GB2531588A

GB2531588A - Battery and method for the production thereof

Info

Publication number: GB2531588A
Application number: GB1418875.9A
Authority: GB
Inventors: Moazzam Ali; Prakash Deep
Original assignee: Technische Universitaet Chemnitz
Current assignee: Technische Universitaet Chemnitz
Priority date: 2014-10-23
Filing date: 2014-10-23
Publication date: 2016-04-27
Anticipated expiration: 2034-10-23
Also published as: GB2531588B; GB201418875D0

Abstract

A thin battery 300, preferably a printed battery, comprises a first substrate 301 and a second substrate 302. A cathode layer 307 and an anode layer 308 are printed on the first substrate 301 and on the second substrate 302, respectively. The binders in the cathode layer 307 and in the anode layer 308 are preferably water insoluble polymers. A separator layer 310, 311 is printed on at least one of the cathode layer 307 and the anode layer 308. The separator layer 310, 311 comprises interconnected water absorbing powders. An electrolyte layer 320 is printed on the at least one separator layer 310, 311. The electrolyte layer 320 comprises water, at least one salt, water insoluble substantially spherical particles 321 and at least one waxy material 322. The first substrate 301 is secured on the second substrate 302 in such a way that the separator layer 310, 311 and the electrolyte layer 320 are sandwiched between the cathode layer 307 and the anode layer 308.

Description

Title: Battery and Method for the Production thereof

CROSS-RELATION TO OTHER APPLICATIONS

[0001] None

FIELD OF THE INVENTION

[0002] The present disclosure relates to a thin battery having a plurality of layers disposed on at least one substrate, in which the layers are produced by printing methods using functional inks

BACKGROUND OF THE INVENTION

[0003] With the development of compact and energy-efficient electronic circuits, the requirement for a power source to drive the electronic circuits has also changed. Recent developments of "use-and-throw-away" electronics, printed on plastic or paper substrates no longer require high energy-density batteries. These use-and-throw-away electronics employ low-energy density, ultra-cheap, thin and mechanically flexible batteries. One potential application of this kind of thin battery is for smart packaging, where the smart package has a shelf life of just a few months. The development of the ultra-cheap thin battery requires a lowering of material and production costs, as well as a reduction in the initial investment costs for production machineries compared to those known in the art.

[0004] As used in this disclosure, the term "thin battery" refers to a battery, which comprises a plurality of layers with a total maximum thickness of 1 mm, excluding the substrate thickness.

[0005] Printing machines have been known for centuries for printing colour inks and are available all over the world. The same existing printing machines can also he used to print electronics devices, by replacing colour inks with so-called functional inks.

[0006] The terms "print," "printability," "printing," printable" and "printed" as used in this disclosure refer to production methods using the functional inks. More specifically these production methods include, but are not limited to, are screen-printing, stencilling, Ilexography, gravure, offset printing and ink-jet printing. These printing methods can he roll-to-roll or sheet-fed or manual.

[0007] The term "ink" as used in this disclosure refers to a material that is in liquid or semi-solid or paste form. It will be understood that, after the printing of the inks on a substrate, a drying or curing process may be required to convert the ink into a solid or a gel form. Typically, heat and/or radiation are used for the drying or curing process. The drying or curing process can he also self-activated.

[0008] In order to produce the thin batteries the following conditions should be fulfilled to reduce cost: * Production in ambient conditions to eliminate the requirement of expensive dean rooms.

* The use of an aqueous based battery to eliminate the requirement of inert environment production or to remove the need for expensive packaging of the produced battery.

All of the layers should be printed from the inks in order to eliminate initial investment cost, as printers all over the world have printing machines.

* Sealing of the battery should be done by a simple roller based laminator. The sealing of the battery is required to prevent the battery from being damaged by ambient conditions. Generally, the sealing of the batteries is done by pattern rollers or pattern plates. In this case, the patterned rollers apply the required pressure or heat only on the adhesive area that surrounds the battery unit cell, but do not apply uniform pressure or heat on the complete area.

[0009] Patterning of a roller or a plate increases the initial investment costs. Therefore, there is a need for a simple lamination method, which requires no patterned roller or patterned plate. The term "unpatterned lamination" as used in this disclosure refers to a lamination method with at least two rollers or two plates system, without any pattern disposed on the rollers or on the plates. This unpatterned lamination uses a uniform pressure and/or heat applied throughout the roller length or throughout the plate area.

[0010] The battery should be mechanically flexible. The mechanically flexible batteries are easier to produce by roll-to-roll production methods. For certain applications, the mechanically flexible batteries are advantageous as they can be place on a curved glass bottle.

[0011] Aqueous based primary and secondary batteries and their production under ambient conditions are known in the art. The term "aqueous battery" as used in this disclosure means that the battery electrolyte is water-based. The thin batteries known in the art can he divided mainly into two categories as shown in FIG. 1 and FIG. 2. FIG.1 shows a cross-sectional view of a typical co-planar structure of a battery unit cell 100, as is known from U.S. Pat. No. 8,029,927 B2. The battery unit cell 100 comprises a bottom substrate 101, which is mechanically flexible. The bottom substrate 101 is typically made of electrically non-conducting materials with sufficient moisture and other gasses barrier properties.

[0012] On top of the bottom substrate 101 is provided a cathode current collecting layer 104 and an anode current collecting layer 103. A cathode layer 107 and an anode layer 108 are provided on top of the cathode current collecting layer 104 and the anode current collecting layer 103, respectively. In certain aspects, the cathode layer 107 and the cathode current collecting layer 104 can be made of the same materials. This means that the same layer will work both as a cathode electrode as well as transfer the generated current outside of the battery unit cell 100. In certain aspects, the anode layer 108 and the anode current collecting layer 103 can be made of the same materials. This means that the same layer will work as an anode electrode as well as transfer the generated current outside of the battery unit cell 100.

[0013] The cathode current collecting layer 104, the anode current collecting layer 103, the cathode layer 107 and the anode layer 108 can he produced by a printing method using the functional inks. In order to create the battery 100, the anode layer 108 and the cathode layer 107 should be connected through an ionically conducting layer 110. In certain batteries, the ionically conducting layer 110 is made of paper substrates soaked with an appropriate water based electrolyte solution. The electrolyte is typically a salt selected based on the chemical reactions involved in the battery. Typically, a piece of paper is first cut into an appropriate size and then placed on top of the cathode layer 107 and the anode layer 108. This process involves a separate machine for cutting paper into a desired shape and then placing the cut paper at the right position. This process can also be done by first placing a sheet of paper on top of the cathode layer 107 and the anode layer 108 and then cutting the sheet of paper by "kiss-cutting" method. In either case, a separate machine is required.

[0014] The battery 100 is scaled with a top substrate 102, using an adhesive layer 105. The adhesive layer 105 is provide around the battery unit cell 100 such that a portion of cathode current collecting layer 104 and a portion of the anode current collecting layer 103 are projecting out of the battery unit cell 100. In this case, the sealing can be done by an "unpatterned lamination" method, as the paper based ionically conducting layer 110 is strong enough to withstand the pressure applied by the laminating rollers uniformly throughout the battery unit cell 100.

[0015] In certain batteries, the ionically conducting layer 110 is made of gel materials, which can be printed directly on top of the cathode layer 107 and the anode layer 108. In this case, the sealing cannot be done by an "unpatterned lamination" method, as applying uniform pressure throughout the battery unit cell 100 will squeeze the gel materials out of their position or out of the scaling area defined by the adhesive layer 105.

[0016] One advantage of the co-planer battery is that the battery 100 has sufficient mechanical flexibility. This kind of battery has a low current density. The reason behind this is the high effective distance between the cathode layer 107 and the anode layer 108. This means internal impedance of the co-planar battery 100 is high and hence the current density is low.

[0017] In order to lower the internal impedance of the battery, a vertical structure is known in the art, as shown in FIG. 2 and denoted 200, such as is known from U.S. Pat. No. 8,574,742 B2. In the vertical structure, a cathode current collecting layer 204 and an anode current collecting layer 203 are provided respectively on a bottom substrate 201 and on a top substrate 202. A cathode layer 207 and an anode layer 208 are provided respectively on top of the cathode current collecting layer 204 and on top of the anode current collecting layer 203. In certain cases, the cathode layer 207 and the cathode current collecting layer 204 can be made of the same materials. This means that the same layer will work as a cathode electrode and the layer will transfer the generated current outside of the battery unit cell 200. In certain cases, the anode layer 208 and the anode current collecting layer 203 can be made of the same materials. This means that the same layer will work as a cathode electrode and the layer will transfer the generated current outside of the battery unit cell 200.

[0018] The cathode layer 207, the anode layer 208, the cathode current collecting layer 204 and the anode current collecting layer 203 can be provided by the printing methods by using the functional inks. In order to complete the battery 200, the anode layer 208 and the cathode layer 207 should be connected through an ionically conducting layer 210.

[0019] The battery 200 is sealed by laminating the top substrate 202 against the bottom substrate 201 using an adhesive layer 205. The adhesive layer 205 is provide around the battery unit cell 200 such that a portion of cathode current collecting layer 204 and a portion of the anode current collecting 203 are outside the battery unit cell 200.

[0020] In certain batteries, the ionically conducting layer 210 is made of paper soaked with an appropriate water based electrolyte solution. The use of paper as an ionically conducting layer 210 requires an addition machine for cutting and placing the paper at the right position. In certain batteries, the ionically conducting layer 210 is made of gel materials, which can be produced by a printing machine using inks As noted above, the disadvantage of the gel materials as electrolytes is that while sealing the battery with an "unpattemed lamination" method i.e. applying a uniform pressure across the battery, the gel materials can leak out of the battery unit cell 200. Therefore, the use of the gel materials as a gel electrolyte requires a customized laminator, with patterned rollers or patterned plates, to apply pressure and/or heat only on the areas where adhesive layer 205 is placed. The other disadvantage with this kind of battery structure is that total thickness of the battery is higher, which lower the mechanical flexibility of the battery.

SUMMARY OF THE INVENTION

[0021] The present invention relates to a thin battery. The thin battery comprises a plurality of layers and at least one of the layers is produced by printing using functional inks. The thin battery comprises a first substrate and a second substrate. A cathode layer is printed on the first substrate. The cathode layer is water insoluble, but is able to absorb water, and is a homogenous blend of at least one cathode active powder, at least one water absorbing material and at least one water insoluble polymeric hinder. An anode layer is printed on the second substrate. The anode layer is water insoluble, but is able to absorb water, and is a homogenous blend of at least one anode active powder, at least one water absorbing material and at least one water insoluble polymeric binder. At least one separator layer is printed either on the cathode layer or on the anode layer or on both the cathode layer and the anode layer. The at least one separator layer comprises at least one water absorbing powder interconnected through an interconnecting material in such a way that the interconnection is not broken in presence of water. At least one electrolyte layer is printed on the at least one separator layer. The electrolyte layer is a homogenous mixture of water, at least one salt, water insoluble substantially spherical particles and at least one waxy material that is substantially ionic conducting. An adhesive layer is provided at least on one of the first substrate and the second substrate around a perimeter of at least one of the cathode layer and the anode layer. The first substrate is secured on the second substrate in such a way that the at least one separator layer and the at least one electrolyte layer are sandwiched between the cathode layer and the anode layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is a cross-sectional view of a prior art thin battery.

[0023] FIG. 2 is a cross-sectional view of another prior art thin battery.

[0024] FIG. 3 is a cross-sectional view of a thin battery, in accordance with an aspect of the present invention.

[0025] FIG. 4A is a cross-sectional view of a recently printed electrolyte layer on top of the separator layer.

100261 FIG. 4B is a cross-sectional view of a first embodiment of the electrolyte layer on top of the separator layer after a period of time.

[0027] FIG. 4C is a cross-sectional view of a second embodiment of the electrolyte layer on top of the separator layer after a period of time.

[0028] FIG. 4D is a cross-sectional view of a third embodiment of the electrolyte layer on top of the separator layer after a period of time.

[0029] FIG. 5 is a flow chart showing a manufacturing process to produce the battery according to one exemplary embodiment of the present disclosure.

[0030] Similar reference numbers are used for similar elements on all figures, except that the reference numbers differ by 100.

IS DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] The invention will now be described in detail. Drawings and examples are provided for better illustration of the invention. It will be understood that the embodiments and aspects of the invention described herein are only examples and do not limit the protector's scope of the claims in any way. The invention is defined by the claims and their equivalents. It will be understood that features of one aspect or embodiment of the invention can be combined with the feature of a different aspect or aspects and/or embodiments of the invention.

[0032] The present invention relates to a thin battery. All layers of the thin battery, including the ionically conducting layer, are produced by printing method from the functional inks The sealing process of the battery is done by laminating top substrate and bottom substrate using an "unpatterned lamination" method, which does not require patterned rollers or patterned plates for lamination. The mechanical flexibility is retained even after using a vertical structure for the battery.

[0033] FIG 3 illustrates a cross sectional view of a thin battery 300 in accordance with one aspect of the invention. The battery 300 includes a bottom substrate 301 and a top substrate 302. The bottom substrate 301 and the top substrate 302 can he mechanically flexible. In one non-limiting example, the bottom substrate 301 and the top substrate 302 can he made of polyester materials. In another aspect, the bottom substrate 301 and the top substrate 302 can be made of polyester film coated with aluminium, aluminium oxide or silica. A cathode current collecting layer 304 is provided on the bottom substrate 301. An anode current collecting layer 303 is provided on the top substrate 302. In one non-limiting aspect, at least one of the cathode current collecting layer 304 and the anode current collecting layer 303 is printed from a functional ink, which is conductive. The functional ink can comprise, but is not limited to, carbon or silver particles. In another aspect, at least one of the cathode current collecting layer 304 and the anode current collecting layer 303 is produced by etching-out a metalized flexible substrate. For example, a copper metalized polyester foil can be etched into a desired pattern to create the combination of either the cathode current collecting layer 304 and the bottom substrate 301 or the anode current collecting layer 303 and the top substrate 302.

[0034] On top of the cathode current collecting layer 304 is printed a cathode layer 307. The cathode layer 307 is printed by using a functional ink which comprises substantially, but is not limited to, at least one cathode active powder, at least one water insoluble polymeric binder and at least one water-absorbing material. On top of the anode current collecting layer 303 is printed an anode layer 308. The anode layer 308 is printed by using a functional ink which comprises substantially, but is not limited to, at least one anode active powder, at least one water insoluble polymeric binder and at least one water absorbing material.

[0035] The anode active powders and the cathode active powders of the thin battery can be selected from an appropriate electrochemical-couple, such as, but not limited to, a zinc-manganese dioxide, lithium manganese oxide-titanium dioxide, lithium manganese oxide-vanadium oxide, etc. The water-insoluble polymeric hinder, in the cathode layer 307 and the anode layer 308, prevents the cathode layer 307 and the anode layer 308 from becoming soft in presence of the aqueous electrolyte. The water-soluble polymeric binder will cause the cathode layer 307 and the anode layer 308 to spread out while laminating the battery 300 with the "unpatterned lamination" method. In one non-limiting example, the water insoluble polymeric hinder can he polystyrene, poly(nlethyl methacrylate) PMMA, ethyl cellulose, polyvinylidene fluoride etc. [0036] The purpose of water-absorbing material in the cathode layer 307 and in the anode layer 308 is to absorb adequate water inside the cathode layer 307 and the anode layer 308. The presence of water in the cathode layer 307 and the anode layer 308 will enhance the ionic mobility of the layer. This enhancement will lower the battery impedance and hence increase the current density. In one non-limiting example, the water absorbing material is polyethylene oxide, polyacrylic acid, polyvinyl alcohol, polyvinylpyrrolidone, cellulose, starch, zeolite, silica gel, etc. [0037] The cathode layer 307 and the anode layer 308 can further comprise electrically conducting particles, which will enhance movement of electrons inside the layer. In one non-limiting example, the electrically conducting particles can be graphite, carbon black, carbon nanotube, graphene etc. The cathode layer 307 and the anode layer 308 can further comprise additives to enhance printability of the inks, to improve surface adhesion, to improve dispersion of the particles in the ink, to increase battery voltage, to increase current density and to lower gas evolution. In one non-limiting example, the cathode layer 307 and the cathode current collecting layer 304 are made of the same materials. That means a single layer will serve the dual purpose of working as a battery electrode and transferring the generated current to outside of the battery unit cell. In one non-limiting example, the anode layer 308 and the anode current collecting layer 303 are made of the same materials. That means a single layer will serve the dual purpose, working as a battery electrode and transferring the generated current to outside of the battery unit cell.

[0038] Separator layers, 310 and 311, are printed on top of at least one of the cathode layer 307 and the anode layer 308. The separator layers 310 and 311 are ionically conducting.

The separator layer 310 and 311 comprise substantially, but are not limited to, at least one water-absorbing powder which are interconnected by interconnecting material in such a way that in presence of water the interconnection is not broken. The water-absorbing powder is substantially water insoluble. This prevents the separator layer 310 and 311 from squeezing out of its position in presence of the water of the electrolyte layer 320, while sealing the battery 300 by using an "unpatterned lamination" method. In one non-limiting example. the water-absorbing powder can be cellulose powder, zeolite powder. silica gel, etc. The interconnecting materials can be a long chain polymeric interconnector, which makes chemical bonds with water absorbing powder. The chemical bond between polymeric interconnector and the water absorbing particles can be an ionic bond, a covalent bond, a van der Waals' interaction or a hydrogen bond. In one non-limiting example, the polymeric interconnector can be selected from ethylcellulose, polystyrene, polyacrylic acid, poly(methyl methacrylate) etc. The separator layers 310 and 311 can further comprise additives to enhance printability of the ink, to improve surface adhesion, to improve dispersion of the water absorbing powder in the ink, to adjust thixotropic properties of the ink and to enhance the bond between the water absorbing powder and the interconnecting materials.

[0039] On top of at least one of the separator layers 310 and 311 is printed at least one electrolyte layer 320. The electrolyte layer 320 substantially comprises, but is not limited to, water, at least one electrolyte salt, water insoluble substantially spherical particles 321 and at least one waxy material 322, which is substantially ionic conducting. The electrolyte salt can be selected based on electrochemistry of the battery. For example, for a zinc-manganese dioxide battery the electrolyte salt can be a zinc chloride salt and for a lithium manganese oxide-titanium dioxide battery the electrolyte salt can be lithium chloride or lithium nitrate or lithium sulphate or a mixture of different lithium salts.

[0040] The waxy material 322 is an ionic conducting polymer or oligomer, which is in wax form in its substantially pure state at ambient conditions. The waxy material 322 can be, but is not limited to, poly(ethylene glycol) or polyethylene oxide. The purpose of the waxy material 322 is to provide smooth slipping of the one separator layer 310 over another one of the separator layers 311 or over another electrode layer 320, when the battery 300 is bent.

[0041] The waxy material 322 can be a mixture of a high molecular weight poly(ethylene glycol) and a low molecular weight poly(ethylene glycol) in one aspect of the invention. Typically, poly(ethylene glycol) with a molecular weight of higher than 5,000 Dalton is solid at ambient conditions. Smaller molecular weight poly(ethylene glycol). i.e. less than 5,000 Dalton, is a waxy solid at ambient conditions. The high molecular weight poly(ethylene glycol) becomes sticky in presence of water. A small quantity of the high molecular weight poly(ethylene glycol) in the electrolyte layer 320, makes the electrolyte layer 320 slightly sticky, as water is present in the electrolyte layer 320. The slight sticky nature of the electrolyte layer 320 keeps the electrolyte layer 320 attached to the separator layers 310 and 311 or to the electrode layer 307 or 308. In one aspect of the disclosure, the ratio of the high molecular weight poly(ethylene glycol) and the small molecular weight poly(ethylene glycol) is 1:9, but this is not limiting of the invention. In a further aspect, the molecular weight of the small molecular weight poly(ethylene glycol) is less than 4,000 Dalton, but this is not limiting of the invention. In a further aspect, the molecular weight of the high molecular weight poly(ethylene glycol) or polyethylene oxide is more than 100,000 Dalton, but this is not limiting of the invention. It will be appreciated that the given molecular weights of poly(ethylene glycol) or polyethylene oxide mentioned here are the number average molecular weights.

[0042] The water insoluble substantially spherical particles 321 can be selected from, but are not limited to, silica gel, zeolite, cellulose powder etc. The purpose of the water-insoluble substantially spherical particles 321 is to prevent the waxy materials 321 from squeezing out of their position when pressure is applied by the "unpatterned lamination" method. The water insoluble substantially spherical particles 321 also work as a ball bearing when the battery 300 is bent. When the electrolyte layer 320 is printed on top of either or both of the separator layers 310 and 311, water along with a major portion of the electrolyte salt is absorbed into the separator layers 310 and 311. Therefore, the waxy material 322 and the water insoluble substantially spherical particles 321 stays mostly on top of the separator layers 310 and 311.

[0043] In this scenario control of the ratio of waxy material 322 and the water-insoluble substantially spherical particles 321 in the electrolyte layer 320 is required to protect the electrolyte layer 320 from being squeezed out of the battery 300. Three different possibilities can arise after printing of the electrolyte layer 420 on top of a separator layer 410, as shown in FIG. 4. For clarity, in FIG. 4 are shown only the separator layer 410 and the electrolyte layer 420. FIG. 4A shows the electrolyte layer 420 and the separator layer 410 just after the electrolyte layer 420 is printed on top of the separator layer 410. After a few seconds, the water in the electrolyte layer 420 is absorbed into the separator layer 410. Some amount of water is also absorbed into the electrode layers too, as the cathode layer (307 in Fig. 3) and the anode layer (308 in Fig. 3) comprise water absorbing materials. Along with the water, a major portion of the electrolyte salt is also absorbed into the separator layer 410. The separator layer 410 becomes saturated with water and, after a certain period of time, the separator layer 410 is unable to absorb more water. Therefore, the amount of water in the printed electrolyte layer 420 should be controlled. After the water saturation of the separator layer 410 is reached, extra water will stay in the electrolyte layer 420. This extra water in the electrolyte layer 420 can cause the electrolyte layer 420 to he easily squeezed out of its position when a uniform pressure is applied on the battery 300 by an "unpatterned lamination". Therefore, the amount of water present in per unit volume of the printed electrolyte layer 420 is selected in such a way that the amount of water is slightly more than the saturation limit of the per unit volume of the separator layer 410. The amount of water in the printed electrolyte layer 420 is controlled by the amount of water in the electrolyte ink as well as by the thickness of the printed electrolyte layer 420. In one aspect, the amount of water in the electrolyte ink is less than 15%, compared to the total weight of the electrolyte ink, but this is not limiting of the invention.

[0044] As mentioned above, after the water in the electrolyte layer 420 is absorbed into the separator layer 410, three possibilities can arise, as shown in FIG. 4B, FIG. 4C and FIG 4D. In FIG. 4B, the thickness of the waxy material 422 along with the left over water and the electrolyte salt is less than the diameter of the water-insoluble substantially spherical particles 421. In this case, when the second separator layer 411 or another electrode is placed on top of the electrolyte layer 420, sufficient ionic connection between the two separator layers 410, 411 or between one separator layer 410 and another electrode is not established. This happens because the water-insoluble substantially spherical particles 421 are solid in nature and are not compressed when a pressure is applied over the battery 300 by an "unpatterned lamination". In FIG. 4C, the thickness of the waxy material 422 along with the left over water and the electrolyte salt is more than the diameter of the water-insoluble substantially spherical particles 421. In this case, some amount of the waxy materials 422 is squeezed out of its position when a uniform pressure is applied over the battery by an "unpattemed lamination".

[0045] In FIG. 4D, the thickness of the waxy material 422 along with the left over water and the electrolyte salt is equal to or slightly more than the diameter of the water-insoluble substantially spherical particles 421. This case generates the best results. In one aspect, the water-insoluble substantially spherical particles 421 arc silica gel of average particle diameter of 50 microns. In this aspect, the weight ratio of poly(ethylene glycol) to the silica gel is in the range of 2 to 18. A theoretical correlation is established to estimate the weight ratio (r) of poly(ethylene glycol) to silica gel, as given by the following equation. 0.68

r= 1.4 3 n * R2 where, R is the radius of the silica gel particle and it is the number of the silica gel particles homogenously distributed in one plane of per unit area of the printed electrolyte layer 420.

[0046] An adhesive layer 305 is provided at least on one of the firs( substrate 301 or the second substrate 302 around a perimeter of at least one of the cathode layer 307 and the anode layer 308. The adhesive layer 305 can be a pressure adhesive or heat activated adhesive or a UV activated adhesive. In a non-limiting aspect, the adhesive layer 305 can also be printed. In another aspect, the adhesive layer 305 can be applied in a form of double-sided tape around the battery unit cell. Finally, the top substrate 302 and the bottom substrate 301 are laminated in such a way that the cathode layer 307 and the anode layer 308 face each other and the separator layer 310 and 311 and the electrolyte layer 320 are sandwiched in between the cathode layer 307 and the anode layer 308. The sealing of the battery 300 can be done by an "unpatterned lamination" machine and by using adhesive layer 305.

[0047] In order to prevent any further leakage of the electrolyte layer 320 by "unpatterned lamination", the total thickness of the adhesive layer 305 is kept just slightly lower than the total thickness of the anode layer 308, the cathode layer 307, the separator layers 310, 311, the electrolyte layer 320, the cathode current collecting layer 304 and the anode current collecting layer 303. In one aspect, the total thickness of the anode layer 308, the cathode layer 307, the separator layers 310, 311, the electrolyte layer 320, the cathode current collecting layer 304 and the anode current collecting layer 303 is around 220 microns and the total thickness of the adhesive layer 305 is 200 microns.

[0048] The thin battery 300 can be produced according to the following exemplary process, as illustrated in FIG. 5: [0049] In the step 530, conductive carbon is printed and dried on a first substrate 301 and on a second substrate 302 as the cathode current collecting layer 304 and as the anode current collecting layer 303, respectively.

[0050] In the step 535, the cathode layer 307 is printed and dried on top of the cathode current collecting layer 304.

[0051] In the step 540, the anode layer 308 is printed and dried on top of the anode current collecting layer 303.

[0052] In the step 545, the at least one separator layers 310 and 311 are printed and dried on at least one of the cathode layer 307 or the anode layer 308.

[0053] In the step 550, the at least one adhesive layer 305 is printed and cured at least on one of the first substrate 301 and the second substrate 302 around a perimeter of at least one of the cathode layer 307 and the anode layer 308.

[0054] In the step 555, at least one electrolyte layer 320 is printed on the at least one separator layer 310 and 311.

[0055] In the step 560, waiting for few seconds until a major portion of the water in the electrolyte layer 320 is absorbed into the separator layer 310 and or 311.

[0056] In the step 565, laminating the first substrate 301 on the second substrate 302 in such a way that the at least one separator layer 310, 311 and the at least electrolyte layer 320 are sandwiched between the cathode layer 307 and the anode layer 308.

[0057] In one non-limiting aspect, the water-absorbing material in the cathode layer 307 and in the anode layer 308 can he different from the water-absorbing powder present in the separator layer 310, 311. In one non-limiting aspect, the-water absorbing material can be water-soluble. In another aspect, the water-absorbing material can be water insoluble. The water-absorbing powder is water insoluble. In one non-limiting aspect, the bottom substrate 301 and the top substrate 302 are a single substrate.

[0058] In order to enhance printability and surface adhesion of the anode layer 308, the cathode layer 307, the separator layers 310, 311 and the electrolyte layer 320 the respective functional inks further comprise at least one additive. The additive can he selected according to the requirement from Evonik TEGO Foamex, TEGO Airex, TEGO Flow, TEGO Glide, TEGO Phobe, TEGO Dispers, TEGO ViscoPlus, TEGO Wet, TEGO Twin etc.

EXAMPLE 1

[0059] A cathode current collecting layer and an anode current collecting layer were printed on two separate 150 micron-thick PET foils by using a screen-printing machine and by using a commercially available conducting carbon ink C210 from Conductive Compounds, Inc. The cathode ink for the cathode layer is prepared by mixing manganese-dioxide particles, cellulose powder and graphite powder in toluene together with PMMA. The anode ink for the anode layer is prepared by mixing zinc particles, cellulose powder and graphite powder in toluene together with PMMA. After printing the cathode layer on top of the cathode current collecting layer, the layer was dried with hot air at 90 °C to remove extra toluene. After printing the anode layer on top of the anode current collecting layer, the layer was dried with hot air at 90 °C to remove extra toluene.

[0060] The separator layer ink was prepared by mixing cellulose power with ethylcellulose in toluene. After printing of the separator layer ink by screen-printing on top of the cathode layer 307 and the anode layer 308 the separator layer ink was dried by hot air at 90 °C to form one of the separator layers 310 and 311. An adhesive layer was printed on the first PET foil forming the first substrate 301, which surrounds the cathode layer 307 in such a way that a portion of the cathode current collecting layer is out of this boundary. Another adhesive layer was printed on the second PET foil forming the second substrate 302, which surrounds the anode layer 308 in such a way, that a portion of the anode current collecting layer projects out of this boundary. The functional ink for the electrolyte layer was prepared by dissolving zinc chloride salt in water and then the functional ink was mixed with polyethylene glycol and silica gel. The electrolyte ink was printed on top of the separator layers 310 and 311. After printing the electrolyte layer, the two PET foils 301 and 302 were laminated in such a way that the cathode layer 307 and the anode layer 308 face each other. The lamination was done by an "unpatterned lamination" machine, which has two smooth rollers. The no-load voltage of the battery 300 was 1.4 Volt and current density of 0.4 mA/cm2.

EXAMPLE 2

[0061] A cathode current collecting layer and an anode current collecting layer were printed on two separate 150 micron-thick PET foils 301, 302 by using a screen-printing machine and by using a commercially available conducting carbon ink C210 from Conductive Compounds, Inc. [0062] The functional ink for the cathode layer 307 was prepared by mixing lithium manganese oxide particles, cellulose powder and graphite powder in toluene together with PMMA. The functional ink for the anode layer 308 is prepared by mixing titanium dioxide particles, cellulose powder and graphite powder in toluene together with PMMA. After printing the cathode layer 307 on top of the cathode current collecting layer 304, the cathode layer was dried with hot air at 90 °C to remove extra toluene. After printing the anode layer 308 on top of the anode current collecting layer 303, the anode layer was dried with hot air at 90 °C to remove extra toluene. The functional layer ink for the separator layer 310, 311, was prepared by mixing cellulose power with ethylcelleluse in toluene. After printing the separator layers 310 and 311 by screen-printing on top of the cathode layer 307 and the anode layer 308 the separator layers 310 and 311 were dried by hot air at 90 °C. An adhesive layer 305 was printed on the first PET foil 301, which surrounds the cathode layer 307 in such a way, that a portion of the cathode current collecting layer is out of this boundary. Another adhesive layer 305 was printed on the second PET foil 302, which surrounds the anode layer 308 in such a way, that a portion of the anode current collecting layer is out of this boundary. The functional ink for the electrolyte layer 320 was prepared by dissolving lithium chloride and lithium sulphate salts in water and mixing it with polyethylene glycol and silica gel. After printing the electrolyte layer 320, the two PET foils 301, 302 were laminated in such a way that the cathode layer 307 and the anode layer 308 face each other. The lamination was done by an "unpatterned lamination" method, which consists of two smooth rollers. The discharge voltage of the battery was found to be 1.1 Volt.

Claims

CLAIMS1. A thin battery (300), comprising: a first substrate (301); a second substrate (302); a cathode layer (307) disposed on the first substrate (301), wherein the cathode layer (307) is water insoluble but water ahsorbable; an anode layer (308) disposed on the second substrate (302), wherein the anode layer (308) is water insoluble but water absorbable; at least one separator layer (310, 311) disposed on at least one of the cathode layer (307) or the anode layer (308), wherein the separator layer (310, 311) comprises at least one water absorbing powder interconnected through at least one interconnecting material in such a way that the interconnection is not broken in the presence of water; and at least one electrolyte layer (320) disposed on at least one of the at least one separator layer (310, 311), the cathode layer (307) or the anode layer (308), wherein the electrolyte layer (320) is a mixture of water, at least one electrolyte salt, water insoluble substantially spherical particles (321) and at least one waxy material which is substantially ionic conducting (322); wherein the first substrate (301) is secured on the second substrate (302) in such a way that the at least one separator layer (310, 311) and the at least one electrolyte layer (320) are sandwiched between the cathode layer (307) and the anode layer (308).
2. The thin battery as claimed in claim 1, further comprising a cathode current collecting layer (304) provided between the cathode layer (307) and the first substrate (301).
3. The thin battery as claimed in claim 1, further comprising an anode current collecting layer (303) provided between the anode layer (308) and the second substrate (302).
4. The thin battery as claimed in claim 1, wherein the cathode layer (307) is a blend of at least one cathode active powder, at least one water absorbing material and at least one water insoluble polymeric hinder;
5. The thin battery as claimed in claim 1. wherein the anode layer (308) is a blend of at least one anode active powder, at least one water absorbing material and at least one water insoluble polymeric binder;
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10.The thin battery as claimed in claims 1, 2 and 3, wherein at least one of the anode layer (308), the cathode layer (307), the at least one separator layer (310, 311), the at least one electrolyte (320), the cathode current collecting layer (304) and the anode current collecting layer (303) are comprised of dried or cured inks.The thin battery as claimed in claims 1, 2 and 3, wherein the cathode current collecting layer (304) and the anode current colleting layer (303) comprise conductive carbon particles.The thin battery as claimed in claims 1, 4 and 5 wherein the at least one of the anode layer (308), the cathode layer (307), the at least one separator layer (310, 311) or the at least one electrolyte layer (320) further comprise at least one additive to enhance printability and surface adhesion.The thin battery as claimed in claims 1, 4 and 5, wherein the at least one of the anode layer (308) or the cathode layer (307) further comprise carbon particles.The thin battery as claimed in claim 1, wherein the first substrate (301) and the second substrate (302) are secured to each other by at least one adhesive layer (305), provided on at least one of the first substrate (301) and the second substrate (302) around a perimeter of at least one of the cathode layer (307) and the anode layer (308).The thin battery as claimed in claim 1, wherein the first substrate (301) and the second substrate (302) form a single substrate.The thin battery as claimed in claim 1, the at least one water absorbing powder is substantially water insoluble.The thin battery as claimed in claim 1, the at least one water absorbing powder is one of a silica gel or a cellulose powder.The thin battery as claimed in claim 1, the size of water insoluble substantially spherical particles (321) is between 1p m and 100 p m.The thin battery as claimed in claims 4 and 5, the at least one water absorbing material is a water-soluble polymer.A method of producing a thin battery (300), comprising: a. providing a cathode current collecting layer (304) on a first substrate (301); b. providing an anode current collecting layer (303) on a second substrate (302); c. printing a cathode layer (307) on the cathode current collecting layer (304), wherein the cathode layer is a blend of at least one cathode active powder, at least one water absorbing material and at least one water insoluble polymeric binder; d. printing an anode layer (308) on the anode current collecting layer (303), wherein the anode layer is a blend of at least one anode active powder, at least one water absorbing material and at least one water insoluble polymeric binder; e. printing at least one separator layer (310, 311) on at least one of the cathode layer (307) or the anode layer (308), wherein the separator layer (310, 311) comprises at least one water-absorbing powder interconnected through at least one interconnecting material in such a way that the interconnection is not broken in the presence of water;
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16.f. printing at least one adhesive layer (305) at least on one of the first substrate (301) and the second substrate (302) around a perimeter of at least one of the cathode layer (307) and the anode layer (308); printing at least one electrolyte layer (320) on the at least one separator layer (310, 311), wherein the electrolyte layer (320) is a mixture of water, at least one salt, water insoluble substantially spherical particles (321) and at least one waxy material which is substantially ionic conducting (322); and h. securing the first substrate (301) on the second substrate (302) in such a way that the at least one separator layer (310, 311) and the at least electrolyte layer (320) are sandwiched between the cathode layer (307) and the anode layer (308).
17. The method of claim 16, further comprising the steps of drying or curing at least one of the anode layer (308), the cathode layer (307), the at least one separator layer (310, 311), the at least one electrolyte layer (320), the cathode current collecting layer (304) and the anode current collecting layer (303).