Electrochemical energy source according to one of the foregoing claims, characterized in that both the electrodes are provided with at least one patterned surface.

12. Electrochemical energy source according to claim 11 , characterized in that the at least one patterned surface of the at least one electrode is provided with multiple cavities.

13. Electrochemical energy source according to claim 12, characterized in that at least a part of the cavities form pillars, trenches, slits, or holes.

14. Electrochemical energy source according to one of the foregoing claims, characterized in that the first electrode and the second electrode each comprises a current collector.

15. Electrochemical energy source according to one claim 14, characterized in that the at least one current collector is made of at least one of the following materials: Al, Ni, Pt, Au, Ag, Cu, Ta, Ti, TaN, and TiN.

16. Electrochemical energy source according to one of the foregoing claims, characterized in that the energy source further comprises at least one electron-conductive barrier layer being deposited between the substrate and at least one electrode, which barrier layer is adapted to at least substantially preclude diffusion of active species of the cell into said substrate.

17. Electrochemical energy source according to claim 16, characterized in that the at least one barrier layer is made of at least one of the following materials: Ta, TaN, Ti, and TiN.

18. Electrochemical energy source according to one of the foregoing claims, characterized in that the substrate comprises Si and/or Ge.

19. Electronic device, comprising at least one electrochemical energy source according to one of the claims 1-18, and at least electronic component connected to said electrochemical energy source.

20. Electronic device according to claim 19, characterized in that the at least one electronic component is at least partially embedded in the substrate of the electrochemical energy source.

21. Electronic device according to claim 19 or 20, characterized in that the at least one electronic component is chosen from the group consisting of: sensing means, pain relief stimulating means, communication means, and actuating means.

22. Electronic device according to one of claims 19-21, characterized in that the electronic device and the electrochemical energy source form a System in Package (SiP).