Improved electrodes for energy storage devices

Abstract

The electrodes are bonded to a protective porous film or coating of boron nitride nanotubes (BNNTs).

Description

[Technical field]

[0001] The present invention relates to protective BNNT-based porous networks or meshes for electrodes for use in energy storage devices, in particular improved metal electrodes including improved S-cathode for metal-sulfur batteries and / or Li, Na, K, Al, Mg, Zn anodes, in particular Li anodes for lithium-sulfur batteries. [Background technology]

[0002] The development of energy storage systems with high energy density, long cycle life, high efficiency, and low cost is important for applications in transportation, grid storage, electric vehicles, and advanced portable electronics. Lithium metal-based batteries, including lithium-sulfur (Li-S) batteries and lithium-air batteries, have a capacity of approximately 650 Wh kg each. -1 and about 950Whkg -1 This is two to three times that of current lithium-ion batteries, and it is considered to be a next-generation battery. In fact, among the current battery systems, Li-S batteries are attractive candidates to function as next-generation batteries with theoretically high energy density. Such batteries have a theoretical specific capacity of 3860 mAhg -1 Lithium metal anodes are an essential component because they have the highest oxidation-reduction potential (-3.04 V vs. standard hydrogen potential) and the lowest redox potential (-3.04 V vs. standard hydrogen potential). In particular, lithium-sulfur (Li-S) technology has a low oxidation-reduction potential (16Li+S 8 →8Li 2 However, the dissolution of intermediate lithium-sulfur polysulfides formed during the charge / discharge process, the so-called shuttle effect, leads to the formation of insulating, insoluble precipitates (e.g., Li 2 S 2 / Li 2S) accumulates on the surfaces of the cathode, anode, and separator during cycling, leading to a continuous increase in the impedance of the battery, causing severe capacity fade and a decrease in the coulombic efficiency of the battery. This means that the active material is poorly recycled, and the discharge capacity and coulombic efficiency decline rapidly. Another problem is related to the formation of dendrites on the lithium metal anode, which can severely limit cycling capabilities and pose safety concerns. Similar issues exist for other metal anodes, including sodium metal electrodes, aluminum metal electrodes, zinc metal electrodes, etc. The dendrite problem is particularly problematic at higher current densities. Such issues mean that lithium-sulfur batteries, despite their promise, are not yet in mass production. Historically, the challenge in developing lithium-sulfur batteries has been to effectively optimize and stabilize the battery components during charge and discharge cycles. Conventional lithium-sulfur batteries tend to fail after a low number of recharge cycles, making them nearly useless for most commercial applications.

[0003] To solve the polysulfide (PS) problem, various strategies have been attempted, including fabrication of carbon-sulfur composites, surface modification of conductive polymers, and modification of electrolytes. Although these approaches lead to improved conductivity, cyclability, and capacity, some challenging issues still exist, such as leakage of polysulfide (PS) into the electrolyte, rapid capacity fading in subsequent cycles, and low lithium-ion conductivity and its stability in the new electrolyte. Recently, the introduction of interlayers, such as carbon paper, carbonized eggshell film, carbon nanotube paper, and acetylene black mesh, between the sulfur cathode and separator has been developed to absorb soluble PS and reuse the absorbed active material. This strategy significantly improves both the rate performance and cycle life of the battery. However, the complexity of the preparation of the interlayer, the weak interaction between the interlayer and polar polysulfide (PS) anions, and the unacceptable thickness and mass of the interlayer have a significant impact on the performance of Li-S batteries.

[0004] Thus, there is a continuing need for further improvements in the performance of S cathode electrodes that at least partially address one or more of the above-mentioned shortcomings or provide a useful alternative. In particular, the development of new lightweight solutions that could mitigate the transport of polysulfides (PS) from the sulfur cathode to the anode would be welcome.

[0005] Moving on to the issue of dendrites, metallic anodes, including Li anodes, have two problems: (1) The virtually infinite relative volume change of the hostless anode that occurs during metal stripping and plating leads to mechanical instability, repeatedly cracking and repairing the passivated solid electrolyte interface (SEI) layer, with the attendant capacity loss over time and reduced cycle life; and (2) uncontrollable formation of metallic dendrites during charge / discharge cycling, resulting in internal short circuits, low coulombic efficiency, poor cycling stability, and serious safety issues. Indeed, the occurrence of cracks during successive cycles of SEI cracking / repairing increases the flux of metal ions to the metal surface, resulting in non-uniform metal deposition and dendrite formation.

[0006] Various attempts to control the formation of undesirable dendrites include the use of new electrolytes and electrolyte additives, solid electrolytes, the addition of artificial physical protective layers, and the design of dendrite-free current collectors. Although these strategies can effectively suppress the formation and growth of metal dendrites, most of them cannot overcome the problem of infinite volume change. Maintaining or complementing the quality and integrity of the SEI layer is critical for the efficient and stable operation of metal anodes. An ideal SEI layer (i) is homogeneous in terms of composition and morphology, preventing metal nucleation and growth only in limited locations; (ii) has a high elastic modulus and dense structure to suppress the formation of dendrites; (iii) is flexible enough to accommodate the interface variations that occur during battery cycling while avoiding repeated failure / repair cycles; and (iv) has high ionic conductivity to promote uniform distribution and transport of metal ions across the electrode surface. Unfortunately, to date, the native SEI layer has lacked one or more of these requirements (as evidenced by poor cycleability), thus highlighting the need for new designs of improved artificial or pseudo-SEI or other structures that possess the above desirable properties or can impart these properties to the native SEI.

[0007] Layered boron nitride (BN) and boron nitride nanotubes (BNNTs) are polymorphs of boron nitride. BNNTs are structurally similar (isostructural) to carbon nanotubes, except that carbon atoms are alternately replaced by nitrogen and boron atoms, whereas layered boron nitride (BN) is structurally similar to graphite, where boron and nitrogen atoms are replaced by carbon atoms. BNNTs resemble rolled graphitic BN sheets (honeycomb BN (h-BN)) that contain N and B atoms instead of C atoms. BNNTs may be single-walled or multi-walled. As a result of the partial ionic character of the BN bond, ionic interactions exist between adjacent BN layers. BNNTs are cylindrical in morphology with submicron diameters and micrometer lengths.

[0008] US Patent Application Publication No. 2019 / 0123324 describes a porous separator for ion batteries comprising a porous scaffold such as a BNNT nanoporous scaffold as a support for a conformal coating of a thermoresponsive polymeric material (polyethylene, possibly chemically modified dopant) that acts as a reversible localized thermoresponsive switching mechanism to reduce temperature and prevent thermal failure and prevent thermal runaway by sterically impeding the flow of ions through the separator as the polymer expands and reduces pore size upon reaching a threshold temperature or by closing the separator pores and blocking the flow of ions in the battery. The improved separator is included between the anode and cathode of the battery. However, the BNNTs are not attached to the battery electrodes and there is no disclosure of a BNNT network / deposit intimately bound or in interfacial contact with one or both of the electrodes. Furthermore, there is no disclosure of a polymer used as a particulate binder dispersed throughout the BNNT network, rather a thermoresponsive conformal film of polymer is required.

[0009] US Patent Application Publication No. 2011 / 0086965 discloses boron nitride nanosheets (BNNS) including three-layer hexagonal boron nitride (h-BN), a form of multi-layered hexagonal boron nitride with some of the layers exfoliated, which can be produced by dispersing virgin hBN powder in an organic solvent and sonicating the dispersion. US 2011 / 0086965 does not discuss boron nitride nanotubes (BNNTs), which, as explained above, are structurally and functionally very different from boron nitride nanosheets BNNS. Summary of the Invention

[0010] In a first aspect, the present invention provides a metal electrode for an energy storage device having a composite of boron nitride nanotubes (BNNTs) and at least one polymeric binder, wherein a coating of the composite is in intimate contact with at least one surface of the electrode as a porous mesh that is selectively permeable to transport metal ions used in the energy storage device, and wherein the composite is physically and / or chemically bonded to the surface of the electrode.

[0011] In a second aspect, the present invention provides an electrode (anode) for an energy storage device comprising a metal-based anode material, the negative electrode having boron nitride nanotubes (BNNTs) bonded thereto in the form of one or more deposits or interlayers of BNNTs having a porous mesh structure.

[0012] In a third aspect, the present invention provides an energy storage device comprising one or more metal or metal-based electrodes according to the first or second aspect, preferably a lithium or sodium metal anode.

[0013] In a fourth aspect, the present invention provides an electronic device comprising a metal or metal-based electrode of the first or second aspect, and / or an energy storage device of the first aspect.

[0014] In a fifth aspect, the present invention provides the use of the electronic device of the fourth aspect in transportation, grid storage, electric vehicle and advanced portable electronics applications.

[0015] In a sixth aspect, the present invention provides a coating of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder as a porous mesh physically and / or chemically bonded to the surface of a metal electrode for preventing the formation of dendrites on an electrode of an energy storage device, preferably the electrode being a Li, Na, K, Al, Mg, or Zn metal anode.

[0016] In a seventh aspect, the present invention provides a coating of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, preferably of a Li, Na, K, Al, Mg, or Zn metal anode, as a porous mesh bonded to the metal electrode for modifying the volume expansion of the metal electrode in an energy storage device.

[0017] In an eighth aspect, the present invention provides a coating of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder as a porous mesh physically and / or chemically bonded to a surface of a metal electrode for enhancing the stability of a native SEI formed on the electrode in an energy storage device.

[0018] In a ninth aspect, the present invention provides a metal-sulfur energy storage device comprising at least one metal electrode having a coating of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, the composite coating being in intimate contact with at least one surface of the electrode as a porous mesh that is selectively permeable to transport metal ions used in the energy storage device, where the composite is physically and / or chemically bonded to the surface of the electrode; and at least one sulfur (S)-based electrode having a film of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, the composite film being in intimate contact with at least one surface of the electrode as a porous network that is selectively permeable to transport metal ions and electrolytes used in the energy storage device, but not permeable to polysulfides.

[0019] In a tenth aspect, the present invention provides a lithium-sulfur energy storage device comprising: at least one lithium metal electrode having a coating of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, the coating of the composite intimately contacting at least one surface of the electrode as a porous mesh that is selectively permeable to lithium ions for use in an energy storage device in which the composite is physically and / or chemically bonded to the surface of the electrode; At least one sulfur (S)-based electrode having a film of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, the film of the composite being in intimate contact with at least one surface of the electrode as a porous network that is selectively permeable to meta-lithium ions and an electrolyte used in the energy storage device, but impermeable to polysulfides; The present invention provides a lithium-sulfur energy storage device comprising:

[0020] Embodiments of the invention are herein described, by way of example only, with reference to the accompanying drawings, in which: [Brief description of the drawings]

[0021] [Figure 1](a) Optical images of an S / graphene electrode (cathode) without and with a film of BNNT porous network with polymer binder (b). The BNNT porous mesh appears gray in the image. (c) SEM image of the porous surface of a regular sulfur / graphene cathode, (d) cross-sectional SEM image showing the BNNT network component, electrode material component, and aluminum current collector component, (e, f) top-view SEM images of the BNNT network on the "protected" S / graphene cathode. The particulate nature of the binder between the BNNT strands or fibers is evident in the form of spheroidal particles in (f) at high magnification. The pore / gap regions of the electrode material surface seen in (c) have been filled to some extent with the composite BNNT / polymer material by the slurry casting fabrication process described herein, resulting in excellent intimate contact between the composite and the electrode material. [Diagram 2] For example, cycling stability in terms of % capacity retention versus cycle number for Li-S coin cells with different thicknesses of BNNT networks on S cathodes based on application of (a) 5 wt % BNNTs in a slurry to the cathode or (b) 10 wt % BNNTs in a slurry to the cathode followed by evaporation of the solvent is shown. The thickness of the film in microns as determined by SEM analysis is shown to the right of each curve, as is the % capacity retention in brackets. The results are compared to an equivalent cell without BNNTs in the S cathode (see the curve labeled "No BNNTs") and clearly show the advantage of the BNNT film in capacity retention over extended cycling, where after 500 cycles as high as 90% capacity retention was possible for a composite film formed from the 5 wt % slurry used to form the 2.3 micron BNNT film, whereas the electrode without the protective BNNT porous network only had a 35% capacity retention. [Diagram 3] (a) SEM and (b) TEM images of the BNNT starting material (without binder) showing the typical length and diameter of the BNNTs used. [Figure 4](a) Comparison of the color of the electrolyte solution of polysulfide solution (intense bright yellow) and the color change of the polysulfide (instantaneous disappearance of bright yellow) upon addition of BNNTs indicating that the polysulfides are adsorbed or captured / retained on the BNNTs. Note that the electrolyte used is the one described in the experimental section. (b) IR spectra of three polysulfide / electrolyte solutions with added 0 mg, 8 mg, and 15 mg of BNNTs. Here, the intensity of the PS8 absorption peak decreases as the concentration of BNNTs increases. This indicates that the PS in the solution is adsorbed or engaged / retained on the BNNTs. (c) Raman spectral analysis of BNNTs recovered from the polysulfide / electrolyte solution experiment, where the bands for BS and NS bonds are shown, indicating the adsorption of sulfur from the polysulfides to the boron and nitrogen atoms of the BNNTs. [Diagram 5] (a) (left panel) shows an SEM analysis of a BNNT / LA133 polymer binder composite film whereby a porous BNNT network is formed from an aqueous solvent system. (b) (right panel) shows an SEM analysis of a BNNT / PVDF polymer binder composite whereby a composite porous network is formed from an organic solvent system. Comparison of the images strongly suggests that the structure, porosity and / or morphology of the porous network of the films in each case is substantially the same, demonstrating comparable performance in terms of polysulfide adsorption / blocking / capture despite the use of different binders. [Figure 6] We show the effect of the ratio of high porosity graphene:high surface area graphene on the specific capacity (mAh / g) in the BNNT network protected S cathode. As can be seen, good specific capacities of about 1000mAh / g are achieved at ratios of 2:8, 4:6, 5:5, and 8:2. However, unexpectedly, a specific capacity of nearly 1400mAh / g is obtained at a ratio of 6:4. [Figure 7](a) Specific capacitance of Test S cathode with BNNTs using various BNNT loading densities, with specific capacitance improved in all cases compared to no BNNTs. BNNT loading densities from about 0.1 to about 0.25 mg / cm2 give good specific capacitance values ​​even at 100 cycles, while (b) shows capacity retention (relative to first cycle capacity) as a function of BNNT loading density (mg / cm2). BNNT loading densities from about 0.1 to about 0.25 mg / cm2 give particularly good performance in terms of capacity retention % compared to the first cycle (see Figure 1). Here, about means ±2%. [Figure 8](a) Cross-sectional and (b) top-view SEM images of coatings of BNNT porous meshes formed directly on lithium films from BNNT / polymer composite slurries using different doctor blade heights. Note that the control and optimization of the thickness of the BNNT porous mesh can be observed more easily and clearly on copper foil than on lithium films, so copper foil can be used as a model of the metal surface for the development of optimized mesh layer thicknesses. Since the film is formed in situ on the metal surface by the slurry technique, it will be appreciated that the composite BNNT porous mesh formed has excellent interfacial contact between the BNNTs and the metal electrode surface, which is substantially flat or planar as is the BNNT / polymer slurry that is placed on top of the electrode as it is formed. Once the solvent evaporates and the film is formed, the BNNTs / polymer are tightly compressed onto the metal electrode surface. This means that there are very few / very small gaps or spaces between the porous networks (typically the gaps / spaces present between the network and the metal surface are on the nanoscale), and these are much smaller than the gaps / spaces present from the preformed composite BNNT / polymer porous network placed on top of the metal electrode surface. Thus, the slurry formation method is useful for producing the excellent interfacial contact observed in the present invention. When the metal electrode is cycled, an SEI (a few nm thick) is formed between the BNNT porous network in intimate contact with the metal surface. This SEI is formed by the reaction between the electrolyte and the metal anode. This SEI is a passivation layer that can protect the metal and provide a pathway for metal ions to the metal electrode. We believe that the BNNT mesh strengthens the SEI and also provides uniform deposition of metal ions across the mesh and SEI. To ensure continuity of attachment with the ultrathin SEI, it is important that the BNNT porous network has as good an interfacial contact as possible with the metal electrode surface. It is believed that before and after SEI formation, the BNNT porous network is bound to the metal electrode surface by one or more physical and / or chemical bonds, and that the bonds are likely strengthened by the SEI upon formation of the SEI. [Figure 9]Voltage profiles of Li-ion plating and peeling cycle performance of symmetric Li coin cells where the lithium foil used in the symmetric cell was coated with BNNTs at different mass loadings and the coating extent of the composite BNNT porous mesh was formed: (a) 0.1 mg / cm2, (b) 0.2 mg / cm2, (c) 0.3 mg / cm2, (d) 0.4 mg / cm2, (e) 0.5 mg / cm2, (f) 1 mg / cm2, (g) 1.5 mg / cm2, and (h) 2 mg / cm2. [Figure 10] Figure 2 shows EIS analysis of Li symmetric coin cells with different BNNT masses added onto the Li chip to form composite BNNT porous mesh coating coverage: (a) 0.1 mg / cm2, (b) 0.2 mg / cm2, (c) 0.3 mg / cm2, (d) 0.4 mg / cm2, (e) 0.5 mg / cm2, (f) 1 mg / cm2, (g) 1.5 mg / cm2, (h) 2 mg / cm2. [Figure 11] 13A-13D are Arrhenius plots constructed according to the Nyquist plots of Li symmetric coin cells with different BNNT mass loadings in the porous mesh on the Li chip. [Figure 12] Long-term cycling performance of symmetric pouch cells with the new lithium film electrode (a) without and (b) with the composite BNNT porous mesh coating. In the absence of the BNNT porous mesh, the overpotential increases with cycling as dendrite formation occurs on the lithium metal, causing cell failure after only 45 cycles. On the other hand, the cell with the BNNT porous mesh coating on the lithium metal maintains a stable overpotential for at least 1000 cycles, indicating a lack of dendrite growth as a result of the protective BNNT mesh on the lithium. [Figure 13]Voltage profiles of plating and delamination cycling performance of symmetric Al and symmetric Zn cells with different metal electrodes: (a) bare Al, (b) Al coated with composite BNNT porous mesh, (c) bare Zn, and (d) Zn coated with composite BNNT porous mesh. BNNT loading of the mesh in each case is 0.4 mg / cm2. [Figure 14] The proposed mechanism for coating the BNNT porous mesh to prevent dendrite growth is to convert the non-uniform lithium ion flow (localized) arriving at the lithium metal anode in a localized manner into a more dispersed lithium ion flow through the mesh to the anode, such that the transport metal ions arriving at the entire lithium surface are more uniformly distributed (delocalized) across the entire surface of the metal electrode. The advantages of this arrangement are explained below. [Figure 15] Exploded view structure of Li-S battery with BNNT porous mesh coating for Li anode protection and BNNT porous network film for S cathode protection. Reversibly trapped PS is observed within the BNNT porous network film. [Figure 16]The capacity and specific capacity of two pouch cells (with and without BNNTs in the cathode) including a 20 cm2 pouch cell with an effective cathode mass loading of 30.4 mAh / g are shown. The bottom line represents the cell without BNNTs, which failed after just over 100 cycles, so the results do not go beyond the dotted line. The data show that the deposition of a film of BNNTs porous network is beneficial to the performance of the cathode, leading to an improved utilization of the sulfur active material, and no adverse effects such as capacitive charge / self-discharge processes are evident. The reversible cycling capacity of the Li-S battery was improved by 15% after 100 cycles with the addition of BNNTs to the cathode. A capacity of 18.9 mAh (622 mAh / gsulfur) was achieved after 100 cycles and 16.7 mAh (550 mAh / gsulfur) after 600 cycles, demonstrating a high level of stability. The capacity retention of the cell without BNNTs falls below the 60% threshold (17.5 mAh, 574 mAh / gsulfur) after 27 cycles, whereas the capacity retention of the cell with BNNTs has since continued to cycle for over 1200 cycles without falling below the 60% capacity threshold. Based on the developed and presented testing procedure, the enhanced capacity retention can be attributed to the presence of the BNNT porous network on the cathode. [Figure 17] Figure 1 shows (a) the capacity retention and (b) coulombic efficiency of Li-S coin cells without BNNT protection and with BNNT protection at both the cathode and anode. The BNNT loadings of the layer and mesh are 0.2mg / cm2 and 0.4mg / cm2, respectively. All tested cells are tested at 25°C at a rate of 0.2. The initial specific capacities of the bare Li-S cell and the cell with BNNT protection on both sides are 1158mAh / g and 1251.6mAh / g, respectively. It can be seen that the unprotected Li-S cell maintains a capacity retention of 74.26% and a coulombic efficiency of 83% after 60 cycles, whereas the BNNT-protected cell shows a higher capacity retention of 95.55% and a higher coulombic efficiency of 96.8% for the same amount of cycles. Although the research is ongoing, the advantages of the composite BNNT porous protection layer on the electrode are clear. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The present invention relates to a film and / or coating of a boron nitride nanotube (BNNT) porous network or mesh for an electrode used in an energy storage device. The BNNT is preferably in the form of a composite BNNT material comprising BNNTs and a polymer binder. The porous network or mesh is selectively permeable to transport metal ions used in the energy storage device. It is understood that the electrode can be used in an energy storage device such as a battery, particularly a rechargeable secondary battery. The electrode can be a sulfur electrode, an alkali metal, particularly sodium or lithium, or a metal electrode such as aluminum, magnesium or zinc.

[0023] Desirably, the BNNTs of the composite are substantially free, and preferably completely free, of impurities such as hexagonal boron nitride (hBN) and / or elemental boron (B). As used herein, BNNTs contain very small amounts of impurities such as metal catalysts, hexagonal boron nitride, and / or elemental boron. Preferred BNNTs are at least 95% pure, at least 96%, at least 97%, at least 98%, or in some cases at least 99% pure.

[0024] Preferably, the composite BNNT porous network or mesh is electrically insulating but permeable to the metal transport ions (e.g., metal ions of metal-based anode materials) used in the particular energy storage device of interest. The porosity / porous structure of the BNNT porous network, mesh, or deposit can be observed using SEM and, if desired, tested with BET analysis.

[0025] Suitably, the binder is present in the composite as solid spheroid-shaped binder particles, which may also be observed in the SEM images provided herein. Desirably, at least a portion of the polymer binder is present in the composite as solid particles that fix or bond the strands of BNNTs in the composite together to form a porous network (for S cathodes) or porous mesh (for metal anodes). A substantial portion of the binder present is present in the form of solid particles, rather than in the form of a distinct conformal coating of polymer on all the BNNT strands, etc. Suitably, the strands of BNNTs in the composite are not completely conformally coated with the polymer binder. It is undesirable to provide a conformal coating of polymer all around the BNNTs, as this may result in excessive thermal expansion of the polymer, which may adversely affect the optimized pore size of the BNNT network / mesh. Incorrect pore size may adversely affect one or more of the reaction rate, the internal resistance of the device, the capacity, and the capacity retention upon cycling.

[0026] Desirably, the composite film is physically and / or chemically bonded to the surface of the electrode, which is the case for an S cathode or a metal anode, as described in more detail below.

[0027] Films of BNNT porous networks, when properly optimized, are particularly useful for blocking polysulfide migration from S cathode materials. Preferred films have optimized BNNT loading, density, and thickness, and synergistically prevent polysulfide diffusion through films of BNNT porous networks by reversibly trapping polysulfides within the porous network while maintaining their activity, i.e., active material can still escape the composite network and return to the cathode mass. Transiently trapped polysulfides can be released from the porous network in a reverse cycle as active S and come into contact with the S cathode material mass. The optimized networks described herein are preferred because they are configured to efficiently and reversibly trap S but not to result in inactive S in the form of PS that is permanently trapped in the BNNT porous network. The functionality of the optimized films of BNNT porous networks described herein is demonstrated by the retention of very good specific capacity (capacity retention) even after multiple cycles due to reversible polysulfide trapping in the films of BNNT porous networks associated with the S cathode (see, e.g., FIG. 7).

[0028] BNNTs in the form of coatings on BNNT porous meshes are also particularly useful for SEI reinforcement and / or prevention of dendrite formation on metal electrodes subject to dendrite formation, such as lithium metal. The preferred coatings of composite BNNT / polymer meshes in this embodiment are optimized with respect to BNNT loading, density, and thickness, which act synergistically to allow transport metal ions to pass through the mesh to the metal electrode surface selectively, but in a manner that distributes the approaching ion flux that reaches the mesh after passing through the mesh uniformly across the surface of the electrode. By distributing the transport metal ions uniformly across the electrode surface, the formation of metal dendrites is significantly reduced. The optimized mesh also has an appropriate thickness to reinforce the native SEI formed on the electrode and protect the electrode from damage due to volume expansion that occurs in hostless electrode materials that contain metals. Mitigating SEI damage in this manner also prevents dendrite formation. The functionality of the optimized coatings on BNNT porous meshes described here is demonstrated by the lack of dendrite formation during metal stripping / plating experiments and the maintenance of low and stable internal resistance, demonstrating very stable overpotentials even after numerous cycles.

[0029] In either case, the composite BNNT / binder material improves the cycling performance of the electrode when used in an energy storage device. The protected electrode material can be provided with a film or coating of the BNNT network or mesh of the present invention and used as the cathode and / or anode of an energy storage device. As an example, a film of the BNNT network is used to protect a sulfur cathode and / or a coating of the BNNT mesh is used to protect a metal anode of a lithium electrode in a metal sulfur energy storage device, such as a lithium sulfur energy storage device. The difference between the film and the coating is in the thickness of the composite on the electrode and / or the density of the BNNTs used. As described herein, S cathodes and metal anodes are advantageous for various reasons, and either type of protected electrode can be used in the device. Preferably, both the BNNT-protected sulfur cathode and the BNNT-protected metal anode are used in improved devices, such as improved lithium sulfur energy storage devices, in which both electrodes (cathode and anode) are protected. We believe that the protected electrodes act synergistically in lithium-sulfur energy storage devices to improve the cycle life performance of lithium-sulfur batteries (see FIG. 17). This effect is also applicable to other metal batteries such as Na, K, AL, and Zn. The BNNT porous network film stabilizes and protects the cathode, while the BNNT mesh coating protects the anode by reducing dendrite formation through strengthening the SEI layer and spreading the metal ion flux reaching the electrode over the entire surface of the electrode. The structure of a Li-S battery with a BNNT protective layer on each electrode is shown in FIG. 15 below. During the operation of a lithium-sulfur battery, lithium ions migrate between the lithium anode and the sulfur cathode. The lithium ions combine with sulfur to produce various lithium polysulfide compounds in the cathode. Some of these polysulfides are soluble in the battery electrolyte and can be deposited on the anode. This leads to a permanent loss of active sulfur from the cathode. After a relatively small number of charging cycles, the loss of active sulfur reduces the battery capacity. The BNNTs in the battery structure function to allow the passage of lithium ions while inhibiting the migration of lithium polysulfides.This promotes the retention of sulfur as an active material in the cathode, helping to maintain the battery capacity during charging and discharging. Additionally, the presence of lithium within the sulfur cathode structure can cause the structure to expand dramatically, compromising the battery's structural integrity and resulting in capacity loss and failure. BNNTs are believed to assist by providing additional structural support to the cathode. This reduces the effects of cathode expansion and contraction, reducing the risk of failure due to mechanical stress. In lithium anodes, lithium ions return to the lithium metal anode during battery cycling. Upon arrival, they can deposit irregularly and grow lithium dendrites at the anode surface. These can damage the insulating separator and cause short circuits and failure. The inclusion of a protective BNNT network / mesh in the anode is believed to result in a uniform ion influx across the anode surface, preventing dendrite formation and anode degradation even after many cycles, preserving the specific capacity and reducing the risk of battery failure over a longer cycle life.

[0030] Because BNNTs conduct heat much more efficiently than copper, it is also believed that BNNTs within the battery structure could help spread the generated heat more evenly, potentially reducing concentrated hot spots and the mechanical and chemical stresses associated with such hot spots. This could further increase the rate of safe charging and reduce the risk of failure. This is an improvement over lithium-ion, where traditional lithium-sulfur batteries can develop concentrated heat spots during charging and discharging, which can increase mechanical and chemical stresses, limit safe charging rates, and increase the risk of failure due to localized excessive heating.

[0031] (electrode) Described herein is an electrode for an energy storage device having a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, the composite in intimate contact with at least one surface of the electrode as a porous network or mesh that is selectively permeable to transport metal ions used in the energy storage device, and at least a portion of the polymer binder is present as particles that fix the strands of BNNTs together to form a porous network or mesh. Also described herein is a sulfur (S)-based electrode for an energy storage device having a composite of boron nanotubes (BNNTs) and at least one polymer binder, the composite in intimate contact with at least one surface of the electrode as a porous network or mesh that is selectively permeable to transport metal ions and electrolytes used in the energy storage device, but not permeable to polysulfides, i.e., the composite is impermeable to polysulfides. Also described herein is a sulfur (S)-based electrode for an energy storage device having a film of a composite of boron nanotubes (BNNTs) and at least one polymer binder, the film of the composite being in intimate contact with at least one surface of the electrode as a porous network and selectively permeable to transport metal ions and electrolytes used in the energy storage device, but not permeable to polysulfides.

[0032] In an S cathode embodiment, the composite film has an average thickness of about 0.9 microns to about 5 microns, preferably about 1.5 microns to about 3.5 microns, and most preferably about 2.5 microns. Desirably, the composite film has an average thickness of about 0.05 mg cm -2 ~about 3.5mgcm -2 , more preferably about 0.05 mg cm -2 ~ approx. 1 mg cm -2 , more preferably about 0.05 mg cm -2 ~about 0.5mgcm -2 , and most preferably about 0.2 to about 0.25 mg cm-2 , and most preferably about 0.2 mg cm -2 In some embodiments, S is about 1 mg cm -2 ~about 5mgcm -2 , preferably about 3 mg cm -2 where about means ±2%.

[0033] Described herein is a metal or metal-based electrode for an energy storage device having a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, the composite in intimate contact with at least one surface of the electrode as a porous mesh that is selectively permeable to transport metal ions used in the energy storage device, and at least a portion of the polymer binder is present as particles that secure strands of BNNTs together to form a porous network or mesh. Described herein is a metal electrode for an energy storage device having a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, the composite coating in intimate contact with at least one surface of the electrode as a porous mesh that is selectively permeable to transport metal ions used in the energy storage device, and the composite is physically and / or chemically bonded to the surface of the electrode.

[0034] Desirably, the composite has an average thickness of about 1 micron to about 50 microns, more preferably about 2 microns to about 25 microns, more preferably about 3 to 10 microns, preferably about 1.5 microns or about 7.5 microns, and most preferably about 5 microns. In some embodiments, the composite coating has a thickness of about 0.2 mg cm -2 ~ approx. 8 mgcm -2 , about 0.1 mg cm -2 ~about 2.5mgcm -2 , more preferably 0.1 to about 2 mg cm -2 , and most preferably about 0.4 mg cm -2These thicknesses and loadings are particularly desirable for meshes for metal electrodes.

[0035] Described herein is an electrode for an energy storage device having boron nitride nanotubes (BNNTs) provided on at least one side of the electrode as a porous network or mesh that is selectively permeable to transport metal ions used in the energy storage device. Suitably, the network or mesh is a composite of BNNTs and a polymer binder.

[0036] Described herein is an electrode for an energy storage device having a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder provided on at least one surface of the electrode as a porous network, mesh, or deposit that is selectively permeable to transport metal ions used in the energy storage device. Most preferably, the binder is present in the BNNT porous network or mesh at a concentration of about 15% or less by weight of the BNNT component, preferably about 10% or less by weight (where about means ±2%). Desirably, a portion of the binder is present in particulate form. More desirably, at least 50% of the binder is present in particulate form. The binder specifically anchors or bonds the BNNT strands or fibers to each other and provides stability to the porous network, mesh, or deposit. In some embodiments, the BNNT strands or fibers are not completely conformally coated with a layer of polymer binder. In some embodiments, less than 75%, less than 50%, or less than 25% of the BNNT strands or fibers are coated with a conformal layer of polymer binder. The composition of the polymer binder is described in detail below. As used herein, in embodiments that include a binder, the term BNNT refers to a composite BNNT / polymer binder, meaning that the binder is present in a porous network or mesh.

[0037] The BNNTs are in intimate contact with the electrode / electrode material. The BNNTs may be physically and / or chemically bonded or fused to the electrode material such that the gaps / spaces present between each component are at the nano-level rather than the micron-level. In some embodiments involving S cathodes, the BNNTs in the film or coating penetrate the pores of the S electrode material, and as a result, become entangled and / or embedded within the surface pores of the BNNT composite component (e.g., BNNTs and binder) and the electrode component. This results in excellent intimate contact between both components in the protected electrode, and in fact the film / coating does not peel off from the electrode, at least under normal cycling conditions.

[0038] (S cathode) In some preferred embodiments, the electrode is a sulfur electrode, e.g., a sulfur cathode for a secondary energy storage device. Thus, in another aspect, the present invention provides an electrode for an energy storage device, comprising a sulfur (S) cathode material having a porous network, mesh, or deposit of boron nitride nanotubes (BNNTs) provided on the S-cathode material. The BNNTs are porous networks, meshes, or deposits that are not permeable to polysulfides but allow the passage of metal transport ions. The BNNTs may prevent the adsorption and / or diffusion of polysulfides into an electrolyte in contact with the electrode, e.g., as found in an energy storage device. In a preferred embodiment, the BNNTs for the S cathode are composites of BNNTs and at least one polymer binder.

[0039] (metal electrode) The electrode may be a metal electrode, particularly an electrode that is problematic in dendrite formation, such as aluminum, zinc, or an alkali metal electrode such as lithium, sodium, potassium, etc., that is involved in the transport of metal ions of these metals. In some preferred embodiments, the electrode is a metal or metal-based electrode for an energy storage device having a composite of boron nitride nanotubes (BNNTs) and a polymer binder provided on at least one surface of the electrode as a selectively permeable porous network for transporting metal ions used in the energy storage device. BNNTs or BNNT / polymer binder composites are particularly useful for lithium electrodes.

[0040] Desirably, the composite BNNT porous network or mesh is flexible and resists cracking or breaking during cycling of the energy storage device during normal operation. -2 ~20mAcm -2 It will be understood to mean charge / discharge in a current density range of 100 times, 500 times, or 1000 times. The flexibility of such a BNNT network or mesh may be demonstrated, for example, as stable electrochemical metal stripping or plating in a symmetric cell, or stable charge / discharge cycling over multiple cycles in an energy storage device, as compared to a comparable system without a BNNT porous network or porous mesh on an electrode. Multiple cycles means at least more than 100, at least more than 500, or at least more than 1000 stripping / plating cycles in a galvanostatic cycling test, or at least more than 100, at least more than 500, or at least more than 1000 charge / discharge cycles in a battery cell.

[0041] Suitably, the BNNT porous network or mesh better controls the undesirable electrode, particularly metal-based anode materials, volume expansion that occurs upon cycling in a cell, compared to a comparable electrode, particularly metal-based anode materials, that does not have a BNNT porous mesh on the electrode. It is believed that the BNNT mesh protects and strengthens the SEI that forms between the metal electrode and the SEI upon cycling. Furthermore, electrodes, particularly metal anodes that do not contain a BNNT component, experience different degrees of volume expansion in different regions of the electrode depending on where the metal ion flux reaching the electrode surface is concentrated. The composite BNNT parts of the present invention homogenize this volume expansion by more uniformly directing the metal ions across the area of ​​the electrode that is in contact with the BNNT porous parts.

[0042] In one embodiment, the electrode material is a sulfur-based electrode material. Desirably, the present invention provides an electrode for an energy storage device comprising an S-cathode material having a porous network of boron nitride nanotubes (BNNTs), preferably a composite BNNT / polymer binder on the S-cathode material. In a related aspect, the present invention provides an energy storage device electrode comprising an S-cathode material having a porous network or deposit of boron nitride nanotubes (BNNTs) on the S-cathode material, preferably a composite BNNT / polymer binder on the S-cathode material.

[0043] In another aspect, the present invention provides a metal or metal-based electrode for an energy storage device having a composite of boron nitride nanotubes (BNNTs) used in the energy storage device to transport metal ions and a polymer binder provided as a selectively permeable porous network on at least one surface of the electrode.

[0044] In a related aspect, the present invention provides a negative electrode (anode) for an energy storage device comprising a metal-based anode material combined with boron nitride nanotubes (BNNTs) in the form of one or more deposits or intermediate layers of BNNTs having a porous mesh structure.

[0045] Preferably, for sulfur-based electrodes, the sulfur is about 0.1 mg cm -2 ~about 5mgcm -2 , more preferably about 0.9 mg cm -2 ~about 2.5mgcm -2 In some embodiments, sulfur is present in the electrode material at an active material loading of about 3 mg cm. -2 In particular, the BNNTs in the film were approximately 0.2 mg cm -2 ~about 0.25mgcm -2 is present in the electrode material at an active material loading of 0.1 to 1000 nm.

[0046] Preferably, the deposit is in the form of one or more layers of boron nitride nanotubes (BNNTs) coating at least one surface of the electrode material.

[0047] It should be understood that the electrodes are formed into blocks or other shaped structures having one or more substantially flat or planar surfaces onto which the BNNTs may be deposited as a film of a composite BNNT porous network or a coating of a composite BNNT porous mesh.

[0048] Suitably, the composite boron nitride nanotube (BNNT) component has an average thickness as described herein. The thickness may be measured by SEM analysis. Particularly preferred thicknesses are in the range of about 1 micron to about 10 microns, where about means ±2%. Particularly preferred BNNT layer thicknesses are in the range of about 1 micron to about 5 microns, which have been found in some embodiments to provide 79-90% capacity retention for the first cycle. In some embodiments, more preferred BNNT layer thicknesses are in the range of about 1.3 microns to about 2.5 microns. In other embodiments, even more preferred BNNT layer thicknesses are in the range of about 1.5 microns to about 2.3 microns, which provide 800-1100 mAhg capacity retention after over 400 cycles, based on initial capacity at a current density of 0.2C. -1Excellent initial specific capacitance and 85-90% capacity retention are obtained. In one embodiment, BNNT layer thicknesses of about 1.5 microns or 2.3 microns are particularly preferred.

[0049] Preferably, the boron nitride nanotubes (BNNTs) are present in the network on the sulfur cathode material in an amount ranging from about 50% to about 95% by weight of the network / deposit, and more preferably in an amount ranging from about 80% to about 90% by weight of the network / deposit.

[0050] In one embodiment, a composite BNNT network or mesh is formed on the electrode surface by casting a solvent-based slurry of BNNTs and binder onto the electrode surface and evaporating the solvent to form a composite BNNT / binder porous network / deposit. Thus, in some embodiments, the network / deposit is a solvent-cast network / mesh with excellent interfacial contact between components with only nano-level gaps / spaces between the components.

[0051] In embodiments that include a binder in the BNNT network / mesh, it will be understood that the slurry from which the network / mesh is prepared essentially comprises / consists of BNNTs, binder, and solvent. Preferred slurries include BNNTs (in the amounts described above for binder concentration), preferably 1 to about 10% by weight of the total slurry in solvent, preferably 3 to 7% by weight of the total slurry in solvent, and most preferably about 5% by weight.

[0052] Desirably, the S electrode includes one or more conductivity enhancers, preferably carbon-based conductivity enhancers, to enhance the electrical conductivity of the S material of the electrode. Preferably, the conductivity enhancer is one or more graphenes, such as highly porous graphene or high surface area graphene. In one embodiment, the preferred conductivity enhancer is a mixture of highly porous graphene and high surface area graphene. The preferred highly porous graphene has a porosity of 300 m 2 / g~800m 2 / g, preferably about 400m 2In one embodiment, the preferred high surface area graphene has a porosity of about 800 m 2 / g~1000m 2 / g, preferably about 833m 2 In one embodiment, the preferred ratio between highly porous graphene and high surface area graphene is 1:9 to 9:1, preferably about 6:4.

[0053] Preferably, the electrode material, preferably a sulfur-based electrode material, is deposited on a current collector, preferably a metal current collector, more preferably a metal foil current collector, most preferably an aluminum foil current collector. Preferably, when the electrode material is a metal or metal-based electrode material, such as Li, K, or Na, it is deposited on a current collector, preferably a metal current collector, more preferably a metal foil current collector, most preferably a copper foil current collector.

[0054] Also described herein are energy storage devices comprising one or more electrodes of the invention described herein. In a related aspect, the invention provides energy storage devices comprising one or more negative electrodes, e.g., lithium metal, potassium metal, or sodium metal electrodes, as described herein.

[0055] In a related aspect, the invention provides an energy storage device including a metal-based anode material, the negative electrode having boron nitride nanotubes (BNNTs) associated therewith in the form of one or more deposits or intermediate layers of a composite BNNT / binder porous mesh.

[0056] Suitably, the preferred energy storage device comprises at least one cathode having a sulfur-based electrode material with a porous deposit of boron nitride nanotubes (BNNTs) on the electrode material, a separator, at least one anode having a lithium, potassium, or sodium metal-based electrode material on the electrode material, and an electrolyte. Suitably, the preferred energy storage device comprises at least one cathode having a sulfur-based electrode material with a porous deposit of boron nitride nanotubes (BNNTs) on the electrode material, a separator, at least one anode having a lithium, metal-based electrode material on the electrode material, and an electrolyte.

[0057] For example, the present invention provides a metal-sulfur energy storage device, comprising: At least one sulfur (S)-based electrode having a film of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, the film of the composite being in intimate contact with at least one surface of the electrode as a porous network that is selectively permeable to transport metal ions and electrolytes used in the energy storage device, but not permeable to polysulfides (impermeable to polysulfides); at least one metal electrode having a coating of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, the coating of the composite intimately contacting at least one surface of the electrode as a porous mesh that is selectively permeable to transport metal ions used in an energy storage device in which the composite is physically and / or chemically bonded to the surface of the electrode; The present invention relates to a metal-sulfur energy storage device comprising:

[0058] For example, the present invention provides a lithium-sulfur energy storage device, comprising: At least one sulfur (S)-based electrode having a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, the composite film being in intimate contact with at least one surface of the electrode as a porous network selectively permeable to transport metal ions and electrolytes used in the energy storage device, but not permeable to polysulfides (impermeable to polysulfides); at least one lithium metal electrode having a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, wherein a coating of the composite is in intimate contact with at least one surface of the electrode as a porous mesh that is selectively permeable to lithium ions that are physically and / or chemically bound to the surface of the electrode; The present invention relates to a lithium-sulfur energy storage device comprising:

[0059] It is desirable for the energy storage device to retain up to 60% of its initial capacity after at least 500 cycles at a current density of 0.2C.

[0060] Desirably, the energy storage device has a capacity of at least 400 mAhg based on the S loading at a temperature of 25° C. and a 0.2 C rate. -1 and preferably at least 900 mAhg based on the amount of S added. -1 The specific capacity is shown.

[0061] Preferably, the device exhibits a capacity of at least 8 mAh. Preferably, the device exhibits a capacity of at least 24 mAh. Preferably, the device exhibits a capacity of at least 32 mAh.

[0062] Described herein is an energy storage device comprising one or more electrodes of the invention described herein. Desirably, the energy storage device comprises one or more negative electrodes for secondary energy storage devices, such as lithium metal or sodium metal electrodes (anodes), or zinc or aluminum metal (anodes). It is understood that the negative electrode is the electrode where oxidation occurs during discharge, i.e., the lithium anode of a Li-S battery, where dissolution of lithium from the anode surface occurs and is incorporated into an alkali metal polysulfide salt. The electrode becomes a cathode during charging, and lithium is plated onto the cathode electrode during charging.

[0063] In a related aspect, the invention provides an energy storage device that includes a metal-based anode material and a negative electrode having associated therewith boron nitride nanotubes (BNNTs) in the form of one or more deposits or intermediate layers of a BNNT porous mesh.

[0064] It is found that Li-S batteries with BNNTs in the cathode and anode exhibit substantially better performance in terms of cycling stability and energy density compared to identical batteries without BNNTs. Indeed, integrating BNNTs into the components and structure of lithium-sulfur batteries is an effective way to stabilize battery components during charging and discharging, creating lithium-sulfur battery cells with cycle lives approaching those of everyday consumer-grade lithium-ion batteries. This offers the possibility that lithium-sulfur batteries can eventually be commercialized and mass-produced.

[0065] (Electronic Devices) Described herein are electronic devices comprising electrodes of the invention and / or energy storage devices of the invention.

[0066] (Application / Use) Described herein are uses of the electronic devices of the present invention in transportation, grid storage, electric vehicle, and portable electronics applications.

[0067] Described herein is the use of one or more BNNT layers, preferably in the form of a composite BNNT / polymer binder porous network, as a polysulfide blocking material for an S cathode of an energy storage device. It is preferred to use one or more BNNT layers, preferably in the form of a composite BNNT / polymer binder porous network, as a polysulfide diffusion blocking coating or reversible trap for polysulfides in a sulfur (S)-based cathode of an energy storage device.

[0068] Described herein is the use of one or more BNNT layers, preferably a composite BNNT / polymer binder porous mesh, as a dendrite growth inhibitor on a metal electrode of an energy storage device. A coating of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder is preferably used as a porous mesh that is physically and / or chemically bonded to the surface of a metal electrode to prevent the formation of dendrites on the electrode in an energy storage device, preferably the electrode being a Li, Na, K, Al, Mg, or Zn metal anode. The physical and / or chemical attachment may include an SEI that forms during cycling.

[0069] Described herein is the use of one or more BNNT layers, preferably a composite BNNT / polymer binder porous mesh, as a dendrite growth inhibitor for a metal electrode of an energy storage device. Described herein is the use of one or more BNNT layers, preferably a composite BNNT / polymer binder porous mesh, as a solid electrolyte interface reinforcement material for a metal electrode of an energy storage device.

[0070] A coating of a composite of boron nitride nanotubes (BNNTs) and at least one polymeric binder as a porous mesh bonded to a metal electrode is preferably used to modify the volume expansion of a metal electrode, preferably a Li, Na, K, Al, Mg, or Zn metal anode, in an energy storage device. A coating of a composite of boron nitride nanotubes (BNNTs) and at least one polymeric binder as a porous mesh physically and / or chemically bonded to the surface of a metal electrode is preferably used to enhance the stability of the native SEI formed on the electrode of an energy storage device.

[0071] (Formation of BNNT porous network, mesh or deposit) Described herein is a slurry for preparing a composite BNNT porous network or mesh for an electrode material comprising boron nitride nanotubes (BNNTs), one or more polymer binders, and one or more solvents. Suitably, the electrode material is an S cathode material, and the BNNTs are provided as a composite film of BNNTs and binder as a porous BNNT network on the electrode surface. Also described herein is a slurry for preparing a coating of a BNNT mesh, preferably a coating of a composite BNNT / polymer binder porous mesh for a metal or metal-based anode material comprising boron nitride nanotubes (BNNTs), one or more polymer binders, and one or more aprotic solvents. Desirably, the solvent is inert to the metal. Suitably, the metal is an alkali metal, particularly sodium or potassium, zinc or aluminum metal.

[0072] Described herein is a method for preparing an electrode for an energy storage device, the electrode comprising an electrode material having associated therewith boron nitride nanotubes (BNNTs) in the form of a porous network or porous mesh of a BNNT / polymer binder composite, the method comprising: (i) preparing a slurry of BNNTs and one or more polymer binders in a solvent; (ii) coating the surface of the electrode with the slurry to a desired thickness; (iii) evaporating the solvent to form a BNNT porous network or mesh on the electrode; Includes.

[0073] Described herein is a method for preparing a negative electrode (anode) comprising a metal-based anode material having attached thereto boron nitride nanotubes (BNNTs) in the form of one or more deposits or interlayers of BNNTs having a porous mesh structure, the method comprising: (i) preparing a slurry of BNNTs and one or more polymer binders in one or more solvents; (ii) coating the surface of a metal-based anode material with the slurry to a desired thickness; (iii) evaporating the solvent to form a metal-based anode material having a surface coating of a composite of BNNTs with a porous mesh structure; Includes. Preferred dimensions are disclosed elsewhere herein. The concentration of BNNTs in the slurry is 10 wt% or less, preferably 7.5 wt% or less, more preferably 5 wt% or less. The amount and thickness of the polymer are described elsewhere herein. Doctor blade techniques may be used to adjust the thickness of the slurry. Preferred thicknesses are described elsewhere herein.

[0074] Description of the Preferred Embodiments The invention will now be described with reference to the following example embodiments, it being understood that the examples are illustrative of the invention described herein and are not intended to limit the invention.

[0075] Embodiment 1 - BNNT Network Films Prevent Polysulfide Shuttling Boron nitride nanotubes (BNNTs) have attracted great attention in various scientific fields due to their exceptional thermal, mechanical, optical and electrical properties, making them more promising nanomaterials compared to other nanotubes. However, boron nitride nanotubes (BNNTs) have never been demonstrated as useful polysulfide blocking materials in S cathodes of batteries, especially in Li|S batteries.

[0076] Herein, we describe a composite boron nitride nanotube / binder film or coating provided on the electrode surface. In the case of the S cathode electrode, the BNNTs are provided as a film of a BNNT porous network. In the case of the metal anode electrode, the BNNTs are provided as a coating of a BNNT porous mesh. The difference in terms refers to the difference in thickness and density of the respective BNNT components. In the case of the S cathode, a dense network of BNNTs is necessary to prevent the PS from diffusing through the network to the electrode, but the thickness is such that the PS is reversibly trapped in the network and not permanently trapped in the network, which results in the generation of inert sulfur over time and a significant decrease in the capacity / capacity surface. Similarly, in the case of the metal anode, the coating of the BNNT porous mesh is of an appropriate thickness to reinforce the SEI of the metal anode while allowing efficient metal ion transport through the mesh. In effect, the mesh serves to divide the metal electrode surface into multiple regions, allowing the ions to be more uniformly distributed as they pass through the mesh.

[0077] The cycling performance of Li-S coin and pouch cells with and without a BNNT interlayer on the cathode was studied in detail. The results clearly show that the BNNT interlayer can significantly improve the cycling stability of Li-S batteries, demonstrating the performance of the interlayer in controlling the polysulfide shuttle and mitigating the adverse effects of polysulfide shuttling.

[0078] Li-S coin cells and Li-S pouch cells incorporating the BNNT / S cathode of the invention have been prepared. In some embodiments, studies examine electrochemical lithium plating and delamination behavior in cells with lithium metal anodes and S cathodes, where the S cathode is protected from cathode mass loss by the polysulfide shuttle by providing a composite BNNT binder network or deposit according to the invention on the S cathode.

[0079] It may be thought that the BNNT interlayer, when provided with the appropriate thickness and / or density, can act as a physical barrier to block the shuttle of polysulfides and / or adsorb polysulfides onto it to prevent diffusion into the electrolyte. However, the preferred porous BNNTs described herein contain channels or pathways for transporting lithium ions, resulting in high cycling stability and high capacity.

[0080] In particular, the present invention provides a cathode comprising a sulfur cathode material combined with a porous film or porous deposit of boron nitride nanotubes (BNNTs). Preferred S cathode materials also include graphene. The porous nature of the film or deposit can be observed from SEM analysis, where the porous nature of the BNNT material is evident. The average pore diameter of the pores in the BNNT material is preferably about 0.1-3 microns, more preferably about 0.5-1.5 microns. The boron and / or nitrogen content of the film / deposit can be confirmed by EDS analysis.

[0081] Boron nitride nanotube (BNNT) films / deposits are designed to be permeable to Li ions, but not Li 2 S 4 Or Li 2 S 6Preferably, the BNNT films / deposits have tunnels, passages or channels arranged and / or dimensioned such that polysulfides, including BNNTs, cannot pass through. As shown by the Raman and IR studies described herein, the BNNT films / deposits block the passage of polysulfides through the films / deposits. It is believed that the polysulfides adsorb to the BNNTs. Thus, the adsorption prevents the diffusion of the polysulfides into the electrolyte.

[0082] In some embodiments, the BNNTs used have an average diameter of about 10 nm to about 250 nm, preferably about 20 to 150 nm. In some embodiments, the BNNTs used have an average length of about 1 micron to about 200 microns, more preferably about 3 microns to about 100 microns. In other embodiments, the length is at least 0.5 microns, more preferably at least 1 micron, and even more preferably at least 10 microns. As can be seen from the SEM and TEM images of the BNNTs in FIG. 3, the diameter of many BNNTs is primarily 20 to 150 nm, and the length is primarily 3 to 100 microns.

[0083] Desirably, the BNNT film / coating is a mixture of BNNTs and one or more binder materials. Suitably, the BNNT porous mesh / network or deposit comprises at least one binder material, preferably a polymeric binder. In a preferred embodiment, a binder is present, suitably a polymeric binder or a mixture of two or more polymeric binders. The binder supports the structure formation and integrity of the BNNT porous mesh / network or deposit. Polymeric binders are particularly preferred because they have an inherent flexibility under typical energy storage device conditions, which is desirable in terms of imparting controllable flexibility to the BNNT structure. In a preferred embodiment, the boron nitride nanotube (BNNT) network / deposit further comprises one or more binders. Preferably, the binder is a polymeric binder, such as PVDF, LA133, PEO or PTFE, or a combination thereof. These binder examples are particularly preferred for BNNTs for S cathode type electrodes. In other embodiments, preferred binders are those that are chemically and / or physically stable in the presence of the metal or metal-based electrode in question, particularly Li, K or Na metals, which are highly reactive materials. Although not essential to the function of the BNNT porous mesh of the present invention, the preferred polymer binders may be permeable to the metal ions in question. In some embodiments, the flexible polymer binder is preferably a natural or synthetic rubber, most preferably a styrene butadiene rubber such as poly(styrene-co-butadiene). These exemplary binders are particularly preferred for metal anodes such as lithium, potassium or sodium.

[0084] Preferably, the binder is present in an amount ranging from 1% to 50% by weight, or 5% to 50% by weight of the BNNT network / deposit. In some embodiments, a binder concentration of 1% to 15% by weight is preferred. In some preferred embodiments, the binder is present in an amount ranging from 10% to 20% by weight of the BNNT network / deposit. In some particularly preferred embodiments, the binder concentration is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15% by weight of the binder relative to the total BNNT component. Most preferably, the binder is present in the BNNT / binder composite at 10% by weight or less, 9% by weight or less, 8% by weight or less, 7% by weight or less, 6% by weight or less, 5% by weight or less, 4% by weight or less, 3% by weight or less, 2% by weight or less, or 1% by weight or less. At least in those embodiments including BNNT / binder composites, a minimum of 0.5 wt. % binder is present.

[0085] Preferably, the boron nitride nanotubes (BNNTs) are present in an amount ranging from about 50% to about 98% by weight of the boron nitride nanotube (BNNT) film or deposit, more preferably 80% to 95% by weight, more preferably 85% to 95% by weight. In some embodiments, the boron nitride nanotubes (BNNTs) are present in an amount of 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95% by weight of the total film / deposit. In other preferred embodiments, the boron nitride nanotubes (BNNTs) are present in an amount ranging from about 88% to about 93% by weight of the total weight of the film / deposit, preferably about 90% by weight of BNNTs. "About" means ±1% of the stated value. Suitably, the remaining % is binder.

[0086] Preferably, at least a portion, preferably a majority, of the binder in the composite BNNT network / deposit is particulate. Preferably, the binder particles are dispersed (preferably uniformly) throughout the composite BNNT / binder network / deposit. The dispersion of the binder can be confirmed by SEM analysis, where individual particles of binder (usually spherical or generally spheroidal particles) are observed to be uniformly dispersed within the BNNT network, i.e., the BNNT fibers / strands that form the network. The contrasting morphology of the binder particles and the BNNT fibers / strands means that the binder and the BNNTs can be easily distinguished in SEM analysis. Desirably, the binder particles adhere or otherwise fix localized areas or regions of the BNNT fibers / strands to provide stability and flexibility to the structure of the porous network. It will be understood that the binder particles fix one or more BNNT fibers / strands together at the location where the binder particle is located. Desirably, the binder does not coat or encapsulate the surface of the BNNT fibers / strands, e.g., within a conformal film of polymer, to any extent that would adversely affect the porosity / pore diameter, particularly the operating temperature of a normal battery or the temperature during thermal runaway. In the present invention, it is desirable that the porosity of the network is always maintained, even when the network / deposit is exposed to heat, e.g., that occurs during the operation of an energy storage device. This is in contrast to the BNNT-polymer composites of US Patent Publication No. 2019 / 0123324, where the opposite result is desired and the polymer is provided as a film / coating on the BNNT scaffold, rather than in a specific form, and the polymer coating expands to reduce the separator pore size, or indeed closes the pores completely to prevent thermal runaway.

[0087] During the preparation of the film / deposit, if an organic solvent system is used to prepare the BNNT / binder mixture, the preferred binder used is PVDF. In some embodiments of the cathode preparation, a water-based system can be used to obtain higher mass loadings of sulfur. Thus, if an aqueous solvent system is used to prepare the BNNT / binder mixture, the preferred binder used is LA133 (acrylonitrile multicopolymer binder). SEM studies show that the porous structure and / or morphology of the film / deposit is the same regardless of the solvent system / binder used. For example, FIG. 8 shows that the film / deposit using LA133 and PVDF has substantially the same structure and morphology despite the different binders used. When a binder is used for the S cathode, the same or a different binder may be used for the BNNT film / deposit. For example, when the S cathode is prepared in an aqueous solution, LA133 may be used as the cathode binder. When an organic solvent is used to form the S cathode, PVDF may be used for the cathode and the BNNT film / deposit.

[0088] In some embodiments, the boron nitride nanotubes (BNNTs) are in the form of a free-standing or self-supporting film disposed in close proximity to the cathode. However, in other preferred embodiments, the film is not a free-standing or self-supporting film in that the BNNT film / deposit is in intimate contact / resting with the S cathode. In some embodiments, the BNNT film / deposit adheres to the S cathode material. It is believed that when the BNNT / polymer slurry is cast during fabrication, the BNNT / polymer material penetrates to some degree into the pores of the S electrode surface. Once the solvent evaporates and the film is formed, strong adhesion occurs between the BNNT / composite film and the S electrode material. In either case, there is at least some, preferably complete, direct interfacial contact between the BNNT film / deposit and the S cathode material. See, for example, FIG. 1(d), which shows the preferred arrangement and intimate interfacial contact between a film of BNNT porous network and the S cathode material.

[0089] The morphology of the BNNT interlayer was investigated by SEM. The thickness of the BNNT interlayer used, for example, in the case of coating on a cathode material, can be controlled by a combination of (i) adjusting the concentration of BNNTs in the interlayer slurry used during formation, and (ii) the height of the doctor blade used to form a uniform coating after applying the BNNT-containing slurry to the S cathode material. The concentration of BNNTs in the slurry affects the density / loading of BNNTs in the final film upon formation. In some embodiments, it is preferred to use a BNNT concentration in the slurry of 15 wt% or less, 10 wt% or less, 7.5 wt% or less, or 5 wt% or less. In some embodiments, a BNNT concentration in the slurry of about 5 wt% is preferred. ("about" here means ±5%).

[0090] The morphology may be described as an irregular network, mesh or sieve of BNNT filaments or strands (depending on the BNNT density / loading used), for example, with multiple filaments or strands arranged in the form of a felt or web. The morphology adopts a tunnel-like, random, fibrous web, honeycomb, or fibrous felt type structure resulting from random superposition of twisted, entangled, or distorted woven yarns or fibrils formed from bundles of BNNT nanotubes, resulting in a structure with channels, passages, or tunnels of dimensions such that Li-ion transport is possible but polysulfides cannot be transported. A BNNT porous network / mesh includes intersecting filaments or strands of BNNTs, a network or grid of connecting, contacting, or intersecting filaments or strands of BNNTs, particularly entangled, intersecting, intertwining, or intertwining filaments of BNNTs. In short, the BNNT yarns, threads, or fibrils are not straight and are not arranged in a regular, repeating, or regular array type structure or arrangement.

[0091] (S-Cathode Electroactive Material Composition) In one embodiment, the present invention provides a sulfur (S)-based cathode comprising a sulfur-cathode material combined with a porous film of boron nitride nanotubes (BNNTs).

[0092] Suitably, the present invention provides a sulfur (S)-based electrode for an energy storage device having a composite film of boron nitride nanotubes (BNNTs) and at least one polymeric binder, the composite film intimately contacting at least one surface of the S electrode as a porous network that is selectively permeable to transport metal ions and electrolytes used in the energy storage device, but impermeable to polysulfides. It is understood that the composite film has tunnels, passages, or channels of dimensions that allow selective passage of transport metal ions through the porous network while reversibly trapping polysulfides within the porous network.

[0093] When a film of a BNNT porous network is used to protect the S electrode material, the density of the BNNTs is such that the channels, pathways, or tunnels reversibly trap the polysulfides. However, the density / thickness of the BNNT porous network film is not so great that it irreversibly traps the polysulfides, which would undesirably lead to deactivation of the active electrode material and loss of capacity over time. The density / thickness of the BNNT porous network film is selected to bring the S back into contact with the active cathode mass upon cycling so that it maintains electrochemical activity despite the mesh. Preferred densities / thicknesses are described elsewhere herein.

[0094] It will be appreciated that the S cathode comprises an electroactive material composition that includes sulfur as the electrochemically active material. In some embodiments, the sulfur is present in an amount ranging from about 60% to about 99% by weight of the electroactive material composition. An amount ranging from about 70% to about 90% by weight is preferred. In one embodiment, 80% by weight sulfur is particularly preferred. The thickness of the sulfur / graphene cathode is suitably in the range of about 5 microns to about 40 microns.

[0095] Preferably, the S cathode also includes a conductivity enhancing material, preferably a carbon-based conductivity enhancing material, such as carbon black, carbon nanotubes (CNTs), carbon nanoparticles, or graphene. In preferred embodiments, the cathode material may include one or more conductivity enhancing agents, such as carbon black (e.g., conductive carbon black such as Ketjen black) or graphene. In some embodiments, the S cathode consists essentially of sulfur and one or more conductivity enhancing agents. In some embodiments, the conductivity enhancing material is present in an amount ranging from 5% to 30% by weight of the electroactive material composition. In some embodiments, the conductivity enhancing material / agent may be present at 10 to 30% by weight of the cathode. In one embodiment, 26% by weight is particularly preferred. Graphene is a particularly preferred conductivity enhancing material. Desirably, when the conductivity enhancing agent is one or more graphenes, the material is present at a concentration of about 0.2 mg cm -2 ~ approx. 0.8 mg cm -2 , about 0.4 mg cm -2 ~0.7mgcm -2 , about 0.5mgcm -2 ~about 0.6mgcm -2 In some embodiments, the mass loading of graphene in the cathode may be 0.6 mg / cm 2The graphene may be a single type of graphene or a mixture of two or more types of graphene, for example highly porous graphene and high surface area graphene. Suitably, the electroactive material composition may comprise a mixture of highly porous graphene and high surface area graphene, for example in a weight percent ratio of 1:9 to 9:1, more preferably 3:7 to 8:2, more preferably 4:6 to 7:3, most preferably a weight ratio of 6:4 being particularly preferred. Suitably, the ratio of highly porous graphene to high surface graphene is 6:4, which gives particularly good performance in terms of highest specific capacitance. Figure 6 shows the effect of various ratios on the specific capacitance. Thus, the weight ratio of the preferred composition is 12 wt% highly porous graphene:8 wt% high surface graphene:80 wt% sulphur. Thus, in a preferred embodiment, the cathode electroactive material composition comprises 12 wt% highly porous graphene:8 wt% high surface graphene:80 wt% sulphur.

[0096] Preferably, the sulfur is about 0.1 mg cm -2 ~ approx. 10 mg cm -2 , 0.5 mg cm -2 ~about 7.5mgcm -2 , about 0.9mgcm -2 ~about 6mgcm -2 , and most preferably about 5 mg cm -2 The preferred electrode has an effective loading of about 1 mg cm -2 ~ approx. 8 mgcm -2 , preferably about 2.5 mg cm -2 ~about 4.5mgcm -2 , and most preferably about 3 mg cm -2 In some embodiments, the mass loading of sulfur in the cathode is from about 0.9 to about 2.4 mg cm -2 The range is.

[0097] Preferably, the boron nitride nanotube (BNNT) film or deposit has a density of about 0.2 mg cm -2 ~about 1.7mgcm -2 , more preferably about 0.1 mg cm -2 ~ approx. 1 mg cm-2 , more preferably about 0.5 mg cm -2 ~about 0.75mgcm -2 has a density of

[0098] In one embodiment, the average thickness of the boron nitride nanotube (BNNT) deposit is about 0.1 microns to about 10 microns. In a preferred embodiment, the average thickness of the boron nitride nanotube (BNNT) deposit is about 0.9 microns to about 5 microns, preferably about 1.5 microns to about 3 microns, and more preferably about 1.75 microns to about 2.5 microns. In some embodiments, an average thickness of about 1.9 microns to 2.3 microns is preferred. In some preferred embodiments, the desired composite film has an average thickness of about 0.9 microns to about 5 microns, preferably about 1.5 microns to about 3.5 microns, and most preferably about 2.5 microns. In some particularly preferred embodiments, an average thickness of about 3.5 microns or less is preferred, as it has been found to provide good protection between sufficient protection to avoid rapid capacity loss and the ability to prevent polysulfide shuttle. However, with thicker layers, the captured / adsorbed polysulfides become inactive because the BNNT layer is too thick to allow the PS to return to the cathode mass, resulting in a decrease in capacity after the first and second cycles. For example, cycling stability results for a single late stage 2.1 V Li-S pouch cell with different thicknesses of BNNT layers on an S cathode show very high capacity retention (>90%) after 50 cycles at 25 °C and 0.2 C for a 2.3 micron thick BNNT interlayer, and good capacity retention (>80%) after 50 cycles at 0.2 C for a 0.9 micron thick BNNT interlayer. This is a significant improvement over a comparable pouch without an interlayer, which shows about 65% capacity retention after 50 cycles.

[0099] In one embodiment, the boron nitride nanotube (BNNT) film / deposit is about 0.075 mg / cm 2 ~about 0.5mg / cm 2 In a preferred embodiment, the boron nitride nanotube (BNNT) film / deposit has a BNNT loading density of about 0.1 mg / cm 2~about 0.3mg / cm 2 , preferably about 0.15 mg / cm 2 ~about 0.25mg / cm 2 The desired composite film has a BNNT loading density of about 0.05 mg cm -2 ~about 3.5mgcm -2 , and more preferably about 0.05 to about 0.5 mg cm -2 , most preferably 0.2 mg cm -2 The surface density or BNNT loading is about 3.5 mg cm -2 The following ranges are particularly preferred when longer cycle life is desired since the films / deposits are dimensioned such that the adsorbed polysulfides can be efficiently returned to the cathodic material upon cycling, i.e., remain active. Here, about means ±2%. In some embodiments, boron nitride nanotube (BNNT) films / deposits have a thickness of about 0.2 mg / cm 2 as has been found to provide particularly good capacity retention of greater than 90% of the initial capacity over at least 10 cycles, at least 20 cycles, at least 50 cycles, at least 200 cycles, or at least 1000 cycles.

[0100] Desirably, the sulfur-based electrode material is deposited on a current collector, preferably an aluminum foil current collector, hi some embodiments, the current collector is a metal (e.g., aluminum) foil current collector that may be coated on one or more sides with a conductive material such as carbon.

[0101] The present invention relates to an energy storage device (e.g., a secondary battery) comprising one or more cathodes of the present invention as described herein. In some embodiments, the device can be a coin cell. In other preferred embodiments, the device can be a pouch cell, such as a single-layer pouch cell. More complex cell arrangements are also envisioned.

[0102] In one embodiment, the present invention provides an energy storage device comprising one or more sulfur (S)-based electrodes of the present invention described herein. For example, the energy storage device may further comprise a separator, at least one metal anode, preferably a lithium or sodium metal anode, and an electrolyte.

[0103] In one embodiment, the energy storage device of the present invention comprises at least one cathode having a sulfur-based electrode material with a porous film of boron nitride nanotubes (BNNTs) on the electrode material, a separator, at least one anode having a lithium metal-based electrode material, and an electrolyte.

[0104] In a preferred embodiment, the energy storage device of the present invention retains up to 60% of its initial capacity after at least 500 cycles at a temperature of 25° C. and a current density of 0.2 C.

[0105] In other embodiments, the device retains up to 60%, up to 70%, up to 80%, up to 90%, up to 100% of the initial capacity after at least 500 cycles at a temperature of 25° C. and a current density of 0.2 C. In other preferred embodiments, the device retains up to 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 100% of the initial capacity after at least 500 cycles at a current density of 0.2 C. These capacity retentions are observed at a temperature of 25° C.

[0106] Preferably, the energy storage device has a capacity of at least 400 mAhg based on the S loading at a 0.2 C rate and a temperature of 25° C. -1 and preferably exhibits a specific capacity of at least 900 mAhg based on S loading. -1 The specific capacity is shown.

[0107] The present invention also relates to an electronic device comprising an inventive cathode as described herein and / or an inventive energy storage device as described herein.

[0108] The present invention also relates to the use of the electronic devices and / or energy storage devices of the present invention in transportation, grid storage, electric vehicles, and advanced portable electronics applications.

[0109] The present invention relates to the use of one or more BNNT layers as a polysulfide blocking coating in the cathode of an energy storage device. The present invention also relates to the use of one or more BNNT layers, preferably a BNNT / polymer binder composite layer, as a polysulfide diffusion blocking coating or reversible trap for polysulfides in the sulfur (S)-based cathode of an energy storage device.

[0110] The present invention further comprises: At least one sulfur (S)-based electrode having a film of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, the film of the composite being in intimate contact with at least one surface of the electrode as a porous network that is selectively permeable to transport metal ions and electrolytes used in the energy storage device, but impermeable to polysulfides; at least one metal electrode having a coating of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, the coating of the composite intimately contacting at least one surface of the electrode as a porous mesh that is selectively permeable to transport metal ions used in an energy storage device, wherein the composite is physically and / or chemically bonded to the surface of the metal electrode; The present invention also extends to a metal-sulfur energy storage device comprising:

[0111] The present invention relates to At least one sulfur (S)-based electrode having a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, the composite film being in intimate contact with at least one surface of the electrode as a porous network that is selectively permeable to transport metal ions and electrolytes used in the energy storage device, but impermeable to polysulfides; at least one lithium metal electrode having a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, wherein a coating of the composite is in intimate contact with at least one surface of the electrode as a porous mesh that is selectively permeable to lithium ions that are physically and / or chemically bound to the surface of the metal electrode; The present invention also extends to a lithium-sulfur energy storage device comprising:

[0112] (Detailed description of the protected S cathode electrode) (Preparation of S cathode) First, graphene and sulfur are mixed and heated at 300°C. The resulting mixture can then be heated, for example, at 300°C for about 24 hours, preferably in an airtight container, to synthesize the S-cathode. Secondly, the resulting graphene / sulfur powder is heated and then mixed with carbon black, a binder, in an organic solvent NMP to form a slurry. Thus, the S-cathode is prepared by mixing a desired amount of sulfur, binder, and conductive additive in an organic solvent, for example, N-methyl-2-pyrrolidone (NMP). The graphene / binder / sulfur slurry is then coated onto a suitable current collector, for example, Al foil, using a doctor blade. The thickness can be controlled by adjusting the height of the blade. The S-cathode is then dried in an oven at 80°C for 12 hours and is ready for coating or bonding with a BNNT interlayer.

[0113] (Preparation of BNNT porous network films for S cathode) The BNNT porous network comprises boron nitride nanotubes (BNNTs) and a binder. For an S cathode, the BNNT composition may comprise about 1 wt% to about 20 wt% BNNTs of the total BNNT composition. An amount of BNNTs ranging from about 2 wt% to about 15 wt% is preferred. An amount ranging from about 5 wt% to about 10 wt% of the total BNNT interlayer composition is preferred. In one embodiment, an amount of BNNTs of about 5 wt% of the total BNNT interlayer composition is particularly preferred. In one embodiment, an amount of binder of 10 wt% is particularly preferred, for example 10 wt% PVDF of the total BNNT interlayer composition. Preferred BNNTs are obtained from BNNTTechnology Limited. Preferred BNNTs are substantially free of impurities such as hexagonal boron nitride and / or elemental boron. The BNNT composition may further comprise one or more binder materials selected from the group consisting of PVDF, PTFE, polyethylene oxide (PEO) and LA133. In some embodiments, LA133 is particularly preferred because it can be used with aqueous solvents / systems such as water.

[0114] In particular, BNNT composites are electrically insulating materials, i.e., they are not electronically conductive. Furthermore, the BNNT composites of the present invention do not include conductivity enhancers, such as carbon-based conductivity enhancers, such as graphene. No additives to enhance conductivity are required, since the transport pathways for metal ions, such as sodium or lithium ions, are open in the porous BNNT composites and are maintained during battery operation. Therefore, graphene is not required in the composites to enhance conductivity.

[0115] The BNNT intermediate layer is prepared by mixing a desired amount of BNNTs and a desired amount of binder in a suitable organic solvent such as N-methylpyrrolidinone (NMP) or deionized water to form a slurry. The resulting slurry is then coated onto the surface of the cathode electrode material, and the thickness of the slurry coating is adjusted as desired, for example by a doctor blade, and then dried, for example in an air oven at 60° C. for 24 hours to remove the solvent, providing a final film of the BNNT porous network on the S cathode material in the form of a film less than 20 microns thick.

[0116] (current collector) The current collector can be any current collector suitable for use with an S cathode. For example, the current collector can be a metal foil, such as aluminum foil, aluminum foam, or conductive carbon cloth. The thickness of the current collector is suitably in the range of about 10 microns to about 100 microns. In one embodiment, the preferred current collector has a thickness of about 20 microns, such as 20 micron aluminum foil. A standard material can be, for example, about 20 micron copper foil, such as 20 micron copper foil, as a current collector for a Li metal anode.

[0117] (Separator) The separator can be any separator suitable for an S cathode. For example, a polypropylene separator such as Celgard 2400 separator (25 micron separator) can be used.

[0118] (electrolyte) The electrolyte can be any electrolyte suitable for the desired battery under consideration. For example, for a Li-S battery, a combination of DOL / DME, particularly Li ionic liquid salt and LiNO 3 Ionic Li salts such as LiNO can be used. 3 The weight ratio of LiNO can be up to 5%. For example, one exemplary electrolyte is 1% by weight of LiNO 3 The compound is 1M LiTFSI in DOL / DME containing

[0119] (Pouch material) The pouch material can be any material suitable for Li-S batteries, such as Al plastic film.

[0120] (Coin cell with BNNT / S-cathode) A Li-S based coin cell was fabricated containing a Li metal anode, a separator, a BNNT-protected S cathode of the present invention, and an electrolyte. In one embodiment, a standard lithium metal chip for coin cells was used as the lithium metal anode, and a 25 micron polypropylene-based separator, e.g., Celgard 2400 separator, was used with the BNNT / S cathode of the present invention. The coin cell contained 1 wt. % LiNO 3 The electrolyte composition was 1M LiTFSI in DOL / DME containing

[0121] Full cells, i.e., Li-S pouch cells, were fabricated in an argon-filled glove box using a lithium metal film as the anode, a 25 micron polypropylene-based separator such as Celgard 2400 separator, and a graphene / S cathode protected with a BNNT interlayer. A commercially available soft Al plastic film was used as the case. The electrolyte, e.g., 1 wt.% LiNO 3 1M LiTFSI in DOL / DME containing, for example, a volume equivalent to about 5 μL / mg to about 50 μL / mg, more preferably about 15 μL / mg, depending on the mass of sulfur. -1 was added appropriately.

[0122] Detailed Description of the Invention Next, Figure 1 shows SEM images of the S / graphene cathode with BNNT composites on the sulfur / graphene cathode (Figure 1b) and the S / graphene cathode without BNNT composites (Figure 1a). Figure 1(c) shows a high magnification top-down view of the sulfur-graphene cathode, revealing the surface porosity of the S cathode material.

[0123] Figure 1(d) shows a side view of the three different layers: (i) the BNNT composite component, (ii) the sulfur / graphene composite component, and (iii) the aluminum foil current collector material. Figure 1(e,f) shows low and high magnification top-down images of the S cathode with the BNNT porous network composite film.

[0124] As is evident from Figure 1(a), Figure 1(e), and (f), it is evident that the BNNT porous network covers the entire cathode material. The enlarged view in Figure 1(f) clearly shows the BNNT porous network formed by the deposited BNNT interlayer. The morphology may be described as a random fiber web, honeycomb, or fiber felt type structure resulting from the random superposition of twisted, entangled, and / or distorted threads or fibrils formed from bundles of BNNT nanotubes. In short, the BNNT yarns, threads, or fibrils are not straight and are not arranged in a regular, repeating, or regular sequence type structure or arrangement. Unique uniformly dispersed solid spheroidal binder particles may also be observed in this image.

[0125] The specific capacity (mAhg based on S) achievable for a Li-S coin cell containing a BNNT / S cathode and an equivalent Li-S coin cell without a BNNT interlayer on the S cathode. -1 ) and specific capacity retention (%) are shown in Figure 2(a) and Figure 2(b).

[0126] Figures 2a and 2b show the performance of coin cells with BNNT interlayers of 5% and 10% by weight relative to the total slurry solution. For the Li-S coin cell in Figure 2(a), the BNNT interlayer was fabricated using a slurry with 5% by weight of BNNTs. All coin and pouch cells are tested at room temperature, approximately 25°C, 0.2C. Varying the doctor blade height resulted in BNNT interlayer thicknesses of X microns (X means that the thickness varies throughout the coating and cannot be reliably measured), 0.9 microns, 1.5 microns, and 2.3 microns, with corresponding capacity retentions (shown as starting specific capacity %) of 40%, 67%, 85%, and 90%, respectively, at 500 cycles, as shown in Figure 2(a). Similarly, Figure 2(b) shows data for a cathode with a BNNT interlayer fabricated using a slurry with 10% by weight of BNNTs. Varying the doctor blade height resulted in BNNT interlayer thicknesses of X microns (X means that the thickness varies throughout the coating and therefore cannot be reliably measured), 2.2 microns, 3.2 microns, and 4.4 microns, with corresponding capacity retentions (shown as starting specific capacity %) of 40%, 79%, 87%, and 92% at 500 cycles, respectively, as shown in Figure 2(a). The data suggest a synergistic effect between the optimal thickness and optimal BNNT concentration in the slurry. In particular, the 2.3 micron film formed from the 5 wt% BNNT slurry gave particularly good capacity over the duration of the cycling study. Furthermore, when the surface of the BNNT-coated sulfur cathode was inspected by SEM (not shown), it is evident that for a blade height of 100 μm, the sulfur cathode was not completely covered, and undesirable large particle agglomerations can be seen on the surface of the BNNT intermediate film made with 10% by weight. Thus, the use of a 10% BNNT by weight slurry results in agglomerations on the surface of the BNNT interlayer. Due to agglomeration, the initial capacity of the BNNT-coated cathode (10%) is not as high as that of the equivalent cathode without the coating. In particular, for the BNNT film used in the experiments reported in Figure 2(a), very little agglomeration is observed on the surface of the BNNT interlayer (5%), which contributes to the high initial capacity.With the BNNT thickness of 10 μm or 20 μm, the capacity retention is good but the capacity decreases. This is attributed to the increased tunnel / path length for lithium ion transport with the increased film thickness. In summary, it was found that thicker BNNT layers result in lower initial capacity but better cycling stability. However, as the thickness of the BNNT layer increases, the cycling stability is improved. Depending on the specific desired battery application, the resulting performance parameters can be tailored as needed.

[0127] Description of the Preferred Embodiments Synthesis of graphene / sulfur cathode: A mixture of 12 wt% highly porous graphene, 8 wt% high surface area graphene (Graphene Supermarket, USA), and 80 wt% sulfur was heated at 300 °C for 24 h in an airtight container for the synthesis of graphene / sulfur electrodes. The graphene / sulfur was coated on an Al foil with a thickness of 20 μm. The resulting graphene / sulfur cathode was then dried at 60 °C for 48 h in a vacuum oven. These electrodes were further coated with a BNNT interlayer.

[0128] Synthesis of BNNT interlayer on cathode: The BNNT interlayer was prepared by mixing a solution of 5 wt% BNNT (BNNT Technology Limited) and 0.5 wt% PVDF binder in N-methylpyrrolidinone (NMP). The slurry was coated on the surface of the graphene / sulfur cathode electrode by a doctor blade with the desired thickness and dried in an air oven at 60 °C for 24 h.

[0129] Fabrication of Li-S coin and pouch cells: Li-S coin cells were fabricated using lithium chips, a Celgard 2400 separator, and a graphene / S cathode with a BNNT interlayer. The electrolyte was 1 wt% LiNO 3 The compound was 1M LiTFSI in DOL / DME containing

[0130] A fully flexible Li-S pouch battery was fabricated in an argon-filled glove box using a lithium film, a Celgard 2400 separator, and a graphene / S cathode with a BNNT interlayer. A commercially available soft Al plastic film was used for the case. The electrolyte was appropriately added according to the mass of sulfur, in this case 15 μL mg -1 It was.

[0131] Results and discussion on protection of S cathode: To coat the BNNT interlayer on the sulfur cathode, a slurry consisting of BNNTs, binder and organic solvent is prepared as exemplified above. In this example, the weight ratio of BNNTs (weight of BNNTs relative to the total weight of the slurry) was controlled to 5%. The blade height is also adjusted to 100 μm, 200 μm, 300 μm and 400 μm to control the thickness of the BNNT interlayer formed. Upon removal of the solvent, the thickness of the final formed interlayer ranges from 0.9 μm to 5 μm depending on the starting concentration of BNNTs in the slurry used.

[0132] It can be observed by SEM that the sulfur cathode is completely covered and a porous network of the BNNT interlayer is formed. As shown in Figure 1d, three separate layers of components can be observed by SEM: the BNNT interlayer, the graphene / sulfur layer, and the Al foil.

[0133] Li-S coin cells with sulfur cathodes coated with the resulting BNNT interlayers were fabricated and tested. The cycling stability of the coin cells was investigated in detail. Figure 2a and Figure 2b compare the specific capacity of Li-S coin cells with and without sulfur cathodes coated with BNNT interlayers. The BNNT interlayer film was fabricated using a slurry with a weight ratio of BNNTs of 5%. First, the Li-S coin cell without the BNNT interlayer shows the worst stability. The cell with the thinnest layer of BNNT layer (note that the thickness cannot be reliably measured in this case because the layer does not completely cover the surface of the sulfur cathode) shows an improvement in stability, but the stability is still insufficient. However, as the thickness of the BNNT layer increases from 0.9 μm to 2.3 μm, the cycling stability (capacity retention) after 500 cycles at 25 °C, 0.2 C increases from 67% to 90%, indicating that the BNNT layer improves the cycling stability of the sulfur cathode.

[0134] A single-layer Li-S pouch battery with a sulfur cathode coated with the resulting BNNT interlayer was fabricated and tested. The cycling stability of the pouch cells was investigated in detail. The BNNT interlayer is fabricated using a slurry in which the weight ratio of BNNTs is 5% of the weight of the total slurry including BNNTs, binder and solvent. The capacity of the pouch cell without the BNNT interlayer drops to 65.2% after 50 cycles, while the pouch cells with 0.9 μm-2.3 μm BNNT layers maintain 82% and 95% of the initial capacity, indicating that the BNNT layer significantly improves the cycling stability of the sulfur cathode.

[0135] (Polysulfide block demonstration) Polysulfide (PS) solution (0.136 mol / L Li in commercial electrolyte) 2 S 8A solution of 1M LiTFSI in DOL / DME containing -1% LiNO3 was prepared and transferred into two bottles. Figure 4(a) shows the polysulfide solution without BNNTs (yellow) and with BNNTs (yellow color has disappeared). The polysulfide solution is yellow due to the presence of PS. However, upon addition of 5 mg of BNNTs, the yellow color disappears immediately, implying the binding of PS with BNNTs such that the dissolved PS is pulled out of the solution. IR analysis was performed on a series of polysulfide solutions with different amounts of BNNTs added (0 mg, 8 mg, and 15 mg of BNNTs added). The IR results in Figure 4(b) show the change in the Li concentration after adding BNNTs to the polysulfide solution. 2 S 8 The results in Fig. 4(c) show a decrease in the intensity of the absorption peaks, indicating that polysulfides are adsorbed on the BNNTs. Raman analysis was also performed. The results in Fig. 4(c) show the BS and NS bonds of the BNNT-polysulfide sample recovered from the BNNT-treated PS solution, further proving that the BNNTs are adsorbing polysulfides. The absorption of PS from the solution onto the BNNTs indicates that the BNNTs are trapping the PS. In an energy storage / battery environment, the adsorption of S onto the BNNT film / deposits prevents the loss of PS into the electrolyte and prevents the loss of cathode mass that may occur upon cycling. With the BNNT composite film with optimized thickness and density, the PS is reversibly trapped by the BNNTs and the PS / S remains electrochemically active.

[0136] Indeed, Figure 7 shows (a) the specific capacity and (b) the capacity retention of the Test S cathode over 100 cycles at various BNNT loading densities of 0.05, 0.1, 0.2, 0.25, and 0.5 mg / cm, respectively. 2 All cells tested in (a) performed acceptable initial specific capacities in the range of 1150–1250 mAh / g. These cells exhibited capacity retention at the 100th cycle of 69.4, 73.7, 85.7, 77.8, and 75.2% (compared to the capacity at the 1st cycle). 2This BNNT loading density gives particularly good performance in terms of capacity retention (see 1st cycle).

[0137] Example 2 - Coating of BNNT mesh controls dendrite formation on metal electrodes During electrochemical metal plating and stripping, or during charge and discharge cycles of an energy device (including electrochemical metal plating and stripping), the metal anode material continually undergoes non-uniform volume expansion and contraction concentrated in various regions throughout the anode, to the extent that the native SEI cracks, fractures, or otherwise damages the material during battery operation. When cracks or fractures form in the native SEI, an uncontrolled influx of large amounts of metal ions reaching certain regions of the anode is readily transported to the metal surface, forming metal nucleation sites on the electrode surface from which dendrites grow. Thus, the instability of the SEI has been a limiting factor in the progress of energy storage devices including metal anodes. Described herein is a metal electrode for an energy storage device having a composite of boron nitride nanotubes (BNNTs) and at least one polymeric binder, wherein a coating of the composite is in intimate contact with at least one surface of the electrode as a porous mesh that is selectively permeable to transport metal ions used in selectively reactive energy storage devices, and wherein the composite is physically and / or chemically bonded to the surface of the electrode. The mesh is configured to distribute metal transport ions across the mesh evenly across the surface of the metal electrode, thereby reducing the formation of metal dendrites.

[0138] The BNNT porous mesh of the present invention has been found to solve the problem of dendrite formation on metal electrodes during electrochemical metal plating and stripping, or during charge and discharge cycles of energy devices involving electrochemical metal plating and stripping. It is believed that the BNNT porous mesh of the present invention comprises one or more tunnels, pathways and / or channels therethrough that are directed, oriented and / or dimensioned to redistribute the concentrated metal ion flux found on one side of the mesh to a more uniformly distributed metal ion flux on the other side of the mesh, thereby distributing the metal ion flux over a larger surface area of ​​the anode. The tunnels, pathways and / or channels therethrough are configured or oriented laterally toward the side of the electrode, i.e., away from any one location or region of the electrode. The direction of the tunnels, pathways and / or channels therethrough takes the concentrated metal ion flux and redistributes it throughout the body of the electrode. That is, the transport through the mesh splits the concentrated metal ion flux into multiple smaller ion fluxes that are spread evenly across the surface of the anode, resulting in homogenous metal plating on the anode surface. In the absence of the BNNT porous mesh coating, the concentrated metal ion fluxes would all target a very localized area of ​​the anode surface, which could cause significant uncontrolled volume expansion. It is believed that the BNNT porous mesh splits the metal surface into more accessible areas to distribute the transported metal ions through the mesh across the metal electrode surface. While this effect can be achieved with a variety of mesh thicknesses, it is preferred to optimize the thickness to ensure fast transport of metal ions through the mesh to ensure good capacity retention and to keep the internal resistance of a device with a protected anode as low as possible. In a preferred embodiment, the BNNT porous mesh composite coating has an average thickness of about 1 micron to about 50 microns, more preferably about 2 microns to about 25 microns, more preferably about 3 to 10 microns, preferably about 1.5 microns or about 7.5 microns, and most preferably about 5 microns. In a preferred embodiment, the composite coating has an average thickness of about 0.2 mg cm -2 ~ approx. 8 mgcm-2 , about 0.1 mg cm -2 ~ approx. 2 mg cm -2 , more preferably about 0.1 to about 2 mg cm -2 , and most preferably about 0.4 mg cm -2 The areal density or BNNT loading is

[0139] In a preferred coating of the composite porous mesh, at least a portion of the polymer binder is present as particles that fix the strands of BNNTs together to form a porous network or mesh. Furthermore, at least a portion of the polymer binder is present as particles that fix the strands of BNNTs together to form a porous mesh. Desirably, the strands of BNNTs are not completely conformally coated with the polymer binder. Suitably, the BNNTs are substantially free, preferably completely free, of hexagonal boron nitride and / or elemental boron impurities. Preferably, the metal is selected from Li, Na, K, Al, and Zn, preferably Li or Na. Desirably, the coating of the composite comprises a polymer binder at a concentration of about 50 wt% or less, preferably 20 wt% or less, preferably 15 wt% or less, preferably about 10 wt% or less. Suitably, the BNNT porous mesh comprises one or more tunnels, pathways and / or channels therethrough that are oriented, oriented and / or dimensioned to delocalize or redistribute concentrated metal ion flux on one side of the mesh into a more evenly distributed metal ion flux on the other side of the porous network / mesh, thereby distributing the metal ion flux across a larger surface area of ​​the electrode.

[0140] Desirably, the BNNT porous mesh for metal electrodes comprises at least one binder, preferably a polymeric binder. A polymeric binder is preferred due to its flexible and / or elastic mechanical properties. Suitably, the polymeric binder may be selected from any binder described herein, but is preferably selected from natural or synthetic rubbers, such as styrene butadiene rubber, poly(vinylidene fluoride-co-hexafluoropropene (PVDF-HFP), poly(3,4-ethylenedioxythiophene)-co-poly(ethylene glycol) (PEDOT-co-PEG), polyethylene glycol (PEG)-polymethylmethacrylate (PMMA), poly(dimethylsiloxane) (PDMS), and combinations thereof. Desirably, the flexible polymeric binder is or comprises poly(styrene-co-butadiene). Preferably, the flexible polymeric binder is poly(styrene-co-butadiene).

[0141] Thus, the present invention provides a BNNT porous mesh for the negative electrode (anode) of an energy storage device, preferably a rechargeable energy storage device. The present invention relates to a protective coating for metal-based anode materials, in which the negative electrode is bonded with boron nitride nanotubes (BNNTs) in the form of one or more deposits or intermediate layers of BNNTs having a porous mesh structure (hereinafter referred to as "BNNT porous mesh"). A preferred BNNT porous mesh of the present invention is a flexible and / or elastic porous mesh. The flexible BNNT porous mesh of the present invention reinforces, supports, scaffolds, and / or strengthens the native solid electrolyte interface (SEI) layer to resist cracking and fracture, thus reducing the opportunity or tendency for site nucleation and subsequent dendrite formation / growth to occur when a concentrated metal ion influx passes through the cracks of the native solid electrolyte interface (SEI). As used herein, "flexible" and / or "elastic" means that the mesh resists cracking or fracture during electrochemical metal plating and stripping, which can be achieved, for example, at 0.1 mAcm. -2 ~20mAcm -2This occurs during charge / discharge cycles in energy storage devices in the current density range of

[0142] Additionally, the BNNT porous mesh of the present invention has been found to have suitable physical and chemical properties for use as one or more of a support, scaffold, or reinforcing structure for an artificial SEI, pseudo-SEI, and / or natural SEI that is reinforced to prevent cracking, fracture, or damage during electrochemical metal plating and peeling. In a preferred embodiment, the BNNT porous mesh mechanically supplements the existing natural SEI. The preferred BNNT porous mesh of the present invention is electronically insulating (i.e., acts as a passivation layer) but ionically conductive, i.e., permeable to the ions of the metal-based anode material but impermeable to the non-transporting metal ion components in electronic and energy storage devices. The preferred BNNT porous mesh has sufficient flexibility to avoid cracking, fracture, or other damage during cycling, and also has sufficient mechanical strength to control or at least reduce the damaging effects on the natural SEI due to volume expansion of metal plating and metal anode materials, e.g., electrochemical metal plating and peeling, or peeling during cycling of energy devices.

[0143] Additionally, it is believed that the mechanical properties of the BNNT porous mesh are such that the BNNT porous mesh can control or more uniformly direct the volumetric expansion of the metal-based anode material across the anode surface area as compared to a comparable metal-based anode material without the BNNT porous mesh. The more uniform or homogeneous control of the volumetric expansion in this manner is believed to reduce the degree of stress and / or strain experienced by the native SEI, making it stronger against cracking, fracture, or other damage that typically occurs during electrochemical metal stripping / plating or cycling operations within energy storage devices.

[0144] Preferably, the BNNT porous mesh comprises at least one distinct layer of BNNTs in direct contact with the electrolyte-facing surface of the metal-based anode material.

[0145] Desirably, the BNNT porous mesh is in the form of a free-standing or free-standing film that is disposed on or adjacent to the electrolyte-facing surface of the metal-based anode material.

[0146] Suitably, the BNNT porous mesh is in the form of a coating directly on the electrolyte-facing surface of the metal-based anode material. The SEI, when formed during cycling, is located between the BNNT porous mesh and the metal anode surface. In some embodiments, the BNNT network / mesh is physically and / or chemically bonded to one or more electrode materials and / or SEI when formed, for example, via physical entanglement or covalent and / or ionic bonds between atoms of the network / mesh and the SEI components. In either case, interfacial / intimate contact between the BNNT layer and the electrode / SEI is desired.

[0147] The BNNT porous mesh is desirably in the form of a three-dimensional (3D) porous film, a porous network / mesh, or a porous deposit of boron nitride nanotube (BNNT) mesh. Desirably, the BNNT porous mesh is uniform throughout its area in one or more of composition, morphology, ionic conductivity, and elastic modulus.

[0148] Suitably, the BNNT porous mesh may include intersecting and / or crossing filaments, particularly intertwining, intersecting, intertwining, or entangled BNNTs, forming a network or grid of connecting, contacting, or intersecting filaments or strands of BNNTs. Desirably, the BNNT porous mesh is a disordered mesh of BNNT filaments or strands. The BNNT porous mesh may comprise one or more tunnels, passages, and / or channels penetrating and traversing the mesh, which are spatially positioned, oriented, directed, and / or dimensioned to redirect, spread, and redistribute a concentrated metal ion flux of metal ions (reaching a particular region of the mesh on the electrolyte side) through the mesh so as to be more uniformly distributed or delivered across the width of the surface of the anode after passing through the BNNT porous mesh, more uniformly and / or more homogeneously. The tunnels, pathways and / or channels therethrough are directed, oriented and / or dimensioned to delocalize or redistribute the concentrated metal ion flux found on one side of the mesh into a more evenly distributed metal ion flux on the other side of the mesh, thereby distributing the metal ion flux over a larger surface area of ​​the anode. This redistribution, diffusion and / or redirection of the metal ion influx advantageously allows the metal ion influx to be split and distributed in a more even and orderly manner over a much larger surface area of ​​the metal anode than would be possible with an anode without the BNNT porous mesh, where the concentrated ion influx tends to be more localized. That is, by passing through the mesh, the concentrated ion influx is delocalized over the entire width of the metal anode surface. Because the metal ions that reach the metal anode surface are delocalized and spread evenly and homogeneously across the anode surface, the volume expansion is better controlled and more consistent and uniform across the anode, thereby minimizing the stresses and strains experienced by the various different components or regions of the SEI that forms at the anode-electrolyte interface during electrochemical metal plating / stripping or charge / discharge cycling in energy storage devices.As a result of the ion redistribution induced by the BNNT porous mesh, the tendency of the SEI to crack or break is significantly reduced due to the reduction in the overall stress experienced by the native SEI. This reduces the opportunity for the nucleation and subsequent growth of metal dendrite sites. That is, the BNNT porous mesh hinders the formation of dendrites by inducing ion delocalization and a more uniform distribution of metal ions passing through the mesh, reaching a larger area of ​​the anode surface compared to that occurring without the BNNT porous mesh. These advantages are clearly observable through stable long-term electrochemical metal plating and peeling in a symmetric cell arrangement or through stable cycling in an energy storage device. The fact that cycling stability is observed infers that dendrite formation has not occurred to the extent that the cell would short-circuit after only a few cycles, as occurs in the absence of a BNNT network / mesh on the metal electrode.

[0149] As a result of the BNNT porous mesh, it is believed that the large flux of metal ions arriving at the mesh is split into multiple smaller, more uniformly directed ion flux streams that traverse the mesh in a manner that results in a more uniform or more homogeneous deposition of metal across the width of the anode surface. In effect, the mesh promotes first more delocalized ion directionality, which in turn promotes more uniform, homogeneous and controlled electrochemical metal plating and more homogeneous and controlled volumetric expansion across the anode, thereby subjecting the native SEI to less damaging stresses and strains.

[0150] A schematic of this ion screening / filtering or control mechanism for the case of a Li metal anode coated with a BNNT porous mesh is shown in Figure 14. Thus, preferably, the pores, tunnels, pathways and / or channels associated with the BNNT porous mesh are dimensioned, oriented, directed and / or oriented to manipulate, control and / or redirect metal ion fluxes attracted to the metal-based anode material by splitting them into more ordered, spatially spread component ion streams through the mesh which have the effect of spreading the ion flow across the surface of the anode material as it passes through the mesh.

[0151] Suitably, the BNNT porous mesh is electrically insulating but permeable to metal transport.

[0152] Preferably, the BNNT porous network / mesh is uniform in one or more of composition, morphology, thickness, ionic conductivity, and mechanical properties. In particular, the composition, thickness, and mechanical properties can be controlled or tailored for any application by varying one or more of the relative concentrations of BNNTs and polymer binder in the mesh slurry, the thickness of the slurry coating, the length and diameter of the BNNTs, etc. The same is true for the BNNT porous network / mesh of the S cathode embodiment.

[0153] Suitably, the BNNT porous mesh is flexible and / or elastic so as to resist cracking or breaking during electrochemical plating and peeling. It is desirable for the BNNT porous mesh to be flexible and / or elastic under electrochemical metal ion plating and peeling conditions. This can be achieved, for example, by using a 1 mAhcm -2 Fixed charge / discharge capacity of 1mAcm -2The BNNT porous mesh is characterized by little or no cracking or breakage after at least 100 charge / discharge cycles at a charge density of 1000 mAhcm. Under these conditions, one cycle takes 2 hours; that is, 1 hour metal plating time and 1 hour metal stripping time. It should be understood that metal ion plating and stripping studies may be performed in a symmetric cell containing a metal electrode. For example, the preferred BNNT porous mesh can be charged at, for example, 1 mAhcm -2 Fixed charge / discharge capacity of 1mAcm -2 The anode material is flexible under lithium ion plating and stripping conditions as evidenced by little or no cracking or breakage after at least 600 charge / discharge cycles at a charge density of 1000. Preferably, the metal-based anode material comprises an alkali metal, such as Li, Na, K, preferably Li or Na, most preferably Li. Suitably, the metal-based anode material comprises lithium metal.

[0154] Preferably, the BNNT porous mesh is physically and / or chemically stable in the presence of metal-based anode materials. Preferably, the BNNT porous mesh is physically and / or chemically stable in the presence of electrolytes or electrolyte systems commonly used in energy storage devices / applications.

[0155] Preferably, the BNNT porous boron nitride nanotubes described herein for any electrode are at least about 0.5 microns long, more preferably at least 1 micron long. In one preferred embodiment, the BNNTs have a length of about 1 to about 50 microns. In one example, BNNTs of about 10 microns long are particularly preferred. The boron nitride nanotubes preferably have a diameter of about 500 nm or less. Preferred diameters range from about 50 nm to about 100 nm, more preferably about 100 nm.

[0156] Desirably, the boron nitride nanotubes are present in the boron nitride nanotube (BNNT) porous mesh in an amount ranging from about 20% to about 95% by weight, preferably from about 50% to about 90% by weight, and most preferably from about 85% to about 98% by weight of the BNNT film or deposit. In some embodiments, 90% by weight of BNNTs is preferred.

[0157] Suitably, the binder is present in the BNNT porous mesh in an amount ranging from about 5% to about 80% by weight of the BNNT porous mesh, more preferably from 10% to 50% by weight of the BNNT porous mesh, preferably about 10% by weight of the BNNT porous mesh. It will be appreciated that the greater the amount of binder, particularly the flexible binder, the greater the flexibility of the mesh. Preferably, the boron nitride nanotubes of the BNNT porous mesh are present in an amount ranging from about 0.2 mg cm -2 ~ approx. 8 mgcm -2 , more preferably about 0.2 mg cm -2 ~about 1.7mgcm -2 , and more preferably about 0.5 to about 0.75 mg cm -2 has a density of

[0158] Preferably, the coating of the boron nitride nanotube (BNNT) mesh has an average thickness of about 0.1 microns to about 100 microns, preferably about 1 micron to about 50 microns, more preferably about 2 microns to about 25 microns, more preferably about 3 microns to about 10 microns, and most preferably about 1 to 10 microns. In some embodiments, the boron nitride nanotube (BNNT) deposit has an average thickness of about 0.9 microns to about 4.4 microns, preferably about 1.9 microns or about 2.3 microns. In other embodiments, the thickness is preferably about 1.5 microns to about 7.5 microns, and most preferably about 5 microns.

[0159] Preferably, the metal or metal-based anode material is deposited on a current collector, preferably copper foil, aluminum foil, carbon cloth, carbon fiber or composite, copper foam, nickel foam. In some embodiments, no current collector is included, for example, when the metal anode is an Al metal anode or a Zn metal anode, no current collector is required.

[0160] The present invention also relates to an energy storage device comprising one or more negative electrodes (anodes) of the present invention.

[0161] The invention extends to an energy storage device comprising one or more metal or metal-based electrodes according to the invention, preferably a lithium or sodium metal anode. Desirably, the energy storage device further comprises at least one cathode, at least one separator and at least one electrolyte. Desirably, the cathode is a sulfur-based or sulfur-graphene cathode, an oxygen cathode, a lithium iron phosphate cathode or a lithium nickel manganese oxide cathode.

[0162] The preferred device has a current of 1mAcm at 25°C. -2 and 1mAhcm -2 The sulfur or sulfur-graphene cathode exhibits stable electrochemical metal plating and exfoliation for at least 100, at least 500, at least 1000 charge-discharge cycles with a fixed charge-discharge capacity. Preferably, the sulfur or sulfur-graphene cathode is provided with a coating of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder in the form of a porous mesh that is selectively permeable to transport metal ions used in energy storage devices.

[0163] In a preferred embodiment, the present invention provides a metal-sulfur energy storage device comprising: at least one metal electrode having a coating of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, the coating of the composite intimately contacting at least one surface of the electrode as a porous mesh that is selectively permeable to transport metal ions used in an energy storage device in which the composite is physically and / or chemically bonded to the surface of the electrode; and at least one sulfur (S)-based electrode having a composite film of boron nitride nanotubes (BNNTs) and at least one polymer binder, the composite film intimately contacting at least one surface of the electrode as a porous network that is selectively permeable to transport metal ions and electrolytes used in the energy storage device, but impermeable to polysulfides.

[0164] In another preferred embodiment, the present invention provides a lithium-sulfur energy storage device comprising: at least one lithium metal electrode having a coating of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, the coating of the composite intimately contacting at least one surface of the electrode as a porous mesh that is selectively permeable to lithium ions for use in an energy storage device in which the composite is physically and / or chemically bonded to the surface of the electrode; At least one sulfur (S)-based electrode having a film of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, the film of the composite being in intimate contact with at least one surface of the electrode as a porous network that is selectively permeable to meta-lithium ions and an electrolyte used in the energy storage device, but impermeable to polysulfides; The present invention relates to a lithium-sulfur energy storage device comprising:

[0165] Preferably, the BNNT loading in the cathode network is about 0.2 mg cm -2 Preferably, the BNNT loading in the anode mesh is about 0.4 mg cm -2 where approximately means ±5%.

[0166] It will be understood that in the embodiments of the energy storage devices described herein, a unit cell comprises one anode and one cathode. Further, an energy storage device in the form of a pack of modules will comprise more than one each of the anodes and cathodes, but will still have an overall ratio of anodes to cathodes of 1:1.

[0167] A preferred energy storage device comprises a metal-based anode material with boron nitride nanotubes (BNNTs) attached to the negative electrode in the form of one or more deposits or interlayers of BNNTs having a porous mesh structure, the BNNT porous mesh being as described in more detail above.

[0168] Desirably, the energy storage device comprises at least one negative electrode (anode) comprising a metal-based anode material to which are bonded boron nitride nanotubes (BNNTs) in the form of one or more deposits or interlayers of BNNTs having a porous mesh structure, a separator between each anode and the cathode, at least one cathode, and an electrolyte. Suitable separators and electrolytes are known in the art.

[0169] Preferably, the energy storage device comprises a sulfur-based or sulfur-graphene cathode, a Li-O 2 The energy storage device includes at least one positive electrode (cathode) that is a catalytic cathode, a lithium iron phosphate cathode, or a lithium nickel manganese oxide cathode.

[0170] The sulfur or sulfur-based cathode of the energy storage device desirably comprises a sulfur cathode material combined with a porous film or porous deposit of boron nitride nanotubes (BNNTs). Such sulfur cathode materials with BNNT intermediate layers are described in detail in Australian Provisional Patent Application No. 2021900777, the contents of which are incorporated herein by reference.

[0171] Suitably, the energy storage device includes an electrolyte or electrolyte system that is compatible with the metal-based anode material, for example in terms of one or more of safety, stability, and energy device performance. For example, ether-based solvents such as DOL or DME, or a mixture of DOL / DME, can be used. These electrolytes can include ionic liquids and / or metal salts as required, preferably salts such as LiNO3 and / or ionic liquids such as LiTFSI in the case of lithium devices. Equivalent or similar sodium analogs can be used for sodium devices. One exemplary electrolyte used herein is 1M LiTFSI in DOL / DME with 1 wt% LiNO3. Such electrolytes can also be used for the S cathode embodiments described herein and the polysulfide absorption experiments described herein.

[0172] Suitably, the preferred composite BNNT porous meshes prevent the formation and growth of dendrites on the anode material during electrochemical metal stripping and plating, such as occurs in the operation of the energy storage device during charge and discharge cycles. Desirably, the composite BNNT porous meshes of the present invention can withstand currents of up to, for example, 1 mAcm. -2 and a current density of 1mAhcm -2Under metal plating and stripping conditions at fixed charge / discharge capacity, for example using 1 hour plating time and 1 hour stripping time, dendrite formation and growth on the anode material during electrochemical metal stripping and plating for at least 60 cycles, more preferably at least 120 cycles, most preferably at least 180 cycles, at least 400 cycles, and most preferably 1000 cycles or more. It will be understood that such metal ion plating and stripping stability performance studies can be carried out in a symmetric metal cell. For example, a symmetric Li-BNNT porous mesh anode|Li-BNNT porous mesh anode cell can be used for cycle stability performance testing of Li metal-BNNT porous mesh electrodes. In preferred such cells, the overvoltage is maintained below 0.5 V for at least 100 cycles, more preferably at least 600 cycles, and most preferably at least 1500 cycles. Preferred systems maintain a stable overvoltage below 0.2 V for at least 100 cycles, more preferably at least 600 cycles, and most preferably at least 1000 cycles. An overpotential of less than 0.5 V during such cycling of electrochemical metal plating and stripping indicates a lack of dendrite formation at the metal anode. Thus, preferred BNNT porous meshes are stable, preferably at room temperature, for at least 100, at least 500, or even at least 1000 cycles of electrochemical metal plating and stripping, as demonstrated electrochemically by the absence of dendrite formation through stable cycling overpotentials of 0.5 V or less.

[0173] The present invention also relates to a slurry for preparing a BNNT porous mesh for metal-based anode materials, comprising boron nitride nanotubes (BNNTs), one or more polymeric binders, and one or more aprotic liquid organic solvents. Suitable binders and BNNTs are described above.

[0174] Suitably, the ratio of the volume of the slurry solvent to the weight of the solid component has a range of 3 mL / g to 20 mL / g, preferably about 5 mL / g to about 10 mL / g, most preferably about 7 mL / g. Suitably, the aprotic solvent is selected from an ether solvent, an ether-based mixed solvent system, a carbonate, N,N-dimethylacetamide (DMAc), and combinations thereof. Suitably, the ether solvent or the ether-based mixed solvent system includes a linear ether or a cyclic ether. Desirably, the ether solvent or the ether-based mixed solvent system is selected from diethyl ether, dioxolane (DOL), tetrahydrofuran (THF), dimethyloxyethane (DME), and combinations thereof. Preferably, the carbonate solvent is selected from diethyl carbonate, dimethyl carbonate, and combinations thereof.

[0175] The present invention also relates to a method for preparing a negative electrode (anode) comprising a metal-based anode material to which are attached boron nitride nanotubes (BNNTs) in the form of one or more deposits or interlayers of BNNTs having a porous mesh structure, the method comprising the steps of: (i) preparing a slurry of BNNTs and binder in one or more aprotic solvents; (ii) coating the surface of a metal-based anode material with the slurry to a desired thickness; (iii) evaporating the solvent to form a metal-based anode material having a deposit of BNNTs with a porous mesh structure; Includes. Suitable slurries are described above, as are those having suitable binders, BNNTs and solvents. Suitably, the BNNTs are present in the slurry at a concentration of about 20% to about 99% by weight of the slurry, preferably about 50% to about 95% by weight, more preferably about 85% to about 95% by weight, and most preferably about 90% by weight. Preferably, the polymeric binder is present in the slurry at a concentration of about 1% to about 80% by weight of the slurry, preferably about 5% to about 50% by weight, more preferably about 5% to about 15% by weight, and most preferably about 10% by weight. Preferably, the coating of the slurry has an initial thickness after coating of about 50 microns to about 1000 microns, more preferably about 100 microns to about 500 microns, and most preferably about 200 microns.

[0176] Preferably, after solvent evaporation, a dry BNNT porous mesh layer is formed having a thickness of about 1 micron to about 50 microns, more preferably about 3 microns to about 40 microns, most preferably about 7 microns to about 40 microns, and most preferably about 8 microns, 11 microns, 25 microns, or 37 microns. In one preferred example, the thickness of the dry BNNT porous mesh layer is about 11 microns.

[0177] A preferred method further comprises providing a metal-based anode material on a negative current collector, such as copper metal, preferably copper foil or aluminum foil. Other suitable current collectors are described above.

[0178] Preferably, the metal or metal-based electrode comprises a transporting ion metal, such as Li, Na, K, Al, and Zn, preferably Li or Na. Suitably, the metal-based anode material is lithium or sodium, preferably lithium.

[0179] The present invention also relates to a slurry for preparing a BNNT porous mesh for metal-based anode materials, comprising boron nitride nanotubes (BNNTs), one or more polymer binders, and one or more aprotic solvents. Desirably, the aprotic solvent is selected from an ether solvent, an ether-based mixed solvent system, a carbonate, N,N-dimethylacetamide (DMAc), and combinations thereof. Preferably, the ether solvent or the ether-based mixed solvent system comprises a linear ether or a cyclic ether. Suitably, the ether solvent or the ether-based mixed solvent system is selected from diethyl ether, dioxolane (DOL), tetrahydrofuran (THF), dimethyloxyethane (DME), and combinations thereof. Desirably, the carbonate solvent is selected from diethyl carbonate, dimethyl carbonate, and combinations thereof.

[0180] The present invention also relates to electronic devices comprising the negative electrode (anode) of the present invention and / or the energy storage device of the present invention. The present invention also relates to the use of the electronic device of the present invention in transportation, grid storage, electric vehicles, and advanced portable electronics applications.

[0181] The present invention also relates to the use of one or more layers of the composite BNNT porous mesh to prevent dendrite formation on a metal-based electrode of an energy storage device. Suitably, the metal-based electrode comprises a Na, K, Al, or Zn metal anode.

[0182] The present invention also relates to the use of one or more layers of the composite BNNT porous mesh to control the volume expansion of a metal-based electrode of an energy storage device.

[0183] The term "about" herein means that the numerical value is to be interpreted as a range defined by a variation of ±0.1%, ±1%, ±5%, or ±10% of the stated value depending on the standard error associated with the measurement method as would be understood by one of ordinary skill in the art. SEM analysis is often used to measure / estimate nano and micron measurements. Embodiment 2 - Materials and Methods

[0184] Fabrication of Li-BNNT anode: Lithium films were supplied by China Energy Lithium Co.,Ltd., and 100 μm thick lithium films were coated on both sides of a copper current collector. The lithium anode was further coated with a BNNT interlayer. The BNNT interlayer was prepared by mixing 90 wt% BNNT, 10 wt% styrene-butadiene rubber (SBR, poly(styrene-co-butadiene) from Sigma-Aldrich) in a tetrahydrofuran (THF, Sigma-Aldrich) solution (5 mL). The slurry was stirred overnight and coated on the surface of the lithium anode with sub-ppm oxygen and water levels in an argon-filled glove box and baked at 60 °C overnight.

[0185] Fabrication of symmetric lithium pouch cells: Symmetric lithium pouch cells were fabricated in an argon-filled glove box. Two Li-BNNT electrodes were cut and combined with a commercially available soft Al plastic film separator (Celgard 2400). 1 mL of electrolyte was dropped into the pouch. The electrolyte was 1 wt% LiNO 3 The pouch cell was sealed in a glove box using a vacuum sealer.

[0186] (Electrochemical measurements) All coin cell and soft package batteries are O 2 and H 2 The cells were assembled in an Ar-filled glove box with O < 1 ppm. The AC impedance of the symmetric Li / Li cell (0.1–10 with an amplitude of 10 mV) was 6 The battery voltage (V) and frequency range (Hz) were investigated using a Solartron 1255B frequency response analyzer. Galvanostatic cycling tests were performed using a Neware 8-channel battery tester.

[0187] (Embodiment 2 - Results and Discussion) To adjust the thickness of the BNNT mesh, the BNNT-SBR slurry was coated on copper foil with various doctor blade gaps controlled at 100 μm, 200 μm, 300 μm, and 400 μm and dried to form a dried final layer of BNNT porous mesh containing BNNTs in a polymer binder matrix. Cross-sectional SEM images of the BNNT mesh on Cu foil created with different gaps were examined as having gaps of (a) 100 microns, (b) 200 microns, (c) 300 microns, and (d) 400 microns. The corresponding thicknesses of the BNNT porous mesh layers after drying were about 8 μm, 11 μm, 25 μm, and 37 μm, corresponding to doctor blade gaps of 100 μm, 200 μm, 300 μm, and 400 μm, respectively. This result clearly indicates that the thickness of the BNNT porous mesh can be easily controlled by adjusting the blade gap during slurry application. In a preferred example, the BNNT slurry is coated onto a lithium film with a 200 μm gap and dried to a thickness of 11 microns.

[0188] Figure 8b shows the nanoscale highly interconnected porous mesh formed by BNNTs, which can be clearly observed. This interconnected porous network of BNNTs porous mesh is believed to uniformly redistribute the ionic flux of metal ions reaching the metal anode surface from the mesh on the electrolyte side. A symmetric lithium pouch cell consisting of two lithium metal electrodes was fabricated to investigate the cycling performance of lithium films with and without BNNT porous mesh. In the first cell, two new lithium films are used as electrodes, and in the second cell, lithium films with BNNT porous mesh are used. Both cells were tested at a charging density of 1 mA cm. -2 and charge / discharge capacity of 1mAhcm -2The cells are tested under the same conditions, fixed at 0.015 V. Thus, one charge / discharge cycle takes 2 h. In Fig. 12a, it can be seen that the overpotential of the cell with fresh lithium film is about 0.1 V for the first 20 cycles. However, the voltage increases in the 30th cycle and reaches 3 V at the 64th cycle, indicating the formation of lithium dendrites. In contrast, the cell with Li-BNNT porous mesh shows a very stable cycling voltage profile for more than 200 cycles after the activation process in the first 10 cycles. In this second cell, the overpotential remains at about 0.015 V for more than 200 cycles, indicating the absence of dendrite formation during cycling. This indicates that the BNNT porous mesh controls the volume expansion and mechanically assists / strengthens the SEI, reducing the cracks and damage required for dendrite growth. In additional data available, not shown here, a stable cycling voltage profile has been observed for more than 400 cycles. The BNNT porous mesh is believed to significantly improve the cycling stability of lithium metal electrodes and prevent dendrite growth by not only protecting and strengthening the SEI, but also by mitigating stress and / or strain on the native SEI via the mechanisms described above, in particular by equalizing the volume expansion throughout the anode. Thus, the preferred BNNT porous mesh limits the distortion of the native solid electrolyte interface (SEI) due to strain and the volume expansion of the metal-based anode material compared to a comparable metal-based anode material without the BNNT porous mesh.

[0189] This may be due to one or more of the following: (1) the electronically insulating yet porous and interconnected BNNT network acts as a screen / mesh that splits / delocalizes the large flux of lithium ions arriving at the electrolyte side mesh into smaller, more uniformly distributed ion streams as they pass through the mesh, resulting in a more uniform and more homogeneous distribution of lithium deposits across the anode surface, overall reducing the chances of dendrite growth / site nucleation; (2) the excellent mechanical properties of the flexible polymer binder with BNNTs allow the formation of a mechanically strong SEI in the lithium electrode, which can accommodate the volumetric changes of lithium during cycling without causing cracks or damage to the SEI. Thus, the BNNT porous mesh is electrically insulating but permeable to the ions of the metal-based anode material.

[0190] FIG. 9 shows the voltage profile of the Li-ion plating and delamination cycling performance of the tested symmetric Li coin cells. The cells were charged at 1 mA / cm 2 current density of 1mAh / cm 2 The lithium foil used in the symmetric cell is (a) 0.1 mg / cm 2 , (b) 0.2 mg / cm 2 , (c) 0.3 mg / cm 2 , (d) 0.4 mg / cm 2 , (e) 0.5 mg / cm 2 , (f) 1 mg / cm 2 , (g) 1.5 mg / cm 2 , and (h) 2 mg / cm 2 The plot shows the BNNTs coated with different mass loadings of 0.1 and 0.2 mg / cm. 2 The plating / peeling overpotential of the Li symmetric cell containing BNNTs increased after 200 hours. 2 The doped cells performed much better in terms of stability and showed a long cycle life of 1400 hours. 2 At a BNNT packing density of 1 mg / cm, a particularly low overpotential of 32 mV is obtained. 2It is also clear that continuing to increase beyond 0.5 increases the overpotential of the cell.

[0191] FIG. 10 shows EIS analysis of Li symmetric coin cells with different BNNT mass loading on the Li chip: (a) bare Li, (b) 0.1 mg / cm 2 , (c) 0.2 mg / cm 2 , (d) 0.3 mg / cm 2 , (e) 0.4 mg / cm 2 , (f) 1 mg / cm 2 , (g) 1.5 mg / cm 2 , (h) 2 mg / cm 2 ,. All coin cells were tested at room temperature, 40, 50, 60, and 70 °C, respectively, to confirm the Li-ion migration rate at a series of different BNNT doping densities. The test frequency range was 1000 kHz to 0.1 Hz. Half cycles at each temperature showed the ionic resistance at the corresponding temperature. The faster the Li-ion migration rate, the larger the decrease in resistance as the temperature increased. The EIS plots were fitted with a fitting software (Zview) to calculate the ionic conductivity.

[0192] Figure 11 shows the Arrhenius plots constructed according to the Nyquist plots of Li symmetric coin cells with different BNNT mass loadings on the Li chip. The loading range of BNNTs is 0.1–2 mg / cm. 2 Li-ions with higher migration rates showed a larger increase in ionic conductivity with increasing temperature, but the logarithm of ionic conductivity is linear with the inverse of temperature. Thus, the higher the slope of these plots, the higher the Li-ion migration rate. 2 When the BNNT loading is less than 1 mg / cm, the slope also increases with increasing BNNT loading. 2 Above 0.4 mg / cm, the slope decreased. 2 The BNNT loading density of 1000 Å results in a particularly high Li-ion transfer rate, which is comparable to the results of symmetric Li coin cells.

[0193] Figure 12 shows the results of (a) without the BNNT porous mesh and (b) with the BNNT porous mesh (the BNNT mass loading in the mesh was 0.4 mg / cm). 2 We show the long-term plating / peeling cycling performance of symmetric pouch cells with pristine lithium film electrodes (without BNNT porous mesh) and pristine lithium film electrodes (without BNNT porous mesh). Their performance is compared in one graph (Fig. 12(c)). In the absence of the BNNT porous mesh, the overpotential increases with cycling as dendrite formation occurs on the lithium metal, resulting in cell failure after 45 cycles. On the other hand, the cell with the coating of the BNNT porous mesh on the lithium metal maintains a stable overpotential for at least 1000 cycles, demonstrating the lack of dendrite growth as a result of the protective coating of the composite BNNT porous mesh on the Li electrode.

[0194] Figure 13 shows the voltage profiles of plating and exfoliation cycling performance of symmetric Al metal and symmetric Zn metal cells (where dendrite growth also occurs during plating / exfoliation / cycling) with different metal electrodes: (a) bare Al, (b) Al with BNNT porous mesh, (c) bare Zn, and (d) Zn with BNNT porous mesh. The cells were charged at 1 mA / cm. 2 current density of 1mAh / cm 2 The meshes were tested at a BNNT loading of 0.4 mg / cm in each case. 2 The symmetric battery with bare Al failed after 80 hours of cycling, while the symmetric battery with the composite BNNT porous mesh coating on Al showed a lower overpotential than the cell with bare Al and stable cycling for 100 hours. Similarly, the bare Zn symmetric cell showed a higher overpotential (0.29 V) than the overpotential of the Zn with composite coating (0.09 V) in the BNNT porous mesh symmetric cell. These results clearly demonstrated that the composite BNNT porous mesh coating can be applied to a variety of metal anodes and can prevent dendrite growth at the metal anodes, as demonstrated by the low and stable overpotential over many cycles.

[0195] In conclusion, tunable coatings of composite BNNT porous meshes containing BNNTs and flexible polymer binders are conveniently designed and synthesized using the scalable methods described herein. SEM images confirm that the BNNT porous meshes consist of a porous interconnected network made of BNNTs in a flexible / elastic polymer matrix, with the polymer present in the form of solid particles between the BNNT strands. Electrochemical results prove that the BNNT porous meshes significantly improve the cycling stability of lithium, aluminum, and zinc metal electrodes, which is clear evidence that dendrite growth is prevented. Furthermore, we believe that the coatings of BNNT porous meshes described herein for protective use with metal anodes have sufficient mechanical strength and sufficient flexibility / elasticity to protect the SEI from cracking, fracture, or other damage that would normally occur during volume expansion. Overall, the mechanical properties and porosity / morphology of the BNNT meshes inhibit dendrite growth during electrochemical metal plating and peeling (stable and low overpotential even at long cycles) and cell cycling (good and stable capacity retention at long cycles). The polymer binder in the mesh allows the mesh to maintain its structural integrity without cracking itself in the presence of volume expansion that occurs during cycling. Furthermore, the binder does not impede the movement of transported ions across the mesh. Thus, the high ionic conductivity of transported metal ions through the coating of the BNNT porous mesh described herein provides delocalized / more uniform ion transport across the electrode surface while better controlling volume expansion, thereby reducing SEI cracking and preventing the formation of dendrite nucleation sites.

Claims

1. 1. A metal electrode for an energy storage device having a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, wherein a coating of the composite is in intimate contact with at least one surface of the electrode as a porous mesh that is selectively permeable to transport metal ions used in the energy storage device, the composite being physically and / or chemically bonded to the surface of the electrode, the composite coating having an average thickness of 1 micron to 50 microns as measured by SEM, and the composite coating having a viscosity of 0.1 mg cm －２ ~8 mg cm －２ An electrode having an areal density or BNNT loading of

2. 10. The electrode of claim 1, wherein at least a portion of the polymer binder is present as particles that anchor BNNTs together to form the porous mesh.

3. 10. The electrode of claim 1, wherein the BNNTs are not fully conformally coated with the polymer binder.

4. 10. The electrode of claim 1, wherein the BNNTs are free of impurities of hexagonal boron nitride and / or elemental boron.

5. 10. The electrode of claim 1, wherein the electrode is selected from a Li electrode, a Na electrode, a K electrode, an Al electrode, and a Zn electrode.

6. 10. The electrode of claim 1, wherein the composite coating comprises the polymer binder at a concentration of 50% by weight or less.

7. 10. The electrode of claim 1, wherein the porous mesh comprises one or more tunnels, pathways and / or channels that are oriented, oriented and / or dimensioned to delocalize or redistribute metal ion flux therethrough that is concentrated on one side of the porous mesh and more evenly distribute the metal ion flux on another side of the porous mesh, whereby the metal ion flux is distributed over a greater surface area of ​​the electrode.

8. The electrode of claim 1, wherein the composite has an average thickness of from 2 microns to 25 microns.

9. The coating of the composite was 0.2 mg cm －２ 10. The electrode of claim 1 having an areal density or BNNT loading of ∼8 mg cm-2.

10. 2. The electrode of claim 1, wherein the polymer binder is selected from styrene butadiene rubber, poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-HFP), poly(3,4-ethylenedioxythiophene)-co-poly(ethylene glycol) (PEDOT-co-PEG), polyethylene glycol (PEG)-polymethyl methacrylate (PMMA), poly(dimethylsiloxane) (PDMS), and combinations thereof.

11. 10. The electrode of claim 1, wherein the metal electrode is deposited on a current collector selected from carbon cloth, carbon fiber, copper foam, nickel foam, and copper foil.

12. A negative electrode (anode) for an energy storage device, comprising a metal-based anode material, the negative electrode having boron nitride nanotubes (BNNTs) bonded thereto in the form of one or more deposits or intermediate layers of BNNTs having a porous mesh structure, the porous mesh structure having an average thickness of 1 micron to 50 microns as measured by SEM, and the one or more deposits or intermediate layers of BNNTs having a porous mesh structure have an average density of 0.1 mg cm －２ Anode with an areal density or BNNT loading of ∼8 mg cm-2.

13. An energy storage device comprising one or more electrodes according to any one of claims 1 to 12.

14. 14. The energy storage device of claim 13 comprising at least one cathode, at least one separator, and an electrolyte.

15. 15. The energy storage device of claim 14, wherein the cathode is a sulfur-based or sulfur-graphene cathode, a lithium iron phosphate cathode, or a lithium nickel manganese oxide cathode.

16. The device is rated at 1 mA cm －２ and a temperature of 25°C. －２ 14. The energy storage device of claim 13, wherein the device exhibits stable electrochemical metal plating and delamination over at least 100 charge / discharge cycles with a fixed charge / discharge capacity.

17. The energy storage device of claim 14, wherein the cathode is a sulfur-based or sulfur-graphene cathode, the sulfur-based or sulfur-graphene cathode being provided with a coating of a composite of boron nitride nanotubes (BNNTs) and at least one polymeric binder in the form of a porous mesh that is selectively permeable to transport metal ions used in the energy storage device.

18. An electronic device comprising an electrode according to any one of claims 1 to 12.

19. 20. Use of the electronic device of claim 18 in transportation, grid storage, electric vehicle, and advanced portable electronics applications.

20. 1. Use of a coating of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder as a porous mesh physically and / or chemically bonded to the surface of a metal electrode for preventing dendrite formation on the electrode of an energy storage device, said porous mesh having an average thickness of 1 micron to 50 microns as measured by SEM, and said composite coating having a density of 0.1 mg cm －２ Use of composite coatings with areal density or BNNT loading of ∼8 mg cm-2.

21. 1. Use of a coating of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder as a porous mesh bonded to a metal electrode for modifying the volume expansion of the metal electrode in an energy storage device, wherein the porous mesh has an average thickness of 1 micron to 50 microns as measured by SEM, and the coating of the composite has a viscosity of 0.1 mg cm －２ Use with an areal density or BNNT loading of ∼8 mg cm-2.

22. 1. Use of a coating of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder as a porous mesh physically and / or chemically bonded to the surface of a metal electrode for enhancing the stability of a native SEI formed on the electrode in an energy storage device, wherein the porous mesh has an average thickness of 1 micron to 50 microns as measured by SEM, and the coating of the composite has a density of 0.1 mg cm －２ Use with an areal density or BNNT loading of ∼8 mg cm-2.

23. 1. A metal-sulfur energy storage device, comprising: At least one metal electrode having a coating of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, said coating of said composite intimately contacting at least one surface of said electrode as a porous mesh that is selectively permeable to transport metal ions used in an energy storage device in which said composite is physically and / or chemically bonded to the surface of said electrode, said composite coating having an average thickness of 1 micron to 50 microns as measured by SEM, and said composite coating having a viscosity of 0.1 mg cm －２ ~8 mg cm －２ at least one metal electrode having an areal density or BNNT loading of at least one sulfur (S)-based electrode having a film of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, said composite film intimately contacting at least one surface of said electrode as a porous network selectively permeable to transport metal ions and electrolytes used in said energy storage device, but impermeable to polysulfides; A metal-sulfur energy storage device comprising:

24. 1. A lithium-sulfur energy storage device comprising: At least one lithium metal electrode having a coating of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, said composite coating intimately contacting at least one surface of said electrode as a porous mesh that is selectively permeable to lithium ions for use in an energy storage device in which said composite is physically and / or chemically bonded to the surface of said electrode, said composite coating having an average thickness of 1 micron to 50 microns as measured by SEM, said composite coating having a density of 0.1 mg cm －２ ~8 mg cm －２ at least one lithium metal electrode having an areal density or BNNT loading of at least one sulfur (S)-based electrode having a film of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, said composite film intimately contacting at least one surface of said electrode as a porous network selectively permeable to meta-lithium ions and an electrolyte used in said energy storage device, but impermeable to polysulfides; 1. A lithium-sulfur energy storage device comprising:

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