EP1515807A4

EP1515807A4 - Conducting polymer-inorganic nanoparticle (cpin) nanoarrays and method of making same and a battery utilizing cpin nanoarrays

Info

Publication number: EP1515807A4
Application number: EP03724453A
Authority: EP
Inventors: Daniel Buttry; John M Pope
Original assignee: Blue Sky Group Inc
Current assignee: Blue Sky Group Inc
Priority date: 2002-05-06
Filing date: 2003-05-06
Publication date: 2005-11-23
Also published as: CN1665605A; WO2003095111A1; AU2003231313A1; EP1515807A1

Abstract

A conducting polymer-inorganic nanoparticle nanoarray is provided. Nanoparticles are formed and capped which provide enhanced properties to the nanoparticles and allow easier handling of them. The capping may be done when the nanoparticles are formed and may functionalize the nanoparticles. The nanoparticles are then bound to conducting polymers in order to produce an electrically conducting matrix which may in turn be electrically bound to a substrate to form an anode or cathode for a Lithium battery. In the matrix the nanoparticles are wired to each other electrically via the capping agent and/or the conducting polymer. The conducting polymer allows for repeated Li+ insertion in use as a battery anode or cathode.

Description

CONDUCTING POLYMER-INORGANIC NANOPARTICLE (CPIN)

NANOARRAYS AND METHOD OF MAKING SAME AND A BATTERY

UTILIZING CPIN NANOARRAYS

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to nanoparticles and nanoparticle composites and in particular to functionalized nanoparticles and nanoarrays and the use of the nanoparticles and functionalized nanoparticles.

As understood herein a nanoparticle is a particle of a compound having a diameter less than 100 nm. Nanoparticles have been used in various ways due to their high surface area and other features in medicine and material science. In the prior art the formation and subsequent handling of the nanoparticles has been problematic. In some instances the chemical compounds which make up the nanoparticle do not readily lend to the formation of aggregate particles of < lOOnm. In other instances the resulting nanoparticle can be readily made, however, the formed nanoparticle cannot be fully utilized due to the properties of the nanoparticle. The formation of Iron based nanoparticles is accomplished through laser ablation to form particles below lOOnm in diameter. However, the Iron nanoparticles have a large surface area and are highly reactive. These particles must be kept extremely dry and out of the presence of oxygen due to being pyrophoric.

It has been suggested that a way to solve the problem of handling is to encase the nanoparticles in salt compounds. The encasement of the particle creates a nanoparticle with a thick crust of another compound effectively limiting the uses of the nanoparticle and creating a much larger particle in the process. While handling is improved, the processing and ultimate use of the WP is greatly complicated.

In order to overcome these problems, it is submitted that to properly form and subsequently use or handle the nanoparticle, the nanoparticle during or after formation is connected/bound to another compound which provides the nanoparticle with stability in that the nanoparticle is nonreactive in the environment, and changes the nanoparticles chemical, physical, mechanical or electrical properties. To accomplish this, the nanoparticle is capped with the other compound. The term capped should be understood to include the chemical bonding of one or a plurality of molecules or compounds to the nanoparticle's surface.

In a preferred embodiment, this capping and other compound also functionalizes the nanoparticle. The functionalization may be for the connection of the nanoparticle to yet other compounds or materials to provide the nanoparticle with another or enhanced physical, chemical, mechanical or electrical property.

By functionalizing the nanoparticle through the capping, the nanoparticle may be handled with relative ease, stored and inserted, connected or bound to other compounds or components. One such functionalized nanoparticle is of nanoparticles of inorganic Li⁺ insertion compounds with an oligomeric chain of derivatives of polythiophene type of compound attached during or after formation. The capped nanoparticle exhibits handling and insertion properties. This type of nanoparticle may also be inserted into a array/matrix of a conducting matrix to form an electrochemical composite. This electronic array in turn utilizes the enhanced properties of the nanoparticle in order to provide desired electrochemical properties. In yet another preferred embodiment, the nanoparticle provides a degree of self assembly to the substrate, composite or array. This self assembly is accomplished via methods and structure described herein.

Such a formed/assembled electrically conductive substrate, composite or array may be used in the formation of a battery anode and/or cathode.

Another aspect of the present invention relates to, self-assembling conducting polymer-inorganic nanoparticle nanoarrays (CPIN nanoarrays): These CPIN nanoarrays are comprised of nanoparticles of inorganic Li⁺ insertion compounds that are "wired" together with oligomeric chains of derivatives of polythiophene. These nanoarrays have extremely high specific energy and specific power due to the unique structural characteristics that derive from the nanoarray. In particular, the use of nanoparticles in CPIN nanoarrays obviates many of the undesirable characteristics of the bulk inorganic Li⁺ insertion compounds.

Production of the inorganic nanoparticles via several approaches including: 1) gas phase reaction of inorganic precursors in a chemical vapor deposition reaction chamber to give homogeneous nucleation of nanoparticles and 2) solution phase sol-gel chemistry. The particles can be capped using capping agents designed to allow, for example, their incorporation into structured nanoarrays. The capped particles can be incorporated into CPIN nanoarrays using a matrix material comprised of, for example, polythiophene oligomeric chains that have been synthesized to bear capping groups and pendent groups suitable for accommodating Li⁺. A range of combinations of inorganic nanoparticles and/or CP oligomers are possible.

The resulting nanoarrays are electrochemically characterized, especially with respect to the reversibility of Li⁺ insertion and expulsion, the potential that prevails during charge and discharge and the current densities that can be attained. The nanoscopic nature of these materials shows electrochemical consequences (e.g. unusual kinetics). Various methods are used to characterize the structural, compositional and electrical properties of the CPIN nanoarrays, especially with respect to how these properties are influenced by the nanoscopic structure. The observed electrochemical behavior is correlated with the structural, compositional and electrical properties of the CPIN nanoarrays.

Lithium secondary batteries have extremely high theoretical specific energy and power. However, these properties have yet to be practically achieved, especially on the cathode side. This is primarily because the electrochemical characteristics of the cathodes in these batteries are limited by several unattractive properties of the compounds used in them. For example, a very common problem with these compounds is that they exhibit substantial volumetric and/or structural changes during repeated Li⁺ insertion and expulsion, with these changes often being irreversible. This can lead, among other things, to loss of electrical connectivity within the cathode resulting in loss of capacity, a phenomenon often called fade. Further, the degree of charging or discharging of such compounds is often purposefully limited to avoid such changes, resulting in specific energies that are well below theoretical values.

The Jahn-Teller distortion that occurs during reduction of manganese oxide is a classic example of a redox-driven structural change. A related example is the redox-driven transition to the (undesirable) spinel structure that occurs in several manganese oxides, even those that have been purposefully prepared to have different (and more desirable) initial structures. A final example is given by the fact that crystalline vanadium pentoxide can be reversibly reduced by one- electron, but not by more, unlike the amorphous xerogel and aerogel materials. A major reason for the irreversibility that occurs during extensive reduction of these transition metal oxides is these redox-driven structural changes. Binders, such as poly(vinylidene fluoride), are often added to address these and other mechanical issues. However, this is undesirable because it leads to a consequent reduction in the specific energy for the cathode.

A second problem with the compounds used in cathodes is that they often have relatively poor electronic conductivities. This is especially true for manganese oxides, materials that are currently receiving intense scrutiny as potential cathode materials. Because of this, carbon is added to enhance the conductivity, which also leads to a reduction in specific energy. A third problem with some cathode materials is that Li⁺ diffusion rates within the material are quite low, thereby limiting the specific power that can be achieved when bulk materials are used to form the cathode. The benefit of the issues described above is that several of the materials that (in theory) have attractive redox and Li⁺ insertion properties exhibit sub-par performance when they are used as bulk materials, especially on repeated cycling.

It is yet another aspect of the present invention to circumvent these undesirable properties. By employing CPIN nanoarrays whose electrochemical reversibility, specific energy and specific power are far superior to those of competing compounds, the problems are addressed.

Nanoscopic arrays of nanoparticles of capped inorganic Li⁺ insertion compounds can be produced, to embed them in matrices containing conducting polymers and or oligomers. Another aspect of the present invention is to characterize the relationship between the details of their structures, composition and electrical properties and their electrochemical behavior. The use of nanoscopic particles leads to several benefits. These include: Nanoscopic particles have critical nucleation radii (CNR) that are larger than the particle diameter. Structural transitions to thermodynamic sink structures (e.g. reversion of various manganese oxides to spinel) can only occur if the particle radius is larger than the critical nucleation radius for that phase. It is possible to eliminate such transitions by using nanoparticles with CNRs larger than the particle radius. This "freezes" the particle into its initially formed state, which may be amorphous or a metastable (or stable) crystalline state.

Charge accommodation of the nanoscopic particles will take place largely at the surface. For example, for a 1 n MnO_> particle, the fraction of Mn(IV) ions at the surface will be 0.5, while for a 10 nm particle it will be 0.05. Further, for a 10 nm particle the fraction of Mn(IV) ions within next-nearest neighbor distance of the surface is 0.75. Thus, a significant fraction of the lattice negative charge for nanoparticles during discharge is either at or very near the surface. This reduces the need for bulk diffusion of Li⁺, greatly increasing the charge and discharge rate of the cathode. This also reduces the volumetric changes and lattice stresses caused by repeated Li⁺ insertion and expulsion.

With nanoscopic particle sizes, the Li⁺ diffusion distances will be significantly reduced. For example, for a 10 nm particle and a bulk diffusion coefficient of Li⁺ in typical insertion materials of approximately 10"¹⁰ cm²/s, the time required for Li⁺ to diffuse a distance equal to the particle radius is 2.5 x 10^~3 s. Thus, Li⁺ diffusion within the particle to compensate reduction of non-surface Mn sites is not a significant kinetic barrier during cycling.

The surface functionality (capping agent) can prevent agglomeration of the nanoparticles, inhibit nanoparticle dissolution and allow the use of rational self- assembly processes when assembling the cathode. Prevention of agglomeration by capping for V2O5 will be described below. Capping will passivate the nanoparticle toward dissolution and other chemical processes. Dissolution is a common problem for various manganese oxides. Finally, and most importantly, capping provides a chemical "handle" that can be used to direct the self- organization of the CPIN nanoarray (e.g. in a self-assembly process). This will be discussed in considerable detail below.

In addition to these properties of the nanoparticles themselves, there are also significant benefits that derive from their incorporation into CPIN nanoarrays. These include:

Wiring the nanoparticles can obviate the need to add carbon filler and ensure good electronic addressability of all of the nanoparticles in the nanoarray. This reduces both the ohmic losses across the cathode and the loss of contact that often results in capacity fade for cathodes. Wiring is considered herein as binding of the nanoparticle to a substrate matrix, composite and/or other nanoparticles electrically.

Nanoscopic particles surrounded by a relatively elastic conducting polymer matrix are sufficiently resilient to reversibly accommodate the volumetric changes that occur during Li⁺ insertion and expulsion. This is important to developing cathodes than can reversibly accommodate large amounts of Li⁺.

Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a nanoparticle reactor;

Fig. 2 shows a photograph of uncapped and capped V205 nanoparticles; Fig. 3 shows a bridged system of nanoparticles;

Fig. 4 shows one embodiment of a synthetic route for a capping compound for a nanoparticle;

Fig. 5 shows a second embodiment of a synthetic route for a capping compound for a nanoparticle;

Fig. 6 shows a third embodiment of a synthetic route for a capping compound for a nanoparticle;

Fig. 7 shows a NMR spectra of a series of Li_xV2θδ xerogel samples at various stages of Li⁺ insertion;

Fig. 8 shows a self assembling matrix system; and

Fig. 9 shows a functionalized nanoparticle.

DETAILED DESCRPTION OF THE INVENTION

A detailed description of the approaches that are used to produce CPIN nanoarrays including the nanoparticles is discussed below.

Nanoparticle Synthesis

Many ways of producing the nanoparticles are envisioned. One particularly useful method of manufacture is via formation in a CVD reactor. The precursors for the nanoparticles may include several compounds which react or bind within the reactor. The apparatus and method using a sole precursor for production is discussed below.

A method of manufacturing the nanoparticles is described but is not meant to limit the envisioned methods of producing the nanoparticles. A unary precursor nanoparticle process reactor is described by its operation. Examples of typical reagents may include but are not limited to the following examples: vanadium oxytriethoxide, aluminum isopropoxide, titanium (IV) isopropoxide, tantalum (V) ethoxide.

This description pertains to the typical operation of the unary precursor particle apparatus for the generation of nanoscopic powders as shown in Fig. 1. The particle precursor material 5 is placed in the precursor vessel 2. Typically these materials are liquids however solids may be used also. The precursor vessel may be heated or cooled to control the vapor pressure of the precursor as appropriate for the precursor in use with a heating element 6. Importantly this allows, via a mass flow controller 3, for metered isobaric delivery of the precursor into the reactor tube 4. Additionally, metering of the precursor by the mass flow controller controls the flow rate of the precursor which, in turn, determines the residence time of the precursor in the heated reactor tube. The residence time is important as this is the time the precursor has to react in the heated zone 7 of the reactor tube. The residence time required for decomposition is dependant on the decomposition kinetics of each precursor. The precursor vapor thus is delivered into the top of the reactor tube. The reactor tube is heated with multi- zone heating elements 8 to allow precise control of the temperature regime along the length of the tube.

The temperature profile of the tube is chosen to affect decomposition of the precursor within the tube. Temperature is typically in the range 300-600 degrees centigrade. Process pressure is carefully controlled and monitored continuously. The pressure is typically maintained in an isobaric manner within a range from 1-50 torr. Process pressure control is achieved by means of an inline throttling valve 9 upstream of the vacuum pump 10. This valve is slaved to a pressure gauge/pressure controller combination 12. Process temperature, pressure and precursor flow rate together control the desired size, morphology, dispersity and extent of agglomerization of the material obtained. Homogenous nucleation of particle growth during precursor decomposition is also realized by the careful control of these parameters. Following particle formation within the reactor tube, a sintered glass disc 11 in the particle trap 13 sequesters the nanoparticulate material. Prior to capture, if desired, particles may be in-flight capped by introduction of the vapor of a capping agent. The amount of cap vapor is controlled in a fashion comparable to the particle precursor reagent. Finally, the collected particles may be recovered directly from the trap. Alternatively, three isolating valves 14, 15, 16 may be closed and the material within the trap handled appropriately if anaerobic handling conditions are required.

Nanoparticles in the 10 to 50 nm size range have been produced. Figure 2 shows TEM images of V2O5 nanoparticles produced via homogeneous nucleation in a CVD reactor. The precursor for these nanoparticles, VO(OCH2CH3)3, was reacted with O2 and H₂0 at low pressure and 400 °C under carefully controlled mass flow conditions to give the nanoparticles shown on the left. The CVD reactor can be run under a variety of conditions to give samples of varying properties. The image on the right of Figure 2 shows nanoparticles that have been capped using SiCl(CHs)3. This capping was done after the nanoparticles were produced via simple exposure of the nanoparticles to the capping reagent in dry toluene. These nanoparticles have been extensively characterized using FTIR, UV-VTS, TEM, electrochemistry and elemental analysis. As can be seen, capping stabilizes the nanoparticles toward agglomeration. Other methods and apparatuses of production are also envisioned for the nanoparticles being produced. A schematic of a surface of a typical capped nanoparticle is shown in Fig. 9. The surface has several molecules or compounds bound to it to functionalize the nanoparticle. Several types of inorganic oxide nanoparticles are produced using the CVD approach, including manganese oxide, vanadium oxide, nickel oxide and cobalt oxide. The third and fourth can be prepared using organometallic precursors, such as the acetates and 2,4-pentanedionates. It is also possible in this reactor to produce mixed metal nanoparticles, given the attractive properties for mixed systems.

Size control of the nanoparticles is readily achieved using temperature and mass flow rate control, both of which are incorporated into the CVD reactor. Note that CVD is usually used for heterogeneous thin film growth. However, due to the control, homogeneous nucleation within the reactor is a possibility.

Inorganic oxide nanoparticles using solution phase approaches are also produced. For example, sol-gel method for producing ZnO nanoparticles. An attraction of this method is that it gives nanoparticles that are weakly capped with poly(vinylpyrrolidone) (PVP). This amide-based capping agent is not strongly bound and is easily displaced by other more strongly coordinating capping agents. Thus, this approach can be used to produce nanoparticles that are easily handled, and can be capped with other reagents during the nanoarray assembly. Several other solution phase approaches are available for producing insertion oxides for Li⁺. In many cases, they produce nanoparticulate materials. Both CVD and solution phase production methods give us the widest possible access to the various types of inorganic oxides that are of use.

Molecular Bridges for CPIN Nanoarray Construction

In many respects, synthesis of the thiophene oligomers is important. The oligomers bear capping groups at both ends and some have pendent groups designed to facilitate Li⁺ diffusion within the material. Bridges are produced that will allow capping of the nanoparticles such that they form 3D structures with high electronic and ionic conductivities and high capacity toward Li⁺ insertion. The structure in Fig. 3 shows an example of a simple bridged system. In this case, a sexithiophene molecular "wire" is used to electronically bridge the nanoparticles while the capping is achieved using the same type of silane coupling chemistry already employed (as in Fig. 2). Other capping chemistries are available. Note that the bridge serves several important purposes including direction of the self-assembly of the nanoarray, stabilization of the nanoparticles and maintenance of the electronic conductivity of the nanoarray. Other bridges to be described below also have structures designed to facilitate Li⁺ accommodation, and to produce capping that is either irreversible (as for the silane system) or moderately reversible.

The sexithiophene system is focused on for several very important reasons. First, there is a rich and varied synthetic chemistry for this material and its derivatives, primarily due to its attractive optical and electronic properties. Second, the six ring system is just large enough to stabilize the cation radical formed during p-doping of the material. Thus, it has very good stability toward repeated oxidation and storage in the p-doped state. Third, the length is just sufficient for bridging between nanoparticles in the 10-50 nm size range. Also, oligomeric ring systems with 2-6 rings between metallic nanoparticles give excellent electronic coupling. A similar approach is suitable for oxide nanoparticles. Fourth, poly(thiophene) and its oligomers are p-doped at potentials that are in the right range (ca. 0.3-0.9 V vs. SCE) to allow them to store charge just as do the Li⁺ insertion compounds in Li secondary battery cathode. Thus, they add charge storage capacity to the material, rather than detracting from it, as is the case for carbon and elastomeric additives.

We turn now to a discussion of the molecular wires that will be synthesized as part of this effort. The first synthetic scheme (as in Fig. 4) shows one synthetic approach to a sexithiophene that bears pendent ether groups and has carboxylic acid (or carboxylate) terminal groups suitable for capping a wide variety of transition metal insertion oxide nanoparticles. This synthesis is a combination of several methods for thiophene oligomer synthesis. These use the widely applied Stille cross coupling reaction. This route uses aldehyde end- capped oligomers. It is particularly noteworthy that the bis(ether)bithiophene is the starting material. The presence of the ether groups pendent from the rings endows this bridge with the ability to accommodate Li⁺ within the interparticle region. This property distinguishes it from the simpler bridge shown in Fig. 5. In addition, the solubility of the oligomers that bear side chains is substantially higher than that for the simple end-capped sexithiophenes. This endows these compounds with distinct advantages when they are being used to produce CPIN nanoarrays, since the various assembly steps will be easier to carry out with more highly soluble bridges.

We have designed an additional route to the target bridge that is based on a slightly different synthetic strategy. The first reaction sequence is shown in Fig. 5; the second is shown in Fig. 6. In this case, protected ester groups are produced prior to the cross coupling reaction. These are then hydrolyzed to the carboxylate. These are similar to the simple silane-capped derivatives shown in Fig. 6 in that their solubility is lower than those bearing side chains. The behavior of these carboxylate-capped sexithiophenes (i.e. without the pendent ester functionalities) is compared with that of the este -bearing derivatives. Enhanced Li⁺ accommodation for the latter is evidenced by lower ionic resistivity, which can be assessed using electrochemical impedance measurements. Finally, several other end-capped oligothiop enes have been prepared, including an aminomethyl derivative. This compound may be suitable for serving as a molecular bridge for transition metal oxides that prefer hard Lewis acid donors, such as high valent Co and Ni. Also, the fact that it is unidentate allows that its binding is more reversible than that of the bidentate carboxylates. This has implications for the assembly approaches that can be used, as described below.

Assembly of the CPIN Nanoarrays

There are several strategies to CPIN nanoarray production. In all, we seek to allow the systems to organize spontaneously via self-assembly processes. In one, the bridges are attached first, followed by assembly. In another, the nanoparticles are assembled prior to attachment of the molecular bridges. In a third, the nanoarrays are grown by sequential layer-by-layer methods. These are described in detail below. Other methods of nanoarray production are also contemplated.

1. Prior Assembly

This approach relies on low temperature physical methods that produce aggregation and/or assembly of the nanoparticles. These include simple solvent evaporation, use of capillary forces and flow induced assembly. Some approaches to self-assembly of colloidal materials produce colloidal "single crystals." In many cases, control of the concentration of the nanoparticle solutions is required prior to these steps. This can be done using centrifuge-redisperse cycles or simple solvent evaporation-redispersion. We also envision using dialysis procedures using very low MW-cutoff membrane materials to produce highly concentrated nanoparticle solutions. All redispersion approaches may require that some measure of coordination from the solvent (or other intentionally added reagent) occur so as to break up interparticle interactions.

Coordinating solvents may be needed to disperse the nanoparticles from the agglomerated states they will be in after synthesis. This will be especially true if the nanoparticles have not been purposefully capped after synthesis. Suitable solvents include THF, acetonitrile (ACN) and various amide solvents (NMP, DMF, formamide), since these are all weakly coordinating. It is important that the solvents not be too strongly coordinating, since they must be displaced by the capping groups at the ends of the sexithiophene bridges during final assembly.

A typical sequence of events for the "prior assembly" method would be the following. First, the nanoparticles would be synthesized using either CVD or solution phase techniques. In both cases, they would be isolated as powders. They would then be redispersed in a weakly coordinating solvent, such as ACN, using ultrasonic irradiation to assist in dispersion if necessary. An aliquot of this solution would be placed on a substrate (e.g. indium-tin oxide glass, mica or a Au thin film with a monolayer of mercaptoundecanoic acid (MUA), which presents carboxylate groups to the solution), and assembly would be allowed to take place in an atmosphere that is nearly saturated with respect to the dispersion solvent. This latter condition is important, because it will ensure that assembly takes place very slowly, which may be necessary to achieve good organization. Assembly is then driven by capillary forces that are accentuated as the volume fraction of nanoparticles increases during solvent evaporation. This general approach has proven to produce nearly perfect single crystal colloidal multilayers over quite large areas for particles in the 100-700 nm range. We use it with much smaller particles (10-50 nm). Thus, considerably lower temperatures may be needed in order to reduce the disordering influence of Brownian motion.

Capping is achieved by exposure of the array to the oligomeric bridge under conditions that will not allow for wholesale dissolution of the array. In one such configuration the array is sandwiched between its own substrate (ITO, mica or SAM-coated Au on mica) and an equally flat, chemically inert second substrate. In the case of mica substrates, the extreme flatness will assist in confining the array. Then, the edge of the sandwich is exposed to a solution of the bridging agent which will be dissolved in a non-coordinating solvent, such as CH2CI2, which is known to dissolve the α-ω-disubstituted aldehyde sexithiophene derivative. In this way, the molecular bridge is allowed to diffuse slowly into the nanoarray, but the confinement and poorly coordinating solvents may prevent dissolution. Either reversible (e.g. carboxylate) or irreversible capping (e.g. silane) can be achieved in this way. Following this treatment, the nanoarray is structurally stable, allowing examination with the characterization methods described below.

2. Prior Attachment of Bridges

In this approach, the α-ω-disubstituted sexithiophene bridging agents are combined with the nanoparticles in solution. There are at least two limiting situations in which this combination can be conducted. In the first, the nanoparticle solution is added slowly to a solution of the molecular bridge. This produces solutions in which the nanoparticles are surrounded by a large number of bridging agents. The number is controllable based on the relative stoichiometries of the bridges and the nanoparticles. These can then be assembled using the methods described above. We believe that this approach is superior to the method described above for several reasons. First, it allows for efficient dispersion of the nanoparticles prior to assembly. Second, it allows for stabilization of the nanoparticles via capping. Third, when the nanoarray is produced, the presence of the bridges will cause the system to establish interparticle distances that are optimized with regard to the length of the bridges. In this case, the initial physical processes that bring the nanoparticles into close proximity are capillary forces that are essentially the same as those described above. However, after the nanoparticles approach each other to molecular scale distances, the α-ω-disubstituted molecular bridges connect the particles. This establishes the interparticle distance and locks the nanoarray into this structure.

The second limiting case in this strategy involves adding the molecular bridge solution to a solution of the nanoparticles. In this case, both ends of a given oligomer will be immediately attached to nanoparticles, producing a dimeric species. Further addition ultimately produces trimers, tetramers, etc. until large aggregates are formed. At some point, these will not be stable in solution, and precipitation occurs. Such a sequence may not give high quality nanoarrays with long range order. However, order may not be a requirement for desirable electrochemical behavior with respect to Li⁺ insertion. Having produced CPIN nanoarrays via the methods described above, we proceed to characterize them using several techniques available.

A typical self-assembling array is shown in Fig. 8 when the polymers are dispersed with the nanoparticles and the self assemble into the array by the polymer interacting with the nanoparticles. The polymers also bind to an electrically conducting substrate.

3. Layer-by-Layer Growth

This method is based on the use of layer-by-layer methods to produce nanoarrays of Au or Ag nanoparticles using sulfur adsorption or Tiθ2 embedded in a polymeric material. A typical protocol is to first prepare a suitable substrate, such as MUA adsorbed on Au (on mica, Si or glass). This substrate is exposed to a dispersion of the uncapped nanoparticles in a weakly coordinating solvent. This leads to adsorption of a first layer of nanoparticles, producing a 2D nanoarray. This is then immersed in a solution of an α-ω-disubstituted sexithiophene, which adsorbs onto the nanoparticles, producing a surface that bears the functional group for that capping agent. This surface is then exposed to the nanoparticle solution again, yielding adsorption of a second layer of nanoparticles. This process can be repeated many times to build up multilayer CPIN nanoarrays.

An advantage of this method is that it is relatively straightforward.

Characterization of CPIN Nanoarrays

Electrochemical Characterization

There are several electrochemical properties that are important to the successful implementation of these CPIN nanoarrays as cathodes in secondary Li⁺ batteries. First, the electrochemical insertion and expulsion of Li⁺ should be fully reversible for many cycles. Second, the potential range over which this occurs should be attractive from the standpoint of use in a Li⁺ secondary battery. Also, this potential should remain relatively stable, especially during discharge. Third, the current density that can be attained should be high, especially during discharge, but ideally during both charge and discharge. These properties can be measured in a straightforward way using traditional electrochemical techniques. Galvanostatic charge-discharge cycling is the most useful method to address the properties listed above. However, ac impedance methods can be very fruitfully applied to develop an understanding of both the ionic and electronic conductivity of thin film samples. Specific electrochemical techniques to be used include cyclic voltammetry for survey work; charge-discharge curves for quantitative assays of charge capacity, discharge potential, and long term reversibility; and ac impedance for characterization of electronic and ionic conductivity.

Several interesting effects are seen in the electrochemical behavior of these materials. First, strong kinetic manifestations of the nanoscopic nature of these particles may be seen. This is caused by the fact that the electrical double layer becomes comparable in length scale to the diffusion layer. Such effects may manifest as very slow apparent electron transfer rate constants for the materials.

A second effect that may be observed for nanoarrays comprised on extremely small nanoparticles is a type of Coulomb trapping effect. This effect can result when the small size of a particle leads to discrete steps in its potential due to capacitive charging effects. In ensembles, it is only observed when the nanoparticle size is extremely monodisperse. The CPIN nanoarray systems are examined for such effects.

Additional Characterization Methods

In addition to electrochemical characterization, we employ a suite of other methods that allow us to fully characterize the structural, compositional and electrical properties of the CPIN nanoarrays. This is important in order to be on sound footing when interpreting the electrochemical behavior for the different structures discussed above. The tools that are applied here include elemental analysis, XRD, SEM-EDS, TEM, FTIR, UV-VIS, ellipsometry, dynamic light scattering, electrical conductivity and TGA/DSC.

Under favorable conditions, a EQCM method allows for measurement of mass gain and loss during redox cycling of thin films. The highly crosslinked nature of the CPIN nanoarrays leads them to behave as rigid films. This is the condition required for use of the EQCM to measure mass changes.

One of the EQCM experiments is the dissection of Li⁺, anion and solvent transport via use of isotopically substituted species, such as ⁶Li⁺ vs. ⁷Li⁺, and deuterated vs. protiated solvents. Measurements of solvent swelling will be important to understanding how the mechanical properties of the polymer matrix influence the accommodation of the reversible volumetric changes that accompany Li⁺ insertion and expulsion, since the swelling provides an indirect measure of the film's mechanical properties.

There is one particularly interesting aspect of the behavior of CPIN nanoarrays that we intend to examine in some detail. The charge compensation processes in such a material will almost necessarily require mixed transport. Consider the material in its fully oxidized form. The inorganic nanoparticles should be electrically neutral, so they will have no counterions. However, the molecular bridges will bear positive charges by virtue of the fact that they will be p-doped. Thus, the material will contain anions under these conditions. Reduction will cause the neutralization of (at least some of) the molecular bridges, which should lead to anion expulsion. Simultaneously, electron injection into the inorganic nanoparticles will require charge accommodation by Li⁺ insertion. Thus, the overall dynamics of the charge-discharge process will be strongly influenced by ionic motion. Understanding how this motion can be controlled by manipulating the CPIN structure is a goal of the characterization. The EQCM measurements, coupled with information from ac impedance experiments, allow us to dissect the effects of ionic motion on the charge- discharge rates in these materials. We turn now to a very brief discussion of NMR as a tool for characterization of Li⁺ insertion compounds.

We have used solid state NMR methods to characterize Li⁺ insertion compounds, such as V2O5, using ⁶Li, ⁷Li and ⁵¹V NMR. This tool allows for facile compositional assessments, study of the structural aspects of Li⁺ insertion (e.g. are there multiple sites at which Li⁺ interacts with the nanoparticles?), and Li⁺ mobility. A unique capability of this method is its ability to probe the distances between electronic spins (either on nanoparticles within the nanoarrays or on the conducting polymer chains) and the various nuclei being examined. Thus, it is ideally suited to the systems we describe here because the length scale over which such interactions are relevant matches the range of the feature sizes of the CPIN nanoarrays. Specifically, we believe we can obtain direct , measurements of the distances between electronic spins and nuclear spins via measurement of their dipolar interactions. Such measurements would be the first of their kind for nanostructured arrays such as those described here. Additional, more routine measurements that can be made using solid state NMR are the characterizations of composition and bond connectivity of the capping agents.

Shown in Fig. 7 the ⁷Li NMR spectra of a series of Li_xN2θs xerogel samples at various stages of Li⁺ insertion (with x = 0.03 (lower), 0.17, 0.55, 0.84, 0.98). These spectra clearly show two resonances, one sharp and one broad. One possible interpretation is that the sharp band is from Li⁺ that is present at surface sites within this high surface area V2O5 xerogel material. To use ΝMR to detect such surface states, then ΝMR may prove to be an extremely valuable tool for assaying the degree to which Li⁺ charge compensation of the nanoparticles occurs by insertion versus simple presence at the particle exterior.

The broader band is due to paramagnetic broadening of some of the charge compensating Li⁺ species. These are likely Li⁺ that have intercalated into the material and are in close proximity to the paramagnetic vanadium (IV) sites. It is possible to use such data to calculate the distances between the Li⁺ species and the paramagnetic sites. This helps us understand if the Li⁺ species are inside of the inorganic nanoparticles or outside, and under what conditions these two states occur. Thus, use of such data helps us understand how the details of local structure influence the Li⁺ in these CPIΝ nanoarrays. The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.

Claims

WHAT WE CLAIM:

1. A process comprising,

forming a plurality of nanoparticles

functionalizing the nanoparticles by binding a compound or molecule to the surface of the nanoparticles,

binding the nanoparticles, the compounds or the molecules to conducting polymers, and

binding the conducting polymers to other nanoparticles, compounds or molecules to thereby form an electrically conducting matrix.

2. A process according to claim 1, wherein the matrix is self-assembling.

3. A process according to claim 1, wherein at least some of the conducting polymers are electrically bound to an electrically conducting substrate.

4. A method of making a composition of matter, comprising;

forming a nanoparticle,

chemically bonding at least one molecule to the nanoparticle substantially during the formation of the nanoparticle to thereby form the composition of matter

wherein the nanoparticle with the chemically bound molecule is more stable than the nanoparticle alone.

5. The method according to claim 4, wherein the nanoparticle is an inorganic Li+ insertion compound.

6. The method according to claim 4, wherein the at least one molecule is an oligomeric chain of derivatives of polythiophene type of compound.

7. A process according to claim 1, wherein the nanoparticles are inorganic Li⁺ insertion compounds.

8. A process according to claim 1, wherein the compounds or molecules are SiCl (CH₈)a.

9. A process according to claim 1, wherein the conducting polymers are oligomeric chain of derivatives of polythiophene type of compound.

10. A method of functionalizing nanoparticles, comprising;

forming the nanoparticles,

chemically binding a compound or molecule to the surface of the nanoparticles to thereby enhance the use of handling the nanoparticles or enhance the nanoparticles physical, chemical, electrical or mechanical properties.

11. A method according to claim 10, wherein the nanoparticles are inorganic Li⁺ insertion compounds.

12. A composition of matter comprising;

a compound or element in a plurality of nanoparticles, and

a conducting polymer bound to the surface of the nanoparticles or to an intermediate compound or molecule which is bound to the surface of the nanoparticles.

13. A composition of matter according to claim 12, wherein the nanoparticles and conducting polymer are electrically connected to thereby form a matrix having the nanoparticles electrically connected to each other.

14. A composition of matter according to claim 12, wherein at least some of the conducting polymers are electrically connected or bound to an electrically conducting substrate.

15. Functionalized nanoparticles comprising;

A compound or element in the form of a plurality of nanoparticles, and

A compound or molecule physically or chemically bound to the surfaces of the nanoparticles,

Wherein the compound or molecule allows the nanoparticles to be more easily handled or processed and substantially prevents agglomeration of the nanoparticles.

16. Functionalized nanoparticles according to claim 15, wherein the compound or molecule facilitates a connection of the nanoparticles to another compound.