Method for assembling and encapsulating lithium microbatteries and microbatteries produced thereby

Abstract

A method of vertically assembling encapsulated single microbatteries, wherein the vertical assembly contains, between the microbatteries, an electrical insulation and/or sealing layer and a metal layer, successively including: a step of stacking and attaching at least two single microbatteries, previously encapsulated, stacked on each other; and forming a metal layer, capable of ensuring the electrical coupling of each of the metal layers of each of the encapsulated single microbatteries. Each of the at least two encapsulated single microbatteries is previously prepared by: forming at least one electrical insulation and/or sealing layer over at least a portion of the lateral sides and of the surface including the current collectors of a microbattery including positive and negative electrodes, an electrolyte, and positive and negative current collectors; making the current collectors of the microbattery accessible; and forming a metal layer extending from the current collectors to the lateral sides of said microbattery.

Claims

1. A method of vertically assembling encapsulated single microbatteries, said vertical assembly containing between the microbatteries at least one of an electrical insulation and sealing layer and a metal layer that contacts at least two microbatteries, said assembly method successively comprising the steps of: (a) stacking and attaching at least two single microbatteries, previously and individually encapsulated, stacked on each other; (b) forming a metal layer that contacts at least two microbatteries, ensuring the electrical coupling of each of the metal layers of each of the individually encapsulated single microbatteries; wherein each of the at least two individually encapsulated single microbatteries is prepared prior to the stacking step (a) by: (i) forming at least one of an electrical insulation and sealing layer over at least a portion of lateral sides and of a surface comprising the current collectors of said single microbattery comprising positive and negative electrodes, an electrolyte, and positive and negative current collectors; (ii) making the current collectors of said microbattery accessible; (iii) forming a metal layer extending from the current collectors of said single microbattery to the lateral sides of said microbattery, wherein the metal layer is a discontinuous metal layer contacting the current collectors of said single microbattery; wherein each single microbattery comprises only one positive electrode, only one electrolyte and only one negative electrode, wherein, prior to the stacking step (a), each single microbattery is formed on a substrate that does not contain any via, wherein each substrate is not a current collector of said microbattery; wherein the metal layer formed in step (iii) is a discontinuous metal layer deposited on a portion of an upper surface and on two lateral sides of the microbattery, thus electrically connecting each current collector to the adjacent lateral side; and wherein the positive and negative current collectors within each single microbattery are not electrically interconnected within said single microbattery.

2. The method of vertically assembling encapsulated single microbatteries of claim 1, wherein the attaching of the encapsulated single microbatteries is performed by means of at least one of non-conductive glue and a non-conductive adhesive film, interposed between two consecutive microbatteries of the stack.

3. The method of vertically assembling encapsulated single microbatteries of claim 2, wherein the gluing is performed with glue comprising a thermal epoxy.

4. The method of vertically assembling encapsulated single microbatteries of claim 1, wherein the electrical insulation and sealing layer is formed by the successive deposition of an electrical insulation layer and of a sealing layer.

5. The method of vertically assembling encapsulated single microbatteries of claim 1, wherein the electrical insulation layer comprises a polymer selected from the group consisting of an epoxy, parylene, an acrylate, a silicone, and mixtures thereof.

6. The method of vertically assembling encapsulated single microbatteries of claim 1, wherein the electrical insulation layer has a thickness in the range from 1 to 5 micrometers.

7. The method of vertically assembling encapsulated single microbatteries of claim 1, wherein the sealing layer comprises at least one dielectric element selected from the group consisting of silicon oxynitride, silicon nitride, silica, alumina, and mixtures thereof.

8. The method of vertically assembling encapsulated single microbatteries of claim 1, wherein the sealing layer has a thickness in the range from 10 to 500 nanometers.

9. The method of vertically assembling encapsulated single microbatteries of claim 1, wherein the step of accessibility of the current collectors is carried out by selective etching.

10. The method of vertically assembling encapsulated single microbatteries of claim 9, wherein the selective etching comprises: a first step of selective etching with a fluorinated SF.sub.6 gas plasma; and a second step of selective etching by a plasma comprising oxygen.

11. The method of vertically assembling encapsulated single microbatteries of claim 1, wherein the metal layer formed in step (iii) is obtained by isotropic deposition, or by atomic layer deposition.

12. The method of vertically assembling encapsulated single microbatteries of claim 1, wherein the metal layer formed in step (iii) comprises at least one element selected from the group consisting of titanium, tungsten, gold, silver, aluminum, and nickel.

13. The method of vertically assembling encapsulated single microbatteries of claim 11, wherein the metal layer formed in step (iii) has a thickness in the range from 100 to 500 nanometers.

14. A vertical stack of individually encapsulated microbatteries, obtained by the method of claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other advantageous aims and aspects of the invention will better appear from the reading of the following detailed description, provided as a non-limiting indication in relation with the accompanying drawings, among which:

(2) FIG. 1 shows a vertical cross-section view of a batch of microbatteries, horizontally arranged in linear fashion.

(3) FIG. 2 shows a vertical cross-section view of single microbatteries, that is, microbatteries dissociated from the linear batch; each contains, on an appropriate support, a central element and lateral current collectors.

(4) FIG. 3 shows a top view of a single microbattery, showing a central element, lateral current collectors on a support.

(5) FIG. 4 shows a vertical cross-section view of a single microbattery, which is totally covered on each of its surfaces with an insulation and/or sealing layer.

(6) FIG. 5 shows a vertical cross-section view of a single microbattery having undergone the deposition of a sealing layer all over the upper surface and the lateral sides.

(7) FIG. 6 shows a vertical cross-section view of a single microbattery having been submitted to a selective etching in order to make the current collectors accessible.

(8) FIG. 7 shows a vertical cross-section view of a single microbattery, which is covered with a metal layer all over the current collectors, over a portion of the upper surface, and all over the lateral sides.

(9) FIG. 8 shows a top view of a microbattery, for which the sealing layer covers the entire microbattery, except for the current collectors and for the region extending from the current collectors to the adjacent lateral sides, which are covered with a metal layer.

(10) FIG. 9 shows a vertical cross-section view of two encapsulated microbatteries, vertically attached to each other by means of glue.

(11) FIG. 10 shows a vertical cross-section view of two microbatteries attached to each other after the deposition of a metal layer which ensures the electrical coupling of the current collectors of each of the microbatteries.

DETAILED DESCRIPTION OF THE INVENTION

(12) A batch of microbatteries is formed in a silicon support (1). On the upper surface of this support are arranged the active elements of the lithium microbattery, that is, the positive electrode, the negative electrode, and the electrolyte, shown in the form of a single element (13, 23, n3) (FIG. 1). Each of the elements is bordered on each side with a current collector (12, 22, n2), including an anode current collector (12a, 22a, n2a) and a cathode current collector (12b, 22b, n2b).

(13) The sawing into single microbatteries exposes lateral sides (FIG. 2). A top view of the microbattery illustrates the central position of the active elements (13) at the center of the support (1), and bordered on each side, at the level of the adjacent lateral sides, by the current collectors (12a and 12b) (FIG. 3).

(14) The method of encapsulating a single microbattery is now described in relation with FIGS. 4 to 8.

(15) The first step of the encapsulation method comprises depositing an electrical insulator layer (14), for example, on each of the microbattery surfaces, thus protecting the active elements (13), the current collectors (12a and 12b), and the adjacent lateral sides (FIG. 4).

(16) The second step of the encapsulation method comprises depositing a sealing layer (15), for example, protecting the upper surface and the lateral sides of the microbattery against attacks particularly originating from water vapor and oxygen (FIG. 5).

(17) A step of selective etching is implemented, to make the current collectors (12a and 12b) accessible, at the level of the upper surface of the microbattery (FIG. 6). Thus, there is no further electrical insulation layer or sealing layer in this location.

(18) The encapsulation method according to the invention ends with a step of depositing a discontinuous metal layer, on a portion of the upper surface and on the two lateral sides of the microbattery, thus electrically connecting each current collector (12a and 12b) to the adjacent lateral side (FIG. 7).

(19) FIG. 8 illustrates the nature of the external structure of the upper surface of the microbattery at the end of this step. The upper surface is coated with a sealing layer (15), except at the level of the region extending from the current collectors (12a and 12b) to the lateral sides of the microbattery, which has a discontinuous metal layer (16a and 16b) deposited thereon.

(20) The method of stacking and encapsulating two microbatteries according to the invention is now described in relation with FIGS. 9 and 10.

(21) Two encapsulated microbatteries are vertically stacked and rigidly attached to each other, or bound to each other by a thermal glue layer, for example non-conductive (17) (FIG. 9). The discontinuous metal layers (16a and 26a) and (16b and 26b) on both sides on each of the microbatteries are not in contact.

(22) The second step of this method comprises depositing a discontinuous metal layer (18a and 18b) over a portion of the upper surface and the respective lateral sides defined by the stack. The discontinuous metal layer (18a and 18b) covers the metal layers (16a and 26a) and (16b and 26b) on each side, on each of the single microbatteries. Thus, at the end of this vertical assembly method, the current collectors (12a and 22a), on one side, and (12b and 22b), on the other side, are now connected to one another.

(23) The different layers which result from the implementation of these 2 methods provide: a good electrical insulation of the active microbattery elements, thus avoiding the occurrence of short-circuits; a good sealing of the microbattery against attacks resulting from water vapor and oxidizing species; an easy connection of the current collectors to other electronic elements, which makes them compatible with the back-end technology; a robustness of the sides of the assembled microbatteries, enabling to stack a significant number of single microbatteries.