FIELD

The present disclosure relates to compositions useful in anodes for lithium ion batteries and methods for preparing and using the same.

BACKGROUND

Various Si-based anode compositions have been introduced for use in lithium-ion batteries. Such compositions are described, for example, in U.S. Patent Nos. 7906238 and 8753545.

SUMMARY

In some embodiments, an electrochemically active material is provided. The electrochemically active material includes composite particles. The composite particles include an alloy material comprising particles. The alloy particles have the formula: SixMyCz, where x, y, and z represent atomic % values and (a) x + y+ z = 100%; (b) x>2y+z; (c) x and y are greater than 0; z is equal to or greater than 0; and (d) M is iron and optionally one or more metals selected from manganese, molybdenum, niobium, tungsten, tantalum, copper, titanium, vanadium, chromium, nickel, cobalt, zirconium, yttrium. The composite particles also include a carbonaceous coating at least partially surrounding the particles, and an organosilane containing surface modifier bonded to an external surface of the composite particles. The organosilane containing surface modifier does not comprise a terminal amino group.

The above summary of the present disclosure is not intended to describe each embodiment of the present disclosure. The details of one or more embodiments of the disclosure are also set forth in the description below. Other features, objects, and advantages of the disclosure will be apparent from the description and from the claims.

DETAILED DESCRIPTION

Electrochemical energy storage has become a critical technology for a variety of applications, including grid storage, electric vehicles, and portable electronic devices. Lithium-ion electrochemical cells are a viable electrochemical energy storage system because of their relatively high energy density and good rate capability.

High energy density anode materials based on silicon (e.g., silicon alloys) can facilitate cost reduction, as well as energy and efficiency improvements of lithium-ion cells. However, such silicon alloys (capacity > about 1100 mAh/g) undergo significant volume change (e.g., up to 140% or more) during charge and discharge cycles.

Conventional negative electrode binders, such as poly(vinylidene fluoride) and sodium carboxymethylcellulose/styrene-butadiene rubber (CMC/SBR) blend, are suitable for use with graphite anode materials. However, they do not perform well in anodes containing more than about 15 wt. %> silicon alloy. Alternative anode binders, such as poly(acrylic acid) lithium salt, enable promising cycle life performance for anodes with high alloy contents (> about 20 wt. %), but they are inherently hygroscopic and brittle, making them difficult to process on an industrial scale. Consequently, high energy density anode materials that perform well in conventional binder systems are desirable.

As used herein,

the terms "lithiate" and "lithiation" refer to a process for adding lithium to an electrode material or electrochemically active phase;

the terms "delithiate" and "delithiation" refer to a process for removing lithium from an electrode material or electrochemically active phase;

the terms "charge" and "charging" refer to a process for providing electrochemical energy to a cell;

the terms "discharge" and "discharging" refer to a process for removing electrochemical energy from a cell, e.g., when using the cell to perform desired work; the phrase "charge/discharge cycle" refers to a cycle wherein an electrochemical cell is fully charged, i.e. the cell attains its upper cutoff voltage and the anode is at about 100%) state of charge, and is subsequently discharged to attain a lower cutoff voltage and the anode is at about 100%> depth of discharge;

the phrase "positive electrode" refers to an electrode (often called a cathode) where electrochemical reduction and lithiation occurs during a discharging process in a full cell; the phrase "negative electrode" refers to an electrode (often called an anode) where electrochemical oxidation and delithiation occurs during a discharging process in a full cell; the term "alloy" refers to a substance that includes any or all of metals, metalloids, semimetals;

the phrase "catenated heteroatom" means an atom other than carbon (for example, oxygen, nitrogen, or sulfur) that is bonded to carbon atoms in a carbon chain so as to form a carbon-heteroatom-carbon chain;

As used herein, the singular forms "a", "an", and "the" include plural referents unless the content clearly dictates otherwise. As used in this specification and the appended embodiments, the term "or" is generally employed in its sense including "and/or" unless the content clearly dictates otherwise.

As used herein, the recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.8, 4, and 5).

Unless otherwise indicated, all numbers expressing quantities or ingredients, measurement of properties and so forth used in the specification and embodiments are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the foregoing specification and attached listing of embodiments can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings of the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claimed embodiments, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

In some embodiments, the present disclosure relates to electrode compositions suitable for use in secondary lithium electrochemical cells (e.g., lithium ion batteries). Generally, the electrode compositions (e.g., negative electrode composition) may include an electrochemically active material that includes silicon alloy particles and a non-metallic electrically conductive layer or coating at least partially covering the alloy particles. As used herein, an "electrically conductive layer" may refer to a layer having a bulk electrical conductivity on the order of about 10-6 ohm-lcm-1 or greater. The active material may further include a coating composition that includes at least one silane of general formula (below).

In some embodiments, the electrochemically active material may include an alloy material having the formula: SixMyCz, where x, y, and z represent atomic % values and (a) x + y+ z = 100%; (b) x>2y+z; (c) x and y are greater than 0; z is equal to or greater than 0; (d) M is iron and optionally one or more metals selected from manganese, molybdenum, niobium, tungsten, tantalum, copper, titanium, vanadium, chromium, nickel, cobalt, zirconium, yttrium, or combinations thereof. In some embodiments, 65% <x < 85%, 70% <x < 80%_, 72% <x < 74%, or 75% <x <77%; 5% <y < 20%, 14% <y < 17%, or 13% <y < 14%; and 5% <z < 15%, 5% <z < 8%, or 9% <z < 12%. In some embodiments, x, y, and z are greater than 0.

In some embodiments, the alloy material may take the form of particles. The particles may have an average diameter (or length of longest dimension) that is no greater than 60 μιτι, no greater than 40 μιτι, no greater than 20 μιτι, or no greater than 10 μιη or even smaller; at least 0.5 μιτι, at least 1 μιτι, at least 2 μιτι, at least 5 μιτι, or at least 10 μιη or even larger; or 0.5 to 10 μιτι, 1 to 10 μιτι, 2 to 10 μιτι, 40 to 60 μιτι, 1 to 40 μιτι, 2 to 40 μιη, 10 to 40 μιη, 5 to 20 μιη, 10 to 20 μιη, 1 to 30 μιη, 1 to 20 μιη, 1 to 10 μιη, 0.5 to 30 μιη, 0.5 to 20 μιη, or 0.5 to 10 μιη.

In some embodiments the alloy material may take the form of particles having low surface area. The particles may have a surface area that is less than 20 m ² /g, less than 12 m ² /g, less than 10 m ² /g, less than 5 m ² /g, less than 4 m ² /g, or even less than 2 m ² /g.

In some embodiments, each of the phases of the alloy material (i.e., active phase, inactive phase, or any other phase of the alloy material) may include or be in the form of one or more grains. In some embodiments, the Scherrer grain size of each of the phases of the alloy material is no greater than 50 nanometers, no greater than 20 nanometers, no greater than 15 nanometers, no greater than 10 nanometers, or no greater than 5 nanometers. As used herein, the Scherrer grain size of a phase of an alloy material is determined, as is readily understood by those skilled in the art, by X-ray diffraction and the Scherrer equation.

In some embodiments, the electrochemically active material may further include a coating at least partially surrounding the alloy material. By "at least partially surrounding" it is meant that there is a common boundary between the coating and the exterior of the alloy material. The coating can function as a chemically protective layer and can stabilize, physically and/or chemically, the components of the particles. Exemplary materials useful for coatings include carbonaceous materials (e.g., carbon black or graphitic carbon), LiPON glass, phosphates such as lithium phosphate (L13PO4), lithium metaphosphate (LiPCb), lithium dithionite (L12S2O4), lithium fluoride (LiF), lithium metasilicate

(Li2SiCb), and lithium orthosilicate (Li4Si04). The coating can be applied by milling, solution deposition, vapor phase processes, or other processes known to those of ordinary skill in the art. In some embodiments, the coating may include a non-metallic, electrically conductive layer or coating. For example, in some embodiments, the coating may include carbon black. The carbon black may be present in an amount of between 0.01 and 20 wt. %, 0.1 and 10 wt. %, or 0.5 and 5 wt. %, based on the total weight of the alloy material and the carbon black. In such embodiments, the coating may partially surround the alloy material. For purposes of the present application, the alloy material and any coatings thereon may be referred to as composite particles.

In some embodiments, the electrochemically active material of the present disclosure may further include an organosilane-containing surface modifier bonded to an external surface of the composite particles. For example, the organosilane containing surface modifier may be bonded to at least a portion of the non-metallic, electrically conductive layer of the composite particles. Generally, it is believed that such surface modification alters the organic chemical makeup of the electrochemically active material's surface, which, in turn, improves its compatibility with conventional process-friendly negative electrode binder materials. Bonding of the organosilane containing surface modifier may be achieved via ionic bonding, dipole-dipole interactions, π-π interactions, hydrogen bonding interactions, covalent bonding, van der Waals forces, or combinations of one or more of these molecular interactions.

The ability to functionalize the surface of the composite particles in this manner is a surprising discovery. Specifically, while silane functionalization of metal and metal oxide surfaces is widely practiced, the effectiveness of silane treatment on non-metallic substrates (e.g. carbon or graphite) is less documented. Kuila et al. reviewed methods of chemical functionalization of graphene {Prog. Mater. Set 2012, 7, 1061-1105), and they discussed nucleophilic substitution on graphene oxide with 3-aminopropyltriethoxysilane, as well as cycloaddition of azidotrimethysilane onto epitaxial graphene. However, both 3- aminopropyltriethoxysilane and azidotrimethysilane contain functional groups that would readily react with graphene oxide. The covalent bonding of organosilane-containing modifiers of the present disclosure onto the electrochemically active materials via alkoxysilane condensation was not expected. In some embodiments, the organosilane containing surface modifier may have the following general formula I:

where R ¹ is a monovalent group (e.g., (i) a hydrogen atom, (ii) an alkyl, cycloalkyl, or aryl group, or (iii) a glycidyl, mercapto, methoxy-PEG or cyano group), or a divalent group such as alkylene or arylene; R ² is a divalent alkylene or arylene group, or a combination thereof, having from 1 to 26, 2 to 22, or 3 to 18 carbon atoms, and optionally includes one or more heteroatoms or functional groups and is optionally substituted with halides; R ³ is an alkyl group having from 1 to 6 or 1 to 4 carbon atoms; Y is a halide, an alkoxy group having from 1 to 4 or 1 to 2 carbon atoms (e.g., a methoxy or ethoxy group), or an acyloxy group having 1 to 7 or 1 to 5 carbon atoms (i.e., -OC(0)R ⁴ wherein R ⁴ is an alkyl group having 1 to 4 carbon atoms); x is 0 or 1; and y is 1 (R ¹ is monovalent) or 2 (R ¹ is divalent). In some embodiments, the organosilane containing surface modifier of formula I does not include terminal amino groups.

In some embodiments, the organosilane containing modifiers may include, individually or in any combination, (3-acetamidopropyl)trimethoxy-silane,

acetoxyethyldimethylchlorosilane, 2-cyanoethyltrimethoxysilane, 3- cyanopropyltrimethoxysilane, 4-cyanobutyltri ethoxy silane, 3- glycidyloxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane,

octadecyltrimethoxy silane, 2-phenylethyltrimethoxy silane, -propyltrimethoxy silane, 3-

(triethoxysilyl)propylsuccinic anhydride, or methoxy poly(ethylene glycol) silanes such as CH30(CH2CH20)nCH2CH ₂ Si(OCH3)3, where n is an integer from 1 to 100 or mixtures thereof.

In some embodiments, the organosilane containing surface modifier may be present in an amount of between 0.1 and 10% wt. %, 0.5 and 8 wt. %, or 1 and 5 wt. %, based on the total weight of the functionalized composite particles. In some embodiments, the organosilane containing surface modifier may be present at an atomic concentration of between 5% and 100%, 10% and 90%, or 15% and 80% on the surface of the

functionalized alloy, based on the observed fractional attenuation of the signal for the metal component M in x-ray photoelectron spectra of surface-treated composite particles of the alloy relative to untreated controls. In some embodiments, the present disclosure is further directed to negative electrode compositions for use in lithium ion batteries. The negative electrode

compositions may include the above-described electrochemically active materials.

Additionally, the negative electrode compositions may include one or more additives such as binders, conductive diluents, fillers, adhesion promoters, thickening agents for dispersion viscosity modification such as carboxymethylcellulose, polyacrylic acid, polyvinylidene fluoride, lithium polyacrylate, carbon black, or other additives known by those skilled in the art. In some embodiments, the negative electrode compositions may include the above-described electrochemically active material in an amount of between 10 and 99 wt. %, 20 and 98 wt. %, 40 and 98 wt. %, 60 and 98 wt. %, 75 and 95 wt. %, or 85 and 95 wt. %, based on the total weight of the negative electrode composition. The negative electrode compositions of the present disclosure, and batteries incorporating these compositions, are readily manufactured with process friendly aqueous binders (e.g., sodium carboxymethylcellulose/styrene butadiene rubber). The electrode compositions exhibit high initial capacities that are retained even after repeated cycling. The surface modifiers discussed herein offer good elasticity and improved adhesion between the composite particles and the binder, thereby enhancing anode capacity retention. The surface modifiers discussed herein may also reduce the direct contact between the composite particles and the electrolyte.

In some embodiments, the negative electrode compositions may include a binder.

Generally, the binder may include polysaccharides and rubber dispersions. The

polysaccharides may include cellulose derivatives, chitin derivatives, pectin derivatives and alginate derivatives. The rubber dispersions may include styrene-butadiene rubber, nitrile rubber, or a combination thereof. Suitable binders may also include water soluble polycarboxylic acids and their salts, such as polyacrylic acid, and lithium polyacrylate.

The binder may be crosslinked. The binder may also include a combination of any two or more of the preceding binders. In some embodiments, the amount of binder in the electrode composition may be at least 3 wt. %, at least 5 wt. %, at least 10 wt. %, or at least 20 wt. % based upon the total weight of the electrode coating; less than 30 wt. %, less than 20 wt. %, or less than 10 wt. %, based upon the total weight of the electrode composition; or between 1 and 30 wt. %, between 3 and 20 wt. %, or between 3 and 10 wt. %, based upon the total weight of the electrode composition. In illustrative embodiments, the negative electrode compositions may include an electrically conductive diluent to facilitate electron transfer from the composition to a current collector. Electrically conductive diluents include, for example, carbons, conductive polymers, powdered metal, metal nitrides, metal carbides, metal silicides, and metal borides, or combinations thereof. Representative electrically conductive carbon diluents include carbon blacks such as Super P and Super S carbon blacks (both from Timcal, Switzerland), Shawinigan Black (Chevron Chemical Co., Houston, Tex.), acetylene black, furnace black, lamp black, graphite, carbon fibers, and combinations thereof. In some embodiments, the conductive carbon diluents may include carbon nanotubes. In some embodiments, the amount of conductive diluent (e.g., carbon nanotubes) in the electrode composition may be at least 2 wt. %, at least 6 wt. %, or at least 8 wt. %, or at least 20 wt. % based upon the total weight of the electrode coating; or between 0.2 wt. % and 80 wt. %, between 0.5 wt. % and 50 wt. %, between 0.5 wt. % and 20 wt. %, or between 1 wt. % and 10 wt. %, based upon the total weight of the negative electrode composition.

In some embodiments, the negative electrode compositions may include graphite to improve the density and cycling performance, especially in calendered coatings, as described in U.S. Patent Application Publication 2008/0206641 by Christensen et al., which is herein incorporated by reference in its entirety. The graphite may be present in the negative electrode composition in an amount of greater than 10 wt. %, greater than 20 wt. %, greater than 50 wt. %, greater than 70 wt. % or even greater, based upon the total weight of the negative electrode composition; or between 20 wt. % and 90 wt. %, between 30 wt. % and 80 wt. %, between 40 wt. % and 60 wt. %, between 45 wt. % and 55 wt.%, between 80 wt. % and 90 wt. %, or between 85 wt. % and 90 wt. %, based upon the total weight of the electrode composition.

In some embodiments, the present disclosure is further directed to negative electrodes for use in lithium ion electrochemical cells. The negative electrodes may include a current collector having disposed thereon the above-described negative electrode composition. The current collector may be formed of a conductive material such as a metal (e.g., copper, aluminum, nickel), or a carbon composite. In some embodiments, the present disclosure further relates to lithium-ion electrochemical cells. In addition to the above-described negative electrodes, the electrochemical cells may include a positive electrode, an electrolyte, and a separator. In the cell, the electrolyte may be in contact with both the positive electrode and the negative electrode, and the positive electrode and the negative electrode are not in physical contact with each other; typically, they are separated by a polymeric separator film sandwiched between the electrodes.

In some embodiments, the positive electrode composition may include an active material. The active material may include a lithium metal oxide. In an exemplary embodiment, the active material may include lithium transition metal oxide intercalation compounds such as L1C0O2, LiCoo.2Nio.8O2, LiMm04, LiFeP0 ₄ , L1 O2, or lithium mixed metal oxides of manganese, nickel, and cobalt in any effective proportion, or of nickel, cobalt, and aluminum in any effective proportion. Blends of these materials can also be used in positive electrode compositions. Other exemplary cathode materials are disclosed in U.S. Patent No. 6,680,145 (Obrovac et al.) and include transition metal grains in combination with lithium-containing grains. Suitable transition metal grains include, for example, iron, cobalt, chromium, nickel, vanadium, manganese, copper, zinc, zirconium, molybdenum, niobium, or combinations thereof with a grain size no greater than about 50 nanometers. Suitable lithium-containing grains can be selected from lithium oxides, lithium sulfides, lithium halides (e.g., chlorides, bromides, iodides, or fluorides), or combinations thereof. The positive electrode composition may further include additives such as binders (such as polymeric binders (e.g., polyvinylidene fluoride), conductive diluents (e.g., carbon, carbon black, flake graphite, carbon nanotubes, conductive polymers), fillers, adhesion promoters, thickening agents for coating viscosity

modification such as carboxymethylcellulose, or other additives known by those skilled in the art. In various embodiments, useful electrolyte compositions may be in the form of a liquid, solid, or gel. The electrolyte compositions may include a salt and a solvent (or charge-carrying medium). Examples of liquid electrolyte solvents include ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, propylene carbonate, fluoroethylene carbonate, tetrahydrofuran (THF), acetonitrile, and

combinations thereof. In some embodiments the electrolyte solvent may comprise glymes, including monoglyme, diglyme and higher glymes, such as tetraglyme. Examples of suitable lithium electrolyte salts include LiPF ₆ , LiBF ₄ , L1CIO4, lithium bis(oxalato)borate, LiN(CF ₃ S0 ₂ ) ₂ , LiN(C ₂ F ₅ S0 ₂ )2, LiAsFe, LiC(CF ₃ S0 ₂ ) ₃ , and combinations thereof.

In some embodiments, the lithium-ion electrochemical cells may further include a microporous separator, such as a microporous material available from Celgard LLC, Charlotte, N.C. The separator may be incorporated into the cell and used to prevent the contact of the negative electrode directly with the positive electrode.

The disclosed lithium ion electrochemical cells can be used in a variety of devices including, without limitation, portable computers, tablet displays, personal digital assistants, mobile telephones, motorized devices (e.g., personal or household appliances, power tools and vehicles), instruments, illumination devices (e.g., flashlights) and heating devices. Multiple lithium ion electrochemical cells of this disclosure can be combined to provide a battery pack.

The present disclosure further relates to methods of making the above-described electrochemically active materials. In some embodiments, the alloy material can be made by methods known to produce films, ribbons or particles of metals or alloys including cold rolling, arc melting, resistance heating, ball milling, sputtering, chemical vapor deposition, thermal evaporation, atomization, induction heating or melt spinning. The above described active materials may also be made via the reduction of metal oxides or sulfides. In some embodiments, the alloy material can be made in accordance with the methods of U.S. Patent 7,871,727, U.S. Patent 7,906,238, U.S. Patent 8,071,238, or U.S. Patent

8,753,545, which are each herein incorporated by reference in their entirety. Any desired coatings may be applied to the alloy material by milling, solution deposition, vapor phase processes, or other processes known to those of ordinary skill in the art. In embodiments in which the coating includes a carbonaceous material or non-metallic, electrically conductive layer, such coating may be applied in accordance with the methods of U.S. Pat. 6,664,004, which is herein incorporated by reference in its entirety.

In some embodiments, the organosilane containing surface modifier may then be bonded to the alloy material (coated or uncoated) by combining the alloy material, an organosilane reagent, and a solvent (e.g., methanol). The reaction mixture may then be subjected to conventional agitation techniques, optionally at elevated temperatures, over time. The resulting surface-modified alloy material may then be isolated by conventional filtration techniques, vacuum dried, and ground. In some embodiments, the organosilane reagents may include, individually or in any combination, (3-acetamidopropyl)trimethoxy- silane, acetoxyethyldimethylchlorosilane, 2-cyanoethyltrimethoxysilane, 3- cyanopropyltrimethoxysilane, 4-cyanobutyltriethoxysilane, 3- glycidyloxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane,

octadecyltrimethoxysilane, 2-phenylethyltrimethoxysilane, -propyltrimethoxysilane, 3- (triethoxysilyl)propylsuccinic anhydride, or methoxy poly(ethylene glycol) silanes such as CH30(CH2CH20)nCH2CH ₂ Si(OCH3)3, where n is an integer from 1 to 100 or mixtures thereof.

The present disclosure further relates to methods of making negative electrodes that include the above-described negative electrode compositions. In some embodiments, the method may include mixing the above-described electrochemically active materials, along with any additives such as binders, conductive diluents, fillers, adhesion promoters, thickening agents for coating viscosity modification and other additives known by those skilled in the art, in a suitable coating solvent such as water or N-methylpyrrolidinone to form a coating dispersion or coating mixture. The dispersion may be mixed thoroughly and then applied to a foil current collector by any appropriate coating technique such as knife coating, notched bar coating, dip coating, spray coating, electrospray coating, or gravure coating. The current collectors may be thin foils of conductive metals such as, for example, copper, aluminum, stainless steel, or nickel foil. The slurry may be coated onto the current collector foil and then allowed to dry in air or vacuum, and optionally by drying in a heated oven, typically at about 80° to about 300°C for about an hour to remove the solvent.

The present disclosure further relates to methods of making lithium ion

electrochemical cells. In various embodiments, the method may include providing a negative electrode as described above, providing a positive electrode that includes lithium, and incorporating the negative electrode and the positive electrode into an electrochemical cell comprising a lithium-containing electrolyte.

In accordance with the compositions and methods of the present disclosure, high energy density electrochemically active materials that exhibit strong capacity retention in negative electrode systems that include conventional, process friendly aqueous binder materials (e.g, carboxymethylcellulose/styrene-butadiene rubber binders) may be obtained. The operation of the present disclosure will be further described with regard to the following detailed examples. These examples are offered to further illustrate various specific embodiments and techniques. It should be understood, however, that many variations and modifications may be made while remaining within the scope of the present disclosure.

Listing of Embodiments

1. An electrochemically active material, the material comprising:

composite particles comprising:

an alloy material comprising particles having the formula: SixMyCz, where x, y, and z represent atomic % values and (a) x + y+ z = 100%; (b) x>2y+z; (c) x and y are greater than 0; z is equal to or greater than 0; and (d) M is iron and optionally one or more metals selected from manganese, molybdenum, niobium, tungsten, tantalum, copper, titanium, vanadium, chromium, nickel, cobalt, zirconium, yttrium;

a carbonaceous coating at least partially surrounding the particles; and an organosilane containing surface modifier bonded to an external surface of the composite particles;

wherein the organosilane containing surface modifier does not comprise a terminal amino group.

2. The electrochemically active material of embodiment 1, wherein 65% <x < 85%, 5% <y < 20%, and 5% <z < 15%.

3. The electrochemically active material according to any one of the previous embodiments, wherein the carbonaceous coating comprises carbon black.

4. The electrochemically active material according to embodiment 3, wherein the carbon black is present in an amount of between 0.1 and 10 wt. %, based on the total weight of the alloy material and the carbon black. 5. The electrochemically active material according to any one of the previous embodiments, wherein the organosilane containing surface modifier has the following general formula:

where R ¹ is a monovalent or divalent group; R ² is a divalent alkylene group, arylene group, or a combination thereof, that includes 2 to 16 carbon atoms and optionally includes one or more heteroatoms or functional groups, and optionally is substituted with halides; R ³ is a an alkyl group having from 1 to 4 carbon atoms; Y is a halide, an alkoxy group having from 1 to 4 carbon atoms, or an acylkoxy group having 1 to 5 carbon atoms; x is 0 or 1; and y is 1 or 2.

6. The electrochemically active material according to embodiment 5, wherein the organo-silane containing surface modifier comprises (3-acetamidopropyl)trimethoxy- silane, acetoxyethyldimethylchlorosilane, 2-cyanoethyltrimethoxysilane, 3- cyanopropyltrimethoxysilane, 4-cyanobutyltriethoxysilane, 3- glycidyloxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane,

octadecyltrimethoxysilane, 2-phenylethyltrimethoxysilane, -propyltrimethoxysilane, 3- (triethoxysilyl)propylsuccinic anhydride, or a methoxy poly(ethylene glycol) silane.

7. The electrochemically active material according to any one of the previous embodiments, the organosilane containing surface modifier is bonded to at least a portion of the carbonaceous coating.

8. A negative electrode composition comprising:

the electrochemically active material according to any one of the previous embodiments; and

a binder comprising carboxymethylcellulose or styrene-butadiene rubber;

wherein the alloy material is present in the negative electrode composition in an amount of greater than 15 wt. %, based on the total weight of the negative electrode composition; and the binder is present in the is present in the negative electrode composition in an amount of between 3 and 20 wt. %, based on the total weight of the negative electrode composition.

9. The negative electrode composition according to embodiment 8, further comprising graphite.

10. A negative electrode comprising:

the negative electrode composition according to any one of embodiments 8-9; and a current collector.

11. An electrochemical cell comprising:

the negative electrode of embodiment 10;

a positive electrode comprising a positive electrode composition comprising lithium; and

an electrolyte comprising lithium.

12. An electronic device comprising the electrochemical cell according to embodiment 11.

13. A method of making an electrochemical cell, the method comprising:

providing a positive electrode comprising a positive electrode composition comprising lithium;

providing a negative electrode according to embodiment 10;

providing an electrolyte comprising lithium; and

incorporating the positive electrode, negative electrode, and the electrolyte into an electrochemical cell.

EXAMPLES

The following examples are offered to aid in the understanding of the present disclosure and are not to be construed as limiting the scope thereof. Unless otherwise indicated, all parts and percentages are by weight. Test Methods and Preparation Procedures

The following test methods and protocols were employed in the evaluation of the illustrative and comparative examples that follow. Unless otherwise indicated, all reagents and chemicals were obtained from Sigma-Aldrich Corporation, USA.

Preparation of electrochemically active material composite particles

Silicon alloy composite particles having the formula Si75.42Fe13.89C10.70 were prepared using procedures disclosed in US 8,071,238 and US 7,906,238, after which the alloy particles were coated with nano-carbon. Elemental silicon powder (325 mesh) was used as received.

Preparation of surface modified electrochemically active materials

Unless otherwise specified, illustrative examples of surface modified

electrochemically active material and comparative examples of surface modified silicon metalloid powder were prepared as follows. 15 g of carbon-coated Si:Fe:C powder (prepared as described above), 5 g organosilane and 30 g methanol were charged to a 4- ounce jar. The reaction mixture was allowed to rotate on a roller for 3 days under ambient conditions. Exemplary organosilane reagents included octadecyltrimethoxysilane, 3- aminopropyltrimethoxysilane, 2-phenylethyltrimethoxysilane, propyltrimethoxysilane, 3- glycidyloxypropyltrimethoxysilane, (2-aminoethyl)(3-trimethoxypropyl)amine and 3- mercaptopropyltrimethoxysilane. The mass ratio of organosilane reagents to carbon-coated Si:Fe:C powder varied between 10% and 66%, while the reaction time varied from 17 hours to 6 days. The surface functionalized anode powder was isolated using filtration with Millipore Type HVLP 0.45 micron membrane and subsequently dried in a vacuum oven at 100° C overnight. The dried materials were finely ground to a powder with a mortar and a pestle. The surface functionalization of elemental Si powder was carried out using the same method.

Surface Analysis Method

The sample surfaces were examined using X-ray Photoelectron Spectroscopy (XPS), also known as Electron Spectroscopy for Chemical Analysis (ESCA). This technique provides an analysis of the outermost 3 to 10 nanometers (nm) of the specimen surface. The photoelectron spectra provide information about the elemental and chemical (oxidation state and/or functional group) concentrations present on a solid surface. It is to all elements in the periodic table except hydrogen and helium with detection limits for most species in the 0.1 to 1 atomic % concentration range. XPS concentrations should be considered semi-quantitative unless standards are included in the data set. Experimental conditions are summarized in the following table.

Surface Analysis Experimental Conditions

Preparation of Electrochemical Coin Half-Cells

Each of the electrochemically active materials were formed into working electrodes by first preparing slurries as follows: 1.5 g of electrochemically active material (surface treated silicon alloy of the present invention, untreated silicon alloy comparative materials, surface treated elemental silicon powder comparative material, or untreated elemental silicon powder comparative material) was first dispersed in 6.52 g of 1-propanol and 2.38 g of water using a MazeruStar speed mixer (Kurabo Industries Ltd., Japan). In the second step, 7.23 g MAG-E graphite (Hitachi Chemical, Japan), 0.9 g KS-6 graphite (TIMREX synthetic graphite, Timcal AG, Switzerland), and 0.1 g conductive carbon (SUPER P from Imerys Graphite and Carbon, Switzerland), 7.03 g of a 1.71 wt% aqueous solution of carboxymethylcellulose (Na-CMC, Daicel 2200, Daicel FineChem Ltd., Japan), and 3.315 g water were added and the ingredients were again mixed. Finally, 0.375 g of 40% aqueous styrene-butadiene rubber (SBR, ZEON Corporation, Japan) was added to the mixing vessel, and the slurry was subjected to a final mix in the MazeruStar. In order to modify the amount of surface-functionalized electrochemically active material in the composite anodes, corresponding amounts of MAG-E was added to or taken out of the formulations. These slurries were then coated onto copper foil to prepare working electrodes, using the following procedure. First, a bead of acetone was dispensed on a clean glass plate and overlaid with a sheet of 15 micron copper foil, which was cleaned with acetone. 25 Using a 6-mil (0.15 mm) coating bar and an EZ coater (Model EC-200 from Chemlnstruments, USA), the slurry was dispensed onto the coating bar and drawn down with a coater speed setting of 2. The composite anode coating was then allowed to dry under ambient conditions overnight, after which it was calendered with a HR01 Hot Rolling Machine (MTI Corporation, USA) to adjust porosity. The coated foil was then dried in a vacuum oven at 120 °C for 2 hours.

To prepare half coin cells, working electrodes were punched from the coated copper foil face down, with white paper underneath, using a 16 mm die, and then the paper was removed. Three matching copper foil pieces were punched (bare current collector) and the average mesh weight was determined. Films of CELGARD 2325 separator material (25 micron microporous trilayer PP/PE/PP membrane, Celgard, USA) were placed between sheets of colored paper and punched out using a 20 mm die, removing the paper afterwards. For each cell, at least 2 separators were cut. Both sides of a lithium foil sheet were rolled and brushed, placed between sheets of plastic film, and counter electrodes were punched out using an 18 mm die, after which the plastic film was removed. Each electrode was weighed separately and the total weight was recorded.

The electrolyte used in coin half-cell preparation was a mixture of 90 wt % of a 1

M solution of LiPF ₆ in 3 :7 (w/w) ethylene carbonate: ethyl methyl carbonate and 10 wt % monofluoroethylene carbonate.

Electrochemical 2325 coin cells were then assembled in this order: 2325 coin cell bottom, 30 mil copper spacer, lithium counter electrode, 33.3 microliters electrolyte, separator, 33.3 microliters electrolyte, separator, grommet, 33.3 microliters electrolyte, working electrode (face down and aligned with lithium counter electrode), 30 mil copper spacer, 2325 coin cell top. The cell was crimped and labelled.

Characterization of Electrochemical Performance (Cycling)

The coin cells were then cycled using a SERIES 4000 Automated Test System

(available from Maccor Inc, USA) according to the following protocol. The first cycle was performed from 5 mV to 0.9 V at C/10 with a trickle discharge to C/40 and a 15 minute rest after discharge/charge. Subsequent cycles (2-100) were performed from 5 mV to 0.9 V at C/4 with a trickle discharge to C/20 and a 15 minute rest after each discharge/charge cycle. Capacity retention over a series of test cycles was recorded.

Results

Surface Analysis

Table 1 shows the atomic percentage of carbon and iron detected on surfaces of examples of surface functionalized electrochemically active material of the present invention, as determined by XPS. The experimental conditions for the preparation of the corresponding functionalization reactions are also indicated in Table 1.

Table 1. Surface Concentration of Carbon and Iron

The higher carbon level observed for the functionalized anode materials is consistent with the occurrence of the surface functionalization reactions. XPS analysis also shows a difference among alkyl, phenyl and hetero-atom-containing surface

functionalities. XPS analysis shows that octadecyltrimethoxysilane functionalized surfaces (Examples 1-3) have the highest levels of surface carbon, and the lowest levels of surface iron. This observation may indicate the presence of octadecyl functional groups on anode surfaces. Fractional attenuation of the XPS signal for the metal component Fe on the surfaces of silane-functionalized anodes confirms the presence of surface modifier. More specifically, 1.2 atomic percent of Fe was detected on the surface of the CE1 while 0 atomic percent of Fe was detected on the surface of Example 1. The 100% absence of any detectable Fe is interpreted as full coverage of the surface by the surface modifier.

Cycling Performance

A summary of the normalized capacity retention of cells made using composite working electrodes comprising various amounts of the surface functionalized silicon alloys of the present invention is provided in Table 2. For comparison, results from cells containing untreated silicon alloys and surface functionalized silicon are also provided.

Table 2. Capacity retention after 50 cycles

Table 3 compares the effect of various organosilane surface treatment reagents on the normalized capacity retention of composite anodes with 20% silicon alloy loading and Na-CMC/SBR binder. The results presented in Table 3 show that composite anodes with octadecyltrimethoxysilane-functionalized silicon alloy (Example 10) had the highest normalized capacity after 60 cycles, while those functionalized with amine-terminated alloy (Examples CE6 and CE7) performed worse than the as-received anode control. Table 3. Capacity retention after 50 cycles

Table 4 compares the effectiveness of organosilane functionalization on 325 mesh Si and carbon-coated Si:Fe:C alloy on the capacity retention of electrochemical cells. All composite anodes were fabricated with 20% silicon or silicon alloy, and Na-CMC/SBR binder as described previously. The effectiveness of organosilane functionalization toward improving the normalized capacity retention of composite anode was only observed for silicon alloy Si:Fe:C.

Table 4. Capacity retention of Electrochemical Cells

Although specific embodiments have been illustrated and described herein for purposes of description of some embodiments, it will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure.