Inorganic composite separator for lithium battery having a three-dimensional electrode

Abstract

The present invention provides a separator for a lithium battery having an electrode with a thickness exceeding 0.1 mm, the separator having the following characteristics: the separator is formed by weaving electrically non-conductive inorganic fibers and optionally mixing non-conductive inorganic particles; the length of the fibers is in the range of 0.5 to 30 mm, and the thickness of the fibers is in the range of 20 to 1500 nm; the fiber material is glass; the pore size of the separator is in the range of 0.02 to 2.5 micrometers, where the pore size of the separator is the average pore size of the separator determined by averaging at least 50 values of the pore diameter read from an electron microscope image; the absorbance of the separator expressed as the weight of the immersion electrolyte 1M LiPF6 in ethylene carbonate / dimethyl carbonate with a volume ratio (v:v) = 1:1 is from 1 to 10 times the weight of the separator.

Description

Detailed Description of the Invention

[0001] [Technical Field] The present invention relates to an inorganic composite separator with adjustable pore size for a rechargeable, particularly high-rate lithium battery cell having spatially arranged three-dimensional (3D) electrodes.

[0002] [Background Art] Many of the currently manufactured rechargeable lithium battery cells are based on very thin sheet-like electrodes made from a mixture of active material, conductive carbon, and an organic binder, which are thinly laminated on a foil of a conductive material, usually aluminum or copper (current collector). The thickness of these planar electrodes is usually around 50 micrometers (rarely exceeding 100 micrometers). The anode and cathode are separated by a thin intermediate layer - separator of a porous and electrically non-conductive material and laminated to each other. The separator is usually a porous foil made of a combination of an organic polymer and / or an inorganic oxide of the polymer. The laminated electrodes separated by the separator are then compressed, sealed, and the space is filled with an electrolyte. As the electrolyte, a non-aqueous solution of a lithium salt is used.

[0003] In the process of charging and discharging these planar electrodes, it is most important to prevent the formation of lithium metal dendrites. Dendrites are formed, for example, during rapid charging or discharging. Lithium metal may deposit on the electrode in the form of dendrites growing through the separator, which may cause an electrical short circuit between the two electrodes. The location with the short circuit is heated, and the elevated temperature causes the organic polymer separator to shrink. This may make the short circuit stronger and cause thermal runaway of the battery.

[0004] Manufacturers are attempting to incorporate inorganic substances into the composition of separators to reduce the shrinkage coefficient. Composite separators must be as thin as possible in order to maintain the high specific capacity of the battery. The typical thickness of current separators is less than 15 micrometers, often less than 10 micrometers, but dendrites sometimes grow to hundreds of micrometers, typically 50 micrometers. For this reason, it is not realistic to use metallic lithium for the cathode in a planar arrangement of thin films where the separator thickness is much smaller than the length of lithium dendrites.

[0005] Commercially used organic polymers shrink at temperatures above 50 °C. Therefore, composite separators containing a combination of inorganic materials and polymers that do not shrink even at high temperatures are being used to reduce the shrinkage of the separator.

[0006] Known composite separators are made as follows: 1) Organic polymers and inorganic fillers, or 2) At least one layer of an inorganic binder completely or partially covered with an organic polymer, or 3) Inorganic materials with varying particle roughness, connected by an organic binder during preparation, and then the organic binder is cured or fired.

[0007] US6432586 and EP1146576 describe ceramic separators for 2D (planar thin film) electrodes coated by lamination of polymer microporous layers. The ceramic layer consists of 20 - 95% non-conductive particles based on Al2O3 or SiO2, CaCO3 or TiO2 with a particle size of 0.001 - 25 micrometers dispersed in a conductive polymer matrix that can be an electrolyte. This thin ceramic layer with a thickness of 0.001 - 50 micrometers prevents lithium dendrites from growing through it. A further polymer layer with a thickness of 5 - 50 micrometers is provided to block the ion flow between the positive and negative electrodes during thermal breakdown.

[0008] The options for inorganic materials for plastic separators are very limited. The materials are required to be electrically non-conductive, not intercalate lithium, be in a stable oxidation state, withstand hydrofluoric acid and the chemical environment, and have a very small particle size.

[0009] As shown in Quantifying the Effect of Separator Thickness on Rate Performance in Lithium-Ion Batteries (Dominik V. Horvath et al 2022 J. Electrochem. Soc. 169 030503), the use of thick layers (up to 16 - 100 μm) of plastic separators dramatically reduces the charge and discharge rate and the capacity utilization. The authors point out that the main cause of the problem is the high resistance of the electrolyte within the separator, not ion diffusion through the separator.

[0010] US2005 / 221192 describes thin-film ceramic separators based on Al2O3 or Zr2O3 and SiO2. Their porosity is 30 - 70%. This separator contains at least two particle size fractions with a difference of at least 10 micrometers. The large particles are Al2O3 or Zr2O3, and the small particles are Zr2O3 and SiO2. The preferred thickness of the separator layer is 10 - 15 micrometers. Preferably, the separator contains a silicone binder to enhance agglomeration and bonding to the electrode. The separator is applied to the electrode as a suspension at a high temperature when a very thin layer of the separator is formed on the electrode at that position.

[0011] EP1803177, US2008032197, and WO2006045339 describe an inorganic separator for thin-film lithium batteries, a method for manufacturing the same, and its use. The separator-electrode unit has an inorganic separator layer and an electrode that includes at least two fractions of metal oxide particles that differ from each other by average particle size and / or different metal oxides, and their active material particles are adhered to the working electrode by an inorganic adhesive. In this way, a separator thickness of less than 15 micrometers can be achieved. The drawback is that a separator containing only a powdered ceramic material has too large a separator weight (g / m 2 2) even if the separator layer is relatively thin.

[0012] As an example of a recent thick-layer separator, WO2019195605 can be cited. This describes a composite separator for primary (non-rechargeable) batteries that includes a layer of glass fibers, a layer of polymer, and optionally a binder. The thickness of the separator layer used in an Al-graphite battery is 60 to 200 micrometers. There may also be multiple layers in which the glass fiber layer is combined with the polymer layer. The glass fiber layer or the polymer layer may include glass paper made from glass fibers, for example SiO2 fibers. This is porous and the pore size is 0.1 to 10 micrometers. Since the glass fiber paper (GFP) is very porous, its use requires a thick separator, and in this case, an excessive amount of electrolyte is required. Therefore, such a strong separator containing only GFP and electrolyte is not commercially viable and is therefore combined with a polymer layer. The cathode is Al. In the present application, it is described that the cathode may also be metallic Li. The anode includes graphite. However, since the electrochemical potential difference between lithium and graphite is only 0.2V, the practical application of Li-graphite batteries is substantially limited.

[0013] Similarly, glass fiber separators designed for lead-acid batteries are not suitable for lithium batteries because their pore sizes are many times larger than the size (around 30 micrometers) necessary to hold mechanically detached parts of the electrodes, separate the lithium electrodes, and protect against the growth of lithium metal dendrites.

[0014] WO2019070945 describes a separator for a Li-S battery that includes a material capable of absorbing and desorbing polysulfides. The composition of the separator reliably reduces sulfur loss from the positive electrode during cycling and improves the cycle life. A lithium-sulfur battery includes a lithium metal negative electrode and a positive electrode containing sulfur, with a space therebetween in which a multifunctional separator is disposed. The separator contains an active material capable of absorbing and desorbing polysulfides, and the electrolyte is in contact with these. The active material of the separator includes a metal nitride or a metal oxynitride, and the porosity of the metal nitride or metal oxynitride is 20% or more. The separator includes a porous support in the form of a microporous sphere formed by mesoporous nanoparticles, porous hollow carbon, graphene oxide layers, porous carbon nanofibers, hollow carbon fibers, metal foams, metal networks, or combinations thereof. Optionally, the porous material includes carbon, graphene, graphene oxide, metal, and combinations thereof, or a polymer coated with an active material. A nitride or oxynitride compound can also function as a separator core, and the core is coated with a coating containing a metal nitride or oxynitride, the composition of which is different from that of the core.

[0015] The problem and formation of dendrites in thick-layer (3D) electrodes are described in WO2010031363. At least one electrode contains an active material in the form of hollow spheres with a wall thickness of at most 10 micrometers and / or an active material in the form of aggregates and / or agglomerates with a size of 30 micrometers, and this active material can absorb and release lithium in the presence of an electrolyte. By pressing this material without an organic binder, a thick electrode with a minimum thickness of 0.5 mm, a high active material content, and a porosity of 25 - 90% of the pressed electrode can be produced. With this three-dimensional electrode, a thick separator with a thickness of 0.1 - 10 mm and a porosity of 30 - 95% can be produced, which contains a highly porous electrically non-conductive ceramic material with pores open. The separator consists of a pressed porous ceramic powder based on Al2O3 or ZrO2, and / or a powder of pyrolysis products, and / or a pressed powder of non-woven glass fibers and / or ceramic fibers. The separator has a non-directional form of pyrolysis products or non-woven glass fibers or ceramic fibers. The advantage of this separator is that its thickness prevents the through-growth of dendrites. However, a major drawback is that the dry powder must be mechanically pressed into its final shape in the manufacturing process, and in the case of a large area, problems occur with mechanical damage to the electrode and the homogeneity of the compressed layer. Such a powder separator consists of non-self-supporting particles and needs to be created in-situ by compression. In this case, the final porosity of the separator can only be adjusted by the final compression. The particle weight is also very large, especially when using ZrO2, and the specific gravity is 5.68 g / cm 3 is.

[0016] EP2727171 describes a Li battery having a three-dimensional electrode as described in EP2371019 and US10581083, and a separator containing a compressed inorganic ceramic material based on glass in the form of Al2O3, SiO2, ZrO2, nanofibers, fibers or organic porous foil is used. Also in this case, the inorganic separator has the same problems related to the inability to adjust the pore size, the structural properties of the separator, and its handling problems.

[0017] As is clear from the cited documents, most known rechargeable lithium battery cells are manufactured based on thin-film planar electrodes. The thickness of these planar electrodes is usually around 50 micrometers (rarely exceeding 100 micrometers). Instead of polymer separators, composite separators containing various polymers or their mixtures and ceramic materials, or combinations of layers of ceramic materials and polymer layers, are used or applied to the electrodes. The preparation of these separators is very complex and often requires the use of various binders and subsequent heat treatment to remove the binders.

[0018] The disadvantage of a battery using a separator containing only inorganic material powder is its large weight.

[0019] The disadvantages of using glass paper in a lithium battery are its large thickness and large pores.

[0020] At present, the thicknesses of the electrodes and the separator are accurately calculated and proportioned, and the transport of lithium ions and the formation of metallic lithium dendrites (= lithium metal dendrites) have been optimized by engineers. Changes in other parameters such as the ratio of the thickness or the capacity mean deterioration of the battery's safety, reliability, and performance. Lithium dendrites are mainly formed during cell charging and grow to a size exceeding 50 micrometers. Their formation strongly depends on the homogeneity of the separator. Lithium dendrites are typically formed at the weakest part of the separator. The thinner the separator, the more difficult it is to ensure homogeneity. Temperature also has a fundamental influence on the formation of dendrites. At sub-zero temperatures, extreme requirements are imposed on the quality of the separator, and at sub-zero temperatures, especially when using graphite as the negative electrode, it is necessary to fundamentally reduce the charging rate.

[0021] The thicker the electrode, the larger the capacity, the higher the lithium content, and the higher the requirements for the separator.

[0022] Typical drawbacks of known separators for lithium accumulators with thick-layer electrodes include the laboriousness of manufacturing the layered composite, the use of inorganic particles in combination with organic polymers and binders, the large weight relative to the layer thickness, the drawback of large pores when using glass paper as the separator or when used as part of a composite separator in combination with an organic polymer, or the problems of pressing and handling of pure powder ceramic separators, as shown by the current state of the art.

[0023] [Disclosure of the Invention] The above-listed drawbacks of separators for lithium batteries having a three-dimensional (thick-layer) electrode with a thickness of at least 0.1 mm, for example, the time-consuming production of the layered composite, the use of inorganic particles in combination with an organic polymer and a binder, the large weight relative to the layer thickness, the drawback of large pores when using glass paper as a separator or when used as part of a composite separator in combination with an organic polymer, or the problems of pressing and handling of ceramic powder separators, are solved by a composite inorganic separator for a lithium battery having a three-dimensional (thick-layer) electrode.

[0024] The separator for a lithium battery according to the present invention is formed by woven non-conductive inorganic fibers, and optionally non-conductive inorganic particles are admixed; here, the length of the fibers is in the range of 0.5 to 30 mm, and the thickness of the fibers is in the range of 20 to 1500 nm; here, the fiber material is glass. The pore size of the separator is in the range of 0.02 to 2.5 micrometers, preferably in the range of 0.02 to 1 micrometer, and the pore size of the separator is defined as the average pore size of the separator determined by the average of the diameter values of at least 50 pores measured from an electron microscope image. The absorption capacity (absorbency) of the separator, expressed as the weight of the electrolyte, immersed in 1 M LiPF6 in EC / DMC (ethylene carbonate / dimethyl carbonate; volume ratio (v:v) = 1:1; specific gravity is 1.3 g / cm 3 , 25 °C) is 1 to 10 times the weight of the separator (i.e., absorbency of 100 to 1000%), preferably 4 to 10 times (i.e., absorbency of 400 to 1000%).

[0025] The porosity of the separator is preferably higher than 20%, preferably higher than 50% (determined by calculation as the ratio of the volume of the separator to the volume of the immersed electrolyte, calculated from the ratio of the weights of the separator before and after immersion in a 1 M LiPF6 electrolyte in EC / DMC).

[0026] The porosity of the non-compressed separator is preferably in the range of 50 to 90%. More preferably, the porosity of the non-compressed separator is higher than 80%, and most preferably in the range of 75 to 90%.

[0027] The porosity of the separator after compression with a force of 100 kPa is preferably in the range of 20 to 55%.

[0028] Preferably, at least 90% by weight of the inorganic fibers have a thickness in the range of 20 to 500 nm.

[0029] The pore size of the separator is preferably in the range of 0.02 to 2.5 micrometers, more preferably in the range of 0.02 to 1 micrometer (i.e., 20 to 1000 nm), and even more preferably in the range of 20 to 500 nm. The pore size of the separator is, in some embodiments, in the range of 20 nm to 150 nm (especially when the separator contains inorganic particles).

[0030] The glass is a silicon dioxide-based material and may contain an admixture of at least one oxide of an element of Group IA, IIA, or IIIA of the periodic table. Preferably, the glass is selected from Group A, C, D, E, R based on aluminosilicate or aluminosilicate having an admixture of alkali oxides such as CaO, MgO, or B2O3. The glass can be, for example, silicate glass, potassium-calcium glass, sodium-calcium glass, borosilicate glass.

[0031] When non-conductive inorganic particles are present, the mass (weight) fraction of the particles relative to the total weight of the separator is at most 20% by weight.

[0032] The non-conductive inorganic particles can be particles having a maximum size in the range of 10 to 700 nm, preferably a maximum of 500 nm, more preferably 200 to 300 nm. Such particles may be formed of a non-conductive metal oxide. In a preferred embodiment, these metal oxides can be, for example, silicon dioxide, aluminum oxide or titanium dioxide.

[0033] The non-conductive inorganic particles can also be glass fibers having a length of up to 20 micrometers, preferably up to 10 micrometers, and a thickness in the range of 20 to 1500 nm.

[0034] The fibers form a macroporous matrix, and the non-conductive inorganic particles are mechanically attached within the structure of the fibers and the macroporous matrix without using any binder. When the inorganic particles completely fill the pores of the matrix, the inorganic particles form a crust having a pore size smaller than the size of the inorganic particles. In this way, the pore size of the separator can be adjusted and optimized.

[0035] The separator does not contain an organic binder. Also, the separator does not contain any inorganic binder. The inorganic binder is a powdery substance and can be used to bind the fibers after contact with a liquid (water).

[0036] The separator according to the present invention is made of only inorganic substances and creates three types of porosity that create the final porosity of the separator. The three types of porosity are the porosity of the matrix, the porosity of the partially reinforced matrix fibers, and the porosity of the completely filled matrix.

[0037] The inorganic material for forming inorganic particles according to the present invention is a ceramic material selected from the group consisting of oxides of silicon, aluminum, zirconium, or titanium, silicates, titanates, aluminosilicates, zirconium silicates, basalt, and / or mixtures thereof, and / or an alumino-borosilicate or aluminosilicate-based glass having a mixture of alkaline oxides such as CaO, MgO or B2O3, which is selected from groups A, C, D, E, R.

[0038] The thickness of the separator after compression with a force of 100 kPa is preferably in the range of 0.050 to 2 mm.

[0039] The separator layer preferably has an areal density in the range of 10 to 200 g / m 2 2.

[0040] In a preferred embodiment, a separator having an areal density of 10 to 200 g / m 2 2 has a porosity in the range of 20 to 95%, more preferably at least 50% without compression, even more preferably 75 to 90% without compression; and a pore size of 50 to 1500 nm, preferably less than 500 nm, most preferably at most 150 nm.

[0041] For a separator for use in a Li-S battery cell, the separator matrix can be further filled with polysulfide-blocking particles such as titanium dioxide, titanium nitride, graphene, zirconium dioxide.

[0042] The separator according to the present invention is prepared by a process in which first glass fibers are dispersed in water, the acidity of the mixture is adjusted to a pH value in the range of 2 to 5, preferably 2.5 to 4, and then the mixture is poured through a sieve, and the resulting layer is dried at a temperature of 100 to 200 °C, thereby forming a macroporous matrix. When the separator also contains inorganic particles, these particles are introduced onto the macroporous matrix in the form of a suspension or an aqueous dispersion. Thereafter, the macroporous matrix, with or without inorganic particles, is calcined at a temperature in the range of 300 to 800 °C.

[0043] Another aspect of the present invention is a lithium battery comprising at least one pair of electrodes separated by the separator according to the present invention, and the thickness of the (compressed) separator is selected such that the ratio to the thickness of the electrodes is 1:2 to 1:10. The electrodes preferably have a thickness of 100 micrometers to 4 mm, more preferably 0.3 to 2 mm, and most preferably 0.5 to 1 mm. The electrode materials for lithium batteries are known to those skilled in the art.

[0044] The advantage of the separator according to the present invention is that it is easy to manufacture. An aqueous suspension of inorganic nanofibers is poured through a sieve and dried. A mesoporous matrix typically having a pore size of 20 to 2500 nm is obtained. This matrix can be used as a separator for low-power batteries, or it can be modified into a form suitable for high-power batteries by flowing an aqueous suspension of non-conductive inorganic particles into it, drying / annealing again, and cutting the separator.

[0045] In this way, the matrix is supplemented with inert and electrically non-conductive particles of inorganic materials having a size of 10 to 700 nanometers that adhere to the fibers by van der Waals forces and / or within the mesoporous structure of the matrix without using any binder. In regions where the pores completely fill the matrix, the particles of the inorganic material form a crust having a pore size smaller than the corresponding size of the applied inorganic material particles. These inorganic materials can preferably be ceramic materials, glass, basalt, and insoluble metal oxides. By structurally modifying the matrix, even with a thickness of several millimeters, a low specific resistance and high mobility of lithium ions when passing through the separator are ensured. Furthermore, structurally modifying the matrix can prevent the growth of lithium metal dendrites, enhance the safety and reliability of the separator, and increase the charge and discharge rate of the accumulator.

[0046] Due to the van der Waals forces and the absence of a chemical binder, the resulting separator has high strength, flexibility, and chemical resistance.

[0047] In this way, layers with different densities and pore sizes can be fabricated in the separator. Pores with a porosity up to 70% smaller than the original fiber matrix can be formed in the gaps between the matrix fibers. In regions where the pores of the matrix are completely filled with particles of the inorganic material, especially on the surface of the matrix, the particles form a crust having a defined pore size smaller than the corresponding size of the applied inorganic material particles. Inside the matrix, depending on the properties of the applied inorganic material particles, these particles adhere more or less to the fibers of the matrix, forming a mesoporous layer with a controlled pore size and density.

[0048] By changing the matrix, the reliability of the separator is improved in terms of electrical separation of the electrodes, ion conductivity, and prevention of dendrite growth through the separator.

[0049] This separator can easily withstand high temperatures of 500°C to 1000°C depending on the inorganic materials used, has a high pressure loss, excellent ionic conductivity, and zero electrical conductivity, and as a result, exhibits excellent separation characteristics.

[0050] Due to the wettable surface of the inorganic material and the completely open pores, the mobility of lithium ions in the separator structure is high, and it is still possible to safely charge the accumulator at a high rate.

[0051] The separator according to the present invention has excellent resistance to the growth of metallic lithium dendrites (=lithium metal dendrites) even at higher battery charging rates. A thickness of 50 to 1000 micrometers, a small pore size, and very good homogeneity are associated with higher battery safety.

[0052] This separator can also be used in a Li-S battery cell that functions as an ion membrane formed on the positive electrode to prevent the movement of polysulfides that break down lithium when the molecule comes into contact with lithium metal. In this case, the matrix additionally contains particles that prevent the movement of polysulfides, selected from the group consisting of metal nitrides or metal oxynitrides, graphene and / or graphene oxide, attached to the nanofibers and electrically non-conductive particles of a glass or ceramic material with a size of 10 to 700 nanometers inside the mesoporous structure.

[0053] The separator is chemically resistant to non-aqueous electrolytes containing fluorine.

[0054] The thickness of the separator is preferably in the range of 50 to 1000 micrometers, the porosity is 20 to 95%, and the pore size is 20 nm to 2500 nm, preferably 70 to 150 nm. The areal density of the separator is preferably in the range of 20 to 500 g / m 2 (weight per unit area).

[0055] The pressure loss of the separator is at least 300 Pa / 100 g / m 2and preferably greater than 1000 Pa / 100 g / m 2 greater.

[0056] Another advantage is the high specific strength of 0.3 to 2.0 km and the high water absorption and strength of the separator that can be compressed up to 70% without any damage.

[0057] [Brief Description of Drawings] FIG. 1 is an SEM image of the upper side of the separator of Example 1, with a size scale bar attached.

[0058] FIG. 2 shows the voltage curve of the cell of Example 1, with charging for 8 hours and discharging for 8 hours.

[0059] FIG. 3 is an electron microscope image showing the structure of the glass-Al2O3 inorganic composite separator of Example 2 (wrapping the fibers and partially filling the pores).

[0060] FIG. 4 is an electron microscope image showing the structure of the glass-Al2O3 inorganic composite separator of Example 3 (wrapping the fibers, filling the pores, and forming a dense and homogeneous Al2O3 crust on the matrix surface).

[0061] FIG. 5 shows the voltage curve of the cell of Example 3 at a charging rate of 1.5 hours and a discharging rate of 1.5 hours.

[0062] FIG. 6 is a cross-sectional electron microscope image of the glass-TiO2 composite separator of Example 4.

[0063] FIG. 7 shows a cross-section of a 446-nm-thick separator having an oriented matrix nanofiber structure filled with TiO2 nanoparticles penetrated to a depth of about 200 micrometers, forming a pore size of about 25 nm (Example 5). The image is by an electron microscope.

[0064] FIG. 8 is an electron microscope image showing a separator matrix having a TiO2 nanoanatase crust on the surface (Example 5).

[0065] Figure 9 shows the graph of the cycle of the cell of Example 5.

[0066] Figure 10 shows the graph of the cycle of the cell of Example 6.

[0067] Figure 11 shows the graph of the cycle of the cell of Example 7 (comparative example).

[0068] Figure 12 shows the graph of the cycle of the cell of Example 8 (comparative example).

[0069] [Example] Method: The composition of the separator (weight % of fibers and weight % of inorganic material) was determined by weight measurement by weighing the components, namely the matrix and the inorganic material, using a precision laboratory balance. The particles of the inorganic material are trapped in the matrix with a weight deviation (loss) of less than 5%.

[0070] Thickness of the separator: Measured using a VEB FENMESGERATEWERK FREIBERG thickness measuring device (contact area 10 cm 2 ), without any pressure applied, and at a constant pressure of 20 kPa. The unit of the value is expressed in mm.

[0071] The thickness measurement of the separator after compressing it with a force of 100 kPa was carried out using an LWBK thickness gauge (AB Lorentzen & Wettre) model 1-2, at a contact pressure of 100 kPa, a contact surface diameter of 16 mm, and a contact surface size of 2 cm 2 under certain conditions. The unit of the value is expressed in mm.

[0072] The areal density was measured by taking a 100×100 mm sample from the separator and weighing it. The sample had a weight closest to 0.01 g. Then the obtained weight was normalized to an area of 1 m 2 . The areal density is in g / m 2 units.

[0073] Absorbency (electrolyte impregnation) was determined by weight measurement as the weight of the electrolyte 1M LiPF6 in EC / DMC (ethylene carbonate / dimethyl carbonate; volume ratio (v:v) = 1:1 and specific gravity 1.3 g / cm 3 ) at 25 °C, related to the weight of the separator before impregnation, in a separator sample of 10×10 cm dimensions. The impregnation of the electrolyte was carried out so that the weight of the impregnated separator became constant. The weight of the impregnated electrolyte was calculated as the difference between the weight of the separator after impregnation and the weight of the (dry) separator before impregnation. The water absorbency was measured using an uncompressed separator.

[0074] The porosity was determined by calculation from the volume (area × thickness), and the volume of the electrolyte calculated from the weight difference of the separator before and after immersion in the electrolyte.

[0075] Porosity [%] = Volume of separator / Volume of electrolyte The following method was used to measure the porosity: 1) Without compression - A 10×10 cm separator having a thickness determined by a thickness gauge is weighed, then immersed in an electrolyte with a specific gravity of 1.3 g / cm 3 and weighed again. In this way, the volume of the electrolyte is determined, the porosity is calculated according to the above formula, and the volume of the separator is calculated as the product of 10×10 cm and the thickness determined by the thickness gauge.

[0076] 2) Compression at 100 kPa - 40 sheets of 10×10 cm separators are weighed, stacked on top of each other between parallel metal plates, and compressed with a force of 100 kPa. The weight and thickness (distance between the plates) of this pack are measured, thereby determining the volume of the separator. The pack of compressed separators is immersed in the electrolyte for 4 hours so that the electrolyte penetrates into the pack. Subsequently, the increase in weight due to the immersion of the electrolyte is measured, and the volume of the electrolyte is calculated by dividing by the specific gravity of the electrolyte. The porosity of the compressed separator is further calculated according to the above formula.

[0077] The pore size was determined by reading the sizes of at least 50 pores from an image using an electron microscope and calculating the average of these sizes.

[0078] The pressure loss was measured with a micromano - meter equipped with a UMK - type inclined arm from Mikrotechna - Modrany, under the set conditions of the rotameter 75 (5 l / min; 0.0167 m / s). Using a so - called calibration plate, the function was checked with calibration values of 300 - 310. The values are represented in Pa / 100 g / m 2 units.

[0079] The strength was measured with a Labor Tech fracture testing machine Labtest 2.005S. The values are specific strengths expressed in km units according to CSN IEC 60050 - 212.

[0080] The electrochemical measurement method was carried out with a BaSyTec Battery Test System. The methods used include potentiometry, amperometry, and voltammetry.

[0081] Example 1: Typically, inorganic silicon dioxide (SiO₂) fibers with a length of 0.5 - 5 mm and a thickness of 20 - 1500 nm were dispersed in water, and the mixture was diluted to adjust its acidity to pH 4. Then, this mixture was dispensed through a sieve, a regular layer was formed on it, which was dried at a temperature of 250 °C, and subsequently fired at a temperature of 700 °C to form a porous separator matrix. The matrix thus produced was cut into separators of the desired shape and used in an accumulator equipped with electrodes with a thickness of 1 mm. The separators showed the following characteristics: Separator thickness without compression - 0.3 mm Separator thickness after compression with a force of 100 kPa - 0.15 mm Areal density - 50 g / m 2 The absorbency of the electrolyte was 1:6.2 based on the weight of the non - compressed separator. Porosity before compression: 79%, porosity after compression with a force of 100 kPa: 40% Pore size statistically determined from an electron microscope <500 nm Separator pressure loss - 720 Pa / 100 g / m 2

[0082] Figure 1 shows a photograph of the upper side of the separator of Example 1 taken with a field emission scanning electron microscope (FE SEM). From the image, it can be seen that the typical pore size is around 500 nm (0.5 μm).

[0083] This separator, along with nickel manganese cobalt lithium oxide (NMC-LiNi x Co (1-x) / 2 Mn (1-x) / 2 O2) as the positive electrode and graphite as the negative electrode, was used to construct a test cell with an electrode thickness of 1 mm (3D), which has excellent discharge performance (maximum peak 1000 A and continuous 50 A), shows full capacity utilization (500 Wh), has a low specific resistance, and a low Columbic loss (<5%).

[0084] Full charge from the discharged state can be achieved at a rate of C / 4 (4 hours). A typical constant-current charge-discharge voltage curve in a relatively slow cycle of 8-hour charge and 8-hour discharge was measured with a commercially available BaSyTec Battery Test System and is shown in Figure 2.

[0085] Example 2: Inorganic glass fibers typically having a length in the range of 0.5 to 5 mm and a thickness in the range of 20 to 1000 nm were dispersed in water, the mixture was diluted, and its acidity was adjusted to pH 2.5. Subsequently, this mixture was poured through a movable fine sieve, where a uniform layer was formed, and then this layer was dried at 150 °C to form a porous matrix. Aluminum oxide ceramic particles with an average particle size of 250 nm were introduced into the matrix by a wet method. The ceramic particles penetrated inside this matrix and covered the fibers. This composite was dried at 350 °C to form a layer of separator matrix, from which a separator of a desired shape was cut out and used in a cell of an accumulator equipped with a three-dimensional electrode with a thickness of 0.5 mm.

[0086] The separator showed the following characteristics: Composition: Glass (90%), Al2O3 (10%) Thickness without compression - 0.32 mm Thickness after compression with a force of 100 kPa - 0.17 mm Areal density of the separator - 45 g / m 2 The absorbency of the electrolyte was 590% by weight based on the weight of the uncompressed separator. Porosity before compression 64%, porosity after compression with a force of 100 kPa 34% Pore size < 300 nm Pressure loss - 950 Pa / 100 g / m 2

[0087] Figure 3 is an image of the upper surface of the separator taken with a field emission scanning electron microscope (FE SEM).

[0088] A battery cell based on the chemical properties (3D) of NMC / graphite with an electrode thickness of 1 mm configured using this separator had excellent discharge performance (maximum 1000 A), full capacity utilization (500 Wh), and low loss (< 4%).

[0089] Charging from the discharged state can be safely performed at a rate of C / 3 (3 hours). When the cell was overcharged at three times the recommended current, penetration of the lithium separator occurred at a voltage of 4.17V.

[0090] Example 3: Typically, inorganic potassium lime glass fibers having a length in the range of 0.5 to 5 mm and a thickness of 20 to 1500 nm were dispersed in water, and this mixture was diluted and its acidity was adjusted to pH 3. Then, this mixture was poured onto a moving screen where a uniform layer was formed, and this layer was dried at 150 °C to form a porous matrix. Aluminum oxide ceramic particles with an average particle size of 250 nm were introduced into the matrix by a wet method. The ceramic particles penetrated into the interior of the matrix, automatically adhered to the fibers, simultaneously saturated the pores of the matrix, and formed a dense and homogeneous Al2O3 crust on the surface. In this way, the pore size of the composite changed to an average of 150 nm (Figure 4). Next, this composite was dried at 350 °C to form a layer, from which a separator was cut out and used in a battery cell with a three-dimensional electrode having a thickness of 0.5 mm.

[0091] The separator showed the following characteristics: Composition: 88% glass, Al2O3 (12%) Thickness without compression - 0.31 mm Thickness after compression with a force of 100 kPa - 0.17 mm Areal density - 57 g / m 2 The absorbency of the electrolyte was 570% by weight based on the weight of the non-compressed separator. Porosity before compression 81%, porosity after compression with a force of 100 kPa 44% Pore size (statistically determined from an electron microscope) approximately 150 nm Pressure loss - 1050 Pa / 100 g / m 2

[0092] Using this separator, a battery cell based on the chemical properties of NMC / graphite with an electrode thickness of 0.5 mm (3D) was constructed. This battery exhibits excellent performance (maximum peak 1000 A and continuous 120 A), high capacity utilization, and relatively low losses.

[0093] Full charge from the discharged state can be achieved at a rate of C / 1.5 (1.5 hours), and even at such a high rate of cycling, lithium dendrites do not penetrate the separator.

[0094] The graph in Figure 5 shows a smooth voltage curve at a current load of 120 A - a charge and discharge time of approximately 1.5 hours.

[0095] Example 4: Typically, inorganic soda lime glass fibers having a length in the range of 0.5 to 5 mm and a thickness in the range of 20 to 1500 nm were dispersed in water, and this mixture was diluted and its acidity adjusted to pH 3. Then, this mixture was poured onto a movable mesh where a uniform layer was formed, and this layer was dried at 150 °C to produce a porous matrix. Ceramic particles of titanium dioxide having a rutile crystal structure with an average particle size of 250 nm were introduced into the matrix by a wet method. The ceramic particles penetrated inside this matrix. Different from the previous examples, the crystals of titanium dioxide were not mechanically pressed onto the fibers of the matrix for adhesion, but its entire volume was saturated, and thus the voids of the composite were changed to an average of 150 nm. Subsequently, this composite was dried at 350 °C to form a layer, from which a separator was cut out in a desired shape and used for a battery cell having a three-dimensional electrode with a thickness of 0.5 mm.

[0096] The separator showed the following characteristics: Composition: 87% glass, TiO2 (13%) Thickness without compression - 0.32 mm Thickness after compression with a force of 100 kPa - 0.18 mm Areal density 60 g / m 2 The absorbency of the electrolyte was 600% by weight based on the weight of the non-compressed separator. Void fraction before compression: 79%, void fraction after compression with a force of 100 kPa: 45% Pore size (statistically determined from electron microscopy): approximately 150 nm Pressure loss - 1030 Pa / 100 g / m 2

[0097] Using this separator, a battery cell based on the chemical properties of NMC / graphite with an electrode thickness of 0.5 mm (3D) was constructed. This battery exhibited stable discharge performance and low losses. The characteristics of this composite separator are comparable to those of the glass - Al2O3 composite separator in Example 2. Figure 6 shows the details of the cross - section of this separator.

[0098] Example 5: Typically, inorganic borosilicate glass fibers having a length in the range of 0.5 - 5 mm and a thickness of 20 - 1500 nm were dispersed in water. This mixture was continuously diluted with distilled water and its acidity was adjusted to pH 2.5. Then, this mixture was poured through a movable mesh where a uniform layer was formed. This layer was dried at 150 °C to produce a porous matrix. Ceramic nanoparticles of titanium dioxide with anatase - type crystal structure and an average particle size of 50 nm were introduced into the matrix by a wet method. The ceramic particles penetrated into the interior of this matrix, mainly saturating the pores at the upper part of the matrix, forming a homogeneous crust, thereby changing the pore size of the composite to an average of 50 nm. Subsequently, this composite was dried at 350 °C to form a layer, from which a separator was cut out in a desired shape and used in a battery with a three - dimensional electrode having a thickness of 0.5 mm.

[0099] The separator showed the following characteristics: Composition: 90% glass, 10% TiO2 Thickness without compression - 0.44 mm Thickness after compression with a force of 100 kPa - 0.17 mm Areal density - 55 g / m 2 The absorbency of the electrolyte was 590 wt% based on the weight of the matrix before compression. Void fraction before compression: 57%, void fraction after compression with a force of 100 kPa: 22% Pore size (statistically determined from electron microscopy): approximately 50 nm Pressure loss - 1270 Pa / 100 g / m 2

[0100] Figure 7 shows a cross-section through a separator with a thickness of 446 nm, having an oriented matrix nanofiber structure filled with TiO2 nanoparticles penetrated to a depth of approximately 200 micrometers, forming a crust with a pore size of approximately 25 nm. A separator of this thickness and such a small pore size is very difficult to manufacture with conventional polymer layers. Since separators with any pore size can be fabricated in this way, the characteristics of the high-speed charge separator can be effectively altered.

[0101] Figure 8 shows an electron microscope image of the surface of a composite separator using anatase nanoparticles with a particle diameter and pore size of less than 50 nm.

[0102] A battery having the chemical properties of NMC / graphite and an electrode thickness of 0.5 mm (3D) configured using this separator showed a clean charge-discharge pattern even at a relatively fast C / 2 cycle rate (Figure 9).

[0103] Full charge from the discharged state can be achieved at a rate of C / 2 (2 hours), and lithium dendrites do not penetrate the separator.

[0104] Example 6: Inorganic glass fibers typically having a length in the range of 0.5 to 5 mm and a thickness of 20 to 1000 nm were dispersed in water, the mixture was diluted, and its acidity was adjusted to pH 2.5. Subsequently, this mixture was poured through a movable mesh where a uniform layer was formed, and this layer was dried at 150 °C to form a porous matrix. Glass short fibers with a typical length of 5 to 10 μm were introduced into the matrix by a wet method. The short fibers penetrated inside the matrix and mechanically bonded with the fibers of the matrix. Subsequently, this composite was dried at 350 °C to form a layer, and separators were cut out therefrom. These separators were used in a battery having a three-dimensional electrode with a thickness of 0.5 mm.

[0105] The separators showed the following properties: Composition: 100% glass Areal density - 55 g / m 2 Thickness without compression - 0.33 mm Thickness after compression with a force of 100 kPa - 0.17 mm The absorbency of the electrolyte was 610 wt% based on the weight of the matrix before compression. Porosity before compression 76%, porosity after compression with a force of 100 kPa 39% Pore size (statistically determined from electron microscopy) < 300 nm Pressure loss - 1050 Pa / 100 g / m 2

[0106] A battery cell based on the chemical properties of NMC / graphite having an electrode thickness of 1 mm (3D) configured using this separator showed stable performance, low loss, and full capacity utilization (comparable to the separator of Example 2). The stable voltage profile of the cycle is evident from Figure 10.

[0107] Example 7 (comparative example): Commercially available glass paper commonly used in high-end lead-acid batteries was used as the separator. These separators were used / tested in a battery having a three-dimensional electrode of NMC / graphite with a thickness of 0.5 mm.

[0108] The separator exhibited the following characteristics: Composition: 93% glass, 7% PVA Thickness without compression - 0.3 mm Areal density - 60 g / m 2 The cell based on the NMC / graphite chemistry with an electrode thickness of 0.5 mm (3D) configured using this separator has virtually unusable characteristics. Even with a very slow charge of 36 hours, the separator already fails at 3.9 V, which subsequently leads to risks of overcharge, a sharp rise in cell temperature, voltage stagnation, as well as cell failure and explosion. The voltage, current, and temperature profiles are shown in Figure 11.

[0109] Example 8 (Comparative Example) A commercially available 23-μm plastic separator was used in a cell otherwise identical based on the NMC / graphite chemistry (3D) with an electrode thickness of 0.5 mm. The superiority of the inorganic separator is evident from the rapid degradation and significantly higher losses compared to the composite separator according to the present invention. With the inorganic separator, the specific resistance does not increase during cycling, and there is no risk of lithium dendrite growth through the separator.

[0110] Figure 12 shows the current, voltage, and temperature curves for the first 300 cycles. The rapid decrease in capacity is evident from the shortening of the cycle length. The losses during cycling also increase with the increase in internal resistance.

[0111] [Industrial Application] The separator according to the present invention can be used in the manufacture of lithium batteries.

Brief Description of the Drawings

[0112]

Figure 2

Figure 5

Figure 9

Figure 10

Figure 11

Figure 12

Claims

1. A separator for a lithium battery having an electrode with a thickness exceeding 0.1 mm, characterized in that the separator is formed by weaving electrically non-conductive inorganic fibers and optionally non-conductive inorganic particles are added; the length of the fibers is in the range of 0.5 to 30 mm, the thickness of the fibers is in the range of 20 to 1500 nm; the material of the fibers is glass; the pore size of the separator is in the range of 0.02 to 2.5 micrometers, where the pore size of the separator is the average pore size of the separator determined by averaging at least 50 values of the pore diameter read from an electron microscope image; the absorbance of the separator expressed as the weight of 1 M LiPF6 of the immersion electrolyte in ethylene carbonate / dimethyl carbonate with a volume ratio (v:v) = 1:1 is 1 to 10 times the weight of the separator.

2. The porosity of the separator measured for the uncompressed separator is in the range of 50 to 90%, and / or the porosity of the separator measured after compressing the separator with a force of 100 kPa is in the range of 20 to 55%, the separator according to claim 1.

3. At least 90% by weight of the fibers have a thickness in the range of 20 to 500 nm, the separator according to claim 1 or 2.

4. The pore size of the separator is in the range of 20 to 1000 nm, more preferably in the range of 20 to 500 nm, even more preferably in the range of 20 nm to 150 nm, the separator according to any one of claims 1 to 3.

5. Characterized by containing a mixture of non-conductive inorganic particles, the weight ratio of the particles to the total weight of the separator being at most 20% by weight, the non-conductive inorganic particles being particles having a maximum size in the range of 10 to 700 nm, preferably at most 500 nm, more preferably having a maximum size of 200 to 300 nm, or glass fibers having a length of at most 20 micrometers, preferably at most 10 micrometers and a thickness in the range of 20 to 1500 nm, the separator according to any one of claims 1 to 4.

6. The non-conductive inorganic particles are made of a ceramic material selected from the group consisting of silicon oxide, aluminum oxide, zirconium oxide, titanium oxide, silicate, titanate, aluminosilicate, zirconium silicate, basalt, and mixtures thereof, and / or an aluminosilicate or aluminosilicate-based glass having a mixture of alkali oxides such as CaO, MgO, or B ２ O ３ The separator according to claim 5, characterized in that it is made of a glass selected from groups A, C, D, E, R based on aluminoborosilicate or aluminosilicate having a mixture of alkali oxides such as the above.

7. The separator according to any one of claims 1 to 6, characterized in that the thickness of the separator after compression with a force of 100 kPa is in the range of 0.050 to 2 mm.

8. The layer of the separator has an area density in the range of 10 to 200 g / m² with a layer thickness of 100 micrometers, and the separator according to any one of claims 1 to 7 is characterized in that. ２ The separator according to any one of claims 1 to 7, characterized in that it has an area density within the range of 10 to 200 g / m² with a layer thickness of 100 micrometers.

9. The separator according to any one of claims 1 to 8, characterized in that the matrix of the separator is further filled with particles that prevent the movement of polysulfide, preferably selected from the group consisting of titanium dioxide, titanium nitride, graphene, and zirconium oxide.

10. A lithium battery comprising at least one pair of electrodes separated by the separator according to any one of the preceding claims, wherein the ratio of the thickness of the separator layer to the thickness of the electrode is in the range of 1:2 to 1:10, and the electrode preferably has a thickness of 100 micrometers to 4 mm, more preferably 0.3 to 2 mm, and most preferably 0.5 to 1 mm.

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