A method for recovering lithium from lithium iron phosphate cathode materials with high selectivity and without acid by mechanical method

Abstract

The present invention discloses a mechanical, acid-free, and highly selective method for recovering lithium from lithium iron phosphate cathode materials. The method comprises the following steps: 1. Mixing the lithium iron phosphate cathode material, a co-grinding agent, and a grinding aid to form a mixture; 2. Ball-milling the mixture at room temperature to obtain a pulverized product; 3. Leaching the pulverized product from step 2 with water to obtain a leachate; and 4. Filtering the leachate to obtain a lithium-containing filtrate. The method of the present invention consumes no acid, has high lithium selectivity, is simple to operate, and has strong controllability.

Description

Technical Field

[0001] The present invention relates to the field of lithium recovery methods, and in particular to a method for recovering lithium from lithium iron phosphate positive electrode materials in an acid-free and highly selective mechanical manner. Background Art

[0002] Lithium iron phosphate (LiFePO4, LFP), first reported in the 1980s, is considered an excellent cathode material for electric vehicles, hybrid electric vehicles, and large-scale energy storage systems. LFP offers the advantages of low toxicity and widespread availability. When used in batteries, these devices exhibit excellent thermal safety and long cycle life.

[0003] New energy vehicles are a strategically emerging pillar industry. Lithium batteries are a core component of new energy vehicles. In recent years, with the widespread adoption of electric vehicles in major Chinese cities, lithium-ion power batteries have also seen rapid growth. The lifespan of lithium-ion power batteries is generally four to five years, so we can foresee that the mass retirement of lithium-ion power batteries from early new energy vehicles is approaching. While lithium-ion batteries are generally considered environmentally friendly and pollution-free, improper recycling can also generate pollution. Large quantities of scrapped lithium-ion batteries lead to environmental pollution and resource waste. It has been reported that future lithium supply crises can only be prevented through 100% lithium-ion battery recycling and a lithium recovery rate of at least 90%. Therefore, recycling spent lithium iron phosphate batteries is essential to preventing environmental pollution and resource depletion. Therefore, harmless treatment and resource utilization of scrapped power battery electrode materials are of paramount importance.

[0004] The difficulty in recycling spent lithium iron phosphate batteries lies in their relatively low extraction efficiency, low recovery selectivity, and the tendency to generate secondary waste. Existing technologies can effectively extract lithium and iron through strong acid treatment and long extraction times. However, the olivine-structured lithium iron phosphate is quite stable, and effective extraction of lithium and iron requires large amounts of strong acid or base. In this case, secondary contamination is inevitable, and the need to handle excessive amounts of acid or base significantly increases process costs. However, mechanochemical activation of spent lithium iron phosphate battery cathode materials reduces activation energy and increases reaction activity, which is expected to help alleviate these issues in the recycling of spent lithium iron phosphate batteries. Mechanical activation can reduce acid consumption, improve lithium recovery selectivity, and reduce secondary pollution emissions.

[0005] Patent application number CN201810014024.0 discloses a method for recovering lithium from lithium iron phosphate cathode materials and a lithium carbonate product. The main process involves mixing the raw materials with concentrated nitric acid at a mass fraction of 15% to 65%, introducing the mixture into a hydrothermal reactor for a hydrothermal reaction, and then producing the lithium carbonate product through a series of operations, including pH adjustment, impurity removal, and filtration. This method is complex and requires a reactor for the hydrothermal reaction, which carries certain risks. Furthermore, the hydrothermal reaction requires high temperatures, which increases recovery costs and places high demands on the reaction equipment.

[0006] Patent application number CN202010760821.0 discloses a method for the comprehensive utilization of waste lithium iron phosphate positive electrode materials. This method uses acid to leach waste lithium iron phosphate positive electrode materials. After adjusting the iron-phosphorus ratio and adjusting the pH value to a strong acid, the leaching solution converts ferrous ions into ferric ions through an oxidation reaction to generate ferric phosphate precipitates. After liquid-solid separation, hydrated ferric phosphate and a lithium-containing solution are obtained. A lithium salt product is then obtained through a series of subsequent operations. Although this method is simple in process, the reaction time is long. Heavy metal precipitants are introduced during the process, which may introduce impurity ions. In addition, the use of reaction conditions such as high acidity can easily cause environmental pollution. Summary of the Invention

[0007] The purpose of the present invention is to provide a mechanical method for recovering lithium from lithium iron phosphate positive electrode materials with high selectivity and acid-free properties, so as to solve the problem of environmental pollution when recovering lithium from lithium iron phosphate positive electrode materials by acid leaching and chemical reaction in the prior art.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is:

[0009] A method for mechanically recovering lithium from lithium iron phosphate cathode materials without acid and with high selectivity comprises the following steps:

[0010] Step 1: taking a lithium iron phosphate positive electrode material, a co-grinding agent, and a grinding aid, wherein the co-grinding agent is an oxidant, and mixing the lithium iron phosphate positive electrode material, the co-grinding agent, and the grinding aid to form a mixture;

[0011] Step 2, ball-milling the mixture in step 1 at room temperature to obtain a pulverized product;

[0012] Step 3, leaching the pulverized product obtained in step 2 with water to obtain a leachate;

[0013] Step 4: Filter the leachate obtained in step 3 to obtain a filtrate which is a lithium-containing solution.

[0014] In the further step 1, the mass ratio of the lithium iron phosphate positive electrode material to the co-grinding agent is 1:1 to 1:10.

[0015] In the further step 1, hydrogen peroxide is used as the grinding aid.

[0016] Furthermore, the mass fraction of hydrogen peroxide used as a grinding aid is 5% to 30%, and the liquid-solid ratio of hydrogen peroxide to the lithium iron phosphate positive electrode material is 0 ml / g to 10 ml / g.

[0017] In the further step 1, the oxidant used in the co-grinding agent is any one of sodium persulfate, ammonium persulfate, potassium persulfate, and sodium peroxide, or any combination thereof in any proportion.

[0018] In the further step 2, the ball milling time is 0 min to 120 min, the ball-to-powder ratio is 5 g / g to 50 g / g, and the ball milling speed is 100 rpm to 700 rpm.

[0019] In the further step 3, deionized water is added to the pulverized product for water leaching, the solid-liquid ratio of the pulverized product to deionized water is 10 g / L~100 g / L, and the leaching is carried out at 10°C~90°C and a stirring speed of 0rpm~500rpm for 0min~120min.

[0020] In the lithium-rich filtrate obtained after filtration in step 4 of the present invention, Li + The leaching rate of Fe is above 90%. 2+ / Fe 3 The leaching rate is below 5%.

[0021] The present invention mechanically ball-mills waste lithium iron phosphate cathode materials from batteries with an oxidant, followed by leaching using deionized water. The ball milling method utilizes mechanical energy as a reaction driving force at room temperature and pressure to destroy the olivine structure of the lithium iron phosphate, thereby enabling a lithium-containing solution to be directly obtained by water leaching in a subsequent step. This method eliminates acid consumption, exhibits high selectivity for the lithium element, and is simple to operate and highly controllable.

[0022] Compared with the prior art, the advantages of the present invention are:

[0023] 1. The method proposed in the present invention is a mechanical method for acid-free and highly selective recovery of lithium iron phosphate positive electrode materials from waste lithium batteries. It has the advantages of zero acid and alkali usage, simple method, reasonable technical route, and environmentally friendly production process. It is a promising method for selectively extracting and recovering valuable metals from waste lithium-ion batteries and conforms to the concept of green chemistry.

[0024] 2. The method of the present invention selectively extracts Li+ from waste lithium iron phosphate battery cathode materials with a leaching rate of over 90% and a Fe2+ / Fe3+ leaching rate of less than 5%. The leaching rates of other valuable metals are relatively low, achieving highly selective extraction of lithium. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a flowchart of the method of the present invention.

[0026] Figure 2 1 is a graph showing the measurement results of the lithium-containing filtrate in an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The present invention will be further described below with reference to the accompanying drawings and examples. Example 1

[0028] like Figure 1 As shown, this embodiment includes the following steps:

[0029] (1) Weigh 1g of waste lithium iron phosphate positive electrode material and 1g of sodium persulfate as a co-grinding agent, put them into a 100ml ball mill, and add 1ml of 30% hydrogen peroxide as a grinding aid into the ball mill.

[0030] (2) Place the ball mill jar in step (1) in a planetary ball mill at room temperature for 5 minutes, control the speed of the planetary ball mill to 500 rpm, and the ball-to-powder ratio to 20 g / g.

[0031] (3) The ball-milled mixture was placed in a 250 ml conical flask, and deionized water was added to the conical flask at a solid-liquid ratio of 30 g / L. The mixture was then leached at 40 °C for 20 min. The leaching process was carried out at a stirring speed of 300 rpm.

[0032] (4) After the leaching in step (3) is completed, the leachate is filtered to obtain a filtrate rich in lithium and iron elements. The filtrate is then subjected to atomic absorption testing.

[0033] like Figure 2 As shown, in the filtrate of step 4, Li + The leaching rate of Fe is 98.3%, 2+ / Fe 3+ The leaching rate is 2.5%. Example 2

[0034] This embodiment includes the following steps:

[0035] (1) Weigh 1g of waste lithium iron phosphate positive electrode material and 1g of sodium persulfate as a co-grinding agent, put them into a 100ml ball mill, and add 2ml of hydrogen peroxide with a mass fraction of 30% as a grinding aid into the ball mill.

[0036] (2) Place the ball mill jar in step (1) in a planetary ball mill at room temperature for 5 minutes, control the speed of the planetary ball mill to 500 rpm, and the ball-to-powder ratio to 20 g / g.

[0037] (3) The ball-milled mixture was placed in a 250 ml conical flask, and deionized water was added to the conical flask at a solid-liquid ratio of 30 g / L. The mixture was then leached at 40 °C for 20 min, with stirring at a speed of 300 rpm during the leaching process.

[0038] (4) After the leaching in step (3) is completed, the leachate is filtered to obtain a filtrate rich in lithium and iron elements. The filtrate is then subjected to atomic absorption testing.

[0039] like Figure 2 As shown, in the filtrate of step 4, Li + The leaching rate of Fe is 99.3%, 2+ / Fe 3+ The leaching rate is 1.5%. Example 3

[0040] This embodiment includes the following steps:

[0041] (1) Weigh 1.5 g of waste lithium iron phosphate battery positive electrode material and 1 g of sodium persulfate as a co-grinding agent, put them into a 100 ml ball mill, and add 1 ml of hydrogen peroxide with a mass fraction of 30% as a grinding aid into the ball mill.

[0042] (2) Place the ball mill jar in step (1) in a planetary ball mill at room temperature for 5 minutes, control the speed of the planetary ball mill to 500 rpm, and the ball-to-powder ratio to 20 g / g.

[0043] (3) The ball-milled mixture was placed in a 250 ml conical flask, and deionized water was added to the conical flask at a solid-liquid ratio of 30 g / L. The mixture was then leached at 25 °C for 20 min, with stirring at a speed of 300 rpm during the leaching process.

[0044] (4) After the leaching in step (3) is completed, the leachate is filtered to obtain a filtrate rich in lithium and iron elements. The filtrate is then subjected to atomic absorption testing.

[0045] like Figure 2 As shown, in the filtrate of step 4, Li + The leaching rate of Fe is 93.3%, 2+ / Fe 3+ The leaching rate is 2.7%. Example 4

[0046] This example includes the following steps:

[0047] (1) Weigh 1g of waste lithium iron phosphate battery positive electrode material and 1g of sodium persulfate as a co-grinding agent, put them into a 100ml ball mill, and add 1ml of hydrogen peroxide with a mass fraction of 30% as a grinding aid into the ball mill.

[0048] (2) Place the ball mill jar in step (1) in a planetary ball mill at room temperature for 5 minutes, control the speed of the planetary ball mill to 500 rpm, and the ball-to-powder ratio to 20 g / g.

[0049] (3) The ball-milled mixture was placed in a 250 ml conical flask, and deionized water was added to the conical flask at a solid-liquid ratio of 30 g / L. The mixture was then leached at 60 °C for 20 min, with stirring at a speed of 300 rpm during the leaching process.

[0050] (4) After the leaching in step (3) is completed, the leachate is filtered to obtain a filtrate rich in lithium and iron elements. The filtrate is then subjected to atomic absorption testing.

[0051] like Figure 2 As shown, in the filtrate of step 4, Li + The leaching rate of Fe is 90%, 2+ / Fe 3+ The leaching rate is 2.5%.

[0052] The embodiments described in the present invention are merely descriptions of the preferred implementation methods of the present invention and are not intended to limit the concept and scope of the present invention. Without departing from the design concept of the present invention, various modifications and improvements made to the technical solutions of the present invention by engineers and technicians in this field should fall within the scope of protection of the present invention. The technical contents for which protection is sought in the present invention have all been recorded in the claims.

Claims

1. A method for mechanically recovering lithium from lithium iron phosphate cathode materials without acid and with high selectivity, characterized in that: The following steps are involved: Step 1: taking a lithium iron phosphate positive electrode material, a co-grinding agent, and a grinding aid, wherein the co-grinding agent is an oxidant, and mixing the lithium iron phosphate positive electrode material, the co-grinding agent, and the grinding aid to form a mixture; Step 2, ball-milling the mixture in step 1 at room temperature to obtain a pulverized product; Step 3, leaching the pulverized product obtained in step 2 with water to obtain a leachate; Step 4: filtering the leachate obtained in step 3 to obtain a filtrate containing lithium; In step 1, the grinding aid is hydrogen peroxide; The mass fraction of hydrogen peroxide as a grinding aid is 5% to 30%, and the liquid-solid ratio of hydrogen peroxide to lithium iron phosphate positive electrode material is 1 ml / 1.5 g to 10 ml / g; In step 1, the mass ratio of the lithium iron phosphate positive electrode material to the co-grinding agent is 1:1 to 1:10; In step 1, the oxidant used in the co-grinding agent is any one of sodium persulfate, ammonium persulfate, potassium persulfate, and sodium peroxide, or any combination thereof in any proportion.

2. The method for mechanically recovering lithium from lithium iron phosphate cathode material with high selectivity and without acid according to claim 1, characterized in that: In step 2, the ball milling time is 0 min to 120 min, the ball-to-powder ratio is 5 g / g to 50 g / g, and the ball milling speed is 100 rpm to 700 rpm.

3. The method for mechanically recovering lithium from lithium iron phosphate cathode material with high selectivity and without acid according to claim 1, characterized in that: In step 3, deionized water is added to the pulverized product for water leaching, the solid-liquid ratio of the pulverized product to deionized water is 10 g / L~100 g / L, and the leaching is carried out at 10°C~90°C and a stirring speed of 0rpm~500rpm for 0min~120min.

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