Electrodes having passivated surfaces and methods of making electrodes having passivated surfaces

Abstract

Electrodes (10), electrochemical cells (20) having the electrodes, and methods (30, 40) of making electrodes are provided. The electrodes (10) include a current collector (200); an active material layer (100) having particles or fibers (101) of active material; and a nonconductive material (102) which partially covers (or passivates) the particles or fibers (101) of the active material layer (100). The electrical cells (20) having the electrodes (10) facilitate battery fabrication by minimizing or eliminating the need for the "formation step" that characterizes prior art battery processing. Aspects of the invention reduce the variation in a battery's performance, improve the yield of the manufacturing line, and / or enhance the stability and safety of batteries having the electrodes provided.

Description

ELECTRODES HAVING PASSIVATED SURFACES ANDMETHODS OF MAKING ELECTRODES HAVING PASSIVATED SURFACESCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority from pending U.S. Provisional Patent Application 63 / 562,768, filed on March 8, 2024, the disclosure of which is included by reference herein in its entirety.BACKGROUND OF THE INVENTIONTechnical Field

[0002] The present disclosure generally relates to electrochemical energy storage devices. More specifically, the present disclosure relates to electrodes for electrochemical energy storage devices, the composition of the electrodes, the structure of the electrodes, methods to make or modify the electrodes, methods to improve manufacturing yield of energy storage devices, and methods to reduce manufacturing cost and manufacturing time for the energy storage devices. The present disclosure also relates to applications of such electrodes and electrochemical cells comprising the electrodes.Description of Related Art

[0003] High energy batteries are widely used nowadays, including sodium-based, lithium-based, and potassium-based batteries. For example, lithium-based batteries have dominated the rechargeable battery market for a long time.

[0004] Currently, prior art battery manufacturing processes include a process referred to as a “formation step,” where the battery is formed via a slow charging process. The formation step is necessary to form a desired solid electrolyte interphase (SEI) that can passivate the electrode surface after the batteries have been assembled. The formation step typically takes up to a few weeks to complete and represents a significant portion ofthe battery manufacturing cost. There is a need to reduce the processing time and cost in the manufacturing of high energy batteries.

[0005] Current manufacturing processes also typically include the use of solvents. The use of these solvents is energy-intensive and may be environmentally unfriendly. An alternative manufacturing process includes a dry electrode process, where the electrode components are mixed without undesirable solvents, rolled into the active material layer, and then laminated onto the current collector. However, the performance of the cells from such dry electrode processes is not stable, and the adoption of such dry electrode processes, for example, in so-called “gigafactories,” has been limited.

[0006] On the other hand, active metal plating or metal dendrite growth, such as lithium plating, sodium plating, or lithium dendrites, at the electrode surface leads to fast degradation of the batteries, large performance variation within a group of batteries, and even thermal runaway and safety events.

[0007] There remains the need in the art for an electrode that has a pre-formed passivation surface or an artificial solid electrolyte interface layer. Such improved electrodes may not need the slow formation step that characterizes prior art processing or can significantly reduce the time and cost of the formation step; reduce the variation of the battery performance in a group, that is especially important for battery packs consisting of multiple batteries; improve the yield of the manufacturing line, including those from dry electrode process; and / or improve cycling stability and safety of the batteries into which such an electrode is used.SUMMARY OF THE INVENTION

[0008] The present disclosure generally relates to electrodes comprising a current collector, an active material layer that comprises active material particles or fibers, and a nonconductive material that partially covers a surface of the active material layer, and thereby passivates the particles or fibers of the active materials at the surface of the active materials layer, for example, passivates the active material from reaction with metals at the surface of the active materials layer. According to aspects of the invention, the nonconductive material may be provided as a thin layer of nonconductive materialor as a thin film of nonconductive material covering the active materials and / or conductive additives. The present invention also relates to an electrochemical cell comprising the disclosed electrodes. In some embodiments, the present invention relates to methods of making such electrodes and applications of such electrodes.

[0009] In one aspect, the at least partial covering or at least partial isolation of the active material in the active material layer by the nonconductive material reduces or minimizes the exposure of the active material particles or fibers in the exposed surface of the active material layer. In one aspect, the reduction or minimization of the exposure of the active material particles or fibers reduces or minimizes the deposition or growth of any undesirable metals, for example, lithium, sodium, and / or zinc, on the active material particles or fibers in the exposed surface of the active material layer. In one aspect, the reduction or minimization of the deposition or growth of any undesirable metals on the active material particles or fibers in the exposed surface of the active material layer is practiced during the charging of a battery having an electrode according to aspects of the invention, for example, during the “formation step” of the battery fabrication process.

[0010] In one aspect, the at least partial covering or the at least partial isolation of the active material of the active material layer by the nonconductive material minimizes or prevents the exposure of active material particles or fibers in the exposed surface of the active material layer substantially “passivates” the exposed surface of the active material layer of the electrode disclosed herein.

[0011] The electrode of present disclosure is composed of: i) a current collector, ii) an active material layer, wherein the active material layer comprises particles or fibers of active material, and one of the active material layer’s surfaces, or a second surface, is in contact with the current collector, and hi) a nonconductive material, wherein the nonconductive material at least partially covers or at least partially isolates the particles or fibers of the active material at the top surface, or a first surface, of the active material layer that is opposite to the current collector. In one aspect, at least partially covers or at least partial isolates comprises at least partially isolating the active material particles or fibers from any metals, for example, lithium, sodium, potassium, vanadium,manganese, nickel, cobalt, iron, aluminum and / or zinc, at the exposed top surface of the active material layer. In one aspect, the nonconductive material partially covers or isolates the particles or fibers of the active material may comprise substantially completely covers or isolates the particles or fibers of the active material at the top surface of the active material layer.

[0012] The current collector can be any commonly used current collector in the art or under development, including, but not limited to, current collectors comprising copper, aluminum, iron, nickel, titanium, carbon, zinc, silver, or composites containing these materials.

[0013] The active material layer contains active material that can reversibly react with an active metal or an active compound, or a composite comprising a combination of active metals or active compounds. According to aspects of the invention, an active metal or an active compound maybe any metal or compound that is prone to react with any active material particles or fibers exposed on the surface of the active material layer.

[0014] In one embodiment of the invention an electrode is provided, the electrode comprising or including a current collector, an active material layer which comprises particles or fibers of active material, wherein one of the active material layer’s surfaces, or a second surface, is in contact with the current collector, and a nonconductive material, wherein the nonconductive material partially covers the particles or fibers of the active material at the top surface, or first surface opposite the second surface, of the active material layer that is opposite to the current collector. In certain embodiments the current collector contains a metal, for example, copper, aluminum, iron, nickel, titanium, or silver. The active material is capable of reversible reaction with an active metal, for example, which may include or may be one of the metals selected from the group consisting of, lithium, sodium, potassium, zinc, magnesium, iron, and aluminum. In certain embodiments the active material is selected from at least one of graphite, hard carbon, silicon, sulfur, an aluminum alloy, tin, iron, or a compound containing an element, for example, one or more of the elements selected from the group of nickel (Ni), cobalt (Co), manganese (Mn), and iron (Fe). In one aspect, the nonconductive material partially covers the particles or fibers of the active material may comprisesubstantially completely covers the particles or fibers of the active material at the top surface of the active material layer.

[0015] In one aspect, the active material layer comprises at least some porosity. For example, in one aspect, the porosity of the active material layer is within the range of 10% to 75%, io%-6o%, io%-5O%, 20%-50%, 30%-50%, 30%-40%, or 40%-50%. According to aspects of the invention, the porosity of the active material layer may be determined by calculating the ratio between the volume occupied by the pores in the active material layer and the total volume of the active material layer. Porosity can be measured by porosimeters, such as, mercury porosimetry or nitrogen gas porosimetry. In one aspect, the total volume of the active material layer (Vt) can be obtained by multiplying the thickness (T) of the active material layer by the width (W) of the active material layer and the length (L) of an active material layer sample, that is,Vt = T x W x L. Equation 1The volume of the solid content (Vs) in the active material layer can be obtained by immersing the sample in a liquid and checking the volume change of the liquid. The volume occupied by the pores (Vp) can be determined by subtracting Vsfrom Vt. Porosity can then be obtained by the ratio of Vp / Vt, orPorosity = Vp / Vt. Equation 2

[0016] In one aspect, the nonconductive material may comprise any nonconductive material or a combination of nonconductive materials known in the art. In certain embodiments, the nonconductive material may include or may be selected from the group consisting of polymers, oxides, sulfides, fluorides, chlorides, carbonates, nitrides, silicates, borates, aluminates, sulfates, phosphates, titanate, zirconate, and mixed-anion compounds. In one aspect, the polymer nonconductive material may comprise one or more of polyethylene (PE), polypropylene (PP), polystyrene (PS), polytetrafluoroethylene (PTFE), polyvinyldifluoride (PVDF), polyacrylic acid (including its esters) (PAA), polyamide (PA), polyester (PES), and poly(terephthalate) (PT).

[0017] In one aspect, the percentage of particles or fibers of the active material that are not covered by the nonconductive materials at the top surface of the active material layer, for example, particles or fibers of the active material exposed on the top surface of the active material layer, is not more than 10%. Preferably, the percentage of particles or fibers of the active material on the top surface of the active material layer that are not covered by the nonconductive materials at the top surface of the active material layer is not more than 5%, or not more than 1%. According to aspects of the invention, the percent of particles or fibers of the active material that are not covered or are exposed on the top surface of the active material layer maybe determined by optical microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X- ray fluorescence, transmission electron microscopy (TEM), or other elemental mapping technologies.

[0018] In certain embodiments, the resistance of the electrode according to aspects of the invention is at least 50% higher than the resistance of a modified electrode where at least some of the covered particles or fibers are removed. The average thickness of the nonconductive material that covers or isolates and the particles or fibers of the active material is between 1 nanometer [nm] and 20 micrometers [pm]. In certain embodiments, an average dimension of the particles or fibers of active material is within the range of 10 nm to 50 pm.

[0019] In certain embodiments, the active material layer has a total conductive surface area that is opposite to the current collector, wherein the conductive surface area covered by the nonconductive material is no less than 70% of the total conductive surface area of the active material layer. Preferably the conductive surface area covered by the nonconductive material is no less than 90% of the total conductive surface area of the active material layer. According to aspects of the invention, the conductive surface area may be determined by electronic conductivity mapping of the active material layer surface, such as Scanning Transmission Electron Microscope Electron Beam-Induced Current (STEM EBIC). The nonconductive material covered areas (Ac) have lower conductivity than the uncovered areas (Au). The coverage ratio (Rc) can then be obtained by:Rc— Ac / (Ac + Au). Equation 3In one aspect, the conductive surface area may originate from the active material particles or fibers and / or the conductive additives that are located at the surface, or first surface, of the active material layer.

[0020] In one embodiment of the invention, the active material layer comprises a lithium compound, wherein the lithium compound comprises at least one of, or may be selected from the group consisting of, a lithium transition metal phosphate (for example, of the formula LiMPO4, where M = Fe, Mn, Ni, or Co), a lithium nickel manganese cobalt oxide (for example, of the formula LiaNixMnyCozO2-b, where o< x,y,z<i, o.5<a<i.5, and -0.5<b<0.5), a lithium cobalt oxide (for example, of the formula LiCoO2), a lithium manganese oxide (for example, of the formula LiMn2O4), a lithium nickel cobalt aluminum oxide (for example, of the formula LiaNixCoyAlzO2-b, where o< x,y,z<i, o.5<a<i.5, and -0.5<b<0.5), a lithium titanate (for example, of the formula Li2TiO3), derivatives of the these lithium compounds, or a mixture of two or more of these lithium compounds.

[0021] In one embodiment of the invention, an electrochemical cell is provided, comprising the electrode disclosed herein, an opposite electrode, and an electrolyte. In certain embodiments, the electrochemical cell may further comprise a separator. In one aspect, the opposite electrode may comprise the electrode disclosed herein. In certain embodiments, the opposite electrode may comprises a lithium-ion compound, wherein the lithium-ion compound comprises at least one of, or is selected from the group consisting of, a lithium transition metal phosphate (for example, of the formula LiMPO4, where M = Fe, Mn, Ni, or Co), a lithium nickel manganese cobalt oxide (for example, of the formula LiaNixMnyCozO2-b, where o< x,y,z<i, o.5<a<i.5, and -0.5<b<0-5), a lithium cobalt oxide (for example, of the formula LiCoO2), a lithium manganese oxide (for example, of the formula LiMn2O4), a lithium nickel cobalt aluminum oxide (for example, of the formula LiaNixCoyAlzO2-b, where o< x,y,z<i, o.5<a<i.5, and -0-5<b<0.5), a lithium titanate (Li2TiO3), derivatives of these lithium-ion compounds, or mixture of two or more of these lithium-ion compounds.

[0022] In one embodiment of the invention, a method of making an electrode is provided, the method comprising or including depositing an active material layer on a current collector, and depositing a nonconductive material on the surface, or a first surface, of the active material layer that is opposite to the current collector, wherein the surface, or first surface, of the conductive material layer is partially covered by the nonconductive material, for example, by an electrostatic process. According to aspects of the methods of invention, the nonconductive material may be provided as a thin layer of nonconductive material or as a thin film of nonconductive material on the active material layer.

[0023] In a further embodiment of the invention, an another electrode is provided, the electrode comprising or including: a current collector; an active material layer, wherein the active material layer comprises particles or fibers of active material, the active material layer having a first surface and a second surface opposite the first surface, wherein the second surface contacts the current collector; and a nonconductive material, wherein the nonconductive material partially covers the particles or fibers of the active material at the first surface of the active material layer. In one aspect, partially covers comprises a percentage of the particles or fibers of the active material that are not covered by the nonconductive materials at the first surface of the active material layer is not more than io%. In another aspect, partially covers comprises a percentage of particles or fibers of the active material that are not covered by the nonconductive materials at the first surface of the active material layer is not more than 1%.

[0024] In one aspect, the nonconductive material of the electrode maybe selected from the group consisting of polymers, oxides, sulfides, fluorides, chlorides, carbonates, nitrides, silicates, borates, aluminates, sulfates, phosphates, and mixed-anion compounds thereof.

[0025] In one aspect, the active material layer may comprise a lithium-ion compound. For example, the lithium-ion compound maybe is selected from the group consisting of a lithium metal phosphate (LiMPO4, M = Fe, Mn, Ni, or Co), a lithium nickel manganese cobalt oxide (LiaNixMnyCozO2, o< x,y,z<i, o.5<a<i.5), a lithium cobalt oxide (LiCoO2), alithium manganese oxide (LiMn2O4), a lithium nickel cobalt aluminum oxide (LiNiCoAlO2), a lithium titanate (Li2TiO3), and derivatives of these lithium-ion compounds.

[0026] In one aspect, a resistance of the electrode is at least 50% higher than the resistance of the electrode after a portion of the covered particles or fibers are removed. In another aspect, an average thickness of the nonconductive material is between 1 nanometer and 20 micrometers. In another aspect, an average thickness of the nonconductive material is between 1 nanometer and 20 micrometers, and a resistance of the electrode is at least 50% higher than a resistance of the electrode after a portion of the covered particles or fibers are removed.

[0027] In one aspect, the active material may be a material capable of reversible reaction with an active metal selected from lithium, sodium, potassium zinc, magnesium, iron, and aluminum. In another aspect, the active material is selected from at least one of graphite, silicon, sulfur, an aluminum alloy, tin, iron, or a compound containing one or more of the elements selected from the group of nickel (Ni), cobalt (Co), manganese (Mn), vanadium (V), and iron (Fe).

[0028] In one aspect, the current collector comprises or contains at least one of copper, aluminum, iron, nickel, titanium, and silver.

[0029] Another embodiment of the invention is an electrochemical cell comprising or including: the electrode disclosed herein; an opposite electrode; and an electrolyte. In one aspect, the electrochemical cell may further include a separator. In one aspect, the opposite electrode may comprise a sodium-ion compound. In one aspect, the opposite electrode may comprise a lithium-ion compound, for example, the lithium-ion compound may be selected from the group consisting of a lithium metal phosphate (LiMPO4, M = Fe, Mn, Ni, or Co), a lithium nickel manganese cobalt oxide (LiaNixMnyCozO2, o< x,y,z<i, o.5<a<i.5), a lithium cobalt oxide (LiCoO2), a lithium manganese oxide (LiMn2O4), a lithium nickel cobalt aluminum oxide (LiNiCoAlO2), a lithium titanate (Li2TiO3), and derivatives of these lithium-ion compounds.

[0030] A further embodiment of the invention is a method of making the electrode , for example, for making the electrode disclosed herein, the method comprising or including: depositing a material having an active material on a current collector to produce an active material layer having a first surface and a second surface, the second surface contacting the current collector; and depositing a nonconductive material on the first surface of the active material layer, wherein the first surface of the active material layer is partially covered by the nonconductive material. In one aspect, depositing the nonconductive material comprises an electrostatic depositing.

[0031] In one aspect, partially covers comprises a percentage of the particles or fibers of the active material that are not covered by the nonconductive material at the first surface of the active material layer is not more than io%. In another aspect, partially covers comprises a percentage of particles or fibers of the active material that are not covered by the nonconductive materials at the first surface of the active material layer is not more than 1%.

[0032] These and other aspects, features, and advantages of this invention will become apparent from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention will be readily understood from the following detailed description of aspects of the invention taken in conjunction with the accompanying drawings in which:

[0034] FIG. 1 is a schematic illustration of a cross-sectional view of an electrode comprising an active material layer and a current collector, according to an aspect of the invention, wherein the active material layer comprises particles or fibers of the active material, and wherein the particles or fibers of the active material are at least partially covered at the top surface of the active material layer by a nonconductive material.

[0035] FIG. 2A and 2B optical micrographs of an uncoated (FIG. 2A) surface of the electrode of FIG. 1 at 40 times optical magnification and a nonconductive material coated (FIG. 2B) surface of the electrode of FIG. 1 according to an aspect of the invention at 40 times optical magnification.

[0036] FIG. 3 is a schematic illustration of the process of measuring the resistance of the electrode shown in FIG. 1 by using a multimeter to connect to the top surface and bottom surface of the nonconductive material covered electrode, according to an aspect of the invention.

[0037] FIG. 4 a schematic illustration of the process of measuring the resistance of an electrode that is modified compared to the electrode shown in FIG. 3 by using a multimeter to connect to the top surface and bottom surface, after the nonconductive material covered particles or fibers are removed with an adhesive tape.

[0038] FIG. 5 is a schematic illustration of an electrochemical cell comprising the electrode shown in FIG. 1, a separator, an opposite electrode, and with an electrolyte added in.

[0039] FIG. 6 is a flow chart illustrating a method of how to make the electrode shown in FIG. 1, according to an aspect of the invention.

[0040] FIG. 7 is a flow chart illustrating a method of how to make the electrode shown in FIG. 1 in a dry electrode manufacturing process, according to another aspect of the invention.

[0041] FIG. 8 is a graph illustrating a comparison of the cycling performance of a group of baseline electrochemical cells and a group of exemplary electrochemical cells according to aspects of the invention.DEFINITIONS

[0042] The following definitions apply herein, including the claims, unless otherwise indicated.

[0043] “Comprising" or " including" are used interchangeably to mean including but not necessarily limited to, and are open-ended terms not intended to exclude additional, unrecited elements or method steps.

[0044] “Top” is used in the context to refer to the top surface of the conductive material which maybe adjacent to the separator or an opposite electrode when equipped in an electrochemical cell; and “bottom” is used in the context to refer to the bottom surface of the conductive material which may be away from the separator or an opposite electrode when provided in an electrochemical cell.

[0045] “Provided” in the context of a method or device disclosed herein may include receiving, obtaining, purchasing, manufacturing, generating, processing, preprocessing, and / or the like, such that the object or material provided is in a state and configuration for other steps to be carried out.

[0046] “Surface area coverage” means the percent of the conductive surface area covered by the nonconductive material. For example, ioo% surface area coverage means all the conductive surface area is covered by the nonconductive material.

[0047] The term “porosity” as used in the context disclosed herein means the ratio of the volume occupied by the pores, Vp, in an active material layer sample and the total volume, Vt, of the active material layer sample. For example, as determined by Equation 1 and Equation 2.

[0048] The expression “reversibly react”” or “reversible reaction” in the context disclosed herein means a reaction in which the reactants and products can interconvert and the reaction can go in both forward and backward directions, depending on the conditions. For example, intercalation of lithium into and out of graphite depending on the electrochemical potential.

[0049] The expressions “conductive surface area” in the context disclosed herein means the area of a surface where a conductive material is present at the surface, for example, the first surface, of the active material layer, for example, graphite particles, conductive additive particles or fibers, doped silicon particle or fibers.DETAILED DESCRIPTION OF THE INVENTION

[0050] The following description of various examples is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. Additionally, the advantages provided by the examples and embodiments described below are illustrative in nature and not all examples and embodiments provide the same advantages or the same degree of advantages.

[0051] The present invention generally relates to electrodes comprising a current collector, an active material layer that comprises active material in the form of particles or fibers, and a nonconductive material that partially covers, or isolates, the particles or fibers of the active materials at the surface of the active materials layer. The present disclosure also relates to electrochemical cells comprising the disclosed electrodes. In some embodiments, the present invention comprises methods of making such electrodes and applications of such electrodes.

[0052] FIG. 1 is a schematic illustration of an electrode 10 comprising an active material layer 100 having a top or first surface 103 and a current collector 200 according to one aspect of the invention, wherein the active material layer 100 comprises particles or fibers 101 of an active material, and wherein the particles or fibers 101 of the active material are partially covered at the top surface, or first surface, 103 of the active material layer 100 by a nonconductive material 102. According to aspects of the invention, the nonconductive material 102 maybe provided as a thin layer of nonconductive material or as a thin film of nonconductive material. The active material layer 100 may typically also have a bottom or second surface 107, opposite the top or first surface 103. An active material layer 100 can be prepared following methods that are commonly used in the art or which are under development. For example, the active material layer 100 may contain particles or fibers 101 of an active material, a binder, and a conductive additive.

[0053] According to aspects of the invention, an active material of the particles or fibers 101 is capable of reversible reaction with an active metal, for example, lithium, sodium, potassium, zinc, magnesium, iron and / or aluminum. An active material isselected from at least one of carbon, such as, a natural graphite, an artificial graphite, and a hard carbon; silicon; sulfur; aluminum; an aluminum alloy; tin; iron; or a compound containing one or more of the elements, or selected from the group of, nickel (Ni), cobalt (Co), manganese (Mn), and iron (Fe). For example, graphite can reversibly react with lithium by reversibly reacting with intercalated lithium ions in interlayer spaces in the graphite; hard carbon can reversibly react with sodium by partially filling pores of the hard carbon with sodium atoms or ions; and silicon can reversibly react with lithium by alloying with lithium, among other types of reversible reactions. In some embodiments, an active material layer too comprises particles or fibers 101 of graphite. In some other embodiments, an active material layer 100 comprises particles or fibers 101 of silicon. In some other embodiments, an active material layer 100 comprises particles or fibers 101 of a silicon-graphite composite. In some embodiments, an active material of the particles or fibers 101 comprises a lithium-ion compound which can be selected from the group consisting of a lithium transition metal phosphate (for example, of the formula LiMPO4, where M = Fe, Mn, Ni, or Co); a lithium nickel manganese cobalt oxide (for example, of the formula LiaNixMnyCozCh-b, where o< x,y,z<i, o.5<a<i.5, and -0.5<b<0.5), a lithium cobalt oxide (for example, of the formula LiCoO2), a lithium manganese oxide (for example, of the formula LiMn2O4), a lithium nickel cobalt aluminum oxide (for example, of the formula LiaNixCoyAlzO2-b, where o< x,y,z<i, o.5<a<i.5, and -0.5<b<0.5), a lithium titanate (for example, of the formula Li2TiO3), or a mixture of one or more of these compounds.

[0054] According to aspects of the intention, the active material layer 100 may have a porous structure. The porosity of the active material layer too may be within the range of 10% to 75%. In other aspects, the active material layer 100 may have a porosity of io%-6o%, io%-5O%, 20%-50%, 30%-50%, 30%-40%, or 40%-50%. According to aspects of the invention, the porosity of the active material layer too maybe determined by Equation 2.

[0055] In one aspect, an average dimension of the particles or fibers 101 of the active material layer is within the range of 10 nanometers [nm] to 50 micrometers [pm]. In some embodiments, the active material layer 100 comprises natural graphite particlesioi with a particle size of 1 - 20 pm. In some other embodiments, the active material layer 100 comprises silicon-graphite composite particles 101 with a particle size of no more than 100 pm. In some embodiments, the active material layer 100 comprises silicon fiber with a diameter between 10 nm to 10 pm. In some embodiments, the active material layer 100 comprises active material particles 101 with a bimodal particle size distribution, such as, having active particles 101 with sizes ranging between 0.1 pm to 10 pm and also between 10 pm to 50 pm. In some embodiments, the active material layer 100 comprises particles 101 of one active material and fibers 101 of another active material.

[0056] According to one aspect of the intention, the expression “nonconductive” means having very low conductivity, for example, less than 1O'6Siemens per centimeter [S / cm] under ambient conditions.

[0057] In one aspect, the nonconductive material 102 selectively covers, or isolates, the particles or fibers 101 of the active materials at the surface 103 of the active material layer 100. In one aspect, selectively covers comprises covering the parties or fibers 101 with nonconductive material 102 while substantially leaving at least some of any pores present open, that is, uncovered by nonconductive material 102. The nonconductive material 102 may comprise, or is selected from the group consisting of, polymers, oxides, sulfides, fluorides, chlorides, bromides, iodides, carbonates, nitrides, silicates, borates, aluminates, sulfates, phosphates, titanates, zirconates, and mixed-anion compounds, or mixtures thereof. Specific examples of the polymers that may comprise the nonconductive material include polyethylene (PE), polypropylene (PP), polystyrene (PS), polytetrafluoroethylene (PTFE), polyvinylidene difluoride (PVDF), polyacrylic acid (including its esters) (PAA), polyamide (PA), poly(terephthalate) (PT). Examples of other nonconductive materials that may be used for aspects of the invention include LiF, Li20, Li2S, Li2CO3, Li3PO4, LiP02F2, A12O3, A1F3, A1PO4, ZnF2, and Zn3(PO4)2.According to one aspect of the invention, a nonconductive material 102 having a lower conductivity, good adhesion, and compatibility with other components of the device is preferred.

[0058] According to aspects of the intention, the current collector 200 shown in FIG. 1 in the electrode 10 can comprise any commonly used current collector material in the art or under development, including, but not limited to, copper, aluminum, iron, nickel, titanium, carbon, zinc, and silver or a composite containing one or more of these conductors, for example, a copper-coated polymer. Current collector 200 can be in the form of a foil, a thin film, a mesh, and / or a foam. Current collector 200 can be a metal, a carbon-coated metal, or a metal-coated polymer, such as, a copper-coated polyethylene terephthalate current collector.

[0059] The nonconductive material 102 covered, or isolated, particles or fibers 101 of the active material layer 100 can be observed by an optical microscope, a scanning electron microscope (SEM), an energy-dispersive X-ray spectroscopy (EDS), or a transmission electron microscopy (TEM). FIGS. 2A and 2B are optical micrographs of a portion of the uncoated top surface, or first surface, 103 of an electrode (FIG. 2A), and of a portion of the coated top surface, or first surface, 103 of an electrode 10 of FIG. 1 (FIG. 2B) according to an aspect of the present invention, respectively, at 40 times optical magnification. The processing and composition of the electrodes shown in FIGS. 2A and 2B are described below in the “Examples of Aspects of the Invention” section, where FIG. 2A is a micrograph of the Example 1 electrode and FIG. 2B is a micrograph of the Example 2 coated electrode.

[0060] The optical comparison of micrographs in FIGS. 2A and 2B reveals that a large percentage of the surface graphite particles 101 on top surface 103 of active material layer 100 of electrode 10 shown in FIG. 2B, according to an aspect of the invention, is covered with nonconductive material 102, where of the surface graphite particles of the surface 103 shown in FIG. 2A are not so covered. According to aspects of the invention, the nonconductive material 102 on the surface 103 may appear as a white dull area of particle contour, while the surface of the graphite particles 101 on the surface 103 shown in FIG. 2A are not so covered, and appear as silver shiny or dark areas of particle contour. The percentage coverage according to aspects of the present invention can be characterized by SEM with EDS to analyze the distribution of the covered material on the surface. For example, both the number of covered particles (Nc) and the number ofuncovered particles (Nu) can be individually counted in a micrograph, and the covered and uncovered ratio can then be calculated. In some embodiments, the percentage of particles or fibers 101 of the active material that are not covered by the nonconductive material 102 at the top surface, or first surface, 103 of the active material layer 100 is no more than 10% (that is, less than 10%). In some embodiments, the percentage of particles or fibers 101 of the active material that are not covered by the nonconductive materials at the top surface 103 of the active material layer 100 is no more than 5% (that is, less than 5%), or no more than 1% (that is, less than 1%). In some embodiments, substantially all the particles or fibers 101 of the active material 100 at the top surface 103 maybe covered.

[0061] The thickness of the nonconductive material 102 that covers the particles or fibers 101 of the active material in the active material layer 100 can be measured under electron microscopy. In some embodiments, the average thickness of the layer or film of nonconductive material 102 that covers the particles or fibers 101 of the active material is between 1 nanometer and 20 micrometers.

[0062] FIG. 3 is a schematic illustration of the process of measuring the electrical resistance of the electrode 10 of FIG. 1 by using a multimeter 110 to connect to the top surface 103 and bottom surface 105 of the current collector 200 of the nonconductive material covered electrode 10, according to an aspect of the invention.

[0063] FIG. 4 is a schematic illustration of the process of measuring the electrical resistance of a modified electrode 10', similar to electrode 10 shown in FIG. 3, but having a portion 108 of the active material layer 100 (in FIG. 3), having some of the nonconductive material 102 and the covered particles or fibers from the top surface 103 removed with an adhesive tape. The portion 108 of the modified active material layer 100' that was removed to produce modified electrode 10' is shown in dashed line in FIG. 4. The removal of the portion 108 yields a modified active material layer 100'. Though the portion 108 has been removed for the modified electrode 10’, the remainder of the original electrode 10 present in modified electrode 10’ is substantially not changed, for example, in this trial, only the coating layer 100 and / or coated particles 101 are removedfrom top surface 103. In this comparative investigation, the removed portion 108 comprises less than 20% of the active material layer 100 in thickness and mass compared to coated electrode 10. For this investigation, the modified electrode 10’ is representative of an uncoated electrode. The electrical resistance across the modified electrode 10’ is measured using a multimeter 110 to connect to a modified top surface 103' and bottom surface 105.

[0064] According to aspects of the invention, a comparison of the resistance across the original electrode 10 shown in FIG. 3, according to aspects of the invention, with the resistance across the modified electrode 10’ having a portion 108 of the active material layer 101 removed, shown in FIG. 4, indicates the relative lack of variation of electrical resistance before material removal. For example, according to one aspect of the invention, the passivation or coating or isolation of the particles or fibers 101 of the active material by the nonconductive material 102 at the surface 103 of the electrode 10 may tend to increase the electrical resistance of electrode 10 at the surface 103. This increase in electrical resistance at the surface 103 can minimize or prevent undesirable metal reactions (for example, lithium plating) with the particles or fibers 101 of active material at the surface 103.

[0065] According to aspects of the invention, the passivation or coating of the particles or fibers 101 of the active material by the nonconductive material 102 at the surface 103 provides an electrode 10 that minimizes or prevents variation in surface electrical resistance across the electrode 10.

[0066] For example, in some embodiments, the resistance of the nonconductive material covered electrode 10 according to aspects of the invention is at least 50% higher than the resistance of the modified electrode 10' after having the portion 108 of active material layer 100 after the covered particles or fibers 101 are removed. In some embodiments, the resistance of the nonconductive material covered electrode 10 is at least 100% higher than the resistance of the modified electrode 10' after having the portion 108 the covered particles or fibers 101 removed. In one aspect, substantially only the active material particles or fibers 101 at the surface 103 may be coated withnonconductive material 102, while the active material particles or fibers 101 in the remainder or in the inside of the active layer 100 may not be coated with nonconductive material 102. In some embodiments, the resistance of the nonconductive material covered electrode 10 is larger than 2 Ohms [Q], while the resistance of the modified electrode 10' after the covered particles or fibers 101 at the surface 103 are removed is less than 1 £1.

[0067] FIG. 5 is a schematic illustration of an electrochemical cell 20 comprising the electrode 10 of FIG. 1, according to an aspect of the invention, a separator 300, an opposite electrode 400, and with an electrolyte 500 added in. In some embodiments, the opposite electrode 400 may comprise a lithium-ion compound, wherein the lithium- ion compound may be, or is selected from the group consisting of, a lithium transition metal phosphate (for example, of the formula LiMPO4, where M = Fe, Mn, Ni, or Co), a lithium nickel manganese cobalt oxide (for example, of the formula LiaNixMnyCozO2-b, where o< x,y,z<i, o.5<a<i.5, and -o.5<b<o.s), a lithium cobalt oxide (for example, of the formula LiCoO2), a lithium manganese oxide (for example, of the formula LiMn204), a lithium nickel cobalt aluminum oxide (for example, of the formula LiaNixCoyAlzO2-b, where o< x,y,z<i, o.5<a<i.5, and -0.5 < <0.5), a lithium titanate (for example, of the formula Li2TiO3), or mixture of or more of these lithium ion compounds.

[0068] The separator 300 may comprise a thin, porous membrane placed between the electrode 10 and the opposite electrode 400. The separator 300 maybe selected from polymers, for example, polyethylene, polypropylene, polyvinylidene difluoride, polyethylene oxide; ceramics, such as glass, LiPONs, Li7La3Zr2Oi2(LLZO), and Li3PS4(LPS); and / or a mixture of a polymer, a mixed ceramic, or a polymer-ceramic composite.

[0069] The electrolyte 500 can be a liquid electrolyte, a gel electrolyte, a solid electrolyte, or a composite electrolyte comprising two or more of a liquid, a gel, or a solid electrolyte. In some embodiments, the electrochemical cell 20 maybe a coin cell. In some alternative embodiments, the electrochemical cell 20 maybe a pouch cell. In some alternative embodiments, the electrochemical cell 20 maybe a cylindrical cell. In some alternative embodiments, the electrochemical cell 20 maybe a prismatic cell.

[0070] FIG. 6 is a flow chart illustrating a method 30 for making the electrode 10 shown in of FIG. 1, according to an aspect of the invention. In one aspect, the method 30 of FIG. 6 maybe characterized as a method according a state-of-the-art manufacturing process. As shown in FIG. 6, in one aspect, the method 30 includes a mixing step 31 comprising the combining of the constituents or ingredients that will eventually comprise the active layer too of electrode 10 shown in FIG. 1. In one aspect, the constituents combined in mixing 31 include active particles or fibers 101, for example, any one or more of the active particles disclosed herein, such as, natural graphite, artificial graphite, hard carbon, silicon powder, carbon-silicon composite, or carbon nanotubes; a conductive additive, such as, carbon black, carbon nanotubes, or graphene; a binder, such, PVDF or CMC; and a solvent, such as, NMP. The mixing 31 may be practiced manually or by automated means, for example, in a specially-designed mixer used in the art, for example, a batch or continuous mixer provided by S. Howes, or its equivalent.

[0071] After mixing the continuants into a slurry in mixing step 31, the slurry is applied to a collector sheet, or current collector, 200 in coating process 33, for example, a collector sheet 200 that will ultimately provide the current collector 200 of electrode 10 shown in FIG 1. The coating process 33 may be practiced by conventional means, for example, manually or by an automated coating device, such as, in a specially-designed coating device mixer used in the art, for example, a continuous coater provided by Durr Systems, Inc., or its equivalent. According to aspects of the invention, the thickness of the slurry on the coated collector sheet 200 may vary from 100 nm to 10 mm, but the coating on the collector sheet 200 typically has a thickness of between 10 pm and 200 pm. The collector sheet 200 may comprise any one or more the materials of the current collector 200 disclosed herein, for example, copper or aluminum.

[0072] As shown in FIG. 6, after coating 33, the slurry coated on the collector sheet 200 is allowed to dry or “cure” in drying process 34. The drying process 34 maybe practiced as room temperature, for example, 65 degrees F to 75 degrees F, but is typically practiced at above room temperature, for example, in an oven or on a “hot plate.” The drying temperature may range from 100 degrees F to 500 degrees F, buttypically drying 34 is practiced at between 150 degrees F and 300 degrees F, for example, at 250 degrees F. In one aspect, drying 34 maybe practiced in a sectional oven, for example, an integrated coating-drying oven provided by Durr Systems, Inc., or its equivalent.

[0073] After drying 34, method 30 proceeds with coating the dried slurry and collector sheet 200 in a coating process 35. According to aspects of the invention, coating 35 may comprise coating dried slurry of active particles or fibers 101 and binder on the collector sheet 200 with a coating material, for example, by means of electrostatic deposition. The coating material may be any one of the nonconducting materials disclosed herein, for example, a PTFE, a PVDF, or a PE.

[0074] In one aspect, the thickness of the coating in coating process 35 may vary from 10 nm to 50 pm, but the coating on the collector sheet 200 typically has a thickness of between 100 nm and 10 pm. In one aspect, coating 35 may be practiced using a conventional electrostatic deposition chamber, for example, a uniquely-designed “home-made” electrostatic deposition chamber equipped with a high voltage supply, a syringe pump and a drum collector, or its equivalent.

[0075] As shown in FIGURE 6, after coating 35, the coated electrode is then processed in a calendaring process 36 to obtain a desired porosity of the electrode 10, for example, the substantially finished electrode 10. As known in the art, the calendaring process 36 is a compaction process that modifies, typically, reduces, the porosity of the treated electrode and reduces the surface roughness of the electrode. As known in the art, calendaring can improve the contact between, for example, the particles or fibers 101, in the electrode 10 and hence enhance the energy density of the electrochemical cell 20, for example, the battery in which the calendared electrode is used. In one aspect, calendaring 36 may be practiced to produce a porosity of the electrode, for example, electrode 10 shown in FIG. 1, from about 10% to about 75%, but the porosity produced by calendaring 36 may typically yield a porosity of 30% to 50%. In one aspect, calendaring 36 may be practiced using a conventional calendaring device, for example, a MSK-E2300A calendaring device provided by MTI Corporation, or its equivalent.

[0076] FIG. 7 is a flow chart illustrating a method 40 for making the electrode 10 shown in FIG. 1 in a dry electrode manufacturing process, according to another aspect of the invention. As shown in FIG. 7, method 40 may begin by a mixing or homogenizing process 41, which maybe similar to mixing process 31 shown and described with respect to FIGURE 6, comprising the combining of the constituents or ingredients that will eventually comprise the active layer 100 of electrode 10 shown in FIG. 1. In one aspect, the constituents combined in mixing 41 include active particles or fibers 101, for example, any one or more of the active particles disclosed herein, such as, natural graphite, hard carbon, or silicon powder; a conductive additive, such as, carbon black, graphene, or carbon nanotubes; and a binder, such, as PTFE. The mixing 41 maybe practiced manually or by automated means, for example, in a specially-designed mixer used in the art, for example, a MSK-PCV-300-LD mixer provided by MTI Corporation, or its equivalent.

[0077] As shown in FIG. 7, according to aspects of the invention, after the mixing 41, the mixed constituents are then treated in a pressing process 42. According to this aspect of the invention, which is different from the process 30 shown in FIG. 6, in process 40, pressing process 42 comprises compressing the mixed constituents from mixing 41 to form a thin film of constituents, for example, a self-standing electrode film. In one aspect, the pressing process 42 may be practiced manually or by automated means, for example, an automated roll mill, as known in the art. The compressing 42 may be practiced specially designed roll mill, for example, a MTI Corporation roll mill provided by MTI Corporation, or its equivalent. In one aspect, after pressing 42, the compressed electrode film may have a thickness from 10 pm to 1 mm, but pressing 42 typically yields a film thickness of between 30 pm and 200 pm.

[0078] After pressing 42, the electrode film produced is coated in a coating process 43. Coating process 43 of method 40 may be similar to coating process 35 of method 30 shown and described with respect to FIG. 6. According to aspects of the invention, coating 43 may comprise coating the electrode film produced in pressing process 42 with a coating material, for example, by means of electrostatic deposition. Typically, during the coating process 43 only one side of the thin film electrode is coated, wherethe opposite side is uncoated. The coating material may be an one of the nonconductive materials disclosed herein, for example, an oxide or a polymer, such as, PVDF or PE. In one aspect, the thickness of the coating provided in process 43 may vary from 10 nm to 100 pm, but the coating 43 may typically provide a thickness of between 100 nm and 10 pm. In one aspect, coating 35 may be practiced using a conventional electrostatic deposition chamber, for example, a uniquely-designed “home-made” electrostatic deposition chamber equipped with a high voltage supply, a syringe pump, and a drum collector, or its equivalent.

[0079] As shown in FIG. 7, after coating 43, the coated thin film electrode is then treated with a lamination process 44 where the coated, thin film electrode is laminated on to a collector sheet, for example, comprising the current collector 200 of electrode 10 in FIG. 1, for example, a metallic sheet, such, as a copper or an aluminum sheet.According to aspects of the invention, during the lamination 44, the uncoated side of the thin film electrode contacts a surface of the collector sheet. As in the coating process 33 of method 30 shown and described with respect to FIG. 6, the collector sheet laminated in lamination process 44 may comprise any one or more the materials of the current collector 200 disclosed herein, for example, copper or aluminum. In one aspect, lamination 44 may be practiced using a conventional lamination device, for example, a JTFM380 lamination device provided by MTI Corporation, or its equivalent. In one aspect, with the completion of lamination 44, a substantially finished electrode 10 according to aspects of the invention may be produced.

[0080] FIG. 8 is a graph 50 illustrating a comparison of the cycling performance of a group of baseline electrochemical cells and a group of exemplary electrochemical cells according to aspect of the invention, for example, electrochemical cell 20 shown and described with respect to FIG. 5. The abscissa or x-axis 51 of graph 50 is in units of numbers of cycles that the subject electrochemical cells were exposed to and the ordinate or y-axis 52 of graph 50 is the “discharge capacity” in units of milliAmp-hours [mAh]. As known in the art, discharge capacity represents the energy that an electrochemical cell can produce, in this case, after the corresponding number of cycles.

[0081] The curves 53 and 54 shown in graph 50 represent the variation in discharge capacity as the number of cycles increases. In FIG. 8, the top four curves 53 represent the performance of electrochemical cells according aspects of the present invention, and the bottom three curves 54 represent the performance of the baseline prior art electrochemical cells. The processing and composition of the electrochemical cells that yielded the performance illustrated in FIG. 8 are described below in the “Examples of Aspects of the Invention” section under the heading Example 5.

[0082] As shown in FIG. 8, in general, with increasing number of cycles, the discharge capacity of these electrochemical cells typically decreases. However, as shown in FIG.8, after the 300 cycles, the top four curves 53 representing electrochemical cells according to aspects of the present invention have greater discharge capacity (in mAh) compared to the bottom three curves 54 of the comparative electrochemical cells. That is, after 300 cycles, all four of the curves 53 of the exemplary electrochemical cells according to aspects of the present invention have higher discharge capacity than all three curves 54 of the comparative electrochemical cells. Furthermore, the variation of the discharge capacity among the electrochemical cells according to aspects of the present invention as indicated by curves 53 is smaller than the variation of the curves 54 of the comparative electrochemical cells.

[0083] In short, as shown in FIG. 8, the performance of electrochemical cells having coated electrodes according to aspects of the present invention, in terms of discharge capacity, is better than the performance of comparative uncoated electrochemical cells after comparable cycling, and the discharge capacity of the coated electrochemical cells according to aspects of the present invention is less variable, that is, more consistent, with increased cycles than the discharge capacity of the comparative uncoated electrochemical cells.Examples of Aspects of the Invention

[0084] The following examples are intended to illustrate certain embodiments of the present invention, but do not exemplify the full scope of the invention.EXAMPLE 1

[0085] In one comparative embodiment, a baseline electrode was prepared first by mixing natural graphite (90 wt%) with carbon black conductive additive (5 wt%) and polyvinylidene difluoride (PVDF) binder (5 wt%) in an N-methylpyrrolidone (NMP) solvent. After stirring overnight at room temperature, the obtained slurry was coated onto a copper current collector sheet with a doctor-blade, as is typical in the art. The slurry and copper current collector sheet were then dried in an oven at 120 degrees C. The dried graphite, PVDF binder, carbon black, and copper current collector sheet was then calendared to a porosity of 40% to provide a graphite comparative baseline electrode having electric conductivity properties similar to electrode 10’ in Figure 4.EXAMPLE 2

[0086] In one exemplary embodiment, the comparative electrode from Example 1 was used as the collector in an electrostatic deposition chamber equipped with a needle, a syringe pump, and a high-voltage module, where the graphite electrode surface was electrostatically coated with PVDF as the coating material to produce a coated electrode according to one aspect of the invention.EXAMPLE 3

[0087] The coated electrode (Example 2) and the uncoated comparison electrode (Example 1) prepared as illustrated in Example 1 and Example 2 were observed under an optical microscope. FIGS. 2A and 2B show optical micrographs of uncoated (FIG. 2A - Example 1) and nonconductive material coated (FIG. 2B - Example 2) surfaces of the electrode of FIG. 1, according to aspects of the invention, at 40 times optical magnification.EXAMPLE 4

[0088] A multimeter was connected to the top surface and bottom surface of the coated electrode of Example 2 - the coated electrode according to an aspect of the invention. Then a portion of the layer of the covered particles or fibers was removed using anadhesive tape (to produce the modified electrode 10’ shown in FIG. 4), and then connected to a multimeter to the top surface and bottom surface again - as shown schematically in FIGURES 3 and 4. The resistance of the nonconductive material covered electrode 10, according to aspects of the invention (as shown in FIG. 3), was 4.9 £1, while the resistance of the modified electrode 10’ after the covered particles or fibers are removed (as shown in FIG. 4) was 0.9 £1.EXAMPLE 5

[0089] The baseline electrode from Example 1 and an exemplary electrode from Example 2 according to aspects of the invention were punched into 14 mm diameter disks and used as electrodes for coin cell assemblies. A commercial LiNio.6Coo.2Mno.2O2 coated aluminum sheet was punched into 12 mm diameter disks and used as the counter electrodes (see counter electrode 400 shown in FIG. 5) for each assembly. The electrodes and the counter electrodes were laid on opposite sides of a polyolefin separator (see separator 300 shown in FIG. 5) for each assembly, and each assembly was soaked with an electrolyte comprised of LiPFe in mixed solvents of ethylene carbonate and dimethyl carbonate (see electrolyte 500 shown in FIG. 5). The above assemblies were put inside a 2032-type coin cell casing compartment with a spacer, a wave spring, and an insulating cap, and sealed with an automatic coin cell presser to make a baseline electrochemical cell and an exemplary electrochemical cell (coin-sized batteries) according to an aspect of the present invention, respectively. The batteries were formed at C / 10 cycling rate for 3 cycles and then cycled at C / 2 constant current - constant voltage charge with C / 10 taping current and 1C constant current discharge between 2.8V and 4.3V for 300 cycles. The discharge capacity of each cell at each cycle was recorded and plotted against the cycle number as shown in FIG. 8.EXAMPLE 6

[0090] In one comparative embodiment, a baseline electrode was prepared by coating a slurry comprising 94 wt% of hard carbon, 4 wt% of graphene conductive carbon, and 2 wt% of a polymeric binder of carboxymethyl cellulose (CMC) in water, on an 8 pm thick copper current collector. The coating of the slurry on the collector leads to theformation of a layer with a thickness of approximately 100 pm. The resulting product is then placed in an extraction oven at a temperature of 50 degrees C for 12 hours, so that the residual water evaporates. The dried sheet is then calendared using a press.EXAMPLE 7

[0091] In one exemplary embodiment of the invention, the comparative sheet prepared as illustrated in Example 6 was used as the collector in an electrostatic deposition chamber equipped with a needle, a syringe pump, and a high voltage module, where the hard carbon electrode surface was electrostatically coated with polyethylene as the coating material.EXAMPLE 8

[0092] In one comparative embodiment of an aspect of the invention, a counter electrode was prepared by coating an ink comprising 90 wt% of a Prussian blue powder (Na2Fe2(CN)6), 5 wt% of an electronic conductor of the carbon nanotube and 5 wt% of a polymeric binder polytetrafluoroethylene (PTFE) onto an aluminum current collector. The resulting product is then placed in an extraction oven at a temperature of 50 degrees C for 12 hours, then calendared using a press.EXAMPLE 9

[0093] In one exemplary embodiment of an aspect of the invention, the electrodes prepared as illustrated in Examples 6 and 7 were punched into 14 mm diameter disks as the anodes for a comparative electrochemical cell and an exemplary electrochemical cell of an aspect of the invention, respectively. The electrodes from Examples 8 were punched into 12 mm diameter disks as the cathode for sodium battery coin cell assembly. The anodes and the cathode were laid on opposite sides of a polyolefin separator and soaked with an electrolyte comprised of NaPFe in mixed solvents of ethylene carbonate and dimethyl carbonate. The above assembly was put inside a 2032- type coin cell casing compartment with a spacer, a wave spring, and an insulating cap, and sealed with an automatic coin cell presser to make a baseline electrochemical celland an exemplary electrochemical cell of an aspect of the invention (coin-sized batteries), respectively.EXAMPLE 10

[0094] In one comparative embodiment, a baseline electrode was prepared first by mixing silicon powder (95 wt%) with Super P Conductive Carbon Black (2 wt%) and PVDF binder (3 wt%) in NMP solvent. After stirring overnight at room temperature, the obtained slurry was coated onto a copper current collector sheet with a doctor-blade. The sheet was then dried in an oven at 120 °C, then calendared to a porosity of 40%.EXAMPLE 11

[0095] In one exemplary embodiment of an aspect of the invention, the comparative sheet prepared as illustrated in Example 10 was used as the collector in an electrostatic deposition chamber equipped with a needle, a syringe pump, and a high voltage module, where the silicon electrode surface was electrostatically coated with PVDF as the coating material.EXAMPLE 12

[0096] The electrodes prepared as illustrated in Examples 10 and 11 were punched into 14 mm diameter disks and used as the electrodes for coin cell assembly. A commercial LiFePO4coated aluminum sheet was punched into 12 mm diameter disks and used as the counter electrode. The electrodes and the counter electrodes were laid on opposite sides of a polyolefin separator and soaked with an electrolyte comprised of LiPF()in mixed solvents of ethylene carbonate and dimethyl carbonate. The above assemblies were put inside a 2032-coin cell casing compartment with a spacer, a wave spring, and an insulating cap, and sealed with an automatic coin cell presser to make a comparative embodiment, and an exemplary electrochemical cell according to an aspect of the invention.EXAMPLE 13

[0097] In one exemplary embodiment of an aspect of the invention, commercial LiCoO2was mixed with carbon nanotube conductive additive and PVDF, then applied onto an aluminum foil to form a LiCoO2electrode. The LiCoO2electrode was used as the collector in an electrostatic deposition chamber equipped with a needle, a syringe pump, and a high voltage module, where the LiCoO2electrode surface was electrostatically coated with an insulating polymer PVDF as the coating material.EXAMPLE 14

[0098] In one exemplary embodiment of an aspect of the invention, natural graphite powder (95 wt%) and carbon nanotube conductive additive (2.5 wt%) were thoroughly mixed and homogenized with PTFE powder (2.5 wt%). The mixture was then pressed between two rollers with a gap distance of 70 micrometers to form a self-standing active material layer film. Next, the active material film was used as the collector in an electrostatic deposition chamber equipped with a needle, a syringe pump, and a high voltage module, where one of its surfaces was electrostatically coated with PVDF as the coating material to obtain a coated active material layer. The one-side coated active material layer was then laminated onto a current collector to make an exemplary electrode of an aspect of the invention, where the uncoated side of the active material layer was in close contact with the current collector.

[0099] According to aspects of the invention, electrodes, electrochemical cells, and methods of making electrodes that overcome the disadvantages of the prior art are provided. For example, aspects of the invention yield electrodes with coated (that is, passivated) surfaces that may facilitate battery fabrication, for example, by obviating the need for the “formation step” that characterizes prior art processing. Aspects of the invention may reduce the variation and increase the capacity of a battery’s performance, may improve the yield of the manufacturing line; and / or may enhance the stability and safety of batteries having the electrodes disclosed herein.

[0100] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein,the singular forms "a", "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0101] The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present disclosure has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the disclosure in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. The embodiments were chosen and described in order to best explain the principles of the disclosure and the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.* * * * *

Claims

CLAIMS1. An electrode (10) comprising: a current collector (200); an active material layer (100), wherein the active material layer (100) comprises particles or fibers (101) of active material, the active material layer (100) having a first surface (103) and a second surface (107) opposite the first surface (103), wherein the second surface (107) contacts the current collector (200); and a nonconductive material (102), wherein the nonconductive material (102) partially covers the particles or fibers (101) of the active material at the first surface (103) of the active material layer (100).

2. The electrode (10) as recited in claim 1, wherein partially covers comprises a percentage of the particles or fibers (101) of the active material that are not covered by the nonconductive material (102) at the first surface (103) of the active material layer (100) is not more than 10%.

3. The electrode (10) as recited in claim 1 or claim 2, wherein partially covers comprises a percentage of particles or fibers (101) of the active material that are not covered by the nonconductive material (102) at the first surface (103) of the active material layer (100) is not more than 1%.

4. The electrode (10) as recited in any one of claims 1 to 3, wherein a resistance of the electrode (10) is at least 50% higher than the resistance of the electrode (10) after a portion of the covered particles or fibers (101) are removed.

5. The electrode (10) as recited in any one of claims 1 to 4, wherein an average thickness of the nonconductive material (102) is between 1 nanometer and 20 micrometers.

6. The electrode (10) as recited in any one of claims 1 to 5, wherein an average thickness of the nonconductive material (102) is between 1 nanometer and 20 micrometers, and a resistance of the electrode (10) is at least 50% higher than a resistance of the electrode (10) after a portion of the covered particles or fibers(101) are removed.

7. The electrode (10) as recited in any one of claims 1 to 6, wherein the active material comprises a material capable of reversible reaction with an active metal selected from lithium, sodium, potassium, zinc, magnesium, iron, and aluminum.

8. The electrode (10) as recited in any one of claims 1 to 7, wherein the active material is selected from at least one of carbon, such as, graphite and hard carbon; silicon; a silicon-graphite composite; sulfur; an aluminum alloy; tin; iron; or a compound containing one or more of the elements selected from the group of nickel (Ni), cobalt (Co), manganese (Mn), and iron (Fe), titanium (Ti), and vanadium (V).

9. The electrode (10) as recited in any one of claims 1 to 8, wherein a porosity of the active material layer (100) is within the range of 10% to 50%.

10. The electrode (10) as recited in any one of claims 1 to 9, wherein the current collector (200) comprises at least one of carbon, copper, aluminum, iron, nickel, titanium, and silver.

11. The electrode (10) as recited in any one of claims 1 to 10, wherein an average dimension of the particles or fibers (101) is within the range of 10 nm to 50 pm.

12. The electrode (10) as recited in any one of claims 1 to 11, wherein the first surface (103) of the active material layer (100) comprises a total conductive surface area, and wherein a conductive surface area covered by the nonconductive material(102) is no less than 70% of the total conductive surface area of the first surface13- The electrode (10) as recited in any one of claims 1 to 12, wherein the first surface (103) of the active material layer (100) comprises a total conductive surface area, and wherein a conductive surface area covered by the nonconductive material(102) is no less than 90% of the total conductive surface area of the first surface(103) of the active material layer (100).

14. The electrode (10) as recited in any one of claims 1 to 13, wherein the nonconductive material (102) is selected from the group consisting of polymers, oxides, sulfides, fluorides, chlorides, carbonates, nitrides, silicates, borates, aluminates, sulfates, phosphates, and mixed-anion compounds thereof.

15. The electrode (10) as recited in claim 14, wherein the polymers comprise one or more of polyethylene (PE), polypropylene (PP), polystyrene (PS), polytetrafluoroethylene (PTFE), polyvinyldifluoride (PVDF), polyacrylic acid (including its esters) (PAA), polyamide (PA), polyester (PES), and poly(terephthalate) (PT).

16. The electrode (10) as recited in any one of claims 1 to 15, wherein the active material layer (100, 100') comprises a lithium-ion compound, wherein the lithium-ion compound is selected from the group consisting of a lithium metal phosphate (LiMPO4, M = Fe, Mn, Ni, or Co), a lithium nickel manganese cobalt oxide (LiaNixMnyCozCb, o< x,y,z<i, o.5<a<i.s), a lithium cobalt oxide (LiCoO2), a lithium manganese oxide (LiMn2O4), a lithium nickel cobalt aluminum oxide (LiNiCoAlO2), a lithium titanate (Li2TiO3), and derivatives of these lithium-ion compounds.

17. The electrode (10) as recited in any one of claims 1 to 16, wherein the nonconductive material (102) partially covers the particles or fibers (101) of the active material comprises the nonconductive material (102) substantially completely covers the particles or fibers (101) of the active material at the first surface (103) of the active material layer (100).

18. An electrochemical cell (20) comprising: the electrode (10) as recited in any one of claims 1 to 17; an opposite electrode (400); and an electrolyte (500).

19. The electrochemical cell (20) as recited in claim 18, further comprising a separator (300).

20. The electrochemical cell (20) as recited in ef claim 18 or claim 19, wherein the opposite electrode (400) comprises a lithium-ion compound, wherein the lithium-ion compound is selected from the group consisting of a lithium metal phosphate (LiMPO4, M = Fe, Mn, Ni, or Co), a lithium nickel manganese cobalt oxide (LiaNixMnyCozCb, o< x,y,z<i, o.5<a<i.s), a lithium cobalt oxide (LiCoO2), a lithium manganese oxide (LiMn2O4), a lithium nickel cobalt aluminum oxide (LiNiCoAlO2), a lithium titanate (Li2TiO3), and derivatives of these lithium-ion compounds.

21. A method of making the electrode (10) recited in claim 1, the method comprising: depositing (33, 43) a material having an active material on a current collector (200) to produce an active material layer (100) having a first surface (103) and a second surface (107), the second surface (107) contacting the current collector (200); and depositing (35, 44) a nonconductive material (102) on the first surface (103) of the active material layer (100), wherein the first surface (103) of the active material layer (100) is partially covered by the nonconductive material (102).

22. The method as recited in claim 21, wherein depositing (33) the nonconductive material (102) comprises an electrostatic depositing.

23. The method as recited in claim 21 or claim 22, wherein partially covered comprises a percentage of particles or fibers (101) of the active material that are not covered by the nonconductive material (102) at the first surface (103) of the active material layer (100) is not more than 10%.

24. The method as recited in any one of claims 21 to 23, wherein partially covers comprises a percentage of particles or fibers (101) of the active material that are not covered by the nonconductive material (102) at the first surface (103) of the active material layer (100) is not more than 1%.

25. The method as recited in any one of claims 21 to 24, wherein the method further comprises, prior to depositing the material having the active material, combining (31, 41) the active material with a binder to produce the material having the active material.

26. The method as recited in claim 25, wherein combining (31, 41) the active material with the binder comprises combining the active material with the binder and a solvent.

27. The method as recited in any one of claims 21 to 26, wherein the method further comprises, after combining, agitating the active material and a binder.

28. The method as recited in any one of claims 21 to 27, wherein the method further comprises, after depositing the nonconductive material on the first surface (103) of the active material layer (100), drying (34) the deposited material on a current collector.

29. The method as recited in any one of claims 21 to 28, wherein the method further comprises, after depositing the nonconductive material on the first surface (103) of the active material layer (100), calendaring (36) the nonconductive material (102) and active material layer (100) to a predetermined porosity.

30. The method as recited in any one of claims 21 to 29, wherein the method further comprises, prior to depositing the material having the active material on thecurrent collector, compressing (42) the material having the active material to form a film of the material having the active material.

31. A method of making an electrode (10), the method comprising: depositing (33, 43) a material having an active material on a current collector (200) to produce an active material layer (100) having a first surface (103) and a second surface (107), the second surface contacting the current collector (200); and depositing (35, 44) a nonconductive material (102) on the first surface (103) of the active material layer (100), wherein the first surface (103) of the active material layer (100) is partially covered by the nonconductive material (102).

32. The method as recited in claim 31, wherein the active material comprises a material capable of reversible reaction with an active metal selected from lithium, sodium, potassium, zinc, magnesium, iron, and aluminum.

33. The method as recited in claim 31 or claim 32, wherein the active material is selected from at least one of graphite, silicon, sulfur, an aluminum alloy, tin, iron, or a compound containing one or more of the elements selected from the group of nickel (Ni), cobalt (Co), manganese (Mn), iron (Fe), titanium (Ti), and vanadium (V).

34. The method as recited in any one of claims 31 to 33, wherein the electrode (10) comprises an electrode for an electrochemical cell (20).

35. The method as recited in any one of claims 31 to 34, wherein the active material comprises particles or fibers of active material, and wherein partially covers comprises a percentage of the particles or fibers (101) of the active material that are not covered by the nonconductive material (102) at the first surface (103) of the active material layer (100) is not more than 10%.

36. The method as recited in any one of claims 31 to 35, wherein the active material comprises particles or fibers of active material, and wherein partially coverscomprises a percentage of particles or fibers (101) of the active material that are not covered by the nonconductive material (102) at the first surface (103) of the active material layer (100) is not more than 1%.

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