Lithium extraction electrode, lithium extraction method, and lithium extraction system

Abstract

A lithium extraction electrode, a lithium extraction method, and a lithium extraction system. The lithium extraction electrode is designed based on a specific structure, and, after a lithium removal reaction is performed, can be directly used in electrochemical lithium extraction of water; after lithium extraction is completed, lithium ions can be directly recycled by means of a reverse reaction, and the lithium ions can be put into a next batch of water for lithium extraction. Thus there is no requirement for replacement or apparatus assistance, and lithium extraction efficiency is high.

Description

A lithium extraction electrode, a lithium extraction method and a lithium extraction system Technical Field

[0001] This article relates to the field of industrial lithium extraction technology, and in particular to a method and system for extracting lithium from electrodes. Background Art

[0002] In the field of lithium extraction from salt lakes, the principle of electrochemical lithium extraction is to set up a working electrode in the lithium extraction water area, enrich the lithium ions in the water area during the discharge process, and then selectively recover the lithium ions into the recovery liquid during the charging process. There is no need to introduce some toxic reagents or high-energy-consuming equipment throughout the process, so it is energy-saving, economical, safe and environmentally friendly.

[0003] However, the lithium extraction efficiency of the working electrode used in the current electrochemical lithium extraction method is very limited. At the same time, the working electrode is prone to saturation and failure, so it needs to be replaced frequently.

[0004] Summary of the Invention

[0005] The purpose of this article is to overcome the shortcomings of the above-mentioned existing technologies and provide a lithium extraction electrode and a lithium extraction method. This method sets an electrode with a specific composition and structure as a working electrode, places it in a lithium-deficient water body to be extracted, and applies electricity. In this way, high-speed lithium extraction can be achieved without the use of additional lithium extraction equipment, and the degree of lithium ion recovery is high.

[0006] To achieve the above objectives, the technical solutions adopted in this paper are:

[0007] A lithium extraction electrode comprises a positive electrode layer, a first monovalent cation membrane, a first transport layer, a negative electrode layer, a second transport layer and a second monovalent cation membrane stacked in sequence; the positive electrode layer and the negative electrode layer are provided with tabs for connecting to a power supply.

[0008] In one embodiment, the positive electrode layer includes a current collector and an active material layer, and the active material is at least one of lithium iron phosphate, lithium iron manganate, lithium iron manganese phosphate, lithium vanadate, and lithium cobaltate;

[0009] In one embodiment, the positive electrode layer includes a first active material layer, a current collector, and a second active material layer in sequence;

[0010] In one embodiment, the thickness of the first active material layer and the second active material layer is 20-30 μm.

[0011] In one embodiment, the total thickness of the active material layer in the positive electrode layer is 40 to 60 μm.

[0012] In one embodiment, the negative electrode layer includes a current collector and an active material layer, and the active material is at least one of graphite, carbon black, and graphene;

[0013] In one embodiment, the negative electrode layer includes a first active material layer, a current collector, and a second active material layer in sequence;

[0014] In one embodiment, the thickness of the first active material layer and the second active material layer is 20-30 μm.

[0015] In one embodiment, the total thickness of the active material layer in the negative electrode layer is 40-60 μm.

[0016] In one embodiment, the first transmission layer and the second transmission layer are at least one of a porous sponge layer and a resin layer, and the average pore size of the first transmission layer and the second transmission layer is 50-200 μm and the porosity is 80-90%.

[0017] In one embodiment, the thickness of the first transmission layer and the second transmission layer is 60-80 μm.

[0018] Another object of this invention is to provide a method for extracting lithium, comprising the following steps:

[0019] Placing the lithium extraction electrode described herein into a soluble metal salt solution, connecting a power source and causing the positive electrode layer in the lithium extraction electrode to undergo a lithium delithiation reaction;

[0020] The lithium extraction electrode after the lithium removal reaction is placed in the water body to be extracted with lithium, and the power is turned on to cause the positive electrode layer in the lithium extraction electrode to undergo lithium insertion reaction;

[0021] The lithium extraction electrode after the lithium extraction reaction is placed in a recovery solution, and the power is turned on to allow the positive electrode layer in the lithium extraction electrode to undergo a lithium de-reaction reaction, thereby completing the lithium extraction.

[0022] The lithium extraction electrode described in this article is arranged in a structure similar to that of a lithium-ion battery, and does not require frequent replacement of lithium extraction electrodes used in conventional electrochemical lithium extraction methods. When the lithium extraction electrode is placed in a soluble metal salt solution and connected to a power source, similar to the lithium deintercalation reaction similar to that of a lithium-ion battery, the positive electrode layer in the lithium extraction electrode will undergo a lithium deintercalation reaction and form a lithium-deficient state. Subsequently, the electrode in the lithium-deficient state is placed in a body of water to be used for lithium extraction. It is only necessary to connect opposite positive and negative power sources to the tabs of the positive and negative electrode sheets respectively to cause the lithium extraction electrode to undergo opposite lithium intercalation reactions. Based on the action of the transport layer and the monovalent cation membrane, the lithium ions in the water body will undergo selective enrichment. After the enrichment is completed, it is only necessary to place the lithium extraction electrode in a recovery solution and connect the opposite positive and negative power sources again to release the enriched lithium ions into the solution, thereby completing the lithium extraction and recovery. The lithium extraction electrode can then be used for the next lithium extraction operation without replacing or processing the electrode layer.

[0023] At the same time, the function of the transport layer is to provide a transmission channel for the lithium-extracted water body during the lithium ion enrichment process, and to promote the contact between the water body and the positive electrode layer, which is similar to the diaphragm layer in the lithium-ion battery. If the pore size is too small, it is not conducive to the transmission of the water body, but if the pore size is too large, it will cause the water body transmission rate to be too fast, which may lead to poor lithium ion enrichment effect and low recovery rate.

[0024] In one embodiment, in the lithium extraction electrode, the positive electrode layer, the first monovalent cation membrane, the first transport layer, the negative electrode layer, the second transport layer and the second monovalent cation membrane are stacked in sequence and wound into a cylindrical shape, with the innermost layer being the positive electrode layer.

[0025] In one embodiment, the lithium extraction electrode after the delithiation reaction is placed in the water body to be extracted with lithium in a direction perpendicular to the direction in which the layers of the lithium extraction electrode are stacked in sequence. When the positive electrode layer in the lithium extraction electrode undergoes a lithium insertion reaction, the water body to be extracted flows from the bottom of the lithium extraction electrode to the upper part.

[0026] In one embodiment, the flow rate of the water to be extracted with lithium is 0.01-0.03 m / s.

[0027] When the lithium extraction electrode described in this article is set up using a winding structure similar to a lithium-ion battery cell, it has a larger contact area than electrodes with other structures. At the same time, the amount of lithium extracted per unit of active material of the positive electrode sheet is greater during a lithium extraction process, and the cylindrical structure can also be provided with multi-layer electrodes. Therefore, the electrode specific surface area is relatively larger, and the thickness of the active material layer on the positive electrode sheet can be set to a relatively low range, thereby reducing the polarization effect during the lithium extraction process. If the thickness of the active material layer is too high, it may cause the lithium extraction electrode to fail to fully exert its lithium extraction efficiency.

[0028] Another object of this article is to provide a lithium extraction system, including a two-pole power supply, the lithium extraction electrode described in this article, and a negative pressure pumping device hermetically connected to the lithium extraction electrode, wherein the positive electrode layer in the lithium extraction electrode is in a lithium-deficient state.

[0029] As mentioned above, the lithium extraction electrode described in this article can be directly placed in the water body to be extracted lithium, such as brine, after undergoing a delithiation reaction in advance. At the same time, the pumping device connected to the lithium extraction electrode is turned on, so that the water body can flow from bottom to top and contact the lithium extraction electrode, thereby maximizing the enrichment of lithium ions in the electrode, and ultimately achieving efficient lithium extraction.

[0030] Compared with the existing technology, the beneficial effects of this article are:

[0031] This article provides a lithium extraction electrode. Based on a specific structural design, it can be directly used in electrochemical lithium extraction from water after a delithiation reaction. At the same time, after the lithium extraction is completed, the lithium extraction electrode can directly recover lithium ions through a reverse reaction and be put into the next batch of water lithium extraction again. There is no need for replacement or device assistance, and the lithium extraction efficiency is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG1 is a schematic cross-sectional view of the lithium extraction electrode described in this article.

[0033] FIG2 is a schematic top view of the lithium extraction electrode described in this article. DETAILED DESCRIPTION

[0034] To better illustrate the purpose, technical solutions and advantages of this article, this article will be further described below with reference to the accompanying drawings and specific embodiments.

[0035] Unless otherwise specified, the materials used in the examples and comparative examples can be obtained through commercial channels.

[0036] Example 1

[0037] An embodiment of the lithium extraction electrode, lithium extraction method, and lithium extraction system described herein, as shown in Figures 1 and 2, includes a positive electrode sheet, a first monovalent cation membrane, a first transport layer, a negative electrode sheet, a second transport layer, and a second monovalent cation membrane stacked in sequence. At the same time, the stacked structural layers can be further stacked twice (that is, as shown in the figure, a stacked layer including a positive electrode sheet and a negative electrode sheet can be stacked twice with another stacked layer of the same structure). This embodiment only shows a lithium extraction electrode prepared by stacking a positive electrode sheet, a first monovalent cation membrane, a first transport layer, a negative electrode sheet, a second transport layer, and a second monovalent cation membrane in sequence. At the same time, each structural layer is wound into a cylindrical shape using a commercial winding machine, with the innermost layer being the positive electrode sheet. After winding, the lithium extraction electrode is provided with a layer of PE film for waterproofing on the outermost layer, and a negative pressure water pump is provided at the top that is sealed and connected to it and can be used for pumping water. The positive and negative electrode sheets are provided with tabs.

[0038] The positive electrode layer is obtained by mixing commercially available lithium iron phosphate, conductive agent carbon black and binder PVDF in a ratio of 97:1.5:1.5, using NMP as solvent and coating it on both sides of a 20 μm thick titanium current collector to form an active material layer. The thickness of the single-side active material layer is 30 μm, and the total thickness of the active material layers on both sides is 60 μm; the negative electrode layer is obtained by mixing commercially available graphite, conductive agent carbon black and binder PVDF in a ratio of 97:1.5:1.5, using NMP as solvent and coating it on both sides of a 20 μm thick titanium current collector to form an active material layer. The thickness of the single-side active material layer is 30 μm, and the total thickness of the active material layers on both sides is 60 μm.

[0039] The first transmission layer and the second transmission layer are porous sponge layers with a thickness of 80 μm, an average pore size of 100 μm, and a porosity of 80%; the first monovalent cation membrane and the second monovalent cation membrane are commercially available sulfonic acid type monovalent cation membranes.

[0040] The lithium extraction method described in this embodiment includes the following steps:

[0041] (1) The lithium extraction electrode described above is placed in a 5 mmol / L sodium chloride solution in a direction perpendicular to the stacking direction of the lithium extraction electrode layers. The tabs on the positive and negative electrode layers are connected to the two poles of the power supply to allow the positive electrode layer in the lithium extraction electrode to undergo a lithium delithiation reaction. The power supply voltage is 1.2 V and the reaction is carried out until the current density is approximately 0.

[0042] (2) The lithium extraction electrode after the delithiation reaction is placed in the brine of the lithium extraction water body in a direction perpendicular to the stacking direction of the lithium extraction electrode layers, and the pole ears on the positive and negative electrode layers are connected to the two poles of the power supply. The connection relationship is opposite to that of step (1). At the same time, the water pump is turned on to allow the brine to enter the lithium extraction electrode at a flow rate of 0.01m / s and flow from the bottom to the top of the lithium extraction electrode, so that the positive electrode layer in the lithium extraction electrode undergoes a lithium insertion reaction; the current and voltage settings of the power supply are the same as those in step (1). When the current density is lower than 0.5A / m 2 , statistical reaction time;

[0043] (3) The lithium extraction electrode after the lithium extraction reaction is placed in another 5mmol / L sodium chloride solution as a recovery solution, and the tabs on the positive and negative electrode layers are connected to the power supply. The connection relationship is the same as step (1), and the positive electrode layer in the lithium extraction electrode undergoes a lithium desorption reaction. The voltage setting of the power supply is the same as step (1). When the current density is about 0, the lithium extraction is completed.

[0044] Example 2

[0045] The only difference between this embodiment and embodiment 1 is that:

[0046] The positive electrode layer is obtained by mixing commercially available lithium iron phosphate, conductive agent carbon black and binder PVDF in a ratio of 97:1.5:1.5 with NMP as solvent and coating it on both sides of a 20 μm thick titanium current collector to form an active material layer. The thickness of the single-side active material layer is 20 μm, and the total thickness of the active material layers on both sides is 40 μm; the negative electrode layer is obtained by mixing commercially available graphite, conductive agent carbon black and binder PVDF in a ratio of 97:1.5:1.5 and coating it on both sides of a 20 μm thick titanium current collector to form an active material layer. The thickness of the single-side active material layer is 20 μm, and the total thickness of the active material layers on both sides is 40 μm.

[0047] The first transmission layer and the second transmission layer are porous resin layers with a thickness of 60 μm. The average pore size of the porous resin layer is 120 μm, and the porosity is 90%.

[0048] The lithium extraction method described in this embodiment includes the following steps:

[0049] (1) The lithium extraction electrode described above is placed in a 5 mmol / L sodium chloride solution in a direction perpendicular to the stacking direction of the lithium extraction electrode layers. The tabs on the positive and negative electrode layers are connected to the two poles of the power supply to allow the positive electrode layer in the lithium extraction electrode to undergo a lithium delithiation reaction. The power supply voltage is 1.2 V and the reaction is carried out until the current density is approximately 0.

[0050] (2) The lithium extraction electrode after the delithiation reaction is placed in the brine of the lithium extraction water body in a direction perpendicular to the stacking direction of the lithium extraction electrode layers, and the pole ears on the positive and negative electrode layers are connected to the two poles of the power supply. The connection relationship is opposite to that of step (1). At the same time, the water pump is turned on to allow the brine to enter the lithium extraction electrode at a flow rate of 0.03m / s and flow from the bottom to the top of the lithium extraction electrode, so that the positive electrode layer in the lithium extraction electrode undergoes a lithium insertion reaction; the current and voltage settings of the power supply are the same as those in step (1). When the current density is lower than 0.5A / m 2 , statistical reaction time;

[0051] (3) The lithium extraction electrode after the lithium extraction reaction is placed in another 5mmol / L sodium chloride solution as a recovery solution, and the tabs on the positive and negative electrode layers are connected to a power supply. The connection relationship is the same as step (1), and the positive electrode layer in the lithium extraction electrode undergoes a lithium desorption reaction. The current and voltage setting of the power supply is the same as step (1), 1.2V, and the reaction is continued until the current density is about 0, that is, the lithium extraction is completed.

[0052] Example 3

[0053] The only difference between this embodiment and embodiment 1 is that:

[0054] The positive electrode layer is obtained by mixing commercially available lithium cobalt oxide, conductive agent carbon black and binder PVDF in a ratio of 97:1.5:1.5 with NMP as solvent and coating it on both sides of a 20 μm thick titanium current collector to form an active material layer. The thickness of the single-side active material layer is 30 μm, and the total thickness of the active material layers on both sides is 60 μm; the negative electrode layer is obtained by mixing commercially available graphite, conductive agent carbon black and binder PVDF in a ratio of 97:1.5:1.5 with NMP as solvent and coating it on both sides of a 20 μm thick titanium current collector to form an active material layer. The thickness of the single-side active material layer is 30 μm, and the total thickness of the active material layers on both sides is 60 μm.

[0055] In steps (1) to (3) of the lithium extraction method, the voltage of the power supply is set to 1.2V.

[0056] Comparative Example 1

[0057] A lithium extraction method comprises the following steps:

[0058] The plate made of commercially available lithium iron phosphate in a lithium-deficient state was used as a lithium extraction electrode. At the same time, the plate made of commercially available graphite in Example 1 was used as a counter electrode and placed in the same brine to be extracted as in Example 1. The lithium extraction electrode and the counter electrode were connected to a power supply and lithium extraction was carried out. The voltage of the power supply was 1.2V. When the current density was lower than 0.5A / m 2 , and the reaction time is calculated; then the lithium-extracted electrode is delithiated according to the same steps as step (3) of Example 1.

[0059] Comparative Example 2

[0060] A lithium extraction method comprises the following steps:

[0061] (1) A waste commercial lithium iron phosphate battery was disassembled, and the battery core was rewound into a cylindrical shape similar to the lithium extraction electrode described in Example 1, and then coated with a PE film to obtain a lithium extraction electrode made from the waste battery core;

[0062] (2) Lithium extraction electrodes were prepared from waste batteries by following the same method as in Example 1. A negative pressure water pump was installed at the top end and was connected to the negative pressure water pump for pumping water. Lithium was extracted by following the same method as in Example 1.

[0063] Effect Example 1

[0064] In order to illustrate the effects of the lithium extraction electrodes and lithium extraction methods described in this article, the brine to be extracted lithium used in each embodiment and comparative example is of the same type. Therefore, before lithium extraction, the concentration of lithium ions in the brine is pre-stated by direct measurement using an atomic absorption spectrophotometer. After the lithium extraction of the lithium extraction electrodes in each embodiment and comparative example is completed, the lithium ion concentration of the brine is counted twice. The recovery rate (%) of the lithium ions in the brine described in each embodiment and comparative example is calculated based on the two statistical values. At the same time, the unit brine lithium extraction rate time (h / L) of each lithium extraction electrode is calculated based on the volume of the brine. The results are shown in Table 1.

[0065] Table 1

[0066] As can be seen from Table 1, the lithium extraction electrodes of the various embodiments described herein have ideal lithium extraction recovery efficiency. After lithium extraction, the recovery rate of lithium ions in the brine can reach more than 88%. At the same time, the lithium extraction time per unit brine can be maintained below 4h / L. The comprehensive effect is far better than the lithium extraction method described in Comparative Example 1 using conventional lithium iron phosphate electrodes and counter electrodes as lithium extraction devices. This type of existing method not only takes a long time per unit, but also has a low lithium extraction efficiency. When the battery cell of a lithium iron phosphate battery is directly used as a lithium extraction device for lithium extraction, although its reaction principle is similar to that of the lithium extraction electrode described herein, the structure of the battery cell is different from that of the lithium extraction electrode described herein, and it cannot effectively carry out selective enrichment of lithium ions. Therefore, its effect is even worse than the single electrode-counter electrode lithium extraction method described in Comparative Example 1.

[0067] Effect Example 2

[0068] In order to explore the influence of the thickness and property parameters of each structural layer in the lithium extraction electrode described in this article on the lithium extraction effect, based on the lithium extraction electrode described in Example 1, the following control group products were set:

[0069] Control group 1: The lithium extraction electrode differs from Example 1 only in that the thickness of the active material layer on one side of the positive electrode sheet is 40 μm, and the total thickness of the active material layers on both sides is 80 μm. The thickness of the active material layer on one side of the negative electrode sheet is 40 μm, and the total thickness of the active material layers on both sides is 80 μm.

[0070] Control Group 2: The lithium extraction electrode differs from Example 1 only in that the thickness of the active material layer on one side of the positive electrode sheet is 10 μm, and the total thickness of the active material layers on both sides is 20 μm. The thickness of the active material layer on one side of the negative electrode sheet is 10 μm, and the total thickness of the active material layers on both sides is 20 μm.

[0071] Control group 3: The only difference from the lithium extraction electrode of Example 1 is that the first transport layer and the second transport layer are porous sponge layers with a thickness of 100 μm.

[0072] Control group 4: The only difference from the lithium extraction electrode of Example 1 is that the first transport layer and the second transport layer are porous sponge layers with a thickness of 50 μm.

[0073] Control group 5: The only difference from the lithium extraction electrode of Example 1 is that the average pore size of the porous sponge layer is 20 μm.

[0074] Control group 6: The only difference from the lithium extraction electrode of Example 1 is that the average pore size of the porous sponge layer is 100 μm.

[0075] Control group 7: The only difference from the lithium extraction electrode of Example 1 is that the average pore size of the porous sponge layer is 200 μm.

[0076] Control group 8: The only difference from the lithium extraction electrode of Example 1 is that the average pore size of the porous sponge layer is 300 μm.

[0077] The lithium extraction electrodes prepared in each control group were subjected to lithium extraction according to the same method as in Example 1, and the lithium extraction effects were statistically analyzed according to the same statistical method as in Effect Example 1. The results are shown in Table 2.

[0078] Table 2

[0079] As can be seen from Table 2, when the active material coating of the positive electrode layer in the lithium extraction electrode described in this article is too little, its lithium extraction saturation is too low, and the lithium ion recovery in the brine cannot be fully realized. If it is too much, the polarization effect of the lithium extraction electrode will be increased, which will in turn cause the lithium extraction efficiency of the lithium extraction electrode to deteriorate and the lithium extraction time to increase. The thickness and pore size of the porous sponge or porous resin layer used as the transport layer will also affect the lithium extraction effect of the lithium extraction electrode. If the thickness is too thin or too thick, or the pore size is too large or too small, it may not be possible to effectively achieve sufficient and rapid transmission of lithium ions, which will ultimately increase the lithium extraction time of the lithium extraction electrode or reduce the lithium ion recovery rate.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this article and are not intended to limit the scope of protection of this article. Although this application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of this article may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of this article.

Claims

1. A lithium extraction electrode, characterized in that: It comprises a positive electrode sheet layer, a first monovalent cation membrane, a first transmission layer, a negative electrode sheet layer, a second transmission layer and a second monovalent cation membrane which are stacked in sequence; the positive electrode sheet layer and the negative electrode sheet layer are provided with pole ears for connecting to a power source.

2. The lithium extraction electrode according to claim 1, characterized in that: The positive electrode layer includes a current collector and an active material layer, and the active material is at least one of lithium iron phosphate, lithium iron manganate, lithium iron manganese phosphate, lithium vanadate, and lithium cobaltate.

3. The lithium extraction electrode according to claim 2, characterized in that: The positive electrode sheet layer includes a first active material layer, a current collector and a second active material layer in sequence; the thickness of the first active material layer and the second active material layer is 20 to 30 μm.

4. The lithium extraction electrode according to claim 3, characterized in that: The total thickness of the active material layer in the positive electrode sheet is 40 to 60 μm.

5. The lithium extraction electrode according to claim 1, characterized in that: The first transmission layer and the second transmission layer are at least one of a porous sponge layer and a resin layer. The average pore size of the first transmission layer and the second transmission layer is 50 to 200 μm, and the porosity is 80 to 90%.

6. The lithium extraction electrode according to claim 5, characterized in that: The thickness of the first transmission layer and the second transmission layer is 60-80 μm.

7. A lithium extraction method, characterized in that: The following steps are involved: Placing the lithium extraction electrode according to any one of claims 1 to 6 into a soluble metal salt solution, connecting a power source and causing the positive electrode layer in the lithium extraction electrode to undergo a lithium desorption reaction; The lithium extraction electrode after the lithium stripping reaction is placed in the water body to be extracted with lithium, and the power is turned on to cause the positive electrode layer in the lithium extraction electrode to undergo lithium insertion reaction; The lithium extraction is completed by placing the lithium extraction electrode after the lithium extraction reaction into a recovery solution, connecting the power supply and causing the positive electrode layer in the lithium extraction electrode to undergo a lithium de-reaction reaction.

8. The lithium extraction method according to claim 7, characterized in that: In the lithium extraction electrode, the positive electrode layer, the first monovalent cation membrane, the first transport layer, the negative electrode layer, the second transport layer and the second monovalent cation membrane are sequentially stacked and wound into a cylindrical shape, with the innermost layer being the positive electrode layer.

9. The lithium extraction method according to claim 7, characterized in that: The lithium extraction electrode after the lithium removal reaction is placed in the water body to be extracted with lithium in a direction perpendicular to the direction in which the layers of the lithium extraction electrode are stacked in sequence. When the positive electrode layer in the lithium extraction electrode undergoes a lithium insertion reaction, the water body to be extracted flows from the bottom of the lithium extraction electrode to the upper part.

10. The lithium extraction method according to claim 9, characterized in that: The flow rate of the water body to be extracted with lithium is 0.01-0.03 m / s.

11. A lithium extraction system, characterized in that: It comprises a two-pole power supply, the lithium extraction electrode according to any one of claims 1 to 6, and a negative pressure water pumping device hermetically connected to the lithium extraction electrode, wherein the positive electrode layer in the lithium extraction electrode is in a lithium-deficient state.

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