阅读说明：本技术 用于电池的纳米多孔分隔器以及相关的制造方法 (Nanoporous separators for batteries and related methods of manufacture ) 是由 史蒂文·A·卡尔森 本杰明·斯隆 大卫·W·埃维森 于 2016-07-11 设计创作，主要内容包括：提供了锂电池,其中所述电池包括阳极、阴极,其中所述阴极包含一种或多种过渡金属、电解质、以及在所述阴极和阳极之间插入的多孔分隔器,其中所述分隔器包含阴离子化合物。还提供了制造此类电池的方法。(A lithium battery is provided, wherein the battery comprises an anode, a cathode, wherein the cathode comprises one or more transition metals, an electrolyte, and a porous separator interposed between the cathode and anode, wherein the separator comprises an anionic compound. Methods of making such batteries are also provided.)

1. A separator for a lithium battery, comprising:

a) an unsupported inorganic oxide layer having a first surface, wherein the inorganic oxide layer comprises:

one or more inorganic oxides; and

an adhesive, and

b) an edge reinforcement area that does not completely cover the first surface.

2. The separator of claim 1, wherein the unsupported inorganic oxide layer comprises boehmite.

3. The separator of claim 1, wherein the adhesive is a polymeric adhesive.

4. The separator of claim 1, wherein the edge reinforcement region comprises a polymer.

5. The separator of claim 4, wherein at least a portion of the polymer of the edge-strengthened region is impregnated in at least a portion of the pores of the inorganic oxide layer.

6. The separator of claim 4, wherein at least a portion of the polymer of the edge-strengthening region is laminated to the inorganic oxide layer.

7. The separator of claim 1, wherein the edge-strengthened region comprises a plurality of portions disposed along two opposing cut edges of the inorganic oxide layer.

8. A lithium battery, comprising: an anode, a cathode, an electrolyte, and the separator of claim 1, wherein the cathode comprises one or more transition metals.

9. A lithium battery as in claim 8, wherein the anode comprises lithium metal.

10. A lithium battery as in claim 8, wherein the cathode comprises one or more transition metals selected from the group consisting of manganese, nickel, and cobalt.

11. The lithium battery as claimed in claim 8, wherein the polymer contained in the edge strengthening region is impregnated in at least a part of the pores of the inorganic oxide layer.

12. A lithium battery as in claim 8, wherein the layer comprising a polymer is laminated to the inorganic oxide layer at an edge strengthening region.

13. The lithium battery of claim 12, wherein the edge strengthening region comprises a plurality of portions disposed along two opposing cut edges of the separator.

Technical Field

The present invention relates generally to the field of batteries and other current generating units such as capacitors and lithium ion capacitors. More particularly, the present invention relates to separators for lithium batteries and related methods of manufacture.

Background

Throughout this application, various patents are referenced by way of reference to notations. The patent disclosures cited in this application are hereby incorporated by reference into this disclosure in order to more fully describe the state of the art to which this invention pertains.

Lithium batteries are widely used in portable electronic devices such as smart phones and portable computers. Among the new applications for lithium batteries are high power batteries for hybrid, plug-in hybrid and electric vehicles. However, the wide acceptance of electric vehicles requires batteries that can be constructed at lower cost and have improved safety features.

Existing methods for manufacturing lithium batteries (including rechargeable and non-rechargeable lithium batteries) and other types of batteries are relatively slow, complex, and expensive. For example, rechargeable lithium ion cells are typically constructed by interleaving strips (strips) of the various layers of the cell to form a stack. These layers may include a plastic separator, a conductive metal substrate coated on both sides with a cathode layer, another plastic separator, and another conductive metal substrate coated on both sides with an anode layer. Such interleaving is typically accomplished on manufacturing equipment that is inefficient and expensive to construct and operate. Thus, there is a need for manufacturing techniques that do not require interleaving discrete battery layers.

As described above, current lithium batteries are assembled using a metal substrate. During the manufacturing process, these metal substrates are typically cut into discrete battery stacks. This is known to form metal debris embedded in the separator or other portions of the finished battery, which can lead to short circuits or other dangerous conditions. Accordingly, there is a need for improved manufacturing techniques that eliminate these safety issues.

In addition, one of the known challenges in reducing the cost of lithium ion batteries is the composition of the cathode. In this regard, cathode materials often account for 30% or more of the total cell cost. Therefore, there is growing interest in using manganese and its oxides as cathode materials, since manganese is much cheaper than other cathode materials and is abundant in nature. However, manganese readily dissolves when used as a cathode in lithium ion batteries, particularly at higher temperatures. During operation, dissolved manganese ions deposit on the separator and anode, resulting in a shortened battery cycle life. Furthermore, this migration problem is not limited to manganese. In this regard, there is also a trend in the battery industry to move to cathodes comprising nickel-manganese-cobalt oxide (NMC), especially nickel-rich NMC. However, nickel ions and cobalt ions, like manganese ions, diffuse through the separator and onto the anode, which shortens the battery cycle life. It would therefore be advantageous if the migration of these metals (e.g., manganese, nickel, and cobalt) could be controlled and eliminated.

Summary of The Invention

It is an object of the invention to provide a battery stack or battery which can be assembled with less complexity and less expensively, and an automated processing device which is faster than processing devices such as those used for portable computer batteries. Another object is to provide a battery that is less expensive to manufacture than existing batteries and that can use transition metals (e.g., manganese, nickel and cobalt) but control the migration of these metals without reducing the cycle life of the battery.

The present invention meets the foregoing objects by the herein described cell stack and cell. The battery stacks and batteries described herein include various coatings and materials, which are described below. Examples of the battery to which the present invention is applied include a single current generating unit, and a plurality of current generating units combined within a case (casting) or a pack (pack). One such battery is a lithium battery, including, for example, rechargeable or secondary lithium ion batteries, non-rechargeable or primary lithium metal batteries, rechargeable lithium metal batteries, and other battery types, such as rechargeable lithium metal alloy batteries.

The battery stack described herein includes a separator, an electrode, and a current collector. The cell stack containing the positive electrode in combination with the cell stack containing the negative electrode form a cell. The battery stacks and batteries described herein include a separator to keep the two electrodes apart so as to prevent electrical shorting, while also allowing transfer of lithium ions and any other ions upon current transport in the electrochemical cell. Examples of separators that can be used for lithium batteries include ceramic separators and polyolefin separators. Ceramic separators include separators comprising inorganic oxides and other inorganic materials.

The battery stacks and batteries described herein include electrodes comprising electroactive materials. The electrode layer may be configured to function as an anode (negative electrode) or a cathode (positive electrode). In a lithium ion battery, for example, an electric current is generated when lithium ions diffuse from an anode to a cathode through an electrolyte. Examples of the electroactive material that can be used for the lithium battery include, for example, lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium nickel manganese cobalt oxide (NMC), and sulfur as the electroactive material of the cathode layer, and lithium titanate, lithium metal, silicon, lithium-intercalated graphite, and lithium-intercalated carbon as the electroactive material of the anode layer.

The battery stacks and batteries described herein also include a current collector, which may be one or more current collection layers adjacent to the electrode layers. One function of the current collector is to provide a conductive path for the current to and from the electrodes and to provide an effective electrical connection to the external circuit to the cell. The current collector may comprise, for example, a single conductive metal layer or coating, such as the sintered metal particle layers discussed herein. As discussed further below, an exemplary conductive metal layer that can function as a current collector is a layer of sintered metal particles comprising nickel, which can be used in either the anode layer or the cathode layer. In embodiments of the invention, the conductive metal layer may comprise aluminum, such as aluminum foil, which may serve as a current collector and a substrate for the positive electrode or cathode layer. In other embodiments, the conductive metal layer may comprise copper, such as copper foil, which may serve as a current collector as well as a substrate for the negative or anode layers.

The batteries described herein also include electrolytes, such as those useful in lithium batteries. Suitable electrolytes include, for example, liquid electrolytes, gel polymer electrolytes, and solid polymer electrolytes. Suitable liquid electrolytes include, for example, LiPF in a mixture of organic solvents₆Solutions of mixtures of such organic solvents as mixtures of ethylene carbonate, propylene carbonate and methylethyl carbonate.

In one embodiment, the invention includes a lithium battery comprising: an anode; a cathode, wherein the cathode comprises one or more transition metals; an electrolyte; and a porous separator interposed between the cathode and the anode, wherein the separator comprises an anionic compound. In one embodiment, the anode comprises lithium metal. In one embodiment, the cathode comprises one or more transition metals selected from manganese, nickel and cobalt. In one embodiment, the porous separator comprises one or more inorganic oxides or inorganic nitrides. In one embodiment, the separator comprises boehmite. In one embodiment, the anionic compound comprises two or more anionic groups. In one embodiment, the anionic groups are selected from sulfonate and carboxylate. In one embodiment, the cation of the anionic group comprises a lithium ion. In one embodiment, the anionic compound comprises greater than about 0.1 wt% of the weight of the porous separator. In one embodiment, the anionic compound is an anthraquinone. In one embodiment, the anionic compound is a photosensitizer. In one embodiment, the photosensitizer is an oxygen scavenger. In one embodiment, the separator comprises a polymer formed by proton absorption by the photosensitizer. In one embodiment, the anionic compound is an oxidant for lithium metal. In one embodiment, the porous separator has an average pore diameter of less than about 100 nm. In one embodiment, a scavenger of HF in the porous separator electrolyte. In one embodiment, the porous separator inhibits migration of transition metal cations through the separator. In one embodiment, the cathode and anode comprise electrode layers, and one or more electrode layers are coated on the separator.

In one embodiment, the invention includes a separator for a current generating unit comprising: one or more inorganic oxides or inorganic nitrides, a binder, and an anionic compound. In one embodiment, the anionic compound is selected from the group consisting of sulfonate and carboxylate. In one embodiment, the anionic compound is an oxidant for lithium metal dendrites. In one embodiment, the anionic compound is a photosensitizer.

In one embodiment, the invention includes a battery stack comprising: the cell stack includes a porous separator, an electrode layer adjacent to the porous separator, a current collector layer coated on the electrode layer, and a reinforcement region along one or more edges of the cell stack, wherein the reinforcement region comprises a polymer. In one embodiment, the reinforcement region comprises a polymer impregnated in the pores of the porous separator. In one embodiment, the reinforcement region comprises a layer of polymer covering the porous separator. In one embodiment, the porous separator further comprises a photosensitizer.

Brief Description of Drawings

The features and advantages of the present disclosure will be more fully understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

fig. 1 is a cross-sectional view of a partially assembled battery stack 1 showing a porous separator 20 coated on a substrate 10 and a release coating 30.

Fig. 2 is a cross-sectional view of the cell stack of fig. 1, with the addition of electrode tracks 40a,40b coated on the porous separator layer 20.

Fig. 3 is a top view of the battery stack shown in fig. 2.

Fig. 4 is a cross-sectional view of the battery stack shown in fig. 2 and 3, with the addition of a current collector layer 50 coated on the electrode tracks and a reinforcement portion 52 coated on the separator layer 20.

Fig. 5 is a top view of the battery stack of fig. 4 with conductive tab patches (tabs) 60 added to the reinforcing portion 52 and also showing cut lines S₁、S₂And S₃The position of (a).

Fig. 6 is a top view of the battery stack assembly shown in fig. 5 after a cutting step is performed.

Detailed Description

The present invention relates to battery stacks for batteries, such as lithium ion batteries and lithium metal batteries, and methods of making such batteries and related nanoporous separators. Other benefits are that the coated cell stacks and cells of the present invention have lower cost and provide improved safety.

The present invention includes, but is not limited to, the following designs for lithium batteries and stacks, and methods of making such batteries. In the following embodiments, the coated stack may be an anode stack or a cathode stack, depending on the electrode material selected.

One aspect of the present invention will be described with reference to a method of manufacturing a lithium battery. One suitable method is described in co-pending U.S. patent application No. 15/130,660, which is incorporated by reference herein in its entirety. The method may use a reusable substrate 10 on which the various layers of the battery stack are coated. Once the battery stack is assembled, the battery layers (e.g., electrodes, separators, current collectors) are disengaged from the substrate 10, and the substrate can be reused to create another battery stack according to the same method. The use of a reusable substrate provides cost savings benefits and reduces waste. It should be noted, however, that this same process can be performed using disposable or non-reusable substrates.

The first step of the method comprises coating the substrate 10 with a release coating 30. The substrate 10 and release coating 30 will be collectively referred to herein as a release layer. Substrate 10 may include any tough, heat resistant film, such as polyethylene terephthalate ("PET"), polyethylene naphthalate ("PEN"), or other polyester film. In a preferred embodiment, the substrate 10 may comprise a 75-125 μm thick PET film. PET provides a tough substrate for the disclosed process because it has high tensile strength and is chemically, thermally and dimensionally stable. Advantageously, due to the thickness, tear resistance and deformation resistance of the PET film, wide rolls (wide rolls), for example, those having a width of 1.5-2.0 meters, can be processed quickly and reliably. For example, the coated cell stack may be processed at a speed of 125 m/min.

A thermally stable and pressure resistant porous separator layer 20 is then coated on the release layer. The coated separator layer 20 can be made thinner than known unsupported separators. The coated separator layer 20 is also highly compatible with roll-to-roll coating methods, such as those described above.

In one embodiment, the separator layer is coated across the full width of the release film at a thickness of 5-8 μm. Fig. 1 shows an example of a cross-sectional view of the assembly 1 after the separator 20 is coated on the substrate 10 and the coating 30 is stripped.

Examples of suitable separator layers 20 for use in the present invention include, but are not limited to, porous separator coatings described in U.S. patent nos. 6,153,337 and 6,306,545 (Carlson et al), 6,488,721 and 6,497,780 (Carlson), and 6,277,514 (Ying et al). Some of these references disclose boehmite ceramic separator layers that are suitable for use in the present invention. See, for example, U.S. patent No. 6,153,337, column 4, lines 16-33, column 8, lines 8-33, column 9, column l.62-column 10, l.22 and column 18, column l.59-column 19, l.13; U.S. patent No. 6,306,545, column 4, l.31-column 5, l.17 and column 10, lines 30-55; and U.S. patent No. 6,488,721, column 37, lines 44-63. U.S. patent No. 6,497,780 discloses boehmite ceramic separator layers, as well as other ceramic separator layers, including those having xerogel or sol-gel structures, which are suitable for use in the present invention. See, for example, U.S. patent No. 6,497,780, column 8, l.66-column 10, l.23 and column 11, l.33-column 12, l.3. U.S. patent No. 6,277,514 teaches the application of one or more protective coatings to a boehmite ceramic separator layer. These protective coatings include inorganic layers designed to protect the surface of a metal anode, such as in a lithium metal anode. See, for example, U.S. patent No. 6,277,514, column 5, lines l.56-6, lines l.42, column 9, lines 14-30, column 10, lines 3-43, column 15, lines 27-56 and column 16, lines 32-42.

Preferred separator layers suitable for use in the present invention are also described in U.S. patent application publication No. 2013/0171500 to Xu et al. One such separator includes a microporous layer comprising (a) at least 50 wt% aluminum boehmite, and (b) an organic polymer, wherein the aluminum boehmite is surface-modified by treatment with an organic acid to form a modified aluminum boehmite. See, for example, sections 28 and 34-36. The organic acid may be a sulfonic acid, preferably an arylsulfonic acid or a toluenesulfonic acid, or a carboxylic acid. The modified boehmite may have 50 to 85% or more preferably 65 to 80% by weight of Al₂O₃And (4) content. The separator may comprise 60 to 90 wt% of the modified alumina, or more preferably 70 to 85 wt% of the modified boehmite. In embodiments of the invention, the microporous layer may be a xerogel layer. The organic polymer may include a polyvinylidene fluoride polymer. The separator layer 20 may also comprise a copolymer of a first fluorinated organic monomer and a second organic monomer.

Other preferred separator layers suitable for use in embodiments of the present invention are described in international application No. WO2014/179355 to Avison et al. The separator layers described in this application include boehmite, various other pigments, and blends thereof. See, for example, WO2014/179355, sections 4-6, 8, 21, 26 and 27. In a preferred embodiment, the separator layer 20 is a nanoporous inorganic ceramic separator. More specifically, a nanoporous battery separator comprises ceramic particles and a polymer binder, wherein the porous separator has a porosity of 35% to 50% and an average pore size of 10-90nm or more preferably 10-50 nm. The ceramic particles may be inorganic oxide particles or inorganic nitride particles. Preferably, the porous ceramic separator exhibits less than 1% shrinkage when exposed to a temperature of 200 ℃ for at least 1 hour. The ceramic particles may include Al₂O₃Or aluminum oxide, AlO (OH) or boehmite, A1N, BN, SiN, ZnO, ZrO₂、SiO₂Or a combination thereof. In a preferred embodiment, the ceramic particles comprise 65-100% boehmite and the remainder, if any, is BN. Alternatively, the ceramic particles may comprise 65-100% boehmite and the remainder, if any, being A1N. The polymeric binder may include polymers such as polyvinylidene fluoride (PVdF) and its copolymers, polyvinyl ethers, urethanes, acrylics, cellulosics, styrene-butadiene copolymers, natural rubber, chitosan, nitrile rubber, silicone elastomers, PEO or PEO copolymers, polyphosphazenes, and combinations thereof.

In one embodiment, the separator layer comprises an inorganic oxide that is surface modified by treatment with an organic sulfonic acid to form a modified inorganic oxide, and further comprises an inorganic oxide that is not surface modified by treatment with an organic sulfonic acid. In one embodiment, the organic sulfonic acid is an aryl sulfonic acid, and more preferably toluene sulfonic acid. In one embodiment, the inorganic oxide comprises boehmite. In one embodiment, boehmite is surface modified by treatment with an organic sulfonic acid to form a modified hydrated alumina. In one embodiment, the ratio by weight of the blend of treated inorganic oxide to untreated inorganic oxide is about 1:3 to 3:1, preferably about 2:3 to 3: 2. In one embodiment, a cross-linking material such as isocyanate is added to provide additional mechanical strength to the separator. Polyfunctional isocyanates are preferred. The weight percent of isocyanate is typically 1% to 10% of the weight of the polymer in the separator, with about 6% by weight being the preferred level.

In one embodiment, the separator is subjected to water extraction to remove any water soluble material, such as organic sulfonic acids, from the separator. This water extraction is preferably done before the separator is used to construct the cell stack. One method for performing such water extraction is to use a water bath immersion at about 80 ℃, which is highly compatible with the high speed manufacturing methods discussed above. In addition, anion treatment (discussed further below) can be applied to the separator at the time of immersion.

Other benefits are that water extraction increases the percent porosity of the separator, which provides better ionic conductivity of the electrolyte, and provides greater mechanical strength (for a given percent porosity) to the separator. For example, some of the organic sulfonic acid that is not covalently bound to the inorganic oxide, or some of the organic sulfonic acid that is strongly bound to the inorganic oxide, may be removed by water extraction. For example, a separator comprising an inorganic oxide treated with an organic sulfonic acid may exhibit a weight loss of about 1% via water extraction. This weight reduction is sufficient to increase the percentage porosity of the separator by 2% to 3% and to increase the mechanical strength of the separator by 10% or more.

In one embodiment of the invention, the separator is dried at a temperature of at least 130 ℃ up to 240 ℃, preferably under vacuum. In one embodiment, this drying at elevated temperature is done for more than 1 hour and preferably more than 3 hours. In one embodiment, vacuum drying is accomplished in a dry cell (cell) comprising electrodes and separators prior to filling the cell with electrolyte. High temperature drying of such separators, especially under vacuum conditions, is useful for increasing the mechanical strength of the separator, typically by at least 10%, and for reducing any residual water content that may degrade the cell, such as in the formation of any HF and other electrolyte salt decomposition products by reaction with water. This reduction in water content in turn causes less dissolution of nickel, manganese and other transition metals in the cathode to prevent their undesirable diffusion through the separator into the anode. This reduction in water content by high temperature drying enabled by the very high thermal stability of the ceramic separator also contributes to a more efficient formation cycle of the battery to form anode and cathode stable layers (discussed further below), commonly referred to as Solid Electrolyte Interface (SEI) layers, which provides longer cycle life and better rate capability.

As the lithium ion battery industry tends to use transition metal cathodes, such as NMC and other transition metals with higher nickel and manganese content, it is desirable to inhibit diffusion and migration of dissolved metal ions (e.g., nickel and manganese ions) into and through the separator to the anode. In one embodiment, a lithium ion battery is constructed using a porous separator comprising a boehmite pigment having an average primary particle size of about 35nm and a cathode comprising nickel-manganese-cobalt oxide (NMC). The small pore size provides for efficient diffusion of small lithium ions (along with their associated complexes with organic carbonates or other electrolyte solvent molecules) with little to no loss in ionic conductivity. It was found that diffusion of manganese and nickel ions from the cathode, including nickel-manganese-cobalt oxide (NMC) cathodes, was suppressed to avoid transport into the separator, and into the anode region where undesirable cell chemical degradation may occur. The suppression of the diffusion of heavy and larger metal ions (e.g., manganese and nickel) is seen, for example, by the disappearance of the coloration of these metal ions in the white separator of the present invention. By comparison, polyolefin and ceramic coated polyolefin separators found no such inhibition when the ceramic coating had pores with diameters as high as 500nm or greater.

If enhanced diffusion inhibition is desired, the porous separator can be treated with anionic, dianionic, and other materials. Such treatment also reduces the pore size and provides charged species on the walls of the pores, which can enhance the cationic nature of the aluminum or other inorganic element of the inorganic oxide or inorganic nitride of the separator. Such treated separators function to scavenge and remove degradation products of lithium salts of HF and other electrolytes (e.g., POF) as compared to known separators₃) And the cycle life is prolonged. Typically, the anionic compound is applied to the separator by a solution comprising at least 2% and preferably 10% or more of the anionic compound. The anionic compound may comprise 0.1 wt% or more of the weight of the separator.

In one embodiment, the treatment of the separator may include a compound that has only one anionic group complexed (or attached) to the aluminum or other cationic group of the separator, and thus no anionic group that remains free to complex with any transition metal cation diffusing from the cathode. For example, the compound having a single anionic group may be an anthraquinone compound, such as anthraquinone-2-sulfonate (AQS). AQS may be a sodium salt, or preferably a lithium salt. Although the separator (after treatment with AQS or another monoanionic compound) does not have an anionic group remaining free in order to complex with the transition metal cation, it can prevent the transition metal cation from diffusing into and through the separator by reducing the pore size, especially when the average pore size is less than about 50nm (diameter) and/or when the anionic compound is relatively large and flat in shape, like AQS and anthraquinone-2, 6-disulfonate (AQdiS). Separators treated with monoanionic compounds (e.g., AQS) will still function as photosensitizers, oxidants of lithium metal, and oxygen scavengers after their reduction, as described below for separators treated with AQdiS and other dianionic compounds.

Alternatively, treatment of the separator uses a compound having two or more anionic groups. In such compounds, one of the anionic groups complexes to the aluminum or other inorganic cationic group of the separator, while the other anionic group remains free and available for complexing with any nickel, manganese, or other transition metal ions from the cathode that can diffuse to the separator.

The anionic group of the compound having two or more anionic groups includes anions selected from the group consisting of sulfonate and carbonate, and combinations thereof. The compound having two or more dianionic groups may include anthraquinone compounds, for example, AQdiS sodium or lithium salts. Aqueous solutions of AQdiS, especially when heated above 80 ℃ to provide higher AQdiS concentrations, are readily incorporated into ceramic separators, such as separators comprising boehmite. Such a composite is not dissolved by an electrolyte used in a lithium battery, and thus remains in the pores of the separator to act as a diffusion inhibitor. When the pores of the ceramic separator are nanoporous, e.g., having an average pore diameter of less than about 100nm, some of the sulfonate groups of the dianionic compound (e.g., ASdiS) are sterically unable to complex to the cationic portion of the separator. This is beneficial because these groups of the compound remain free to complex with nickel ions, manganese ions and other transition metal ions and reduce their unwanted diffusion into the anode.

Some dianionic compounds suitable for use in the present invention, such as anthraquinone compounds having two or more dianionic groups, have useful characteristics in addition to reducing diffusion of transition metal cations into the anode. These additional useful features include, for example, use as a photoinitiator, and for reacting with and oxidizing any lithium metal in contact with the separator. AQdiS has a moderate intensity absorption peak at about 320nm up to about 400nm and is an effective photosensitizer for uv curing to photopolymerize monomers and oligomers. This characteristic is useful in conjunction with the edge strengthening procedure described herein, and is useful for improving the overall mechanical strength of the separator. Treatment of a ceramic separator (e.g., a ceramic separator comprising boehmite) with a hot aqueous solution of AQdiS can provide a strongly absorbing AQdiS photosensitizer with an optical density of 0.3, or higher than the optical density of the separator before treatment.

It is generally understood that the safety of lithium batteries can be improved by reducing or eliminating the oxygen present in the electrolyte, since lower oxygen content reduces the flammability. In this regard, photosensitization by AQdiS involves the photoinduced reduction of AQdiS, and generally involves the extraction of hydrogen atoms from photosensitized compounds. In the presence of oxygen, the transient photoreduced AQdiS is re-oxidized back to the original AQdiS. This type of reversible reaction of the photosensitizer is useful for removing oxygen from the system (e.g., in the battery electrolyte). Certain anthraquinone compounds (e.g., AQdiS) are reduced by contact with lithium metal and can be used to oxidize any lithium metal dendrites in contact therewith. Because the reduced anthraquinone compound can oxidize back to the original anthraquinone compound in the presence of any oxygen, a single anthraquinone compound can reduce a significant amount of lithium metal atoms over the life of the battery, provided there is oxygen available to oxidize the original anthraquinone compound.

The separator may also be rolled to further reduce its pore size in order to improve the separator's suppression of diffusion of manganese ions and other large, heavy metal ions and to increase the separator's mechanical strength. For example, calendering to reduce the thickness of the separator by about 8% was found to increase the tensile strength of the boehmite separator by about 15%.

In one embodiment, the separator is coated with a lithium metal layer to "prelithiate" the cell, such as a cell containing silicon at the anode. In this regard, when a lithium ion cell is first charged, lithium ions diffuse from the cathode and are introduced into the anode where they are reduced to lithium metal. Therefore, decomposition products of lithium metal and an electrolyte, which are called Solid Electrolyte Interface (SEI), are easily formed at the surface of the anode, wherein a thin SEI layer contains lithium and an electrolyte reaction component. As a result of the SEI layer formation, a portion of the lithium introduced into the cell via the cathode is irreversibly bound and thus removed from the cycling operation, i.e., from the capacity available to the user. This process can consume about 10% to 20% of the lithium ion cell capacity, and up to 50%, depending on the amount of silicon in the oxy group. It is therefore advantageous to "prelithiate" (i.e., make more lithium available as the anode active material) the anode in order to minimize lithium consumption for the first charge-discharge cycle and thus minimize irreversible capacity loss.

Thermal runaway and other heat-related safety issues of lithium ion batteries and other lithium-based batteries are well known. Thus, a thin safety shutdown layer (not shown) may optionally be applied to one side of the separator 20 of the coated stack. The safety shutdown layer rapidly terminates the operation of the battery when the temperature of the single cell reaches a temperature of 100 to 150 c, preferably 105 to 110 c. In a preferred embodiment, such a safety shutdown layer has a thickness of 0.5 to 5 microns. The safety shutdown layer coating may comprise an aqueous or alcoholic solvent so that it can be conveniently applied during the stripping, cutting or other converting steps without the need to use a coater and to apply excessive mechanical stress on the coated stack to which the release substrate is not attached. The safety shutdown layer may comprise particles selected from polymer particles (e.g., styrene acrylic polymer particles, polyethylene particles, and fluorinated polymers and copolymers) and wax particles, alone or blended with one another.

A suitable safety shutdown layer is described in U.S. patent No. 6,194,098 to Ying et al. Specifically, Ying teaches a protective coating for a battery separator (e.g., a boehmite ceramic separator) comprising polyethylene beads. See, e.g., Ying, column 10, l.66-column 14, l.19. When the threshold temperature is reached, the polyethylene beads melt and the cell is terminated. Other suitable safety shutdown layers, particularly those suitable for use with ceramic separators and other separators (e.g., plastic separators), are described in U.S. patent 9,070,954 to Carlson et al. Carlson describes microporous polymer shutdown coatings, see, e.g., column 2, l.15-column 3, l.28, which can incorporate the disclosed coated stacks and methods.

As shown in fig. 2 and 3, one or more electrodes 40a,40b are then coated on the separator layer 20. Suitable materials and methods for coating electrodes directly onto nanoporous separators are described in, for example, U.S. patent No. 8,962,182 (see, for example, column 2, l.24-column 3, l.39, column 4, lines 49-56, column 5, lines 9-65 and column 6, column l.2-column 8, l.7), U.S. patent No. 9,065,120 (see, for example, column 3, lines 12-65, column 4, lines 18-61, column 8, column l.2-column 9, l.31, column 9, lines 42-67 and column 14, lines 6-23), U.S. patent No. 9,118,047 (see, for example, column 2, l.24-column 3, l.33, column 4, lines 36-51 and columns 5, l.3-6, l.21) and column 9,209,446 (see, for example, column 2, l.20-42, lines 1-56, column 5, lines 16-31 and column 7, l.1-column 8, l.65). These patents and applications referenced herein are incorporated by reference in their entirety.

The electrode coatings 40a,40b may be applied to the entire surface of the separator layer 20, in lanes (lane) or strips (strip) to the separator layer 20, or in patches or rectangles to the separator layer 20, depending on the end use requirements. The cathode coating may be applied from a pigment dispersion comprising water or an organic solvent, such as N-methylpyrrolidone (NMP), and contains an electroactive or cathode active material in the form of a pigment, a conductive carbon pigment, and an organic polymer. The anodic coating can be applied from a pigment dispersion comprising an organic solvent or water and contains an electroactive or anodically active material in the form of a pigment, a conductive carbon pigment and an organic polymer. These electrode pigments are particles typically 0.5 to 5 microns in diameter. Preferably, the conductive pigments and other pigments of the electrodes 40a,40b do not penetrate into or through the separator layer 20.

In the embodiment shown in fig. 2 and 3, the electrodes are coated with lanes 40a,40 b. The electrode tracks 40a,40b may be deposited using a slot die coater or other methods known in the art. Fig. 2 shows an example of a cross-sectional view of a part of the assembly 1 after the electrodes 40a,40b have been coated. Fig. 3 shows the same assembly 1 in top view. Two lanes 40a and 40b are shown in fig. 2 and 3 for ease of illustration. However, it should be understood that additional or fewer tracks, for example, 1-15 tracks (or even more), may be coated across the full width of the assembly in order to maximize the yield or volumetric output of the number of individual cell stacks that may be cut from the assembly.

In this regard, the electrode layers are coated in lanes 40a,40b at the width desired for the final coated stack design and the cell end use. In one embodiment, the lanes 40a,40b preferably have a width W of 12cm to 25cm₁And are at a distance W of 2cm to 4cm from each other₂And (4) separating.

In one embodiment shown in fig. 4, a current collection layer 50 is applied to the electrode side of the assembly, which in this case includes the substrate 10, release coating 30, separator 20, and electrodes 40a,40 b. Methods of coating current collection layers and materials for forming such layers are disclosed in co-pending U.S. patent application No. 15/130,660.

For example, the current collector layer 50 may include nickel metal. A nickel current collection layer is preferred because it can be used as a current collection layer in either an anode stack or a cathode stack. In addition, nickel is generally less likely to be oxidized and more electrochemically stable than copper, aluminum, or other metals used for the current collector layer. However, as discussed below, copper, aluminum, and other materials may also be used.

To improve the mechanical integrity of the coated stack, a strengthening region 52 (shown in fig. 4) may be added to the coated stack. The reinforced areas 52 preferably cover the entire surface of the separator 20 between the electrode tracks 40a,40 b. At the end of the process, when the stack is cut to its final width, the strengthened region 52 will become the edge of the coated stack or a region near the edge of the coated stack. The coating including reinforced areas 52 provides much greater mechanical strength, particularly tear resistance and tensile strength, to the coated stack. This is important after the coated stack becomes unsupported after it has been detached from the strong release substrate. When they are unsupported, the coated stack, especially the electrode layers, can become brittle (in the absence of strengthened areas) and can even crack or tear during processing. The presence of the mechanically strong edge strengthened region 52 minimizes (and may even eliminate) the problem of tearing during the process of breaking away, cutting, stamping, tabbing, and stacking into the final single cell. This method of edge strengthening is also applicable to unsupported separators, such as ceramic separators.

In one embodiment, a polymer is used to strengthen the strengthened region 52. The polymer may be impregnated in the pores of the separator 20 and/or coated on the separator 20. Alternatively, such reinforcement may be provided by heating the overlying layer, for example a porous polymer safety shutdown layer (discussed above), so as to melt the polymer of the edge region of the separator into the pores or into the thin layer overlying the separator. Such methods include "sandwich" structures in which a porous polymer layer (e.g., a breaker layer) is between two inorganic separators. By heating the edge region, this three-layer structure is laminated and strengthened in the edge region. Alternatively, the reinforcement of the edges of the separator may be provided by exploiting the photoactive properties of the photosensitizer (discussed above) that is complexed to the separator. For example, during the conversion process, a liquid containing a photo-curable compound, such as 1, 6-hexanediol diacrylate (HDDA), may be coated on the edge-strengthened region, and then cured by absorbing ultraviolet light by a photosensitizer in the separator. Additional photosensitizers may be added to the liquid containing the radiation curable compound for additional curing efficiency and for the case when the edge strengthening is above the spacer layer and in the pores of the spacer.

After coating to provide the current collector layer 50, a second electrode layer (not shown) may be coated on the current collector layer 50. In a preferred embodiment, such a second electrode layer is coated in lanes of substantially the same width as the lanes of the first electrode layer 40a,40b and directly covers the locations of the first electrode layer. This provides an anode stack and a cathode stack with electrode coatings on both sides of the current collector, which is the most typical cell assembly configuration for the electrode, i.e., electrode coatings on both sides of the current collector layer. After coating of the second electrode, the coated stack on the release substrate is preferably calendered to densify the second electrode.

The assembly is then prepared for tabbing, i.e. electrical interconnection. In the embodiment shown in fig. 5, patches 60 of conductive material have been applied at the desired tab locations to achieve high conductivity in these areas. The patch 60 is in electrical contact with the current collector 50. It should be understood that the arrangement and number of conductive patches 60 will vary depending on the particular cell design. As will be discussed further below, the embodiment shown in fig. 5 represents a patch 60 configuration for a cylindrical or "jellyroll" design.

In one embodiment, the next step is to release the coated battery stack from the release substrate 10 so that the coated stack can be converted into a finished single cell. As discussed above, to save cost, the substrate 10 may be reused to make another coated stack. Preferably, the release substrate 10 is cleaned and inspected prior to each reuse.

The next step is to cut the coated stack assembly 1 to the desired width. In the embodiment shown in fig. 5, through the region of the separator layer 20 that does not contain an electrode or current collector layer (i.e., S)₁、S₂And S₃) To complete the cut. Since only the separator layer 20 and the reinforcing areas 52 are cut layers, there is no possibility of conductive debris or chips being generated from, for example, an electrode or current collector layer. In contrast, in prior art methods, the cutting is typically performed through a metal layer or a conductive metal foil layer. However, cutting these metal layers creates conductive debris (e.g., metal pieces or chips) that can cause the cell to fail during manufacturing or during use due to short circuits, which can lead to ignition or explosion of the cell. Thus, the possibility of such dangerous situations is avoided using the present invention.

The embodiment shown in fig. 6 provides a coated stack 70 for a jellyroll structure. In this regard, the coated stack 70 will be wound into a jellyroll structure with a coated stack of opposite polarity and packaged in a cylindrical shell. The discontinuous coated stack 70 may be tabbed or welded using conventional methods.

While the preferred embodiments of the present invention have been shown and described in detail, various modifications and improvements therein will be apparent to those skilled in the art. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.