GB2590393A

GB2590393A - Component

Info

Publication number: GB2590393A
Application number: GB1918467.0A
Authority: GB
Inventors: John Alexander Samuel
Original assignee: Dyson Technology Ltd
Current assignee: Dyson Technology Ltd
Priority date: 2019-12-16
Filing date: 2019-12-16
Publication date: 2021-06-30
Also published as: GB201918467D0; WO2021123734A1

Abstract

A component 100 comprising a current collector 102 adhered to a substrate 104. The mean crystallite size of the current collector 102 is limited such that the strength of the adhesion between the current collector and the substrate is at least 0.8 N/mm2. The current collector may comprise platinum, with a mean crystallite size is ≥ 50nm. The component can also be part an assembly where the assembly is a cathode which comprises LiCoO2.The assembly may also be used as a part of a battery.

Description

COMPONENT

Technical Field

The present invention relates to a component comprising a current collector and a substrate, and articles incorporating the component.

Background

Current collectors for use in batteries (such as lithium-ion batteries) are typically formed on substrates. During charging and discharging of a battery, the battery cell may undergo expansion and contraction; adhesion of a current collector to the underlying substrate should be sufficient such that the substrate and current collector remain adhered throughout this cycling process. Moreover, components comprising substrates adhered to current collectors are often subjected to roll-to-roll processing, and the adhesion strength must be sufficient to prevent del aminati on of the layers.

Summary

At its most general, the invention provides a component comprising a current collector adhered to a substrate, wherein the mean crystallite size of the current collector is limited such that the strength of the adhesion between the current collector and the substrate is at least 0.8 Nimm2.

The inventors have established that limiting the crystallite size in a current collector improves adhesion of the current collector to the substrate.

A second aspect of the invention provides an assembly comprising a component according to the first aspect and an electrode adhered to the current collector on a side opposite to the substrate.

A third aspect of the invention provides a battery comprising an assembly according to the second aspect.

Further features and advantages of the invention will become apparent from the following description of preferred embodiments of the invention, given by way of example only, which is made with reference to the accompanying drawings.

To the extent that they are compatible, optional or preferable features of each aspect of the invention may be combined with other aspects of the invention defined herein.

Brief Description of the Drawings

Figure 1 shows a schematic cross-sectional view of a component according to embodiments of the invention Figures 2a to 2d each show a schematic cross-sectional view of an assembly according to embodiments of the invention.

Figure 3 shows a schematic cross-sectional view of a battery according to embodiments of the invention

Detailed Description

The inventors have established that a lower crystallite size in the current collector improves adhesion of the current collector to the substrate. The crystallite size of the current collector may be reduced by lowering the power or increasing the pressure during deposition of the metal on the substrate.

Figure 1 shows a component 100 comprising a substrate layer 102 and a current collector layer 104 disposed on the substrate layer 102. In an embodiment, the substrate is formed from PET and the current collector is formed from platinum with a mean crystallite size of about 24.7 nm, but other materials may be used as discussed in detail herein.

For the avoidance of doubt, the adhesion strength referred to herein is a tensile 30 adhesion The mean crystallite size may be obtained by application of the Schen-er equation to X-ray diffraction data.

In some cases, the current collector comprises platinum, copper, nickel and/or aluminium. In some cases, the current collector may essentially consist of one of these metals.

In some cases, the strength of the adhesion between the current collector and the substrate is at least 0.5 N/mm2, 0.8 N/mm2, 1.0 N/mm2, 1.25 N/mm2, 1.5 N/mm2, 1.75 N/mm2, or most suitably at least about 2.0 N/mm2.

In some cases, the current collector essentially consists of platinum and the mean crystallite size of the platinum is less than or equal to about 50nm, 40nm, 30nm or 25 nm.

In some cases, a surface of the current collector opposite to the surface adhered to the substrate has a surface roughness of Xs, where Xs < 100 nm. This may be referred to herein as a top surface, for ease of reference. This "top" designation does not reflect any required orientation of the component in use, and merely reflects that the surface is opposite to a "bottom" surface which contacts the substrate. The top surface may be configured to support an electrode in use. In some cases, the top surface of the current collector may have a surface roughness of greater than 1 nm, for example greater than 5 nm.

It has been found that the roughness of the top surface of the current collector is an important factor in manufacturing products incorporating a thin layer of crystalline electrode material on the current collector. Ensuring that the surface of the current collector is extremely smooth results in a crystalline electrode with surprisingly few defects. Conversely, when the surface of the current collector is relatively rough there is a surprisingly profound effect on the likelihood of delamination of the layer of crystalline material from the current collector. If the top surface is too smooth however the current collector can become too difficult to handle and process.

Particularly in applications where the current collector is stored in layers that are in contact with each other, for example when the current collector is an elongate film supplied on a drum or roller, it may be that the surface roughness needed for easing handling decreases as the thickness of the current collector increases. For thick films of current collector, the minimum roughness required may be lower than for very thin films. It may be the case that the product of the thickness of the current collector and Xs (i.e. the thickness of the substrate multiplied by Xs) is no more than 105 nm2. Preferably, the product of the thickness of the current collector and Xs is no more than 5 x 104 nm2. In some cases, it may be that Xs is no more than 10% of the thickness of the current collector.

The surface roughness may be measured by a profilometer. The surface roughness may be measured by means of calculating the RMS roughness. The RIMS roughness may be calculated as the deviation in height from a perfectly smooth external surface. It will be understood that a perfectly smooth external surface is perfectly flat when the mid-plane of the substrate is transformed onto a flat plane. The surface roughness may be measured by means of calculating the arithmetic average of the absolute values of profile heights (above the minimum height measured) over an evaluation length of a sample.

In some cases, the substrate comprises one or more materials selected from: a polymer material, a semiconductor wafer, plastic film, metal foil, thin glass, mica and a polyimide material. In some cases, the substrate may comprise polyethylene terephthalate (PET), or polyethylene naphthalate (PEN). PEN and PET are reasonably flexible, and have a relatively high tensile strength due to their semi-crystalline structure In some cases, the substrate may have a thickness of less than about 100 um, suitably less than about 50 pm, and optionally more than about 0.5 um, more than about 1 um, or possibly more than about 10 um.

In some cases, the current collector may be thin layer. In some cases, the thickness of the current collector may be less than about 100 pm, suitably less than about 50 pm, less than about 10 pm, less than about 5 pm or possibly less than about I p.m. Generally, a thin current collector is advantageous as it minimises the overall mass of the battery in which it employed. Typically, the current collector will be at least 500 nm thick, and possibly I pm or thicker. There is a lower limit on how thin the current collector can be before its mechanical strength and other physical properties make it unsuitable for use.

In some cases, the component has a laminate structure with a layer of substrate being adhered to a layer of current collector. In some such cases, the thickness of the current collector layer is less than about 100 pm, and/or the thickness of the substrate layer is from about 0.5 p.m to about 100 p.m.

In some cases, the component may comprise, or be in the form of, a sheet, optionally an elongate sheet. Such a sheet may be provided in the form of a roll. This facilitates simple storage and handling of the substrate.

In some cases, the invention provides an assembly comprising a component described herein an electrode adhered to the current collector on a side opposite to the substrate. In some cases, the assembly may comprise a laminate structure comprising (in order) a substrate layer, a current collector layer adhered to the substrate layer, and an electrode layer on (e.g. abutting) the current collector layer. (Throughout this specification, reference to an element being adhered to another element indicates direct adhesion (i.e. abutting contact between the layers).

In some cases, the electrode is a cathode and comprises LiCo02. In some such cases, the thickness of the cathode is less than about 10 p.m. In some cases, the thickness of the cathode is from about 50 nm, 100 nm or 500 nm to about 1 p.m, 5 p.m or 10 p.m.

In some cases, the mean crystallite size of the cathode (suitably LiCo02) is in the range of about 10 nm to about 30 nm, suitably in the range of about 14 nm to about 25 nm.

At least a portion of and optionally all the electrode material may have a crystalline "layered oxide" structure. Such "layered oxide" structures are important when manufacturing solid-state batteries. A layered oxide structure allows for lithium ions to more easily de-intercalate from the crystal structure, resulting in a faster charging, higher capacity solid-state battery. It will be understood that intercalation refers to a property of a material that allows ions to readily move in and out of the material without the material changing its phase (chemical and crystalline structure) For example, a solid-state intercalation film remains in a solid-state during discharging and charging of an energy-storage device.

In some cases, it may be that Xs (the surface roughness of the current collector top surface) is no more than 10 % of the thickness of the first electrode crystalline layer deposited on the current collector. For very thin electrode crystalline layers, from say lOnm to 100nm thick, it may be that Xs is no more than 50% of the thickness of the first electrode crystalline layer. For electrode crystalline layers, with a thickness of from 100nm to 1pm thick, it may be that Xs is no more than 10 % of the thickness of the first electrode crystalline layer.

Figure 2a shows an assembly 210 according to an embodiment of the invention, comprising a component 100, comprising a substrate layer 102 and a current collector layer 104 disposed on the substrate, and an electrode layer 106 disposed on the current collector layer 104 on the opposite side from the substrate layer 102. In an embodiment the substrate layer 102 is formed from PET, the current collector is formed from platinum with a mean crystallite size of about 24.7 nm, and the electrode layer is a LiCo02 cathode, but other materials may be used as discussed herein.

In some cases, the assembly further comprises an electrolyte on the opposite side of the electrode from the current collector. In some such cases, the assembly may comprise a laminate structure comprising the following layers, in order: (a) a substrate layer, (b) a current collector layer, (c) a cathode layer, and (d) an electrolyte layer. In some cases, there may be intermediate layers between the layers recited above. In other cases, the recited layers may be in a directly abutting relationship and in some cases, the layers may be adhered to each adjacent layer. An example of such an assembly 220 is illustrated schematically in Figure 2d, in which the electrolyte layer 108 is disposed on a surface of the cathode layer 106 opposite to the current collector 104. The electrolyte layer may be LiPON, but other materials can be employed, as discussed herein. (Figure 2b employs the same reference numerals as earlier figures and description of these elements is provided in detail above.) The electrolyte may comprise a solid layer, and may be referred to as a fast ion conductor. A solid electrolyte layer may have structure which is intermediate between that of a liquid electrolyte, which for example lacks a regular structure and includes ions which may move freely, and that of a crystalline solid. A crystalline material for example has a regular structure, with an ordered arrangement of atoms, which may be arranged as a two dimensional or three dimensional lattice. Ions of a crystalline material are typically immobile and may therefore be unable to move freely throughout the material.

In some cases, the electrolyte may have a thickness in the range of about 0.1 p.m to about 10 pm. The electrolyte may comprise, or optionally be formed of any suitable material which is ionically conductive, but which is also an electrical insulator, such as lithium phosphorous oxynitride (LiPON).

In some cases, the assembly further comprises a second electrode on the opposite side of the electrolyte layer from the first electrode. In some such cases, the second electrode is an anode, and may suitably comprise, or optionally be formed of graphite, silicon and/or indium tin oxide. In some such cases, the assembly may comprise a laminate structure comprising the following layers, in order: (a) a substrate layer, (b) a current collector layer, (c) a cathode layer, (d) an electrolyte layer, and (e) an anode layer. In some cases, there may be intermediate layers between the layers recited above. In other cases, the recited layers may be in a directly abutting relationship and in some cases, the layers may be adhered to each adjacent layer.

S

Any assembly with an anode layer may further include a current collector associated with the anode. This may be a further layer of a metal, for example, nickel, disposed on a surface of the anode opposite to the electrolyte An example of such an assembly is illustrated schematically in Figure 2c, in which the anode layer 110 is disposed on the opposite surface of the electrolyte layer 106 from the cathode layer 104. The anode layer may be graphite, but other materials can be employed, as discussed herein. (Figure 2c employs the same reference numerals as earlier figures and description of these elements is provided in detail above.) A further assembly 250 is illustrated in Figure 2d. In this assembly, a laminate structure consisting of the following abutting layers, in order is provided: a substrate 102, suitably formed from PET; a current collector 104, suitably formed from 111-strained nickel; a cathode layer 106, suitably formed from LiCo02; an electrolyte layer 108, suitably formed from LiPON; an anode layer 110, suitably formed from graphite; a second electrolyte layer 108', suitably formed from UPON; a second cathode layer 106', suitably formed from LiCo07; and a second current collector layer 104', suitably formed from 111-strained nickel. Although not illustrated, any assembly with an anode layer may include a current collector associated with the anode. This may be a further layer of a metal, for example, nickel, disposed within the anode (e.g, bisecting the anode, in a plane parallel to the other layers.

Further, as will be envisaged, in further embodiments, the assembly may comprise further layers stacked above 104', repeating the order shown in Figure 2d.

In all cases described herein, the component or assembly may be flexible, such that it can be rolled and processed on roll-to-roll apparatus (also known as reel-to-reel apparatus).

A further aspect of the invention provides a battery comprising a least one assembly described herein In some cases, the battery comprises a plurality of assemblies.

Such a battery 300 is illustrated in Figure 3, where two assemblies 240a and 240b are illustrated. (The reference numerals from previous figures are used again in Figure 3. The two assemblies and constituent elements have been denoted as "a" and "b" suffixes on the reference numerals.) An electrically insulating material 302 is arranged between the assemblies. The electrically insulating material 302 may be an ink, such as a dielectric ink. A suitable dielectric ink is DM-IN1-7003, available from Dycotec Materials Ltd., Unit 12 Star West, Westmead Industrial Estate, Westlea, Swindon, SNS 7SW, United Kingdom. In general, the electrically insulating material 302 may be any suitable dielectric material. A dielectric material is for example an electrical insulator which may be polarized upon application of an electric field. Such a dielectric material typically also has a low electrical conductivity.

In the battery of Figure 3, two assemblies are illustrated. In other, non-illustrated embodiments, there may be a single assembly, and in other embodiments, there may be more than two assemblies.

Measurement of adhesion strength Adhesion strength may be measured by any known technique in the art. A suitable technique is described below, which uses an Elcometer 510.

In this example method for measuring the tensile adhesion, a dolly is fastened to the current collector using an adhesive (such as araldite), which is allowed to cure and set. Once fully cured, the Elcometer applies a perpendicular pulling force which gradually increases over time. The force required to separate the current collector from the substrate can be established.

Example

Pt current collectors that were deposited on glass or silica wafers had different crystallite sizes, obtained by altering the power and/or pressure during deposition of the platinum.

The adhesion strength was measured using the Elcometer 510 (as described above) and the results are provided in Table 1.

Crystallography Physical Adhesion Mean crystallite Crystallite Elcometer strength / size / nm strain / 510 test N/mm 24.7 0.461 Pass 2.14 71 0.06 Fail 0.2 58 0.468 Fail 54 0.382 Fail 0.606 Fail 0.58 Fail

Table 1

The mean crystallite size is obtained by application of the Scherrer equation to X-ray diffraction data It can be seen that the adhesion strength was greatest when the mean crystallite size was less than 25nm.

Throughout this specification, reference to an element being "on" another element is to be understood as including direct or indirect contact. In other words, an element on another element may be either touching the other element, or not in contact the other element but, instead, generally supported by an intervening element (or elements) but nevertheless located above, or overlapping, the other element. In some cases, the elements are adjacent i.e. in direct contact or abutting. In some cases, the materials may adhere to one another. Where there are a number of stacked materials (such as in the laminate structures described herein), some of the layers may adhere to one another but others need not adhere.

The above embodiments are to be understood as illustrative examples of the invention. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

Claims

CLAIMSA component comprising a current collector adhered to a substrate, wherein the mean crystallite size of the current collector is limited such that the strength of the adhesion between the current collector and the substrate is at least 0.8 N/mm2. 3. 4, 6. 7.
A component according to claim 1, wherein the current collector comprises platinum, copper, nickel and/or aluminium.
A component according to claim 1 or claim 2, wherein the strength of the adhesion between the current collector and the substrate is at least 2.0 N/mm2.
A component according to claim 1, wherein the current collector substantially consists of platinum and the mean crystallite size of the platinum is less than or equal to about 50 nm.
A component according to any preceding claim, wherein a surface of the current collector opposite to the surface adhered to the substrate has a surface roughness of Xs, where Xs < 100 nm.
A component according to any preceding claim, wherein the substrate comprises one or more materials selected from: a polymer material, a semiconductor wafer, plastic film, metal foil, thin glass, mica and a polyimide material.
A component according to any preceding claim, wherein the component has a laminate structure and wherein the thickness of the current collector layer is less than about 100 pm A component according to any preceding claim, wherein the component has a laminate structure and wherein the substrate has a thickness of from 0.5 pm to 100 pm.
An assembly comprising a component according to any one of claims 1 to 8 and an electrode adhered to the current collector on a side opposite to the substrate.
S
10. An assembly according to claim 9, wherein the electrode is a cathode which comprises LiCo02.
11. An assembly according to claim 10, wherein the cathode is provided as a layer on the current collector, and wherein the thickness of the cathode is less than about 10 nm.
12. An assembly according claim 10 or claim 11, wherein mean crystallite size of the cathode is in the range of 10 nm to 30 nm.
13. An assembly according to any of claims 9 to 12, further comprising an electrolyte on the opposite side of the electrode from the current collector.
14. An assembly according to claim 13, further comprising a second electrode on the opposite side of the electrolyte from the first electrode
15. An assembly according to claim 14, wherein the second electrode is an anode which comprises graphite.
16. A battery comprising an assembly according to any one of claims 9 to 15.
17. A battery according to claim 16, where the battery comprises a plurality of assemblies according to any one of claims 9 to 15.