Monolithic sulfur flake cathode based on hyperbranched superstructure and method of making the same

Abstract

The invention relates to a cathode for a rechargeable battery having a monolithic sulfur-structured cathode body, i.e. a sulfur wafer, comprising a heterogeneously branched and / or hyperbranched structure of twinned sulfur crystals as active electrode material.

Description

[0001] This invention relates to advanced positive-cathodes for alkaline ion and / or alkaline earth ion sulfur batteries and batteries having said positive-cathodes, more specifically, to lithium-sulfur secondary batteries exhibiting branched and / or hyperbranched monolithic cathode superstructures, and even more particularly, to methods for producing the same monolithic sulfur allotropic structure.

[0002] Due to the rapid growth of electric vehicles and the development of market demand for portable electronic devices, there is an increasing demand for advanced rechargeable batteries with higher energy to meet the growing needs of electric vehicle users for a wider operating radius, or, with the development of the portable electronic device industry, for longer battery life.

[0003] KAI XI et al., "Binder-free three-dimensional sulfur / few-layer graphenefoam cathode with enhanced high-rate capability for rechargeable lithium-sulphur batteries", NANOSCALE, vol. 6, January 1, 2014 (2014-01-01), pp. 5746-5753, disclose a three-dimensional graphene foam framework on which sulfur is deposited. THGsi is achieved by loading sulfur onto an independent, porous, and interconnected 3D network of FLG (multilayer graphene) via a sulfur solution infiltration method. As can be seen from the extracted Figure 7, this structure is a sulfur-layered framework composed of a graphene network / foam. Therefore, the structural integrity (self-support) / structural framework of the cathode does not originate from sulfur, but from the graphene foam. Compared to the disclosure according to the present invention, the structural framework of the cathode is actually provided by the sulfur crystals / crystallinity themselves.

[0004] WO 2011 / 147924 A1 discloses the application of expanded graphite in lithium / sulfur solid composite batteries. According to page 13, the lithium cathode is actually made from a slurry containing sulfur and expanded graphite, which is cast onto a substrate or placed in a mold, and some or all of the liquid medium is removed from the slurry to form a solid composite material. Therefore, WO 2011 / 147924 A1 teaches the production of a sulfur cathode from a slurry, and thus from a suspension of solid particles that are dried and thus compacted into a solid composite material. This means that although the sulfur particles may be crystalline, the cathode comprises smaller crystalline plates with interfaces. Conversely, according to the invention, a macroscopic crystalline sulfur structure is provided, i.e., a crystalline monolayer sulfur structure cathode body, which is a grown sulfur wafer.

[0005] US 2013 / 164626 A1 discloses a binderless sulfur-carbon nanotube composite cathode for rechargeable lithium-sulfur batteries. The sulfur-carbon composite material is provided in the form of carbon nanotube sheets, on which sulfur nucleates from an aqueous solution. Through the self-organization of these layered carbon nanotubes, a solid electrode material is formed without any binder (paragraph 70).

[0006] Therefore, it is a single sulfur crystal on a carbon nanotube (paragraph 16). However, these crystals are nanocrystals (paragraph 86). Therefore, a cathode in which the framework is composed of self-supporting crystalline sulfur itself is not disclosed, and thus a crystalline monolithic sulfur structure cathode body (i.e., a grown sulfur wafer) is not disclosed.

[0007] Recently, in line with the trend towards smaller and more compact energy carriers, this paper defines an energy carrier as a battery with high volumetric capacity, expressed in Wh / L, and lightweight as a battery with high gravimetric energy content, expressed in Wh / kg. There is a particular bias in understanding the definition of the term "high-energy battery," where the ideal requirement for a battery is high gravimetric energy in Wh / kg. However, in reality, because available space (e.g., the available space / volume for inserting the battery into a smartphone, laptop, or electric vehicle platform) is a more limiting factor than weight, the requirement for volumetric capacity is actually higher. Therefore, batteries with both high volumetric and high gravimetric energy content are needed—LiS lithium-sulfur batteries are one of the most promising post-lithium battery types, based on a multi-step redox conversion reaction with a theoretical energy content of 1672 mAh / g, based on the transfer of 2 electrons per sulfur atom, S8 + 16Li + + 16e - → 8Li2S, therefore each S8 molecule has a total of 16 electrons, producing approximately 2650 Wh / kg and approximately 2860 Wh / l.

[0008] Clearly, LiS batteries still need to address several limiting factors related to sulfur, such as low ionic and electronic conductivity, low density, volume fluctuations of 79% orthorhombic α-allotropy and 70% monoclinic β-allotropy, and low areal-effective mass utilization coefficient. Existing inventions and patents related to lithium-sulfur batteries demonstrate and confirm that proposed solutions and subsequent claims cannot adequately address the specific properties of sulfur because they focus on adapting existing slurry-based battery production methods used in conventional lithium-ion batteries. In current state-of-the-art lithium-ion batteries, a TM transition metal is preferred as the cathode, with a true density of 5.1 g / cm³. 3 Within the range of (LiCoO2), with sulfur at 2.07 g / cm³. 3Compared to more than twice the volumetric energy density, very advanced concepts and subsequent methods are needed to unlock the theoretical potential of sulfur as a cathode active material in order to compete with current lithium-ion battery chemistry in terms of volumetric energy density.

[0009] This unique patent addresses the need for safe, economical, and environmentally friendly sulfur cathodes while respecting nature by eliminating the use of transition metals (TMs). These sulfur cathodes possess high volumetric and gravimetric energy content, and their production involves extensive mining, refining, and chemical processing to produce and subsequently transport the precursors required for the synthesis of conventional cathodes in state-of-the-art lithium-ion batteries. Sulfur is inexpensive, abundant, and non-toxic; most importantly, its global presence is primarily as a byproduct (waste) of chemical refining, such as natural gas. Therefore, from the outset, lithium-sulfur batteries have had the most positive environmental impact on the planet.

[0010] To optimize lithium-sulfur battery technology, it is essential to fully understand the characteristics of sulfur allotropes, the subsequent production processes and related parameters, and their impact on the electrochemical and chemical processes within the battery.

[0011] Although lithium-sulfur batteries are expected to have three times the energy content of state-of-the-art lithium-ion batteries, their practical application is hampered by a number of scientific and technological problems that need to be properly addressed. Therefore, we have summarized the challenges associated with the commercialization of lithium-sulfur batteries, defined here as an experimental 20Ah lithium-sulfur pouch cell with the following parameters: 700 / 700 / 700 (Wh / kg, Wh / l, 700x cycle life at 80% DoD and 1C rate). We start with the most challenging one, number 1.

[0012] 1. Non-uniform current distribution and its impact on the cathode:

[0013] This is the most problematic issue, becoming a major concern as the size / area of ​​the electrode increases along with the type, location, and size of the current collector foil, for example, from laboratory-scale microcells to more practical pouch cells of tens of ampere-hours. This process is characterized by structural and morphological changes in the sulfur composite cathode, and subsequently, a redistribution of existing electron (provided by conductive additives) and ion distribution channels or pathways (provided by open voids in the electrolyte-impregnated cathode) within the cathode. The current collector foil establishes numerous electrical contact points between the active material and the supporting materials (such as conductive additives and binders in the composite cathode), enabling electrons to flow into and out of the electrode through external circuitry, collectively forming a functional ion / electron transport system.

[0014] During the cycling (charging and discharging) of LiS cells, repeated volume fluctuations in the cathode occur, which further translate into excessive mechanical forces. These forces profoundly affect the structural integrity of sulfur composite cathodes by disrupting the existing established bonds between sulfur / binder / additives during expansion (discharging) and contraction (charging). This difference is characteristic of active materials with high volume changes such as S (79%), Si (276%), Sn (260%), etc.

[0015] An effective electron conduction path within the sulfur composite cathode, along with the ion channels of this invention (defined herein as tortuosity factors), is an essential component of a successful high-energy and cycle-life LiS cell. Therefore, the ion / electron tortuosity must be as short as possible to fully realize the potential of sulfur.

[0016] The most common formulation used to make cathodes starts with the use of sulfur, which means that the cathode is made of denser S8 in a “charged state”, so all internal structures, joints and materials in the cathode must be able to withstand the expansion during the first formatting cycle (discharge).

[0017] If the cathode is constructed in the "discharge state," it will use Li₂S with a density less than S₈, therefore this type of cathode must withstand the shrinkage during charging. From a technical perspective, it is advantageous to manufacture sulfur cathodes starting with Li₂S because higher calendering forces can be applied, resulting in a denser cathode structure, and in particular, a good interconnection structure of active material-binder-additives can be produced. This is in contrast to the charged-state cathode, where the calendering-compacting process needs to retain the space / porosity required for further expansion into Li₂S during discharge.

[0018] In continuous cycling, the electronic conductivity path is constantly disrupted and rebuilt with each complete cycle. This negative impact can be partially compensated by using long-range conductive additives such as CNTs or carbon fibers.

[0019] 2. Non-uniform current distribution and its impact on the electrolyte:

[0020] Similar to the previous section, the volume fluctuations of the cathode also affect the presence, distribution, and exchange of electrolytes between the internal structure of the electrode and the immersion septum. This is because during expansion / contraction (discharge / charge cycle), the change in cathode porosity occurs in such a way that the non-uniform current distribution in the cathode plane begins to create areas where electrolytes are discharged from the deep surface of the cathode interior, and begins to negatively affect the effective ion conduction pathways in these areas, which further translates into the loss of active material and low utilization levels of active material.

[0021] This process differs significantly from the effect of porosity blockage on Li2S precipitation during discharge. The lithium metal foil—the anode—is stripped away during discharge, thus reducing the anode's thickness as lithium ions transfer to the cathode and react with sulfur. To achieve this, the cathode must be able to accommodate the reaction products—a buffering effect where the anode's volume / thickness loss during discharge is compensated by an increase in the cathode's volume, and vice versa during charging.

[0022] The open porosity of the sulfur cathode has a significant impact on all parameters of a LiS cell, therefore a thorough understanding of the conversion reaction is crucial. This conversion reaction occurs via a reversible phase transition—during discharge, solid S8 transforms into liquid PS (polysulfide), and subsequently PS transforms into solid Li2S, which precipitates from the electrolyte. According to the present invention, it has been found that in order to minimize the variation in cathode thickness to below 30%, a cathode structure with a customized porosity needs to be designed to accommodate and compensate for internal volume fluctuations.

[0023] 3. Sulfur volume expansion:

[0024] The periodic expansion-contraction cycle occurring in the sulfur cathode is defined here as orthogonal-αS8 15.49 cm. 3 / mol- Fully charged state and Li2S 27.68 cm 3 / mol- Complete discharge state, where the volume change is 79%, but according to known actual conditions, 16.38 cm 3 / mol of monoclinic-β sulfur precipitates first upon recharging, thus limiting the volume fluctuation of the sulfur cathode to 70%.

[0025] Conventional slurry-based processes for manufacturing sulfur cathodes cannot produce complex electrode structures with customized porosities required to effectively contain sulfur and provide precise buffer space within the internal porosity, with minimal impact on variations in cathode thickness. Currently, slurry-based cathodes limit porosity to approximately 45%. Beyond this point, any further increase in porosity is driven by reducing rolling pressure, leading to low compaction density and excessive dead volume / weight space that needs to be filled with electrolyte and subsequently loses structural integrity.

[0026] This is because cathode calendering is an important part of the process and is crucial for establishing an effective current conduction path (network mechanism), which is provided by the interaction of adjacent particulate sulfur / binder / additive in the slurry.

[0027] Sulfur cathodes must provide pathways for ion and electron conduction, with expansion during discharge being the most challenging aspect due to the pore blockage (ion blocking) effect. This occurs at areas with abundant active surfaces where short-chain sulfur compounds begin to precipitate, severely limiting ion diffusion / lithium-ion tortuosity (Li ion tortuosity) within the deep cathode structure. + (tortuosity), and then restricts the flow of current because of the need for ion and electron flow.

[0028] Therefore, a finely tuned production process is preferred to balance the high electronic conductivity and denser structure present under high pressure calendering, while reducing ion current exchange, thereby achieving an appropriate balance that is neither too high nor too low.

[0029] Traditionally, these limitations have been apparent through strict constraints on the potential for achieving full discharge of sulfur, but a great deal of effort has been required to understand the interactions of the lithium-metal anode because its structural integrity is loosened during electroplating / stripping, for example, during discharge, lithium peels off the surface of the foil, while on the opposite side, the cathode expands so finely that the lithium-metal foil becomes completely dense, so all changes result in changes in thickness. Because there is no internal structure to buffer changes in volume / thickness, when the cathode expands, the anode contracts, lithium peels off, and there is a synergistic effect between the electrodes.

[0030] 4. The low electrical conductivity of sulfur:

[0031] Sulfur is one of the best electrical insulators, with a conductivity of 5 × 10⁻⁶. -30 S / cm (charge-delithiation state), while Li₂S (discharge-delithiation state) is 3.6 × 10⁻⁶. -7 S / cm, therefore, in order to become the active part of the multi-electron redox reaction, according to the prior art, it is necessary to add a large amount of conductive additives to the cathode during production, or to use conductive polymers as a coating on the sulfur particles, and to apply various encapsulation or permeation methods, such as containing and fixing sulfur in a porous but conductive structure (e.g., micron-porous carbon derived from CDC carbide).

[0032] 5. Polysulfide dissolution (PS shuttle) and loss of active sulfur:

[0033] PS is an intermediate product of the sulfur redox reaction, defined as Li₂S. x , 4≤n≤8, it is freely soluble in ordinary liquid electrolytes. During cycling, the sulfur active material present in the cathode undergoes a phase transition defined as solid-liquid (first, dissolution phase) and liquid-solid (second, precipitation phase) during discharge, and then the reverse occurs during charging.

[0034] The loss of active sulfur in the cathode and the subsequent migration of PS species between electrodes are commonly referred to as PS polysulfide shuttle, which leads to high self-discharge, rapid capacity decay, lithium metal poisoning, and low coulombic efficiency. Various strategies have been applied in the literature to address PS shuttles, defined as composite cathodes having a large-to-medium-to-microporous matrix of sulfur encapsulated in a conductive polymer and / or permeated with sulfur. Electrolytes are optimized using solvents with limited PS solubility, PS anchoring additives (introducing functional groups or doping strategies), or binders. The most common approach is to deposit a functional PS shuttle interlayer on a separator or the surface of the sulfur cathode.

[0035] The PS cycle is a process driven by a concentration gradient between electrodes, which is determined by solvated PS anions (such as S8) that have high solubility in the electrolyte. 2- S6 2- and S4 2- The anion species is provided to diffuse freely from the cathode to the anode, where it interacts with the lithium metal anode and is reduced to short-chain PS, which then precipitates on the surface of the lithium metal as an insoluble deposit.

[0036] This is because the solubility of Li₂S₂ / Li₂S is very limited. The PS shuttle cycle ends with the subsequent reaction of the already precipitated Li₂S with the long-chain PS present in the electrolyte, generating soluble medium-chain ions again, which then diffuse back into the cathode and are oxidized.

[0037] 6. Sulfur particle aggregation – melting

[0038] Sulfur-based composite slurries consist of various basic structures and morphologies, defined here as active materials and conductive additives, each of which can coexist as primary particles of various shapes, such as (0D, 1D, 2D, 3D), nano- to micron-sized aggregates and clusters. Aggregates are structures formed by electrostatic interactions within particles, conductive additives, binders, and / or technical processing additives (such as thickeners, dispersants, or bridging polymers), while clusters are formed by linking aggregates into more complex structures, with clusters held together by van der Waals interactions.

[0039] All these components are now part of the cathode paste, which is then applied to the current collector foil primarily by a slot die coater. During the drying of the thick coating, the binder migrates, which further leads to coating inconsistencies and microstructural defects.

[0040] As the solvent evaporates from the wet electrode during drying, internal stress is generated on the flat surface of the electrode due to the shrinkage effect, which leads to crack formation, propagation, and even peeling off from the current collector foil.

[0041] Electrode drying is a complex three-phase boundary layer process (TPB) because it involves heat and mass transfer in the solid, liquid, and vapor phases, defined as solvent evaporation, binder diffusion and migration, and particle deposition. During drying, binder migration forms a gradient structure in which the presence of binder and other additives (e.g., electroactive polymers) varies between the top and bottom electrode structures. Simultaneously, solvent evaporation during drying is responsible for pore formation and stabilization processes by emptying pores toward the top surface without disrupting the surrounding structure.

[0042] The final manufacturing step that defines the electrochemical properties of the battery is electrode calendering, as it has a significant impact on porosity and tortuosity. During electrode compaction, it leads to a reduction in electrode thickness and porosity, thereby increasing the surface active mass loading (mg / cm²). 2 And by increasing electrode density, a higher volumetric capacity of mAh / cm³ can be achieved. 3 .

[0043] Calendering influences electrode morphology by altering the distribution of particles / aggregates / clusters; higher pressure results in fewer individual particles and more complex clusters. Sulfur-based cathodes are highly specialized cases due to the solid-liquid-solid phase transition, requiring unique solutions to address the challenges associated with the sulfur melting process. This process is characterized by the aggregation and melting of sulfur particles, followed by rapid particle size growth and reduced battery capacity, a consequence of repeated dissolution and precipitation of sulfur during prolonged cycling.

[0044] The original morphology of the deposited sulfur composite cathode is destroyed by the melting process as small nanoparticles reform into larger micron particles upon recharging. During this process, the surrounding sulfur material is removed, leaving empty voids previously occupied by active sulfur clusters. These active sulfur clusters then affect the ion diffusion path, and mass transport kinetics become increasingly restricted because the active surface of the molten sulfur is smaller than the high surface area of ​​the original nano-sulfur.

[0045] Traditional lithium-ion chemistry does not undergo a phase transition during cycling, so melting is only a specific process for lithium-sulfur batteries. Therefore, it is necessary to develop a new type of battery casing that is different from traditional cylindrical or prismatic pouch batteries.

[0046] 7. Low volumetric capacity (mAh / cm³) 3 :

[0047] In existing technologies, sulfur has a low electrical conductivity of 5×10⁻⁶. -30The S / cm ratio in the cathode is compensated by adding supporting additives (such as binders, various conductive additives and / or multifunctional binders) to the composition, for example, 70% by weight, while the other 30% is used for 20% conductive additives and 10% for binders, whereas in conventional lithium-ion batteries, the active material content in the cathode is about 95% by weight.

[0048] For example, electron conductivity in 10 -4 S / cm to approximately 10 -2 The NCA cathode with a S / cm ratio depends on the discharge state (lithiation). Therefore, in order to improve the electronic conductivity, effective mass capacity, and utilization of the sulfur-based composite cathode, more conductive additives need to be added to the composite cathode, averaging 20% ​​per weight.

[0049] The main obstacle to lithium-sulfur is the presence of additives with very low mass density; based on the current weight content of 20% conductive carbon additive, its average density is 0.25 g / cm³. 3 In conventional lithium-ion batteries with NCA cathodes, the mass density is less than 3%, therefore the calculated true density of sulfur is 2.07 g / cm³. 3 The actual density of disulfide is 1.66 g / cm³. 3 The amount of binder required in sulfur cathodes is typically as high as 10 wt.%, and billions of contact points are established in sulfur and advanced nano-carbon materials with high specific surface area to exchange electrons, where all these dead volume / weight materials present in the cathode will further reduce the ratio between active and inactive support materials.

[0050] This inevitably reduces the overall energy density of the battery. Adding 20 wt.% carbon conductive additive to the cathode slurry will readily occupy over 50% of the cathode volume, further translating to a thicker cathode. This creates another significant problem, as the existence of these dead volumes / spaces is solely due to the excessive low-density carbon significantly increasing the electrode volume / thickness. Therefore, more electrolyte must be filled into the voids, thus affecting the E / S ratio and mAh / cm². 2 Effective mass loading per unit area and in mAh / cm² 3 A tight balance is achieved between the unit volume loads.

[0051] 8. Low sulfur utilization rate

[0052] To explore the theoretical potential of sulfur as an energy carrier, significant changes should be made to the cathode structure, such as electrodes with customized properties defined as aligned porosity, low ionic and electronic tortuosity factors, and low dead volume / weight of additives and materials.

[0053] The shift from randomly oriented electrode microstructures in current lithium-ion batteries to next-generation engineered 3D electrode structures with near-unit tortuosity clearly demonstrates their potential to improve battery capacity, particularly during high charge / discharge rates, by enhancing active material utilization and increasing areal and volumetric capacity (mAh / cm²). 2 and mAh / cm 3 Increase battery capacity based on ).

[0054] The sulfur-specific complex redox reaction is carried out on the basis of the exchange of ions / electrons provided by a well-interconnected electrode structure, which then mediates an electrochemical reaction with S8 / Li2S particles. In this case, if their surfaces are not in direct electrical contact and are isolated from the conductive network, chemical steps are required from PS dissolved in the surrounding electrolyte or from sulfur.

[0055] Constructing well-organized cathodes with customized properties (e.g., vertically aligned open pores) allows for the creation of cathodes with the desired internal pore network to accommodate sulfur and shorten ion conduction paths—torsion. Current wet slurry-based cathode production methods have failed to successfully establish 3D sulfur composite cathodes due to the random distribution of their internal structure / pores and composition, leading to non-uniform electron / ion flow and subsequent pore blockage effects. Furthermore, non-uniform expansion during discharge hinders lithium ion diffusion from the overall cathode, where Li₂S precipitation occurs on the surrounding structure, which serves as part of the conductive network.

[0056] The technologies and processes used to manufacture 3D structured electrodes can be summarized as: co-extrusion, cryogenic casting, laser structuring / ablation, magnetic or electric field alignment of active materials or additives present in the slurry, sacrificial pore-forming agents, active or inactive template-assisted methods, filtration methods, or semi-solid electrode concepts.

[0057] 9. Volume / weight (ml / g) of sulfur electrolytes with excessively high E / S ratios.

[0058] The electrolyte in a lithium-ion battery does not actively participate in the energy storage reaction. It should promote reversible metal plating / stripping, solvation and desolvation, and most importantly, ion transfer—the movement of ions between electrodes—the ion current. Only lithium-ion cations are charge carriers. Therefore, the electrolyte content in the battery must be kept as low as possible, and the LTN (lithium transfer number) must be close to uniform. Thus, cations dominate as charge carriers on inactive anions.

[0059] Traditionally, laboratory-scale batteries have an E / S ratio between 6 and 18 ml / g. Therefore, obtaining a commercially acceptable lithium-sulfur battery at such a low ratio is "infeasible" due to the excessive amount of dead volume / weight electrolyte in the cathode; a more practical ratio is < 3 ml / g. In principle, there are limiting factors for the E / S ratio, namely the size / shape of the material in the cathode, because the shape of the particles during cathode production determines the electrode porosity, which plays a crucial role in electrode kinetics as it determines the amount of electrolyte in the battery. For sulfur-based cathodes produced via conventional slurry casting and subsequent calendering processes, the optimal possible porosity is approximately 50%.

[0060] 10. Excess lithium on the anode

[0061] Due to the continuous consumption of lithium during battery cycling, defined here as the rapid degradation / depletion of the electrolyte caused by the formation of a thick and porous SEI layer and moss-like lithium structure across the entire thickness of the anode, followed by expansion exceeding 100% of the original thickness of the lithium metal foil through the accumulation of electrochemically inaccessible dead lithium.

[0062] Lithium loss needs to be compensated for by introducing an additional amount of lithium, which will make up for the loss when using conventional anode materials such as graphite in existing lithium-ion chemistry. There is minimal lithium loss during cycling, with most of the loss occurring during the formation of the SEI layer during the formatting protocol. However, this changes for active materials such as silicon anodes or lithium-rich high-energy layered high-voltage cathodes, where lithium loss is significant (both at the cathode and anode). To address these issues, new methods for introducing lithium into existing lithium-ion batteries have been developed, such as mechanically activated stabilized lithium metal powder covered by a protective layer, enabling it to withstand existing slurry-based battery manufacturing processes.

[0063] Using lithium metal foil as the anode will have a significant impact on the final battery parameters, but this is mainly a theoretical impact, because the cathode and anode of an electrochemical battery must have a properly balanced volumetric capacity (mAh / cm³). 3 The volumetric capacity was then converted to different electrode loads and thicknesses, thus using high-capacity lithium metal foil with a theoretical volumetric capacity of 2062 mAh / cm³. 3 While ordinary graphite anodes have a capacity of 837 mAh / cm³. 3 Silicon has a capacity of 8334 mAh / cm³. 3 Obviously, by increasing the capacity on the anode side, it is still necessary to balance this additional anode capacity by increasing the cathode load or using a cathode with a higher capacity. However, there is still a critical cathode thickness of 120 μm and a porosity as low as 30%, which limits the overall parameters of the cell.

[0064] It is important to understand that the rearrangement of the lithium metal foil structure into a highly porous and moss-like anode, and the presence of inactive lithium, will reduce the final volumetric capacity (mAh / cm³). 3 This makes it unable to compete with advanced graphite anodes.

[0065] WO 2019 / 081367 A1 teaches cathodes composed of nanotubes and nanofibers, which are formed as a 3D structure of mesh or fabric. Sulfur is the active component in the cathode.

[0066] To address the aforementioned problems, the present invention aims to provide a positive electrode, preferably for use in alkaline-ion sulfur batteries, which exhibits improved cycle life, gravimetric and volumetric energy content, and utilization of surface active material.

[0067] To achieve these and other objectives, a cathode for use, for example, in lithium-sulfur batteries is provided as a cathode having a monolithic structure, which is preferably defined herein as a sulfur or sulfur-based heterostructure host structure and branched and / or hyperbranched sulfur (see...). Figure 2 A combination of sulfur-based or sulfur-supported structures, which work together to form a self-supporting sulfur or sulfur-based structure (also known as a sulfur wafer), which can provide long-range electron conduction paths within its internal and / or external structure.

[0068] The cathode of the present invention comprises a crystalline monolithic sulfur structure cathode body. Preferably, the monolithic sulfur structure cathode body comprises a heterogeneously branched and / or hyperbranched structure of twinned sulfur crystals as the active electrode material. These structures may also be referred to as substructures. Preferably, they are referred to as crystals, thus the active electrode material is obtained by crystal growth, preferably from seed crystals. Preferably, the macroscopic structure of the monocrystalline-(crystal)-sulfur structure is a system of twinned growth, symbiosis, interfusion, or twinned crystals.

[0069] Optionally, the cathode of the present invention can be described as including a grown monolithic sulfur structure cathode body, i.e., a crystalline sulfur wafer, preferably including a heterobranched and / or hyperbranched structure of twinned sulfur crystals as active electrode materials.

[0070] According to the invention, the wafer is a paste-free structure, and therefore not made from paste, but from a suspension of particles. Preferably, the wafer is a symbiotic / twin crystal structure / crystal system. The wafer can preferably be grown from numerous small (nano) seeds, preferably from sulfur seeds. Preferably, these seeds are aligned. Alignment can be achieved, for example, by electrostatically supporting the arrangement of the seeds. For this purpose, the seeds can be attached to a carrier that can be affected by a magnetic or electric field.

[0071] The growth of the crystal wafer can be carried out at temperatures in the presence of monoclinic thioallotropes, preferably at least in a metastable state. The seed crystal can also be referred to as the first-generation crystalline substrate, which can provide a 1D needle / rod / wire / tubular structure. As the crystal grows, further elongation occurs, and the basic or single seed crystal becomes polycrystalline. The connection of the initial basic seed structure is not mediated by the presence of binders or other reagents, but rather by the direct symbiosis of the crystal structures, thus resulting in crystal twinning / branching / hyperbranching.

[0072] Therefore, a self-standing 3D monolithic polycrystalline sulfur wafer with a preferred customized porosity is formed. The monolithic structure according to the invention is formed without the aid of a binder, but has a direct intercrystalline twinning / branching mechanism, which can also be characterized as a PAC-free particle-aggregate-cluster, a feature of slurry electrodes in known prior art methods for producing lithium-ion batteries.

[0073] Lithium-sulfur batteries with a cathode exhibiting a weight ≥1200 mAh / g and a capacity ≥1200 mAh / cm³ at 0.2C. 3 and area ≥10 mAh / cm 2 Capacity, with battery level ≥600 Wh / kg.

[0074] Preferably, the present invention includes an environmentally friendly (slurry-free) electrode and a method for manufacturing the same, wherein a self-supporting monolithic sulfur and / or monolithic branched and / or hyperbranched sulfur or sulfur-based structure is produced by a slurry-free method. The product of this method is preferably an electrode, wherein all precursors and materials used in the production process become components of the final sulfur cathode.

[0075] Preferably, the component is the active component of the electrode, capable of storing and transferring energy, and preferably without phase change (no interface, therefore no interparticle exchange of electrons / ions). Therefore, binders and / or other filler materials may not meet this definition.

[0076] Compared with the definition of the prior art in existing inventions relating to this lithium-sulfur battery, our invention demonstrates the direct use of sulfur as a component for manufacturing advanced preferred all-sulfur or almost all-sulfur (sulfur-based, preferably more than 82% sulfur, more preferably more than 95% or 98% or 99% or 99.9% sulfur) cathode heterostructures.

[0077] Total sulfur may mean "only sulfur, except for unavoidable impurities".

[0078] This type of electrode is highly advantageous compared to common wet slurry-based coatings. For slurry-based electrodes, the active sulfur and / or sulfur carrier present in the cathode slurry, as well as inactive components (e.g., binders, conductive additives, and / or technical additives), must participate in the process of forming a supporting internal electrode structure (e.g., a specific type of host structure) to accommodate sulfur, which is primarily carbon-based.

[0079] However, such known cathodes consist of a compressed particle + binder structure, which forces electrons to pass through several particle-particle or particle-binder-particle barriers. On the one hand, the binder consumes a significant amount of space that cannot be used for active electrode materials.

[0080] According to the present invention, when storing or releasing energy (battery charging, discharging), the active electrode material is preferably an active substance during electrochemical redox reactions.

[0081] This directly leads to a reduction in the weight and volumetric capacity of the cathode. On the other hand, the energy loss in this known electrode is detectable and is directly related to the movement of electrons through the aforementioned barrier.

[0082] Therefore, the object of the present invention is to provide an electrode, particularly a cathode, which has high weight and volumetric capacity and less energy loss compared with prior art electrodes.

[0083] According to the invention, twinning can specifically refer to the interconnection of crystals or crystal portions, preferably formed by the growth of crystals to further form crystalline portions. Twinning can, for example, be achieved by growing at least a second-generation crystal on a first-generation crystal (see example...). Figure 2 Alternatively, twinning can occur through the coexistence of individual crystals, whereby the portions fuse into a single crystalline unit as at least one crystal grows. According to the invention, crystal twinning preferably exists within the branched or hyperbranched portions of a sulfur crystal. Preferably, at least two generations of crystals are stacked on top of each other in the twinned portion. Also preferably, two or more surrounding / adjacent crystals twinnize through fusion as described above.

[0084] This objective is achieved by means of a cathode according to the present invention.

[0085] According to the present invention, a cathode is provided, preferably for use in a rechargeable battery, having a monolithic sulfur structure cathode body, i.e., a sulfur wafer, the sulfur wafer comprising a heterobranched and / or hyperbranched structure of twinned sulfur crystals as active electrode materials.

[0086] Compared to powder-based electrodes formed from slurry, this invention can be said to (almost) achieve unimpeded passage of electrons through the electrode.

[0087] According to the present invention, the sulfur wafer preferably comprises / has a sulfur structure having structural features of grown crystalline sulfur entities.

[0088] More preferably, the sulfur wafer comprises a monolithic sulfur or structure containing the properties described in the present invention.

[0089] Furthermore, according to the present invention, the sulfur wafer can be a monolithic sulfur-based structure, a grown sulfur crystal structure, and / or a second-generation sulfur structure grown on a substrate of first-generation sulfur crystals and / or sulfur nanotubes and / or sulfur microtubes and / or sulfur nanofibers and / or sulfur microfibers (in any combination). Such a structure can be a superstructure, and therefore a branched and / or hyperbranched sulfur structure, particularly a needle-like structure (see...). Figure 2 ).

[0090] A single-piece sulfur structure is preferably used to form the cathode.

[0091] Therefore, according to the present invention, a cathode is provided, which is preferably made of a single crystalline entity. Such a crystalline entity may include or be made of sulfur monomeric structures, preferably primarily made of sulfur.

[0092] The monolithic structure may include a superstructure.

[0093] The term "superstructure" here preferably refers to a more advanced structure, particularly a dendritic system and / or a branched and / or hyperbranched system, which, according to one embodiment, can encounter heterostructures. Such a system can be formed, for example, by second-generation crystal growth as described above.

[0094] The term “superstructure” can also (additionally or alternatively) refer to a combination of different types of sulfur or sulfur-based materials in an overall structure.

[0095] The term "heterogeneous" (structurally) herein preferably refers to a description using at least one, preferably two or more, structures, namely sulfur nanotubes and / or microtubes and / or nanowires and / or nanorods and nanofibers and / or microfibers as a substrate for growing secondary crystalline sulfur structures thereon, preferably in the form of 1D needle-like and / or 2D sheet-like and / or branched and / or hyperbranched crystalline structures. Such secondary sulfur structures can lead to dendritic and / or branched (secondary) structures. Figure 2 ).

[0096] Heterogeneous preference refers to structures provided by stacking at least 3 layers of aligned / interwoven hollow tubular sulfur nanofibers / microfibers and / or layers and / or nano / microtubes.

[0097] Preferably, there are 3-200 stacked layers, more preferably, 80 layers interwoven between 15° and 120° and contained within a monolithic sulfur structure.

[0098] According to the present invention, heterogeneity can preferably mean that the monolithic sulfur structure contains at least two different allotropes (different solids) of sulfur, and / or the macroscopic structure of the monolithic sulfur cathode contains a generally non-uniformly distributed porosity, and / or the macroscopic structure of the monolithic sulfur structure contains a branched and / or hyperbranched crystal structure with single / variable / variable density and / or single / variable / variable distribution and / or single / variable / variable shape and / or single / variable / variable porosity.

[0099] According to the present invention, the term "monolithic" is preferred by its usual definition, meaning made into a single / unique entity.

[0100] However, according to the present invention, this single / unique body is not made by compression, compaction, and / or with powder and binder, but rather by crystal growth from a corresponding mother liquor, preferably a single crystal. Therefore, the monolayer of the present invention can be described as a monolayer grown or cultivated from one or more sulfur seeds and / or on a sulfur micro / nanotube and / or fibrous substrate.

[0101] According to one embodiment of the present invention, this substrate can provide structural integrity to the monolithic sulfur structure of the present invention, thereby enabling the monolithic sulfur structure of the present invention to be self-supporting. The substrate can also constitute an active electrode material.

[0102] According to another embodiment of the invention, monolayers derived from sulfur seed crystals can also result in self-supporting monolayer sulfur structures. Preferably, crystallization occurs in layers to enhance structural integrity. Self-supporting can also be referred to as self-standing.

[0103] Through the above production method, the dead volume within the monolithic sulfur structure, and therefore the dead volume (which can also be described as porosity) within the cathode, is reduced to a very low percentage (less than 50%, preferably 30%). The low percentage of open (lithium ion-accessible) porosity resulting from the engineered internal cathode structure is still sufficient to carry enough electrolyte to allow for adequate reaction kinetics with ions from the electrolyte and to allow for volume fluctuations during cycling.

[0104] Therefore, the weight and volumetric capacity are significantly increased, preferably reaching a minimum of 1200 mAh / g at 0.2C, with a volume ≥1200 mAh / cm³. 3 Area ≥10 mAh / cm² 2 Capacity, with battery level ≥600 Wh / kg.

[0105] Therefore, not only is the monolithic sulfur structure of the present invention a binder-free structure, but it also preferably has a controllable low porosity, which can increase the capacity of the monolithic sulfur cathode of the present invention.

[0106] Furthermore, the crystallized or grown monolithic sulfur structure comprises far fewer, almost no, phase transition surfaces that need to be traversed by electrons traveling between the cathode and anode, because the monolithic crystalline body of the present invention is grown from a single seed crystal and / or a polycrystalline system of sulfur. Preferably, a heterostructure is formed from aligned crystals that collaboratively form a branched structure, and preferably has engineered internal electrode porosity that exhibits high porosity uniformity in size, shape, and / or location within the electrode.

[0107] This structure preferably has a good balance of uniformity represented by aligned crystals, but also heterogeneity represented by structural anisotropy, which may be crucial for allowing, to some extent, an internal volume self-compensation mechanism, under which fluctuations in sulfur (sulfur structural volume) during cycling are preferably compensated within a monolithic sulfur body.

[0108] Monolithic bodies may contain macroscopic cracks or fragments, such as unavoidable fracture points or structural defects, which arise during the further processing of the monolith into the final cathode after monolithic growth. However, these cracks and defects preferably do not dissolve the overall effect / characteristics of the cathode, and preferably none of these defects are comparable in degree to those of a compressed powder + binder cathode.

[0109] Fragments / segments are preferably binder-free and can be 10 times larger than grains from powder-based sulfur + binder cathodes. 5 times.

[0110] In this invention, "binder-free" specifically refers to the structural integrity of the crystalline monolayer sulfur structure cathode being independent of any adhesive. Therefore, the process of fixing the cathode body internally together involves no or substantially no adhesive. Consequently, the cathode body is preferably binder-free internally, especially since the cathode body is a grown entity that provides structural integrity of the cathode body or its fragments / pieces through its lattice / crystalline structure.

[0111] According to a preferred embodiment of the invention, the monolithic superstructure is heterogeneous. According to the invention, heterogeneity can be represented by a non-uniform crystalline (sulfur) pattern within the monolithic electrode body.

[0112] However, according to the present invention, heterogeneity can also refer to branched or hyperbranched crystal structures, which can be obtained, for example, by second-generation crystal growth of sulfur crystals on first-generation sulfur crystals and / or sulfur-based and / or sulfur-containing substrates, particularly as described above.

[0113] This first-generation sulfur crystal and / or sulfur-based and / or sulfur-containing substrate can be one or more layers of aligned and / or interwoven hollow sulfur nanotubes and / or sulfur nanofibers and / or dispersed sulfur crystals, preferably (after second-generation crystal growth) contained within a monolithic heterogeneous sulfur structure. Sulfur nanotubes or nanofibers can be fabricated using a MHDES magnetohydrodynamic electrospinning (melt spinning) process. This process can be based on the Lorentz law, which applies to paramagnetic sulfur materials in a molten state at the desired temperature. The aforementioned tubes can be manufactured according to WO 2019 / 081367.

[0114] First-generation sulfur crystals can be formed through (direct) crystal printing.

[0115] Therefore, hollow 1D sulfur fibers (nanotubes) preferably aligned can be manufactured by advanced melt electrospinning, which are preferably in the form of continuous fabric as a precursor for constructing a monolithic sulfur cathode.

[0116] Nanofibers can be an intermediate in the production of nanotubes. The same applies to microtubes and microfibers.

[0117] The diameter range of these tubes and fibers is preferably from 120 nm (nanotubes) to 25 µm (microtubes).

[0118] The cathode, comprising a combination of hollow and solid sulfur active materials, will preferably further include or consist of sulfur nanotubes and / or microtubes and / or nanorods or microrods or wires and / or nanosheets or microsheets. As previously mentioned, its monolithic sulfur structure preferably comprises 8-65% wt. of monoclinic sulfur allotropes, more preferably 35% or more of monolithic sulfur allotropes. Therefore, the ratio between hollow and solid active sulfur is preferably 65 / 35, defined herein as an example of a monolithic sulfur wafer having 65% wt. of sulfur nanotubes (hollow) and 35% wt. of sulfur nanowires (solid), forming a branched and / or hyperbranched structure that together forms the active material. A preferred ratio may be in the range of 50 / 50 to 90 / 10.

[0119] The cathode having only solid sulfur active material will be further composed of sulfur nano or micro rods or wires and / or nano or micro sheets as described above, preferably having a monolithic sulfur structure comprising 64% wt. to 99.9% wt. of monoclinic sulfur allotropes, more preferably 98%, which is defined herein as the example (solid) sulfur nanowires forming branched and / or hyperbranched structures to collectively form the active sulfur material.

[0120] According to embodiments of the present invention, the monolithic sulfur structure is self-supporting or self-supporting, and thus the monolithic sulfur structure is provided independently of any type of support (preferably an internal support) on which the electrode material is carried.

[0121] According to one embodiment, the cathode is a structure containing only sulfur, apart from unavoidable impurities. The aforementioned structural entity can provide a cathode without a free active element (sulfur), for example, a carbon substructure to which sulfur can be attached.

[0122] According to another embodiment, structural integrity is provided by the sulfur crystals and / or polycrystalline structure themselves, provided by a dendritic crystal system based on sulfur and / or substrate as described above.

[0123] According to a preferred embodiment, a monolithic sulfur superstructure is formed, wherein the monolithic sulfur crystals are grown from seed crystals consisting mainly of 1D and 2D particles or on nanotube / microtube / nanofiber / microfiber entities in a sulfur-containing process liquid at a temperature preferably between 95°C and 120°C.

[0124] According to embodiments of the invention, a protective layer for the monolithic sulfur body can be provided on its surface, comprising one or more suitable polymers having ionic and / or electronic conductivity, preferably one or more polymers having mixed ionic / electronic conductivity, a metallic-decorated rGO, and / or a metal oxide layer, to maintain the integrity of the sulfur structure. This means that complete encapsulation of the entire monolithic sulfur body by applying suitable polymer and / or metal oxide layers as a single layer or composite layer is more effective than conventional PS anti-dissolution methods applied to single composite sulfur particles, and the monolithic sulfur wafer of our invention significantly reduces the polysulfide dissolution effect.

[0125] The layer and / or multiple layers (composite materials) may also be conductive layers (electron and ion transport layers), wherein one or more rGO layers of polymer and / or metal oxide and / or metal decoration may be made by spraying, dip coating and / or chemical oxidative polymerization and / or electrochemical methods (such as EPD), wherein one or more suitable materials to be deposited or co-deposited must be polarizable (positive or negative charge carriers) or have the ability to maintain induced dipoles.

[0126] The preferred composite encapsulation layer further comprises a combination of at least three types of layers that synergistically form a functional protective composite layer, namely a) a sulfur-rich crosslinked polymer and / or copolymer layer, b) a layer formed by using a suitable oxidant such as Mn. 7+ Metal oxides chemically generated by direct oxidation of sulfur, preferably MnO2 layers, and c) deposition via cathodic EPDR electrophoresis and M x+ The reduction method and subsequent electrochemical deoxygenation of GO involves depositing a metal-decorated rGO layer from positively charged metal cations adsorbed on a graphene oxide layer. The adsorbed metal cations are reduced to metal-decorated rGO, wherein the preferred cation is Fe. 2+However, it is not limited to rFeGO. The preferred arrangement of such composite layers is a+b+c, but it is not limited to any combination, such as three layers b+a+c or two layers such as a+c.

[0127] According to embodiments of the present invention, an electron and ion transport layer is provided on the surface of a monolithic chalcogenide through a preferably uniform, preferably π-electron conjugated polymer and / or metal and / or metal oxide conductive layer.

[0128] According to an embodiment of the present invention, the polymer conductive layer is photochemically crosslinked with the surface of an existing monolithic sulfur body, wherein the free electrons for the reaction are provided by photoexcited sulfur diradicals, and the energy source for excitation may be intense pulsed light and / or laser beams and / or gamma rays.

[0129] The conductive polymer is preferably rich in sulfur and insoluble in electrolytes, and can be selected from the group consisting of: PANI (polyaniline), PPY (polypyrrole), PTH (polythiophene), PEDOT (poly(3,4-ethylenedioxythiophene), poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), PAN (poly(1-acrylonitrile), poly(3,4-ethylenedioxythiophene)-co-poly(ethylene glycol) (PEDOT-co-PEG), poly(styrene) (PPV), poly(3-hexylthiophene-2,5-diyl) (P3HT), and poly(9,9-dioctylfluorene-cofluorene-comethylbenzoate) (PFM).

[0130] Introducing iodine into the sulfur melt before it is processed into sulfur nanotubes and / or microtubes can reduce its viscosity.

[0131] A battery, preferably a lithium-sulfur electrochemical battery, wherein the cathode preferably exceeds threshold parameters, defined herein as having a weight ≥ 1200 mAh / g and a volume ≥ 1200 mAh / cm³ at 0.2C. 3 Area ≥10 mAh / cm² 2 The capacity, wherein when the battery level is ≥600 Wh / kg, may include the cathode of the present invention having the following preferred parameters:

[0132] The cathode has a single-sided thickness between 50 μm and 250 μm, and / or a monolithic sulfur wafer, preferably exhibiting a heterogeneous structure provided by stacking at least ≥ 3 layers of aligned / interwoven hollow tubular sulfur fibers, the diameter of which is preferably in the range of 120 nm (nanotube) to 85 μm (microtube). The active sulfur content in the cathode is preferably ≥ 85% wt., more preferably 90%, and wherein the monolithic sulfur wafer preferably provides a substrate for the co-occurrence of secondary active materials (preferably sulfur nanorods and / or nanotubes) to form a branched and / or hyperbranched heterogeneous monolithic sulfur body for the cathode, wherein the alignment of the resulting monoliths is preferably ≥ 85%, and preferably the reproducibility of the battery capacity between each manufactured cathode, expressed herein by volume and area loading, exhibits a high uniformity of ≥ 99.2% and a capacity mismatch deviation of less than 0.8%.

[0133] According to the present invention, the cathode preferably has a monolithic and / or heterogeneous sulfur wafer cathode.

[0134] According to one aspect, the invention also relates to a method for producing a monolithic sulfur crystal cathode, wherein the sulfur has fibrous and / or hollow fibrous properties, preferably derived from an advanced melt spinning method, derived from a liquid sulfur melt exhibiting paramagnetic properties at a preferred temperature between 119°C and 415°C at 1.01325 bar or between 140°C and 650°C at 10 bar, and preferably subsequently subjected to a combination of stretching, stretching, and / or quenching cycles of the resulting sulfur fibers and / or sulfur nanotubes or microtubes.

[0135] According to another aspect, the present invention may also relate to a method for producing a branched and / or hyperbranched monolithic sulfur cathode having a self-supporting sulfur substrate, a secondary sulfur structure coexisting within available voids present in the substrate, and synergistically providing and / or engineering a branched monolithic sulfur cathode with a customized porosity capable of internally compensating for sulfur volume changes during cycling.

[0136] According to another aspect, the present invention may also relate to a solvent-free and / or slurry-free and / or IR-free drying and / or calendering and / or binder-free electrode production method for constructing a monolithic sulfur wafer cathode as described herein, the method preferably further comprising bonding the monolithic sulfur wafer cathode to a current collector foil and / or substrate coated with a conductive adhesive layer having a conductive filler and a polymer matrix.

[0137] Preferably, the (heterogeneous) monolithic sulfur body entering the cathode and subsequent battery production process, also referred to as a monolithic sulfur structure, is preferably composed of ≥96% wt., more preferably 98% wt. of sulfur, and preferably exhibits self-supporting properties in a manner applicable to laser cutting and pick-and-place production processes.

[0138] According to a preferred embodiment, the cathode has a symmetrical shape with a standard dimensional deviation of ≤15%, more preferably ≤1.5%, and is therefore preferably represented by a) a circle, b) a square, c) a hexagon, d) an octagon, and other subsequent symmetrical shapes that can accommodate an equal number of current collector fins, and is thus defined as each single electrode having ≥2 fins symmetrically distributed on the current collector foil / substrate.

[0139] Preferably, the cathode includes a primary supporting positive electrode material comprising a (heterogeneous) monolith composed of sulfur nanotubes as components (sulfur wafers), wherein the cathode preferably has a shape and size that matches the net shape of the current collector foil including conductive additives, and the cathode may additionally or alternatively include a secondary positive electrode material, i.e., a sulfur cathode material co-occurring within the primary positive electrode material of the monolithic sulfur wafer.

[0140] The final monolithic sulfur wafer assembled into a cathode may include Figure 1 Any combination of the following structures arranged in the order of the given text. Any feature A through H is disclosed individually, and separate units are permitted, and should not be construed as being disclosed only in combinations A through H, but also as separate features:

[0141] A. Preferably, the primary cathode material comprises or is composed of crystalline sulfur, such as nanotubes or microtubes and / or nanowires or microwires and / or nanorods or microrods and / or nanosheets or microsheets representing a 2D structure, and / or sulfur nanofibers or microfibers as components (hollow structure), thus being sulfur wafers (3D sulfur structure), wherein the cathode preferably has a shape and size that matches the net shape of the current collector foil including conductive additives and binders.

[0142] B. If such a material is applicable, preferably, the secondary cathode material comprises a sulfur allotrope, wherein more preferably, monolithic 1D rods and / or 1D needles and / or 2D sheets are co-occurring within the body of the monolithic sulfur wafer A, i.e., the primary cathode material. The secondary cathode material is preferably applied to the primary cathode material of nanotubes / microtubes and / or nanofibers / microfibers. Material B may be at least partially arranged inside material A, particularly within the internal voids of the structure of A, reducing the original porosity of A, and preferably also interconnecting / bridging the pores and / or the sides of individual pores.

[0143] C. Assembled monolithic sulfur cathode.

[0144] D. A conductive adhesive layer with a thickness of ≤10 μm and more preferably 6 μm, wherein a patterned surface may optionally be present.

[0145] E. Preferably, the final cathode comprises a current collector foil with a thickness between 8 and 20 μm, more preferably 12 μm.

[0146] F. Preferably, the thickness of the intermediate cathode / ion-permeable transition layer is between 2 and 10 μm, more preferably 5 μm.

[0147] G. Preferably, the thickness of the inseparable electrically insulating but ion-permeable layer supported by the cathode is between 8 and 25 μm, more preferably 14 μm.

[0148] H. A heterogeneous monolithic sulfur wafer having A and preferred B.

[0149] Figure 2 This illustrates the basic principles of dendritic polymers, and thus, branched or hyperbranched structures. Starting with a primary substrate structure, which can be a (monolithic) filament or crystal structure itself of sulfur nanotubes / microtubes and / or nanofibers / microfibers, preferably, 1D (one-dimensional, therefore growing / already grown along one axis, thus forming needle-like / tubular) branches of the deposited crystalline material grow / arrange on the primary substrate structure (second-generation twinning or crystal growth). This process can be repeated to grow third-generation or higher twins, wherein preferably, the next-generation 1D structure grows at least partially, preferably primarily, and most preferably only on the last-generation twin below.

[0150] This method can also be used to interconnect individual sulfur nanotubes / microtubes and / or nanofibers / microfibers, thereby expanding the electron / ion exchange network.

[0151] With this arrangement, sulfur structures can be grown on sulfur-based structures to form monolithic sulfur (slurry-free) structures (engineered structures with customized porosity).

Claims

1. A cathode for a rechargeable battery, having A crystalline monolithic sulfur structure cathode, wherein the monolithic sulfur structure cathode is a grown sulfur wafer comprising a heterogeneous branched structure of twinned sulfur crystals, and the monolithic sulfur structure cathode serves as an active electrode material. The heterogeneous branched structure refers to: Using sulfur nanotubes and / or microtubes and / or nanorods and / or nanofibers and / or microfibers as a substrate, branched structures are grown thereon; and / or The monolithic sulfur-structured cathode comprises a combination of at least two sulfur allotropes with different crystal lattices; and / or The macroscopic structure of the monolithic sulfur-structured cathode includes a branched structure with varying density and / or distribution and / or shape and / or porosity.

2. The cathode according to claim 1, Its features are, The sulfur wafers are obtained by aligned seed growth.

3. The cathode according to claim 1, Its features are, The monolithic sulfur structure cathode comprises at least three layers of aligned and / or interwoven hollow tubular sulfur nanotubes and / or nanofibers and / or microtubes and / or microfibers.

4. The cathode according to claim 1, Its features are, The cathode has a combination of hollow sulfur active material and solid sulfur active material.

5. The cathode according to claim 4, Its features are, The weight ratio between hollow sulfur active material and solid sulfur active material is 65:

35.

6. The cathode according to claim 1, Its features are, The monolithic sulfur-structured cathode contains 64 wt% to 99.9 wt% of monoclinic sulfur allotropes, and / or the sulfur content present in the monolithic crystalline cathode is ≥85 wt%.

7. The cathode according to claim 1, Its features are, The monolithic sulfur-structured cathode contains 98 wt% monoclinic sulfur allotropes, and / or the sulfur content present in the monolithic crystalline cathode is ≥85 wt%.

8. The cathode according to claim 1, Its features are, The monolithic sulfur structure cathode is self-supporting.

9. The cathode according to claim 1, Its features are, The monolithic sulfur structure cathode is provided independently of any kind of internal support, and the electrode material will be carried and / or supported in or on the support.

10. The cathode according to claim 1, Its features are, The monolithic sulfur structure cathode is provided independently of any kind of heterogeneous support, and the electrode material will be carried and / or supported in or on the support.

11. The cathode according to claim 1, Its features are, The structural integrity of sulfur wafers is provided by the polycrystalline structure, and therefore by the grown crystalline entity itself.

12. The cathode according to claim 1, Its features are, A monolithic sulfur-structured cathode maintains an electron and ion transport layer on its surface.

13. A battery having a cathode according to any one of claims 1 to 12.

14. A method for producing a branched monolithic sulfur structure cathode, said monolithic sulfur structure cathode being a sulfur wafer, wherein aligned monolithic sulfur crystals are grown directly from seed crystals present in a sulfur-containing mother liquor at a temperature of 95°C to 120°C.

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