Lithium supplementing agent and preparation method therefor, positive electrode sheet, and secondary battery

Abstract

The present application belongs to the technical field of energy storage, and provides a lithium supplementing agent. The lithium supplementing agent comprises a sulfide composite material, the sulfide composite material comprising: a first sulfide, and a second sulfide doped in the first sulfide. The first sulfide comprises lithium sulfide, and the second sulfide is selected from at least one of a metal sulfide other than lithium sulfide, and an organic sulfide. The present application can solve the problems in the existing technology that positive electrode lithium supplementation is prone to gas generation, has a poor lithium replenishment effect, and is not conducive to effectively improving the overall performance of a battery.

Description

Lithium replenishing agent and its preparation method, positive electrode sheet and secondary battery Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a lithium replenishing agent and its preparation method, a positive electrode sheet, and a secondary battery. Background Technology

[0002] Lithium-ion batteries are widely used in the new energy field, such as as batteries for new energy vehicles. During the charging and discharging process, a certain amount of active lithium from the positive electrode is irreversibly consumed on the negative electrode surface to form an SEI (solid electrolyte interphase) film, resulting in problems such as low initial cycle efficiency and poor cycle life.

[0003] Currently, the primary methods to improve first-cycle efficiency are pre-lithiation or the addition of lithium replenishing agents. Common lithium replenishment methods include positive electrode lithium replenishment and negative electrode lithium replenishment. Negative electrode lithium replenishment often uses lithium powder or lithium foil as replenishing agents, which can easily lead to safety hazards. Positive electrode lithium replenishment often uses lithium-rich compounds and binary lithium compounds as replenishing agents, which can be added directly during the slurry mixing process. This method is simple to operate and has a higher safety profile, making it a current focus of attention.

[0004] However, current cathode lithium replenishment methods suffer from problems such as easy gas generation and poor lithium replenishment effect, which are not conducive to the effective improvement of the overall battery performance.

[0005] Summary of the Invention

[0006] In view of the technical problems existing in the background art, this application provides a lithium replenishing agent and its preparation method, a positive electrode sheet, a secondary battery and an electrical device, aiming to solve the problem that the overall performance of the battery cannot be effectively improved in the related art.

[0007] In a first aspect, embodiments of this application provide a lithium replenishing agent, comprising: a sulfide composite material, the sulfide composite material comprising: a first sulfide and a second sulfide doped in the first sulfide; wherein the first sulfide comprises lithium sulfide, and the second sulfide is selected from at least one of metal sulfides and organic sulfides other than lithium sulfide.

[0008] In the technical solution of this application embodiment, the lithium sulfide in the lithium replenishing agent can be used for lithium replenishment. After the lithium is removed, the remaining sulfur bonds with the second sulfide to form, for example, polysulfides, etc., to avoid the formation of elemental sulfur after the lithium in the lithium sulfide is removed, reduce the amount of elemental sulfur dissolved in the electrolyte, and reduce the amount of elemental sulfur deposited through the separator onto the negative electrode or the separator, thereby reducing the impact of residual elemental sulfur on battery performance, improving battery performance stability, and effectively improving battery performance overall.

[0009] In some embodiments, the metal sulfide includes at least one of sodium sulfide, calcium sulfide, and potassium sulfide; and / or,

[0010] The organosulfur compound includes at least one of: ammonium sulfide, sodium dithiocarbamate, and potassium sodium dithiocarbamate; and / or,

[0011] In this sulfide composite material, the mass ratio of the second sulfide to the first sulfide is (60-80):(15-30); and / or,

[0012] In this sulfide composite material, the molar ratio of sulfur in the second sulfide to that in the first sulfide is (0.1-0.31):(1.0-1.1).

[0013] In this embodiment, by controlling the mass ratio of the second sulfide to the first sulfide to be (60-80):(15-30), and / or controlling the molar ratio of sulfur in the second sulfide to the first sulfide to be (0.1-0.31):(1.0-1.1), both lithium replenishment and sulfur fixation effects can be achieved.

[0014] In some embodiments, the lithium replenishing agent further includes: a carbon coating layer coated on the surface of a sulfide composite material;

[0015] In this lithium replenishing agent, the carbon coating layer accounts for 5% to 10% of the total mass.

[0016] In this embodiment, by coating the sulfide composite material with a carbon coating layer, the electron conductivity efficiency of the lithium supplement can be effectively improved. By controlling the mass percentage of the carbon coating layer to be 5% to 10%, the electron conductivity efficiency can be effectively improved without affecting lithium-ion transport.

[0017] In some embodiments, the median particle size D50 of the lithium supplement is 3 μm to 12 μm; and / or,

[0018] The specific surface area of ​​the lithium supplement is 2m². 2 / g~10m 2 / g.

[0019] In this embodiment, the D50 particle size and specific surface area of ​​the lithium supplement are both within a suitable range, which makes the lithium supplement have a high compaction density, thereby improving the energy density.

[0020] Secondly, embodiments of this application provide a method for preparing a lithium supplement, comprising:

[0021] The first lithium source and the first sulfur source are mixed and subjected to a first reaction process to obtain a first reaction solution;

[0022] The first reaction solution is mixed with a reducing agent, a pH adjuster and a second sulfide, and then subjected to a first purification treatment to obtain a sulfide composite material;

[0023] The first reaction solution includes a first sulfide, which contains lithium sulfide, and the second sulfide is selected from at least one of metal sulfides other than lithium sulfide and organic sulfides.

[0024] In the technical solution of this application embodiment, the sulfide composite material can be prepared by combining the second sulfide with the first sulfide. The preparation method is simple and easy to implement.

[0025] In some embodiments, the first purification process includes:

[0026] Concentrate the first reaction solution to obtain crystals of the first sulfide and the second sulfide; and / or,

[0027] The method for preparing the lithium supplement further includes:

[0028] The crystallized material is subjected to solid-liquid separation, and the separated solid material is washed and dried; and / or,

[0029] The preparation method of this lithium supplement also includes:

[0030] A lithium supplement is prepared by mixing carbon materials with sulfide composite materials and subjecting the mixture to a second reaction treatment; and / or,

[0031] The second reaction process includes grinding and calcination. The grinding time is 1 to 2 hours, and the calcination is carried out in a protective atmosphere at a temperature of 200°C to 300°C for 5 to 8 hours.

[0032] In this embodiment, the first purification process is simple and easy to implement, and can improve the purity of the sulfide composite material at a low cost. Subsequent solid-liquid separation, washing, drying, and the second reaction treatment are also simple, enabling the preparation of a high-purity sulfide composite material and obtaining a lithium supplement with improved product quality. Through grinding and calcination, on the one hand, the sulfide composite material can be further fused to obtain a more uniformly mixed sulfide composite material; on the other hand, carbon material can be coated onto the sulfide composite material, forming a carbon coating layer on the surface of the sulfide composite material after calcination, thereby improving the electron conductivity of the lithium supplement. Calcination in a protective atmosphere allows for further control of humidity and oxygen content during calcination, further improving the purity of the obtained lithium supplement.

[0033] In some embodiments, the method for preparing the lithium supplement satisfies at least one of the following conditions:

[0034] (1) The temperature of the first reaction treatment is 30℃~60℃ and the time is 30min~60min;

[0035] (2) Concentration is performed by vacuum concentration at a temperature of 50℃~80℃, and / or the final concentration solution has a Baume degree of 45~50.

[0036] (3) The first sulfide and the second sulfide are crystallized by cooling. The crystallization temperature is 10℃~25℃ and the cooling rate is 10℃ / h~15℃ / h.

[0037] (4) The mass ratio of sulfide composite material to carbon material can be (90-95):(5-10);

[0038] (5) The grinding time is 1h to 2h, and / or the calcination temperature is 200℃ to 300℃ and the time is 5h to 8h.

[0039] In this embodiment, controlling the temperature of the first reaction treatment to 30℃~60℃ and the time to 30min~60min helps to increase the reaction rate of the first sulfur source and the first lithium source and ensure their complete reaction. Vacuum concentration helps to increase the concentration rate and effectively reduce the concentration temperature, minimizing damage to the sulfide composite material caused by high temperatures. Simultaneously, controlling the concentration temperature and the Baume degree of the concentrated solution, and using cooling to induce the crystallization of lithium sulfide and the second sulfide, helps to increase the crystallization rate of lithium sulfide and the second sulfide, while also ensuring complete crystallization and reducing impurity precipitation. By performing solid-liquid separation on the crystallized material, and washing and drying the separated solid material, a mixed crystalline material of the first sulfide and the second sulfide with high purity can be obtained. This lithium supplement can be prepared by mixing carbon materials with the sulfide composite material and then performing a second reaction treatment.

[0040] In some embodiments, the method for preparing the lithium supplement satisfies at least one of the following conditions:

[0041] (1) The first lithium source includes at least one of lithium sulfate, lithium oxalate and lithium carbonate, and the first sulfur source includes at least one of barium sulfide and calcium sulfide;

[0042] (2) The purity of the first lithium source and the first sulfur source is greater than or equal to 99.5%;

[0043] (3) The content of magnetic foreign matter in the first lithium source and the first sulfur source is less than 1 ppm;

[0044] (4) The reducing agent includes at least one of hydrazine hydrate and sulfite;

[0045] (5) The pH adjuster includes hydroxides selected from lithium hydroxide and / or hydroxides of the metal corresponding to the second sulfide;

[0046] (6) Carbon materials include: CNTs and / or graphene.

[0047] In this embodiment, using the aforementioned first sulfur source and first lithium source, barium sulfate precipitate, barium oxalate, and / or barium carbonate precipitate can be obtained, thereby reducing impurities in the first reaction solution. Controlling the purity of both the first lithium source and the first sulfur source to be greater than or equal to 99.5% is beneficial for reducing impurity content and improving the purity of the lithium supplement agent. Controlling the magnetic foreign matter content of the first lithium source and the first sulfur source to be less than 1 ppm reduces the introduction of magnetic foreign matter and reduces battery performance degradation caused by magnetic foreign matter when the lithium supplement agent is applied to the battery. The presence of the reducing agent and hydroxide is beneficial for the purification of the first sulfide and the second sulfide and for reducing impurities. Simultaneously, the addition of hydroxide helps to inhibit the hydrolysis of the first sulfide and the second sulfide, and the addition of the reducing agent helps to effectively prevent the oxidation of sulfur ions, thereby maintaining the performance stability of the first sulfide and the second sulfide in the sulfide composite material. Using hydrazine hydrate as a reducing agent to generate nitrogen gas during the reaction helps to avoid introducing new impurities into the sulfide composite material. The pH adjuster is a hydroxide, which helps to effectively inhibit the hydrolysis of the corresponding metal sulfide and / or lithium sulfide.

[0048] Thirdly, embodiments of this application provide a positive electrode sheet, including a current collector and a positive electrode material disposed on at least one side of the current collector along its thickness direction, the positive electrode material including the lithium supplement agent as described in the first aspect.

[0049] In this embodiment, the positive electrode contains the aforementioned lithium replenishing agent, thus possessing the advantages of a lithium replenishing agent.

[0050] Fourthly, embodiments of this application provide a secondary battery, including a positive electrode, a negative electrode, and a separator; wherein the positive electrode is the positive electrode as described in the third aspect.

[0051] In this embodiment, the secondary battery includes the aforementioned positive electrode sheet, thus possessing the advantages of a positive electrode sheet.

[0052] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0053] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0054] Figure 1 is a schematic flowchart of a method for preparing a lithium supplement provided in an embodiment of this application. Detailed Implementation

[0055] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0056] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0057] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0058] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0059] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0060] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple groups" refers to two or more (including two groups), and "multiple pieces" refers to two or more (including two pieces).

[0061] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0062] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0063] Among common cathode lithium replenishment materials, lithium-rich compounds such as lithium iron phosphate and lithium nickel oxide have problems such as high price, poor air stability, complex preparation, easy gas generation and residue, which cannot effectively improve the overall performance of the battery.

[0064] To address the aforementioned technical problems, this application provides a lithium replenishing agent and its preparation method, a positive electrode sheet, and a secondary battery. In this lithium replenishing agent, lithium sulfide is used for lithium replenishment. After lithium removal from the lithium sulfide, the remaining sulfur bonds with a second sulfide to form, for example, polysulfides. This prevents the formation of elemental sulfur after lithium removal from the lithium sulfide, reduces the amount of elemental sulfur dissolved in the electrolyte, and reduces the amount of elemental sulfur deposited across the separator onto the negative electrode or the separator. This reduces the impact of residual elemental sulfur on battery performance, improves battery performance stability, and effectively enhances overall battery performance.

[0065] The electrical devices provided in this application embodiment can be, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Among them, electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0066] In a first aspect, embodiments of this application provide a lithium replenishing agent, which includes: a sulfide composite material, the sulfide composite material including: a first sulfide and a second sulfide doped in the first sulfide. The first sulfide includes lithium sulfide, and the second sulfide is selected from at least one of metal sulfides other than lithium sulfide and organic sulfides.

[0067] The second sulfide comprises at least one of metal sulfides other than lithium sulfide and organic sulfides. The second sulfide can be any sulfide that can bond with the sulfur after lithium sulfide delithiation to fix the sulfur (such as elemental sulfur) after lithium sulfide delithiation, so as to prevent the elemental sulfur after lithium sulfide delithiation from being dissolved or deposited on the membrane.

[0068] The principle of the second sulfide fixing sulfur after lithium delithiation is explained below:

[0069] When the lithium replenishing agent provided in this application embodiment is used in the positive electrode material, the lithium sulfide in the lithium replenishing agent can be used for lithium replenishment. After the lithium is removed, the remaining sulfur can bond with the second sulfide, for example, to form a polysulfide. This avoids the formation of elemental sulfur after the lithium in the lithium sulfide is removed. Taking advantage of the fact that the product of sulfur and the second sulfide has a lower solubility in the electrolyte than elemental sulfur in the electrolyte, for example, polysulfides are not easy to dissolve in the electrolyte and will not pass through the separator to deposit on the negative electrode or the separator. This avoids elemental sulfur dissolving in the electrolyte, passing through the separator and depositing on the negative electrode or the separator, thereby reducing the impact of residual elemental sulfur on battery performance and improving battery performance stability. Overall, this can effectively improve battery performance.

[0070] In some embodiments, the metal sulfide may include at least one of sodium sulfide, calcium sulfide, and potassium sulfide; and / or, the organic sulfide may include at least one of ammonium sulfide, sodium dithiocarbamate, and potassium dithiocarbamate.

[0071] In some embodiments, in the sulfide composite material, the mass ratio of the second sulfide to the first sulfide is (60-80):(15-30). For example, the mass ratio of the second sulfide to the first sulfide is 60:15, 60:18, 60:20, 60:23, 60:25, 60:28, 60:30, 65:16, 65:17, 65:20, 65:22, 65:25, 65:28, 65:30, 70:15, 70:18, 70:20, 70:23, 70:25, 70:29, 70:30, 75:15, 75:17, 75:20, 75:22, 75:25, 75:28, 75:30, 80:15, 80:17, 80:21, 80:24, 80:25, 80:28, or 80:30.

[0072] In these embodiments, by controlling the mass ratio of the second sulfide to the first sulfide to be (60-80):(15-30), both lithium replenishment and sulfur fixation effects can be achieved.

[0073] In some embodiments, in the sulfide composite material, the molar ratio of sulfur in the second sulfide to that in the first sulfide is (0.1–0.31):(1.0–1.1). For example, the molar ratio of sulfur in the second sulfide to that in the first sulfide can be 0.1:1.0, 0.2:1.0, 0.3:1.0, 0.1:1.1, 0.2:1.1, 0.3:1.1, or 0.31:1.1.

[0074] In these embodiments, by controlling the molar ratio of sulfur in the second sulfide to that of the first sulfide to be (0.1–0.31):(1.0–1.1), both lithium replenishment and sulfur fixation effects can be achieved.

[0075] In some embodiments, the lithium supplement further includes a carbon coating layer that coats the surface of the sulfide composite material.

[0076] In these embodiments, by coating the sulfide composite material with a carbon coating layer, the electron conduction efficiency of the lithium supplement can be effectively improved.

[0077] In some embodiments, the carbon coating layer comprises 5% to 10% of the lithium supplement by mass. For example, the carbon coating layer may comprise 5%, 6%, 7%, 8%, 9%, or 10% by mass.

[0078] In these embodiments, the carbon coating accounts for 5% to 10% of the mass, which can effectively improve electron conduction efficiency without affecting lithium-ion transport.

[0079] In some embodiments, the D50 particle size of the lithium supplement is 3 μm to 12 μm; and / or,

[0080] The specific surface area of ​​the lithium supplement is 2m². 2 / g~10m 2 / g.

[0081] For example, the D50 particle size of this lithium replenisher can be 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, or 12 μm. The D50 particle size can be obtained using a laser particle size analyzer, and it represents the particle size corresponding to a cumulative volume distribution percentage of 50% for the lithium replenisher. As another example, the specific surface area of ​​this lithium replenisher can be 2 m². 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g or 10m 2 / g.

[0082] In these embodiments, the D50 particle size and specific surface area of ​​the lithium supplement are within a suitable range, which makes the lithium supplement have a high compaction density, thereby improving the energy density.

[0083] In some embodiments, the magnetic foreign matter content of the lithium replenisher is 0.11 ppm to 0.20 ppm. For example, the magnetic foreign matter content of the lithium replenisher can be 0.11 ppm, 0.12 ppm, 0.13 ppm, 0.14 ppm, 0.15 ppm, 0.16 ppm, 0.17 ppm, 0.18 ppm, 0.19 ppm, or 0.20 ppm. This can reduce the impact of magnetic foreign matter on battery performance.

[0084] In some embodiments, the water content of the lithium supplement is 125 ppm to 530 ppm. For example, the water content of the lithium supplement can be 125 ppm, 127 ppm, 130 ppm, 140 ppm, 150 ppm, 160 ppm, 170 ppm, 180 ppm, 190 ppm, 200 ppm, 210 ppm, 215 ppm, 220 ppm, 225 ppm, 230 ppm, 240 ppm, 247 ppm, 260 ppm, 270 ppm, 280 ppm, 290 ppm, 296 ppm, 311 ppm, 312 ppm, 340 ppm, 350 ppm, 370 ppm, 390 ppm, 400 ppm, 410 ppm, 420 ppm, 430 ppm, 440 ppm, 450 ppm, 459 ppm, 470 ppm, 785 ppm, 500 ppm, 527 ppm, or 530 ppm.

[0085] In these embodiments, the lithium replenishing agent has a low moisture content, which can effectively reduce the hydrolysis of lithium sulfide and second sulfide, thereby improving the lithium replenishment effect.

[0086] In some embodiments, the compaction density of the lithium replenishing agent is 2.01 g / mL to 2.15 g / mL. For example, the compaction density of the lithium replenishing agent may be 2.01 g / mL, 2.03 g / mL, 2.05 g / mL, 2.10 g / mL, 2.11 g / mL, 2.13 g / mL, 2.14 g / mL, or 2.15 g / mL.

[0087] In these embodiments, the lithium supplement has a large compaction density and a high energy density.

[0088] Secondly, embodiments of this application provide a method for preparing a lithium supplement, as shown in Figure 1. The preparation method includes the following steps S11 to S12:

[0089] S11. The first lithium source and the first sulfur source are mixed and subjected to a first reaction to obtain a first reaction solution. The first reaction solution includes a first sulfide, which includes lithium sulfide, and the second sulfide is selected from at least one of metal sulfides and organic sulfides other than lithium sulfide.

[0090] The first reaction can be a double displacement reaction.

[0091] In some embodiments, the first lithium source includes at least one of lithium sulfate, lithium oxalate, and lithium carbonate, and the first sulfur source includes at least one of barium sulfide and calcium sulfide.

[0092] In these embodiments, when the first lithium source and the first sulfur source are used, the first reaction process undergoes a metathesis reaction to obtain a lithium sulfide solution and barium sulfate, barium oxalate or calcium sulfate precipitate, which facilitates the subsequent solid-liquid separation to obtain lithium sulfide with higher purity.

[0093] In some embodiments, the molar ratio of sulfur in the first sulfur source to lithium in the first lithium source can be 0.5:(1.0 to 1.1). For example, the molar ratio of sulfur in the first sulfur source to lithium in the first lithium source can be 0.5:1.0 or 0.5:1.1, etc.

[0094] In these embodiments, the first sulfur source and the first lithium source are facilitated to react in a stoichiometric ratio, thereby obtaining lithium sulfide with high purity and avoiding the formation of lithium polysulfides or other impurities.

[0095] In some embodiments, the purity of both the first lithium source and the first sulfur source is greater than or equal to 99.5%. Here, purity refers to mass fraction; that is, the mass fraction of both the first lithium source and the first sulfur source is greater than or equal to 99.5%, meaning the mass fraction of impurities is less than or equal to 0.5%.

[0096] In these embodiments, the purity of the reaction product lithium sulfide can be improved and the introduction of impurities can be reduced.

[0097] In some embodiments, the magnetic foreign matter content of the first lithium source and the first sulfur source is less than 1 ppm. Here, the magnetic foreign matter content refers to the mass content; that is, the mass content of the magnetic foreign matter in the first lithium source and the first sulfur source is less than 1 ppm, meaning the mass content of the magnetic foreign matter is less than or equal to 1 ppm.

[0098] In these embodiments, by controlling the content of magnetic foreign matter in the first lithium source and the first sulfur source to be less than 1 ppm, it is beneficial to reduce the content of magnetic foreign matter, reduce the content of magnetic foreign matter in the final product, or reduce the difficulty of removing magnetic foreign matter in the final product.

[0099] In some embodiments, the temperature of the first reaction treatment can be 30°C to 60°C, and the time can be 30 min to 60 min. For example, the temperature of the first reaction treatment can be 30°C, 40°C, 50°C, or 60°C, and the time can be 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, or 60 min, etc.

[0100] In these embodiments, by controlling the temperature of the first reaction treatment to be 30°C to 60°C and the time to be 30 min to 60 min, the first sulfur source and the first lithium source can react rapidly, thereby improving the reaction efficiency.

[0101] S12. The first reaction solution is mixed with a reducing agent, a pH adjuster and a second sulfide, and then purified to obtain a sulfide composite material.

[0102] The addition of a reducing agent effectively prevents the oxidation of sulfide ions, thereby maintaining the performance stability of the first and second sulfides in the sulfide composite material. Since the first and second sulfides hydrolyze in water to form hydroxides, the pH adjuster can include hydroxides. The addition of hydroxides effectively inhibits the hydrolysis of the first and second sulfides during the first purification process. The presence of the reducing agent and hydroxides facilitates the purification of the first and second sulfides, reducing impurities.

[0103] In some embodiments, the reducing agent may include at least one of hydrazine hydrate and sulfite.

[0104] In these embodiments, hydrazine hydrate acts as a reducing agent to generate nitrogen gas without introducing new impurities into the sulfide composite material.

[0105] There are no specific limitations on the concentration and amount of the reducing agent mentioned above, as long as the reduction effect can be achieved and oxidation of the sulfide composite material can be prevented.

[0106] In some embodiments, when the reducing agent includes hydrazine hydrate, a hydrazine hydrate solution is mixed with a first reaction solution, a pH adjuster, and a second sulfide. The mass fraction of hydrazine hydrate in the hydrazine hydrate solution can be 20% to 30%. For example, the mass fraction of hydrazine hydrate in the hydrazine hydrate solution can be 20%, 22%, 25%, 28%, or 30%, etc. The solvent used in the hydrazine hydrate solution can be the same as the solvent in the first reaction solution.

[0107] In some embodiments, the pH adjuster includes a hydroxide selected from lithium hydroxide and / or hydroxides of metals corresponding to metal sulfides.

[0108] In these embodiments, the addition of hydroxides can effectively inhibit the hydrolysis of the corresponding metal sulfides and / or lithium sulfides.

[0109] In some embodiments, to further reduce the introduction of impurities, the aforementioned hydroxide can be battery grade.

[0110] In some embodiments, the molar ratio of the reducing agent, hydroxide ions in the hydroxide, lithium sulfide, and sulfur in the second sulfide is (0.05–0.1):(0.02–0.05):(1.0–1.1):(0.1–0.31). For example, the molar ratio of the reducing agent, hydroxide ions in the hydroxide, lithium sulfide, and sulfur in the second sulfide can be 0.05:0.02:1.0:0.1, 0.05:0.03:1.0:0.1, 0.05:0.05:1.0:0.1, 0.05:0.02:1.1:0.1, 0.05:0.02:1.0:0.2, 0.05:0.02:1.0:0.31, 0.05:0.03:1.1:0.2, or 0.05:0.03:1.1:0. 0.31, 0.05:0.05:1.1:0.2, 0.05:0.05:1.1:0.31, 0.08:0.02:1.0:0.1, 0.08:0.03:1.0:0.1, 0.08:0.03:1.1:0.1, 0.08:0.03:1.1:0.2, 0.1:0.02:1.0:0.1, 0.1:0.05:1.0:0.1, 0.1:0.05:1.1:0.2, or 0.1:0.05:1.0:0.31, etc.

[0111] In these embodiments, by controlling the molar ratio of reducing agent, hydroxide ions in hydroxide, lithium sulfide, and sulfur in second sulfide within the above-mentioned range, the introduction of impurities can be minimized while effectively preventing oxidation and hydrolysis of lithium sulfide and second sulfide.

[0112] In some embodiments, the first purification process in S12 includes:

[0113] The first reaction solution is concentrated to obtain crystals of the first sulfide and the second sulfide, thereby purifying the first sulfide and the second sulfide.

[0114] In these embodiments, the first and second sulfides can be purified by dissolving and crystallizing them using a first reaction solution. This first purification process is simple, easy to implement, and can improve the purity of sulfide composite materials at a low cost.

[0115] In some embodiments, the above concentration is vacuum concentration, and the concentration temperature is 50°C to 80°C.

[0116] In some embodiments, the Baume degree of the final concentrate after concentration is 45 to 50. For example, the concentration temperature can be 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, or 80°C, etc. As another example, the Baume degree of the final concentrate after concentration can be 45, 46, 47, 48, 49, or 50, etc.

[0117] In these embodiments, vacuum concentration can effectively reduce the concentration temperature and minimize the damage to sulfide composite materials caused by high temperatures. At the same time, by controlling the temperature and the Baumé degree of the final concentrate, lithium sulfide and the second sulfide can be effectively crystallized and precipitated, and impurity precipitation can be reduced.

[0118] In some embodiments, the first sulfide and the second sulfide can be crystallized by cooling, with the crystallization temperature being 10°C to 25°C and the cooling rate being 10°C / h to 15°C / h. For example, the crystallization temperature can be 10°C, 12°C, 15°C, 17°C, 19°C, 20°C, 22°C, 24°C, or 25°C, etc. Again, for example, the cooling rate can be 10°C / h, 12°C / h, 13°C / h, 14°C / h, or 15°C / h.

[0119] In these embodiments, the first sulfide and the second sulfide are crystallized by cooling at a temperature of 10°C to 25°C and a cooling rate of 10°C / h to 15°C / h, which allows lithium sulfide and the second sulfide to crystallize out of the first reaction solution in proportion, reducing losses.

[0120] In some embodiments, the method for preparing the lithium supplement further includes solid-liquid separation of the crystallized material and washing and drying of the separated solid material.

[0121] In these embodiments, a mixed crystalline material of the first and second sulfides with high purity can be obtained by performing solid-liquid separation on the crystallized material, and by washing and drying the separated solid material. This solid-liquid separation process, washing, and drying process is simple and easy to implement.

[0122] In order to further reduce the introduction of impurities, before the concentration process to crystallize lithium sulfide and the second sulfide from the reaction solution to obtain the sulfide composite material, the preparation method may further include: filtering the reaction solution with a filter element with a pore size of 20 nm to 50 nm to remove impurities from the reaction solution.

[0123] In some embodiments, the solid-liquid separation described above can be centrifugal separation. Centrifugal separation is a convenient and quick method for separating solids and liquids from crystallized materials, and it can reduce impurities.

[0124] In some embodiments, the separated solid material is washed with a first solvent, which may include at least one of methanol, ethanol, and glycerol, and the volume of the first solvent is 3 to 6 times the volume of the solid material. For example, the volume of the first solvent may be 3, 4, 5, or 6 times the volume of the solid material, etc.

[0125] In these embodiments, using a first solvent to wash the separated solid materials can reduce residual moisture. Simultaneously, by controlling the volume of the first solvent, moisture in the solid materials can be effectively washed away, further reducing residual moisture.

[0126] In some embodiments, the drying temperature is 50°C to 80°C, and the time is 3 hours to 6 hours; the drying method can be vacuum drying or atmospheric pressure drying under a protective gas. For example, the drying temperature can be 50°C, 51°C, 53°C, 55°C, 56°C, 58°C, 60°C, 62°C, 65°C, 67°C, 69°C, 70°C, 71°C, 74°C, 76°C, 78°C, 79°C, or 80°C, and the drying time can be 3 hours, 4 hours, 5 hours, or 6 hours. The protective gas used during atmospheric pressure drying can be selected from at least one of nitrogen, argon, and helium.

[0127] In some embodiments, the residual amount (by mass fraction) of the first solvent in the solid material after drying is less than 0.3%.

[0128] Furthermore, the solvent used in the first reaction process in S11 is not specifically limited. All solvents that can dissolve lithium sulfide and the second sulfide, and that can crystallize lithium sulfide and the second sulfide in proportion by concentration, are within the scope of protection of this application.

[0129] In some embodiments, the solvent used in the first reaction treatment described above may include at least one selected from distilled water, deionized water, pure water, methanol, ethanol, and glycerol. That is, the solvent in the first reaction solution may be selected from at least one selected from distilled water, deionized water, pure water, methanol, ethanol, and glycerol.

[0130] In these embodiments, methanol, ethanol, and glycerol have low boiling points, which facilitates subsequent concentration and crystallization.

[0131] In some embodiments, as shown in FIG1, the method for preparing the lithium supplement may further include:

[0132] S13. Mix carbon materials with sulfide composite materials and perform a second reaction treatment to prepare a lithium supplement.

[0133] In these embodiments, the lithium supplement can be prepared by mixing carbon materials with sulfide composite materials and then subjecting the mixture to a second reaction treatment. This second reaction treatment process is simple and can produce carbon-coated materials with high purity.

[0134] The specific composition of the carbon material is not specified.

[0135] In some embodiments, the carbon material includes CNTs (Carbon Nanotubes) and / or graphene.

[0136] In some embodiments, the mass ratio of the sulfide composite material to the carbon material can be (90-95):(5-10). For example, the mass ratio of the sulfide composite material to the carbon material can be 90:5, 90:6, 90:7, 90:8, 90:9, 90:10, 91:5, 91:6, 91:7, 91:8, 91:9, 91:10, 92:5, 92:6, 92:7, 92:8, 92:9, 92:10, 95:5, 95:6, 95:7, 95:8, 95:9, or 95:10, etc.

[0137] In some embodiments, the second reaction process described above includes grinding and calcination.

[0138] In these embodiments, the grinding and calcination processes promote further fusion of the sulfide composite material, resulting in a more uniformly mixed composite. Furthermore, they allow for the coating of the sulfide composite material with a carbon coating layer, thereby improving the electronic conductivity of the lithium supplement. Calcination under an inert gas atmosphere further controls humidity and oxygen content, reducing hydrolysis and oxidation of the sulfide composite material.

[0139] In some embodiments, the grinding time can be 1 to 2 hours. Ball milling can be used to mix the carbon material with the mixed crystals of lithium sulfide and the second sulfide.

[0140] In some embodiments, the grinding balls used in the ball milling method can be ceramic balls, which can grind the material to a particle size of 2μm to 10μm.

[0141] In some embodiments, the calcination temperature can be 200°C to 300°C, and the time can be 5 to 8 hours. For example, the calcination temperature can be 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C, or 300°C, and the time can be 5 hours, 6 hours, 7 hours, or 8 hours, etc.

[0142] Furthermore, in some embodiments, to further reduce hydrolysis and oxidation of the sulfide composite material, the humidity inside the calcination furnace is below 0.1%, the oxygen content is below 1 ppm, and the furnace pressure is 200 Pa to 400 Pa during calcination. Simultaneously, to further reduce impurities introduced during calcination, the preparation method may further include: promptly removing waste gas from the furnace using an induced draft fan during calcination, and cooling the material to a temperature ≤50°C after calcination before discharge. Calcination can be carried out under a protective atmosphere. The protective atmosphere may include at least one of nitrogen, argon, and helium.

[0143] Furthermore, in order to reduce iron impurities in the lithium replenishing agent and prepare a lithium replenishing agent that meets the requirements, the preparation method may further include, after discharge, screening and iron removal of the discharged material to obtain the lithium replenishing agent.

[0144] To prevent hydrolysis and oxidation of the sulfide composite material in the lithium supplement, the screening and iron removal processes described above can be carried out in a constant temperature and humidity chamber. The humidity in the chamber is less than or equal to 10%, and the temperature is between 20°C and 30°C.

[0145] During sieving, a 100-200 mesh sieve can be used to obtain the lithium supplement.

[0146] When removing iron, an electromagnetic separator can be used.

[0147] Among them, the process from discharge to screening can be carried out by negative pressure conveying.

[0148] In the method for preparing lithium supplement provided in the embodiments of this application, a first reaction solution is prepared, which includes a first sulfide, which includes lithium sulfide. Then, the first reaction solution and the second sulfide are mixed in the presence of a reducing agent and a pH adjuster. After a first purification treatment, a sulfide composite material with high purity can be prepared. The preparation method is simple and convenient, and the obtained sulfide composite material has high purity.

[0149] Thirdly, embodiments of this application provide a positive electrode sheet, including a current collector and a positive electrode material disposed on at least one side of the current collector along its thickness direction, the positive electrode material including the lithium supplement agent as described in the third aspect.

[0150] Fourthly, embodiments of this application provide a secondary battery, including a positive electrode, a negative electrode, and a separator;

[0151] The positive electrode sheet is the positive electrode sheet as described in the third aspect.

[0152] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0153] Example 1

[0154] The preparation method of the lithium supplement provided in Example 1 is as follows:

[0155] Barium sulfide, lithium sulfate, and methanol were mixed and stirred at 45°C for 45 min to obtain a precipitate and a first reaction solution. The mixture was filtered, and 25% (mass fraction) hydrazine hydrate and battery-grade lithium hydroxide were added to the first reaction solution. Sodium sulfide (second sulfide) was then added, and the mixture was stirred until dissolved. The solution was then precisely filtered using a 30 nm filter. The resulting filtrate was concentrated under vacuum at 70±1°C until the final concentration reached a Baumé degree of 47.3. The solution was then cooled to 20°C at a cooling rate of 13°C / h. The cooled crystals were centrifuged and then washed with anhydrous methanol, the volume of which was five times the volume of the crystals. They were then dried under vacuum or nitrogen protection at 70°C for 5 hours, stopping when the methanol content in the crystals was below 0.3% (mass fraction), yielding a sulfide composite material. After drying, the sulfide composite material was mixed with graphene at a mass ratio of 93:7 for 1.5 hours, with ceramic balls added during the mixing process for grinding until the particle size was 6.1 μm. After grinding, the material was calcined in a nitrogen-protected furnace. During calcination, the nitrogen flow rate was controlled to maintain a furnace humidity below 0.1% and an oxygen content below 1 ppm, with a furnace pressure of 300 Pa. Exhaust gas was exhausted through a blower. The calcination temperature was 250°C for 6 hours. After calcination, the material was cooled to ≤50°C before being discharged. The discharged material is screened for iron removal and packaged to obtain lithium supplement. The screening is carried out using a 150-mesh sieve, and the iron removal is carried out using an electromagnetic iron separator. Screening, iron removal and packaging are all carried out in a constant temperature and humidity room, with humidity controlled at ≤10% and temperature at 25±5℃.

[0156] The main components of barium sulfide and lithium sulfate are ≥99.5% (by mass fraction), the content of magnetic foreign matter is less than 1 ppm, and the molar ratio of added barium sulfide, lithium sulfate, hydrazine hydrate and lithium hydroxide is 1:1.05:0.08:0.04. In the lithium supplement, the molar ratio of lithium sulfide to sodium sulfide is 1:0.18.

[0157] Example 2

[0158] The preparation method of the lithium supplement provided in Example 2 is as follows:

[0159] Barium sulfide, lithium sulfate, and methanol were mixed and stirred at 30°C for 30 minutes to obtain a precipitate and a first reaction solution. The mixture was filtered, and 20% (mass fraction) hydrazine hydrate and battery-grade lithium hydroxide were added to the first reaction solution. Sodium sulfide (second sulfide) was then added, and the mixture was stirred until dissolved. The solution was then precisely filtered using a 20nm filter. The resulting filtrate was concentrated under vacuum at 50°C until the final concentration reached a Baume degree of 45. The solution was then cooled to 10°C at a rate of 10°C / h. The obtained crystals were centrifuged and dried, then washed with anhydrous methanol in an amount six times the volume of the crystals. They were then dried under vacuum or nitrogen protection at 50°C for 6 hours, stopping when the methanol content in the crystals was below 0.3% (mass fraction), yielding a sulfide composite material. After drying, the sulfide composite material was mixed with CNTs at a mass ratio of 90:10 for 1 hour, with ceramic balls added during the mixing process for grinding until the particle size was 2.6 μm. After grinding, the material was calcined in a nitrogen-protected furnace. During calcination, the nitrogen flow rate was controlled to maintain a furnace humidity below 0.1% and an oxygen content below 1 ppm, with a furnace pressure of 200 Pa. Exhaust gas was exhausted through a blower. The calcination temperature was 200°C for 5 hours. After calcination, the material was cooled to ≤50°C before being discharged. The discharged material is screened for iron removal and packaged to obtain lithium supplement. The screening is carried out using a 100-mesh sieve, and the iron removal is carried out using an electromagnetic iron separator. Screening, iron removal and packaging are all carried out in a constant temperature and humidity room, with humidity controlled at ≤10% and temperature at 25±5℃.

[0160] The main components of barium sulfide and lithium sulfate are ≥99.5% (by mass fraction), the content of magnetic foreign matter is less than 1 ppm, and the molar ratio of added barium sulfide, lithium sulfate, reducing agent and lithium hydroxide is 1:1.0:0.05:0.02. In the lithium supplement, the molar ratio of lithium sulfide to sodium sulfide is 1:0.29.

[0161] Example 3

[0162] The preparation method of the lithium supplement provided in Example 3 is as follows:

[0163] Barium sulfide, lithium sulfate, and methanol were mixed and stirred at 60°C for 60 min to obtain a precipitate and a first reaction solution. The mixture was filtered, and 30% (mass fraction) hydrazine hydrate and battery-grade lithium hydroxide were added to the first reaction solution. Sodium sulfide (second sulfide) was then added, and the mixture was stirred until dissolved. The solution was then precisely filtered using a 50 nm filter. The resulting filtrate was concentrated under vacuum at 80°C until the final concentrate had a Baumé degree of 50. The concentrate was then cooled to 25°C at a rate of 15°C / h. The obtained crystals were centrifuged and dried, then washed with anhydrous methanol in an amount three times the volume of the crystals. They were then dried under vacuum or nitrogen protection at 80°C for 3 hours, stopping when the methanol content in the crystals was below 0.3% (mass fraction), yielding a sulfide composite material. After drying, the sulfide composite material was mixed with graphene at a mass ratio of 95:5 for 2 hours, with ceramic balls added during the mixing process for grinding until the particle size was 10 μm. After grinding, the material was calcined in a nitrogen-protected furnace. During calcination, the nitrogen flow rate was controlled to maintain a furnace humidity below 0.1%, an oxygen content below 1 ppm, and a furnace pressure of 400 Pa. Exhaust gas was exhausted through a blower. The calcination temperature was 300°C for 8 hours. After calcination, the material was cooled to ≤50°C before being discharged. The discharged material is screened for iron removal and packaged to obtain lithium supplement. The screening is carried out using a 200-mesh sieve, and the iron removal is carried out using an electromagnetic iron separator. Screening, iron removal and packaging are all carried out in a constant temperature and humidity room, with humidity controlled at ≤10% and temperature at 25±5℃.

[0164] The main components of barium sulfide and lithium sulfate are ≥99.5% (by mass fraction), the content of magnetic foreign matter is less than 1 ppm, and the molar ratio of added barium sulfide, lithium sulfate, reducing agent and lithium hydroxide is 1:1.1:0.1:0.05. In the lithium supplement, the molar ratio of lithium sulfide to sodium sulfide is 1:0.1.

[0165] Example 4

[0166] The preparation method of the lithium supplement provided in Example 4 is the same as that of the lithium supplement provided in Example 1, except that:

[0167] The molar ratio of added barium sulfide, lithium sulfate, reducing agent and lithium hydroxide is 1:0.9:0.05:0.02.

[0168] Example 5

[0169] The preparation method of the lithium supplement provided in Example 5 is the same as that of the lithium supplement provided in Example 1, except that:

[0170] The molar ratio of added barium sulfide, lithium sulfate, reducing agent and lithium hydroxide is 1:1.0:0.04:0.02.

[0171] Example 6

[0172] The preparation method of the lithium supplement provided in Example 6 is the same as that of the lithium supplement provided in Example 1, except that:

[0173] The molar ratio of added barium sulfide, lithium sulfate, reducing agent and lithium hydroxide is 1:1.0:0.05:0.01.

[0174] Example 7

[0175] The preparation method of the lithium supplement provided in Example 7 is the same as that of the lithium supplement provided in Example 1, except that:

[0176] The reducing agent is replaced with sodium sulfite instead of hydrazine hydrate.

[0177] Example 8

[0178] The preparation method of the lithium supplement provided in Example 8 is the same as that of the lithium supplement provided in Example 1, except that:

[0179] Replace lithium hydroxide with sodium hydroxide.

[0180] Example 9

[0181] The preparation method of the lithium supplement provided in Example 9 is the same as that of the lithium supplement provided in Example 1, except that:

[0182] The molar ratio of barium sulfide to sodium sulfide is 1:0.05.

[0183] Example 10

[0184] The preparation method of the lithium supplement provided in Example 10 is the same as that of the lithium supplement provided in Example 1, except that:

[0185] The molar ratio of barium sulfide to sodium sulfide is 1:0.32.

[0186] Example 11

[0187] The method for preparing the lithium supplement provided in Example 11 is as follows:

[0188] Barium sulfide, lithium sulfate, and methanol were mixed and stirred at 45°C for 45 min to obtain a precipitate and a first reaction solution. The mixture was filtered, and 25% (mass fraction) hydrazine hydrate and battery-grade calcium hydroxide were added to the first reaction solution. Then, calcium sulfide (second sulfide) was added, stirred until dissolved, and then precisely filtered using a 30 nm filter. The resulting filtrate was concentrated under vacuum at 70±1°C until the final concentration reached a Baumé degree of 47.3. The concentrate was then cooled to 20°C at a rate of 13°C / h. The cooled crystals were centrifuged and then washed with anhydrous methanol, the volume of which was five times the volume of the crystals. They were then dried under vacuum or nitrogen protection at 70°C for 5 hours, stopping when the methanol content in the crystals was below 0.3% (mass fraction), yielding a sulfide composite material. After drying, the sulfide composite material was mixed with graphene at a mass ratio of 93:7 for 1.5 hours, with ceramic balls added during the mixing process for grinding until the particle size was 6.1 μm. After grinding, the material was calcined in a nitrogen-protected furnace. During calcination, the nitrogen flow rate was controlled to maintain a furnace humidity below 0.1% and an oxygen content below 1 ppm, with a furnace pressure of 300 Pa. Exhaust gas was exhausted through a blower. The calcination temperature was 250°C for 6 hours. After calcination, the material was cooled to ≤50°C before being discharged. The discharged material is screened for iron removal and packaged to obtain lithium supplement. The screening is carried out using a 150-mesh sieve, and the iron removal is carried out using an electromagnetic iron separator. Screening, iron removal and packaging are all carried out in a constant temperature and humidity room, with humidity controlled at ≤10% and temperature at 25±5℃.

[0189] The main contents of barium sulfide and lithium sulfate are ≥99.5% (by mass fraction), the content of magnetic foreign matter is less than 1 ppm, the molar ratio of added barium sulfide, lithium sulfate, reducing agent and lithium hydroxide is 1:1.05:0.08:0.04, and the molar ratio of lithium sulfide to calcium sulfide is 1:0.18.

[0190] Example 12

[0191] The method for preparing the lithium supplement provided in Example 12 is as follows:

[0192] Barium sulfide, lithium sulfate, and methanol were mixed and stirred at 45°C for 45 min to obtain a precipitate and a first reaction solution. The mixture was filtered, and 25% (mass fraction) hydrazine hydrate and battery-grade potassium hydroxide were added to the first reaction solution. Potassium sulfide (second sulfide) was then added, and the mixture was stirred until dissolved. The solution was then precisely filtered using a 30 nm filter. The resulting filtrate was concentrated under vacuum at 70±1°C until the final concentration reached a Baumé degree of 47.3. The solution was then cooled to 20°C at a rate of 13°C / h. The cooled crystals were centrifuged and then washed with anhydrous methanol, the volume of which was five times the volume of the crystals. They were then dried under vacuum or nitrogen protection at 70°C for 5 hours, stopping when the methanol content in the crystals was below 0.3% (mass fraction), yielding a sulfide composite material. After drying, the sulfide composite material was mixed with graphene at a mass ratio of 93:7 for 1.5 hours, with ceramic balls added during the mixing process for grinding until the particle size was 6.1 μm. After grinding, the material was calcined in a nitrogen-protected furnace. During calcination, the nitrogen flow rate was controlled to maintain a furnace humidity below 0.1% and an oxygen content below 1 ppm, with a furnace pressure of 300 Pa. Exhaust gas was exhausted through a blower. The calcination temperature was 250°C for 6 hours. After calcination, the material was cooled to ≤50°C before being discharged. The discharged material is screened for iron removal and packaged to obtain lithium supplement. The screening is carried out using a 150-mesh sieve, and the iron removal is carried out using an electromagnetic iron separator. Screening, iron removal and packaging are all carried out in a constant temperature and humidity room, with humidity controlled at ≤10% and temperature at 25±5℃.

[0193] The main contents of barium sulfide and lithium sulfate are ≥99.5% (by mass fraction), the content of magnetic foreign matter is less than 1 ppm, the molar ratio of added barium sulfide, lithium sulfate, reducing agent and lithium hydroxide is 1:1.05:0.08:0.04, and the molar ratio of lithium sulfide to potassium sulfide is 1:0.18.

[0194] Comparative Example 1

[0195] The method for preparing the lithium supplement provided in Comparative Example 1 is as follows:

[0196] Barium sulfide, lithium sulfate, and methanol were mixed and stirred at 45°C for 45 min to obtain a precipitate and a first reaction solution. The mixture was filtered, and 25% (mass fraction) hydrazine hydrate and battery-grade lithium hydroxide were added to the first reaction solution. After dissolution by stirring, the solution was precisely filtered using a 30 nm filter. The resulting filtrate was concentrated under vacuum at 70±1°C until the final concentration reached a Baumé degree of 47.3. The solution was then cooled to 20°C at a rate of 13°C / h. The obtained crystals were centrifuged and dried, then washed with anhydrous methanol in an amount five times the volume of the crystals. They were then dried under vacuum or nitrogen protection at 70°C for 5 hours, stopping when the methanol content in the crystals was below 0.3% (mass fraction), yielding lithium sulfide. After drying, lithium sulfide was mixed with graphene at a mass ratio of 93:7 for 1.5 hours, with ceramic balls added during the mixing process for grinding until the particle size was 6.1 μm. After grinding, the material was calcined in a nitrogen-protected furnace. During calcination, the nitrogen flow rate was controlled to maintain a furnace humidity below 0.1% and an oxygen content below 1 ppm, with a furnace pressure of 300 Pa. Exhaust gas was exhausted through a blower. The calcination temperature was 250°C for 6 hours. After calcination, the material was cooled to ≤50°C before being discharged. The discharged material is screened for iron removal and packaged to obtain lithium supplement. The screening is carried out using a 150-mesh sieve, and the iron removal is carried out using an electromagnetic iron separator. Screening, iron removal and packaging are all carried out in a constant temperature and humidity room, with humidity controlled at ≤10% and temperature at 25±5℃.

[0197] The main contents of barium sulfide and lithium sulfate are ≥99.5% (by mass fraction), the content of magnetic foreign matter is less than 1 ppm, and the molar ratio of added barium sulfide, lithium sulfate, hydrazine hydrate and lithium hydroxide is 1:1.05:0.08:0.04.

[0198] Test methods and test results

[0199] 1. Testing of the chemical composition and physicochemical properties of lithium supplements

[0200] The lithium supplements provided in Examples 1-12 and Comparative Example 1 were tested for chemical composition and physicochemical properties. The specific test results are shown in Table 1 below.

[0201] Table 1

[0202] In Table 1 above, the amounts of calcium, magnesium, zinc, copper, nickel, and cobalt in the lithium supplement were determined by inductively coupled plasma atomic emission spectrometry, the amount of barium was determined by sulfuric acid titration, and the content of lithium hydroxide was determined by automatic potentiometric titration.

[0203] In Table 1, the moisture content of the lithium supplement was obtained by the KF method; the magnetic foreign matter in the lithium supplement was collected by a magnet, dissolved in aqua regia, and tested on an atomic absorption spectrometer; the BET specific surface area was obtained by testing with a BET analyzer and nitrogen multi-point adsorption method; the pH value of the lithium supplement was obtained by acid-base potentiometric titration and tested with a pH meter; the D50 particle size was obtained by laser particle size analyzer, and the D50 particle size represents the particle size corresponding to a cumulative volume distribution percentage of 50% for the lithium supplement.

[0204] In Table 1, the method for measuring compacted density is as follows: a compaction density meter is used for testing, the test pressure is 3T, and the compaction time is 30S.

[0205] As shown in Table 1, the D50 particle size of the lithium supplements provided in Examples 1-12 ranges from 3.2 μm to 11.5 μm, with most concentrated between 6.2 μm and 7.2 μm; the specific surface area of ​​the lithium supplements provided in Examples 1-12 is 2 m². 2 / g~10m 2 The values ​​are between / g, and mostly concentrated at 6.1m. 2 / g~6.8m 2 The lithium replenishing agents provided in Examples 1-12 have a compaction density of 2.01 g / mL to 2.15 g / mL, which are suitable for D50 particle size, specific surface area and compaction density, which is beneficial to improving the energy density of the lithium replenishing agent when applied to secondary batteries and providing a better lithium replenishment effect.

[0206] The lithium replenishing agents provided in Examples 1-12 have low magnetic foreign matter content and low moisture content. For example, the magnetic foreign matter content is less than 0.18 ppm, or even as low as 0.12 ppm, and the moisture content is less than 550 ppm, or even as low as 201 ppm. This helps to reduce the performance degradation of the lithium replenishing agent caused by the introduction of magnetic foreign matter and moisture.

[0207] The pH value of the lithium replenishing agents provided in Examples 1-5 and Examples 7-12 is controlled below 12.8, and the content of LiOH can also be basically controlled at the ppm level. This can inhibit the hydrolysis of lithium sulfide to generate LiOH to a certain extent, thereby maintaining a high lithium replenishment effect and avoiding the reduction of the specific capacity during the first charge and discharge.

[0208] The lithium supplement provided in Example 6 has a relatively high LiOH content, reaching 8.70%. This may be because, with a low pH adjuster, the hydrolysis of lithium sulfide during the reaction is difficult to suppress, resulting in the generation of more LiOH, which in turn increases the pH value.

[0209] Comparing Example 4 and Example 1, the Ba element content of the lithium supplement agent increased when the amount of lithium sulfate provided in Example 4 was less, indicating that when the amount of the first lithium source added is less, impurities are easily introduced into the lithium supplement agent.

[0210] Comparing Example 5 and Example 1, when the reducing agent provided in Example 5 was less, the moisture content, pH value and LiOH content of the lithium supplement all increased, indicating that a small amount of lithium sulfide and sodium sulfide were oxidized and hydrolyzed, introducing impurity LiOH.

[0211] Comparing Example 6 and Example 1, when the pH adjuster provided in Example 6 was insufficient, the hydrolysis of lithium sulfide during the reaction was difficult to suppress, resulting in the generation of more LiOH and an increase in pH value.

[0212] Comparing Example 9 and Example 1, when the amount of sodium sulfide provided in Example 9 was insufficient, the moisture content and pH value of the lithium supplement were significantly increased, and the LiOH content also showed an increasing trend. This indicates that the addition of sodium sulfide has an inhibitory effect on both the moisture content and the LiOH content, and can regulate the pH value.

[0213] Comparing Example 10 and Example 1, when the amount of sodium sulfide provided in Example 10 was higher, the pH value and moisture content of the lithium supplement were significantly reduced. At the same time, the LiOH content was also reduced. This also shows that sodium sulfide has a regulatory effect on the pH value, moisture content and LiOH content of the lithium supplement.

[0214] 2. Electrical performance tests of lithium supplements

[0215] (1) The lithium replenishing agents provided in Examples 1-12 and Comparative Example 1 were incorporated into the positive electrode active material to prepare the positive electrode material. The lithium replenishing agent and the positive electrode active material (such as lithium iron phosphate) were mixed at a mass ratio of 3:97 to obtain a mixture. The mixture, SP and PVDF were prepared into a positive electrode material at a mass ratio of 80:10:10 and coated onto the positive electrode current collector. Then, a coin cell was prepared using 1 mol / L lithium hexafluorophosphate as the electrolyte and lithium sheet as the negative electrode. Charge and discharge tests were conducted at a rate of 0.1C (voltage range of 2V to 4.0V). The test results are shown in Table 2 below.

[0216] Table 2

[0217] As shown in Table 2, the lithium replenishing agents provided in Examples 1-12 are composite materials of lithium sulfide and second sulfide. Therefore, the initial charge specific capacity and initial discharge specific capacity of Examples 1-12 are lower than those of Comparative Example 1. Combining Tables 2 and 1, it can be seen that in Examples 1-3, 7-9, and 11-12, when the molar ratio of reducing agent, hydroxide ions in hydroxide, lithium sulfide, and sulfur in second sulfide is (0.05-0.1):(0.02-0.05):(1.0-1.1):(0.1-0.31), the initial charge specific capacity of the lithium replenishing agent provided in this application can be maintained at over 600 mAh / g, which is comparable to that of Comparative Example 1, and the lithium replenishing agent can maintain a good lithium replenishing effect.

[0218] Comparing Example 4 and Comparative Example 1, it can be seen that when the amount of lithium sulfate provided in Example 4 is insufficient, barium sulfide impurities are introduced to a certain extent, and the content of lithium sulfide is reduced, resulting in a certain degree of decrease in the first charge specific capacity and the first discharge specific capacity of the lithium replenishing agent.

[0219] Comparing Example 5 and Comparative Example 1, it can be seen that when the reducing agent provided in Example 5 is insufficient, it causes hydrolysis and oxidation of lithium sulfide and sodium sulfide to a certain extent, reducing the first charge specific capacity and first discharge specific capacity of the lithium replenishment agent.

[0220] Comparing Example 6 and Comparative Example 1, it can be seen that when the amount of lithium hydroxide provided in Example 6 is insufficient, a large amount of lithium sulfide hydrolyzes, generating a large amount of lithium hydroxide, which results in a significant reduction in both the initial charge specific capacity and the initial discharge specific capacity of the lithium replenishing agent.

[0221] (2) The lithium replenishing agents provided in Examples 1 to 12 and the lithium replenishing agent provided in Comparative Example 1 (carbon content of CNT is 8% (mass fraction)) were mixed with lithium iron phosphate at a mass ratio of 3:97. The mixture was then mixed with SP and PVDF at a mass ratio of 90:5:5 to prepare a positive electrode sheet. Then, the other steps were the same as in (1) to prepare a coin cell. The coin cell was first charged at 25°C at a voltage of 2V to 4.0V and 1C, and then discharged at 1C. Starting from the second cycle, the coin cell was cycled at a voltage of 2V to 3.75V. After 100 cycles of 1C charge and discharge at 25°C, the separator was disassembled and the number of black spots on the separator was counted. The number of black spots in Examples 1 to 3 were 1, 1 and 2, respectively. The number of black spots on the separator corresponding to the lithium replenishing agent of lithium sulfide (carbon content of CNT is 8% (mass fraction)) was 23. The dissolved elemental sulfur content in the electrode liquid of the coin cell was measured. The measurement results are shown in Table 3 below.

[0222] Table 3

[0223] As shown in Table 3, the elemental sulfur content in the electrolyte of the coin cells with the lithium replenishing agents provided in Examples 1 to 12 does not exceed 300 ppm, which is much lower than the elemental sulfur content in the electrolyte of Comparative Example 1 (1058 ppm). This indicates that the lithium replenishing agents provided in Examples 1 to 12 can significantly reduce the generation of elemental sulfur, thereby improving the overall battery performance.

[0224] A comparison of the coin cell with the lithium replenishing agent provided in Example 5 and the coin cell with the lithium replenishing agent provided in Example 1 shows that, with less reducing agent provided in Example 5, the hydrolysis and oxidation of lithium sulfide and sodium sulfide are caused to a certain extent, thereby reducing the amount of fixed sulfur element in sodium sulfide, resulting in an increase in the elemental sulfur content in the electrolyte of the coin cell with the lithium replenishing agent provided in Example 5.

[0225] A comparison of the coin cell with the lithium replenishing agent provided in Example 6 and the coin cell with the lithium replenishing agent provided in Example 1 shows that when the amount of lithium hydroxide provided in Example 6 is insufficient, a large amount of lithium sulfide hydrolyzes, and at the same time, some sodium sulfide hydrolyzes as well. As a result, the elemental sulfur content in the electrolyte of the coin cell with the lithium replenishing agent provided in Example 6 is significantly higher than that in the electrolyte of the coin cell with the lithium replenishing agent provided in Example 1.

[0226] A comparison of the coin cell with the lithium replenishing agent provided in Example 9 and the coin cell with the lithium replenishing agent provided in Example 1 shows that when the amount of sodium sulfide provided in Example 9 is relatively small, the proportion of lithium sulfide is relatively large. The small amount of sodium sulfide makes it difficult to fix sulfur to the greatest extent, resulting in an increase in the elemental sulfur content in the electrolyte of the coin cell with the lithium replenishing agent provided in Example 9 compared to the elemental sulfur content in the electrolyte of the coin cell with the lithium replenishing agent provided in Example 1.

[0227] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A lithium supplement, characterized in that, include: A sulfide composite material, the sulfide composite material comprising: a first sulfide and a second sulfide doped in the first sulfide; The first sulfide includes lithium sulfide, and the second sulfide is selected from at least one of metal sulfides other than lithium sulfide and organic sulfides.

2. The lithium supplement agent according to claim 1, characterized in that, The metal sulfide includes at least one of sodium sulfide, calcium sulfide, and potassium sulfide; and / or, The organosulfur compound includes at least one of ammonium sulfide, sodium dithiocarbamate, and potassium sodium dithiocarbamate; and / or, In the sulfide composite material, the mass ratio of the second sulfide to the first sulfide is (60-80):(15-30); and / or, In the sulfide composite material, the molar ratio of sulfur in the second sulfide to that in the first sulfide is (0.1-0.31):(1.0-1.1).

3. The lithium supplement according to claim 1 or 2, characterized in that Also includes: A carbon coating layer, wherein the carbon coating layer is coated on the surface of the sulfide composite material; In the lithium replenishing agent, the carbon coating layer accounts for 5% to 10% of the total mass.

4. The lithium supplement agent according to claim 1 or 2, characterized in that, The lithium supplement has a D50 particle size of 3 μm to 12 μm; and / or, The specific surface area of the lithium supplementing agent is 2 m 2 / g ~ 10 m 2 / g.

5. A method for producing a lithium supplement, characterized by, include: The first lithium source and the first sulfur source are mixed and subjected to a first reaction process to obtain a first reaction solution; The first reaction solution is mixed with a reducing agent, a pH adjuster and a second sulfide, and then subjected to a first purification treatment to obtain a sulfide composite material; The first reaction solution includes a first sulfide, which contains lithium sulfide, and the second sulfide is selected from at least one metal sulfide other than lithium sulfide.

6. The method of claim 5, wherein the lithium supplement is prepared by the steps of: The first purification process includes the following steps: Concentrate the first reaction solution to obtain crystals of the first sulfide and the second sulfide; and / or, The method for preparing the lithium supplement further includes: The crystallized material is subjected to solid-liquid separation, and the separated solid material is washed and dried; and / or, The method for preparing the lithium supplement further includes: The lithium supplement is prepared by mixing carbon materials with the sulfide composite material and subjecting it to a second reaction treatment; and / or The second reaction treatment includes grinding and calcination. The grinding time is 1 to 2 hours, and the calcination is carried out in a protective atmosphere at a temperature of 200°C to 300°C for 5 to 8 hours.

7. The method of claim 6, wherein the lithium supplement is prepared by the steps of: The method for preparing the lithium supplement meets at least one of the following conditions: ​ (1) The temperature of the first reaction treatment is 30℃~60℃ and the time is 30min~60min; (2) The concentration is vacuum concentration, the concentration temperature is 50℃~80℃, and / or the Baume degree of the concentrated solution is 45~50. (3) Cooling the concentrate to obtain crystals of the first sulfide and the second sulfide; (4) The mass ratio of the sulfide composite material to the carbon material is (90-95):(5-10).

8. The process for the preparation of a lithium supplement according to any one of claims 5 to 7, characterized in that, The method for preparing the lithium supplement meets at least one of the following conditions: (1) The first lithium source includes at least one of lithium sulfate, lithium oxalate and lithium carbonate, and the first sulfur source includes at least one of barium sulfide and calcium sulfide. (2) The purity of the first lithium source and the first sulfur source is greater than or equal to 99.5%; (3) The magnetic foreign matter content of the first lithium source and the first sulfur source is less than 1 ppm; (4) The reducing agent includes at least one of hydrazine hydrate and sulfite; (5) The pH adjuster includes hydroxides selected from lithium hydroxide and / or hydroxides of the metals corresponding to the metal sulfide; (6) The carbon material includes: CNT and / or graphene.

9. A positive electrode sheet characterized by comprising: It includes a current collector and a positive electrode material disposed on at least one side of the current collector along its thickness direction, the positive electrode material including the lithium supplement as described in any one of claims 1 to 4.

10. A secondary battery characterized by comprising: Includes positive electrode plate, negative electrode plate and separator; The positive electrode sheet is the positive electrode sheet as described in claim 9.

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