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 a protective BNNT-based porous network or mesh for electrodes used in energy storage devices, and to an improved metal electrode, particularly an improved S-cathode and / or Li, Na, K, Al, Zn anode for metal-sulfur batteries, and especially a Li anode 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 crucial 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, each have a capacity of approximately 650 Wh / kg. -1 and approximately 950 Whkg -1 It can supply a specific energy of 3860mAhg, which is 2-3 times that of current lithium-ion batteries, and is considered a next-generation battery. In fact, among current battery systems, Li-S batteries are an attractive candidate to function as next-generation batteries with theoretically high energy density. Such a battery has a theoretical specific capacity of 3860mAhg -1Lithium metal anodes are essential components because they have a high potential and the lowest redox potential (-3.04V compared to a standard hydrogen potential electrode). In particular, lithium sulfur (Li-S) technology is based on the multi-step electrochemical reaction 16Li + S8 → 8Li2S. However, the dissolution of lithium sulfur polysulfide intermediate products formed during the charge / discharge process, the so-called shuttle effect, leads to the accumulation of insulating and insoluble precipitates (e.g., Li2S2 / Li2S) on the surfaces of the cathode, anode, and separator during the cycle, resulting in a continuous increase in battery impedance, causing a serious decrease in capacity and Coulombic efficiency of the battery. This means that the active material is not recycled well, and the discharge capacity and Coulombic efficiency decline rapidly. Another problem is related to the formation of dendritic crystals on lithium metal anodes, which significantly limits the cycle capability and can raise safety concerns. Similar problems exist with other metal anodes, including sodium metal electrodes, aluminum metal electrodes, and zinc metal electrodes. The dendritic crystal problem becomes particularly problematic at high current densities. These problems mean that despite the potential of lithium-sulfur batteries, they are not yet mass-produced. 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 small number of recharge cycles, making them largely useless for most commercial applications.

[0003] To address the polysulfide (PS) problem, various strategies have been attempted, including the fabrication of carbon-sulfur composites, surface modification of conductive polymers, and modification of electrolytes. While these approaches lead to improvements in conductivity, cycleability, and capacity, several challenging issues remain, such as the leakage of polysulfide (PS) into the electrolyte, rapid capacity degradation in subsequent cycles, and the low lithium-ion conductivity and stability of the new electrolyte. Recently, the introduction of an intermediate layer such as carbon paper, carbonized eggshell film, carbon nanotube paper, or 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 preparing the intermediate layer, the weak interaction between the intermediate layer and polar polysulfide (PS) anions, and unacceptable intermediate layer thickness and mass significantly impact the performance of Li-S batteries.

[0004] Therefore, 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 aforementioned drawbacks, or provide useful alternatives. In particular, the development of new lightweight solutions that can mitigate the transport of polysulfides (PS) from the sulfur cathode to the anode would be welcome.

[0005] Now we move on to the dendritic crystal problem. Metal anodes, including Li anodes, have two problems: (1) The virtually infinite relative volume changes of the hostless anode that occur during metal delamination and plating lead to mechanical instability, causing repeated cracking and repair of the passivated solid electrolyte interface (SEI) layer, resulting in capacity loss and reduced cycle life over time. (2) Uncontrolled metal dendritic crystal formation occurs during charge / discharge cycles, leading to internal short circuits, low Coulomb efficiency, poor cycle stability, and serious safety problems. In fact, when cracks occur during a continuous cycle of SEI cracking / repairing, the flux of metal ions to the metal surface increases, resulting in heterogeneous metal deposition and dendritic crystal formation.

[0006] Various attempts to control the formation of undesirable dendritic crystals include the use of new electrolytes and electrolyte additives, solid electrolytes, the addition of artificial physical protective layers, and the design of current collectors without dendritic crystals. While these strategies can effectively suppress the formation and growth of metal dendritic crystals, most cannot overcome the problem of infinite volume changes. Maintaining or complementing the quality and integrity of the SEI layer is crucial for the efficient and stable operation of the metal anode. 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 modulus and dense structure to suppress dendritic crystal formation; (iii) has sufficient flexibility to accommodate interface fluctuations that occur during battery cycling while avoiding repeated failure / repair cycles; and (iv) has high ionic conductivity to promote the uniform distribution and transport of metal ions across the entire electrode surface. Unfortunately, to date, natural SEI layers lack one or more of these requirements (indicated by their low cycle capacity), thus highlighting the need for new designs of improved artificial SEI or pseudo-SEI or other structures that possess the desirable characteristics described above, or that can impart these characteristics to natural SEI.

[0007] Layered boron nitride (BN) and boron nitride nanotubes (BNNTs) are polymorphs of boron nitride. BNNTs are structurally similar to carbon nanotubes (isostructure), except that carbon atoms are alternately substituted with nitrogen and boron atoms, while layered boron nitride (BN) is structurally similar to graphite, where boron and nitrogen atoms are substituted with carbon atoms. BNNTs are analogous to rolled graphite-like BN sheets (honeycomb BN(h-BN)) containing nitrogen and boron atoms instead of carbon atoms. BNNTs can be monolayered or multilayered. Ionic interactions exist between adjacent BN layers as a result of the partial ionic properties of the BN bonds. BNNTs are cylindrical in shape, with a diameter of submicrons and a length of micrometers.

[0008] U.S. Patent Application Publication No. 2019 / 0123324 describes a porous separator for an ion battery comprising a porous scaffold, such as a BNNT nanoporous scaffold, as a support for a conformal coating of a thermoresponsive polymer material (polyethylene, possibly a chemically modified dopant) that functions as a reversible localized thermoresponsive switching mechanism that lowers temperature, prevents thermal failure, and prevents thermal runaway by sterically obstructing the flow of ions through the separator or by closing the pores of the separator and blocking the flow of ions within the battery as the polymer expands and reduces pore size when it reaches a threshold temperature. The improved separator is placed 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 that is closely bound or interfacially in contact with one or both 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 the polymer is required.

[0009] U.S. Patent Application Publication No. 2011 / 0086965 discloses boron nitride nanosheets (BNNS) containing trilayer hexagonal boron nitride (h-BN), which is a form of multilayer hexagonal boron nitride in which a portion of the layer has been exfoliated, and which can be manufactured by dispersing unused hBN powder in an organic solvent and by sonicating the dispersion. As explained above, U.S. Patent Application Publication No. 2011 / 0086965 does not discuss boron nitride nanotubes (BNNTs), which are structurally and functionally very different from boron nitride nanosheets (BNNS). [Overview of the Initiative]

[0010] In a first aspect, the present invention provides a sulfur (S)-based electrode for an energy storage device having a film of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, wherein the composite film is a porous network that is selectively permeable to transport metal ions and electrolytes used in the energy storage device but impermeable to polysulfides, and is in close contact with at least one surface of the S electrode. Preferably, the composite BNNT porous network film is directly attached to the S cathode such that substantial interfacial contact exists between the entire composite film and the entire S cathode surface. Preferably, there are no microgaps or microspaces (at a level of 0.5 microns or more) between the film and the S cathode surface.

[0011] In a second aspect, the present invention provides a sulfur (S)-based cathode comprising a sulfur cathode material bonded to a porous membrane of boron nitride nanotubes (BNNTs).

[0012] In a third aspect, the present invention provides an energy storage device comprising one or more sulfur (S)-based electrodes as described in the first or second aspect.

[0013] In a fourth aspect, the present invention provides an electronic device comprising a sulfur (S)-based cathode according to the first or second aspect, and / or an energy storage device according to the third aspect.

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

[0015] In a sixth aspect, the present invention provides the use of one or more BNNT layers as a polysulfide diffusion blocking film or a reversible polysulfide trap in a sulfur(S)-based cathode of an energy storage device.

[0016] In a seventh aspect, the present invention relates to a metal sulfur energy storage device, At least one sulfur (S)-based electrode having a film of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, wherein the composite film is a BNNT porous network that is selectively permeable to transport metal ions and electrolytes used in energy storage devices but impermeable to polysulfides, and is in close contact with at least one surface of the electrode, and At least one metal electrode having a coating of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, wherein the composite coating is in close contact with at least one surface of the electrode as a porous mesh that is selectively permeable to transport metal ions used in energy storage devices in which the composite is physically and / or chemically bonded to the surface of the metal electrode, We provide a metal sulfur energy storage device equipped with the following features.

[0017] In the eighth aspect, the present invention relates to a lithium sulfur energy storage device, At least one sulfur (S)-based electrode having a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, wherein the film of the composite is a porous network that is selectively permeable to transport metal ions and electrolytes used in energy storage devices but impermeable to polysulfides, and is in close contact with at least one surface of the electrode, and At least one lithium metal electrode having a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, wherein the coating of the composite is in close contact with at least one surface of the electrode as a porous mesh that is selectively permeable to lithium ions to which the composite is physically and / or chemically bonded, We provide a lithium-sulfur energy storage device equipped with the following features.

[0018] Preferably, the coating of the composite BNNT porous mesh is configured to reversibly capture polysulfides, meaning that during the cycle, the captured sulfur (in the form of polysulfides) remains active, meaning that the polysulfides can return to / escape from the porous network and come into contact with the S cathode mass so that elemental S can participate in the redox reaction formed at the cathode. A film of BNNT porous network in which PS is permanently captured is undesirable because the cathode material becomes inactive and its capacity decreases as the cycle continues.

[0019] Embodiments of the present invention will be described in this specification simply as examples, with reference to the accompanying drawings. [Brief explanation of the drawing]

[0020] [Figure 1] (a) Optical image of an S / graphene electrode (cathode) without film of a BNNT porous network with polymer binder, and (b) Optical image of an S / graphene electrode (cathode) with film of a BNNT porous network with polymer binder. The BNNT porous mesh appears gray in the image. (c) SEM image of the porous surface of a normal sulfur / graphene cathode, (d) Cross-sectional SEM image showing BNNT network components, electrode material components, and aluminum current collector components, (e, f) Top surface SEM image of a BNNT network on a "protected" S / graphene cathode. The particulate nature of the binder between BNNT strands or fibers is evident at high magnification in the form of spheroidal particles in (f). The pore / gap regions on the electrode material surface seen in (c) are filled to some extent with the composite BNNT / polymer material by the slurry casting manufacturing process described herein, resulting in excellent close contact between the composite and the electrode material. [Figure 2]For example, cycle stability in terms of capacity retention (%) over the number of cycles is shown for Li-S coin cells with BNNT networks of different thicknesses on the S cathode, based on (a) coating the cathode with 5 wt% BNNT in the slurry and (b) 10 wt% BNNT in the slurry onto the cathode, followed by evaporation of the solvent. The film thickness determined by SEM analysis is shown to the right of each curve in microns, and the % capacity retention in parentheses is also shown. The results are compared with equivalent cells without BNNT on the S cathode (see curve labeled "No BNNT"), clearly demonstrating the advantage of BNNT films in capacity retention over long cycles. After 500 cycles, a composite film formed from 5 wt% slurry used to form a 2.3 micron BNNT film achieved a high capacity retention of 90%, compared to only 35% for electrodes without a protective BNNT porous network. [Figure 3] (a) SEM image of BNNT starting material (without binder) showing the typical length and diameter of the BNNT used, and (b) TEM image. [Figure 4] (a) A comparison of the color of the polysulfide solution electrolyte (deep bright yellow) and the change in the color of the polysulfide when BNNT is added (instantaneous disappearance of bright yellow), indicating that the polysulfide is adsorbed or captured / retained on BNNT. Note that the electrolyte used is the one described in the experiment section. (b) IR spectra of three polysulfide / electrolyte solutions with 0 mg, 8 mg, and 15 mg of BNNT added are shown. Here, the intensity of the PS8 absorption peak decreases as the concentration of BNNT increases. This indicates that PS in the solution is adsorbed or engaged / retained with BNNT. (c) Raman spectral analysis of BNNT recovered from the polysulfide / electrolyte solution experiment is shown, showing BS and NS bond bands, indicating the adsorption of sulfur from the polysulfide to the boron and nitrogen atoms of BNNT. [Figure 5](a) (Left panel) shows SEM analysis of a film of a BNNT / LA133 polymer binder composite, where the porous BNNT network is formed from an aqueous solvent system. (b) (Right panel) shows SEM analysis of a BNNT / PVDF polymer binder composite, where the porous network of the composite is formed from an organic solvent system. Comparing the images, the structure, porosity, and / or morphology of the porous network of the film are substantially the same in each case, strongly suggesting that despite the use of different binders, they exhibit equivalent performance in terms of polysulfide adsorption / blocking / capture. [Figure 6] This figure shows the effect of the ratio of highly porous graphene to highly surface area graphene on the specific capacity (mAh / g) in a BNNT network-protected S-cathode. As can be seen from the figure, good specific capacities of approximately 1000 mAh / g are achieved with ratios of 2:8, 4:6, 5:5, and 8:2. However, unexpectedly, a specific capacity of nearly 1400 mAh / g is obtained with a ratio of 6:4. [Figure 7] (a) The specific volume of the test S cathode with BNNT using various BNNT addition densities, where the specific volume is improved in all cases compared to the case without BNNT. BNNT addition densities of approximately 0.1 to approximately 0.25 mg / cm2 give good specific volume values ​​even after 100 cycles. On the other hand, (b) shows the volume retention rate (relative to the volume of the first cycle) as a function of the BNNT addition density (mg / cm2). BNNT addition densities of approximately 0.1 to approximately 0.25 mg / cm2 give particularly good performance in terms of volume retention rate % compared to the first cycle (see Figure 1). Here, approximately means ±2%. [Figure 8](a) a cross-sectional view and (b) a top SEM image of a coating of BNNT porous mesh directly formed on a lithium film from a BNNT / polymer composite slurry using different doctor blade heights. Note that copper foil can be used as a model of the metal surface for developing the thickness of the optimized mesh layer, as controlling and optimizing the thickness of the BNNT porous mesh is easier and clearer to observe on copper foil than on lithium film. Since the film is formed in situ on the metal surface by slurry technique, it will be understood that the formed composite BNNT porous mesh has excellent interfacial contact between the BNNT and the metal electrode surface, which is substantially flat or planar as well as the BNNT / polymer slurry placed on the electrode at the time of formation. Once the solvent evaporates and the film is formed, the BNNT / polymer is tightly compressed on the metal electrode surface. This means that there are very few / very small gaps or spaces between the porous network (typically the gaps / spaces present between the network and the metal surface are nanoscale), and these are much smaller than the gaps / spaces present from the pre-formed composite BNNT / polymer porous network placed on the metal electrode surface. Therefore, the slurry formation method is useful for generating the excellent interfacial contact observed in the present invention. When the metal electrode is circulated, a SEI (several nanometers thick) is formed between the BNNT porous network in close 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. The inventors believe that the BNNT mesh reinforces the SEI and also enables uniform deposition of metal ions across the mesh and the SEI. To ensure the continuity of adhesion by the ultrathin SEI, it is important that the BNNT porous network has as good an interfacial contact as possible with the metal electrode surface. Before and after SEI formation, the BNNT porous network is physically and / or chemically bonded to the metal electrode surface in one or more ways, and it is likely that this bond is reinforced by the SEI during its formation. [Figure 9]These are the voltage profiles of the Li-ion plating and stripping cycle performance of symmetric Li coin-type batteries, where lithium foil used in symmetric batteries is coated with BNNTs of different mass dopings, (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, forming a range of coatings of a composite BNNT porous mesh. [Figure 10] EIS analysis of Li symmetric coin batteries with different BNNT masses added to Li chips to form coating areas of composite BNNT porous mesh: (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 11] This is an Arrhenius plot created according to the Nyquist plot of Li symmetric coin cells with different BNNT mass dopings in a porous mesh on a Li chip. [Figure 12] This shows the long-term cycle performance of symmetric pouch cells with novel lithium film electrodes, with (a) no composite BNNT porous mesh coating and (b) composite BNNT porous mesh coating. In the absence of the BNNT porous mesh, dendritic crystal formation occurs on the lithium metal, and the overvoltage increases with the cycles, resulting in cell failure after only 45 cycles. On the other hand, the cell coated with the BNNT porous mesh on the lithium metal maintains a stable overvoltage for at least 1000 cycles, indicating the absence of dendritic crystal growth as a result of the protective BNNT mesh on the lithium. [Figure 13]The voltage profiles of the plating and stripping cycle performance of symmetric Al batteries and symmetric Zn batteries with different metal electrodes are shown. (a) bare Al, (b) Al coated with a composite BNNT porous mesh, (c) bare Zn, and (d) Zn coated with a composite BNNT porous mesh. The amount of BNNT added to the mesh in each case is 0.4 mg / cm2. [Figure 14] The proposed mechanism for coating with a BNNT porous mesh prevents dendritic crystal growth by transforming a heterogeneous (localized) lithium ion flow reaching the lithium metal anode in a localized manner into a more dispersed lithium ion flow reaching the anode through the mesh. This allows transport metal ions reaching the entire lithium surface to be more uniformly distributed (delocalized) across the entire surface of the metal electrode. The advantages of this configuration are described below. [Figure 15] This is an exploded view of a Li-S battery structure with a BNNT porous mesh coating for lithium anode protection and a BNNT porous network film for S cathode protection, where reversibly trapped PS is observed within the BNNT porous network film. [Figure 16]The capacitive and specific capacitive data for two pouch cells (one with BNNT in the cathode and one without) containing a 20cm² pouch cell with an effective cathode mass doping of 30.4mAh / g are shown. The bottom line represents the cell without BNNT, which failed slightly after 100 cycles, so the result does not exceed the dotted line. The data indicates that the deposition of the BNNT porous network film is beneficial to the cathode performance, leading to improved utilization of the sulfur active material, and that adverse effects such as capacitive charging / self-discharging processes are not evident. The reversible cycle capacity of the Li-S battery improved by 15% after 100 cycles with BNNT added to the cathode. A capacity of 18.9mAh (622mAh / gsulfur) was achieved after 100 cycles, and a capacity of 16.7mAh (550mAh / gsulfur) was achieved after 600 cycles, demonstrating a high level of stability. The capacity retention rate of cells without BNNTs fell below the 60% threshold (17.5 mAh, 574 mAh / gsulfur) after 27 cycles, while the capacity retention rate of cells containing BNNTs continued for over 1200 cycles without ever falling below the 60% capacity threshold. Based on the developed and presented test procedures, the improvement in retention capacity is thought to be due to the presence of the BNNT porous network on the cathode. [Figure 17] The (a) capacity retention rate and (b) Coulomb efficiency of Li-S coin cells with and without BNNT protection, and with BNNT protection on both the cathode and anode, are shown. The BNNT doping rates for the layer and mesh are 0.2 mg / cm² and 0.4 mg / cm², respectively. All tested cells are tested at a rate of 0.2 at 25°C. The initial specific capacities of the bare Li-S cells and the cells with BNNT protection on both sides are 1158 mAh / g and 1251.6 mAh / g, respectively. The unprotected Li-S cell maintains a capacity retention rate of 74.26% and a Coulomb efficiency of 83% after 60 cycles, while the BNNT-protected cell shows a higher capacity retention rate of 95.55% and a higher Coulomb efficiency of 96.8% after the same number of cycles. Although the research is ongoing, the advantages of the composite BNNT porous protective layer on the electrodes are clear. [Modes for carrying out the invention]

[0021] The present invention relates to films and / or coatings of boron nitride nanotube (BNNT) porous networks or porous meshes for electrodes used in energy storage devices. The BNNTs are preferably in the form of a composite BNNT material comprising BNNTs and a polymer binder. The porous network or porous mesh is selectively permeable to transport metal ions used in energy storage devices. It should be understood that the electrodes may be used in energy storage devices such as batteries, particularly rechargeable secondary batteries. The electrodes may be sulfur electrodes, alkali metals, particularly sodium or lithium, or metal electrodes such as aluminum, magnesium or zinc.

[0022] Preferably, the BNNT of the composite is substantially free, and preferably completely free, of impurities such as hexagonal boron nitride (hBN) and / or elemental boron (B). The BNNT used herein contains only very small amounts of impurities such as metal catalysts, hexagonal boron nitride, and / or elemental boron. Preferred BNNT has a purity of at least 95%, at least 96%, at least 97%, at least 98%, or possibly at least 99%.

[0023] Preferably, the composite BNNT porous network or porous mesh is electrically insulating but permeable to metal transport ions used in the specific energy storage device in question (e.g., metal ions in metal-based anode materials). The porous / porous structure of the BNNT porous network, mesh, or deposit can be observed using SEM and, if necessary, tested by BET analysis.

[0024] Ideally, the binder exists in the composite as solid ellipsoidal binder particles, which can also be observed in the SEM images provided herein. Preferably, at least a portion of the polymer binder exists in the composite as solid particles that fix or adhere together the strands of BNNT in the composite to form a porous network (in the case of an S-cathode) or porous mesh (in the case of a metal anode). The substantial portion of the binder present exists in the form of solid particles rather than in the form of a distinct conformal coating of polymer over all BNNT strands, etc. Ideally, the strands of BNNT in the composite are not fully conformal coated with polymer binder. Conformal coating of polymer around all of the BNNT is undesirable because it may lead to excessive thermal expansion of the polymer, which can adversely affect the optimized pore size of the BNNT network / mesh. Inaccurate pore size can adversely affect one or more of the reaction rate, internal resistance of the device, capacity, and capacity retention rate during cycling.

[0025] Ideally, the composite film is physically and / or chemically bonded to the electrode surface. This is true for S-cathodes or metal anodes, as will be explained in more detail later.

[0026] When properly optimized, the BNNT porous network film is particularly useful in blocking the migration of polysulfides from the S cathode material. A preferred film has an optimized BNNT content, density, and thickness, and synergistically prevents the diffusion of polysulfides through the BNNT porous network film by reversibly trapping polysulfides within the porous network while maintaining its activity, i.e., by allowing the active material to still escape from the composite network and return to the cathode mass. The temporarily trapped polysulfides can be released from the porous network as active S in the reverse cycle and come into contact with the S cathode material mass. The optimized network described herein is preferred because it efficiently and reversibly traps S but does not produce inactive S in the form of PS that is permanently trapped in the BNNT porous network. The functionality of the optimized BNNT porous network film described herein is demonstrated by its excellent specific volume (capacity retention rate) even after numerous cycles, due to the reversible polysulfide capture in the BNNT porous network film associated with the S cathode (see, for example, Figure 7).

[0027] BNNT in the form of a coating on a BNNT porous mesh is also particularly useful for SEI strengthening and / or preventing dendritic crystal formation on metal electrodes subject to dendritic crystal formation, such as lithium metal. The preferred coating of the composite BNNT / polymer mesh in this embodiment is optimized with respect to the amount, density, and thickness of BNNT added, which work synergistically to allow transport metal ions to pass through the mesh to the metal electrode surface selectively, but uniformly disperse the approaching ion flux that reaches the mesh after passing through it, across the entire electrode surface. By uniformly dispersing transport metal ions across the entire electrode surface, the formation of metal dendritic crystals is significantly reduced. The optimized mesh also has an appropriate thickness to strengthen the innate SEI formed on the electrode and protect the electrode from damage caused by volume expansion that occurs in hostless electrode materials containing metal. Mitigating SEI damage in this way also prevents dendritic crystal formation. The functionality of the optimized coating of the BNNT porous mesh described herein is demonstrated by exhibiting very stable overpotential even after numerous cycles, with the absence of dendritic crystal formation during metal stripping / plating experiments and the maintenance of low and stable internal resistance.

[0028] In both cases, the composite BNNT / binding material improves the cycle performance of the electrodes when used in energy storage devices. The protected electrode material is provided with a film or coating of the BNNT network or mesh of the present invention and can be 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 the 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 lies in the thickness of the composite on the electrode and / or the density of the BNNT used. As described herein, both S cathodes and metal anodes have advantages for various reasons, and both types of protective electrodes can be used in devices. Preferably, both BNNT-protected sulfur cathodes and BNNT-protected metal anodes are used in improved devices, such as improved lithium sulfur energy storage devices, where both electrodes (cathode and anode) are protected. The inventors believe that the protected electrodes work synergistically within the lithium-sulfur energy storage device to improve the cycle life performance of lithium-sulfur batteries (see Figure 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, and the BNNT mesh coating protects the anode by reducing dendritic crystal formation through reinforcement of the SEI layer and spreading the metal ion flux reaching the electrode across the entire electrode surface. The structure of a Li-S battery with a BNNT protective layer on each electrode is shown in Figure 15 below. During operation of the lithium-sulfur battery, lithium ions move between the lithium anode and the sulfur cathode. The lithium ions combine with sulfur to form various lithium polysulfide compounds in the cathode. Some of these polysulfides are soluble in the battery electrolyte and can deposit on the anode. This leads to the permanent loss of active sulfur from the cathode. With relatively few charge cycles, the loss of active sulfur reduces the battery capacity. BNNTs within the battery structure function to allow the passage of lithium ions while suppressing the movement of lithium polysulfide.This promotes the retention of sulfur as an active material in the cathode, helping to maintain battery capacity during charging and discharging. Furthermore, the presence of lithium within the sulfur cathode structure can cause the structure to expand dramatically, compromising the structural integrity of the battery and potentially leading to capacity loss or failure. BNNTs are thought to assist by providing additional structural support to the cathode. This reduces the effects of cathode expansion and contraction, thereby lowering the risk of failure due to mechanical stress. In the lithium anode, during battery cycling, lithium ions return to the lithium metal anode. Upon arrival, they deposit irregularly, and lithium dendritic crystals can grow on the anode surface. These can damage the insulating separator and cause short circuits and failures. By including a protective BNNT network / mesh in the anode, uniform ion inflow occurs across the entire anode surface, preventing dendritic crystal formation and anode degradation even after many cycles, maintaining specific capacity and reducing the risk of battery failure over a longer cycle life.

[0029] Because BNNT conducts heat far more efficiently than copper, it is thought that BNNT within the battery structure can help dissipate the generated heat more evenly, potentially reducing concentrated hot spots and the mechanical and chemical stress associated with such hot spots. This could further improve safe charging speeds and reduce the risk of failure. This is an improvement over lithium-ion batteries, which can develop concentrated heat spots during charging and discharging, increasing mechanical and chemical stress, limiting safe charging speeds, and increasing the risk of failure due to localized overheating.

[0030] (electrode) This specification describes an electrode for an energy storage device having a composite of boron nitride nanotubes (BNNTs) and at least one polymeric binder, wherein the composite is in intimate contact with at least one surface of the electrode as a porous network or porous mesh that is selectively permeable for transporting metal ions used in the energy storage device, and at least a portion of the polymeric binder exists as particles that hold the strands of the BNNTs together to form the porous network or porous mesh. This specification also describes a sulfur (S)-based electrode for an energy storage device having a composite of boron nitride nanotubes (BNNTs) and at least one polymeric binder, wherein the composite is in intimate contact with at least one surface of the electrode as a porous network or porous mesh that is selectively permeable for transporting metal ions and electrolytes used within the energy storage device but is impermeable to polysulfides, i.e., the composite is impermeable to polysulfides. This specification also describes a sulfur (S)-based electrode for an energy storage device having a film of a composite of boron nitride nanotubes (BNNTs) and at least one polymeric binder, wherein the film of the composite is in intimate contact with at least one surface of the electrode as a porous network and is selectively permeable for transporting metal ions and electrolytes used within the energy storage device but is impermeable to polysulfides.

[0031] In embodiments of the S cathode, the film of the composite has an average thickness of from about 0.9 microns to about 5 microns, preferably from about 1.5 microns to about 3.5 microns, and most preferably about 2.5 microns. Desirably, the film of the composite is from about 0.05 mg cm -2 to about 3.5 mg cm -2 , more preferably from about 0.05 mg cm -2 to about 1 mg cm -2 , more preferably from about 0.05 mg cm -2 to about 0.5 mg cm -2 , and most preferably from about 0.2 to about 0.25 mg cm-2 Most preferably about 0.2 mg / cm² -2 It has a surface density or BNNT addition amount. In some embodiments, S is about 1 mg cm -2 ~about 5mgcm -2 Preferably about 3 mg / cm² -2 It exists in the amount added. Here, "approximately" means ±2%.

[0032] This specification describes 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, wherein the composite is in close 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 fix the strands of BNNTs together to form a porous network or porous mesh. This specification also describes a metal electrode for an energy storage device having a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, wherein the coating of the composite is in close 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.

[0033] Preferably, 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 coating of the composite is about 0.2 mg cm -2 ~approximately 8 mg / cm² -2 Approximately 0.1 mg / cm² -2 ~about 2.5mgcm -2 More preferably 0.1 to approximately 2 mg / cm² -2 Most preferably about 0.4 mg / cm² -2It has a surface density or BNNT content. These thicknesses and content levels are particularly desirable for meshes for metal electrodes.

[0034] This specification describes electrodes for energy storage devices having boron nitride nanotubes (BNNTs) provided on at least one side of the electrode as a porous network or porous mesh that is selectively permeable to transport metal ions used in energy storage devices. Preferably, the network or mesh is a composite of BNNTs and a polymer binder.

[0035] This specification describes electrodes for energy storage devices 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 energy storage devices. Most preferably, the binder is present in the BNNT porous network or mesh at a concentration of about 15% by weight or less, preferably about 10% by weight or less (where about means ±2%) of the BNNT component. Preferably, a portion of the binder is present in particulate form. More preferably, at least 50% of the binder is present in particulate form. The binder particularly fixes or adheres the BNNT strands or fibers to each other, providing stability to the porous network, mesh, or deposit. In some embodiments, the BNNT strands or fibers are not fully 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 including a binder, the term BNNT means composite BNNT / polymer binder, and means that the binder is present in a porous network or porous mesh.

[0036] BNNTs are in close contact with the electrode / electrode material. BNNTs can be physically and / or chemically bonded or fused to the electrode material such that the gaps / spaces between each component are at the nanoscale rather than the micronscale. In some embodiments, including S cathodes, BNNTs in a film or coating penetrate into the pores of the S electrode material, resulting in the BNNT composite (e.g., BNNTs and a binder) and the electrode component becoming entangled and / or embedded within the surface pores. This results in excellent tight contact between both components within the protected electrode, and in fact, the film / coating does not peel off the electrode, at least under normal cycling conditions.

[0037] (S cathode) In some preferred embodiments, the electrode is a sulfur electrode, for example, a sulfur cathode for a secondary energy storage device. Thus, in another embodiment, 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 an S-cathode material. The BNNTs are a porous network, mesh, or deposit that is not permeable to polysulfides but allows the passage of metal transport ions. The BNNTs can prevent the adsorption and / or diffusion of polysulfides to the electrolyte in contact with the electrode, as seen, for example, in an energy storage device. In a preferred embodiment, the BNNTs for the S-cathode are a composite of BNNTs and at least one polymer binder.

[0038] (metal electrode) The electrodes may be metal electrodes, particularly those with problems in dendritic crystal formation, such as aluminum, zinc, or alkali metal electrodes such as lithium, sodium, and potassium, which are involved in the transport of metal ions. In some preferred embodiments, the electrodes are metal or metal-based electrodes for energy storage devices 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 energy storage devices. BNNTs or BNNT / polymer binder composites are particularly useful for lithium electrodes.

[0039] Ideally, the composite BNNT porous network or porous mesh should be flexible and resistant to cracking or fracture during the cycling of an energy storage device under normal operation. This is 0.1 mAcm -2 ~20mAcm -2 This would be understood to mean charging / discharging within a given current density range. The flexibility of such BNNT networks or meshes can be demonstrated, for example, as stable electrochemical metal stripping or plating in symmetric cells, or stable charge / discharge cycles over multiple cycles in energy storage devices, compared to equivalent systems without a porous BNNT network or porous mesh on electrodes. Multiple cycles means at least 100, at least 500, or at least 1000 stripping / plating cycles in constant current cycling tests, or at least 100, at least 500, or at least 1000 charge / discharge cycles in battery cells.

[0040] Ideally, a BNNT porous network or mesh better controls undesirable electrode expansion, particularly in metal-based anode materials, during cycling within a cell, compared to equivalent electrodes without a BNNT porous mesh on the electrode, especially in metal-based anode materials. The BNNT mesh is thought to protect and strengthen the SEI formed between the metal electrode and the SEI during cycling. Furthermore, in electrodes, particularly metal anodes without a BNNT component, varying degrees of volume expansion occur in different regions of the electrode, depending on where the metal ion flux reaching the electrode surface is concentrated. The composite BNNT component of the present invention equalizes this volume expansion by more uniformly directing metal ions across the entire region of the electrode in contact with the BNNT porous component.

[0041] In one embodiment, the electrode material is a sulfur-based electrode material. Preferably, 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 related embodiments, 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), preferably a composite BNNT / polymer binder on the S-cathode material.

[0042] 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 energy storage devices to transport metal ions and a polymer binder provided as a selectively permeable porous network on at least one surface of the electrode.

[0043] In related embodiments, the present invention provides an anode for an energy storage device comprising a metal-based anode material, the anode being coupled to boron nitride nanotubes (BNNTs) in the form of one or more deposits or intermediate layers of BNNTs having a porous mesh structure.

[0044] Preferably, in the case of a sulfur-based electrode, the sulfur content is about 0.1 mg / cm³. -2 ~about 5mgcm -2 More preferably about 0.9 mg / cm² -2 ~about 2.5mgcm -2 The active material is present in the electrode material at an amount of added sulfur. In some embodiments, sulfur is present at about 3 mg / cm³. -2 The amount of active material added was approximately 0.2 mg / cm³, particularly BNNT in the film. -2 ~about 0.25mgcm -2 The active material is present in the electrode material at the amount added.

[0045] 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.

[0046] It should be understood that the electrodes are formed into one or more substantially flat or planar block or other shaped structures on which BNNT can be deposited as a film of a composite BNNT porous network or as a coating of a composite BNNT porous mesh.

[0047] Appropriately, the composite boron nitride nanotube (BNNT) component has an average thickness as described herein. The thickness can 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 in some embodiments have been found to give a capacity retention rate of 79 to 90% with respect to the first cycle. In some embodiments, a more preferred BNNT layer thickness is in the range of about 1.3 microns to about 2.5 microns. In other embodiments, an even more preferred BNNT layer thickness is in the range of about 1.5 microns to about 2.3 microns, which, based on the initial capacity at a current density of 0.2C, gives 800 to 1100 mAhg after more than 400 cycles. -1Excellent initial specific capacity and a capacity retention rate of 85-90% are obtained. In one embodiment, a BNNT layer thickness of about 1.5 microns or 2.3 microns is particularly preferred.

[0048] Preferably, boron nitride nanotubes (BNNTs) are present in the network on the sulfur cathode material in amounts ranging from about 50% to about 95% by weight of the network / deposit, and more preferably in amounts ranging from about 80% to about 90% by weight of the network / deposit.

[0049] In one embodiment, a composite BNNT network or mesh is formed on the electrode surface by casting a solvent-based slurry of BNNT and a binder onto the electrode surface and evaporating the solvent to form a porous network / deposit of composite BNNT / binder. Thus, in some embodiments, the network / deposit is a solvent-cast network / mesh with excellent interfacial contact between components, having only nanoscale gaps / spaces between components.

[0050] In embodiments in which a binder is included in the BNNT network / mesh, it will be understood that the slurry in which the network / mesh is prepared substantially consists of / comprises BNNT, binder, and solvent. A preferred slurry contains BNNT (in the amounts described above for the binder concentration), but also contains preferably 1 to about 10% by weight of the total slurry in the solvent, preferably 3 to 7% by weight of the total slurry in the solvent, most preferably about 5% by weight.

[0051] Preferably, the S electrode contains one or more conductivity enhancers, preferably carbon-based, to enhance the conductivity of the S material of the electrode. Preferably, the conductivity enhancers are 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 is 300m 3 / g~800m 3 / g, preferably about 400m 3It has a porosity of / g. In one embodiment, preferred high surface area graphene is about 800m 2 / g~1000m 2 / g, preferably about 833m 2 It has a surface area of ​​ / g. 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.

[0052] 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, and 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, and most preferably a copper foil current collector.

[0053] Furthermore, this specification also describes energy storage devices comprising one or more electrodes of the present invention as described herein. In a related embodiment, the present invention provides an energy storage device comprising one or more negative electrodes as described herein, for example, lithium metal, potassium metal, or sodium metal electrodes.

[0054] In related embodiments, the present invention provides an energy storage device comprising a metal-based anode material, wherein the anode has boron nitride nanotubes (BNNTs) in the form of one or more deposits or intermediate layers of a composite BNNT / binder porous mesh.

[0055] Preferably, a preferred energy storage device comprises at least one cathode having a sulfur-based electrode material having a porous deposit of boron nitride nanotubes (BNNTs) on an electrode material, a separator, at least one anode having a lithium, potassium, or sodium metal-based electrode material on an electrode material, and an electrolyte. Preferably, a preferred energy storage device comprises at least one cathode having a sulfur-based electrode material having a porous deposit of boron nitride nanotubes (BNNTs) on an electrode material, a separator, at least one anode having a lithium, metal-based electrode material on an electrode material, and an electrolyte.

[0056] For example, the present invention is a metal sulfur energy storage device, At least one sulfur (S)-based electrode having a film of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, wherein the composite film is in close 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 an energy storage device but impermeable to polysulfides (i.e., 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, wherein the composite coating is in close contact with at least one surface of the electrode as a porous mesh that is selectively permeable to transport metal ions used in energy storage devices in which the composite is physically and / or chemically bonded to the surface of the electrode, This relates to a metal sulfur energy storage device equipped with the following features.

[0057] For example, the present invention is a lithium-sulfur energy storage device, At least one sulfur (S)-based electrode having a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, wherein the film of the composite is a porous network that is selectively permeable to transport metal ions and electrolytes used in energy storage devices but impermeable to polysulfides (impermeable to polysulfides), and is in close contact with at least one surface of the electrode, and At least one lithium metal electrode having a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, wherein the coating of the composite is in close contact with at least one surface of the electrode as a porous mesh that is selectively permeable to lithium ions to which the composite is physically and / or chemically bonded, This relates to a lithium-sulfur energy storage device equipped with the following features.

[0058] Energy storage devices should ideally retain up to 60% of their initial capacity even after at least 500 cycles at a current density of 0.2C.

[0059] Preferably, the energy storage device has a capacity of at least 400 mAhg based on the amount of S added, at a rate of 0.2C at a temperature of 25°C. -1 This indicates the specific capacity, preferably at least 900 mAhg based on the amount of S added. -1 This indicates the specific capacity.

[0060] Preferably, the device has a capacity of at least 8 mAh. Preferably, the device has a capacity of at least 24 mAh. Preferably, the device has a capacity of at least 32 mAh.

[0061] This specification describes an energy storage device comprising one or more electrodes of the present invention as described herein. Preferably, the energy storage device comprises one or more negative electrodes for a secondary energy storage device, for example, a lithium metal or sodium metal electrode (anode), or a zinc or aluminum metal (anode). It should be understood that the negative electrode is the lithium anode of a Li-S battery, which is an electrode that undergoes oxidation during discharge, i.e., lithium dissolution occurs from the anode surface 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.

[0062] In related embodiments, the present invention provides an energy storage device comprising a negative electrode to which a metal-based anode material and boron nitride nanotubes (BNNTs) in the form of an intermediate layer of one or more deposits or a BNNT porous mesh are bonded.

[0063] Li-S batteries with BNNTs in the cathode and anode have been found to perform substantially better in terms of cycle stability and energy density compared to identical batteries without BNNTs. In fact, integrating BNNTs into the components and structure of lithium-sulfur batteries is an effective way to stabilize the battery components during charging and discharging, creating lithium-sulfur battery cells with cycle life close to that of everyday consumer-grade lithium-ion batteries. This opens up the possibility of lithium-sulfur batteries finally being commercialized and mass-produced.

[0064] (Electronic devices) This specification describes electronic devices including the electrodes and / or energy storage devices of the present invention.

[0065] (Application / Use) This specification describes the use of the electronic devices of the present invention in transportation, grid storage, electric vehicles, and portable electronics applications.

[0066] This specification describes the use of one or more BNNT layers, preferably in the form of a composite BNNT / polymer binder porous network, as a polysulfide barrier material for the S cathode of an energy storage device. It is preferable 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 a reversible polysulfide trap in the sulfur (S)-based cathode of an energy storage device.

[0067] This specification describes the use of one or more BNNT layers, preferably composite BNNT / polymer binder porous meshes, as dendritic crystal growth inhibitors on metal electrodes of energy storage devices. A coating of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder is preferably used as a porous mesh physically and / or chemically bonded to the surface of a metal electrode to prevent dendritic crystal formation on the electrode within the energy storage device, preferably the electrode being a Li, Na, K, Al, Mg, or Zn metal anode. Physical and / or chemical adhesion may include SEIs formed during the cycle.

[0068] This specification describes the use of one or more BNNT layers, preferably composite BNNT / polymer binder porous mesh, as a dendritic crystal growth inhibitor for metal electrodes in energy storage devices. This specification describes the use of one or more BNNT layers, preferably composite BNNT / polymer binder porous mesh, as a solid electrolyte interface reinforcing material for metal electrodes in energy storage devices.

[0069] It is preferable to correct the volume expansion of metal electrodes, preferably Li, Na, K, Al, Mg, or Zn metal anodes in energy storage devices, by using 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. It is also preferable to enhance the stability of the innate SEI formed on the electrodes of energy storage devices by using 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 the metal electrode.

[0070] (Formation of BNNT porous networks, meshes, or deposits) This specification describes slurries for preparing composite BNNT porous networks or porous meshes for electrode materials, comprising boron nitride nanotubes (BNNTs), one or more polymer binders, and one or more solvents. Preferably, the electrode material is an S-cathode material, and the BNNTs are provided as a film of a composite of BNNTs and a binder as a porous BNNT network on the electrode surface. Also described herein are slurries for preparing coatings of BNNT meshes, preferably coatings of composite BNNT / polymer binder porous meshes for metal or metal-based anode materials, comprising boron nitride nanotubes (BNNTs), one or more polymer binders, and one or more aprotic solvents. Preferably, the solvent is inert to the metal. Preferably, the metal is an alkali metal, particularly sodium or potassium, zinc or aluminum metal.

[0071] This specification describes a method for preparing electrodes for energy storage devices, the electrodes comprising an electrode material in which boron nitride nanotubes (BNNTs) are associated in the form of a porous network or a porous mesh of a BNNT / polymer binder composite, the method is described below. (i) A step of preparing a slurry of BNNT and one or more polymer binders in a solvent, (ii) The step of coating the surface of the electrode with a slurry to a desired thickness, (iii) Evaporating the solvent to form a BNNT porous network or porous mesh on the electrode, Includes.

[0072] This specification describes a method for preparing a negative electrode (anode) comprising a metal-based anode material to which boron nitride nanotubes (BNNTs) in the form of one or more deposits or intermediate layers of BNNTs having a porous mesh structure are bonded, and this method is (i) The step of preparing a slurry of BNNT and one or more polymer binders in one or more solvents, (ii) The step of coating the surface of a metal-based anode material with a slurry to a desired thickness, (iii) Evaporating the solvent to form a metal-based anode material having a surface coating of a BNNT composite material having a porous mesh structure, Includes. Preferred dimensions are disclosed elsewhere in this specification. The BNNT concentration in the slurry is 10% by weight or less, preferably 7.5% by weight or less, and more preferably 5% by weight or less. The amount and thickness of the polymer are described elsewhere in this specification. The slurry thickness can be adjusted using doctor blade technique. Preferred thicknesses are described elsewhere in this specification.

[0073] (Description of preferred embodiments) The present invention will be described with reference to the following embodiments. It should be understood that the embodiments are illustrative of the present invention as described herein and are not intended to limit it.

[0074] (Embodiment 1 - The BNNT network film prevents polysulfide shuttle.) Boron nitride nanotubes (BNNTs) have attracted considerable attention in various scientific fields due to their exceptional thermal, mechanical, optical, and electrical properties, making them more promising as nanomaterials compared to other nanotubes. However, BNNTs have not yet been demonstrated as a useful polysulfide shielding material for the S cathode of batteries, particularly in Li|S batteries.

[0075] This specification describes composite boron nitride nanotube / binding film or coating provided on electrode surfaces. For S-cathode electrodes, BNNT is provided as a film of a porous BNNT network. For metal anode electrodes, BNNT is provided as a coating of a porous BNNT mesh. The difference in terminology refers to the difference in thickness and density of the respective BNNT components. In the case of S-cathodes, a high-density network of BNNT is required to prevent PS from diffusing into the electrode through the network, but its thickness is such that PS is reversibly trapped within the network, not permanently trapped, resulting in the generation of inert sulfur over time and a significant decrease in capacity / capacitance surface. Similarly, in the case of metal anodes, a coating of a porous BNNT mesh is of a suitable thickness to enhance the SEI of the metal anode while enabling efficient metal ion transport through the mesh. In fact, the mesh serves to divide the metal electrode surface into multiple regions, allowing for more uniform dispersion of ions as they pass through the mesh.

[0076] The cycle performance of Li-S coin cells and pouch cells with and without a BNNT interlayer on the cathode was studied in detail. The results clearly demonstrate that the BNNT interlayer can significantly improve the cycle stability of Li-S cells, demonstrating the interlayer's performance in controlling the polysulfide shuttle and mitigating the adverse effects of polysulfide reciprocation.

[0077] Li-S coin batteries and Li-S pouch batteries incorporating the BNNT / S cathode of the present invention were prepared. In some embodiments, the study investigates the electrochemical lithium plating and delamination behavior in batteries having a lithium metal anode and an S cathode, in which the S cathode is protected from cathode mass loss by polysulfide shuttles by providing a composite BNNT binder network or deposit according to the present invention on the S cathode.

[0078] The BNNT intermediate, when provided with appropriate thickness and / or density, can be thought to act as a physical barrier blocking 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 cycle stability and high capacity.

[0079] In particular, the present invention provides a cathode comprising a sulfur cathode material bonded to a porous film or porous deposit of boron nitride nanotubes (BNNTs). Graphene is also included as a preferred S-cathode material. The porous nature of the film or deposit can be observed from SEM analysis, which clearly demonstrates the porous nature of the BNNT material. The average pore diameter of the BNNT material is preferably about 0.1 to 3 microns, more preferably about 0.5 to 1.5 microns. The boron and / or nitrogen components of the film / deposit can be confirmed by EDS analysis.

[0080] The boron nitride nanotube (BNNT) film / deposit preferably has tunnels, passages, or channels that are positioned and / or sized to allow Li ions to pass through, but not polysulfides containing Li2S4 or Li2S6. As shown by the Raman and IR studies described herein, the BNNT film / deposit prevents the passage of polysulfides through the film / deposit. It is thought that the polysulfides are adsorbed onto the BNNTs. Therefore, adsorption prevents the diffusion of polysulfides into the electrolyte.

[0081] 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 Figure 3, many BNNTs have a diameter of mainly 20 to 150 nm and a length of mainly 3 to 100 microns.

[0082] Preferably, the BNNT film / coating is a mixture of BNNT and one or more binder materials. Preferably, the BNNT porous mesh / network or deposit comprises at least one binder material, preferably a polymer binder. In preferred embodiments, a binder is present, preferably a polymer binder or a mixture of two or more polymer binders. The binder supports the structural formation and integrity of the BNNT porous mesh / network or deposit. Polymer binders are particularly preferred because they have inherent flexibility under typical energy storage device conditions, which is desirable in that they impart controllable flexibility to the BNNT structure. In preferred embodiments, the boron nitride nanotube (BNNT) network / deposit further comprises one or more binders. Preferably, the binder is a polymer binder such as PVDF, LA133, PEO, or PTFE, or a combination thereof. Examples of these binders 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 substantially highly reactive materials. Although not essential to the functionality of the BNNT porous mesh of the present invention, preferred polymer binders may be permeable to the metal ions in question. In some embodiments, the flexible polymer binder is preferably natural or synthetic rubber, most preferably styrene-butadiene rubber such as poly(styrene-co-butadiene). Examples of these binders are particularly preferred for metal anodes such as lithium, potassium, or sodium.

[0083] Preferably, the binder is present in an amount ranging from 1% to 50% by weight, or 5% to 50% by weight, of the boron nitride nanotube (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 boron nitride nanotube (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 in an amount of 10% or less by weight, 9% or less by weight, 8% or less by weight, 7% or less by weight, 6% or less by weight, 5% or less by weight, 4% or less by weight, 3% or less by weight, 2% or less by weight, or 1% or less by weight. In embodiments containing a BNNT / binding agent complex, at least 0.5% by weight of the binding agent is present.

[0084] Preferably, boron nitride nanotubes (BNNTs) are present in amounts ranging from about 50% to about 98% by weight, more preferably 80% to 95% by weight, and more preferably 85% to 95% by weight of the film or deposit. In some embodiments, boron nitride nanotubes (BNNTs) are present in amounts ranging from 85% to 86% to 87% to 88% to 89% to 90% to 91% to 92% to 93% to 94% to 95% by weight of the total film / deposit. In other preferred embodiments, boron nitride nanotubes (BNNTs) are present in amounts ranging from about 88% to about 93% by weight, preferably about 90% by weight of BNNTs, of the total weight of the film / deposit. "Approximately" means ±1% of the stated values. Appropriately, the remaining % is a binder.

[0085] Preferably, at least a portion, preferably most, of the binder in the composite BNNT network / sediment is particulate. Preferably, the binder particles are dispersed (preferably uniformly) throughout the composite BNNT / binder network / sediment. The dispersion of the binder can be confirmed by SEM analysis, where individual binder particles (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 morphologies of the binder particles and the BNNT fibers / strands mean that the binder and BNNT can be easily distinguished by SEM analysis. Preferably, the binder particles provide stability and flexibility to the porous network structure by adhering or otherwise fixing local areas or regions of the BNNT fibers / strands. It will be understood that the binder particles fix one or more BNNT fibers / strands together at the location where the binder particles are located. Preferably, the binder does not coat or encapsulate the surface of the BNNT fibers / strands, for example, within a conformal film of a 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 generated, for example, during the operation of an energy storage device. This is in contrast to the BNNT polymer composite in U.S. Patent Application Publication 2019 / 0123324, where the opposite result is desired, and the polymer is provided not in a specific form but as a film / coating on a BNNT scaffold, and the polymer coating expands to reduce the pore size of the separator or actually completely closes the pores to prevent thermal runaway.

[0086] When an organic solvent system is used to prepare the BNNT / binder mixture during film / deposit preparation, the preferred binder used is PVDF. In some embodiments of cathode preparation, a water-based system can be used to obtain a higher mass of sulfur. Therefore, when 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 are the same regardless of the solvent system / binder used. For example, Figure 8 shows that films / deposits using LA133 and PVDF have 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 can be used for the BNNT film / deposit. For example, when the S cathode is prepared in aqueous solution, LA133 can be used as the cathode binder. When an organic solvent is used to form the S cathode, PVDF can be used for both the cathode and the BNNT film / deposit.

[0087] In some embodiments, the boron nitride nanotubes (BNNTs) are in the form of an independent or self-supporting film positioned in close proximity to the cathode. However, in other preferred embodiments, the film is not independent or self-supporting, in that the BNNT film / deposit is in close contact / resting with the S cathode. In some embodiments, the BNNT film / deposit adheres to the S cathode material. When the BNNT / polymer slurry is cast during manufacturing, it is assumed that the BNNT / polymer material penetrates to some extent into the pores of the S electrode surface. As the solvent evaporates and the film is formed, strong adhesion occurs between the BNNT / composite film and the S electrode material. In any case, there is at least some, preferably complete, direct interfacial contact between the BNNT film / deposit and the S cathode material. See, for example, Figure 1(d) which shows a preferred arrangement and close interfacial contact between the BNNT porous network film and the S cathode material.

[0088] The morphology of the BNNT intermediate layer was investigated by SEM. The thickness of the BNNT intermediate layer used can be controlled, for example, in the case of coating on a cathode material, by a combination of (i) adjusting the concentration of BNNT in the intermediate layer 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 BNNT in the slurry affects the density / amount of BNNT added in the final film during formation. In some embodiments, it is preferable to use BNNT concentrations in the slurry of 15% by weight or less, 10% by weight or less, 7.5% by weight or less, or 5% by weight or less. In some embodiments, the BNNT concentration in the slurry is preferably about 5% by weight (where "about" means ±5%).

[0089] The morphology can be described, for example, as an irregular network, mesh, or sieve of BNNT filaments or strands (depending on the BNNT density / addition amount used), having multiple filaments or strands arranged in the form of a felt or web. The morphology employs tunnel-like, random, fibrous web, honeycomb, or fibrous felt-type structures formed from bundles of BNNT nanotubes, resulting from a random overlap of twisted, tangled, or distorted yarns or fibrils, resulting in structures with channels, passages, or tunnels of dimensions such that Li ions can be transported, but polysulfides cannot. BNNT porous networks / meshes include intersecting filaments or strands of BNNT, networks or grids of connected, contacting, or intersecting filaments or strands of BNNT, in particular entangled, intersecting, entangled, or intertwined BNNT filaments. In short, the BNNT yarns, threads, or fibrils are not straight and are not arranged in regular, repeating, or regular arrangement-type structures or arrangements.

[0090] (S-cathode electroactive material composition) In one embodiment, the present invention provides a sulfur (S)-based cathode comprising a sulfur-cathode material bonded to a porous film of boron nitride nanotubes (BNNTs).

[0091] More precisely, the present invention provides a sulfur (S)-based electrode for an energy storage device having a film of a composite of boron nitride nanotubes (BNNTs) and at least one polymeric binder, wherein the composite film is in close contact with 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 should be understood that the composite film has tunnels, passages, or channels of such dimensions that transported metal ions can selectively pass through the porous network while reversibly trapping polysulfides within the porous network.

[0092] When a BNNT porous network film is used to protect the S electrode material, the density of the BNNT is such that the channels, pathways, or tunnels reversibly trap polysulfides. However, a density / thickness of the BNNT porous network film is undesirable because it is not high enough to irreversibly capture polysulfides, leading to deactivation of the active electrode material and loss of capacity over time. The density / thickness of the BNNT porous network film is selected so that, despite the mesh, electrochemical activity is maintained and S returns to contact the active cathode mass during cycling. Preferred densities / thicknesses are described elsewhere in this specification.

[0093] It will be understood that the S cathode comprises an electroactive material composition containing sulfur as an electrochemically active substance. In some embodiments, 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 of sulfur is particularly preferred. The thickness of the sulfur / graphene cathode is appropriately in the range of about 5 microns to about 40 microns.

[0094] 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 Ketjenblack) or graphene. In some embodiments, the S-cathode consists substantially 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 in 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. Preferably, if the conductivity-enhancing agent is one or more graphenes, the material is present in about 0.2 mg cm³ -2 ~approximately 0.8 mg / cm² -2 Approximately 0.4 mg / cm² -2 ~0.7 mg / cm -2 , about 0.5mgcm -2 ~about 0.6mgcm -2 It may be present in that amount. In some embodiments, the mass amount of graphene added to the cathode is 0.6 mg / cm³. 2Graphene can be a single type of graphene or a mixture of two or more types of graphene, for example, highly porous graphene and highly surface area graphene. Preferably, the electroactive material composition may contain a mixture of highly porous graphene and highly surface area graphene, for example, in a weight % ratio of 1:9 to 9:1, more preferably 3:7 to 8:2, more preferably 4:6 to 7:3, and most preferably 6:4 by weight. Preferably, the ratio of highly porous graphene to highly surface area graphene is 6:4, which provides particularly excellent performance with respect to the highest specific capacity. Figure 6 shows the effect of various ratios on specific capacity. Therefore, a preferred weight ratio of composition is 12 wt% highly porous graphene: 8 wt% highly surface area graphene: 80 wt% sulfur. Thus, in a preferred embodiment, the cathode electroactive material composition contains 12 wt% highly porous graphene: 8 wt% highly surface area graphene: 80 wt% sulfur.

[0095] Preferably, the sulfur content is about 0.1 mg / cm³. -2 ~approximately 10 mg / cm² -2 , 0.5 mg cm -2 ~about 7.5mgcm -2 , about 0.9mgcm -2 ~about 6mgcm -2 Most preferably about 5 mg / cm² -2 It is present in the electrode material at an effective additive amount of approximately 1 mg cm³. -2 ~approximately 8 mg / cm² -2 Preferably about 2.5 mg cm -2 ~about 4.5mgcm -2 Most preferably about 3 mg cm -2 The electrode contains sulfur with a sulfur mass addition amount of . In some embodiments, the sulfur mass addition amount in the cathode is about 0.9 to about 2.4 mg cm³. -2 It is within the range.

[0096] Preferably, the boron nitride nanotube (BNNT) film or deposit is approximately 0.2 mg / cm². -2 ~about 1.7mgcm -2 More preferably about 0.1 mg / cm² -2 ~approximately 1 mg cm-2 More preferably about 0.5 mg / cm² -2 ~about 0.75mgcm -2 It has a density of .

[0097] 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 film of the desired composite 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 because it has been found to provide a good balance between sufficient protection to avoid rapid capacity loss and the ability to prevent polysulfide shuttle. However, in thicker layers, the BNNT layer is too thick, preventing the PS from returning to its cathode mass, and the captured / adsorbed polysulfides become inactive, resulting in a decrease in capacity after the first and second cycles. For example, the cycle stability results for a single late-stage 2.1VLi-S pouch battery with BNNT layers of different thicknesses on the S cathode showed very high capacity retention (over 90%) after 50 cycles at 25°C and 0.2C with a 2.3-micron thick BNNT interlayer, and good capacity retention (over 80%) after 50 cycles at 0.2C with a 0.9-micron thick BNNT interlayer. This is a significant improvement compared to an equivalent pouch without an interlayer, which showed a capacity retention of approximately 65% ​​after 50 cycles.

[0098] In one embodiment, the boron nitride nanotube (BNNT) film / deposit is approximately 0.075 mg / cm³. 2 ~about 0.5mg / cm 2 It has a BNNT doping density of approximately 0.1 mg / cm³. In a preferred embodiment, the boron nitride nanotube (BNNT) film / deposit contains approximately 0.1 mg / cm³. 2~about 0.3mg / cm 2 Preferably about 0.15 mg / cm³ 2 ~about 0.25mg / cm 2 It has a BNNT addition density of approximately 0.05 mg / cm². The desired composite film is approximately 0.05 mg / cm². -2 ~about 3.5mgcm -2 More preferably about 0.05 to about 0.5 mg / cm² -2 Most preferably 0.2 mg cm -2 It has a surface density or BNNT content of approximately 3.5 mg / cm². -2 The following range is particularly preferred when a longer cycle lifetime is desired, as the film / deposit size is determined so that the adsorbed polysulfides can efficiently return to the cathode material during cycling, i.e., maintain their activity. Here, "approximately" means ±2%. In some embodiments, the boron nitride nanotube (BNNT) film / deposit is approximately 0.2 mg / cm³. 2 This is because it has a BNNT doping density, which has been shown to give a particularly good capacity retention rate of over 90% of the initial capacity over at least 10 cycles, at least 20 cycles, at least 50 cycles, at least 200 cycles, and at least 1000 cycles.

[0099] Preferably, the sulfur-based electrode material is deposited on a current collector, preferably an aluminum foil current collector. In some embodiments, the current collector is a metal (e.g., aluminum) foil current collector that can have one or more surfaces coated with a conductive material such as carbon.

[0100] The present invention relates to an energy storage device (e.g., a secondary battery) comprising one or more cathodes as described herein. In some embodiments, the device may be a coin cell. In other preferred embodiments, the device may be a pouch cell, such as a single-layer pouch cell. More complex cell arrangements are also conceivable.

[0101] In one embodiment, the present invention provides an energy storage device comprising one or more sulfur (S)-based electrodes of the present invention as 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.

[0102] In one embodiment, the energy storage device of the present invention comprises at least one cathode having a sulfur-based electrode material having a porous film of boron nitride nanotubes (BNNTs) on an electrode material, a separator, at least one anode having a lithium metal-based electrode material, and an electrolyte.

[0103] In a preferred embodiment, the energy storage device of the present invention retains up to 60% of its initial capacity even after at least 500 cycles at a temperature of 25°C and a current density of 0.2C.

[0104] In other embodiments, the device retains up to 60%, 70%, 80%, 90%, or 100% of its initial capacity after at least 500 cycles at a temperature of 25°C and a current density of 0.2C. In other preferred embodiments, the device retains up to 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% of its initial capacity after at least 500 cycles at a current density of 0.2C. These capacity retention rates are observed at a temperature of 25°C.

[0105] Preferably, the energy storage device has a 0.2C rate, a temperature of 25°C, and a capacity of at least 400 mAhg based on the amount of S added. -1 It shows the specific capacity, preferably at least 900 mAhg based on S addition. -1 This indicates the specific capacity.

[0106] The present invention also relates to electronic devices including the cathode and / or energy storage device of the present invention as described herein.

[0107] 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.

[0108] 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 BNNT / polymer binder composite layers, as a polysulfide diffusion blocking coating or a reversible polysulfide trap in the sulfur(S)-based cathode of an energy storage device.

[0109] The present invention further, At least one sulfur (S)-based electrode having a film of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, wherein the composite film is in close 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 energy storage devices 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, wherein the composite coating is in close contact with at least one surface of the electrode as a porous mesh that is selectively permeable to transport metal ions used in energy storage devices in which the composite is physically and / or chemically bonded to the surface of the metal electrode, This also extends to metal-sulfur energy storage devices that incorporate these features.

[0110] The present invention At least one sulfur (S)-based electrode having a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, wherein the film of the composite is a porous network that is selectively permeable to transport metal ions and electrolytes used in energy storage devices but impermeable to polysulfides, and is in close contact with at least one surface of the electrode, and At least one lithium metal electrode having a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, wherein the coating of the composite is in close contact with at least one surface of the electrode as a porous mesh that is selectively permeable to lithium ions to which the composite is physically and / or chemically bonded, This also extends to lithium-sulfur energy storage devices that incorporate these features.

[0111] (Detailed description of the protected S cathode electrode) (Preparing the S cathode) First, graphene and sulfur are mixed and heated at 300°C. The resulting mixture can then be heated, preferably in an airtight container, at 300°C for approximately 24 hours to synthesize an S-cathode. Secondly, the resulting graphene / sulfur powder is heated and then mixed with carbon black, a binder in the organic solvent NMP, to form a slurry. Thus, the S-cathode is prepared by mixing desired amounts of sulfur, a binder, and a conductive additive in an organic solvent, such as N-methyl-2-pyrrolidone (NMP). The graphene / binder / sulfur slurry is then coated onto a suitable current collector, such as Al foil, using a doctor blade. The thickness can be controlled by adjusting the blade height. Next, the S-cathode is dried in an oven at 80°C for 12 hours, preparing it for coating or bonding with a BNNT intermediate layer.

[0112] (Preparation of the BNNT porous network film for the S cathode) The BNNT porous network comprises boron nitride nanotubes (BNNTs) and a binder. In the case of an S cathode, the BNNT composition may contain about 1% to about 20% by weight of BNNTs in total. A preferred amount of BNNT is in the range of about 2% to about 15% by weight. A preferred amount is in the range of about 5% to about 10% by weight of the total BNNT intermediate layer composition. In one embodiment, an amount of BNNT of about 5% by weight of the total BNNT intermediate layer composition is particularly preferred. In one embodiment, an amount of 10% by weight of binder is particularly preferred, for example, 10% by weight of PVDF in total BNNT intermediate layer composition. Preferred BNNTs are available from BNNT Technology Limited. Preferred BNNTs are substantially free of impurities such as hexagonal boron nitride and / or elemental boron. The BNNT composition may further contain 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 an aqueous solvent / system such as water.

[0113] In particular, BNNT composites are electrical insulating materials, meaning they are not electronically conductive. Furthermore, the BNNT composites of this invention do not contain conductivity enhancers such as carbon-based conductivity enhancers like graphene. In porous BNNT composites, transport pathways for metal ions such as sodium ions or lithium ions are open and retained during battery operation, so additives to enhance conductivity are not necessary. Therefore, graphene is not required in the composite to enhance conductivity.

[0114] The BNNT intermediate layer is prepared by mixing a desired amount of BNNT 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, the thickness of the slurry coating is adjusted as desired, for example by a doctor blade, and then the solvent is removed by drying, for example, in an air oven at 60°C for 24 hours to provide a final film of the BNNT porous network on the S cathode material in the form of a film with a thickness of less than 20 microns.

[0115] (Current collector) The current collector can be any current collector suitable for use with an S cathode. For example, the current collector may be a metal foil such as aluminum foil or aluminum foam, or a conductive carbon cloth. The thickness of the current collector is suitable in the range of about 10 microns to about 100 microns. In one embodiment, a preferred current collector thickness is about 20 microns, for example, 20-micron aluminum foil. A standard material for the current collector of a Li metal anode may be a copper foil of about 20 microns, for example, about 20 microns.

[0116] (Separator) The separator can be any separator suitable for an S cathode. For example, a polypropylene separator such as a Celgard 2400 separator (25 micron separator) can be used.

[0117] (electrolyte) The electrolyte can be any electrolyte suitable for the desired battery under consideration. For example, in the case of a Li-S battery, a DOL / DME combination, particularly a Li ionic liquid salt and an ionic Li salt such as LiNO3, can be used, and appropriately, the weight ratio of LiNO3 can be up to 5%. For example, one exemplary electrolyte is 1M LiTFSI in DOL / DME containing 1 wt% LiNO3.

[0118] (Pouch material) The pouch material can be any material suitable for Li-S batteries, such as aluminum plastic film.

[0119] (Coin cell with BNNT / S-cathode) A Li-S based coin cell was fabricated comprising a Li metal anode, a separator, the BNNT-protected S cathode of the present invention, and an electrolyte. In one embodiment, a standard lithium metal chip for coin batteries was used as the lithium metal anode, and a 25-micron polypropylene-based separator, such as the Celgard 2400 separator, was used together with the BNNT / S cathode of the present invention. The coin cell was filled with an electrolyte composition of 1 M LiTFSI in DOL / DME containing 1 wt% LiNO3.

[0120] Full cells, i.e., Li-S pouch cells, were manufactured in an argon-filled glove box using a lithium metal film as the anode, a 25-micron polypropylene-based separator such as a Celgard 2400 separator, and a graphene / S cathode protected by a BNNT intermediate layer. A commercially available flexible Al plastic film was used for the case. The electrolyte, e.g., 1M LiTFSI in DOL / DME containing 1 wt% LiNO3, was added in a volume corresponding to, for example, about 5 μL / mg to about 50 μL / mg, more preferably about 15 μL mg, depending on the mass of sulfur. -1 It was added appropriately.

[0121] (Detailed description of the invention) Next, Figure 1 shows SEM images of an S / graphene cathode containing a BNNT composite on a sulfur / graphene cathode (Figure 1b) and an S / graphene cathode without a BNNT composite (Figure 1a). Figure 1(c) is a high-magnification top view of the sulfur graphene cathode, clearly showing the porosity of the surface of the S cathode material.

[0122] Figure 1(d) is a side view showing three different layers: (i) BNNT composite components, (ii) sulfur / graphene composite components, and (iii) aluminum foil current collector material. Figures 1(e, f) are low-magnification and high-magnification top views of an S cathode with a film of the BNNT porous network composite.

[0123] As is evident from Figures 1(a), 1(e), and (f), a BNNT porous network clearly covers the entire cathode material. The enlarged view of Figure 1(f) clearly shows the BNNT porous network formed by the deposited BNNT intermediate layer. This morphology can be described as a random fibrous web, honeycomb, or fibrous felt-type structure resulting from a random superposition of twisted, tangled, 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 arrangement type structure or configuration. Unique, uniformly dispersed solid spheroidal binder particles can also be observed in this image.

[0124] Specific capacity (mAhg based on S) achievable with a Li-S coin cell containing a BNNT / S cathode and an equivalent Li-S coin cell without the BNNT intermediate layer on the S cathode. -1 A comparison of the volume retention rate (%) and specific volume retention rate (%) is shown in Figures 2(a) and 2(b).

[0125] Figures 2a and 2b show the performance of coin cells with BNNT interlayers at weight ratios of 5% and 10% of the total slurry solution. In the Li-S coin cell in Figure 2(a), the BNNT interlayer was fabricated using a slurry with a BNNT weight ratio of 5%. All coin and pouch type batteries are tested at room temperature of approximately 25°C and 0.2C. Varying the doctor blade height resulted in BNNT interlayer thicknesses of X microns (where X is the thickness across the coating, meaning reliable measurement is not possible), 0.9 microns, 1.5 microns, and 2.3 microns, yielding corresponding capacity retention rates (shown as initial ratio capacity %) of 40%, 67%, 85%, and 90% after 500 cycles, respectively, as shown in Figure 2(a). Similarly, Figure 2(b) shows data for cathodes with BNNT interlayers fabricated using a slurry with a BNNT weight ratio of 10%. Varying the doctor blade height resulted in BNNT interlayer thicknesses of X microns (where X is the thickness across the entire coating, making reliable measurement impossible), 2.2 microns, 3.2 microns, and 4.4 microns, yielding corresponding volume retention rates (shown as initial relative volume %) of 40%, 79%, 87%, and 92% after 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, a 2.3-micron film formed from a 5 wt% BNNT slurry provided particularly good capacity over the duration of the cycle study. Furthermore, when the surface of the BNNT-coated sulfur cathode was examined by SEM (not shown), it was clear that the sulfur cathode was not completely covered when the blade height was 100 μm, and undesirable aggregation of large particles was observed on the surface of the BNNT interlayer film prepared with a 10% wt% BNNT weight ratio. Therefore, using a slurry with a 10% wt% BNNT weight ratio results in aggregation on the surface of the BNNT interlayer. Due to aggregation, the initial volume of the BNNT-coated cathode (10%) is not as high as that of an equivalent uncoated cathode. In particular, in the BNNT film used in the experiment reported in Figure 2(a), almost no aggregation was observed on the surface of the BNNT intermediate layer (5%), which contributes to the high initial volume.When the BNNT thickness is 10 μm or 20 μm, capacity retention is good, but capacity decreases. This is thought to be because the tunnel / path length for lithium ion transport increases with film thickness. In summary, it was found that thicker BNNT layers result in lower initial capacity but improved cycle stability. However, it was found that cycle stability improves with increasing BNNT layer thickness. Depending on the specific desired battery application, the resulting performance parameters can be adjusted as needed.

[0126] (Description of preferred embodiments) Synthesis of graphene / sulfur cathodes: A mixture consisting of 12 wt% highly porous graphene, 8 wt% high surface area graphene (Graphene Supermarket, USA), and 80 wt% sulfur was heated in an airtight container at 300°C for 24 hours for the synthesis of graphene / sulfur electrodes. The graphene / sulfur was coated onto a 20 μm thick aluminum foil. The resulting graphene / sulfur cathodes were then dried in a vacuum oven at 60°C for 48 hours. These electrodes were further coated with a BNNT intermediate layer.

[0127] Synthesis of the BNNT intermediate layer on the cathode: The BNNT intermediate layer was prepared by mixing a solution of 5 wt% BNNT (BNNT Technology Limited) and 0.5 wt% N-methylpyrrolidinone (NMP) as a PVDF binder. The slurry was coated to the desired thickness on the surface of the graphene / sulfur cathode electrode using a doctor blade and dried in an air oven at 60°C for 24 hours.

[0128] Li-S coin cell and pouch cell manufacturing: Li-S coin cells were manufactured using a lithium chip, a Celgard 2400 separator, and a graphene / S cathode with a BNNT interlayer. The electrolyte was 1M LiTFSI in DOL / DME containing 1 wt% LiNO3.

[0129] A fully flexible Li-S pouch battery was fabricated in an argon-filled glove box using a graphene / S cathode with a lithium film, Celgard 2400 separator, and BNNT intermediate layer. A commercially available flexible 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 That was the case.

[0130] Results and Discussion Regarding Protection of S Cathodes: To coat the sulfur cathode with a BNNT intermediate layer, a slurry consisting of BNNT, a binder, and an organic solvent was prepared as illustrated above. In this example, the weight ratio of BNNT (weight of BNNT relative to the total weight of the slurry) was controlled to 5%. The blade height was also adjusted to 100 μm, 200 μm, 300 μm, and 400 μm to control the thickness of the BNNT intermediate layer formed. After removing the solvent, the final thickness of the intermediate layer formed ranged from 0.9 μm to 5 μm, depending on the initial concentration of BNNT in the slurry used.

[0131] SEM can be used to observe that the sulfur cathode is completely covered and that a porous network of BNNT intermediate layers is formed. As shown in Figure 1d, three distinct layers of the constituent material can be observed by SEM, which are the BNNT intermediate layer, the graphene / sulfur layer, and the Al foil.

[0132] Li-S coin cells with sulfur cathodes coated with the obtained BNNT interlayer were fabricated and tested. The cycle stability of the coin cells was investigated in detail. Figures 2a and 2b compare the specific capacity of Li-S coin cells with and without a sulfur cathode coated with a BNNT interlayer. The BNNT interlayer film was fabricated using a slurry with a BNNT weight ratio of 5%. First, the Li-S coin cell without the BNNT interlayer showed the worst stability. Cells with the thinnest BNNT layer (note that in this case, the thickness cannot be reliably measured because the layer does not completely cover the surface of the sulfur cathode) showed improved stability, but the stability was still insufficient. However, as the thickness of the BNNT layer increased from 0.9 μm to 2.3 μm, the cycle stability (capacity retention rate) after 500 cycles at 25°C and 0.2C increased from 67% to 90%, indicating that the BNNT layer improves the cycle stability of the sulfur cathode.

[0133] Single-walled Li-S pouch batteries with sulfur cathodes coated with the obtained BNNT interlayer were fabricated and tested. The cycle stability of the pouch cells was investigated in detail. The BNNT interlayer was fabricated using a slurry in which the weight ratio of BNNT was 5% of the total slurry weight, including BNNT, binder, and solvent. The capacity of pouch cells without the BNNT interlayer decreased to 65.2% after 50 cycles, while pouch cells with BNNT layers of 0.9 μm to 2.3 μm maintained 82% and 95% of their initial capacity, respectively, indicating that the BNNT layer significantly improves the cycle stability of the sulfur cathode.

[0134] (Demonstration of polysulfide blocks) A polysulfide (PS) solution (1M LiTFSI in DOL / DME containing 0.136 mol / L Li2S8-1%LiNO3 in a commercially available electrolyte) was prepared and transferred to two bottles. Figure 4(a) shows the polysulfide solution without BNNT (yellow) and the polysulfide solution with BNNT (yellow color disappears). The polysulfide solution is yellow because of the presence of PS. However, upon addition of 5 mg of BNNT, the yellow color immediately disappears, indicating binding of PS to BNNT such that dissolved PS is drawn out of the solution. IR analysis was performed on a series of polysulfide solutions with different amounts of BNNT added (0 mg, 8 mg, and 15 mg of BNNT). The IR results in Figure 4(b) show a decrease in the intensity of the Li2S8 absorption peak after adding BNNT to the polysulfide solution. This indicates that the polysulfide is adsorbed onto BNNT. Raman analysis was also performed. The results in Figure 4(c) show the BS and NS bonds of the BNNT polysulfide sample recovered from the BNNT-treated PS solution, further demonstrating that BNNT adsorbs polysulfides. The absorption of PS from the solution into BNNT indicates that BNNT is trapping PS. In energy storage / battery environments, the adsorption of S onto the BNNT film / deposit prevents the loss of PS into the electrolyte and prevents the loss of cathode mass that may occur during cycling. With BNNT composite films of optimized thickness and density, PS is reversibly trapped by BNNT, and PS / S maintains electrochemical activity.

[0135] In fact, Figure 7 shows (a) specific volume and (b) volume retention of the test S cathode at various BNNT doping densities over 100 cycles. The BNNT doping densities are 0.05, 0.1, 0.2, 0.25, and 0.5 mg / cm³, respectively. 2 All cells tested in (a) performed with an acceptable initial specific capacity in the range of 1150–1250 mAh / g. These cells showed capacity retention rates of 69.4%, 73.7%, 85.7%, 77.8%, and 75.2% at 100 cycles (compared to the capacity at 1 cycle). Approximately 0.1–0.25 mg / cm³ 2The BNNT doping density provides particularly good performance in terms of volume retention (see cycle 1).

[0136] (Embodiment 2 - Coating of BNNT mesh controls the formation of dendritic crystals on metal electrodes) During electrochemical metallization and deplating, or during the charging and discharging cycles of an energy device (including electrochemical metallization and deplating), the metal anode material undergoes continuous, non-uniform volume expansion and contraction concentrated in various regions of the anode to the extent that it causes cracks, fractures, or other damage to the innate SEI during battery operation. When cracks or fractures form in the innate SEI, an uncontrolled influx of large amounts of metal ions reaching specific regions of the anode is easily transported to the metal surface, forming metal nucleation sites on the electrode surface from which dendritic crystals grow. Thus, SEI instability has been a limiting factor in the progress of energy storage devices containing 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 polymer binder, wherein the coating of the composite is in close contact with at least one surface of the electrode as a porous mesh that is selectively permeable to transport metal ions used in a selectively reactive energy storage device, and the composite is physically and / or chemically bonded to the surface of the electrode. The mesh is configured to uniformly distribute metal transport ions across the entire surface of the metal electrode, thereby reducing the formation of metal dendritic crystals.

[0137] The BNNT porous mesh of the present invention has been found to solve the problem of dendritic crystal 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. The BNNT porous mesh of the present invention comprises one or more tunnels, pathways and / or channels through which the concentrated metal ion flux observed on one side of the mesh is directed, oriented, and / or sized to redistribute to a more uniformly dispersed metal ion flux on the other side of the mesh, thereby dispersing the metal ion flux over a wider surface area of ​​the anode. The tunnels, pathways and / or channels through which they pass are configured or oriented laterally toward the side of the electrode, i.e., away from any one position or region of the electrode. The orientation of the tunnels, pathways and / or channels through which they pass receives the concentrated metal ion flux and redistributes it throughout the body of the electrode. In other words, transport through the mesh divides the concentrated metal ion flux into multiple smaller ion fluxes, which spread uniformly across the entire surface of the anode, resulting in a homogeneous metallic coating on the anode surface. Without the BNNT porous mesh coating, the concentrated metal ion flux would all target very localized areas on the anode surface, potentially causing significant and uncontrollable volume expansion. The BNNT porous mesh is thought to divide the metal surface into more accessible areas, thus dispersing the transported metal ions across the entire surface of the metal electrode through the mesh. While this effect can be achieved with various mesh thicknesses, it is preferable to optimize the thickness to ensure high-speed transport of metal ions through the mesh, ensure good capacity retention, and keep the internal resistance of a device with a protected anode as low as possible. In preferred embodiments, the coating of the BNNT porous mesh 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 preferred embodiments, the coating of the composite has an average thickness of about 0.2 mg cm -2 ~approximately 8 mg / cm²-2 Approximately 0.1 mg / cm² -2 ~approximately 2 mg cm -2 More preferably about 0.1 to about 2 mg / cm² -2 Most preferably about 0.4 mg / cm² -2 It has a surface density or BNNT content.

[0138] In a preferred coating of the composite porous mesh, at least a portion of the polymer binder exists as particles that fix the BNNT strands together to form a porous network or porous mesh. Furthermore, at least a portion of the polymer binder exists as particles that fix the BNNT strands together to form a porous mesh. Preferably, the BNNT strands are not completely conformally coated with the polymer binder. Preferably, the BNNTs are substantially free of hexagonal boron nitride and / or elemental boron impurities, preferably completely free. Preferably, the metal is selected from Li, Na, K, Al, and Zn, preferably Li or Na. Preferably, the coating of the composite contains the polymer binder at a concentration of about 50% by weight or less, preferably 20% by weight or less, preferably 15% by weight or less, and preferably about 10% by weight or less. Ideally, the BNNT porous mesh has one or more tunnels, pathways and / or channels through it that are directed, oriented, and / or sized to delocalize or redistribute a concentrated metal ion flux on one side of the mesh to a more uniformly distributed metal ion flux on the opposite side of the porous network / mesh, thereby distributing the metal ion flux over a larger surface area of ​​the electrode.

[0139] Preferably, the BNNT porous mesh for the metal electrode contains at least one binder, preferably a polymer binder. The polymer binder is preferred because of its flexible and / or elastic mechanical properties. Suitably, the polymer binder can be selected from any of the binders described herein, but preferably from natural rubber or synthetic rubber, 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)-polymethyl methacrylate (PMMA), poly(dimethylsiloxane) (PDMS) and combinations thereof. Preferably, the flexible polymer binder is poly(styrene-co-butadiene) or contains poly(styrene-co-butadiene). Preferably, the flexible polymer binder is poly(styrene-co-butadiene).

[0140] Therefore, the present invention provides a BNNT porous mesh for use as the negative electrode (anode) of an energy storage device, preferably a rechargeable energy storage device. The present invention relates to a protective coating for a metal-based anode material, and the negative electrode has boron nitride nanotubes (BNNTs) in the form of one or more deposits or intermediate layers of BNNTs having a porous mesh structure bonded thereto (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 strengthens, supports, scaffolds, and / or reinforces the natural solid electrolyte interface (SEI) layer to resist cracking and fracture, and thus reduces the chance or tendency for site nucleation and subsequent dendrite formation / growth that occurs when concentrated metal ion influx passes through cracks in the natural 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 is, for example, 0.1 mA cm -2 ~20 mA cm -2This occurs during charge-discharge cycles in energy storage devices within a given current density range.

[0141] Furthermore, the BNNT porous mesh of the present invention has been found to possess physical and chemical properties suitable for use as one or more supports, scaffolding, or reinforcing structures for artificial SEIs, pseudo-SEIs, and / or natural SEIs to reinforce them in order to prevent cracking, fracturing, or damage during electrochemical metal plating and delamination. In preferred embodiments, the BNNT porous mesh mechanically supplements an existing natural SEI. The preferred BNNT porous mesh of the present invention is electronically insulating (i.e., functions as a passivation layer) but ionically conductive, i.e., permeable to ions in metal-based anode materials but impermeable to non-transport metal ion components in electronic and energy storage devices. The preferred BNNT porous mesh has sufficient flexibility to avoid cracking, fracturing, or other damage during cycling, and also has sufficient mechanical strength to control or at least mitigate the damaging effects on natural SEIs due to volume expansion of metal plating and metal anode materials, such as during electrochemical metal plating and delamination, or delamination during cycling of energy devices.

[0142] Furthermore, the mechanical properties of the BNNT porous mesh suggest that, compared to equivalent metal-based anode materials without the BNNT porous mesh, the BNNT porous mesh can control or more uniformly guide the volume expansion of the metal-based anode material across the entire anode surface area. This more uniform or homogeneous control of volume expansion is thought to reduce the degree of stress and / or strain experienced by the natural SEI, thereby strengthening it against cracks, fractures, or other damage that typically occur during electrochemical metal delamination / plating or cycling operations within energy storage devices.

[0143] Preferably, the BNNT porous mesh comprises at least one separate layer of BNNT in direct contact with the surface facing the electrolyte of the metal-based anode material.

[0144] Preferably, the BNNT porous mesh is in the form of a freestanding or self-supporting film placed on or in close proximity to the electrolyte-facing surface of the metal-based anode material.

[0145] Ideally, the BNNT porous mesh is in the form of a direct coating on the electrolyte-facing surface of the metal-based anode material. The SEI, when formed during the cycle, 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 it is formed, for example, through interatomic physical entanglement or covalent and / or ionic bonds between the network / mesh and the SEI components. In any case, interfacial contact / close contact between the BNNT layer and the electrode / SEI is desirable.

[0146] The BNNT porous mesh is preferably in the form of a three-dimensional (3D) porous film, a porous network / mesh, or a porous deposit of boron nitride (BNNT) mesh. Preferably, the BNNT porous mesh is uniform throughout its region in one or more of the following: composition, morphology, ionic conductivity, and elastic modulus.

[0147] Suitablely, a BNNT porous mesh may include intersecting and / or intersecting filaments, particularly entangled, intersecting, entangled, or intertwined BNNTs, forming a network or grid of connected, contacting, or intersecting filaments or strands of BNNTs. Preferably, a BNNT porous mesh is a disordered mesh of BNNT filaments or strands. A BNNT porous mesh is thought to comprise one or more tunnels, passages, and / or channels that penetrate and traverse the mesh, which are spatially positioned, oriented, directed, and / or dimensionally positioned to redistribute, spread, and redistribute more uniformly and / or homogeneously, so as to redistribute concentrated metal ion fluxes (reaching specific regions of the mesh on the electrolyte side) through the mesh so as to be more uniformly distributed or delivered across the entire width of the anode surface after passing through the BNNT porous mesh. The tunnels, pathways, and / or channels through them are directed, oriented, and / or dimensional to delocalize or redistribute the concentrated metal ion flux observed on one side of the mesh to the more uniformly distributed metal ion flux on the other side of the mesh, thereby dispersing the metal ion flux over a wider surface area of ​​the anode. This redistribution, diffusion, and / or redirection of the metal ion inflow advantageously allows the metal ion inflow to be divided and distributed more uniformly and orderly over a much wider surface area of ​​the metal anode than is possible in anodes without a BNNT porous mesh, where concentrated ion inflows tend to be more localized. In other words, by passing through the mesh, concentrated ion inflows are delocalized across the entire width of the metal anode surface. Metal ions reaching the metal anode surface are delocalized and spread uniformly and homogeneously across the entire anode surface, resulting in better controllable volume expansion, greater consistency and uniformity across the entire anode, thereby minimizing stress and strain on various different parts or regions of the SEI formed at the anode-electrolyte interface during electrochemical metal plating / stripping or charge / discharge cycles in energy storage devices.The redistribution of ions caused by the BNNT porous mesh reduces the overall stress on the native SEI, thus significantly reducing the tendency of the SEI to crack or fracture. This reduces the opportunity for nucleation and subsequent growth of metal dendritic crystal sites. In other words, the BNNT porous mesh prevents dendritic crystal formation by inducing ion delocalization and by reaching a wider area of ​​the anode surface through a more uniform distribution of metal ions passing through the mesh compared to what would occur without the BNNT porous mesh. These advantages are clearly observable through stable, long-term electrochemical metal plating and delamination in symmetric cell configurations, or through stable cycling in energy storage devices. The fact that cycling stability is observed suggests that dendritic crystal formation does not occur to the extent that the cell shorts out after only a few cycles, which would occur without the BNNT network / mesh on the metal electrode.

[0148] As a result of the BNNT porous mesh, it is thought that the large metal ion flux reaching the mesh is divided into multiple smaller, more uniformly directed ion fluxes that traverse the mesh in a way that the metal is deposited more uniformly or more homogeneously across the entire width of the anode surface. In effect, the mesh first promotes more delocalized ion directivity, which in turn promotes more uniform, homogeneous, and controlled electrochemical metallization and more homogeneous and controlled volume expansion across the entire anode, thereby subjecting the innate SEI to less damaging stress and strain.

[0149] A schematic diagram of this ion screening / filtering or control mechanism in the case of a Li metal anode coated with a BNNT porous mesh is shown in Figure 14. Preferably, the pores, tunnels, pathways and / or channels associated with the BNNT porous mesh are sized, oriented, directed and / or oriented to manipulate, control and / or redirect the metal ion flux attracted to the metal-based anode material by splitting it into a more ordered, spatially spread ion flow of constituent components through the mesh, which has the effect of spreading the ion flow across the entire surface of the anode material as it passes through the mesh.

[0150] Ideally, BNNT porous mesh is electrically insulating but permeable to metal transport.

[0151] Preferably, the BNNT porous network / mesh is uniform in one or more of the following: composition, morphology, thickness, ionic conductivity, and mechanical properties. In particular, the composition, thickness, and mechanical properties can be controlled or adjusted to suit any application by changing one or more of the following: the relative concentration of BNNT to polymer binder in the mesh slurry, the thickness of the slurry coating, the length and diameter of the BNNTs, etc. The same applies to the BNNT porous network / mesh of the S-cathode embodiment.

[0152] Ideally, the BNNT porous mesh is flexible and / or elastic to resist cracking or fracture during electrochemical plating and stripping. It is desirable that the BNNT porous mesh be flexible and / or elastic under electrochemical metal ion plating and stripping conditions. This is, for example, 1 mAhcm. -2 With a fixed charge / discharge capacity of 1mAcm -2This is demonstrated by the absence of little to no cracks or damage after at least 100 charge / discharge cycles at a charge density of . Under these conditions, one cycle takes 2 hours; that is, the metal plating time is 1 hour and the metal stripping time is 1 hour. It should be understood that metal ion plating and stripping studies can be carried out in a symmetric cell containing metal electrodes. For example, a preferred BNNT porous mesh is, for example, 1 mAh cm. -2 With a fixed charge / discharge capacity of 1mAcm -2 The material is flexible under lithium-ion plating and stripping conditions, as demonstrated by little or no cracking or breakage after at least 600 charge / discharge cycles at a given charge density. Preferably, the metal-based anode material contains alkali metals, such as Li, Na, and K, preferably Li or Na, most preferably Li. Suitablely, the metal-based anode material contains lithium metal.

[0153] Preferably, the BNNT porous mesh is physically and / or chemically stable in the presence of a metal-based anode material. Preferably, the BNNT porous mesh is physically and / or chemically stable in the presence of an electrolyte or electrolyte system commonly used in energy storage devices / applications.

[0154] Preferably, for any electrode, the boron nitride nanotubes of the BNNT porous described herein are at least about 0.5 microns in length, more preferably at least 1 micron. In one preferred embodiment, the BNNTs are about 1 to about 50 microns in length. In one example, BNNTs with a length of about 10 microns are particularly preferred. The boron nitride nanotubes preferably have a diameter of about 500 nm or less. The preferred diameter is in the range of about 50 nm to about 100 nm, and more preferably about 100 nm.

[0155] Preferably, the boron nitride nanotubes are present in the BNNT porous mesh in an amount in the range of about 20 wt% to about 95 wt%, preferably in an amount of about 50 wt% to about 90 wt%, most preferably in an amount of about 85 wt% to about 98 wt% of boron nitride nanotube (BNNT) film or deposit. In some embodiments, 90 wt% of BNNT is preferred.

[0156] Suitably, the binder is present in the BNNT porous mesh in an amount ranging from about 5 wt% to about 80 wt% of the BNNT porous mesh, more preferably from 10 wt% to 50 wt% of the BNNT porous mesh, preferably about 10 wt% of the BNNT porous mesh. It will be appreciated that as the amount of binder, particularly a flexible binder, increases, the flexibility of the mesh becomes greater. Preferably, the boron nitride nanotubes of the BNNT porous mesh are about 0.2 mg cm -2 ~ about 8 mg cm -2 、 more preferably about 0.2 mg cm -2 ~ about 1.7 mg cm -2 、 more preferably about 0.5 to about 0.75 mg cm -2 having a density of.

[0157] Preferably, the coating of the boron nitride nanotube (BNNT) mesh has an average thickness of about 0.1 micron 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, most preferably about 1 - 10 microns. In some embodiments, the boron nitride nanotube (BNNT) deposit has an average thickness of about 0.9 micron 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, most preferably about 5 microns.

[0158] 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, foamed copper, or foamed nickel. In some embodiments, no current collector is included; for example, if the metal anode is an Al metal anode or a Zn metal anode, a current collector is not required.

[0159] The present invention also relates to an energy storage device comprising one or more anodes.

[0160] The present invention extends to energy storage devices comprising one or more metal or metal-based electrodes, preferably lithium or sodium metal anodes, according to the present invention. Preferably, the energy storage device further comprises at least one cathode, at least one separator, and at least one electrolyte. Preferably, the cathode is sulfur-based or sulfur-graphene cathode, oxygen cathode, lithium iron phosphate cathode, or lithium nickel-manganese oxide cathode.

[0161] A preferred device is 1 mAcm² at a temperature of 25°C. -2 The charge density and 1 mAhcm -2 With a fixed charge-discharge capacity, it exhibits stable electrochemical metal plating and delamination for at least 100, at least 500, and at least 1000 charge-discharge cycles. Preferably, the sulfur or sulfur graphene cathode is coated with a composite of boron nitride nanotubes (BNNTs) in the form of a porous mesh that is selectively permeable to transport metal ions used in energy storage devices, and at least one polymer binder.

[0162] In a preferred embodiment, the present invention is a metal sulfur energy storage device, At least one metal electrode having a coating of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, wherein the composite coating is in close contact with at least one surface of the electrode as a porous mesh that is selectively permeable to transport metal ions used in energy storage devices in which the composite is physically and / or chemically bonded to the surface of the electrode, The invention relates to 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, wherein the composite film is in close 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.

[0163] In another preferred embodiment, the present invention is a lithium-sulfur energy storage device, At least one lithium metal electrode having a coating of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, wherein the composite coating is in close contact with at least one surface of the electrode as a porous mesh that is selectively permeable to lithium ions used in energy storage devices 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, wherein the composite film is a porous network that is selectively permeable to metalithium ions and electrolytes used in energy storage devices but impermeable to polysulfides, and is in close contact with at least one surface of the electrode, and This extends to lithium-sulfur energy storage devices that include the following features.

[0164] Preferably, the amount of BNNT added to the cathode network is about 0.2 mg / cm³. -2 Preferably, the amount of BNNT added to the anode mesh is about 0.4 mg / cm³. -2 Here, "approximately" means ±5%.

[0165] In embodiments of energy storage devices described herein, it will be understood that a unit cell comprises one anode and one cathode. Furthermore, energy storage devices in the form of a pack of modules will comprise two or more anodes and cathodes, but the overall ratio of anodes to cathodes will still be 1:1.

[0166] A preferred energy storage device comprises a metal-based anode material, with the anode bonded to one or more boron nitride nanotubes (BNNTs) in the form of deposits or intermediate layers of BNNTs having a porous mesh structure. The BNNT porous mesh is described in further detail above.

[0167] Preferably, the energy storage device comprises at least one anode comprising a metal-based anode material, the anode being bonded to one or more boron nitride nanotubes (BNNTs) in the form of one or more deposits or intermediate layers of BNNTs having a porous mesh structure; a separator between each anode and cathode; at least one cathode; and an electrolyte. Suitable separators and electrolytes are known in the art.

[0168] Preferably, the energy storage device comprises at least one positive electrode (cathode), which is a sulfur-based or sulfur-graphene cathode, a catalytic cathode for Li-O2 energy storage devices, a lithium iron phosphate cathode, or a lithium nickel manganese oxide cathode.

[0169] The sulfur or sulfur-based cathode of an energy storage device preferably comprises a sulfur cathode material bonded to a porous film or porous deposit of boron nitride nanotubes (BNNTs). Such a sulfur cathode material having a BNNT intermediate layer is described in detail in Australian Provisional Patent Application No. 2021900777, which is incorporated herein by reference.

[0170] Suitablely, the energy storage device includes an electrolyte or electrolyte system that is compatible with the metal-based anode material in terms of one or more of the following respects: safety, stability, and energy device performance. For example, ether-based solvents such as DOL or DME, or mixtures of DOL / DME, can be used. These electrolytes may optionally include ionic liquids and / or metal salts, 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 in sodium devices. One example electrolyte used herein is 1M LiTFSI in DOL / DME containing 1 wt% LiNO3. Such electrolytes can also be used in the S cathode embodiments and polysulfide absorption experiments described herein.

[0171] Preferably, the preferred composite BNNT porous mesh prevents electrochemical metal delamination and the formation and growth of dendritic crystals on the anode material during plating, such as during the operation of energy storage devices during charge and discharge cycles. Preferably, the composite BNNT porous mesh of the present invention has a density of, for example, 1 mAcm -2 Current density and 1 mAhcm -2Under metal plating and stripping conditions with fixed charge / discharge capacities, for example, using a plating time of 1 hour and a stripping time of 1 hour, it is possible to prevent the formation and growth of dendritic crystals 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 at least 1000 cycles. It will be understood that such metal ion plating and stripping stability performance studies can be carried out in symmetric metal cells. 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 a preferred such cell, the overvoltage is maintained below 0.5V for at least 100 cycles, more preferably at least 600 cycles, and most preferably at least 1500 cycles. A preferred system maintains a stable overvoltage below 0.2V for at least 100 cycles, more preferably at least 600 cycles, and most preferably at least 1000 cycles. If the overpotential during electrochemical metallization and stripping in such cycles is less than 0.5V, it indicates a lack of dendritic crystal formation at the metal anode. Therefore, a preferred BNNT porous mesh is preferably stable at room temperature for at least 100 cycles, at least 500 cycles, and even at least 1000 cycles of electrochemical metallization and stripping, as is electrochemically demonstrated by the absence of dendritic crystal formation through stable cycle overpotentials of 0.5V or less.

[0172] The present invention also relates to a slurry for preparing a boron nitride (BNNT) porous mesh for metal-based anode materials, comprising boron nitride nanotubes (BNNTs), one or more polymer binders, and one or more aprotic liquid organic solvents. Suitable binders and BNNTs are described above.

[0173] Preferably, the ratio of the volume of the slurry solvent to the weight of the solid component is in the range of 3 mL / g to 20 mL / g, preferably about 5 mL / g to about 10 mL / g, and most preferably about 7 mL / g. Preferably, the aprotic solvent is selected from ether solvents, ether-based mixed solvent systems, carbonates, N,N-dimethylacetamide (DMAc), and combinations thereof. Preferably, the ether solvent or ether-based mixed solvent system includes linear ethers or cyclic ethers. Preferably, the ether solvent or 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.

[0174] The present invention also relates to a method for preparing a negative electrode (anode) comprising a metal-based anode material to which boron nitride nanotubes (BNNTs) in the form of one or more deposits or intermediate layers of BNNTs having a porous mesh structure are bonded. (i) The step of preparing a slurry of BNNT and a binder in one or more aprotic solvents, (ii) The step of coating the surface of a metal-based anode material with a slurry to a desired thickness, (iii) Evaporating the solvent to form a metal-based anode material having deposits of BNNT having a porous mesh structure, Includes. A suitable slurry, as well as one having a suitable binder, BNNT, and solvent, is described above. Preferably, the BNNT is present in the slurry at a concentration of about 20% to about 99% by weight, 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 polymer binder is present in the slurry at a concentration of about 1% to about 80% by weight, 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 slurry coating 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.

[0175] 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, most preferably about 8 microns, 11 microns, 25 microns, or 37 microns. In a preferred example, the thickness of the dry BNNT porous mesh layer is about 11 microns.

[0176] A preferred method further includes the step of providing a metal-based anode material on a negative electrode current collector such as copper metal, preferably copper foil or aluminum foil. Other suitable current collectors are described above.

[0177] Preferably, the metal or metal-based electrode contains transport ion metals, such as Li, Na, K, Al, and Zn, and preferably Li or Na. Suitablely, the metal-based anode material is lithium or sodium, and preferably lithium.

[0178] The present invention also relates to a slurry for preparing a porous mesh of boron nitride (BNNT) for metal-based anode materials, comprising boron nitride nanotubes (BNNT), one or more polymer binders, and one or more aprotic solvents. Preferably, the aprotic solvent is selected from ether solvents, ether-based mixed solvent systems, carbonates, N,N-dimethylacetamide (DMAc), and combinations thereof. Preferably, the ether solvent or ether-based mixed solvent system comprises a linear ether or a cyclic ether. Suitablely, the ether solvent or 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.

[0179] The present invention also relates to electronic devices including the anode and / or energy storage device of the present invention. The present invention also relates to the use of the electronic devices of the present invention in transportation, grid storage, electric vehicles, and advanced portable electronics applications.

[0180] The present invention also relates to the use of one or more layers of composite BNNT porous mesh to prevent the formation of dendritic crystals on metal-based electrodes of energy storage devices. Preferably, the metal-based electrode comprises a Na, K, Al, or Zn metal anode.

[0181] The present invention also relates to the use of one or more layers of composite BNNT porous mesh for controlling the volume expansion of metal-based electrodes in energy storage devices.

[0182] The term "approximately" here means that the 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, which would be understood by those skilled in the art. SEM analysis is often used to measure / estimate nano- and micron-scale measurements. (Embodiment 2 - Materials and Methods)

[0183] Li-BNNT Anode Fabrication: Lithium film was supplied by China Energy Lithium Co., Ltd., and a 100 μm thick lithium film was coated on both sides of the copper current collector. The lithium anode was further coated with a BNNT interlayer. The BNNT interlayer was prepared by mixing 90 wt% BNNT and 10 wt% styrene-butadiene rubber (SBR, poly(styrene-co-butadiene) from Sigma-Aldrich) in a tetrahydrofuran (THF, Sigma-Aldrich) solution (5 mL). This slurry was stirred overnight and coated onto the surface of the lithium anode in an argon-filled glove box with oxygen and water levels below ppm, and then calcined overnight at 60°C.

[0184] Fabrication of symmetric lithium pouch cells: Symmetric lithium pouch cells were fabricated in a glove box filled with argon. Two Li-BNNT electrodes were cut and combined with a commercially available flexible Al plastic film separator (Celgard 2400). 1 mL of electrolyte was dropped into the pouch. The electrolyte was 1 M LiTFSI in DOL / DME containing 1 wt% LiNO3. The pouch cells were sealed in the glove box using a vacuum sealer.

[0185] (Electrochemical measurement) All coin-cell and soft-package batteries were assembled in an Ar-filled glove box with O2 and H2O < 1 ppm. The AC impedance of the symmetrical Li / Li cell was 0.1-10 mV at an amplitude of 10 mV. 6 The frequency range (in Hz) was investigated using a Solartron 1255B frequency response analyzer. Constant current cycle tests were performed using a Neware 8-channel battery tester.

[0186] (Embodiment 2 - Results and Discussion) To adjust the thickness of the BNNT mesh, BNNT-SBR slurry was coated onto copper foil with various doctor blade gaps controlled to 100 μm, 200 μm, 300 μm, and 400 μm, and dried to form a dried final layer of BNNT porous mesh containing BNNT 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 thicknesses of the corresponding BNNT porous mesh layers after drying were approximately 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 demonstrates that the thickness of the BNNT porous mesh can be easily controlled by adjusting the blade gap during slurry coating. 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.

[0187] Figure 8b shows a highly interconnected porous mesh at the nanoscale, clearly observable, formed from BNNTs. This porous network of interconnected BNNT mesh is thought to uniformly redistribute the ion flux of metal ions from the electrolyte-side mesh to the metal anode surface. Symmetric lithium pouch cells consisting of two lithium metal electrodes were fabricated, and the cycling performance of lithium films with and without the BNNT porous mesh was investigated. In the first cell, two new lithium films were used as electrodes, while in the second cell, a lithium film with the BNNT porous mesh was used. Both cells were charged to a charge density of 1 mAcm². -2 and charge / discharge capacity 1mAhcm -2The cells are tested under the same fixed conditions. Therefore, one charge / discharge cycle takes 2 hours. In Figure 12a, we can see that the overvoltage of the cell with the new lithium film is approximately 0.1V in the first 20 cycles. However, the voltage increased at cycle 30, reaching 3V at cycle 64. This indicates the formation of lithium dendritic crystals. In contrast, the cell with the Li-BNNT porous mesh shows a very stable cycle voltage profile over more than 200 cycles after an activation process in the first 10 cycles. In this second cell, the overvoltage remains at approximately 0.015V over more than 200 cycles, indicating no dendritic crystal formation during the cycles. This indicates that the BNNT porous mesh controls volume expansion and mechanically assists / reinforces the SEI, mitigating the cracks and damage necessary for dendritic crystal growth. Additional data available, not shown here, shows a stable cycle voltage profile observed over 400 cycles. BNNT porous mesh is thought to not only protect and strengthen the SEI, but also to significantly improve the cycle stability of lithium metal electrodes and prevent dendritic crystal growth by reducing the stress and / or strain on the innate SEI through the above mechanism, particularly by homogenizing the volume expansion of the entire anode. Therefore, a preferred BNNT porous mesh limits strain and the strain on the innate solid electrolyte interface (SEI) due to volume expansion of the metal-based anode material compared to an equivalent metal-based anode material without the BNNT porous mesh.

[0188] This is thought to be due to one or more of the following: (1) The electrically insulated, porous, interconnected BNNT network acts as a screen / mesh that divides / delocalizes the large flux of lithium ions reaching the mesh on the electrolyte side into smaller, more uniformly distributed ion flows as they pass through the mesh, resulting in a more uniform and homogeneous distribution of lithium deposits across the anode surface, and an overall reduction in the opportunity for dendritic crystal growth / site nucleation. (2) The excellent mechanical properties of the flexible polymer binder containing BNNTs create a mechanically strong SEI on the lithium electrode, which can accommodate volume changes of lithium during the cycle without causing cracks or damage to the SEI. Thus, the BNNT porous mesh is electrically insulating but permeable to ions in the metal-based anode material.

[0189] Figure 9 shows the voltage profiles of the Li-ion plating and stripping cycle performance of the tested symmetrical Li coin cell. The cell voltage was 1 mA / cm². 2 Current density, 1 mAh / cm² 2 It is tested at a capacity of (a) 0.1 mg / cm³. The lithium foil used in the symmetric cell is (a) 0.1 mg / cm³. 2 (b) 0.2 mg / cm³ 2 (c) 0.3 mg / cm³ 2 (d) 0.4 mg / cm³ 2 (e) 0.5 mg / cm³ 2 (f) 1 mg / cm³ 2 (g) 1.5 mg / cm³ 2 , and (h) 2 mg / cm³ 2 The samples are coated with different mass amounts of BNNT, such as 0.1 and 0.2 mg / cm³. The plots show BNNT at different concentrations. 2 This shows that the plating / stripping overpotential of the Li-added symmetric cell increased after 200 hours. On the other hand, BNNT was 0.3-2 mg / cm³. 2 The added cells exhibited significantly superior performance in terms of stability, showing a long cycle life of 1400 hours. (Approximately 0.4 mg / cm³) 2 At this BNNT packing density, a particularly low overpotential of 32mV is obtained. Furthermore, with a BNNT addition of 1mg / cm³, a very low overpotential is achieved. 2It is also clear that if the value continues to increase beyond a certain point, the cell's overvoltage will increase.

[0190] Figure 10 shows the EIS analysis of Li symmetric coin batteries with different BNNT masses added to the Li chip. (a) Bare Li, (b) 0.1 mg / cm³ 2 (c) 0.2 mg / cm³ 2 (d) 0.3 mg / cm³ 2 (e) 0.4 mg / cm³ 2 (f) 1 mg / cm³ 2 (g) 1.5 mg / cm³ 2 (h)2 mg / cm³ 2 All coin cells were tested at room temperature and at 40, 50, 60, and 70°C, respectively, to determine 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 a cycle at each temperature showed the ionic resistance at the corresponding temperature. The faster the Li ion migration rate, the greater the decrease in resistance as the temperature increased. The EIS plots were fitted using fitting software (Zview) and the ionic conductivity was calculated.

[0191] Figure 11 shows Arrhenius plots created according to Nyquist plots of Li symmetric coin cells with different BNNT mass doping amounts on a Li tip. The BNNT doping range is 0.1–2 mg / cm³. 2 Li ions with higher migration velocities showed a greater increase in ionic conductivity as the temperature increased, but the logarithm of ionic conductivity has a linear relationship with the reciprocal of temperature. Therefore, a higher slope of these plotted lines indicates a higher migration velocity of Li ions. BNNT addition amount: 0.5 mg / cm 2 If the value is less than 1 mg / cm³, the slope increases as the amount of BNNT added increases. 2 Beyond this point, the slope decreased. (Approximately 0.4 mg / cm²) 2 The BNNT doping density resulted in particularly high Li ion transport rates, which are consistent with the results obtained in symmetrical Li-coin batteries.

[0192] Figure 12 shows (a) the case without a BNNT porous mesh and (b) the case with a BNNT porous mesh (the amount of BNNT added to the mesh is 0.4 mg / cm³). 2 This shows the long-term plating / stripping cycle performance of symmetric pouch cells with new lithium film electrodes (and a BNNT porous mesh). Their performance is compared in one graph (Figure 12(c)). In the absence of the BNNT porous mesh, dendritic crystal formation occurs on the lithium metal, and the overvoltage increases with the cycles, resulting in cell failure after 45 cycles. On the other hand, cells coated with a BNNT porous mesh on the lithium metal maintain a stable overvoltage for at least 1000 cycles, demonstrating the absence of dendritic crystal growth as a result of the protective coating of the composite BNNT porous mesh on the Li electrode.

[0193] Figure 13 shows the voltage profiles of the plating and stripping cycle performance of symmetric Al metal cells and symmetric Zn metal cells with different metal electrodes (where dendritic crystal growth also occurs during plating / stripping / cycling), as follows: (a) bare Al, (b) Al with BNNT porous mesh, (c) bare Zn, (d) Zn with BNNT porous mesh. The cells are rated at 1 mA / cm². 2 Current density, 1 mAh / cm² 2 The test is conducted at the specified volume. The amount of BNNT added to the mesh is 0.4 mg / cm³ in each case. 2 The symmetrical battery with bare Al failed after 80 hours of cycling, while the symmetrical battery with a composite BNNT porous mesh coating on Al exhibited lower overvoltages than the bare Al cell and showed stable cycling for 100 hours. Similarly, the bare Zn symmetrical battery showed a higher overvoltage (0.29V) than the Zn with the composite coating of the BNNT porous mesh symmetrical battery (0.09V). These results clearly demonstrate that the composite BNNT porous mesh coating can be applied to various metal anodes and can prevent dendritic crystal growth on metal anodes, as demonstrated by the low and stable overvoltages over many cycles.

[0194] In conclusion, a tunable coating of a composite BNNT porous mesh containing BNNT and a flexible polymer binder is conveniently designed and synthesized using the expandable method described herein. SEM images confirm that the BNNT porous mesh consists of an interconnected network of porous BNNTs made within a flexible / elastic polymer matrix, with the polymer present in the form of solid particles between the BNNT strands. Electrochemical results demonstrate that the BNNT porous mesh significantly improves the cycle stability of lithium, aluminum, and zinc metal electrodes, which is clear evidence that dendritic crystal growth is prevented. Furthermore, the inventors believe that the BNNT porous mesh coating described herein for protective use with metal anodes possesses sufficient mechanical strength and flexibility / elasticity to protect the SEI from cracking, fracture, or other damage that typically occurs during volume expansion. Overall, the mechanical properties and porosity / morphology of the BNNT mesh suppress dendritic crystal growth during electrochemical metal plating and delamination (stable and low overpotential even in long-term cycles) and cell cycling (good stable capacity retention in long-term cycles). The polymer binder within the mesh allows the mesh to maintain its structural integrity without cracking, even in the presence of volume expansion during cycling. Furthermore, the binder does not hinder the movement of transport ions across the mesh. In other words, the high ionic conductivity of transport metal ions through the coating of the BNNT porous mesh described herein leads to delocalized / more uniform ion transport across the entire electrode surface, while better controlling volume expansion, thereby reducing SEI cracks and preventing the formation of dendritic crystal nucleation sites.

Claims

1. A sulfur (S)-based electrode for an energy storage device having a film of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, wherein the film of the composite is in close contact with at least one surface of the sulfur (S)-based 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, The composite film has an average thickness of 0.9 to 5 microns, as measured by SEM. The composite film is 0.1 mg cm －２ ~3.5 mg cm －２ An electrode having a surface density or BNNT content.

2. The electrode according to claim 1, wherein the BNNT of the composite does not contain impurities such as hexagonal boron nitride (hBN) and / or elemental boron (B).

3. The electrode according to claim 1, wherein at least a portion of the polymer binder is present in the composite as solid particles that fix or adhere together with the BNNTs in the composite to form the porous network.

4. The electrode according to claim 1, wherein the BNNTs in the composite film are not completely conformally coated with the polymer binder.

5. The electrode according to claim 1, wherein the composite film has an average thickness of 1.5 microns to 3.5 microns.

6. The surface density of the composite film or the amount of BNNT added is 0.1 mg / cm². －２ The electrode according to claim 1, wherein the concentration is ~1.0 mg cm⁻².

7. The amount of S in the electrode is 1 mg cm －２ The electrode according to claim 1, which is present in an added amount of ~8 mg cm⁻².

8. The electrode according to claim 1, wherein the composite film contains the polymer binder at a concentration of 15% by weight or less of the weight of the composite.

9. The electrode according to claim 1, wherein the composite film is physically and / or chemically bonded to the surface of the electrode.

10. The electrode according to claim 1, wherein the composite film includes pores having an average pore diameter of 0.1 to 3 microns.

11. The electrode according to claim 1, wherein the polymer binder comprises PVDF, PEO, PTFE, or acrylonitrile multicopolymer.

12. The electrode according to claim 1, wherein the electrode comprises one or more conductivity enhancers selected from carbon black, carbon nanotubes, carbon nanoparticles, and graphene.

13. The aforementioned conductivity enhancer is 0.2 mg cm －２ ~0.6 mg cm －２ The electrode according to claim 12, wherein one or more graphene particles are present in an amount.

14. The electrode according to claim 13, wherein the electrode is a sulfur graphene-based electrode material, and the graphene is a mixture of highly porous graphene having a porosity of 300 m³ / g to 800 m³ / g and high surface area graphene having a surface area of ​​800 m² / g to 1000 m² / g.

15. The electrode according to claim 14, wherein the weight ratio of high-porosity graphene to high-surface-area graphene is 1:9 to 9:

1.

16. It comprises a sulfur cathode material bonded to a porous membrane of boron nitride nanotubes (BNNTs), The porous membrane has an average thickness of 0.9 microns to 5 microns, as measured by SEM. The porous membrane is 0.1 mg cm －２ ~3.5 mg cm －２ A sulfur (S)-based electrode having a surface density or BNNT content.

17. An energy storage device comprising one or more sulfur (S)-based electrodes according to any one of claims 1 to 16.

18. An energy storage device according to claim 17, Separator and, At least one metal anode, Electrolytes, An energy storage device that further enhances these features.

19. The energy storage device according to claim 17, wherein the device retains up to 60% of its initial capacity in cycle 1 for at least 500 cycles at a temperature of 25°C and a current density of 0.2C.

20. At a rate of 0.2 C at a temperature of 25 °C, having a specific capacity of at least 400 mAh g based on the S addition amount, the energy storage device according to claim 17. －１ ​

21. An electronic device comprising a sulfur (S)-based electrode according to any one of claims 1 to 16.

22. Use of the electronic device according to claim 21 in transportation, grid storage, electric vehicles, and portable electronics applications.

23. A metal sulfur energy storage device, At least one sulfur (S)-based electrode having a film of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, wherein the composite film is in close contact with at least one surface of the at least one sulfur (S)-based 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, and the composite film has an average thickness of 0.9 to 5 microns as measured by SEM, and the composite film has a density of 0.05 mg cm². －２ ~3.5 mg cm －２ A sulfur (S)-based electrode having a surface density or BNNT content, At least one metal electrode having a coating of a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, wherein the coating of the composite is in close contact with at least one surface of the at least one metal electrode as a porous mesh that is selectively permeable to transport metal ions used in energy storage devices in which the composite is physically and / or chemically bonded to the surface of the at least one metal electrode, A metal sulfur energy storage device equipped with the following features.

24. A lithium-sulfur energy storage device, At least one sulfur (S)-based electrode having a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, wherein the film of the composite is in close contact with at least one surface of the at least one sulfur (S)-based 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, the film of the composite has an average thickness of 0.9 to 5 microns as measured by SEM, and the film of the composite is 0.05 mg cm² －２ ~3.5 mg cm －２ A sulfur (S)-based electrode having a surface density or BNNT content, At least one lithium metal electrode having a composite of boron nitride nanotubes (BNNTs) and at least one polymer binder, wherein the coating of the composite is in close contact with at least one surface of the at least one lithium metal electrode as a porous mesh that is selectively permeable to lithium ions to which the composite is physically and / or chemically bonded, A lithium-sulfur energy storage device equipped with the following features.

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