Patent Application
20180331400
This application claims the priority benefit of French Application for Patent No. 1754148, filed on May 11, 2017, the disclosure of which is hereby incorporated by reference in its entirety to the maximum extent allowable by law.
The present application relates to a lithium battery.
It is known to use lithium batteries in electronic devices such as laptops, mobile phones and tablet computers.
There are a number of types of lithium battery such as a lithium-ion battery, a lithium-polymer battery or a lithium-metal battery. Each of these types of battery is characterized by the materials composing the various elements of the battery.
A lithium-metal or lithium-ion battery may be formed from a cathode made of lithium cobalt oxide (LiCoO2), an electrolyte made of lithium phosphorus oxynitride (LiPON) and an anode. In the case of a lithium-metal battery, the anode is made of lithium (Li). In the case of a lithium-ion battery, the anode is a lithium intercalation compound or a compound that allows an alloy to be formed with lithium, for example LiFePO4, graphite, Li4Ti5O12 or a TiSi or TiGe alloy. The whole lot is encapsulated in a protective layer. LiPON is a solid electrolyte allowing thin and flexible lithium batteries to be produced. The small thickness of these batteries allows them to be integrated into thin devices. The flexibility of these batteries allows them to be integrated into flexible devices. For example, such batteries may be integrated into the strap of a wristwatch in order to power the electronic circuitry of the watch. Moreover, it is also possible to stack these batteries to form a compact module in which the batteries are connected in series and/or in parallel.
In known lithium-metal and lithium-ion batteries using LiCoO2 by way of cathode material, protuberances frequently form in the encapsulating layer during charging cycles and in particular during the first charging cycle. These protuberances result from gas bubbles trapped under the encapsulating layer and can cause various problems. When the battery is deformed, for example when it is bent, cracks may form in the encapsulating layer, thus exposing the anode, cathode and/or electrolyte layers of the battery to open air. These protuberances also make it difficult, or even impossible, to stack a plurality of batteries to produce a compact module of a plurality of batteries connected in series and/or parallel.
The present application aims to decrease, or even suppress, these protuberances.
In an embodiment, a lithium-metal or lithium-ion battery comprises a stack including a cathode layer made of LiCoO2, an anode layer and an electrolyte layer made of LiPON between the anode and cathode layers; an encapsulating layer covering the stack; and an interface layer made of a material that is configured to capture oxygen and placed under the encapsulating layer.
According to one embodiment, the interface layer is made of a material configured to capture oxygen via an oxidation chemical reaction.
According to one embodiment, said material is a metal chosen from the group comprising copper, aluminum, zinc and titanium.
According to one embodiment, said material is a substoichiometric metal oxide.
According to one embodiment, said material is aluminum oxide.
According to one embodiment, the encapsulating layer is adhesively bonded to the stack by an adhesive layer.
According to one embodiment, the encapsulating layer comprises an aluminum film coated with a film of polyethylene terephthalate.
According to one embodiment, the encapsulating layer has a thickness smaller than 150 μm.
These features and advantages, and others, will be described in detail in the following description of particular embodiments, which description is given without limitation and with reference to the appended figures, in which:
The figures have not been drawn to scale and, for the sake of clarity, only those elements that are useful to understanding the described embodiments have been shown and described in detail. In particular, the topology, as seen from above, of the anode and cathode contacts of the batteries described below has not been described in detail since it is within the capabilities of a person skilled in the art to adapt this topology to the targeted application and in particular depending on the way in which the battery must be connected.
In the following description, when the terms “left”, “right”, “upper”, “lower”, “flank”, etc. are used, reference is being made to the orientation of the elements in question in the corresponding figures. Unless otherwise specified, the expression “about” means to within 10% and preferably to within 5%.
For a battery, the term “anode” means the negative electrode and the term “cathode” means the positive electrode.
On most of the carrier 3 (on the right in the figure) is placed a conductive layer 5 that is optionally arranged on a binding layer 7. The conductive layer 5 is made of a metal, for example of platinum, and has a thickness comprised between 50 nm and 10 μm and, for example, of about 100 nm. The binding layer 7 is made of lithium cobalt oxynitride (LiCoON) and has a thickness comprised between 50 nm and 10 μm and, for example, of about 1 μm. The conductive layer 5 is a cathode contact layer. On a small portion of the carrier 3 (on the left in the figure) is placed a conductive layer 9 that is optionally arranged on a binding layer 11. The material of the conductive layer 9 is preferably identical to that of the conductive layer 5. The material of the binding layer 11 is preferably identical to that of the binding layer 7. A metal layer section 13, which is for example made of copper, straddles one end of the conductive layer 9 and the carrier 3. The layer 13 has a thickness comprised between 50 nm and 10 μm and is, for example, about 500 nm. The layers 9 and 13 form an anode contact.
On most of the conductive layer 5 rests a stack 14 comprising a cathode layer 15 made of lithium cobalt oxide (LiCoO2), an electrolyte layer 17 made of lithium phosphorus oxynitride (LiPON), and an anode layer 19 that is, for example, made of lithium (Li). The lower face of the cathode layer 15 makes contact with the cathode contact layer 5. The cathode layer 15 has a thickness comprised between 2 and 50 μm and, for example, of about 10 μm. The electrolyte layer 17 is between the cathode layer 15 and the anode layer 19 and separates these layers 15 and 19 from each other. The lower face of the layer 17 makes contact with the layer 15 and the upper face of the layer 17 makes contact with the layer 19. In the example shown, the electrolyte layer 17 juts out from one side of the stack 14 (to the right of the layer 15 in the figure), on the conductive layer 5, and on another side of the stack 14 (to the left of the layer 15 in the figure), on the carrier 3, without making contact with the layer 13. The electrolyte layer 17 has a thickness comprised between 0.5 and 5 μm and for example of about 2 μm. The anode layer 19 covers most of the electrolyte layer 17. The anode layer 19 juts out from one side of the stack 14 (to the left in the figure) and extends as far as to the copper layer 13. The anode layer 19 has a thickness comprised between 50 nm and 20 μm and, for example, of about 5 μm.
An encapsulating layer 21 covers the various elements of the battery and in particular the layers 15, 17 and 19 of the stack 14 in such a way as to leave accessible only a portion of the conductive layer 5 and a portion of the conductive layer 9. The free portion of the layer 5 forms a zone allowing for a cathode contact redistribution 23 and the free portion of the layer 9 forms a zone allowing for an anode contact redistribution 25.
The encapsulating layer 21, for example, consists of an aluminum film covered with a film of polyethylene terephthalate (PET), also known by the abbreviation PET-alu. When the layer 21 is of PET-alu, the aluminum film is always separated from the anode layer 19 by at least one adhesive layer. For example, the aluminum film is adhesively bonded to the stack 14 by an adhesive film, and the PET film is adhesively bonded to the aluminum film by an adhesive layer. The encapsulating layer 21 is, for example, deposited by lamination. The encapsulating layer 21 has a thickness comprised between 5 and 150 μm and for example of about 100 μm. Such a PET-alu encapsulating layer 21 is flexible and therefore particularly suitable for lithium batteries intended to conform to the shape of the electronic devices into which they will be integrated.
As indicated above, during the charging cycles of a battery of the type of that in
The battery 26 comprises the same elements, referenced by the same references, as the battery 1 of
Tests have shown that oxygen is released by the cathode layer 15 made of LiCoO2 during battery charging cycles and mainly during the first charging cycle. In the battery 1 of
The layer 27 is made of a material liable to oxidize. This material is, for example, a metal chosen from the group comprising copper, titanium, aluminum and zinc. By way of example, the thickness of an interface layer 27 made of copper is comprised between 100 nm and 1 μm and is, for example, 500 nm. In the case of a metal layer 27 made of copper or titanium of a thickness of 100 nm, tests have shown a decrease of 42% in the number and/or size of the bubbles with respect to the case of a battery of the type of that in
Particular embodiments have been described. Various variants and modifications will seem obvious to those skilled in the art. In particular, although an embodiment has been described in which the encapsulating layer is of PET-alu, this encapsulating layer could be made of other materials, for example a film of polyvinylidene chloride (PVDC) coated with a film of mica.
The carrier may either be made of an insulator, for example of mica or of another ceramic such as zirconia or alumina, or be made of a conductor, for example of aluminum or another metal, coated with an insulating layer, or indeed of a semiconductor, for example of silicon, coated with an insulating layer.
Furthermore, an interface layer 27 such as described with reference to
| Number | Date | Country | Kind |
|---|---|---|---|
| 1754148 | May 2017 | FR | national |
