Capacity recovery methods and applications of single-crystal cathode materials in spent sodium-ion batteries

Abstract

This invention discloses a method for capacity recovery of single-crystal cathode material from spent sodium-ion batteries and its application. The capacity recovery method includes: washing and drying the impurity-containing single-crystal cathode material from spent sodium-ion batteries using an aqueous solution containing a first sodium source to obtain a first material; and thoroughly mixing the first material with a second sodium source and additives, followed by calcination to obtain a single-crystal cathode material with recovered capacity. The capacity recovery method provided by this invention has a simple process and readily available raw materials. Furthermore, this method can restore the capacity of the single-crystal cathode material obtained from spent sodium-ion batteries to near its pre-cycling level and maintain high cycle stability, allowing it to be reused in sodium-ion batteries, achieving cascade utilization of the material and maximizing its benefits.

Description

Technical Field

[0001] This invention belongs to the field of new materials technology, specifically relating to a method and application for capacity recovery of single-crystal cathode material in waste sodium-ion batteries. Background Technology

[0002] Lithium-ion batteries dominate the portable electronics market and also show great promise for applications in electric vehicles. However, due to the scarcity of lithium resources, lithium prices have risen sharply in recent years, prompting many companies to begin recycling and utilizing materials used in lithium-ion batteries. Nevertheless, the limited availability of lithium resources and the relatively poor safety and low-temperature performance of lithium-ion batteries still restrict their application in stationary energy storage. Considering the abundance of sodium resources and its better safety and low-temperature performance, sodium-ion batteries have a greater advantage in the energy storage field.

[0003] While the development of sodium-ion batteries has been slower than that of lithium-ion batteries, it has accelerated significantly in recent years, with many companies already in mass production. Therefore, it is essential to consider the recycling and reuse of materials from used sodium-ion batteries. This would not only reduce environmental pollution from discarded sodium-ion batteries but also generate economic benefits. The current trend in sodium-ion battery cathode materials is towards single-crystal materials, making it necessary to provide a method for recycling single-crystal cathode materials from discarded sodium-ion batteries.

[0004] In the recycling of lithium-ion batteries, the cathode material is generally extracted and separated to recover various metal elements. Similarly, in sodium-ion batteries, extraction and separation techniques are ultimately used to recover the corresponding metal elements. However, directly using this recycling method does not fully utilize the materials and cannot maximize efficiency. Summary of the Invention

[0005] The main objective of this invention is to provide a method and application for capacity recovery of single-crystal cathode materials in waste sodium-ion batteries, so as to overcome the shortcomings of the prior art.

[0006] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0007] This invention provides a method for capacity recovery of single-crystal cathode material in spent sodium-ion batteries, comprising:

[0008] Provides single-crystal cathode materials containing impurities from waste sodium-ion batteries;

[0009] The impurity-containing single-crystal cathode material is washed and dried using an aqueous solution containing a first sodium source to obtain the first material;

[0010] Furthermore, the first material is thoroughly mixed with the second sodium source and additives, and then calcined to obtain a single-crystal cathode material with capacity recovery; wherein the calcination process is a two-stage calcination process.

[0011] The present invention also provides a single-crystal cathode material prepared by the aforementioned capacity recovery method.

[0012] The present invention also provides the application of the aforementioned capacity recovery method in the recycling of sodium-ion batteries.

[0013] This invention also provides a method for the cascade utilization of single-crystal cathode materials from waste sodium-ion batteries, comprising:

[0014] The aforementioned capacity recovery method is used to restore the capacity of the single-crystal cathode material in waste sodium-ion batteries. Then, the materials are assembled into sodium-ion batteries, thereby realizing the cascade utilization of the single-crystal cathode material in waste sodium-ion batteries.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] (1) The capacity recovery method provided by the present invention has a simple process, readily available raw materials, and can be completed with existing equipment conditions, which is conducive to industrial production;

[0017] (2) The capacity recovery method provided by the present invention can save raw material costs and precursor synthesis costs, greatly reduce the front-end cost of cathode material synthesis, make full use of resources, and is more environmentally friendly.

[0018] (3) The present invention uses single crystal materials from waste sodium-ion batteries. Since the crystal structure has been formed, only a lower calcination temperature and a shorter calcination time are required, which can reduce electricity costs, thereby further reducing production costs and improving economic and environmental benefits.

[0019] (4) The capacity recovery method provided by the present invention can restore the capacity of the single crystal cathode material obtained from the waste sodium-ion battery to a level close to that before the material was cycled, and can maintain a high cycle stability, so that it can be reused in sodium-ion batteries, thereby achieving the cascade utilization of the material and maximizing the benefits. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a comparison chart of the first charge-discharge capacity curves of the finished material and the recycled material before restoration in Embodiment 1 of the present invention at a current density of 0.1C (1C = 130mA / g);

[0022] Figure 2 This is a SEM image of the recycled material in Embodiment 1 of the present invention;

[0023] Figure 3 This is a SEM image of the finished material in Embodiment 1 of the present invention;

[0024] Figure 4 This is an XRD comparison diagram of the finished material and recycled material in Embodiment 1 of the present invention with the initial material that has not undergone charge-discharge cycles;

[0025] Figure 5 This is a comparison chart of the cycle performance of the finished material and the initial material in Embodiment 1 of the present invention at a current density of 1C. Detailed Implementation

[0026] In view of the deficiencies of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. This invention uses single-crystal cathode material from waste sodium-ion batteries as the main raw material, and sodium citrate and other materials as sodium sources. The preparation method involves washing and drying the single-crystal cathode material recovered from waste sodium-ion batteries, then fully mixing it with a certain proportion of sodium sources and additives, and finally calcining it at high temperature to obtain the final material. Therefore, the process is simple, the raw materials are readily available, and it can be completed with existing equipment conditions, which is conducive to industrial production.

[0027] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Specifically, as one aspect of the technical solution of this invention, a method for capacity recovery of single-crystal cathode material in waste sodium-ion batteries includes:

[0029] Provides single-crystal cathode materials containing impurities from waste sodium-ion batteries;

[0030] The impurity-containing single-crystal cathode material is washed and dried using an aqueous solution containing a first sodium source to obtain the first material;

[0031] Furthermore, the first material is thoroughly mixed with the second sodium source and additives, and then calcined to obtain a single-crystal cathode material with capacity recovery; wherein the calcination process is a two-stage calcination process.

[0032] The capacity recovery method provided by this invention can restore the capacity of single-crystal cathode material obtained from waste sodium-ion batteries to a level close to that before the material was cycled, and can maintain high cycle stability, so that it can be reused in sodium-ion batteries, achieving the cascade utilization of materials and maximizing benefits.

[0033] This invention utilizes residual conductive agent and binder as carbon sources to restore the capacity of single-crystal cathode materials through a single sintering process; it also incorporates sodium citrate or sodium hydroxide during water washing to prevent the complete removal of sodium ions from the material; and employs relatively low-temperature and short-time processes throughout the entire recycling and preparation process.

[0034] In some preferred embodiments, the impurities in the impurity-containing single-crystal cathode material include conductive agents and binders; the impurities mainly include C and H elements.

[0035] In some preferred embodiments, the first sodium source includes sodium citrate and / or sodium hydroxide, but is not limited thereto.

[0036] Furthermore, the first sodium source is sodium citrate.

[0037] In some preferred embodiments, the mass ratio of the first sodium source to water in the aqueous solution containing the first sodium source is less than or equal to 10%.

[0038] In some preferred embodiments, the drying process is carried out at a temperature of 120–160°C.

[0039] In some preferred embodiments, the capacity recovery method specifically includes:

[0040] The first material is thoroughly mixed with the second sodium source and additives using any one of the following methods: ball milling, sand milling, or air jet milling, to obtain the second material.

[0041] Furthermore, the second sodium source includes any one or a combination of two or more of sodium citrate, sodium acetate, sodium carbonate, and sodium hydroxide, and is not limited thereto.

[0042] Furthermore, the additives include citric acid and any one or more combinations of oxides, hydroxides, acetates, carbonates, and nitrates containing W, Sn, Cu, Al, Zn, Co, Ti, Mg, Si, Ca, K, or Zr, and are not limited thereto.

[0043] Specifically, the additive is used to assist in sodium supplementation and to restore and improve the structural stability of the material.

[0044] Furthermore, the particle size of the second material is 2-10 μm.

[0045] Furthermore, the mass ratio of the additive to the first material is 0.15 to 5.0:100.

[0046] In some preferred embodiments, the capacity recovery method specifically includes: calcining the second material at 400-650°C for 3-5 hours in a dry atmosphere, followed by a second calcination at 750-950°C for 8-12 hours to obtain a single-crystal cathode material with recovered capacity.

[0047] Furthermore, the drying atmosphere includes any one or a combination of two or more of the following: a dry air atmosphere, a dry oxygen atmosphere, or a dry nitrogen atmosphere, and is not limited thereto.

[0048] In some preferred embodiments, the capacity of the impurity-containing single-crystal cathode material is ≤110mAh / g.

[0049] In some preferred embodiments, the capacity of the impurity-containing single-crystal cathode material before cycling is ≥140mAh / g.

[0050] In some preferred embodiments, the capacity of the capacity-recovered single-crystal cathode material is ≥130mAh / g.

[0051] In some preferred embodiments, the molar ratio of sodium to non-sodium metal elements in the capacity-recovering single-crystal cathode material is 0.91-0.97:1.

[0052] In some more specific embodiments, the capacity recovery method for the single-crystal cathode material in the spent sodium-ion battery includes the following steps:

[0053] Step 1: The impurity-containing single-crystal cathode material recovered from waste sodium-ion batteries is washed with water and dried to obtain material A1 (the aforementioned "first material");

[0054] Step 2: Mix material A1 thoroughly with a certain proportion of sodium source and additives to obtain mixture A2 (the aforementioned "second material");

[0055] Step 3: After high-temperature calcination of mixture A2, finished material A3 (the aforementioned "capacity-recovered single-crystal cathode material") is obtained.

[0056] Preferably, in step 1, the single-crystal cathode material is a layered transition metal oxide with the chemical formula Na. x Ni a Fe b Mn c Cu d Mg e Zn fO2, where 0.9≤x≤1.1, 0≤a≤0.6, 0≤b≤0.6, 0≤c≤1.0, 0≤d≤0.2, 0≤e≤0.3, and 0≤f≤0.1.

[0057] Preferably, in step 1, during the water washing process, sodium citrate or sodium hydroxide, especially sodium citrate, is generally added at a mass percentage of no more than 10.0%.

[0058] Preferably, in step 1, the drying temperature is generally 120-160℃.

[0059] Preferably, in step 2, the sodium source is any one or a combination of two or more of sodium citrate, sodium acetate, sodium carbonate, and sodium hydroxide.

[0060] Preferably, in step 2, the additive includes citric acid and any one or more of oxides, hydroxides, acetates, carbonates and nitrates containing W, Sn, Cu, Al, Zn, Co, Ti, Mg, Si, Ca, K and Zr.

[0061] Preferably, in step 2, the sodium source is described as a molar ratio, generally based on the ICP test results of material A1 in step 1. The sodium element is added to achieve a molar ratio of 0.91-0.97:1 with other non-sodium metal elements, i.e., a sodium ratio of 0.91-0.97. For example, if the recovered cathode material containing impurities has a sodium ratio of 1.02, after washing and drying, some sodium is removed, and the molar ratio of sodium to other metal elements in the obtained material A1 is 0.8:1, then sodium can be added to achieve a sodium ratio of 0.97:1. The additive is described as a mass percentage, generally 0.15%-5.0%.

[0062] Preferably, in step 2, the mixing method is mainly ball mill, sand mill or air jet mill mixing, which can make the mixing effect more thorough and uniform. Since it is a single crystal material, there is no need to consider the morphology and particle breakage, only to control a certain particle size.

[0063] Preferably, in step 3, the atmosphere for high-temperature calcination is dry air, oxygen, or nitrogen. To reduce costs and improve efficiency, dry air is generally chosen.

[0064] Preferably, in step 3, the high-temperature calcination temperature is divided into two stages. The first stage is a pre-calcination treatment at 400-650℃ for 3-5 hours. This stage can remove the moisture and carbon dioxide generated during the pre-calcination process, which is beneficial to stabilizing the subsequent high-temperature calcination environment of the material and improving the uniformity of the elements in the additives entering the material. The second stage is at 750-950℃ for 8-12 hours. After the calcination is completed, the material is allowed to cool naturally in the furnace.

[0065] This invention uses single-crystal materials from waste sodium-ion batteries as the main raw material and sodium citrate as the sodium source. The preparation method involves washing and drying the single-crystal cathode material recovered from waste sodium-ion batteries, then fully mixing it with a certain proportion of sodium source and additives, and finally calcining it at high temperature to obtain the final material. Therefore, the process is simple, the raw materials are readily available, and it can be completed with existing equipment, which is conducive to industrial production.

[0066] By directly utilizing single-crystal materials from spent sodium-ion batteries, a simple water washing and drying process yields single-crystal materials containing missing sodium and small amounts of conductive agents and binders. These conductive agents and binders primarily contain C and H elements, thus serving as inorganic carbon sources to improve the sintering environment. This eliminates the need for new raw materials in precursor synthesis, saving both raw material and precursor synthesis costs, significantly reducing the initial precursor cost for cathode material synthesis. During the water washing process, to prevent complete sodium ion release and protect the material structure, a washing solution prepared with sodium citrate or sodium hydroxide is added. Furthermore, since the recycled materials from the batteries already possess a formed crystal structure, a high-temperature, long-duration calcination process is unnecessary for slow crystallization. Lower calcination temperatures and shorter times are sufficient to replenish sodium and restore the material's capacity, thereby reducing electricity costs, improving resource utilization, and ultimately making the process more environmentally friendly. To simplify the process, a single calcination is used. However, if too much sodium is added, the residual sodium will be too high, affecting the overall performance of the material. Adding a dealkali reduction process would increase the cost of recycling. Therefore, sodium is only added until the molar ratio of sodium to other non-sodium metal elements is 0.91-0.97:1, i.e., the sodium ratio is 0.91-0.97. This avoids excessive sodium, eliminates the need for secondary processes, and improves economic efficiency.

[0067] Therefore, this method can restore the capacity of single-crystal cathode materials obtained from waste sodium-ion batteries and maintain high cycle stability, allowing them to be reused in sodium-ion batteries. This achieves the goal of cascade utilization of materials, further reducing costs, and improving resource utilization and economic benefits.

[0068] Another aspect of the present invention provides a single-crystal cathode material prepared by the aforementioned capacity recovery method.

[0069] Another aspect of the present invention provides the use of the aforementioned capacity recovery method in the recycling of sodium-ion batteries.

[0070] Another aspect of this invention provides a method for the cascade utilization of single-crystal cathode materials from waste sodium-ion batteries, comprising:

[0071] The aforementioned capacity recovery method is used to restore the capacity of the single-crystal cathode material in waste sodium-ion batteries. Then, the materials are assembled into sodium-ion batteries, thereby realizing the cascade utilization of the single-crystal cathode material in waste sodium-ion batteries.

[0072] The technical solution of the present invention will be further described in detail below with reference to several preferred embodiments and accompanying drawings. This embodiment is implemented on the premise of the technical solution of the invention, and provides detailed implementation methods and specific operation processes. However, the protection scope of the present invention is not limited to the following embodiments.

[0073] Unless otherwise specified, the experimental materials used in the examples below can be purchased from conventional biochemical reagent companies.

[0074] Example 1

[0075] (1) 100g of impurity-containing single crystal cathode material (i.e., material after charge-discharge cycle) obtained from waste sodium-ion batteries was mixed with 5g of sodium citrate, washed with water, and dried at 140°C to obtain material A1;

[0076] (2) Take material A1 and test its sodium content to be 0.75. Then, according to the test results, mix 50g of material A1 with 8.13g of sodium citrate (sodium supplemented to 0.95), 1.5g of citric acid and 0.3g of magnesium oxide in a ball mill to obtain mixture A2.

[0077] (3) In dry air, the mixture A2 is pre-calcined at 500°C for 4 hours, then calcined at 800°C for 9 hours, and then cooled naturally in the furnace to obtain the finished material A3.

[0078] Testing and characterization: The obtained finished materials were assembled into sodium-ion coin cells for charge-discharge testing, and the morphology of the materials was observed under a scanning electron microscope and analyzed by XRD. The materials after washing and drying in step (1) were also tested for comparison. Figure 1 The figure shows the first charge-discharge capacity curve of the finished material at a current density of 0.1C (1C = 130mA / g). It can be seen that the specific capacity of the material was restored to 132.51mAh / g after being processed by this process. Figure 2 The image shown is an electron microscope image of the recycled material. It can be seen that obvious structural cracks appeared in the material after cycling. Figure 3 It can be seen that the cracks in the restored material have basically disappeared, and the morphology has been improved; Figure 4 The XRD patterns of the restored finished material and recycled material are compared with the initial material. It can be seen from the figure that the diffraction peaks and intensities of the restored finished material are basically similar to those of the initial material, indicating that the structure and sodium content of the material have been restored. Figure 5The graph shows a comparison of the cycle performance of the finished material and the initial material at a current density of 1C. It can be seen that the capacity retention rate of the material after 100 charge-discharge cycles is 87.92%, which is close to the capacity retention rate of 90.51% of the initial material, indicating that the structural stability of the material has been restored.

[0079] Example 2

[0080] (1) 100g of impurity-containing single-crystal cathode material recovered from waste sodium-ion batteries is mixed with 10g of sodium hydroxide, washed with water, and dried at 120°C to obtain material A1;

[0081] (2) Take material A1 and test its sodium content to be 0.81. Then, according to the test results, mix 50g of material A1 with 4.59g of sodium acetate (sodium supplemented to 0.93), 1.5g of citric acid and 0.2g of cobalt nitrate in a ball mill to obtain mixture A2.

[0082] (3) In dry air, the mixture A2 is pre-calcined at 400°C for 5 hours, then calcined at 750°C for 12 hours, and then cooled naturally in the furnace to obtain the finished material A3.

[0083] The obtained finished materials were assembled into sodium-ion button batteries and charged and discharged at a current density of 0.1C (1C = 130mA / g). The specific capacity was restored to 137.42mAh / g.

[0084] Example 3

[0085] (1) 100g of impurity-containing single-crystal cathode material recovered from waste sodium-ion batteries is mixed with 1g of sodium citrate, washed with water, and dried at 160°C to obtain material A1;

[0086] (2) Take material A1 and test its sodium content to be 0.68. Then, according to the test results, mix 50g of material A1 with 7.38g of sodium carbonate (sodium supplemented to 0.97), 2.5g of citric acid and 1.5g of copper acetate in a ball mill to obtain mixture A2.

[0087] (3) In dry air, the mixture A2 is pre-calcined at 650°C for 3 hours, then calcined at 950°C for 8 hours, and then cooled naturally in the furnace to obtain the finished material A3.

[0088] The obtained finished materials were assembled into sodium-ion button batteries and charged and discharged at a current density of 0.1C (1C = 130mA / g). The specific capacity was restored to 135.56mAh / g.

[0089] Example 4

[0090] (1) 100g of impurity-containing single crystal cathode material recovered from waste sodium-ion batteries was mixed with 5g sodium citrate and 1g sodium hydroxide, washed with water, and dried at 140°C to obtain material A1.

[0091] (2) Take material A1 and test its sodium content to be 0.77. Then, according to the test results, mix 50g of material A1 with 2.63g of sodium hydroxide (sodium supplemented to 0.91), 1.5g of citric acid and 0.3g of calcium carbonate in a ball mill to obtain mixture A2.

[0092] (3) In dry air, the mixture A2 is pre-calcined at 500°C for 4 hours, then calcined at 800°C for 9 hours, and then cooled naturally in the furnace to obtain the finished material A3.

[0093] The obtained finished materials were assembled into sodium-ion button batteries and charged and discharged at a current density of 0.1C (1C = 130mA / g). The specific capacity was restored to 130.15mAh / g.

[0094] Comparative Example 1 (The method is the same as in Example 1, except that a sodium source is missing during the water washing process)

[0095] (1) 100g of impurity-containing single-crystal cathode material recovered from waste sodium-ion batteries was washed with water and dried at 140°C to obtain material A1.

[0096] (2) Take material A1 and test its sodium content to be 0.56. Then, according to the test results, mix 50g of material A1 with 16.55g of sodium citrate (sodium supplemented to 0.95), 1.5g of citric acid and 0.3g of magnesium oxide in a ball mill to obtain mixture A2.

[0097] (3) In dry air, the mixture A2 is pre-calcined at 500°C for 4 hours, then calcined at 800°C for 9 hours, and then cooled naturally in the furnace to obtain the finished material A3.

[0098] The obtained finished materials were assembled into sodium-ion button batteries and charged and discharged at a current density of 0.1C (1C = 130mA / g). The specific capacity was restored to 121.06mAh / g.

[0099] Comparative Example 2 (the method is the same as in Example 1, except that a single-stage calcination is used in step 3)

[0100] (1) 100g of impurity-containing single-crystal cathode material recovered from waste sodium-ion batteries was mixed with 5g of sodium citrate, washed with water, and dried at 140°C to obtain material A1;

[0101] (2) Take material A1 and test its sodium content to be 0.75. Then, according to the test results, mix 50g of material A1 with 8.13g of sodium citrate (sodium supplemented to 0.95), 1.5g of citric acid and 0.3g of magnesium oxide in a ball mill to obtain mixture A2.

[0102] (3) In dry air, the mixture A2 is calcined at 800℃ for 9 hours and then cooled naturally in the furnace to obtain the finished material A3.

[0103] The obtained finished materials were assembled into sodium-ion button batteries and charged and discharged at a current density of 0.1C (1C = 130mA / g). The specific capacity was restored to 126.31mAh / g.

[0104] Comparative Example 3 (The method is the same as in Example 1, except that sodium was supplemented in excess).

[0105] (1) 100g of impurity-containing single-crystal cathode material recovered from waste sodium-ion batteries was mixed with 5g of sodium citrate, washed with water, and dried at 140°C to obtain material A1;

[0106] (2) Take material A1 and test its sodium content to be 0.75. Then, according to the test results, mix 50g of material A1 with 11.39g of sodium citrate (sodium added to 1.03), 1.5g of citric acid and 0.3g of magnesium oxide in a ball mill to obtain mixture A2.

[0107] (3) In dry air, the mixture A2 is pre-calcined at 500°C for 4 hours, then calcined at 800°C for 9 hours, and then cooled naturally in the furnace to obtain the finished material A3.

[0108] The obtained finished materials were assembled into sodium-ion button batteries and charged and discharged at a current density of 0.1C (1C = 130mA / g). The specific capacity recovered to 126.37mAh / g, and the first-time efficiency was low at 85.11%, indicating that although the capacity was high when sodium was added, it affected the discharge capacity. It also indicates that there was too much sodium residue on the surface of the material.

[0109] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0110] It should be understood that the technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made to the technical solutions of the present invention without departing from the spirit and scope of the claims are within the scope of protection of the present invention.

Claims

1. A method for capacity recovery of single-crystal cathode material in waste sodium-ion batteries, characterized in that, include: A single-crystal cathode material containing impurities from waste sodium-ion batteries is provided; wherein, the impurities in the single-crystal cathode material include conductive agents and binders; the impurities mainly include C and H elements; The impurity-containing single-crystal cathode material is washed and dried using an aqueous solution containing a first sodium source to obtain the first material; Furthermore, the first material is thoroughly mixed with the second sodium source and additives, and subjected to a first calcination treatment at 400-650℃ for 3-5 hours in a dry atmosphere, followed by a second calcination treatment at 750-950℃ for 8-12 hours, thereby obtaining a single-crystal cathode material with capacity recovery; wherein, the additives include citric acid and any one or more combinations of oxides, hydroxides, acetates, carbonates, and nitrates containing W, Sn, Cu, Al, Zn, Co, Ti, Mg, Si, Ca, K, or Zr.

2. The capacity recovery method according to claim 1, characterized in that: The first sodium source includes sodium citrate and / or sodium hydroxide.

3. The capacity recovery method according to claim 1, characterized in that: The first sodium source is sodium citrate.

4. The capacity recovery method according to claim 1, characterized in that: The mass ratio of the first sodium source to water in the aqueous solution containing the first sodium source is less than or equal to 10%.

5. The capacity recovery method according to claim 1, characterized in that: The drying process is carried out at a temperature of 120~160℃.

6. The capacity recovery method according to claim 1, characterized in that, Specifically, it includes: The first material is thoroughly mixed with the second sodium source and additives using any one of the following methods: ball milling, sand milling, or air jet milling, to obtain the second material.

7. The capacity recovery method according to claim 6, characterized in that: The second sodium source includes any one or a combination of two or more of sodium citrate, sodium acetate, sodium carbonate, and sodium hydroxide.

8. The capacity recovery method according to claim 6, characterized in that: The particle size of the second material is 2-10 μm.

9. The capacity recovery method according to claim 6, characterized in that: The mass ratio of the additive to the first material is 0.15~5.0:

100.

10. The capacity recovery method according to claim 1, characterized in that: The dry atmosphere includes any one or a combination of two or more of the following: dry air atmosphere, dry oxygen atmosphere, or dry nitrogen atmosphere.

11. The capacity recovery method according to claim 10, characterized in that: The drying atmosphere is a dry air atmosphere.

12. The capacity recovery method according to claim 1, characterized in that: The capacity of the impurity-containing single-crystal cathode material is ≤110 mAh / g.

13. The capacity recovery method according to claim 1, characterized in that: The capacity of the single-crystal cathode material with capacity recovery is ≥130 mAh / g.

14. The capacity recovery method according to claim 1, characterized in that: The molar ratio of sodium to non-sodium metal elements in the single-crystal cathode material with capacity recovery is 0.91-0.97:

1.

15. A single-crystal cathode material prepared by the capacity recovery method according to any one of claims 1-14.

16. Use of the capacity recovery method according to any one of claims 1-14 in the recycling of sodium-ion batteries.

17. A method for the tiered utilization of single-crystal cathode material in waste sodium-ion batteries, characterized in that, include: The capacity recovery method according to any one of claims 1-14 is used to restore the capacity of the single-crystal cathode material in the waste sodium-ion battery, and then the sodium-ion battery is formed by assembly, thereby realizing the cascade utilization of the single-crystal cathode material in the waste sodium-ion battery.

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