WO2016062756A1 - Electrode precursor structure comprising functional release layer - Google Patents

Electrode precursor structure comprising functional release layer Download PDF

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Publication number
WO2016062756A1
WO2016062756A1 PCT/EP2015/074341 EP2015074341W WO2016062756A1 WO 2016062756 A1 WO2016062756 A1 WO 2016062756A1 EP 2015074341 W EP2015074341 W EP 2015074341W WO 2016062756 A1 WO2016062756 A1 WO 2016062756A1
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release layer
release
layer
carrier substrate
electrode precursor
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PCT/EP2015/074341
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French (fr)
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Oliver Gronwald
Klaus MÜHLBACH
Yuriy V. Mikhaylik
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Basf Se
Sion Power Corporation
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Priority to US201462068014P priority
Priority to US62/068,014 priority
Priority to US62/068,009 priority
Application filed by Basf Se, Sion Power Corporation filed Critical Basf Se
Publication of WO2016062756A1 publication Critical patent/WO2016062756A1/en

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    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • C09J5/00Adhesive processes in general; Adhesive processes not provided for elsewhere, e.g. relating to primers
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00Secondary cells; Manufacture thereof
    • H01M10/05Accumulators with non-aqueous electrolyte
    • H01M10/052Li-accumulators
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    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2/00Constructional details or processes of manufacture of the non-active parts
    • H01M2/14Separators; Membranes; Diaphragms; Spacing elements
    • H01M2/16Separators; Membranes; Diaphragms; Spacing elements characterised by the material
    • H01M2/164Separators; Membranes; Diaphragms; Spacing elements characterised by the material comprising non-fibrous material
    • H01M2/1653Organic non-fibrous material
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
    • H01M4/02Electrodes composed of or comprising active material
    • H01M4/13Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134Electrodes based on metals, Si or alloys
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
    • H01M4/02Electrodes composed of or comprising active material
    • H01M4/13Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139Processes of manufacture
    • H01M4/1395Processes of manufacture of electrodes based on metals, Si or alloys
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
    • H01M4/02Electrodes composed of or comprising active material
    • H01M4/36Selection of substances as active materials, active masses, active liquids
    • H01M4/362Composites
    • H01M4/366Composites as layered products
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
    • H01M4/02Electrodes composed of or comprising active material
    • H01M4/36Selection of substances as active materials, active masses, active liquids
    • H01M4/38Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/381Alkaline or alkaline earth metals elements
    • H01M4/382Lithium
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00Electrodes
    • H01M4/02Electrodes composed of or comprising active material
    • H01M4/36Selection of substances as active materials, active masses, active liquids
    • H01M4/38Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/40Alloys based on alkali metals
    • H01M4/405Alloys based on lithium
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    • C09JAdhesives; non-mechanical aspects of adhesive processes in general; adhesive processes not provided for elsewhere; use of material as adhesives
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    • C09J2205/302Process for debonding adherents
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    • C09DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09JAdhesives; non-mechanical aspects of adhesive processes in general; adhesive processes not provided for elsewhere; use of material as adhesives
    • C09J2205/00Other features
    • C09J2205/30Other features of adhesive processes in general
    • C09J2205/31Use of irradiation
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01MPROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00Secondary cells; Manufacture thereof
    • H01M10/05Accumulators with non-aqueous electrolyte
    • H01M10/056Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0565Polymeric materials, e.g. gel-type or solid-type
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    • H01M2300/00Electrolytes
    • H01M2300/0085Immobilising or gelification of electrolyte

Abstract

Described are an electrode precursor structure, an electrode obtainable from said electrode precursor structure, a process for preparing the electrode structure and an electrochemical cell comprising said electrode and the use of a polymer comprising UV-VIS cleavable bonds in the production of a release layer for electrode structures.

Description

Electrode precursor structure comprising functional release layer

The present invention relates to an electrode precursor structure comprising:

at least one active material comprising lithium metal or lithium alloy,

a carrier substrate, and

one or more release layers adhering to the carrier substrate,

wherein said one release layer or at least one of said more than one release layers a) is a release layer which comprises one or more polymers with UV-VIS cleavable bonds, wherein the adhesion to the carrier substrate is reducible by UV-VIS cleaving said bonds,

or

b) is a release layer obtainable by exposing to UV-VIS radiation a release layer as defined under item a) so that the UV-VIS cleavable bonds are cleaved.

The present invention also relates to an electrode structure obtainable by providing or preparing the inventive electrode precursor structure, wherein said one release layer or at least one of said more than one release layers is a release layer obtainable by exposing to UV-VIS radiation a release layer as defined above, item a) so that the UV-VIS cleava- ble bonds are cleaved, and removing the carrier substrate from said one release layer or said at least one of said more than one release layers. The present invention further relates to an electrochemical cell comprising at least one inventive electrode structure. The present invention also relates to an electrochemical cell obtainable by contacting an inventive electrode structure, wherein said one release layer or at least one of said more than one release layers is a release layer obtainable by exposing to UV-VIS radiation a release layer as defined above, item a) so that the UV-VIS cleavable bonds are cleaved, with a non-aqueous electrolyte, so that the release layer is at least partially, preferably completely, dissolved in the non-aqueous electrolyte. Furthermore, the present invention relates to a battery comprising at least one inventive electrochemical cell, to a process for preparing an inventive electrode structure, and to the use of a polymer comprising UV- VIS cleavable bonds in the production of a release layer for electrode structures.

Rechargeable lithium - sulfur (Li/S) batteries are believed to be very promising alternative power sources for long driving range (> 300 km) pure electric vehicles (PEV's) and plug- in electric vehicles (PHEV) since current lithium-ion batteries (LIB) based on intercalation materials can potentially provide only energy densities up to 200 Wh kg"1. This novel type of battery system offers much higher energy density and is relatively inexpensive. Theoretical energy density values can approach 2500 Wh kg"1 with practical values of 500 to 600 Wh kg"1 assuming the complete electrochemical conversion of sulfur (S8) to lithium sulfide (Li2S). Therefore, Li/S batteries have been investigated for mobile and portable applications, especially high energy applications.

Lithium as anode material offers several advantages over other materials due to its negative electrochemical potential and in combination with other materials its wide electrochemical window, its light weight and thus highest gravimetric energy density among all metallic anode materials. The active cathode material in lithium sulfur batteries consists of sulfur. Concentration of sulfur in the cathode can vary between 30 to 80 wt%. Due to the electronically insulation properties of sulfur the presence of further additives is required. As conductive additives carbon (20-60 wt%) and in order to ensure the mechanical integrity of the cathode layer additional binders (1-10 wt%) are employed. Currently quick capacity fading and low sulfur utilization are the main obstacles for using Li/S as rechargeable system. Only about 50 % or ~ 800 mAhg"1 of 1672 mAhg"1 as theoretical capacity can be used. Reason is the "polysulfide shuttle" mechanism. The elemental sulfur molecules accept electrons during the first discharge process and are gradually converted from higher order to lower order polysulfides. Lower polysulfides with less than three sulfur atoms (Li2S3) are insoluble in the electrolyte so that the following reduction step to the insoluble and electronically non-conductive Li2S2 is hampered. Thus low discharge efficiencies are observed at rates higher than C/10. In addition, the polysulfides are not transformed to elemental sulfur during the charging cycles. Instead of being oxidized to sulfur in the final step, the higher order polysulfides constantly diffuse to the anode where they are being gradually reduced by the elemental lithium to lower polysulfides in a parasitic reaction. The soluble lower polysulfides then diffuse back to the cathode thus establishing the "polysulfide shuttle". Insoluble lower polysulfides precipitate from the electrolyte and accumulate on the anode side. In summary, the mechanism reduces charge efficiency and causes corrosion on anode and cathode. As result Li/S batteries suffer from capacity fading and a lack of cycle lifetime. Typical state of the art Li/S battery systems can reach lifetimes of 50 - 80 cycles.

One concept for improving the lithium-sulfur system is based on special protected anodes manufactured by thin layer technology. These anodes consist of a lithium layer (25 μιτι thickness) and anode stabilizing laminate (ASL, 2 to 3 μιτι thickness) based on alternating polymer/ceramic composite on copper as current collector. The lithium is vapor deposited (VDLi) while the ASL polymer layers are being generated by flash evaporation. The multilayer anode is sealed on the top by a polymer gel pad for additional protection and as separator replacement. The cathode is comprised of 55 wt% sulfur as active material and 40 wt% carbon matrix. Due to the applied pressure of 10 kg/cm2 anode and cathode have to be pressure stable. The pressure is required to allow the formation of smoother surface during lithium deposition and for keeping the ceramic in place.

In the manufacturing process copper is deposited on optical grade PET carrier substrate coated with polyvinylalcohol as release layer, then thin layers of lithium as vapor deposit- ed lithium (VDLi) and ceramic layers such as lithium oxide as anode stabilization layers (ASL) are deposited. Since thicknesses of these layers account for the range of few micrometers, it is important to provide carrier substrates with extremely smooth surface. One solution approach is given by a process called "manufacturing process for inverted protected lithium anodes - iPLA". Here, the carrier substrate (optical grade PET) is coat- ed first with polymer as release layer (Gel) to provide a smooth surface. Upon the polymer subsequently a ceramic layer (Li20), lithium (VDLi) and copper (Cu) are deposited. Finally, the multilayer anode is delaminated from the carrier substrate. Depending on the adhesion force, the release layer might remain on the electrode or stay on the carrier substrate. Therefore, it was an object of the present invention to facilitate and control the delamina- tion process in order to obtain a defined electrode structure.

This object is achieved by an electrode precursor structure comprising:

at least one active material comprising lithium metal or lithium alloy,

- a carrier substrate, and

one or more release layers adhering to the carrier substrate,

wherein said one release layer or at least one of said more than one release layers a) is a release layer which comprises one or more polymers with UV-VIS cleavable bonds, wherein the adhesion to the carrier substrate is reducible by UV-VIS cleaving said bonds,

or

b) is a release layer obtainable by exposing to UV-VIS radiation a release layer as defined under item a) so that the UV-VIS cleavable bonds are cleaved.

In the meaning of the present invention, the electrode precursor structure according to alternative b) is an electrode structure, wherein said one release layer or at least one of said more than one release layers b) is a release layer obtainable by exposing to UV-VIS radiation a release layer (intermediate release layer) which comprises one or more polymers with UV-VIS cleavable bonds, wherein the adhesion to the carrier substrate is reducible by UV-VIS cleaving said bonds, so that the UV-VIS cleavable bonds are cleaved.

It has surprisingly been found that delamination (release) process is facilitated by photo induced cleavage of the release layer polymer matrix. Without wishing to be bound to any particular theory, it is believed that a lower degree of crosslinking will soften the release layer and ease the release step. The present invention offers the advantage that the sensitive ceramic layer of the released anode is protected by a polymer layer during the following handling procedure of the cell assembly. As a consequence, the polymer release layer is integrated in the electrochemical cell. According to one option of the present invention, the polymer layer performs as gel protection layer for the anode. According to another option of the present invention, complete dissolution of the release layer in the electrolyte is achieved. For this option, the polymer release layer has to be soluble in the cell electrolyte and is not allowed to interfere with the electrochemical performance. The present invention also generally relates to electrode structures for use in electrochemical cells, and particularly to material precursor layers for use in electrode structures in electrochemical cells. The subject matter of the present invention involves, in some cases, interrelated products, alternative solutions to a particular problem, and/or a plurali- ty of different uses of one or more systems and/or articles.

In certain embodiments, an electrode precursor is provided. In some embodiments, the electrode precursor comprises an electroactive layer comprising an electroactive material, a carrier substrate, and a release layer adhered to the carrier substrate, wherein the release layer comprises a polymer comprising a UV-VIS cleavable bond. In certain embodiments, a method of fabricating an electrode precursor is provided. In some embodiments, the method comprises contacting a release layer with a carrier substrate, wherein the release layer comprises a polymer comprising a UV-VIS cleavable bond, and attaching an electroactive layer comprising lithium metal or lithium alloy to the release layer directly or to the release layer via an intervening layer. In certain embodiments described above and/or herein, the method comprises exposing the one or more release layers to UV-VIS radiation such that the UV-VIS cleavable bond is cleaved.

In certain embodiments described above and/or herein, the method comprises removing the carrier substrate from the release layer. In certain embodiments described above and/or herein, the release layer is a first release layer, the electrode precursor comprising a second release layer positioned adjacent the first release layer.

In certain embodiments described above and/or herein, the step of attaching the electroactive layer to the release layer comprises attaching the electroactive layer directly to the release layer.

In certain embodiments described above and/or herein, the step of attaching the electroactive layer to the release layer comprises attaching the electroactive layer to the release layer via an intervening layer. In certain embodiments described above and/or herein, the intervening layer is a lithium ion conducting protective layer.

In certain embodiments described above and/or herein, adhesion to the carrier substrate is reduced by cleaving the UV-VIS cleavable bonds via UV-VIS.

In certain embodiments described above and/or herein, the release layer is formed by exposing the release layer to UV-VIS radiation such that the UV-VIS cleavable bond is cleaved.

In certain embodiments described above and/or herein, the carrier substrate comprises a film selected from the group consisting of polymer films, metalized polymer films, ceramic films and metal films.

In certain embodiments described above and/or herein, the UV-VIS cleavable bonds are carbon-oxygen bonds.

In certain embodiments described above and/or herein, the release layer comprises one or more photo cleavable units selected from the group consisting of o-Nitrobenzyl alcohol, alpha-Ketoester, and Benzyl alcohol.

In certain embodiments described above and/or herein, the release layer comprises a first surface and a second surface, wherein the first surface and/or the second surface has a mean peak to valley roughness between about 0.1 μιτι and about 1 μητι.

In certain embodiments described above and/or herein, the electrode or electrode precursor comprises at least one Li ion conducting layer adjacent the release layer.

In certain embodiments described above and/or herein, the electrode or electrode precursor comprises at least one Li metal layer adjacent the release layer.

In certain embodiments described above and/or herein, the electrode or electrode precursor comprises at least one current collector layer adjacent the release layer.

In certain embodiments described above and/or herein, the release layer comprises a gel polymer layer. In certain embodiments described above and/or herein, the at least one Li ion conducting layer is a ceramic layer.

In certain embodiments described above and/or herein, the at least one Li ion conducting layer has a thickness greater than a mean peak to valley roughness of the one or more release layers.

In certain embodiments described above and/or herein, the thickness of the at least one Li ion conducting layer is at least two times greater than the mean peak to valley roughness of the one or more release layers.

In certain embodiments described above and/or herein, the thickness of the at least one Li ion conducting layer is between about 0.1 μιτι and about 5 μιτι.

In certain embodiments described above and/or herein, the release layer comprises an amorphous polymer.

In certain embodiments described above and/or herein, an adhesive strength between the release layer and the at least one Li ion conducting layer is greater than an adhesive strength between the release layer and the carrier substrate.

In certain embodiments described above and/or herein, the release layer is a separator.

In certain embodiments described above and/or herein, the release layer is conductive to lithium ions.

In certain embodiments described above and/or herein, the release layer comprises a lithium salt.

In certain embodiments described above and/or herein, the mean peak to valley roughness of the release layer is less than the mean peak to valley roughness of the carrier substrate.

In certain embodiments described above and/or herein, the step of exposing the one or more release layers to UV-VIS radiation comprises directing UV-VIS radiation through the carrier substrate onto the release layer. In certain embodiments described above and/or herein, the step of removing the carrier substrate from the release layer comprises peeling off the carrier substrate from the release layer.

In certain embodiments described above and/or herein, an electrochemical cell comprises at least one electrode or electrode precursor as described above and/or herein.

In certain embodiments involving an electrochemical cell described above and/or herein, the electrochemical cell comprises an electrolyte.

In certain embodiments involving an electrochemical cell described above and/or herein, the release layer is a gel polymer layer.

In certain embodiments involving an electrochemical cell described above and/or herein, the release layer is configured such that when the UV-VIS cleavable bonds are cleaved and the release layer is in contact with a non-aqueous electrolyte, the release layer is at least partially dissolved in the non-aqueous electrolyte.

In certain embodiments involving an electrochemical cell described above and/or herein, the UV-VIS cleavable bonds are cleaved, with a non-aqueous electrolyte, such that the release layer is completely dissolved in the non-aqueous electrolyte.

In certain embodiments involving an electrochemical cell described above and/or herein, the electrochemical cell comprises at least one cathode comprising sulfur.

In certain embodiments involving an electrochemical cell described above and/or herein, the cathode comprises elemental sulfur.

In certain embodiments, a battery comprises an electrochemical cell described above and/or herein.

Throughout the present text, the term "embodiment" is used to describe or define a preferred aspect of the present invention. The disclosure of the present invention must not be restricted to the sum of the individual embodiments described herein, but is intended to cover any combination of any embodiments with one another. Thus, an "embodiment" or a "set of embodiments" of the present invention typically characterizes one or a number of specific aspects of the generic teaching of the present invention. These specific aspects (i.e. embodiments) can typically be combined in order to give even more specific (and, thus, even more preferred) teachings. Likewise, preferred "aspects" of the present invention as defined herein can be combined with each other and/or with "embodiments" of the present invention. Particularly preferred aspects of the invention are defined in the claims as attached.

Any suitable material can be used as a carrier substrate. Preferably, the carrier substrate is made from a polymeric material. In a preferred aspect of the present invention, the carrier substrate comprises a polyester such as a polyethylene terephthalate (PET) (e.g., optical grade polyethylene terephthalate), polyolefins, polypropylene, nylon, polyvinyl chloride, and polyethylene (which may optionally be metalized). In another preferred aspect of the present invention, the carrier substrate comprises a metal or a ceramic material.

Accordingly, the present invention also relates to an electrode precursor structure as described herein, wherein the carrier substrate is selected from the group consisting of polymer films, metalized polymer films, ceramic films and metal films.

Any UV-VIS cleavable bonds are suitable for application in the present invention. However, it is preferred that the UV-VIS cleavable bonds are carbon-oxygen bonds. UV-VIS cleavable bonds are incorporated in the release layer by means of photo cleavable units. Exemplary photo cleavable groups are disclosed in J. Chem. Soc, Perkin Trans. 1 , 2002, 125-142 and in Polym. Chem., 2013, 4, 5026-5037. Preferably, photo cleavable units are selected from the group consisting of o-nitrobenzyl alcohol, alpha-ketoester, benzyl alcohol, truxillic acid derivatives, azobenzene and a-cyclodextrin (a-CD) host-guest complexes.

Accordingly, the present invention also relates to an electrode precursor structure as described herein, wherein said UV-VIS cleavable bonds are carbon-oxygen bonds. The present invention also relates to an electrode precursor structure as described herein, wherein said one release layer or at least one of said more than one release layers comprises one or more photo cleavable units selected from the group consisting of o- nitrobenzyl alcohol, alpha-ketoester, benzyl alcohol, truxillic acid derivatives, azobenzene and a-cyclodextrin (a-CD) host-guest complexes.

In a preferred aspect of the present invention, the surface of the release layer has a mean peak to valley roughness (Rz) of less than or equal to about 2 μητι, less than or equal to about 1.5 μητι, less than or equal to about 1 μητι, less than or equal to about 0.9 μητι, less than or equal to about 0.8 μητι, less than or equal to about 0.7 μητι, less than or equal to about 0.6 μητι, or less than or equal to about 0.5 μιτι. Correspondingly, the surface of the release layer preferably exhibits an Rz of greater than or equal to about 0.1 μητι, greater than or equal to about 0.2 μητι, greater than or equal to about 0.4 μητι, greater than or equal to about 0.6 μητι, greater than or equal to about 0.8 μητι, or greater than or equal to about 1 μητι. Combinations of the above-noted ranges are possible (e.g., an Rz of greater than or equal to about 0.1 μιτι and less than or equal to about 1 μητι). Preferably, the mean peak to valley roughness of the release layer is less than the mean peak to valley roughness of the carrier substrate.

The surface roughness (e.g., the mean peak to valley roughness (Rz)) may be calculated, for example, by imaging the surface with a non-contact 3D optical microscope (e.g., an optical profiler). Briefly, an image may be acquired at a magnification between about 5X and about 1 10X (e.g., an area of between about 50 micrometer x 50 micrometer and about 1.2 mm x 1.2 mm) depending on the overall surface roughness. Those skilled in the art would be capable of selecting an appropriate magnification for imaging the sample. The mean peak to valley roughness can be determined by taking an average of the height difference between the highest peaks and the lowest valleys for a given sample size (e.g., averaging the height difference between the five highest peaks and the five lowest valleys across the imaged area of the sample) at several different locations on the sample (e.g., images acquired at five different areas on the sample).

Accordingly, the present invention also relates to an electrode precursor structure as described herein, wherein the mean peak to valley roughness of said one release layer or at least one of said more than one release layers on one or both sides of the layer is in the range of from 0.1 μιτι to 1 μητι. The present invention also relates to an electrode precursor structure as described herein, wherein the mean peak to valley roughness of said one release layer or at least one of said more than one release layers is less than the mean peak to valley roughness of the carrier substrate.

Preferably, the electrode precursor structure of the present invention further comprises at least one Li ion conducting layer. Preferably, the at least one Li ion conducting layer is a ceramic layer. Preferably, the thickness of the at least one Li ion conducting layer is greater, more preferably at least two times greater, than the mean peak to valley roughness of said one release layer or at least one of said more than one release layers. In view of the above, the thickness of the at least one Li ion conducting layer preferably is less than or equal to about 5 μητι, less than or equal to about 2 μητι, less than or equal to about 1.5 μητι, less than or equal to about 1.4 μητι, less than or equal to about 1.3 μητι, less than or equal to about 1.2 μητι, less than or equal to about 1.1 μητι, less than or equal to about 1 μητι, less than or equal to about 0.9 μητι, less than or equal to about 0.8 μητι, less than or equal to about 0.7 μητι, less than or equal to about 0.6 μητι, less than or equal to about 0.5 μητι, less than or equal to about 0.4 μητι, less than or equal to about 0.3 μητι, less than or equal to about 0.2 μητι, less than or equal to about 0.1 μητι, less than or equal to about 50 nm, or less than or equal to about 30 nm. Correspondingly, the thickness of the at least one Li ion conducting layer preferably is greater than or equal to about 10 nm, greater than or equal to about 30 nm, greater than or equal to about 50 nm, greater than or equal to about 0.1 μιτι, greater than or equal to about 0.2 μητι, greater than or equal to about 0.3 μιτι, greater than or equal to about 0.4 μητι, greater than or equal to about 0.6 μητι, greater than or equal to about 0.8 μιτι, greater than or equal to about 1 μητι, greater than or equal to about 1.2 μιτι, greater than or equal to about 1.4 μιτι, or greater than or equal to about 1.5 μιτι. Combinations of the above are possible (e.g., a thickness of the at least one Li ion conducting layer may be less than or equal to about 5 μιτι and greater than or equal to about 0.1 μιτι).

It is also preferred that the electrode precursor structure of the present invention further comprises at least one Li metal layer.

Furthermore, it is preferred that the electrode precursor structure of the present invention further comprises at least one current collector. Materials for the current collector are preferably selected from metals (e.g., copper, nickel, aluminum, passivated metals, and other appropriate metals); metallized polymers; electrically conductive polymers; poly- mers including conductive particles dispersed therein; and other appropriate materials. In a preferred aspect of the present invention, the current collector is deposited onto the electrode layer using physical vapor deposition, chemical vapor deposition, electrochemical deposition, sputtering, doctor blading, flash evaporation, or any other appropriate deposition technique for the selected material. Alternatively, the current collector might be formed separately and bonded to the electrode structure.

Accordingly, the present invention also relates to an electrode precursor structure as described herein, further comprising at least one Li ion conducting layer, wherein preferably the at least one Li ion conducting layer is a ceramic layer, wherein preferably the thickness of the at least one Li ion conducting layer is greater, more preferably at least two times greater, than the mean peak to valley roughness of said one release layer or at least one of said more than one release layers. The present invention also relates to an electrode precursor structure as described herein, wherein the thickness of the at least one Li ion conducting layer is between 0.1 μιτι and 5 μιτι. Further, the present invention relates to an electrode precursor structure as described herein, further comprising at least one Li metal layer. Furthermore, the present invention relates to an electrode precursor structure as described herein, further comprising at least one current collector.

Conductivity of the release layer may be provided either through intrinsic lithium ion conductivity of the material in the dry state, or the release layer may comprise a polymer that is capable of being swollen by an electrolyte to form a gel polymer exhibiting conductivity in the wet state. Preferably, the polymer is an amorphous polymer. Preferably, the release layer exhibits conductivities of greater than or equal to about 10~7 S/cm, greater than or equal to about 10~6 S/cm, greater than or equal to about 10~5 S/cm, greater than or equal to about 10~4 S/cm, greater than or equal to about 10 3 S/cm, greater than or equal to about 10"2 S/cm, greater than or equal to about 10"1 S/cm in either the dry or wet state. Correspondingly, the release layer preferably exhibits conductivities of less than or equal to about 10~1 S/cm, less than or equal to aboutI O"2 S/cm, less than or equal to about 10 3 S/cm in either the dry or wet state. Combinations of the above are possible (e.g., a conductivity of greater than or equal to about 10~4 S/cm and less than or equal to about 10~1 S/cm).

In a preferred aspect of the present invention, the release layer includes a polymer that is conductive to certain ions (e.g., alkali metal ions) but is also substantially electrically conductive. Preferred electrically conductive polymers (also known as electronic polymers or conductive polymers) are doped with lithium salts selected from the group consisting of LiSCN, LiBr, Lil, LiCI04, LiAsF6, LiS03CF3, LiS03CH3, LiBF4, LiB(Ph)4, LiPF6, LiC(S02CF3)3, and LiN(S02CF3)2). Preferred conductive polymers are selected from the group consisting of poly(acetylene)s, poly(pyrrole)s, poly(thiophene)s, poly(aniline)s, poly(fluorene)s, polynaphthalenes, poly(p-phenylene sulfide), and poly(para-phenylene vinylene)s. Electrically-conductive additives may also be added to polymers to form electrically-conductive polymers.

Accordingly, the present invention also relates to an electrode precursor structure as described herein, wherein said one release layer or at least one of said more than one release layers forms a gel polymer layer upon contact with the electrolyte of an electrochemical cell. The present invention also relates to an electrode precursor structure as described herein, wherein said one release layer or at least one of said more than one release layers comprises an amorphous polymer. Further, the present invention relates to an electrode precursor structure as described herein, wherein upon contact with the electrolyte of an electrochemical cell said one release layer or at least one of said more than one release layers is conductive to lithium ions and/or wherein said one release layer or at least one of said more than one release layers comprises a lithium salt. The present invention also relates to an electrode precursor structure as described herein, wherein said one release layer or at least one of said more than one release layers functions as a separator. The percent difference in adhesive strength between the release layer and the two surfaces with which the release layer is in contact may be calculated by taking the difference between the adhesive strengths at these two interfaces. For instance, for a release layer positioned between two layers (e.g., between a carrier substrate and a Li ion conducting layer), the adhesive strength of the release layer on the first layer (e.g., a carrier sub- strate) can be calculated, and the adhesive strength of the release layer on the second layer (e.g., a Li ion conducting layer) can be calculated. The smaller value can then be subtracted from the larger value, and this difference divided by the larger value to determine the percentage difference in adhesive strength between each of the two layers and the release layer. In a preferred aspect of the present invention, this percent difference in adhesive strength is greater than or equal to about 20%, greater than or equal to about 30%, greater than or equal to about 40%, greater than or equal to about 50%, greater than or equal to about 60%, greater than or equal to about 70%, or greater than or equal to about 80%. The percentage difference in adhesive strength may be tailored by methods described herein, such as by choosing appropriate materials for each of the layers. In another preferred aspect of the present invention, an adhesive strength between the release layer and the Li ion conducting layer is greater than an adhesive strength between the release layer and the carrier substrate.

Adhesion and/or release between a release layer and components of an electrochemical cell may involve associations such as adsorption, absorption, Van der Waals interactions, hydrogen bonding, covalent bonding, ionic bonding, cross linking, electrostatic interactions, and combinations thereof. The type and degree of such interactions can also be tailored by methods described herein.

The adhesive strength may also be determined by a peel adhesion test (e.g., FINAT Test Method No. 2 (FTM 2)). Briefly, the peel adhesion test uses a tensile testing machine to measure the force required to peel a first layer (e.g., a polymer layer) from a second layer (e.g., an ion conducting layer, a carrier substrate), by removing the first layer from the second layer at a 90° angle at a constant speed (e.g., between about 0.505 mm/min and about 1 143 mm/min). Those skilled in the art would be capable of selecting an appropriate speed for the test based upon the relative adhesion strength and/or film mechanical strength of the first and second layers. Preferably, the adhesive strength is determined by a peel adhesion test by removing the first layer from the second layer at a 90° angle at a constant speed of about 254 mm/min

Accordingly, the present invention also relates to an electrode precursor structure as described herein, wherein an adhesive strength between said one release layer or at least one of said more than one release layers and the at least one Li ion conducting layer is greater than an adhesive strength between said one release layer or at least one of said more than one release layers and the carrier substrate.

In another aspect, the present invention relates to an electrode structure obtainable by providing or preparing an electrode precursor structure according to the present invention, wherein said one release layer or at least one of said more than one release layers is a release layer obtainable by exposing to UV-VIS radiation a release layer as defined above so that the UV-VIS cleavable bonds are cleaved and

removing the carrier substrate from said one release layer or said at least one of said more than one release layers.

Such electrode structure is an electrode structure comprising:

at least one electrode comprising lithium metal or lithium alloy,

and

one or more release layers, wherein said one release layer or at least one of said more than one release layers is a release layer obtainable by exposing to UV-VIS radiation a release layer (intermediate release layer) which comprises one or more polymers with UV-VIS cleavable bonds, so that the UV-VIS cleavable bonds are cleaved. In a further aspect, the present invention relates to an electrochemical cell comprising at least one electrode structure according of the invention.

In a preferred aspect of the present invention, the electrochemical cell as described herein further comprises an electrolyte. The electrolyte may comprise one or more ionic electrolyte salts to provide ionic conductivity and one or more liquid electrolyte solvents, gel polymer materials, or polymer materials. Preferred non-aqueous electrolytes include organic electrolytes comprising one or more materials selected from the group consisting of liquid electrolytes, gel polymer electrolytes, and solid polymer electrolytes. Non-aqueous liquid electrolyte solvents include, but are not limited to, non-aqueous organic solvents, which are preferably selected from the group consisting of N-methyl acetamide, acetonitrile, acetals, ketals, esters, carbonates, sulfones, sulfites, sulfolanes, aliphatic ethers, acyclic ethers, cyclic ethers, glymes, polyethers, phosphate esters, siloxanes, dioxolanes, N-alkylpyrrolidones, substituted forms of the foregoing, and blends thereof. Preferred acyclic ethers are selected from the group consisting of diethyl ether, dipropyl ether, dibutyl ether, dimethoxymethane, trimethoxymethane, dimethoxyethane, diethoxyethane, 1 ,2-dimethoxypropane, and 1 ,3-dimethoxypropane. Preferred cyclic ethers are selected from the group consisting of tetrahydrofuran, tetrahydropyran, 2- methyltetrahydrofuran, 1 ,4-dioxane, 1 ,3-dioxolane, and trioxane. Preferred polyethers are selected from the group consisting of diethylene glycol dimethyl ether (diglyme), triethylene glycol dimethyl ether (triglyme), tetraethylene glycol dimethyl ether (tetraglyme), higher glymes, ethylene glycol divinylether, diethylene glycol divinylether, triethylene glycol divinylether, dipropylene glycol dimethyl ether, and butylene glycol ethers. Preferred sulfones are selected from the group consisting of sulfolane, 3-methyl sulfolane, and 3-sulfolene. Fluorinated derivatives of the foregoing may also be used as liquid electrolyte solvents. Mixtures of the solvents described herein can also be used.

Preferred mixtures of solvents are selected from 1 ,3-dioxolane and dimethoxyethane, 1 ,3- dioxolane and diethyleneglycol dimethyl ether, 1 ,3-dioxolane and triethyleneglycol dimethyl ether, and 1 ,3-dioxolane and sulfolane. The weight ratio of the two solvents in the mixtures preferably vary from about 5 : 95 to 95 : 5.

Preferred gel polymer electrolytes are selected from the group consisting of polyethylene oxides, polypropylene oxides, polyacrylonitriles, polysiloxanes, polyimides, polyphosphazenes, polyethers, sulfonated polyimides, perfluorinated membranes (NAFION resins), polydivinyl polyethylene glycols, polyethylene glycol diacrylates, polyethylene glycol dimethacrylates, derivatives of the foregoing, copolymers of the foregoing, crosslinked and network structures of the foregoing, and blends of the foregoing. Preferred solid polymer electrolytes are selected from the group consisting of polyethers, polyethylene oxides, polypropylene oxides, polyimides, polyphosphazenes, polyacrylonitriles, polysiloxanes, derivatives of the foregoing, copolymers of the foregoing, crosslinked and network structures of the foregoing, and blends of the foregoing.

Preferably, the non-aqueous electrolyte comprises at least one lithium salt. Preferably, the at least one lithium salt is selected from the group consisting of LiN03, LiPF6, LiBF4, UCIO4, LiAsF6, Li2SiF6, LiSbF6, LiAICI4, lithium bis-oxalatoborate, UCF3SO3, LiN(S02F)2, LiC(CnF2n+iS02)3, wherein n is an integer in the range of from 1 to 20, and (CnF2n+iS02)m I-i with n being an integer in the range of from 1 to 20, m being 1 when X is selected from oxygen or sulfur, m being 2 when X is selected from nitrogen or phos- phorus, and m being 3 when X is selected from carbon or silicon.

Accordingly, the present invention also relates to an electrochemical cell as described herein, wherein the electrochemical cell comprises an electrolyte.

In a preferred aspect of the present invention, the release layer forms a gel upon contact with the electrolyte. Accordingly, the present invention also relates to an electrochemical cell as described herein, wherein said one release layer or said at least one of said more than one release layers forms a gel polymer layer upon contact with electrolyte.

In a further aspect, the present invention relates to an electrochemical cell obtainable by contacting an electrode structure of the invention, wherein said one release layer or at least one of said more than one release layers is a release layer obtainable by exposing to UV-VIS radiation a release layer as defined above so that the UV-VIS cleavable bonds are cleaved, with a non-aqueous electrolyte, so that the release layer is at least partially, preferably completely, dissolved in the non-aqueous electrolyte.

Preferably, the electrochemical cell as described herein, further comprising at least one cathode comprising sulfur as electroactive material. "Electroactive sulfur-containing materials" as used herein relates to cathode active materials which comprise the element sulfur in any form, wherein the electrochemical activity involves the breaking or forming of sulfur-sulfur covalent bonds. Preferred electroactive sulfur-containing materials are selected from elemental sulfur and organic materials comprising sulfur atoms and carbon atoms, which may or may not be polymeric. Organic materials include those further comprising heteroatoms, conductive polymer segments, composites, and conductive polymers.

Preferably, the sulfur-containing material, in its oxidized form, comprises a polysulfide moiety, Sm, selected from the group consisting of covalent Sm moieties, ionic Sm moie- ties, and ionic Sm2" moieties, wherein m is an integer equal to or greater than 3. Preferably, m of the polysulfide moiety Sm of the sulfur-containing polymer is an integer equal to or greater than 6. More preferably, m of the polysulfide moiety Sm of the sulfur-containing polymer is an integer equal to or greater than 8. In a preferred aspect of the present invention, the sulfur-containing material is a sulfur-containing polymer. In another pre- ferred aspect of the present invention, the sulfur-containing polymer has a polymer backbone chain and the polysulfide moiety Sm is covalently bonded by one or both of its terminal sulfur atoms as a side group to the polymer backbone chain. In yet another preferred aspect of the present invention, the sulfur-containing polymer has a polymer backbone chain and the polysulfide moiety Sm is incorporated into the polymer backbone chain by covalent bonding of the terminal sulfur atoms of the polysulfide moiety.

Preferably, the electroactive sulfur-containing material comprises more than 50% by weight of sulfur. More preferably, the electroactive sulfur-containing material comprises more than 75% by weight of sulfur. Most preferably, the electroactive sulfur-containing material comprises more than 90% by weight of sulfur. The nature of the electroactive sulfur-containing materials useful in the practice of this invention may vary widely, as known in the art. In a preferred aspect of the present invention, the electroactive sulfur-containing material comprises elemental sulfur. In another preferred aspect of the present invention, the electroactive sulfur-containing material comprises a mixture of elemental sulfur and a sulfur-containing polymer. Accordingly, the present invention also relates to an electrochemical cell as described herein, further comprising at least one cathode comprising sulfur as a cathode active species, wherein preferably the cathode includes elemental sulfur as a cathode active species. In a further aspect, the present invention also relates to a battery comprising at least one electrochemical cell of the invention.

In another aspect, the present invention relates to a process for preparing an electrode structure of the invention, comprising in ascending order the steps of

- preparing or providing a carrier substrate,

preparing or providing one or more release layers as herein,

contacting said one release layer or one of the more than one release layers with the carrier substrate so that said one release layer or one of the more than one release layers adheres to the carrier substrate.

- optionally preparing or providing a lithium conductive layer

preparing or providing at least one active material comprising lithium metal or lithium alloy,

optionally preparing or providing the current collector.

Preferably, the process for preparing an electrode structure of the invention comprises the following further steps:

exposing said one release layer or one of the more than one release layers adhering to the carrier substrate to UV-VIS radiation so that the UV-VIS cleavable bonds are cleaved,

optionally, after cleaving said bonds removing the carrier substrate from said one release layer or said one of the more than one release layers.

Preferably, in the process for preparing an electrode structure of the invention as described herein, said step of exposing said one release layer or said one of the more than one release layers to UV-VIS radiation is carried out by directing UV-VIS radiation through the carrier substrate onto said one release layer or said one of the more than one release layers.

Preferably, in the process for preparing an electrode structure of the invention as described herein, said step of removing the carrier substrate from said one release layer or one of the more than one release layers is carried out by peeling off the carrier substrate from said one release layer or said one of the more than one release layers. In another aspect, the present invention relates to the use of a polymer comprising UV- VIS cleavable bonds in the production of a release layer for electrode structures.

The present invention is further illustrated by the following examples and figures.

FIG. 1A shows an electrode precursor structure including an electroactive material layer, an optional intervening layer, a release layer, and a carrier substrate according to one set of examples of the present invention;

FIG. 1 B shows an electrode formed by the use of the release layer and carrier substrate shown in FIG. 1A according to one set of examples of the present invention;

FIG. 2 is an exemplary schematic of the synthesis of 2-Nitro-1 ,3-benzenedimethanol. FIG. 3 is an exemplary schematic of the synthesis of o-nitro-benzyl (ONB) moieties.

FIG. 1A shows an electrode precursor structure according to one set of examples of the present invention that includes a release layer. As shown in the illustrative example of FIG. 1A, electrode precursor structure 10 includes several layers that are stacked together to form an electrode 12 (e.g., an anode or a cathode). Electrode 12 can be formed by positioning the layers on a carrier substrate 20. For example, electrode 12 may be formed by first positioning one or more release layers 24 on a surface of carrier substrate 20. As described in more detail hereinabove and below, the release layer serves to subsequently release the electrode 12 from the carrier substrate 20 so that the carrier substrate is not incorporated into the final electrochemical cell. To form the electrode, an electrode com- ponent such as optional intervening layer 26 (e.g., an ion conductive layer, such as a Li ion conductive layer described herein) can be positioned adjacent the release layer on the side opposite the carrier substrate. Subsequently, an electroactive material layer 28 may be positioned adjacent optional intervening layer 26, or on the release layer directly in examples in which the intervening layer is not present. As such, in some examples, electroactive material layer 28 is positioned directly adjacent one or more release layers 24. In some examples, an optional current collector (not shown) may be positioned adjacent surface 29 of electroactive material layer 28.

After electrode precursor structure 10 has been formed, the carrier substrate 20 may be released from the electrode through the use of release layer 24. As described herein, this release process may be facilitated by exposing at least a portion of the electrode precur- sor structure, and/or the release layer within the structure, to UV-VIS radiation. This exposure may, in some examples, cleave a photo-cleavable bond within the release layer. Release layer 24 can be either released along with the carrier substrate 20 so that the release layer is not a part of the final electrode structure, or the release layer 24 may remain a part of the final electrode structure 12 as shown illustratively in FIG. 1 B.

The positioning of the release layer during release of the carrier substrate can be varied by tailoring the chemical and/or physical properties of the release layer. For example, if it is desirable for the release layer 24 to be part of the final electrode structure 12, as shown in FIG. 1 B, the release layer 24 may be tailored to have a greater adhesive affinity to optional intervening layer 26 or electroactive material layer 28 relative to its adhesive affinity to carrier substrate 20. On the other hand, if it is desirable for the release layer to not be part of an electrode structure, the release layer may be designed to have a greater adhesive affinity to carrier substrate 20 relative to its adhesive affinity to optional intervening layer 26 or electroactive material layer 28 (e.g., when no intervening layer is present). In the latter case, when a peeling force is applied to carrier substrate 20 (and/or to the electrode), the release layer is released from optional intervening layer 26 or electroactive material layer 28 (e.g., when no intervening layer is present) and remains on substrate 20.

In certain examples, carrier substrate 20 is left intact with electrode 12 as a part of elec- trade precursor structure 10 after fabrication of the electrode, but before the electrode is incorporated into an electrochemical cell. For instance, electrode precursor structure 10 may be packaged and shipped to a manufacturer who may then incorporate electrode 12 into an electrochemical cell. In such examples, electrode precursor structure 10 may be inserted into an air and/or moisture-tight package to prevent or inhibit deterioration and/or contamination of one or more components of the electrode precursor structure. Allowing carrier substrate 20 to remain attached to electrode 12 can facilitate handling and transportation of the electrode. For instance, carrier substrate 20 may be relatively thick and have a relatively high rigidity or stiffness, which can prevent or inhibit electrode 12 from distorting during handling. In such examples, carrier substrate can be removed by the manufacturer before, during, or after assembly of an electrochemical cell.

Although FIG. 1A shows release layer 24 positioned between carrier substrate 20 and optional intervening layer 26, in other examples the release layer may be positioned between other components of an electrode. For example, the release layer may be positioned adjacent surface 29 of electroactive material layer 28, and the carrier substrate may be positioned on the opposite side of the electroactive material layer (not shown). In some such examples, an electrode may be fabricated by first positioning one or more release layers onto a carrier substrate, followed by positioning of an electroactive material layer on the release layer. Afterwards, any other suitable layers such as a current collec- tor may be positioned on the electroactive material layer. To form the electrode, the carrier substrate can be removed from the electroactive material layer via the release layer. The release layer may remain with the electrode or may be released along with the carrier substrate.

It should be understood that when a portion (e.g., layer, structure, region) is "on", "adja- cent", "above", "over", "overlying", or "supported by" another portion, it can be directly on the portion, or an intervening portion (e.g., layer, structure, region) also may be present. Similarly, when a portion is "below" or "underneath" another portion, it can be directly below the portion, or an intervening portion (e.g., layer, structure, region) also may be present. A portion that is "directly on", "immediately adjacent", "in contact with", or "direct- ly supported by" another portion means that no intervening portion is present. It should also be understood that when a portion is referred to as being "on", "above", "adjacent", "over", "overlying", "in contact with", "below", or "supported by" another portion, it may cover the entire portion or a part of the portion.

It should be understood, therefore, that in the examples illustrated in FIGs. 1A and 1 B and in other examples described herein, one or more additional layers may be positioned between the layers shown in the figures. For example, one or more additional layers (e.g., a second release layer) may be positioned between electroactive material layer 28 and release layer 24, and/or one or more additional layers (e.g., a second release layer) may be positioned between release layer 24 and carrier substrate 20. Furthermore, one or more layers may be positioned between other components of the cell.

Although FIGs. 1A and 1 B show a single release layer 24 as part of electrode precursor structure 10, any suitable number of release layers may be used. For example, a release system may include 2, 3, 4 or more layers. The number of layers used in a release system may depend at least in part on whether the release layer(s) is to be incorporated into the final electrochemical cell, or whether the release layer(s) is removed along with the carrier substrate.

In other examples, however, more than one release layer is used to fabricate a component of an electrochemical cell. For instance, a first release layer may be positioned adjacent a carrier substrate and may have, for example, a relatively high adhesive affinity to the carrier substrate. The first release layer may be chosen because it is compatible with certain processing conditions, but it may have a relatively high adhesive affinity to a second surface (e.g., optional intervening layer 26 or the electroactive material layer of FIG. 1A). In such examples, the release layer would not allow release of the carrier substrate. Thus, a second release layer may be positioned between the first release layer and the second surface to allow adequate release of the carrier substrate. In one example, the second release layer has a relatively high adhesive affinity to the first release layer, but a relatively low adhesive affinity to the second surface. As such, the application of a force could allow removal of the carrier substrate and both release layers from the second surface. In another example, the second release layer has a relatively low adhesive affinity to the first release layer and relatively high adhesive affinity to the second surface. In such examples, the application of a force could allow removal of the carrier substrate and the first release layer, which the second release layer and the second surface remain intact. Other configurations of release layers are also possible.

In certain examples, the electrode precursor structure as described herein comprises one or more release layers (e.g., a first release layer and a second release layer adjacent the first release layer). The release layer may be ionically conductive.

Evaluation of photoactive release layer polymers 1. Precursor Synthesis

The two step synthesis of 2-Nitro-1 ,3-benzenedimethanol (3) as key precursor was carried out as follows (Figure 2). As initial step 1 ,3-dimethyl-2-nitrobenzene (1 ) was oxidized with KMn04 to 2-Nitro-isophthalic acid (2) and subsequently reduced with borane- tetrahydrofuran complex to yield 2-Nitro-1 ,3-benzenedimethanol (3).

Figure imgf000023_0001

Synthesis of 2-Nitro-1 ,3-benzenedimethanol (3) 1.1. Synthesis of 2-Nitro-isophthalic acid (2)

A stirred mixture of 15.8 g (0.105 mol) 1 ,3-dimethyl-2-nitrobenzene (1), 800 ml water and 6.4 g (0.16 mol) sodium hydroxide was heated to 95 °C, then 66 g (0.418 mol) KMn04 was added in portions over a period of three hours. The resulting mixture was refluxed for another 20 hours, cooled and filtered and dried to give 16.5 g (0.078 mol, 53 %, M = 21 1.13 g/mol)) 2-Nitro-isophthalic acid (2) as white pure solid. H-NMR (d5-THF, 500 MHz): δ = 8.2 ppm (2 H, m, aromatic), 7.7 ppm (1 H, m, aromatic).

1.2 Synthesis of 2-Nitro-1 ,3-benzenedimethanol (3)

A solution of 21.2 g (0.1 mol) 2-Nitro-isophthalic acid (2) in 100 ml of THF was cooled to 0 °C and 500 ml (0.5 mol) 1 N borane-tetrahydrofuran was added dropwise over one hour. The mixture was allowed to warm slowly to 25 °C and stirred for 36 hours. 85 ml methanol was added slowly and the mixture was filtered and evaporated. The residue was dissolved in 160 ml ethyl acetate and washed with 40 ml water, dried over MgS04, filtered and evaporated to yield a yellow solid which was further purified by chromatography over silica (cyclohexane / ethylacetate) to give 9.9 g (0.055 mol; M = 179.13 g/mol) 2-Nitro-1 ,3- benzenedimethanol (3). Mp: 99 °C. H-NMR (d5-THF, 500 MHz): δ = 7.5 - 7.6 ppm (3 H, m, aromatic), 4.6 ppm (4 H, d, -CH2OH), 4.5 ppm (2 H, bs, -CH2OH).

2. Preparation of functional polymer release layers

For formulation of release layer films 2-Nitro-1 ,3-benzenedimethanol (3) was combined with Lupranat M50W as crosslinking building block and Pluriol 6000 as structural motif for conferring lithium ion conductivity (Figure 3). All three components were combined in equimolar ratios (mol/mol) and same weight ratios (wt/wt).

Figure imgf000024_0001

Lupranat M50 2-Nitro-1 ,3-benzene-dimethanol (3) Pluriol E 6000

Formulation of o-nitro-benzyl (ONB) moieties containing release layer layers The three components were prepared as 30 wt% solutions in diglyme, then casted on the carrier substrate (glass, nickel or PET) at 50 °C and dried in vacuum overnight. Free standing films were obtained by immersion of the coated substrate in water after film drying. 2.1 Preparation of free standing films

1 g of 30 wt% Pluriol E 6000 solution in dioxolane was mixed with 1 g of 30 wt% solution of 2-Nitro-1 ,3-benzenedimethanol (3) in diglyme and subsequently 0.45 g Lupranat M50W were added. The solution was coated as 100 μιτι film on glass by the means of doctor blading and dried. Then the coated glass plate was submerged in water and the freestanding film after obtained delamination and drying under vacuum.

2.2 Preparation of films coated on nickel substrate

1 g of 30 wt% Pluriol E 6000 solution in dioxolane was mixed with 1 g of 30 wt% solution of 2-Nitro-1 ,3-benzenedimethanol (3) in diglyme and subsequently 0.45 g Lupranat M50W were added. The solution was coated as 60 μιτι film on glass by the means of doctor blading and dried. The coated nickel substrates were dried over a period of 24 hours under vacuum at 80° and used for conductivity measurements.

3. Photoisomerization

The photoisomerization treatment was carried out with UV-F 450 lamp from Panacol- Elosol GmbH which provides UV-A (315 bis 380) nm with intensities up to 200mW/cm2. 4. Lithium ion conductivity

The evaluation of lithium ion conductivity was performed in Pouch cells (10 cm x 10 cm) with nickel electrodes. The films were placed in between two nickel plates (3.6 cm x 3.4 cm) and a Celgard 2325 separator or directly coated nickel electrodes were used. Then 0.5 ml electrolyte 1 ,2-dimethyl ether / 1 ,3-dioxolane (1 : 1 , vol, vol), 16 wt% lithium bis trifluoromethanesulfonimide (LiTFSI), 4 wt% LiN02 and 1 wt% guanidiumnitrate (DD 16-4- 1 ) were added before the Pouch bag was sealed. The pure electrolyte conductivity DD 16-4-1 accounts for 8.37 χ 10~3 S/cm. The cells were allowed to rest for two hours to complete the solvent take up. 5 kg weight were placed to exert pressure on the cell (5 kg / 15 cm2 = 0.33 kg/cm2) then the ionic conductivity was determined using impedance spectroscopy (Zahner IM6eX) in the frequency range from 10Hz to 1 Mhz with an amplitude of 50 mV. From the Nyquist diagram the ohmic resistance was determined and the conductivity of the sample calculated. Table 1 summarizes the results obtained.

Table 1 : Conductivities of o-nitro-benzyl (ONB) moieties containing release layers

Film No. UV irradiation composition type σ [S/cm]

1 Yes 1 : 1 : 1 (wt : wt: wt) Ni-coated 1.0 x 10~4

2 Yes 1 : 1 : 1 (wt : wt: wt) Ni-coated 2.6 x 10~4

3 Yes 1 : 1 : 1 (mol : mol: mol) Ni-coated 6.7 x 10~4

4 Yes 1 : 1 : 1 (mol : mol: mol) Ni-coated 9.3 x 10~4

Results and discussion

1. Conductivity

Lithium ion conductivities of o-nitro-benzyl (ONB) moieties containing release layers after UV treatment resulted in values in the range of 1.0 χ 10"4 to 9.3 χ 10~4 S/cm thus being sufficient for electrochemical operation in lithium-sulfur cells.

2. Adhesion properties - Releasability

All crosslinked ONB polyimide films were subjected to simple testing procedure regarding their release ability. The release ability on optical grade PET and glass surface was tested by peeling off a Tesa tape sticking on the polymer surface. Table 2 summarizes the release properties depending on their composition. As result, UV treatment weakens the release layer network and allows releasability from PET carrier.

Table 2: Adhesion properties o-nitro-benzyl (ONB) moieties containing release layers Film No. UV irradiation composition Release PET

1 No 1 : 1 : 1 (wt : wt: wt)

2 Yes 1 : 1 : 1 (wt : wt: wt)

3 No 1 : 1 : 1 (mol : mol: mol)

4 Yes 1 : 1 : 1 (mol : mol: mol)

(/ release, no release)

Summary

O-nitro-benzyl (ONB) moieties containing release layers have been synthesized and evaluated regarding their potential to perform as release layers in lithium sulfur cells. UV treatment was found to improve the release layer functionality and in addition, lithium ion conductivities of the resulting being sufficient for electrochemical operation in lithium- sulfur cells.

Claims

An electrode precursor structure comprising:
at least one active material comprising lithium metal or lithium alloy, a carrier substrate, and
one or more release layers adhering to the carrier substrate,
wherein said one release layer or at least one of said more than one release layers a) is a release layer which comprises one or more polymers with UV-VIS cleavable bonds, wherein the adhesion to the carrier substrate is reducible by UV-VIS cleaving said bonds,
or
b) is a release layer obtainable by exposing to UV-VIS radiation a release layer as defined under item a) so that the UV-VIS cleavable bonds are cleaved.
The electrode precursor structure according to claim 1 , wherein the carrier substrate is selected from the group consisting of polymer films, metalized polymer films, ceramic films and metal films.
The electrode precursor structure according to claim 1 or 2, wherein said UV-VIS cleavable bonds are carbon-oxygen bonds.
The electrode precursor structure according to any of claims 1 to 3, wherein said one release layer or at least one of said more than one release layers comprises one or more photo cleavable units selected from the group consisting of o- nitrobenzyl alcohol, alpha-ketoester, benzyl alcohol, truxillic acid derivatives, azobenzene and a-cyclodextrin (a-CD) host-guest complexes.
The electrode precursor structure according to any of claims 1 to 4, wherein the mean peak to valley roughness of said one release layer or at least one of said more than one release layers on one or both sides of the layer is in the range of from 0.1 pm to 1 pm.
The electrode precursor structure according to any of claims 1 to 5, further comprising at least one Li ion conducting layer.
7. The electrode precursor structure according to any of claims 1 to 6, further comprising at least one Li metal layer.
8. The electrode precursor structure according to any of claims 1 to 7, further comprising at least one current collector.
The electrode precursor structure according to any of claims 1 to 8, wherein said one release layer or at least one of said more than one release layers forms a gel polymer layer upon contact with the electrolyte of an electrochemical cell.
The electrode precursor structure according to any of claims 6 to 9, wherein the at least one Li ion conducting layer is a ceramic layer.
The electrode precursor structure according to any of claims 6 to 10, wherein the thickness of the at least one Li ion conducting layer is greater than the mean peak to valley roughness of said one release layer or at least one of said more than one release layers.
The electrode precursor structure according to any of claims 6 to 1 1 , wherein the thickness of the at least one Li ion conducting layer is at least two times greater than the mean peak to valley roughness of said one release layer or at least one of said more than one release layers.
The electrode precursor structure according to any of claims 6 to 12, wherein the thickness of the at least one Li ion conducting layer is between 0.1 μηι and 5 μιτι.
The electrode precursor structure according to any of claims 1 to 13, wherein said one release layer or at least one of said more than one release layers comprises an amorphous polymer.
The electrode precursor structure according to any of claims 6 to 14, wherein an adhesive strength between said one release layer or at least one of said more than one release layers and the at least one Li ion conducting layer is greater than an adhesive strength between said one release layer or at least one of said more than one release layers and the carrier substrate. The electrode precursor structure according to any of claims 1 to 15, wherein said one release layer or at least one of said more than one release layers functions as a separator.
The electrode precursor structure according to any of claims 1 to 16, wherein upon contact with the electrolyte of an electrochemical cell said one release layer or at least one of said more than one release layers is conductive to lithium ions and/or wherein said one release layer or at least one of said more than one release layers comprises a lithium salt.
The electrode precursor structure according to any of claims 1 to 17, wherein the mean peak to valley roughness of said one release layer or at least one of said more than one release layers is less than the mean peak to valley roughness of the carrier substrate.
An electrode structure obtainable by
providing or preparing an electrode precursor structure according to any of claims 1 to 18, wherein said one release layer or at least one of said more than one release layers is a release layer obtainable by exposing to UV-VIS radiation a release layer as defined in claim 1 , item a) so that the UV-VIS cleavable bonds are cleaved
and
removing the carrier substrate from said one release layer or said at least one of said more than one release layers.
An electrochemical cell comprising at least one electrode structure according to claim 19.
The electrochemical cell according to claim 20, wherein the electrochemical cell comprises an electrolyte.
22. The electrochemical cell according to claim 21 , wherein said one release layer or said at least one of said more than one release layers forms a gel polymer layer upon contact with electrolyte. An electrochemical cell obtainable by contacting an electrode structure according to any of claims 1 to 18, wherein said one release layer or at least one of said more than one release layers is a release layer obtainable by exposing to UV-VIS radiation a release layer as defined in claim 1 , item a) so that the UV-VIS cleavable bonds are cleaved, with a non-aqueous electrolyte, so that the release layer is at least partially, preferably completely, dissolved in the non-aqueous electrolyte.
The electrochemical cell according to any of claims 20 to 23, further comprising at least one cathode comprising sulfur as electroactive material, wherein preferably the cathode includes elemental sulfur as electroactive material.
A battery comprising at least one electrochemical cell according to any of claims 20 to 24.
26. Process for preparing an electrode precursor structure according to any of claims 1 to 19, comprising in ascending order the steps of
preparing or providing a carrier substrate,
- preparing or providing one or more release layers as defined in claim 1 , item a),
contacting said one release layer or one of the more than one release layers with the carrier substrate so that said one release layer or one of the more than one release layers adheres to the carrier substrate.
- optionally preparing or providing a lithium conductive layer
preparing or providing at least one active material comprising lithium metal or lithium alloy,
optionally preparing or providing the current collector
The process according to claim 26, comprising the following further steps:
exposing said one release layer or one of the more than one release layers adhering to the carrier substrate to UV-VIS radiation so that the UV-VIS cleavable bonds are cleaved,
optionally, after cleaving said bonds removing the carrier substrate from said one release layer or said one of the more than one release layers.
28. The process according to claim 27, wherein said step of exposing said one release layer or said one of the more than one release layers to UV-VIS radiation is carried out by directing UV-VIS radiation through the carrier substrate onto said one release layer or said one of the more than one release layers.
29. The process according to claim 27 or 28, wherein said step of removing the carrier substrate from said one release layer or one of the more than one release layers is carried out by peeling off the carrier substrate from said one release layer or said one of the more than one release layers.
30. Use of a polymer comprising UV-VIS cleavable bonds in the production of a release layer for electrode structures.
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