Negative electrode for sodium-ion battery, method for manufacturing same, and sodium-ion battery including same

Abstract

The present invention relates to a negative electrode for a sodium-ion battery, a method for manufacturing the negative electrode, and a sodium-ion battery comprising the negative electrode, wherein the negative electrode comprises: a negative electrode current collector; and a negative electrode active material layer positioned on at least one surface of the negative electrode current collector, and the negative electrode active material layer comprises hard carbon particles and graphite particles.

Description

Negative electrode for a sodium ion battery, method for manufacturing the same, and sodium ion battery including the same

[0001] The present invention relates to a negative electrode for a sodium ion battery, a method for manufacturing the negative electrode, and a sodium ion battery comprising the negative electrode.

[0002] Sodium is an alkali metal element located adjacent to lithium metal in the periodic table and possesses similar physical and chemical properties. The content of sodium in the Earth's crust is 2.74%, which is much higher than the content of lithium, which is 0.0065%. Sodium-ion batteries have a long cycle life, excellent low-temperature performance, good high-output discharge performance, and excellent safety. Therefore, in specific applications (e.g., start-stop power, large-scale energy storage, home energy storage, electric two-wheelers, etc.), sodium-ion batteries are considered a potential substitute for lithium-ion batteries.

[0003] Among various cathode materials for sodium ion batteries, hard carbon materials are considered to be the most likely to be industrialized first as cathode materials for sodium ion batteries due to their advantages of low cost, excellent electrical conductivity, environmental friendliness, and abundant supply.

[0004] However, in the case of hard carbon materials, the material itself has high mechanical strength, large particle size, and an irregular edge shape in its geometric form. Consequently, when rolling the cathode, the compaction density is low, resulting in an excessively low volume energy density of the cathode and a high liquid injection coefficient. Furthermore, hard carbon materials have a low carbonization temperature and a low degree of graphitization, and their poor electrical conductivity leads to a high resistivity of the electrode. Consequently, the initial efficiency of the sodium-ion battery is low and the scaling performance is poor. These shortcomings clearly hinder the application and development of hard carbon-based sodium-ion batteries.

[0005] One embodiment provides a negative electrode for a sodium ion battery, said negative electrode can achieve high pressure density, peel strength, and low resistivity by mixing graphite particles among hard carbon particles of the negative electrode active material layer.

[0006] Another embodiment provides a method for manufacturing the above-mentioned cathode.

[0007] Another embodiment provides a sodium ion battery comprising the above-mentioned cathode, wherein the sodium ion battery can achieve high initial Coulomb efficiency, energy density and capacity retention rate, and a low liquid injection factor.

[0008] A cathode according to one embodiment comprises: a cathode current collector; and a cathode active material layer located on at least one surface of the cathode current collector; wherein the cathode active material layer comprises hard carbon particles and graphite particles.

[0009] The particle size D of the above hard carbon particles 50 The particle size is 5 μm to 15 μm, and the particle size D of the graphite particles. 10 is 1 μm to 8 μm, and particle size D 50 It can be 3 μm to 15 μm.

[0010] The particle size D of the above hard carbon particles 50 The particle size is 5 μm to 15 μm, and the particle size D of the graphite particles. 10 It is 1 μm to 3 μm, and particle size D 50 It can be 3 μm to 5 μm.

[0011] In the above-mentioned cathode active material layer, the content of graphite particles may be 0.5% to 20% by weight based on 100% by weight of hard carbon particles.

[0012] The thickness of the above negative electrode active material layer may be 20 μm to 200 μm.

[0013] The above-mentioned negative electrode active material layer comprises a first sub-negative electrode active material layer and a second sub-negative electrode active material layer, wherein the first sub-negative electrode active material layer is located on at least one surface of the negative electrode current collector, and the second sub-negative electrode active material layer is located on the first sub-negative electrode active material layer, wherein the first sub-negative electrode active material layer comprises hard carbon particles and graphite particles, and the second sub-negative electrode active material layer may comprise graphite particles.

[0014] The above-mentioned negative active material layer comprises a first sub-negative active material layer, a second sub-negative active material layer, and a third sub-negative active material layer, wherein the third sub-negative active material layer is located on at least one surface of the negative current collector, the first sub-negative active material layer is located on the third sub-negative active material layer, the second sub-negative active material layer is located on the first sub-negative active material layer, the first sub-negative active material layer comprises hard carbon particles and graphite particles, and the second sub-negative active material layer and the third sub-negative active material layer may comprise graphite particles.

[0015] The above-mentioned cathode active material layer may further include a binder and optionally a conductive material.

[0016] In the above cathode active material layer, based on 100 weight% of hard carbon particles, the content of graphite particles may be 5 weight% to 10 weight%.

[0017] A method for manufacturing a negative electrode for a sodium ion battery according to one embodiment comprises: a step of preparing a negative electrode active material layer slurry comprising hard carbon particles, graphite particles, a binder, and optionally a conductive material; a step of applying the negative electrode active material layer slurry to at least one surface of a negative electrode current collector; and a step of drying and roll-pressing the negative electrode current collector coated with the negative electrode active material layer slurry.

[0018] A sodium ion battery according to one embodiment includes the aforementioned negative electrode; a positive electrode; and a separator located between the negative electrode and the positive electrode.

[0019] A negative electrode for a sodium ion battery and a method for manufacturing the same according to one embodiment can provide a negative electrode having high pressure density, peel strength, and low resistivity.

[0020] A sodium ion battery according to one embodiment can achieve high initial Coulomb efficiency, energy density and capacity retention rate, and a low liquid injection factor.

[0021] FIGS. 1a to 1d are schematic cross-sectional views of a negative electrode for a sodium ion battery according to one embodiment.

[0022] FIGS. 2a to 2d are schematic diagrams illustrating a coating process for manufacturing a negative electrode for a sodium ion battery according to one embodiment.

[0023] FIGS. 3 to 6 are structural diagrams of a sodium ion battery according to one embodiment.

[0024] Hereinafter, an embodiment of the present invention will be described in detail. However, the following embodiment is merely an example and the present invention is not limited thereto, and the present invention is limited only by the claims.

[0025] Hereinafter, various embodiments of the present invention will be fully described with reference to the drawings. However, the present invention may be implemented in various different forms and should not be interpreted as being limited to the embodiments described herein. Rather, embodiments are provided to make the present invention thorough and complete and to sufficiently convey the scope of the present invention to those skilled in the art. In the drawings, the sizes of layers and regions may be exaggerated for clarity. Also, in the drawings, some details may be omitted for convenience. Therefore, the drawings should not be interpreted as limiting the present invention in any aspect.

[0026] Unless otherwise specified, when a part such as a layer, membrane, region, plate, etc. is described as being located "on" another part, it may indicate not only a case where the part is "direct" to the other part, but also a situation where another part exists between them.

[0027] Unless otherwise specified, the terms “on ……” or “on ……” in this specification may mean positioned above the target part or positioned below the target part, and do not necessarily mean positioned above the target part with respect to the direction of gravity.

[0028] Unless otherwise specified, the term "A or B" may mean "a, or B, or A and B."

[0029] In the specification, "combination thereof" may mean a mixture of components, a laminate, a composite, a copolymer, an alloy, a comixture, or a reaction product.

[0030] Even if terms such as "identical," "equivalent," or "equivalent" are used in the description of an embodiment, it should be understood that slight differences may exist. Accordingly, if one component or value is described as identical to another component or value, it should be understood to mean that the one component or value is identical to the other component or value within an expected manufacturing or operational tolerance range (e.g., ±10%).

[0031] In the description of one embodiment, where the terms "approximately" or "substantially" are used with numerical values, it should be understood that the relevant numerical values ​​include a tolerance of ±10% near the specified values.

[0032] Unless otherwise defined, "particle size D 50"This may refer to the diameter of the particle at which the cumulative volume in the particle size distribution is 50 volume percent. The particle size distribution can be measured by methods known to those skilled in the art. For example, the particle size distribution can be measured using a particle size analyzer, transmission electron microscope images, or scanning electron microscope images. As another method, the particle size distribution is determined by measuring the particle size using a Dynamic Light Scattering (DLS) measuring device, calculating the number of particles in each particle size range through data analysis, and then the particle size D 50 It can also be calculated. Optionally, the particle size distribution can be measured using laser diffraction. When measuring the particle size distribution by laser diffraction, for example, the particles to be measured are dispersed in a dispersion medium, the dispersion medium is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac's MT 3000), and ultrasound at approximately 28 kHz is irradiated at an output of 60 W to determine the particle size D based on the particle size distribution at 50% of the measuring device. 50 Calculate.

[0033] Unless otherwise defined, "particle size D 10 "It can refer to the diameter of the particle size at which the cumulative volume in the particle size distribution is 10 volume%. The particle size distribution is particle size D 50 It is measured according to the method described in.

[0034] Hereinafter, a negative electrode for a sodium ion battery according to one embodiment of the present invention will be described.

[0035] A negative electrode for a sodium ion battery according to one embodiment comprises a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector. The negative electrode active material layer comprises hard carbon particles and graphite particles.

[0036] Hard carbon can be used as a negative electrode material for sodium-ion batteries, but because hard carbon has high mechanical strength and many grain edges, when rolling the negative electrode active material layer containing hard carbon, the reaction force of the hard carbon particles against the rollers increases, and sufficient sliding does not occur between the particles, resulting in a high porosity and thick thickness of the negative electrode active material layer and a low compacted density of the negative electrode. On another aspect, hard carbon materials have a high degree of disorder and a low degree of graphitization. In the microstructure, the carbon atomic layers of hard carbon are stacked and cross-linked with each other, so the elastic deformation is large and the repulsive force is also large. Consequently, when rolling, the compacted density decreases, which lowers the volumetric energy density of the battery and increases the liquid injection amount. In addition, the conductivity of hard carbon materials is generally relatively low and significantly lower than that of graphite, and the porosity of the negative electrode active material layer containing hard carbon materials is high and the contact between hard carbon particles is poor, resulting in high internal resistance of the negative electrode and poor kinetic performance. Consequently, the initial Coulomb efficiency of the sodium-ion battery is low and the rate performance is reduced.

[0037] In the prior art, a method has been proposed to improve the pressure density of a cathode containing hard carbon using nanomaterials such as nano oxides and sulfides. However, in this prior art, oxides such as silica, aluminum oxide, and molybdenum disulfide, and sulfides are insulating materials, so their addition can lower the conductivity of the cathode and degrade the initial Coulomb efficiency and magnification performance. In addition, since the particle size of the nanomaterial is nanoscale (e.g., less than 1 μm), the nanomaterial cannot sufficiently fill the gaps between the hard carbon particles.

[0038] According to one embodiment of the present invention, a negative electrode for a sodium ion battery (specifically, a negative electrode active material layer) is manufactured by mixing graphite particles with hard carbon particles, thereby realizing a negative electrode having high pressure density, high peel strength, and low resistivity, and improving the energy density, initial Coulomb efficiency, and scaling performance of a sodium ion battery including said negative electrode, reducing the amount of liquid injected, and reducing the cost.

[0039] In one embodiment of the present invention, the graphite particles may be micrometer-sized graphite particles. For example, the particle size D of the graphite particles 10 µm can be about 1 µm to about 8 µm, and the particle size D of the graphite particles 50 µm can be about 3 µm to about 15 µm. For example, the particle size D of the graphite particles 10 µm may be about 1 µm to about 7 µm, about 1 µm to about 6 µm, about 1 µm to about 5 µm, about 1 µm to about 4 µm, or about 1 µm to about 3 µm. For example, the particle size D of the graphite particles 50 It may be about 3 µm to about 15 µm, about 3 µm to about 14 µm, about 3 µm to about 13 µm, about 3 µm to about 12 µm, about 3 µm to about 11 µm, about 3 µm to about 10 µm, about 3 µm to about 9 µm, about 3 µm to about 8 µm, about 3 µm to about 7 µm, about 3 µm to about 6 µm, or about 3 µm to about 5 µm.

[0040] Particle size D of graphite particles 10 can be about 1 μm to about 3 μm. For example, the particle size D of graphite particles 50 µm can be about 3 µm to about 5 µm. For example, the particle size D of graphite particles 10 can be about 1.2 μm to about 2.8 μm, about 1.4 μm to about 2.6 μm, about 1.6 μm to about 2.4 μm, about 1.8 μm to about 2.2 μm, or about 2.0 μm. For example, the particle size D of the graphite particles50 It may be about 3.2 μm to about 4.8 μm, about 3.4 μm to about 4.6 μm, about 3.6 to about 4.4 μm, about 3.8 μm to about 4.2 μm, or about 4.0 μm.

[0041] Within the above range, small-sized graphite particles can fill the pores between the hard carbon particles and between the hard carbon particles and the current collector, thereby improving the lubricity of the hard carbon particles. By mixing large-sized graphite particles with hard carbon particles and forming a uniform layered structure with the hard carbon particles, the contact points between the hard carbon particles and the separator can be reduced, and the edges of the hard carbon particles can be prevented from damaging the separator. Through this structure, the smoothness of the cathode active material layer can be improved, the situation in which the hard carbon particles are damaged under high roll press pressure can be reduced, and at the same time, damage to the separator caused by the hard carbon particles can be prevented. If the particle size of the graphite particles is too large, it is difficult to fill the pores between the hard carbon particles and between the hard carbon particles and the current collector. If the particle size of the graphite particles is too small, the dispersibility of the graphite particles is poor, and they can easily aggregate to form secondary particles. When preparing the cathode active material layer slurry, bubbles can easily remain inside the slurry, resulting in uneven dispersion of the graphite particles and the formation of bubbles on the electrode surface.

[0042] In one embodiment of the present invention, the particle size D of the hard carbon particles 50The particle size is approximately 5 μm to approximately 15 μm, and may be, for example, approximately 6 μm to approximately 14 μm, approximately 7 μm to approximately 13 μm, approximately 8 μm to approximately 12 μm, approximately 9 μm to approximately 11 μm, or approximately 10 μm. When hard carbon particles having the above particle size range are used, a synergistic effect can be obtained in which the hard carbon particles and graphite particles fill the pores and are uniformly stacked. When small-sized graphite particles are sufficiently filled into the pores between the hard carbon particles and between the hard carbon particles and the current collector, they provide lubrication and bearing effects, and in a high-pressure roll press, they can fill and flatten the irregularities on the surface of the hard carbon particles, reduce frictional resistance, and lower the coefficient of friction. At the same time, large-sized graphite particles and hard carbon particles can form a uniform and tight stacked structure. The graphite particles have high sphericity and good flexibility, which improves the smoothness of the cathode and reduces the risk of hard carbon particles piercing and damaging the separator. Under the pressure of a relatively large roll press, the graphite particles provide better buffering, which can prevent the hard carbon particles from being destroyed at high pressure.

[0043] In a cathode according to one embodiment, based on 100 weight% of hard carbon particles, the content of graphite particles may be about 0.5 weight% to about 20 weight%, for example, about 1 weight% to about 19 weight%, about 2 weight% to about 18 weight%, about 3 weight% to about 17 weight%, about 4 weight% to about 16 weight%, about 5 weight% to about 15 weight%, about 6 weight% to about 14 weight%, about 7 weight% to about 13 weight%, about 8 weight% to about 12 weight%, about 9 weight% to about 11 weight%, or about 10 weight%. When the content of graphite particles is within the above range based on 100 weight% of hard carbon particles, the graphite particles can be sufficiently filled into the pores between the hard carbon particles and between the hard carbon and the current collector, and the capacity and energy density of the sodium ion battery can be prevented from being reduced by excessively introducing graphite having low sodium storage activity.

[0044] In one embodiment of the present invention, the thickness of the negative electrode active material layer may be about 20 μm to about 200 μm. For example, the thickness of the negative electrode active material layer may be about 30 μm to about 180 μm, about 40 μm to about 1600 μm, about 60 μm to about 140 μm, or about 80 μm to about 120 μm.

[0045] There are no particular restrictions on the source of the hard carbon particles of the present invention, and they can be purchased commercially or obtained through self-production. For example, hard carbon particles can be obtained by carbonizing needle coke, asphalt tar, petroleum coke, starch, coconut shells, phenolic resin, epoxy resin, rice straw, wood, or a combination thereof.

[0046] As described above, a negative electrode for a sodium ion battery according to one embodiment comprises a negative electrode current collector and a negative electrode active material layer located on at least one surface of the negative electrode current collector. The negative electrode active material layer comprises hard carbon particles and graphite particles, and may further comprise a binder and optionally a conductive material.

[0047] For example, in the cathode active material layer, the weight ratio of hard carbon particles, conductive material, and binder may be (85 to 99):(0 to 5):(1 to 10).

[0048] The binder can bond the negative electrode active material particles (i.e., hard carbon particles and graphite particles) to each other and also attach the negative electrode active material to the current collector. The binder may include a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0049] The non-aqueous binder may include polyvinyl chloride, carboxylated polyvinyl chloride, polyfluoroethylene, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0050] The water-based binder may include styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic acid rubber, butyl rubber, fluororubber, polyoxyethylene, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic acid resin, phenolic resin, epoxy resin, polyvinyl alcohol, or a combination thereof.

[0051] When an aqueous binder is used as a cathode binder, it may further include a cellulose-based compound capable of imparting viscosity. The cellulose-based compound may include carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, alkali metal salts thereof, or combinations thereof. The alkali metal may include Na, K, Li, or combinations thereof.

[0052] The dry binder may include a fibrous polymer material. For example, the dry binder may include polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyoxyethylene, or a combination thereof.

[0053] A conductive material can impart conductivity to an electrode. The conductive material may include any material that conducts electrons without causing chemical changes (e.g., unwanted chemical changes in a sodium-ion battery). Non-limiting examples of conductive materials may include carbon materials, at least one of carbon black, acetylene black, Ketjenblack, SuperP, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials, including at least one of copper, nickel, aluminum, and silver in the form of metal powder or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0054] In one embodiment, since graphite particles have excellent conductivity, they can partially or entirely replace the conductive material and do not significantly affect the electrochemical performance of the battery. That is, the negative electrode active material layer of one embodiment may not include a separate conductive material.

[0055] The present invention does not impose any special limitations on the composition of the negative current collector, and the negative current collector can be selected from among the negative current collectors generally used in the field, and includes but is not limited to aluminum foil or carbon-coated aluminum foil, and its thickness d may be less than 20 μm.

[0056] Hereinafter, a cathode according to one embodiment of the present invention will be described with reference to the drawings.

[0057] FIGS. 1a to 1d are schematic cross-sectional views of a negative electrode for a sodium ion battery according to one embodiment.

[0058] Referring to FIG. 1a, in the above embodiment, the cathode active material layer may have a single-layer structure, and the single-layer structure may include a mixture of hard carbon particles and graphite particles, a binder, and optionally a conductive material. For example, the cathode (20) may include a cathode current collector (21) and a cathode active material layer (22) located on at least one surface of the cathode current collector (21), and the cathode active material layer (22) has a single-layer structure and includes hard carbon particles (221) and graphite particles (222).

[0059] As illustrated in FIG. 1a, in the above embodiment, the graphite particles (222) of small particle size can sufficiently fill the pores between the hard carbon particles (221) to provide lubrication, reduce the friction coefficient between the hard carbon particles (221), and increase sliding friction and rolling friction. The graphite particles (222) and the hard carbon particles (221) can sufficiently slide under a roll press to fill the pores between particles, reduce the particle spacing, increase the contact area between particles, and reduce the porosity of the cathode active material layer (22), thereby improving the pressure density of the cathode active material layer (22) and reducing the liquid injection coefficient. In addition, the conductivity of the graphite particles is much better than that of the hard carbon particles, and the graphite particles (222) with small particle sizes fill the pores, while the graphite particles (222) with large particle sizes and the hard carbon particles (221) form a uniform stacked structure, thereby making the contact between particles tighter and reducing the contact impedance. Accordingly, the electron transfer capability of the negative electrode (20) is significantly improved, and the electrical resistivity is reduced, so that the initial Coulomb efficiency and scaling performance of the battery can be improved.

[0060] Referring to FIG. 1b, in the above embodiment, the negative active material layer may have a two-layer structure. For example, the negative electrode (20) may include a negative current collector (21) and a negative active material layer (22) located on at least one surface of the negative current collector, and the negative active material layer (22) may include a first sub-negative active material layer (210) and a second sub-negative active material layer (220). The first sub-negative active material layer (210) may be located on at least one surface of the negative current collector (21), and the second sub-negative active material layer (220) may be located on the first sub-negative active material layer (210). The first sub-negative active material layer (210) may include hard carbon particles (221) and graphite particles (222), and the second sub-negative active material layer (220) may include graphite particles (222). In other words, the negative electrode active material layer (22) may include a first sub-negative electrode active material layer (210) comprising hard carbon particles (221) and graphite particles (222), and a second sub-negative electrode active material layer (220) comprising graphite particles (222).

[0061] In addition to realizing the beneficial effects realized in one embodiment of FIG. 1a, one embodiment of FIG. 1b can further prevent the edges of hard carbon particles (221) from poking the separator (30) by arranging a second sub-negative active material layer (220) containing graphite particles (222) in contact with the separator (30).

[0062] Referring to FIG. 1c, in the above embodiment, the negative active material layer may have a two-layer structure. For example, the negative electrode (20) may include a negative current collector (21) and a negative active material layer (22) located on at least one surface of the negative current collector, and the negative active material layer (22) may include a first sub-negative active material layer (210) and a second sub-negative active material layer (220). The second sub-negative active material layer (220) may be located on at least one surface of the negative current collector (21), and the first sub-negative active material layer (210) may be located on the second sub-negative active material layer (220). The first sub-negative active material layer (210) may include hard carbon particles (221) and graphite particles (222), and the second sub-negative active material layer (220) may include graphite particles (222). In other words, the negative electrode active material layer (22) may include a first sub-negative electrode active material layer (210) comprising hard carbon particles (221) and graphite particles (222), and a second sub-negative electrode active material layer (220) comprising graphite particles (222).

[0063] Referring to FIG. 1d, in the above embodiment, the negative active material layer may have a three-layer structure. For example, the negative electrode (20) may include a negative current collector (21) and a negative active material layer (22) located on at least one surface of the negative current collector, and the negative active material layer (22) may include a first sub-negative active material layer (210), a second sub-negative active material layer (220), and a third sub-negative active material layer (230). The third sub-negative active material layer (230) may be located on at least one surface of the negative current collector (21), the first sub-negative active material layer (210) may be located on the third sub-negative active material layer (230), and the second sub-negative active material layer (220) may be located on the first sub-negative active material layer (210). The first sub-negative active material layer (210) may include hard carbon particles (221) and graphite particles (222), and the second sub-negative active material layer (220) and the third sub-negative active material layer (230) may include graphite particles (222). In other words, the negative active material layer (22) may include a second sub-negative active material layer (220) and a third sub-negative active material layer (230) containing graphite particles (222), and a first sub-negative active material layer (210) located between the second sub-negative active material layer (220) and the third sub-negative active material layer (230) while containing hard carbon particles (221) and graphite particles (222).

[0064] In addition to realizing the beneficial effects realized in one embodiment of FIG. 1b, one embodiment of FIG. 1d can further improve the adhesion between the cathode active material layer (22) and the cathode current collector (21) by arranging a third sub-cathode active material layer (230) containing graphite particles (222) while in contact with the cathode current collector (21), thereby improving the peel strength of the cathode.

[0065] A method for manufacturing a cathode according to one embodiment of the present invention will be described below with reference to the drawings.

[0066] FIGS. 2a to 2d are schematic diagrams illustrating a coating process for manufacturing a negative electrode for a sodium ion battery according to one embodiment.

[0067] Referring to FIG. 2a, a cathode active material layer slurry comprising hard carbon particles, graphite particles, a binder, and optionally a conductive material is applied onto a cathode current collector using a single-layer coating method, and then a cathode can be obtained through drying, roll pressing, vacuum drying, and cutting. The cathode obtained through the coating process of FIG. 2a corresponds to the cathode shown in FIG. 1a.

[0068] Referring to FIG. 2b, a first sub-negative active material layer slurry and a second sub-negative active material layer slurry can be applied onto a negative current collector using a two-layer coating method to form a first sub-negative active material layer located on at least one surface of the negative current collector and a second sub-negative active material layer located on the first sub-negative active material layer. The first sub-negative active material layer slurry may include hard carbon particles, graphite particles, a binder, and optionally a conductive material, and the second sub-negative active material layer slurry may include graphite particles, a binder, and optionally a conductive material. The negative electrode obtained through the coating process of FIG. 2b corresponds to the negative electrode shown in FIG. 1b.

[0069] Referring to FIG. 2c, a first sub-negative active material layer slurry and a second sub-negative active material layer slurry can be applied onto a negative current collector using a two-layer coating method to form a first sub-negative active material layer located on at least one surface of the negative current collector and a second sub-negative active material layer located on the first sub-negative active material layer. The first sub-negative active material layer slurry comprises graphite particles, a binder, and optionally a conductive material, and the second sub-negative active material layer slurry comprises hard carbon particles, graphite particles, a binder, and optionally a conductive material. The negative electrode obtained through the coating process of FIG. 2c corresponds to the negative electrode shown in FIG. 1c.

[0070] Referring to FIG. 2d, a first sub-negative active material layer slurry, a second sub-negative active material layer slurry, and a third sub-negative active material layer slurry can be applied onto a negative current collector using a three-layer coating method to form a third sub-negative active material layer located on at least one surface of the negative current collector, a first sub-negative active material layer located on the third sub-negative active material layer, and a second sub-negative active material layer located on the first sub-negative active material layer. The first sub-negative active material layer slurry may comprise hard carbon particles, graphite particles, a binder, and optionally a conductive material, and the second sub-negative active material layer and the third sub-negative active material layer slurry may comprise graphite particles, a binder, and optionally a conductive material. The negative electrode obtained through the coating process of FIG. 2d corresponds to the negative electrode shown in FIG. 1d.

[0071] A cathode active material layer with a different structure can be obtained through the coating process illustrated in FIGS. 2a to 2d. For example, a two-layer cathode active material layer comprising a lower layer and an upper layer can be obtained through a two-layer coating method. The lower layer is a hard carbon / graphite layer acting as a sodium-storage active layer, which can ensure a higher sodium storage capacity (generally 300 mAh / g or more). The upper layer is a graphite layer acting as a smooth buffer layer, which prevents direct contact between the hard carbon particles and the separator, reduces the risk of puncturing the separator, and reduces the risk of the hard carbon particles being crushed under high roll pressure. For example, a three-layer cathode active material layer comprising a lower layer, an intermediate layer, and an upper layer can be obtained through a multilayer coating method. The lower layer is a graphite layer acting as a high-peel strength layer, which can improve the peel strength of the cathode active material layer. The middle layer is a hard carbon / graphite layer that acts as a sodium storage active layer and can ensure a high sodium storage capacity (typically 300 mAh / g or more). The upper layer is a graphite layer that acts as a smooth buffer layer and can prevent direct contact between the hard carbon and the separator, reduce the risk of puncturing the separator, and reduce the risk of hard carbon particles being crushed under high roll pressure.

[0072] Hereinafter, a sodium ion battery including a negative electrode for a sodium ion battery according to one embodiment of the present invention will be described.

[0073] A sodium ion battery according to one embodiment of the present invention may include a negative electrode, a positive electrode, a separator located between the negative electrode and the positive electrode, and an electrolyte for impregnating the negative electrode and the positive electrode.

[0074] The negative electrode may be the negative electrode for the sodium ion battery described above.

[0075] The present invention does not particularly limit the composition and structure of the anode and may refer to general anodes in the field. Specifically, the anode may include an anode current collector and an anode active material layer located on at least one surface of the anode current collector.

[0076] In one embodiment, the positive active material layer comprises a positive active material, a conductive material, and a binder.

[0077] Specifically, the positive electrode active material includes, but is not limited to, layered metal oxides, polyanionic compounds, Prussian blue / white compounds, or combinations thereof.

[0078] The present invention does not particularly limit the composition and structure of the separator, but may select a separator commonly used in the field, and includes, but is not limited to, polypropylene (PP) separators and polyethylene (PE) separators. For example, it may include a separator comprising two layers or multiple layers of polyethylene, polypropylene, and polyvinylidene fluoride, and may be, for example, a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator, etc.

[0079] There are no particular limitations on the type of electrolyte of the present invention, and an electrolyte generally used in the field may be selected. It includes, but is not limited to, one or more sodium salts of NaPF6, NaFSI, NaDFOB, and NaPO2F2, solvents such as propylene carbonate (PC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and diethyl carbonate (DEC), and one or more additives of fluoroethylene carbonate (FEC), ethylene sulfate (DTD), propylene-1,3-sulfonic acid lactone (PST), and ascorbic acid (VC).

[0080] The present invention does not particularly limit the method of manufacturing a sodium ion battery, and it can be manufactured by referring to general methods in the field.

[0081] In one embodiment, a sodium ion battery can be manufactured through the following steps: slurry homogenization → coating → roll press → cutting → stacking → electrode tab welding → aluminum plastic film heat sealing → liquid injection → formation and grading.

[0082] A sodium ion battery according to one embodiment of the present invention will be described below with reference to the drawings.

[0083] FIGS. 3 to 6 are structural diagrams of a sodium ion battery according to one embodiment.

[0084] FIG. 3 shows a cylindrical battery, FIG. 4 shows a prismatic battery, and FIG. 5 and FIG. 6 show a pouch-type battery. Referring to FIG. 3 to FIG. 6, a sodium ion battery (100) may include an electrode assembly (40) and a case (50). The electrode assembly (40) may include a positive electrode (10), a negative electrode (20), and a separator (30) between the positive electrode (10) and the negative electrode (20). The electrode assembly (40) may be accommodated in the case (50). The positive electrode (10), the negative electrode (20), and the separator (30) may be impregnated with an electrolyte (not shown). As shown in FIG. 3, the sodium ion battery (100) may include a sealing member (60) that seals the case (50). In FIG. 4, the sodium ion battery (100) may include a positive lead tab (11), a positive terminal (12), a negative lead tab (21), and a negative terminal (22). As illustrated in FIG. 5 and FIG. 6, the sodium ion battery (100) may include an electrode tab (70) illustrated in FIG. 6 or a positive electrode tab (71) and a negative electrode tab (72) illustrated in FIG. 5, and the electrode tabs (70 / 71 / 72) may include electrode tabs (70 / 71 / 72) that form an electrical path for guiding the current formed in the electrode assembly (40) to the outside.

[0085] The present invention will be described in more detail below with reference to specific examples. However, these examples are provided for illustrative purposes only and should not be interpreted as limiting the present invention in any way.

[0086] Example 1

[0087] Step 1: Preparation of a negative electrode for a sodium-ion battery

[0088] Particle size D 50 These 10 µm hard carbon particles, Super P (SP), sodium carboxymethylcellulose (CMC), and styrene-butadiene rubber (SBR) were dispersed in pure water in a weight ratio of 96.5:1:1.0:1.5. Then, particle size D 10This is 2 μm, and particle size D 50 Graphite particles of 4 μm were added, and the weight ratio of the graphite particles (mass) to the hard carbon particles was 5:100. The mixture was uniformly dispersed using a stirrer to prepare a cathode active material layer slurry with a solid content of 45%.

[0089] Using the single-layer coating method illustrated in Fig. 2a, the cathode active material layer slurry was coated on both sides of an aluminum foil with a thickness of 13 μm as a cathode current collector, dried for 10 minutes at 100°C, and then a cathode was obtained through roll pressing, vacuum drying, and cutting.

[0090] Step 2: Preparation of the anode

[0091] Particle size D 50 This is a layered oxide NaNi with a thickness of 8±1 µm. 0.33 Fe 0.33 Mn 0.34 O2 (NFM), SP, and polyvinylidene fluoride (PVDF) were dispersed in N-methyl-2-pyrrolidone (NMP) in a weight ratio of 97.7:1.0:1.3 and uniformly dispersed using a stirrer to prepare an anode active material layer slurry with a solid content of 65%.

[0092] The above-mentioned positive active material layer slurry was applied to both sides of an aluminum foil with a thickness of 13 μm as a positive current collector, and a general positive coating process in the field was used for the application process. The NFM positive was obtained by drying at 120°C for 10 minutes, followed by roll pressing and cutting.

[0093] Step 3: Assembly of the sodium-ion battery

[0094] The cathode obtained in Step 1, the anode obtained in Step 2, and the separator were stacked in a Z-type stacking manner, and processes such as tab welding → aluminum plastic film heat sealing → liquid injection (electrolyte injection) → formation and capacity grading were carried out to finally manufacture a pouch cell. The electrolyte comprises 10 wt% NaPF6, 50 wt% propylene carbonate (PC), 35 wt% ethyl methyl carbonate (EMC), 4 wt% fluoroethylene carbonate (FEC), 0.4 wt% 1-propene-1,3-sulfone (PST), and 0.6 wt% ethylene sulfate (DTD) in weight percent.

[0095] Example 2

[0096] The present embodiment provides a cathode and a sodium ion battery, and the method of manufacturing the same is substantially the same as in Example 1, but the difference is that in the manufacturing process of the cathode, the mixing weight ratio of graphite particles and hard carbon particles is 6:100.

[0097] Example 3

[0098] The present embodiment provides a cathode and a sodium ion battery, and the method of manufacturing the same is substantially the same as in Example 1, but the difference is that in the manufacturing process of the cathode, the mixing weight ratio of graphite particles and hard carbon particles is 7.5:100.

[0099] Example 4

[0100] The present embodiment provides a cathode and a sodium ion battery, and the method of manufacturing the same is substantially the same as in Example 1, but the difference is that in the manufacturing process of the cathode, the mixing weight ratio of graphite particles and hard carbon particles is 10:100.

[0101] Example 5

[0102] This embodiment provides a negative electrode and a sodium ion battery, and the method of manufacturing the same is substantially the same as in Example 1, but the difference is that D of the hard carbon particles 50Adjusted to 15 μm, and D of the graphite particles 50 Adjusted to 12 μm, and D of the graphite particles 10 The value was adjusted to 6 μm.

[0103] Example 6

[0104] This embodiment provides a negative electrode and a sodium ion battery, and the method of manufacturing the same is substantially the same as in Example 1, but the difference is that D of the hard carbon particles 50 Adjusted to 5 μm, and D of graphite particles 50 Adjusted to 3 μm, and D of the graphite particles 10 The value was adjusted to 1 μm.

[0105] Example 7

[0106] The present embodiment provides a cathode and a sodium ion battery, and the method of manufacturing the same is substantially the same as in Example 1, but the difference is that in the process of manufacturing the cathode, the mixing weight ratio of hard carbon, SP, CMC, and SBR is 97.5:0:1.0:1.5, and the mixing weight ratio of graphite particles and hard carbon particles is 10:100.

[0107] Example 8

[0108] The present embodiment provides a negative electrode and a sodium ion battery, and the method of manufacturing the same is substantially the same as that of Example 4, but the difference is that in the process of manufacturing the negative electrode, the two-layer coating method shown in FIG. 2b is used, and a hard carbon / graphite mixed slurry is applied to the lower layer and a graphite slurry is applied to the upper layer. The graphite slurry is prepared such that the weight ratio of graphite:CMC:SBR is 97.5:1.0:1.5 and the solid content is 45%.

[0109] Example 9

[0110] The present embodiment provides a negative electrode and a sodium ion battery, and the method of manufacturing the same is substantially the same as that of Example 4, but the difference is that in the process of manufacturing the negative electrode, the multilayer coating method shown in FIG. 2c is used, and a graphite slurry is applied to the bottom layer and a hard carbon / graphite mixed slurry is applied to the top layer. The graphite slurry was prepared such that the weight ratio of graphite:CMC:SBR is 97.5:1.0:1.5 and the solid content is 45%.

[0111] Example 10

[0112] The present embodiment provides a cathode and a sodium ion battery, and the method of manufacturing the same is substantially the same as that of Example 4, but the difference is that in the process of manufacturing the cathode, the multilayer coating method shown in FIG. 2d is used, the bottom layer is coated with a graphite slurry, the middle layer is coated with a hard carbon / graphite mixed slurry, and the top layer is coated with a graphite slurry. The graphite slurry was prepared such that the weight ratio of graphite:CMC:SBR is 97.5:1.0:1.5, and the solid content is 45%.

[0113] Comparative Example 1

[0114] The present comparative example provides a negative electrode and a sodium ion battery, and the method of manufacturing the same is substantially the same as Example 1, but the difference is that graphite material is not added during the manufacturing process of the negative electrode.

[0115] Comparative Example 2

[0116] The present comparative example provides a cathode and a sodium ion battery, and the method of manufacturing the same is substantially the same as Example 1, but the difference is that in the process of manufacturing the cathode, graphite particles were replaced with a mixed material of nano SiO2 and MoS2 in which the mass ratio of SiO2 to MoS2 is 3:1.

[0117] Comparative Example 3

[0118] The present comparative example provides a negative electrode and a sodium ion battery, the method of manufacturing thereof is substantially the same as Example 1, the difference being that in the process of manufacturing the negative electrode, graphite particles are used to form a nanographene sheet of equal mass (particle size D 50 It was replaced with 300 nm.

[0119] Comparative Example 4

[0120] The present comparative example provides a negative electrode and a sodium ion battery, the method of manufacturing thereof is substantially the same as that of Example 1, the difference being that in the process of manufacturing the negative electrode, graphite particles are equal mass of nanofullerene C60 (particle size D 50 It was replaced with 300 nm.

[0121] Comparative Example 5

[0122] The present comparative example provides a negative electrode and a sodium ion battery, and the method of manufacturing the same is substantially the same as Example 6, the difference being that in the process of manufacturing the negative electrode, graphite particles were not added to the lower hard carbon / graphite layer, and only the hard carbon layer was used.

[0123] Comparative Example 6

[0124] The present comparative example provides a negative electrode and a sodium ion battery, and the method of manufacturing the same is substantially the same as Example 7, the difference being that in the process of manufacturing the negative electrode, graphite particles were not added to the hard carbon / graphite layer of the intermediate layer, and only the hard carbon layer was used.

[0125]

[0126] Evaluation example

[0127] Evaluation of cathode pressure density

[0128] The cathodes of the examples and comparative examples were each rolled while gradually applying pressure from 0 to 50 t, and after measuring the electrode thickness, the maximum pressure density that the electrode can achieve was determined by comprehensively considering the surface condition of the electrode, and the value was listed in Table 1.

[0129] Evaluation of cathode electrical resistivity

[0130] The total electrical resistivity of the cathodes of the above examples and comparative examples, i.e., the sum of the electrical resistance of the active material layer, the contact resistance between the active material layer and the current collector, and the resistance of the current collector, was directly measured using the double-plane controllable pressure disc electrode resistance method with a BER series multifunction electrode resistance meter, and the values ​​were listed in Table 1.

[0131] Peel strength evaluation

[0132] The cathodes of the above examples and comparative examples were cut into samples of 25 mm × 150 mm in size and fixed to the center of a 30 mm × 200 mm slide glass with tape. Then, the 90° peel strength was measured while peeling the cathode current collector from the cathode active material layer using a universal testing machine (UTM). The results are shown in Table 1.

[0133] Evaluation of initial Coulomb efficiency of a battery

[0134] In a constant current charge / discharge mode, the sodium ion batteries of the examples and comparative examples were charged to an upper limit voltage of 3.8V at a current density of 0.2C, then constant voltage charging was performed at 3.8V until a cutoff current of 0.05C was reached, and then discharged again at 0.2C until a cutoff voltage of 2.0V was reached. After recording the initial charge capacity (Q1) and initial discharge capacity (Q2) of the battery, the initial Coulomb efficiency of the battery was calculated according to Q2 / Q1. The results are shown in Table 2.

[0135] Evaluation of liquid injection coefficient

[0136] A fresh cell was taken immediately after assembly and weighed, and the total weight (g1) was recorded. After disassembling the cell, the weight of the dry electrode (g2) and the weight of the structural member (g3) were measured to obtain the amount of liquid injected (g = g1 - g2 - g3). Then, the injection liquid coefficient was calculated using [amount of liquid injected / cell capacity], with the unit being g / Ah. The results are shown in Table 2.

[0137] Energy density evaluation

[0138] The energy density of each of the sodium ion batteries of the above examples and comparative examples was measured. The measurement results are shown in Table 2.

[0139] The energy density was calculated by Equation 1.

[0140] [Equation 1]

[0141] Energy density (ampere-hours / liter (Ah / L)) = [(negative electrode area capacity / total thickness of the cell) × average voltage]

[0142] Area capacity in Equation 1 (milliampere-hour / square centimeter (mAh / cm²)) 2 )) is the value obtained by dividing the total amount of current passing through the battery by the geometric area of ​​the electrode.

[0143] Capacity retention rate evaluation

[0144] The sodium ion batteries of the above examples and comparative examples were charged and discharged 200 times at 25°C under 2C charging conditions (CC / CV, 4.45V, 0.025C cut-off) and 2.0C discharging conditions (CC, 2.5V cut-off), and the capacity retention rate was evaluated according to Equation 1.

[0145] [Equation 1]

[0146] Capacity Retention Rate (%) = (Discharge Capacity after 200 Cycles / Discharge Capacity after 1 Cycle) × 100

[0147] No. Cathode pressure density (g / cm²) 3Electrical resistivity of the cathode (mΩ·cm) Peel strength (N / m) Example 1 1.0 80.3 618.9 Example 2 1.1 20.3 319.5 Example 3 1.1 50.2 621.4 Example 4 1.2 10.2 023.8 Example 5 1.1 00.3 719.2 Example 6 1.0 70.3 418.4 Example 7 1.1 60.2 522.6 Example 8 1.0 70.2 123.4 Example 9 1.0 80.2 124.2 Example 101.130.2025.5 Comparative Example 10.920.5215.7 Comparative Example 21.060.5817.4 Comparative Example 31.010.4218.0 Comparative Example 41.050.5917.2 Comparative Example 51.030.3315.6 Comparative Example 61.030.2818.4

[0148] As shown in Table 1, the cathodes of Examples 1 to 10 exhibit higher pressure density, lower electrical resistivity, and higher peel strength than the cathodes of Comparative Examples 1 to 6. This is because the pressure density and peel strength of the cathode can be effectively improved and electrical resistance reduced by mixing the graphite particles described above into the hard carbon cathode active material layer and filling the pores of the hard carbon particles with the graphite particles.

[0149] In addition, as shown in Table 1, the peel strength of Example 10 is the highest, which is because a third sub-negative active material layer containing graphite particles is formed in contact with the negative current collector, thereby effectively improving the adhesion between the negative active material layer and the negative current collector.

[0150] In addition, the cathodes of Comparative Examples 3 and 4, which have nanoscale graphene and fullerene C60 added, exhibit lower pressure densities than the cathodes of Examples 1 to 10.

[0151] No. Liquid injection coefficient (g / Ah) 0.2C Initial Coulomb efficiency (%) Energy density (Wh·L) -1) 2C Capacity Retention Rate (%) Example 1 4.986.82 10.385.6 Example 2 4.787.12 15.286.4 Example 3 4.487.02 15.788.1 Example 4 4.486.92 19.489.6 Example 5 4.887.22 09.885.9 Example 6 5.186.42 08.485.2 Example 74.187.62 3.591.8 Example 8 4.986.32 16.390.4 Example 9 4.986.12 15.990.1 Example 104.786.5213.589.8 Comparative Example 16.578.1196.675.3 Comparative Example 25.584.3205.480.0 Comparative Example 35.783.2209.683.4 Comparative Example 45.584.2205.681.2 Comparative Example 55.687.1214.388.5 Comparative Example 65.687.4210.587.5

[0152] As shown in Table 2, the cathodes of Examples 1 to 10 exhibit a lower liquid injection coefficient than the cathodes of Comparative Examples 1 to 6.

[0153] In addition, the sodium ion batteries of Comparative Examples 1 and 2, which do not have graphite added to the negative electrode active material layer or only have nano SiO2 and MoS2 added, exhibit relatively low energy density and capacity retention rate.

[0154] In addition, the sodium ion batteries of Comparative Examples 3 and 4, which have nanoscale graphene and fullerene C60 added to the negative electrode active material layer, exhibit a higher liquid injection coefficient than the sodium ion batteries of Examples 1 to 10.

[0155] A cathode according to one embodiment can achieve high pressure density, peel strength, and low resistivity by mixing graphite particles with hard carbon particles. A sodium ion battery including the cathode according to one embodiment can achieve high initial Coulomb efficiency, energy density, capacity retention rate, and a low liquid injection factor.

[0156] Although one embodiment of the present invention has been described above, the scope of the present invention is not limited thereto, and various modifications may be made within the scope of the claims, the detailed description of the present invention, and the drawings, and such modifications are also included within the scope of the present invention.

[0157] [Explanation of the symbol]

[0158] 100: Sodium ion battery 10: Positive electrode

[0159] 11: Positive lead tab 12: Positive terminal

[0160] 20: Cathode 21: Cathode current collector

[0161] 22: Cathode active material layer 210: First sub-cathode active material layer

[0162] 220: Second sub-negative electrode active material layer 230: Third sub-negative electrode active material layer

[0163] 221: Hard carbon particles 222: Graphite particles

[0164] 30: Separator 40: Electrode assembly

[0165] 50: Case 60: Sealing member

[0166] 70: Electrode tab 71: Positive electrode tab

[0167] 72: Cathode electrode tab

Claims

1. In a negative electrode for a sodium ion battery, The above cathode is, cathode current collector; and A negative electrode active material layer located on at least one surface of the above-mentioned negative electrode current collector; comprising The above-described negative electrode active material layer comprises hard carbon particles and graphite particles, for a sodium ion battery negative electrode.

2. In Paragraph 1, Particle size D of hard carbon particles 50 The is 5 μm to 15 μm, and Particle size D of the above graphite particles 10 is 1 μm to 8 μm, and particle size D 50 A negative electrode for a sodium ion battery, having a thickness of 3 μm to 15 μm.

3. In Paragraph 1, Particle size D of hard carbon particles 50 The is 5 μm to 15 μm, and Particle size D of the above graphite particles 10 It is 1 μm to 3 μm, and particle size D 50 A negative electrode for a sodium ion battery, having a thickness of 3 μm to 5 μm.

4. In Paragraph 1, A negative electrode for a sodium ion battery, wherein, in the above negative electrode active material layer, the content of graphite particles is 0.5% to 20% by weight based on 100% by weight of hard carbon particles.

5. In Paragraph 1, A negative electrode for a sodium ion battery, wherein the thickness of the negative electrode active material layer is 20 μm to 200 μm.

6. In Paragraph 1, The above negative electrode active material layer includes a first sub-negative electrode active material layer and a second sub-negative electrode active material layer, and The first sub-negative active material layer is located on the at least one surface of the negative current collector, and the second sub-negative active material layer is located on the first sub-negative active material layer. The first sub-negative active material layer comprises hard carbon particles and graphite particles, and The above second sub-negative active material layer comprises graphite particles, a negative electrode for a sodium ion battery.

7. In Paragraph 1, The above-mentioned negative electrode active material layer includes a first sub-negative electrode active material layer, a second sub-negative electrode active material layer, and a third sub-negative electrode active material layer, and The third sub-negative active material layer is located on at least one surface of the negative current collector, the first sub-negative active material layer is located on the third sub-negative active material layer, and the second sub-negative active material layer is located on the first sub-negative active material layer. The first sub-negative active material layer comprises hard carbon particles and graphite particles, and A negative electrode for a sodium ion battery, wherein the second sub-negative active material layer and the third sub-negative active material layer comprise graphite particles.

8. In Paragraph 1, The above negative electrode active material layer further comprises a binder and optionally a conductive material, for a negative electrode for a sodium ion battery.

9. In Paragraph 1, A negative electrode for a sodium ion battery, wherein, in the above negative electrode active material layer, the content of graphite particles is 5% to 10% by weight based on 100% by weight of hard carbon particles.

10. A method for manufacturing a negative electrode for a sodium ion battery, A step of preparing a negative electrode active material layer slurry comprising hard carbon particles, graphite particles, a binder, and optionally a conductive material; A step of applying the above-mentioned cathode active material layer slurry to at least one surface of a cathode current collector; and A method for manufacturing a negative electrode for a sodium ion battery, comprising the step of drying and roll-pressing the negative current collector coated with the negative active material layer slurry.

11. In sodium ion batteries, A cathode according to any one of claims 1 to 9; Anode; and A sodium ion battery comprising a separator located between the cathode and the anode.

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