Flexible lithium battery

The present invention relates to a flexible lithium battery comprising a first current collector layer and a second current collector layer, wherein the first current collector layer has a first outer surface and a first inner surface, and the second current collector layer has a second outer surface and a second inner surface; there is a glue frame sandwiched between the first inner surface and the second inner surface to form a sealed and enclosed space, wherein there is an electrochemical system layer disposed in this sealed and enclosed space, with the electrochemical system layer comprising a first active material layer, a second active material layer, and an electrically insulating layer disposed between the first active material layer and the second active material layer; and there is a flexible adhesive layer disposed between the first inner surface and the first active material layer and/or between the second inner surface and the second active material layer, wherein this flexible adhesive layer consists of an adhesive and an electrically conductive additive, with the adhesive consisting of a linearly structured colloid and a stereoscopically structured colloid.

BACKGROUND OF THE INVENTION

Field of Invention

The present invention relates to a battery structure, in particular to a flexible lithium battery.

Related Art

In human technology requirements, various wearable electronic devices are correspondingly developed. In order to make the wearable electronic devices conform to the trend of thin and lightweight, the space distribution in the electronic device becomes an important issue. A flexible battery which can be arranged on a non-plane may be one of the solutions to this problem. Please refer toFIG. 1, which is a cross-sectional view of a structure of the conventional flexible lithium battery. As shown, such a flexible lithium battery10includes a first current collecting layer12, a second current collecting layer14and a glue frame16sandwiched between the first current collecting layer12and the second current collecting layer14to form an enclosed space18. A first active material layer20, an electrical insulation layer22and a second active material layer24are sequentially arranged in the enclosed space18. An electrochemical system layer26is formed by the first active material layer20, the electrical insulation layer22and the second active material layer24. The first active material layer20is contacted to the first current collecting layer12, and the second active material layer24is contacted to the second current collecting layer14. The flexible lithium battery10is characterized in that the whole can be dynamic bending. However, during bending the current collecting layer12,14is easily separated from the adjacent active material layers20,24to cause a short circuit.

In view of the above factors, the invention provides a brand-new flexible lithium battery in order to overcome the aforementioned problems.

SUMMARY OF THE INVENTION

It is a primary objective of this invention to provide a flexible lithium battery, and a flexible adhesive layer is arranged between the current collecting layer and the active material layer, to avoid a short circuit caused by separating of the current collecting layer and the active material layer during the battery is bent.

Also, it is another objective of this invention to provide a flexible lithium battery. The electrochemical system layer and the flexible adhesive layer are sealed in the enclosed space, which forming by the first current collecting layer, the second current collecting layer and the glue frame.

In order to implement the abovementioned, this invention discloses a flexible lithium battery. The battery includes a first current collecting layer and a second current collecting layer, wherein the first current collecting layer has a first outer surface and a first inner surface, and the second current collecting layer has a second outer surface and a second inner surface, and a glue frame sandwiched between the first inner surface and the second inner surface. The glue frame is closed-structure and its upper and lower surface is adhered to the first inner surface and the second inner surface, respectively. Therefore, an enclosed space is formed by the glue frame, the first current collecting layer and the second current collecting layer. An electrochemical system layer and at least one flexible adhesive layer are disposed in the enclosed space and adjacent to the inner surface of the glue frame. The electrochemical system layer includes a first active material layer, a second active material layer, and an electrically insulating layer disposed between the first active material layer and the second active material layer. The flexible adhesive layer is disposed between the first inner surface and the first active material layer and/or between the second inner surface and the second active material layer. The flexible adhesive layer is composed of an adhesive and an electrically conductive additive, with the adhesive consisting of a linearly structured colloid and a stereoscopically structured colloid.

Wherein the stereoscopically structured colloid is made of a cross-linked polymer. The cross-linked polymer is selected from epoxy, acrylic acid resin, polyacrylonitrile (PAN) and combinations thereof with network-structure, or polyimide (PI) and derivatives thereof with ladder-structure.

Wherein the weight ratio of the electrically conductive additive to the adhesive is from 1:1 to 7:3.

Wherein the weight ratio of the electrically conductive additive to the stereoscopically structured colloid is from 5:2 to 7:3.

Wherein the weight ratio of the linearly structured colloid to the stereoscopically structured colloid is from 3:2 to 9:1.

Wherein a thickness of the flexible adhesive layer is 4-10 μm.

Wherein a shape of the electrically conductive additive is spherical shape, tubular shape or sheet-like shape, or a combination thereof.

Wherein the electrically conductive additive with spherical shape is a carbon black.

Wherein an average particle size of the electrically conductive additive with spherical shape is 40 nm.

Wherein a surface area of the electrically conductive additive with spherical shape is 60-300 m2/g.

Wherein the electrically conductive additive with tubular shape is a carbon tube.

Wherein a diameter the electrically conductive additive with tubular shape is 5-150 nm, and a length the electrically conductive additive with tubular shape is 5-20 nm.

Wherein a surface area of the electrically conductive additive with tubular shape is 20-400 m2/g.

Wherein the electrically conductive additive with sheet-like shape is graphite, graphene or a combination thereof.

Wherein an average particle size of the electrically conductive additive with sheet-like shape is 3.5 nm.

Wherein a surface area of the electrically conductive additive with sheet-like shape is 20 m2/g.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides a flexible lithium battery to solve the problem of the short circuit caused by separating of the current collecting layer and the active material layer during the battery is bent.

Please refer toFIG. 2, as shown, the flexible lithium battery30according to the invention mainly consists of a first current collecting layer12, a second current collecting layer14, a glue frame16and an electrochemical system layer26. The first current collecting layer12has a first outer surface a and a first inner surface b. The second current collecting layer has a second outer surface c and a second inner surface d. The a glue frame16is sandwiched between the first inner surface b and the second inner surface d. More specifically, the glue frame16is closed-structure and its upper and lower surface is adhered to the first inner surface b of the first current collecting layer12and the second inner surface d of the second current collecting layer14, respectively. Therefore, an enclosed space18is formed by the glue frame16, the first current collecting layer12and the second current collecting layer14. The electrochemical system layer26is disposed in the enclosed space18and adjacent to the inner surface e of the glue frame16. In the direction from the first current collecting layer12to the second current collecting layer14, the electrochemical system layer26includes a first active material layer20, a second active material layer24, and an electrically insulating layer22disposed between the first active material layer20and the second active material layer24. A first flexible adhesive layer32is disposed between the first inner surface b and the first active material layer20. As the same with the first active material layer20, the first flexible adhesive layer32is adjacent to the inner surface e of the glue frame16. The first flexible adhesive layer32is composed of an adhesive and an electrically conductive additive34, with the adhesive consisting of a linearly structured colloid and a stereoscopically structured colloid.

The electrochemical system layer26and the first flexible adhesive layer32are completely sealed within the first current collecting layer12, the second current collecting layer14and the glue frame16. And the glue frame16is still a flexible sealing glue after polymerization reactions. Therefore, the electrochemical system layer26and the first flexible adhesive layer32are not damaged easily after being bent for many times.

The weight ratio of the electrically conductive additive to the adhesive is from 1:1 to 7:3. The weight ratio of the electrically conductive additive to the stereoscopically structured colloid is from 5:2 to 7:3. The weight ratio of the linearly structured colloid to the stereoscopically structured colloid is from 3:2 to 9:1. The thickness of the first flexible adhesive layer32is 4-10 μm.

The shape of the electrically conductive additive34is spherical shape, tubular shape or sheet-like shape, or a combination thereof. For example, when the shape of the electrically conductive additive34is spherical shape, the electrically conductive additive34may be the carbon black. An average particle size of the electrically conductive additive34with spherical shape is 40 nm. A surface area of the electrically conductive additive34with spherical shape is 60-300 m2/g. When the shape of the electrically conductive additive34is tubular shape, the electrically conductive additive34may be the is carbon tube. A diameter the electrically conductive additive with tubular shape is 5-150 nm, and a length the electrically conductive additive with tubular shape is 5-20 nm. A surface area of the electrically conductive additive with tubular shape is 20-400 m2/g. When the shape of the electrically conductive additive34is sheet-like shape, the electrically conductive additive34may be graphite, graphene or a combination thereof. An average particle size of the electrically conductive additive34with sheet-like shape is 3.5 nm. A surface area of the electrically conductive additive with sheet-like shape is 20 m2/g.

When the stereoscopically structured colloid is made of a cross-linked polymer. The cross-linked polymer is selected from epoxy, acrylic acid resin, polyacrylonitrile (PAN) and combinations thereof with network-structure, or polyimide (PI) and derivatives thereof with ladder-structure.

According to the invention, the characteristic of the cross-linked polymer has good thermal stability and thermal tolerance is utilized. During heat treatment in the assembling process of the flexible battery, such as the hot-pressing process, since the cross-linked polymer can withstand high temperatures without melting, and compared with the linear polymer, the cross-linked polymer having more stereoscopically structured branching, so that under the process conditions of high temperature (or high temperature and pressure), the cross-linked polymer can impede crystalline of the linear polymer. Therefore, the crystal size and degree of crystallinity of the linear polymer are limited. The sterically hindered caused by crystallization is reduced, so that ions can pass more smoothly.

The electrically conductive additive34is capable of improving electrical conduction characteristics between the first active material layer20and the first current collecting layer12. The space required to be filled with the linearly structured colloid and the stereoscopically structured colloid is further reduced due to the presence of the electrically conductive additive34. For example, the space, which need to be filled with the linearly structured colloid and the stereoscopically structured colloid, will be the pitch T between the two adjacent electrically conductive additives34. Therefore, the crystallization caused by heat treatment or pressurization treatment of the linearly structured colloid can be effectively avoided to increase the flexibility, as shown inFIG. 3.

Referring toFIG. 3, when the battery is bent by the external force, the electrically conductive additive34can also serve as a bearing point for the first flexible adhesive layer32. That is, when the size of the electrically conductive additive34is small and the number of doping is large enough, the number of bearing points is relatively large. So that the deformation of the adhesive layer between any two bearing points is significantly reduced compared with that of an adhesive without adding the electrically conductive additive34. In view of the above, the adhesive condition of the first flexible adhesive layer32and the first inner surface b of the first current collecting layer12, and the first active material layer20are much improved.

Although the electrically conductive additive34and the adhesive layer described above are only present on a single-side of the electrically insulating layer22of the flexible lithium battery30, the persons skilled in this art may also arrange the same structure on the other side as well. For example, as shown inFIG. 4, a second flexible adhesive layer36may be disposed between the second inner surface d and the second active material layer24alone or alternatively together with the first flexible adhesive layer32. The composition of the second flexible adhesive layer36is the same as that of the first first flexible adhesive layer32.