Battery cathode materials, sodium-ion batteries and electrical equipment

Abstract

The present application provides a battery positive electrode material, a sodium ion battery, and an electrical device, wherein the sodium content of the outer region of the battery positive electrode material on the side close to the inner region of the particle is greater than the sodium content of the particle surface; the inner region of the particle refers to the area within the radius from the center of the particle to the surface of the particle, and the outer region of the particle refers to the area within the radius from the 90% radius to the surface of the particle. Because the sodium content of the outer region of the battery positive electrode material on the side close to the inner region of the particle is greater than the sodium content of the particle surface, the sodium content on the surface of the battery positive electrode material is low, which reduces the content of alkaline substances generated when the battery positive electrode material is exposed to air, avoids the phenomenon of slurry gelation in the homogenization process of the battery positive electrode material, avoids the presence of excessive alkaline substances leading to battery capacity loss, battery cycle performance deterioration, and battery flatulence, thereby improving the battery's specific capacity, cycle life, and battery safety performance.

Description

Technical Field

[0001] The present application relates to the field of batteries, and in particular to a battery positive electrode material, a sodium ion battery and an electrical device. Background Art

[0002] Secondary batteries, especially sodium-ion batteries, not only have the advantages of abundant sodium resource reserves, widespread distribution, low cost, no development bottlenecks, environmental friendliness, and compatibility with existing lithium-ion battery production equipment, but also have good power characteristics, wide temperature range adaptability, safety performance, and no over-discharge issues. However, the surface sodium of the positive electrode material used in sodium-ion batteries easily reacts with carbon dioxide and water in the air to form alkaline sodium hydroxide and sodium carbonate, which increases the alkalinity of the positive electrode material surface. Therefore, when the positive electrode material is homogenized, the structure of the adhesive PVDF changes in a high alkaline environment, causing the slurry to gel, which is not conducive to the coating process. At the same time, the high alkalinity of the battery positive electrode material surface will increase the irreversible capacity loss of the battery, deteriorate the battery cycle performance, and cause battery flatulence. Therefore, the problem of reducing the residual alkalinity on the surface of the battery positive electrode material needs to be solved urgently. Summary of the Invention

[0003] The present application provides a battery positive electrode material, a sodium ion battery and an electrical device to solve the problem that the surface of the existing battery positive electrode material has high residual alkalinity, causing slurry gelation and deterioration of electrochemical performance.

[0004] Based on the above problems, the present application provides a battery positive electrode material, the battery positive electrode material chemical formula includes Na x TMO2, where 0.9<x<1.1, TM is a transition metal;

[0005] The sodium content in the outer region of the particle of the battery positive electrode material on the side close to the inner region of the particle is greater than the sodium content on the surface of the particle; the inner region of the particle refers to the area within the radius from the center of the particle to 90% in the direction from the center of the particle to the surface of the particle; the outer region of the particle refers to the area within the radius from 90% to the surface of the particle.

[0006] Preferably, the sodium content in the inner region of the particle is evenly distributed, and the sodium content in the inner region of the particle is greater than that in the outer region of the particle.

[0007] Preferably, the sodium content in the inner region of the particle of the battery positive electrode material is recorded as A, and the sodium content in the outer region of the particle is recorded as a, then 1

[0008] Preferably, the crystal structure space group of the battery positive electrode material consists of one or more of R-3m, R3m, P63 / mmc and P63mc.

[0009] ​Preferably, the secondary particles of the battery positive electrode material include spherical structures and quasi-spherical particles, and the particle size Dv50 of the battery positive electrode material is 1 μm to 20 μm, and Dv99 is 10 μm to 30 μm.

[0010] Preferably, the specific surface area of the battery positive electrode material is 0.005m 2 / g~10m 2 / g.

[0011] Preferably, the tap density of the battery positive electrode material is 1 g / cm 3 ~3g / cm 3 , compacted density is 2g / cm 3 ~4g / cm 3 .

[0012] Preferably, TM is selected from at least one of Mn, Fe, Ni, Li, Cu, Zn, Co and Ti.

[0013] The present application also provides a sodium ion battery, which includes the above-mentioned battery positive electrode material.

[0014] The present application also provides an electrical device, which includes the above-mentioned sodium ion battery, and the sodium ion battery serves as a power supply for the electrical device.

[0015] The battery positive electrode material, sodium ion battery and electrical equipment provided by the present application have a lower sodium content on the surface of the battery positive electrode material because the sodium content on the side of the outer region of the battery positive electrode material particles close to the inner region of the particles is greater than the sodium content on the surface of the particles, thereby reducing the content of alkaline substances generated when the battery positive electrode material is exposed to air, thereby avoiding the phenomenon of slurry gelation during the homogenization process of the battery positive electrode material, and avoiding the consequences of battery capacity loss, battery cycle performance deterioration and battery flatulence due to the presence of excessive alkaline substances, thereby improving the battery's specific capacity, cycle service life and battery safety performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings constituting part of the present application are used to provide a further understanding of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation of the present application. In the drawings:

[0017] Figure 1 The figure shows the SEM surface morphology of the positive electrode material of the battery according to one embodiment of the present application.

[0018] Figure 2 The figure shows the distribution trend of sodium in the positive electrode material of the battery in Example 1 of the present application.

[0019] Figure 3The 100-cycle retention rate curves of the positive electrode materials of Example 1 and Comparative Example 1 of the present application are shown. DETAILED DESCRIPTION

[0020] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0021] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0022] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0023] As analyzed in the background technology of this application, the surface of the battery positive electrode material in the prior art has high-energy sodium. During the homogenization process, sodium reacts with oxygen and water in the air to form alkaline compounds such as sodium hydroxide and sodium carbonate, resulting in an increase in the alkalinity of the surface of the battery positive electrode material. During the homogenization process of the battery positive electrode material, slurry gel appears, which is not conducive to coating. In addition, when the battery is charged and discharged, the formation of alkaline compounds on the surface consumes active sodium, increases the irreversible capacity loss of the battery, and deteriorates the cycle performance of the battery. In addition, sodium carbonate decomposes into carbon dioxide gas, causing the battery to swell and posing a safety hazard. In order to solve these problems, the present application provides a battery positive electrode material, a sodium ion battery, and an electrical device.

[0024] Reference Figure 1 One embodiment of the present application provides a battery positive electrode material, the chemical formula of which includes Na x TMO2, where 0.9 < x < 1.1, TM includes transition metals;

[0025] The sodium content in the outer region of the particle of the battery positive electrode material on the side close to the inner region of the particle is greater than the sodium content on the surface of the particle; the inner region of the particle refers to the area within the radius from the center of the particle to 90% in the direction from the center of the particle to the surface of the particle; the outer region of the particle refers to the area within the radius from 90% to the surface of the particle.

[0026] In this embodiment, since the sodium content on the side of the outer region of the battery positive electrode material close to the inner region of the particle is greater than the sodium content on the surface of the particle, the sodium content on the surface of the battery positive electrode material is relatively low. This reduces the content of alkaline substances generated when the battery positive electrode material is exposed to air, thereby avoiding the phenomenon of slurry gelation during the homogenization process of the battery positive electrode material, and avoiding the consequences of battery capacity loss, battery cycle performance deterioration, and battery flatulence caused by the presence of excessive alkaline substances, thereby improving the battery's specific capacity, cycle service life, and battery safety performance.

[0027] In another embodiment, in order to further reduce the amount of residual alkali on the surface of the positive electrode material of the battery and give full play to the capacity of the positive electrode material, the sodium content in the inner region of the particle is evenly distributed, and the sodium content in the inner region of the particle is greater than the sodium content in the outer region of the particle; the sodium content in the inner region of the particle of the positive electrode material of the battery is recorded as A, and the sodium content in the outer region of the particle is recorded as a, then 1 is satisfied.

[0028] The sodium content on the surface of the battery positive electrode material is not necessarily lower. When the surface sodium content is too low, the conductivity of the battery positive electrode material deteriorates. It also reduces the sodium ion migration rate during the charge and discharge process, which is not conducive to the battery capacity and the fast charging performance of the battery. Therefore, in another embodiment, the sodium content on the surface of the battery positive electrode material accounts for 8% to 20% of the total sodium content of the battery positive electrode material. When the surface sodium content is lower than 10%, the conductivity and ion conductivity of the battery positive electrode material decrease. When the surface sodium content is higher than 20%, the pH of the battery positive electrode material is too high, the slurry gels severely, and the electrochemical performance of the battery deteriorates.

[0029] In another embodiment, the crystal structure space group of the battery positive electrode material is composed of one or more of R-3m, R3m, P63 / mmc, and P63mc. The presence of the above space groups can increase the rate of sodium ion insertion and extraction in the battery positive electrode material and also improve the interlayer stability of the battery positive electrode material. The crystal structure of the battery positive electrode material can be obtained by XRD (X-ray diffraction) analysis.

[0030] In another embodiment, the secondary particles of the battery positive electrode material are spherical in structure, and the particle size Dv50 is 1μm to 20μm, for example, 1μm, 5μm, 8μm, 12μm, 15μm, 20μm; Dv99 is 10μm to 30μm, for example, 10μm, 15μm, 18μm, 25μm, 30μm. If the particle size Dv50 of the battery positive electrode material is too small, the specific surface area will be too large, which will lead to excessive side reactions and a decrease in the battery cycle performance. If the particle Dv50 is too large, the migration path of the sodium ions on the positive electrode sheet will be too long, which is not conducive to the charge and discharge rate of the battery, and the battery cycle performance will also be affected. In another embodiment, the specific surface area of the battery positive electrode material is 0.005m 2 / g~10m 2 / g, for example, 0.005m 2 / g, 0.5m 2 / g, 2m 2 / g、5m 2 / g、8m​2 / g、10m 2 / g. The battery positive electrode material within this specific surface area range has better electrochemical charge and discharge performance and cycle performance.

[0031] In another embodiment, the tap density of the positive electrode material of the battery is 1 g / cm 3 ~3g / cm 3 , compacted density is 2g / cm 3 ~4g / cm 3 Within the above-mentioned range of tapped and compacted density, the battery can have a high gram capacity while ensuring that the positive electrode sheet has a suitable porosity, ensuring the positive electrode sheet's ability to retain liquid and avoiding the phenomenon of rapid capacity decay and increased internal resistance during battery cycling. In some embodiments, the true density of the battery positive electrode material is 2 g / cm 3 ~4g / cm 3 .

[0032] In some embodiments, Na in the chemical formula of the positive electrode material x The TM in TMO2 can be selected from at least one of Mn, Fe, Ni, Li, Cu, Zn, Co, and Ti. These metal elements can increase the specific capacity of the battery positive electrode material or improve the stability of the battery positive electrode material. In one embodiment, the battery positive electrode material described above can be obtained by the following steps:

[0033] S1, reacting and dispersing Na-TM oxide and molybdenum salt in an organic solvent to obtain a dispersion;

[0034] S2. Filtering the dispersion to obtain a battery positive electrode material precursor;

[0035] S3. calcining the battery positive electrode material precursor to obtain the battery positive electrode material.

[0036] In step S1, the Na-TM oxide can be obtained by thoroughly mixing a sodium salt and a TM metal oxide and then calcining them. The sodium salt can be sodium citrate, sodium hydroxide, sodium nitrate, or sodium carbonate. The organic solvent can be ethanol or propanol, and the molybdenum salt is ammonium molybdate tetrahydrate. The pH of the dispersion is controlled between 8 and 10, and the pH of the dispersion can be adjusted using aqueous ammonia. In step S3, the calcination temperature is 700-1000°C for 6-24 hours. After calcination, the calcined product can be washed with an alcohol solution to remove any Na2MoO4 impurities. After drying, a pure battery positive electrode material is obtained.

[0037] In the above-mentioned process of preparing the battery positive electrode material, the battery positive electrode material precursor is a substance in which a molybdenum salt is uniformly wrapped in a Na-TM oxide. During the calcination of the battery positive electrode material precursor, the molybdenum salt is converted into molybdenum trioxide, and the molybdenum trioxide reacts with the sodium element on the surface of the Na-TM oxide. Under high temperature conditions, the sodium element inside the Na-TM oxide migrates to the surface, thereby obtaining a battery positive electrode material with a low surface sodium content.

[0038] The present application also provides a sodium ion battery, comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, wherein the positive electrode sheet comprises the above-mentioned battery positive electrode material. The sodium ion battery comprising the battery positive electrode material of the present application has high specific capacity, cyclability, and low gas production.

[0039] The present application also provides an electrical device, which includes the above-mentioned sodium ion battery, and the sodium ion battery serves as a power supply for the electrical device.

[0040] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0041] Example 1

[0042] 1) Preparation of battery positive electrode materials: Raw materials (NH4)6Mo7O 24 4H2O (ammonium molybdate tetrahydrate) and NaNi 0.33 Fe 0.33 Mn 0.33 O2 (Dv50 is 10μm) is placed in an ethanol solution with a concentration of 4wt%, and the pH is adjusted to 9 with ammonia water to obtain a dispersion. The dispersion is ultrasonically treated and then filtered to obtain a battery positive electrode material precursor. The obtained battery positive electrode material precursor is calcined at 800℃ for 10 hours, and after cooling, the calcined product is washed with an ethanol solution and dried to obtain a battery positive electrode material with a low surface sodium content. The prepared battery positive electrode material has an A / a of 1.3, a Dv50 of 10μm, and a specific surface area of 5m 2 / g, and the metal elements it contains are Na, Ni, Fe and Mn.

[0043] 2) Preparation of positive electrode sheet:

[0044] The battery positive electrode material, conductive carbon black and binder PVDF prepared in step 1) are dispersed in solvent NMP and mixed evenly to obtain a positive electrode slurry (wherein the weight ratio of the positive electrode material, conductive carbon black and binder PVDF is 96:2:2); the positive electrode slurry is evenly coated on the positive electrode current collector aluminum foil, and after drying, cold pressing, slitting and cutting, a positive electrode sheet is obtained. The compaction density of the positive electrode sheet is 3g / cm 3 .

[0045] 3) Preparation of negative electrode sheets: The negative electrode active material graphite, conductive carbon black, thickener CMC and binder SBR are dispersed in a solvent deionized water in a weight ratio of 96:1:1:2 and mixed evenly to obtain a negative electrode slurry; the negative electrode slurry is evenly coated on the negative electrode current collector copper foil; after drying, cold pressing, slitting, and cutting, the negative electrode sheet is obtained.

[0046] 4) Preparation of sodium ion battery: The positive electrode sheet, the separator and the negative electrode sheet are stacked in sequence, and the separator adopts PP / PE / PP composite film. Then, the battery cell is wound into a battery cell and placed in a battery casing. After the top and side sealing and the injection of electrolyte (the preparation method of the electrolyte is: ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a mass ratio of 30:40:30 to obtain a non-aqueous organic solvent. 1 mol / L NaPF6 is dissolved in the above-mentioned non-aqueous organic solvent and mixed evenly to obtain an electrolyte), etc., a sodium ion battery is made.

[0047] Example 2

[0048] The same as Example 1, except that during the preparation of the battery positive electrode material, the raw material NaNi 0.33 Fe 0.33 Mn 0.33 O2 is replaced by NaNi 0.33 Co 0.33 Ti 0.33 O.

[0049] Example 3 is the same as Example 1, except that during the preparation of the positive electrode material of the battery, the raw material NaNi 0.33 Fe 0.33 Mn 0.33 O2 is replaced by NaNi 0.5 Zn 0.5 O2.

[0050] Example 4

[0051] The same as Example 1, except that during the preparation of the battery positive electrode material, the raw material NaNi 0.33 Fe 0.33 Mn 0.33 O2 is replaced by NaNi 0.7 Co 0.1 Cu 0.2 O2.

[0052] Example 5

[0053] Same as Example 1, except that during the preparation of the positive electrode material of the battery, NaNi 0.33 Fe 0.33 Mn0.33 The Dv5 of O2 is 1μm.

[0054] Example 6

[0055] Same as Example 1, except that during the preparation of the positive electrode material of the battery, NaNi 0.33 Fe 0.33 Mn 0.33 The Dv5 of O2 is 5μm.

[0056] Example 7

[0057] Same as Example 1, except that during the preparation of the positive electrode material of the battery, NaNi 0.33 Fe 0.33 Mn 0.33 The Dv5 of O2 is 12μm.

[0058] Example 8

[0059] Same as Example 1, except that during the preparation of the positive electrode material of the battery, NaNi 0.33 Fe 0.33 Mn 0.33 The Dv5 of O2 is 15μm.

[0060] Example 9

[0061] Same as Example 1, except that during the preparation of the positive electrode material of the battery, NaNi 0.33 Fe 0.33 Mn 0.33 The Dv5 of O2 is 20μm.

[0062] Example 10

[0063] The same as Example 1, except that the calcination temperature is 700° C., and the A / a of the obtained battery positive electrode material is 0.8.

[0064] Example 11

[0065] The same as Example 1, except that the calcination temperature is 750° C., and the A / a of the obtained battery positive electrode material is 1.1.

[0066] Example 12

[0067] The same as Example 1, except that the calcination temperature is 850° C., and the A / a of the obtained battery positive electrode material is 1.5.

[0068] Example 13

[0069] The same as Example 1, except that the calcination temperature is 1000° C., and the A / a of the obtained battery positive electrode material is 1.8.

[0070] Example 14

[0071] The same as Example 1, except that the cold pressing pressure was adjusted during the preparation of the positive electrode sheet to obtain a compaction density of 1 g / cm 3 .

[0072] Example 15

[0073] The same as Example 1, except that the cold pressing pressure was adjusted during the preparation of the positive electrode sheet to obtain a compaction density of 2 g / cm 3 .

[0074] Example 16

[0075] The same as Example 1, except that the cold pressing pressure was adjusted during the preparation of the positive electrode sheet, and the compaction density of the positive electrode sheet was 4g / cm 3 .

[0076] Example 17

[0077] The same as Example 1, except that the cold pressing pressure was adjusted during the preparation of the positive electrode sheet to obtain a compaction density of 6 g / cm 3 .

[0078] Comparative Example 1

[0079] The positive electrode material provided is NaNi 0.33 Fe 0.33 Mn 0.33 O2. The sodium content in the outer region of the battery positive electrode material particles, which is closer to the inner region of the particles, is less than the sodium content on the particle surface. The positive electrode material is made into a sodium ion battery, and the battery manufacturing method is the same as Example 1.

[0080] The characteristic parameters of the battery positive electrode materials prepared in the above Examples 1-17 and Comparative Example 1, as well as the test data of the prepared sodium ion batteries are recorded in Table 1, wherein the specific method of the battery test is:

[0081] 1) Specific Capacity Test: Place the battery on a Xinwei charge and discharge tester at room temperature, charge at 0.33C to 4.0V, and discharge at 0.33C to 1.5V. The discharge capacity is the specific capacity value.

[0082] 2) 100-cycle capacity retention test: The battery was placed on a Xinwei charge-discharge tester at room temperature, charged at 0.33C to 4.0V, and then discharged at 0.33C to 1.5V. This cycle was repeated, with one charge-discharge cycle being considered one cycle. The ratio of the discharge capacity in grams per cycle to the discharge capacity in grams per cycle was the capacity retention rate.

[0083] 3) Volume expansion test: Tested by battery volume expansion rate tester.

[0084] Table 1 Characteristics of battery cathode materials and battery performance

[0085]

[0086]

[0087] According to the comparison of the data of Examples 1-17 and Comparative Example 1 in Table 1, it can be seen that the battery material with low surface sodium content provided by the present application has a lower pH value, that is, its alkalinity is low. When the surface sodium content is low, the battery capacity can be increased, the battery cycle life can be increased, and the battery gas production can be reduced. Figure 3 The capacity attenuation rate of comparative example 1 is significantly greater than the cycle capacity attenuation rate of embodiment 1.

[0088] According to the data of Examples 5 to 9 in Table 1, it can be seen that as the specific surface area of the battery positive electrode material increases, the gas production rate of the battery will increase accordingly. This is because the effective area where the electrolyte and the battery positive electrode material can react increases, thereby increasing the occurrence of side reactions and causing gas production. However, when the specific surface area of the battery positive electrode material is too small or too large, it will cause the battery cycle performance and battery gram capacity to decay. Based on the battery gas production rate, battery cycle performance and battery gram capacity, the specific surface area of the battery positive electrode material is preferably 0.5 to 8 m 2 / g.

[0089] In summary, the battery positive electrode material provided by the present application has a lower sodium content on the surface of the battery positive electrode material because the sodium content on the side of the outer region of the battery positive electrode material close to the inner region of the particle is greater than the sodium content on the surface of the particle. This reduces the content of alkaline substances generated when the battery positive electrode material is exposed to air, thereby avoiding the phenomenon of slurry gelation during the homogenization process of the battery positive electrode material, and avoiding the consequences of battery capacity loss, battery cycle performance deterioration, and battery bloating due to the presence of excessive alkaline substances, thereby improving the battery's specific capacity, cycle service life, and improving the battery's safety performance.

[0090] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A battery positive electrode material, characterized in that: The general chemical formula of the battery positive electrode material is Na x TMO2, where 0.9 < x < 1.1, TM includes transition metals; The sodium content in the outer region of the battery positive electrode material particle close to the inner region of the particle is greater than the sodium content on the particle surface; the inner region of the particle refers to the area within the range of 90% radius from the center of the particle to the surface of the particle, and the sodium content of the inner region of the particle is uniformly distributed; the outer region of the particle refers to the area within the range of 90% radius to the surface of the particle; The sodium content in the inner region of the particles of the battery positive electrode material is denoted as A, and the sodium content in the outer region of the particles is denoted as a, then 1 satisfies the crystal structure space group of the battery positive electrode material and is composed of one or more of R-3m, R3m, P63 / mmc and P63mc.

2. The battery positive electrode material according to claim 1, characterized in that: The secondary particles of the battery positive electrode material include spherical structures and quasi-spherical structures. The particle size Dv50 of the battery positive electrode material is 1 μm to 20 μm, and Dv99 is 10 μm to 30 μm.

3. The battery positive electrode material according to claim 2, characterized in that: TM is selected from at least one of Mn, Fe, Ni, Li, Cu, Zn, Co and Ti.

4. The battery positive electrode material according to claim 3, characterized in that: The specific surface area of the battery positive electrode material is 0.005m 2 / g~10m 2 / g.

5. The battery positive electrode material according to claim 3, characterized in that: The tap density of the battery positive electrode material is 1 g / cm 3 ~3g / cm 3 , compacted density is 2g / cm 3 ~4g / cm 3 .

6. The battery positive electrode material according to any one of claims 1 to 5, characterized in that The invention comprises the battery positive electrode material according to any one of claims 1 to 6.

7. A sodium ion battery, characterized in that: The sodium ion battery according to claim 7 is included, and the sodium ion battery serves as a power supply for the electrical equipment.

8. An electrical device, characterized in that: ​

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