Method for recovering lithium resource in waste lithium battery for lithium supplement of negative electrode of lithium battery

Abstract

The invention discloses a method for recovering a lithium resource in a waste lithium battery for lithium supplement of a negative electrode of the lithium battery, and belongs to the technical field of lithium battery recovery. An anode of a waste lithium battery is recycled, a circuit is externally connected to control the amount of electrodeposited lithium on an aluminum foil, a layer of aluminum-lithium alloy is formed on the surface of the aluminum foil, and the aluminum-lithium alloy is used as a modification layer on the surface of a cathode of the lithium ion battery, so that a lithium supplementing effect is provided for lithium loss caused by an SEI film formed on the cathode, and the aluminum-lithium alloy can also be used as a part of a cathode material; and high reversible capacity is provided. The recycling method is easy to operate, invalid waste of the positive electrode in the waste battery is avoided, compared with a common negative electrode lithium supplementing method, the pre-lithiation degree can be accurately controlled, the used aluminum foil is low in price, the production cost is reduced, operation is easy, and potential safety hazards are small.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery recycling, and in particular relates to a method for recycling lithium resources in waste lithium batteries for lithium battery negative electrode replenishment. Background Art

[0002] Lithium-ion batteries (LIBs) are considered to be one of the most promising electrochemical energy storage systems due to their high energy density, long cycle life, and no memory effect. However, the formation of the solid electrolyte interface (SEI) on the negative electrode of lithium-ion batteries consumes a large amount of lithium ions, resulting in low first coulombic efficiency (ICE) and severe energy density attenuation. In order to solve the above problems, additional active lithium ions are introduced through various lithium sources. These additional lithium ions are used to sacrifice the formation of SEI, which ultimately leads to an increase in battery capacity and energy density.

[0003] At present, the common method of using negative electrode lithium replenishment is to directly mix lithium metal materials such as lithium foil and lithium powder into the negative electrode or press them on the surface of the negative electrode active material. If the lithium replenishment is insufficient, the first coulomb efficiency of the battery cannot be fully improved. If the lithium replenishment is excessive, a metal lithium plating layer may be formed on the surface of the negative electrode. Lithium foil needs to be extremely thin to achieve accurate lithium compensation. Lithium foil with a thickness of less than 20 μm is mechanically brittle. Due to the safety hazards of lithium powder being too active, FMC proposed a lithium carbonate-coated lithium powder solution (SLMP) to improve the stability of lithium powder. However, lithium carbonate will inhibit the lithium replenishment effect while protecting lithium metal, and a static pressure process is required to activate SLMP and a large amount of toxic and harmful solvents such as toluene are required for dispersion. Therefore, it is necessary to develop a negative electrode lithium replenisher with accurate lithium compensation, good stability and safety to improve battery performance. Summary of the invention

[0004] The purpose of the present invention is to propose a method for recycling lithium resources in waste lithium batteries for lithium battery negative electrode replenishment. The positive electrode of the waste lithium battery is recycled as the positive electrode, and the degree of pre-lithiation on the aluminum foil is controlled by an external circuit, and the aluminum-lithium alloy formed on the surface of the aluminum foil replenishes the lithium of the lithium battery negative electrode.

[0005] In order to achieve the above-mentioned invention object, the present invention provides the following technical solution: a method for recovering lithium resources from waste lithium batteries for replenishing lithium in the negative electrode of lithium batteries, comprising the following steps:

[0006] Step 1: Set the surface density to 2 ~ 6 mg / cm 2 The aluminum foil is used as the negative electrode, the positive electrode of the discarded lithium battery is used as the positive electrode, and the separator of the discarded lithium battery is used as the separator. After adding the electrolyte, a half-cell is assembled, and the aluminum foil is pre-lithiated by a current of 0.1 to 1.0 mA to ensure that the pre-lithiation degree is 20% to 60%;

[0007] Step 2, using the pre-lithiated aluminum foil in step 1 as a modification layer on the surface of the negative electrode of the lithium-ion battery to assemble a full battery.

[0008] Preferably, in step 1, the aluminum foil is pre-lithiated by a current of 0.1 to 0.5 mA to ensure that the degree of pre-lithiation is 20% to 60%.

[0009] Preferably, in step 1, the discarded lithium battery positive electrode is a discharged electrode.

[0010] Preferably, in step 1, the positive electrode of the discarded lithium battery is selected from any one of lithium iron phosphate, ternary lithium and lithium iron manganese phosphate.

[0011] Preferably, in step 2, the negative electrode of the whole battery is a graphite electrode.

[0012] Specifically, the surface density of active materials in graphite pole pieces is 5 ~ 15 mg / cm 2 .

[0013] Preferably, in step 2, the positive electrode of the full battery is selected from any one of lithium iron phosphate, ternary lithium and lithium manganese iron phosphate.

[0014] Specifically, the surface density of the active material in the positive electrode is 10 ~ 30 mg / cm 2 .

[0015] Preferably, the pre-lithiated aluminum foil is laminated to the negative electrode surface of the full battery by roller pressing to achieve lithium replenishment.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] The present invention can accurately control the amount of electrodeposited lithium on the aluminum foil through in-situ pre-lithiation, form a layer of aluminum-lithium alloy on the surface of the aluminum foil, and form a strong connection with the bottom layer of the aluminum foil, so that they have good conductivity. Using the aluminum-lithium alloy as a modification layer on the surface of the negative electrode of a lithium-ion battery not only provides a lithium replenishment effect for the lithium loss caused by the formation of the SEI film at the negative electrode, but also can be used as a part of the negative electrode material to provide a high reversible capacity. In addition, the lithium replenishment method avoids the ineffective waste of the positive electrode in waste batteries by recycling the pre-lithiated aluminum foil of the positive electrode of the lithium battery, and the aluminum foil used is cheap, thereby reducing the cost of battery materials. Compared with the commonly used negative electrode lithium replenishment method, this method has higher stability and safety, and the process conditions during use are also simpler and more convenient. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is the first cycle charge and discharge curve of the pre-lithiated aluminum foil used for lithium replenishment of the negative electrode of a lithium iron phosphate full battery in Example 1.

[0019] Figure 2This is the first cycle charge and discharge curve of the pre-lithiated aluminum foil used for lithium replenishment of the negative electrode of a lithium iron phosphate full battery in Example 2.

[0020] Figure 3 This is the first cycle charge and discharge curve of the pre-lithiated aluminum foil used for lithium replenishment of the negative electrode of a lithium iron phosphate full battery in Example 3.

[0021] Figure 4 This is the XRD pattern of the pre-lithiated aluminum foil in Example 3.

[0022] Figure 5 This is the first cycle charge and discharge curve of the lithium iron phosphate full battery of comparative example 1.

[0023] Figure 6 This is the first cycle charge and discharge curve of the lithium iron phosphate half-cell of comparative example 2. DETAILED DESCRIPTION

[0024] The preferred embodiments of the present invention are described in detail below so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0025] The lithium replenishment method of the present invention recycles the positive electrode pre-lithiation aluminum foil of the lithium battery. The recycling method is simple to operate, avoids the ineffective waste of the positive electrode in the waste battery, and the aluminum foil used is cheap, which reduces the battery material cost. Compared with the commonly used negative electrode lithium replenishment method, this method has higher stability and safety, can achieve accurate control of the pre-lithiation degree, and the process conditions during use are also simpler and more convenient.

[0026] The surface density of the aluminum foil used in the present invention is 2 to 6 mg / cm 2 The aluminum foil with this surface density has a moderate thickness and can be used as a negative electrode active material while replenishing lithium to improve the battery energy density. The external circuit current is 0.1 ~ 1.0 mA, preferably 0.1 ~ 0.5 mA, under which condition the pre-lithiation of the aluminum foil surface is more uniform. The pre-lithiation degree of the aluminum foil is 20% ~ 60%, preferably 30% ~ 50%, under which condition the aluminum-lithium alloy foil can have good mechanical properties and excellent lithium replenishment effect.

[0027] The discarded lithium battery positive electrode is the electrode after discharge. The positive electrode types include lithium iron phosphate, ternary lithium and lithium manganese iron phosphate and other positive electrode materials. The discarded diaphragm can completely cover the positive electrode surface. By using the discarded lithium-rich electrode and diaphragm, the recycling cost is greatly saved and the secondary use of discarded batteries is realized.

[0028] The electrolyte is a diluted conventional lithium-ion battery electrolyte. This is because lithium salts will precipitate out after the waste lithium battery electrodes are dried. The use of diluted electrolyte can promote the dissolution of lithium salts and is beneficial to the diffusion of lithium ions during the charging and discharging process.

[0029] The surface density of active materials in graphite pole pieces is 5 ~ 15 mg / cm 2 Aluminum-lithium alloy can be used as a lithium supplement and negative electrode at the same time. By reasonably matching it with the graphite negative electrode of this surface density, it is helpful to reduce the process cost of the negative electrode.

[0030] The surface density of active material in the positive electrode is 10 ~ 30 mg / cm 2 Since aluminum itself has a high theoretical specific capacity, aluminum-lithium alloy can be used as a negative electrode while supplementing lithium, which is beneficial to increasing the capacity of the negative electrode. Therefore, a positive electrode sheet with a larger surface density of active material is used in combination.

[0031] The pre-lithiated aluminum foil is rolled and bonded to the surface of the negative electrode to achieve lithium replenishment, which is beneficial to improving the contact between the aluminum-lithium alloy and the electrode, reducing the ohmic impedance, and also conducive to the stability of the electrode performance.

[0032] Example 1

[0033] (1) Set the surface density to 3 mg / cm 2 The aluminum foil is used as the negative electrode, the discarded lithium battery positive electrode is used as the positive electrode, and the discarded diaphragm is used as the diaphragm. After a small amount of electrolyte is replenished, the battery is assembled. The aluminum foil is embedded with lithium (aluminum-lithium alloy foil) through a current of 0.3 mA, and the pre-lithiation degree is 30%.

[0034] (2) The surface density of the active material is 7 mg / cm 2 The surface density of graphite pole pieces and active materials is about 16 mg / cm 2 The lithium iron phosphate electrode was placed in a vacuum drying oven and dried at 80°C for 4 hours. The pre-lithiation battery was then disassembled in a vacuum glove box filled with argon. The aluminum-lithium alloy foil was taken out, rolled and bonded to the surface of the graphite electrode. After adding the diaphragm and electrolyte, it was assembled into a full battery with the dried lithium iron phosphate positive electrode.

[0035] Figure 1 The first cycle charge and discharge curve of the pre-lithiated aluminum foil used for lithium supplementation of the negative electrode of a full lithium iron phosphate battery in Example 1. It can be seen from the figure that the battery is charged and discharged at 0.05C, and the charge capacity is 156 mAh g -1 , the discharge capacity is 142 mAh g -1 The coulombic efficiency is 91%, which is about 15 mAh g higher than that of comparative example 1. -1 This part of the capacity is provided by the active lithium released from the aluminum-lithium alloy and is used to sacrifice the SEI formed at the negative electrode.

[0036] Example 2

[0037] This embodiment is basically the same as the embodiment 1, except that the pre-lithiation degree of the aluminum foil is 40% by changing the lithium insertion time.

[0038] Figure 2 The first cycle charge and discharge curve of the pre-lithiated aluminum foil used for lithium supplementation of the negative electrode of a lithium iron phosphate full battery in Example 2. It can be seen from the figure that the battery is charged and discharged at 0.05C, and the charge capacity is 160 mAh g -1 , the discharge capacity is 148 mAh g -1 , the coulombic efficiency is 92%. Compared with comparative example 1, the discharge capacity is about 21 mAh g higher. -1 This part of the capacity is provided by the active lithium released from the aluminum-lithium alloy and is used to sacrifice the SEI formed at the negative electrode.

[0039] Example 3

[0040] This embodiment is basically the same as the embodiment 1, except that the pre-lithiation degree of the aluminum foil is 50% by changing the lithium insertion time.

[0041] Figure 3 The first cycle charge and discharge curve of the pre-lithiated aluminum foil used for lithium supplementation of the negative electrode of a full lithium iron phosphate battery in Example 3. It can be seen from the figure that the battery is charged and discharged at 0.05C, and the charge capacity is 160 mAh g -1 , the discharge capacity is 153 mAh g -1 The coulombic efficiency is 95.6%. Compared with the comparative example 1, the discharge capacity is about 26 mAh g -1 This part of the capacity is provided by the active lithium released from the aluminum-lithium alloy. The coulombic efficiency is equivalent to that of comparative example 2, indicating that the lithium consumed by the formation of SEI at the negative electrode has been fully replenished.

[0042] Figure 4 This is the XRD diagram of the pre-lithiated aluminum foil of Example 3. It can be seen from the figure that the Al-Li alloy formed by the pre-lithiated aluminum foil has the chemical composition of LiAl.

[0043] Comparative Example 1

[0044] The surface density of the active material is about 7 mg / cm 2 The surface density of the graphite negative electrode sheet and active material is about 16 mg / cm 2 The lithium iron phosphate positive electrode sheet was placed in a vacuum drying oven at 80°C and dried for 4 h, and the full battery was assembled.

[0045] Figure 5 This is the charge and discharge curve of the lithium iron phosphate full battery at 0.05C. It can be seen from the figure that the battery is charged and discharged at 0.05C, and the charge capacity is 156 mAh g -1 , the discharge capacity is 127 mAh g-1 , the Coulomb efficiency is only 81.4%.

[0046] Comparative Example 2

[0047] The surface density of the active material is about 16 mg / cm 2 The lithium iron phosphate positive electrode sheet was placed in a vacuum drying oven at 80°C for 4 hours, and metallic lithium was used as the negative electrode to assemble a half-cell.

[0048] Figure 6 This is the charge and discharge curve of the lithium iron phosphate full battery at 0.05C. It can be seen from the figure that the battery is charged and discharged at 0.05C, and the charge capacity is 158 mAh g -1 , the discharge capacity is 150 mAh g -1 , the Coulomb efficiency is 95.0%.

Claims

1. A method for recovering lithium resources from discarded lithium batteries for lithium battery negative electrode replenishment, characterized in that: The steps include: Step 1: Set the surface density to 2 ~ 6 mg / cm 2 The aluminum foil is used as the negative electrode, the positive electrode of the discarded lithium battery is used as the positive electrode, and the separator of the discarded lithium battery is used as the separator. After adding the electrolyte, a half-cell is assembled, and the aluminum foil is pre-lithiated by a current of 0.1 to 1.0 mA to ensure that the pre-lithiation degree is 20% to 60%; Step 2, using the pre-lithiated aluminum foil in step 1 as a modification layer on the surface of the negative electrode of the lithium-ion battery to assemble a full battery.

2. The method according to claim 1, characterized in that In step 1, the aluminum foil is pre-lithiated by a current of 0.1 to 0.5 mA to ensure that the degree of pre-lithiation is 20% to 60%.

3. The method according to claim 1, characterized in that In step 1, the positive electrode of the discarded lithium battery is the discharged electrode.

4. The method according to claim 1, characterized in that In step 1, the positive electrode of the waste lithium battery is selected from any one of lithium iron phosphate, ternary lithium and lithium manganese iron phosphate.

5. The method according to claim 1, characterized in that In step 2, the negative electrode of the whole battery is a graphite electrode.

6. The method according to claim 5, characterized in that The surface density of active material in graphite pole piece is 5 ~ 15mg / cm 2 .

7. The method according to claim 1, characterized in that In step 2, the positive electrode of the full battery is selected from any one of lithium iron phosphate, ternary lithium and lithium manganese iron phosphate.

8. The method according to claim 7, characterized in that The surface density of the active material in the positive electrode is 10 ~ 30 mg / cm 2 .

9. The method according to claim 1, characterized in that The pre-lithiated aluminum foil is rolled and laminated onto the negative electrode surface of the lithium full battery to achieve lithium replenishment.

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