Method for preparing basic lithium iron phosphate from waste lithium iron phosphate cathode powder and regenerating lithium iron phosphate

Abstract

The application belongs to the technical field of waste lithium battery positive electrode material recycling, and specifically discloses a method for preparing basic lithium iron phosphate from waste lithium iron phosphate positive electrode powder, which comprises the following steps: subjecting the waste lithium iron phosphate positive electrode powder to acid leaching treatment, and performing solid-liquid separation to obtain a leaching solution; subjecting the leaching solution to oxidation treatment, and then performing precipitation treatment with sodium hydroxide, and performing solid-liquid separation to obtain a lithium solution and iron-phosphorus slag; subjecting the slurry formed by slurrying the iron-phosphorus slag and a lithium source to hydrothermal treatment at a temperature of 200 DEG C or above to obtain the basic lithium iron phosphate. The application also comprises a scheme for preparing lithium iron phosphate by mixing and reacting the basic lithium iron phosphate and a carbon source. The scheme can obtain basic lithium iron phosphate with high phase purity, and further can prepare regenerated lithium iron phosphate material with better performance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of recycling waste lithium battery positive electrode materials, and particularly relates to the field of recycling and regenerating waste lithium iron phosphate positive electrode powder. BACKGROUND

[0002] As a typical lithium ion battery positive electrode material, lithium iron phosphate has the characteristics of structural stability, long cycle life and low cost, and is widely used in electric vehicles and energy storage systems. In recent years, with the rise in prices of transition metals nickel, cobalt and manganese and the popularization and application of blade batteries, the market share of lithium iron phosphate has been increasing, which has also led to an increase in the number of waste lithium iron phosphate batteries year by year. Compared with lithium cobaltate and nickel-cobalt-manganese lithium batteries, although lithium iron phosphate batteries have lower resource and environmental hazards, improper disposal can still cause resource waste and environmental pollution.

[0003] As the component with the highest content in waste lithium iron phosphate batteries, the recycling of lithium iron phosphate positive electrode waste has great recycling value. Wet recycling is the mainstream process for recycling lithium iron phosphate positive electrode waste, including leaching and regeneration processes. Most wet recycling processes leach lithium iron phosphate positive electrode waste, and then obtain lithium carbonate and iron phosphate products through a step-by-step precipitation method. Finally, the recycled lithium carbonate and iron phosphate are mixed and solid-phase sintered to regenerate lithium iron phosphate. This method realizes the closed-loop recycling of lithium iron phosphate, but the solid-phase sintering method for preparing lithium iron phosphate has high requirements for the morphology and composition of iron phosphate, which means that the regeneration process is difficult to control and the cost is high. Another wet recycling process is to leach lithium, iron and phosphorus in lithium iron phosphate positive electrode waste into the solution at the same time, and then adjust the pH value of the leaching solution to regenerate lithium iron phosphate by a hydrothermal method. This method avoids the preparation process of iron phosphate, but in order to ensure the purity of the regenerated lithium iron phosphate, three times the stoichiometric amount of lithium needs to be added in the hydrothermal process. Although the remaining lithium after the hydrothermal reaction can be further recycled, the entire process is still complex. Therefore, under the premise of preparing pure-phase lithium iron phosphate, it is urgent to develop a more efficient wet recycling process while reducing lithium consumption. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application aims to provide a method for preparing alkali lithium iron phosphate from waste lithium iron phosphate positive electrode powder, which aims to prepare alkali lithium iron phosphate from waste lithium iron phosphate and improve the phase purity thereof.

[0005] The second object of the present application is to provide a method for regenerating waste lithium iron phosphate positive electrode powder, which aims to prepare alkali lithium iron phosphate from waste lithium iron phosphate positive electrode powder and further regenerate it into lithium iron phosphate material.

[0006] A method for preparing alkali lithium iron phosphate from waste lithium iron phosphate positive electrode powder, which comprises the following steps: subjecting the waste lithium iron phosphate positive electrode powder to acid leaching treatment to obtain a leaching solution through solid-liquid separation;

[0007] The leaching solution is subjected to oxidation, alkali precipitation, solid-liquid separation to obtain a lithium solution and an iron-phosphorus residue; the slurry formed by the iron-phosphorus residue and a lithium source is subjected to hydrothermal treatment at a temperature of 200 DEG C or above to obtain an iron lithium phosphate hydroxide.

[0008] The waste lithium iron phosphate positive electrode powder is subjected to leaching and then oxidation treatment, and then subjected to precipitation treatment with an alkali solution, and further combined with subsequent hydrothermal treatment and joint control of hydrothermal reaction parameters such as temperature, so that the waste lithium iron phosphate positive electrode powder can be used to prepare the iron lithium phosphate hydroxide, and through optimization of the hydrothermal reaction parameters, the phase purity and crystallinity of the iron lithium phosphate hydroxide can be further synergistically controlled. Further, the regenerated lithium iron phosphate formed by the prepared iron lithium phosphate hydroxide can obtain a regenerated lithium iron phosphate material with better electrochemical performance.

[0009] In the present application, the joint of the oxidation, alkali precipitation and subsequent hydrothermal reaction parameters of the acid leaching solution is the key to successfully inducing the iron lithium phosphate hydroxide and further improving the phase purity, crystallinity and electrochemical performance.

[0010] In the present application, the waste lithium iron phosphate positive electrode powder can be obtained by known methods, for example, it can be a positive electrode material obtained by stripping from a waste lithium iron phosphate battery positive electrode sheet;

[0011] In the present application, the content of the lithium iron phosphate active material in the waste lithium iron phosphate positive electrode powder is not particularly required, and considering the economic benefits of the recycling process, the content of the active material can be 60-95 wt.%, in addition, the positive electrode powder can also contain at least one of a conductive agent, a binder, a separator and an electrolyte.

[0012] In the present application, the acid solution in the acid leaching stage is an aqueous solution of a strong inorganic acid;

[0013] In the present application, the strong inorganic acid is at least one of hydrochloric acid and sulfuric acid;

[0014] In the present application, the concentration of the strong inorganic acid in the acid solution is not particularly required, and considering the processing cost, it can be 1-5 M, and further can be 2-3 M;

[0015] In the present application, a reducing agent can also be added in the acid leaching stage; the reducing agent can be any component that can avoid oxidation of divalent iron, for example, at least one of ascorbic acid and citric acid; the amount of the reducing agent can be adjusted as needed, for example, the amount is 5-10 wt.% of the waste lithium iron phosphate positive electrode powder.

[0016] In the present application, the liquid-solid ratio in the acid leaching stage can be adjusted as needed, and considering the processing cost, for example, it can be 5-20 mL / g, and further can be 5-10 mL / g;

[0017] In the present application, the temperature and time of the acid leaching stage can be adjusted according to conventional principles, for example, when the temperature is lower, the time can be generally extended to obtain the desired leaching effect, and considering the preparation efficiency, the temperature of the acid leaching stage can be 50-80℃. The time of the acid leaching stage is 1-3h.

[0018] In the present application, an oxidizing agent is added to the leaching solution for oxidation treatment. The oxidizing agent is a component that can oxidize Fe 2+ to Fe 3+ , for example, at least one of hydrogen peroxide and an oxidizing atmosphere.

[0019] In the present application, the amount of the oxidizing agent is not less than the theoretical amount required to oxidize Fe 2+ in the leaching solution to Fe 3+ , and considering the processing cost, it can be 1-10 times the theoretical amount.

[0020] In the present application, after the leaching solution is subjected to oxidation treatment, a basic substance or a basic solution thereof is added for the basic precipitation treatment.

[0021] In the present application, the basic substance used in the basic precipitation stage is at least one of sodium hydroxide, potassium hydroxide, and aqueous ammonia, and sodium hydroxide is preferred. The present application shows that using sodium hydroxide for basic precipitation treatment can improve the phase purity and crystallinity of the lithium iron phosphate hydroxide, which is helpful to further improve the phase and crystallinity of the regenerated lithium iron phosphate, and further improve the electrochemical performance of the regenerated lithium iron phosphate.

[0022] In the present application, the concentration of the basic solution is not particularly limited, and considering the processing efficiency and cost, it can be 0.01-5M, and further can be 0.1M to saturated concentration.

[0023] In the present application, the basic substance is used to control the pH of the basic precipitation reaction, and preferably, the pH at the end of the basic precipitation reaction is stabilized at 2-4, and further can be 2.8-3.2.

[0024] In the present application, the iron-phosphorus slag is a composite of iron phosphate and a small amount of iron hydroxide. In the present application, the iron-phosphorus slag and the lithium source are further subjected to a hydrothermal reaction, and the combined control of the hydrothermal reaction parameters can induce the formation of lithium iron phosphate hydroxide phase, and improve the phase purity and crystallinity.

[0025] In the present application, the lithium source can be a material capable of providing lithium known in the industry, for example, a material containing at least one of lithium hydroxide, lithium phosphate, lithium carbonate. Considering the treatment effect and cost, the lithium source used in the present application will be the lithium liquid collected for precipitation treatment to obtain lithium source solids, such as lithium precipitation process with phosphoric acid, lithium precipitation process with carbonization, and then the iron phosphate slag and lithium source are slurried with water.

[0026] In the present application, the molar ratio of Fe / Li in the slurry of the iron phosphate slag and the lithium source is 1:1 to 1.05.

[0027] In the present application, the iron phosphate slag and the lithium source are subjected to hydrothermal treatment, which can obtain basic lithium iron phosphate at a molar ratio close to the theoretical molar ratio of iron and lithium, and finally obtain regenerated lithium iron phosphate.

[0028] In the present application, the temperature, liquid-solid ratio and time of the hydrothermal reaction process are optimized and controlled, which is helpful to further cooperate with the precipitation process of sodium hydroxide, and can further synergistically improve the phase purity and crystallinity of the basic lithium iron phosphate, and then finally improve the phase and crystallinity of the prepared lithium iron phosphate and the electrochemical performance.

[0029] Preferably, the hydrothermal temperature is 220-280℃, and further preferably 225-245℃. It has been found that at the preferred hydrothermal reaction temperature, the phase purity and crystallinity of the basic lithium iron phosphate can be further improved in combination with other process parameters.

[0030] Preferably, the solid-liquid ratio in the slurry is 0.1-3g / mL, preferably 1.8-2.5g / mL, and further preferably 1.9-2.1g / mL. It has been found that at the preferred solid-liquid ratio, the phase purity and crystallinity of the basic lithium iron phosphate can be further improved in combination with other process parameters.

[0031] Preferably, the hydrothermal reaction time is 2-14h, preferably 4-10h, and further preferably 5-7h. It has been found that at the preferred conditions, the phase purity and crystallinity of the basic lithium iron phosphate can be further improved in combination with other process parameters, and then the electrochemical performance of the subsequently prepared material, especially the specific capacity, is improved.

[0032] As a scheme of the same inventive concept, the present application also provides a method for regenerating waste lithium iron phosphate positive electrode powder, which comprises the following steps: preparing basic lithium iron phosphate from waste lithium iron phosphate positive electrode powder by the method of the present application; and compounding and calcining the basic lithium iron phosphate and a carbon source to obtain regenerated lithium iron phosphate.

[0033] In the present application, thanks to the preparation process of basic lithium iron phosphate, further calcination transformation treatment can successfully prepare lithium iron phosphate at a ratio close to the theoretical Fe:Li (1:1), which can reduce the lithium usage by 60% compared to the existing hydrothermal method for preparing lithium iron phosphate. Moreover, it helps to jointly improve the phase purity, grain and electrochemical performance of regenerated lithium iron phosphate.

[0034] In the present application, the carbon source is not particularly required and can be a conventional organic matter capable of providing C, such as at least one of glucose, sucrose, and starch.

[0035] The weight ratio of basic lithium iron phosphate to carbon source is 1:0.1-0.2.

[0036] The atmosphere in the calcination stage is a protective atmosphere.

[0037] The calcination temperature is 500-800℃, and further can be 550-650℃.

[0038] Preferably, the calcination time is 2-14h, preferably 4-10h, and further preferably 5-7h.

[0039] The present application also provides regenerated lithium iron phosphate prepared by the method.

[0040] In the present application, the preparation process can impart special results and surface properties to the regenerated lithium iron phosphate. More importantly, the material with the said characteristics prepared by the preparation method can exhibit better electrochemical performance.

[0041] The present application also provides a lithium ion battery comprising the regenerated lithium iron phosphate of the present application in the positive electrode.

[0042] In the present application, the lithium ion battery can comprise the regenerated lithium iron phosphate of the present application in the positive electrode, and other results, components and ingredients can be conventional in the industry.

[0043] Advantages

[0044] The present application oxidizes the spent lithium iron phosphate leaching solution, precipitates it with sodium hydroxide, further controls the subsequent hydrothermal treatment and hydrothermal reaction parameters, and can prepare basic lithium iron phosphate from spent lithium iron phosphate positive electrode powder. It also helps to improve the phase purity and crystallinity, and further carbonates the calcination to regenerate high-purity lithium iron phosphate with high purity, crystallinity and high electrochemical performance. Compared with the existing hydrothermal method for preparing lithium iron phosphate, the lithium usage can be reduced by 60%. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 shows the XRD patterns of the hydrothermal products obtained at different pH values of the leaching solution. Figure 1 Figure 2 shows the XRD patterns of the hydrothermal products obtained at different solid-liquid ratios.

[0046] Figure 3 shows the XRD patterns of the hydrothermal products obtained at different hydrothermal temperatures. Figure 2 Figure 4 shows the cycle performance of lithium iron phosphate prepared using the lithium iron phosphate hydroxide obtained at different hydrothermal times as the precursor.

[0047] Figure 5 shows the XRD patterns of the hydrothermal products obtained at different hydrothermal times. Figure 3 Figure 6 shows the XRD patterns of the hydrothermal products obtained at different hydrothermal times.

[0048] Figure 4 Figure 7 shows the XRD patterns of the hydrothermal products obtained at different hydrothermal times.

[0049] Figure 8 shows the cycle performance and rate performance of lithium iron phosphate prepared using the lithium iron phosphate hydroxide obtained at different hydrothermal times as the precursor. (a) shows the cycle performance, and (b) shows the rate performance. Figure 5 Figure 9 shows the XRD patterns of the hydrothermal products obtained at different hydrothermal times.

[0050] Figure 6 Figure 10 shows the cycle performance and rate performance of lithium iron phosphate prepared using the lithium iron phosphate hydroxide obtained at different hydrothermal times as the precursor. (a) shows the cycle performance, and (b) shows the rate performance.

[0051] Figure 11 shows the XRD patterns of the hydrothermal products obtained at different hydrothermal times. Figure 7 Figure 12 shows the cycle performance and rate performance of lithium iron phosphate prepared using the lithium iron phosphate hydroxide obtained at different hydrothermal times as the precursor. (a) shows the cycle performance, and (b) shows the rate performance.

[0052] The present application will be described in detail below with reference to specific examples.

[0053] The lithium iron phosphate positive electrode waste material can be obtained from the positive electrode sheet of the waste lithium iron phosphate battery based on known processes, and contains lithium iron phosphate active material, and also allows the presence of conductive agents and adhesive agents and other components. In the following examples, as a typical enumeration, the content of lithium iron phosphate active material in the lithium iron phosphate positive electrode waste material is between 80-90wt%.

[0054] The present application is a method for preparing lithium iron phosphate hydroxide and regenerating lithium iron phosphate from waste lithium iron phosphate positive electrode powder, which comprises the following steps:

[0055] 1) The waste lithium iron phosphate positive electrode powder is added to a dilute sulfuric acid solution for leaching, and after filtration, a leaching solution rich in lithium, iron and phosphate ions is obtained. Then an oxidizing agent is added for oxidation treatment to obtain an oxidation solution;

[0056] 2) The composition of the oxidation solution in step 1 is adjusted using sodium hydroxide to obtain a filter residue rich in iron and phosphorus compounds and a lithium filtrate;

[0057] 3) Lithium phosphate is prepared by adding sodium phosphate to the lithium-rich filtrate and heating and stirring; ​​​

[0058] 4) mixing the residue of 2) and lithium phosphate homogeneously, and obtaining basic lithium iron phosphate through hydrothermal reaction;

[0059] 5) mixing the basic lithium iron phosphate and carbon source such as glucose aqueous solution homogeneously through ultrasonic, and obtaining carbon-coated lithium iron phosphate after drying and calcining.

[0060] In the above treatment method, preferably, the Fe, P and Li contents in the waste lithium iron phosphate positive electrode powder are 23-28%, 12-16% and 3-4% respectively, and the main impurity is graphite, accounting for about 20-30%.

[0061] In the above treatment method, preferably, when the waste lithium iron phosphate positive electrode powder is leached by using dilute sulfuric acid solution, the sulfuric acid concentration in the leaching process is 1-3 mol / L, the solid-liquid ratio of the leaching solution is 5-20 ml / g, the leaching time is 1-3 hours, and the leaching temperature is 50-80℃.

[0062] In step 2), the pH value of the oxidation solution is adjusted to 2-4 by using sodium hydroxide solution as the control end point.

[0063] In the above treatment method, preferably, when the lithium phosphate is precipitated by using sodium phosphate, the amount of sodium phosphate used in the precipitation process is 1-2 times the stoichiometric amount, and the precipitation temperature is 70-95℃. The precipitation time is 1-3 hours.

[0064] 3Li + +Na3PO4=Li3PO4↓+3Na +

[0065] In the above treatment method, preferably, when the basic lithium iron phosphate is prepared through hydrothermal reaction, the reaction temperature is 200-230℃, the solid-liquid ratio is 0.1-3 g / mL, preferably 1.8-2.5 g / mL, and further preferably 1.9-2.1 g / mL, the hydrothermal time is 2-14 h, preferably 4-10 h, and further preferably 5-7 h.

[0066] In the above treatment method, preferably, the mass ratio of the carbon source glucose and the basic lithium iron phosphate is 0.1-0.2:1.

[0067] In the above treatment method, preferably, the basic lithium iron phosphate is calcined at 500-800℃ for 2-10 hours to obtain lithium iron phosphate.

[0068] In the treatment method of the present application, the leaching rates of lithium, iron and phosphorus are greater than or equal to 99%.

[0069] The application provides a method for preparing alkali lithium iron phosphate from waste lithium iron phosphate positive electrode powder and regenerating lithium iron phosphate. First, lithium, iron and phosphorus elements in lithium iron phosphate positive electrode waste are leached into a solution, then iron and phosphorus in the leaching solution are precipitated by adjusting the pH value, and lithium in the filtrate is precipitated in the form of lithium phosphate after filtration. Then, the two precipitates are mixed, alkali lithium iron phosphate is prepared by a hydrothermal method, and finally, lithium iron phosphate is regenerated by taking the alkali lithium iron phosphate as a precursor. The method avoids preparing high-quality iron phosphate, and the phosphorus and iron elements can be used economically and effectively; by introducing alkali lithium iron phosphate, the consumption of lithium is reduced. Compared with the existing hydrothermal method, the amount of lithium is reduced by 2 times, and the economy is greatly improved.

[0070] The application prepares micron-level spherical alkali lithium iron phosphate by a hydrothermal method, and obtains lithium iron phosphate with similar structure on this basis, which exhibits excellent electrochemical performance.

[0071] The electrochemical performance of the regenerated lithium iron phosphate is tested by a blue electric tester at normal temperature and pressure to test the cycle and rate performance of the battery. The positive electrode sheet, the conductive carbon black and the PVDF are uniformly mixed and dried to prepare (the mass ratio is 8:1:1). Then, the button cell assembled by using the regenerated lithium iron phosphate material is subjected to charge-discharge cycle by using a current of 1C; the rate performance of the button cell assembled by using the regenerated lithium iron phosphate material is tested by using currents of 0.2C, 0.5C, 1C, 2C and 5C.

[0072] The following is a typical case:

[0073] Example 1:

[0074] Step (1):

[0075] Take 8wt.% of lithium iron phosphate, ascorbic acid, and a 2mol / L sulfuric acid solution into a 500mL beaker, respectively, set the temperature of the water bath to 60℃, and set the stirring rate to 400rpm. When the temperature of the water bath rises to the set temperature, take 10ml / g of lithium iron phosphate positive electrode waste into the beaker, set the reaction time to 2h, and filter after the reaction. Then, an oxidizing agent (hydrogen peroxide, wherein H2O2 is 1-1.5 times the molar amount of Fe in the positive electrode waste) is added for oxidation treatment, and Fe 3+ oxide solution is obtained.

[0076] Step (2):

[0077] A saturated sodium hydroxide solution (labeled as lye) is configured, the pH value of the oxidation solution is adjusted to be stable at 3, then filtration is performed, and the filtrate (lithium solution) and the filter residue (iron and phosphorus residue) are enriched, respectively.

[0078] Sodium phosphate is added to the filtrate, the reaction temperature is set to 90℃, and the reaction time is set to 2h. After the reaction, filtration is performed, and lithium phosphate is obtained.

[0079] Step (3):

[0080] The filter residue and lithium phosphate (prepared in step 2) were added into a reaction kettle, mixed, and the solid-liquid ratio was controlled to be 2 g / mL with water. The hydrothermal reaction temperature was set to be 230°C, and the reaction time was 10 hours. After the reaction, the reaction kettle was cooled to room temperature and filtered to obtain the basic iron lithium phosphate.

[0081] Step (4):

[0082] A certain amount of glucose was dissolved, and the basic iron lithium phosphate was added into the glucose aqueous solution (the weight ratio of the basic iron lithium phosphate to the glucose was 1:0.15), ultrasonically mixed, dried, and then calcined at 600°C under an argon atmosphere for 5 hours to obtain the lithium iron phosphate (regenerated lithium iron phosphate).

[0083] Example 2:

[0084] Compared with Example 1, the only difference is that in step (2), potassium hydroxide solution was used as the alkali solution. The remaining experimental steps and conditions are the same as those in Example 1.

[0085] Example 3:

[0086] Compared with Example 1, the only difference is that in step (2), saturated ammonia water was used as the alkali solution. The remaining experimental steps and conditions are the same as those in Example 1.

[0087] Table 1 shows the impurity element content in the basic iron lithium phosphate obtained after hydrothermal treatment when using different alkali solutions to adjust the pH value of the leaching solution. As can be seen from Table 1, the impurity element content in the basic iron lithium phosphate obtained after hydrothermal treatment is the lowest and the purity is the highest when using sodium hydroxide solution to adjust the pH value of the leaching solution. Similar results can also be obtained from the corresponding XRD patterns. Figure 1 ).

[0088] Table 1 Impurity element content (pH = 3)

[0089]

[0090] The electrochemical performance of the regenerated lithium iron phosphate obtained in Examples 1-3 was tested according to the above method, and the results are shown in Figure 2 As can be seen from the figure, the electrochemical performance of the regenerated lithium iron phosphate obtained in Example 1 is better. In summary, according to Examples 1-3, using sodium hydroxide for precipitation reaction and further combining with hydrothermal reaction can control the impurity phase, improve the phase purity and crystallinity of the basic iron lithium phosphate, and further improve the performance of the regenerated lithium iron phosphate.

[0091] Example 4:

[0092] The difference between Example 1 and Example 2 is that the solid-liquid ratio of the hydrothermal reaction for preparing the basic lithium iron phosphate in step (3) is different; specifically, the solid-liquid ratio is 2 g / mL.

[0093] The experimental steps and conditions before hydrothermal reaction are the same as those in Example 1. The filter residue and lithium phosphate are added into the inner liner of the reaction kettle and mixed uniformly, the solid-liquid ratio of the slurry at the initial stage of the hydrothermal reaction is controlled to be 1.5 g / mL, the hydrothermal reaction temperature is set to be 230°C, and the reaction time is 10 hours. The remaining experimental steps and conditions are the same as those in Example 1.

[0094] Example 5:

[0095] The difference between Example 1 and Example 2 is that the solid-liquid ratio of the hydrothermal reaction for preparing the basic lithium iron phosphate in step (3) is different; specifically, the solid-liquid ratio is 2 g / mL.

[0096] The experimental steps and conditions before hydrothermal reaction are the same as those in Example 1. The filter residue and lithium phosphate are added into the inner liner of the reaction kettle and mixed uniformly, the solid-liquid ratio of the slurry at the initial stage of the hydrothermal reaction is controlled to be 0.7 g / mL, the hydrothermal reaction temperature is set to be 230°C, and the reaction time is 10 hours. The remaining experimental steps and conditions are the same as those in Example 1.

[0097] Example 6:

[0098] The difference between Example 1 and Example 2 is that the solid-liquid ratio of the hydrothermal reaction for preparing the basic lithium iron phosphate in step (3) is different; specifically, the solid-liquid ratio is 2 g / mL.

[0099] The experimental steps and conditions before hydrothermal reaction are the same as those in Example 1. The filter residue and lithium phosphate are added into the inner liner of the reaction kettle and mixed uniformly, the solid-liquid ratio of the slurry at the initial stage of the hydrothermal reaction is controlled to be 0.1 g / mL, the hydrothermal reaction temperature is set to be 230°C, and the reaction time is 10 hours. The remaining experimental steps and conditions are the same as those in Example 1.

[0100] Figure 3 The XRD patterns of the basic lithium iron phosphate obtained under different solid-liquid ratios of the hydrothermal reaction are shown in the figure. As can be seen from the figure, the basic lithium iron phosphate with higher pure phase can be obtained by controlling the solid-liquid ratio of the hydrothermal reaction to be 2 g / mL.

[0101] Example 7:

[0102] The difference between Example 1 and Example 2 is that the solid-liquid ratio of the hydrothermal reaction for preparing the basic lithium iron phosphate in step (3) is different; specifically, the solid-liquid ratio is 2 g / mL.

[0103] The experimental steps and conditions before hydrothermal reaction are the same as those in Example 1. The filter residue and lithium phosphate are added into the inner liner of the reaction kettle and mixed uniformly, the solid-liquid ratio of the slurry at the initial stage of the hydrothermal reaction is controlled to be 2 g / mL, the hydrothermal reaction temperature is set to be 200°C, and the reaction time is 10 hours. The remaining experimental steps and conditions are the same as those in Example 1.

[0104] Example 8:

[0105] Compared with Example 1, the difference is only that the hydrothermal temperature of preparing the basic lithium iron phosphate in step (3) is different; specifically, the hydrothermal temperature is 210℃.

[0106] The experimental steps and conditions before hydrothermal treatment are the same as those in Example 1. The filter residue and lithium phosphate are added into the reactor liner and mixed, the solid-liquid ratio of the slurry at the initial stage of hydrothermal treatment is 2 g / mL, the hydrothermal reaction temperature is set to 210℃, and the reaction time is 10 hours. The remaining experimental steps and conditions are the same as those in Example 1.

[0107] Figure 4 The XRD patterns of the basic lithium iron phosphate obtained at different hydrothermal reaction temperatures are shown in the figure. As can be seen from the figure, when the reaction temperature is lower, the reaction is incomplete, and there are still impurities. Therefore, controlling the reaction temperature to 230℃ can obtain basic lithium iron phosphate with better pure phase.

[0108] Example 9:

[0109] Compared with Example 1, the difference is only that the reaction time of the hydrothermal reaction is different; specifically, the reaction time is 6 hours.

[0110] The experimental steps and conditions before hydrothermal treatment are the same as those in Example 1. The filter residue and lithium phosphate are added into the reactor liner and mixed, the solid-liquid ratio is controlled to 2 g / mL, the hydrothermal reaction temperature is set to 230℃, and the reaction time is 6 hours. The remaining experimental steps and conditions are the same as those in Example 1.

[0111] Example 10:

[0112] Compared with Example 1, the difference is only that the reaction time of the hydrothermal reaction is different; specifically, the reaction time is 2 hours.

[0113] The experimental steps and conditions before hydrothermal treatment are the same as those in Example 1. The filter residue and lithium phosphate are added into the reactor liner and mixed, the solid-liquid ratio is controlled to 2 g / mL, the hydrothermal reaction temperature is set to 230℃, and the reaction time is 2 hours. The remaining experimental steps and conditions are the same as those in Example 1.

[0114] Figure 5 The XRD and SEM patterns of the basic lithium iron phosphate obtained at different hydrothermal reaction times are shown in the figure. As can be seen from the figure, controlling the reaction time of the hydrothermal reaction to 6 hours can obtain basic lithium iron phosphate with uniform morphology and good crystallinity.

[0115] Figure 6 The XRD pattern of the lithium iron phosphate prepared by taking the basic lithium iron phosphate obtained at different hydrothermal reaction times as the precursor is shown in the figure.

[0116] Figure 7Fig. 6 is a graph of cycle performance and rate performance of lithium iron phosphate prepared from different hydrothermal time of basic lithium iron phosphate. As can be seen from the graph, the electrochemical performance of lithium iron phosphate prepared by using basic lithium iron phosphate obtained by hydrothermal reaction for 6 hours as precursor is the best. Therefore, the conditions listed in Example 9 are the best reaction conditions for hydrothermal reaction, and the lithium iron phosphate obtained after calcination has the best performance.

[0117] In addition, in the present application, the basic lithium iron phosphate prepared by the hydrothermal method is used as a precursor to regenerate lithium iron phosphate, which can exhibit better electrochemical performance and lower cost compared to lithium iron phosphate obtained by the process of preparing lithium iron phosphate by the hydrothermal method.

Claims

1. A method for preparing basic lithium iron phosphate from waste lithium iron phosphate cathode powder, characterized by, The waste lithium iron phosphate positive electrode powder is subjected to acid leaching treatment, and solid-liquid separation to obtain a leaching solution; a reducing agent is added in the acid leaching stage; The lithium solution and iron-phosphorus slag are obtained by adding an oxidizing agent to the leaching solution for oxidation, alkali precipitation, and solid-liquid separation; the slurry formed by slurrying the iron-phosphorus slag and a lithium source is subjected to hydrothermal treatment at a temperature of 200°C or higher to obtain basic lithium iron phosphate; The alkali used in the alkali precipitation stage is at least one of sodium hydroxide, potassium hydroxide, and ammonia water; The solid-liquid ratio in the slurry is 0.1-3 g / mL.

2. The method of claim 1, wherein the spent lithium iron phosphate cathode powder is prepared by the steps of: a) mixing the spent lithium iron phosphate cathode powder with a solvent to form a mixture; b) adding a base to the mixture; c) stirring the mixture; d) filtering the mixture; and e) drying the mixture. The waste lithium iron phosphate positive electrode powder is obtained by stripping the positive electrode material from the waste lithium iron phosphate battery positive electrode sheet.

3. The method of claim 1, wherein the spent lithium iron phosphate cathode powder is prepared by the steps of: a) mixing the spent lithium iron phosphate cathode powder with a solvent to form a mixture; b) adding a base to the mixture; c) stirring the mixture; d) filtering the mixture; and e) drying the mixture. The waste lithium iron phosphate positive electrode powder contains 60-95 wt.% of lithium iron phosphate active material.

4. The method for preparing basic lithium iron phosphate from waste lithium iron phosphate cathode powder as described in claim 3, characterized in that, The waste lithium iron phosphate positive electrode powder further contains at least one of a conductive agent, a binder, a separator, and an electrolyte.

5. The method for preparing basic lithium iron phosphate from waste lithium iron phosphate cathode powder as described in claim 1, characterized in that, The acid used in the acid leaching stage is an aqueous solution of inorganic strong acid.

6. The method for preparing basic lithium iron phosphate from waste lithium iron phosphate cathode powder as described in claim 5, characterized in that, The inorganic strong acid is at least one of hydrochloric acid and sulfuric acid.

7. The method for preparing basic lithium iron phosphate from waste lithium iron phosphate cathode powder as described in claim 5, characterized in that, The concentration of the inorganic strong acid in the acid is 1-5 M.

8. The method for preparing basic lithium iron phosphate from waste lithium iron phosphate cathode powder as described in claim 1, characterized in that, The reducing agent is at least one of ascorbic acid and citric acid.

9. The method for preparing basic lithium iron phosphate from waste lithium iron phosphate cathode powder as described in claim 1, characterized in that, The liquid-solid ratio in the acid leaching stage is 5-20 mL / g. The temperature in the acid leaching stage is 50-80°C. The time in the acid leaching stage is 1-3 h.

10. The method for preparing basic lithium iron phosphate from waste lithium iron phosphate cathode powder as described in claim 1, characterized in that, The oxidizing agent is at least one of hydrogen peroxide and an oxidizing atmosphere.

11. The method for preparing basic lithium iron phosphate from waste lithium iron phosphate cathode powder as described in claim 1, characterized in that, The alkali used in the alkali precipitation stage is sodium hydroxide.

12. The method for preparing basic lithium iron phosphate from waste lithium iron phosphate cathode powder as described in claim 1, characterized in that, The pH at the end of the alkali precipitation reaction is 2-4.

13. The method for preparing basic lithium iron phosphate from waste lithium iron phosphate cathode powder as described in claim 1, characterized in that, The lithium source is a material containing at least one of lithium hydroxide, lithium phosphate, and lithium carbonate.

14. The method for preparing basic lithium iron phosphate from waste lithium iron phosphate cathode powder as described in claim 1, characterized in that, The lithium source is lithium phosphate formed by precipitation of lithium liquid through phosphatization or lithium carbonate formed by precipitation of lithium liquid through carbonization.

15. The method for preparing basic lithium iron phosphate from waste lithium iron phosphate cathode powder as described in claim 1, characterized in that, In the slurry, the molar ratio of Fe / Li in the iron-phosphorus slag and the lithium source is 1:1-1.

05.

16. The method for preparing basic lithium iron phosphate from waste lithium iron phosphate cathode powder as described in claim 1, characterized in that, In the slurry, the solid-liquid ratio is 1.8-2.5 g / mL.

17. The method of claim 1, wherein the spent lithium iron phosphate cathode powder is prepared by the steps of: a) mixing the spent lithium iron phosphate cathode powder with a solvent to form a mixture; b) heating the mixture to a temperature of about 400 °C to about 600 °C; c) cooling the mixture to room temperature; and d) washing the mixture with water. In the slurry, the solid-liquid ratio is 1.9-2.1 g / mL.

18. The method for preparing basic lithium iron phosphate from waste lithium iron phosphate cathode powder as described in claim 1, characterized in that, The hydrothermal temperature is 220-280°C.

19. The method for preparing basic lithium iron phosphate from waste lithium iron phosphate cathode powder as described in claim 1, characterized in that, The hydrothermal temperature is 225-245°C.

20. The method for preparing basic lithium iron phosphate from waste lithium iron phosphate cathode powder as described in claim 1, characterized in that, The hydrothermal time is 2-14 h.

21. The method for preparing basic lithium iron phosphate from waste lithium iron phosphate cathode powder as described in claim 1, characterized in that, The hydrothermal time is 4-10 h.

22. The method for preparing basic lithium iron phosphate from waste lithium iron phosphate cathode powder as described in claim 1, characterized in that, The hydrothermal time is 5-7 h.

23. A method for recycling a waste lithium iron phosphate cathode powder, the method comprising: The waste lithium iron phosphate positive electrode powder is subjected to the method according to any one of claims 1-22 to obtain basic lithium iron phosphate, the basic lithium iron phosphate and a carbon source are compounded and calcined to obtain regenerated lithium iron phosphate. ​ 24. The method for regenerating waste lithium iron phosphate cathode powder as described in claim 23, characterized in that, The carbon source is at least one of glucose, sucrose, and starch. The weight ratio of the basic lithium iron phosphate to the carbon source is 1:0.1-0.

2. The atmosphere in the calcination stage is a protective atmosphere. The calcination temperature is 500-800°C. The calcination time is 2-14 h.

25. The method for regenerating waste lithium iron phosphate cathode powder as described in claim 24, characterized in that, The calcination time is 4-10 h.

26. The method for regenerating waste lithium iron phosphate cathode powder as described in claim 25, characterized in that, The calcination time is 5-7 h.

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