Negative electrode sheet and sodium ion battery

Abstract

A negative electrode sheet and a battery comprising the negative electrode sheet. The negative electrode sheet comprises a negative electrode active material, the negative electrode active material comprising hard carbon and graphite. In an XRD pattern of the negative electrode active material, the intensity of a (002) crystal plane diffraction peak having a diffraction angle 2θ of 21.5°-25° is I1, and the intensity of a (002) crystal plane diffraction peak having a diffraction angle 2θ of 25.5°-27° is I2, satisfying: 0 < I1 / I2 ≤ 0.65. The negative electrode active material can effectively improve the conductivity of negative electrode sheets, and improve the performance of contact surfaces of electrode sheets and electrolytes, so as to enhance the sodium storage dynamic performance and the initial coulombic efficiency of the negative electrode sheets, thus obtaining sodium ion batteries having high specific capacities and good rate capabilities.

Description

Anode sheet and sodium-ion battery Technical Field

[0001] The present disclosure relates to the field of battery technology, and in particular to a negative electrode sheet and a sodium ion battery including the negative electrode sheet.

[0002] Background of the Invention

[0003] In recent years, sodium-ion batteries (SIBs) have attracted widespread attention as the optimal energy storage device for large-scale applications due to their abundant sodium resources and low cost. However, due to the large radius of sodium ions, they are difficult to embed into the interlayers of carbonaceous materials. Therefore, the development of suitable anode materials is crucial for promoting the commercial application of SIBs.

[0004] Although previous studies have shown that a variety of materials (such as hard carbon, soft carbon, sulfide, oxide, phosphorus, tin, etc.) can be used as negative electrodes to store sodium ions, only hard carbon negative electrodes have shown great development potential in practical applications. On the one hand, hard carbon has a large interlayer spacing, can store a large amount of sodium ions, and can also withstand the repeated insertion and extraction of sodium ions during charge and discharge, so it has a higher specific capacity and better cycle stability; on the other hand, hard carbon precursors are abundant and the sodium storage platform is low. Using it as a negative electrode material is conducive to the development of sodium-ion batteries with both low cost and high energy density. Despite this, hard carbon negative electrodes also have problems such as low initial coulombic efficiency, poor sodium storage kinetics, and insufficient capacity.

[0005] Therefore, solving the above-mentioned problems of hard carbon is very important for inventing a battery with high specific capacity, high cycle stability and good rate performance.

[0006] Summary of the Invention

[0007] The present disclosure aims to overcome the aforementioned problems of the prior art by providing a negative electrode sheet and a sodium-ion battery comprising the same. This disclosure can effectively enhance the conductivity of the negative electrode sheet and improve the performance of the interface between the electrode sheet and the electrolyte, thereby improving the negative electrode sheet's sodium storage kinetics and initial coulombic efficiency. This results in a sodium-ion battery with high specific capacity and excellent rate performance.

[0008] The inventors of the present disclosure have discovered that improving the sodium storage kinetics and initial coulombic efficiency of the negative electrode sheet can improve the specific capacity and rate performance of the battery. In order to improve the sodium storage kinetics and initial coulombic efficiency of the negative electrode sheet, the conductivity of the negative electrode sheet can be improved, the interface performance between the electrode sheet and the electrolyte can be improved, and the utilization rate of the active material in the negative electrode sheet can be increased, thereby improving the specific capacity of the battery; at the same time, the high conductivity and good interface performance of the negative electrode sheet can also reduce the polarization of the battery and reduce the side reactions of the electrolyte, thereby improving the rate performance of the battery. The inventors of the present disclosure have discovered a negative electrode sheet that can improve the conductivity of the negative electrode sheet and enhance the performance of the contact surface between the electrode sheet and the electrolyte, and has specific characteristics.

[0009] In order to achieve the above-mentioned purpose, the first aspect of the present disclosure provides a negative electrode sheet, wherein the negative electrode sheet includes a negative electrode active material, and the negative electrode active material includes hard carbon and graphite. In the XRD spectrum of the negative electrode active material, the intensity of the (002) crystal plane diffraction peak with a diffraction angle 2θ located at 21.5°-25° is I1, and the intensity of the (002) crystal plane diffraction peak with a diffraction angle 2θ located at 25.5°-27° is I2, satisfying: 0<I1 / I2≤0.65.

[0010] A second aspect of the present disclosure provides a sodium ion battery, wherein the sodium ion battery includes the negative electrode sheet described in the first aspect of the present disclosure.

[0011] Through the above technical solution, the present disclosure has at least the following advantages compared with the prior art:

[0012] (1) The negative electrode sheet disclosed herein has high electrical conductivity;

[0013] (2) The negative electrode sheet disclosed herein has good sodium storage kinetics;

[0014] (3) The initial coulombic efficiency of the negative electrode sheet disclosed herein is high;

[0015] (4) The negative electrode sheet disclosed herein has a high specific capacity;

[0016] (5) The specific capacity of the battery disclosed herein is high;

[0017] (6) The battery disclosed herein has good rate performance;

[0018] (7) The battery disclosed herein has high cycle stability;

[0019] (8) The battery disclosed herein has a long cycle life.

[0020] Other features and advantages of the present disclosure will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG1 is a SEM image of the negative electrode active material in Example 1 of the present disclosure.

[0022] FIG2 shows an XRD pattern of the negative electrode active material in Example 1 of the present disclosure.

[0023] FIG3 shows a particle size distribution diagram of graphite in the negative electrode active material in Example 1 of the present disclosure (it can be seen from the figure that the median particle size Dv50 of the graphite is 12.97 μm).

[0024] FIG4 shows a particle size distribution diagram of the hard carbon in the negative electrode active material in Example 1 of the present disclosure (it can be seen from the figure that the median particle size Dv50 of the hard carbon is 4.97 μm).

[0025] FIG5 shows a particle size distribution diagram of the negative electrode active material in Example 1 of the present disclosure (it can be seen from the figure that the median particle size Dv50 of the negative electrode active material is 5.2 μm).

[0026] FIG6 is a graph showing the cycle performance of the negative electrode active material in Example 1 of the present disclosure at a current density of 20.5 mA / g. DETAILED DESCRIPTION

[0027] The following describes the specific embodiments of the present disclosure in detail. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure and are not intended to limit the present disclosure.

[0028] In a first aspect, the present disclosure provides a negative electrode sheet, wherein the negative electrode sheet includes a negative electrode active material, wherein the negative electrode active material includes hard carbon and graphite, and wherein in an XRD pattern of the negative electrode active material, the intensity of the (002) crystal plane diffraction peak at a diffraction angle 2θ of 21.5°-25° is I1, and the intensity of the (002) crystal plane diffraction peak at a diffraction angle 2θ of 25.5°-27° is I2, satisfying the following conditions: 0<I1 / I2≤0.65. As shown in FIG2 , when the negative electrode active material satisfies 0<I1 / I2≤0.65, it indicates that the hard carbon and graphite in the negative electrode active material are well matched, which can ensure that the negative electrode active material has the advantages of a large interlayer spacing and high conductivity, thereby improving the interface performance between the electrode and the electrolyte. Moreover, the large interlayer spacing and high conductivity can increase the sodium storage capacity and sodium storage kinetics of the negative electrode active material, thereby increasing the specific capacity and initial coulombic efficiency of the negative electrode sheet and improving the rate performance of the battery.

[0029] In the XRD pattern of the negative electrode active material, the half-maximum width of the (002) crystal plane diffraction peak at 25.5°-27° can be 0.1° to 1°. Within this range, the negative electrode active material facilitates sodium ion deintercalation, electrolyte infiltration, sodium ion deintercalation, and electron transfer, while also improving the structural stability of the negative electrode active material, thereby improving sodium storage kinetics and increasing sodium storage capacity.

[0030] In the present disclosure, through the coordinated combination of the above-mentioned characteristics of the negative electrode active material, the graphite and the hard carbon can be uniformly mixed together (Figure 1), which can improve the conductivity of the negative electrode active material and improve the interface performance of the electrode and the electrolyte, thereby improving the utilization rate of the active material and reducing the side reactions of the electrolyte and the polarization of the battery, thereby improving the initial coulombic efficiency, rate performance, specific capacity and cycle life of the battery.

[0031] By using a negative electrode active material with the above-mentioned specific characteristics in the negative electrode sheet, it has been possible to achieve better sodium storage kinetics and initial coulombic efficiency than the existing technology. To further improve the effect, one or more of the technical features can be further optimized.

[0032] The negative electrode active material may satisfy: 0<I1 / I2≤0.65 (e.g., 0.01, 0.015, 0.02, 0.025, 0.03, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65).

[0033] In one embodiment, the negative electrode active material satisfies the following relationship: 0.03≤I1 / I2≤0.45.

[0034] In one example, based on the total weight of the negative electrode active material, the weight content A of the hard carbon is 91 wt % ≤ A ≤ 99 wt % (e.g., 91 wt %, 92 wt %, 93 wt %, 94 wt %, 95 wt %, 96 wt %, 97 wt %, 98 wt %, 99 wt %), and the weight content B of the graphite is 1 wt % ≤ B ≤ 9 wt % (e.g., 1 wt %, 2 wt %, 3 wt %, 4 wt %, 5 wt %, 6 wt %, 7 wt %, 8 wt %, 9 wt %);

[0035] and / or, the median particle size Dv50 of the negative electrode active material is ≤12 μm;

[0036] and / or, the median particle size Dv50 of the graphite is ≥5.2 μm;

[0037] and / or, the median particle size Dv50 of the graphite is not less than the median particle size Dv50 of the hard carbon;

[0038] And / or, the negative electrode active material has an electrical conductivity C of ≥35 S / cm at a pressure of 50 MPa.

[0039] When the total weight of the negative electrode active material is used as a benchmark, the weight content A of the hard carbon is 91wt%≤A≤99wt%, and the weight content B of the graphite is 1wt%≤B≤9wt%, since the sodium storage capacity of the hard carbon in the negative electrode active material is significantly higher than that of graphite, and the conductivity of graphite is significantly higher than that of hard carbon, when the weight contents of both are simultaneously limited to the above-mentioned specific range, the performance of hard carbon and graphite can be comprehensively utilized, which is beneficial to improving the sodium storage kinetics and high sodium storage capacity of the negative electrode sheet.

[0040] When the median particle size Dv50 of the negative electrode active material is ≤12μm, wherein the median particle size Dv50 of the graphite is ≥5.2μm, and the median particle size Dv50 of the graphite is not less than the median particle size Dv50 of the hard carbon, through the above control, it is possible to ensure that the negative electrode sheet has good sodium storage dynamics and a smaller amount of graphite can better connect more hard carbon, so that the percentage of the sodium storage active material hard carbon in the negative electrode active material is higher, thereby improving the conductivity of the negative electrode active material while ensuring its high specific capacity, thereby improving the specific capacity and rate performance of the battery; in addition, graphite can improve the interface performance between the electrode sheet and the electrolyte, thereby reducing polarization and reducing the side reactions of the electrolyte, thereby improving the initial coulombic efficiency, capacity and cycle stability of the battery.

[0041] In order to meet the requirements of the negative electrode sheet for the conductivity of the negative electrode active material, the conductivity C of the negative electrode active material under a pressure of 50 MPa is limited to ≥35S / cm. Moreover, when the conductivity C of the negative electrode active material is ≥35S / cm, it is conducive to the rapid transmission of electrons and ions in the electrode, thereby improving the rate performance of the battery.

[0042] In one example, the conductivity C of the negative electrode active material under a pressure of 50 MPa is 40S / cm-70S / cm (for example, 40S / cm, 45S / cm, 50S / cm, 55S / cm, 60S / cm, 65S / cm, 70S / cm). Controlling the conductivity of the negative electrode active material within the above range is beneficial to overcoming the problem of poor sodium storage kinetics of hard carbon, thereby further improving the rate performance, specific capacity and initial coulombic efficiency of the battery. The conductivity can be measured with reference to the method described in GB / T 24525-2009 "Graphite Anode Materials for Lithium-ion Batteries", for example: using PRCD1100 (IEST-Yuanneng Technology), the powder is placed in a test mold, and a program is set to pressurize (for example, from 1kN to 2kN, 3kN, 4kN, 5kN) to obtain the powder conductivity.

[0043] In one embodiment, based on the total weight of the negative electrode active material, the weight content A of the hard carbon is 95.5 wt% to 98.5 wt%, and the weight content B of the graphite is 1.5 wt% to 4.5 wt%. When the weight content A of the hard carbon and the weight content B of the graphite are limited to the above-specified ranges, the combined performance of the sodium storage kinetics and sodium storage capacity of the negative electrode sheet can be further improved.

[0044] According to a specific embodiment, the median particle size Dv50 of the hard carbon is 1.5 μm-13 μm (eg, 1.5 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm).

[0045] In one embodiment, the hard carbon has a median particle size Dv50 of 3 μm to 8 μm.

[0046] According to a specific embodiment, the median particle size of the graphite is 10 μm<Dv50≤20 μm (for example, 10.5 μm, 12 μm, 15 μm, 17 μm, 20 μm).

[0047] In one embodiment, the median particle size Dv50 of the graphite is 11 μm to 16 μm. Within this range, it is possible to improve the sodium storage kinetics and increase the sodium storage capacity.

[0048] In one example, the difference between the median particle size Dv50 of the graphite and the median particle size Dv50 of the hard carbon is 0μm-12μm (for example, 0μm, 0.01μm, 0.1μm, 0.5μm, 1μm, 3μm, 5μm, 8μm, 10μm). When the difference between the median particle size Dv50 of the graphite and the median particle size Dv50 of the hard carbon is 0μm, it means that the median particle size Dv50 of the graphite is equal to the median particle size Dv50 of the hard carbon. When the difference between the median particle size Dv50 of the graphite and the median particle size Dv50 of the hard carbon is controlled within the above range, it can ensure that the negative electrode active material has high conductivity and good processing performance while having a high proportion of hard carbon, which can further improve the specific capacity, sodium storage kinetics and initial coulombic efficiency of the negative electrode active material.

[0049] In one embodiment, the median particle size Dv50 of the graphite is greater than the median particle size Dv50 of the hard carbon by a difference of 1.5 μm to 8.5 μm.

[0050] In one embodiment, the median particle size Dv50 of the graphite is greater than the median particle size Dv50 of the hard carbon by 2 μm to 5 μm.

[0051] In one embodiment, the negative electrode active material has a median particle size Dv50 of 1.5 μm to 12 μm (e.g., 1.5 μm, 2 μm, 5 μm, 7 μm, 10 μm, 12 μm). When the median particle size of the negative electrode active material is controlled within the above range, it can further ensure that it has higher sodium storage kinetics and better processing performance.

[0052] In the present disclosure, the median particle size Dv50 can be obtained by testing with a laser particle size analyzer.

[0053] In one embodiment, the specific surface area of ​​the graphite is ≤9.6m 2 / g, the specific surface area of ​​the hard carbon is 0.5m 2 / g-26m 2 / g.

[0054] In one example, the specific surface area of ​​the hard carbon is greater than the specific surface area of ​​the graphite.

[0055] In one embodiment, the specific surface area of ​​the graphite is ≤9.6m 2 / g, the specific surface area of ​​the hard carbon is 0.5m 2 / g-26m 2 / g, and the specific surface area of ​​the hard carbon is greater than that of the graphite. When the specific surface areas of the graphite and the hard carbon meet the above-mentioned limitations, the occurrence of side reactions during sodium storage can be reduced, thereby improving the initial coulombic efficiency. When the specific surface area of ​​the hard carbon is greater than that of the graphite, the diffusion rate of lithium ions can be increased, thereby improving the dynamic performance of the battery. Therefore, when the specific surface areas of the graphite and hard carbon, as well as their relative size, are simultaneously controlled, the battery performance can be further improved.

[0056] In one embodiment, the specific surface area of ​​the graphite is 0.5 m 2 / g-7m 2 / g (for example, 0.5m 2 / g、1m 2 / g, 2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 Controlling the specific surface area of ​​graphite within the above range can improve the infiltration of the electrolyte, increase the deintercalation of sodium, and improve the kinetics of sodium electrolyte.

[0057] In one embodiment, the specific surface area of ​​the hard carbon is 0.5 m 2 / g-26m 2 / g (for example, 0.5m 2 / g、1m2 / g、5m 2 / g、10m 2 / g、15m 2 / g, 20m 2 / g, 25m 2 / g, 26m 2 / g).

[0058] In one embodiment, the specific surface area of ​​the hard carbon is 1 m 2 / g-10m 2 / g (for example, 1m 2 / g, 2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g、10m 2 Controlling the specific surface area of ​​hard carbon within the above range can improve the infiltration of electrolyte, enhance the deintercalation of sodium, and improve the kinetics of sodium battery.

[0059] In one embodiment, the specific surface area of ​​the hard carbon is greater than the specific surface area of ​​the graphite by a difference of 0.5 m 2 / g-7m 2 / g (for example, 0.5m 2 / g、1m 2 / g, 2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 Controlling the difference between the specific surface area of ​​hard carbon and the specific surface area of ​​graphite within the above range can improve electrolyte infiltration. Furthermore, the synergistic combination of hard carbon and graphite allows the graphite and hard carbon to be uniformly mixed, thereby increasing the conductivity of the negative electrode active material and improving the interface properties between the electrode and the electrolyte. This increases the utilization rate of the active material and reduces electrolyte side reactions and battery polarization, thereby improving the initial coulombic efficiency, rate capability, specific capacity, and cycle life of the battery.

[0060] In one embodiment, the Raman spectrum of the negative electrode active material satisfies: ID / IG ≤ 0.56 (for example, 0.56, 0.55, 0.5, 0.45, 0.4, 0.35, 0.3, 0.25, 0.2, 0.15, 0.1, 0.05). When the Raman spectrum of the negative electrode active material satisfies: ID / IG ≤ 0.56, it indicates that the negative electrode active material has fewer defects. When the Raman spectrum of the negative electrode active material satisfies: ID / IG > 0.56, the negative electrode active material has more defects and relatively low conductivity, and more defects will increase the side reactions between the negative electrode and the electrolyte. When the Raman spectrum of the negative electrode active material satisfies: ID / IG ≤ 0.56, it indicates that the negative electrode active material has fewer defects and higher conductivity, and fewer defects can reduce the side reactions between the negative electrode and the electrolyte, thereby enabling the negative electrode sheet to have a higher initial coulombic efficiency and sodium storage kinetics, and thus enabling the battery to have a higher specific capacity and rate performance.

[0061] The ID refers to the 1300cm in the Raman spectrum. -1 to 1400cm -1 The peak intensity of the inner D peak; the IG refers to the 1500cm in the Raman spectrum -1 to 1650cm -1 Peak intensity of inner G peak.

[0062] In one embodiment, the Raman spectrum of the negative electrode active material satisfies the following formula: 0.2≤ID / IG≤0.45. When the Raman spectrum of the negative electrode active material satisfies the above specific formula, side reactions between the negative electrode and the electrolyte can be further reduced, the initial coulombic efficiency and sodium storage kinetics of the negative electrode sheet can be further improved, thereby further improving the specific capacity and rate performance of the battery.

[0063] According to a specific embodiment, the degree of graphitization of the negative electrode active material is ≥ 90% (e.g., 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%). When the degree of graphitization of the negative electrode active material is ≥ 90%, it indicates that the negative electrode active material has few defects and a high degree of graphitization, thereby improving the conductivity of the negative electrode sheet.

[0064] In one example, the graphitization degree of the negative electrode active material is 92%-97%.

[0065] According to a specific embodiment, the compaction density of the negative electrode sheet is ≥1g / cm 3 When the compaction density of the negative electrode sheet is ≥1g / cm 3 When the battery is heated, the specific capacity of the battery can be improved.

[0066] In one embodiment, the compaction density of the negative electrode sheet is 1 g / cm 3-1.3g / cm 3 (For example, 1g / cm 3 , 1.1g / cm 3 , 1.2g / cm 3 , 1.3g / cm 3 ).

[0067] In one example, the graphite includes at least one of natural graphite and artificial graphite.

[0068] In one example, the natural graphite includes one or more of flake graphite, earthy graphite, and block graphite.

[0069] In one example, the artificial graphite includes one or more of single crystal graphite, polycrystalline graphite, pyrolytic graphite, highly oriented pyrolytic graphite, and graphite fiber.

[0070] The negative electrode active material can be prepared by the following method:

[0071] a) solution mixing: adding the graphite and the hard carbon to a certain amount of deionized water and stirring them continuously to uniformly mix them to obtain a mixed solution, and drying the mixed solution under stirring to obtain a powder;

[0072] b) Ball milling: The powder and zirconium beads are placed in a ball mill, and a certain amount of solvent is added, followed by ball milling.

[0073] In one embodiment, the drying process is to dry the water in the mixed solution.

[0074] In one example, the drying conditions are: temperature of 20°C-80°C (for example, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C), and time of 12h-48h (for example, 12h, 15h, 20h, 25h, 30h, 35h, 40h, 45h, 48h).

[0075] In one example, the weight ratio of the powder to the zirconium beads is 0.3-2.1 (e.g., 0.3, 0.4, 0.5, 0.7, 1, 1.2, 1.5, 1.8, 2, 2.1).

[0076] In one example, the solvent is ethanol or water.

[0077] In one embodiment, the ball milling treatment conditions are: a rotation speed of 200r / min-1200r / min (for example, 200r / min, 300r / min, 400r / min, 500r / min, 600r / min, 700r / min, 800r / min, 900r / min, 1000r / min, 1100r / min, 1200r / min), and a time of 6h-24h (for example, 6h, 8h, 10h, 12h, 15h, 18h, 20h, 22h, 24h).

[0078] In one embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on one or both sides of the negative electrode current collector. The negative electrode active material layer includes the negative electrode active material.

[0079] According to a specific embodiment, based on the total weight of the negative electrode active material layer, the weight content of the negative electrode active material is 90wt%-98wt% (for example, 90wt%, 90.5wt%, 91wt%, 91.5wt%, 92wt%, 92.5wt%, 93wt%, 93.5wt%, 94wt%, 94.5wt%, 95wt%, 95.5wt%, 96wt%, 96.5wt%, 97wt%).

[0080] In one example, based on the total weight of the negative electrode active material layer, the weight content of the negative electrode active material is 92 wt %-96 wt %.

[0081] In one example, the negative electrode active material layer includes a binder, a conductive agent, and a thickener.

[0082] In one example, the binder is selected from one or more of styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), polytetrafluoroethylene, and polyethylene oxide.

[0083] In one example, the conductive agent is selected from one or more of conductive carbon black, carbon fiber, Ketjen black, acetylene black, carbon nanotubes and graphene.

[0084] In one example, the thickener is one or more of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose.

[0085] According to a specific embodiment, based on the total weight of the negative electrode active material layer, the weight content of the binder is 1.5wt%-4.8wt% (for example, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 4.8wt%), the weight content of the conductive agent is 0wt%-5.2wt% (for example, 0wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, 5.2wt%), and the weight content of the thickener is 0.5wt%-2.8wt% (for example, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 2.8wt%). When the weight content of the conductive agent is 0wt%, it means that there is no conductive agent in the negative electrode active material layer. In the case where the negative electrode active material layer does not contain a conductive agent, the conductivity of the negative electrode sheet can still meet the requirements of the battery.

[0086] In one example, based on the total weight of the negative electrode active material layer, the weight content of the binder is 2 wt%-2.9 wt%, the weight content of the conductive agent is 1.5 wt%-3.5 wt%, and the weight content of the thickener is 0.5 wt%-2 wt%.

[0087] In one example, the negative electrode current collector is selected from aluminum foil.

[0088] A second aspect of the present disclosure provides a sodium ion battery, wherein the sodium ion battery includes the negative electrode sheet described in the first aspect of the present disclosure.

[0089] The materials of the battery except the negative electrode sheet can be prepared according to the methods in the art, and can achieve the effects of high specific capacity, stable cycle performance and good rate performance.

[0090] The sodium ion battery disclosed herein contains the negative electrode sheet disclosed herein, so the specific capacity, cycle stability and rate performance of the battery are improved.

[0091] In one embodiment, the sodium ion battery includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte.

[0092] The positive electrode sheet may be a conventional positive electrode sheet in the art. For example, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer located on one side or both sides of the positive electrode current collector.

[0093] In one embodiment, the positive electrode active material layer includes a positive electrode active material, a binder, and a conductive agent.

[0094] In one embodiment, the positive electrode active material includes one or more of sodium-containing transition metal oxides, polyanion materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian blue materials.

[0095] The sodium-containing transition metal oxides include (Ni, Fe, Mn) oxides; for example: NaFe 1 / 3 Ni 1 / 3 Mn 1 / 3 O2、NaNi 0.6 Fe 0.25 Mn 0.15 O2、NaCu 0.22 Fe 0.3 Mn 0.48 O2.

[0096] In one example, the electrolyte includes an electrolyte salt, an organic solvent, and an additive.

[0097] In one example, the electrolyte salt includes one or more of NaPF6, NaBF4, NaClO4, NaCF3SO3, NaAlO4, NaAlCl4, Na(CF3SO2)2N, NaBOB, and NaDFOB.

[0098] In one example, the organic solvent includes one or more of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

[0099] In one example, the additive includes one or more of 1,3-propane sultone (PS), diethylene glycol sulfate (DTD), propene sultone (PST), maleic anhydride, citraconic anhydride, succinic anhydride, succinonitrile (SN), adiponitrile (ADN), ethylene glycol bis(propionitrile) ether (EGBE), hexane tricarbonitrile (HTCN), fluorobenzene, and DENE.

[0100] In one example, based on the total weight of the electrolyte, the weight content of the electrolyte salt is 10wt%-15wt% (for example, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%), the weight content of the organic solvent is 70wt%-89wt% (for example, 70wt%, 72wt%, 75wt%, 78wt%, 80wt%, 82wt%, 85wt%, 88wt%, 89wt%), and the weight content of the additive is 0.1wt%-15wt% (for example, 0.1wt%, 0.5wt%, 1wt%, 3wt%, 5wt%, 8wt%, 10wt%, 12wt%, 15wt%).

[0101] The material of the isolation membrane can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0102] The present disclosure will be described in detail below through examples. The examples described in this disclosure are only a portion of the examples of the present disclosure, not all of the examples. Based on the examples in this disclosure, all other examples obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this disclosure.

[0103] The following examples are used to illustrate the negative electrode sheet of the present disclosure.

[0104] Example 1

[0105] (1) Preparation of ingredients:

[0106] Negative electrode active material: 95 parts by weight (median particle size Dv50 is 5.2 μm, conductivity is 70 S / cm, and degree of graphitization is 93.5%), of which the weight content of hard carbon A is 97% (median particle size Dv50 is 4.97 μm, specific surface area is 5.9 m 2 / g), the weight content of graphite (artificial graphite) B is 3% (median particle size Dv50 is 6.03μm, specific surface area is 1.28m 2 / g);

[0107] Binder: SBR 2.55 parts by weight;

[0108] Thickener: CMC is 1.45 parts by weight;

[0109] Conductive agent: 1 part by weight of conductive carbon black;

[0110] Negative electrode current collector: aluminum foil.

[0111] (2) Preparation of negative electrode active materials

[0112] a) solution mixing: adding the graphite and the hard carbon to 30 mL of deionized water and stirring continuously to uniformly mix them to obtain a mixed solution, drying the mixed solution under stirring, evaporating the water to dryness, and obtaining a powder;

[0113] b) Ball milling: The powder and zirconium beads of different sizes were placed in a ball mill, wherein the weight ratio of the powder to the zirconium beads was 0.5. After adding a certain amount of ethanol, the mixture was ball milled at a speed of 600 r / min for 12 h.

[0114] (3) Preparation of negative electrode sheet

[0115] The negative electrode active material of step (2) is dispersed in the thickener glue, and then a binder is added thereto and stirred at a speed of 800 r / min for 3 hours to obtain a negative electrode slurry. The negative electrode slurry is coated on one side of the surface of the negative electrode current collector and placed in a vacuum dry oven and baked at 120°C for 12 hours to obtain a negative electrode sheet, wherein the compaction density of the negative electrode sheet is 1.15 g / cm 3 .

[0116] Example 2 group

[0117] This example group was carried out with reference to Example 1, except that the weight content A of the hard carbon and / or the weight content B of the graphite were changed. See Table 1 for details.

[0118] Example 3 group

[0119] This example group was carried out with reference to Example 1, except that the median particle size Dv50 of graphite and / or the median particle size Dv50 of hard carbon were changed. See Table 1 for details.

[0120] Example 4 Group

[0121] This example group was carried out with reference to Example 1, except that the specific surface area of ​​hard carbon and / or the specific surface area of ​​graphite were changed. See Table 1 for details.

[0122] Example 5 Group

[0123] This example group was carried out with reference to Example 1, except that the graphitization degree of the negative electrode active material was changed. See Table 1 for details.

[0124] Example 6

[0125] The method was carried out in accordance with Example 1, except that the negative electrode active material layer did not include a conductive agent. The contents of the components in the negative electrode active material layer were as follows: negative electrode active material: 96 parts by weight (median particle size Dv50 of 5.2 μm, conductivity of 70 S / cm, degree of graphitization of 93.5%), wherein the weight content of hard carbon A was 97% (median particle size Dv50 of 4.97 μm, specific surface area of ​​5.9 m 2 / g), the weight content of graphite (artificial graphite) B is 3% (median particle size Dv50 is 6.03μm, specific surface area is 1.28m 2 / g);

[0126] Binder: SBR 2.55 parts by weight;

[0127] Thickener: CMC is 1.45 parts by weight.

[0128] Comparative Example 1

[0129] The same method was used as in Example 1, except that the graphite was replaced with the same weight portion of hard carbon. For details, see Table 1.

[0130] Comparative Example 2

[0131] The same process was carried out as in Example 1, except that the weight content of the hard carbon was adjusted to change I1 / I2. For details, see Table 1.

[0132] Table 1

[0133] Preparation Example

[0134] Batteries were prepared using the negative electrode sheets obtained in the examples and comparative examples in the following manners.

[0135] (1) Positive electrode

[0136] The positive electrode active material (layered ternary NaFe 1 / 3 Ni 1 / 3 Mn 1 / 3 O2), binder (PVDF), and conductive agent (conductive carbon black) are mixed in a mass ratio of 96:2:2. N-methylpyrrolidone is added and stirred in a vacuum mixer until a uniform positive electrode slurry is formed. The positive electrode slurry is evenly coated on both sides of the positive electrode current collector (aluminum foil). The coated aluminum foil is baked in an oven and then dried in a 120°C oven for 8 hours. The desired positive electrode sheet is then obtained by roller pressing and slitting.

[0137] (2) Negative electrode

[0138] The negative electrode sheets obtained in the above embodiments and comparative examples were used respectively.

[0139] (3) Electrolyte

[0140] The electrolyte contains a mixture of ethylene carbonate and diethyl carbonate (volume ratio is 1:1) in which NaClO4 (1 mol / L) and fluoroethylene carbonate (wherein the weight content of fluoroethylene carbonate in the electrolyte is 5%) are dissolved.

[0141] (4) Diaphragm

[0142] The diaphragm is made of fiberglass.

[0143] (5) Preparation of sodium ion batteries

[0144] The positive electrode sheet of step (1), the separator of step (4), and the negative electrode sheet of step (2) are stacked in order, ensuring that the separator is located between the positive and negative electrode sheets to play an isolating role, and then a bare battery cell is obtained by winding. The bare battery cell is placed in an aluminum-plastic film shell, and the electrolyte of step (3) is injected into the dried bare battery cell. After vacuum packaging, standing, forming, shaping, and sorting, the desired battery is obtained.

[0145] Test Case

[0146] 1. Button batteries were prepared from the negative electrodes of the embodiment and the comparative example and the following tests were performed:

[0147] (1) Preparation of button batteries

[0148] 1) Negative electrode

[0149] The negative electrode sheets obtained in the above embodiments and comparative examples were used respectively.

[0150] 2) Electrolyte

[0151] The electrolyte contains a mixture of ethylene carbonate and diethyl carbonate (volume ratio is 1:1) in which NaClO4 (1 mol / L) and fluoroethylene carbonate (wherein the weight content of fluoroethylene carbonate in the electrolyte is 5%) are dissolved.

[0152] 3) Diaphragm

[0153] The diaphragm is made of fiberglass.

[0154] 4) Button battery preparation

[0155] The negative electrode sheet of step 1), the separator of step 3) and the sodium metal sheet are sequentially placed in a button cell, and then the electrolyte of step 2) is added and sealed.

[0156] (2) Test the prepared button battery

[0157] 1) Initial Coulombic efficiency test

[0158] Performance testing was conducted at a temperature of 25°C, a voltage range of 0-2V, and a current density of 20.5 mA / g. Initial coulombic efficiency (%) of a button cell = first cycle charge capacity / first cycle discharge capacity * 100%.

[0159] 2) Specific capacity test

[0160] Performance testing was conducted at a temperature of 25°C, with a voltage range of 0 to 2 V and a current density of 20.5 mA / g. Coin cell specific capacity (mAh / g) = first cycle charge capacity / mass of negative electrode active material in the negative electrode sheet.

[0161] 2. The batteries of the embodiment and comparative example were tested as follows:

[0162] (1) Rate performance test

[0163] The test temperature was 25°C. Under the voltage range of 0-2V, one cycle performance test was carried out at current densities of 8mA / g, 200mA / g, 500mA / g, and 1000mA / g, respectively. The charging capacity was recorded as Q1, and the charging capacity Q1 is the rate performance at different current densities.

[0164] (2) Cyclic stability test

[0165] The coin cell battery was tested at a temperature of 25°C, with a voltage range of 0-2V and a current density of 20.5 mA / g for 80 cycles. Capacity retention (%) after 80 cycles = discharge capacity at the 80th cycle / charge capacity at the first cycle * 100%.

[0166] The obtained results are recorded in Table 2.

[0167] Table 2

[0168] As can be seen from Table 2, it can be seen from the comparative examples and the examples that the initial coulombic efficiency of the negative electrode sheet of the example is improved, the specific capacity of the battery made from the negative electrode sheet of the example is improved, the capacity retention rate is improved, and the rate performance is improved, indicating that the negative electrode sheet of the present disclosure and the sodium ion battery including the negative electrode sheet improve the specific capacity and rate performance of the battery by improving the conductivity of the negative electrode sheet and improving the interface performance between the electrode sheet and the electrolyte.

[0169] The preferred embodiments of the present disclosure are described in detail above, but the present disclosure is not limited thereto. Within the technical concept of the present disclosure, various simple variations of the technical solution of the present disclosure may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed by the present disclosure and fall within the scope of protection of the present disclosure.

Claims

1. A negative electrode sheet, characterized in that: The negative electrode sheet includes a negative electrode active material, and the negative electrode active material includes hard carbon and graphite. In the XRD spectrum of the negative electrode active material, the intensity of the (002) crystal plane diffraction peak with a diffraction angle 2θ located at 21.5°-25° is I1, and the intensity of the (002) crystal plane diffraction peak with a diffraction angle 2θ located at 25.5°-27° is I2, satisfying: 0<I1 / I2≤0.

65.

2. The negative electrode sheet according to claim 1, wherein: In the XRD spectrum of the negative electrode active material, the half-peak width of the (002) crystal plane diffraction peak at 25.5°-27° is 0.1°-1°; And / or, the negative electrode active material satisfies: 0.03≤I1 / I2≤0.

45.

3. The negative electrode sheet according to claim 1 or 2, wherein: Based on the total weight of the negative electrode active material, the weight content A of the hard carbon is 91wt%≤A≤99wt%, and the weight content B of the graphite is 0wt%<B≤9wt%; and / or, the median particle size Dv50 of the negative electrode active material is ≤12 μm; And / or, the median particle size Dv50 of the graphite is ≥5.2 μm; and / or; the median particle size Dv50 of the graphite is not less than the median particle size Dv50 of the hard carbon; And / or, the conductivity C of the negative electrode active material under a pressure of 50 MPa is ≥ 35 S / cm.

4. The negative electrode sheet according to any one of claims 1 to 3, wherein: Based on the total weight of the negative electrode active material, the weight content A of the hard carbon is 95.5%wt%-98.5wt%, and the weight content B of the graphite is 1.5wt%-4.5wt%; and / or, the median particle size Dv50 of the hard carbon is 1.5 μm-13 μm; And / or, the median particle size of the graphite is 10 μm<Dv50≤20 μm; And / or, the median particle size Dv50 of the graphite is greater than the median particle size Dv50 of the hard carbon by a difference of 0 μm to 12 μm.

5. The negative electrode sheet according to any one of claims 1 to 4, wherein: The median particle size Dv50 of the graphite is 11 μm-16 μm; and / or, the median particle size Dv50 of the hard carbon is 3 μm-8 μm; And / or, the median particle size Dv50 of the graphite is greater than the median particle size Dv50 of the hard carbon by a difference of 1.5 μm to 8.5 μm.

6. The negative electrode sheet according to any one of claims 1 to 5, wherein: The conductivity of the negative electrode active material at a pressure of 50 MPa is 40 S / cm-70 S / cm; And / or, the median particle size Dv50 of the negative electrode active material is 1.5 μm-12 μm.

7. The negative electrode sheet according to any one of claims 1 to 6, wherein: The specific surface area of ​​the graphite is ≤9.6m 2 / g, the specific surface area of ​​the hard carbon is 0.5m 2 / g-26m 2 / g; And / or, the specific surface area of ​​the hard carbon is greater than the specific surface area of ​​the graphite.

8. The negative electrode sheet according to any one of claims 1 to 7, wherein: The specific surface area of ​​the graphite is 0.5 m 2 / g-7m 2 / g; And / or, the specific surface area of ​​the hard carbon is 1m 2 / g-10m 2 / g; And / or, the specific surface area of ​​the hard carbon is greater than the specific surface area of ​​the graphite by a difference of 0.5 m 2 / g-7m 2 / g.

9. The negative electrode sheet according to any one of claims 1 to 8, wherein: The Raman spectrum of the negative electrode active material satisfies: ID / IG≤0.56, preferably 0.2≤ID / IG≤0.45; And / or, the graphitization degree of the negative electrode active material is ≥90%, preferably 92%-97%.

10. The negative electrode sheet according to any one of claims 1 to 9, wherein: The compaction density of the negative electrode sheet is ≥1g / cm 3 , preferably 1g / cm 3 -1.3g / cm 3 .

11. The negative electrode sheet according to any one of claims 1 to 10, wherein: The graphite includes at least one of natural graphite and artificial graphite; Preferably, the natural graphite includes one or more of flake graphite, earthy graphite and block graphite; Preferably, the artificial graphite includes one or more of single crystal graphite, polycrystalline graphite, pyrolytic graphite, highly oriented pyrolytic graphite and graphite fiber.

12. The negative electrode sheet according to any one of claims 1 to 11, wherein: The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer located on one side or both sides of the negative electrode current collector, wherein the negative electrode active material layer comprises a negative electrode active material, a binder, a conductive agent and a thickener.

13. The negative electrode sheet according to claim 12, wherein: Based on the total weight of the negative electrode active material layer, the weight content of the negative electrode active material is 90wt%-98wt%; And / or, based on the total weight of the negative electrode active material layer, the weight content of the binder is 1.5wt%-4.8wt%, the weight content of the conductive agent is 0wt%-5.2wt%, and the weight content of the thickener is 0.5wt%-2.8wt%.

14. The negative electrode sheet according to claim 12, wherein: Based on the total weight of the negative electrode active material layer, the weight content of the negative electrode active material is 90wt%-98wt%.

15. A sodium ion battery, characterized in that: The sodium ion battery comprises the negative electrode sheet according to any one of claims 1 to 14.

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