Carbon-based negative electrode material and preparation method thereof, sodium-ion battery and electric equipment

Abstract

The invention relates to the technical field of sodium-ion batteries, in particular to a carbon-based negative electrode material and a preparation method thereof, a sodium-ion battery and electric equipment. The discharge sodium ion flux coefficient FNa < + > of the carbon-based negative electrode material is 40-100 m < 2 > / (mol.h); fNa < + > = (m * SBET * CNa * MNa) / (C2 * h2); m is the mass of the carbon-based negative electrode material in the half cell; the SBET is the specific surface area of the carbon-based negative electrode material; cNa is 1166 mAh / g; the content of MNa is 22.99 g / mol; c2 is the second cycle discharge capacity of the half cell; h2 is the second cycle discharge time of the half cell. According to the invention, the relationship between the electrochemical performance of the carbon-based negative electrode material and the sodium ion flux is constructed, and the discharge sodium ion flux coefficient of the carbon-based negative electrode material is controlled, so that the carbon-based negative electrode material with high capacity and good low-temperature performance can be screened out.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a carbon-based negative electrode material and a preparation method thereof, a sodium ion battery and an electrical device. Background Art

[0002] Under low temperature conditions, the migration rate of ions and electrons within sodium-ion batteries decreases, leading to increased sodium ion migration barriers at various electrode interfaces and slow chemical diffusion within the bulk of the electrode material. This increases battery impedance and polarization, leading to decreased battery capacity, reduced charge and discharge efficiency, and sodium precipitation on the surface of the negative electrode material. Therefore, the development of low-temperature-resistant sodium-ion battery negative electrode materials has important research significance and practical application value.

[0003] At present, the technical means to improve the low-temperature performance of the negative electrode materials of sodium ion batteries include: reducing the particle size, increasing the interlayer spacing, pore formation, doping, introducing defect sites, increasing surface dangling bonds, or coating the surface of the carbon material to change the stability of the SEI film generated by the contact between the electrode material and the electrolyte, and reducing the apparent activation energy Ea during the sodium ion transport process at each interface. However, the negative electrode materials obtained by the above methods generally have a low capacity, generally less than 300mAh / g. Carbon-based materials with higher specific capacity (>300mAh / g) usually have poor low-temperature performance. This is because the platform capacity of high-capacity carbon-based materials is longer, the platform voltage is lower, and it is closer to the potential of metallic sodium deposition. When charging at low temperatures, metallic sodium is more likely to precipitate on the surface of the negative electrode material, resulting in interface deterioration.

[0004] Therefore, it is of great significance to screen sodium ion battery anode materials with both good low-temperature performance and high capacity.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The first purpose of the present invention is to provide a carbon-based negative electrode material for sodium ion batteries. By constructing the relationship between the electrochemical performance and sodium ion flux of the carbon-based negative electrode material and controlling the size of the discharge sodium ion flux coefficient of the carbon-based negative electrode material, the low-temperature performance and electrochemical performance can be judged, and a carbon-based negative electrode material with both high capacity and good low-temperature performance can be screened out.

[0007] The second object of the present invention is to provide a method for preparing a carbon-based negative electrode material, wherein the carbon-based negative electrode material prepared by this method has high capacity and good low-temperature performance.

[0008] A third object of the present invention is to provide a sodium ion battery having both high capacity and excellent low-temperature performance.

[0009] A fourth object of the present invention is to provide an electrical device.

[0010] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted:

[0011] The present invention first provides a carbon-based negative electrode material, wherein the discharge sodium ion flux coefficient F of the carbon-based negative electrode material is Na+ 40~100m 2 / (mol·h); and the F Na+ Satisfies the following relationship: F Na+ =(m×S BET ×C Na ×M Na ) / (C2×h2); wherein the carbon-based negative electrode material is made into a half-cell, m is the mass of the carbon-based negative electrode material in the half-cell, in g; S BET is the specific surface area of ​​the carbon-based negative electrode material, in m 2 / g;C Na is the theoretical specific capacity of sodium, which is 1166 mAh / g; M Na is the molar mass of sodium, which is 22.99 g / mol; C2 is the second-week discharge capacity of the half-cell, in mAh; h2 is the second-week discharge time of the half-cell, in h.

[0012] Furthermore, the sodium ion flux coefficient F of the discharge platform section of the carbon-based negative electrode material is Na+平 100~200m 2 / (mol·h); the F Na+平 Satisfies the following relationship: F Na+平 =(m×S BET ×C Na ×M Na ) / (C 平 ×h 平 ); among them, C 平 is the second-week platform discharge capacity of the half-cell, in mAh; h 平 is the second-cycle platform discharge time of the half-cell, in hours.

[0013] Furthermore, the sodium ion flux coefficient F of the carbon-based negative electrode material in the discharge slope section is Na+斜 300~1000m 2 / (mol·h); and the F Na+斜 Satisfies the following relationship: F Na+斜 =(m×S BET ×C Na ×M Na ) / (C 斜 ×h 斜 ); among them, C斜 is the second cycle ramp discharge capacity of the half-cell, in mAh; h 斜 is the second cycle ramp discharge time of the half-cell, in hours.

[0014] Furthermore, the specific surface area S of the carbon-based negative electrode material BET 5~20m 2 / g.

[0015] Furthermore, the particle size of the carbon-based negative electrode material is in the range of 0.5 to 13 μm.

[0016] Furthermore, the median particle size of the carbon-based negative electrode material is 3 to 6 μm.

[0017] The present invention further provides a method for preparing a carbon-based negative electrode material, comprising the following steps: pre-carbonizing a precursor material and then acid-washing to obtain a carbon precursor; crushing the carbon precursor and then carbonizing it, and cooling it to obtain the carbon-based negative electrode material.

[0018] Furthermore, the precursor material includes at least one of asphalt, coal-based materials, biomass materials, starch and its derivatives, lignin and its derivatives, cellulose and its derivatives, resin and its derivatives.

[0019] Furthermore, the pre-carbonization temperature is 300-900° C., and the holding time is 2-12 hours.

[0020] Furthermore, the pre-carbonization is carried out in an inert atmosphere.

[0021] Furthermore, the acid used for pickling includes at least one of hydrochloric acid solution, nitric acid solution, sulfuric acid solution and hydrofluoric acid solution.

[0022] Furthermore, the ash content in the carbon precursor is ≤1%.

[0023] Furthermore, the carbonization temperature is 1100° C. to 1600° C., and the holding time is 1 to 12 hours.

[0024] Furthermore, the carbonization is carried out in an inert atmosphere.

[0025] The present invention further provides a sodium ion battery comprising a carbon-based negative electrode material.

[0026] The present invention also provides an electrical device comprising a sodium ion battery.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The present invention constructs the relationship between the electrochemical performance of the carbon-based negative electrode material and the sodium ion flux, and controls the discharge sodium ion flux coefficient F of the carbon-based negative electrode material.Na+ 40~100m 2 / (mol·h), carbon-based negative electrode materials with both high capacity and good low-temperature performance can be screened out.

[0029] (2) The present invention controls the sodium ion flux coefficient F of the discharge platform section of the carbon-based negative electrode material. Na+ Flat meet 100 ~ 200m 2 / (mol·h), sodium ion flux coefficient F in the discharge ramp Na+ Inclined to meet 300~1000m 2 / (mol·h), which can achieve better high capacity and low temperature performance.

[0030] (3) The present invention provides a method for preparing a carbon-based negative electrode material. The prepared carbon-based negative electrode material has high capacity and good low-temperature performance. The preparation method is simple to operate, has a short process flow, and is easily scalable to mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 A schematic diagram of defining the slope section and platform section provided by the present invention. DETAILED DESCRIPTION

[0033] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. Those who do not specify specific conditions in the embodiments are carried out according to normal conditions or the conditions recommended by the manufacturer. Those whose reagents or instruments are not specified by the manufacturer are conventional products that can be purchased commercially.

[0034] Unless otherwise specified, in the present invention, terms such as "first aspect," "second aspect," "third aspect," and "fourth aspect" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor as implicitly indicating the importance or quantity of the technical features indicated. Furthermore, terms such as "first," "second," "third," and "fourth" serve only as non-exhaustive enumeration and description, and should not constitute closed-ended limitations on quantity.

[0035] Unless otherwise specified, the terms "include" and "comprising" used in the present invention may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0036] Unless otherwise specified, in the present invention, "one or more" or "at least one" refers to any one, any two, or any two or more of the listed items. Among them, "several" refers to any two or any two or more.

[0037] In a first aspect, the present invention provides a carbon-based negative electrode material, wherein the discharge sodium ion flux coefficient F of the carbon-based negative electrode material is Na+ 40~100m 2 / (mol·h), including but not limited to 40m 2 / (mol·h), 45m 2 / (mol·h), 50m 2 / (mol·h), 55m 2 / (mol·h), 60m 2 / (mol·h), 65m 2 / (mol·h), 70m 2 / (mol·h), 75m 2 / (mol·h), 80m 2 / (mol·h),85m 2 / (mol·h), 90m 2 / (mol·h),95m 2 / (mol·h), 100m 2 / (mol·h) or the range between any two of them.

[0038] It can be understood that the sodium ion flux coefficient refers to the equivalent area of ​​the interface through which 1 mol of sodium ions pass per unit time.

[0039] The F Na+ Satisfies the following relationship: F Na+ =(m×S BET ×C Na ×M Na) / (C2×h2).

[0040] The carbon-based negative electrode material is made into a half-cell, and m is the mass of the carbon-based negative electrode material in the half-cell, in g.

[0041] S BET is the specific surface area of ​​the carbon-based negative electrode material, in m 2 / g.

[0042] C Na is the theoretical specific capacity of sodium, and C Na It is 1166mAh / g.

[0043] M Na is the molar mass of sodium, and M Na It is 22.99g / mol.

[0044] C2 is the discharge capacity of the half-cell in the second cycle, in mAh.

[0045] h2 is the second cycle discharge time of the half-cell, in hours.

[0046] It is understandable that the charge and discharge specific capacity and charge and discharge time are usually based on the discharge curve data of the second week of half-cell testing.

[0047] During the charge and discharge process, solvated and desolvated sodium ions are transported at the electrolyte-solid electrolyte membrane interface, within the solid electrolyte membrane, at the solid electrolyte-material surface interface, and within the bulk of the material. This transport process is accompanied by changes in the transfer medium and the interfacial area, resulting in changes in the sodium ion transport interface flux per unit time and current density. The size of each transport interface is related to the intrinsic properties of the material, and we call this flux coefficient the sodium ion flux coefficient of the negative electrode material.

[0048] By constructing the relationship between the electrochemical properties of carbon-based negative electrode materials and the sodium ion flux, the present invention can obtain a formula for the discharge sodium ion flux coefficient. By calculating and comparing the sizes of the discharge sodium ion flux coefficients of different carbon-based negative electrode materials, the low-temperature performance and rate performance of the materials are summarized, and carbon-based negative electrode materials with both high capacity and good low-temperature performance are screened out.

[0049] In some specific embodiments, when the discharge sodium ion flux coefficient F of the carbon-based negative electrode material is satisfied Na+ 40~100m 2 / (mol·h), the material has an appropriate specific surface area. Half-cell measurements show high first-cycle coulombic efficiency, a discharge voltage of 50-75mV, and a reversible specific capacity of 320-400mAh / g. When the cell is operated at -20°C and a 0.1C rate, and the coulombic efficiency is ≥99.5%, the capacity retention rate is ≥75%. The 26700 cell maintains over 90% of its capacity after 1500 cycles at a 3C rate at room temperature.

[0050] When the discharge sodium ion flux coefficient of the carbon-based negative electrode material is low, it means that during the desolvation process of the solvated sodium ions at the negative end, the sodium ions require more energy to be transported at each interface, that is, it is more difficult to desolvate. The material exhibits a low specific surface area (≤5m 2 / g). Half-cell discharge voltage during the first cycle was low (≤50mV), and the discharge plateau was close to the sodium metal nucleation potential. At higher rates, excessive polarization caused overpotential sodium deposition, which manifested as widespread deposition on the electrode. Capacity retention was low during both low- and room-temperature cycling tests.

[0051] When the discharge sodium ion flux coefficient of the carbon-based negative electrode material is high, it means that during the desolvation process of the solvated sodium ions at the negative end, the sodium ions require less energy to be transported at each interface, that is, it is easier to desolvate. However, at this time, the specific surface area of ​​the material is too large (≥20m 2 / g), a large number of bubbles will be generated during the pulping process, pinholes or pore-like low-density areas are likely to appear on the surface of the electrode, and point-like sodium precipitation is likely to occur during the charge and discharge cycle; the coulombic efficiency of the half-cell measured in the first week is low (≤80%), the discharge voltage in the first week is large (≥75mV), and the reversible specific capacity is small (≤320mAh / g).

[0052] In some specific embodiments, in order to obtain better high capacity and low temperature performance, the discharge platform sodium ion flux coefficient F of the carbon-based negative electrode material is Na+平 100~200m 2 / (mol·h); including but not limited to 100m 2 / (mol·h), 110m 2 / (mol·h), 120m 2 / (mol·h), 130m 2 / (mol·h), 140m 2 / (mol·h), 150m 2 / (mol·h), 160m 2 / (mol·h), 170m 2 / (mol·h), 180m 2 / (mol·h), 190m 2 / (mol·h), 200m 2 / (mol·h) or the range between any two of them.

[0053] The carbon-based negative electrode material is made into a half-cell, the F Na+平 Satisfies the following relationship: F Na+平 =(m×S BET ×C Na ×M Na ) / (C 平 ×h 平 ). Among them, C 平 is the second-week platform discharge capacity of the half-cell, in mAh; h 平 is the second cycle platform discharge time of the half-cell, in h. m is the mass of the carbon-based negative electrode material in the half-cell, in g. BET is the specific surface area of ​​the carbon-based negative electrode material, in m 2 / g. C Na The theoretical specific capacity of sodium is 1166 mAh / g. Na is the molar mass of sodium, which is 22.99 g / mol.

[0054] It can be understood that the second-week discharge capacity can be divided into discharge ramp capacity and discharge platform capacity, and the second-week discharge time can be divided into discharge ramp time and discharge platform time. Figure 1 As shown, the discharge curve with a voltage higher than 0.08V is defined as a slope segment, and the discharge curve with a voltage lower than 0.08V is defined as a platform segment.

[0055] The electrochemical curves of different negative electrode material platform segments are used to calculate the apparent sodium ion flux coefficient, which is well correlated with the performance of the material reaction at the battery cell end.

[0056] In some specific embodiments, in order to obtain better high capacity and low temperature performance, the sodium ion flux coefficient F of the discharge slope section of the carbon-based negative electrode material is Na+斜 300~1000m 2 / (mol·h); including but not limited to 300m 2 / (mol·h), 350m 2 / (mol·h), 400m 2 / (mol·h), 450m 2 / (mol·h), 500m 2 / (mol·h), 550m 2 / (mol·h), 600m 2 / (mol·h), 650m 2 / (mol·h), 700m 2 / (mol·h), 750m2 / (mol·h), 800m 2 / (mol·h),850m 2 / (mol·h), 900m 2 / (mol·h),950m 2 / (mol·h), 1000m 2 / (mol·h) or the range between any two of them.

[0057] The carbon-based negative electrode material is made into a half-cell, the F Na+斜 Satisfies the following relationship: F Na+斜 =(m×S BET ×C Na ×M Na ) / (C 斜 ×h 斜 ); among them, C 斜 is the second cycle ramp discharge capacity of the half-cell, in mAh; h 斜 is the second cycle ramp discharge time of the half-cell, in h. m is the mass of the carbon-based negative electrode material in the half-cell, in g. BET is the specific surface area of ​​the carbon-based negative electrode material, in m 2 / g. C Na The theoretical specific capacity of sodium is 1166 mAh / g. Na is the molar mass of sodium, which is 22.99 g / mol.

[0058] In some specific embodiments, the specific surface area S of the carbon-based negative electrode material is BET 5~20m 2 / g, including but not limited to 5m 2 / g、6m 2 / g、8m 2 / g、10m 2 / g、12m 2 / g、13m 2 / g、15m 2 / g、18m 2 / g, 20m 2 / g, or any range of values ​​between them.

[0059] In some specific embodiments, the particle size of the carbon-based negative electrode material is in the range of 0.5 to 13 μm, including but not limited to any point value of 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 10 μm, 12 μm, 13 μm or a range value between any two of them.

[0060] It is understandable that the particle size distribution of carbon-based negative electrode materials determines the range of all particle sizes in the material. For example, graphite is graded during processing to remove excess fine powder particles to improve the processing performance of slurry coating. However, the compaction density of hard carbon particles themselves is low, less than 1.2g / cm 3 In order to improve the compaction of hard carbon materials, it is necessary to mix large and small particles and limit the particle size range. The compaction density of conventional high-capacity hard carbon materials is 0.9g / cm 3 The compacted density of the material of the present invention is 0.91 to 0.95 g / cm 3 within the range.

[0061] In some specific embodiments, the median particle size D50 of the carbon-based negative electrode material is 3 to 6 μm, including but not limited to any point value of 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, and 6 μm, or a range value between any two of them.

[0062] It is understandable that the size of the median particle size of the carbon-based negative electrode material will also affect the specific surface area of ​​the material as a whole. When using the same material precursor and the same preparation process, the smaller the particle size, the larger the specific surface area of ​​the material. And the smaller the particle size, the shorter the ion diffusion path, the higher the efficiency, the less obstruction, the better the kinetic performance, and the better the low-temperature performance and rate performance of the material. But the smaller the better, if the median particle size is too small, the processing performance of the slurry coating will also deteriorate. Therefore, choosing the right particle size and specific surface area can ensure both good processing performance and good electrochemical performance.

[0063] In a second aspect, the present invention provides a method for preparing the above-mentioned carbon-based negative electrode material, comprising the following steps: pre-carbonizing the precursor material and then acid-washing to obtain a carbon precursor; crushing the carbon precursor and then carbonizing it, and cooling it to obtain the carbon-based negative electrode material.

[0064] Acid washing and purification can remove most of the ash. Ash is an inorganic component, primarily composed of metal oxides and metal salts. It has no electrochemical activity in the material, reducing the material's specific capacity, electronic and ionic conductivity, and worsening the material's kinetic performance. This increases the battery's impedance, leading to increased internal resistance during charge and discharge, and increased temperature rise during charge and discharge cycles. Some metal oxides in the ash gain electrons at the negative electrode and are reduced to elemental metal, resulting in an excessively large K value and reduced battery safety. Reducing the ash content can improve the material's electrochemical performance at low temperatures.

[0065] It is understandable that the pre-carbonization temperature is lower and the high-temperature carbonization temperature is higher. Pre-carbonization can remove most of the volatiles in the material (water, carbon dioxide, carbon monoxide, methane, etc.). On the one hand, it can prevent the excessive volatiles during high-temperature carbonization from causing the material to be secondary activated, resulting in low carbon yield and excessive specific surface area after activation. On the other hand, it can prevent the large amount of volatiles during high-temperature carbonization from corroding the carbonization equipment, shortening the service life of the equipment and increasing the maintenance cost of the equipment.

[0066] The carbon-based negative electrode material produced by this method has high capacity and good low-temperature performance.

[0067] Furthermore, the preparation method is simple to operate, has a short process flow, and is easy to implement in batch production.

[0068] In some specific embodiments, the precursor material includes at least one of asphalt, coal-based materials, biomass materials, starch and its derivatives, lignin and its derivatives, cellulose and its derivatives, resin and its derivatives.

[0069] In some specific embodiments, the biomass material includes at least one of coconut shells, apricot shells, walnut shells, bamboo and hazelnut shells, but is not limited thereto.

[0070] In some specific embodiments, the pre-carbonization temperature is 300-900° C., including but not limited to any one of 300° C., 400° C., 500° C., 600° C., 700° C., 800° C., and 900° C., or any range therebetween, preferably 400-600° C. The pre-carbonization holding time is 2-12 h, including but not limited to any one of 2 h, 3 h, 5 h, 6 h, 8 h, 10 h, and 12 h, or any range therebetween.

[0071] In some specific embodiments, the pre-carbonization is performed in an inert atmosphere; the inert atmosphere may be, for example, at least one of nitrogen, argon, and helium.

[0072] In some specific embodiments, the acid used for pickling includes at least one of hydrochloric acid solution, nitric acid solution, sulfuric acid solution and hydrofluoric acid solution.

[0073] In some specific embodiments, the molar concentration of the acid used in the pickling is 1 to 5 mol / L.

[0074] In some specific embodiments, the ash content of the carbon precursor is ≤1%, preferably ≤0.5%. This is beneficial for improving the low-temperature performance, rate performance, and self-discharge of the battery cell (low K value).

[0075] Among them, ash refers to the inorganic matter remaining after high-temperature burning, and the ash content is expressed as a mass fraction.

[0076] In some specific embodiments, the carbonization temperature is 1100° C. to 1600° C., including but not limited to any one of 1100° C., 1200° C., 1300° C., 1400° C., 1500° C., and 1600° C., or any range therebetween. The carbonization holding time is 1 to 12 hours, including but not limited to any one of 1 hour, 2 hours, 3 hours, 5 hours, 6 hours, 8 hours, 10 hours, and 12 hours, or any range therebetween.

[0077] In some specific embodiments, the carbonization is performed in an inert atmosphere, wherein the inert atmosphere may be, for example, at least one of nitrogen, argon, and helium.

[0078] In some specific embodiments, the particle size of the pulverized carbon precursor is in the range of 0.5 to 13 μm, and the median particle size is 3 to 6 μm.

[0079] In a third aspect, the present invention provides a sodium ion battery comprising the above-mentioned carbon-based negative electrode material.

[0080] This sodium-ion battery has both high capacity and excellent low-temperature performance and has broad application prospects.

[0081] In a fourth aspect, the present invention provides an electrical device comprising the above-mentioned sodium ion battery.

[0082] Among them, electrical equipment includes any equipment or devices that use the above-mentioned sodium ion batteries, such as electric vehicles, electric motorcycles, electric bicycles, power tools, starting power supplies, energy storage systems, electronic products, office equipment, etc., but is not limited to these.

[0083] The embodiments of the present invention will be described in detail below with reference to the examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention. Where specific conditions are not specified in the examples, the methods were performed according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments are not specified, they are all commercially available conventional products.

[0084] Example 1

[0085] The preparation method of the carbon-based negative electrode material provided in this embodiment includes the following steps: pre-carbonizing the coal-based material at 500°C under a nitrogen atmosphere for 8 hours. Then, the pre-carbonized material is pickled with a sulfuric acid solution having a molar concentration of 2 mol / L to obtain a carbon precursor, wherein the ash content is 0.4%. After the carbon precursor is crushed, it is carbonized at 1400°C for 6 hours under a nitrogen atmosphere to obtain a carbon-based negative electrode material. The specific surface area S of the carbon-based negative electrode material is 2000 nm. BET , particle size D1, particle size D10, particle size D50, particle size D90, and particle size D99 are shown in Table 4.

[0086] A button half-cell was fabricated using the carbon-based negative electrode material prepared in this example, and charge-discharge tests were conducted. The steps were as follows: NMP (N-methylpyrrolidone) was used as the solvent, PVDF (polyvinylidene fluoride) as the binder, conductive carbon black SP as the conductive agent, and the carbon-based negative electrode material prepared in this example as the negative electrode active material. The raw materials were weighed in a ratio (mass percentage) of 95%:2%:3% for negative electrode active material:conductive agent:binder. The solvent was then added and stirred to obtain a uniform negative electrode slurry. The negative electrode slurry was then coated on both surfaces of a negative electrode current collector (copper foil) and dried to obtain a negative electrode sheet. A sodium sheet was used as the counter electrode. The negative electrode sheet and counter electrode were assembled in an argon glove box with a nominal capacity of 200 mAh / g and a voltage range of 0-2 V. After the button half-cell was allowed to rest for 2 hours, a charge-discharge cycle was performed. The cells were discharged at a rate of 0.1C to 0 V, allowed to rest for 10 minutes, and then discharged at a rate of 0.02C to 0 V. The second week discharge curve data was used for formula calculation.

[0087] Discharge sodium ion flux coefficient F of carbon-based negative electrode materials Na+ The calculation method is: F Na+ =(m×S BET ×C Na ×M Na ) / (C2×h2). Where C2 is the discharge capacity of the coin cell in the second cycle, in mAh. h2 is the discharge time of the coin cell in the second cycle, in hours.

[0088] Sodium ion flux coefficient F in the discharge platform section of carbon-based anode materials Na+平 The calculation method is: F Na+ The following relationship is satisfied: Na+平 =(m×S BET ×C Na ×M Na ) / (C 平 ×h 平 ). Among them, C 平 The second-week platform discharge capacity of the half-cell, in mAh. 平The second-cycle platform discharge time of the button half-cell, in hours.

[0089] Sodium ion flux coefficient F during discharge ramp of carbon-based anode materials Na+斜 The calculation method is: F Na+ Slant = (m × S BET ×C Na ×M Na ) / (C 斜 ×h 斜 ). Among them, C 斜 The second cycle slope discharge capacity of the half-cell, in mAh. 斜 The second cycle ramp discharge time of the button half-cell, in hours.

[0090] In the above three calculation formulas, m is the mass of the carbon-based negative electrode material in the buckle half-cell, in g. BET The specific surface area of ​​carbon-based negative electrode materials is in m 2 / g. C Na are the theoretical specific capacities of sodium, and C Na =1166mAh / g. M Na are the molar masses of sodium, and M Na =22.99 g / mol.

[0091] Example 2

[0092] The preparation method of the carbon-based negative electrode material provided in this embodiment includes the following steps: pre-carbonizing starch at 400°C under an argon atmosphere for 4 hours. Then, the pre-carbonized material is acid-washed with a hydrochloric acid solution with a molar concentration of 3 mol / L to obtain a carbon precursor, in which the ash content is 0.5%. The carbon precursor is crushed and carbonized, and then carbonized at 1600°C for 4 hours under an argon atmosphere to obtain a carbon-based negative electrode material. The specific surface area S of the carbon-based negative electrode material is 2000 nm. BET , particle size D1, particle size D10, particle size D50, particle size D90, and particle size D99 are shown in Table 4.

[0093] The carbon-based negative electrode material prepared in this embodiment was used to prepare a button half-cell according to the method of Example 1. The discharge sodium ion flux coefficient F of the carbon-based negative electrode material was calculated according to the method of Example 1. Na+ , the sodium ion flux coefficient F of the discharge platform section of carbon-based negative electrode materials Na+平 and the sodium ion flux coefficient F of the discharge ramp of carbon-based negative electrode materials Na+斜 .

[0094] Example 3

[0095] The preparation method of the carbon-based negative electrode material provided in this embodiment includes the following steps: pre-carbonizing the phenolic resin at 600°C under a nitrogen atmosphere for 12 hours. Then, the pre-carbonized material is pickled with a hydrofluoric acid solution having a molar concentration of 2 mol / L to obtain a carbon precursor, wherein the ash content is 0.8%. The carbon precursor is crushed and carbonized, and then carbonized at 1200°C for 10 hours under a nitrogen atmosphere to obtain a carbon-based negative electrode material. The specific surface area S of the carbon-based negative electrode material is 2000 nm. BET , particle size D1, particle size D10, particle size D50, particle size D90, and particle size D99 are shown in Table 4.

[0096] The carbon-based negative electrode material prepared in this embodiment was used to prepare a button half-cell according to the method of Example 1. The discharge sodium ion flux coefficient F of the carbon-based negative electrode material was calculated according to the method of Example 1. Na+ , the sodium ion flux coefficient F of the discharge platform section of carbon-based negative electrode materials Na+平 and the sodium ion flux coefficient F of the discharge ramp of carbon-based negative electrode materials Na+斜 .

[0097] Comparative Example 1

[0098] The negative electrode material is hard carbon, and its specific surface area S BET , particle size D1, particle size D10, particle size D50, particle size D90, and particle size D99 are shown in Table 4.

[0099] The negative electrode material of this comparative example was used to prepare a button half-cell according to the method of Example 1. The discharge sodium ion flux coefficient F of the carbon-based negative electrode material was calculated according to the method of Example 1. Na+ , the sodium ion flux coefficient F of the discharge platform section of carbon-based negative electrode materials Na+平 and the sodium ion flux coefficient F of the discharge ramp of carbon-based negative electrode materials Na+斜 .

[0100] Comparative Example 2

[0101] The negative electrode material is hard carbon, and its specific surface area S BET , particle size D1, particle size D10, particle size D50, particle size D90, and particle size D99 are shown in Table 4.

[0102] The negative electrode material of this comparative example was used to prepare a button half-cell according to the method of Example 1. The discharge sodium ion flux coefficient F of the carbon-based negative electrode material was calculated according to the method of Example 1. Na+ , the sodium ion flux coefficient F of the discharge platform section of carbon-based negative electrode materials Na+平 and the sodium ion flux coefficient F of the discharge ramp of carbon-based negative electrode materials Na+斜 .

[0103] Comparative Example 3

[0104] The negative electrode material is hard carbon, and its specific surface area S BET , particle size D1, particle size D10, particle size D50, particle size D90, and particle size D99 are shown in Table 4.

[0105] The negative electrode material of this comparative example was used to prepare a button half-cell according to the method of Example 1. The discharge sodium ion flux coefficient F of the carbon-based negative electrode material was calculated according to the method of Example 1. Na+ , the sodium ion flux coefficient F of the discharge platform section of carbon-based negative electrode materials Na+平 and the sodium ion flux coefficient F of the discharge ramp of carbon-based negative electrode materials Na+斜 .

[0106] C2, h2, C in each embodiment and each comparative example 平 、h 平 、C 斜 、h 斜 See Table 1. m, S in each embodiment and each comparative example BET 、C Na 、M Na See Table 2. The F values ​​of each group calculated in each embodiment and each comparative example are as follows: Na+ , each group F Na+平 , each group F Na+斜 And each F Na+ The average value of each F Na+平 The average value of each F Na+斜 The average values ​​are shown in Table 3.

[0107] Among them, each embodiment and each comparative example were respectively used to obtain four sets of second-week discharge curve data, and the F Na+ , each group F Na+平 And each group F Na+斜 The values ​​of F are calculated and four groups of F are obtained. Na+ The average value of the four groups F Na+斜 The average value of the four groups F Na+平 The average value of .

[0108] Table 1 C2, h2, C in each embodiment and each comparative example 平 、h 平 、C 斜 、h 斜 data

[0109]

[0110]

[0111] Table 2 m, S in each embodiment and each comparative example BET 、C Na 、M Nadata

[0112]

[0113] Table 3 F per group Na+ 、F Na+平 、F Na+斜 and its average value

[0114]

[0115]

[0116] The specific surface area S of the carbon-based negative electrode materials prepared in each embodiment and each comparative example BET , particle size D1, particle size D10, particle size D50, particle size D90, and particle size D99 are shown in Table 4.

[0117] Table 4 Specific surface area and particle size of various carbon-based negative electrode materials

[0118]

[0119] The test results of the maximum upper limit voltage when the coulombic efficiency of the buckle half-cells prepared in each embodiment and each comparative example is greater than 99.5% are shown in Table 5.

[0120] Table 5 Test results of the maximum upper limit voltage when the coulombic efficiency of each buckle half-cell is greater than 99.5%

[0121]

[0122]

[0123] Table 5 shows that the maximum upper voltage limit required to achieve a Coulombic efficiency of ≥99.5% for each material at -20°C and a 0.1C rate varies significantly. The material with good low-temperature performance reaches a maximum upper voltage limit of 3.8V, while the material with poor low-temperature performance only reaches 3.3V. A Coulombic efficiency of 99.5% or higher at this higher upper voltage limit indicates higher capacity and longer cycle life at low temperatures.

[0124] Among them, the maximum upper limit voltage of Comparative Example 1 and Comparative Example 2 is about 3.4V, which is significantly lower than that of Example 1, Example 2, and Example 3.

[0125] The main problem with Comparative Example 3 is that although it has excellent low-temperature performance, it cannot also provide good high-temperature performance.

[0126] Furthermore, the carbon-based negative electrode materials obtained in each embodiment and each comparative example were used to make battery cells, and the steps are as follows: the ambient temperature, humidity and cleanliness are controlled to meet the standards (the required temperature is 25±5°C, the humidity is ≤10% RH, and the cleanliness is 100,000 grade). The negative electrode sheet, the positive electrode sheet and the diaphragm obtained by the above processing are assembled in the form of positive electrode-diaphragm-negative electrode-diaphragm. After the tabs are welded and glued, a bare cell can be obtained. The bare cell is placed in a steel shell and then injected with a carbonate electrolyte (the injected electrolyte is the Zhongke Haina HNE400R001 model). After sealing, it is subjected to high-temperature standing treatment, and then subjected to formation, aging, and capacity separation processes to obtain a finished sodium ion battery.

[0127] The test results of the capacity retention rate of each battery cell under different upper limit voltage conditions of -20℃ 0.1C rate, the charge and discharge efficiency under different upper limit voltage conditions of -20℃ 0.1C rate, the 25-week cycle retention rate of -20℃ 0.1C rate, and the performance summary of different materials under different temperature and rate conditions are shown in Tables 6, 7, 8, and 9, respectively.

[0128] Table 6 Capacity retention test results at -20℃ 0.1C rate and different upper limit voltage conditions

[0129]

[0130]

[0131] Table 7 -20℃ 0.1C rate charge and discharge efficiency test results under different upper limit voltage conditions

[0132]

[0133] Table 8 -20℃ 0.1C rate 25-week cycle retention test results

[0134]

[0135] Table 9 Summary of performance of different materials under different temperature and rate conditions

[0136]

[0137]

[0138] It can be seen from the various tables that the discharge sodium ion flux coefficient F of the carbon-based negative electrode materials prepared in each embodiment is Na+ Meet 40~100m 2 / (mol·h), sodium ion flux coefficient F in the discharge platform section Na+平 Meet 100~200m 2 / (mol·h), sodium ion flux coefficient F in the discharge ramp Na+斜Meet 300~1000m 2 / (mol·h), combining high capacity with good low-temperature performance. However, the flux coefficients of Comparative Examples 1 and 2 do not meet the requirements, and the low-temperature performance is significantly reduced. The flux coefficient of Comparative Example 3 does not meet the requirements, and both the 60°C storage retention -7D and 60°C storage recovery -7D do not meet the requirements.

[0139] Specifically, referring to Table 6, the capacity retention rates of cells made of different materials under different upper voltage conditions are compared at -20°C and 0.1C rate. Except for Comparative Example 1 (the capacity retention rate at 3.8V is reduced), the capacity retention rates of other materials increase or decrease with the increase of the upper voltage. Comparing the capacity retention rates of different materials under the same voltage conditions, it can be seen that the material with better low-temperature performance has a higher capacity retention rate at 3.8V. Materials with good low-temperature performance also have a higher room temperature recovery rate.

[0140] As shown in Table 7, under the same test conditions as above, the coulombic efficiency of all materials decreases as the upper limit voltage increases. The coulombic efficiency of different materials under the same upper limit voltage conditions varies significantly.

[0141] Refer to Table 8. Using the same test conditions as above, the initial capacity retention and capacity retention after 25 cycles of each material were compared to determine the differences in low-temperature cycling performance. Materials with good low-temperature performance have high capacity retention rates at both the first and 25 weeks, indicating low capacity decay.

[0142] See Table 9 for comprehensive evaluation data on battery cells with different materials, including room temperature cycling at different rates, 40°C high-temperature cycling, -20°C low-temperature cycling, and 60°C high-temperature storage for 7 days. Materials with poor low-temperature performance have good high-temperature cycling and storage performance, while materials with the best low-temperature performance have poor high-temperature cycling and storage performance. This allows us to screen out negative electrode materials with good low-temperature performance that meet the requirements for high-temperature cycling and storage.

[0143] It is understandable that materials with good low-temperature performance do not necessarily have good high-temperature performance. When cycling under high-temperature conditions, the battery capacity decays rapidly and the service life is short. The 60°C storage retention-7D and 60°C storage recovery-7D data of Comparative Example 3 do not meet the requirements, indicating that the negative electrode surface of the material has many side reactions in a high-temperature environment, consuming a large amount of electrolyte and sodium ions, and generating gas inside the battery. When the battery temperature rise (heat generated by the battery itself in a certain temperature environment) is high, there is a risk of thermal runaway (spontaneous combustion).

[0144] In summary, the present invention constructs the relationship between the electrochemical performance and sodium ion flux of carbon-based negative electrode materials and controls the size of the discharge sodium ion flux coefficient of carbon-based negative electrode materials, thereby judging the quality of low-temperature performance and electrochemical performance, and screening out carbon-based negative electrode materials with both high capacity and good low-temperature performance.

[0145] Although the present invention has been illustrated and described using specific embodiments, it should be appreciated that the above embodiments are merely intended to illustrate the technical solutions of the present invention rather than to limit them. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents, without departing from the spirit and scope of the present invention. However, these modifications or replacements do not deviate from the essence of the corresponding technical solutions within the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A carbon-based negative electrode material, characterized in that The discharge sodium ion flux coefficient F of the carbon-based negative electrode material Na+ 40~100m 2 / (mol·h); And the F Na+ Satisfies the following relationship: F Na+ =(m×S BET ×C Na ×M Na ) / (C2×h2); Wherein, the carbon-based negative electrode material is made into a half-cell, m is the mass of the carbon-based negative electrode material in the half-cell, in g; S BET is the specific surface area of ​​the carbon-based negative electrode material, in m 2 / g; C Na is the theoretical specific capacity of sodium, which is 1166 mAh / g; M Na is the molar mass of sodium, which is 22.99 g / mol; C2 is the discharge capacity of the half-cell in the second cycle, in mAh; h2 is the second cycle discharge time of the half-cell, in hours.

2. The carbon-based negative electrode material according to claim 1, characterized in that The sodium ion flux coefficient F of the discharge platform section of the carbon-based negative electrode material Na+平 100~200m 2 / (mol·h); The F Na+平 Satisfies the following relationship: F Na+平 =(m×S BET ×C Na ×M Na ) / (C 平 ×h 平 ); Among them, C 平 The second-week platform discharge capacity of the half-cell, in mAh; h 平 is the second-cycle platform discharge time of the half-cell, in hours.

3. The carbon-based negative electrode material according to claim 1, characterized in that: The sodium ion flux coefficient F of the carbon-based negative electrode material in the discharge slope section Na+斜 300~1000m 2 / (mol·h); And the F Na+斜 Satisfies the following relationship: F Na+斜 =(m×S BET ×C Na ×M Na ) / (C 斜 ×h 斜 ); Among them, C 斜 is the second cycle ramp discharge capacity of the half-cell, in mAh; h 斜 is the second cycle ramp discharge time of the half-cell, in hours.

4. The carbon-based negative electrode material according to any one of claims 1 to 3, characterized in that The specific surface area S of the carbon-based negative electrode material BET 5~20m 2 / g.

5. The carbon-based negative electrode material according to any one of claims 1 to 3, characterized in that: The particle size of the carbon-based negative electrode material is in the range of 0.5 to 13 μm.

6. The carbon-based negative electrode material according to any one of claims 1 to 3, characterized in that: The median particle size of the carbon-based negative electrode material is 3 to 6 μm.

7. The method for preparing a carbon-based negative electrode material according to any one of claims 1 to 6, wherein: The steps include: The precursor material is pre-carbonized and then acid-washed to obtain a carbon precursor; The carbon precursor is crushed and then carbonized, and then cooled to obtain the carbon-based negative electrode material.

8. The method for preparing a carbon-based negative electrode material according to claim 7, characterized in that: At least one of the following conditions is met: (1) The precursor material includes at least one of asphalt, coal-based materials, biomass materials, starch and its derivatives, lignin and its derivatives, cellulose and its derivatives, and resin and its derivatives; (2) The pre-carbonization temperature is 300-900° C., and the holding time is 2-12 hours; (3) the pre-carbonization is carried out in an inert atmosphere; (4) the acid used for pickling includes at least one of hydrochloric acid solution, nitric acid solution, sulfuric acid solution and hydrofluoric acid solution; (5) The ash content in the carbon precursor is ≤1%; (6) The carbonization temperature is 1100° C. to 1600° C., and the holding time is 1 to 12 hours; (7) The carbonization is carried out in an inert atmosphere.

9. A sodium ion battery, characterized in that: The method comprises the carbon-based negative electrode material according to any one of claims 1 to 6.

10. An electrical device, characterized in that: Comprising the sodium ion battery as claimed in claim 9.

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