The improvements generally relate to the field of energy storage devices, and more specifically to pseudocapacitive batteries.
Electrochemical capacitors combine both electric double layer (EDL) and Faradaic mechanisms to maintain high power densities, but at energy densities that exceed the performance of purely EDL-based capacitors. This improvement is often accomplished by utilizing redox-active nanoparticles at the electrode surface, which store additional electrons in a Faradaic manner that mimics EDL charge storage “pseudocapacitively.” It is desirable to maintain the high power performance of electrochemical capacitors while pushing towards the energy density regime typically occupied by batteries. A great deal of research is currently focused on realizing a high performance pseudocapacitance energy storage enabled by nanomaterials. However, despite extensive experimental activity, the physics which underlie a pseudocapacitive response in a given nanomaterial system are not well understood. Recently, it was proposed that suitably engineered conducting nanoparticles might be tailored to exhibit a near ideal pseudocapacitive response through the use of “quantized capacitance”—an observable Faradaic mechanism in nanoparticles arising from electron-electron interactions related to Coulomb blockade. However, the energy and power density capabilities of “quantized capacitance” have yet to be fully explored.
Therefore, improvements are needed.
In accordance with one aspect, there is provided an energy storage device, comprising a first electrode having a plurality of electrons stored thereon, a second electrode having a plurality of holes stored thereon, the second electrode spaced from the first electrode to define a volume therebetween, a supporting medium disposed in the volume between the first electrode and the second electrode, the supporting medium comprising at least one counterion species, and a plurality of nanoparticle elements provided in the volume, adjacent at least one of the first electrode and the second electrode, the plurality of nanoparticle elements configured to store the electrons therein at different energy levels using quantized capacitance.
In some embodiments, the plurality of nanoparticle elements are made of at least one of carbon, semi-metallic elements, semiconducting elements, and metallic elements.
In some embodiments, each nanoparticle element of the plurality of nanoparticle elements has a size distribution lower than 100 nm.
In some embodiments, each of the first electrode and the second electrode comprises a current collector, and the plurality of nanoparticle elements are deposited onto the current collector of at least one of the first electrode and the second electrode.
In some embodiments, at least one of the first electrode and the second electrode comprises a current collector coated with a conductive material, and the plurality of nanoparticle elements are deposited onto the conductive material.
In some embodiments, the plurality of nanoparticle elements are embedded or dispersed in the supporting medium.
In some embodiments, the supporting medium is one of an electrolytic medium and a dielectric medium.
In some embodiments, the supporting medium is in at least one of a liquid state and a solid state.
In some embodiments, the supporting medium is an immiscible electrolyte.
In some embodiments, the supporting medium is one of static and non-static.
In some embodiments, the plurality of nanoparticle elements are configured to be displaced within the supporting medium.
In some embodiments, the first electrode and the second electrode are printed onto a substrate.
In some embodiments, the first electrode, the second electrode, and the supporting medium are made of a flexible material.
In some embodiments, the plurality of nanoparticle elements are separated from one another by the supporting medium.
In some embodiments, the plurality of nanoparticle elements comprises a first plurality of nanoparticle elements and a second plurality of nanoparticle elements, the energy storage device further comprising a separating member disposed within the volume at a substantially equal distance from the first electrode and the second electrode, the separating member configured to separate the first plurality of nanoparticle elements from the second plurality of nanoparticle elements.
In some embodiments, the energy storage device further comprises a network of conductive material provided within the volume between the first electrode and the second electrode, the plurality of nanoparticle elements distributed within the network of conductive material.
In accordance with another aspect, there is provided a method for providing an energy storage device. The method comprises providing a first electrode having a plurality of electrons stored thereon, providing a second electrode having a plurality of holes stored thereon, spacing the second electrode from the first electrode to define a volume therebetween, disposing a supporting medium in the volume between the first electrode and the second electrode, and providing a plurality of nanoparticle elements in the volume, adjacent at least one of the first electrode and the second electrode, and separated from one another by the supporting medium, the plurality of nanoparticle elements configured to store the electrons therein at different energy levels.
In some embodiments, providing the plurality of nanoparticle elements in the volume comprises depositing the plurality of nanoparticle elements onto a current collector of at least one of the first electrode and the second electrode.
In some embodiments, providing the plurality of nanoparticle elements in the volume comprises depositing the plurality of nanoparticle elements onto a conductive material coated on a current collector of at least one of the first electrode and the second electrode.
In some embodiments, providing the plurality of nanoparticle elements in the volume comprises providing a network of conductive material within the volume, and distributing the plurality of nanoparticle elements within the network of conductive material
Many further features and combinations thereof concerning embodiments described herein will appear to those skilled in the art following a reading of the instant disclosure.
In the figures,
Herein, it is proposed to improve energy density and power density storage capabilities for an electrochemical system, and more particularly provide a combination of high power density and high energy density, making use of quantized capacitance and its pseudocapacitive features. As used herein, the term “energy density” refers to how much energy a given system stores, while the term “power density” refers to how fast the system charges and discharges. The level of energy density and power density achievable by a given system may vary depending on the application.
Using suitably sized engineered nanostructures may allow to boost the energy storage of electrons across a wide voltage range (i.e., with the entire voltage range, whose value may vary depending on the application, being used to store energy) and such energy storage can in turn be employed as a pseudocapacitive battery or in devices such as capacitors, conventional batteries, flow battery designs, and the like. As used herein, the term “pseudocapacitive” refers to the successive storage of charge through multiple electron transfer events (often referred to as Faradaic) in an electrochemical system that mimics the current-voltage properties of a classical capacitor. For instance, a specific application of the energy storage device proposed herein may be to replace the metals in existing energy storage devices with carbon materials during electrode manufacturing, thereby allowing to engineer metal-free batteries and to resolve sustainability challenges. Existing manufacturing processes used for existing battery technology or energy storage systems of similar configuration (e.g., ultracapacitors) may be adapted for application to the energy storage device described herein.
In
The investigation is motivated by developments in the usage of graphitic nanoparticles, where these particles have been utilized electrochemically to great effect by tuning both their dimensionality and laminate packing. It has also been shown that carbon nanostructures can store high densities of electrons. Additionally, from a pseudocapacitive perspective, graphite or graphene is a bulk conductor, which through sufficient nanostructuring can provide quantized capacitance charging states that are accessible electrochemically. Moreover, graphitic nanoparticles can be resolved down to one atomic layer such that all atoms equally participate in charge storage. In other words, there is no internal region in such a two-dimensional (2D) material and therefore the charge storage as function solely of the nanoparticle volume is maximized compared to, for example, a conducting sphere, where net charge aggregates towards the surface. Driven by these developments, a quantized capacitance energy storage scheme is proposed herein.
In particular, an energy storage device having at least one of its electrode terminals modified to utilize a mechanism (referred to herein as the “Coulomb blockade” mechanism) is proposed herein. In turn, energy storage of various systems may be enhanced using the systems and methods described herein. As used herein, the term “Coulomb blockade” refers to the energetic quantization of electron addition and removal in suitably sized engineered nanostructured materials. In energy storage devices, electrons are transferred to and stored in the nanostructured materials. Forced to be in close proximity to each other in such nanostructured materials, electrons experience strong mutual repulsion. Hence, the next electron is to be added at a higher voltage level than previous electrons. This leads to a split in the system's energy level (referred to herein as “energy level splitting”) at equal distance over a wide voltage range, allowing for increased electron storage potential within the nanostructured materials. The term “Coulomb blockade” thus refers to the manner in which electrons are stored at different energy levels in the nanostructured materials. As used herein, the term “quantized capacitance” refers to a process via which Coulomb blockade is used to store energy.
In general, the Coulomb blockade mechanism can be realized in a device that stores a matching number of charges on both of its electrode terminals (the charges on both terminals being of opposite polarity), where at least one of the terminals is modified with conducting or semi-conducting nanoparticles or nanostructures (referred to herein as “nanostructured elements” or “nanostructured materials”). As will be described below, it is thus proposed herein to construct at least one of the energy storage device's electrode terminals of conducting or semi-conducting nanostructured elements that utilize the Coulomb blockade mechanism. It is further proposed herein for the energy storage device to include a supporting medium (which may be a dielectric or electrolytic media) in which the nanoparticle elements may be partially or fully embedded, which provide a reorganization response with the addition or removal of electrons from such a nanostructure. The nanostructured elements may also be separated by non-conducting media to allow for electron tunneling and storage, to promote electron-electron interactions in such a nanostructure. As will be described further below, the non-conducting media may be made of a non-conducting material including, but not limited to, a Solid Electrolyte Interphase (SEI) layer, electrolytic media, coating, core-shell, ligand, grafting, or non-conducting layer. The design of the device's electrode and criteria to engineer the device's components will be described further below.
To explore the physical feasibility of a quantized capacitance storage mechanism, the volumetric energy density limits that would be provided by this scheme are first described with reference to
Fundamentally, the volumetric energy storage density of a system is a product of the density at which electrons are stored and the voltage V at which the electrons are placed. In a capacitive system, this is summarized by E=½CV2=½QV, where C is the capacitance and Q is the charge stored (Q=CV). In one embodiment and as illustrated in
Nanoscale graphitic systems can store one (1) electron for approximately every ten (10)_carbon atoms. This achievable ratio, when applied to graphene or graphene nanodisks as in 202, results in a surface electron storage density of σe≈4 q/nm2, where q=1.6×10−19 C is the elementary charge. Although this electron density is less than the theoretical maximum of fully intercalated graphite in batteries, it is still a significant storage density for supercapacitor systems. To induce quantized capacitance, it is desirable for a nanoparticle to be separated from other similar particles by a supporting medium 206 (also referred to herein as an “electrically insulating medium”), since this promotes electron-electron interactions and enables one to tune the storage voltage. The dielectric properties of the insulating medium 206, which may be a dielectric media or an electrolyte, also impact the voltage storage properties associated with quantized capacitance, as will also be discussed further below. The supporting medium 206 can be as thin as 1 nm. Thus, when combining the proposed graphene nanodisks 202 with a supporting medium 206 separating the nanodisks 202, one obtains the electron density trend presented in plot 300 of
It is desirable for the electrolyte fraction present in the porous electrode to be assessed because, to arrive at a plausible energy storage technology, it is desirable for the packing density of nanoparticles to be increased (compared to existing approaches). This is desirable to increase volumetric energy densities via the energy storage mechanism proposed herein, similar to the manner in which it is desirable to increase the molar concentration of redox species to increase the volumetric energy density in a flow battery. An effective thickness (d) for a graphene nanodisk as in 202 corresponding to d≈0.4 nm, roughly equal to the spacing between graphite sheets, is assumed, and the total volume is varied from 2 times to 20 times the reactant (nanodisks) volume. Accordingly, at a storage voltage of Vd=5 V, one obtains the volumetric energy density trends presented in plot 300 of
It is noted that a factor of ¼, being the product of two ½ multipliers, is appended to the energy density expression in Eq. (1). The first ½ multiplier from the equal volume of opposite charge that is to be stored at a cathode of the energy storage device. The second ½ multiplier arises from the manner in which charge is stored via quantized capacitance, being added in equal degrees at higher and lower voltages for a given terminal, just like a regular capacitor. From the plot 300 of
An overview on the mechanism giving rise to quantized capacitance (i.e. referred to herein as the “quantized capacitance redox mechanism”) will now be provided. The primary energy density assumption is that the redox potentials of nanoparticles exhibiting quantized capacitance can be pushed towards encompassing a bias window of near 5 V. This is arguably the maximum achievable bias window for most state-of-the-art electrolyte systems. The manner in which energy storage at this voltage limit of near 5 V may be accomplished via quantized capacitance will now be described.
When an electrode is biased towards electron storage, the potential difference will raise the Fermi energy level in the electrode relative to nanoparticles in the electrolyte, as shown in
A tunneling electron transfer process between the electrode and nanoparticle dispersion is considered. Hence, the Coulomb blockade mechanism of multiple electron storage in a dielectric medium can be described by the Gerischer-Hopfield model and the multiple redox peaks as in 406 presented in plot 410 of
Equations (5) and (6) thus express the density of electronic states for successive redox events.
The single-particle redox levels are then related by:
εred,N+1−εred,N=U
εox,N−εred,N+1=2λ (7)
It is assumed that wavefunction quantization contributions to the total energy arising from an electron addition or removal event are negligible. Crucially, one can engineer A and U to tune the redox peak placement in a quantized capacitance system to encompass a target V−,max placement voltage for a given number of electrons (see
The operational voltage tuning capabilities associated with the energy storage device will now be described. First, it is desirable to arrive at a nanodisk electron storage density of around 4 q/nm2 for the proposed energy storage mechanism. Second, it is desirable to tune the charging energy parameter U such that this density of electrons is stored and removed at a bias of about 2.5 V on a given terminal relative to the fully discharged state (for a total of about 5 V across both terminals). From Eqs. (2) and (3), one can see that the solvent dielectric constant (ϵr) and nanodisk radius (r) are two physical means for accomplishing this. In
The reorganization energy λ of a given particle is also dependent on the radius and dielectric medium of such a nanodisk. Its outer-sphere contribution can be directly computed from Eq. (4) and is plotted as a function of ϵr for various nanodisk radii in plot 520 of
Lastly, it should be recognized that the classical estimates in
The volumetric energy density assessment concludes with electrolyte considerations in quantized capacitance (i.e. a consideration of how electrolyte stability impacts upon energy storage via the mechanism proposed herein). Charge storage via quantized capacitance occurs over two electrodes. One electrode serves as the negative (−) terminal by gaining electrons during charging, while the other serves as the positive (+) terminal by giving up electrons during charging. Since opposite charges are stored on both electrodes, the device's terminals will be biased in opposite directions with respect to their fully discharged configuration. Hence, the overall cell potential in Eq. (1) is the addition of the biases on both electrodes as described by:
V
d
=|V
+,max
|+|V
−,max| (8)
This voltage splitting arrangement relates directly to how positive and negative charges can be stored. It is well known that carbon nanostructures excel at storing electrons. Indeed, an electron storage density of about 4 q/nm2 can be routinely achieved. However, the propensity for electron removal from carbon nanostructures is more challenging. For example, while one can place up to about seven electrons on a C60 molecule, only up to three electrons can typically be removed. Whether one is considering fullerenes or another carbon nanostructure, this difficultly arises when the removal of electrons from the electrolyte (breakdown) occurs at an earlier potential than the removal of further electrons from the intended (carbon) nanostructure. On the other hand, it is possible to attain stability upon removal of high densities of electrons in bulk graphitic systems. For example, in BrC8 graphite sheets give up to about 4.8 q/nm2. More recently, similar success has been found in FeCl3-doped graphene. Comparatively, in C60 the ratio of electrons that can be removed (even in the presence of counterions) is around one for every 20 atoms, versus one for every eight atoms in BrC8. The challenge is how to achieve the electron-electron removal capabilities of graphite or graphene in a smaller nanostructure where the V+,max storage voltage can be tuned following the description herein prior to reaching electrolyte breakdown.
The contrasting ability of graphite to give up more electrons than C60 is due to the energies at which electron removal can be accessed. Since electrons are well delocalized in graphene/graphite, the quantization and electron-electron interaction energetic costs associated with electron removal (or addition) are much less than in C60. The comparative electronic structure plots for graphene and C60 in
Now, in
To overcome these electrolyte stability issues, which compete with the electron storage and removal, multiple engineering avenues for the proposed energy storage system may be possible. First, one may attempt to engineer an electrolyte that has a large stability window that is directly symmetric about the Dirac cone of graphene or graphite (at about 5 eV), as shown in
Second, one may independently tune the nanodisk dimensions on each electrode to fit a given electrolyte stability window alignment. This scenario is shown in
Power density, namely the manner in which the power performance targeted in
In order for quantized capacitance to persist, it is desirable for particles to be separated by a reasonable tunneling barrier. This is necessary to promote Coulombic interactions between electrons on a nanoparticle and thereby arrive at a “quantized” value of U as described by Eq. (3). By tuning U, one is able to engineer the storage voltage for a target electron density σe, as discussed herein. However, this tunneling process cannot be so slow as to render the power density impractical (see
Assuming that the temperature is held fixed at about 300 K, the interparticle electronic coupling (|Mip|) and classical Marcus-Hush reorganization energy (λc=2λ) primarily dominate the diffusion of electrons via Eqs. (9) and (10). To first order, the electronic coupling is further dependent upon the tunneling barrier width W and height Vb between the particles in the manner of:
In plot 710 of
Based on the estimates in
Turning now to
The two electrodes 802a, 802b of the energy storage device 800 are connected to an external power circuit 804 configured for charging and discharging the device 800. In the illustrated embodiment, the power circuit 804 comprises a battery 805 electrically coupled (e.g., via conductors, or the like) to the electrodes 802a, 802b and configured to supply power to the energy storage device 800 for allowing electrons to flow (e.g., along direction of arrows A when in the charging mode illustrated in
At least one of the terminals of the electrodes 802a, 802b of the energy storage device 800 is modified with (i.e. contains) nanostructured materials or elements 806 (e.g., metallic, semi-metallic, conducting, or semi-conducting nanoparticles) to enable the Coulomb blockade mechanism. In some embodiments, the nanostructured materials 806 are arranged to form nanoparticle layers 807a, 807b that are positioned adjacent the terminals of electrodes 802a, 802b, respectively, for energy storage. Although
Furthermore, in some embodiments, the Coulomb blockade effect may be a standalone storage mechanism or operate in conjunction with other storage mechanisms. For instance, the energy storage device described herein (e.g., device 800 of
Still referring to
A separating member 810 (also referred to herein as a “separator”) may be positioned in the supporting medium 808, at a substantially equal distance (not shown) from the electrodes 802a, 802b. The separating member 810 is configured to prevent the electrodes 802a, 802b from coming into electrical contact with one another, thus preventing short-circuiting of the terminals of the electrodes 802a, 802b. The separating member 810 is preferably made of a porous material to allow anions and cations present in the supporting medium 808 to pass through the separating member 810. In some embodiments, the separating member 810 is a polymer matrix. In other embodiments, the separating member 810 is a filter paper. Any other suitable porous material may apply. While
Each electrode 802a, 802b further comprises a current collector (not shown) configured to conduct and bridge the flow of electrons 812 between the supporting medium 808 and the terminals of the electrodes 802a, 802b. The nanostructured materials 806 may be deposited directly on the respective current collector or deposited onto a conductive material (not shown) coated onto the respective current collector. The current collector at the negative terminal of electrode 802a receives electrons 812 under the potential bias such that the electrons 812 can tunnel and be stored in the nanostructured materials 806. The opposite (i.e. positive) terminal of electrode 802b exhibits the reverse process of extracting the electrons 812 (depicted as holes 814 in
It should be understood that, while the nanostructured materials 806 are illustrated as having a spherical shape in
In one embodiment illustrated in
Apart from the use of quantized graphitic nanoparticles, the scheme in
It should be noted that the shape of the voltammogram 912 (and more particularly that of the upper and lower portions thereof) may vary, depending on the separation U between the overlapping electron transfer current peaks (see
Furthermore, the volume region (i.e. the supporting medium, reference 808 in
Moreover, it should be understood that any suitable supporting medium 808 may apply. In one embodiment, an electrolytic media having the simplified construction of
It should be noted that the energy storage device's housing (reference 801 in
Referring now to
In one embodiment, the MXene sheets 1010 of the MXene composite layer 1002 are vertically aligned, as illustrated in
Referring now to
First, it should be noted that the electrolytic media containing the nanostructured materials (reference 806 in
While the embodiments of
It should also be noted that there is a possibility of combining the proposed quantized capacitance setup within other emerging EDL technologies. For example, rather than utilizing a single electrode setup, a matrix of nanodisks could be imbedded between stacked electrically conductive MXenes sheets or similarly electrically conductive materials, as illustrated in
Referring now to
In both the proposed energy storage device and existing technologies, such as redox-polymer batteries, redox centres are dispersed in a supporting medium, with operation facilitated by the classical diffusion of counterions and the tunneling (outer-sphere transfer) diffusion of electrons. Unlike redox-polymer batteries, quantized capacitance is capable of producing multiple redox reactions on a single site, in such a manner that the Faradaic current is able to mimic a pseudocapacitive response as shown in
Returning to the Ragone plot 100 in
The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. Still other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, considering a review of this disclosure.
Various aspects of the systems and methods described herein may be used alone, in combination, or in a variety of arrangements not specifically discussed in the embodiments described in the foregoing and is therefore not limited in its application to the details and arrangement of components set forth in the foregoing description or illustrated in the drawings. For example, aspects described in one embodiment may be combined in any manner with aspects described in other embodiments. Although embodiments have been shown and described, it will be apparent to those skilled in the art that changes, and modifications may be made without departing from this invention in its broader aspects. The scope of the following claims should not be limited by the embodiments set forth in the examples but should be given the broadest reasonable interpretation consistent with the description.
The present application claims the benefit of U.S. Provisional Patent Application No. 63/354,325 filed on Jun. 22, 2022, the contents of which are hereby incorporated by reference.
Number | Date | Country | |
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63354325 | Jun 2022 | US |