Battery cell separator

Abstract

A separator for a secondary battery cell comprises a primary layer comprising a porous secondary battery separator material, a thermal stability coating applied to the primary layer on a surface of the primary layer that will face an anode within the secondary battery cell, at least one of a first edge and a second edge of the primary layer comprising an uncoated region in which the thermal stability coating is not applied, and a metallic coating applied to the primary layer within the uncoated region.

Description

INTRODUCTION

[0001] The present invention relates generally to a separator for an electrochemical energy storage device, such as a Li-ion battery cell, and more particularly to a separator having a thermal stability coating in combination with a metallic coating.

[0002] The current generation of Li-ion batteries uses separators made of porous polyolefin, which are susceptible to thermal shrinkage at high temperatures and can cause an electrical short circuit between the positive and negative electrodes or the corresponding current collectors. A ceramic coating on the separator prevents direct contact and ensures thermal stability. However, separators that combine porous polyolefin and ceramic materials cannot be tested using non-destructive techniques.

[0003] While current separators serve their purpose, there is a need for a new and improved battery cell separator that includes a metallic coating in conjunction with the ceramic coating to provide thermal stability while allowing the separator to be inspected using non-destructive techniques, such as X-rays.

[0004] Known separators for battery cells and battery cells as such are described, for example, in CN 1 14 204 206 A, US 2009 / 0081 535 A1 and US 2021 / 0 367 308 A1. SUMMARY

[0005] According to several aspects of the present disclosure, a separator for a secondary battery cell comprises a primary layer comprising a porous secondary battery separator material, a thermal stability coating applied to the primary layer on a surface of the primary layer that will face an anode within the secondary battery cell, at least one of a first edge and a second edge of the primary layer comprising an uncoated region in which the thermal stability coating is not applied, and a metallic coating applied to the primary layer on the anode-facing surface of the primary layer within the uncoated region. The separator further comprises a gap between the thermal stability coating and the metallic coating.

[0006] In another aspect, the porous accumulator separator material is a porous polyolefin comprising polyethylene (PE), polypropylene (PP), or a PE / PP hybrid.

[0007] In another aspect, the thermal stability coating is a ceramic material, a metal oxide / metal hydroxide, or a pore-controllable polyamine (PAI) layer.

[0008] According to another aspect, the metallic coating is a polymeric binder having metal particles suspended therein, a metal layer applied to the primary layer by electrodeless plating, or a metal layer applied to the primary layer by vapor deposition.

[0009] In another aspect, the metallic coating comprises aluminum, stainless steel, iron, or iron oxide.

[0010] In another aspect, the separator further comprises an electrically insulating coating applied over the uncoated portion of the primary layer and the metallic coating.

[0011] In another aspect, the primary layer is approximately ten micrometers thick, the thermal stability coating is approximately three micrometers thick, the width of the metallic coating is at least ten micrometers, and the width of the gap between the thermal stability layer and the metallic coating is at least one micrometer.

[0012] According to several aspects of the present disclosure, a secondary battery cell comprises an anode layer, a cathode layer, and a separator disposed between the anode layer and the cathode layer, the separator comprising a primary layer comprising a porous secondary battery separator material, a thermal stability coating applied to the primary layer on a surface of the primary layer facing the anode, at least one of a first edge and a second edge of the primary layer comprising an uncoated region in which the thermal stability coating is not applied, and a metallic coating applied to the primary layer on the anode-facing surface of the primary layer within the uncoated region. The separator further comprises a gap between the thermal stability coating and the metallic coating.

[0013] Not according to the invention, a vehicle comprises at least one accumulator cell suitable for storing electrical energy for the vehicle, wherein the accumulator cell has an anode layer, a cathode layer and a separator arranged between the anode layer and the cathode layer, wherein the separator comprises a primary layer comprising a porous polyolefin comprising polyethylene (PE), polypropylene (PP) or a PE / PP hybrid, a heat stability coating comprising a ceramic material, a metal oxide / metal hydroxide or a layer of a pore-controllable polyamine (PAI) applied to the primary layer on a surface of the primary layer facing the anode, wherein at least one of a first edge and a second edge of the primary layer comprises an uncoated region in which the heat stability coating is not applied, and a metallic coating,which is applied to the primary layer on the anode-facing surface of the primary layer within the uncoated area.,

[0014] Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are for purposes of illustration only and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The drawings described herein are for illustrative purposes only and are not intended to limit the scope of the present disclosure in any way. Fig. 1 shows a vehicle having a battery system with at least one battery cell according to an exemplary embodiment of the present disclosure in a schematic view. Fig. 2 shows a battery cell having a separator according to an exemplary embodiment in a cut-off schematic view. Fig. 3 shows a cathode layer, a separator and an anode layer of the accumulator cell, which in Fig. 2 is shown in a sectional view along line 3-3 of Fig. 2. Fig. 4 shows an enlarged part of the Fig. 3 shown separator, which is represented by the circled part of Fig. 3, which begins with “ Fig. 4”. Fig. Figure 5 shows an enlarged view similar to that of Fig. 4, wherein the separator comprises an electrically insulated coating over the uncoated portion of the primary layer.

[0016] The figures are not necessarily to scale, and some features may be larger or smaller, for example, to show details of specific components. In some cases, well-known components, systems, materials, or methods are not described in detail to avoid obscuring the present disclosure. Therefore, the specific structural and functional details disclosed herein are not to be considered limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present disclosure. DETAILED DESCRIPTION

[0017] The following description is merely exemplary and is not intended to limit the disclosure, application, or uses. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, summary, or the following detailed description. It should be understood that throughout the drawings, corresponding reference characters designate like or corresponding parts and features.As used herein, the term module refers to any hardware, software, firmware, electronic control component, processing logic, and / or processor device, individually or in any combination, including, but not limited to: an application-specific integrated circuit (ASIC), an electronic circuit, a processor (common, dedicated, or group), and memory that executes one or more software or firmware programs, combinational logic circuitry, and / or other suitable components that provide the described functionality. Although the figures shown herein represent an example with particular arrangements of elements, in actual embodiments, additional intermediate elements, devices, features, or components may be present. It is also understood that the figures are for illustrative purposes only and may not be drawn to scale.

[0018] As used herein, the term "vehicle" is not limited to motor vehicles. While the present technology is primarily described herein in the context of motor vehicles, it is not limited to motor vehicles. The concepts may be used in a variety of applications, including aircraft, watercraft, other vehicles, and non-vehicle consumer electronics components.

[0019] Lithium-ion batteries and battery cells generally have one of three conventional shapes: cylindrical, prismatic, or pouch. Each of these battery types offers a number of advantages and disadvantages. The battery type determines many production factors; for example, each battery shape can have a different temperature distribution and heat transfer model.

[0020] A cylindrical cell consists of plate-shaped anodes, separators, and cathodes rolled and packaged in a cylindrical can. This type is one of the first mass-produced batteries. Cylindrical cells are well suited to automated production and offer good mechanical stability. The round shape of the battery distributes the internal pressure caused by side reactions almost evenly across the cell circumference, allowing the cell to withstand higher internal pressures without deformation. However, when cylindrical cells are combined into packs and modules, the circular cross-section of the cell does not allow for full utilization of the available space, resulting in low packing density for cylindrical cells.However, thermal management of a pack of cylindrical cells can be easier because the cavities allow easy circulation of coolant around the cells within a battery pack.

[0021] Prismatic cells consist of large sheets of anodes, cathodes, and separators that are rolled and pressed into a cubic metal or hard plastic casing. The electrodes can also be assembled by stacking layers on top of each other instead of in a jelly-roll arrangement. Portions of the electrode and separator plates of a prismatic cell located near the container corners may be subject to greater stress. This can damage electrode coatings and lead to uneven electrolyte distribution. When prismatic cells are combined into packs, the box-like shape of the cells allows for optimal use of the available space. However, this efficient use of space comes at the cost of less efficient thermal management, as there are no voids between the cells, as is the case with a pack of cylindrical cells.

[0022] Pouch cells do not have a rigid enclosure and instead use a sealed, flexible film as a cell container. This packaging reduces weight and results in flexible cells that easily fit into the available space of a given product. However, pouch cells can expand with gas during charging and discharging. The electrode and separator layers of a pouch cell are stacked and do not have a jelly-roll arrangement. For pouch cells, a cell expansion of 8% to 10% must be considered during battery and product development. Furthermore, pouch cells require a support structure due to the soft construction of the cell, and the cell should not be placed near sharp edges.

[0023] According to an exemplary embodiment of the present disclosure, Fig. 1 shows a vehicle 10 with an associated accumulator system 11 for storing electrical energy and supplying the vehicle 10 with it. In general, the accumulator system 11 cooperates with other systems within the vehicle 10 to supply energy to an electric drive system within the vehicle and / or the various systems within the vehicle 10. The vehicle 10 generally includes a chassis 12, a body 14, front wheels 16, and rear wheels 18. The body 14 is arranged on the chassis 12 and essentially encloses components of the vehicle 10. The body 14 and the chassis 12 together can form a frame. The front wheels 16 and the rear wheels 18 are each rotatably coupled to the chassis 12 in the region of a corner of the body 14.

[0024] In various embodiments, the vehicle 10 is an autonomous vehicle, and the system 11 is integrated into the autonomous vehicle 10. For example, an autonomous vehicle 10 is a vehicle 10 that is automatically controlled to transport passengers from one location to another. The vehicle 10 is shown as a passenger car in the illustrated embodiment; however, it should be understood that any other vehicle, including motorcycles, trucks, sport utility vehicles (SUVs), recreational vehicles (RVs), etc., may also be used. In one exemplary embodiment, the vehicle 10 is equipped with a so-called level four or level five automation system.A Level Four system indicates a "high degree of automation" and refers to the driving mode-specific execution of all aspects of the dynamic driving task by an automated driving system, even if a human driver does not respond appropriately to a request for intervention. A Level Five system indicates "full automation," meaning that an automated driving system fully executes all aspects of the dynamic driving task under all road and environmental conditions that can be handled by a human driver. The novel aspects of the present disclosure are also applicable to non-autonomous vehicles.

[0025] As shown, the vehicle 10 generally includes a propulsion system 20, a transmission system 22, a steering system 24, a braking system 26, a sensor system 28, an actuator system 30, at least one data storage device 32, a controller 34, and a wireless vehicle communication module 36. In an embodiment where the vehicle 10 is an electric vehicle, the propulsion system may include one or more electric motors connected to and powered by the battery system 11, and a transmission system 22 may not be present. The propulsion system 20, in various embodiments, may include an internal combustion engine, an electric machine, such as a traction motor, and / or a fuel cell propulsion system. The transmission system 22 is configured to transfer the power of the propulsion system 20 to the front wheels 16 and the rear wheels 18 of the vehicle according to selectable gear ratios.According to various embodiments, the transmission system 22 may be a stepped automatic transmission, a continuously variable transmission, or other suitable transmission. The braking system 26 is configured to provide braking torque to the front wheels 16 and the rear wheels 18 of the vehicle. In various embodiments, the braking system 26 may include friction brakes, an electromechanical brake, a regenerative braking system such as an electric machine, and / or other suitable braking systems. The steering system 24 influences the position of the front wheels 16 and the rear wheels 18. Although a steering wheel is shown for illustrative purposes, the steering system 24 may not include a steering wheel in some embodiments contemplated by the present disclosure, such as a fully autonomous vehicle.

[0026] The sensor system 28 includes one or more sensing devices 40a-40n that sense observable conditions of the external environment and / or the internal environment of the vehicle 10. The sensing devices 40a-40n may include, but are not limited to, radar, lidar, global positioning systems, optical cameras, thermal cameras, ultrasonic sensors, and / or other sensors. In an exemplary embodiment, the plurality of sensing devices 40a-40n includes an engine speed sensor, an engine torque sensor, an electric drive motor voltage and / or current sensor, an accelerator pedal position sensor, a coolant temperature sensor, a cooling fan speed sensor, and / or a transmission oil temperature sensor. The actuator system 30 includes one or more actuator devices 42a-42n that control one or more vehicle features, such as, but are not limited to, the drive system 20, the transmission system 22, the steering system 24, and the braking system 26.

[0027] The vehicle controller 34 includes at least one processor 44 and a computer-readable storage device or medium 46. The at least one data processor 44 may be any custom or off-the-shelf processor, a central processing unit (CPU), a graphics processing unit (GPU), an auxiliary processor among multiple processors associated with the vehicle controller 34, a semiconductor-based microprocessor (in the form of a microchip or chipset), a macroprocessor, any combination thereof, or generally any device for executing instructions. The computer-readable storage device or medium 46 may include volatile and non-volatile memory, such as read-only memory (ROM), random access memory (RAM), and keep-alive memory (KAM). A KAM is persistent or non-volatile memory that can be used to store various operating variables while the at least one data processor 44 is powered off.The computer-readable storage device or medium 46 may be implemented using any number of known storage devices such as PROMs (Programmable Read Only Memory), EPROMs (Electrically Erasable PROMs), EEPROMs (Electrically Erasable PROMs), flash memory, or other electrical, magnetic, optical, or combination storage devices capable of storing data, some of which represent executable instructions used by the control unit 34 in controlling the vehicle 10.

[0028] The instructions may comprise one or more separate programs, each comprising an ordered list of executable instructions for implementing logical functions. When executed by the at least one processor 44, the instructions receive and process signals from the sensor system 28, execute logic, calculations, methods, and / or algorithms to automatically control the components of the vehicle 10, and generate control signals for the actuator system 30 to automatically control the components of the vehicle 10 based on the logic, calculations, methods, and / or algorithms. Even if only one controller 34 in Fig. 1, embodiments of the vehicle 10 may include any number of controllers 34 that communicate and cooperate via any suitable communication medium or combination of communication media to process the sensor signals, perform logic, calculations, methods and / or algorithms, and generate control signals to automatically control features of the vehicle 10.

[0029] The wireless communication module 36 is configured to wirelessly transmit and receive information to and from other remote entities 48, such as, but not limited to, other vehicles ("C2C communication"), infrastructure ("C21" communication), remote systems, remote servers, cloud computing, and / or personal devices. In an exemplary embodiment, the communication system 36 is a wireless communication system configured to communicate over a wireless local area network (WLAN) using IEEE 802.11 standards or using radio data communication. However, additional or alternative communication methods, such as Dedicated Short Range Communication (DSRC), are also contemplated within the scope of this disclosure.DSRC channels refer to short- to medium-range, one-way or two-way wireless communication channels specifically designed for use in vehicles, along with a corresponding set of protocols and standards.

[0030] The vehicle controller 34 is a non-generalized electronic control device including a preprogrammed digital computer or processor, a memory or non-transitory computer-readable medium used to store data such as control logic, software applications, instructions, computer code, data, lookup tables, etc., and a transmitter / receiver device (or input / output ports). Computer-readable media includes any type of media accessible by a computer, such as read-only memory (ROM), random access memory (RAM), a hard disk drive, a compact disc (CD), a digital video disc (DVD), or any other type of storage. A "non-transitory" computer-readable medium excludes wired, wireless, optical, or other communication connections that carry transitory electrical or other signals.A non-transitory computer-readable medium includes media on which data can be permanently stored and media on which data can be stored and later overwritten, such as a rewritable optical disk or an erasable storage device. Computer code includes all types of program code, including source code, object code, and executable code.

[0031] With reference to Fig. 2, a battery cell 50 for the battery system 11 comprises an anode layer 52, a cathode layer 54, and a separator 56 disposed between the anode layer 52 and the cathode layer 54. The battery cell 50 shown is a cylindrical lithium-ion battery cell (Li-ion battery cell). It is understood that the novel features of the present disclosure are applicable to any type of battery cell 50 having an anode 52, a cathode 54, and a separator 56 disposed therebetween, as well as to non-Li-ion battery cells.

[0032] With further reference to Fig. 2 and Fig. 3 and Fig. 4, the separator 56 includes a primary layer 58 comprising a porous battery separator material 60. In an exemplary embodiment, the porous battery separator material 60 is a porous polyolefin comprising polyethylene (PE), polypropylene (PP), or a PE / PP hybrid. The porous primary layer 58 serves to contain electrolyte and prevent physical contact (electron-conducting contact) between the anode layer 52 and the cathode layer 54. Multiple battery cells 50 may be arranged for current flow in series or parallel, or in any suitable combination thereof, to meet the electrical potential and power requirements of the battery system 11.

[0033] The lithium-ion battery cell 50 generally functions by the reversible passage of lithium ions between a negative electrode (anode layer 52) and a positive electrode (cathode layer 54). The primary layer 58 of the separator is impregnated with an electrolyte solution suitable for transferring lithium ions between the anode layer 52 and the cathode layer 54. Both the anode layer 52 and the cathode layer 54 are further supported on or bonded to a metallic current collector (typically copper for the anode layer 52 and aluminum for the cathode layer 54).During battery operation, the current collectors associated with the anode layer 52 and the cathode layer 54 are connected by a controllable and interruptible external circuit that allows an electron current to flow between the anode layer 52 and the cathode layer 54 to electrically balance the associated transport of lithium ions through the battery cell 50. Many different materials can be used to manufacture these various components of a lithium-ion battery.But in general, the anode layer 52 typically comprises a lithium intercalation material or an alloy host material, the cathode layer 54 typically comprises a lithium-containing active material capable of storing lithium at a higher potential (relative to a lithium metal reference electrode) than the host material of the anode layer 52, and the electrolyte solution typically contains one or more lithium salts dissolved and ionized in a non-aqueous solvent. Contact of the anode layer 52 and the cathode layer 54 with the electrolyte creates an electrical potential between the anode layer 52 and the cathode layer 54, which is maintained by electrochemical reactions within the battery cell 50 when an electron flow is utilized in an external circuit between the anode layer 52 and the cathode layer 54.

[0034] The lithium-ion battery cell 50 or a plurality of lithium-ion battery cells 50 connected in series or parallel for current flow (or a combination thereof) can be used to reversibly supply power to an associated load device. The battery system 11 supplies electrical energy to a load device, e.g., an electric motor, on demand until the lithium content of the anode layer 52 (the negative electrode) is depleted to a predetermined level. The battery cell 50 can then be recharged by flowing a suitable direct electrical current in the reverse direction between the anode layer 52 and the cathode layer 54.

[0035] At the beginning of the discharge, the anode layer 52 contains a high concentration of intercalated lithium, while the cathode layer 54 is relatively depleted. Creating a closed external circuit between the anode layer 52 and the cathode layer 54 under these conditions causes the transport of intercalated lithium from the anode layer 52. The intercalated lithium is oxidized to lithium ions and electrons.The lithium ions are transported from the anode layer 52 (the negative electrode) to the cathode layer 54 (the positive electrode) through the ion-conducting electrolyte solution contained in the pores of the porous polyolefin primary layer 58 of the separator 56. At the same time, the released electrons are transferred through the external circuit from the anode layer 52 (the negative electrode) to the cathode layer 54 (the positive electrode) (via the current collectors) to balance the overall reaction taking place in the electrochemical storage cell 50. The lithium ions are incorporated into the material of the cathode layer 54 through an electrochemical reduction reaction. The flow of electrons through the external circuit can power a load device until the content of intercalated lithium in the anode layer 52 falls below a usable level or the power demand no longer exists.

[0036] The battery cell 50 can be recharged after a partial or complete discharge of its available capacity. To recharge or re-energize the lithium-ion battery cell 50, an external power source is connected to the cathode layer 54 and the anode layer 52 to reverse the electrochemical reactions of the battery discharge. This means that during charging, the lithium in the cathode layer 54 is oxidized to produce lithium cations and electrons. The cations are transported through the separator 56 to the anode layer 52, and the electrons migrate through the external circuit to the anode layer 52. At the surface of the anode layer 52, the lithium cations are reduced to lithium by combining with the available electrons within the anode layer 52, and the lithium content of the anode layer 52 increases.Overall, the charging process reduces the lithium content in the cathode layer 54 and increases the lithium content in the anode layer 52.

[0037] The separator 56 serves an important function in the battery cell 50. In many lithium-ion battery designs, the anode layer 52 and the cathode layer 54 are formed as thin, densified, polymer-bonded, particulate material layers on their respective current collectors (e.g., copper or aluminum foils), and each cell 50 is assembled with a thin, porous polyolefin separator 56 sandwiched between the opposing electrode layers. Thus, the pores and surfaces of the polyolefin primary layer 58 of the separator 56 are filled and contacted with a lithium ion-containing, non-aqueous electrolyte, which contacts and wets the opposing anode layer 52 and cathode layer 54 to enable the flow of lithium ions and counterions through the pores of the separator 58 and between the anode layer 52 and cathode layer 54.However, the polymeric primary layer 58 of the separator 56 resists the flow of electrons directly between the anode layer 52 and the cathode layer 54.

[0038] The properties of the separator 56 play an important role in determining the thermal response of the battery cell 50 during an abuse event. Commercially available, state-of-the-art polyolefin-based separators 56 are generally made of polyethylene (PE), polypropylene (PP), or hybrids of PE and PP. While PE- and PP-based materials offer excellent mechanical properties, they are susceptible to thermal failure due to their relatively low transition temperatures (135°C for PE and 165°C for PP). Additionally, polyolefin-based materials generally exhibit poor wetting properties with carbonate-based electrolytes used in Li-ion battery cells 50. By layering PP and PE, the difference in melting points between PP and PE can be utilized, with PE used as a shutdown layer and PP used to protect structural integrity.Unfortunately, such protection is only effective below the melting point of PP.

[0039] The separator 56 of the present disclosure further includes a thermal stability coating 62 applied to the primary layer 58 on a surface 64 of the primary layer 58 facing the anode layer 52. In an exemplary embodiment, the thermal stability coating 62 comprises a thin layer of a ceramic material such as silicon dioxide or aluminum oxide, or a thin layer of metal oxides or metal hydroxides such as boehmite. In a non-limiting example, the primary layer 58 is surface-coated with polymer-bonded particles of such ceramic materials or metal oxides. The thermal stability coating 62 increases the strength of the separator 56, increases the dimensional stability of the separator 56 at high temperatures (above which polymers such as PE or PP would be in a molten state), and increases the electrolyte retention capacity of the primary layer 58 of the separator 56.In another exemplary embodiment, the thermal stability coating comprises a pore-controlled polyamine (PAI). The PAI is applied to the primary layer 58 using a phase transfer and gravure printing process. The PAI provides a pore-controllable structure with different pore sizes. For example, the pore size can vary between 0.02 micrometers, 0.17 micrometers, and 0.85 micrometers. The PAI thermal stability coating 62 provides the advantage of "guest-host transition," in which the PAI undergoes a reversible transition, increasing thermal stability, and "pore on / off," in which ion transfer through the separator can be selectively turned on or off by using the PAI to close the pores in the primary PE layer 58.

[0040] With further reference to Fig. 2, the battery cell 50 includes a plurality of alternating layers of anode layer 52 / separator 56 / cathode layer 54 wound into a cylindrical shape. As shown, the battery cell 50 includes a first end 66 having a positive cap 68 electrically connected to a positive tab 70 connected to the cathode layer 54(s). The battery cell 50 further includes a second end 72 having a negative cap 74 electrically connected to a negative tab 76 connected to the anode layer 52(s). The primary layer 58 of the separator 56 includes a first edge 78 extending circumferentially around the cylindrical battery cell 50 adjacent the first end 66 of the battery cell 50 and a second edge 80 extending circumferentially around the cylindrical battery cell 50 adjacent the second end 72.In an exemplary embodiment, at least one of the first edge 78 and the second edge 80 of the primary layer 58 of the separator 56 includes an uncoated region 82 in which the thermal stability coating 62 is not applied. The battery cell 50 may include an uncoated region 64 adjacent to one or both of the first and second edges 78, 80.

[0041] During manufacturing, there is a risk that the first and second edges 78, 80 of the separator 56 may be damaged by impacts against other objects, etc. Therefore, for quality control purposes during mass production, it is desirable to test the finished battery cells 50 to ensure that the first and second edges 78, 80 have not been damaged. Non-destructive testing methods, such as X-ray inspection, are not feasible due to the nature of the primary layer 58 and the thermal stability coating 62 made of polymer and ceramic / metal oxide. Thus, periodic random disassembly processes (destructive testing) are typically performed to visually determine whether the manufactured battery cells 50 have damaged / defective separators 56. This involves the loss of the disassembled battery cell 50 and does not allow for 100% testing of the manufactured battery cells 50.

[0042] In order to allow each battery cell 50 to be tested using non-destructive techniques (X-ray testing), the separator 56, in an exemplary embodiment, comprises a metallic coating 84 applied to the primary layer 58 on the surface 64 of the primary layer 58 facing the anode layer 52 within the uncoated area 82. Referring again to Fig. 4, in an exemplary embodiment, the width of the metallic coating 84 is at least ten micrometers, as indicated at 86, and the separator 56 includes a gap 96 of at least one micrometer between the metallic coating 84 and the thermal stability coating 62, as indicated at 88. Thus, the minimum width of the uncoated region 82 is at least eleven micrometers, as indicated at 90.

[0043] The metallic coating 84 can be any metallic material that can be detected using x-ray techniques. In an exemplary embodiment, the metallic coating 84 comprises aluminum or stainless steel. Aluminum is often the metallic material used for the metallic coating 84 due to its electrochemical stability. However, compared to other metallic materials, aluminum tends to exhibit a weak response when applied to x-ray techniques. When using aluminum, image processing techniques and algorithms can be used to improve the response of aluminum in x-ray images. A metallic coating of iron (Fe) or iron oxide (FeO2) provides optimal visibility using x-ray techniques and has no negative impact on the performance of the battery cell 50.In contrast to aluminum, iron-based metal oxides are stable in the anode potential of the lithium-ion battery cell 50.

[0044] The metallic coating 84 can be applied to the surface 64 of the primary layer 58 facing the anode layer 52 using any known methods or processes. In one exemplary embodiment, the metallic coating 84 comprises metallic particles or powders suspended in a matrix or binder of polymeric material. During application, the polymeric material is a liquid slurry into which the metallic particles / powders are mixed along with a surfactant and a rheology modifier. The slurry containing the metallic particles / powders and other ingredients is then applied to the surface 64 of the primary layer 58 facing the anode layer 52 using wet coating and solvent drying techniques.This application method reduces the occurrence of metallic contamination, and the metallic coating 84 can be fabricated and applied simultaneously with the thermal stability coating 62. However, in other embodiments, the metallic coating 84 can be applied to the surface 64 of the primary layer 58 facing the anode layer 52 using electrodeless plating techniques or by vacuum deposition, such as (but not limited to) physical vapor deposition (PVD) or chemical vapor deposition (CVD).

[0045] Physical vapor deposition techniques such as electron beam physical vapor deposition (EB-PVD), magnetron sputtering, and pulsed laser deposition (PLD) can be used to deposit binderless, ceramic (inorganic) thin films that offer better thickness and morphology control than slurry coating techniques. Among thin film deposition techniques, EB-PVD is a fast (2 nm / s) and scalable process that produces a dense, uniform ceramic layer and requires no post-treatment. It utilizes an electron beam (EB) source capable of vaporizing a target at a very high speed (approximately 2 nm / s) and depositing it onto a solid, large surface area, or roll-to-roll fabrication, which is required for large-scale battery production.

[0046] As in Fig. 2, the positive tab 70 (cathode tab) is located at the first end 66 of the battery cell 50 and the negative tab 76 (anode tab) is located at the second end 72 of the battery cell 50. In other embodiments where the negative tab 76 is located at the same end of the battery cell 50 as the positive tab 70, the separator 56 further includes an electrically insulating coating 98 applied over the uncoated region 82 of the primary layer 58 and the metallic coating 84.

[0047] With further reference to Fig.4, in an exemplary embodiment, the primary layer 58 is approximately ten micrometers thick, as indicated at 92, and the thermal stability coating 62 is approximately three micrometers thick, as indicated at 94, where the term "approximately" as used herein is defined as plus or minus two micrometers. It will be understood by those skilled in the art that the primary layer 58 and the thermal stability layer 62 may have other thicknesses depending on design constraints / requirements.

Claims

[1] Separator (56) for a battery cell (50), comprising: a primary layer (58) comprising a porous accumulator separator material (60), a thermal stability coating (62) applied to the primary layer (58) on a surface (64) of the primary layer (58) that will face an anode (52) in the battery cell (50), wherein at least one of a first edge (78) and a second edge (80) of the primary layer (58) comprises an uncoated region (82) in which the thermal stability coating (62) is not applied, and a metallic coating (84) applied to the primary layer (58) on the anode-facing surface (64) of the primary layer (58) within the uncoated area (82), further comprising a gap (96) between the thermal stability coating (62) and the metallic coating (84). [2] The separator (56) of claim 1, wherein the porous accumulator separator material (60) is a porous polyolefin comprising polyethylene (PE), polypropylene (PP), or a PE / PP hybrid. [3] Separator (56) according to claim 1, wherein the heat stability coating (62) consists of a ceramic material, a metal oxide / metal hydroxide or a layer of pore-controllable polyamine (PAI). [4] Separator (56) according to claim 1, wherein the metallic coating (84) a polymeric binder with metal particles suspended therein, a metal layer applied to the primary layer by electrodeless plating, or a metal layer deposited onto the primary layer by vapor deposition. [5] Separator (56) according to claim 1, wherein the metallic coating (84) comprises aluminum, stainless steel, iron or iron oxide. [6] The separator (56) of claim 1, further comprising an electrically insulating coating (98) applied over the uncoated portion (82) of the primary layer (58) and the metallic coating (84). [7] Separator (56) according to claim 1, wherein: the primary layer (58) is ten micrometers thick, the thermal stability layer (62) is three micrometers thick, the width (86) of the metallic coating (84) is at least ten micrometers and the width (88) of the gap (96) between the thermal stability layer (62) and the metallic coating (84) is at least one micrometer. [8] A storage cell (50) comprising an anode layer (52), a cathode layer (54) and a separator (56) disposed between the anode layer (52) and the cathode layer (54), the separator (56) comprising: a primary layer (58) comprising a porous accumulator separator material (60), a thermal stability coating (62) applied to the primary layer (58) on a surface (64) of the primary layer (58) facing the anode, wherein at least one of a first edge (78) and a second edge (80) of the primary layer (58) comprises an uncoated region (82) in which the thermal stability coating (62) is not applied, and a metallic coating (84) applied to the primary layer (58) on the anode-facing surface (64) of the primary layer (58) within the uncoated area (82), wherein the separator (56) has a gap (96) between the thermal stability coating (58) and the metallic coating (84).

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