Negative electrode for sodium-ion batteries, method of manufacturing the same, and sodium-ion battery comprising the same

Abstract

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

Description

Technical Field

[0001] Examples of this disclosure relate to a negative electrode for a sodium-ion battery and a sodium-ion battery including the negative electrode. Background Technology

[0002] Sodium is an alkali metal element, adjacent to lithium in the periodic table, and possesses similar physicochemical properties. Furthermore, sodium constitutes 2.74% of the Earth's crust, far exceeding lithium's 0.0065%. Sodium-ion batteries exhibit long cycle life, excellent low-temperature performance, good high-power discharge performance, and superior safety. Therefore, in certain specific applications (such as start-stop power supplies, large-scale energy storage, home energy storage, and electric two-wheelers), sodium-ion batteries are considered a potential alternative to lithium-ion batteries.

[0003] Among the many anode materials for sodium-ion batteries, hard carbon materials are considered the most likely to be industrialized first for sodium-ion secondary batteries due to their advantages such as low cost, good conductivity, environmental friendliness, and abundant sources.

[0004] However, hard carbon anode materials have high mechanical strength, large particle size, and irregular angular morphology, resulting in low compaction density during rolling. This leads to excessively low volumetric energy density and a high liquid injection coefficient. Furthermore, hard carbon materials have low carbonization temperatures, low graphitization degrees, and poor electrical conductivity, resulting in high electrode resistivity. This leads to low initial efficiency and poor rate performance in sodium-ion batteries. These shortcomings significantly hinder the application and development of hard carbon-based sodium-ion batteries. Summary of the Invention

[0005] One example embodiment provides a negative electrode for sodium-ion batteries that achieves high compaction density, peel strength, and low resistivity by incorporating graphite particles into the hard carbon particles of the negative electrode active material layer.

[0006] Another example embodiment provides a method for manufacturing the above-described negative electrode.

[0007] Another example embodiment provides a sodium-ion battery including the above-described negative electrode, which achieves high initial coulombic efficiency, energy density and capacity retention, as well as a low fill factor.

[0008] The negative electrode according to an example embodiment includes: a negative current collector; and a negative active material layer located on at least one surface of the negative current collector, the negative active material layer comprising hard carbon particles and graphite particles.

[0009] In the example embodiment, the hard carbon particles have a particle size D50 of 5 μm to 15 μm, and the graphite particles have a particle size D10 of 1 μm to 8 μm and a particle size D50 of 3 μm to 15 μm.

[0010] In the example embodiment, the hard carbon particles have a particle size D50 of 5 μm to 15 μm, and the graphite particles have a particle size D10 of 1 μm to 3 μm and a particle size D50 of 3 μm to 5 μm.

[0011] In an example embodiment, the content of graphite particles in the negative electrode active material layer is from 0.5 wt% to 20 wt%, based on 100 wt% hard carbon particles.

[0012] In the example embodiment, the thickness of the negative electrode active material layer is in the range of 20 μm to 200 μm.

[0013] In an example embodiment, the negative electrode active material layer includes a first sub-negative electrode active material layer and a second sub-negative electrode active material layer. 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. The first sub-negative electrode active material layer includes hard carbon particles and graphite particles, and the second sub-negative electrode active material layer includes graphite particles.

[0014] In an example embodiment, the 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. The third sub-negative electrode active material layer is located on at least one surface of the negative electrode current collector. The first sub-negative electrode active material layer is located on the third sub-negative electrode active material layer, and the second sub-negative electrode active material layer is located on the first sub-negative electrode active material layer. The first sub-negative electrode active material layer includes hard carbon particles and graphite particles, and the second and third sub-negative electrode active material layers include graphite particles.

[0015] In an example embodiment, the negative electrode active material layer further includes a binder and an optional conductive material.

[0016] In an example embodiment, the content of graphite particles in the negative electrode active material layer is 5 wt% to 10 wt%, based on 100 wt% hard carbon particles.

[0017] The method for manufacturing a negative electrode for a sodium-ion battery as described above, according to an example embodiment, includes: preparing a negative electrode active material layer slurry, the negative electrode active material layer slurry comprising hard carbon particles, graphite particles, a binder, and optionally a conductive material; coating the negative electrode active material layer slurry onto at least one surface of a negative electrode current collector; and baking and rolling the negative electrode current collector coated with the negative electrode active material layer slurry.

[0018] A sodium-ion battery according to an example embodiment includes: a negative electrode as described above; a positive electrode; and a separator located between the negative electrode and the positive electrode. Attached Figure Description

[0019] Figures 1A to 1D This is a schematic cross-sectional view showing the negative electrode for a sodium-ion battery according to an example embodiment.

[0020] Figures 2A to 2D This is a schematic diagram illustrating a coating process for manufacturing a negative electrode for a sodium-ion battery according to an example embodiment.

[0021] Figures 3 to 6 This is a schematic diagram of the structure of a sodium-ion battery according to an example embodiment. Detailed Implementation

[0022] Example embodiments of the present disclosure are described in detail below. However, these embodiments are presented by way of example, and the present disclosure is not limited thereto, and is limited only by the scope of the appended claims.

[0023] In the following description, various exemplary embodiments of the present disclosure will be described more fully with reference to the accompanying drawings. However, the present disclosure may be embodied in many different forms and should not be construed as limiting itself to the exemplary embodiments set forth herein. Rather, these embodiments are provided so that the present disclosure will be thorough and complete, and these exemplary embodiments will fully convey the scope of the present disclosure to those skilled in the art. In the drawings, the dimensions of layers and regions may be exaggerated for clarity. Furthermore, some details may be omitted in the drawings for ease of illustration. Therefore, the drawings should not be construed as limiting the present disclosure in any way.

[0024] Unless otherwise stated herein, when a part such as a layer, membrane, region, plate, etc., is described as being disposed “on” another part, it means not only that the part is “directly on” the other part, but also that there are other parts between them.

[0025] Unless otherwise stated herein, the terms "on" or "above" in this specification may refer to being positioned above or below the target part, and not necessarily to being positioned on the upper side of the target part based on the direction of gravity.

[0026] Unless otherwise stated, the term "A or B" may mean "including A, including B, or including both A and B".

[0027] In this specification, "combination thereof" may mean a mixture, stack, complex, copolymer, alloy, blend, or reaction product of the components.

[0028] Although the terms “same,” “equal,” or “equivalent” are used in the description of the example embodiments, it should be understood that some minor deviations may exist. Therefore, when an element or value is said to be the same as another element or value, it should be understood that one element or value is the same as the other element or value within the expected range of manufacturing or operating tolerances (e.g., ±10%).

[0029] Unless otherwise defined herein, “particle size D50” can refer to the diameter of particles that constitute 50% of the total volume in the particle size distribution. Particle size distribution can be measured by methods known to those skilled in the art. For example, particle size distribution can be measured using a particle size analyzer, transmission electron microscopy (TEM) images, or scanning electron microscopy (SEM) images. Alternatively, particle size distribution can be obtained by measuring particle size using a measuring device that utilizes dynamic light scattering, performing data analysis to count the number of particles in each particle size range, and then calculating the particle size D50 from this data. Optionally, particle size distribution can be measured using laser diffraction. When measuring particle size distribution by laser diffraction, for example, the particle size D50 can be calculated based on the 50% particle size distribution in the measuring device by dispersing the particles to be measured in a dispersion medium, introducing the dispersion medium into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), and irradiating the device with ultrasound at an output of approximately 28 kHz at 60 W.

[0030] Unless otherwise defined herein, “particle size D10” may refer to the diameter of particles that constitute 10% of the total volume in the particle size distribution. The particle size distribution may be obtained by the method described in particle size D50.

[0031] In the following, a negative electrode for a sodium-ion battery according to an exemplary embodiment of the present disclosure will be described.

[0032] The negative electrode for a sodium-ion battery according to an example embodiment includes 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 includes hard carbon particles and graphite particles.

[0033] Hard carbon materials can be used as anode materials in sodium-ion batteries. However, due to the high mechanical strength and numerous angular particles of hard carbon, the reaction force of hard carbon particles on the rollers is significant during the rolling process of the anode active material layer containing hard carbon. This makes it difficult for the particles to slide sufficiently, resulting in high porosity and a large thickness of the anode active material layer, leading to a low compaction density of the anode. Furthermore, hard carbon materials have high disorder and low graphitization. In their microstructure, the stacking and cross-linking of carbon atom layers in hard carbon result in large elastic strain and rebound, further contributing to a low compaction density during rolling. This leads to a lower volumetric energy density and a larger electrolyte injection volume in the battery. In addition, the electrical conductivity of hard carbon materials is generally poor, far inferior to graphite. The high porosity of the anode active material layer containing hard carbon and the poor contact between hard carbon particles result in high internal resistance and poor kinetic properties of the anode. This leads to a low initial coulombic efficiency and poor rate performance in sodium-ion batteries.

[0034] In existing technologies, methods have been proposed to improve the compaction density of negative electrodes, including hard carbon, using nanomaterials such as nano-oxides and sulfides. However, in these existing technologies, since oxides and sulfides such as silicon oxide, aluminum oxide, and molybdenum disulfide are insulating materials, their addition leads to a decrease in the conductivity of the negative electrode and a deterioration in the initial coulombic efficiency and rate performance. Furthermore, because the particle size of nanomaterials is on the nanoscale (e.g., less than 1 micrometer), the nanomaterials cannot effectively (e.g., adequately) fill the gaps between hard carbon particles.

[0035] According to exemplary embodiments of this disclosure, incorporating graphite particles into hard carbon to prepare a negative electrode (specifically, a negative electrode active material layer) for a sodium-ion battery can achieve a negative electrode with high compaction density, high peel strength, and low resistivity. Furthermore, it can improve the energy density, first coulombic efficiency, and rate performance of the sodium-ion battery including the negative electrode, reduce its electrolyte injection volume, and lower costs.

[0036] In the exemplary embodiments of this disclosure, the graphite particles are micron-sized graphite particles. Specifically, the particle size D10 of the graphite particles can be from about 1 μm to about 8 μm, and the particle size D50 of the graphite particles can be from about 3 μm to about 15 μm. For example, the particle size D10 of the graphite particles can be from about 1 μm to about 7 μm, from about 1 μm to about 6 μm, from about 1 μm to about 5 μm, from about 1 μm to about 4 μm, or from about 1 μm to about 3 μm. For example, the particle size D50 of the graphite particles can be from about 3 μm to about 15 μm, from about 3 μm to about 14 μm, from about 3 μm to about 13 μm, from about 3 μm to about 12 μm, from about 3 μm to about 11 μm, from about 3 μm to about 10 μm, from about 3 μm to about 9 μm, from about 3 μm to about 8 μm, from about 3 μm to about 7 μm, from about 3 μm to about 6 μm, or from about 3 μm to about 5 μm.

[0037] Preferably, the particle size D10 of the graphite particles can be from about 1 μm to about 3 μm. Preferably, the particle size D50 of the graphite particles can be from about 3 μm to about 5 μm. For example, the particle size D10 of the graphite particles can be from about 1.2 μm to about 2.8 μm, from about 1.4 μm to about 2.6 μm, from about 1.6 μm to about 2.4 μm, from about 1.8 μm to about 2.2 μm, or about 2.0 μm. For example, the particle size D50 of the graphite particles can be from about 3.2 μm to about 4.8 μm, from about 3.4 μm to about 4.6 μm, from about 3.6 μm to about 4.4 μm, from about 3.8 μm to about 4.2 μm, or about 4.0 μm.

[0038] Within the aforementioned range, small-diameter graphite particles can fill the pores between hard carbon particles and between hard carbon particles and the current collector, improving the lubricity of the hard carbon particles. Large-diameter graphite particles, when combined with hard carbon particles, can form a uniform packing structure, reducing the contact points between the hard carbon particles and the separator, and preventing the sharp edges of the hard carbon particles from damaging the separator. This structure improves the smoothness of the negative electrode active material layer, reduces the likelihood of hard carbon particles breaking under high roller pressure, and prevents damage to the separator caused by hard carbon particles. If the graphite particle size is too large, it is difficult to fill the pores between hard carbon particles and between hard carbon particles and the current collector; if the graphite particle size is too small, the graphite particles have poor dispersibility, easily agglomerate to form secondary particles, and air bubbles are easily retained inside the slurry during the preparation of the negative electrode active material slurry, resulting in uneven dispersion of graphite particles and the formation of air bubbles on the electrode surface.

[0039] In the exemplary embodiments of this disclosure, the particle size D50 of the hard carbon particles can be from about 5 μm to about 15 μm, for example, from about 6 μm to about 14 μm, from about 7 μm to about 13 μm, from about 8 μm to about 12 μm, from about 9 μm to about 11 μm, or about 10 μm. Using hard carbon particles with the above-mentioned particle size range enables the hard carbon particles and graphite particles to form a synergistic effect of pore filling and uniform packing. Small-diameter graphite particles can fully fill the pores between hard carbon particles and between hard carbon particles and the current collector, acting as lubricants and bearings. Under heavy-load rolling pressure, they fill and improve the uneven surface roughness of the hard carbon particles, reducing frictional resistance and decreasing the coefficient of friction. Simultaneously, large-diameter graphite particles can form a uniform and dense packing structure with the hard carbon particles. Graphite particles have high roundness and good flexibility, which can improve the smoothness of the negative electrode, reduce the risk of hard carbon particles puncturing the diaphragm, and under high roller pressure, graphite particles can play a good buffering role to prevent hard carbon particles from breaking under high roller pressure.

[0040] In the negative electrode according to the example embodiment, based on 100 wt% hard carbon particles, the content of graphite particles can be in the range of about 0.5 wt% to about 20 wt%, for example, it can be about 1 wt% to about 19 wt%, about 2 wt% to about 18 wt%, about 3 wt% to about 17 wt%, about 4 wt% to about 16 wt%, about 5 wt% to about 15 wt%, about 6 wt% to about 14 wt%, about 7 wt% to about 13 wt%, about 8 wt% to about 12 wt%, about 9 wt% to about 11 wt%, or about 10 wt%. When the content of graphite particles based on 100 wt% hard carbon particles is within the above range, the graphite particles can be sufficiently filled into the pores between the hard carbon particles and between the hard carbon particles and the current collector, while avoiding the reduction in sodium-ion battery capacity and energy density due to the excessive introduction of graphite with low sodium storage activity.

[0041] In the exemplary embodiments of this disclosure, the thickness of the negative electrode active material layer is in the range of about 20 μm to about 200 μm. For example, the thickness of the negative electrode active material layer can 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.

[0042] This disclosure does not impose any particular restrictions on the source of hard carbon particles; they can be obtained commercially or by self-production. For example, hard carbon particles can be obtained by carbonizing one or more of the following: needle coke, pitch tar, petroleum coke, starch, coconut shell, phenolic resin, epoxy resin, straw, and wood.

[0043] As described above, the negative electrode for a sodium-ion battery according to an example embodiment includes a negative current collector and a negative active material layer located on at least one surface of the negative current collector. The negative active material layer includes hard carbon particles and graphite particles, and may also include a binder and optional conductive material.

[0044] For example, in the negative electrode active material layer, the mass ratio of hard carbon material, conductive agent and binder can be (85~99):(0~5):(1~10).

[0045] The binder can adhere the negative electrode active material particles (i.e., hard carbon particles and graphite particles) to each other and to the negative electrode active material to the current collector. The binder may include at least one of non-aqueous binders, aqueous binders, dry binders, and combinations thereof.

[0046] Non-aqueous adhesives may include at least one of polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, and combinations thereof.

[0047] The waterborne adhesive may be or include at least one of styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepoxychloropropane, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0048] When an aqueous binder is included as the negative electrode binder, a cellulose compound capable of imparting viscosity may also be included. The cellulose compound may include at least one of carboxymethyl cellulose, hydroxypropyl methylcellulose, methylcellulose, and their alkali metal salts. The alkali metal may include at least one of Na, K, and Li.

[0049] Dry adhesives can be or include polymeric materials capable of being fibrous. For example, dry adhesives can be or include at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, and combinations thereof.

[0050] Conductive materials can impart conductivity to electrodes. Any material that does not cause chemical changes (e.g., does not cause undesirable chemical changes in a sodium-ion battery) and conducts electrons can be included in the battery. Non-limiting examples of conductive materials may include: carbon-based materials, such as at least one of carbon black, acetylene black, Ketjen black, Super P, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials, including at least one of copper, nickel, aluminum, silver, etc., in the form of metal powder or metal fibers; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0051] In an exemplary embodiment, because graphite has good electrical conductivity, it can replace some or all of the conductive materials without significantly affecting the electrochemical performance of the battery. That is, the negative electrode active material layer in the exemplary embodiment may not include a dedicated conductive material.

[0052] This disclosure does not impose any particular limitation on the composition of the negative electrode current collector. The negative electrode current collector can be selected from negative electrode current collectors commonly used in the art, including but not limited to aluminum foil or carbon-coated aluminum foil, with a thickness d < 20 μm.

[0053] The negative electrode according to an exemplary embodiment of the present disclosure will now be described with reference to the accompanying drawings.

[0054] Figures 1A to 1D This is a schematic cross-sectional view showing the negative electrode for a sodium-ion battery according to an example embodiment.

[0055] Reference Figure 1AIn this example embodiment, the negative electrode active material layer may have a monolayer structure comprising a mixture of hard carbon particles and graphite particles, as well as a binder and optional conductive material. For example, the negative electrode 20 may include a negative electrode current collector 21 and a negative electrode active material layer 22 located on at least one surface of the negative electrode current collector 21, the negative electrode active material layer 22 having a monolayer structure and comprising hard carbon particles 221 and graphite particles 222.

[0056] like Figure 1A As shown in this example embodiment, the small-diameter graphite particles 222 fully fill the pores between the hard carbon particles 221, acting as a lubricant, reducing the coefficient of friction between the hard carbon particles 221, and increasing sliding and rolling friction. This allows the graphite particles 222 and hard carbon particles 221 to slide fully under roller pressure, filling the pores between particles, reducing the particle gaps, increasing the contact area between particles, and decreasing the porosity of the negative electrode active material layer 22. This, in turn, increases the compaction density of the negative electrode active material layer 22 and reduces the liquid injection coefficient. Furthermore, since graphite has significantly better conductivity than hard carbon, and the small-diameter graphite particles 222 fill the pores while the large-diameter graphite particles 222 and hard carbon particles 221 form a uniform packing structure, the contact between particles is tighter, and the contact resistance is reduced. Therefore, the electron transport capability of the negative electrode 20 is significantly improved, and the resistivity is reduced, thereby improving the initial coulombic efficiency and rate performance of the battery.

[0057] Reference Figure 1B In this example embodiment, the negative electrode active material layer may have a double-layer structure. For example, the negative electrode 20 may include a negative electrode current collector 21 and a negative electrode active material layer 22 located on at least one surface of the negative electrode current collector. The negative electrode active material layer 22 includes a first sub-negative electrode active material layer 210 and a second sub-negative electrode active material layer 220. The first sub-negative electrode active material layer 210 is located on at least one surface of the negative electrode current collector 21, and the second sub-negative electrode active material layer 220 is located on the first sub-negative electrode active material layer 210. The first sub-negative electrode active material layer 210 includes hard carbon particles 221 and graphite particles 222, and the second sub-negative electrode active material layer 220 includes graphite particles 222. In other words, the negative electrode active material layer 22 includes a first sub-negative electrode active material layer 210 containing hard carbon particles 221 and graphite particles 222 and a second sub-negative electrode active material layer 220 containing graphite particles 222.

[0058] Besides being able to achieve Figure 1A In addition to the beneficial effects achieved by the example embodiments, Figure 1B The example embodiment can further prevent the sharp edges of the hard carbon particles 221 from piercing the diaphragm 30 by providing a second sub-negative electrode active material layer 220 containing graphite particles 222 in contact with the diaphragm 30.

[0059] Reference Figure 1C In this example embodiment, the negative electrode active material layer may have a double-layer structure. For example, the negative electrode 20 may include a negative electrode current collector 21 and a negative electrode active material layer 22 located on at least one surface of the negative electrode current collector. The negative electrode active material layer 22 includes a first sub-negative electrode active material layer 210 and a second sub-negative electrode active material layer 220. The second sub-negative electrode active material layer 220 is located on at least one surface of the negative electrode current collector 21, and the first sub-negative electrode active material layer 210 is located on the second sub-negative electrode active material layer 220. The first sub-negative electrode active material layer 210 includes hard carbon particles 221 and graphite particles 222, and the second sub-negative electrode active material layer 220 includes graphite particles 222. In other words, the negative electrode active material layer 22 includes a first sub-negative electrode active material layer 210 containing hard carbon particles 221 and graphite particles 222 and a second sub-negative electrode active material layer 220 containing graphite particles 222.

[0060] Reference Figure 1D In this example embodiment, the negative electrode active material layer may have a three-layer structure. For example, the negative electrode 20 may include a negative electrode current collector 21 and a negative electrode active material layer 22 located on at least one surface of the negative electrode current collector. The negative electrode active material layer 22 includes a first sub-negative electrode active material layer 210, a second sub-negative electrode active material layer 220, and a third sub-negative electrode active material layer 230. The third sub-negative electrode active material layer 230 is located on at least one surface of the negative electrode current collector 21, the first sub-negative electrode active material layer 210 is located on the third sub-negative electrode active material layer 230, and the second sub-negative electrode active material layer 220 is located on the first sub-negative electrode active material layer 210. The first sub-negative electrode active material layer 210 includes hard carbon particles 221 and graphite particles 222, and the second sub-negative electrode active material layer 220 and the third sub-negative electrode active material layer 230 both include graphite particles 222. In other words, the negative electrode active material layer 22 includes a second sub-negative electrode active material layer 220 and a third sub-negative electrode active material layer 230 containing graphite particles 222, and a first sub-negative electrode active material layer 210 containing hard carbon particles 221 and graphite particles 222 and located between the second sub-negative electrode active material layer 220 and the third sub-negative electrode active material layer 230.

[0061] Besides being able to achieve Figure 1B In addition to the beneficial effects achieved by the example embodiments, Figure 1D The example embodiment can further enhance the adhesion between the negative electrode active material layer 22 and the negative electrode current collector 21 by providing a third sub-negative electrode active material layer 230 containing graphite particles 222 in contact with the negative electrode current collector 21, thereby improving the peel strength of the negative electrode.

[0062] A method for manufacturing a negative electrode according to an exemplary embodiment of the present disclosure will now be described with reference to the accompanying drawings.

[0063] Figures 2A to 2D This is a schematic diagram illustrating a coating process for manufacturing a negative electrode for a sodium-ion battery according to an example embodiment.

[0064] Reference Figure 2A A single-layer coating method can be used to coat a slurry containing hard carbon particles, graphite particles, a binder, and optional conductive materials onto a negative electrode current collector. The negative electrode is then obtained through baking, rolling, vacuum baking, and cutting. Figure 2A The negative electrode obtained by the coating process corresponds to Figure 1A The negative electrode shown.

[0065] Reference Figure 2B A double-layer coating method can be used to coat a first sub-negative electrode active material layer slurry and a second sub-negative electrode active material layer slurry onto the negative electrode current collector, thereby forming a first sub-negative electrode active material layer located on at least one surface of the negative electrode current collector and a second sub-negative electrode active material layer located on the first sub-negative electrode active material layer. The first sub-negative electrode active material layer slurry comprises hard carbon particles and graphite particles, as well as a binder and optional conductive material, and the second sub-negative electrode active material layer slurry comprises graphite particles, as well as a binder and optional conductive material. Figure 2B The negative electrode obtained by the coating process corresponds to Figure 1B The negative electrode shown.

[0066] Reference Figure 2C A double-layer coating method can be used to coat a first sub-negative electrode active material layer slurry and a second sub-negative electrode active material layer slurry onto the negative electrode current collector, thereby forming a first sub-negative electrode active material layer located on at least one surface of the negative electrode current collector and a second sub-negative electrode active material layer located on the first sub-negative electrode active material layer. The first sub-negative electrode active material layer slurry comprises graphite particles, a binder, and optional conductive materials, while the second sub-negative electrode active material layer slurry comprises hard carbon particles and graphite particles, a binder, and optional conductive materials. Figure 2C The negative electrode obtained by the coating process corresponds to Figure 1C The negative electrode shown.

[0067] Reference Figure 2DA three-layer coating method can be used to coat a first sub-negative electrode active material layer slurry, a second sub-negative electrode active material layer slurry, and a third sub-negative electrode active material layer slurry onto a negative electrode current collector, thereby forming a third sub-negative electrode active material layer located on at least one surface of the negative electrode current collector, a first sub-negative electrode active material layer located on the third sub-negative electrode active material layer, and a second sub-negative electrode active material layer located on the first sub-negative electrode active material layer. The first sub-negative electrode active material layer slurry comprises hard carbon particles and graphite particles, as well as a binder and optional conductive material. The second and third sub-negative electrode active material layer slurries comprise graphite particles, as well as a binder and optional conductive material. Figure 2D The negative electrode obtained by the coating process corresponds to Figure 1D The negative electrode shown.

[0068] Through such Figures 2A to 2D The coating process shown can yield negative electrode active material layers with different structures. For example, a double-layer coating method can produce a double-layer negative electrode active material layer including a bottom layer and a top layer. The bottom layer is a hard carbon / graphite layer serving as a sodium storage active layer, ensuring a high sodium storage capacity (typically above 300 mAh / g); the top layer is a graphite layer serving as a smoothing buffer layer, preventing direct contact between hard carbon particles and the separator, thus reducing the risk of separator puncture and the risk of hard carbon particle breakage under high roller pressure. Alternatively, a multi-layer coating method can produce a three-layer negative electrode active material layer including a bottom layer, an intermediate layer, and a top layer. The bottom layer is a graphite layer serving as a high peel strength layer, improving the peel strength of the negative electrode active material layer; the intermediate layer is a hard carbon / graphite layer serving as a sodium storage active layer, ensuring a high sodium storage capacity (typically above 300 mAh / g); the top layer is a graphite layer serving as a smoothing buffer layer, preventing direct contact between hard carbon particles and the separator, thus reducing the risk of separator puncture and the risk of hard carbon particle breakage under high roller pressure.

[0069] In the following, a sodium-ion battery including a negative electrode for a sodium-ion battery according to an exemplary embodiment of the present disclosure will be described.

[0070] A sodium-ion battery according to an example embodiment of the present disclosure may include a negative electrode, a positive electrode, a separator located between the negative electrode and the positive electrode, and an electrolyte impregnating the negative electrode and the positive electrode.

[0071] The negative electrode can be the negative electrode used in sodium-ion batteries as described above.

[0072] This disclosure does not impose any particular limitation on the composition and structure of the positive electrode, which can be referred to with reference to conventional positive electrode compositions in the art. Specifically, the positive electrode includes a positive current collector and a layer of positive active material located on at least one surface of the positive current collector.

[0073] In an example embodiment, the positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder.

[0074] Specifically, the positive electrode active material includes, but is not limited to, one or more of layered metal oxides, polyanionic compounds, and Prussian blue / white compounds.

[0075] This disclosure does not impose any particular limitation on the composition and structure of the diaphragm, which can be selected from diaphragms conventionally used in the art, including but not limited to polypropylene (PP) diaphragms, polyethylene (PE) diaphragms, or composite diaphragms. For example, it may include diaphragms comprising two or more layers of polyethylene, polypropylene, and polyvinylidene fluoride, such as polyethylene / polypropylene double-layer diaphragms, polyethylene / polypropylene / polypropylene triple-layer diaphragms, polypropylene / polypropylene / polypropylene triple-layer diaphragms, etc.

[0076] This disclosure does not impose any particular limitation on the type of electrolyte, which may be selected from electrolytes commonly used in the art, including but not limited to one or more sodium salts such as NaPF6, NaFSI, NaDFOB, and NaPO2F2, and one or more solvents such as propylene carbonate (PC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and diethyl carbonate (DEC), and one or more additives such as fluoroethylene carbonate (FEC), ethylene sulfate (DTD), propylene-1,3-sulfonyl lactone (PST), and ascorbic acid (VC).

[0077] This disclosure does not impose any particular limitation on the method of manufacturing sodium-ion batteries, which can be manufactured by referring to conventional methods in the art.

[0078] In the example embodiment, a sodium-ion battery can be prepared by the following steps: homogenization → coating → rolling → cutting → stacking → electrode welding → heat sealing aluminum-plastic film → electrolyte injection → formation and capacity testing, etc.

[0079] A sodium-ion battery according to an exemplary embodiment of the present disclosure will now be described with reference to the accompanying drawings.

[0080] Figures 3 to 6 This is a schematic diagram of the structure of a sodium-ion battery according to an example embodiment.

[0081] Figure 3 A cylindrical battery is shown. Figure 4 A prismatic battery is shown. Figure 5 and Figure 6 A pouch-type battery is shown. (See reference) Figures 3 to 6The sodium-ion battery 100 may include an electrode assembly 40 and a housing 50. The electrode assembly 40 includes a positive electrode 10 and a negative electrode 20, and a separator 30 between the positive electrode 10 and the negative electrode 20. The electrode assembly 40 is housed within the housing 50. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). Figure 3 As shown, the sodium-ion battery 100 may include a sealing member 60 of a sealed housing 50. Figure 4 In this sodium-ion battery 100, a positive electrode lead connector 11, a positive electrode terminal 12, a negative electrode lead connector 21, and a negative electrode terminal 22 may be included. For example... Figure 5 and Figure 6 As shown, the sodium-ion battery 100 may include Figure 6 The electrode terminal 70 shown, or for example Figure 5 The positive electrode terminal 71 and negative electrode terminal 72 shown form an electrical path for guiding the current formed in the electrode assembly 40 to the outside of the sodium-ion battery 100.

[0082] The present disclosure will be described in more detail below with reference to specific examples. However, it should be understood that these examples are provided for illustrative purposes only and should not be construed as limiting the present disclosure in any way.

[0083] Example 1 Step 1: Preparation of the negative electrode for sodium-ion batteries Hard carbon particles with a particle size D50 of 10 μm, Super P (SP), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were dispersed in pure water at a mass ratio of 96.5:1:1.0:1.5. Then, graphite particles with a particle size D10 of 2 μm and a D50 of 4 μm were added, with the ratio of graphite particles to hard carbon particles being 5:100. The mixture was then uniformly dispersed using a mixer to form a negative electrode active material slurry with a solid content of 45%.

[0084] The above-mentioned negative electrode active material layer slurry is processed using, as follows: Figure 2A The single-layer coating method shown is applied to both surfaces of a 13μm thick aluminum foil that serves as the negative electrode current collector. The foil is baked at 100°C for 10 minutes, and then rolled, vacuum baked, and cut to obtain the negative electrode.

[0085] Step 2: Preparation of the positive electrode Layered oxide NaNi with a particle size D50 of 8±1 μm 0.33 Fe 0.33 Mn 0.34O2 (NFM), SP and PVDF are dispersed in NMP at a mass ratio of 97.7:1.0:1.3 and uniformly dispersed by a mixer to form a positive electrode active material slurry with a solid content of 65%.

[0086] The above-mentioned positive electrode active material slurry was coated onto both surfaces of a 13 μm thick aluminum foil serving as the positive electrode current collector. The coating process was a conventional positive electrode coating process in the art. After baking at 120°C for 10 minutes, the electrode was rolled and cut to obtain the NFM positive electrode.

[0087] Step 3: Assembly of Sodium-ion Batteries The negative electrode obtained in step one, the positive electrode obtained in step two, and the separator are stacked by Z-shaped winding. The process involves electrode tab welding, heat sealing of the aluminum-plastic film, electrolyte injection, and formation and capacity testing to finally obtain a soft-pack battery cell. The electrolyte comprises, by weight percentage, 10 wt% NaPF6, 50 wt% PC, 35 wt% EMC, 4 wt% FEC, 0.4 wt% PST, and 0.6 wt% DTD.

[0088] Example 2 This example provides a negative electrode and a sodium-ion battery, the preparation method of which is basically the same as that of Example 1, except that in the preparation process of the negative electrode, the particle mass ratio of graphite particles to hard carbon particles is 6:100.

[0089] Example 3 This example provides a negative electrode and a sodium-ion battery, the preparation method of which is basically the same as that of Example 1, except that in the preparation process of the negative electrode, the particle mass ratio of graphite particles to hard carbon particles is 7.5:100.

[0090] Example 4 This example provides a negative electrode and a sodium-ion battery, the preparation method of which is basically the same as that of Example 1, except that in the preparation process of the negative electrode, the particle mass ratio of graphite particles to hard carbon particles is 10:100.

[0091] Example 5 This example provides a negative electrode and a sodium-ion battery, which are prepared in a manner that is basically the same as in Example 1, except that the D50 of the hard carbon particles is adjusted to 15 μm, the D50 of the graphite particles is adjusted to 12 μm, and the D10 of the graphite particles is adjusted to 6 μm.

[0092] Example 6 This example provides a negative electrode and a sodium-ion battery, which are prepared in a manner that is basically the same as in Example 1, except that the D50 of the hard carbon particles is adjusted to 5 μm, the D50 of the graphite particles is adjusted to 3 μm, and the D10 of the graphite particles is adjusted to 1 μm.

[0093] Example 7 This example provides a negative electrode and a sodium-ion battery, the preparation method of which is basically the same as that of Example 1. The difference is that in the preparation process of the negative electrode, the mass ratio of hard carbon, SP, CMC and SBR is 97.5:0:1.0:1.5, and the particle mass ratio of graphite particles to hard carbon particles is 10:100.

[0094] Example 8 This example provides a negative electrode and a sodium-ion battery, the preparation method of which is basically the same as that in Example 4, except that in the preparation process of the negative electrode, a method such as... Figure 2B The double-layer coating method shown uses a hard carbon / graphite mixed slurry as the bottom layer and a graphite slurry as the top layer. The graphite slurry is prepared according to a mass ratio of graphite:CMC:SBR of 97.5:1.0:1.5 and has a solid content of 45%.

[0095] Example 9 This example provides a negative electrode and a sodium-ion battery, the preparation method of which is basically the same as that in Example 4, except that in the preparation process of the negative electrode, a method such as... Figure 2C The multi-layer coating method shown employs a graphite slurry as the bottom layer and a hard carbon / graphite mixed slurry as the top layer. The graphite slurry is prepared according to a graphite:CMC:SBR mass ratio of 97.5:1.0:1.5, with a solid content of 45%.

[0096] Example 10 This example provides a negative electrode and a sodium-ion battery, the preparation method of which is basically the same as that in Example 4, except that in the preparation process of the negative electrode, a method such as... Figure 2D The multilayer coating method shown employs a graphite slurry as the bottom layer, a hard carbon / graphite mixed slurry as the middle layer, and a graphite slurry as the top layer. The graphite slurry is prepared according to a graphite:CMC:SBR mass ratio of 97.5:1.0:1.5. The solid content is 45%.

[0097] Comparison Example 1 This comparative example provides a negative electrode and a sodium-ion battery, the preparation method of which is basically the same as that of Example 1, except that no graphite material is added during the preparation of the negative electrode.

[0098] Comparison Example 2 This comparative example provides a negative electrode and a sodium-ion battery, the preparation method of which is basically the same as that of Example 1. The difference is that in the preparation process of the negative electrode, the graphite particles are replaced with a mixed material of nano-SiO2 and MoS2, and the mass ratio of SiO2 to MoS2 is 3:1.

[0099] Compare Example 3 This comparative example provides a negative electrode and a sodium-ion battery, the preparation method of which is basically the same as that of Example 1. The difference is that in the preparation process of the negative electrode, the graphite particles are replaced with nano-graphene sheets of the same mass (particle size D50 is 300nm).

[0100] Compare Example 4 This comparative example provides a negative electrode and a sodium-ion battery, the preparation method of which is basically the same as that of Example 1. The difference is that in the preparation process of the negative electrode, the graphite particles are replaced with the same mass of nano-fullerene C60 (particle size D50 is 300 nm).

[0101] Compare Example 5 This comparative example provides a negative electrode and a sodium-ion battery, the preparation method of which is basically the same as that of Example 6. The difference is that in the preparation process of the negative electrode, no graphite particles are added to the bottom hard carbon / graphite layer, and it is only a hard carbon layer.

[0102] Comparison Example 6 This comparative example provides a negative electrode and a sodium-ion battery, the preparation method of which is basically the same as that of Example 7. The difference is that in the preparation process of the negative electrode, no graphite particles are added to the intermediate hard carbon / graphite layer, and it is only a hard carbon layer.

[0103] Evaluation Example Evaluation of negative electrode compaction density The negative electrodes of the example and comparative examples were gradually pressurized under pressure ranging from 0 to 50 t to roll and the electrode thickness was measured. Then, combined with the electrode surface condition, the maximum compaction density that the electrode can achieve was determined, and the value is listed in Table 1.

[0104] Evaluation of negative electrode resistivity Test method: The overall resistivity of the negative electrode of the above examples and comparative examples was directly measured using the dual-plane controllable pressure disk electrode resistance method with a BER series multi-functional electrode resistance meter. The resistivity was measured as the sum of the 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. The values ​​are listed in Table 1.

[0105] Peel strength evaluation The negative electrodes of the above examples and comparative examples were cut into samples measuring 25mm × 150mm. The samples were fixed to the center of a 30mm × 200mm glass slide using adhesive tape. The 90-degree peel strength was then measured while peeling the negative electrode current collector from the active material layer of the negative electrode using a universal testing machine (UTM). The results are shown in Table 1.

[0106] First Coulomb Efficiency Evaluation of Battery Test method: Under constant current charge-discharge mode, the sodium-ion batteries of the example and comparative examples were charged to the upper limit voltage of 3.8V at a current density of 0.2C, then charged at a constant voltage of 3.8V to the cutoff current of 0.05C, and then discharged at 0.2C to the cutoff voltage of 2.0V. The initial charge capacity Q1 and the initial discharge capacity Q2 of the battery were recorded, and the initial coulombic efficiency of the battery was calculated based on Q2 / Q1. The results are shown in Table 2.

[0107] Evaluation of injection coefficient Test method: Weigh a fresh battery cell and record the total weight as g1. After disassembling the battery cell, weigh the dry electrode g2 and the structural components g3. Obtain the electrolyte injection volume g = g1 - g2. g3; then the injection coefficient is calculated by dividing the injection volume by the cell capacity, in g / Ah. The results are shown in Table 2.

[0108] Energy density evaluation The energy density of the sodium-ion batteries in the examples and comparative examples above was measured. The measurement results are shown in Table 2.

[0109] Energy density is calculated using Equation 1.

[0110] Equation 1 Energy density (Ah / L) = [(Area capacity of negative electrode / Total thickness of cell unit) × Average voltage] The areal capacity (milliampere-hours / square centimeter (mAh / cm²)) in Equation 1 2 The value is obtained by dividing the total current passing through the battery by the geometric area of ​​the battery's electrodes.

[0111] Capacity retention evaluation 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 cutoff) and 2.0C discharging conditions (CC, 2.5V cutoff), and the capacity retention was evaluated according to Equation 1.

[0112] Equation 1 Capacity retention rate = (Discharge capacity after 200 cycles / Discharge capacity after 1 cycle) × 100% Table 1

[0113] As shown in Table 1, the negative electrodes of Examples 1 to 10 exhibit higher compaction density, lower resistivity, and higher peel strength than the negative electrodes of Comparative Examples 1 to 6. This is because graphite particles, as described above, are incorporated into the hard carbon negative electrode active material layer. The graphite particles fill the pores between the hard carbon particles, effectively increasing the compaction density and peel strength of the negative electrode and reducing the resistivity.

[0114] Furthermore, as shown in Table 1, Example 10 exhibits the highest peel strength because a third sub-anode active material layer containing graphite particles is formed in contact with the negative electrode current collector, effectively improving the adhesion between the negative electrode active material layer and the negative electrode current collector.

[0115] Furthermore, the negative electrodes of Comparative Examples 3 and 4, which incorporate nanoscale graphene and fullerene C60, exhibited lower compaction densities than the negative electrodes of Examples 1 to 10.

[0116] Table 2

[0117] As shown in Table 2, the negative electrodes of Examples 1 to 10 exhibited lower injection coefficients than the negative electrodes of Comparative Examples 1 to 6.

[0118] In addition, the sodium-ion batteries in Comparative Example 1 and Comparative Example 2, which did not add graphite or only added nano-SiO2 and MoS2 to the negative electrode active material layer, exhibited lower energy density and capacity retention.

[0119] Furthermore, the sodium-ion batteries in Comparative Examples 3 and 4, which added nanoscale graphene and fullerene C60 to the negative electrode active material layer, exhibited a higher liquid injection coefficient than the sodium-ion batteries in Examples 1 to 10.

[0120] The negative electrode according to the example embodiment achieves high compaction density, peel strength, and low resistivity by incorporating graphite particles into hard carbon particles. The sodium-ion battery including this negative electrode according to the example embodiment achieves high initial coulombic efficiency, energy density, capacity retention, and low fill factor.

[0121] Although exemplary embodiments of the present disclosure have been described above, the present disclosure is not limited thereto, and modifications may be made in any form within the scope of the claims, the detailed description of the present disclosure, and the accompanying drawings, and such modifications also fall within the scope of the present disclosure.

Claims

1. A negative electrode for a sodium-ion battery, characterized in that, The negative electrode includes: Negative current collector; and A negative electrode active material layer is located on at least one surface of the negative electrode current collector. The negative electrode active material layer includes hard carbon particles and graphite particles.

2. The negative electrode according to claim 1, characterized in that, The particle size D50 of the hard carbon particles ranges from 5 μm to 15 μm, and The graphite particles have a particle size D10 of 1 μm to 8 μm and a particle size D50 of 3 μm to 15 μm.

3. The negative electrode according to claim 1, characterized in that, The particle size D50 of the hard carbon particles ranges from 5 μm to 15 μm, and The graphite particles have a particle size D10 of 1 μm to 3 μm and a particle size D50 of 3 μm to 5 μm.

4. The negative electrode according to claim 1, characterized in that, In the negative electrode active material layer, the content of graphite particles is from 0.5 wt% to 20 wt%, based on 100 wt% hard carbon particles.

5. The negative electrode according to claim 1, characterized in that, The thickness of the negative electrode active material layer is in the range of 20 μm to 200 μm.

6. The negative electrode according to claim 1, characterized in that, The negative electrode active material layer includes a first sub-negative electrode active material layer and a second sub-negative electrode active material layer. 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. The first sub-anode active material layer includes hard carbon particles and graphite particles, and The second sub-anode active material layer includes graphite particles.

7. The negative electrode according to claim 1, characterized in that, The 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. The third sub-negative electrode active material layer is located on at least one surface of the negative electrode current collector, the first sub-negative electrode active material layer is located on the third sub-negative electrode active material layer, and the second sub-negative electrode active material layer is located on the first sub-negative electrode active material layer. The first sub-anode active material layer includes hard carbon particles and graphite particles, and The second and third sub-anode active material layers comprise graphite particles.

8. The negative electrode according to claim 1, characterized in that, The negative electrode active material layer also includes a binder and an optional conductive material.

9. The negative electrode according to claim 1, characterized in that, In the negative electrode active material layer, the content of graphite particles is 5 wt% to 10 wt%, based on 100 wt% hard carbon particles.

10. A method for manufacturing a negative electrode for a sodium-ion battery according to claim 1, the method comprising: A negative electrode active material layer slurry is prepared, wherein the negative electrode active material layer slurry includes hard carbon particles, graphite particles, a binder, and optional conductive materials; The negative electrode active material layer slurry is coated onto at least one surface of the negative electrode current collector; and The negative electrode current collector coated with the negative electrode active material layer slurry is baked and rolled.

11. A sodium-ion battery, the sodium-ion battery comprising: The negative electrode according to any one of claims 1 to 9; Positive electrode; as well as A diaphragm is located between the negative electrode and the positive electrode.

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