Composite negative electrode material, negative electrode plate and sodium ion battery

Abstract

The invention provides a composite negative electrode material which is used for manufacturing a negative electrode plate and is a mixed particle of large-particle hard carbon and a small-particle carbon material, the small-particle carbon material accounts for 5-20% of the mass of the mixed material, and the particle size distribution characteristic parameter D50 of the small-particle carbon material is 0.1-0.8 time of the particle size distribution characteristic parameter D50 of the large-particle hard carbon. The invention also provides a negative plate which is prepared from the composite negative electrode material. The invention also provides a sodium ion battery which comprises the negative plate. According to the invention, a mode of mixing large particles and small particles is adopted, and due to a shorter ion transmission path, the small particles are smaller in polarization in a charging and discharging process, higher in retention rate during rate charging and low-temperature charging, and smaller in temperature rise; and the small particles can fill large particle accumulation gaps, so that the compaction density is improved, and the energy density is further improved.

Description

Technical Field

[0001] The present invention relates to the field of new materials and new energy technologies, and in particular to a sodium ion battery and its negative electrode sheet and material capable of improving high-rate charging and low-temperature charging performance, increasing negative electrode compaction density and battery energy density. Background Art

[0002] At present, in the field of sodium-ion battery technology, hard carbon negative electrode materials are highly favored due to their unique sodium storage properties and structural advantages. Hard carbon materials exhibit two different voltage regions during the charging process: a slope region and a platform region. Generally, the energy density of the negative electrode is improved by increasing the capacity of the platform region. However, the potential of the negative electrode platform region (~0.1V vs Na+ / Na) is close to the sodium metal deposition threshold (0V). Under high-rate charging or low-temperature conditions, the polarization phenomenon of hard carbon negative electrode materials is particularly significant, which may cause the negative electrode potential to be lower than 0V, resulting in sodium precipitation, thereby leading to a decrease in high-rate charging and low-temperature charging performance, which is mainly manifested in a decrease in capacity retention rate, an increase in temperature rise, and even thermal runaway when the battery is charged at a high rate or at a low temperature.

[0003] In addition, the general compaction density of hard carbon anodes is less than 1.0 g / cc, which limits the energy density and practical application of batteries.

[0004] Therefore, developing new technologies to improve the rate and low-temperature performance of sodium batteries; increasing the compaction density of hard carbon negative electrode materials and thus increasing energy density are of great significance for promoting the commercialization of sodium-ion battery technology.

[0005] CN 116947012 A adopts a method of first preparing large, medium and small particles and then adding a binder and sintering to prepare a composite material, which improves the compaction density of the material. However, the preparation process is long and multiple sintering increases energy consumption; CN 116387472A adopts a mixture of soft carbon, hard carbon and solid electrolyte to prepare a slurry. The solid electrolyte only provides ion transport and does not provide capacity. Adding a solid electrolyte will further reduce the energy density; CN 115513440 A mentions the use of soft carbon and hard carbon coating sintering or soft carbon and hard carbon physical mixing methods. However, it is difficult to ensure uniformity of the coating, and physical mixing also requires reasonable grading to be effective.

[0006] Therefore, how to improve high-rate charging and low-temperature charging performance, and increase the negative electrode compaction density and battery energy density are issues that the sodium-ion battery industry urgently needs to solve. Summary of the Invention

[0007] A main purpose of the present invention is to overcome at least one of the defects of the above-mentioned prior art and provide a composite negative electrode material, negative electrode sheet and sodium ion battery that can improve high-rate charging and low-temperature charging performance, increase the negative electrode compaction density and battery energy density.

[0008] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0009] According to one aspect of the present invention, a composite negative electrode material is provided for making a negative electrode sheet, which is a mixture of large-particle hard carbon and small-particle carbon material. The small-particle carbon material accounts for 5-20% of the mass of the mixed material, and the particle size distribution characteristic parameter D50 of the small-particle carbon material is 0.1-0.8 times the D50 of the large-particle hard carbon.

[0010] According to a specific embodiment of the present invention, the particle size of the large particle hard carbon is in the range of 2-16 μm, and the particle size of the small particle carbon material is in the range of 0.5-5 μm; the specific surface area of the large particle hard carbon is less than 6 m 2 / g, the specific surface area of small-particle carbon materials is greater than that of large-particle hard carbon and is less than 30m 2 / g; the tap density of large-particle hard carbon is greater than 0.7g / cm 3 .

[0011] According to a specific embodiment of the present invention, the preparation of the composite negative electrode material includes the following steps:

[0012] a. Preparation of small particle carbon materials:

[0013] Select spherical soft carbon or hard carbon raw materials;

[0014] Using methane or acetylene as the carbon source, the temperature is 400-600℃, and a nano-carbon layer is deposited by CVD method. The thickness of the carbon layer is controlled at 50-200nm.

[0015] Screening to select small particles that meet the particle size parameter requirements;

[0016] b. Physically blending large hard carbon particles and small carbon particles according to the mass ratio.

[0017] According to another aspect of the present invention, a negative electrode sheet is provided, which is prepared from the above-mentioned composite negative electrode material.

[0018] According to a specific embodiment of the present invention, the uniformly mixed composite negative electrode material is directly used during the homogenization.

[0019] According to a specific embodiment of the present invention, the large-particle and small-particle carbon materials are fed separately.

[0020] According to another aspect of the present invention, a sodium ion battery is provided, comprising the above-mentioned negative electrode sheet.

[0021] As can be seen from the above technical solutions, the advantages and positive effects of the composite negative electrode material, negative electrode sheet and sodium ion battery of the present invention are:

[0022] The present invention adopts a mixing method of large particles and small particles. Due to the shorter ion transmission path, the small particles have less polarization during charging and discharging, higher retention rate during rate charging and low-temperature charging, and smaller temperature rise; small particles can fill the gaps in the accumulation of large particles, thereby increasing the compaction density and further increasing the energy density. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a simplified schematic diagram of the particle stacking model.

[0024] Figure 2 This is an electron microscope image of the electrode of Example 2.

[0025] Figure 3 This is an electron microscope image of the electrode of Example 4.

[0026] Figure 4 This is an electron microscope image of the electrode of comparative example 1.

[0027] Figure 5 3. It is a comparison chart of the charge and discharge curves of Comparative Example 1, Example 2, and Example 4.

[0028] Figure 6 This is a comparison chart of the temperature rise of the large charging surface of Example 1, Example 2, and Example 4.

[0029] Figure 7 This is a comparison chart of low-temperature charging curves of Comparative Example 1, Example 2, and Example 4. DETAILED DESCRIPTION

[0030] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be embodied in many forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the concepts of the example embodiments to those skilled in the art. Like reference numerals in the figures represent like or similar structures, and thus their detailed description will be omitted.

[0031] The following is an explanation of the professional terms used in the claims and description of the present invention.

[0032] 1. Particle size distribution parameters (D10, D50, D90)

[0033] D10: defined as the equivalent particle size value corresponding to when the cumulative volume distribution percentage reaches 10% (unit: μm).

[0034] D50: (Median particle size): The equivalent particle size value when the cumulative volume distribution percentage is 50%, which characterizes the average particle size of the material.

[0035] D90: defined as the equivalent particle size value when the cumulative volume distribution percentage reaches 90%.

[0036] This parameter is measured by laser diffraction (GB / T 19077-2016) and is used to measure the overall distribution characteristics of particles.

[0037] 2. Compacted Density

[0038] Definition: The mass per unit volume of the electrode sheet after the roll pressing process (unit: g / cc)

[0039] The calculation formula is:

[0040] Compaction density = surface density / (pole thickness - current collector thickness)

[0041] This parameter reflects the filling density of the active material in the electrode and directly affects the volume energy density of the battery. For example, the compaction density of the hard carbon negative electrode of the sodium ion battery needs to be ≥0.8g / cm 3 , in order to take into account both high capacity and ion transmission efficiency.

[0042] 3. Specific surface area (BET Surface Area)

[0043] Definition: Surface area per unit mass of material (unit: m 2 / g), as measured by the nitrogen adsorption BET method (GB / T 19587-2017). A high specific surface area can accelerate ion transport, but it can easily lead to electrolyte decomposition side reactions, reducing coulombic efficiency.

[0044] In a specific technical solution of the present invention, a 26700 cylindrical battery was used to verify its performance. The production conditions of the 26700 cylindrical battery are as follows: O3-NaNi1 / 3Fe1 / 3Mn1 / 3O2 is used as the positive electrode active material, and an appropriate electrolyte is selected. The positive electrode slurry consists of positive electrode active material: PVDF: SP: CNT in a ratio of 95.5:2:2:0.5. It is wet-mixed and evenly coated on an aluminum foil current collector. After drying and roller pressing, it forms a surface density of 32mg / cm 2 , compacted density is 3.0g / cm 3 The negative electrode slurry is made from a mixture of negative electrode active material (CMC, SBR, SP) in a ratio of 93.7:1.5:2. This is then coated onto an aluminum foil current collector, dried, and rolled to form the negative electrode. The positive electrode, separator, and negative electrode are wound sequentially into a battery cell and packaged into a 26700 steel case with a liquid injection volume of 14.5 ± 0.3 g. The battery is formed at 25°C with a charge current of 0.05C and a charge cutoff voltage of 2.3V. After formation, the battery is allowed to rest at 45°C for capacity separation and aging, and then assembled.

[0045] Pole compaction density

[0046] The coated negative electrode sheet is rolled using a JZLB2 600*650-C roller press, with a hydraulic cylinder pressure of 9 MPa and a gap setting of 1.790 mm between the drive side and the non-drive side. After rolling, the electrode sheet needs to be bent twice without leaking or breaking.

[0047] Electrode electron microscope test

[0048] The pole piece before rolling was cut into standard size samples (CP samples), and electron microscope photos of the interface were taken to compare the different particle stacking states.

[0049] Battery Test

[0050] Battery testing was conducted in accordance with the group standard T / CIAPS0031-2023, "General Specification for Sodium-Ion Batteries." The rate charging conditions were 1.5C charging and 0.5C discharging at 25°C, with the discharge capacity recorded. Low-temperature charging conditions were 0.5C charging at -10°C and 0.5C discharging at 25°C, with the discharge capacity recorded.

[0051] The capacity retention rate is calculated as follows:

[0052] 1.5C charging capacity retention rate: 1.5C charging, 0.5C discharging capacity / 0.5C charging, 0.5C discharging capacity;

[0053] -10℃ charge capacity retention rate: -10℃ 0.5C charge, 25℃ 0.5C discharge capacity / 25℃ 0.5C charge, 0.5C discharge capacity;

[0054] Large surface temperature rise: Place the temperature measuring wire on the middle of the large surface of the battery to record the battery temperature. The maximum temperature measured during the charging stage minus the charging starting temperature is the large surface temperature rise during the charging stage.

[0055] The present invention has the following technical effects:

[0056] 1) A mixture of large and small particles is used. Due to the shorter ion transmission path, the small particles have smaller polarization during the charge and discharge process. Through the study of the particle accumulation model, the D50 of the small particles is controlled to be 0.2-0.4 times the D50 of the large particles. The small particles occupy part of the surface of the large particles. During high-rate charging or low-temperature charging, the sodium ions can be quickly "embedded" into the negative electrode material instead of sodium precipitation, realizing effective sodium storage in the negative electrode under high-rate charging and low-temperature charging conditions, thereby improving the capacity retention rate of the battery at high-rate and low-temperature charging, while alleviating the heat generation problem caused by sodium precipitation.

[0057] 2) Using a mixture of large and small particles, based on the Furnas close packing theory model, the proportion of small particles in the total particle mass is controlled to be 5%-20%. Small particles can fill the gaps between large particles, thereby increasing the compaction density and thus the energy density.

[0058] 3) This method has simple process, low cost and is easy to mass produce.

[0059] The technical effects are demonstrated below in combination with different embodiments and comparative examples.

[0060] First, in all cases, small carbon particles were prepared:

[0061] Small particle carbon material A:

[0062] The hard carbon particles (D50 = 1.39 μm) were ultrasonically cleaned with ethanol and vacuum dried, and then uniformly dispersed in the quartz boat of the chemical vapor deposition (CVD) reactor. The reaction chamber was evacuated to a vacuum degree of ≤10 Pa, and then replaced with inert gas three times to eliminate residual oxygen. The temperature was raised to the deposition temperature of 600 ° C at a rate of 15 ° C / min, and a mixture of acetylene gas (flow rate 100 sccm) and carrier gas argon (flow rate 200 sccm) was introduced to maintain the reaction pressure at 450 ± 50 Pa. The deposition treatment lasted for 2.5 hours. After the reaction was completed, it was naturally cooled to room temperature under an argon atmosphere to obtain composite particles with a uniform surface coating of an amorphous carbon layer. TEM characterization showed that the coating thickness was 90-110 nm. The large particles and fine powder were removed by sieving and sorting. The particle size of the tested material was D10 = 0.83 μm, D50 = 1.39 μm, D90 = 2.72 μm, and the specific surface area was 7.97 m 2 / g. Recorded as small particle carbon material A.

[0063] Small particle carbon material B:

[0064] The soft carbon particles (D50 = 2.70 μm) were ultrasonically cleaned with ethanol and vacuum dried, and then evenly dispersed in the quartz boat of the chemical vapor deposition (CVD) reactor. The reaction chamber was evacuated to a vacuum degree of ≤10 Pa, and then replaced with inert gas three times to eliminate residual oxygen. The temperature was raised to the deposition temperature of 500 ° C at a rate of 15 ° C / min, and a mixture of acetylene gas (flow rate 100 sccm) and carrier gas argon (flow rate 200 sccm) was introduced to maintain the reaction pressure at 400 ± 50 Pa. The deposition treatment was carried out for 2.5 hours. After the reaction was completed, it was naturally cooled to room temperature under an argon atmosphere to obtain composite particles with a uniform surface coating of an amorphous carbon layer. TEM characterization showed that the coating thickness was 80-100 nm. The large particles and fine powder were removed by sieving and sorting. The particle size of the tested material was D10 = 0.53 μm, D50 = 2.71 μm, D90 = 4.92 μm, and the specific surface area was 27.01 m 2 / g. Recorded as small particle carbon material B.

[0065] Example 1

[0066] The large-particle hard carbon material was selected, and its particle size distribution was: D10 = 2.25 μm, D50 = 5.67 μm, D90 = 9.94 μm, and the specific surface area was 5.28 m 2 / g, and the tap density is 0.81g / cm 3 9.5 kg of large-grain hard carbon and 0.5 kg of small-grain carbon material A were placed in an SHR25A-B high-speed mixer and mixed at 500 rpm for 15 minutes. Once uniformly mixed, the composite negative electrode material was obtained. 26700 cylindrical batteries were fabricated with this material and their performance was tested.

[0067] Example 2

[0068] The large-particle hard carbon material was selected, and its particle size distribution was: D10 = 2.25 μm, D50 = 5.67 μm, D90 = 9.94 μm, and the specific surface area was 5.28 m 2 / g, and the tap density is 0.81g / cm 3 9 kg of large-grain hard carbon and 1 kg of small-grain carbon material A were placed in an SHR25A-B high-speed mixer and mixed at 500 rpm for 15 minutes. Once uniformly mixed, the composite negative electrode material was obtained. This material was used to fabricate 26700 cylindrical batteries and test their performance. Electron microscopy was performed on the negative electrode sheet before roller pressing.

[0069] Example 3

[0070] The large-particle hard carbon material was selected, and its particle size distribution was: D10 = 2.25 μm, D50 = 5.67 μm, D90 = 9.94 μm, and the specific surface area was 5.28 m 2 / g, and the tap density is 0.81g / cm 3 8.5 kg of large-grain hard carbon and 1.5 kg of small-grain carbon material A were placed in an SHR25A-B high-speed mixer and mixed at 500 rpm for 15 minutes. Once uniformly mixed, the composite negative electrode material was obtained. 26700 cylindrical batteries were made with this mixture and their performance was tested.

[0071] Example 4

[0072] The large-particle hard carbon material was selected, and its particle size distribution was: D10 = 2.25 μm, D50 = 5.67 μm, D90 = 9.94 μm, and the specific surface area was 5.28 m 2 / g, and the tap density is 0.81g / cm 3 8 kg of large-grain hard carbon and 2 kg of small-grain carbon material A were placed in an SHR25A-B high-speed mixer and mixed at 500 rpm for 15 minutes. Once uniformly mixed, the composite negative electrode material was obtained. 26700 cylindrical batteries were fabricated with this material and their performance was tested. Electron microscopy examination of the negative electrode sheet before roller pressing was performed.

[0073] Example 5

[0074] The large-particle hard carbon material was selected, and its particle size distribution was: D10 = 2.21 μm, D50 = 4.32 μm, D90 = 8.98 μm, and the specific surface area was 7.21 m 2 / g, and the tap density is 0.83g / cm 3 8 kg of large-particle hard carbon and 2 kg of small-particle carbon material B were used to make 26700 cylindrical batteries. The materials were added in sequence during the homogenization stage, and the battery performance was tested after the production was completed.

[0075] Example 6

[0076] The large-particle hard carbon material was selected, and its particle size distribution was: D10 = 2.89 μm, D50 = 8.32 μm, D90 = 14.26 μm, and the specific surface area was 4.51 m 2 / g, and the tap density is 0.78g / cm 3 8 kg of large-particle hard carbon and 2 kg of small-particle carbon material B were used to make 26700 cylindrical batteries. The materials were added in sequence during the homogenization stage, and the battery performance was tested after the production was completed.

[0077] Comparative Example 1

[0078] The same large-particle hard carbon material as in Example 1 was selected, except that the small-particle carbon material was not added, and 26700 cylindrical batteries were directly made. The front electrode sheet before rolling was selected for electron microscopy testing, and 26700 was used for battery performance testing.

[0079] Comparative Example 2

[0080] The difference from Example 1 is that 7 kg of large-grained hard carbon and 3 kg of small-grained carbon material A are put into a high-speed mixer for mixing. Other conditions are the same as those in Example 1.

[0081] Comparative Example 3

[0082] The difference from Example 1 is that 5 kg of large-grained hard carbon and 5 kg of small-grained carbon material A are put into a high-speed mixer for mixing. Other conditions are the same as those in Example 1.

[0083]

[0084] Table 1: Comparison of test results for each case

[0085] As can be seen from Table 1, using the methods in the examples, the compaction density can all be achieved to be greater than 1.0g / cc. The compaction density of Example 2 can reach 1.1g / cc. Comparative Example 1 uses only large-particle hard carbon, and the compaction density can only reach 0.98g / cc, indicating that the patented method can effectively improve the compaction density of the electrode. According to the group standard T / CIAPS0031-2023 "General Specification for Sodium Ion Batteries", charging at a rate of 1.5C can achieve a capacity retention rate of greater than 92% and a battery large surface temperature rise of less than 4°C; charging at a low temperature of -10°C can achieve a capacity retention rate of greater than 93% and a battery large surface temperature rise of less than 1°C. The small-particle carbon material content in Comparative Examples 2 and 3 reaches 30% and 50%, respectively. Although the capacity retention rate at 1.5C charging and -10°C is significantly improved, the compaction density is much lower than that of the pure large-particle hard carbon in Comparative Example 1, which cannot meet the requirements of sodium ion battery negative electrode materials.

[0086] Figure 1 It is a simplified schematic diagram of the particle stacking model. Figure 2 、 Figure 3 、 Figure 4 The electron microscope images of the electrodes of Example 2, Example 4 and Comparative Example 1 respectively show that Figure 2 、 Figure 3 Small and medium-sized particles are effectively filled in the gaps, which is conducive to achieving denser stacking of particles.

[0087] Figure 5 It can be seen that the charging curve voltage of Comparative Example 1 is higher in the 2.5-3.2V stage, indicating that the charging polarization of Comparative Example 1 is higher. Example 2 and Example 4 can effectively reduce polarization and slowly release sodium, thereby improving the capacity retention rate of rate charging and low-temperature charging and reducing the charging temperature rise, which is consistent with the results in Table 1.

[0088] Figure 6 The temperature rise curves of the large surface of Comparative Example 1, Example 2, and Example 4 in the 1.5C charging stage are shown. It can be seen that the temperature rise of Example 2 and Example 4 is significantly lower than that of Comparative Example 1, indicating that the method of this patent can effectively reduce the temperature rise of the large surface of the battery during high-rate charging.

[0089] Figure 7 The charge and discharge curves for Comparative Example 1, Example 2, and Example 4 at -10°C are shown. It can be seen that the charge capacity of Examples 2 and 4 at -10°C is significantly lower than that of Comparative Example 1, but the discharge capacity is similar, indicating that Examples 2 and 4 have higher coulombic efficiency at -10°C. The high charge capacity of Comparative Example 1 at low temperatures may be due to sodium precipitation, which leads to the consumption of "active sodium" in the battery system, resulting in a decrease in coulombic efficiency and long-term performance. Examples 2 and 4 can effectively alleviate this situation.

[0090] Those skilled in the art will appreciate that the specific structures and processes described in the above detailed embodiments are merely illustrative and non-limiting. Furthermore, those skilled in the art may combine the various technical features described above in various possible ways to create new technical solutions or make other modifications, all of which fall within the scope of the present invention.

Claims

1. A composite negative electrode material for making a negative electrode sheet, characterized in that: The particles are mixed particles of large hard carbon particles and small carbon particles. The small carbon particles account for 5-20% of the mixed material mass. The particle size distribution characteristic parameter D50 of the small carbon particles is 0.1-0.8 times the D50 of the large hard carbon particles.

2. The composite negative electrode material according to claim 1, wherein: The particle size range of large-particle hard carbon is 2-16μm, and the particle size range of small-particle carbon material is 0.5-5μm; the specific surface area of large-particle hard carbon is less than 6m2 / g, and the specific surface area range of small-particle carbon material is greater than the specific surface area of large-particle hard carbon and less than 30m2 / g; the tap density of large-particle hard carbon is greater than 0.7g / cm3.

3. The composite negative electrode material according to claim 1 or 2, characterized in that: The preparation of the composite negative electrode material comprises the following steps: a. Preparation of small particle carbon materials: Select spherical soft carbon or hard carbon raw materials; Using methane or acetylene as the carbon source, the temperature is 400-600℃, and a nano-carbon layer is deposited by CVD method. The thickness of the carbon layer is controlled at 50-200nm. Screening to select small particles that meet the particle size parameter requirements; b. Physically blending large hard carbon particles and small carbon particles according to the mass ratio.

4. A negative electrode sheet, characterized in that: Prepared from the composite negative electrode material according to any one of claims 1 to 3.

5. The negative electrode sheet according to claim 4, characterized in that: The uniformly mixed composite negative electrode material is directly used during homogenization.

6. The negative electrode sheet according to claim 4, characterized in that: The large-particle and small-particle carbon materials are fed separately.

7. A sodium ion battery, characterized in that: A negative electrode sheet comprising any one of claims 4 to 6.

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