WO2024074618A1

WO2024074618A1 - Electrochemical cell

Info

Publication number: WO2024074618A1
Application number: PCT/EP2023/077581
Authority: WO
Inventors: Sang Eun Cheon; Billy GRUNDSTRÖM; Valeria DE VELASCO BERMUDEZ; Nicolas POTIN
Original assignee: Northvolt Ab
Priority date: 2022-10-06
Filing date: 2023-10-05
Publication date: 2024-04-11

Abstract

An electrochemical cell having a stacked configuration. The cell comprises a positive electrode; a negative electrode; a separator arranged between the positive electrode and the negative electrode; a sealant disposed between a peripheral region of the positive electrode and a peripheral region of the negative electrode; a first polymer layer located on an outward facing side of the positive electrode; and a second polymer layer located on an outward facing side of the negative electrode.

Description

ELECTROCHEMICAL CELL

TECHNICAL FIELD

The present disclosure relates to an electrochemical cell having a stacked configuration and to a battery module comprising a plurality of said electrochemical cells. The cell includes a positive electrode and a negative electrode, and a polymer layer on an outward facing side of at least one of the electrodes.

BACKGROUND

Rechargeable or secondary batteries find widespread use as electrical power supplies and energy storage systems. For example, in automobiles, battery packs being formed of a plurality of battery modules, wherein each battery module includes a plurality of electrochemical cells, are expected as a means of effective utilization of electric power, also in the viewpoint of air pollution prevention. Several different form factors exist for the electrochemical cells applied in secondary batteries depending on their intended application field. In automotive applications, the most common cell types are cylindrical, prismatic and pouch cells. A further concept for automotive applications is large format flat, thin cells, which in general include a single positive electrode and a single negative electrode and in which the upper and lower surfaces are formed by the current collector foils, which serve as cell housing and also act as the terminals for the cell. Such cells can be serially stacked with direct contact between the cell terminals, thereby eliminating the need for an outside can, bus bars, or other terminal attachments. However, in order to prevent short-circuiting, the current collector foils have to be sealed with a sealant, such as an adhesive. There is still a need for improvements to make electrochemical cells, in particular large format electrochemical cells, durable and stable, and thereby better usable in practice.

SUMMARY

In view of the above-outline requirements, an object of the present invention is to provide an electrochemical cell and a battery module having long lifetime and high safety.

Furthermore, it is an object of the present invention to provide an electrochemical cell and a battery module which have high energy and performance, have a low weight, are of simple structure and allow reduced hardware costs and simplified production processes, and at the same time have long lifetime and high safety. One or more of these objects may be achieved by an electrochemical cell and a battery module according to the independent claims. The independent claims and the claims depending therefrom can be combined in any technologically suitable and sensible way, thereby providing further embodiments of the invention. The description, particularly in relation to the drawings, provides further details characterizing embodiments of the invention.

According to a first aspect of the present disclosure, there is provided an electrochemical cell having a stacked configuration, comprising a positive electrode; a negative electrode; a separator arranged between the positive electrode and the negative electrode; a sealant disposed between a peripheral region of the positive electrode and a peripheral region of the negative electrode; a first polymer layer located on an outward facing side of the positive electrode; and a second polymer layer located on an outward facing side of the negative electrode.

Such an electrochemical cell can benefit from a reduced risk of damage during manufacture, particularly when manually handling components of the cell. In one specific example, this can result from a reduced likelihood of the foil substrate being wrinkled or suffering from other surface defects during manufacture. Also, advantageously, the electrochemical cell can have a relatively light weight.

The positive electrode and the negative electrode may each comprise a connection portion that protrudes laterally from a side of the electrochemical cell to provide an electrical connection for the respective electrode.

The connection portions of each electrode may protrude beyond the associated polymer layer.

The electrochemical cell may further comprise a connection portion that is distinct from, and electrically connected to, each of the positive and negative electrodes. The connection portion may protrudes laterally from a side of the electrochemical cell.

The connection portions may protrude laterally from two adjoining edges of the electrochemical cell. The connection portions may protrude laterally from part, but not all of, each of the two adjoining edges of the electrochemical cell.

Each of the positive electrode and the negative electrode may comprise a plurality of distinct connection portions.

The first polymer layer and the second polymer layer may each have a thickness in the range of 10 pm to 80 pm.

The positive electrode may comprise a first foil substrate and a first active material. The negative electrode may comprise a second foil substrate and a second active material. The first foil substrate and the second foil substrate may each have a thickness in the range of 0.1 pm to 40 pm.

The first and I or second polymer layers may be electrically conductive.

The first and the second polymer layers may be electrical insulators. The first polymer layer may be located on only part of the positive electrode in order to expose a part of the positive electrode. The second polymer layer may be located on only part of the negative electrode in order to expose a part of the negative electrode. The exposed part of the negative electrode may be configured to be aligned with an exposed part of a positive electrode of a neighbouring electrochemical cell when the electrochemical cells are provided in a stack. The exposed part of the positive electrode is configured to be aligned with an exposed part of a negative electrode of a neighbouring electrochemical cell when the electrochemical cells are provided in the stack.

The first and I or second polymer layer may comprise one or more channels through the thickness of the polymer layer.

The one or more channels may extend through the entire thickness of the polymer layer.

The one or more channels may extend partially through the thickness of the polymer layer.

The one or more channels may take a path that starts and I or ends at a peripheral edge of the polymer layer. The first and I or second polymer layer may comprise one or more indentations I protrusions in an outward facing side of the polymer layer to provide mechanical engagement with a polymer layer of an adjacent cell in a stack.

The one or more indentations I protrusions may be for interlocking with corresponding protrusions I indentations of the polymer layer of an adjacent cell in the stack.

The sealant may comprise: a first adhesive layer and a second adhesive layer, wherein the first adhesive layer is disposed at a peripheral region of the positive electrode on an inward facing side of the positive electrode, and the second adhesive layer is disposed at a peripheral region of the negative electrode on an inward facing side of the negative electrode; and a first sealing layer and a second sealing layer, wherein the first sealing layer is disposed on the first adhesive layer such that the first adhesive layer is sandwiched between the first sealing layer and the positive electrode, and the second sealing layer is disposed on the second adhesive layer such that the second adhesive layer is sandwiched between the second sealing layer and the negative electrode.

The sealant joins a periphery of the positive electrode to a periphery of the negative electrode and may hence be stacked between portions of the positive and the negative electrode that are aligned in the stacking direction. The present inventors advantageously found that by applying at least a two-layer sealant, i.e. an adhesive layer and a sealing layer, at the peripheral edge of each electrode, sufficient insulation and bonding strength can be provided to thereby ensure a stable and durable sealing and joining of the positive electrode and the negative electrode and to achieve high safety and long lifetime.

In an embodiment, at least one of the first adhesive layer and the second adhesive layer, preferably both layers, is disposed along the entire outer peripheral edge of the positive electrode and the entire outer peripheral edge of the negative electrode, respectively (i.e., along all four sides assuming a rectangular shape of the electrode substrates). By this, the bonding strength between the positive electrode and the negative electrode is further increased.

The first and second adhesive layers mainly function to provide sufficient adhesion of the sealant to the respective electrode. Accordingly, the first adhesive layer and the second adhesive layer each comprise an adhesive material, which may be the same or different, and is preferably selected from materials which exhibit adhesive properties and binding force sufficient to attach directly to the electrode and to ensure a strong and durable interfacial bond between the electrode and the adhesive layer. Preferred examples of suitable adhesive materials include, but are not limited to, polyolefins, for example, polyethylene or polypropylene, functionalized polyolefins, for example, ethylene- or propylene copolymers with monomers containing one or more of carboxylate, epoxy, nitrile, imine, maleicanhydride and hydroxyl functional groups, polyvinyl alcohols, polyamides, polyacrylnitrile, epoxy resins, (meth)acrylates, and derivatives thereof.

In an embodiment, the first adhesive layer and the second adhesive layer comprise the same adhesive material, in order to simplify production processes.

A thickness of the first adhesive layer and a thickness of the second adhesive layer may be the same or different. Preferably the first adhesive layer and the second adhesive layer have the same thickness. In a preferred embodiment, the first adhesive layer and the second adhesive layer each have a thickness of less than or equal to 40 pm, preferably in the range of 0.5 pm to 40 pm, more preferably in the range of 15 pm to 40 pm. By this, the overall weight and thickness of the electrochemical cell and the battery module can be decreased, and material costs can be saved.

The first and second sealing layers mainly function to provide good sealing properties to the sealant. Accordingly, the first sealing layer and the second sealing layer each comprise a sealing material, which may be the same or different, and is preferably selected form materials that exhibit insulation properties, stickiness, especially when heated, and chemical resistance, especially against degradation by the electrolyte. In a preferred embodiment, the first sealing layer and the second sealing layer comprise the same sealing material, in order to simplify production processes.

In a preferred embodiment, the first sealing layer and the second sealing layer each comprise as a sealing material one or more selected from polyolefins, in particular polyethylene, polypropylene and cast polypropylene (CPP), functionalized polyolefins, in particular polyolefin copolymers with monomers containing one or more of carboxylate, epoxy, nitrile, imine, maleicanhydride and hydroxyl functional groups, and epoxy resins, wherein CPP is particularly preferred, as CPP has excellent insulation properties and high chemical resistance, and because it becomes sticky when heated. Particularly preferably, the first sealing layer and the second sealing layer each comprise at least CPP, and optionally one or more materials selected from polyolefins, in particular polyethylene or polypropylene, functionalized polyolefins, in particular polyolefin copolymers with monomers containing one or more of carboxylate, epoxy, nitrile, imine, maleicanhydride and hydroxyl functional groups, and epoxy resins. That is, in a further preferred embodiment, the first sealing layer and the second sealing layer each comprise, or consist of, CPP. In another further preferred embodiment, the first sealing layer and the second sealing layer each comprise, or consist of, CPP and one or more materials selected from polyolefins, in particular polyethylene or polypropylene, functionalized polyolefins, in particular polyolefin copolymers with monomers containing one or more of carboxylate, epoxy, nitrile, imine, maleicanhydride and hydroxyl functional groups, and epoxy resins.

A thickness of the first sealing layer and a thickness of the second sealing layer may be the same or different. Preferably the first sealing layer and the second sealing layer have the same thickness. In a preferred embodiment, the first sealing layer and the second sealing layer each have a thickness in the range of 20 pm to 200 pm, more preferably in the range of 30 pm to 150 pm, and even more preferably in the range of 40 pm to 80 pm. For example, each layer may have a thickness of 40 pm, or 80 pm. If the thicknesses of the first and second sealing layer are below this range, sealing performance during cycling may not be ensured and electrolyte leakage may occur. If the thicknesses are above the defined range, the cell becomes too thick so that the overall battery module dimension is affected. In a further preferred embodiment, the thickness of the first sealing layer is greater than the thickness of the first adhesive layer and/or the thickness of the second sealing layer is greater than the thickness of the second adhesive layer. By this configuration, it is possible to take advantage of the good sealing properties imparted by the sealing material, while at the same time sufficient adhesion to the electrodes is ensured.

In a further embodiment, the first sealing layer has substantially (i.e. , within the given error limits of the production process) the same width as the first adhesive layer, measured from the outer peripheral edge to the inner peripheral edge of the first sealing layer and perpendicular to the stacking direction of the cell. Likewise, the second sealing layer has substantially the same width as the second adhesive layer, measured from the outer peripheral edge to the inner peripheral edge of the second sealing layer and perpendicular to the stacking direction of the cell, which is preferably the same width as the width of the first sealing layer. In an embodiment, at least one of the first sealing layer and the second sealing layer has an inner peripheral edge that surrounds the separator at an outer peripheral edge of the separator. This means, the inner peripheral edge of at least one of the first sealing layer and the second sealing layer, preferably of both sealing layers, surrounds and directly contacts the outer peripheral edge of the separator, whereby the separator is sealed relative to the positive electrode and the negative electrode in order to properly isolate the positive electrode and the negative electrode. This configuration allows the cell to be thinner.

In another embodiment, in order to seal the separator relative to the positive electrode and the negative electrode and to properly isolate the positive electrode and the negative electrode, the separator at least partly extends through the first sealing layer and the second sealing layer such that the separator is sandwiched at an outer peripheral edge thereof between the first sealing layer and the second sealing layer. For example, the separator can entirely extend through the first sealing layer and the second sealing layer, such that the first and second sealing layers are completely separated from each other by the separator and such that they sandwich the separator at the outer peripheral edge thereof over their entire width (i.e. from their outer peripheral edge to their inner peripheral edge). Alternatively, the separator extends through the first sealing layer and the second sealing layer only to a certain extent, such that the first and second sealing layers sandwich the separator at the outer peripheral edge thereof only over a part of their width (i.e. from their inner peripheral edge to the outer peripheral edge of the separator).

In an embodiment, at least one of the first sealing layer and the second sealing layer, preferably both sealing layers, has an outer peripheral edge that protrudes outward relative to a peripheral edge of the positive electrode and the negative electrode. By this configuration, the outer edges of the positive electrode and the negative electrode can be prevented from coming into contact, thereby providing additional protection against shortcircuiting. For example, according to this embodiment one or both of the first and second sealing layer may extend to the outside of the positive and/or negative electrode, in order to provide additional insulation when assembling two or more of the electrochemical cells into a battery pack or module.

In an embodiment, at least a portion of the positive and/or negative electrode may protrude laterally beyond the sealant arranged at the peripheral region of said electrodes. The protruding electrode portion may hence form an overhang, or extension, protruding from the sealant in a direction orthogonal to the stacking direction. One or both electrodes may protrude on one or several sides for the cell. In an example, the positive and the negative electrode may protrude from different sides of the cell, such as opposing sides, to allow the cell to be electrically accessed from different sides. The protruding electrode portion(s) may be formed of the entire edge of the electrode facing that particular side of the cell or be cut into one or several tab portions. The protruding electrode portion(s) may for example be used as a current collector acting as a terminal of the cell, or as a voltage pickup means for a battery management system (BMS) or the like. In an embodiment, the protruding portions of two or more cells arranged in a stack may be connected to each other to provide a parallel connection between the cells. The stack may hence comprise a combination of series and parallel connected cells.

As outlined above, by applying at least a two-layer sealant at the peripheral edge of each electrode, i.e., an adhesive layer and a sealing layer, a stable and durable sealing and joining of the positive electrode and the negative electrode is ensured. This arrangement is therefore particularly suitable for providing a single-layer, flat, large format electrochemical cell in which the upper and lower surfaces are electrically isolated and act as positive and negative terminals for the cell.

Therefore, according to a preferred embodiment of the electrochemical cell, the cell is a single-layer, large format electrochemical cell including a single positive electrode, a single negative electrode, which serve as a cell housing, a separator arranged between the single positive electrode and the single negative electrode, and a sealant disposed between the positive electrode and the negative electrode as describe above. According to a further preferred embodiment, the single positive electrode includes a first foil substrate, which may be formed of a first electrically-conducive material, and a first active material layer disposed on an inward facing side of the first foil substrate, and the single negative electrode includes a second foil substrate, which may be formed of a second electrically-conducive material, and a second active material layer disposed on an inward facing side of the second foil substrate, wherein the outward facing sides of the electrode substrates act as the negative and positive cell terminals, respectively.

Advantageously, due to the large surface area of such a cell a large capacity in a single electrode pair is ensured. Also, because of the large surface area heat is efficiently released from the cell and heat generation is prevented, thereby increasing safety and life time of the cell. Further, since the electrochemical cell according to this embodiment includes a single pair of electrodes of one positive electrode and one negative electrode, the structure and the production process becomes less complex, and material and production cost are reduced.

Further advantageously, such cells can be serially stacked with direct contact between the cell terminals, thereby eliminating the need for an outside can or cell housing, bus bars, or other terminal attachments. Additionally, since the direct contact occurs immediately adjacent to the active material sites, cell resistance is greatly reduced. In case two or more of the cells comprises electrodes with overhanging portions, i.e., terminal portions that protrude beyond the sealant and towards the lateral side of the cells, these portions may be utilised to provide parallel connections between cells in the stack.

According to a further aspect of the present disclosure, there is provided a battery module comprising a plurality of electrochemical cells, wherein each of the electrochemical cells has a stacked configuration and comprises: a positive electrode; a negative electrode; a separator arranged between the positive electrode and the negative electrode; and a sealant disposed between a peripheral region of the positive electrode and a peripheral region of the negative electrode; wherein: the plurality of electrochemical cells are provide in a stack; and the battery module further comprises a first polymer layer located on an outward facing side of the positive electrode of a first electrochemical cell in the stack; and a second polymer layer located on an outward facing side of the negative electrode of a last electrochemical cell in the stack.

The battery module may further comprise an intermediate polymer layer between each adjacent electrochemical cell in the stack.

Also disclosed herein is a battery module that comprises a plurality of electrochemical cells according to the present disclosure, i.e., at least two, preferably more than two, electrochemical cells according to the present disclosure. In a preferred embodiment, the battery module comprises a plurality of single-layer electrochemical cells according to the present disclosure, which are serially stacked with direct contact to each other, such that there is direct contact between cell terminals of adjacent cells.

In the context of the present disclosure, the terms “large format cell” and “large surface area” may be understood as referring to cells having a width and/or length (as seen in a direction orthogonal to the stacking direction) in the order of magnitude of meters (m), or at least tenths of metres. Hence, a large format cell may refer to a cell having a minimum length and width in the range of, for instance, 0.3 - 2 m, such as 0.3 x 0.3 m, 0.6 x 0.6 m, 0.6 x 0.72 m, 0.8 x 0.8 m, 0.5 x 1.2 m, 1.2 x 1.5 m, and 1.5 x 2 m.

There is also disclosed a method of manufacturing a plurality of electrochemical cells, the method comprising: arranging components of the electrochemical cells into respective stacks of components; sealing some, but not, all sides of each stack of components in order to leave an opening in one of the sides of each stack; injecting electrolyte into the opening of each stack; and sealing the openings in each stack.

The method may further comprise aligning the plurality of partially sealed stacks of components and holding them in a fixture, before injecting electrolyte into the opening of each stack.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is a side sectional view of an electrochemical cell according to an embodiment of the present disclosure;

Fig. 2 is a side sectional view of an electrochemical cell according to another embodiment of the present disclosure;

Fig. 3 is a side sectional view of a battery module according to an embodiment of the present disclosure; and Fig. 4 illustrates schematically a method of manufacturing an electrochemical cell according to an embodiment of the present disclosure;

Fig. 5 illustrates an example apparatus that can be used to inject electrolyte into a plurality of electrochemical cells as a single operation; and

Fig. 6 shows a plan view of an electrochemical cell according to another embodiment of the present disclosure.

DETAILED DESCRIPTION

The technical solutions of the embodiments of this application will be described in more detail below with reference to the accompanying drawings, which show merely exemplary embodiments of this application. The features of various embodiments can be combined to form further exemplary aspects of the present disclosure that may not be explicitly described or illustrated. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present invention without making creative efforts shall fall within the protection scope of the present disclosure.

Fig. 1 is a side sectional view of a single-layer electrochemical cell according to an embodiment of the present disclosure.

Fig. 1 schematically shows a single-layer electrochemical cell 10, which is for example a lithium ion cell, comprising a single positive electrode 11 and a single negative electrode 13 each having a layered structure; and a separator 15 disposed between the single positive electrode 11 and the single negative electrode 13. The positive electrode 11 , the negative electrode 13 and the separator 15 are arranged in a stacked configuration, that is, in a single positive electrode-separator-single negative electrode stack. A sealant is disposed between a peripheral region of the positive electrode 11 and a peripheral region of the negative electrode 13. In this example, the sealant is provided by first and second adhesive layers 16, 18 and first and second sealing layers 17, 19 such that the sealant joins a periphery of the positive electrode 11 to a periphery of the negative electrode 13. In another example, the sealant may not include an adhesive layer. In which case, for example, a dry lamination technique can be used for providing the sealant. In one implementation this can include performing electrospinning. The voids 20 indicated in Fig. 1 may be filled with a liquid electrolyte. The electrochemical cell 10 also includes a first polymer layer 21 and a second polymer layer 22. The first polymer layer 21 is located on an outward facing side of the positive electrode 11 (that is, a side facing away from the separator 15 in the cell stack). The second polymer layer 22 is located on an outward facing side of the negative electrode 13.

The single positive electrode 11 (that is, the cathode) includes a first foil substrate 12a, which may be formed of a first electrically conductive material, and a first active material layer 12b disposed on an inward facing side of the first foil substrate 12a (that is, a side facing the separator 15 and the negative electrode 13 in the cell stack). The first foil substrate 12a preferably is a metal foil substrate formed of a first electrically conductive material such as aluminum, without being limited thereto. The first active material layer 12b preferably comprises a first active material selected from a lithiated metal oxide, and in particular from a lithium transition metal composite oxide, wherein the metal preferably includes one or more of nickel (Ni), cobalt (Co) and manganese (Mn). According to a preferred example, the positive electrode 11 is formed of an aluminum foil and has an active material layer comprising a lithium transition metal composite oxide disposed on the inward facing side. In embodiments, the first electrically conductive material of the first foil substrate 12a may be coated on one or both sides thereof with an oxidation- preventing treatment, such as chromate treatment or treatment with chromium compounds. In further embodiments, a conductive material layer may additionally be disposed on an inward facing side of the first foil substrate 12a, such that the conductive material layer is sandwiched between the first foil substrate 12a and the first active material layer 12b, in order to enhance cell performance.

The single negative electrode 13 (that is, the anode) includes a second foil substrate 14a, which may be formed of a second electrically conductive material and a second active material layer 14b disposed on an inward facing side thereof (that is, a side facing the separator 15 and the positive electrode 11 in the cell stack). The second foil substrate 14a preferably is a metal foil substrate formed of a second electrically conductive material such as copper or copper-clad aluminum, without being limited thereto. The second active material layer 14b preferably comprises a second active material selected from graphite or silicon, or mixtures thereof. According to a preferred example, the negative electrode 13 is formed of a copper foil and has an active material layer comprising graphite disposed on the inward facing side. In embodiments, the second electrically conductive material of the second foil substrate 14a can be coated on one or both sides thereof with an oxidationpreventing treatment, such as chromate treatment or treatment with chromium compounds. The outward facing sides of first and second foil substrates 12a, 14a can act as the negative and positive cell terminals, respectively.

The first active material layer 12b and the second active material layer 14b preferably are not applied such that they cover the entire inward facing sides of the first foil substrate 12a and the second foil substrate 14a, respectively. As shown in Fig. 1 , the first active material layer 12b is applied only to a central region of the first foil substrate 12a, such that a region exists at the outer peripheral edge 12c of the first foil substrate 12a, which is free of the first active material (i.e., a region onto which the first active material layer 12b is not applied). Likewise, the second active material layer 14b is applied only to a central region of the second foil substrate 14a, such that a region exists at the outer peripheral edge 14c of the second foil substrate 14a, which is free of the second active material (i.e., a region onto which the second active material layer 14b is not applied). The anode electrode is typically larger than the cathode.

A first adhesive layer 16 is disposed at an outer peripheral region 12c of the first foil substrate 12a on an inward facing side thereof (i.e., a side facing the separator 15 and the second foil substrate 14a in the cell stack). A second adhesive layer 18 is disposed at the outer peripheral region 14c of the second foil substrate 14a on an inward facing side thereof (i.e., a side facing the separator 15 and the first foil substrate 12a in the cell stack). As will be discussed in more detail below, the outer peripheral regions 12c, 14c of the foil substrates 12a, 14a at which the adhesive layers 16, 18 are disposed can be: at the outer peripheral edge of the foil substrate 12a, 14a (as shown in Figure 1 for the right-hand edge of the first foil substrate 12a and for the left-hand edge of the second foil substrate 14a); or spaced apart from the outer peripheral edge of the foil substrate 12a, 14a (as shown in Figure 1 for the left-hand edge of the first foil substrate 12a and for the right-hand edge of the second foil substrate 14a. Spacing the adhesive layers 16, 18 from the outer peripheral edge of a foil substrate 12a, 14a provides an electrical connection for the associated electrode 11 , 13.

In this example, the first adhesive layer 16 and the second adhesive layer 18 attach directly to the first foil substrate 12a and the second foil substrate 14a, respectively. According to the embodiment of Fig. 1 , the first adhesive layer 16 is applied to the inward facing side of first foil substrate 12a only at a region within the outer peripheral region 12c of the first foil substrate 12a that is free of the first active material. Likewise, the second adhesive layer 18 is applied to the inward facing side of second foil substrate 14a only at a region within the outer peripheral region 14c of the second foil substrate 14a which is free of the second active material 14b.

Preferably, the first adhesive layer 16 and the second adhesive layer 18 are applied along the entire length of the outer peripheral region 12c of the first foil substrate 12a and the entire length of the outer peripheral region 14c of the second foil substrate 14a, respectively (i.e. , along all four sides assuming a rectangular shape of the electrode substrates). By this, the bonding strength between the first foil substrate 12a and the second foil substrate 14a is further increased.

Further preferably, the first adhesive layer 16 and the second adhesive layer 18 each has a thickness measured in the stacking direction Z of the cell of less than or equal to 40 pm, for example in the range of 0.5 pm to 40 pm, more preferably in the range of 15 pm and 40 pm. By this, the overall weight and thickness of the electrochemical cell and the battery module can be decreased, and material costs can be saved.

The first and second adhesive layers 16, 18 mainly function to provide sufficient adhesion of the sealant to the first and second foil substrates 12a, 14a. Accordingly, the first adhesive layer 16 and the second adhesive layer 18 may each comprise a material, which may be the same or different, with adhesive properties and binding force sufficient to attach directly to the electrode substrates, and which can ensure a strong and durable interfacial bond between the electrode substrates and the adhesive layers. More preferably, the first adhesive layer 16 and the second adhesive layer 18 comprise the same adhesive material to simplify production processes.

Preferred examples of suitable adhesive materials include, but are not limited to, polyolefins (for example, ethylene- or propylene-based polymers), functionalized polyolefins (for example, ethylene- or propylene copolymers with monomers containing one or more of carboxylate, epoxy, nitrile, imine, maleicanhydride and hydroxyl functional groups), polyvinyl alcohols, polyamides, polyacryl nitrile, epoxy resins, (meth)acrylates, and derivatives thereof.

Referring to Fig. 1 , a first sealing layer 17 is disposed on the first adhesive layer 16 such that the first adhesive layer 16 is sandwiched between the first sealing layer 17 and the first foil substrate 12a, and a second sealing layer 19 is disposed on the second adhesive layer 18 such that the second adhesive layer 18 is sandwiched between the second sealing layer 19 and the second foil substrate 14a. The first sealing layer 17 and the second sealing layer 19 attach directly to the first adhesive layer 18 and the second adhesive layer 19, respectively.

The first and second sealing layers 17, 19 mainly function to provide good sealing properties of the sealant. Accordingly, the first sealing layer 17 and the second sealing layer 19 may each comprise a material, which may be the same or different, and which exhibits insulation properties, stickiness, especially when heated, and chemical resistance, especially against degradation by the electrolyte. Preferably, the first sealing layer 17 and the second sealing layer 19 comprise the same sealing material to simplify production processes.

Further preferably, the first sealing layer 17 and the second sealing layer 19 each comprise as the sealing material one or more selected from polyolefins, in particular polyethylene, polypropylene and cast polypropylene (CPP), functionalized polyolefins, in particular polyolefin copolymers with monomers containing one or more of carboxylate, epoxy, nitrile, imine, maleicanhydride and hydroxyl functional groups, and epoxy resins, wherein CPP is particularly preferred, because CPP has excellent insulation properties and high chemical resistance, and because it becomes sticky when heated. Particularly preferably, the first sealing layer 17 and the second sealing layer 19 each comprise at least CPP as sealing material, and optionally one or more materials selected from polyolefins, in particular polyethylene or polypropylene, functionalized polyolefins, in particular polyolefin copolymers with monomers containing one or more of carboxylate, epoxy, nitrile, imine, maleicanhydride and hydroxyl functional groups, and epoxy resins. That is, in an exemplary embodiment, the first sealing layer 17 and the second sealing layer 19 each comprise, or consist of, a CPP layer. In another exemplary embodiment, the first sealing layer 17 and the second sealing layer 19 each comprise, or consist of, a CPP layer and one or more material layers selected from polyolefins, in particular polyethylene or polypropylene, functionalized polyolefins, in particular polyolefin copolymers with monomers containing one or more of carboxylate, epoxy, nitrile, imine, maleicanhydride and hydroxyl functional groups, and epoxy resins.

As shown in the embodiment of Fig. 1 , the first sealing layer 17 has the same width as the first adhesive layer 16, and the second sealing layer 19 has the same width as the second adhesive layer 18, each measured from an outer peripheral edge 17a, 19a to an inner peripheral edge 17b, 19b of the sealing layers and perpendicular to the stacking direction Z of the cell. This is however only exemplary, and the first and second sealing layers 17, 19 can independently from each other have a greater or smaller width than the first and second adhesive layers 16, 18.

As further shown in the embodiment of Fig. 1 , the thickness of the first sealing layer 17 is preferably greater than the thickness of the first adhesive layer 16, and the thickness of the second sealing layer 19 is preferably greater than the thickness of the second adhesive layer 18, each measured in measured in the stacking direction Z of the cell. By this configuration, it is possible to take advantage of the good sealing properties imparted by the sealing material, while at the same time sufficient adhesion to the electrodes is ensured.

Further preferably, the thickness of the first sealing layer 17 and the thickness of the second sealing layer 19, measured in the stacking direction Z of the cell, is each in the range of 20 pm to 200 pm, more preferably in the range of 30 pm to 150 pm, and even more preferably in the range of 40 pm to 80 pm, for example 40 pm, or 80 pm. Further preferably the first sealing layer and the second sealing layer have the same thickness. If the thickness of each of sealing layers 17, 19 is below this range, the sealing performance during cycling may not be ensured and electrolyte leakage may occur. If the thickness of each of sealing layers 17, 19 If is above this range, the cell becomes too thick so that the overall battery module dimension is affected.

According to another embodiment not shown in Fig. 1 , at least one of outer peripheral edges 17a, 19a of the first sealing layer 17 and the second sealing layer 19, preferably both outer peripheral edges, protrudes outward relative to outer peripheral edges 12c, 14c of the first and second foil substrate 12a, 14a, respectively. By this configuration, the outer edges of the first and second foil substrate 12a, 14a, which act as the negative and positive cell terminals, can be prevented from coming into contact, thereby providing additional insulation and protection against short-circuiting. For example, according to this embodiment one or both of the first and second sealing layer 17, 19 may extend to the outside of the first and second foil substrate 12a, 14a, respectively, in order to provide additional insulation when assembling two or more cells 10 into a battery pack or module. As a further example, one or both of the first and second sealing layers 17, 19 may extend to the outside of the first and second foil substrate 12a, 14a, respectively on some, but not all, of the edges of the first and second foil substrate 12a, 14a. For instance, a sealing layer 17, 19 may extend to the outside of an associated foil substrate 12a, 14a, on three of the four edges of a rectangular foil substrate 12a, 14a. The first foil substrate 12a and first active material layer 12b are spaced apart and isolated from the second foil substrate 14a and second active material layer 14b by the separator 15. The separator 15 is not specifically limited, and is made of an electrically isolating and permeable material that isolates the positive electrode 11 from the negative electrode to prevent electrical shortcircuiting and allows the passing through of ions provided in the electrolyte. For example, the separator 15 may have a 3-layer structure comprising for example a base film, which includes a polyolefin and a non-woven material, a ceramic layer coated on the base film, and a layer including polyvinylidenfluorid and acrylate binder coated on the ceramic layer.

As shown in the embodiment of Fig. 1 , the separator 15 entirely extends through the first sealing layer 17 and the second sealing layer 19, such that the first and second sealing layers 17, 19 are completely separated from each other by the separator 15. According to this configuration, the separator 15 is sandwiched at an outer peripheral edge 15a between the first and second sealing layers 17, 19 over their entire width (i.e. from their outer peripheral edge 17a, 19a to their inner peripheral edge 17b, 19b), whereby a seal exists between the first foil substrate 12a/first active material layer 12b of the positive electrode 11 and the separator 15, and between the second foil substrate 14a/second active material layer 14b of the negative electrode 13 and the separator 15. By this configuration, a hermetic seal about a periphery of the cell can be achieved to properly isolate the positive electrode 11 and the negative electrode 13.

The present disclosure is however not limited to this configuration. According to another embodiment not shown in Fig. 1 , the separator 15 does not entirely extend through the first sealing layer 17 and the second sealing layer 19, but only to a certain extent. According to this embodiment, the separator 15 is sandwiched at the outer peripheral edge 15a between the first and second sealing layers 17, 19 only over a part of their width (i.e. from their inner peripheral edge 17b, 19b to the outer peripheral edge 15a of the separator). This configuration likewise achieves a hermetic seal about a periphery of the cell proper to properly isolate the positive electrode 11 and the negative electrode 13.

According to still another embodiment not shown in Fig. 1 , at least one of the first sealing layer 17 and the second sealing layer 19 has an inner peripheral edge 17b, 19b that surrounds an outer peripheral edge 15a of the separator 15. This means, the inner peripheral edge 17b, 19b of at least one of the first sealing layer 17 and the second sealing layer 19, preferably of both sealing layers, surrounds and directly contacts the outer peripheral edge 15a of the separator 15, whereby the separator 15 is sealed relative to the positive electrode 11 and the negative electrode 13 in order to properly isolate the positive electrode 11 and the negative electrode 13. This configuration allows the cell to be thinner.

By applying the two-layer sealant including first adhesive 16 and first sealing layer 17 and second adhesive 18 and second sealing layer 19 at the peripheral regions of the first and second foil substrate 12a, 14a, respectively, as shown for example in Fig. 1 , a stable and durable sealing and joining of the positive and negative electrodes 11 , 13 is ensured, as the adhesive layers provide a strong bonding to the electrode substrates and the sealing layers provide good insulation properties and high chemical resistance. By this safety and lifetime of the cell are increased.

As indicated above, at least a portion 1 T of a peripheral region of the positive electrode 11 protrudes outwardly from the edge of the sealant (formed of the first adhesive layer 16 and the first sealing layer 17). Similarly, at least a portion 13’ of a peripheral region of the negative electrode 13 protrudes outwardly from the edge of the sealant (formed of the second adhesive layer 18 and the second sealing layer 19). The protruding electrode portions 1 T, 13’ hence form overhangs, or terminal extensions, protruding from the sealant in a direction orthogonal to the stacking direction. The protruding electrode portions 1 T, 13’ may also be referred to as connection portions because they each provide an electrical connection for the associated electrode 11 , 13. This can be especially useful in examples where the associated polymer layers 21 , 22 and not electrically conductive.

The protruding portions 1 T, 13’ in this example are formed of a portion of the electrode that is not covered with any active material layer 12b, 14b. In the present example, each of the positive and the negative electrodes 11 , 13 comprises a respective overhanging portion 1 T, 13’ arranged to protrude on opposite sides of the cell 10. However, it will be appreciated that the lateral extension of the electrodes 11 , 13 need not necessarily be defined by the position of the sealant at the peripheral edges, as indicated in Fig. 1.

The first polymer layer 21 is located on an outward facing side of the positive electrode 11 , more particularly on an outward facing side of the first foil substrate 12a for the example of Fig. 1. The second polymer layer 22 is located on an outward facing side of the negative electrode 13, more particularly on an outward facing side of the second foil substrate 14a for the example of Fig. 1. The first and second polymer layers 21 , 22 could be, for example polyamide (Nylon), PET or any other suitable polymer. As will be discussed in more detail below, use of the polymer layers 21 , 22 can assist with the manufacture of the electrochemical cell. This can include a reduction or avoidance of wrinkles in the positive and the negative electrodes 11 , 13, which in turn can negatively affect the performance of the cell. Furthermore, use of the first and second polymer layers 21 , 22 can enable thinner foil substrates 12a, 14a to be used such that, overall, the weight of the electrochemical cell 10 can be reduced.

The polymer layers 21 , 22 may be provided as a tape. That is, the polymer layers 21 , 22 may including an adhesive for attaching to the respective electrode 11 , 13. In some examples, an adhesive can be applied to an electrode 11 , 13 followed by a polymer film.

In another example, the foil substrate 12a, 14a can be deposited on to the polymer layer 21 , 22 during manufacture of the cell 10, rather than applying the polymer layer 21 , 22 to the foil substrate 12a, 14a. Such deposition methods are known in the art. Such an example can be particularly suitable for providing the sealant without any adhesive layers 16, 18. For instance, physical vapour deposition (PVD) can be used to provide the sealant.

The first polymer layer and the second polymer layer can each have a thickness in the range of 10 pm to 100 pm. In some applications, a thickness in one of the following ranges can function particularly well: 10 pm to 80 pm, 10 pm to 60 pm, 15 pm to 40 pm, and 15 pm to 25 pm.

The inclusion of the polymer layers 21 , 22 can enable the thickness of the associated foil substrates 12a, 14a (and therefore also the thickness of the electrodes 11 , 13) to be reduced when compared with a cell that does not have polymer layers. This is because the polymer layer 21 , 22 can compensate for any loss of structural integrity that may result from having a thinner foil substrate 12a, 14a. The thickness of a foil substrate in a cell that does not have polymer layers may be 15 pm to 20 pm. Whereas, for a cell 10 that does have polymer layers 21 , 22 (such as the one of Fig. 1), the thickness of the foil substrates 12a, 14a may be reduced to a value in the range of 0.1 pm to 40 pm, 1 pm to 20 pm, or 2 pm to 10 pm. For example, the thickness of the foil substrates 12a, 14a may be one of 10 pm, 5 pm, or 2 pm. This low thickness of the foil substrates 12a, 14a can assist with avoiding wrinkles in the foil as the cell 10 is manufactured. The presence of such wrinkles will represent an unevenness in the surface of the electrodes 11 , 13 in the electrochemical cell 10, which can degrade the performance of the electrochemical cell 10. For instance, an unevenness in the surface of an electrode can degrade the quality and predictability of the reaction in the electrochemical cell 10. Furthermore, an inconsistency in the surface of the electrodes between cells can also result in unpredictable performance of the electrochemical cell 10 and inconsistent performance for different cells 10.

These issues can be particularly problematic for electrochemical cells that have relatively large electrodes. Examples of such large cells may have a largest lateral dimension in the range of 0.3 m - 2 m. The cell may, for instance, be formed of electrodes having a rectangular or quadratic shape with sides measuring 0.3 x 0.3 m, 0.6 x 0.6 m, 0.6 x 0.72 m, 0.8 x 0.8 m, 0.5 x 1 .2 m, 1.2 x 1.5 m, or 1.5 x 2 m. It will however be appreciated that the electrodes (and thus the resulting cell) may have other shapes as well, conforming to e.g., circles, ovals, or T-shapes.

In some examples, the first and I or second polymer layers 21 , 22 can be electrically conductive. In this way the electrical connection between adjacent cells in a stack can be increased. Such electrical connection (through direct contact between the polymer layers 21 , 22 of adjacent cells 10 in a stack), can supplement the electrical connections that are available using the protruding electrode portions 11’, 13’ that are identified above and discussed in more detail below. Alternatively, electrical connection through direct contact between the electrically conductive polymer layers 21 , 22 of adjacent cells 10 may be provided as an alternative to the use of protruding electrode portions 11’, 13’. That is, an outer peripheral edge of the foil substrates 12a, 14a may be aligned with the outer peripheral edges 17a, 19a of the sealing layers around substantially all of the perimeter of the foil substrates 12a, 14a.

Furthermore, use of electrically conductive polymer layers 21 , 22 enables the upper and lower surfaces of the cell 10 to act as positive and negative terminals for the cell. Such cells can therefore be serially stacked with direct contact between the cell terminals, thereby eliminating the need for an outside can or cell housing, bus bars, or other terminal attachments. Advantageously, since the direct contact occurs immediately adjacent to the active material sites, cell resistance is greatly reduced.

Further, since the electrochemical cell according to the embodiment shown in Fig. 1 includes a single pair of electrodes of one positive electrode and one negative electrode, the structure and the production process becomes less complex, and material and production cost are reduced. Advantageously, due to the large surface area of the cell a large capacity in the single electrode pair is ensured. Additionally, because of the large surface area of the cell heat is efficiently released from the cell and heat generation is prevented, thereby increasing safety and life time of the cell.

If electrically non-conductive polymer layers 21 , 22 are used, then the electrical connection to the electrodes are provided by the protruding electrode portions 11’, 13’ that protrude from one or more sides of the cell 10, as identified above. In this way, the positive electrode 11 and the negative electrode 13 each comprise a connection portion 11’, 13’ that protrudes laterally beyond the associated sealant 17, 19 in order to provide an accessible electrical connection for the respective electrode 11 , 13. In this example, the outer peripheral edges of the connection portions 11’, 13’ align with outer peripheral edges of the associated polymer layer 21 , 22. Although it will be appreciated from Fig. 2 that in another example the outer peripheral edges of the connection portions 11’, 13’ can protrude laterally beyond the outer peripheral edges of the associated polymer layer 21 , 22. Either way, each of the connection portions 1 T, 13’ are unitary with the associated foil substrate 12a, 14a.

Fig. 6 shows a plan view of an electrochemical cell according to another embodiment of the present disclosure. In this example, the first and second polymer layers only partially cover the outer surfaces of their associated electrodes. The first polymer layer 121 and the first foil substrate 112a of the first electrode are visible in Fig. 6. The second layer and the second foil substrate are not visible in Fig. 6 because they are on the underside of the cell as it is shown in Fig. 6. A protruding electrode portion 113’ (that is similar to the one that is shown in Fig. 1) is also visible in Fig. 6.

In this example, the first polymer layer 121 and the second polymer layer are electrical insulators, such that an electrical current cannot pass through them when the cell is arranged in a stack.

By using a first polymer layer 121 that is located on only part of the first electrode, a window is provided through or past the first polymer layer 121. It will be appreciated that the same is true for the second polymer layer and the second electrode. In this way, the electrodes of adjacent cells can directly, galvanically, contact each other through the windows in the polymer layers. As indicated above, providing direct contact between the electrodes can eliminate the need for an outside can or cell housing, bus bars, or other terminal attachments and it can also advantageously reduce the cell resistance. Nonetheless, the presence of the polymer layers over part of their associated electrodes can still provide sufficient strength in order to maintain the structural integrity of the cell. The polymer layer can also provide the functionality of a protective layer in the regions where it is present.

In this example, the first polymer layer 121 and the second polymer layer contact the outer surfaces of their associated electrodes only at peripheral regions of the electrodes. As a result of this arrangement, a central region of the outer surface of each electrode is exposed at the regions of the cell where the polymer layers are absent. However, it will be appreciated that the polymer layers can partially cover any region of its associated electrode as long as at least part of the exposed region of electrode will coincide with the exposed region of the neighbouring electrode when the cells are arranged in a stack. In this way, the exposed part of the negative electrode of a given cell is configured to be aligned with the positive electrode of a neighbouring electrochemical cell when the electrochemical cells are provided in a stack; and the exposed part of the positive electrode of the given cell is configured to be aligned with the negative electrode of a neighbouring electrochemical cell when the electrochemical cells are provided in the stack.

In another example, not shown in the figures, the cell can include one or more connection portions that that are distinct from, and electrically connected to, each of the positive and negative electrodes. Such connection portions also protrude from one or more sides of the cell 10 such that they provide an accessible electrical connection for the respective electrode 11 , 13. For instance, such a connection portion may be provided as a piece of nickel (or other suitable electrically conductive material) that is laminated in to the cell during manufacture.

Due to the large form factor of the cell 10, it can be advantageous to include one or more connection portions 1 T, 13’ for providing an electrical connection to the respective electrodes 11 , 13. For example, a connection portion 1 T, 13’ may protrude laterally from two adjoining edges of the cell 10. In some examples, such a connection portion may protrude laterally from two adjoining edges of the sealant 17 and the corresponding polymer layer 21 , 22. In an example where the cell 10 has a generally rectangular shape (not withstanding any connection portions 1 T, 13’), such adjoining edges define a corner of the cell 10. In which case, a connection portion can be considered as having an ‘L’ shape that extends around a corner of the cell 10. Such an ‘L’ shaped connection portion can protrude laterally from part, but not all of, each of the two adjoining edges of the cell 10. In some examples, one or both of the positive electrode 11 and the negative electrode 13 have a plurality of distinct connection portions. That is, a single electrode 11 , 13 can have a plurality of connection portions that are spaced apart from each other around the periphery of the electrode 11 , 13. This can be useful for improving the electrical connection to the cell

10, and in some applications can be considered as improving the versatility of the cell 10 because it can conveniently be connected to in one of a number of different positions around the cell. One or more of the connection portions that are disclosed in this document can be provided at a central region of a peripheral edge of an electrode 11 , 13, such that the connection portion extends from a part of, but not all of, the peripheral edge.

It will be appreciated from the above discussion that one or more connection portions (which may also be referred to as tabs) may be provided in a number of different ways in order to improve the electrical connection to the cell. For instance, they may be provided along the entire length of a cell, they maybe arranged along two sides (thereby forming an L-shape), and they may or may not be notched. Such tabs could also be used with an electrically conductive polymer layer 21 , 22 to further increase the level of conduction that can be achieved when connecting cells together in a stack.

Fig. 2 is a side sectional view of a cell 10 according to an embodiment of the present disclosure, which is similar to the cell that is discussed above with reference to Fig. 1. The cell 10 may hence comprise a positive electrode 11 and a negative electrode 13, wherein each may have a layered structure (not shown), as well as a separator 15 disposed therebetween. A sealant 25, 26 may be arranged at the peripheral regions of the positive electrode 11 and the negative electrode 13, forming a stacked structure with the respective electrodes 11 , 13. The sealant may be formed of a single layer as shown in Fig. 2, or it may be provided as a stack of adhesive and sealing layers as in Fig. 1.

As indicated above, in this example the outer peripheral edges of the connection portions 1 T, 13’ protrude laterally beyond the outer peripheral edges of the associated polymer layer 21 , 22. When viewed from above, at least a portion of the peripheral edge of an electrode 11 , 13 (more particularly, a peripheral edge of a connection portion 11’, 13’ of the electrode

11 , 13) is located outside the footprint of the associated polymer layer 21 , 22. Such an example can further improve the quality of the electrical connection to the electrodes 11 , 13 that is achievable. Such an electrical connection may to an external device, or may be to another cell in a stack of cells that can be provided as part of a battery module. An example of such a battery module is discussed in more detail below. Fig. 3 shows is side sectional view of a battery module 30 according to an embodiment of the present disclosure.

The battery module 30 includes a plurality of electrochemical cells, which are each similar to the electrochemical cell 10 that is illustrated in Fig. 2. Only two electrochemical cells 10a, 10b are shown in Fig. 3 as a stack to assist with the ease of illustration. However, it will be appreciated that the battery module 30 may include more than two electrochemical cells stacked together.

In the same way as described above, each electrochemical cell 10a, 10b has a stacked configuration that comprises: a positive electrode 11a, 11 b; a negative electrode 13a, 13b; a separator 15a, 15b; and a sealant.

The plurality of electrochemical cells 10a, 10b are provided in a stack such that the outward facing side of one electrochemical cell is positioned adjacent to the outward facing side of a neighbouring electrochemical cell. In this example, each individual electrochemical cell includes a first polymer layer 21 a, 21b and a second polymer layer 22a, 22b. Therefore, the plurality of electrochemical cells 10a, 10b are provided in a stack such that the outward facing side of a polymer layer of one electrochemical cell is positioned adjacent to the outward facing side of a polymer layer of a neighbouring electrochemical cell. In the example, of Fig. 3, the outward facing side of a second polymer layer 22a of one electrochemical cell 10a is positioned adjacent to the outward facing side of a first polymer layer 21b of a neighbouring electrochemical cell 10b such that the negative electrode 13a of the first electrochemical cell 10a is closest to the positive electrode 11b of the second electrochemical cell 10b. Indeed, if electrically conductive polymer layers are used, then these two electrodes will be in direct electrical contact with each other. This can be useful if the cells in the stack are to be connected in series with each other.

More generally, the battery module 30 of Fig. 3 can be considered as having a first polymer layer 21a located on an outward facing side of the positive electrode 11a of a first electrochemical cell 10a in the stack; and a second polymer layer 22b located on an outward facing side of the negative electrode 13b of a last electrochemical cell 10b in the stack. The battery module 30 also includes an intermediate polymer layer 22a, 21b between each adjacent electrochemical cell 10a, 10b in the stack. In Fig. 3, the intermediate polymer layer 22a, 21 b comprises a first polymer layer of one of the cells back-to-back with a second polymer layer of the other cell such that it has twice the thickness of the polymer layers 22a, 22b on the outer faces of the stack. However, it will be appreciated that in other examples, the intermediate polymer layer can have any suitable thickness or properties, which may or may not be the same as the outermost polymer layers in the stack. Indeed, in some examples, the stack may not have any intermediate polymer layers at all such that all of the cells in the stack are in direct contact with each other such that they are serially connected together.

In examples where the cells in the stack are electrically isolated from each other by non- electrically conductive polymer layers, then electrical connection to the electrode of each cell can be provided by connection portions 11a’, 13a’, 11b’, 13b’. In the following description, these connection portions will be referred to as tabs.

The tabs can advantageously improve the quality of the electrical contact that can be made to an electrode. In some applications, the direct metal to metal electrode contact between the faces of adjacent cells, which may rely on contact pressure between the surfaces, may not provide a sufficiently reliable connection. For relatively thick foil substrates, the tabs may be self-supporting such that they can be welded or otherwise electrically connected (in series or parallel) without difficulty. As another example, especially for relatively thick foil substrates, tabs may be bolted together. For instance, holes can be provided through the tabs in a plurality of cells such that when the cells are arranged in the stack the holes are aligned and a bolt can be located through the holes in order to electrically connect the tabs together. If a relatively thin foil is used, then the tabs can be structurally more reliable if they are provided with some mechanical support. For instance, the polymer layer can extend over at least a portion, if not all, of the foil substrate as shown in Fig. 1.

In some applications, welding can be made more complicated if the polymer layer extends all the way over the tabs, especially if the polymer layer is an electrical insulator. In which case, it can be beneficial to extend the sealant peripherally outwards such that it overlaps with at least some, or all, of the tab. This can provide sufficient structural support such that riveting can be used to provide an electrical connection to the cell. Known clamping or stamping techniques can also be used to provide electrical connections between the tabs in such examples because the sealant is on the inward facing surface (i.e. towards the separator 15) of each electrode tab such that the outward facing surfaces (i.e. away from the separator 15) of the electrode tabs on adjacent cells can be brought into direct contact with each other. It will be appreciated that a series or parallel connection between the cells in the stack (or a combination of series and parallel connections between the cells) can be accomplished by appropriate connection to the tabs of the cells.

In some applications, temporary structural support can be provided to the tabs by a removable support structure. Such a removable support structure may be provided as a removable tape (such as an insulation tape) that is initially included on the tabs during manufacture and then removed before an electrical connection is made to the tab.

In some examples, an outer surface of the first and I or second polymer layers of any of the cells disclosed herein can be patterned such that it has at least one discontinuity in the outer surface. Such patterns therefore can include one or more indentations into (e.g. scratches) and I or one or more protrusions from the plane of the outer surface of the polymer layer. As will be discussed below, such patterns can improve the ability to cool a cell and I or can provide for mechanical engagement with a neighbouring cell in a stack.

Such a polymer layer can include one or more channels that extend from a surface of the polymer layer through the thickness of the polymer layer. Such channels can assist with dissipating heat that is generated by the cell by providing an airflow path through the cell. Beneficially, such channels may take a path that starts and I or ends at a peripheral edge of the polymer layer. In this way, heat that is generated at one location in the cell can be transferred by airflow through the channel to another part of the cell, preferably to an end of the channel that is located outside the footprint of the electrode. It will be appreciated that the cross-sectional shape of a channel can take any suitable form, such as a rectangle, a square or a circle.

A channel can extend through the entire thickness of the polymer layer or it can extend partially through the thickness of the polymer layer. If a channel extends only partially through the thickness of the polymer layer, then it can extend from either an inward facing surface of the polymer layer or an outward facing surface of the polymer layer. If a channel extends from an inward facing surface, then the channel will be adjacent to an associated electrode, and therefore may be better located to remove any heat that is generated by the cell.

Additionally or alternatively, a pattern can be implemented that provides mechanical engagement with a polymer layer of an adjacent cell in a stack. This can provide additional 1 fixation strength between adjacent cells. In one example such a pattern can be implemented as an interlocking sawtooth structure such that the teeth of one polymer layer engage with the teeth of a neighbouring cell in the stack and relative movement of the cells (in the plane of the cells) is inhibited. In this way, the one or more indentations I protrusions in a polymer layer are for interlocking with corresponding protrusions I indentations of a polymer layer of an adjacent cell in a stack.

The manufacture of the electrochemical cells that are disclosed herein can include a step of electrolyte filling. That is, filling the voids 20 that are shown in Fig. 1 with electrolyte such that pores inside the electrodes 11 , 13 and the separator 15 are filled with the electrolyte.

Fig. 4 illustrates schematically a method of manufacturing an electrochemical cell according to an embodiment of the present disclosure. The electrochemical cell can be any cell disclosed herein.

At step 40, the method includes arranging components of the electrochemical cell in a stack of components. As will be appreciated from the description of electrochemical cells in this document, these components can include a positive electrode, a negative electrode and a separator (that is positioned between the positive electrode and the negative electrode). Optionally, the components can also include a first polymer layer located on an outward facing side of the positive electrode and a second polymer layer located on an outward facing side of the negative electrode. Depending upon the specific construction of the electrochemical cell, the sealant can be considered as a component that is arranged in the stack of components at step 40. Alternatively, the sealant can be provided at steps 41 and 43, as discussed below.

At step 41 , the method involves sealing some, but not all, of the sides of the stack of components in order to leave an opening in one of the sides. In one example according to the present disclosure, this step can include initially sealing three sides of the cell (for example using the first and second adhesive layers 16, 18 and the first and second sealing layers 17, 19) to join three of the four sides of the periphery of rectangular positive and negative electrodes 11 , 13) . In this way, the entire fourth side provides the opening. In an alternative implementation, the fourth side can be partially sealed such that the opening is provided in some, but not all, of the fourth side. Then, at step 42, the method involves injecting electrolyte into the opening. This step can be performed in a vacuum condition, if appropriate. In this way, the electrolyte is provided into the void I cavity within the electrochemical cell such that electrolyte is also provided into pores inside the electrodes and the separator.

Once the electrolyte has been injected, the manufacturing process can continue at step 43 by closing I sealing the opening. As discussed above, sealing the opening may involve closing the fourth side or closing the unsealed portion of the fourth side if it was partially sealed at step 41 .

Beneficially, such a process can be used to inject electrolyte into a plurality of cells as part of a single operation. That is, step 42 may include the steps of: aligning a plurality of partially sealed electrochemical cells, each of which has an opening (in some examples by holding the plurality of electrochemical cells in a fixture); and then injecting the electrolyte into the openings of the plurality of electrochemical cells as a single operation.

Fig. 5 illustrates an example apparatus that can be used to inject electrolyte into a plurality of electrochemical cells 52 as a single operation. Fig. 5 shows a plurality of partially sealed electrochemical cells 52, each of which has an opening 53. As discussed above, the openings 53 are provided by an earlier processing step of sealing some, but not all, of the sides of the stack of electrochemical cell components. The plurality of electrochemical cells are held by a single fixture 54. Then electrolyte can be added through the opening 53 in each of the cells 53 at the same time through a number of nozzles 51. In this example, a plurality of nozzles 51 are mounted on a nozzle mounted plate 50 that can be positioned over the plurality of electrochemical cells 52 such that the nozzles 51 align with the openings 53 in the electrochemical cells 52. In this way, many cells can be filled at the same time therefore improving the efficiency of the manufacturing process.

In prismatic cells, the electrode thickness must be kept low, due to the fact that there can be about 100 layers in a jelly roll and therefore any increase in the thickness of an individual cell multiplies out to a significant increase in the thickness of the cell. Therefore, any increase in thickness of a cell is a substantial consideration for prismatic cells, which furthermore can limit volumetric energy density. In comparison, the cells disclosed in this document can have a large thin format, which means that an increase in the thickness of an individual electrochemical cell has a reduced impact because each cell is only a single layer. Therefore, for electrochemical cells disclosed herein, the calendaring ratio (compression before and after) may be decreased, which results in a low density of active material. In turn, this leads to improved electrode soaking and a more uniform electrochemical reaction. Yet further, the reduced density of the cell can result in the materials being less stressed and therefore a longer lifecycle of the cell.

Due to the lower density of the electrode, a lower vacuum pressure can be used when filling the cell with electrolyte. This represents a yet further improvement in the manufacturing process.

A still further advantage of the lower density electrodes can be a reduction in the amount of swelling that is experienced by the electrode material during use, and therefore a less massive mechanical frame structure can be required for an associated battery pack.

Examples disclosed herein relate to an electrochemical cell that can have a relatively large surface area. For example, 3m² which is about 80 times larger than a standard pouch size. Also, heat release efficiency can be improved, which can improve the safety of the electrochemical cell and I or can result in longer cell life.

In relation to safety, a relatively simple electrochemical cell can be provided, which can benefit from a relatively simple I efficient manufacturing process, which can also be relatively low cost.

Furthermore, there is no limitation on the chemistry that can be used by the cell.

Suitable anode materials include carbon based materials such as graphite, as well as silicon-based anodes.

Therefore, typical electroactive materials used in the cathode may include lithium ion cathodes such as lithium iron phosphate, nickel-cobalt-manganese (NMC) composite oxides and lithium NMC (Li-NMC) composite oxides such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMn2O4), lithium nickel cobalt oxide (LiNixCo1-xO2 (0<x<1) or LiNi1-x-yCoxAlyO2 ((0<x<0.2, 0<y<0.1)) as well as lithium nickel cobalt manganese (NCM) oxide (LiNi1-x-yCoxMnyO2 (0<x+y<1)).

Additionally, as energy density is not so critical, sodium ion cathodes may also be used such as P2-type, P3 type, 03 type and polyanion materials including sodium iron manganese oxides, sodium vanadium phosphates, Prussian blue analogues (such as sodium manganese iron cyanate).

Particularly suitable lower energy density materials that may be used include:: i. LFP: 140-150 mAh/g (low voltage) ii. NMC811: 190 mAh/g iii. Na-ion 140 mAh/g (low voltage)

Therefore, an increased thickness (e.g. 50% for Na, 30% for LFP) that is required for comparable levels of loading is considered acceptable.

To summarise, one or more of the examples disclosed herein can provide one or more of the following advantages:

• Lighter weight per cell. This can be achieved because the thickness of the foil substrate can be reduced, such that it is replaced by a polymer layer. For example, the thickness of the foil substrate can be reduced from 40 pm to (for example) 15 pm, and the reduced thickness foil substrate can be used with a polymer layer that is, for example, 10 pm thick. Overall, this results in a lighter cell.

• An improvement in safety. There can be a reduced risk of damaging the cell during manufacture, particularly when manually handling components of the cell during manufacture. In one specific example, this can result from a reduced likelihood of the foil substrate being wrinkled or suffering from other surface defects during manufacture.

• Reduced risk of corrosion of the foil substrate because it is coated I covered by a polymer layer.

• Improved electrical connection to the cell, at least in part due to the provision of laterally extending connection regions that in some examples are unitary with the corresponding electrode. Although the invention has been described above with regard to its preferred embodiments, which represent the best mode for carrying out the invention, it is understood that various changes as would be obvious to one of ordinary skill in this art can be made without departing from the scope of the disclosure, which is set forth in the appended claims.

Claims

Claims An electrochemical cell having a stacked configuration, comprising a positive electrode; a negative electrode; a separator arranged between the positive electrode and the negative electrode; a sealant disposed between a peripheral region of the positive electrode and a peripheral region of the negative electrode; a first polymer layer located on an outward facing side of the positive electrode; and a second polymer layer located on an outward facing side of the negative electrode. The electrochemical cell of claim 1 , wherein the positive electrode and the negative electrode each comprise a connection portion that protrudes laterally from a side of the electrochemical cell to provide an electrical connection for the respective electrode. The electrochemical cell of claim 2, wherein the connection portions of each electrode protrude beyond the associated polymer layer. The electrochemical cell of claim 1 , further comprising a connection portion that is distinct from, and electrically connected to, each of the positive and negative electrodes, wherein the connection portion protrudes laterally from a side of the electrochemical cell. The electrochemical cell of any one of claims 2 to 4, wherein the connection portions protrude laterally from two adjoining edges of the electrochemical cell. The electrochemical cell of claim 5, wherein the connection portions protrudes laterally from part, but not all of, each of the two adjoining edges of the electrochemical cell. The electrochemical cell of any one of claims 2 to 6, wherein each of the positive electrode and the negative electrode comprise a plurality of distinct connection portions. The electrochemical cell of any preceding claim, wherein the first polymer layer and the second polymer layer each have a thickness in the range of 10 pm to 80 pm. The electrochemical cell of any preceding claim, wherein: the positive electrode comprises a first foil substrate and a first active material; the negative electrode comprises a second foil substrate and a second active material; and the first foil substrate and the second foil substrate each have a thickness in the range of 0.1 pm to 40 pm. The electrochemical cell of any preceding claim, wherein the first and I or second polymer layers are electrically conductive. The electrochemical cell of any one of claims 1 to 9, wherein: the first and the second polymer layers are electrical insulators; the first polymer layer is located on only part of the positive electrode in order to expose a part of the positive electrode; the second polymer layer is located on only part of the negative electrode in order to expose a part of the negative electrode; the exposed part of the negative electrode is configured to be aligned with an exposed part of a positive electrode of a neighbouring electrochemical cell when the electrochemical cells are provided in a stack; and the exposed part of the positive electrode is configured to be aligned with an exposed part of a negative electrode of a neighbouring electrochemical cell when the electrochemical cells are provided in the stack. The electrochemical cell of any preceding claim, wherein the first and / or second polymer layer comprise one or more channels through the thickness of the polymer layer. The electrochemical cell of claim 12, wherein the one or more channels extend through the entire thickness of the polymer layer. The electrochemical cell of claim 12, wherein the one or more channels extend partially through the thickness of the polymer layer. The electrochemical cell of any one of claims 12 to 14, wherein the one or more channels take a path that starts and / or ends at a peripheral edge of the polymer layer. The electrochemical cell of any preceding claim, wherein the first and / or second polymer layer comprise one or more indentations / protrusions in an outward facing side of the polymer layer to provide mechanical engagement with a polymer layer of an adjacent cell in a stack. The electrochemical cell of claim 16, wherein the one or more indentations / protrusions are for interlocking with corresponding protrusions / indentations of the polymer layer of the adjacent cell in the stack. A battery module comprising a plurality of electrochemical cells, wherein each of the electrochemical cells has a stacked configuration and comprises: a positive electrode; a negative electrode; a separator arranged between the positive electrode and the negative electrode; and a sealant disposed between a peripheral region of the positive electrode and a peripheral region of the negative electrode; wherein:

RECTIFIED SHEET (RULE 91) ISA/EP the plurality of electrochemical cells are provide in a stack; and the battery module further comprises a first polymer layer located on an outward facing side of the positive electrode of a first electrochemical cell in the stack; and a second polymer layer located on an outward facing side of the negative electrode of a last electrochemical cell in the stack. The battery module of claim 18, further comprising an intermediate polymer layer between each adjacent electrochemical cell in the stack.

RECTIFIED SHEET (RULE 91) ISA/EP