Column-shaped silicon anode with a carbon fiber mesh on top and this encompassing lithium-ion batteries

Abstract

Lithium-ion batteries are provided that include a columnar silicon anode featuring a carbon fiber network on exposed surfaces of the anode. The columnar silicon is fabricated by plasma vapor deposition. Also disclosed are methods for forming the carbon fiber network, which generally involve spraying a dilute carbon fiber precursor solution containing carbon nanotubes, an optional polymeric dispersant, and a solvent, followed by gentle evaporation at elevated temperature to remove the solvent and form the carbon fiber network. The carbon fiber network is uniformly and multidirectionally distributed across the exposed surfaces of the columnar silicon anode.The presence of the carbon fiber mesh provides high-performance electronic pathways to improve battery performance, especially at higher currents.

Description

INTRODUCTION

[0001] The present disclosure relates generally to anodes for liquid-based, gel-based, or solid-state lithium-ion batteries, and more particularly to anodes formed from columnar silicon having a carbon fiber network thereon, and to lithium-ion batteries comprising the same.

[0002] Lithium-ion batteries with silicon anodes (Si anodes) represent a promising energy storage technology as they have a high gravimetric theoretical storage capacity for lithium (Li) (4200 mAh g -1 for Li 4,4 Si) compared to conventionally used graphite anodes (372 mAh g -1 ) and at the same time have a relatively low discharge voltage (the average delithiation voltage of Si is 0.4 V).

[0003] However, it is known that silicon's ability to absorb large amounts of lithium causes the material to undergo enormous volume changes during lithiation and delithiation, which can be as high as approximately 400% or more, as occurs during battery cycling. The stress and strain resulting from this volume change can lead to electrode fracture and electrical insulation from the underlying current collector upon repeated cycling, resulting in delamination of the deposited silicon film from the current collector. Furthermore, the silicon anode is subject to mechanical fracture and instability of the solid electrolyte interphase (SEI) layers formed during the intercalation / deintercalation processes.

[0004] In addition, silicon anodes naturally have low electrical conductivity at room temperature (<10 -5Siemens per centimeter (S / cm)), which is significantly lower than that of carbon and graphite (10-10 4 S / cm). When working with liquid electrolyte (or solid electrolyte or gel electrolyte), the low electrical conductivity of silicon can degrade the performance of the lithium-ion battery and make its practical high-performance application difficult.

[0005] Accordingly, it is desirable to mitigate the problems arising from the expansion and contraction of the silicon anode during lithium-ion battery cycling to maximize capacity and minimize failures, as well as improve their performance for high-power applications. SUMMARY

[0006] In an exemplary embodiment, a columnar silicon anode for a lithium-ion battery comprises a plurality of spherical silicon columns; and a carbon fiber mesh on exposed surfaces of the spherical silicon columns. Silicon in the plurality of spherical silicon columns is greater than 97 weight percent, and the carbon fiber mesh is approximately 0.05 weight percent to less than 3 weight percent, wherein the weight percents are based on a total weight of the plurality of spherical silicon columns and the carbon fiber mesh.

[0007] The carbon fiber network is random and multidirectional. In one or more aspects, the carbon fiber network further comprises a polymer additive in an amount of greater than 0 to 3 weight percent. The carbon fiber network comprises carbon nanotubes, wherein the carbon nanotubes have a length of greater than about 1 micrometer (µm), a diameter of about 1 nm to about 6 nm, and a thickness of less than 0.1 nanometer (nm). The carbon nanotubes may comprise single-walled carbon nanotubes, double-walled carbon nanotubes, and / or multi-walled carbon nanotubes. In some aspects, the carbon fiber network comprises one or more carbon additive materials.

[0008] The plurality of spherical silicon columns can be deposited onto an anode current collector by direct current magnetron sputtering. Each of the plurality of spherical silicon columns comprises dimensions a and b with lengths within a range of approximately 0.5 to 40 micrometers (µm). The columnar silicon anode has an areal capacitance of approximately 0.5 to approximately 20 milliampere-hours per square centimeter. The lithium-ion battery comprising the columnar silicon anode can be used with liquid, solid, or gel-based electrolytes.

[0009] In one or more embodiments, a method for forming a carbon fiber network on a columnar silicon anode for a lithium-ion battery comprises providing a columnar silicon anode on an anode current collector, the columnar silicon anode comprising a plurality of spherical silicon columns deposited on the anode current collector by plasma vapor deposition. A carbon fiber precursor solution having a solids content of less than 10 weight percent is applied to exposed surfaces of the columnar silicon anode. The carbon fiber precursor solution comprises carbon nanotubes, a polymeric dispersant, and a solvent.The applied carbon fiber precursor solution, the columnar silicon anode, and the anode current collector are exposed to an elevated temperature for a time effective to evaporate the solvent and form the carbon fiber network on the exposed surfaces. The carbon fiber network is random and multidirectional and comprises more than 0 to less than 3 weight percent based on the total weight of the carbon fiber network and the columnar silicon anode. The columnar silicon anode comprises silicon in an amount of more than 97 weight percent based on the total weight of the carbon fiber network and the columnar silicon anode.

[0010] The elevated temperature may be 80°C to 90°C and the solvent may comprise water or N-methyl-2-pyrrolidone.

[0011] The anode current collector has a surface roughness Rz in a range of 0.1 µm to 12 µm.

[0012] The polymeric dispersant comprises poly(vinylidene fluoride) (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), poly(tetrafluoroethylene) (PTFE), sodium carboxymethylcellulose (CMC), styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), or styrene-ethylene-butylene-styrene copolymer (SEBS). The carbon nanotubes have a diameter of approximately 1 to approximately 6 nanometers (nm), a thickness of less than 0.1 nm, and a length of greater than 1 µm. The carbon fiber precursor solution may further comprise a carbon material containing acetylene black, graphene, and / or graphite.

[0013] In one or more embodiments, a rechargeable lithium-ion battery comprises a cathode current collector having a thickness of about 4 to about 30 µm and externally connected to a load, the cathode current collector comprising aluminum; a cathode on the cathode current collector; an anode current collector having a thickness of about 4 to about 30 µm and externally connected to a load, the anode current collector being made of one or more materials selected from a group consisting of copper, stainless steel, nickel, iron, titanium, tin (Sn), and alloys thereof, and the anode current collector having a surface roughness Rz in a range of 0.1 µm to 12 µm; a columnar silicon anode on the anode current collector comprising a plurality of spherical silicon columns and a carbon fiber mesh on exposed surfaces of the spherical silicon columns.

[0014] The columnar silicon anode is applied by plasma vapor deposition and has a thickness in a range of 1 µm to about 80 µm, wherein the columnar silicon anode comprises silicon in an amount greater than 97% by weight, and wherein the columnar silicon anode has an areal capacity of about 0.5 to about 20 mAh / cm 2 has.

[0015] A porous separator is located between the cathode and the columnar silicon anode.

[0016] In one or more aspects, the lithium-ion battery may further comprise a liquid electrolyte in the cathode, the columnar silicon anode, and the porous separator, wherein the liquid electrolyte comprises a lithium salt and an organic solvent, wherein the liquid electrolyte comprises a lithium salt, an organic solvent, and an optional additive, wherein the lithium salts are LiPF6, LiBF4, lithium bis(oxalato)borate, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiAsF6, LiC(CF3SO2)3, LiClO4, Li 1+x Al x Ti 2-x (PO4)3 and LiTFSI, and wherein the organic solvent comprises ethylene carbonate, diethyl carbonate, propylene carbonate, fluoroethylene carbonate (FEC), and combinations thereof.

[0017] The separator is a solid electrolyte and is located in the cathode and the columnar silicon anode, wherein the solid electrolyte is selected from a group consisting of pseudobinary sulfide, pseudoternary sulfide, pseudoquaternary sulfide, halide-based solid electrolyte, and hydride-based solid electrolyte.

[0018] The foregoing features and advantages, as well as other features and advantages of the disclosure, will be readily apparent from the following detailed description when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Further features, advantages and details are listed only as examples in the following detailed description, which refers to the drawings in which: Fig. 1 schematically illustrates a columnar silicon anode layer having a cobweb-like carbon network thereon on a copper current collector according to one or more embodiments of the present disclosure; Fig. 2 schematically illustrates a single silicon column according to one or more embodiments of the present disclosure; Fig. 3 is a top-down scanning electron micrograph showing a columnar surface of a silicon anode including the cobweb-like carbon fiber network thereon in accordance with one or more embodiments of the present disclosure; Fig. 4 schematically illustrates a liquid electrolyte-based lithium-ion battery structure with a silicon anode according to one or more embodiments of the present disclosure; Fig. 5 graphically illustrates room temperature cycling for a lithium-ion battery construction having a columnar silicon anode with and without the cobweb-like carbon fiber network according to one or more embodiments of the present disclosure; Fig. 6 graphically illustrates the performance level for a lithium-ion battery construction having a columnar silicon anode with and without the cobweb-like carbon fiber network according to one or more embodiments of the present disclosure; Fig. 7 graphically illustrates the discharge curve for a lithium-ion battery construction having a columnar silicon anode with and without the cobweb-like carbon fiber network according to one or more embodiments of the present disclosure; and Fig. 8 schematically illustrates a solid-state electrolytic battery structure with a silicon anode according to one or more embodiments of the present disclosure. DETAILED DESCRIPTION

[0020] The following description is merely exemplary and is not intended to limit the present disclosure, its application, or uses.

[0021] According to exemplary embodiments, liquid- or solid-state lithium-ion battery constructions comprising a columnar silicon anode with a cobweb-like carbon fiber mesh thereon are disclosed. The cobweb-like carbon fiber mesh on the columnar silicon anode, which is highly conductive, enhances the battery's performance, particularly at higher currents. Furthermore, the cobweb-like carbon fiber mesh can serve as a protective layer for the columnar silicon anode of the lithium-ion battery to mitigate silicon powdering that can occur during cycling due to volumetric expansion and contraction, thus effectively improving the battery's cyclability and operating life.Consequently, the columnar silicon anode with the cobweb-like carbon fiber network can be advantageously implemented in lithium-ion batteries for high-performance and high-energy consumption applications.

[0022] Conventional techniques related to the manufacture of lithium-ion batteries may, but need not, be described herein. Furthermore, the various tasks and process steps described herein may be integrated into a more comprehensive method or process with additional steps or functions not further described herein. In particular, various steps in the manufacture of lithium-ion batteries are well known, and thus, for the sake of brevity, many conventional steps are only briefly mentioned here or omitted entirely without providing the known process details.

[0023] Spatially relative terms, e.g., "beneath," "under," "lower," "above," "upper," and the like, may be used herein for convenience to describe the relationship of one element or feature to one or more other elements or features, as illustrated in the figures. It is to be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation, in addition to the orientation illustrated in the figures. For example, if the device in the figures is turned over, elements described as being "below" other elements or features, or "below" other elements or features, would then be oriented "above" the other elements or features. Thus, the term "below" can encompass both the above and below orientations.The device may be oriented differently (rotated by 90 degrees or in other orientations) and the spatially relative descriptors used here may be interpreted accordingly.

[0024] The following definitions and abbreviations are to be used for the interpretation of the claims and the description. As used herein, the terms "comprises," "comprising," "includes," "including," "has," "comprising," "having," "contains," or "containing," or any other variation thereof, are intended to encompass non-exclusive inclusion. For example, a composition, mixture, process, method, article, or device that includes a list of elements is not necessarily limited to those elements, but may also include other elements not expressly listed or included in such composition, mixture, process, method, article, or device.

[0025] The terms "a / an" do not imply a limitation of quantity, but denote the presence of at least one of the referenced items. The term "or" means "and / or" unless the context clearly indicates otherwise. When reference is made throughout the specification to "an aspect," this means that a particular element (e.g., a feature, structure, step, or property) described in connection with the aspect is included in at least one of the aspects described herein and may or may not be present in other aspects. Furthermore, it is to be understood that the described elements in the various aspects may be combined in any suitable manner. Furthermore, the terms "upper," "lower," "top," "bottom," "left," and "right," and their derivatives, refer to the described structures as oriented in the figures of the drawings.The same numbers in the different figures may refer to the same component or part of it.

[0026] When an element, such as a layer, film, region, or substrate, is described as being "on" another element, it may be directly on top of the other element, or there may be intervening elements. Conversely, when an element is described as being "directly on" another element, there are no intervening elements.

[0027] Unless otherwise indicated herein, all examination standards are the most recent standard in effect on the filing date of this application or, if priority is claimed, the filing date of the earliest priority application in which the examination standard appears.

[0028] Unless otherwise defined, technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

[0029] With reference now to Fig. Figure 1 schematically illustrates a cross-sectional view of a columnar silicon anode 10 according to the present disclosure provided on an anode current collector 12. Both anode and cathode current collectors for lithium-ion batteries are generally selected to be electrochemically stable to oxidation and reduction environments during battery charging and discharging. The columnar silicon anode 10 includes a plurality of silicon columns 14 and a cobweb-like carbon fiber network 16 formed on exposed surfaces of each silicon column 14 and bridging adjacent silicon columns 14. The silicon columns 14 are generally spherical columnar structures that provide a high interface area to facilitate charge transfer and may have low porosity to increase energy density.The spider web-like carbon fiber network 16, which is applied to the silicon pillars 14, has a significantly higher electronic conductivity than a silicon semiconductor and provides advantageous electronic conduction paths for high-performance silicon anodes.

[0030] As in Fig. 2, the dimensions a and b of a spherical silicon column 14 generally have lengths within a range of about 0.5 to about 40 micrometers (µm). For example, dimension a may have a length dimension of 3.5 µm and dimension b may have a length dimension of 3.0 µm. Depending on the deposition parameters, the areal capacitance provided by a columnar silicon anode comprising the layer of silicon columns 14 may range between 0.5 and about 20 milliampere-hours per square centimeter (mAh / cm 2). In one or more embodiments, the columnar silicon anode is configured to have an areal capacity of about 2 to about 4 mAh / cm 2 In one or more embodiments, the resulting silicon columns 14 are greater than about 99 weight percent (wt%) silicon.

[0031] Reference to the term "cobweb-like" is not intended to imply that the cobweb-like carbon fiber network 16 on the silicon pillars 14 assumes a particular shape and configuration. The cobweb-like carbon fiber network 16 is generally a non-repeating pattern of randomly applied carbon fibers and is non-directional to provide strength and reinforcement in multiple directions. In one or more embodiments, the cobweb-like carbon fiber network 16 is greater than about 0.05 weight percent (wt. %) to less than about 3 wt. % based on the total weight of the silicon pillars 14 and the cobweb-like carbon fiber network 16.

[0032] In one or more embodiments, the anode current collector 12 is roughened to increase its surface area and improve adhesion for the attachment and growth of the spherical silicon pillars 16 thereon. In one or more embodiments, the anode current collector 12 has a surface roughness (Rz) in a range of about 0.1 micrometers (µm) to about 12 µm. The anode current collector 12 may have a thickness of about 4 µm to about 30 µm and may be in the form of a foil. For example, the anode current collector 12 may have a thickness of about 14 µm. The anode current collector 12 is made of one or more materials selected from the group consisting of copper, stainless steel, nickel-iron, titanium, tin, and their alloys. In other designs, the current collector is a coated graphene foil or a carbon-coated stainless steel foil.

[0033] The process for forming the columnar silicon anode 10 having a plurality of silicon columns 14 and the cobweb-like carbon fiber mesh 16 thereon generally involves cleaning the surface of the anode current collector 12 with a suitable solvent, such as isopropyl alcohol, to remove contaminants and oxides. The surface is then rinsed with distilled water and dried.

[0034] The plurality of silicon pillars 14 may be deposited onto the cleaned anode current collector 12 using plasma vapor deposition (PVD). PVD generally involves depositing silicon onto a substrate (e.g., the anode current collector 12) via vapor deposition or sputtering of a silicon target material. For example, the PVD process may be a pulsed direct current (DC) magnetron sputtering process in an inert atmosphere using a silicon target (e.g., n-type; 99.995%). During sputtering, silicon is ejected from the silicon target material and deposited onto the anode current collector 12. As is generally known in the art, the plurality of silicon pillars 14 (i.e., a columnar silicon structure) may be formed by controlling deposition parameters such as temperature, deposition rate, gas composition, and the like.The resulting columnar silicon structure can be annealed to remove residual stresses and promote further growth of the columnar structures.

[0035] Once the plurality of silicon pillars 14 are formed on the anode current collector 12, the cobweb-like carbon fiber network 16 is deposited thereon by mixing a dilute precursor solution comprising carbon nanotubes, a polymeric dispersant, and a processing solvent such as water, N-methyl-2-pyrrolidone, or a similar solvent in which the polymeric dispersant is soluble. The total solids content (carbon nanotube and polymeric dispersant) within the precursor solution is generally low. In one or more embodiments, the total solids content is less than 10 wt.%. In one or more other embodiments, the total solids content is less than 3 wt.%, and in one or more further embodiments, the total solids content is less than 1 wt.%.The precursor solution can be sprayed onto the plurality of silicon columns 14 and then subjected to gentle solvent evaporation at elevated temperatures of approximately 80°C to 90°C, for example, for a period of time sufficient to completely remove the solvent. Once the solvent is removed, the cobweb-like carbon fiber network 16 forms. As mentioned above, in one or more embodiments, the cobweb-like carbon fiber network 16 is greater than 0.05 to less than 3 weight percent based on the total weight of the plurality of silicon columns 14 and the cobweb-like carbon fiber network 16. The silicon content in the columnar silicon anode 10 is greater than 97 weight percent based on the total weight of the plurality of silicon columns 14 and the cobweb-like carbon fiber network 16.The amount of carbon deposited during the formation of the cobweb-like carbon fiber network can be easily determined by thermogravimetric analysis, which is an analytical technique that involves monitoring the weight change upon application of heat and / or pyrolysis.

[0036] In one or more embodiments, the cobweb-like carbon fiber network 16 is formed from carbon nanotubes (CNTs), which may include single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), multi-walled carbon nanotubes (MWCNTs), or combinations thereof. Carbon nanotubes are generally cylindrical carbon structures with diameters in the nanometer range (typically a few nanometers) and lengths ranging from micrometers to millimeters. SWCNTs specifically refer to nanotubes consisting of a single layer of graphene rolled into a seamless cylinder, while DWCNTs comprise two concentric cylindrical layers, and multi-walled CNTs refer to more than two concentric cylindrical layers.Suitable SWCNTs, DWCNTs, and multi-walled carbon nanotubes for forming the cobweb-like carbon fiber network generally have a length greater than about 1 micrometer (µm), a diameter of about 1 nm to about 6 nm, and a thickness of less than 0.1 nanometers (nm), although larger or smaller diameters and thicknesses may be used. Alternatively, vapor-drawn carbon fibers having the dimensions noted above may also be used. In one or more embodiments, mixtures of the carbon nanotubes may be mixed with other types of carbon additives in the precursor solution during formation of the cobweb-like carbon fiber network (e.g., Super P™, commercially available from TIMCAL; Ketjenblack, a type of acetylene black commercially available from Cabot Corporation; acetylene black; conductive graphite agents such as KS-6, KS-15, SO, SEG-6, and the like; and graphene).

[0037] Exemplary polymeric dispersants include, but are not limited to, poly(vinylidene fluoride) (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), poly(tetrafluoroethylene) (PTFE), sodium carboxymethylcellulose (CMC), styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), styrene-ethylene-butylene-styrene copolymer (SEBS), and the like. The polymeric dispersant assists in the dispersion of the carbon nanotubes (i.e., prevents aggregation) in the precursor solution.

[0038] Fig. Figure 3 is a scanning electron micrograph showing a top surface of an exemplary columnar silicon anode 14 with the cobweb-like carbon fiber network 16 thereon. As shown, the cobweb-like carbon fiber network is randomly formed directly on the exposed surfaces of each silicon column and also bridges surfaces on adjacent silicon columns. The cobweb-like carbon fiber network is random and multidirectional.

[0039] Fig. 4 illustrates an exemplary liquid-based lithium-ion battery cell 50. The lithium-ion battery cell 50, also referred to as an electrochemical cell, comprises a single cell, but may also comprise more than one cell. The lithium-ion battery cell 50 generally includes an anode current collector 52, which is typically a copper current collector, and a cathode current collector 54, which is typically an aluminum current collector. The anode and cathode current collectors 52 and 54, respectively, are externally connectable to a load or a charging source (not shown), as appropriate. A columnar silicon anode, including the cobweb-like carbon fiber mesh thereon 56, overlies the anode current collector 52, and a lithium-containing metal oxide-based cathode 58 overlies the cathode current collector 54.A porous plastic spacer or separator 60 is provided between the columnar silicon anode with the cobweb-like carbon fiber mesh 56 thereon and the cathode 58. A liquid electrolyte 62 is dispersed in the porous plastic spacer or separator 60, the silicon anode layer 56, and the lithium-containing metal oxide-based composite layer 58.

[0040] The lithium-containing metal oxide-based cathode 58 generally comprises an active cathode material in a range of 30 to 98 wt.%, a conductive additive in a range of 0 to 30 wt.%, and a binder in a range of 0 to 20 wt.%, wherein the weight percentages are based on a total weight of the lithium-containing metal oxide-based cathode 58. The lithium-containing metal oxide-based cathode may have a thickness in a range of approximately 10 µm to approximately 500 µm, e.g., 40 µm.

[0041] Exemplary active cathode materials include, but are not limited to, lithium-containing metal oxide-based composites such as lithium cobalt oxide (LCO), lithium nickel manganese cobalt oxide (NMC), lithium iron phosphate (LFP), lithium manganese oxide-lithium manganese iron phosphate (LMO-LMFP), lithium manganese oxide (LMO), lithium nickel cobalt alumina (NCA), lithium titanate (LTO), and the like.

[0042] The conductive additive comprises one or more materials selected from a group consisting of carbon black, graphite, graphene, graphene oxide, Super P (SP), acetylene black, carbon nanofibers, carbon nanotubes, and other electronically conductive additives.

[0043] Examples of binders include one or more materials selected from a group consisting of polytetrafluoroethylene (PTFE), sodium carboxymethylcellulose (CMC), styrene-butadiene rubber (SBR), poly(vinylidene fluoride) (PVDF), nitrile-butadiene rubber (NBR), styrene-ethylene-butylene-styrene copolymer (SEBS), styrene-butadiene-styrene copolymer (SBS), and other suitable binders.

[0044] An exemplary separator 60 according to one or more embodiments may comprise polyethylene (PE), polypropylene (PP), polyacetylene, combinations thereof, or the like. The separator generally has a porosity of approximately 40 to 60% and a thickness of approximately 8 to 20 μm.

[0045] The liquid electrolyte 62 is a liquid medium that allows the movement of lithium ions between the lithium-containing metal oxide-based cathode 58 and the columnar silicon anode, including the cobweb-like carbon fiber mesh 56 thereon. The liquid electrolyte 62 generally comprises a lithium salt, an organic solvent, and additives. Examples of suitable salts include LiPF6, LiBF4, lithium bis(oxalato)borate, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiAsF6, LiC(CF3SO2)3, LiClO4, Li 1+x Al x Ti 2-x (PO4)3 and LiTFSI. Examples of organic solvents include ethylene carbonate, diethyl carbonate, propylene carbonate, fluoroethylene carbonate (FEC), and combinations thereof.

[0046] When the liquid-based lithium-ion battery cell 50 is fully charged, lithium ions will have been transported from the lithium-containing metal oxide-based cathode layer 58 via the liquid electrolyte 62 into the columnar silicon anode including the cobweb-like carbon fiber network 56 thereon (including the cobweb-like carbon fiber network thereon) to form a lithium-silicon compound such as Li 21 Si5, which has a significantly higher maximum capacity than that of a graphite anode.

[0047] The electrochemical properties of a liquid-based lithium-ion battery cell comprising a columnar silicon anode with and without the cobweb-like carbon fiber network were evaluated; the results are presented in Fig. 6-8. In the following experiments, the lithium-ion battery cell comprised a copper current collector with a thickness of 20 µm, the same columnar silicon anode with and without the cobweb-like carbon fiber mesh, a separator with a porosity of 45% formed from polyacetylene and polypropylene with a thickness of 20 µm, and a cathode formed from LMFP / LMO / SP / PVDF=46 / 46 / 4 / 4 (wt%) with a loading of approximately 1.1 mAh / cm 2 , and a cathode current collector made of aluminum with a thickness of 20 µm.

[0048] In Fig. 5, the room temperature cycling performance was evaluated for the lithium-ion battery designs comprising the silicon anode without the cobweb-like carbon network (Si-w / oC; Si without C) and the designs comprising the silicon anode with the cobweb-like carbon network (Si-w / C; Si with C). After approximately 60 cycles, the lithium-ion battery comprising the Si-w / oC anode began to show a loss in percentage capacity retention compared to the same lithium-ion battery design comprising the Si-w / oC anode, which worsened after 100 cycles. The percentage capacity retention of the Si-w / oC deteriorated significantly to approximately 70% after 100 cycles, presumably due to the loss of electronic contact due to volumetric expansion.In contrast, the percentage capacity retention for the lithium-ion battery comprising the Si-w / C anode was essentially linear and was approximately 88% after 100 cycles, advantageously demonstrating improved electronic conduction and protection from volumetric expansion during charging resulting from the presence of the cobweb-like carbon fiber network.

[0049] Fig. Figure 6 graphically illustrates the performance of lithium-ion battery designs that include the silicon anode without the cobweb-like carbon network (Si-w / oC) and the designs that include the silicon anode with the cobweb-like carbon network (Si-w / C). Discharge performance in lithium-ion batteries generally refers to how well the battery can deliver charge at different rates or currents, often referred to as the C-current rate (i.e., it is a measure of how quickly the battery can discharge without losing its capacity and power). The C-rate represents the current at which a battery discharges relative to its rated capacity. For example, a battery discharged at a 1 C rate will take one hour to fully discharge, while a 2 C rate would discharge the battery in half an hour. Higher C-rates, such as 5 C or 10 C, represent much faster discharge rates.As graphically shown, the percentage capacity retention was measured for 3 cycles at the different rates as shown. At the higher C rates, the percentage capacity retention was significantly lower for the lithium-ion battery with the Si-w / oC anode than for the lithium-ion battery with the Si-w / C anode, with the difference increasing as the C rate increased. The cobweb-like carbon fiber network on the columnar silicon anode clearly improves the battery's discharge capability, especially at the 15 C rate and the 20 C rate, as graphically shown.

[0050] In Fig. Figure 7 graphically shows the discharge curves at the 15C rate for the lithium-ion battery designs comprising the silicon anode without the cobweb-like carbon network (Si-w / oC) and designs comprising the silicon anode with the cobweb-like carbon network (Si-w / C). The discharge curve of a lithium-ion battery refers to the relationship between the battery voltage and the remaining capacity during a discharge cycle. It illustrates how the battery voltage decreases as the capacity is depleted. As shown, capacity retention was significantly higher in the lithium-ion battery with the Si-w / C anode.

[0051] Fig.Figure 8 illustrates a solid-state lithium-ion battery 100 according to one or more other embodiments. The solid-state lithium-ion battery 100 includes an anode current collector 102 and a cathode current collector 104. A columnar silicon anode comprising the previously described cobweb-like carbon fiber mesh 106 is provided on the anode current collector 102, and a cathode 108 is provided on the cathode current collector 104. A separator 110 consisting of a solid electrolyte 112 is located between the columnar silicon anode comprising the cobweb-like carbon fiber mesh 106 and the cathode 108, which may also comprise a solid electrolyte 112.

[0052] The cathode 108 in the solid-state battery 100 may include solid electrolyte (ranging from 1 to 50 wt.%), cathode active material ranging from 30 to 98 wt.%, conductive additive ranging from 0 to 30 wt.%, and a binder ranging from 0 to 20 wt.%. In some examples, the cathode 108 has a thickness ranging from 10 µm to 500 µm (e.g., 40 µm).

[0053] In some examples, the cathode active material comprises one or more materials selected from a group consisting of a rock salt layer oxide, spinel, a polyanion cathode, a lithium transition metal oxide, a surface coated and / or doped cathode material, and a low voltage cathode material.

[0054] Examples of rock salt layer oxides include LiCoO2, LiNi x Mn y Co1- x-y O2, LiNi x Mn- y Al1- x-y O2, LiNi x Mn1- xO2, Li 1+x MO2. Examples of spinel include LiMn2O4, Li-Ni 0,5 Mn 1,5 O4. Examples of polyanion cathodes include LiV2(PO4)3. Examples of surface-coated and / or doped cathode materials include LiNbO3-coated LiMn2O4, Li2ZrO3, or Li3PO4-coated LiNi x Mn y Co1- x-y O2 and Al-doped LiMn2O4. Examples of low-voltage cathode materials include lithium-containing metal oxides / sulfides (e.g., LiTiS2), lithium sulfide, and sulfur.

[0055] In some examples, the conductive additive comprises one or more materials selected from a group consisting of carbon black, graphite, graphene, graphene oxide, Super P, acetylene black, carbon nanofibers, carbon nanotubes, and other electronically conductive additives. Examples of binders include one or more materials selected from a group consisting of polytetrafluoroethylene (PTFE), sodium carboxymethylcellulose (CMC), styrene-butadiene rubber (SBR), poly(vinylidene fluoride) (PVDF), nitrile-butadiene rubber (NBR), styrene-ethylene-butylene-styrene copolymer (SEBS), styrene-butadiene-styrene copolymer (SBS), and other suitable binders.

[0056] In some examples, the solid electrolyte in the separator layer and / or cathode electrode is selected from a group consisting of pseudobinary sulfide, pseudoternary sulfide, pseudoquaternary sulfide, halide-based solid electrolyte, and hydride-based solid electrolyte.

[0057] Examples of pseudobinary sulfides include Li2S-P2S5 system (Li3PS4, Li7P3S 11 and Li 9,6 P3S 12 ), Li2S-SnS2 system (Li4SnS4), Li2S-SiS2 system, Li2S-GeS2 system, Li2S-B2S3 system, Li2S-Ga2S3 system, Li2S-P2S3 system, Li2S-Al2S3 system. Examples of pseudoternary sulfides include Li2O-Li2S-P2S5 system, Li2S-P2S5-P2O5 system, Li2S-P2S5-GeS2 system (Li 3,25 Ge 0,25 P 0,75 S4 and Li 10 GeP2S 12 ), Li2S-P2S5-LiX (X = F, Cl, Br, I) system (Li6PS5Br, Li6PS5Cl, L7P2S8I and Li4PS4I), Li2S-As2S5-SnS2 system (Li 3,833 SnN 0,833 ASo 0,166S4), Li2S-P2S5-Al2S3 system, Li2S-LiX-SiS2 (X = F, Cl, Br, I) system and 0.4LiI 0.6Li4SnS4 and Li 11 Si2PS 12 Examples of pseudoquaternary sulfides include Li2O-Li2S-P2S5-P2O5 system, Li 9,54 Si 1,74 P 1,44 S 11,7 Cl 0,3 , Li7P 2,9 Mn 0,1 S 10,7 I 0,3 and Li 10,35 Sn 0,27 S 1,08 ]P 1,65 S 12 .

[0058] Examples of halide-based solid electrolytes include Li3YCl6, Li3InCl6, Li3YBr6, Li11, Li2CdCl4, Li2MgCl4, Li2Cdl4, Li2ZnI4, and Li3OCl. Examples of halide-based solid electrolytes include LiBH4, LiBH4-LiX (X = Cl, Br, or I), LiNH2, Li2NH, LiBH4-LiNH2, and Li3AlH6. In other examples, other types of solid electrolytes with low grain boundary resistance can also be used.

[0059] While the above disclosure has been described with reference to exemplary embodiments, it will be appreciated by those skilled in the art that various changes may be made and equivalent elements may be substituted without departing from its scope. Furthermore, many changes may be made to adapt a particular situation or material to the teachings of the disclosure without departing from its essential scope. Therefore, the present disclosure is not intended to be limited to the particular embodiments disclosed, but is intended to include all embodiments falling within its scope.

Claims

[1] A columnar silicon anode for a lithium-ion battery, comprising: a plurality of spherical silicon columns; and a carbon fiber mesh on exposed surfaces of the spherical silicon columns; wherein the silicon in the plurality of spherical silicon columns is more than 97 weight percent, and wherein the carbon fiber network is approximately 0.05 weight percent to less than 3 weight percent, the weight percents being based on a total weight of the plurality of spherical silicon columns and the carbon fiber network. [2] The columnar silicon anode according to claim 1, wherein the carbon fiber network is random and multidirectional. [3] The columnar silicon anode of claim 1, wherein the carbon fiber mesh further comprises a polymer additive in an amount of more than 0 to 3% by weight. [4] The columnar silicon anode of claim 1, wherein the carbon fiber network comprises carbon nanotubes, the carbon nanotubes having a length of more than about 1 micrometer (µm), a diameter of about 1 nm to about 6 nm, and a thickness of less than 0.1 nanometer (nm). [5] The columnar silicon anode of claim 4, wherein the carbon nanotubes comprise single-walled carbon nanotubes, double-walled carbon nanotubes and / or multi-walled carbon nanotubes. [6] A columnar silicon anode according to claim 4, further comprising one or more carbon additives. [7] A columnar silicon anode according to claim 1, wherein the plurality of spherical silicon columns are deposited on an anode current collector by DC magnetron sputtering. [8] The columnar silicon anode of claim 1, wherein the silicon anode has an areal capacitance of about 0.5 to about 20 milliampere hours per square centimeter. [9] A method for forming a carbon fiber network on a columnar silicon anode for a lithium-ion battery, the method comprising: Providing a columnar silicon anode on an anode current collector, the columnar silicon anode comprising a plurality of spherical silicon columns deposited on the anode current collector by plasma vapor deposition; Applying a carbon fiber precursor solution having a solids content of less than 10 weight percent to exposed surfaces of the columnar silicon anode, wherein the carbon fiber precursor solution comprises carbon nanotubes, a polymeric dispersant, and a solvent; and Exposing the applied carbon fiber precursor solution, the columnar silicon anode, and the anode current collector to an elevated temperature for a period of time effective to evaporate the solvent and form the carbon fiber network on the exposed surfaces, wherein the carbon fiber network is random and multidirectional and amounts to more than 0 to less than 3 weight percent based on a total weight of the carbon fiber network and the columnar silicon anode, and wherein the columnar silicon anode comprises silicon in an amount of more than 97 weight percent based on the total weight of the carbon fiber mesh and the columnar silicon anode. [10] The method of claim 9, wherein the carbon nanotubes have a diameter of about 1 to about 6 nanometers (nm), a thickness of less than 0.1 nm, and a length of more than 1 µm.

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