Lithium supplement material, preparation method thereof and secondary battery

Abstract

The invention relates to the technical field of lithium battery materials, in particular to a lithium supplementing material, a preparation method thereof and a secondary battery. The method comprises the following steps: mixing an iron salt solution, a first precipitator and a first complexing agent for precipitation reaction to form an iron core; then adding a dispersing agent and stirring; continuously adding a lithium salt solution, a second precipitator and a second complexing agent, and continuously reacting to obtain reaction slurry containing a lithium shell; according to the method, the iron-based hydroxide with proper granularity is regulated and controlled through wet precipitation, a dispersing agent is used as a core site, the iron-based hydroxide is used as a template to form a lithium carbonate shell on the outside, and a Fe / Li core shell with a controllable structure is formed, so that the problem of non-uniform solid-phase mixing in the preparation process of the lithium supplementing material is solved; further washing and drying the reaction slurry to obtain a precursor material containing a core-shell structure; according to the method, the formation of an impure phase in the sintering process is avoided, and the capacity release after the lithium supplementing material is added into the battery is facilitated.

Description

Technical Field

[0001] This invention relates to the technical field of lithium battery materials, specifically to a lithium replenishment material, its preparation method, and a secondary battery. Background Technology

[0002] Lithium-ion batteries are currently the most promising and fastest-growing rechargeable batteries, possessing numerous advantages such as high specific energy, low self-discharge, good cycle performance, and no memory effect. However, during the first charge and discharge process, a solid electrolyte interphase (SEI) forms at the interface of the negative electrode material. The formation of the SEI is an irreversible process, and the lithium ions (chemical formula: Li+) used to form the SEI cannot be inserted into the positive electrode material during discharge, resulting in a loss of battery capacity.

[0003] Studies have found that the formation of the SEI (Sediment-Insulated Electrode) consumes some lithium ions in the cathode material, leading to irreversible capacity loss. Therefore, this capacity loss can be compensated for by pre-replenishing lithium. Pre-replenishing lithium technology mainly falls into two categories: one is lithium replenishment technology for the anode material, which has high requirements for the operating environment and is difficult to commercialize; the other is lithium replenishment technology for the cathode material, which has relatively lower requirements, is simpler, and the replenishing agent is generally a lithium-rich cathode material with an anti-fluorite structure, such as Li. X MO4 (M = Fe, Co, Mn). Among them, lithium iron ferrite (chemical formula: Li5FeO4) is the preferred choice for lithium supplementation because it has the advantages of simple synthesis process, low material price and high safety of lithium supplementation.

[0004] Currently, lithium iron ferrite (LFP) has poor air stability and easily reacts with water and carbon dioxide in the air to form the LiFeO2 phase. This results in low purity and reduced capacity of LFP, increasing the difficulty of industrial mass production. At the same time, the poor conductivity of LFP limits the capacity release of secondary batteries during high-rate charging. Summary of the Invention

[0005] To address the technical challenge of improving the product quality of lithium iron ferrite as a lithium supplement material, the present invention aims to provide a lithium supplement material, its preparation method, and a secondary battery. The specific technical solution adopted is as follows: In a first aspect, embodiments of the present invention provide a method for preparing a lithium-supplementing material, the method comprising: S1. Iron salt solution, first precipitant and first complexing agent are mixed to carry out precipitation reaction to form iron core; then a dispersant is added and stirred; lithium salt solution, second precipitant and second complexing agent are added and the reaction is continued to obtain a reaction slurry containing a lithium shell, wherein the particle size of the iron core is larger than a preset first target value, the first target value is configured based on the dispersant system of corresponding concentration, so that the iron core adsorbs lithium ions of lithium salt solution to form a lithium shell; S2. The reaction slurry is washed and dried to obtain a precursor material containing a core-shell structure, which consists of iron-based hydroxide, organic carbon and lithium carbonate from the inside out. S3. The precursor material is calcined under an inert protective gas to obtain a lithium supplement material, which is a linkage structure in which carbon grows on the outer surface of lithium iron ferrite.

[0006] In an optional embodiment, step S1 includes: In the first stage, a bottom liquid is reserved in the reactor. Iron salt solution, first precipitant and first complexing agent are introduced into the reactor to precipitate and react to form iron nuclei. Feeding is stopped after the particle size D50 of the iron nuclei reaches the first target value. In the second stage, the dispersant is introduced into the reactor and stirred for a preset time; In the third stage, a lithium salt solution, a second precipitant, and a second complexing agent are added. The reaction is stopped when the molar ratio of lithium ions to iron ions reaches the second target value to obtain a reaction slurry.

[0007] In one optional embodiment, during the first stage of the precipitation reaction, the pH of the reaction system is controlled to be 8-11; the temperature to be 30-70°C; the stirring speed to be 200-1500 rpm; the ammonia concentration to be 1-20 g / L; and the first target value D50 to be 0.5-10 μm.

[0008] In one alternative embodiment, the dispersant includes one of polyvinyl alcohol, polyvinylpyrrolidone, methylcellulose, carboxymethylcellulose, polyethylene, polypropylene, and polystyrene.

[0009] In one optional embodiment, the pH of the reaction system in the third stage is controlled to be 7.5~10.5, the temperature to be 40~70℃, the stirring speed to be 200~1000rpm, and the ammonia concentration to be 0~10g / L.

[0010] In an optional embodiment, in step S1, the iron salt solution and the lithium salt solution are introduced into the reaction vessel at a molar ratio of iron ions to lithium ions of 1:5 to 5.5.

[0011] In an optional embodiment, in step S1, the metal ion concentration of the iron salt solution is 0.5~5 mol / L; the solution concentration of the first precipitant is 0.1~40 mol / L; and the solution concentration of the first complexing agent is 0.1~1 mol / L.

[0012] In one optional embodiment, the first precipitant is one of sodium hydroxide, lithium hydroxide solution, and potassium hydroxide; the second precipitant is one of sodium carbonate, potassium carbonate, sodium bicarbonate, oxalic acid, and sodium oxalate; and both the first and second complexing agents are one of ammonia, sodium citrate, disodium ethylenediaminetetraacetate, and imidazole.

[0013] Secondly, embodiments of the present invention also provide a lithium replenishment material, which is prepared by any of the preparation methods described in the first aspect.

[0014] Thirdly, embodiments of the present invention also provide a secondary battery, which includes the lithium replenishment material of the second aspect.

[0015] The present invention has the following beneficial effects: 1. This invention involves mixing an iron salt solution, a first precipitant, and a first complexing agent to form an iron core through a precipitation reaction; subsequently, a dispersant is added and stirred; then, a lithium salt solution, a second precipitant, and a second complexing agent are added, and the reaction continues to obtain a reaction slurry containing a lithium shell. This step uses wet precipitation to control the particle size of iron-based hydroxides, using the dispersant as core sites and the iron-based hydroxides as templates to form a lithium carbonate shell on the outside, forming a controllable Fe / Li core-shell structure, overcoming the problem of uneven solid-phase mixing during the preparation of lithium-replenishing materials; further, the reaction slurry is washed and dried to obtain a precursor material containing a core-shell structure; the precursor material is calcined under an inert protective gas to obtain the lithium-replenishing material. Because the method can ensure uniform solid-phase mixing and avoid the formation of impurity phases during sintering, it is beneficial to the capacity release after the lithium-replenishing material is added to the battery.

[0016] 2. The preparation method of the present invention involves adding a dispersant and stirring after forming an iron-based hydroxide. Based on the uniform adsorption of the dispersant on the iron core, a lithium salt solution is then added to form a lithium shell structure, which allows the lithium shell to diffuse during the subsequent sintering process, forming a linkage structure where carbon grows on the outer surface of lithium-rich lithium iron ferrite. This improves the stability of the lithium supplementation material structure. Lithium-rich lithium iron ferrite is less likely to form a LiFeO2 phase with water and carbon dioxide in the air, thereby greatly extending the storage time of lithium-rich lithium iron ferrite in a humid air environment.

[0017] 3. The preparation method of the present invention can realize the preparation of high-quality lithium-rich lithium iron oxide in a reaction vessel. The preparation method is simple and stable, and it is easy to realize the industrial production of lithium-rich materials, which is conducive to the large-scale application of such materials. Attached Figure Description

[0018] To more clearly illustrate the technical solutions and advantages 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 of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 A flowchart illustrating a method for preparing a lithium supplement material according to an embodiment of the present invention; Figure 2 This is a SEM image of a lithium replenishment material provided in one embodiment of the present invention; Figure 3 This is an XRD pattern of a lithium supplement material provided in one embodiment of the present invention. Detailed Implementation

[0020] To further illustrate the technical means and effects adopted by the present invention to achieve its intended purpose, the following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation, structure, features, and effects of a lithium replenishment material, its preparation method, and a secondary battery according to the present invention. In the following description, different "one embodiment" or "another embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0021] 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 invention pertains.

[0022] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0023] The following description, in conjunction with the accompanying drawings, details a lithium replenishment material, its preparation method, and a specific solution for a secondary battery provided by the present invention.

[0024] Please see Figure 1 , Figure 1 This is a flowchart illustrating a method for preparing a lithium-supplementing material according to an embodiment of the present invention. The preparation method specifically includes: S1. Iron salt solution, first precipitant and first complexing agent are mixed to form iron cores through precipitation reaction; then a dispersant is added and stirred; lithium salt solution, second precipitant and second complexing agent are added to continue the reaction to obtain a reaction slurry containing a lithium shell, wherein the particle size of the iron core is larger than a preset first target value, the first target value is configured based on the dispersant system of corresponding concentration, so that the iron core adsorbs lithium ions from the lithium salt solution to form a lithium shell.

[0025] Specifically, the first precipitant and the first complexing agent can be prepared into a solution. In a reaction vessel, the iron salt solution, the first precipitant, and the first complexing agent are mixed to allow the mixed solution to undergo a precipitation reaction, producing Fe(OH)₂. x x is 2 and 3, meaning the precipitation reaction produces ferric hydroxide and ferrous hydroxide. During the precipitation reaction, samples are taken for analysis to determine the particle size of the iron cores. Once the particle size of the iron cores reaches the preset target value, a dispersant is added and stirred to ensure uniform mixing of the dispersant in the solution where iron cores have been formed. After stirring the dispersant, a lithium salt solution, a second precipitant, and a second complexing agent are added to continue the reaction, resulting in a reaction slurry containing a lithium shell.

[0026] It is understandable that the first target value can be selected based on actual needs. For example, if the iron core particle size is small, the surface energy of the reaction system is large, and the corresponding dispersant concentration will be high; conversely, a lower concentration dispersant system will be configured. The dispersant can form a sufficient adsorption layer on the iron core surface, making the reaction system stable and preventing agglomeration, while not inhibiting the subsequent directional enrichment and deposition growth of lithium ions on the outer surface of the iron core. The smaller the iron core, the larger the specific surface area and the higher the surface energy, requiring a higher dispersant surface coverage to achieve electrostatic or steric stabilization. When the dispersant concentration is fixed, there is a minimum particle size. Below this particle size, the dispersant is difficult to form an adsorption layer, the iron core is prone to agglomeration or excessive occupation of effective sites by the dispersant, resulting in a decrease in the effective adsorption of lithium ions on the iron core surface, and homogeneous deposition in the bulk solution phase, failing to form a dense and continuous lithium shell. Conversely, if the particle size is much larger than required, the diffusion path for downstream shell growth becomes longer, the shell thickness uniformity deteriorates, and the Fe / Li diffusion coupling efficiency of subsequent solid-phase reactions decreases, thereby increasing the risk of local component deviation and impurity phases during sintering.

[0027] In implementation, the first target value can be determined by quantitative dispersant addition and particle size backpropagation. Under the target ionic strength and pH, the adsorption capacity and steady-state potential of the candidate dispersant are titrated to determine the critical adsorption capacity and corresponding concentration required to achieve stable dispersion. Then, the specific surface area of ​​the iron core (estimated by the expected particle size distribution or BET) is used to evaluate whether the dispersant required per unit volume of the system is sufficient to form a continuous adsorption layer. With this as a constraint, the corresponding minimum particle size is solved and used as the first target value.

[0028] It should be noted that the iron salt solution can be prepared as ferric chloride solution, ferric nitrate solution, ferrous sulfate solution, etc., as long as it can undergo a precipitation reaction to generate iron nuclei; no specific restrictions are imposed here. The first precipitant can be prepared as one of sodium hydroxide, lithium hydroxide solution, or potassium hydroxide; the first complexing agent can be prepared as one of ammonia, sodium citrate, disodium ethylenediaminetetraacetate, or imidazole. In step S1, the metal ion concentration of the iron salt solution is 0.5~5 mol / L; the concentration of the first precipitant solution is 0.1~40 mol / L; and the concentration of the first complexing agent solution is 0.1~1 mol / L.

[0029] For example, step S1 includes: In the first stage, a bottom liquid is reserved in the reactor. An iron salt solution, a first precipitant, and a first complexing agent are then introduced into the reactor to precipitate and form iron nuclei. Feeding is stopped once the particle size D50 of the iron nuclei reaches the first target value. The bottom liquid can be hot pure water or a solution prepared from the first precipitant and / or the first complexing agent, as long as the precipitation reaction occurs after each solution is introduced.

[0030] Furthermore, in the first stage of precipitation reaction, firstly, based on the consideration of sufficient precipitation and morphology of nuclear iron ions, the reaction pH is controlled to be >8, preferably 8~11; secondly, based on the consideration of nuclear particle growth state, the ammonia concentration and reaction temperature are controlled to control the primary particle stacking and growth rate, with priority given to controlling the ammonia concentration, as the higher the ammonia concentration, the slower the deposition rate, and the ammonia concentration is 1~20g / L; secondly, the reaction temperature is controlled, as the lower the temperature, the slower the reaction rate, and the relatively finer the primary stacking; thirdly, based on morphology control, the stirring speed is adjusted, within a certain range, the higher the stirring speed, the more rounded the morphology, with the preferred stirring speed being 200~1500rpm.

[0031] In the second stage, the dispersant is introduced into the reactor and stirred for a preset time. The dispersant includes one of polyvinyl alcohol, polyvinylpyrrolidone, methylcellulose, carboxymethylcellulose, polyethylene, polypropylene, and polystyrene. Mechanical stirring is used, and the preset stirring time can be set based on the amount of solution introduced to ensure the dispersant is thoroughly mixed in the solution.

[0032] In the third stage, a lithium salt solution, a second precipitant, and a second complexing agent are added. The reaction is stopped when the molar ratio of lithium ions to iron ions reaches the second target value to obtain a reaction slurry.

[0033] In the third stage, shell growth control is based on the first principle: pH is selected within an appropriate range of 7.5 to 10.5; the second principle is to achieve reasonable core-shell growth by controlling the lithium salt flow rate. Generally, the lower the lithium salt flow rate, the more favorable it is for shell growth. The preferred lithium salt flow rate is 0.5 to 500 L / h. Secondly, the stirring speed is controlled. To achieve uniform core-shell growth, the preferred speed is 200 to 1000 rpm. The third principle is to control the growth rate. The ammonia concentration is prioritized to control the ion deposition rate. The preferred ammonia concentration is 0 to 10 g / L. Secondly, the reaction temperature is controlled. The preferred temperature is 40 to 70℃.

[0034] The second target value can be set to 5-5.5. For example, setting it to 5 means that when preparing the reaction slurry in the reactor, the iron salt solution and lithium salt solution can be introduced into the reactor at a molar ratio of iron ions to lithium ions of 1:5. The lithium salt solution can be prepared as lithium chloride solution, lithium sulfate solution, etc., without specific restrictions. The second precipitant is one of sodium carbonate, potassium carbonate, sodium bicarbonate, oxalic acid, and sodium oxalate. The second complexing agent is also one of ammonia, sodium citrate, disodium ethylenediaminetetraacetate, and imidazole. When considering the washing and sintering losses of lithium ions, the molar ratio of iron ions to lithium ions can be appropriately increased to 1:5.5.

[0035] S2. The reaction slurry is washed and dried to obtain a precursor material containing a core-shell structure, which consists of iron-based hydroxide, organic carbon, and lithium carbonate from the inside out.

[0036] Specifically, the core-shell structure is Fe(OH). x @Organic Carbon@Li₂CO₃, where x is 2 or 3, represents a core-shell structure where lithium carbonate coats organic carbon, and organic carbon coats iron-based hydroxides. The detergent can be one of pure water, alkaline solution, or sodium carbonate solution; the washing equipment can be one of a centrifuge, washing pot, filter press, or vacuum filter; the drying equipment can be one of an oven, tray dryer, freeze dryer, flash dryer, or spray dryer. After washing, drying is performed at a temperature set between 80 and 300°C.

[0037] S3. The precursor material is calcined under an inert protective gas to obtain a lithium supplement material, which is a linkage structure in which carbon grows on the outer surface of lithium iron ferrite.

[0038] Specifically, the inert protective gas is one of argon, helium, and nitrogen, the sintering temperature is set to 700~1200℃, and the sintering time is 1~40h. After calcination of the precursor material, some of the carbon source is converted into carbon material and covers the outer surface of lithium-rich lithium iron ferrite, preventing lithium-rich lithium iron ferrite from combining with water and carbon dioxide in the air to form the LiFeO2 phase.

[0039] Compared to the traditional physical mixing of iron and lithium, this invention generates in-situ iron cores, adds a dispersant to achieve dispersion, and forms organic carbon as adsorption sites to adsorb lithium ions onto the surface of the iron cores, gradually growing to form a lithium shell with a stable structure. During the subsequent sintering process, the organic carbon gradually decomposes at high temperatures to form a carbon layer, and the lithium shell gradually penetrates into the iron core, forming a coating structure. This method solves the problem of inhomogeneity in traditional physical mixing of iron and lithium, as well as the targeting problem that occurs during sintering. This method results in uniform lithium diffusion in the formation of the lithium shell and after subsequent sintering, more uniform iron-lithium mixing, better thermodynamic diffusion, and fewer impurities in the formed product.

[0040] It is understandable that iron nuclei with a particle size larger than a preset threshold are first formed in the reaction system, giving their surfaces strong adsorption sites and charge distribution characteristics. When the lithium salt solution is added, the outer surface of the iron nuclei preferentially adsorbs lithium ions from the solution. Under the combined action of the second precipitant and the second complexing agent, lithium ions are gradually deposited on the outer layer of the iron nuclei, thus forming a uniform lithium shell. Since this lithium shell grows from the surface of the iron nuclei, it can achieve a gradual coverage "from the inside out," ensuring that lithium elements are uniformly distributed on the outer layer of the iron nuclei at the microscale, rather than exhibiting large agglomerations or uneven deposition.

[0041] Compared to traditional physical mixing, this invention achieves in-situ growth of lithium to form a lithium shell. The mixing of iron and lithium is no longer limited by the uneven mixing caused by concentration differences resulting from physical stirring. The core-shell structure of this invention plays a stabilizing role during calcination. The iron core, as the inner core, maintains the integrity of the particle skeleton, allowing iron and lithium to achieve uniform solid solution through a shorter diffusion path during high-temperature reaction. The outer organic carbon is transformed into a carbon phase during calcination. This method of sequentially growing the lithium shell from the iron core outward not only improves the mixing uniformity of iron and lithium in the precursor but also effectively reduces the formation of impurity phases caused by local concentration differences during sintering. Ultimately, a composite structure of lithium-rich lithium iron ferrite and carbon is obtained, thereby improving the structural stability and electrochemical performance of the lithium supplementation material.

[0042] Based on the same technical concept as the preparation method, this embodiment of the invention also provides a lithium replenishment material, which is prepared by any of the preparation methods.

[0043] Based on the same technical concept as the preparation method, embodiments of the present invention also provide a secondary battery, which includes the above-mentioned lithium replenishment material.

[0044] The technical solution of the present invention will be described in detail below through specific embodiments and comparative examples.

[0045] Example 1: The preparation of lithium supplementation materials includes the following steps: (1) Add 20L of hot water and 32% alkaline solution to a 50L reactor as the base liquid, adjust the pH of the base liquid to 8, and control the temperature inside the reactor to 50℃.

[0046] (2) In the first stage, a 2 mol / L ferric chloride solution was prepared, and ferric chloride solution, 32% alkaline solution and 8w% ammonia water were introduced into the reaction vessel. The flow rate of the ferric chloride solution was 2 L / h, the pH value of the reaction system was 7.5~9.0, the ammonia concentration was 5~7 g / L, the stirring speed was 600 rpm, and the temperature of the reaction system was 60℃. When the D50 of the precipitated particles was 5.0 μm, the second stage was started. In the second stage, the stirring speed was increased to 1000 rpm, a 10 w% carboxymethyl cellulose solution was introduced, and the third stage was carried out after stirring for 2 hours. In the third stage, a 4 mol / L lithium chloride solution was prepared, and lithium chloride solution, 2 mol / L sodium carbonate solution, and 8 w% ammonia water were introduced into the reactor. The flow rate of the lithium chloride solution was 1 L / h, the pH value of the reaction system was 10.0~11.0, the ammonia concentration was 1~3 g / L, the stirring speed was 500 rpm, and the temperature of the reaction system was 55℃. When the Li / Fe molar ratio introduced into the reactor reached 5, the reaction was terminated.

[0047] (3) After the reaction is complete, wash the product using a filter press and then spray dry it at 200°C to obtain Fe(OH). x @Organic carbon@Li2CO3 precursor material.

[0048] (4) The precursor from step (3) was calcined at 800°C for 20 hours under argon protection to obtain a lithium supplement material with carbon coating on lithium iron ferrite.

[0049] Example 2: The preparation of lithium supplementation materials includes the following steps: (1) Add 40L of hot water and 32% alkaline solution to a 100L reactor as the base liquid, adjust the pH of the base liquid to 9, and control the temperature inside the reactor to 60℃.

[0050] (2) In the first stage, a 2 mol / L ferric sulfate solution was prepared, and ferric sulfate solution, 32% alkaline solution and 8w% ammonia water were introduced into the reaction vessel. The flow rate of the ferric sulfate solution was 10 L / h, the pH value of the reaction system was 9.0~10.0, the ammonia concentration was 3~4 g / L, the stirring speed was 400 rpm, and the temperature of the reaction system was 60℃. When the D50 of the precipitate particles was 4.0 μm, the second stage was started. In the second stage, the stirring speed was increased to 600 rpm, a 5 w% polyvinylpyrrolidone solution was introduced, and the third stage was carried out after stirring for 3 hours. In the third stage, a 4 mol / L lithium sulfate solution was prepared, and lithium sulfate solution, 2 mol / L sodium carbonate solution, and 8 w% ammonia water were introduced into the reactor. The flow rate of the lithium salt solution was 2 L / h, the pH value of the reaction system was 10.0~11.0, the ammonia concentration was 1~3 g / L, the stirring speed was 500 rpm, and the temperature of the reaction system was controlled at 55℃. When the Li / Fe molar ratio introduced into the reactor reached 5, the reaction was terminated.

[0051] (3) After the reaction is complete, Fe(OH) is obtained by washing with a filter press and freeze-drying. x @Organic carbon@Li2CO3 precursor materials.

[0052] (4) The precursor from step (3) was calcined at 850°C for 15 hours under nitrogen protection to obtain a lithium supplement material with carbon coating on lithium iron ferrite.

[0053] Example 3: The preparation of lithium supplementation materials includes the following steps: (1) Add 100L of hot water and 32% alkaline solution to a 200L reactor as the base liquid, adjust the pH of the base liquid to 10, and control the temperature inside the reactor to 60℃.

[0054] (2) In the first stage, a 2 mol / L ferric nitrate solution was prepared, and ferric nitrate solution, 32% alkaline solution and 8w% ammonia water were introduced into the reaction vessel. The flow rate of the ferric nitrate solution was 10 L / h, the pH value of the reaction system was 10.0~11.0, the ammonia concentration was 6~7 g / L, the stirring speed was 300 rpm, and the temperature of the reaction system was 60℃. When the D50 of the precipitate particles was 3.0 μm, the second stage was started. In the second stage, the stirring speed was increased to 500 rpm, a 15 w% polyvinyl alcohol solution was introduced, and the mixture was stirred for 3 hours before proceeding to the third stage. In the third stage, a 4 mol / L lithium nitrate solution was prepared, and lithium nitrate solution, 2 mol / L sodium carbonate solution, and 8 w% ammonia water were introduced into the reactor. The flow rate of the lithium salt solution was 10 L / h, the pH value of the reaction system was 10.0~11.0, the ammonia concentration was 1~3 g / L, the stirring speed was 600 rpm, and the temperature of the reaction system was 55℃. When the Li / Fe molar ratio introduced into the reactor reached 5, the reaction was terminated.

[0055] (3) After the reaction is complete, Fe(OH) is obtained by washing in a washing pot and spray drying at 180°C. x @Organic carbon@Li2CO3 precursor materials.

[0056] (4) The precursor from step (3) was calcined at 900°C for 10 hours under nitrogen protection to obtain a lithium supplement material with carbon coating on lithium iron ferrite.

[0057] Example 4: The preparation of lithium supplementation materials includes the following steps: (1) Add 150L of hot water and 32% alkaline solution to a 500L reactor as the base liquid, adjust the pH of the base liquid to 10, and control the temperature inside the reactor to 60℃.

[0058] (2) In the first stage, a 2 mol / L ferric chloride solution was prepared, and ferric chloride solution, 32% alkaline solution and 8w% ammonia water were introduced into the reaction vessel. The flow rate of the ferric chloride solution was 10 L / h, the pH value of the reaction system was 10.0~11.0, the ammonia concentration was 6~7 g / L, the stirring speed was 300 rpm, and the temperature of the reaction system was 60℃. When the D50 of the precipitated particles was 8.0 μm, the second stage was started. In the second stage, the stirring speed was increased to 500 rpm, a 10 w% polyvinyl alcohol solution was introduced, and the third stage was carried out after stirring for 3 hours. In the third stage, a 4 mol / L lithium chloride solution was prepared, and lithium chloride solution, 2 mol / L ammonium bicarbonate solution, and 8 w% ammonia water were introduced into the reactor. The flow rate of the lithium salt solution was 20 L / h, the pH value of the reaction system was 10.0~11.0, the ammonia concentration was 1~3 g / L, the stirring speed was 600 rpm, and the temperature of the reaction system was 55℃. When the Li / Fe molar ratio introduced into the reactor reached 5, the reaction was terminated.

[0059] (3) After the reaction is complete, Fe(OH) is obtained by washing with a centrifuge and spray drying at 200℃. x @Organic carbon@Li2CO3 precursor materials.

[0060] (4) The precursor from step (3) was calcined at 1000°C for 8 hours under nitrogen protection to obtain a lithium supplement material with carbon coating on lithium iron ferrite.

[0061] Example 5: The preparation of lithium supplementation materials includes the following steps: (1) 10m 3 Add 6m to the reactor 3 Hot water and a 32% alkaline solution were used as the base solution. The pH of the base solution was adjusted to 8, and the temperature inside the reactor was controlled at 55°C.

[0062] (2) In the first stage, a 2 mol / L ferrous sulfate solution was prepared, and ferrous sulfate solution, 32% alkaline solution and 8w% ammonia water were introduced into the reaction vessel. The flow rate of the ferrous sulfate solution was 10 L / h, the pH value of the reaction system was 10.0~11.0, the ammonia concentration was 6~7 g / L, the stirring speed was 150 rpm, and the temperature of the reaction system was 60℃. When the D50 of the precipitate particles was 10.0 μm, the second stage was started. In the second stage, the stirring speed was increased to 200 rpm, an 8% polyvinyl alcohol solution was introduced, and the third stage was carried out after stirring for 3 hours. In the third stage, a 4 mol / L lithium sulfate solution was prepared, and lithium sulfate solution, 2 mol / L ammonium bicarbonate solution, and 8 w% ammonia water were introduced into the reactor. The flow rate of the lithium salt solution was 100 L / h, the pH value of the reaction system was 10.0~11.0, the ammonia concentration was 1~3 g / L, the stirring speed was 230 rpm, and the temperature of the reaction system was 55℃. The reaction was terminated when the Li / Fe molar ratio introduced into the reactor reached 5.

[0063] (3) After the reaction is complete, Fe(OH) is obtained by washing with a centrifuge and drying in a continuous oven at 180°C. x @Organic carbon@Li2CO3 precursor materials.

[0064] (4) The precursor from step (3) was calcined at 1000°C for 8 hours under nitrogen protection to obtain a lithium supplement material with carbon coating on lithium iron ferrite.

[0065] Comparative Example 1: The preparation of lithium supplementation materials includes the following steps: (1) Li:Fe Weigh lithium hydroxide and iron oxide in a stoichiometric ratio of 5.02:1 and grind them in a ball mill for 5 hours.

[0066] (2) The ground sample was placed in a crucible and calcined at 800°C for 20 hours under argon protection to obtain the lithium supplement material Li5FeO4.

[0067] Comparative Example 2: The preparation of lithium supplementation materials includes the following steps: (1) Li:Fe Weigh lithium hydroxide and iron oxide in a stoichiometric ratio of 5.02:1, weigh 5w% glucose together and grind them in a ball mill for 5h.

[0068] (2) The ground sample was placed in a crucible and calcined at 800°C for 20 hours under argon protection to obtain the lithium supplement material Li5FeO4@C.

[0069] Please see Figure 2 , Figure 2 The image shows a SEM image of the lithium replenishment material prepared in Example 1. As can be seen from the image, the lithium replenishment material has a linked structure where carbon is grown on the outer surface of lithium iron phosphate. With this structure, the capacity of the lithium replenishment material is more easily released after being added to the battery, thus achieving a better lithium replenishment effect.

[0070] Please see Figure 3 , Figure 3The image shows the XRD pattern of the lithium replenishment material prepared in Example 1. X-ray diffraction analysis was performed on the lithium replenishment material prepared in Example 1. The horizontal axis represents twice the diffraction angle; the vertical axis represents the diffraction intensity, reflecting the strength of the diffraction signal at that angle. The image shows that the lithium replenishment material contains fewer impurity phases, indicating good preparation quality.

[0071] To further verify the lithium replenishment effect of the lithium replenishment material proposed in the embodiments of the present invention, the lithium replenishment material was added to the battery and a charge-discharge test was carried out. The test results are shown in Table 1.

[0072] Table 1

[0073] As can be seen from the data in Table 1, the lithium replenishing materials prepared by the methods used in Examples 1-5 of this invention, after being added to the battery, showed no significant capacity decay after 24-48 hours of 0.1C charging, and the capacity remained similar to that of the initial charge, indicating that the capacity of the lithium replenishing materials was fully released and achieved a good lithium replenishment effect. In contrast, the lithium replenishing material prepared by the method in Comparative Example 1 showed a significant capacity decay after 24 hours, failing to achieve a good lithium replenishment effect. The composite lithium replenishing material prepared in Comparative Example 2 showed less capacity decay after 24 hours, indicating that carbon coating was effective; however, the significant capacity decay after 36 hours showed that the carbon coating effect of this process was far inferior to that of the examples.

[0074] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of the present invention.

Claims

1. A method for preparing a lithium-supplementing material, characterized in that, The method includes: S1. Iron salt solution, first precipitant and first complexing agent are mixed to carry out precipitation reaction to form iron core; then a dispersant is added and stirred; lithium salt solution, second precipitant and second complexing agent are added and the reaction is continued to obtain a reaction slurry containing a lithium shell, wherein the particle size of the iron core is larger than a preset first target value, the first target value is configured based on the dispersant system of corresponding concentration, so that the iron core adsorbs lithium ions of the lithium salt solution to form a lithium shell; S2. The reaction slurry is washed and dried to obtain a precursor material containing a core-shell structure, wherein the core-shell structure consists of iron-based hydroxide, organic carbon and lithium carbonate from the inside out. S3. The precursor material is calcined under an inert protective gas to obtain a lithium-replenishing material, wherein the lithium-replenishing material is a linkage structure in which carbon grows on the outer surface of lithium iron ferrite.

2. The method for preparing the lithium-supplementing material according to claim 1, characterized in that, Step S1 includes: In the first stage, a bottom liquid is reserved in the reactor, and the iron salt solution, the first precipitant and the first complexing agent are introduced into the reactor to precipitate and react to form iron nuclei. Feeding is stopped after the particle size D50 of the iron nuclei reaches the first target value. In the second stage, the dispersant is introduced into the reaction vessel and stirred for a preset time; In the third stage, the lithium salt solution, the second precipitant, and the second complexing agent are added, and the reaction is stopped when the molar ratio of lithium ions to iron ions reaches the second target value to obtain the reaction slurry.

3. The method for preparing the lithium-supplementing material according to claim 2, characterized in that, During the precipitation reaction in the first stage, the pH of the reaction system is controlled to be 8~11; the temperature to be 30~70℃; the stirring speed to be 200~1500rpm; the ammonia concentration to be 1~20g / L; and the first target value D50 to be 0.5~10μm.

4. The method for preparing the lithium-supplementing material according to claim 2, characterized in that, The dispersant includes one of polyvinyl alcohol, polyvinylpyrrolidone, methylcellulose, carboxymethylcellulose, polyethylene, polypropylene, and polystyrene.

5. The method for preparing the lithium-supplementing material according to claim 2, characterized in that, In the third stage, the pH of the reaction system is controlled at 7.5~10.5, the temperature at 40~70℃, the stirring speed at 200~1000rpm, and the ammonia concentration at 0~10g / L.

6. The method for preparing the lithium-supplementing material according to claim 1, characterized in that, In step S1, the iron salt solution and the lithium salt solution are introduced into the reaction vessel at a molar ratio of iron ions to lithium ions of 1:5~5.

5.

7. The method for preparing the lithium-supplementing material according to claim 1, characterized in that, In step S1, the concentration of metal ions in the iron salt solution is 0.5~5 mol / L; the concentration of the first precipitant solution is 0.1~40 mol / L; and the concentration of the first complexing agent solution is 0.1~1 mol / L.

8. The method for preparing the lithium-supplementing material according to claim 1, characterized in that, The first precipitant is one of sodium hydroxide, lithium hydroxide solution, and potassium hydroxide; the second precipitant is one of sodium carbonate, potassium carbonate, sodium bicarbonate, oxalic acid, and sodium oxalate; the first complexing agent and the second complexing agent are both one of ammonia, sodium citrate, disodium ethylenediaminetetraacetate, and imidazole.

9. A lithium supplementation material, characterized in that, The lithium replenishing material is prepared by any one of the preparation methods described in claims 1 to 8.

10. A secondary battery, characterized in that, The secondary battery includes the lithium replenishment material as described in claim 9.

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