Large battery pack anode containing silicon particles

Abstract

This document describes a large anode containing a high weight percentage of silicon suitable for use in lithium-ion energy storage devices and battery packs, and a method for manufacturing the same. The anode material described herein may include a film cast onto a current collector substrate, the film comprising a plurality of active material particles and a conductive polymer film coated on the active material particles. In some embodiments, the conductive polymer film comprises polyacrylonitrile (PAN). Methods for manufacturing the anode material may include preparing a slurry comprising active material particles and a conductive polymer material, casting the slurry onto a current collector substrate, and subjecting the composite material to drying and heat treatment.

Description

[0001] This case is a divisional application of the applicant’s patent application No. 201780072661.7 filed on October 13, 2017, entitled “Anode of a Large Battery Pack Containing Silicon Particles”, the entire contents of which are incorporated herein by reference.

[0002] Cross-reference to related applications

[0003] This application claims priority to U.S. Provisional Patent Application No. 62 / 407,938, filed October 13, 2016, the entire contents of which are incorporated herein by reference.

[0004] Statement on Federally Funded Research

[0005] This invention was made with government support under authorization number DE-SC0013852 granted by the Department of Energy. The government owns certain rights to this invention. Technical Field

[0006] This disclosure relates to energy storage devices such as lithium-ion electrochemical cells and battery packs. More specifically, this disclosure relates to the variable-scale production of silicon anode electrode sheets suitable for, for example, lithium-ion energy storage devices and battery packs. Background Technology

[0007] Battery packs are ubiquitous in today's society, powering everything from hearing aids to smartphones, forklifts, and even vehicles. Today's battery pack technologies range from heavy, large, and inexpensive lead-acid battery packs to lighter, smaller, and more expensive lithium-ion battery packs (LIBs). Nevertheless, rechargeable LIBs have dominated the portable electronics market for nearly a decade, and more recently they have gained significant attention in the electric vehicle sector and specialized markets, including military applications. Small improvements in materials processing and device manufacturing have increased energy density by approximately 5% to 6% annually—a slow and incremental process. To date, the main success of improvements in Li-ion technology has been in modifying first-generation materials and packing them into smaller, safer packages. Existing battery packs remain heavy, large, expensive, and unsafe, creating barriers to the power / cost requirements of next-generation applications. Achieving future energy storage goals requires breakthroughs in next-generation electrode materials. The introduction of active materials with higher energy densities is essential.

[0008] Recently, silicon has been identified as one of the most attractive high-energy anode materials for lithium-ion batteries (LIBs). Silicon boasts a low operating voltage and a capacity of 3579 mAh / g. -1The high theoretical specific capacity of Si—nearly ten times higher than that of existing graphite anodes—has spurred extensive research efforts aimed at developing viable Si-based electrodes. Despite these advantages, numerous challenges, primarily related to the material's significant volume expansion, hinder its commercialization. Commercial graphite electrodes expand by approximately 10% to 13% during lithium intercalation, while Si expands by nearly 300%, leading to structural degradation and instability in the crucial solid electrolyte interphase (SEI). This instability ultimately reduces battery life to suboptimal levels. The degradation of active materials can be mitigated by introducing materials smaller than 150 nm or through the design of electrode structures with nanostructures capable of reducing expansion. Unfortunately, the electrode structures proposed in previous work lack sufficiently high coulombic efficiency, mainly because the volume changes during Si alloying and dealloying make the SEI at the Si-electrolyte interface mechanically unstable.

[0009] Many efforts aimed at utilizing silicon in the anode operation of lithium-ion battery packs combine silicon with conventional active materials. This provides higher capacity while minimizing the drawbacks of silicon materials (e.g., volume expansion, active material utilization, etc.). In existing graphite electrodes, mixtures of nano-silicon (nano-Si) particles have been implemented in commercial practice to increase the capacity of current anodes. However, this approach is limited to containing only about 5% (by mass) of nano-silicon active material. Due to the large volume expansion and contraction of Si during lithiation and delithiation, any amount exceeding this 5% limit would disrupt the conventional network of the electrode.

[0010] The applicant's preliminary work has demonstrated impressive long-term cycling stability of the nano-Si electrode / room-temperature ionic liquid (RTIL or IL) system, and, normalized to the quality of the electroactive material, its combination with a commercially available "L333" cathode for Li-ion batteries provides 1.35 times the specific energy of current prior art. When combined with an imide-based RTIL electrolyte, the nano-silicon-cyclized polyacrylonitrile (nSi-cPAN) electrode maintains an average half-cell coulombic efficiency above 99.97% due to the robust electrode structure and the cooperative effect of forming a stable solid electrolyte interphase (SEI) layer. Internationally published patent application number WO2016 / 123396 (the entire contents of which are incorporated herein by reference) describes the composition of the material formed during the combination and utilization of an nSi-cPAN electrode and a RTIL electrolyte of a specific composition in a Li-ion battery pack. Specifically, this application discloses the composition of the SEI formed between the nSi-cPAN electrode and the RTIL electrolyte.

[0011] Following the demonstration of the nSi-cPAN system, the applicant developed a "micron-Si" (μSi) anode. The utilization of μSi is made possible by leveraging the mechanical strength of the cPAN coating. By encapsulating μSi particles within an elastic, conductive coating matrix, the fragmentation of large Si particles is accommodated. This mechanism has been termed "self-contained fragmentation." The fragmented silicon particles remain adhered to the cPAN coating matrix, enabling long-term, full utilization of the material with minimal capacity degradation. This mechanism is validated by the electrode's ability to retain its capacity after multiple cycles, demonstrating that even after fragmentation, the silicon particles remain within the electronically conductive cPAN matrix. This... Figure 1 The composition of the material formed by electrochemically pulverizing large silicon particles within a cPAN matrix is ​​shown in and described in internationally published patent application number WO 2016 / 123396.

[0012] While the development of the nSi-RTIL system and μSi-cPAN electrode has enabled record-breaking performance in Li-ion full cells with silicon anodes (high-quality silicon loading, unconditioned / unlithiated silicon anodes, long cycle life, and high energy), this performance has only been demonstrated on a laboratory scale. The anodes used to demonstrate these inventions, although containing over 70% silicon relative to the total anode mass, are too thin for commercial applications; they are “desktop” demonstrations for proof of concept and feasibility. The pastes used to manufacture these anodes contain 12.5 to 25% by weight of solids (extremely low solids content unsuitable for commercial manufacturing). Laboratory-standard current collector substrates (thickness greater than 25 to 30 micrometers) and low electrode coating thickness (resulting in ~2 mAh·cm⁻¹) are also present. -2 The small electrode area and low current (suitable for coin cell demonstrations, in the microampere range) allow for such demonstrations. However, transitioning these technologies from desktop to commercial production lines presents a whole new set of challenges.

[0013] Commercial anodes must provide at least 2 mAh·cm -2 The areal capacity allows it to be paired with cathodes to improve the energy density and cost of large Li-ion battery packs. This means that previously developed anodes must be scaled up (by a factor of 2 for most metrics, including mass loading and thickness, to achieve attractive energy densities) and processed in a commercially viable manner. Commercial anodes must also be developed to achieve their areal capacity (mAh·cm²). -2 The anode is kept consistent throughout the anode sheet to properly match the cathode capacity when stacked or wound in pouch or cylindrical cells, respectively. As the anode is scaled up to commercial levels, the adhesion between the cladding and the current collector substrate, the physical properties of the cladding, and even the anode electrochemistry all change. It is well known that at values ​​greater than 2 to 3 mAh·cm⁻¹... -2Achieving a viable high-performance silicon anode under high areal capacity load is very difficult, especially for anodes containing a high-quality percentage of silicon material (greater than 10% by weight). This is due to adhesion (between the electrode and the copper current collector substrate) and cohesion (maintaining electrode structural integrity within the electrode itself) problems caused by the expansion and contraction of the silicon active material during lithiation and delithiation, respectively. Summary of the Invention

[0014] This document describes various embodiments of methods and material compositions used to facilitate consistent and high-quality commercial-scale Si-cPAN anodes for Li-ion battery packs. In some embodiments, the anode comprises a film cast onto a current collector substrate, the film comprising active material particles (e.g., silicon particles) and a conductive polymer film coating layer on the active material particles. In some embodiments, the conductive polymer film coating layer comprises a thermoplastic material that, upon treatment, becomes a cyclized, non-plastic ladder-shaped compound. Such an anode can be introduced into an energy storage device along with a cathode and an electrolyte.

[0015] A method for manufacturing the anode disclosed herein is also described. In some embodiments, the method includes the step of preparing a slurry comprising an active material, additive powder, polymer powder, and a solvent. The slurry is then mixed for a period of time, followed by casting the slurry onto a current collector substrate. Drying and heating steps are then performed.

[0016] This invention also includes the following items:

[0017] 1. An energy storage device, the energy storage device comprising:

[0018] cathode;

[0019] Electrolytes; and

[0020] An anode comprising a film having a thickness of 10 to 80 micrometers, cast onto a surface with a roughness R. z On a current collector substrate larger than 1.5 micrometers, the film comprises:

[0021] A) a plurality of active material particles, wherein the active material particles comprise at least one of silicon, hard carbon, graphite, graphene, germanium, titanium dioxide, tin, magnesium, antimony, and lead; and

[0022] B) A conductive polymer film coating layer on the active material particles, the conductive polymer film coating layer comprising a thermoplastic polymer that, after treatment, becomes a cyclized, non-plastic ladder compound.

[0023] 2. The energy storage device according to Project 1, wherein the anode comprises 30-60% by weight of silicon particles and the areal weight capacity of the anode is 1.3 to 1.6 times the areal weight capacity of the cathode.

[0024] 3. The energy storage device according to Project 1, wherein the anode comprises 60% or more silicon particles and the areal weight capacity of the anode is 1.6 to 2.0 times the areal weight capacity of the cathode.

[0025] 4. The energy storage device according to Project 1, wherein the thermoplastic polymer that becomes a cyclized, non-plastic ladder compound after treatment comprises polyacrylonitrile.

[0026] 5. The energy storage device according to Project 1, wherein the electrolyte comprises an imide-based room temperature ionic liquid.

[0027] 6. The energy storage device according to Project 1, wherein the porosity of the anode membrane is between 50-70%.

[0028] 7. The energy storage device according to Project 1, wherein the arithmetic mean height Sa is less than three times the resulting interface ratio Sdr.

[0029] 8. A method of manufacturing an anode, wherein the anode comprises a membrane having a thickness of 10 to 80 micrometers, cast onto a current collector substrate, the membrane comprising a plurality of active materials and a thermoplastic polymer that, after treatment, becomes a cyclized, non-plastic ladder compound, the method comprising:

[0030] A) A slurry is prepared by placing a mixture of active material, additive powder and polymer powder in a solvent capable of dissolving the polymer powder. The slurry has a Brinell viscosity of 2000-6000 cP at room temperature using a #64 spindle at 20 to 100 RPM.

[0031] B) Mix the slurry for 1 to 4 hours;

[0032] C) The slurry is cast onto the current collector substrate;

[0033] D) Dry the cast film; and

[0034] E) Apply heat to the cast film at a temperature of 200 to 400°C for 1 to 12 hours.

[0035] 9. The method according to Item 8, wherein the active material comprises at least one of silicon, hard carbon, graphite, germanium, titanium dioxide, tin, magnesium, antimony, and lead.

[0036] 10. The method of claim 8, wherein the thermoplastic polymer that becomes a cyclized, nonplastic ladder compound after treatment comprises polyacrylonitrile.

[0037] 11. The method according to item 8, wherein the additive powder comprises lithium metal powder.

[0038] 12. The method according to item 8, wherein the additive powder comprises lithium nitride.

[0039] 13. The method according to item 8, wherein the additive powder comprises oxalic acid.

[0040] 14. The method according to Item 8, wherein the application of heat of 200 to 400°C is carried out under vacuum or an inert gas flow.

[0041] 15. An energy storage device comprising an anode, a cathode, and an electrolyte manufactured according to the method of item 8, wherein the areal weight capacity of the anode is 1.3 to 2.0 times that of the areal weight capacity of the cathode. Attached Figure Description

[0042] Figure 1 To illustrate the cycling data of a μSi-cPAN half-cell containing a fluorinated electrolyte additive, a pair of graphs are shown, illustrating rapid CE stabilization achieved using the applicant's previously disclosed μSi-cPAN / mRTIL system.

[0043] Figure 2 High-resolution transmission electron microscopy (HR-TEM) images of nanospherical silicon particles coated in polyacrylonitrile are provided.

[0044] Figure 3 The graph illustrates a full-cell pouch three-electrode experiment with a micron-sized silicon (anode) and an NMC

[622] (cathode) working electrode and a lithium counter electrode, where the N / P ratio is 0.9.

[0045] Figure 4 To illustrate the cycling data of pouch cells, a pair of graphs were used to compare the effects of low N / P ratios and sufficient N / P ratios.

[0046] Figure 5 Graphs showing the half-cell cycling performance of silicon / PAN anodes are provided, highlighting the performance of 1 to 3 micrometer silicon particles (D50 size) on a range of copper with different surface roughness, as well as surface morphology images of various copper materials with different surface roughness (b)-(e).

[0047] Figure 6 To illustrate the curves of a full cell (coin) containing silicon / carbon active material, PAN conductive binder (normalized to total anode coating mass, 30 to 35% silicon) and NMC

[622] cathode, the anode current collector roughness was compared.

[0048] Figure 7A summary of various copper types, their associated roughness parameters, and representative surface profilometer spectra for the first copper type (“OM10um (rough)” copper) is provided.

[0049] Figure 8 The diagram illustrates the heating process of polyacrylonitrile.

[0050] Figure 9 SEM and EDS (with mapping) of polymer-driven nanocomposites containing silicon and PAN after heat treatment under argon atmosphere are provided.

[0051] Figure 10 A pair of graphs illustrating the electrochemical performance of a PAN / Si nanocomposite anode subjected to heat treatment at 300°C in argon (top) and air (bottom) environments, followed by heat treatment at 600°C in argon.

[0052] Figure 11 To compare the cyclization curves in a vacuum furnace and a tube furnace under an argon flow, high CE and high capacity are shown when cyclizing under either environment.

[0053] Figure 12 A series of graphs show the first cycle voltage curves of a full cell containing a nickel-rich NCM cathode and a Si-cPAN anode, wherein the anode component was heat-treated under various procedures.

[0054] Figure 13 To illustrate the method described in this article (6mAh / cm²) 2 A graph of an exemplary half-cell containing an anode of 30 to 35% silicon (normalized to total anode mass) generated by a load.

[0055] Figure 14 To illustrate a pair of graphs for a single-stacked bag of full cells containing exemplary anodes as described herein, these anodes are mass-produced and suitable for commercial-grade performance (commercial mass load, commercially viable auxiliary components). Detailed Implementation

[0056] The following description details various embodiments of methods related to the production of commercial-scale Si-cPAN electrodes, the electrochemical effects associated with some or all of these methods, and various embodiments of the composition of the resulting materials. The description is divided into several sections according to the steps used to manufacture the electrode, with each step describing the physical parameters that can be used to obtain improved battery pack performance.

[0057] Typically, Si-based electrodes are fabricated by mixing a polymer binder (such as polyvinylidene fluoride, polyacrylic acid, styrene-butadiene rubber, or carboxymethyl cellulose), conductive additives (usually carbon black), and Si particles in an organic solvent such as N-methylpyrrolidone (NMP) to produce a viscous slurry. The slurry is then scraped onto a copper foil current collector and dried to form the anode electrode. The embodiments described herein relate to the fabrication of a polymer-driven composite Si anode, which differs significantly from conventional methods.

[0058] Surprisingly, the method described in this paper is compatible with conventional manufacturing infrastructure, allowing the Li-ion market to obtain the first truly “insertion-type” high-load silicon anode. Other silicon anode production methods are cost- and resource-intensive, providing significant value for the method discussed below. As described in more detail below, silicon active material is coated in a conductive polymer such as polyacrylonitrile (PAN), cast onto copper foil, then treated under heat, and paired with a cathode in a specific manner to achieve full-cell performance.

[0059] This document discusses polyacrylonitrile (PAN) as an exemplary conductive polymer used in the disclosed methods, but other polymers may be used. Other suitable polymers include, but are not limited to, poly(acrylic acid) (PAA), carboxymethyl cellulose (CMC), and alginate. PAN is a resinous, fibrous organic polymer made from a mixture of monomers and acrylonitrile as the main component. PAN fibers are chemical precursors to high-quality carbon fibers upon appropriate modification, and they are commercially used in many high-tech and common everyday applications.

[0060] Many types of active materials can also be used under the methods described herein. Silicon is discussed as an exemplary anodic active material used under this method, including any silicon morphology capable of being integrated into the anode paste and electrode sheet. Silicon morphologies include, but are not limited to, nanospheres, nanowires, nanorods, whiskers, “coral” silicon, microsphere silicon, and large-particle silicon materials with various nanoscale features. Silicon-graphite, silicon-graphene, silicon-hard carbon, and other silicon-carbon composites are also non-exhaustive exemplary anodic active materials used under the methods described herein. Mixtures of silicon and carbonaceous materials such as graphite or hard carbon are also non-exhaustive exemplary anodic active materials.

[0061] Large-volume slurry mixing

[0062] To mass-produce Si-cPAN electrodes, the methods described herein typically begin with the preparation of a slurry. The slurry is usually prepared by mixing active materials, polymers, auxiliary materials, and additives in a solvent. The resulting slurry preferably possesses specific rheological properties to provide the highest electrochemical cycling performance in Li-ion battery packs. In some embodiments, the composition of the materials added to the solvent comprises about 10 to about 50 wt% PAN and about 50 to about 90 wt% active material. In some embodiments, the slurry contains about 30 to about 60 wt% solids in about 70 to about 40 wt% of solvent.

[0063] The active materials used in the preparation of the slurry may include combinations of materials with different compositions. For example, carbonaceous active materials (graphite, graphene, hard carbon, etc.) may be incorporated to form a silicon:carbonaceous material weight ratio of 10:90 or 90:10. An exemplary commercial Si:cPAN anode may include a Si:carbonaceous material:PAN weight ratio of 30:55:15. Other exemplary weight ratios include 40 to 80 wt% silicon, 5 to 50 wt% carbonaceous material, and 10 to 20 wt% PAN. The carbonaceous material may include a mixture of active materials and conductive additives, including but not limited to carbon black or carbon nanotubes.

[0064] A mixture of active material and conductive binder powder is dispersed in a solvent to form a slurry. In some embodiments, the solvent is chosen such that it can dissolve the conductive binder. For example, when using a PAN polymer, N,N-dimethylformamide (DMF, 99%) is an exemplary solvent used in the methods described herein. Other suitable solvents include, but are not limited to, dimethyl sulfone (DMSO2), dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMAc), ethylene carbonate (EC), and propylene carbonate (PC).

[0065] Slurry viscosity determines the mixing quality, coating quality, and the ability to form large films on current collector substrates. Exemplary slurry viscosities can be determined using a Brinell viscometer (spindle 64) (all measurements were performed at room temperature 23°C). Slurry viscosity is determined by the solvent / polymer mass ratio, polymer chain length, and solvent mass relative to the total slurry mass. The exemplary slurries prepared using the materials and methods described herein exhibit significantly more Newtonian properties than conventional Li-ion anode slurries. A Newtonian fluid is a fluid in which the viscous stress generated by fluid flow is linearly proportional to the range of strain rate or fluid deformation. This means that when shear forces are applied to the slurries described herein, the slurry does not exhibit as much shear thinning as conventional Li-ion anode slurries. This has implications for anode mixing and coating processes, as the slurry can be mixed at much higher RPMs and can be successfully coated at very low thicknesses. The low shear thinning properties of the slurry can be investigated using a Brinell viscometer, a commonly used instrument in rheological characterization. In some embodiments, the slurry has a Brinell viscosity between 3000 and 6000 centipoise (cP) at room temperature between 12 and 100 RPM (steel ingot #64), with a variation of less than 1000 cP for a given slurry mixture. The relatively small viscosity variation over a range of shear forces (described by spindle speed in RPM) indicates the Newtonian nature of the slurry. Other exemplary slurries have viscosities in the range of 3500 to 5000 cP at room temperature between 20 and 100 RPM.

[0066] Slurry mixing parameters affect the performance of the resulting anode. Besides mass percentage, powder mixing, and slurry viscosity, slurry mixing time and slurry volume are also important factors determining the quality of polymer coating on the active material. Slurry time is crucial for achieving uniform polymer coating on suspended active material particles. In some embodiments, a slurry mixing time of up to 12 hours is sufficient. In other embodiments, with appropriate equipment, a lower mixing time (e.g., 2 hours) is adequate.

[0067] Slurry mixing can be performed on a variety of equipment. Vacuum and non-vacuum planetary centrifugal mixers (e.g., "ThinkyMixer" or "ross" mixers), slurry planetary dispersion vacuum mixers, dual planetary dispersion mixers, homogenizers, and simple stirring with a stirring rod on a stirring plate in a beaker can all create adequate mixing conditions.

[0068] Slurry volume is important because a sufficient amount of material must be present to produce adequate mixing. Slurry volume also affects the electrochemical performance of the resulting anode. If the slurry volume is too low, a significant portion of the material will not undergo agitation / mixing, resulting in an inability to apply a uniform coating. For example, a mixture of 200 mg of active material plus polymer powder and 1.6 g of solvent (87.5% solvent by weight of total slurry mass) will not mix properly. Regardless of the mixing method, there will not be enough slurry in this case to produce adequate mixing. A slurry using 1.2 g of active material plus polymer powder in 8.4 g of solvent (87.5% solvent by weight of total slurry mass) will mix well, as will a slurry using 1.2 g of active material plus polymer powder in 4–6 g of solvent, resulting in a uniform polymer coating on the active material. However, this solids content (12.5% ​​by weight solids) is unsuitable for coating on large-scale manufacturing equipment. The viscosity of these slurries is too low to be coated using roll-to-roll methods (e.g., comma bars, slot dies, etc.).

[0069] As the anolyte mass load increases, the quality of the PAN coating on the silicon material resulting from the above parameters becomes increasingly important. Microscopy, such as transmission electron microscopy, can be used to determine the coating uniformity and thickness to confirm whether an appropriate coating has been obtained. A PAN coating resulting in strong morphology retention throughout the electrochemical cycle should be at least 3 to 5 nanometers thick, covering all surfaces of the active material particles and present throughout the entire electrode. An example of an exemplary coating formed using the above method is shown in [examples omitted]. Figure 2 In the middle, electron energy loss spectroscopy (EELS) highlights the silicon and PAN coating (d). A uniform 3 to 5 nm coating is present on the particles throughout the electrode matrix.

[0070] When preparing the slurry, it is also appropriate to add electrode additives that can enhance the performance of the full-cell Li-ion battery pack. Exemplary electrode additives include, but are not limited to, lithium metal powder (such as stabilized lithium metal powder, SLMP) and lithium nitride (Li3N), as well as other high-lithium-content powders and salts. These dry powders can be added directly to the slurry and mixed with other slurry components. Oxalic acid can also be added to the slurry to improve dispersion and adhesion properties.

[0071] Generally, the polymer is dissolved in a solvent. The slurry is then mixed to ensure that the polymer material fully coats the active material powder dispersed in the polymer / solvent solution.

[0072] Electrode coating

[0073] After mixing the slurry, the slurry is cast onto the current collector substrate using, for example, a roll-to-roll coating method. A roll-to-roll coating machine can be used to produce hundreds of meters of electrode in a single run. The roll-to-roll coating process is determined by the physical properties of the slurry (e.g., shear, viscosity, etc.). The current collector foil is pulled through the coating machine at a speed of 0.2 to 50 meters per minute, and the coated foil passes through a dryer set at a temperature of 30 to 70°C for water-based slurries and 110 to 160°C for solvent-based slurries. For the purposes of the technology described in this application, although it is a solvent-based system, the dryer temperature should be set to 30 to 70°C.

[0074] Important factors for electrode coating include the areal mass loading of silicon per square centimeter, the capacity provided, and how these figures match the cathode used in a full cell. To pair with high-energy cathode materials containing “nickel-rich NMC” (nickel-manganese-cobalt oxide cathodes), the areal capacity of the anode should be 1.3 to 2.0 times that of the cathode. This factor is known in industry as the “N / P ratio” (negative electrode capacity / positive electrode capacity). In conventional Li-ion batteries containing graphite anodes, the N / P ratio is typically 1.1 to 1.2 and is set to avoid lithium plating on the anode during cycling. The N / P ratio envisioned for the system described herein is designed to cover efficiency losses during the initial cycling process and “fix” the anode half-cell voltage between 0.01 and 1.5 V (relative to Li / Li). + If the N / P ratio is too low, the anode half-cell voltage will drop below 0.01V (due to complete and excessive lithiation of silicon) and the anode will be destroyed. This is in Figure 3 The diagram is shown in the image. Figure 4 A comparison is shown between a cell with a poor N / P ratio and a cell with a strong N / P ratio. A higher relative N / P ratio also prevents wrinkling and deformation of the anode film due to the expansion and contraction of the silicon material present in the film. The ideal N / P ratio depends on the silicon mass loading relative to the total anode film mass. If the anode film contains 20 to 50 wt% silicon, the N / P ratio should be 1.2 to 1.6. If the anode film contains more than 50 wt% silicon, the N / P ratio should be greater than 1.6. In some embodiments, the weight percentage of silicon in the anode can be added to "1" to obtain the minimum N / P ratio of the system. In other words, if the anode contains 40 wt% silicon, the resulting full-cell system should have an N / P ratio greater than 1.4.

[0075] Current collector substrate

[0076] The current collector substrate (typically a metal foil) is used to move electrons from the outside of the battery to the electrodes and vice versa. Electrode slurry is cast onto the foil as a coating of uniform thickness. For a Li-ion battery pack to function properly, the electrode coating should adhere sufficiently to the current collector foil and maintain this adhesion throughout the cycle. In alloyed electrodes such as silicon, this is particularly challenging when using large electrodes (which tend to be very thick), given the expansion properties of the active material. A conductive binder is responsible for adhering the anode film to the current collector substrate; in large electrodes, sufficient binder must be present to allow adhesion. In the silicon plus PAN system described herein, 10 to 25% PAN is the minimum permissible polymer content relative to the total anode coating mass. This is unique for scaled-up, large silicon anodes with a thickness greater than 5 micrometers.

[0077] Significantly and surprisingly, the physical properties of the current collector substrate are highly important to the performance of the resulting anode sheet. Along with the anode composition, the physical properties of the current collector substrate affect battery life. Copper foil is an exemplary current collector substrate and is most commonly used in conventional Li-ion batteries. This article discusses the properties of copper foil.

[0078] For anolyte adhesion, an important physical property of copper is its surface roughness. One measure of roughness is the ten-point height or maximum height (R0). z This is the root mean square value. R z Defined as the average number of peaks and valleys in a given scan region, at least five consecutive points are measured (five highest peaks + five highest values ​​= 10 points). For some embodiments of the anode described herein, in order to maintain adhesion throughout the cycle, copper R... z It should be at least 1.5 micrometers. Other embodiments with larger active materials may require higher surface roughness, up to 6 to 7 micrometers. Other embodiments with nanoscale active materials require R... z The value is greater than 0.5 micrometers. The copper foil used in conventional / previously commercialized Li-ion anodes typically has an R value of 0.5 micrometers or less. z value.

[0079] Another measure of surface roughness is the arithmetic mean height (Sa), which represents the height difference at each point compared to the arithmetic mean of the surface. Yet another measure of surface roughness is the ratio of the resulting interface area (Sdr), which is the percentage of the surface area contributed by the texture relative to the area defined by the plane (i.e., a perfectly level surface has Sdr = 0). Each of these parameters and their relative magnitudes are important to the performance of the system described in this paper.

[0080] As mentioned earlier, the copper surface roughness required for feasible performance largely depends on the size of the active material. Current data indicate that if the electrode film expansion is less than 50% along the z-axis (perpendicular to the electrode substrate) and the active material particle size is greater than 500 nanometers, the surface roughness R... z Copper with a particle size greater than 0.5 micrometers will provide the best performance. If the electrode film expands by more than 50% along the z-axis (perpendicular to the electrode substrate) and the active material particle size is greater than 500 nanometers, the surface roughness R... z Copper with a diameter greater than 2 micrometers will provide the best performance.

[0081] Unfortunately, higher surface roughness is associated with a necessary increase in thickness, which is detrimental to battery pack energy density because a thicker current collector (an auxiliary material that does not contribute to battery capacity) will occupy space without providing energy. The improved adhesion on a rougher copper surface is explained by the increased surface area available for adhesion between the conductive polymer and copper. (Reference) Figure 5 Various copper surfaces were imaged under an optical microscope for comparison.

[0082] Figure 5 The performance of a half-cell containing a silicon-plus-PAN anode is also shown, confirming that, based on the active material morphology and anode film structure, appropriate copper surface roughness is clearly required to maintain adhesion to the anode film during many charge-discharge cycles. In the half-cell, the first-cycle coulombic efficiency (CE) is higher, and the CE stabilizes much faster in cells containing rougher copper foil; this is attributed to maintaining electron contact and faster electron transport within the cell. The CE behavior and associated electron transport / adhesion properties are manifested in full-cells with active material particles larger than 500 nanometers, such as… Figure 6 As shown in the figure. In the presence of R z In full cells with an anode current collector film of 1 micrometer or less, the battery performance gradually declines and eventually collapses within 50 cycles.

[0083] Figure 7 This document provides a summary of various copper types, their associated roughness parameters, and representative surface profilometer spectra for the first copper type (“OM10um (rough)” copper). The copper types indicated by shaded font (“OM10um (rough)” and “VL10|23um” copper) offer optimal performance across a range of silicon material types and anolyte microstructures. Figure 7The materials shown generally perform best in the scaled-up electrode systems described herein. Therefore, a new parameter, Sa / Sdr, is used to describe the copper foil with optimal performance based on the roughness parameter. Sa / Sdr describes the ratio of the average height of peaks and valleys on the foil surface to the percentage of surface roughness caused by roughness. In other words, a high Sa / Sdr means that the copper surface has very high peaks with low frequencies relative to the total roughness, where a Sa / Sdr close to 1 indicates a more uniform distribution of peak / valley heights on the copper surface. A Sa / Sdr close to 1 is found to be advantageous, and for a range of silicon material types and anode film compositions and microstructures, a Sa / Sdr below 3 is found to be sufficient for high performance.

[0084] Electrode rolling

[0085] In some implementations, the electrodes are coated and then dried on a roll-to-roll coating apparatus, with the dryer temperature set to 30 to 70°C and an airflow. After casting the slurry onto the current collector foil and drying / evaporating the solvent, a conventional graphite anode is calendered to approximately 70% of its original film thickness. This calendering produces a porosity of approximately 40% to 50%. This method provides a higher degree of particle contact while still allowing sufficient electrolyte permeation. When the porosity exceeds 50%, conventional anodes will lack sufficient mechanical strength to withstand the production and operation of the battery pack. The system described herein differs. The electrodes require higher porosity to accommodate the volumetric expansion of the silicon material, and a higher interfilm surface area facilitates the formation of a robust SEI layer and faster Li... + Ion transport. The anodes described herein, including silicon-cPAN anodes, are rolled to a porosity of 40% to 70%. Exemplary porosities of Si-cPAN composites will be 50% to 60%. This contrasts with conventional graphite anodes, which have a porosity of approximately 30% to 40%. Conventional electrodes containing silicon (currently up to 15% by weight of Si) (PAA, CMC, SBR, etc. binders) have porosities in the range of 40% to 50%. Active materials exhibiting higher expansion require electrodes with higher porosities.

[0086] Electrode heat treatment

[0087] A key aspect of the anode described herein lies in the ability of the conductive polymer binder to act as both a binder material and an electronically conductive matrix capable of providing efficient charge transfer throughout the composite. As mentioned above, large-scale fabrication of this type of high-performance anode film is indeed difficult and requires an understanding of many challenges, but the need to process numerous conductive polymers to achieve electronic conductivity adds another layer of complexity. The exemplary conductive polymers discussed herein (e.g., PAN) can be heated in a reducing atmosphere or in a vacuum to exhibit electronic conductivity. Simultaneously, the processable polymer ensures that the polymer matrix does not become too brittle due to the mechanical effects of battery cycling (caused by heat treatment at very high temperatures or in inappropriate atmospheres). Moreover, the processing should be carried out so that the auxiliary components of the electrode (i.e., copper) remain unaffected and in a state suitable for battery operation.

[0088] Many conductive polymers can undergo chemical transformations to acquire electronic conductivity; however, most require the addition of cross-linking agents to catalyze these chemical reactions. PAN copolymers are unique because they become autocatalyzed through a heat treatment process. PAN is a unique linear, semi-crystalline organic polymer with the molecular formula (C3H3N). n The molecular structure of PAN consists of carbon chains with coordinating nitrile groups. PAN's chemistry is of particular interest due to its unique autocatalytic cyclization and cross-linking processes, which are stabilized by heat. PAN chains degrade before reaching a molten state, and this degradation process (often referred to as "cyclization") transforms the linear PAN chains into a thermally stable conjugated ladder structure that does not flow or dissolve. This... Figure 8 The diagram illustrates this. This thermal stabilization allows the fibers to withstand carbonization and graphitization temperatures (approximately 1000 to 3000°C) and produce high-performance carbon fibers without excessive weight loss or chain breakage.

[0089] Thermal stabilization of PAN refers to the low-temperature (typically 200 to 300°C) transformation of polymer fibers into high-temperature elastic fibers. This transformation is necessary for the fibers to withstand carbonization (800 to 1300°C) and graphitization (1300 to 3000°C) as well as to achieve the highest possible carbon yield and excellent properties. The main chemical reactions involved in this process are known to be cyclization, dehydrogenation, oxidation, and crosslinking, which lead to the formation of a thermally stable conjugated ladder structure.

[0090] Cycloning is a crucial reaction in the PAN stabilization process and a primary focus of the anodic treatment described in this paper. Cycloning occurs when nitrile bonds (C≡N) react and crosslink between PAN molecules, resulting in a stable conjugated ladder polymer with double bonds (C=N) and fused pyridine rings. The thermal stability of the stabilized fibers is attributed to the ladder structure formed through the cyclization of nitrile groups, allowing the stabilized PAN to operate at high temperatures with minimal volatilization of the carbonaceous material. Cycloning is the reason for the color variation of the stabilized fibers, ranging from white to yellow to brown to black. Cycloning is exothermic and can damage the fibers if it proceeds too rapidly. The fibers may shrink excessively, losing significant mass, and may even melt and fuse together. Conversely, if the stabilization process is too conservative (both in terms of time and heat), the fibers will only be partially stabilized. Unlike dehydrogenation, cyclization does not require the presence of oxygen and can therefore be carried out in an inert atmosphere. The reaction atmosphere is important in the method described herein because the anode copper foil current collector involves heat treatment of the PAN, and any exposure to oxygen at temperatures above 100°C will cause the foil to oxidize, leading to defect problems (electronic resistance and electrochemical side reactions).

[0091] In the embodiments described herein, PAN is treated only to its stabilization (specifically, "cyclization") stage, and the resulting pyridine-based conjugated polymer is then applied as an electrode binder / coating with robust mechanical and inherent electronic properties. The deviation from conventional stabilization procedures (oxidation, dehydrogenation, and cyclization for carbonization and graphitization) aimed at achieving high carbon yields and high-performance carbon is to avoid forming a highly oriented (base-plane aligned), rigid, and brittle coating around an active material prone to high expansion and contraction.

[0092] Stabilizing PAN from a linear molecule to a ladder-like polymer compound via cyclization can be performed by heating in an inert environment at 100 to 500 °C. An exemplary temperature for the cyclization heat treatment of PAN is 300 °C at a rate of 5 °C / min, with a holding time at the peak temperature ranging from 2 to 12 hours. Running a series of temperatures allows for the determination of the optimal peak electrochemical performance of the PAN / silicon configuration. Figure 9 Scanning electron microscopy (SEM) images and energy-dispersive spectroscopy (EDS) analyses of some of these polymer-driven nanocomposite samples are shown. PAN / silicon samples were tested using the methods described above, while others underwent subsequent treatment to carbonize PAN and were held for 1 hour at peak temperatures of 500 °C, 600 °C, 700 °C, 800 °C, 900 °C, and 1000 °C under the same argon atmosphere. Similarly, this second-stage heating was maintained at a heating rate of 5 °C / min. Figure 10 and Figure 11 The electrochemical data from various heat treatment tests are illustrated.

[0093] In addition to processing parameters such as heating time and temperature, the equipment used and the resulting atmosphere are also important. As discussed above, the anode should be processed under a vacuum or inert gas flow. Argon and nitrogen are exemplary inert gas atmospheres, and pressures of 20 to 80 PSI will provide the most constant heating conditions. Heat treatment under vacuum also achieves proper cyclization conditions and high-performance anodes. These atmospheres can be provided in a range of equipment types, including tube furnaces, glove boxes, vacuum furnaces, or other controlled atmosphere furnaces. The gas flow during heat treatment allows for improved heating and electrochemical performance because byproducts of the polymer chemical reaction (including hydrogen degassing during PAN cyclization) are flushed away from the system and therefore cannot react with the electrode or current collector substrate. The gas flow through a tube furnace should be set at 100 to 1,000 liters per hour for optimal performance. A single roll or multiple rolls of anodes can be processed in a single furnace. Controlled atmosphere furnaces can also be added to industry-standard roll-to-roll coating systems used for electrode fabrication. Typically, the electrodes are passed through a drying oven immediately after coating; alternatively, they can be passed through a controlled atmosphere furnace after initial drying, with conditions set to initiate a polymer chemical transformation (i.e., PAN cyclization) before being wound onto a reel. Instead of this apparatus, tube furnaces offer a commercially viable method for processing large rolls of anodes containing silicon / polyacrylonitrile composites.

[0094] Of particular importance, especially when it comes to commercial-scale manufacturing, it has been found that heating time and heating rate should be adjusted according to the anode microstructure and size. Specifically, anode thickness, PAN weight percentage, and the amount of anode material being treated all affect these processing parameters. Figure 12 As shown, a heating time of only 2 hours is sufficient to obtain appropriate electrochemical performance.

[0095] Electrochemical performance

[0096] Figure 13 Exemplary data for a micron-sized silicon:polyacrylonitrile (Si:PAN) anode half-cell fabricated using the methods described herein are presented. The mass loading, processing, and composition of the resulting material are sufficient for commercial use. Figure 14 Exemplary data for a full cell comprising the exemplary anode described herein and a “nickel-rich” high-energy cathode (“NMC

[622] ”) are presented.

[0097] As can be understood from the foregoing, specific embodiments of the invention have been described herein for illustrative purposes, but various modifications may be made without departing from the scope of the invention. Therefore, the invention is not limited except for the appended claims.

Claims

1. An anode, said anode comprising: A membrane, having a thickness of 10 to 80 micrometers, is cast onto a surface roughness... R z On a current collector substrate larger than 1.5 micrometers, wherein the arithmetic mean height of the current collector substrate is... Sa The size is smaller than the interface area ratio generated by the current collector substrate. Sdr Three times that of the membrane, which comprises: A) Multiple active material particles; and B) A conductive polymer film coating layer disposed on the active material particles, the conductive polymer film coating layer comprising a thermoplastic polymer, wherein the thermoplastic polymer is processed to become a cyclized, non-plastic ladder compound.

2. The anode according to claim 1, wherein the plurality of active material particles are selected from silicon, hard carbon, graphite, graphene, germanium, titanium dioxide, tin, magnesium, antimony, lead, and combinations thereof.

3. The anode according to claim 1, wherein the plurality of active material particles comprise particles selected from silicon particles, silicon-carbon composite material particles, and combinations thereof.

4. The anode according to claim 3, wherein the particles are selected from silicon nanospheres, silicon nanowires, silicon nanorods, silicon whiskers, "coral" silicon, microspheres, silicon-graphite, silicon-graphene, silicon-hard carbon, and combinations thereof.

5. The anode of claim 3, wherein the anode comprises 30-60% by weight of silicon particles.

6. The anode of claim 3, wherein the anode comprises 60% or more silicon particles by weight.

7. The anode of claim 1, wherein the thermoplastic polymer comprises polyacrylonitrile.

8. The anode according to claim 1, wherein the porosity of the anode film is between 50% and 70%.

9. An energy storage device, the energy storage device comprising: Anode, the anode comprising: A membrane, having a thickness of 10 to 80 micrometers, is cast onto a surface roughness... R z On a current collector substrate larger than 1.5 micrometers, wherein the arithmetic mean height of the current collector substrate is... Sa The size is smaller than the interface area ratio generated by the current collector substrate. Sdr Three times that of the membrane, which comprises: A) A plurality of active material particles, wherein the active material comprises silicon and carbonaceous active materials; and B) A conductive polymer film coating layer disposed on the active material particles, the conductive polymer film coating layer comprising a thermoplastic polymer, wherein the thermoplastic polymer is processed to become a cyclized, non-plastic ladder compound. cathode; and Electrolytes.

10. The energy storage device of claim 9, wherein the electrolyte comprises an imide-based room-temperature ionic liquid.

11. A method for manufacturing an anode, the method comprising: A slurry is prepared by combining active materials, additive powders, polymer powders, and a solvent capable of dissolving the polymer powders. The slurry is cast onto a current collector substrate to form a cast film, wherein the current collector substrate includes a surface roughness... R z Greater than 1.5 micrometers, and wherein the arithmetic mean height of the current collector substrate is... Sa The size is smaller than the interface area ratio generated by the current collector substrate. Sdr Three times that of the membrane, wherein the membrane comprises a thermoplastic polymer that is processed to become a cyclized, nonplastic ladder-shaped compound; Dry the cast film; and The cast film is heated, wherein the film has a thickness of 10 to 80 micrometers.

12. The method of claim 11, wherein the heating comprises applying heat to the cast film at a temperature of 200 to 400°C for a period of 1 to 12 hours.

13. The method of claim 12, wherein the heating is performed under a vacuum or an inert gas flow.

14. The method of claim 11, wherein the slurry has a Brinell viscosity of 2000-6000 cP, measured at room temperature using a #64 spindle at 20 to 100 RPM.

15. The method of claim 11, wherein the active material comprises silicon and carbonaceous active materials.

16. The method of claim 11, wherein the active material comprises 40 to 80% by weight of silicon, 5 to 50% by weight of carbonaceous material and 10 to 20% by weight of polyacrylonitrile.

17. The method of claim 15, wherein the weight ratio of silicon:carbon material:polymer powder is 30:55:15, and wherein the polymer powder is polyacrylonitrile.

18. The method of claim 11, wherein the additive powder comprises a material selected from lithium metal powder, lithium nitride, oxalic acid, and combinations thereof.

19. The method according to claim 11, wherein the solvent is selected from N,N-dimethylformamide, dimethyl sulfone, dimethyl sulfoxide, N-methyl-2-pyrrolidone, N,N-dimethylacetamide, ethylene carbonate, propylene carbonate, and combinations thereof.

20. The method of claim 11, wherein the active material is selected from silicon, hard carbon, graphite, graphene, germanium, titanium dioxide, tin, magnesium, antimony, lead, and combinations thereof.

21. The method of claim 20, wherein the active material comprises silicon or a silicon-carbon composite material.

22. The method according to claim 21, wherein the silicon or silicon-carbon composite material is selected from nanosphere silicon, nanowire silicon, nanorod silicon, whisker silicon, "coral" silicon, microsphere silicon, silicon-graphite, silicon-graphene, silicon-hard carbon, and combinations thereof.

23. The method of claim 11, wherein the thermoplastic polymer comprises polyacrylonitrile.

24. The method of claim 11, wherein the active material comprises active material particles with a particle size greater than 500 nanometers.

25. A method for manufacturing an energy storage device, the method comprising: The anode is manufactured according to the method of any one of claims 11-24; The anode, cathode, and electrolyte are disposed within the housing.

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