A negative electrode sheet and a sodium-ion battery

Abstract

This application belongs to the field of new energy battery technology, specifically relating to a negative electrode sheet and a sodium-ion battery. This application provides a negative electrode sheet, including a negative electrode current collector and a negative electrode active layer. The negative electrode active material includes a core and a coating layer covering at least a portion of the surface of the core. The core includes a first disordered carbon material, and the coating layer includes a second disordered carbon material. The thickness of the coating layer is denoted as P nm, where 5 ≤ P ≤ 200. The particle size of the negative electrode active material satisfies: (Dv60 / Dv10) × (Dv90 / Dv40) ≤ 20. The negative electrode active material in the negative electrode sheet provided by this application has a consistent ion diffusion path, reducing ion transport resistance, constructing an electronic conductivity network, and is beneficial to the battery's low-temperature cycling and low-temperature discharge power performance.

Description

Technical Field

[0001] This application belongs to the field of new energy battery technology, specifically relating to a negative electrode and a sodium-ion battery. Background Technology

[0002] Sodium-ion batteries have shown great potential in extreme environments such as electric vehicles in cold regions, deep-space and deep-sea equipment, and cold-region communication base stations due to the abundance and low cost of sodium resources and their inherent superior low-temperature migration characteristics compared to lithium-ion batteries. However, existing sodium-ion batteries exhibit problems at low temperatures, such as sluggish sodium-ion desolvation kinetics and hindered sodium-ion diffusion within the bulk material. These problems lead to a sharp increase in internal resistance, deterioration in discharge power performance, and a reduction in cycle life. Summary of the Invention

[0003] Therefore, the technical problem to be solved by this application is to overcome the defects of low discharge power and poor cycle performance of batteries at low temperatures in the prior art, thereby providing a negative electrode and a sodium-ion battery.

[0004] Therefore, this application provides the following technical solution.

[0005] According to an embodiment of this application, in a first aspect, a negative electrode sheet is provided, comprising a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector, the negative electrode active layer comprising a negative electrode active material, the negative electrode active material comprising a core and a coating layer covering at least a portion of the surface of the core, the core comprising a first disordered carbon material, the coating layer comprising a second disordered carbon material, the thickness of the coating layer denoted as P nm, 5 ≤ P ≤ 200, and the particle sizes Dv10, Dv40, Dv60 and Dv90 of the negative electrode active material satisfying: (Dv60 / Dv10) × (Dv90 / Dv40) ≤ 20; And / or, 1μm≤Dv10≤4μm; and / or, 2μm≤Dv40≤7μm; and / or, 5μm≤Dv60≤9μm; and / or, 7μm≤Dv90≤16μm.

[0006] According to an embodiment of this application, in a second aspect, a sodium-ion battery is also provided, comprising a positive electrode, a separator, an electrolyte, and the negative electrode described in the first aspect.

[0007] The technical solution of this application has the following advantages: The negative electrode sheet provided in this application includes a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material includes a core and a coating layer covering at least a portion of the surface of the core. The core includes a first disordered carbon material, and the coating layer includes a second disordered carbon material. The thickness of the coating layer is denoted as P nm, where 5 ≤ P ≤ 200. The particle sizes Dv10, Dv40, Dv60, and Dv90 of the negative electrode active material satisfy: (Dv60 / Dv10) × (Dv90 / Dv40) ≤ 20. 1μm≤Dv10≤4μm; and / or, 2μm≤Dv40≤7μm; and / or, 5μm≤Dv60≤9μm; and / or, 7μm≤Dv90≤16μm.

[0008] This study found that (Dv60 / Dv10)×(Dv90 / Dv40)≤20 can ensure the uniformity of particle size distribution of the negative electrode active material, indicating that there is neither excessive fine powder nor excessive coarse powder. The uniformly distributed negative electrode active material has a consistent ion diffusion path, which can reduce ion transport resistance and construct an effective electronic conductivity network. This allows the negative electrode active material to have good transport rate even at low temperatures, which is beneficial to the low-temperature cycling and low-temperature discharge power performance of the battery. Simultaneously, this negative electrode active material can also form a uniform and dense structure. A better solid electrolyte interphase (SEI) film on the negative electrode side reduces interfacial impedance, minimizes polarization, and improves the battery's low-temperature cycling and low-temperature discharge power performance. Furthermore, when 1μm≤Dv10≤4μm; and / or 2μm≤Dv40≤7μm; and / or 5μm≤Dv60≤9μm; and / or 7μm≤Dv90≤16μm, a reasonable particle size distribution can ensure a certain compaction density, which is beneficial to cycle stability and low-temperature performance. At the same time, the negative electrode active material has good processability, which facilitates production.

[0009] Additional aspects and advantages of the embodiments of this application will be described and shown in part in the following description, or illustrated by practice of the embodiments of this application. Detailed Implementation

[0010] The following embodiments are provided to better understand this application and are not limited to the preferred embodiments described herein. They do not constitute a limitation on the content and scope of protection of this application. Any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining features of this application with other prior art, falls within the scope of protection of this application.

[0011] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0012] To address the issues of poor low-temperature discharge power performance and low-temperature cycle performance of sodium-ion batteries in related technologies, according to an embodiment of this application, in a first aspect, a negative electrode sheet is provided, comprising a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector, the negative electrode active layer comprising a negative electrode active material, the negative electrode active material comprising a core and a coating layer covering at least a portion of the surface of the core, the core comprising a first disordered carbon material, the coating layer comprising a second disordered carbon material, the thickness of the coating layer denoted as P nm, 5≤P≤200, and the particle sizes Dv10, Dv40, Dv60 and Dv90 of the negative electrode active material satisfying: (Dv60 / Dv10)×(Dv90 / Dv40)≤20; 1μm≤Dv10≤4μm; and / or, 2μm≤Dv40≤7μm; and / or, 5μm≤Dv60≤9μm; and / or, 7μm≤Dv90≤16μm.

[0013] This study found that Dv60 / Dv10 reflects the distribution amount of fine powder in the negative electrode active material, while Dv90 / Dv40 reflects the distribution amount of coarse powder. By satisfying (Dv60 / Dv10)×(Dv90 / Dv40)≤20, the uniformity of particle size distribution of the negative electrode active material can be guaranteed, indicating that there is neither an excessive amount of fine powder nor an excessive amount of coarse powder. The product of the two, (Dv60 / Dv10)×(Dv90 / Dv40), acts as a magnifying glass for the distribution morphology of the negative electrode active material. If there is too much coarse powder or too much fine powder, then (Dv60 / Dv10) will be less than or equal to 20. The ratio (Dv90 / Dv40) can spike to over 20; however, a uniformly distributed negative electrode active material has a consistent ion diffusion path, which reduces ion transport resistance and constructs an effective electronic conductivity network, enabling the negative electrode active material to maintain a good transport rate even at low temperatures, thus benefiting the battery's low-temperature cycling and low-temperature discharge power performance. Simultaneously, a negative electrode active material with a uniform particle size distribution can also help form a uniform and dense solid electrolyte interphase (SEI) film on the negative electrode side, thereby reducing interfacial impedance and polarization, which also benefits the battery's low-temperature cycling and low-temperature discharge power performance. Exemplarily, the particle size of the negative electrode active material can be measured using conventional testing methods in the art, such as a Malvern Mastersizer 3000 laser particle size analyzer.

[0014] If (Dv60 / Dv10) × (Dv90 / Dv40) is greater than 20, it indicates poor uniformity of particle size distribution of the negative electrode active material, significant differences in ion diffusion paths, and increased ion transport resistance, which is detrimental to the battery's low-temperature cycling and low-temperature discharge power performance. It is understood that in this application, Dv10 is the particle size corresponding to a cumulative volume distribution percentage of 10% for the negative electrode active material, Dv40 is the particle size corresponding to a cumulative volume distribution percentage of 40% for the negative electrode active material, Dv60 is the particle size corresponding to a cumulative volume distribution percentage of 60% for the negative electrode active material, and Dv90 is the particle size corresponding to a cumulative volume distribution percentage of 90% for the negative electrode active material. For example, (Dv60 / Dv10)×(Dv90 / Dv40) can be 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, etc., or a value within the range of any two of the above values.

[0015] Further, 1μm ≤ Dv10 ≤ 4μm, and / or 2μm ≤ Dv40 ≤ 7μm, and / or 5μm ≤ Dv60 ≤ 9μm, and / or 7μm ≤ Dv90 ≤ 16μm. This facilitates the processing of the negative electrode active material and reduces production difficulty. For example, Dv10 can be 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, etc., or a value within the range of any two of the above values. For example, Dv40 can be 2μm, 2.5μm, 3μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, etc., or a value within the range of any two of the above values. For example, Dv60 can be 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, or a value within the range of any two of the above values. For example, Dv90 can be 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, or a value within the range of any two of the above values.

[0016] Meanwhile, controlling the thickness P of the coating layer to satisfy 5 ≤ P ≤ 200 can further improve ion diffusion efficiency. Thus, while fully leveraging the improved effect of the negative electrode active material with good particle size uniformity, it also enhances kinetic performance, which is beneficial for the battery's low-temperature cycling and low-temperature discharge power performance. Exemplarily, the thickness P of the coating layer can be measured using conventional methods in the art, such as transmission electron microscopy (TEM). Exemplarily, the thickness P (in nm) of the coating layer can be 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, or a value within any two of the above ranges.

[0017] In some embodiments, in the Raman spectrum of the second disordered carbon material, 0.7 ≤ J2 ≤ 1.2, J2 = I D2 / I G2 , wherein, the I D2 This indicates that the Raman displacement is at 1300 cm. -1 -1400cm -1 The peak intensity of the Raman peak at the location, I G2 This indicates that the Raman displacement is at 1500 cm. -1 -1650cm -1 The peak intensity of the Raman peak at the location; can further improve the high-temperature storage performance of the battery. In the Raman spectrum of the second disordered carbon material, 0.7≤J2≤1.2 indicates that the defects in the coating layer are smaller and the stability of the second disordered carbon material is better. Further controlling 0.0035≤J2 / P≤0.24 can improve the ion diffusion efficiency while ensuring the coating effect and improving the stability of the negative electrode active material, thereby improving the high-temperature storage, low-temperature cycling and low-temperature discharge power performance of the battery. Exemplarily, the Raman spectrum of the second disordered carbon material can be measured by conventional methods in the art, such as testing with a Raman spectrometer; Exemplarily, I D2 (unit: cm) -1 () can be 1300, 1305, 1310, 1315, 1320, 1325, 1330, 1335, 1340, 1345, 1350, 1355, 1360, 1365, 1370, 1375, 1380, 1385, 1390, 1395, 1400, etc., or values ​​within the range of any two of the above values. For example, I G2 (unit: cm) -1The ) can be 1500, 1510, 1520, 1530, 1540, 1550, 1555, 1560, 1565, 1570, 1575, 1580, 1585, 1590, 1595, 1600, 1605, 1610, 1615, 1620, 1630, 1640, 1650, etc., or values ​​within the range of any two of the above values. For example, J2 can be 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, etc., or values ​​within the range of any two of the above values.

[0018] In some implementations, 5 ≤ (Dv60 / Dv10) × (Dv90 / Dv40) ≤ 20; this can further increase the compaction density of the material and improve its conductivity, thereby further improving the low-temperature cycling and low-temperature discharge power performance of the battery.

[0019] In some embodiments, in the Raman spectrum of the first disordered carbon material, J1=I D1 / I G1 , wherein, the I D1 This indicates that the Raman displacement is at 1300 cm. -1 -1400cm -1 The peak intensity of the Raman peak at the location, I G1 This indicates that the Raman displacement is at 1500 cm. -1 -1650cm -1 The peak intensity of the Raman peak at the location; J1 is greater than J2; in some embodiments, 0.8 ≤ J1 ≤ 2.5. Thus, a coating layer with lower defect levels (especially when 0.8 ≤ J1 ≤ 2.5, 0.7 ≤ J2 ≤ 1.2) can compensate for the core defect level, improve the high-temperature storage performance of the battery, optimize the interface of the negative electrode active material, reduce impedance, and further improve the low-temperature cycling and low-temperature discharge power performance of the battery. Exemplarily, the Raman spectrum of the first disordered carbon material can be measured using conventional methods in the art, for example, by testing with a Raman spectrometer; Exemplarily, I D1 (unit: cm) -1 () can be 1300, 1305, 1310, 1315, 1320, 1325, 1330, 1335, 1340, 1345, 1350, 1355, 1360, 1365, 1370, 1375, 1380, 1385, 1390, 1395, 1400, etc., or values ​​within the range of any two of the above values. For example, I G1 (unit: cm) -1The ) can be 1500, 1510, 1520, 1530, 1540, 1550, 1555, 1560, 1565, 1570, 1575, 1580, 1585, 1590, 1595, 1600, 1605, 1610, 1615, 1620, 1630, 1640, 1650, etc., or values ​​within the range of any two of the above values. For example, J1 can be 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, etc., or values ​​within the range of any two of the above values.

[0020] In some embodiments, the negative electrode active material contains a first element, which includes Ca and Fe. Based on the mass of the negative electrode active material, the mass content of Ca is less than or equal to 500 ppm, and the mass content of Fe is less than or equal to 100 ppm. Exemplarily, the mass content of Ca and the mass content of Fe can be measured using conventional methods in the art, such as inductively coupled plasma optical emission spectrometry (ICP-OES). Exemplarily, the mass content of Ca (in ppm) can be 0.05, 0.1, 0.5, 1, 5, 10, 50, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 250, 300, 350, 400, 450, 500, etc., or values ​​within the range of any two of the above values. For example, the Fe mass content (in ppm) can be 0.05, 0.1, 0.5, 1, 5, 10, 50, 100, or a value within any two of the above ranges. By controlling the Ca content in the negative electrode active material to less than or equal to 500 ppm and the Fe content to less than or equal to 100 ppm, the low Ca and Fe content can maintain the structural stability of the carbon material, optimize the distribution of sodium storage active sites, reduce irreversible capacity loss during the first charge and discharge process, improve the first coulombic efficiency, low-temperature discharge power, and low-temperature cycle performance, and improve the battery's thermal safety and high-temperature storage performance.

[0021] According to an embodiment of this application, in a second aspect, a sodium-ion battery is also provided, comprising a positive electrode, a separator, an electrolyte, and the negative electrode described in the first aspect.

[0022] It is understood that the sodium-ion battery provided in this application has good low-temperature cycling and low-temperature discharge power performance because it has the negative electrode sheet described in the first aspect.

[0023] In some embodiments, the negative electrode sheet further includes a conductive agent, which includes carbon nanotubes; the number 'a' of carbon nanotubes is 5-180 within a 5μm × 5μm scanning electron microscope range. Further research in this application has found that adding carbon nanotubes to the negative electrode sheet allows these excellent one-dimensional conductors to interconnect like "wires," thus connecting with the negative electrode active material and forming a three-dimensional conductive network. This helps electrons quickly travel from the current collector to the carbon material surface, significantly reducing the charge transfer impedance of the negative electrode, thereby reducing the battery's internal resistance and improving its low-temperature cycle performance and low-temperature discharge power performance. Furthermore, controlling the number of carbon nanotubes to 5-180, particularly within the range of 13-42, effectively leverages the advantages of carbon nanotubes while avoiding excessive side reactions between the carbon nanotubes with their large specific surface area and the electrolyte, thus ensuring the battery's high-temperature storage performance. Exemplarily, the mass content 'a%' of the carbon nanotubes can be obtained using conventional testing methods in the art. For example, using a scanning electron microscope, the number of carbon nanotubes can be measured within a 5μm × 5μm area. Five areas can be randomly selected, and the average value can be taken to obtain the number of carbon nanotubes. For example, the number 'a' of carbon nanotubes can be 5, 13, 30, 42, 60, 120, 150, 180, etc., or a value within any two of the above ranges.

[0024] In some embodiments, the diameter of the carbon nanotubes is denoted as c nm, and the tap density of the negative electrode active material is denoted as b g / cm³. 3 The following conditions must be met: 0.01 ≤ b / c ≤ 0.3; in some embodiments, 4 ≤ c ≤ 60; in some embodiments, 0.5 ≤ b ≤ 1.2. This application research found that when 0.01 ≤ b / c ≤ 0.3, especially when 4 ≤ c ≤ 60 and 0.5 ≤ b ≤ 1.2 are met, carbon nanotubes can uniformly fill the gaps in the negative electrode active material, forming an effective conductive network, which is beneficial to the low-temperature discharge power and low-temperature cycle performance of the battery. If b / c is greater than 0.3, the carbon material and carbon nanotubes are prone to agglomeration and cross-linking, which is not conducive to the transmission of electrons in the conductive network, increasing impedance and polarization, thus affecting the low-temperature discharge power and low-temperature cycle performance of the battery. For example, b / c can be 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, or a value within the range of any two of the above values.

[0025] For example, the tap density of the negative electrode active material is bg / cm³. 3 It can be obtained by conventional testing methods in the art. For example, it can be measured using a tap density tester; exemplarily, the tap density of the negative electrode active material (unit: bg / cm³) 3The ) can be 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, etc., or a value within the range of any two of the above values.

[0026] For example, the diameter of the carbon nanotube can be obtained by testing methods conventional in the art. For instance, the diameter of the carbon nanotube can be measured by observing its cross-section or longitudinal section using a transmission electron microscope (TEM). For example, the diameter (in nm) c of the carbon nanotube can be 4, 5, 8, 10, 12, 15, 18, 20, 23, 25, 27, 30, 33, 35, 37, 40, 45, 50, 55, 60, etc., or a value within any two of the above ranges. Furthermore, controlling the diameter c of the carbon nanotubes to satisfy 4≤c≤60 allows the carbon nanotubes to achieve both good high-temperature and low-temperature performance. On the one hand, carbon nanotubes with a suitable diameter can be uniformly dispersed in the slurry and avoid agglomeration, thereby forming a uniform conductive network in the negative electrode. On the other hand, it can increase the number of contact points between the carbon nanotubes and the negative electrode active material, effectively helping electron transport. Moreover, the carbon nanotubes have good flexibility, which can ensure the flexibility and compaction density of the negative electrode, thus benefiting the battery's low-temperature discharge power, low-temperature cycling, and high-temperature storage performance.

[0027] In some embodiments, the length of the carbon nanotubes is 1 μm-100 μm. Exemplarily, the length of the carbon nanotubes can be obtained by conventional testing methods in the art. For example, it can be measured using a scanning electron microscope (SEM) or an atomic force microscope (AFM). Exemplarily, the length of the carbon nanotubes (in μm) can be 1, 3, 5, 8, 10, 12, 15, 18, 20, 23, 25, 27, 30, 40, 50, 60, 70, 80, 90, 100, or a value within any two of the above ranges.

[0028] In some embodiments, the negative electrode sheet further includes a binder, which includes at least one selected from polyvinyl alcohol, polyacrylic acid, sodium polyacrylate, sodium alginate, sodium carboxymethyl cellulose, and styrene-butadiene rubber. The mass content of the binder, based on the mass of the negative electrode active layer, is denoted as m%, satisfying 0.5 ≤ m ≤ 4. This can further improve the low-temperature discharge power and low-temperature cycle performance of the battery. Exemplarily, the mass content of the binder can be obtained by conventional testing methods in the art, such as thermogravimetric analysis (TGA). Exemplarily, the mass content m% of the binder can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, or a value within any two of the above ranges.

[0029] In some embodiments, the binder comprises sodium polyacrylate, with the sodium content (k%) denoted by the mass of the sodium polyacrylate, satisfying 1 ≤ k ≤ 15. Sodium ions in sodium polyacrylate can participate in the formation of the SEI film, improving its stability and ionic conductivity while reducing sodium ion transport resistance. Simultaneously, compared to polyacrylic acid, the polymer chains of sodium polyacrylate change from a coiled to an extended shape, allowing for more uniform bonding with the negative electrode active material. This helps the conductive network better transport electrons, improving the battery's low-temperature discharge power and low-temperature cycle performance. Furthermore, the tight bonding between sodium polyacrylate and the negative electrode active material also enhances the mechanical properties of the negative electrode active layer, effectively improving the structural stability of the negative electrode during cycling, which also benefits the battery's low-temperature discharge power and low-temperature cycle performance. In addition, controlling the sodium content (k) in the sodium polyacrylate can reduce the viscosity of the negative electrode active layer slurry, increase the ion diffusion rate, and reduce side reactions, which is beneficial for the battery's high-temperature storage, low-temperature discharge power, and low-temperature cycle performance.

[0030] For example, the mass content k of sodium in the sodium polyacrylate can be obtained by conventional testing methods in the art. For instance, after the battery is discharged to 0% SOC, the negative electrode is dissected, the powder is scraped off, and the content is measured using inductively coupled plasma (ICP). For example, the mass content k% of sodium in the sodium polyacrylate can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, etc., or a value within any two of the above ranges.

[0031] In some implementations, 0.5 ≤ (k×m) ≤ 30. This reduces the amount of binder used while maintaining battery capacity and energy density, further shortening ion and electron transport paths and improving the structural stability of the negative electrode, thereby enhancing the battery's low-temperature discharge power and low-temperature cycle performance. For example, k×m can be 0.5, 1, 2, 3, 4, 5, 8, 10, 12, 15, 18, 20, 22, 25, 28, 30, or a value within any two of the above ranges.

[0032] In some embodiments, the porosity of the positive electrode is denoted as V. 正 The porosity of the negative electrode sheet is denoted as V. 负 The porosity of the membrane is denoted as V. 隔 %, satisfying H≥0.9, H=1 / S; S=|(V 负 -V 正 )| / V 隔 +|(V 负 -V 隔 )| / V 正 +|(V正 -V 隔 )| / V 负 .

[0033] Further research in this application revealed that the porosity of the positive electrode, negative electrode, and separator affects the ion conduction rate. A higher degree of porosity matching between the positive electrode, negative electrode, and separator results in better electrolyte wettability, smoother ion transport paths, and reduced likelihood of localized blockages or dead zones, thereby lowering ion diffusion resistance and improving the battery's low-temperature discharge power and low-temperature cycle performance. Specifically, V 负 -V 正 This reflects the difference in porosity between the positive and negative electrodes. If the difference is too large, a membrane with higher porosity can dilute the adverse effects of this difference, thereby helping ions to be smoothly transported from the negative electrode to the positive electrode through the membrane, i.e., |(V 负 -V 正 )| / V 隔 If the value is small, similarly, if the difference between the negative electrode and the membrane is large (V... 负 -V 隔 Sodium ions may clog the negative electrode side, but this adverse effect can be diluted by the higher porosity of the positive electrode. If the difference between the positive electrode and the separator is large (V... 正 -V 隔 A negative electrode with higher porosity can also dilute this adverse effect. Ultimately, H ≥ 0.9, especially when 0.9 ≤ H ≤ 20, indicates that sodium ions have a good transport rate in the overall combination of the positive electrode, separator, and negative electrode. Smooth ion transport and low diffusion resistance are beneficial to the battery's low-temperature cycling and low-temperature discharge power performance. For example, H can be 0.9, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 10, 15, 18, 20, etc., or a value within any two of the above ranges.

[0034] For example, the porosity V of the positive electrode sheet 正 It can be obtained by testing methods conventional in the art. For example, it can be measured using a true density meter. In some embodiments, 25 ≤ V 正 A porosity ≤40% ensures smooth ion channels and low diffusion resistance while providing a buffer space for the positive electrode active material, improving its stability during cycling. Furthermore, moderate porosity promotes good contact between the positive electrode active material and the positive electrode active layer, enabling the formation of a continuous conductive network and preventing excessive electrolyte wetting of the positive electrode, thus suppressing side reactions and benefiting the battery's low-temperature discharge power, low-temperature cycling, and high-temperature storage performance. For example, the porosity V of the positive electrode is... 正 % can be 25%, 28%, 30%, 32%, 35%, 37%, 40%, etc., or a value within the range of any two of the above values.

[0035] For example, the porosity V of the negative electrode sheet 负 It can be obtained by testing methods conventional in the art. For example, it can be measured using a true density meter. In some embodiments, 35 ≤ V 负 ≤50. This ensures good contact between the negative electrode active materials, forming a continuous conductive network and preventing excessive electrolyte wetting in the negative electrode sheet, thus suppressing side reactions. Simultaneously, it further guarantees smooth ion channels, low diffusion resistance, and provides buffer space for the negative electrode active materials, ensuring their stability and contributing to the battery's low-temperature discharge power, low-temperature cycling, and high-temperature storage performance. For example, the porosity V of the negative electrode sheet... 负 % can be 35%, 38%, 40%, 42%, 45%, 47%, 50%, etc., or a value within the range of any two of the above values.

[0036] For example, the porosity V of the membrane 隔 It can be obtained by testing methods conventional in the art. For example, it can be measured using a true density meter. In some embodiments, 40 ≤ V 隔 ≤60; thus, the separator possesses good structural and thermal stability, ensuring battery safety while allowing for uniform electrolyte wetting and ion migration uniformity. This reduces ion diffusion resistance, improves interfacial contact properties, and benefits the battery's low-temperature discharge power and low-temperature cycle performance. For example, the separator's porosity V 隔 % can be 40%, 42%, 45%, 48%, 50%, 52%, 55%, 57%, 60%, etc., or a value within the range of any two of the above values.

[0037] In some embodiments, the electrolyte includes a sulfur-containing additive, which includes at least one of 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, vinyl sulfate, vinyl disulfate, methanedisulfonate, ethylene sulfate, and mannitol carbonate sulfate; the mass content of the sulfur-containing additive is 0.1%-5% based on the mass of the electrolyte. The sulfur-containing additive provided in this application has high electrochemical activity due to the sulfur-oxygen bond, and can preferentially form a stable SEI film on the negative electrode side surface, thereby reducing direct contact between the negative electrode active material and the electrolyte, preventing electrolyte decomposition and gas generation, reducing side reactions, and improving the high-temperature storage performance of the battery. Furthermore, controlling the mass content of the sulfur-containing additive to 0.1%-5% can form a more uniform and dense SEI film, providing effective protection on the negative electrode side, further reducing side reactions. Simultaneously, the generated SEI film has a moderate thickness, with a short ion migration distance and low ion migration resistance, reducing the battery's internal resistance, which is beneficial for the battery's high-temperature storage, low-temperature discharge power, and low-temperature cycle performance.

[0038] For example, the mass content of the sulfur-containing additive can be obtained by testing methods conventional in the art. For example, it can be determined by gas chromatography (GC); for example, the mass content of the sulfur-containing additive can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc., or a value within the range of any two of the above values.

[0039] In some embodiments, the 1,3-propanesulfonate lactone content is 0.1%-5% based on the mass of the electrolyte; further, it is 1%-3%. This can further improve the uniformity and density of the SEI film and its ion transport performance, and further improve the battery's high-temperature storage, low-temperature discharge power, and low-temperature cycling performance.

[0040] In some embodiments, the electrolyte includes sodium hexafluorophosphate, and the mass content of sodium hexafluorophosphate is denoted as f%, based on the mass of the electrolyte, satisfying 5 ≤ f ≤ 25. Sodium hexafluorophosphate can efficiently dissolve and dissociate sodium ions, enabling rapid intercalation and deintercalation and conduction of sodium ions. Controlling the mass content of sodium hexafluorophosphate can further improve the ion transport rate, which is beneficial to the low-temperature discharge power and low-temperature cycle performance of the battery. Exemplarily, the mass content f of sodium hexafluorophosphate can be obtained by conventional testing methods in the art. For example, it can be measured by gas chromatography (GC). Exemplarily, the mass content f% of sodium hexafluorophosphate can be 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, etc., or a value within any two of the above values.

[0041] In some embodiments, the electrolyte further includes a functional salt, which includes at least one selected from sodium perchlorate, sodium tetrafluoroborate, sodium bis(trifluoromethanesulfonyl)imide, and sodium difluorosulfonylimide. Adding a functional salt can further improve the interfacial kinetics of the electrolyte, which is beneficial for the battery's high-temperature storage, low-temperature discharge power, and low-temperature cycling performance. In some embodiments, the mass content of sodium difluorosulfonylimide is denoted as g%, based on the mass of the electrolyte, satisfying 1 ≤ g ≤ 20; this can further improve the ion transport rate, which is beneficial for the battery's low-temperature discharge power and low-temperature cycling performance. Exemplarily, the mass content g of sodium difluorosulfonylimide can be obtained by conventional testing methods in the art. For example, it can be measured using gas chromatography (GC); exemplaryly, the mass content g% of sodium difluorosulfonylimide can be 1%, 3%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, etc., or values ​​within any two of the above ranges.

[0042] Furthermore, in some embodiments, 0.05 ≤ g / f ≤ 0.9. This application's research found that although sodium bis(fluorosulfonyl)imide can further improve interfacial kinetics, it may corrode the positive electrode current collector, thus affecting the stability of the positive electrode. Sodium hexafluorophosphate, on the other hand, can form a stable passivation film on the exposed surface of the positive electrode current collector, reducing the possibility of sodium bis(fluorosulfonyl)imide corroding the current collector. Therefore, controlling 0.05 ≤ g / f ≤ 0.9 can fully utilize the improving effects of sodium bis(fluorosulfonyl)imide and sodium hexafluorophosphate, protecting the positive electrode current collector, improving conductivity, enhancing interfacial kinetics and thermal stability, reducing side reactions, and benefiting the battery's high-temperature storage, low-temperature discharge power, and low-temperature cycle performance. Exemplarily, g / f can be 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or a value within any two of the above ranges.

[0043] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector, the positive active layer comprising a positive active material; the positive active material includes at least one of O3-type layered oxide and P2-type layered oxide. O3-type layered oxide has a higher mass ratio of sodium ions than P2-type layered oxide, which helps to improve capacity, while P2-type layered oxide has higher conductivity, which can improve the battery's low-temperature cycling and low-temperature discharge power performance.

[0044] Furthermore, in some embodiments, the structural formula of the O3-type layered oxide is Na. x Fe y Ni z Mn r M p O2; wherein M includes at least one of Ti, Cu, Mg, Ca, Cr, Co, Ce, Zn, Pd, Al and Mo; x satisfies: 0.8≤x<1, y satisfies: 0.20≤y≤0.35, z satisfies: 0.23≤z≤0.35, r satisfies: 0.24≤r≤0.36, and p satisfies: 0≤p≤0.2.

[0045] Furthermore, in some embodiments, the structural formula of the P2-type layered oxide is Na. w Fe t Ni u Mn v Cu j N qO2, wherein N includes at least one of Mg, Ca, Cr, Co, Ce, Zn, Pd, Ti, Al and Mo; wherein w satisfies: 0.2≤w<0.8, wherein t satisfies: 0≤t≤0.3, wherein u satisfies: 0≤u≤0.3, wherein v satisfies: 0<v≤0.8, wherein j satisfies: 0.2≤j≤0.6, and wherein q satisfies: 0≤q≤0.2.

[0046] In some embodiments, the positive electrode active material includes O3-type layered oxide and P2-type layered oxide. Based on the mass of the positive electrode active material, the mass content of the P2-type layered oxide is denoted as d%, and the mass content of the O3-type layered oxide is denoted as (1-d)%, satisfying 0 < d ≤ 50. Furthermore, combining O3-type and P2-type layered oxides can leverage the advantages of both, increasing capacity while maintaining high conductivity, which is beneficial for low-temperature cycling and low-temperature discharge power performance of the battery. Exemplarily, the mass content d% of the P2-type layered oxide can be obtained by conventional testing methods in the art. For example, it can be measured using X-ray diffraction (XRD). Exemplarily, the mass content d% of the P2-type layered oxide can be 0.1%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc., or values ​​within any two of the above ranges.

[0047] In some embodiments, the median volumetric particle size of the positive electrode active material is 3 μm-7 μm. This results in good dispersibility of the positive electrode active material, ensuring electrode uniformity and avoiding excessive contact with the electrolyte, thus reducing side reactions. Simultaneously, the positive electrode active material also exhibits good structural stability and a short ion diffusion path, which is beneficial for the battery's high-temperature storage, low-temperature cycling, and low-temperature discharge power performance. Exemplarily, the median volumetric particle size of the positive electrode active material can be obtained by conventional testing methods in the art. For example, it can be measured using a Malvern Mastersizer 3000 laser particle size analyzer. Exemplarily, the median volumetric particle size of the positive electrode active material can be 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, or a value within any two of the above ranges.

[0048] In some embodiments, the separator includes a base membrane and a coating disposed on at least one surface of the base membrane. The coating includes a ceramic layer and a first adhesive layer. The coating has a porous structure with a pore size ≥ 0.5 μm. Within an optional range of 100 μm × 100 μm on the coating surface, the difference between the maximum and minimum pore diameters is 1 μm-9 μm. In particular, when the pore size of the coating is 0.5 μm-20 μm, the pore size distribution in the coating is uniform, and the interfacial impedance is consistent, which is beneficial to the low-temperature discharge power and low-temperature cycle performance of the battery. Exemplarily, the pore size of the coating can be 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 25 μm, 30 μm, etc., or values ​​within any two of the above ranges.

[0049] For example, the pore size of the coating can be obtained by testing methods conventional in the art. For instance, the method for testing the pore size of the coating includes: taking a photograph of the coating surface using a scanning electron microscope (SEM); randomly selecting a 100μm × 100μm range from the obtained SEM image; and measuring the pore size of each pore. When the pore size of all tested pores is greater than 0.5μm, it can be considered that the pore size of the pores on the diaphragm meets the aforementioned condition. It can be understood that within the 100μm × 100μm range, the difference between the maximum diameter and the minimum diameter of the tested pores is the difference between the maximum diameter and the minimum diameter of the pores in the diaphragm.

[0050] In some embodiments, the coating thickness on the base film side is 1 μm-5 μm. This shortens the ion transport path while ensuring the coating's improved performance, which is beneficial for the battery's low-temperature discharge power and low-temperature cycling performance. Exemplarily, the coating thickness on the base film side can be measured using conventional testing methods in the art. For example, it can be measured by taking a cross-section of the separator in the thickness direction using a scanning electron microscope (SEM). Exemplarily, the coating thickness (in μm) on the base film side can be 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or a value within any two of the above ranges.

[0051] In some embodiments, the thickness of the separator is 9 μm-17 μm. This further shortens the ion transport path, improves the ion transport rate, and is beneficial to the low-temperature discharge power and low-temperature cycle performance of the battery. Exemplarily, the thickness of the separator can be measured using conventional testing methods in the art. For example, it can be measured by taking a cross-section of the separator in the thickness direction using a scanning electron microscope (SEM). Exemplarily, the thickness of the separator (in μm) can be 9, 10, 11, 12, 13, 14, 15, 16, 17, etc., or a value within any two of the above ranges.

[0052] In some embodiments, the first adhesive layer comprises polyvinylidene fluoride and / or polymethyl methacrylate.

[0053] In some embodiments, the diaphragm further includes a second adhesive layer comprising polyvinylidene fluoride and / or polymethyl methacrylate.

[0054] In some embodiments, the ceramic layer comprises at least one of alumina, boehmite, magnesium oxide, magnesium hydroxide, barium sulfate, barium titanate, zinc oxide, calcium oxide, silicon dioxide, silicon carbide, and boron nitride.

[0055] In some embodiments, the base film may be made of at least one of polyethylene (PE), polypropylene (PP), or a composite base film of polyethylene and polypropylene. The base film may be a single-layer film or a multi-layer composite film, without particular limitation. When the base film is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0056] In some embodiments, the coating further includes an adhesive, which includes at least one of polyvinylidene fluoride adhesives and polyacrylate adhesives; the coating is applied according to conventional processes in the art, such as gravure coating, transfer coating, dip coating and spraying, for single-sided or double-sided coating.

[0057] In some embodiments, the conductive agent further includes at least one of acetylene black, conductive carbon black, Ketjen black, conductive graphite, carbon nanotubes, conductive carbon fibers, and graphene.

[0058] According to an embodiment of this application, a third aspect also provides a method for preparing a negative electrode active material, comprising the following steps: (1) The first precursor is subjected to first carbonization and mixed with acid to obtain the first disordered carbon material precursor; (2) The first disordered carbon material precursor and the coating agent are mixed and sintered to obtain the negative electrode active material.

[0059] In some embodiments, the first precursor includes at least one of coconut shell, rice husk, peanut shell, walnut shell, bamboo, cellulose, lignin, hazelnut shell, bituminous coal, sub-bituminous coal, and anthracite.

[0060] In some embodiments, the first carbonization is carried out under a protective atmosphere, which includes at least one of a nitrogen atmosphere and an inert atmosphere.

[0061] In some embodiments, the protective atmosphere includes at least one of a nitrogen atmosphere and an inert atmosphere.

[0062] In some embodiments, the heating rate of the first carbonization is 1-5 °C / min.

[0063] In some embodiments, the temperature of the first carbonization is 400-600°C.

[0064] In some embodiments, the first carbonization time is 1-8 hours.

[0065] In some embodiments, the acid includes at least one of nitric acid, hydrochloric acid, and hydrofluoric acid.

[0066] Mixing with acid can further remove impurities from the first disordered carbon material precursor and reduce the calcium and iron content in the first disordered carbon material precursor, so that the calcium and iron content in the final negative electrode active material meets specific requirements (based on the mass of the negative electrode active material, the mass content of Ca is less than or equal to 500 ppm and the mass content of Fe is less than or equal to 100 ppm). While ensuring the stability of the first disordered carbon material, mixing with acid can activate and enhance the active sites of the first disordered carbon material, reduce irreversible capacity loss during the first charge and discharge process, improve the first coulombic efficiency, low-temperature discharge power and low-temperature cycle performance, and improve the thermal safety performance and high-temperature storage performance of the battery.

[0067] In some embodiments, the concentration of the nitric acid is 6-10 mol / L; in some embodiments, the concentration of the hydrochloric acid is 5-10 mol / L; and in some embodiments, the concentration of the hydrofluoric acid is 3-7 mol / L.

[0068] In some embodiments, the acid includes nitric acid, hydrochloric acid, and hydrofluoric acid.

[0069] In some embodiments, the coating agent includes at least one of asphalt, resin, tar, and starch.

[0070] In some embodiments, the sintering is carried out under a protective atmosphere, which includes at least one of a nitrogen atmosphere and an inert atmosphere.

[0071] In some embodiments, the sintering heating rate is 3-7°C / min.

[0072] In some embodiments, the sintering temperature is 1000-1500°C.

[0073] In some embodiments, the sintering time is 3-8 hours.

[0074] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application. Where specific experimental steps or conditions are not specified in the embodiments and comparative examples, they can be performed according to the conventional experimental steps or conditions described in the literature in the art. Reagents or instruments used, unless otherwise specified, are all commercially available conventional reagent products. In all embodiments and comparative examples of this application, the unit % represents mass percentage.

[0075] Example 1 This embodiment provides a method for preparing a battery, including the following steps: (1) Preparation of negative electrode Preparation method of negative electrode active material: Coconut shell is crushed and heated to 600℃ at a heating rate of 2℃ / min under nitrogen atmosphere and held for 4h. It is then mixed with a mixed acid (composed of nitric acid, hydrochloric acid, and hydrofluoric acid, with nitric acid concentration of 8mol / L, hydrochloric acid concentration of 7mol / L, and hydrofluoric acid concentration of 5mol / L), rinsed with water until neutral, and dried at 80℃ to obtain a first disordered carbon material precursor. The first disordered carbon material precursor is mixed with asphalt and heated to 1300℃ at a heating rate of 4℃ / min under nitrogen atmosphere, held for 5h, cooled to room temperature, demagnetized, and sieved to obtain the negative electrode active material. The negative electrode active material prepared in this embodiment includes a core and a coating layer covering at least a portion of the surface of the core. The thickness P of the coating layer is 100nm. The core includes a first disordered carbon material, and the coating layer includes a second disordered carbon material. In the Raman spectrum of the first disordered carbon material, J1 is 1.2, and J1=1. D1 / I G1 I D1 Raman displacement at 1350cm -1 The peak intensity of the Raman peak at the location, I G1 This indicates that the Raman displacement is at 1580 cm. -1 The peak intensity of the Raman peak at the location; in the Raman spectrum of the second disordered carbon material, J2 is 0.9, J2=I D2 / I G2 I D2 Raman displacement at 1350cm -1 The peak intensity of the Raman peak at the location, I G2 This indicates that the Raman displacement is at 1580 cm. -1 The peak intensity of the Raman peak at the location; J2 / P=0.009; It should be noted that the coconut shell used in this embodiment contains Ca and Fe. By mixing with mixed acid, the mass content of Ca in the obtained negative electrode active material is 100ppm and the mass content of Fe is 20ppm.

[0076] The aforementioned negative electrode active material, acetylene black, carbon black, sodium carboxymethyl cellulose, and polyacrylic acid were added to a vacuum mixer in a mass ratio of 94:3.5:0.5:0.5:1.5, along with an appropriate amount of deionized water. The mixture was thoroughly mixed under vacuum until a uniform, free-flowing negative electrode slurry with a solid content of 48 wt% was formed. The negative electrode slurry was then uniformly coated onto an aluminum foil with a thickness of 12 μm. After drying, rolling, and slitting, the negative electrode sheet was obtained.

[0077] (2) Preparation of positive electrode sheet The positive electrode active material (Na) 0.63 Mn 0.68 Cu 0.32 O2), polyvinylidene fluoride, and acetylene black were added to a vacuum mixer in a mass ratio of 93:2:5, along with an appropriate amount of N-methylpyrrolidone (NMP). The mixture was thoroughly stirred under vacuum until a uniform, free-flowing positive electrode slurry was formed, with a solid content of 60 wt%. The positive electrode slurry was then uniformly coated onto an aluminum foil with a thickness of 12 μm, followed by drying, rolling, and slitting to obtain the positive electrode sheet.

[0078] (3) Electrolyte preparation In an argon glove box with a water content of <0.1ppm and an oxygen content of <0.1ppm, the solvent is added and stirred to dissolve the electrolyte. Then, NaPF6 is added to obtain the electrolyte. The mass content of NaPF6 is f%, and the solvent is propylene carbonate, methyl ethyl carbonate and diethyl carbonate in a mass ratio of 3:5:2.

[0079] (4) Diaphragm The diaphragm used includes a polyethylene base membrane and an adhesive layer disposed on both sides of the polyethylene base membrane. The adhesive layer contains polyvinylidene fluoride. The thickness of the adhesive layer on the base membrane side is 1 μm, and the thickness of the diaphragm is 9 μm.

[0080] (5) Preparation of pouch cells The above-obtained positive electrode, negative electrode and separator are stacked to obtain bare cells, then the tabs are welded on, and aluminum-plastic film is used for encapsulation. Cells with qualified moisture content are injected into the above-obtained electrolyte. After aging, formation, secondary sealing, sorting and OCV processes, soft pack batteries are obtained.

[0081] The preparation methods of Examples 2-7 and Comparative Example 1 are basically the same as those of Example 1, with differences shown in Table 1-2. " / " indicates that the item does not exist. In Table 1-2, Dv10 is the particle size corresponding to a cumulative volume distribution percentage of 10% for the negative electrode active material, Dv40 is the particle size corresponding to a cumulative volume distribution percentage of 40% for the negative electrode active material, Dv60 is the particle size corresponding to a cumulative volume distribution percentage of 60% for the negative electrode active material, and Dv90 is the particle size corresponding to a cumulative volume distribution percentage of 90% for the negative electrode active material; UDI = (Dv60 / Dv10) × (Dv90 / Dv40); a represents the number of carbon nanotubes, c nm is the diameter of the carbon nanotubes, and b g / cm³ is the number of nanotubes. 3 The tap density of the negative electrode active material is given, m% is the mass content of the binder, k% is the mass content of sodium in sodium polyacrylate, and V is the mass content of sodium in sodium polyacrylate. 正 % represents the porosity of the positive electrode, V 负 % represents the porosity of the negative electrode, V 隔 % represents the porosity of the membrane, S = |(V 负 -V 正 )| / V 隔 +|(V 负 -V 隔 )| / V 正 +|(V 正 -V 隔 )| / V 负 f% represents the mass content of sodium hexafluorophosphate, g% represents the mass content of sodium difluorosulfonamide, d% represents the mass content of P2-type layered oxides, PS represents 1,3-propanesulfonate lactone, DTD represents vinyl sulfate, and NaFSI represents sodium difluorosulfonamide.

[0082] Example 8 This embodiment provides a method for preparing a battery. The difference from Embodiment 1 is that carbon nanotubes of the same mass are used to replace the carbon black in step (1). The length of the carbon nanotubes is 50 μm. The other parameters of the carbon nanotubes are detailed in Table 1.

[0083] The preparation methods of Examples 9-13 are basically the same as those of Example 8, with the differences shown in Tables 1-2. The mass content of carbon nanotubes is controlled by adjusting the content of the negative electrode active material. The carbon nanotubes in Examples 9-10 have a tube length of 50 μm; the carbon nanotubes in Example 11 have a tube length of 100 μm; and the carbon nanotubes in Example 12 have a tube length of 1 μm.

[0084] Example 14 This embodiment provides a method for preparing a battery, which differs from Embodiment 1 in that sodium polyacrylate is used in place of sodium carboxymethyl cellulose and polyacrylic acid in step (1) by mass.

[0085] The preparation methods of Examples 15-19 are basically the same as those of Example 8. The differences are shown in Tables 1-2. The mass content of sodium polyacrylate is controlled by adjusting the content of the negative electrode active material.

[0086] The preparation methods of Examples 20-29 are basically the same as those of Example 1. The differences are shown in Tables 1-2.

[0087] Example 30 This embodiment provides a method for preparing a battery. The difference from Embodiment 1 is that the negative electrode sheet and the separator in step (4) are different. The negative electrode sheet is detailed in Table 1-2. Step (4) in this embodiment is as follows: The diaphragm includes a polyethylene base membrane and a coating disposed on one side of the polyethylene base membrane. The coating has a thickness of 3 μm and includes a ceramic layer and a first adhesive layer. The first adhesive layer contains polyvinylidene fluoride, and the thickness ratio of the ceramic layer to the first adhesive layer is 2:1. A second adhesive layer is disposed on the surface of the base membrane away from the coating. The second adhesive layer contains polyvinylidene fluoride and has a thickness of 1 μm. The thickness of the diaphragm is 11 μm.

[0088] The preparation methods of Examples 31-32 are basically the same as those of Example 30. The differences are shown in Tables 1-2.

[0089] Table 1. Variables in the Examples and Comparative Examples 1

[0090] Table 2 Variables for Example and Comparative Example 2

[0091] Test case The batteries provided in each embodiment and comparative example were subjected to performance tests. The specific test methods are as follows: (1) Low temperature discharge power performance test: Under (25+2)℃ environment, standard constant current 1C discharge to 2V, rest for 30min; then 1C standard constant current constant voltage charge to 3.9V, cut-off current 0.05C, rest for 30min; then standard constant current 1C discharge to 2V, obtain the actual capacity C0 of the cell; rest for 30min; standard constant current constant voltage charge to 3.9V, cut-off current 0.05C, use 1C0 discharge to 80% SOC; -20℃ stand for 4h; discharge with constant current 18C0, constant current density for 2s, sample every 50ms, record the voltage at 2s.

[0092] (2) Low temperature cycling performance test: Under (25+2)℃ environment, discharge to 2V with standard constant current 1C and rest for 30min; then charge to 3.9V with standard constant current constant voltage 1C, cut-off current 0.05C and rest for 30min; then discharge to 2V with standard constant current 1C and obtain the actual capacity C0 of the cell; rest for 30min; charge the battery to 3.9V with standard constant current constant voltage and cut-off current 0.05C; stand at -10℃ for 4h; (a) discharge to 2V with standard constant current 0.5C and rest for 10min; (b) charge to 3.9V with standard constant current constant voltage 0.5C and cut-off current 0.05C and rest for 10min; repeat cycle (a)-(b) 50 times, low temperature cycling performance (%) = discharge capacity of the 50th cycle / discharge capacity of the 3rd cycle.

[0093] (3) High temperature storage performance test: Under (25±2)℃ environment, 1C constant current discharge to 2V, rest for 30min; then 1C constant current and constant voltage charge to 3.9V, 0.05C cutoff, rest for 30min; 1C constant current discharge to 2V, obtain the initial capacity C0 of the cell; rest for 30min, 1C0 constant current and constant voltage charge to 3.9V, 0.05C0 cutoff, then rest for 30 days under 80℃ environment; after 30 days, take it out, stand at (25±2)℃ for 1h, 1C0 constant current discharge to 2V, rest for 30min, 1C0 constant current and constant voltage charge to 3.9V, cutoff current 0.05C0, rest for 30min, 1C0 constant current discharge to 2V to obtain capacity C2, high temperature storage performance (%) = C2 / C0.

[0094] The specific test results are shown in Table 3.

[0095] Table 3 Test results of the examples and comparative examples

[0096] As can be seen from Tables 1-3, compared to Comparative Example 1 ((Dv60 / Dv10)×(Dv90 / Dv40) greater than 20), the low-temperature discharge power and low-temperature cycling performance of Examples 1-32 were improved to varying degrees. This indicates that controlling the uniformity of the particle size distribution of the negative electrode active material can reduce ion transport resistance and construct an effective electronic conductivity network.

[0097] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A negative electrode sheet, comprising a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector, the negative electrode active layer comprising a negative electrode active material, characterized in that, The negative electrode active material includes a core and a coating layer covering at least a portion of the surface of the core. The core includes a first disordered carbon material, and the coating layer includes a second disordered carbon material. The thickness of the coating layer is denoted as P nm, where 5 ≤ P ≤ 200. The particle sizes Dv10, Dv40, Dv60, and Dv90 of the negative electrode active material satisfy: (Dv60 / Dv10) × (Dv90 / Dv40) ≤ 20. 1μm≤Dv10≤4μm; and / or, 2μm≤Dv40≤7μm; and / or, 5μm≤Dv60≤9μm; and / or, 7μm≤Dv90≤16μm.

2. The negative electrode sheet according to claim 1, characterized in that, In the Raman spectrum of the second disordered carbon material, 0.7 ≤ J2 ≤ 1.2, J2 = I D2 / I G2 , wherein, the I D2 This indicates that the Raman displacement is at 1300 cm. -1 -1400cm -1 The peak intensity of the Raman peak at the location, I G2 This indicates that the Raman displacement is at 1500 cm. -1 -1650cm -1 The peak intensity of the Raman peak at the location; preferably, 0.0035 ≤ J2 / P ≤ 0.24; Preferably, 5 ≤ (Dv60 / Dv10) × (Dv90 / Dv40) ≤ 20; Preferably, in the Raman spectrum of the first disordered carbon material, J1=I D1 / I G1 , wherein, the I D1 This indicates that the Raman displacement is at 1300 cm. -1 -1400cm -1 The peak intensity of the Raman peak at the location, I G1 This indicates that the Raman displacement is at 1500 cm. -1 -1650cm -1 The peak intensity of the Raman peak at the location; J1 is greater than J2; Preferably, 0.8 ≤ J1 ≤ 2.5; Preferably, the negative electrode active material contains a first element, which includes Ca and Fe. Based on the mass of the negative electrode active material, the mass content of Ca is less than or equal to 500 ppm and the mass content of Fe is less than or equal to 100 ppm.

3. A sodium-ion battery, characterized in that, Includes a positive electrode, a separator, an electrolyte, and a negative electrode as described in any one of claims 1-2; Preferably, the negative electrode further includes a conductive agent, which includes carbon nanotubes; the number a of carbon nanotubes is 5 to 180 within a 5μm×5μm range under a scanning electron microscope. Preferably, the negative electrode sheet further includes a binder, which includes at least one of polyvinyl alcohol, polyacrylic acid, sodium polyacrylate, sodium alginate, sodium carboxymethyl cellulose, and styrene-butadiene rubber; the mass content of the binder is denoted as m% based on the mass of the negative electrode active layer, satisfying 0.5≤m≤4.

4. The sodium-ion battery according to claim 3, characterized in that, The adhesive includes sodium polyacrylate, and the mass content of sodium element is denoted as k% based on the mass of sodium polyacrylate, satisfying 1≤k≤15; And / or, within a 5μm × 5μm range under a scanning electron microscope, the number a of carbon nanotubes is 13-42; And / or, the diameter of the carbon nanotubes is denoted as c nm, and the tap density of the negative electrode active material is denoted as b g / cm³. 3 The condition is satisfied that 0.01 ≤ b / c ≤ 0.3; And / or, the length of the carbon nanotubes is 1μm-100μm.

5. The sodium-ion battery according to claim 4, characterized in that, 4≤c≤60； And / or, 0.5 ≤ b ≤ 1.2; And / or, 0.5≤(k×m)≤30.

6. The sodium-ion battery according to any one of claims 3-5, characterized in that, The porosity of the positive electrode is denoted as V. 正 The porosity of the negative electrode sheet is denoted as V. 负 The porosity of the membrane is denoted as V. 隔 %, satisfying H≥0.9, H=1 / S; S=|(V 负 -V 正 )| / V 隔 +|(V 负 -V 隔 )| / V 正 +|(V 正 -V 隔 )| / V 负 。 7. The sodium-ion battery according to claim 6, characterized in that, 0.9 ≤ H ≤ 20; and / or, 25 ≤ V 正 ≤40; and / or, 35≤V 负 ≤50; and / or, 40≤V 隔 ≤60.

8. The sodium-ion battery according to any one of claims 3-5, characterized in that, It also meets at least one of the following conditions: (1) The electrolyte includes a sulfur-containing additive, which includes at least one of 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, vinyl sulfate, vinyl disulfate, methylene disulfonate, ethylene sulfate, and mannitol carbonate sulfate; the mass content of the sulfur-containing additive is 0.1%-5% based on the mass of the electrolyte; (2) The electrolyte includes sodium hexafluorophosphate. The mass content of sodium hexafluorophosphate is denoted as f%, based on the mass of the electrolyte, and satisfies 5≤f≤25. Preferably, the electrolyte also includes a functional salt, which includes at least one of sodium perchlorate, sodium tetrafluoroborate, sodium bis(trifluoromethanesulfonyl)imide, and sodium bis(fluorosulfonyl)imide. (3) The positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one side surface of the positive current collector, the positive active layer including a positive active material; the positive active material includes at least one of O3 type layered oxide and P2 type layered oxide; (4) The diaphragm includes a base membrane and a coating disposed on at least one side of the base membrane. The coating includes a ceramic layer and a first adhesive layer. The coating has a porous structure and the pore size of the coating is ≥0.5μm. Within an optional range of 100μm×100μm on the surface of the coating, the difference between the maximum diameter of the pore and the minimum diameter of the pore is 1μm-9μm. Preferably, the pore size of the coating is 0.5μm-20μm.

9. The sodium-ion battery according to claim 8, characterized in that, Based on the mass of the electrolyte, the mass content of the 1,3-propanesulfonate lactone is 0.1%-5%; And / or, based on the mass of the electrolyte, the mass content of sodium difluorosulfonamide is recorded as g %, satisfying 1≤g≤20; And / or, the positive electrode active material includes O3-type layered oxide and P2-type layered oxide. Based on the mass of the positive electrode active material, the mass content of the P2-type layered oxide is denoted as d%, and the mass content of the O3-type layered oxide is denoted as (1-d)%, satisfying 0 < d ≤ 50. And / or, the median particle size of the positive electrode active material is 3μm-7μm; And / or, the thickness of the coating on one side of the base film is 1μm-5μm; And / or, the thickness of the diaphragm is 9μm-17μm; And / or, the ceramic layer comprises at least one of alumina, boehmite, magnesium oxide, magnesium hydroxide, barium sulfate, barium titanate, zinc oxide, calcium oxide, silicon dioxide, silicon carbide, and boron nitride.

10. The sodium-ion battery according to claim 9, characterized in that, Based on the mass of the electrolyte, the mass content of the 1,3-propanesulfonate lactone is 1%-3%; And / or, 0.05 ≤ g / f ≤ 0.9; And / or, the structural formula of the O3-type layered oxide is Na x Fe y Ni z Mn r M p O2; wherein M includes at least one of Ti, Cu, Mg, Ca, Cr, Co, Ce, Zn, Pd, Al and Mo; x satisfies: 0.8≤x<1, y satisfies: 0.20≤y≤0.35, z satisfies: 0.23≤z≤0.35, r satisfies: 0.24≤r≤0.36, and p satisfies: 0≤p≤0.2; And / or, the structural formula of the P2 type layered oxide is Na w Fe t Ni u Mn v Cu j N q O2, wherein N includes at least one of Mg, Ca, Cr, Co, Ce, Zn, Pd, Ti, Al and Mo; wherein w satisfies: 0.2≤w<0.8, wherein t satisfies: 0≤t≤0.3, wherein u satisfies: 0≤u≤0.3, wherein v satisfies: 0<v≤0.8, wherein j satisfies: 0.2≤j≤0.6, and wherein q satisfies: 0≤q≤0.2.

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