Multi-layer electrode for a battery

Abstract

The present disclosure relates to a secondary solid-state battery. This battery includes a current collector comprising a poly-3,4-ethylenedioxythiphenpolystyrenesulfonate layer (PEDOT-PSS layer) in direct surface contact with a negative electrode. The battery also includes a positive electrode and a solid electrolyte separator between the positive and negative electrodes. The PEDOT-PSS layer can be compressed and expanded in response to the expansion and contraction of the negative electrode. In some embodiments, the current collector may include a carrier film on which the PEDOT-PSS layer is coated. A cell stack of several assemblies further comprises the positive electrode, the solid electrolyte separator, the negative electrode, and the current collector, with some adjacent pairs being separated by carbon fiber papers.

Description

FIELD OF TECHNOLOGYThis disclosure relates to solid-state batteries (SSBs) and, more particularly, to mitigating issues associated with volume changes during battery charging and discharging in SSBs, particularly those employing metallic anodes such as lithium (Li) or silicon (Si).GENERAL STATE OF THE ARTSSBs can provide increased specific energy density and volumetric energy density. The use of metal anodes such as Li or Si in SSBs was helpful to achieve these energy density metrics. These anodes are sometimes challenging due to the substantial volume change experienced during charging and discharging cycles.To maintain interfacial contact within the cells and compensate for these volume changes, stack pressures in the range of 5-50 MPa are typically required. Nevertheless, performance degradation is still possible in Li- or Si-based SSBs. This problem is attributed in part to voltage variation and associated accumulation of strain in the electrodes during operation.SUMMARYThis disclosure describes a design of a secondary SSB in which a current collector, a layer of poly-3,4-ethylenedioxythiphene polystyrene sulfonate (PEDOT-PSS), is integrated into the negative electrode. The negative electrode is deposited on this PEDOT-PSS layer, which is structured to expand and contract in response to the respective expansion and contraction of the negative electrode, thereby coping with the expansion involved in the operation of the battery.The positive electrode and the negative electrode are separated by a solid electrolyte separator in the proposed battery configuration. The current collector can be further improved by adding a carrier film on which the PEDOT-PSS layer is coated, which contributes to the mechanical integrity of the current collector.This carrier film may be a polyimide substrate that provides insulating and structural advantages for the overall battery design. An electrode assembly is provided by the composition of the positive electrode, the solid electrolyte separator, the negative electrode and the current collector.The disclosure further provides a secondary SSB comprised of a plurality of such electrode assemblies. Each assembly includes positive and negative electrodes, a solid electrolyte separator, and a current collector in direct face contact with the negative electrode, the negative electrode positioned between the solid electrolyte separator and the current collector.In addition to these elements, the battery configuration described may include carbon fiber papers interleaved with the electrode assemblies. These carbon fiber papers function as additional spacers and stabilizers so that not all adjacent pairs of electrode assemblies are in direct contact. Some are separated by one of these carbon fiber papers.In another embodiment of the secondary SSB, the battery includes positive and negative electrodes, a solid electrolyte separator, and a current collector formed by a PEDOT-PSS layer coated on a support sheet. The carrier film is in direct surface contact with the negative electrode, wherein the negative electrode is located between the solid electrolyte separator and the current collector. The carrier film in this embodiment may be a polyimide substrate that adds a layer of structural integrity to the battery.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1A is a schematic cross-section of a current collector including carbon fiber paper; FIG. 1B is a schematic cross-section of an anode coated on a current collector; FIG. 2A is a schematic cross-section of a single cell assembly with a carbon fiber paper current collector; FIG. 2B is a schematic cross-section of a cell stack assembly with a carbon fiber paper current collector; FIG. 3 is a schematic cross section of carbon fiber paper as a strain buffer in a cell stack of a secondary SSB; FIG. 4 is a schematic cross section of an elastic material interposed between two metal foils; FIG. 5 is a schematic cross-section of a metal foam coated with a microporous layer; and FIG. 6 is a schematic cross-section of a conductive polymer current collector in a cell of a secondary SSB.DETAILED DESCRIPTIONEmbodiments are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments may take various and alternative forms. The figures are not necessarily to scale. Some features could be exaggerated or minimized to show details of specific components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art.Various features illustrated and described with respect to any of the figures may be combined with features illustrated in one or more other figures to produce embodiments that are not expressly illustrated or described. The illustrated combinations of features provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of this disclosure may be desirable for specific applications or implementations.Measures that can mitigate stress fluctuations, reduce the accumulation of strain, and reduce the need for stack pressure are desirable. Such measures could improve cycle stability and battery life, which represents a significant advance in battery technology. The disclosed embodiments may alleviate the challenges associated with volume change of SSBs. They introduce an elastic and conductive layer which can serve as a current collector or separate strain buffer. This layer can be used in SSBs that exhibit a significant volume change during charging and discharging, such as those based on metal anodes such as Li metal and Si.The electrical conductivity of this layer should exceed 1 S / cm, ideally 10 S / cm. To accommodate the change in volume of the SSB anode, the elasticity of the layer should be able to accommodate strains, for example, a 40% strain at a compressive stress of 1.5 MPa. Ideally, the layer should have a compressive modulus of elasticity in the range between 1 and 10 MPa and a range of elongation (up to 60%). The thickness of the layer should be small, ideally less than 80 microns in an uncompressed state.In one embodiment, carbon fiber paper may be used as the current collector. A microporous layer consisting of nano-sized carbon particles is coated on the carbon fiber paper to ensure a smooth surface for coating the electrode, for example, the anode Si layer.In another embodiment, a metal foam may be used as the main elastic component, on which a microporous (carbon) layer is coated to adjust the surface roughness and improve the electrical contact. The elastic properties of the metal foam can be designed as required. A microporous layer composed of nano-sized carbon particles is used to ensure a smooth surface for coating the anode Si layer.In another embodiment, a sandwich configuration of resilient material between two metal layers is contemplated. In this embodiment, an elastic material (such as silicone rubber) is interposed between two metal foils. The metal foils provide an electrical connection and the spring-like middle layer contracts as the electrode expands, thereby releasing the stress of the electrode active materials. As the active materials contract, the layer returns to maintain the particles in intimate contact. The properties of the elastic material, such as the modulus of elasticity and thickness, can be adjusted to meet the requirements for expansion and contraction. The thickness of the metal foil could be in the range of 2-5 μm to minimize the overall thickness of the current collector. The metal foils could be the same metal (such as Cu foils or Al foils) or different metals (one side could be a Cu foil, the other side an Al foil).These elastic and conductive layers can be used not only as a direct substitute for the metal foil current collectors in the current battery manufacture (i.e., copper foil on the anode and aluminum foil on the cathode), but also as a strain buffer layer between individual cells. The latter can be more cost-effective for the case of the SSB electrode which has smaller volume changes during charging and discharging. The number of such stretch buffer layers and their locations must be carefully considered to achieve optimum performance and minimum cost enhancement.The disclosure relates to cycle stability, thereby increasing the life of metal anode-based SSBs. Another potential advantage of the disclosure is the reduction of operating stack pressure, which is currently a challenge for battery packaging in electric vehicles. This disclosure has the potential to lower the stack pressure to less than 1 MPa, thereby facilitating the packaging of the battery.Moreover, the contemplated embodiments do not increase the complexity of battery manufacture. For example, the new current collector is a direct substitute for the current metal foil in the roll-to-roll process. The stretch buffer layer can be easily inserted between the individual cells.FIG. 1A provides an illustrated embodiment of the carbon fiber paper. This carbon fiber paper, designated by reference numeral 10, is a composite structure comprising a core carbon fiber layer 12 encapsulated between two microporous layers, designated by reference numerals 14 and 16, respectively. The microporous layers 14 and 16 comprise a plurality of nano-sized carbon particles 18 effectively embedded therein. The typical thickness of the microporous layer is in the range of 1-10 μm.The presence of these microporous layers 14, 16 on both sides of the carbon fiber layer 12 not only contributes to the improved mechanical stability of the carbon fiber paper 10, but also serves to make its surface smoother. This improved surface smoothness is advantageous when a subsequent coating of an anode Si layer is performed, because it helps adhesion and uniform coverage of the layer.In one embodiment, the carbon fiber paper 10 serves as the current collector within the construct of an SSB. In this function, it is configured such that one of the microporous layers, for example 14, is in direct face contact with a negative electrode, while the other microporous layer, for example 16, is in direct face contact with a negative electrode or a positive electrode. The result of this arrangement ensures that the surfaces of the current collector are smoother than the surfaces of a single carbon fiber.Turning to FIG. 1B, the process of coating an anode Si slurry, designated by the reference numeral 20, onto the carbon fiber paper 10 is illustrated. Once deposited, the anode Si slurry 20 takes on the role of the negative electrode.In particular, the incorporation of nano-sized carbon particles 18 into the microporous layers 14, 16 serves to improve conductivity and promote efficient electron transfer within the battery. In certain embodiments, the carbon fiber layer 12 could take the form of a metal foam such as Cu or Al. The dimensions of this metal foam layer could be such that its thickness exceeds that of each of the microporous carbon layers 14, 16.Following the coating process, the solid electrolyte separator is applied so that it directly contacts the Si anode 20. Moreover, in some configurations, a positive electrode may be incorporated into the battery structure that is arranged to be in direct face contact with the solid electrolyte separator on the other side.This set-up configuration forms an integrated cell assembly that includes the positive electrode coated on a current collector, which may be the carbon fiber paper 10, the solid electrolyte separator, and the negative electrode that may be applied as a Si slurry to a current collector. Multiple such cell assemblies may be assembled together with carbon fiber papers in an interleaved manner. Adjacent pairs of the electrode assemblies may be separated by one of the carbon fiber papers.Continuing with FIG. 2A, a battery cell structure is illustrated in the mentioned embodiment. The battery cell includes the carbon fiber paper 10 as a base layer. Over this base layer is deposited an anode Si layer 22, which is the negative electrode in this battery cell structure. The anode Si layer 22 directly interfaces with the microporous layer 14 of the carbon fiber paper 10 taking advantage of the smoother surface provided by the microporous layer.A solid electrolyte separator 24 is applied following the Si anode layer 22, which directly forms an interface with the Si anode layer 22. The solid electrolyte separator 24 facilitates ion transport between the electrodes of the battery while preventing direct electronic contact therebetween.A cathode layer 26 is applied to the solid electrolyte separator 24, forming the positive electrode of the battery cell structure. The completed structure is then completed with a current collector, thereby forming a single battery cell. The aluminum foil which is usually used at present can be used as a cathode current collector. A current collector 10 made of carbon fiber paper may also be used for the cathode. This configuration constitutes a continuous cell assembly that integrates a positive electrode (cathode layer 26), a solid electrolyte separator 24, and a negative electrode (anode Si layer 22).Turning to FIG. 2B, an embodiment of the bipolar arrangement of the battery cells is illustrated. Here, another complete battery cell structure, similar to that shown in FIG. 2A, is shown stacked over the existing structure. Each cell in the stack maintains the same order of layers as a single cell starting with the carbon fiber paper current collector 10 at the base, followed by a Si anode layer 22, a solid electrolyte separator 24, and a cathode layer 26, then repeating the structure. At the end, the battery cell can be completed with a carbon fiber paper 10.This bipolar stack configuration allows for improved energy density by allowing for the series connection of multiple cells. The bipolar configuration allows anodes and cathodes to share current collectors, reducing the overall weight and volume of the battery, resulting in a more compact and efficient design. As a result, in such a configuration, a plurality of electrode assemblies and carbon fiber papers are accommodated in an interleaved manner, with only some adjacent pairs of the electrode assemblies being separated by one of the carbon fiber papers. This compact arrangement of layers in the bipolar configuration optimizes the performance and efficiency of the battery.The elastic and conductive carbon fiber structure can be used not only as a current collector but also as a strain buffer layer. Referring now to FIG. 3, an expanded battery pack is illustrated. The configuration begins with a carbon fiber paper, designated by reference numeral 30, which serves as the base layer.This layer is followed by two or more individual battery cells, which are designated by reference numeral 32. Each of these individual cells 32 includes a plurality of components: a Si anode 34, a solid electrolyte separator 36, a cathode 38, and a substrate layer. The cathode substrate may be an aluminum (Al) foil 40 and the anode substrate may be a Cu foil 42. On these components is placed another layer of carbon fiber paper 30, followed by a subsequent single cell 32.In this particular arrangement, the Si anode 34 is coated on the Cu foil 42 according to conventional battery fabrication techniques. However, what distinguishes this structure is the integration of the carbon fiber paper 30 as a strain buffer layer. The role of this layer is to help relieve mechanical stresses, thereby promoting overall durability and longevity of the battery cell.In particular, it is not necessary to include the carbon fiber paper 30 for each individual cell 32. Depending on experimental regulations and the desired properties of the battery, this layer may be included, for example, after 3 to 5 individual cells each. The exact placement is determined based on experimental results. By reducing the number of carbon fiber papers 30 in the stack, the configuration becomes more compact, thereby improving the volumetric energy density of the battery.The complete structure represents a secondary SSB. A plurality of electrode assemblies are incorporated therein, each of which includes a positive and a negative electrode, a solid electrolyte separator 36 located between the positive and negative electrodes, and a current collector in direct face contact with the negative electrode. In this configuration, the negative electrode (Si anode 34) is disposed between the solid electrolyte separator 36 and the current collector (carbon fiber paper 30).The configuration of the secondary SSB also employs carbon fiber papers 30 interleaved with the electrode assemblies. In this embodiment, some but not all adjacent pairs of the electrode assemblies are separated by one of the carbon fiber papers 30.In an additional aspect of the illustrated embodiment, the current collector may include a carrier foil to aid in structural integrity and better adhesion to the negative electrode. A practicable choice for this carrier film could be a polyimide substrate because of its mechanical and thermal stability. This polyimide substrate could be coated with a layer of poly-3,4-ethylenedioxythiophene-polystyrenesulfonate, a conductive polymer, to increase the current collecting capacity of the current collector.Reference is now made to Figure 4 which illustrates a configuration of a resilient material 40 sandwiched between two metal foils 42 and 44. In particular, in this configuration, an elastomeric material, such as silicone rubber, is used as the central layer, thereby creating an elastic structure that can be matched to the expansion and contraction behavior of the battery components.The role of the metal foils 42 and 44 is varied. Primarily, they serve as conductors that provide an electrical connection. In addition, they act in conjunction with the resilient material 40 to form a compressible structure. This "spring-like" middle layer is configured to contract as the electrode expands during charging cycles, thereby releasing the strain to which the active electrode materials are exposed. Conversely, it will rebound or expand as the active material shrinks during discharge cycles, thereby ensuring that the particles remain in intimate contact.These adaptive behaviors are helpful to maintain the integrity of the battery and improve its durability and performance. It should be noted that the properties of the resilient material 40, such as its modulus of elasticity and thickness, can be accurately designed to meet the specific requirements of the battery for expansion and contraction.In order to maintain the compact configuration of the battery and minimize the overall thickness of the current collector, the thickness of the metal foils 42 and 44 may be kept within the range of 2 ~ 5 μm. This careful balance ensures that the battery maintains its energy density while incorporating the strain relief advantages of the resilient layer 40.Depending on design needs and performance requirements, the metal foils 42 and 44 may be made of the same material or different materials. In some configurations, both could be Cu, Al, or any other conductive material that meets application requirements. In other cases, the metal foils may be made of different materials to optimize certain properties, such as conductivity, mechanical strength, or corrosion resistance.A secondary SSB configuration includes this current collector configuration with an elastomeric material interposed between two metal foils. In this configuration, the negative electrode and the positive electrode are separated by a solid electrolyte separator, and each of the metal foils of the current collector is in direct surface contact with a positive or negative electrode.The entire configuration consisting of the positive and negative electrodes, the solid electrolyte separator, and the uniquely configured current collector forms an electrode assembly. The battery may further include a plurality of these electrode assemblies and carbon fiber papers interleaved with the electrode assemblies. This arrangement ensures that some, but not all, adjacent pairs of electrode assemblies are separated by one of the carbon fiber papers, thereby improving the mechanical stability and performance of the battery.Referring now to FIG. 5, a novel configuration configuration is illustrated. Here, a metal foam 50 serves as the primary elastic component, enveloped by two microporous layers 52 and 54. These microporous layers are made of nano-sized carbon particles and provide a number of functionalities to the overall system.The microporous layers 52 and 54 serve as an important interface and contribute to both the mechanical and electrical properties of the assembly. They serve to adjust the surface roughness of the metal foam 50, thereby providing a more uniform and conductive surface. This smooth surface is ideal for subsequent coating of the anode Si layer, which contributes to improvement of adhesion and uniformity thereof. The microporous layers 52 and 54 also play a central role in improving electrical contact and thus contribute to conductivity within the assembly.The metal foam 50 at the core of this embodiment was chosen for its inherent elasticity. This resiliency enables it to respond to the expansion and contraction of the electrodes during the charge-discharge cycles of the battery, thereby improving durability and reliability. The elastic properties of this metal foam 50 can be carefully designed to meet the desired specifications, thereby ensuring optimum performance in response to the mechanical behavior of the active material.The described configuration is integrated into a secondary SSB in which a current collector comprises this metal foam 50 interposed between the microporous layers 52 and 54. The positive electrode and the negative electrode are separated by a solid electrolyte separator, and each of the microporous layers of the current collector is in direct face contact with a positive or negative electrode.The entirety of this assembly, comprising the positive and negative electrodes, the solid electrolyte separator, and the uniquely configured current collector, forms a cell assembly. The battery design may include multiple such cell assemblies. Further, carbon fiber papers may be interleaved with these assemblies so that not all adjacent pairs of electrode assemblies are in direct contact. Instead, some are separated by a carbon fiber paper that provides additional mechanical stability and improves overall battery performance.Referring now to FIG. 6, a secondary SSB cell configuration 60 is introduced. In this embodiment, a stretch buffer layer and a current collector in a one layer 62 of poly-3,4-ethylenedioxythiphene polystyrene sulfonate (PEDOT-PSS) form a basic component. The anode layer 64, which may be a Si anode, may be directly coated on this PEDOT-PSS layer.The PEDOT-PSS layer 62 is itself coated on a carrier film 66, such as an insulating polyimide substrate. This polyimide substrate serves to provide structural support for the PEDOT-PSS layer 62, thereby improving the overall mechanical stability of the SSB cell 60.However, this carrier film 66 may be either held in the SSB stack or removed depending on the specific battery configuration. For example, it could be removed in a bipolar stack configuration to optimize space and material efficiency.To further increase the mechanical strength of conductive polymer current collector (PEDOT-PSS) 62, the layer may be reinforced with other porous substrates or polymeric materials. These could include, but are not limited to, expanded polytetrafluoroethylene (e-PTFE), glass fibers, cellulose substrate, or polyvinylidene fluoride hexafluoropropylene (PVDF-HFP). These reinforcements ensure that the current collector is reliable and is capable of withstanding the mechanical stresses during battery operation.The SSB cell 60 as a whole is composed of a positive electrode 68, a solid electrolyte separator 70, a negative electrode 64, and the current collector 62. the current collector 62 containing the PEDOT-PSS layer is in direct surface contact with the negative electrode 64. the negative electrode 64, in turn, is positioned between the solid electrolyte separator 70 and the current collector 62.The assembly including the positive electrode 68, the solid electrolyte separator 70, the negative electrode 64, and the current collector 62 forms a cell assembly. These assemblies may be used to generate a secondary SSB that includes multiple such assemblies. Further, carbon fiber papers may be interleaved with these assemblies so that not all adjacent pairs of electrode assemblies are in direct contact. Instead, some are separated by a carbon fiber paper that provides additional mechanical stability and improves overall battery performance.While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The terms used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of these disclosed subject matters.As described above, the features of various embodiments may be combined to form further embodiments of the disclosure that may not be expressly described or illustrated. While various embodiments could have been described as providing or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art will understand that one / more features or characteristics may be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes may include, but are not limited to, strength, durability, marketability, appearance, packaging, size, serviceability, weight, mikroability, ease of assembly, etc. Thus, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.

Claims

A secondary all-solid-state battery comprising: a current collector including a poly-3,4-ethylenedioxythiphene polystyrenesulfonate layer; a negative electrode coated on the poly-3,4-ethylenedioxythiphene polystyrenesulfonate layer such that the poly-3,4-ethylenedioxythiphene polystyrenesulfonate layer is configured to be compressed or expanded in response to expansion and contraction of the negative electrode; a positive electrode; and a solid electrolyte separator between the positive and negative electrodes.The secondary all-solid-state battery of claim 1, wherein the current collector further includes a carrier sheet.The secondary all-solid-state battery of claim 2, wherein the carrier film is a polyimide substrate.The secondary all-solid-state battery of claim 2, wherein the poly-3,4-ethylenedioxythiphene polystyrenesulfonate layer is coated on the support film.The secondary all-solid-state battery of claim 1, wherein the positive electrode, the solid electrolyte separator, the negative electrode, and the current collector form an electrode assembly further comprising a plurality of the electrode assemblies and carbon fiber papers interleaved with the electrode assemblies.The secondary all solid state battery of claim 5, wherein the carbon fiber papers are interleaved with the electrode assemblies such that some, but not all, adjacent pairs of the electrode assemblies are separated by one of the carbon fiber papers.A secondary all-solid-state battery comprising: a plurality of electrode assemblies, each of the electrode assemblies including positive and negative electrodes, a solid electrolyte separator between the positive and negative electrodes, and a current collector in direct surface contact with the negative electrode such that the negative electrode is between the solid electrolyte separator and the current collector; and carbon fiber papers interleaved with the electrode assemblies such that some, but not all, adjacent pairs of the electrode assemblies are separated by one of the carbon fiber papers.The secondary all-solid-state battery of claim 7, wherein the current collector includes a poly-3,4-ethylenedioxythiphene polystyrenesulfonate layer.The secondary all-solid-state battery of claim 8, wherein the current collector further includes a carrier sheet.The secondary all-solid-state battery of claim 9, wherein the carrier film is a polyimide substrate.The secondary all-solid-state battery of claim 10, wherein the poly-3,4-ethylenedioxythiphene polystyrenesulfonate layer is coated on the support film.A secondary all-solid-state battery comprising: positive and negative electrodes; a solid electrolyte separator between the positive and negative electrodes; and a support sheet and a poly-3,4-ethylenedioxythiphenpolystyrene layer coated on the support sheet to form a current collector in direct face contact with the negative electrode such that the negative electrode is between the solid electrolyte separator and the current collector.The secondary all-solid-state battery of claim 12, wherein the carrier film is a polyimide substrate.The secondary all-solid-state battery of claim 12, wherein the positive electrode, the solid electrolyte separator, the negative electrode, and the current collector form an electrode assembly further comprising a plurality of the electrode assemblies and carbon fiber papers interleaved with the electrode assemblies.The secondary all solid state battery of claim 14, wherein the carbon fiber papers are interleaved with the electrode assemblies such that some, but not all, adjacent pairs of the electrode assemblies are separated by one of the carbon fiber papers.

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