Sodium-ion battery anode and its preparation method, sodium-ion battery

Abstract

This invention provides a sodium-ion battery negative electrode and its preparation method, as well as a sodium-ion battery. The sodium-ion battery negative electrode includes a current collector having a first outer surface and a second outer surface disposed opposite to each other; a negative electrode active material layer disposed on the first outer surface and / or the second outer surface of the current collector; and a sodium-containing compound layer disposed on the outer surface of the negative electrode active material layer away from the current collector. The sodium-containing compound layer of this invention can release sodium ions during the first charge-discharge process of the sodium-ion battery to replenish sodium in the negative electrode material, thereby compensating for the initial irreversible sodium consumption of the negative electrode material and improving the energy density of the sodium-ion battery. The negative electrode active material layer and the sodium-containing compound layer in this application are in interfacial contact, which, compared to the prior art where sodium-replenishing additives are physically doped into the interior of the negative electrode material layer, exhibits superior cycle stability and electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and more specifically, to a sodium-ion battery negative electrode and its preparation method, and a sodium-ion battery. Background Technology

[0002] With socio-economic development, the cost, development, and application of lithium-ion batteries will be severely limited in the future. Researchers worldwide are focusing on developing a battery that can replace lithium-ion batteries and be mass-produced and applied.

[0003] Sodium-ion batteries are one of the most promising options. Their working principle is similar to lithium-ion batteries; they are rechargeable batteries that rely on the movement of sodium ions between the positive and negative electrodes to complete charging and discharging. However, due to the large atomic radius of sodium ions, they cannot efficiently intercalate and deintercalate at the graphite negative electrode material, affecting the battery's conductivity. Furthermore, in commonly used sodium-ion battery negative electrodes, during the first charge and discharge process of the rechargeable battery, the electrolyte solvent inevitably reacts at the interface between the negative electrode and the electrolyte, forming a solid electrolyte interphase (SEI) film covering the surface of the negative electrode. The formation of the SEI film consumes some sodium... + This causes the positive electrode to become active Na + The loss of sodium during the initial charge and discharge cycle increases the irreversible capacity loss. Therefore, it is necessary to replenish sodium in the negative electrode material.

[0004] Currently, there are two main methods for replenishing sodium in sodium-ion batteries: The first is to add sodium-rich materials to the positive electrode, releasing sodium through an electrochemical reaction during the first charge cycle. However, this method is inefficient, and the added sodium introduces unavoidable inactive substances, which affect the overall energy density of the product. The second method is to directly add sodium-replenishing additives to the negative electrode material through dispersion mixing.

[0005] For example, patent CN108878780A discloses a method for replenishing sodium in the negative electrode of a sodium-ion battery. In an inert atmosphere, solid metallic sodium is melted at a certain temperature to obtain liquid sodium. The liquid metallic sodium is then uniformly added to the surface of the negative electrode sheet, allowing the liquid metallic sodium to penetrate into the gaps between the negative electrode materials. After drying, a sodium-replenished negative electrode sheet is obtained.

[0006] However, this sodium replenishment method has the following problems: due to the high activity and low safety of elemental sodium, it affects subsequent battery assembly processes.

[0007] For example, CN110690437 discloses a sodium-ion battery negative electrode sheet, which uses carbon-coated sodium phosphide as a sodium supplement additive, and physically does the carbon-coated sodium phosphide into the negative electrode active material to prepare the sodium-ion battery negative electrode sheet.

[0008] While this method addresses the safety issue of sodium as a sodium supplement additive, the preparation process of carbon-coated sodium supplement additives is complex and prone to uneven coating, leading to poor long-term cycle performance of the battery. Furthermore, when physically doping the sodium supplement additive into the negative electrode material, the additive undergoes volume changes during the sodium supplementation process, resulting in poor electrical contact between the negative electrode material and the current collector.

[0009] In summary, existing technologies for adding sodium to the negative electrode of sodium-ion batteries suffer from problems such as poor operational safety, poor electrochemical performance, and poor cycle stability. Therefore, this invention aims to provide a sodium-ion battery negative electrode, its preparation method, and a sodium-ion battery to address these issues. Summary of the Invention

[0010] The main objective of this invention is to provide a sodium-ion battery anode and its preparation method, as well as a sodium-ion battery, to solve the problems existing in the prior art when adding sodium to the sodium-ion battery anode, such as poor operational safety, poor electrochemical performance, or poor cycle stability.

[0011] To achieve the above objectives, according to one aspect of the present invention, a sodium-ion battery negative electrode is provided, comprising: a current collector having a first outer surface and a second outer surface disposed opposite to each other; a negative electrode active material layer disposed on the first outer surface and / or the second outer surface of the current collector; and a sodium-containing compound layer disposed on the outer surface of the negative electrode active material layer away from the current collector.

[0012] Furthermore, the ratio of the thickness of the negative electrode active material layer to the thickness of the sodium-containing compound layer is 0.5 to 10:1.

[0013] Furthermore, the ratio of the thickness of the negative electrode active material layer to the thickness of the sodium-containing compound layer is 1 to 5:1.

[0014] Furthermore, the thickness of the negative electrode active material layer is 3–15 μm.

[0015] Furthermore, the thickness of the sodium-containing compound layer is 0.5–15 μm.

[0016] Furthermore, the sodium-containing compound in the sodium-containing compound layer is selected from one or more of sodium phosphide, sodium nickelate, sodium chromate, sodium oxide, sodium sulfide, sodium carbonate, sodium fluoride, or sodium hydroxide.

[0017] Furthermore, the sodium-containing compound is selected from one or more of sodium phosphide, sodium oxide, or sodium sulfide.

[0018] Furthermore, the sodium-containing compounds include sodium phosphide, sodium oxide, and sodium sulfide, and the weight ratio of sodium phosphide, sodium oxide, and sodium sulfide is 1–3:1:1–2.

[0019] Furthermore, the negative electrode active material in the negative electrode active material layer is selected from one or more of hard carbon, soft carbon, artificial graphite, or natural graphite.

[0020] Furthermore, the negative electrode active material in the negative electrode active material layer is selected from hard carbon.

[0021] Furthermore, the specific surface area of ​​hard carbon is ≤10m². 2 / g, tap density is 0.85~1g / cm³ 3 The particle size is 5–10 μm and the interlayer spacing is 0.38–0.4 nm.

[0022] Furthermore, the current collector is selected from one or more of copper foil, aluminum foil, cobalt foil, nickel foil or silver foil, and is more preferably aluminum foil.

[0023] To achieve the above objectives, according to one aspect of the present invention, a method for preparing a sodium-ion battery negative electrode is provided, comprising: providing a current collector having a first outer surface and a second outer surface disposed opposite to each other; disposing a negative electrode active material layer on the first outer surface and / or the second outer surface of the current collector; and disposing a sodium-containing compound layer on the outer surface of the negative electrode active material layer away from the current collector.

[0024] Further, the preparation method includes the following steps: coating a first slurry containing a negative electrode active material onto a first outer surface and / or a second outer surface of a current collector, and after a first drying, obtaining a current collector with a negative electrode active material layer disposed on the first outer surface and / or the second outer surface; coating a second slurry containing a sodium compound onto the outer surface of the negative electrode active material layer away from the current collector, and after a second drying, obtaining a sodium-ion battery negative electrode.

[0025] Furthermore, the first slurry is prepared by the following steps: the negative electrode active material, the first conductive agent and the first binder are first mixed and then first ground to obtain the first slurry.

[0026] Furthermore, the second slurry is prepared by the following steps: under an inert atmosphere, a sodium-containing compound, a second conductive agent, and a second binder are mixed and then subjected to a second grinding to obtain the second slurry.

[0027] Furthermore, the weight ratio of the negative electrode active material, the first conductive agent, and the first binder is 6-8:1-2:0.5-1.

[0028] Furthermore, the weight ratio of the sodium-containing compound, the second conductive agent, and the second binder is 6–8:1–2:0.5–1.

[0029] Furthermore, the first conductive agent and the second conductive agent are each independently selected from one or more of acetylene black, conductive carbon black, or carbon nanotubes.

[0030] Furthermore, the first adhesive and the second adhesive are each independently selected from one or more of polyvinylidene fluoride solution, styrene-butadiene rubber, carboxymethyl cellulose, or polyacrylic acid.

[0031] Furthermore, both the first and second adhesives are polyvinylidene fluoride solutions, and the mass concentration of polyvinylidene fluoride in the polyvinylidene fluoride solution is 50–100 mg / mL.

[0032] Furthermore, the viscosity of the first slurry is 2000-10000 mPa·s at 25°C; the D50 particle size of the solids in the first slurry is 5 μm-10 μm.

[0033] Furthermore, the viscosity of the second slurry is 2000–10000 mPa·s at 25°C; the D50 particle size of the solids in the first slurry is 5 μm–10 μm.

[0034] Furthermore, the temperature of the first drying is 50–90°C; the time of the first drying is 24–48 h, more preferably 24–36 h.

[0035] Furthermore, the temperature for the second drying is 50–90°C, more preferably 60–80°C; and the drying time is 24–48 h, more preferably 24–36 h.

[0036] According to another aspect of the present invention, a sodium-ion battery is provided, comprising the sodium-ion battery negative electrode described above.

[0037] The sodium-ion battery negative electrode of the present invention includes a current collector, a negative electrode active material layer, and a sodium-containing compound layer. The sodium-containing compound layer of the present invention can release sodium ions during the first charge and discharge process of the sodium-ion battery to replenish sodium in the negative electrode material, thereby compensating for the first irreversible sodium consumption of the negative electrode material and improving the energy density of the sodium-ion battery. The negative electrode active material layer and the sodium-containing compound layer of the present application are in interfacial contact. Compared with the prior art when the sodium replenishing additive is physically doped into the interior of the negative electrode material layer, it has better cycle stability and electrochemical performance. Attached Figure Description

[0038] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0039] Figure 1 A schematic diagram of the structure of a sodium-ion battery negative electrode in one embodiment of the present invention is shown.

[0040] Figure 2 A schematic diagram of the structure of the negative electrode of a sodium-ion battery in another embodiment of the present invention is shown.

[0041] The above figures include the following reference numerals: 10, current collector; 20, negative electrode active material layer; 30, sodium-containing compound layer. Detailed Implementation

[0042] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0043] As described in the background section of this application, existing technologies for adding sodium to the negative electrode of sodium-ion batteries suffer from problems such as poor operational safety, poor electrochemical performance, or poor cycle stability. To address this issue, this application provides a sodium-ion battery negative electrode, such as... Figure 1 As shown, it includes a current collector 10 having a first outer surface and a second outer surface disposed opposite to each other; a negative electrode active material layer 20 disposed on the first outer surface and / or the second outer surface of the current collector 10; and a sodium-containing compound layer 30 disposed on the outer surface of the negative electrode active material layer 20 away from the current collector 10.

[0044] The sodium-ion battery negative electrode of the present invention includes a current collector, a negative electrode active material layer, and a sodium-containing compound layer. The sodium-containing compound layer of the present invention can release sodium ions during the first charge and discharge process of the sodium-ion battery to replenish sodium in the negative electrode material, thereby compensating for the first irreversible sodium consumption of the negative electrode material and improving the energy density of the sodium-ion battery. The negative electrode active material layer and the sodium-containing compound layer of the present application are in interfacial contact. Compared with the prior art when the sodium replenishing additive is physically doped into the interior of the negative electrode material layer, it has better cycle stability and electrochemical performance.

[0045] Compared to the co-doping method used in existing technologies when adding sodium to the negative electrode material, this application sets an independent sodium-containing compound layer 30 on the outer surface of the negative electrode active material layer 20. This is based on the applicant's discovery that when sodium-adding additives are physically doped into the interior of the negative electrode material layer, the sodium ions in the additives undergo significant volume changes during the sodium addition process. This leads to gaps between the negative electrode material and the current collector, resulting in poor electrical contact and loss of electrical contact between the negative electrode. Consequently, the electrochemical performance of the battery product deteriorates, and the cycle stability is poor. Simultaneously, the sodium ions from the additives also leave voids inside the negative electrode material, creating gaps and reducing the battery's energy density. Furthermore, by independently setting the sodium-containing compound layer on the outer surface of the negative electrode material layer, this application achieves excellent conductivity and stability without the need for coating the sodium-containing compound, and avoids the problems of uneven coating and complex operation associated with coating processes. Based on the above structure, when the sodium-containing compound in the sodium-containing compound layer undergoes volume changes during sodium replenishment, it will not affect the internal structure of the negative electrode material layer, nor will it affect the contact between the negative electrode material layer and the current collector. This layered sodium-ion battery negative electrode has excellent cycle stability and electrochemical performance.

[0046] To further improve the cycle stability and electrochemical performance of the sodium-ion battery anode, in a preferred embodiment, the ratio of the thickness of the anode active material layer 20 to the thickness of the sodium-containing compound layer 30 is 0.5 to 10:1, for example, 0.5:1, 1:1, 1.5:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, preferably 1:5 to 1. When the ratio of the thickness of the anode active material layer 20 to the thickness of the sodium-containing compound layer 30 is too low, the sodium-containing compound layer will undergo significant volume changes during battery charge-discharge cycles, resulting in poor long-cycle performance. When the ratio is too high, the sodium replenishment effect will be poor, leading to a lack of significant improvement in the first-cycle coulombic efficiency of the sodium-ion battery.

[0047] In a preferred embodiment, the thickness of the negative electrode active material layer 20 is 3–15 μm. Limiting the thickness of the negative electrode active material layer within this range effectively balances the energy density and conductivity of the sodium-ion battery. When the negative electrode material layer is too thin, the battery capacity will be too low, affecting the energy density; when the thickness of the negative electrode active material layer is too thick, the electrolyte will have difficulty penetrating, affecting the conductivity.

[0048] In a preferred embodiment, the thickness of the sodium-containing compound layer 30 is 0.5–15 μm. Limiting the thickness of the sodium-containing compound layer within this range results in superior electrochemical performance. Both excessively thick and excessively thin sodium-containing compound layers negatively impact the first-cycle efficiency and first-cycle discharge specific capacity of the sodium-ion battery. This is because: when the sodium-containing compound layer is too thin, it cannot effectively compensate for the initial irreversible sodium consumption of the negative electrode material; when the sodium-containing compound layer is too thick, the replenishment of sodium in the sodium-containing compound layer results in a large volume change, affecting battery stability and consequently impacting the first-cycle efficiency and first-cycle discharge specific capacity of the sodium-ion battery.

[0049] In a preferred embodiment, the sodium-containing compound in the sodium-containing compound layer 30 is selected from one or more of sodium phosphide, sodium nickelate, sodium chromate, sodium oxide, sodium sulfide, sodium carbonate, sodium fluoride, or sodium hydroxide. The sodium-containing compounds selected in this invention have high air stability, high safety, and high conductivity. During sodium replenishment, these compounds can provide more active sodium ions, thereby mitigating defects in the negative electrode active material layer and reducing side reactions with the electrolyte to a certain extent.

[0050] To further improve the electrochemical performance of the negative electrode in sodium-ion batteries, the sodium-containing compound in the sodium-containing compound layer 30 is preferably one or more of sodium phosphide, sodium oxide, or sodium sulfide. Sodium phosphide, sodium oxide, and sodium sulfide not only serve as sodium sources to replenish the active sodium in the negative electrode active material layer, but also possess reversible sodium storage electrochemical activity, enabling them to store sodium ions and participate in the battery cycle as active materials. This further improves the battery's first-cycle coulombic efficiency and first-cycle discharge specific capacity.

[0051] The reaction equation for sodium supplementation using sodium phosphide is: Na3P → 3 / x Na + +3 / xe - +Na x P; The reaction formula for sodium storage using sodium phosphide is: Na x P+3 / x Na + +3 / xe - →Na3P.

[0052] The reaction equation for sodium supplementation using sodium oxide is: Na₂O → 2 / x Na + +2 / xe - +Na x O; The reaction formula for sodium storage using sodium oxide is: Na x O+2 / x Na + +2 / xe - →Na2O.

[0053] The reaction equation for sodium supplementation using sodium sulfide is: Na₂S → 2 / x Na + +2 / xe - +Na x S; The reaction formula for sodium storage using sodium sulfide is: Na x S+2 / x Na + +2 / xe - →Na2S.

[0054] In a preferred embodiment, the sodium-containing compound layer 30 comprises sodium phosphide, sodium oxide, and sodium sulfide, wherein the weight ratio of sodium phosphide, sodium oxide, and sodium sulfide is 1–3:1:1–2. For example, the ratios can be 1:1:1; 1.5:1:1; 2:1:2; 2.5:1:1; 3:1:1; 1:1:2; 1.5:1:2; 2:1:2; 2.5:1:2; 3:1:2; 1:1:1.5; 1.5:1:1.5; 2:1:1.5; 3:1:1.5.

[0055] Sodium phosphide has the highest sodium ion content among the aforementioned sodium-containing compounds, resulting in the best sodium replenishment effect. However, sodium phosphide undergoes significant volume changes during the electrochemical reactions of sodium replenishment and storage, exhibiting the largest volume expansion among the three, which can easily lead to a decrease in battery capacity retention under long-term cycling. Sodium sulfide has the best stability among the three and is less prone to volume expansion. However, sodium sulfide is toxic, and excessive use can be harmful to test personnel and the test environment; therefore, the amount added should not be too large. Sodium oxide has a better sodium replenishment effect than sodium sulfide due to the difference in electronegativity between oxygen and sulfur atoms, and it is easier to release sodium ions. However, the resulting volume expansion is greater than that of sodium sulfide, leading to a decrease in battery capacity retention under long-term cycling. Nevertheless, it is superior to sodium phosphide and is non-toxic.

[0056] In summary, the volume expansion rates of sodium phosphide, sodium oxide, and sodium sulfide during the electrochemical reaction process of sodium replenishment and storage are ranked as follows: sodium phosphide > sodium oxide > sodium sulfide. Their sodium replenishment effectiveness is ranked as follows: sodium phosphide > sodium oxide > sodium sulfide. This invention achieves superior sodium replenishment activity and volume stability in the sodium-containing compound layer 30 when replenishing sodium in a sodium-ion battery by synergistically combining sodium phosphide, sodium oxide, and sodium sulfide and simultaneously controlling their proportions. This results in a sodium-ion battery with excellent first-week coulombic efficiency and long-term capacity retention.

[0057] In a preferred embodiment, the negative electrode active material in the negative electrode active material layer 20 is selected from one or more of hard carbon, soft carbon, artificial graphite, or natural graphite. The aforementioned negative electrode active material of this application has superior battery capacity and can improve the energy density of sodium-ion batteries.

[0058] Preferably, the negative electrode active material in the negative electrode active material layer 20 is hard carbon. Hard carbon materials have a large interlayer distance and many lattice defects, which provides abundant sites for sodium ions, enabling them to exhibit high reversible capacity when used as a negative electrode in sodium-ion batteries.

[0059] To further improve the reversible capacity of sodium-ion batteries, hard carbon with a specific surface area of ​​<10 m² is preferred. 2 / g, tap density is 0.85~1g / cm³ 3 The particle size is 5–10 μm and the interlayer spacing is 0.38–0.4 nm.

[0060] In a preferred embodiment, the current collector is selected from one or more of copper foil, aluminum foil, cobalt foil, nickel foil, or silver foil, and more preferably aluminum foil. When aluminum foil is used as the current collector, it exhibits superior conductivity, stability, and mechanical strength.

[0061] In a preferred embodiment, such as Figure 2 As shown, the negative electrode of a sodium-ion battery includes a current collector 10, a negative electrode active material layer 20, and a sodium-containing compound layer 30. The current collector 10 has a first outer surface and a second outer surface disposed opposite to each other. The negative electrode active material layer 20 is disposed on the first outer surface and the second outer surface of the current collector 10, and the sodium-containing compound layer 30 is correspondingly disposed on the outer surfaces of the negative electrode active material layer 20 on both sides of the current collector. This invention provides a negative electrode active material layer 20 on both the first and second outer surfaces of the current collector, and a sodium-containing compound layer 30 is disposed on the outer surface of each negative electrode active material layer 20. This allows for more efficient utilization of the current collector during subsequent sodium-ion battery manufacturing processes, simplifies subsequent sodium-ion battery manufacturing steps, and saves material and process costs.

[0062] The present invention also provides a method for preparing the above-mentioned sodium-ion battery negative electrode, comprising providing a current collector 10 having a first outer surface and a second outer surface disposed opposite to each other; disposing a negative electrode active material layer 20 on the first outer surface and / or the second outer surface of the current collector 10; and disposing a sodium-containing compound layer 30 on the outer surface of the negative electrode active material layer 20 away from the current collector 10.

[0063] Based on the reasons stated above, the sodium-ion battery of the present invention features a stacked negative electrode configuration, with a sodium-containing compound layer 30 disposed on the outer surface of the negative electrode active material layer 20. The negative electrode active material layer 20 is disposed on the first and / or second outer surfaces of the current collector 10. The sodium-containing compound layer can release sodium ions during the first charge and discharge process of the sodium-ion battery to replenish sodium in the negative electrode material, thereby compensating for the initial irreversible sodium consumption of the negative electrode material and improving the energy density of the sodium-ion battery. In this application, the negative electrode active material layer and the sodium-containing compound layer are in interfacial contact, which, compared to the prior art where sodium-replenishing additives are physically doped into the interior of the negative electrode material layer, exhibits superior cycle stability and electrochemical performance.

[0064] In one embodiment, a first slurry containing a negative electrode active material is coated onto the first outer surface and / or the second outer surface of the current collector 10. After drying, a current collector 10 with a negative electrode active material layer 20 disposed on the first outer surface and / or the second outer surface is obtained. Preferably, the thickness of the first slurry coating is 5–100 μm, more preferably 5–25 μm. This invention uses a coating method to deposit the negative electrode active material layer on the first outer surface and / or the second outer surface of the current collector, which allows for precise control of the thickness of the negative electrode active material layer. Furthermore, by controlling the coating thickness of the first slurry within the aforementioned range, the energy density and conductivity of the material can be balanced.

[0065] In one embodiment, a second slurry containing a sodium compound is coated onto the outer surface of the negative electrode active material layer 20 away from the current collector 10, and after drying, a sodium-ion battery negative electrode is obtained. Preferably, the thickness of the second slurry coating is 0.5–100 μm, more preferably 5–25 μm. This invention uses a coating method to deposit the sodium compound layer on the outer surface of the negative electrode material layer, which allows for precise control of the thickness of the sodium compound layer. Furthermore, by controlling the coating thickness of the first slurry within the aforementioned range, the first-cycle efficiency and first-cycle discharge specific capacity of the sodium-ion battery can be improved.

[0066] In one embodiment, the first slurry is prepared by the following steps: mixing the negative electrode active material, the first conductive agent, and the first binder, followed by a first grinding, to obtain the first slurry.

[0067] Preferably, the weight ratio of the negative electrode active material, the first conductive agent, and the first binder is 6-8:1-2:0.5-1. The present invention controls the negative electrode active material, the first conductive agent, and the first binder within the above range in order to further improve the conductivity of the negative electrode active material, and at the same time control the viscosity of the first slurry to improve the adhesion between the negative electrode active material layer and the current collector.

[0068] Preferably, the first grinding speed is 300-500 r / min, and the first grinding time is 36-60 min. By controlling the grinding speed and time within the above range, the present invention can ensure that the solid substances in the first slurry are fully ground, resulting in uniform particle size and better dispersibility of solid substances in the slurry. Consequently, the slurry has better coatability and can be uniformly and smoothly coated on the surface of the current collector.

[0069] To further improve the adhesion between the negative electrode active material layer and the current collector, the viscosity of the first slurry is preferably 2000-10000 mPa·s at 25°C; more preferably 3000-7000 mPa·s; and the D50 particle size of the solids in the first slurry is 5 μm-10 μm.

[0070] In a preferred embodiment, the second slurry is prepared by the following steps: under an inert atmosphere, a sodium-containing compound, a second conductive agent, and a second binder are mixed and then subjected to a second grinding to obtain the second slurry.

[0071] Preferably, the weight ratio of the sodium-containing compound, the second conductive agent, and the second binder is 6-8:1-2:0.5-1. The present invention controls the sodium-containing compound, the second conductive agent, and the second binder within the above range in order to further improve the conductivity of the sodium-containing compound, while controlling the viscosity of the second slurry to improve the adhesion between the sodium-containing compound layer and the negative electrode active material layer.

[0072] Preferably, the second grinding speed is 300-500 r / min, and the second grinding time is 36-60 min. By controlling the grinding speed and time within the above range, the present invention can ensure that the solid substances in the second slurry are fully ground, resulting in uniform particle size and better dispersibility of solid substances in the slurry. Consequently, the slurry has better coating properties and can be uniformly and smoothly coated on the surface of the negative electrode active material layer.

[0073] To further improve the adhesion between the sodium-containing compound layer and the negative electrode material layer, the viscosity of the second slurry is preferably 2000-10000 mPa·s at 25°C; more preferably 3000-7000 mPa·s; and the D50 particle size of the solids in the second slurry is 5 μm-10 μm.

[0074] To further improve the conductivity of sodium-ion batteries, the first conductive agent and the second conductive agent are each independently selected from one or more of acetylene black, conductive carbon black, or carbon nanotubes; preferably, the first conductive agent and the second conductive agent are acetylene black.

[0075] To further improve the adhesion between layers in the material, the first adhesive and the second adhesive are each independently selected from one or more of polyvinylidene fluoride solution, styrene-butadiene rubber, carboxymethyl cellulose or polyacrylic acid. More preferably, both the first adhesive and the second adhesive are polyvinylidene fluoride solutions, and the mass concentration of polyvinylidene fluoride is 50-100 mg / mL, wherein the solvent of the polyvinylidene fluoride solution is N-methylpyrrolidone.

[0076] In a preferred embodiment, the first drying temperature is 50–90°C; the first drying time is 24–48 h, more preferably 24–36 h. By limiting the first drying temperature and time within the above ranges, the present invention can obtain a suitable curing effect, control the thickness of the negative electrode active material layer, and improve the adhesion between the negative electrode active material layer and the current collector.

[0077] In a preferred embodiment, the second drying temperature is 50–90°C, more preferably 60–80°C; the second drying time is 24–48 h, more preferably 24–36 h. By limiting the second drying temperature and time within the above ranges, the present invention can obtain a suitable curing effect, control the thickness of the sodium-containing compound, and improve the adhesion between the sodium-containing compound layer and the negative electrode active material layer.

[0078] The present invention also provides a sodium-ion battery, which includes the sodium-ion battery negative electrode described above.

[0079] Based on the reasons stated above, the sodium-ion battery of the present invention has superior cycle stability and electrochemical performance.

[0080] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0081] Example 1

[0082] like Figure 1 As shown, the negative electrode of the sodium-ion battery includes a current collector 10, a negative electrode active material layer 20, and a sodium-containing compound layer 30. The current collector 10 has a first outer surface and a second outer surface disposed opposite to each other. The negative electrode active material layer 20 is disposed on the first outer surface of the current collector 10, and the sodium-containing compound layer 30 is disposed on the outer surface of the negative electrode active material layer 20.

[0083] Preparation of the first slurry containing the negative electrode active material: hard carbon powder (particle size 10 μm, specific surface area 10 m²) 2 / g, compacted density is 1g / cm³ 3 ), acetylene black and polyvinylidene fluoride solution (solvent is N-methylpyrrolidone, polyvinylidene fluoride mass concentration is 50 mg·mL), -1After being mixed in a weight ratio of 8:1:1, the mixture was subjected to a first grinding process for 48 hours at a grinding speed of 400 r / min to obtain a first slurry. The viscosity of the first slurry was 5000 mPa·s at 25°C, and the D50 particle size of the solids in the first slurry was 8 μm.

[0084] Preparation of a second slurry containing sodium compounds: Under an inert atmosphere, sodium compounds (sodium phosphide powder, sodium oxide powder, sodium sulfide powder), acetylene black, and polyvinylidene fluoride solution (solvent is N-methylpyrrolidone, and the mass concentration of polyvinylidene fluoride is 50 mg·mL⁻¹) are added. -1 The mixture was then subjected to a second grinding process at a weight ratio of 8:1:1 for 48 hours at a grinding speed of 400 r / min to obtain a second slurry. The sodium-containing compounds contained sodium phosphide, sodium oxide, and sodium sulfide in a weight ratio of 2:1:1. The viscosity of the second slurry was 5000 mPa·s, and the D50 particle size of the solids in the second slurry was 8 μm.

[0085] A first slurry containing a negative electrode active material is coated onto the first outer surface of an aluminum foil current collector 10, and then subjected to a first drying process at a temperature of 60°C for 24 hours to obtain a negative electrode active material layer 20 coated on the first outer surface of the current collector.

[0086] A second slurry containing a sodium compound is coated onto the outer surface of the above-mentioned negative electrode active material layer 20 to form a sodium compound layer 30. After a second drying process, the drying temperature is 60°C and the drying time is 24 hours, resulting in a sodium-ion battery negative electrode.

[0087] In this embodiment, the thickness ratio of the negative electrode active material layer to the sodium-containing compound layer is 1:1, the thickness of the negative electrode active material layer is 5 μm, and the thickness of the sodium-containing compound layer is 5 μm.

[0088] Example 2

[0089] The only difference from Example 1 is that the weight ratio of sodium phosphide, sodium oxide and sodium sulfide in the sodium-containing compound is 1:1:1.

[0090] Example 3

[0091] The only difference from Example 1 is that the weight ratio of sodium phosphide, sodium oxide and sodium sulfide in the sodium-containing compound is 1:1:2.

[0092] Example 4

[0093] The only difference from Example 1 is that the weight ratio of sodium phosphide, sodium oxide and sodium sulfide in the sodium-containing compound is 3:1:1.

[0094] Example 5

[0095] The only difference from Example 1 is that the weight ratio of sodium phosphide, sodium oxide and sodium sulfide in the sodium-containing compound is 4:1:1.

[0096] Example 6

[0097] The only difference from Example 1 is that the sodium-containing compound is sodium phosphide.

[0098] Example 7

[0099] The only difference from Example 1 is that the sodium-containing compound is sodium carbonate.

[0100] Example 8

[0101] The only difference from Example 1 is that the thickness ratio of the negative electrode active material layer to the sodium-containing compound layer obtained in this example is 0.5:1, the thickness of the negative electrode active material layer is 5 μm, and the thickness of the sodium-containing compound layer is 10 μm.

[0102] Example 9

[0103] The only difference from Example 1 is that the thickness ratio of the negative electrode active material layer to the sodium-containing compound layer obtained in this example is 10:1, the thickness of the negative electrode active material layer is 5 μm, and the thickness of the sodium-containing compound layer is 0.5 μm.

[0104] Example 10

[0105] The only difference from Example 1 is that the thickness ratio of the negative electrode active material layer to the sodium-containing compound layer obtained in this example is 5:1, the thickness of the negative electrode active material layer is 5 μm, and the thickness of the sodium-containing compound layer is 1 μm.

[0106] Example 11

[0107] The only difference from Example 1 is that the thickness ratio of the negative electrode active material layer to the sodium-containing compound layer obtained in this example is 4:1, the thickness of the negative electrode active material layer is 5 μm, and the thickness of the sodium-containing compound layer is 20 μm.

[0108] Example 12

[0109] The only difference from Example 1 is that the thickness ratio of the negative electrode active material layer to the sodium-containing compound layer obtained in this example is 15:1, the thickness of the negative electrode active material layer is 15 μm, and the thickness of the sodium-containing compound layer is 1 μm.

[0110] Comparative Example 1

[0111] The difference from Example 1 is that the sodium-ion battery anode prepared in this example does not include a sodium-containing compound layer, and the thickness of the active layer of the anode material is 10 μm.

[0112] Comparative Example 2

[0113] In an inert atmosphere, hard carbon powder, sodium-containing compounds (sodium phosphide powder, sodium oxide powder, sodium sulfide powder), acetylene black, and polyvinylidene fluoride solution (solvent is N-methylpyrrolidone, and the mass concentration of polyvinylidene fluoride is 50 mg·mL⁻¹) are added. -1 The mixtures were ground in a weight ratio of 4:4:1:1 to obtain a slurry for the negative electrode material. The sodium phosphide powder, sodium oxide powder, and sodium sulfide powder in the sodium-containing compound were in a weight ratio of 2:1:1. The grinding time was 48 hours and the grinding speed was 400 r / min.

[0114] The above-mentioned negative electrode material is coated onto the surface of an aluminum foil current collector with a slurry, and then dried at a temperature of 60°C for 24 hours to obtain a sodium-ion battery negative electrode, wherein the thickness of the negative electrode material coating is 10 μm.

[0115] Performance testing:

[0116] Button cell preparation method: The sodium-ion battery negative electrode of the above embodiment and comparative example is cut into small circular pieces with a diameter of about 1 cm using a cutting machine to be used as the negative electrode. A metallic sodium sheet is used as the counter electrode, Celgard2500 is used as the separator, and EC / DMC / EMC 1:1:1 (W / W) + 1M NaPF6 is used as the electrolyte. The button cell is assembled in a glove box under an argon atmosphere, requiring that the water and oxygen content in the glove box be less than 0.1 ppm.

[0117] Electrochemical performance testing: The assembled battery was subjected to constant current charge-discharge testing using a LANDCT 2001A tester (Wuhan Landian Electronics Co., Ltd.). The test temperature was 25℃, the test voltage range was 0.01~3.0V, the test current density was 0.1C, and the nominal specific capacity was set to 530mAh / g. The test results are shown in Table 1.

[0118] Table 1

[0119]

[0120]

[0121] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A sodium-ion battery negative electrode, characterized in that, The negative electrode of the sodium-ion battery includes: A current collector (10) having a first outer surface and a second outer surface disposed opposite to each other; A negative electrode active material layer (20) disposed on the first outer surface and / or the second outer surface of the current collector (10); A sodium-containing compound layer (30) disposed on the outer surface of the negative electrode active material layer (20) away from the current collector (10); The ratio of the thickness of the negative electrode active material layer (20) to the thickness of the sodium-containing compound layer (30) is 1 to 5:1; the thickness of the negative electrode active material layer (20) is 3 to 15 μm; the thickness of the sodium-containing compound layer (30) is 0.5 to 15 μm; The sodium-containing compound in the sodium-containing compound layer (30) is a combination of sodium phosphide, sodium oxide and sodium sulfide, and the weight ratio of the sodium phosphide, the sodium oxide and the sodium sulfide is 1 to 3:1:1 to 2.

2. The sodium-ion battery negative electrode according to claim 1, characterized in that, The negative electrode active material in the negative electrode active material layer (20) is selected from one or more of hard carbon, soft carbon, artificial graphite or natural graphite.

3. The sodium-ion battery negative electrode according to claim 2, characterized in that, The negative electrode active material in the negative electrode active material layer (20) is selected from the hard carbon; the specific surface area of ​​the hard carbon is ≤10m². 2 / g, tap density is 0.85~1g / cm³ 3 The particle size is 5~10μm and the interlayer spacing is 0.38~0.4nm.

4. The sodium-ion battery negative electrode according to claim 1, characterized in that, The current collector is selected from one or more of copper foil, aluminum foil, cobalt foil, nickel foil or silver foil.

5. The sodium-ion battery negative electrode according to claim 4, characterized in that, The current collector is the aluminum foil.

6. A method for preparing a sodium-ion battery negative electrode according to any one of claims 1 to 5, characterized in that, The preparation method of the negative electrode of the sodium-ion battery includes: Providing a current collector (10) having a first outer surface and a second outer surface disposed opposite to each other; Disposing a negative electrode active material layer (20) on the first outer surface and / or the second outer surface of the current collector (10); Disposing a sodium-containing compound layer (30) on the outer surface of the negative electrode active material layer (20) away from the current collector (10).

7. The method for preparing a sodium-ion battery negative electrode according to claim 6, characterized in that, The preparation method includes the following steps: Coating a first slurry containing a negative electrode active material on the first outer surface and / or the second outer surface of the current collector (10), and after first drying, obtaining the current collector (10) with the negative electrode active material layer (20) disposed on the first outer surface and / or the second outer surface; Coating a second slurry containing a sodium-containing compound on the outer surface of the negative electrode active material layer (20) away from the current collector (10), and after second drying, obtaining the negative electrode of the sodium-ion battery.

8. The method for preparing a sodium-ion battery negative electrode according to claim 7, characterized in that, The first slurry is prepared by the following steps: mixing the negative electrode active material, a first conductive agent and a first binder first and then performing first grinding to obtain the first slurry; The second slurry is prepared by the following steps: under an inert atmosphere condition, mixing the sodium-containing compound, a second conductive agent and a second binder second and then performing second grinding to obtain the second slurry; The weight ratio of the negative electrode active material, the first conductive agent and the first binder is 6 to 8:1 to 2:0.5 to 1; The weight ratio of the sodium-containing compound, the second conductive agent and the second binder is 6 to 8:1 to 2:0.5 to 1; The first conductive agent and the second conductive agent are each independently conductive carbon black and / or carbon nanotubes; the conductive carbon black is acetylene black; The first binder and the second binder are each independently selected from one or more of polyvinylidene fluoride solution, styrene-butadiene rubber, carboxymethyl cellulose or polyacrylic acid.

9. The method for preparing a sodium-ion battery negative electrode according to claim 8, wherein the first binder and the second binder are both polyvinylidene fluoride solutions, and the mass concentration of polyvinylidene fluoride in the polyvinylidene fluoride solution is 50~100 mg / mL.

10. The method for preparing a sodium-ion battery negative electrode according to claim 7, characterized in that, The viscosity of the first slurry is 2000~10000 mPa•s at 25℃; the D50 particle size of the solids in the first slurry is 5μm~10μm. The viscosity of the second slurry is 2000~10000 mPa•s at 25°C; the D50 particle size of the solids in the first slurry is 5μm~10μm.

11. The method for preparing a sodium-ion battery negative electrode according to claim 7, characterized in that, The temperature of the first drying process is 50~90℃; the drying time is 24~48h.

12. The method for preparing a sodium-ion battery negative electrode according to claim 11, characterized in that, The first drying time is 24~36 hours.

13. The method for preparing a sodium-ion battery negative electrode according to claim 7, characterized in that, The second drying temperature is 50~90℃; the second drying time is 24~48h.

14. The method for preparing a sodium-ion battery negative electrode according to claim 13, characterized in that, The second drying temperature is 60~80℃, and the second drying time is 24~36h.

15. A sodium-ion battery, characterized in that, The sodium-ion battery includes the sodium-ion battery negative electrode as described in any one of claims 1 to 5.

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