HK1242475B - A composition - Google Patents

Description

Composition

Technical Field

The present invention relates to electrode compositions and methods for preparing electrode compositions.

Background Art

There is a need for simple methods to improve the performance of electronic materials used in batteries, capacitors, supercapacitors, and other energy storage and conversion systems. One such example is the silicon-based anode for lithium-ion batteries, which are considered a very promising technology due to their higher theoretical energy storage density (3,400-4,200 mAh/g) compared to conventional graphite lithium batteries (350-370 mAh/g).

The capacity of a lithium-ion battery depends on how many lithium ions the positive and negative electrodes can store. Using silicon and carbon particles, which aid conductivity, in the negative electrode significantly increases battery capacity because one silicon atom can bond to up to 3.75 lithium ions, while with a graphite negative electrode, six carbon atoms are needed for every lithium atom.

Unfortunately, a consequence of this increased capacity is that the silicon in the negative electrode expands and contracts by as much as 400% during charge/discharge cycling. This level of repeated expansion and contraction during charge/discharge leads to structural instability. This results in reduced capacity and shortened battery life because the silicon electrode loses stability and deteriorates physical properties after short recharge cycles. Maintaining steric stability during lithiation is a challenge for all types of silicon materials, including their various oxides, composites, and alloys. Other examples of electrode active materials with similar expansion/contraction characteristics during charge/discharge include tin- and germanium-based negative electrode materials and sulfur-based positive electrode materials.

Maintaining the structural integrity of the negative electrode active material during charge/discharge is not the only limitation encountered by electrode materials. New cathode materials with higher energy density also have integrity issues as a result. Manganese and/or nickel dissolution occurs in cathodes based on lithium manganese nickel oxide materials. In addition to structural loss, this dissolution due to the electrolyte can lead to the formation of a thick solid electrolyte interface (SEI) layer and electrolyte depletion. Both of these issues limit the performance and cycle life of the battery.

The present invention seeks to address at least some of the above-mentioned shortcomings of the prior art.

The reference to any prior art in the specification is not an acknowledgment or suggestion that the prior art forms part of the common general knowledge in any jurisdiction, or that it could reasonably be expected that the prior art would be understood by a person skilled in the art to be relevant and/or combinable with other prior art.

Summary of the Invention

In one aspect of the present invention, an electrode is provided, comprising: an active material having a surface and a metal-ligand complex bound to the surface of the active material, the metal-ligand complex comprising at least one ligand coordinately bonded to a metal ion; and wherein the metal ion is bound to the surface of the active material via a coordination bond.

The electrode can be a negative electrode or a positive electrode.

In another aspect of the present invention, an electrochemical cell is provided, comprising a negative electrode, a positive electrode, and an electrolyte disposed between the negative electrode and the positive electrode; wherein at least one of the negative electrode or the positive electrode is an electrode as previously defined.

Therefore, at least one of the negative electrode and the positive electrode includes an active material having a surface and a metal-ligand complex bound to the surface of the active material, the metal-ligand complex including at least one ligand coordinately bonded to a metal ion, and wherein the metal ion is bound to the surface of the active material through a coordinate bond.

In another aspect of the present invention, a precursor composition for manufacturing an electrode is provided, the precursor composition comprising: an active material having a surface, a metal-ligand complex bound to the surface of the active material, the metal-ligand complex comprising at least one ligand coordinatedly bonded to a metal ion; wherein the metal ion is bound to the surface of the active material via a coordination bond.

In another aspect of the present invention, there is provided use of the precursor composition described above in the manufacture of an electrode.

In yet another aspect of the present invention, a method for manufacturing an electrode is provided, comprising: manufacturing the electrode from the precursor composition described above.

In another aspect of the present invention, a method for manufacturing an electrode is provided, comprising: forming a precursor composition containing an active material, and manufacturing an electrode from the precursor composition, wherein the method comprises contacting a metal-ligand complex with the surface of the active material, the metal-ligand complex comprising at least one ligand that coordinately bonds with a metal ion, and the metal ion is bound to the surface of the active material through a coordination bond.

In another aspect of the present invention, a method for improving electrode performance is provided, comprising contacting the surface of an electrode active material with a metal ligand complex, the metal ligand complex comprising at least one ligand that coordinately bonds with a metal ion, wherein the metal ion is bound to the surface of the active material through a coordination bond.

Further aspects of the invention and further embodiments of the aspects described in the preceding paragraphs will become apparent from the following description, given by way of example, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a graph showing the zeta potential distribution of metal complex-coated silicon and a control. The left peak shows the Si nanoparticles before metal ligand complex coating. The right peak shows the zeta potential of the metal complex-coated Si nanoparticles changing from negative to positive.

FIG2 is a graph showing the charge/discharge cycling stability of metal-ligand complex-coated Si and a control with similar mass loading.

3 is a graph showing charge/discharge cycling data for metal ligand complex coated Si and a control using ball milling.

4 is a graph showing the charge/discharge cycle stability of metal ligand complex coated micron-sized Si (1-3 um) and control (1-3 um).

5 is a graph showing charge/discharge cycle data of metal ligand complex coated Si and a control with different slurry formulations of Si:Super-P:PAA, wherein Si:Super-P:PAA = 70:20:10 (wt %).

6 is a graph showing the charge/discharge cycling stability of various concentrations (10, 25, and 50 mM) of metal complex coatings and a control on Si with and without washing.

7 is a graph of the 0.5C charge/discharge cycling stability of metal-ligand complex-coated Si and a control after 0.1C activation.

8 is a graph showing the long-term cycling stability of metal oxide cathodes coated with metal ligand complexes compared to those without the metal ligand complexes (control).

9 is a graph showing the long-term cycling stability of metal oxide cathodes coated with metal ligand complexes using aqueous binders compared to those without the metal ligand complexes (control).

10 is a graph showing the supercapacitor charge/discharge cycling stability of metal ligand complex coated Si-based cells at 20 C compared to those without the metal ligand complex (control).

11 is a graph showing supercapacitor charge/discharge cycle stability of metal ligand complex coated Si-based cells at 60 C compared to those without metal ligand complex (control).

DETAILED DESCRIPTION

The present invention is based, at least in part, on the fact that electrodes that include a metal-ligand complex in the electrode active material have numerous benefits over conventional electrodes that do not include this feature.

Without wishing to be bound by theory, the inventors believe that the use of metal-ligand complexes as additives to electrode active materials provides effective strong binding to the surface of the active material, thereby improving the performance of devices such as batteries, capacitors, supercapacitors, and other energy storage and conversion systems that include these electrodes. This increase in performance may include providing higher energy density, faster charge and discharge cycles, stabilization of the active material during charge and/or discharge, and providing longer cycle life.

It is believed that the metal-ligand complex functions to alleviate the strains induced by the cyclic embedding of electrolytes, such as small charge-carrying ions, such as lithium, commonly used in electrochemical cells, on the active particles. In other words, the metal-ligand complex functions to alleviate the stresses and strains associated with the expansion and contraction of the active material by effectively bridging the surface of the active material particles and preventing or mitigating the effects of any surface defects, such as cracks or fissures, in the active material. Additionally, the metal-ligand complex can serve as a general barrier coating to maintain the structural integrity of the active material.

In one aspect of the present invention, an electrode is provided comprising an active material having a surface and a metal-ligand complex bound to the surface of the active material, wherein the metal-ligand complex comprises at least one ligand that coordinately bonds with a metal ion, and wherein the metal ion is bound to the surface of the active material via a coordinate bond.

As used herein, the term "active material" is intended to include any component of an electrode that participates in the electrochemical charge and discharge reactions. An active material may also be referred to as an intercalation material or compound, which is a material or compound that is capable of undergoing intercalation and deintercalation of electrolyte ions to achieve charge and discharge cycles.

The term "surface," as used herein with respect to the surface of an active material as described above, is intended to encompass the surface of any particle, fiber, or other material, including porous materials, that participates in electrochemical discharge and charge reactions. In one embodiment, the surface of an active material is that portion of the active material that presents electron-donating groups to which metal ions can coordinately bond. For example, when the active material is silicon, the relevant surface may be the exterior surface of each individual silicon particle.

With respect to metal-ligand complexes bound to the surface of an active material and metal ions bound to the surface of an active material via coordination bonds, the term "bound" as used herein is intended to include both cases where the metal ion of the metal-ligand complex has a coordination bond directly to the surface of the active material, and where the metal ion of the metal-ligand complex has a coordination bond to at least one intermediate or compound that itself interacts with the surface of the active material. For example, in the latter case, the metal ion of the metal-ligand complex can be incorporated into a hydrophobic ligand such as a fatty acid or other hydrophobic entity such as a phenylbutadiene fragment. In this case, hydrophobic interactions may exist between the relatively hydrophobic active material and the hydrophobic fragments of the substituted metal-ligand complex. Alternatively, the metal ion of the metal-ligand complex has a coordination bond to one or more binder materials, and the binder material is bound to the surface of the active material via one or more other non-covalent interactions, such as ionic interactions, hydrophobic interactions, van der Waals interactions, and hydrogen bonds. In either case, the metal-ligand complex formed on the surface of one active material particle can bind to the surface of other active material particles to provide the effects described herein. In a preferred embodiment, the metal ion has a coordinate bond to the surface of the active material.

The present invention thus relates to metal-ligand complex compositions that can be used as components of electrodes, particularly those that bind or coat electrode active materials. In various embodiments, the metal-ligand complexes formed in accordance with the present invention that bind to active materials can:

Improve the adhesion and bonding of various components or other materials in batteries,

While still being flexible enough to be wound or curled into the proper shape,

Improve or increase ionic and electronic conductivity,

Improve or maintain the stability of active materials,

Reduce the solubility of certain active materials,

Extend the cycle life of batteries, capacitors, supercapacitors, etc., and

Reduce overall material waste.

Metal-ligand complexes broadly include metal ions having one or more coordination sites occupied by a ligand and one or more coordination sites available for binding to the surface of an electrode active material directly or through an intermediate.

In embodiments, the surface of the active material is partially coated with a metal-ligand complex layer. However, in alternative embodiments, the surface is completely coated with a metal-ligand complex layer. It will be appreciated that the extent of coating or layer formation of the metal-ligand complex around the active material particles will depend on the amount of metal-ligand complex added and the number of electron-donating sites on the active material surface. In either case, the metal-ligand complex is sufficiently bound to form a network within the active material, thereby bridging between individual particles of the active material and allowing for better adaptation to cycling stresses during charge and discharge operations.

In embodiments, if the metal ligand complex does form a relatively complete layer or coating around the active material particles, the thickness of the metal ligand complex layer is less than about 750 nm, preferably less than about 500 nm, more preferably less than about 250 nm, even more preferably less than about 100 nm, still even more preferably less than about 50 nm, still more preferably less than about 20 or about 10 nm, and most preferably less than about 5 nm. A layer at the lower end of this range would be one in which the metal ligand complex is directly bonded to the active material. However, in embodiments in which the metal ligand complex is part of a coordination polymer as described below, the layer will necessarily be much thicker, but it is expected to still be less than 5000 nm, preferably less than 1000 nm, and more preferably less than 500 nm. Therefore, the thickness of the coating can be customized for a specific application.

As previously discussed, the electrode includes an active material that is at least partially coated with a metal-ligand complex. However, the electrode may include other active materials. The other active material may be an active material different from the first active material, in which case the other active material may or may not be coated with the metal-ligand complex. Alternatively or in addition, the other active material may be the same material as the active material, but uncoated. Thus, in one embodiment, the electrode further includes a second active material. The first active material and the second active material may be the same or different.

In a first exemplary embodiment, the first active material and the second active material are identical. In this embodiment, only the first active material is coated with the metal-ligand complex. That is, the second active material is not coated with the metal-ligand complex.

In a second exemplary embodiment, the first active material and the second active material are different. In this embodiment, both the first active material and the second active material are coated with a metal-ligand complex.

In a third exemplary embodiment, the first active material and the second active material are different. In this embodiment, the first active material is coated with a metal-ligand complex. The second active material is not coated with a metal-ligand complex.

It will be apparent to those skilled in the art that these embodiments are exemplary and not intended to be limiting. It will be understood that other active materials, such as a third or fourth active material, may also be included. Although the first active material is at least partially coated, it will be appreciated that the second, third, and fourth active materials may be present as part of the electrode in any combination of coated or uncoated.

Generally, for those embodiments having at least a first active material and a second active material, it is preferred that the weight ratio of the first active material to the second active material is from about 10:1 to about 1:10. More preferably, the weight ratio is from about 5:1 to 1:5. Even more preferably, the weight ratio is from about 3:1 to about 1:3.

In one embodiment, the active material is bound to the metal-ligand complex through an intermediate agent, such as, for example, a binder or a ligand designed to bind directly to the surface of the active material.

In an embodiment, the metal of the metal-ligand complex is selected from chromium, ruthenium, iron, cobalt, aluminum, zirconium and rhodium. Preferably, the metal is chromium.

The metal may be present in any suitable oxidation state. For example, chromium is known to have the following oxidation states: I, II, III, IV, V, or VI. In embodiments where the metal ion is a chromium ion, the preferred oxidation state of chromium is III.

When in contact with the active material, the metal ion can be combined with a coordinating or non-coordinating counterion (e.g., an anion selected from the group consisting of chloride, acetate, bromate, nitrate, perchlorate, alum, fluoride, formate, sulfide, iodide, phosphate, nitrite, iodate, chlorate, bromate, chlorite, carbonate, bicarbonate, hypochlorite, hypobromite, cyanate, oxalate, and sulfate). In one embodiment, the counterion is a non-coordinating anion. In another embodiment, the counterion is a coordinating anion. The present invention is not limited by the counterion, and a vast array of such counterions are known to those skilled in the art and will depend in part on the choice of metal ion.

In certain embodiments, mixtures of different metal ions may be used, for example, to form a plurality of metal-ligand complexes. In these cases, preferably at least one metal ion is chromium.

In one embodiment, the metal forming the metal-ligand complex is different from the metal forming the active material. For example, if a chromium metal-ligand complex is used, the active material forming the negative electrode is not chromium metal.

In an embodiment, the weight percent of the metal-ligand complex in the electrode composition (defined as a dried and fully formed electrode material cast on a current collector) is between 0.01% and 10%. Preferably, the weight percent of the metal-ligand complex is between 0.1% and 5%. More preferably, the weight percent of the metal-ligand complex is between 0.5% and 3%.

In a preferred embodiment, the metal-ligand complex is not incorporated into the active material by a melt process. That is, the metal of the metal-ligand complex is not melted together with the active material, as this would not result in the formation of the desired metal-ligand complex and binding to the surface of the active material as described herein. Preferably, the metal-ligand complex is incorporated into the active material in the liquid phase, i.e., in the presence of a suitable solvent for forming the liquid phase.

In a specific embodiment, when the metal-ligand complex is a chromium metal-ligand complex, the active material does not include aluminum or iron as additional materials.

It is known that metals form many metal-ligand complexes. Preferred ligands for forming metal-ligand complexes are those that include nitrogen, oxygen, or sulfur as groups that form coordinate bonds. More preferably, the groups that form coordinate bonds include oxygen or nitrogen. Even more preferably, the groups that form coordinate bonds are oxygen-containing groups. Still even more preferably, the oxygen-containing groups are selected from the group consisting of oxides, hydroxides, water, sulfates, carbonates, phosphates, or carboxylates.

In embodiments, the ligand is a mono-, di- or tri-atom ligand.Preferably, the ligand is an oxygen-containing species such as an oxide, hydroxide or water, wherein the group forming the coordinate bond is oxygen.

Preferably, the ligand is an oxygen-containing ligand.

The metal ligand complex layer can be further stabilized by cross-linking the metal ions to each other to form larger oligomeric metal ligand complexes. Thus, in a preferred embodiment, the metal ligand complex is an oligomeric metal ligand complex.

In one embodiment, the ligand of the metal-ligand complex is a bridging moiety that coordinately bonds to at least two metal ions, such as oxo-, hydroxyl-, carboxyl-, sulfur-, and phosphorus-ligands. Preferably, this results in the formation of an oligomeric metal-ligand complex. In an exemplary embodiment, the metal-ligand complex is an oxygen-bridged chromium (III) complex. Preferably, the metal-ligand complex is an oligomeric oxygen-bridged chromium (III) complex.

The oligomeric metal ligand complexes can be further polymerized with one or more bridging conjugates such as carboxylic acids, sulfates, phosphates and other multidentate polymeric ligands to form polymeric metal ligand complexes from the oligomeric metal ligand complex clusters.

In an embodiment, the metal ligand complex forms a coordination bond with another component of the electrode. Such further components may include another active material or a binder material. In some cases, for example, when the active material is in the form of a population of particles, the metal ligand forms a coordination bond with adjacent particles in the population of particles. In another example, if there are two active materials, the metal ligand forms another coordination bond with the second active material. Alternatively, the coordination bond may be formed between the metal ion and a component of the electrode.

In certain embodiments, a mixture of different ligands can be used. Different ligands can have different functions, such as forming a plurality of different metal-ligand complexes, bridging between metal-ligand complexes, crosslinking metal ions, changing the hydrophobicity/hydrophilicity of metal-ligand complexes, or providing a surface for forming coordinate bonds with electrode components. Some of these embodiments can result in indirect binding of metal-ligand complexes to the active material via coordinate covalent bonds from one ligand to another, the properties of which can be the same or different, which are bonded to the surface of the active material.

It will be appreciated by those skilled in the art that an electrode can be a negative electrode or a positive electrode and can be formed of materials commonly used for either of the two. In either case, the active material comprises a surface, and the metal ions can form a coordination bond directly or indirectly with the surface. In one embodiment, the surface of the active material comprises nitrogen, oxygen, sulfur, hydroxyl or a carboxylic acid with a lone electron pair for forming a coordination bond. Preferably, the surface comprises an oxygen class. Oxygen classes are preferred because the surface of the active material can generally be easily oxidized, thereby comprising an oxide layer, or may have been considered an oxide. Therefore, in a preferred embodiment, the active material surface is an oxide surface or is suitable for becoming an oxide surface.

In embodiments, active material (or the first active material or the second active material) is selected from the group consisting of metal, intermetallic compound, metalloid and carbon. The electrode can be a negative pole, in which case the active material is typically selected from silicon, silicon-containing materials (its oxides, compounds and alloys), tin, tin-containing materials (its oxides, compounds and alloys), germanium, germanium-containing materials (its oxides, compounds and alloys), carbon and graphite. Preferably, when the electrode is a negative pole, the active material comprises silicon and/or carbon. Silicon can be in the form of pure silicon, its various oxides (SiO, SiO ₂ etc.), its alloys (Si-Al, Si-Sn etc.) and compounds (Si-C, Si-graphene etc.). Preferably, carbon is in the form of graphite, super-P carbon, graphene, carbon nanotubes, carbon nanofibers, acetylene black, Ketjenblack (Ketjenblack, KB), and more preferably in the form of graphite.

In one embodiment, when the electrode is a negative electrode, the first active material comprises silicon.

In another embodiment, wherein the electrode is a negative electrode, there is a first active material and a second active material, at least one of which comprises silicon. Preferably, in this embodiment, the first active material comprises silicon and the second active material comprises carbon.

When the electrode is a positive electrode, the active material (or the first active material or the second active material) is selected from sulfur, _LiFePO4 (LFP), mixed metal oxides including cobalt, lithium, nickel, iron, and/or manganese, and carbon. Preferably, the carbon is in the form of one or more carbon particles selected from graphite, Super-P carbon, graphene, carbon nanotubes, carbon nanofibers, acetylene black, and Ketjen black (KB); more preferably, it is in the form of graphite.

It will be appreciated from the disclosure herein that the active materials used to form the negative and/or positive electrodes are not particularly limited, and any such materials used in the prior art are suitable, particularly those used in lithium-ion batteries, and more particularly those using silicon-based negative electrodes.

In embodiments, the metal-ligand complex bridges separate portions of the active material, such as adjacent particles, or, in the case where the active material is in particulate form, bridges between regions of a particle. Without wishing to be bound by theory, the inventors believe that bridging between separate portions of the electrode active material helps to reduce cycling stresses caused by electrode volume expansion and contraction resulting from charge/discharge operations. Bridging between separate portions of the active material can result from direct interactions between the metal-ligand complex on the separate portions of the active material, or, alternatively, from indirect interactions between the metal-ligand complex and another intermediate compound, such as a binder. Therefore, it is preferred that the electrode additionally include a binder compound.

As discussed above, in some cases, bridging interactions can occur between the metal-ligand complex and the binder. Thus, in certain embodiments, the metal-ligand complex includes a coordination bond to the binder portion. Preferably, the coordination bond is formed between the metal ion of the metal-ligand complex and the binder portion.

In certain embodiments, the binder is capable of cross-linking the metal ions in the metal ligand complex layer to form a metal ligand/binder complex capable of binding the active material. Preferred binder moieties include carbenes, conjugated dienes, polyaromatics and heteroaromatics, nitrogen-containing groups, oxygen-containing groups, or sulfur-containing groups. Even more preferably, the binder moiety is an oxygen-containing group. Most preferably, the binder moiety is at least one of a carboxyl group, a hydroxyl group, an aldehyde group, and a carbonyl group.

In embodiments, the adhesive compound is a polymer. In embodiments where it is desired to form a coordination bond between the metal ligand complex and the adhesive, preferred polymers are those comprising oxygen species such as acrylate, carboxyl, hydroxyl or carbonyl moieties. These groups can form a coordination bond with metal gold water ions. However, other polymers without these groups can also be used, depending on specific criteria, and for example, suitable polymers can be polyvinylidene fluoride (PVDF) or styrene-butadiene rubber. In any case, if the coordination bond between the metal ligand complex and the adhesive is desired, it is more preferred that the adhesive be selected from polyvinyl pyrrolidone, carboxymethyl cellulose, polyacrylic acid (PAA), poly(methacrylic acid), polymethyl methacrylate, polyacrylamide, polypyrrole, polyacrylonitrile (polyacrylonitride), maleic anhydride copolymers, including poly(ethylene and maleic anhydride) and other copolymers, polyvinyl alcohol, carboxymethyl chitosan, natural polysaccharides, xanthan gum, alginate, polyimide. Most preferably, the adhesive is PAA. In optional embodiments, if the adhesive moiety is desired to contain nitrogen atoms, suitable polymers are polyacrylonitrile.

The binder is typically present in an amount from about 2 wt% to about 40 wt%, preferably from about 5 wt% to about 30 wt%, and most preferably from about 5 wt% to about 20 wt% of the current collector electrode material.

In certain embodiments, the electrode is formed from an active material initially provided as primary particles having a primary particle size. The active material can be combined with other components and then formed around a suitable current collector into the electrode. During the process of manufacturing the electrode (whether by casting or other manufacturing methods), the primary particles of the active material can aggregate to form aggregated secondary particles having a secondary particle size.

The term particle is generally intended to include materials of many different shapes. The primary particles can have any shape, for example, spherical, cylindrical, rod-like, wire-like, tubular. The primary particles can be porous or non-porous.

Preferably, the primary particles of the active material are nano-sized. The term "nano-sized" is intended to include a number average particle size from about 1 nm to about 1000 nm. In this case, the primary particles of the active material are nano-shaped particulate materials, such as nanoparticles, carbon nanotubes, graphene sheets, carbon-based nanocomposites, nanorods, nanowires, nanolattices, nano core-shell structures and other hollow nanostructures. It is generally preferred that the shape of the primary particles is substantially spherical.

Preferably, the primary particles have a number average particle size of at least 10 nm. More preferably, the particles have a number average particle size of at least 30 nm. Even more preferably, the particles have a number average particle size of at least 50 nm. Most preferably, the particles have a number average particle size of at least 70 nm.

Preferably, the primary particles have a number average particle size of up to 10 μm. More preferably, the particles have a number average particle size of up to 5 μm. Even more preferably, the particles have a number average particle size of up to 4 μm. An advantage of the present invention is that the inclusion of the metal ligand complex provides benefits in operation when used with larger or coarse active material particles as well as smaller particles. For example, it is standard to reduce the size of silicon particles used to produce negative electrodes to the range of hundreds of nanometers. The Examples section herein shows that such a reduction is not necessary for the present invention to work, and that surprisingly good results can indeed be obtained with silicon in the low micron particle size range.

It should be understood that the number average diameter of the primary particles has a lower limit selected from any one of about 10 nm, 30 nm, 50 nm or 70 nm and an upper limit selected from any one of about 10 μm, 5 μm, 4 μm or 1000 nm, 900 nm, 700 nm, 500 nm or 300 nm. The selection may depend on the application of the active material and the electrode.

As discussed above, after fabrication of the electrode, primary particles of the active material may have aggregated to form aggregated secondary particles.

In certain embodiments, the metal-ligand complex is applied to the primary particles prior to any aggregation, in which case at least a portion of the surface of the primary particles is coated with the metal-ligand complex.Preferably, the primary particles are encapsulated by the metal-ligand complex.

In an alternative embodiment, the metal-ligand complex is applied after at least some of the primary particles have been aggregated. In this case, at least a portion of the surface of the secondary particles is coated with the metal-ligand complex. Preferably, the secondary particles are encapsulated by the metal-ligand complex. The secondary particles can be porous or non-porous.

It should also be understood that other electrode structures are contemplated besides those in which the active material is provided as particles. For example, the active material can have a porous morphology. In this embodiment, the surface of the porous active material is at least partially coated with a metal-ligand complex.

In yet other embodiments, the surface of the active material displays nanostructured or nanopatterned features. The term "nanopattern" is intended to encompass features having a size range of 1-1000 nm. In these embodiments, the surface of these nanostructured or nanopatterned features is at least partially coated with a metal-ligand complex.

As discussed above, the electrode material or component to which the metal-ligand complex is bound is an active material. An active material is any part or component of an electrode required for the electrochemical charge and discharge reactions. The electrode can be a negative electrode, in which case the active material is typically selected from silicon, silicon-containing materials (oxides, composites, and alloys thereof), tin, tin-containing materials (oxides, composites, and alloys thereof), germanium, germanium-containing materials (oxides, composites, and alloys thereof), carbon, or graphite. Alternatively, the electrode can be a positive electrode, in which case the active material is typically selected from a metal oxide or mixed metal oxide, carbon, or graphite. In particular, mixed lithium oxide materials (wherein lithium oxide is mixed with other oxides such as manganese, cobalt, nickel, etc.) are used.

The metal-ligand complex can coordinate with any electron-donating groups on the surface of the active material, allowing the metal-ligand complex to bind to the active material. As a result of our oxygen-containing atmosphere, even active materials that are reportedly devoid of electron-donating groups often possess such groups. Thus, the active material includes a surface with electron-donating groups, and the metal ions of the metal-ligand complex layer are bound to these electron-donating groups of the active material via coordination bonds. Suitable electron-donating surface moieties include oxides.

In the case of almost no or no electron-donating groups on the active material surface, the ligand of the metal ligand ligand can also be a hydrophobic ligand (RX), wherein X is coordinated to the metal ion, so wherein X can be any electron-donating group that can form a coordination bond with the metal ion. Group "R" can be independently selected from alkyl, heteroalkyl, alkenyl, alkynyl, cycloalkyl, heterocycloalkyl, alkylcycloalkyl, heteroalkylcycloalkyl, aryl, heteroaryl, aralkyl and heteroaralkyl, and the group can be optionally substituted. According to this embodiment, preferably "R" has more hydrophobic properties. In addition, the R group can also include a group selected from a conjugated diene-containing group, a polyaromatic or heteroaromatic-containing group, a nitrogen-containing group, an oxygen-containing group or a sulfur-containing group. Preferably, "R" group is a short polymer, for example, a shorter version of a polymeric binder such as polyvinylidene fluoride (PVDF), poly (styrene butadiene), polyethylene and its copolymers, polypropylene and its copolymers and polyvinyl chloride.

The metal-ligand complex layer can partially coat the active material, or the coating can completely encapsulate the active material. This allows the properties of the active material to be adjusted. For example, a complete encapsulation layer can prevent degradation or dissolution of the active material and can also be used to prevent undesirable reactions in other components of the battery (for example, when manganese dissolves in the electrolyte, excessive SEI layer growth is deposited at the negative electrode). However, in cases where only minimal modification of the properties of the system/material/component is required (for example, minimal damage to conductivity), only partial coating may be required.

The metal ligand complex composition can be coated or applied to the active material of the electrode to form a thin film on the surface of the active material. The film can be formed into a monolayer. However, if necessary, thicker films can also be prepared. Depending on the formulation used and/or the polymeric ligands present together, such as adhesives, the thickness of these coatings can be increased. This can be achieved in the following ways: by forming a larger complex of a combination metal ligand complex and a polymeric ligand, such as an adhesive, on the surface of the active material, and/or by applying alternating coatings, such as additional metal ligand complexes, polymers or adhesives or nanoparticles, such as aluminum oxide, titanium oxide, to form a multilayer laminate structure on the surface of the active material. Additional coatings can be used to change overall coating properties. Therefore, the properties of the active material and the electrode, such as its structural integrity, can be adjusted by controlling the layer thickness of the metal ligand complex composition.

The present invention will now be described with particular reference to forming a coating on a silicon anode material. However, it should be understood that the basic concepts of the present invention can be applied to, but not limited to, any other material or component if a coating is required to maintain or enhance the pre-existing structure and/or properties of the applied battery material or component.

Silicon anodes comprising metal ligand complexes can be manufactured in various ways. For example, three key components are typically required when producing silicon anode slurry: (i) silicon particles, (ii) carbon particles, and (iii) a binder such as polyacrylic acid (PAA). The metal ligand complex can be added to silicon particles to form an activated silicon material, which can then be combined with carbon particles and PAA. Alternatively or additionally, the carbon particles can be coated with the metal ligand complex and then combined with silicon particles and PAA. Alternatively, the metal ligand complex can be combined with PAA to form a polymeric metal ligand complex, which is then combined with silicon particles and carbon particles in any order. Alternatively, the metal ligand complex can be added directly to a pre-existing mixture of silicon particles, carbon particles, and PAA and mixed therewith.

In the case of silicon-based anodes, the ability of the metal-ligand complex to form coordination bonds with neighboring particles creates a stable structure that can form and reform these bonds in a dynamic chemical environment. Both the negative and positive electrodes allow lithium ions to enter and exit the interior of the active particles that make up these electrodes. During insertion (or intercalation), ions move into the electrode. In the reverse process, extraction (or deintercalation), ions move out of the electrode. When a lithium-ion battery is discharging, positive lithium ions move from the negative electrode (in this case, silicon) and into the positive electrode (the lithium-containing compound). When the battery is charging, the opposite occurs.

When charging, silicon expands to store lithium ions. Accommodating the expansion that accompanies lithium absorption has always been a challenge in designing high-capacity lithium-ion negative electrode materials. Silicon has the highest capacity among lithium-ion storage materials, but when fully charged, its volume expands by 3-4 times. This expansion quickly destroys the electrical contact in the negative electrode. The metal ligand complex described in the present invention forms coordination forces between the various components of the silicon negative electrode material. Without wishing to be bound by theory, the inventors believe that this combination can resist expansion and contraction within the active material. In addition, even if some of these coordination bonds break during expansion, the coordination bonds can be formed again after contraction. Therefore, the present invention provides electrodes with higher stability and longer life. In addition, the metal ligand complex does not act as an insulator and allows electrons to move freely.

The advantages of metal ligand complex coatings are not limited to the negative electrode. The above advantages also allow for more efficient positive electrode performance. New positive electrode materials based on mixed lithium oxides containing a mixture of cobalt, lithium and nickel have stability problems. These mainly involve dissolving manganese and/or nickel from the solid into the electrolyte, which deposits on the negative electrode material and, as mentioned above, causes excessive SEI layer growth in the negative electrode. It has been shown that a thin deposit of aluminum oxide on the positive electrode material increases stability, but there is currently no cost-effective method for achieving such a coating. The metal ligand complex of the present invention can be applied to the active material to act as a diffusion barrier and chemically lock the manganese oxide near the surface. In addition, the stronger interaction between the different components of the electrode allows for improved efficiency of electron transfer, thereby resulting in longer battery life.

The present invention is not limited to batteries, but is equally applicable to capacitors and supercapacitors, as well as other energy storage and conversion systems. In fact, any arrangement using electrodes can benefit from including the metal-ligand complexes described herein. Due to the basic concept of metal-ligand complexes, the performance enhancement features are also applicable.

Metal-ligand complexes are discussed below.

The present inventors have discovered that providing conditions for forming electron-donating groups that bridge or otherwise connect or bond two or more metal ions generally results in the formation of a metal-ligand complex. One method can be to provide a pH below pH 7, preferably a pH of about 1.5-6, and preferably a pH of about 2-5, to the composition formed by contacting the metal-ligand complex with the surface of the active material to hydroxylate the chromium (III) ion.

Various chromium salts such as chromium chloride, chromium nitrate, chromium sulfate, and chromium perchlorate can be used to form metal-ligand complexes. These salts are mixed with alkaline solutions such as potassium hydroxide, sodium bicarbonate, sodium sulfite, and ammonia to form different metal-ligand complexes. Organic reagents that can serve as bases, such as ethylenediamine, di(3-aminopropyl)diethylamine, pyridine, imidazole, etc., can also be used. The size and structure of the metal-ligand complex can be controlled by changes in pH, temperature, solvent, and other conditions.

In particular, by varying the metal salt and the reaction environment, the binding of the metal ligand complex to oxides (e.g., silica) and other solid matrices can be tuned and a coordination sphere can be provided to bind other components, such as nanoparticles, to the matrix surface, i.e., additional active material particles or particles of a second active material or other active materials of the electrode. Although the individual coordination interactions between the metal ligand complex and a given active material are relatively weak, the diversity of the coordination forces results in very strong interactions. Individually, each coordination interaction may be broken individually due to some point local stress source. However, this local stress source is unlikely to break all of the multiple coordination bonds. Therefore, after relaxation, the broken bonds, such as bonds to the active material surface, can be reformed, thereby alleviating stress through future cycles.

The metal ligand complex can be further stabilized by cross-linking the metal ions to form larger oligomeric metal ligand complexes. Therefore, in one embodiment, the metal ligand complex is an oligomeric metal ligand complex. This oligomeric metal ligand complex can be pre-formed and applied to the active material, or formed in situ on the surface of the active material. In this case, the ligand can form multiple coordination bonds with a variety of metal ions to effectively bridge or cross-link metal ions. In other words, the ligand can form a coordination bond with two or more metal ions, thereby connecting one metal ion to another metal ion.

Exemplary oxygen-bridged chromium structures are provided below:

When applied to an active material, at least one of the water or hydroxyl groups on each metal-ligand complex is replaced by a coordination bond to the surface of the active material, such as a silica/silicon particle. This is shown below, where "X" represents a coordination bond to the active material surface.

It should also be recognized that multiple water or hydroxyl groups may be replaced by coordination bonds to the surface of the active material, for example, each chromium ion may form a coordination bond to the surface of the active material.

Furthermore, water and/or hydroxyl groups may be replaced by a coordinate bond with another component of the electrode, such as an additional active material or a binder.

Multiple oligomeric metal ligand complexes can be further cross-linked with each other using larger multidentate ligands such as binders to form larger oligomeric metal ligand complexes. Therefore, in another embodiment, the metal ligand complex is a polymeric metal ligand complex. Such a polymeric metal ligand complex can be preformed and applied to the active material, or formed in situ on the surface of the active material. In this case, the multidentate ligand is able to form multiple coordination bonds in multiple metal ligand complexes to effectively bridge or cross-link metal ions across a large distance or between the first and second active materials.

Metal-ligand complexes, oligomeric metal-ligand complexes, and polymeric metal-ligand complexes can be further masked with ligands of varying hydrophobicity to alter the overall hydrophilicity/hydrophobicity of these complexes. Thus, in another embodiment, metal-ligand complexes, oligomeric metal-ligand complexes, and polymeric metal-ligand complexes can be masked versions of these metal-ligand complexes. Such masked metal-ligand complexes can be preformed and applied to the active material, or formed in situ to alter the surface properties of the active material. In this case, the masking ligand can alter the surface properties of the first active material to more effectively bind to the second active material.

In another aspect of the present invention, an electrochemical cell is provided, comprising: a negative electrode, a positive electrode, and an electrolyte disposed between the negative electrode and the positive electrode; wherein at least one of the negative electrode or the positive electrode is an electrode as previously defined.

Thus, at least one of the negative electrode and the positive electrode includes an active material having a surface and a metal-ligand complex bound to the surface of the active material, the metal-ligand complex including at least one ligand coordinately bonded to a metal ion; and wherein the metal ion is bound to the surface of the active material through a coordinate bond.

In yet another aspect of the present invention, a precursor composition for manufacturing an electrode is provided. The precursor composition includes: an active material having a surface; and a metal-ligand complex bound to the surface of the active material, the metal-ligand complex including at least one ligand that coordinately bonds with a metal ion; wherein the metal ion is bound to the surface of the active material via a coordinate bond. Various features of the precursor composition are as previously described with respect to the electrode.

As previously mentioned, the precursor composition may also comprise a binder compound.

In an embodiment, the active material is provided in the form of particles having a primary particle size as defined hereinbefore.

In another aspect of the present invention, there is provided use of the precursor composition described above for manufacturing an electrode.

In yet another aspect of the present invention, there is provided a method for manufacturing an electrode, comprising manufacturing the electrode from the precursor composition described above.

In another aspect of the present invention, a method for manufacturing an electrode is provided, comprising: forming a precursor composition comprising an active material and manufacturing an electrode from the precursor composition, wherein the method comprises contacting a metal-ligand complex with the surface of the active material, the metal-ligand complex comprising at least one ligand that coordinately bonds with a metal ion, and the metal ion is bound to the surface of the active material through a coordination bond.

The method of making an electrode may further include the step of casting the precursor composition onto a current collector to form the electrode.

It should be understood that the metal-ligand complex can be applied to the active material surface at any stage of the process. For example, in a first illustrative embodiment, the active material is coated with the metal-ligand complex prior to the step of forming the precursor composition. In a second illustrative embodiment, the metal-ligand complex is mixed into the precursor composition. In a third illustrative embodiment, the metal-ligand complex is added during the step of forming the electrode. In a fourth illustrative embodiment, the metal-ligand complex is added to the binder to form a metal-binder complex prior to the step of forming the electrode. In a fifth illustrative embodiment, the metal-ligand complex is applied to the active material after the electrode is formed.

In embodiments, the step of fabricating the electrode comprises casting the electrode from the precursor composition.

In another aspect of the present invention, a method for improving electrode performance is provided, comprising coating the surface of an electrode active material with a metal ligand complex layer, the metal ligand complex comprising at least one ligand that coordinates and bonds with a metal ion; wherein the metal ion forms a coordination bond with the surface of the active material.

As a result of coating the surface of the electrode active material, the electrode exhibits improved performance compared to an uncoated electrode. In certain embodiments, the improved performance is at least one selected from the group consisting of: higher first cycle discharge capacity, higher first cycle efficiency, and higher capacity after 500 deep charge/discharge cycles at 100% depth of charge. Preferably, the improved performance is higher capacity after 500 deep charge/discharge cycles.

In one embodiment, the capacity after 500 deep charge/discharge cycles at 100% depth of charge is at least 5%, even more preferably at least 7%, and most preferably at least 9% greater than that of the uncoated electrode.

In another embodiment, the capacity after 500 deep charge/discharge cycles at 100% depth of charge is at least 30%, even more preferably at least 50%, and most preferably at least 70% greater than that of the uncoated electrode.

It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All these different combinations constitute various alternative aspects of the invention.

Example

Example 1: Preparation of Metal-Ligand Complex Solution

Three different metal-ligand complex solutions are described. Depending on the salt, base, final pH, and other ligands used, the metal-ligand complex solutions exhibit different binding properties specifically tailored to the active material being coated.

Solution 1

In this example, chromium perchlorate hexahydrate (45.9 g) was dissolved in 480 mL of purified water and mixed thoroughly until all solids dissolved. Similarly, 8 mL of ethylenediamine solution was added to 490 mL of purified water. The solutions were combined and stirred overnight at room temperature before equilibration to a pH of approximately 4.5.

Solution 2

In this example, chromium chloride hexahydrate (26.6 gm) was dissolved in 500 mL of purified water and mixed thoroughly until all solids dissolved. The pH was slowly adjusted to 4.5 with 1 M NaOH or LiOH.

Solution 3

In this example, chromium chloride hexahydrate (45.9 g) was dissolved in 480 mL of purified water and mixed thoroughly until all solids were dissolved. Similarly, 8 mL of ethylenediamine solution was added to 490 mL of purified water. The combined solutions were stirred overnight at room temperature and then equilibrated to a pH of approximately 3.8.

Example 2: Preparation of Metal-Ligand Complex-Coated Silicon Nanoparticles

A. Preparation of Metal-Ligand Complex Silicon Slurry

In this example, a 50 mM (final concentration) metal complex (Solution 1) was used. Silicon (Si) nanopowder (100 nm size) was purchased from MTI, USA. A 20% w/v silicon nanoparticle slurry was prepared by mixing dried silicon nanopowder with 7.5% isopropanol at pH 4.3 in ddH ₂ O in a round-bottom flask. The slurry was placed under vacuum for 5 minutes, and then a 100 mM metal ligand complex solution was added. The flask was heated to 40° C. and the slurry was mixed at 400 rpm for 5 minutes using a mechanical overhead mixer with an axial flow impeller. The impeller was removed and the solution was vacuumed again for 10 minutes. The impeller was replaced and the slurry was allowed to mix overnight at 40° C. and 400 rpm. The overnight slurry was transferred to a centrifuge tube and centrifuged at 10,000 g for 10 minutes to separate the solid from the solution. 70% of the supernatant was removed from the starting volume and replaced with ddH ₂ O at pH 4.3. The pellet was resuspended using physical stirring and high-frequency bath sonication for 10 minutes. This wash step was repeated, and after a third centrifugation step, the supernatant was removed from the solution. _ddH₂O at pH 4.3 was added to the slurry until a solids content of 20% w/v was reached. The slurry was again bath sonicated for 10 minutes to fully disperse the particles. Various concentrations of the metal-ligand complex (50 mM, 25 mM, and 10 mM) were used in combination with various numbers of wash steps to coat Si nanoparticles.

B. Zeta Potential, SEM, and ICP-AES Analysis of Metal-Ligand Complex-Coated Silicon Nanoparticles

The zeta potential of Si nanoparticles coated with metal ligand complexes and controls (Si nanoparticles in water) was analyzed using a Malvern zeta potential analyzer. The zeta potential distribution curve is shown in Figure 1, which shows that the zeta potential of Si coated with metal ligand complexes is shifted to a more positive value compared to the control (negative charge). This supports the formation of a positively charged metal complex coating on the surface of the Si nanoparticles, and the overall offset of the zeta potential can vary depending on the conditions used. Scanning electron microscopy (SEM) studies also show that the coating is too thin for the SEM instrument to resolve (resolution <10 nm). Inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis of metal complex activated silicon nanoparticles was performed by Spectrometer Services Pty Ltd (Victoria, Australia). Based on the apparent density of the starting material, the thickness of the metal ligand complex layer was estimated to be <5 nm based on the estimated 1% absorption of the original metal ligand complex solution.

Example 3: Fabrication and testing of coin cell batteries with and without metal ligand complex-coated silicon nanoparticles Si anode without metal-ligand complex

A. Preparation of Battery Slurry

Metal ligand complex-coated silicon nanoparticles were prepared as described in Example 2. TIMCAL graphite & Super P conductive carbon black were purchased from MTI Corporation in the United States, and poly(acrylic acid) (PAA) with an average Mw of 450,000 Daltons was purchased from Sigma-Aldrich. The metal ligand complex-coated silicon nanoparticles were transferred to a side-arm flask with a magnetic stir bar. The mass of Super P carbon equivalent to the dry weight of the metal ligand complex-coated silicon nanoparticles was weighed and transferred to the same flask. The slurry was diluted to 15% w/v solid content by adding 15% isopropanol in _ddH2O . The slurry flask was placed on a heated stirrer and mixed at 40°C and 400rpm for 5 minutes. The flask was placed under vacuum and mixing continued for another 5 minutes. The vacuum device was removed and the slurry was mixed again for 1 hour. 450kDa poly(acrylic acid) equivalent to half the mass of SuperP carbon was weighed and added to the slurry. The slurry was mixed overnight at 40°C and 400rpm. A slurry with a ratio of Si:Super-P:PAA of 40:40:20 (wt%) was obtained. The amounts of Si, Super P and PAA were adjusted to produce different slurry formulations.

B. Fabrication and Testing of Metal-Ligand Complex-Coated Si Anodes in Coin Cells

Si particles were coated with a metal ligand complex at a concentration of 50 mM and washed twice to remove unreacted metal ligand complex solution. The slurry mixing procedure was the same as described in the previous example, and the ratio of Si:Super-P:PAA was set to 40:40:20 (wt%). The Si slurry was used to make electrodes and assemble button cells. The Si slurry was cast onto a copper (Cu) foil used as a current collector to form a Si electrode. The Si electrode was then dried, rolled and cut under vacuum for assembly of button cells. A Si electrode with uncoated Si as the active material was made and used as a control, which had a similar mass loading (2.22-2.37 mg/ ^cm2 ) as the metal ligand-coated Si electrode. Lithium (Li) metal was used as the counter electrode, and 1 M _LiPF6 /EC:DEC:DMC=1:1:1 with 10% FEC was used as the electrolyte for assembling button cells. For charge/discharge cycling tests, coin cells were activated at 0.01C (1C = 4200 mAh/g) for two cycles and then cycled at 0.5C (1C = 4200 mAh/g) for long-term stability testing. The C rate is based on the mass of the Si particles in the electrode. The voltage range for the charge/discharge tests was 0.005–1.50 V relative to Li. Charge/discharge tests were performed on a computer-controlled Neware multichannel battery tester. Three replicate cells were prepared and tested for each condition.

Table 1 summarizes the charge/discharge cycle test data of the metal ligand complex-coated Si and the control, and Figure 2 shows the long-term cycle stability comparison of the metal ligand complex-coated Si and the control. The data show that the metal ligand complex-coated Si has a higher discharge capacity, higher charge/discharge efficiency, and better high-rate capacity retention. The cycle stability test shows that the metal ligand complex-coated Si has excellent long-term stability. The capacity of the metal ligand complex-coated Si is still significantly higher than that of the control after 500 deep cycles (100% DOD-deep discharge) at 0.5°C (1C=4200mAh/g).

Table 1 Charge/discharge cycle data of chromium metal complex-coated Si and controls with similar mass loadings

*Data are based on the average of 3 replicate cells, and the metal-ligand complex-coated Si and the control have similar mass loadings (2.22-2.37 mg/cm ² ).

Example 4: Fabrication and testing of Si anode using metal-ligand complexes and ball milling

This example aims to optimize the process for mixing Si slurry and observe the effect of ball milling on the charge/discharge cycling performance of Si anodes with metal-ligand complexes.

As above, Si particles were coated with 50 mM chromium metal ligand complex and washed twice. The slurry mixing procedure was the same as described in the previous example, and the ratio of Si:Super-P:PAA was set to 40:40:20 (wt%). Ball milling was used to process Si slurries with and without metal ligand complexes. The procedures for making Si electrodes and assembling button cells were the same as described in the previous example. For charge/discharge cycle testing, the button cells were activated at 0.03C (1C = 4200 mAh/g) for 2 cycles and then cycled at 0.5C (1C = 4200 mAh/g) for long-term stability testing. The voltage range of the charge/discharge test was 0.005-1.50 V compared to Li.

Table 2 summarizes the data of the charge/discharge cycle tests of the metal complex-coated Si and the control, and Figure 3 shows the long-term cycling stability comparison of the metal ligand complex-coated Si and the control. The data show that the performance of the Si negative electrode is significantly improved by using ball milling, and the metal ligand complex-coated Si (with a high mass loading of 27%) outperforms the control in terms of discharge capacity, charge/discharge efficiency, and high capacity retention. After 500 deep charge/discharge cycles (100% DOD) at 0.5°C, the capacity of the metal ligand complex-coated Si is still significantly higher than that of the control.

Table 2 Discharge/charge cycle data of Si coated with metal complexes prepared by ball milling and control

*Data are based on the average of 3 replicate cells and the mass loading of the metal-ligand complex-coated Si is 27% higher than the control. ^#Ball milling was used to process the slurry.

Example 5: Comparison of micron-sized and nano-sized particles using silicon particles with larger particle size (1-3 μm) performance

This example compares the charge/discharge cycling performance of larger micron-sized silicon particles with and without metal-ligand complexes.

The procedures for preparing the slurry, fabricating the coin cell, and testing the coin cell were the same as those discussed in Examples 3 and 4. Micron-sized silicon particles with a particle size of 1-3 μm were sourced from US Research Namomaterials and coated with 25 mM of the metal-ligand complex and washed once. Table 3 summarizes the charge/discharge cycling test data for the metal-ligand complex-coated Si (1-3 μm) and the control (1-3 μm), and Figure 4 shows a comparison of the long-term cycling stability of the metal-ligand complex-coated Si (1-3 μm) and the control (1-3 μm). The data show that the metal-ligand complex-coated Si has higher discharge capacity, higher charge/discharge efficiency, and higher capacity retention than the control. Cycling stability testing demonstrates that the metal-ligand complex-coated Si has good stability, with the capacity of the metal-ligand complex-coated Si remaining significantly higher than the control after 100 deep charge/discharge cycles (100% DOD - deep discharge) at 0.5C (1C = 4200 mAh/g).

Compared to the 100 nm Si nanoparticles used in Example 4, micron-sized (1-3 μm) Si particles have higher initial discharge capacity and charge/discharge efficiency. Compared to nanosized particles, micron-sized Si particles also have the advantages of lower cost, easier handling and fewer safety issues. Therefore, from the perspective of practical application in the battery industry, micron-sized Si particles are preferred. The great challenge of using large micron-sized Si particles is the exacerbation of expansion and stability problems. Current data show that the cycle stability of micron-sized Si particles can be significantly improved by using a metal ligand complex coating.

Table 3 Discharge/charge cycle data of micron-sized (1-3 μm) Si with or without metal-ligand complexes

*Data are based on the average of 4 replicate cells.

Example 6: Preparation and testing of a slurry having a metal-ligand complex and Si:Super-P:PAA=70:20:10 Preparation of Si negative electrode

This example investigates the effect of variations in slurry formulation on the charge/discharge cycling performance of Si anodes with metal-ligand complexes.

As described above, Si particles were coated with 50 mM metal-ligand complex and washed twice. The slurry mixing procedure was the same as described in Example 4, except that the Si:Super-P:PAA ratio was adjusted to 70:20:10 (wt%). The procedures for fabricating Si electrodes and assembling coin cells were the same as described in the previous examples. For charge/discharge cycling tests, coin cells were activated at 0.03C (1C = 4200 mAh/g) for 2 cycles and then cycled at 0.5C (1C = 4200 mAh/g) for long-term stability testing. The voltage range for charge/discharge testing was 0.005-1.50 V vs. Li.

Table 4 summarizes the charge/discharge cycle test data of the metal ligand complex-coated Si and the control, and Figure 5 shows the long-term cycling stability comparison of the metal ligand complex-coated Si and the control. The data show that the initial capacity of the metal ligand complex-coated Si at 0.03C and 0.5C is much higher than that of the control, and the capacity of the metal ligand complex-coated Si is similar to that of the control after more than 200 deep cycles (100% DOD) at 0.5C. This shows that the slurry formulation plays an important role in optimizing the performance of the Si cathode with the metal ligand complex and allows for a level of control over the performance.

Table 4 Charge/discharge cycle data of metal complex coated Si with Si:Super-P:PAA=70:20:10 slurry formulation and control

*Data are based on the average of 3 replicate cells, and the metal-ligand complex-coated Si and the control have similar mass loadings.

Example 7: Fabrication and testing of Si anodes coated with metal-ligand complexes at different concentrations

This example investigates the effects of metal ligand complex concentration and the need for a washing step on the charge/discharge cycling performance of Si anodes.

Si particles were coated with various concentrations of metal ligand complexes, namely 50 mM, 25 mM and 10 mM. The effect of a washing step after the coating step was also studied. For the 50 mM metal ligand complex experiment, two washes were performed after the coating step to remove excess metal ligand complex. For the 25 mM metal complex experiment, one wash and no wash were performed, respectively. For the 10 mM metal ligand complex experiment, no wash was performed. The slurry mixing procedure was the same as in the previous example, with the Si:Super-P:PAA ratio set to 40:40:20 (wt%). The slurry was provided for ball milling, electrode fabrication and button cell assembly. The procedures for fabricating Si electrodes and assembling button cells were the same as described in the previous example. For the charge/discharge cycle test, the button cells were activated at 0.03C (1C = 4200 mAh/g) for two cycles and then cycled at 0.5C (1C = 4200 mAh/g) for long-term stability testing. The voltage range of the charge/discharge tests was 0.005–1.50 V versus Li.

Table 5 summarizes the charge/discharge cycling test data for metal-ligand complex-coated Si and a control, and Figure 6 shows a comparison of the long-term cycling stability of the metal-ligand complex-coated Si and the control. The data show that the metal-ligand complex-coated Si (with 20-27% higher mass loading) exhibits higher discharge capacity, better charge/discharge efficiency, better high-capacity retention, and better long-term cycling stability than the control. The beneficial effects of the metal-ligand complex coating tend to decrease with decreasing metal complex concentration, indicating that the metal-ligand complex coating effectively improves the charge/discharge performance of the Si anode. The data also show that both the metal-ligand complex concentration and the washing step have a significant impact on the performance of the Si anode. A Si anode coated with 25 mM metal complex and washed once exhibited similar long-term cycling stability at 0.5 C as a Si anode coated with 50 mM metal complex and washed twice, but the 0.03 C discharge capacity of 25 mM/1 wash was significantly lower than that of 50 mM/2 washes. The data indicate that optimal coating conditions (concentration, pH, and temperature, etc.) of the slurry formulation used can maximize the performance of the Si anode and eliminate the need for a washing step.

Table 5 Charge/discharge cycle data of Si coated with different concentrations (10 mM, 25 mM and 50 mM) of metal ligand complexes and controls

*Data are based on the average of 3 replicate cells, and the mass loading of the metal-ligand complex-coated Si is 20–27% higher than the control.

Example 8: Fabrication and testing of Si negative electrodes for coin cells activated at different charge/discharge rates

This example investigates the rapid activation or fast charge/discharge capability of Si anodes with metal-ligand complexes.

As described in Example 2, Si particles were coated with 50 mM metal ligand complex and washed twice. The slurry mixing procedure was the same as described in Example 3, and the ratio of Si:Super-P:PAA was set to 40:40:20 (wt%). The procedures for fabricating Si electrodes and assembling button cells were the same as described in the previous examples. For charge/discharge tests, the button cells were charged/discharged at 0.01C and 0.03C (1C = 4200 mAh/g), respectively. The voltage range of the charge/discharge tests was 0.005-1.50 V compared to Li. The capacity and charge/discharge efficiency of the metal ligand complex coated Si and the control were obtained at two different rates (0.01C and 0.03C) for comparison.

Table 6 summarizes the charge/discharge test data of the metal ligand complex-coated Si and the control at two different rates (0.01C and 0.03C). The data show that the metal ligand complex-coated Si (mass loading is 20-27% higher than the control) has higher discharge capacity and better charge/discharge efficiency than the control at 0.01C and 0.03C. When the charge/discharge rate increases from 0.01C to 0.03C, the capacity retention rate of the metal ligand complex-coated Si is 88%, which is significantly higher than the 58% of the control. This shows that the metal ligand complex coating can enable the Si negative electrode to activate faster or charge/discharge faster.

Table 6 Charge/discharge cycle data of metal ligand complex coated Si and control tested at two different charge/discharge rates (0.01C and 0.03C)

*Data are based on the average of 3 replicate cells, and the mass loading of the metal-ligand complex-coated Si is 20–27% higher than the control.

Example 9: Fabrication and testing of Si negative electrodes for button cells using binders of different molecular weights

This example compares the effects of different molecular weight polyacrylic acid binders (100 kD and 450 kD) on the charge/discharge cycle performance of a Si negative electrode with a metal ligand complex. The procedures for preparing the slurry, making button cells, and testing the button cells were the same as those shown in Examples 3 and 4. The data in Table 7 show that higher molecular weight PAA binders work better with the metal ligand complex in terms of improving discharge capacity, charge/discharge efficiency, and high capacity retention. PAA binders with higher molecular weights have more binding sites for binding to the metal ligand complex and Si particles, which leads to multiple interactions between the binder and the Si particles and a stronger resulting bond. Therefore, the molecular weight of the binder affects, to some extent, the efficiency and strength of the metal ligand complex in stabilizing the structure of the Si particles and improving the performance of the Si negative electrode.

Table 7 Discharge/charge cycle data of Si coated with metal ligand complexes of PAA binders with different molecular weights and a control with 450k-PAA

*Data are based on the average of 3 replicate cells, and the mass loading of the Si anode with the metal-ligand complex is 25% higher than the control.

Example 10: Fabrication and testing of Si anodes for coin cells using different binders

This example compares the effects of polyacrylic acid (PAA) and polyvinyl alcohol (PVA) binders on the charge/discharge cycling performance of Si anodes coated with metal ligand complexes. The procedures for preparing the slurry, fabricating the button cells, and testing the button cells were the same as those shown in Examples 2, 3, and 4. The data in Table 8 show that the PVA binder has similar or slightly better charge/discharge performance than the PAA binder of similar molecular weight. This example also demonstrates that the metal ligand complex works with different polymer binders to improve the charge/discharge performance of Si anodes. As can be seen from Examples 9 and 10, the choice of binder type and molecular weight can be used in conjunction with the use of the metal ligand complex.

Table 8 Charge/discharge cycle data of Si coated with metal ligand complexes with different binders (PAA and PVA) and control with PAA binder

*Data are based on the average of 3 replicate cells, and the mass loading of the Si anode with the metal-ligand complex is 25% higher than the control.

Example 11: Fabrication and testing of Si anodes using different orders of metal-ligand complex addition

This example compares the effect of different addition orders of metal ligand complexes on the charge/discharge cycle performance of Si negative electrodes. The procedures for preparing slurries, making button cells, and testing button cells were the same as those shown in Examples 2, 3, and 4. Three different addition orders of metal ligand complexes were compared to a control without metal ligand complexes. Si activation was performed by coating Si particles using a 50mM/2 wash metal ligand complex procedure, first by premixing Si and SPC particles (Si+SPC), then adding 4mM metal ligand complex, and SPC activation was performed by coating SPC particles using a 50mM/2 wash metal ligand complex procedure. The data in Table 9 show that the optimal performance in improving discharge capacity, charge/discharge efficiency, and high capacity retention using metal ligand complexes can also be controlled by the order in which the composite active materials are formed.

Table 9 Discharge/charge cycle data of Si with different addition orders of metal ligand complexes and controls without metal ligand complexes

*Data are based on the average of 3 replicate cells, and the mass loading of the Si anode with the metal-ligand complex is 25% higher than the control.

Example 12: Fabrication and testing of Si negative electrodes for button cells using different metal-ligand complexes

In this embodiment, the effect of different anions (Cl and ClO ₄ ) present in different metal ligand complexes was studied. 100 nm Si particles were coated with the two different metal ligand complexes described in Example 1 (solutions 1 and 3), and the procedures for preparing the slurry, making button cells, and testing the button cells were the same as those shown in Examples 2 and 3. The data in Table 10 show that the CrCl _3- based metal ligand complex has similar performance to the Cr(ClO ₄ ) _3- based metal ligand complex in terms of discharge capacity and coulombic efficiency at 0.03C, and both show better performance than the control. When the charge/discharge rate is increased to 0.5C, the Cr(ClO ₄ ) ₃ -based metal ligand complex shows better performance than CrCl ₃ in terms of discharge capacity and capacity retention. This shows that the use of metal ligand complexes, although it varies with the choice of counter ion, does not rely on the choice of counter ion to achieve improved negative electrode performance.

Table 10 Discharge/charge cycle data of Si with different metal ligand complexes and control

Example 13: Testing fast activation at 0.1C using the Si negative electrode of a button cell

Activation/formation by charge/discharge is an important step in battery manufacturing. For Si anode-based batteries, due to the high resistance associated with the Si anode, battery activation typically requires very low charge/discharge rates (less than 0.1C). From a battery manufacturing perspective, faster activation is preferred because it can shorten battery formation time and reduce manufacturing costs.

This example investigates the feasibility of activating Si negative electrode-based button cells at a charge/discharge rate of 0.1C and compares the 0.5C cycling performance of Si cells with and without metal ligand complexes after 0.1C activation. The procedures for preparing the slurry and making the button cells were the same as those shown in Examples 3 and 4. For the charge/discharge cycling test, the button cells were activated at 0.1C (1C = 4200mAh/g) for 2 cycles and then cycled at 0.5°C (1C = 4200mAh/g) for long-term stability testing. The C rate is based on the mass of Si particles in the electrode. The voltage range of the charge/discharge test was 0.005-1.50V compared to Li. Figure 7 shows a comparison of the long-term cycling stability of Si coated with the metal ligand complex and the control at 0.5°C after 0.1C activation. It can be seen that the Si negative electrode is activated at a faster rate of 0.1C and exhibits similar performance to the Si negative electrode activated at a slower rate (0.03C in Figure 3). The cycling stability test also showed that the metal ligand complex-coated Si has excellent long-term stability, and the capacity of the metal ligand complex-coated Si is still significantly higher than that of the control after 500 deep cycles (100% DOD-deep discharge) at 0.5C (1C=4,200mAh/g).

Example 14: Fabrication and testing of coin cells with and without metal ligands using a PVDF/NMP-based process Metal oxide cathodes based on bulk complexes

To investigate the effect of metal-ligand complexes on the performance of stable metal oxide cathodes, lithium mixed metal oxide particles were coated with metal-ligand complexes, and electrodes and coin cells were fabricated for charge/discharge cycling tests.

Lithium mixed metal oxide particles were purchased from MTI (USA) and had a composition of Li(NiCoMn) _O₂ (Ni:Co:Mn = 1:1:1). The procedure for coating the metal oxide particles with the metal-ligand complex was the same as described in Example 2-A. To prepare the slurry, polyvinylidene fluoride (PVDF) was used as a binder, N-methyl-2-pyrrolidone (NMP) as a solvent, and super-C45 carbon as a conductor, all purchased from MTI. The ratio of oxide:super-C45:PVDF was 85:7:8 (wt%). The slurry preparation procedure was the same as described in Example 3-A.

The metal oxide slurry was sent out for making electrodes and assembling button cells. The slurry was cast onto aluminum (Al) foil used as a current collector to form the electrode. The cast electrode was then dried, rolled and cut under vacuum for assembly of button cells. Electrodes with uncoated metal oxide as the active material were manufactured and used as controls, which had similar mass loadings (about 13 mg/ ^cm2 ) as the metal ligand complex coated electrodes. Lithium (Li) metal was used as the counter electrode, and 1M _LiPF6 /EC:DEC:DMC=1:1:1 was used as the electrolyte for assembling button cells. For charge/discharge cycle testing, the button cells were activated at 0.1C (1C=150mAh/g) for 3 cycles and then cycled at 0.5C (1C=150mAh/g) for long-term stability testing. The C rate is based on the mass of the metal oxide particles in the electrode. The voltage range of the charge/discharge test was 2.5-4.2V compared to Li. Charge/discharge tests were performed on a computer-controlled Neware multi-channel battery tester. Three replicate cells were prepared and tested for each condition.

Figure 8 shows a comparison of the long-term cycling curves of the metal ligand complex coated metal oxide positive electrode and the control. In this example, the discharge capacity of the control for the first 100-150 cycles is slightly higher than that of the metal ligand complex coated positive electrode, which may be solved by further optimizing the coating conditions for more efficient diffusion of lithium ions. After 200 cycles, the metal ligand complex coated positive electrode begins to show significantly improved stability relative to the control. After 450 deep cycles (100% DOD-depth of discharge) at 0.5°C, the capacity of the metal ligand complex coated positive electrode is still significantly higher than the control. The improvement in cycling stability by the metal ligand complex is believed to be due to the inhibition of structural changes and/or the reduction of metal element dissolution into the electrolyte due to the metal ligand complex coating on the metal oxide particles.

Example 15: Fabrication and testing of button cells with and without gold using a water-based adhesive process Metal oxide cathodes based on ligand complexes

The lithium-ion battery industry widely uses organic solvent-based processes to produce metal oxide cathodes. However, aqueous processes using water-soluble binders are more preferred due to cost and environmental considerations. This example investigates the compatibility of metal-ligand complexes with aqueous binder-based processes for cathode production, as well as their impact on stabilizing the performance of the resulting metal oxide cathodes.

Poly(acrylic acid) (PAA) with a molecular weight of 450,000 Daltons was purchased from Sigma-Aldrich and used as an aqueous binder to mix the metal oxide slurry. The procedures for preparing the slurry, making button cells, and testing the button cells were the same as those shown in Example 14. Table 11 summarizes the charge/discharge cycle test data of the metal ligand complex-coated metal oxide positive electrode and the control, and Figure 9 shows the long-term cycle stability comparison of the metal ligand complex-coated positive electrode and the control. The data show that the metal ligand complex-coated positive electrode has a higher discharge capacity and better capacity retention when the charge/discharge rate increases. The cycle stability test shows that the metal ligand complex-coated positive electrode has better stability than the control, and the capacity of the metal ligand complex-coated positive electrode is still significantly higher than the control after 250 deep cycles (100% DOD-discharge depth) at 0.1C (1C=150mAh/g).

Table 11 Charge/discharge cycle data of metal oxide cathodes with metal ligand complexes and controls

Example 16: Fabrication and testing of Si anodes in supercapacitors with activated carbon (AC) as positive electrodes

This example involves fabricating supercapacitors using Si negative electrode and activated carbon (AC) as positive electrode and studying the effect of metal ligand complex coating on the electrochemical performance of Si-AC supercapacitors.

As described in Example 3, Si particles were coated with 50 mM metal ligand complex and washed twice. The slurry mixing procedure was the same as described in the previous example, and the ratio of Si:Super-P:PAA was set to 40:40:20 (wt%). Ball milling was used to process Si slurries with and without metal ligand complex. The procedure for making Si electrodes was the same as described in the previous example. 90% activated carbon (AC, Norit 30) was mixed with 10% PVDF binder using NMP as a solvent to form a positive electrode slurry, and the slurry was then cast onto Al foil to form the positive electrode. The AC electrode was then dried under vacuum, rolled, and cut for button cell assembly. The mass loading of the Si electrode was controlled at 0.32-0.76 mg/ ^cm2 , and the mass loading of the AC electrode was controlled at 3.69-8.73 mg/ ^cm2 . To assemble the coin cells, an AC electrode was used as the positive electrode, Si was used as the negative electrode, and 1M _LiPF₆ /EC:DEC:DMC (1:1:1) with 10% FEC was used as the electrolyte. For charge/discharge cycling testing, the coin cells were activated for three cycles at a current density of 0.08 A/g, which is approximately 2.0 C based on the total mass of active materials on the negative and positive electrodes. After activation, the coin cells were cycled at 20 C and 60 C for long-term stability testing. The charge/discharge tests were conducted over a voltage range of 2.0 to 4.5 V.

Figures 10 and 11 show a comparison of the long-term cycling stability of Si-AC cells with metal-ligand complex-coated Si and a control at 20C (500 cycles) and 60C (1,000 cycles), respectively. The data demonstrate that the charge/discharge cycling stability of Si-AC cells is significantly enhanced by the use of metal-ligand complex-coated Si. The capacity retention of the metal-ligand complex-coated Si-based cells is significantly higher than that of the control after 1,000 deep charge/discharge cycles (100% DOD) at 20°C and 10,000 deep charge/discharge cycles (100% DOD) at 60C.

Claims (30)

1. Electrodes, including: Active materials with surfaces; and A metal ligand complex that binds to the surface of the active material, wherein the metal ligand complex comprises at least one ligand that is coordinated and bonded to a metal ion; The metal ions therein bind to the surface of the active material through coordination bonds. 2. The electrode of claim 1, wherein the surface is encapsulated by a metal ligand complex layer. 3. The electrode of claim 2, wherein the thickness of the metal ligand complex layer is less than 1000 nm. 4. The electrode of claim 1 further comprises a second active material. 5. The electrode of claim 4, wherein the surface of the second active material does not bind to the metal ligand complex. 6. The electrode of claim 1, wherein the metal ligand complex is selected from the group consisting of chromium, ruthenium, iron, cobalt, aluminum, zirconium, and rhodium. 7. The electrode of claim 6, wherein the metal is a chromium ion. 8. The electrode of claim 7, wherein the chromium ion is a chromium III ion. 9. The electrode of claim 1, wherein the ligand comprises atoms selected from nitrogen, oxygen, or sulfur that form coordinate bonds with the metal ion. 10. The electrode of claim 1, wherein the ligand is a monoatomic ligand, a diatomic ligand, or a triatomic ligand. 11. The electrode of claim 10, wherein the ligand is of an oxygen-containing species; and wherein the coordinate bond is formed between the oxygen atom and the metal ion. 12. The electrode of claim 1, wherein the ligand is a bridging compound coordinated with at least two metal ions. 13. The electrode of claim 1, wherein the metal ligand complex is an oxygen-bridged chromium III complex. 14. The electrode of claim 1, wherein the surface of the active material is an oxide surface. 15. The electrode of claim 1, wherein the active material is selected from the group consisting of metals, intermetallic compounds, metalloids, and carbon. 16. The electrode of claim 15, wherein the active material is selected from the group consisting of: silicon, silicon-containing materials including oxides, complexes and alloys of silicon, tin, tin-containing materials including oxides, complexes and alloys of tin, germanium, germanium-containing materials including oxides, complexes and alloys of germanium, carbon, graphite, sulfur, _LiFePO4 , and mixed metal oxides including one or more of cobalt, lithium, nickel, iron and manganese. 17. The electrode of claim 1, wherein when the electrode is a negative electrode, the active material is selected from the group consisting of silicon and carbon. 18. The electrode of claim 1, wherein when the electrode is a positive electrode, the active material is selected from the group consisting of _LiFePO4 and mixed metal oxides including one or more of cobalt, lithium, nickel, iron and manganese. 19. The electrode of claim 4, wherein the second active material is carbon. 20. The electrode of claim 1, wherein the metal ligand complex is an oligomeric metal ligand complex. 21. The electrode of claim 1, wherein the metal ligand complex provides a surface that forms a coordination bond with another component of the electrode. 22. Electrochemical cells, including: negative electrode, Positive electrode, and The electrolyte placed between the negative and positive electrodes; Wherein, at least one of the negative electrode and the positive electrode is an electrode according to any one of claims 1-21. 23. A precursor composition for manufacturing an electrode, said precursor composition comprising: Active materials with a surface; A metal ligand complex that binds to the surface of the active material, wherein the metal ligand complex comprises at least one ligand that is coordinated and bonded to a metal ion; The metal ions therein bind to the surface of the active material through coordination bonds. 24. Use of the precursor composition of claim 23 in the manufacture of an electrode. 25. A method of manufacturing an electrode, comprising: manufacturing the electrode from the precursor composition of claim 23. 26. A method for manufacturing an electrode, comprising: Forming a precursor composition containing an active material, and Electrodes are manufactured from the precursor composition. The method includes contacting a metal ligand complex with the surface of the active material, the metal ligand complex comprising at least one ligand coordinated to the metal ion, and The method further includes binding the metal ions to the surface of the active material via coordination bonds. 27. The method of claim 25 or 26, wherein the step of manufacturing the electrode comprises casting the electrode from the precursor composition. 28. Methods for improving electrode performance include: The surface of the electrode active material is brought into contact with a metal ligand complex, wherein the metal ligand complex includes at least one ligand that is coordinated and bonded to a metal ion; The metal ions therein bind to the surface of the active material through coordination bonds. 29. The method of claim 28, wherein the electrode exhibits improved performance compared to an untreated electrode, and the improved performance is at least one selected from the group consisting of: higher first-cycle discharge capacity, higher first-cycle efficiency, and higher capacity after 500 deep charge/discharge cycles at 0.5C with 100% depth of charge. 30. The method of claim 29, wherein the improved performance is a higher capacity after 500 deep charge/discharge cycles at 0.5C with 100% depth of charge, and the capacity is at least 5% greater than that of the uncoated electrode.