Negative electrode material for an electrochemical lithium-ion battery cell, electrochemical lithium-ion battery cell, and method for producing an electrochemical battery cell

Abstract

Negative electrode material for an electrochemical lithium-ion battery cell, comprising: a polymeric ultra-thin conformal coating on a surface of the negative electrode material selected from the group consisting of: silicon, silicon-containing alloys, tin-containing alloys, and combinations thereof, wherein the coating has a thickness of less than or equal to about 50 nm and is capable of reversibly elongating by at least 50% from a contracted state to an expanded state in at least one direction to minimize or prevent breakage of the negative electrode material during lithium-ion cycling; characterized in that the polymeric ultra-thin conformal coating comprises a TEMPO methacrylate.

Description

TECHNICAL FIELD

[0001] The present invention relates to electrode materials for electrochemical devices and in particular to a negative electrode material according to the preamble of claim 1 for an electrochemical lithium-ion battery cell, as is essentially known from US 2016 / 0 111 700 A1.

[0002] Comparable negative electrode materials can also be found in the documents US 2011 / 0 129 729 A1, US 2016 / 0 093 879 A1 and CN 103 682 354 A. BACKGROUND

[0003] High-energy-density electrochemical cells such as lithium-ion batteries and lithium-sulfur batteries can be used in a wide variety of consumer products and vehicles, such as hybrid electric vehicles (HEVs) and electric vehicles (EVs). Typical lithium-ion and lithium-sulfur batteries include a first electrode (e.g., a cathode), a second electrode (e.g., an anode), an electrolyte material, and a separator. Often, a stack of battery cells is electrically connected to increase overall power. Conventional lithium-ion and lithium-sulfur batteries rely on the flow of lithium ions from a negative electrode to a positive electrode and back again. A separator and an electrolyte are placed between the negative and positive electrodes. The electrolyte can conduct lithium ions and can be in solid or liquid form.When charging a battery, lithium ions move from a cathode (positive electrode) to an anode (negative electrode), and when discharging a battery, they move in the opposite direction.

[0004] Contact between the anode and cathode materials and the electrolyte can create an electrical potential between the electrodes. When an electron current is generated between the electrodes in an external circuit, the potential is maintained by electrochemical reactions within the battery cells. Each of the negative and positive electrodes within a stack is connected to a current collector (typically a metal, such as copper for the anode and aluminum for the cathode). During battery use, the current collectors connected to the two electrons are interconnected via an external circuit, allowing the current generated by the electrons to be transported between the electrodes to compensate for the transport of the lithium ions.

[0005] Typical electrochemically active materials for forming an anode include lithium-graphite intercalation compounds, lithium-silicon alloys, lithium-tin alloys, and lithium alloys. While graphite compounds are the most common, anode materials with high specific capacity (compared to conventional graphite) have recently been of growing interest. For example, silicon has the highest known theoretical charge capacity for lithium, making it one of the most promising materials for rechargeable lithium-ion batteries. However, current silicon-containing anode materials suffer from significant weaknesses. The large volume changes that occur during the intercalation and release of lithium (e.g., lithium alloying or de-alloying) (e.g.,Volume expansion / contraction of the silicon-containing materials leads to cracking in the anode, a decline in electrochemical cyclic performance and a reduced Coulomb charge capacity (capacity fade) as well as a limited cycle life.

[0006] It would be desirable to develop high-performance negative electrode materials consisting of silicon or other negative electrode materials that expand during the lithium cycle for use in high-performance lithium-ion batteries. These materials overcome the current weaknesses that prevent widespread commercial use, particularly in automotive applications. For long-term and effective use, silicon-containing anode materials would need to exhibit minimal capacity decay and optimal charge capacity for extended use in lithium-ion batteries. SUMMARY

[0007] According to the invention, a negative electrode material for an electrochemical lithium-ion cell is presented, which is characterized by the features of claim 1.

[0008] Furthermore, an electrochemical lithium-ion battery cell with the features of claim 5 is presented.

[0009] Furthermore, according to the invention, a method for producing an electrochemical battery cell is presented, which is characterized by the features of claim 6.

[0010] Further areas of application will become apparent from the description presented herein. The description and specific examples in this summary are for illustrative purposes only. DRAWINGS

[0011] The drawings described herein are for illustrative purposes only. Figure 1 is a schematic diagram of an electrochemical battery cell; Figure 2 is a schematic representation of the volumetric expansion of an electroactive material consisting of silicon during lithium ion intercalation / alloying. Figure 3 is a schematic representation of an electrode material in an electrochemical battery cell comprising an ultra-thin conformal coating according to certain aspects of the present invention that can minimize or prevent breakage of the electrode material during lithium-ion cycling. Figure 4 shows an X-ray photon spectroscopy (XPS) of a polymeric ultrathin conformal coating of silicon on a copper substrate. Figure 5 shows an infrared spectroscopy of an organic polymeric coating of a siloxane on a silicon surface. Figure 6 shows comparative electrochemical behavior for a reference and two comparative samples prepared according to certain aspects of the present invention with a polymeric ultrathin conformal coating on silicon with thicknesses of 5 nm and 10 nm.

[0012] Corresponding reference numbers identify corresponding parts in the various views of the drawings. DETAILED DESCRIPTION

[0013] In this invention, the numerical values ​​represent both approximate measurements or limits of ranges to accommodate minor deviations from the specific values ​​and embodiments that approximately have the stated value, as well as those that exactly have the stated value. Contrary to the application examples provided at the end of the detailed description, all numerical values ​​of parameters (e.g., quantities or conditions) in this specification, including the appended claims, are to be understood in all cases by the term "approximate," regardless of whether or not "approximately" actually appears before the numerical value. "Approximately" indicates that the disclosed numerical value allows for some imprecision (with some approximation to exactness in the value; approximately or realistically close to the value; approximately).If the imprecision provided by "about" is not otherwise understood by those skilled in the art to have this ordinary meaning, then "about," as used herein, indicates at least variations resulting from ordinary measurement techniques and the use of such parameters. For example, "about" may encompass a variation of less than or equal to 5%, possibly less than or equal to 4%, possibly less than or equal to 3%, possibly less than or equal to 2%, possibly less than or equal to 1%, possibly less than or equal to 0.5%, and in certain aspects, possibly less than or equal to 0.1%.

[0014] Furthermore, the invention of ranges includes the invention of all values ​​and further subdivided ranges within the entire range, including the endpoints and subranges specified for the ranges.

[0015] Exemplary embodiments will now be described in more detail with reference to the accompanying drawings.

[0016] The present technology relates to improved electrochemical cells, including batteries, particularly lithium-ion batteries and lithium-sulfur batteries, which can be used in vehicle applications. An exemplary and schematic representation of a battery 20 is shown in Fig. 1. The battery may be a lithium-ion electrochemical cell or a lithium-sulfur electrochemical cell. The battery 20 includes a negative electrode 22, a positive electrode 24, and a separator 30 (e.g., a microporous polymeric separator) disposed between the two electrodes 22, 24. The separator 26 includes an electrolyte 30, which may also be present in the negative electrode 22 and the positive electrode 24. A negative electrode current collector 32 may be disposed at or near the negative electrode 22, and a positive electrode current collector 34 may be positioned at or near the positive electrode 24. The negative electrode current collector 32 and the positive electrode current collector 34 each collect the electrons and transport the free electrons to and from an external circuit 40.An interruptible external circuit 40 and load 42 connects the negative electrode 22 (via its current collector 32) and the positive electrode 24 (via its current collector 34). Each of the negative electrode 22, the positive electrode 24, and the separator 26 may further include the electrolyte 30, which can conduct lithium ions. The separator 26, which serves as both an electrical insulator and a mechanical support, is sandwiched between the negative electrode 22 and the positive electrode 24 to prevent physical contact and thereby avoid the occurrence of a short circuit. In addition to providing a physical barrier between the two electrodes 22, 24, the separator 26 may provide a minimal resistance path for the internal passage of the lithium ions (and associated anions) to facilitate the operation of the battery 20.

[0017] Battery 20 can generate an electric current during discharge through reversible electrochemical reactions that occur when external circuit 40 is closed (to connect negative electrode 22 and positive electrode 34) when negative electrode 22 contains a relatively larger amount of intercalated / diffused lithium. The chemical potential difference between positive electrode 24 and negative electrode 22 drives the electrons generated by the oxidation of the intercalated / diffused lithium at negative electrode 22 through external circuit 40 to positive electrode 24. Lithium ions also generated at the negative electrode are simultaneously transferred to positive electrode 24 through electrolyte 30 and separator 26.The electrons flowing through the external circuit 40 and the lithium ions migrating through the separator 26 in the electrolyte 30 form intercalated lithium at the positive electrode 24. The electrical current flowing through the external circuit 18 can be used and conducted by the load 42 until the intercalated / diffused lithium in the negative electrode 22 is depleted and the capacity of the battery 20 decreases.

[0018] The battery 20 can be recharged and used at any time by connecting an external power source to the lithium-ion battery 20 to reverse the electrochemical reactions of the battery discharge. Connecting an external power source to the battery 20 forces the otherwise non-spontaneous oxidation of intercalated lithium at the positive electrode 24 to generate electrons and lithium ions. The electrons, which flow through the external circuit 40 back to the negative electrode 22, and the lithium ions, which are transported by the electrolyte 30 through the separator 26 back to the negative electrode 22, reconnect at the negative electrode 22 and refill it with stored / diffused lithium for consumption in the next battery discharge cycle. The external power source that may be used to charge the battery 20 may vary in size, construction, and specific end use of the battery 20. Some notable and exemplary external sources include an AC wall outlet and a motor vehicle alternator. In many lithium-ion battery and lithium-sulfur battery configurations, the negative current collector 32, the negative electrode 22, the separator 26, the positive electrode 24, and the positive current collector 34 are each fabricated as relatively thin sheets (e.g., a few micrometers or a millimeter or less in thickness) and assembled in layers that are electrically connected together in parallel to provide a suitable power package.

[0019] Furthermore, the battery 20 may include a variety of other components that, although not illustrated here, are well known to those skilled in the art. For example, the lithium-ion battery 20 may include a housing, seals, end caps, and any other conventional components or materials that may be located within the battery 20, including between or around the negative electrode 22, the positive electrode 24, and / or the separator 26, for example. As noted above, the size and shape of the battery 20 may vary depending on the particular application for which it is designed. Battery-powered vehicles and portable consumer electronic devices, for example, are two examples where the battery 20 would likely have a different size, capacity, and power output.The battery 20 may also be connected in series or parallel with other similar lithium-ion cells or batteries to produce a greater voltage output and power density if required by the load 42.

[0020] Accordingly, the battery 20 can generate electrical power at a load 42, which can be operatively connected to the external circuit 40. The load 42 can be powered entirely or partially by the electrical current passed through the external circuit 40 as the lithium-ion battery 20 discharges. While the load 42 can be any number of electrically powered devices, some specific examples of power-consuming load devices include an electric motor for a hybrid vehicle or for an electric car, a laptop computer, a tablet computer, a mobile phone, and a cordless power tool or household appliances, as examples. However, the load device 42 can also be a power generating device that charges the battery 20 to store the energy.

[0021] Any suitable electrolyte 30 capable of conducting lithium ions between the negative electrode 22 and the positive electrode 24 may be used in the lithium-ion battery 20, either in solid form or in solution. In certain aspects, the electrolyte solution may be an anhydrous liquid electrolyte solution comprising a lithium salt dissolved in an organic solvent or a mixture of organic solvents. Numerous conventional non-aqueous liquid electrolyte solutions 30 may be used in the lithium-ion battery 20. A notable list of lithium salts that may be dissolved in an organic solvent to form the non-aqueous liquid electrolyte solution includes LiPF6, LiClO4, LiAlCl4, LiIl, LiBr, LiSCN, LiBF4, LiB(C6H5)4, LiAsF6, LiCF3SO3, LiN(CF3SO2)2, and combinations thereof.These and similar lithium salts can be dissolved in a variety of organic solvents, including various alkyl carbonates such as cyclic carbonates (ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC)), acyclic carbonates (dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC)), aliphatic carboxylic acid esters (methyl formate, methyl acetate, methyl propionate), γ-lactones (γ-butyrolactone, γ-valerolactone), chain ethers (1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane), cyclic ethers (tetrahydrofuran, 2-methyltetrahydrofuran) and mixtures thereof.

[0022] The separator 30, in one embodiment, may comprise a microporous, polymeric separator comprised of a polyolefin. The polyolefin may be a homopolymer (derived from a single constituent monomer) or a heteropolymer (derived from more than one constituent monomer), which may be either linear or branched. When a heteropolymer is derived from two constituent monomers, the polyolefin may adopt any copolymer chain arrangement, including that of a block copolymer or a random copolymer. Likewise, a polyolefin that is a heteropolymer derived from more than two constituent monomers may also be a block copolymer or a random copolymer. In certain aspects, the polyolefin may be polyethylene (PE), polypropylene (PP), or a blend of PE and PP.

[0023] When the separator 30 is a microporous polymeric separator, it may be a single layer or a multi-layer laminate manufactured via either a dry or a wet process. For example, in one embodiment, a single layer of the polyolefin may constitute the entire microporous polymeric separator 30. In other aspects, the separator 30 may be a fibrous membrane having a multitude of pores extending between opposing surfaces and may, for example, have a thickness of less than one millimeter. However, as another example, the microporous polymeric separator 30 may also be composed of multiple separate layers of the same or dissimilar polyolefin.The microporous polymeric separator 30 may comprise other polymers besides the polyolefin, such as, but not limited to, polyethylene terephthalate (PET), polyvinylidene fluoride (PVDF), cellulose, and / or a polyamide. The polyolefin layer and any other polymer layers may also be included in the microporous polymeric separator 30 as a fibrous layer to provide the microporous polymeric separator 30 with suitable structural and porosity characteristics. Various common polymers and commercial products for forming the separator 30 are considered, as are the many manufacturing processes that can be used to produce such a microporous polymeric separator 30.

[0024] In a lithium-ion battery, the positive electrode 24 may be formed from a lithium-based active material that allows sufficient intercalation and disintercalation of lithium when serving as the positive terminal of the lithium-ion battery 20. The positive electrode 24 may include a polymer binder to structurally hold the lithium-based active material together. An exemplary common class of known materials that may be used to form the positive electrode 24 are layered lithium transition metal oxides. For example, in certain embodiments, the positive electrode 24 may include at least one spinel comprising a transition metal, such as lithium manganese oxide (Li (1+x) Mn (2-x) O4), where 0 ≤ x ≤ 1, where x is typically less than 0.15 including LiMn2O4, lithium manganese nickel oxide (LiMn (2-x) Ni x O4), where 0 ≤ x ≤ 1 (e.g. LiMn 1,5 Ni 0,5O4), lithium cobalt oxide (LiCoO2), lithium manganese oxide (LiMn2O4), lithium nickel oxide (LiNiO2), a lithium nickel manganese cobalt oxide (Li(Ni x Mn y Co z )O2), where 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, and x + y + z = 1 including LiMn 0‚33 Ni 0,33 Co 0,33 O2, lithium-rich nickel-cobalt metal oxide (LiNi (1-x-y) Co x M yO2), where 0 <x<1, y<1 und M Al, Mn oder dergleichen sein kann, sonstige bekannte Lithiumübergangsmetalloxide oder -mischoxide, Lithiumeisenphosphate oder ein Lithiumeisen-Polyanionoxid wie zum Beispiel Lithiumeisenphosphat (LiFePO4) oder Lithiumeisenfluorphosphat (Li2FePO4F). Solche aktiven Materialien können mit mindestens einem polymeren Bindemittel vermischt werden, beispielsweise durch Schlickergießen aktiver Materialien mit solchen Bindemitteln, wie Polyvinylidenfluorid (PVDF), Ethylen-Propylen-DienKautschuk (EPDM) oder Carboxymethoxylcellulose (CMC). Der positive Stromabnehmer 34 kann aus Aluminium oder jedem beliebigen anderen geeigneten elektrisch leitenden Material bestehen.

[0025] In a lithium-sulfur battery, the positive electrode contains sulfur-based compounds for a positive active material. A sulfur-based compound can be selected from at least one of: elemental sulfur, Li2S n(where n is greater than or equal to 1), Li2S n (where n is greater than or equal to 1), dissolved in a catholyte, an organosulfur compound and a carbon-sulfur polymer ((C2S x ) n : where x = 2.5, and n is 2 or greater). The positive electrode may also include electrically conductive materials that facilitate the movement of electrons within the positive electrode. For example, electrically conductive materials may include graphite, carbonaceous materials, or a conductive polymer. Carbonaceous materials may be used as examples. ® , Denka Black ®, acetylene black, carbon, carbon black, and the like. Examples of a conductive polymer include polyaniline, polythiophene, polyacetylene, polypyrrole, and the like. The conductive material can be used singly or as a mixture of two or more materials. The positive electrode can also include a polymeric binder, as described above.

[0026] In certain aspects, the present invention provides improved negative electrodes (e.g., anode). The electrochemically active negative electrode material can be selected from the group consisting of silicon, silicon-containing alloys, tin-containing alloys, and combinations thereof. Silicon particles can, by way of example, contain silicon or silicon-containing binary and ternary alloys and / or tin-containing alloys such as Si-Sn, SiSnFe, SiSnAl, SiFeCo, SnO2, and the like. Such negative electrode materials suffer from significant volume expansion during lithium cycling (e.g., they can absorb the onset of lithium ions during charging of the electrochemical cell ("intercalation") and release lithium ions again during discharging of the electrochemical cell ("de-intercalation"), or even lithium alloying / de-alloying).

[0027] For example, as in Figure 2, a particle 100 consisting of silicon-containing material undergoes a significant volume expansion during lithium-ion incorporation or lithium alloying. In an initial state 110 prior to lithium-ion incorporation or reaction, the particle 100 is in a first contracted state. After lithium-ion insertion / incorporation or alloying, the particle 100 is in a second expanded state 120. For example, if the particle is a silicon particle (Si) in the first contracted state 110, after the incorporation of lithium ions, it forms Li 4,4Si (corresponding to the second expanded state 120). The volume of a silicon particle 100 after lithium intercalation in the second expanded state 120 can be up to four (4) times (400%) larger than the volume of the silicon particle 100 in the first contracted state 110. As is evident, the first contracted state 110 can correspond to the volume of the particle 100 before lithium intercalation or after lithium extraction. In a conventional system such as in Figure 2, the extent of volume expansion that occurs can bring the particle 100 into a third state 130, wherein the particle 100 mechanically disintegrates and breaks into several smaller fragments or pieces 132. If the particle 100 breaks into smaller pieces 132 in the third state 130, these pieces are smaller pieces 132 and can no longer sustain the performance of the electrochemical cell.Thus, it is desirable to avoid fragmentation and breakage associated with the third state 130.

[0028] According to various aspects of the present teachings, an electrode material in an electrochemical cell includes an ultrathin conformal coating capable of minimizing or preventing the cracking of the negative electrode material during lithium-ion cycling. For example, as shown in Figure 3, a particle 140 of the electrode material has an ultrathin, polymeric, flexible, conformal coating 142 disposed thereon. It should be noted that the features in Figure 3 are not necessarily drawn to scale, but are for illustrative purposes only.

[0029] The ultra-thin conformal coating is applied to exposed areas of a surface of the electrode material so that it is thin but largely covers the exposed areas of the surface of the material.In certain variations, the polymeric ultra-thin conformal coating is applied to greater than or equal to about 50% of the exposed area of ​​the negative electrode material, possibly greater than or equal to about 75% of the exposed surface, possibly greater than or equal to about 90% of the exposed surface, possibly greater than or equal to about 95% of the exposed surface, possibly greater than or equal to about 97% of the exposed surface, possibly greater than or equal to about 98% of the exposed surface, possibly greater than or equal to about 99% of the exposed surface, possibly greater than or equal to about 99.5% of the exposed surface, and in certain aspects, 100% of the exposed area of ​​the negative electrode material is coated with the polymeric ultra-thin conformal coating.

[0030] In certain preferred aspects, a surface of a silicon and / or tin negative electrode material has an ultra-thin conformal surface coating that is flexible and minimizes or prevents breakage of the negative electrode material during lithium-ion cycling in the electrochemical cell. In the event of minor degradation of the active electrode material, the flexible polymer coating can help maintain the structural integrity of the electrode.In certain variations, an average thickness of the surface coating on the negative electrode material is ultra-thin and thus has an average thickness of less than or equal to about 50 nm, possibly less than or equal to about 35 nm, possibly less than or equal to about 30 nm, possibly less than or equal to about 25 nm, possibly less than or equal to about 20 nm, possibly less than or equal to about 15 nm, possibly less than or equal to about 10 nm, possibly less than or equal to about 9 nm, possibly less than or equal to about 8 nm, possibly less than or equal to about 7 nm, and possibly less than or equal to about 6 nm. In certain variations, an ultra-thin coating is greater than or equal to about 5 nm to less than or equal to about 50 nm.

[0031] In certain variations, the thickness of the ultra-thin conformal surface coating varies across the surface of the electroactive material only to a maximum of less than or equal to approximately 100% (a thickness difference from the thinnest portion of the coating to the thickest portion of the coating is ≤ 100%). This ensures that the coating thickness is relatively uniform and maintains coverage over the surface of the electrode material in both the expanded and contracted states. The ultra-thin conformal surface coating provides sufficient coverage of the exposed surface areas to protect the negative electrode material during large volume expansion and to keep it intact without cracking and degrading performance in the electrochemical cell, while maintaining lithium-ion diffusion values ​​and minimizing the electrical impedance at the electroactive material surface to increase electrode integrity.

[0032] In certain aspects, the polymeric ultra-thin conformal coating is flexible and can therefore reversibly elongate by at least 50% from a contracted state to an expanded state in at least one direction to minimize or prevent the fracture of the negative electrode material or to hold the fractured electrode particles together to maintain both ionic and electrical conductivity during lithium-ion cycling. In certain variations, a Young's modulus of the polymeric ultra-thin conformal coating can be less than or equal to about 2 GPa when the coating is saturated with liquid electrolytes, and in certain preferred variations, less than or equal to about 1 GPa. By reversibly elongating in at least one direction, it is meant that the polymeric conformal coating can extend in at least one direction from an initial point (e.g., the initial length L i) to an extended point (e.g. the extended length L e ) and return to or at least close to the starting point without mechanical breakage or failure. Thus, an elongation of at least 50% Le−LiLi≥50%, If in one example the initial average thickness of the ultrathin conformal coating corresponds to a Li of 5 nm, that a 50% strain results in an extended length L eof approximately 7.5 nm. Thus, the flexible polymeric ultrathin conformal coating provides the ability to expand and contract with the active electrode material during lithium cycling.Depending on the electroactive material used, the ultra-thin conformal coating can reversibly elongate by at least 75% from a contracted state to an expanded state in at least one direction, possibly by at least 100% from a contracted state to an expanded state in at least one direction, possibly by at least 125% from a contracted state to an expanded state in at least one direction, possibly by at least 150%, possibly by at least 175%, and in certain variations up to 200% or more elongation from a contracted state to an expanded state in at least one direction to minimize or prevent breakage of the negative electrode material during lithium-ion cycling.The ultra-thin conformal polymer coating desirably has a lithium ion conductivity or diffusion rate greater than that of the electrode material, for example, greater than 10. -12 up to 10 -14 cm 2 / s.

[0033] In certain variations, the average particle diameter of the negative electrode active material may be greater than or equal to about 5 nanometers to less than or equal to about 200 nanometers. As mentioned above, the present technology is particularly suitable for use with negative electrode materials for the negative electrode 22 selected from the group consisting of: silicon, silicon-containing alloys, tin-containing alloys, and combinations thereof. Materials usable for forming the negative electrode 22 include, for example, lithium-silicon and silicon-containing binary and ternary alloys and / or tin-containing alloys such as Si-Sn, SiSnFe, SiSnAl, SiFeCo, SnO 2mand the like. The negative electrode material may consist of greater than or equal to about 50% to less than or equal to about 90% of an electroactive material (e.g., silicon-containing or tin-containing particles), possibly greater than or equal to about 5% to less than or equal to about 30% of an electrically conductive material, and a binder. Suitable electrically conductive materials may be selected from graphite, carbon black, powdered nickel, metal particles, conductive polymers, or any combination thereof.Suitable binders may include a polymer material and an extractable plasticizer to form a porous composite, such as halogenated hydrocarbon polymers (such as poly(vinylidene chloride) and poly((dichloro-1,4-phenylene)ethylene), fluorinated urethanes, fluorinated epoxies, fluorinated acrylics, copolymers of halogenated hydrocarbon polymers, epoxies, ethylene-propylene-diamine termonomer (EPDM), ethylene-propylene-diamine termonomer (EPDM), polyvinylidene difluoride (PVDF), hexafluoropropylene (HFP), ethylene-acrylic acid copolymer (EAA), ethylene-vinyl acetate copolymer (EVA), EAA / EVA copolymers, PVDF / HFP copolymers, CMC (carboxyl-methyl cellulose), and mixtures thereof. The negative electrode current collector 32 may be made of copper or any other suitable electrically conductive material. as is known to experts.

[0034] An electrode can be prepared by mixing the electroactive material, such as silicon-containing particles, with a polymeric ultrathin conformal coating in a slurry with a polymeric binder compound, a non-aqueous solvent, optionally a plasticizer, and optionally, if necessary, electrically conductive particles. The slurry can be mixed or stirred and then thinly applied to a substrate using a doctor blade. The substrate can be a removable substrate or, alternatively, a functional substrate such as a current collector (such as a metallic grid or mesh layer) attached to one side of the electrode foil. In one variation, heat or radiation can be applied to volatilize the solvent from the electrode foil, leaving a solid residue.The electrode foil can be further consolidated, where heat and pressure are applied to the foil for sintering and calendering. In other variations, the foil can be air-dried at moderate temperatures to form self-supporting foils. If the substrate is removable, it is removed from the electrode foil, which is then further laminated to a current collector. With each substrate type, it may be necessary to extract or remove the remaining plasticizer before incorporation into the battery cell.

[0035] A battery can thus be assembled in a layered cell structure comprising an anode layer, a cathode layer, and an electrolyte / separator between the anode and cathode layers. The anode and cathode layers each comprise a current collector. A negative anode current collector can be a copper collector foil, which can be in the form of an open grid or a thin film. The current collector can be connected to an external current collector strip.

[0036] For example, in certain variations, an electrode membrane such as an anode membrane comprises the electrode active material (e.g., silicon) dispersed in a polymeric binder matrix over a current collector. The separator can then be disposed over the negative electrode element, which is covered with a positive electrode membrane comprising a composition of a finely divided lithium intercalation compound in a polymeric binder matrix. A positive current collector, such as an aluminum collector foil or grid, completes the assembly. Strips of the current collector elements form respective terminals of the battery. A protective packing material covers the cell and prevents the ingress of air and moisture. An electrolyte suitable for lithium-ion transport is injected into this pocket in the separator (and also absorbed into the positive and / or negative electrodes).In certain aspects, the laminated battery is further hermetically sealed before use.

[0037] In certain variations, the present invention provides an electroactive material for an electrochemical cell, such as a lithium-ion battery. A negative electrode material may be comprised of, for example, silicon, silicon alloys, tin, and its alloys. In certain variations, the negative electrode material is comprised of silicon. The electrode material has a polymeric ultra-thin conformal surface coating thereon, which may have a thickness of less than or equal to about 50 nm and is capable of reversibly elongating by at least 50% from a contracted state to an expanded state in at least one direction to minimize or prevent breakage of the negative electrode material during lithium-ion cycling within the electrochemical cell.In certain variations, the electroactive material consisting of silicon, silicon alloys, tin, and its alloys is deposited in a preformed electrode layer, and the polymeric ultrathin conformal coating is applied to at least one surface of the preformed electrode layer. In other variations, the polymeric ultrathin conformal coating is deposited on a plurality of particles consisting of silicon, silicon alloys, tin, and its alloys, which can subsequently be incorporated into the electrode. In certain aspects, the polymeric ultrathin conformal coating is ultrathin and formed by an atomic layer deposition process.

[0038] In other aspects, the present invention provides a method for producing a negative electrode for an electrochemical battery cell, including a polymerization process where one or more precursors are reacted on a surface of a negative electrode material selected from the group consisting of: silicon, silicon-containing alloys, tin-containing alloys, and combinations thereof. The precursor can, in certain variations, be an initiator or a monomer. The polymerization forms a polymeric ultrathin conformal coating, as described above.The polymerization can occur by a process selected from the group consisting of: layer-by-layer polymerization, which can be carried out as vapor reactants via atomic layer deposition, anionic polymerization, cationic polymerization, and radical polymerization, although only radical polymerization is used in the invention to form the polymeric ultra-thin conformal coating. The polymerization can be carried out by a process selected from the group consisting of: physical vapor deposition (PVD), chemical vapor deposition (CVD), molecular layer deposition (MLD), layer-by-layer deposition (LBL), chemical vapor infiltration, and wet chemistry.

[0039] In a variation not according to the invention, the polymerization process comprises a layer-by-layer polymerization. In certain aspects, the layer-by-layer process may occur in an atomic layer deposition (ALD) reactor, wherein a first gaseous precursor (e.g., an alkyllithium, such as lithium tert-butoxide - LiO t Bu) and a second gaseous precursor (e.g., a linear or cyclic siloxane) are introduced sequentially into the reactor. The linear or cyclic siloxane can be linear siloxane polymers [-SiRR'O-] (with various alkyl and aryl R and R' side groups), silsesquioxane polymers, silalkylene polymers [-Si(CH3)2(CH2) m-] and any copolymers of the above. In one example, the second gaseous precursor can be a cyclic methylsiloxane. Trimethylaluminum (TMA) can also be used as a precursor. Using alkyllithium as an initiator, the cyclic siloxane or linear siloxane can be polymerized into the polymeric coating in situ on the particles or any other substrate for various applications.

[0040] In certain variations, a gaseous polymerization / deposition process for layer-by-layer polymerization not according to the invention includes atomic layer deposition (ALD), wherein the first gaseous precursor is first applied to the surface of the negative electrode material. In any of the processes described herein, the negative electrode material desirably has at least 1% of the exposed surface area containing active hydrogen or hydroxyl groups. This amount of active groups at the surface helps ensure coverage levels with the polymeric coating discussed above, for example, that more than 90% of the exposed surface area is covered by the polymeric coating. If necessary, the surface of the electrode-active material may be activated prior to polymerization by conventional methods known in the art, for example, by plasma treatment, oxidation, or other chemical treatment.Thus, in this polymerization process not according to the invention, the polymeric ultra-thin conformal surface coating is built up layer by layer, so that the first gaseous precursor is first reacted with the active groups on the surface of the negative electrode material.

[0041] In other variations, the polymerization process comprises a free-radical polymerization process. The precursors can include an initiator and a monomer. While the precursors can be in either a gaseous / vapor or liquid state, in most cases the precursors are in a vapor or gaseous state due to the temperatures to which they are heated, and the carrier gas (e.g., Ar) carries them into the reactor. In certain variations, the initiator is selected from the group consisting of: azoisobutylnitrile, dicumyl peroxide, persulfate, and combinations thereof. The monomer can comprise an acrylate monomer or a methacrylate monomer. According to the invention, the monomer is 4-methacryloyloxy-2,2,6,6-tetramethylpiperidine-1-oxy (TEMPO methacrylate), which forms a semiconducting polymer. Such a free-radical polymerization process is carried out in an oxygen-free and anhydrous environment.For example, the radical polymerization process can be carried out in an inert gas environment (e.g., nitrogen, argon). The initiator, monomer, and the active particles are mixed and reacted with each other at suitable temperatures to form the coating layer on the surface of the particles. Thus, the resulting polymeric ultrathin conformal coating, in certain variations, comprises a semiconducting methacrylate polymer.

[0042] In other variations, the polymerization process according to the invention comprises an anionic polymerization. The precursors may include an initiator and a monomer. While the precursors may be in either a gaseous / vapor or liquid state, due to the temperatures to which they are heated, in most cases the precursors are in a vapor or gaseous state, and the carrier gas (e.g., Ar) carries them into the reactor. In certain variations, the initiator is selected from the group consisting of: Grignard reactants, metal alkoxides, amides, cyanides, and combinations thereof. Suitable examples of such initiators may be sec-butyllithium, diphenylmethyl-Na, and NaNH2. The monomer may be selected from the group consisting of: vinylpyridine, cyclic siloxane, cyanoacrylate, propylene oxide, vinylsilane, and combinations thereof.Suitable examples of such monomers may be vinylpyridine, cyclic siloxane with various alkyl and aryl groups, such as methyl, ethyl, phenyl, and the like. Such an anionic polymerization process not according to the invention can be carried out in an oxygen-free and anhydrous environment. For example, the anionic polymerization process can be carried out in an inert gas environment (e.g., nitrogen, argon). Thus, in certain variations, the resulting polymeric ultrathin conformal coating comprises a polymer selected from the group consisting of: vinylpyridine, cyclic dimethyl siloxane, and combinations thereof.

[0043] In still further variations, the polymerization process according to the invention may comprise a cationic polymerization. The precursors may include an initiator and a monomer. While the precursors may be in either a gaseous / vapor or liquid state, in most cases the precursors are in a vapor or gaseous state due to the temperatures to which they are heated, and the carrier gas (e.g., Ar) carries them into the reactor. In certain variations, the initiator is a protic acid. Suitable examples of such an initiator may be phosphoric acid, sulfuric acid, fluoro- and trifluoromethanesulfonic acid. Other initiators may be Lewis acids such as SnCl4, AlCl3, BF3, and TiCl4. The monomer may be selected from the group consisting of lactones, lactams, and combinations thereof. Suitable examples of such monomers may be oxirane, oxazoline, and tetrahydrofuran.Such a cationic polymerization process not according to the invention can be carried out in an oxygen-free and water-free environment. For example, the radical polymerization process can be carried out in an inert gas environment (e.g., nitrogen, argon). Thus, the resulting polymeric ultrathin conformal coating, in certain variations, consists of a polymer such as polycaprolactam (or nylon) or polyethylene oxide. Example 1

[0044] Samples are prepared for comparison purposes. Sample A is prepared according to certain aspects of the present teachings and contains a silicon anode material with a coating of linear and cyclic siloxane deposited onto the silicon particles by ALD. For Sample A, the silicon electrode material is coated with linear and cyclic siloxane deposited via an aqueous atomic layer deposition process. The precursors include a cyclic methyl siloxane, lithium tert-butoxide, and trimethylaluminum (TMA). The deposition temperature for the substrate may be approximately 80°C. The annealing temperature for the trimethylaluminum (TMA) and cyclic methyl siloxane precursors may also be around 80°C, and the annealing temperature for the lithium tert-butoxide precursor is around 160°C. The carrier gas (Ar) flow rate is approximately 20 SCCM.For each precursor, the initial purge time is approximately 0.015 seconds, the exposure time is approximately 20 seconds, and the purge duration is approximately 20 seconds. All precursors are alternately introduced into the deposition chamber, and each precursor passes through the purge-exposure pump, resulting in a cycle. A typical reaction for coating formation is: n4[(CH3)SiO]n→LiOtBu(g) n[(CH3)2SiO]4. A siloxane layer with a thickness of approximately 0.15 nm is deposited on electrode surfaces (half an inch in diameter) in each cycle. The total thickness of the formed polymeric surface coating is 5 nm after 33 cycles.

[0045] The structural characterization of the polymeric siloxane coatings is described in the Fig. 3 and Fig.4. XPS results in Figure 4 show that the silicon-containing polymer coating was deposited on a copper substrate. The X-axis (150) is the binding energy (eV), while the Y-axis (152) is c / s. The typical Si signal (a small peak around 103 eV) was detected on Cu. Figure 5 shows a siloxane coating with Si-O and CH bonds deposited on a silicon surface of the active material. The X-axis (160) is the wavenumber (cm -1 ), while the Y-axis (162) is the absorption. Example 2 (not according to the invention)

[0046] Si thin-film electrodes (~100 nm) are deposited onto copper current collectors by RF magnetron sputtering and tested in coin cells for electrochemical characterization. Polymer coatings were fabricated using the ALD process described above in Example 1. A control sample is pure silicon (Si) anode material (incorporated into a negative electrode). Sample A is a silicon material with a polymeric ultrathin conformal coating deposited thereon by ALD (as described in the process in Example 1) to a thickness of 5 nm. Sample B is a silicon material with a polymeric ultrathin conformal coating deposited thereon by ALD (as described in the process in Example 1) to a thickness of 10 nm.

[0047] Battery half-cells with silicon (either reference samples or samples AB) as the working electrodes and Li foil as the counter electrode are used with an electrolyte containing 1M LiPF6 EC at 50% and 50% DEC and a separator. The Si electrodes (or polymer-coated Si electrodes) serve as the working electrodes, and pure lithium metal foil serves as the counter and reference electrodes in CR2032 button cells. A separator (CELGARD™, USA) is placed between the working electrode and the lithium foil, and 1M LiPF6 in ethylene carbonate and dimethyl carbonate (EC:DMC in a 1:1 volume ratio, BASF) serves as the electrolyte. An uncoated portion of the electrode is connected to an external terminal. The electrolyte and separator are placed between the surfaces of the respective positive and negative electrodes to form a complete battery cell.The Arbin Battery Test System (BT-2000) is used for cyclic testing of button cells using the constant current method (at a rate of C / 3) and a voltage window between 0.05 V and 1.5 V. The EIS study is performed in two-electrode button cells at the assigned voltage. The button cells are left to rest for 24 hours until they stabilize.

[0048] Electrochemical measurements are carried out with a constant current density of 10 mA / g -1 (approximately C / 10) relative to the mass of the positive electrode in the operating voltage range of 3 V to approximately 4.8 V for full cells. A cycle test of the battery is performed. Charge-discharge cycles are repeated 20 times under ambient conditions.

[0049] The charge and discharge profiles of the electrochemical performance of the reference sample and samples AB are shown in Figure 6. In Figure 6, a left y-axis shows the retention capacity (300) normalized in capacity starting with unit 1, a right y-axis shows the cycle efficiency % (310), while the cycle number is shown on the x-axis (320). A charge rate of C / 10 is used, and up to 20 cycles are tested. Charge capacity and discharge capacity are shown as fixed data points (reference = 322, sample A = 324, sample B = 326), while the coulombic efficiency (CE) is shown as open data points (reference = 332, sample A = 334, sample B = 336).

[0050] Different coatings (e.g., Samples A and B) exhibit different functionality. The polymeric coatings according to certain aspects of the present invention exhibit both improved cycling performance and coulombic efficiency. The coating thickness impacts cell performance. Thus, the ideal thickness depends on several factors, including the anode chemistry, particle size, and coating chemistry. The polymeric ultra-thin conformal coating improves cycling efficiency and retention capacity. Thus, polymeric coatings provide improved cycling stability of silicon anodes. The polymeric ultra-thin conformal coating is believed to provide additional mechanical stability to the underlying electrode material to stabilize the negative electrode material during expansion and contraction.

[0051] In certain variations, a lithium-ion battery comprising an electroactive material according to the invention having a polymeric ultra-thin conformal surface coating to minimize or prevent breakage of the negative electrode material during lithium-ion cycling can maintain charge capacity within 80% of the original charge capacity for greater than or equal to about 500 hours of battery operation, possibly greater than or equal to about 1000 hours of battery operation, possibly greater than or equal to about 1500 hours of battery operation, and in certain aspects, greater than or equal to about 2000 hours or more of battery operation (active cycling operation).

[0052] In certain variations, the lithium-ion battery comprising an electroactive material according to the invention having a polymeric ultra-thin conformal surface coating to minimize or prevent breakage of the negative electrode material during lithium-ion cycling can maintain charge capacity within 80% of an original charge capacity for at least 1000 deep discharge cycles, possibly more than or equal to about 2000 deep discharge cycles, possibly more than or equal to about 3000 deep discharge cycles, possibly more than or equal to about 4000 deep discharge cycles, and in certain variations possibly more than or equal to about 5000 deep discharge cycles.

Claims

[1] Negative electrode material for an electrochemical lithium-ion battery cell, comprising: a polymeric ultra-thin conformal coating on a surface of the negative electrode material selected from the group consisting of: silicon, silicon-containing alloys, tin-containing alloys, and combinations thereof, wherein the coating has a thickness of less than or equal to about 50 nm and is capable of reversibly elongating by at least 50% from a contracted state to an expanded state in at least one direction to minimize or prevent breakage of the negative electrode material during lithium-ion cycling; characterized by , that the polymeric ultra-thin conformal coating comprises a TEMPO methacrylate. [2] The electrode material of claim 1, wherein the polymeric ultra-thin conformal coating is applied to more than or equal to 50% of the exposed surface of the negative electrode material, or optionally to more than or equal to 99% of the exposed area of ​​the negative electrode material. [3] The electrode material according to claim 1, wherein the thickness is greater than or equal to 5 nm to less than or equal to 50 nm. [4] The electrode material of claim 1, wherein the polymeric ultra-thin conformal coating comprises a methacrylate polymer. [5] Electrochemical lithium-ion battery cell, comprising: a negative electrode comprising the electrode material according to claim 1; a positive electrode comprising a positive electroactive material comprising lithium; a separating device; and an electrolyte, wherein the polymeric ultra-thin coating minimizes or prevents breakage of the negative electrode material during lithium-ion cycling to substantially maintain the charge capacity of the lithium-ion electrochemical cell for greater than or equal to about 500 hours of operation. [6] Method for producing an electrochemical battery cell comprising the negative electrode material according to claim 1, wherein the method comprises radically polymerizing one or more precursors on a surface of the negative electrode to form the polymeric ultra-thin conformal coating, so that a negative electrode material according to claim 1 is obtained.

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