A method for preparing a uniform and controllable prelithiated electrode

Abstract

The present invention discloses a method for preparing a uniform and controllable prelithiated electrode sheet. The preparation method includes, in an inert environment, immersing the electrode sheet with a lithiumophilic coating after the second rolling into molten liquid lithium, and then performing surface extrusion and the third curing. The method of the present invention can uniformly embed the molten metal lithium into the lithiumophilic coating on the electrode sheet by means of immersion. By controlling the thickness of the lithiumophilic coating, the solid content of the slurry during coating, the pressure of the second rolling, and the immersion time, the control of the precise prelithiation amount can be achieved; compared with the traditional prelithiation method, the present invention is easier to achieve uniform and precise prelithiation control, and is more conducive to improving the first-cycle discharge capacity of the battery, thereby enhancing the energy density of the lithium-ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium - ion batteries, and particularly to a method for preparing a uniform and controllable prelithiated electrode. Background Art

[0002] Due to advantages such as high energy density, long cycle life, and no memory effect, lithium - ion batteries have currently become one of the most important electrochemical devices and are widely used in the fields of electric vehicles, consumer electronics, energy storage, etc. With the continuous optimization of materials, manufacturing processes, product designs, etc., the energy density of lithium - ion batteries is getting higher and higher, and the user experience in the fields of consumer electronics and electric vehicles is getting better and better. In order to enable lithium - ion batteries to have a broader application market and better user experience, higher energy density is the goal that all practitioners in the lithium - ion battery industry are constantly striving for.

[0003] Currently, one of the most important ways to improve the energy density of lithium - ion batteries is prelithiation. During the first charge of a lithium - ion battery, the organic electrolyte will be reduced and decomposed on the surface of the negative electrode to form a solid electrolyte interphase (SEI) film, permanently consuming a large amount of lithium from the positive electrode, resulting in a low initial Coulomb efficiency (ICE) of the first cycle and reducing the capacity and energy density of the lithium - ion battery. As a negative electrode material, graphite will cause 5% - 10% irreversible lithium loss during the first cycle, while for the high - capacity negative electrode material silicon, it will cause 15% - 35% irreversible lithium loss during the first cycle. To solve this problem, prelithiation technology has been studied. By prelithiating the electrode material to compensate for lithium, the irreversible lithium loss caused by the formation of the SEI film is offset, so as to improve the initial efficiency of the battery and further increase the energy density of the battery.

[0004] Currently, the methods for negative electrode prelithiation mainly include metal lithium prelithiation, electrochemical prelithiation, organolithium compound prelithiation, etc. Currently, the most common methods for negative electrode metal lithium prelithiation in the prior art are lithium - sheet prelithiation and lithium - powder prelithiation. However, lithium sheets cannot be made thin, uniform, and have a small error amount, resulting in inaccurate control and uneven prelithiation when using lithium - sheet prelithiation; lithium - powder prelithiation has a high risk during the implementation process due to the high activity of lithium powder, and good prelithiation uniformity cannot be achieved either. The process of electrochemical prelithiation is relatively complex, increasing the process flow and cost of battery manufacturing. Organolithium compound prelithiation may introduce other elements that do not provide capacity, thus having some adverse effects on improving the energy density of lithium - ion batteries. Summary of the Invention

[0005] The present invention discloses a method for preparing a uniform and controllable pre-lithiated electrode sheet to address the problems in the prior art. This method can achieve the infiltration of molten liquid metal lithium into the lithiumophilic coating of the negative electrode sheet, thereby realizing the uniformity of pre-lithiation on the negative electrode sheet. Moreover, factors such as the thickness of the lithiumophilic coating, the solid content of the coating slurry, the rolling pressure, and the infiltration time can be controlled to precisely control the required lithium intercalation amount. Compared with other methods, it can more significantly improve the Coulombic efficiency of the lithium-ion battery in the first cycle, and further enhance the energy density of the lithium-ion battery.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for preparing a uniform and controllable pre-lithiated electrode sheet provided by the present invention, the preparation method comprising: in an inert environment, infiltrating the electrode sheet with a lithiumophilic coating after the second rolling into molten liquid metal lithium, and then performing surface extrusion and third curing.

[0008] The above design of the present invention: By performing the second rolling on the electrode sheet with a lithiumophilic coating, the bonding strength between the lithiumophilic coating and the active material layer can be enhanced. However, with the increase of the rolling pressure during the second rolling, the lithium loading capacity of the lithiumophilic coating will decrease. Therefore, according to the actual coating situation, a pressure of 0 ton - 5 tons can be applied to the lithiumophilic coating to enhance the bonding strength between the lithiumophilic coating and the active material layer on the basis of a certain lithium loading capacity of the lithiumophilic coating; then infiltrate the electrode sheet with a lithiumophilic coating into molten liquid metal lithium to make the molten metal lithium uniformly infiltrate into the lithiumophilic coating. Through surface extrusion and third curing, during the surface extrusion process, it is not only beneficial to remove the molten metal lithium adsorbed on the surface of the lithiumophilic coating, but also beneficial to the more stable existence of metallic lithium in the lithiumophilic coating; in addition, factors such as the thickness of the lithiumophilic coating, the solid content of the coating slurry, the pressure of the second rolling, and the infiltration time can be controlled to precisely control the required lithium intercalation amount.

[0009] As a further solution, the mass ratio of the solid content of the slurry of the lithiumophilic coating is 10% - 30%. The solid content of the slurry of the lithiumophilic coating will affect the porosity of the lithiumophilic coating. When the mass ratio of the solid content of the slurry is small, there are more voids in the cured lithiumophilic coating, more infiltrated metallic lithium, and stronger lithium loading capacity. However, if the solid content of the slurry is too low, the coatability of the lithiumophilic coating slurry will decrease; conversely, when the mass ratio of the solid content of the slurry is larger, there are fewer voids in the cured lithiumophilic coating, resulting in a decrease in the lithium loading capacity, and it will also affect the coatability of the lithiumophilic coating slurry.

[0010] As a further solution, the pressure of the second rolling is 0 ton - 5 tons; the thickness of the lithiumophilic coating is 5 μm - 30 μm; the infiltration time is 6 s - 50 s; the pressure of surface extrusion is 0 kg - 100 kg. The thickness of the lithiumophilic coating, the pressure of the second rolling, the pressure of surface extrusion, and the infiltration time will all directly affect the lithium loading of the lithiumophilic coating. When other conditions are the same, the lithium loading of the lithiumophilic coating increases with the increase in the thickness of the lithiumophilic coating, decreases with the increase in the pressure of the second rolling, and increases with the increase in the infiltration time when not fully infiltrated (it will not increase after full infiltration). When the infiltrated electrode sheet is subjected to surface extrusion, the pressure of surface extrusion can not only remove the excess molten metallic lithium on the surface of the lithiumophilic coating, but also make the metallic lithium in the lithiumophilic coating more stable to a certain extent.

[0011] As a further solution, the mass ratio of the solid content of the slurry of the lithiumophilic coating is 15% - 25%. This is beneficial to obtaining a suitable porosity of the lithiumophilic coating on the basis of better coating operability.

[0012] As a further solution, the pressure of the second rolling is 1 ton - 3 tons; the thickness of the lithiumophilic coating is 10 μm - 20 μm; the infiltration time is 10 s - 25 s. This is more conducive to the infiltration operation, improves production efficiency and obtains a lithium loading that can be accurately controlled, and can also reduce the occurrence of powder falling off the lithiumophilic coating due to too small pressure of the second rolling.

[0013] As a further solution, the lithiumophilic coating includes a lithiumophilic material.

[0014] As a further solution, the lithiumophilic material includes one or more of porous carbon, carbon fiber, hard carbon, soft carbon, carbon nanotube, graphene, petroleum coke, and carbon black. The lithiumophilic material has good affinity with molten metallic lithium, and the molten metallic lithium can be quickly infiltrated, which is beneficial to the preparation of the electrode sheet with uniform lithium intercalation.

[0015] As a further solution, the lithiumophilic material includes porous carbon. The texture of porous carbon is more conducive to realizing the process of pre-lithiation of molten liquid lithium by infiltration.

[0016] As a further solution, the condition for the third curing is cold air.

[0017] As a further solution, the preparation method further includes:

[0018] S1: Coating the negative electrode slurry on both sides of the current collector, performing the first curing, and the first rolling to obtain an electrode sheet with an active material coating;

[0019] S2: Coating the lithiumophilic material on the electrode sheet with an active material layer, performing the second curing, and the second rolling to obtain an electrode sheet with an active material coating and a lithiumophilic coating.

[0020] As a further solution, the temperature of the first curing is 60°C - 80°C, and the time of the first curing is 5 min - 7 min; the pressure of the first rolling is 9 tons - 11 tons; the temperature of the second curing is 50°C - 70°C, and the time of the second curing is 1 min - 2 min. Excellent adhesion between the current collector, the active material coating, and the lithium-philic coating can be achieved, and a better lithium-philic coating can be obtained, providing an embedding basis for the embedding of metallic lithium, and also promoting better and more uniform contact between the metallic lithium in the lithium-philic coating and the active material in the active material coating, thereby facilitating the improvement of the first-cycle Coulombic efficiency of the battery and further enhancing the energy density of the battery.

[0021] As a further solution, the thickness of the current collector is 6 μm - 10 μm; the thickness of the active material coating is 100 μm - 200 μm.

[0022] As a further solution, the current collector is a copper foil.

[0023] As a further solution, the active material layer includes a negative active material; as a further solution, the negative active material includes one or more of graphite, hard carbon, silicon monoxide, and silicon-carbon composite materials.

[0024] The present invention also provides a system for the preparation method of the prelithiated electrode.

[0025] As a further solution, the system includes a coating system, a wetting system, and a transportation system;

[0026] The wetting system is in an inert gas atmosphere environment;

[0027] In the advancing direction of the current collector, the coating system is sequentially provided with a first coating device, a second coating device, and a rolling device; an oven is provided between the first coating device and the second coating device, and between the second coating device and the rolling device; the first coating device and the second coating device are respectively used for coating both sides of the current collector or the electrode.

[0028] In the advancing direction of the electrode with the active material coating and the lithium-philic coating, the wetting system is sequentially provided with a heating tank body, at least 2 pressing roller shafts, and a cold air box; the pressing roller shafts are respectively located on both sides of the electrode with the active material coating and the lithium-philic coating.

[0029] The transportation system includes a device for winding and unwinding the current collector or the electrode and a traveling device, a first guiding and traction roller shaft, and a second guiding and traction roller shaft;

[0030] The first guiding and traction roller shaft and the second guiding and traction roller shaft are arranged behind the rolling equipment of the coating system. The first guiding and traction roller shaft is used to guide the electrode sheet with the active material coating to travel towards the coating system again; the second guiding and traction roller shaft is used to guide the electrode sheet with the active material coating and the lithiumophilic coating to travel towards the infiltration system.

[0031] For the pre-lithiation method of the present invention, a set of related pre-lithiation pipeline production line system has been developed; the coating system in the present invention can achieve staged coating of the active material coating and the lithiumophilic coating in one system, reducing the equipment cost; and the coating system can also achieve double-sided coating. In the infiltration system, using a pressure roller shaft between the heating tank and the cold air box can remove the metallic lithium liquid adsorbed on the surface of the electrode sheet, making the pre-lithiation amount precisely controllable, and to a certain extent, making the metallic lithium exist more stably in the lithiumophilic coating, and can also provide a traction effect; the first guiding and traction roller shaft can not only guide the electrode sheet coated only with the active material coating back into the coating system for coating the lithiumophilic coating, which is beneficial to reducing the equipment cost and the floor area of the system, but also when the equipment is in the stage of preparing to coat the lithiumophilic coating, the first guiding and traction roller shaft can also have the functions of winding and unwinding, providing time preparation for coating the lithiumophilic coating; while the second guiding and traction roller shaft realizes the connection of the two systems, thus forming a pre-lithiation pipeline, and also has the functions of winding and unwinding, which is beneficial to providing time preparation for infiltration. And the number and length of the ovens in the present invention can be designed according to the production speed.

[0032] As a further solution, the oven in the coating system is an oven having at least a first passage and a second passage for the input and output of the electrode sheet. The oven is arranged between the first coating device and the second coating device; the first passage of the oven is used for the curing of the current collector or the electrode sheet after being coated by the first coating device, and the second passage of the oven is used for the curing of the other side of the current collector or the electrode sheet after being coated by the second coating device. The multi-passage oven can realize the curing of the coatings applied step by step using the same oven. When the current collector is coated with the slurry on the upper layer by the first coating device, it is input and output through the first passage of the oven to realize the curing of the upper layer coating slurry. Subsequently, the lower layer coating slurry of the current collector is coated by the second coating device, and then through the input and output of the second passage of the oven, the curing of the lower layer coating slurry is realized. The multi-passage oven is beneficial to reducing the equipment cost, the occupied area of the equipment and the production energy consumption.

[0033] As a further solution, the transportation system includes a coating system traction roller shaft group for traction the current collector or the electrode sheet to travel through the coating system and change the traveling direction of the current collector or the electrode sheet.

[0034] As a further solution, the traction roller shaft group of the coating system is arranged in the coating system, and the traction roller shaft group of the coating system includes at least two traction roller shafts of the coating system.

[0035] As a still further solution, the traction roller shafts of the coating system include a first traction roller shaft of the coating system and a second traction roller shaft of the coating system. The first traction roller shaft of the coating system and the second traction roller shaft of the coating system are arranged between the oven and the second coating device. The first traction roller shaft of the coating system and the second traction roller shaft of the coating system are used to change the traveling direction of the current collector or the electrode sheet. The first traction roller shaft of the coating system and the second traction roller shaft of the coating system can also cooperate with the second coating device to coat the other side of the current collector or the electrode sheet, so as to realize the step-by-step coating on both sides of the current collector or the electrode sheet. It can also cooperate with the use of a multi-pass oven, which is beneficial to the full curing of the coating layer in the oven, greatly reducing the floor area of the equipment and reducing the production energy consumption.

[0036] As a further solution, the transportation system includes a traction roller shaft group of the infiltration system, which is used to traction the electrode sheet with an active material coating and a lithium-philic coating from the second guiding traction roller shaft through the infiltration system.

[0037] As a further solution, the traction roller shaft group of the infiltration system is arranged in the infiltration system, and the traction roller shaft group of the infiltration system includes at least five traction roller shafts of the infiltration system.

[0038] As a still further solution, the traction roller shafts of the infiltration system include a first traction roller shaft of the infiltration system, a second traction roller shaft of the infiltration system, a third traction roller shaft of the infiltration system, a fourth traction roller shaft of the infiltration system, and a fifth traction roller shaft of the infiltration system. The first traction roller shaft of the infiltration system is arranged between the second guiding traction roller shaft and the second traction roller shaft of the infiltration system for traction. The second traction roller shaft of the infiltration system, the third traction roller shaft of the infiltration system, the fourth traction roller shaft of the infiltration system, and the fifth traction roller shaft of the infiltration system are arranged in the heating tank body, wherein the second traction roller shaft of the infiltration system and the fifth traction roller shaft of the infiltration system are located on the same horizontal plane, and the third traction roller shaft of the infiltration system and the fourth traction roller shaft of the infiltration system are located below the horizontal plane of the second traction roller shaft of the infiltration system and the fifth traction roller shaft of the infiltration system. The first traction roller shaft of the infiltration system cooperates with the second guiding traction roller shaft to traction the electrode sheet with an active material coating and a lithium-philic coating into the infiltration system for pre-lithiation.

[0039] As a further solution, the transportation system further includes an unwinder and a winder. The unwinder is arranged in front of the first coating device in the coating system. The winder is arranged behind the cold air box in the infiltration system. One end of the current collector or the electrode sheet in the coating system is connected to the unwinder. One end of the electrode sheet with an active material coating and a lithium-philic coating that has been fully infiltrated with molten lithium in the infiltration system is connected to the winder.

[0040] The features and beneficial effects of the present invention are as follows:

[0041] (1) The method of the present invention can uniformly embed molten metallic lithium into the lithiumophilic coating on the electrode sheet by infiltration. By controlling the thickness of the lithiumophilic coating, the solid content of the coating slurry, the pressure of the second rolling, and the infiltration time, precise control of the lithium insertion amount can be achieved.

[0042] (2) A production line for the method of the present invention has been developed, which is conducive to realizing the streamlined production of pre-lithiated electrode sheets.

[0043] (3) Compared with the traditional pre-lithiation method, the present invention can pre-lithiate uniformly and precisely control the pre-lithiation amount, which is more conducive to improving the first-cycle discharge capacity of the battery and enhancing the energy density of the battery. Description of the Drawings

[0044] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0045] Figure 1 It is a schematic diagram of the pre-lithiated electrode sheet provided by the embodiment of the present invention.

[0046] Figure 2 It is a schematic diagram of the equipment for the method of preparing the pre-lithiated electrode sheet provided by the embodiment of the present invention.

[0047] Figure 3 It is a comparison chart of the first charge-discharge curves of three kinds of battery cells obtained by three different pre-lithiation methods provided by Embodiment 1 of the present invention.

[0048] Figure 4 It is a comparison chart of the first charge-discharge curves of three kinds of battery cells obtained by three different pre-lithiation methods provided by Embodiment 2 of the present invention.

[0049] Among them, the above-mentioned drawings include the following reference numerals:

[0050] 1 - Coating system; 2 - Infiltration system; 3 - Transportation system; 11 - Current collector; 12 - First coating equipment; 13 - Oven; 14 - Second coating equipment; 15 - Rolling equipment; 21 - Electrode sheet with active material coating and lithium - philic coating; 22 - Heating tank body; 23 - Press roller shaft; 24 - Cold air box; 31 - Unwinder; 32 - First coating system traction roller shaft; 33 - Second coating system traction roller shaft; 34 - First guiding traction roller shaft; 35 - Second guiding traction roller shaft; 36 - First infiltration system traction roller shaft; 37 - Second infiltration system traction roller shaft; 38 - Third infiltration system traction roller shaft; 39 - Fourth infiltration system traction roller shaft; 310 - Fifth infiltration system traction roller shaft; 311 - Rewinder; Ⅰ - Route 1; Ⅱ - Route 2. Detailed implementation mode

[0051] To facilitate the understanding of a method for preparing a uniform and controllable pre - lithium electrode sheet of the present invention, the method for preparing the pre - lithium electrode sheet of the present invention will be described more comprehensively below. Embodiments of the present invention are given, but the scope of the present invention is not limited thereby. The relational terms such as "first", "second", and "third" in the description and claims of the present invention are only used to distinguish one procedure with the same name from another, and do not necessarily require or imply any such actual relationship or order between these procedures. For example, "the first rolling" and "the second rolling" only represent the distinction between two rolling procedures, and do not require or imply that the first rolling must or has been experienced before the second rolling.

[0052] We also pre - lithium the negative electrode of the battery using the equipment of the present invention. The pre - lithium process is mainly divided into two routes, including Route 1 (Ⅰ) and Route 2 (Ⅱ). From Figure 2 As can be seen from the equipment flow chart of the method for preparing a pre - lithium electrode sheet provided in the embodiment of the present invention, the system of the preparation method of the present invention mainly includes a coating system 1, an infiltration system 2, and a transportation system 3.

[0053] Among them, Route 1 (Ⅰ) is mainly realized in the coating system 1. Through the cooperation between the coating system 1 and the transportation system 3, the coating of the current collector 11 or the electrode sheet is achieved. The transportation system 3 includes a coating system traction roller shaft group for pulling the current collector 11 or the electrode sheet to travel through the coating system 1 and change the traveling direction of the current collector 11 or the electrode sheet. The coating system traction roller shaft group includes at least 2 coating system traction roller shafts. The coating system 1 includes a first coating device 12, an oven 13, a second coating device 14, and a rolling device 15; the transportation system 3 includes an unwinder 31, a first coating system traction roller shaft 32, a second coating system traction roller shaft 33, and a first guiding traction roller shaft 34. The unwinder 31 releases the current collector 11. Through the actions of the unwinder 31, the first coating system traction roller shaft 32, and the second coating system traction roller shaft 33, the current collector 11 or the electrode sheet travels in the coating system 1. The current collector 11 passes through the first coating device 12 to complete the coating of the negative electrode slurry on one side of the current collector 11 to obtain an electrode sheet with a single-sided active material coating. Then, it enters the first passage of the oven 13 and the coated negative electrode slurry is cured in the oven 13. Subsequently, it exits the oven 13 from the first passage of the oven 13. Then, through the first coating system traction roller shaft 32 and the second coating system traction roller shaft 33, the advancing direction of the electrode sheet with a single-sided active material coating is changed. It passes through the second coating device 14 to complete the coating of the negative electrode slurry on the other side of the electrode sheet with a single-sided active material coating. After the electrode sheet with an active material coating after coating the negative electrode slurry enters the second passage of the oven 13 again and the coated negative electrode slurry is cured in the oven 13, it then exits the oven 13 from the second passage of the oven 13. The cured electrode sheet with an active material coating undergoes the first rolling by the rolling device 15 to complete the coating of the negative electrode slurry and obtain an electrode sheet with a double-sided active material coating. Subsequently, it is connected to the unwinder 31 of the transportation system 3 through the first guiding traction roller shaft 34. By repeating the above operations, the coating of the lithiumophilic material is completed in the coating system 1, and an electrode sheet 21 with an active material coating and a lithiumophilic coating is further obtained. Among them, the first coating device 12 and the second coating device 14 are respectively located on both sides of the current collector 11 or the electrode sheet to achieve double-sided coating; the electrode sheet with an active material coating after completing the coating of the negative electrode slurry passes through the rolling device 15 to increase the adhesion between the active materials and between the coating and the current collector 11. The electrode sheet with an active material coating is coated with the lithiumophilic material again through the coating system 1 to obtain an electrode sheet 21 with an active material coating and a lithiumophilic coating. The obtained electrode sheet 21 with an active material coating and a lithiumophilic coating passes through the rolling device 15. Within a certain pressure of the rolling device 15, while the lithiumophilic coating can have a certain lithium-carrying capacity, the lithiumophilic coating and the active material layer also have excellent bonding strength.

[0054] Route 2 (II) is mainly implemented in the infiltration system 2. The pre-lithiation process of the electrode sheet 21 with an active material coating and a lithiumophilic coating is completed through the mutual cooperation between the infiltration system 2 and the transportation system 3. The transportation system 3 includes an infiltration system traction roller shaft group for traction the electrode sheet 21 with an active material coating and a lithiumophilic coating to travel through the infiltration system 2 from the second guiding traction roller shaft 35. The infiltration system traction roller shaft group includes at least 5 infiltration system traction roller shafts. The infiltration system includes a heating tank 22 and a cold air box 24; the transportation system 3 includes a second guiding traction roller shaft 35, a first infiltration system traction roller shaft 36, a second infiltration system traction roller shaft 37, a third infiltration system traction roller shaft 38, a fourth infiltration system traction roller shaft 39, a fifth infiltration system traction roller shaft 310, and a unwinder 311. The electrode sheet 21 with an active material coating and a lithiumophilic coating after the second rolling by the rolling equipment 15 in the coating system 1 is guided and tractioned to the infiltration system 2 through the second guiding traction roller shaft 35 of the transportation system 3. In an inert environment, the electrode sheet 21 with an active material coating and a lithiumophilic coating passes through the second guiding traction roller shaft 35 and the first infiltration system traction roller shaft 36 in sequence. The first infiltration system traction roller shaft 36 changes the advancing direction of the electrode sheet 21 with an active material coating and a lithiumophilic coating, and then enters the heating tank 22. The heating tank 22 includes a second infiltration system traction roller shaft 37, a third infiltration system traction roller shaft 38, a fourth infiltration system traction roller shaft 39, and a fifth infiltration system traction roller shaft 310. Among them, the second infiltration system traction roller shaft 37 and the fifth infiltration system traction roller shaft 310 are located on the same horizontal plane, and the third infiltration system traction roller shaft 38 and the fourth infiltration system traction roller shaft 39 are located below the horizontal plane of the second infiltration system traction roller shaft 37 and the fifth infiltration system traction roller shaft 310; the molten lithium in the heating tank 22 can be formed into a molten state of liquid lithium by heating, and the electrode sheet 21 with an active material coating and a lithiumophilic coating is infiltrated in the heating tank 22 to promote the lithium metal to enter the lithiumophilic coating. After infiltration, the pressing roller shafts 23 located on both sides of the electrode sheet 21 with an active material coating and a lithiumophilic coating are used for extrusion, which can not only remove the molten lithium adsorbed on the surface of the electrode sheet, but also help to stably store the lithium metal in the lithiumophilic coating, so as to realize the control of the accurate lithium intercalation amount. Then it enters the cold air box 24 to cool and solidify the lithium metal in the lithiumophilic coating, and then the winder 311 is used for winding. The process of preparing the pre-lithiated electrode sheet is completed, and the pre-lithiated negative electrode sheet is obtained as Figure 1 shown.

[0055] We first compared the initial efficiency of the battery assembled with the molten lithium uniformly pre-lithiated electrode sheet, the ordinary lithium metal sheet pre-lithiated electrode sheet, and the non-pre-lithiated electrode sheet of the present invention through two specific experiments, as shown in Examples 1-2.

[0056] Example 1:

[0057] When the solid content of the slurry for coating the lithiumophilic coating is 20%, the pressure for the second roll pressing of the lithiumophilic coating is 0 ton, and the thickness is 10 μm, after the lithiumophilic coating is completely wetted, the measured lithium loading per unit area is 0.16 mg / cm 2 When using an unprelithiated graphite negative electrode (the electrode sheet specification is 10 cm × 10 cm, one negative electrode sheet is coated on one side, and three negative electrode sheets are coated on both sides) to assemble a full cell with ternary materials (the NP (negative electrode reversible surface capacity / positive electrode reversible surface capacity) ratio is 1.1), the battery is named G-NCM. The first charge capacity of the G-NCM battery is 2.41 Ah, the first discharge capacity is 2.11 Ah, and the capacity loss is 0.3 Ah, that is, the total capacity to be intercalated with lithium is 0.3 Ah. According to the specific capacity of lithium being 3860 mAh / g, the amount of metallic lithium that needs to be compensated is 78 mg, the amount of lithium compensation required for each side of the negative electrode sheet is 11.14 mg, and the coating thickness of the lithiumophilic coating should be controlled at 7 μm.

[0058] Select a copper foil with a thickness of 8 μm, coat graphite slurry on the surface of the copper foil, control the single-sided active material surface density at 10 mg / cm 2 , control the coating speed at 5 m / min, the oven length at 30 m, and the temperature at 70 °C. Through the cooperation of the unwinder and the rewinder, the copper foil passes through the first coating equipment, the oven, the second coating equipment, the oven, and the rolling equipment in sequence, so that both sides of the copper foil are coated with the negative electrode slurry, and a pole piece with an active material coating is obtained. Among them, the pressure of the rolling equipment is 10 tons.

[0059] We coat the pole piece with the active material coating again using the coating system for the second coating, coat the lithiumophilic material porous carbon slurry, control the coating speed at 10 m / min, the oven length at 30 m, and the temperature at 60 °C. Through the cooperation of the unwinder and the rewinder, the pole piece with the active material coating passes through the first coating equipment, the oven, the second coating equipment, the oven, and the rolling equipment in sequence, so that both sides of the pole piece with the active material coating are coated with the lithiumophilic material, and a pole piece with a lithiumophilic coating is obtained. The pressure for the second roll pressing of the lithiumophilic coating by the rolling equipment is 0 ton, and the thickness of the lithiumophilic coating is controlled at 7 μm.

[0060] Finally, we use the wetting system for prelithiation. Under an argon atmosphere, the metallic lithium is heated to a molten state using a heating tank to obtain liquid metallic lithium. Through the cooperation of the unwinder and the rewinder, the pole piece with the lithiumophilic coating passes through the heating tank, the pressure roller shaft, and the cold air box in sequence to obtain a prelithiated negative electrode pole piece. The negative electrode pole piece is assembled with ternary materials into a full cell (NP ratio is 1.1), and the battery is named G / Li liquid-NCM. The first charge and discharge tests are carried out.

[0061] In addition, we use the method of pressing lithium metal flakes on the graphite surface for lithium compensation. Lithium metal flakes with a thickness of 20 μm are used. Similarly, the lithium metal content to be compensated is 78 mg, and the lithium compensation amount required for each side of the negative electrode sheet is 11.14 mg. Therefore, a lithium metal flake with a thickness of 20 μm and an area of 10.43 cm 2 (3.48 cm × 3 cm) needs to be pressed on each side of the negative electrode sheet. Similarly, it is assembled with the ternary material to form a full cell (NP ratio is 1.1), and the battery is named G / Li flake-NCM. The first charge-discharge test is carried out.

[0062] Example 2:

[0063] When the solid content of the slurry for coating the lithiumophilic coating is 20%, the pressure of the second rolling of the lithiumophilic coating is 0 ton, and the thickness is 10 μm, after the lithiumophilic coating is completely infiltrated, the measured lithium loading per unit area is 0.16 mg / cm 2 . When using a silicon monoxide-graphite negative electrode without pre-lithiation (the electrode sheet specification is 10 cm × 10 cm, one side of one negative electrode sheet is coated, and both sides of three negative electrode sheets are coated) to assemble a full cell with the ternary material (NP (negative electrode reversible surface capacity / positive electrode reversible surface capacity) ratio is 1.1), the battery is named G&SiO-NCM. The first charge capacity of the G&SiO-NCM battery is 2.42 Ah, the first discharge capacity is 1.89 Ah, and the capacity loss is 0.53 Ah, that is, the total capacity that should be intercalated with lithium is 0.53 Ah. According to the specific capacity of lithium being 3860 mAh / g, the amount of lithium metal to be compensated is 137 mg, and the lithium compensation amount required for each side of the negative electrode sheet is 19.57 mg. The coating thickness of the lithiumophilic coating should be controlled at 12 μm.

[0064] Copper foil with a thickness of 8 μm is selected, and silicon monoxide-graphite slurry (where the mass ratio of silicon monoxide is 15%) is coated on the copper foil surface. The single-sided active material surface density is controlled at 7.2 mg / cm 2 , the coating speed is controlled at 5 m / min, the oven length is 30 m, and the temperature is 70 °C. Through the cooperation of the unwinder and the winder, the copper foil passes through the first coating equipment, the oven, the second coating equipment, the oven and the rolling equipment in sequence, so that both sides of the copper foil are coated with the negative electrode slurry, and an electrode sheet with an active material coating is obtained. Among them, the pressure of the rolling equipment is 10 tons.

[0065] We use the coated electrode sheet with the active material coating for a second coating using the coating system, and coat the lithiumophilic material porous carbon slurry. The coating speed is controlled at 10 m / min, the oven length is 30 m, and the temperature is 60 °C. Through the cooperation of the unwinder and the rewinder, the electrode sheet with the active material coating passes through the first coating equipment, the oven, the second coating equipment, the oven, and the rolling equipment in sequence, so that both sides of the electrode sheet with the active material coating are coated with the lithiumophilic material, obtaining an electrode sheet with a lithiumophilic coating. The pressure of the rolling equipment for the second rolling of the lithiumophilic coating is 0 tons, and the thickness of the lithiumophilic coating is controlled at 12 μm.

[0066] Finally, we use the infiltration system for prelithiation. Under an argon atmosphere, the metallic lithium is heated to a molten state using a heating tank to obtain liquid metallic lithium. Through the cooperation of the unwinder and the rewinder, the electrode sheet with the lithiumophilic coating passes through the heating tank, the pressure roller shaft, and the cold air box in sequence, obtaining the prelithiated negative electrode sheet. The prelithiated negative electrode sheet and the ternary material are assembled into a full cell (NP ratio is 1.1), and the battery is named G&SiO / Li liquid-NCM. The first charge-discharge test is carried out.

[0067] In addition, we use the method of pressing a metallic lithium sheet on the surface of silicon suboxide-graphite for lithium compensation. A metallic lithium sheet with a thickness of 20 μm is used. Similarly, the content of metallic lithium that needs to be compensated is 137 mg, and the lithium compensation amount required for each side of the negative electrode sheet is 19.57 mg. Therefore, a metallic lithium sheet with a thickness of 20 μm and an area of 18.32 cm 2 (4.58 cm × 4 cm) needs to be pressed on each side of the negative electrode sheet. Similarly, it is assembled with the ternary material into a full cell (NP ratio is 1.1), and the battery is named G&SiO / Li sheet-NCM. The first charge-discharge test is carried out.

[0068] In order to further optimize the conditions of the preparation method of the present invention to obtain a prelithiated negative electrode sheet with better electrochemical performance, based on Example 1, porous carbon is used as the lithiumophilic coating material, and the active material coating and the lithiumophilic coating are coated using the method conditions of Example 1. The effects of the thickness of the lithiumophilic coating, the solid content of the coating slurry, the second rolling pressure, and the infiltration time on prelithiation are further explored, as shown in Examples 3 - 12.

[0069] Example 3:

[0070] When the thickness of the lithiumophilic coating is 5 μm, the solid content of the coating slurry is 20%, and the pressure of the second rolling of the lithiumophilic coating is 0 tons, the time required for the lithiumophilic coating to achieve complete infiltration in the molten metallic lithium is 6 s, and the lithium loading per unit area after complete infiltration is 0.08 mg / cm 2 .

[0071] Example 4:

[0072] When the thickness of the lithiumophilic coating is 10 μm, the solid content of the coating slurry is 20%, and the pressure of the second rolling of the lithiumophilic coating is 0 ton, the time required for the lithiumophilic coating to achieve complete infiltration in molten metallic lithium is 10 s, and the lithium loading per unit area after complete infiltration is 0.16 mg / cm 2 .

[0073] Example 5:

[0074] When the thickness of the lithiumophilic coating is 15 μm, the solid content of the coating slurry is 20%, and the pressure of the second rolling of the lithiumophilic coating is 0 ton, the time required for the lithiumophilic coating to achieve complete infiltration in molten metallic lithium is 15 s, and the lithium loading per unit area after complete infiltration is 0.24 mg / cm 2 .

[0075] Example 6:

[0076] When the thickness of the lithiumophilic coating is 20 μm, the solid content of the coating slurry is 20%, and the pressure of the second rolling of the lithiumophilic coating is 0 ton, the time required for the lithiumophilic coating to achieve complete infiltration in molten metallic lithium is 25 s, and the lithium loading per unit area after complete infiltration is 0.31 mg / cm 2 .

[0077] Example 7:

[0078] When the solid content of the lithiumophilic coating slurry is 10%, it is difficult to coat normally due to too low slurry viscosity.

[0079] Example 8:

[0080] When the solid content of the lithiumophilic coating slurry is 15%, the thickness is 10 μm, and the pressure of the second rolling of the lithiumophilic coating is 0 ton, the time required for the lithiumophilic coating to achieve complete infiltration in molten metallic lithium is 7 s, and the lithium loading per unit area after complete infiltration is 0.17 mg / cm 2 .

[0081] Example 9:

[0082] When the solid content of the lithiumophilic coating slurry is 30%, it is difficult to coat normally due to too high slurry viscosity.

[0083] Example 10:

[0084] When the lithiumophilic coating is rolled for the second time with a pressure of 1 ton, the solid content of the coating slurry is 20%, and the thickness is 10 μm, the time required for the lithiumophilic coating to achieve complete infiltration in molten metallic lithium is 15 s, and the lithium loading per unit area after complete infiltration is 0.14 mg / cm 2 .

[0085] Example 11:

[0086] When the lithiumophilic coating is roll-pressed for the second time with a pressure of 3 tons, the solid content of the coating slurry is 20%, and the thickness is 10 μm, the time required for the lithiumophilic coating to achieve complete infiltration in molten metallic lithium is 20 s, and the lithium loading per unit area after complete infiltration is 0.13 mg / cm 2 .

[0087] Example 12:

[0088] When the lithiumophilic coating is roll-pressed for the second time with a pressure of 5 tons, the solid content of the coating slurry is 20%, and the thickness is 10 μm, the time required for the lithiumophilic coating to achieve complete infiltration in molten metallic lithium is 40 s, and the lithium loading per unit area after complete infiltration is 0.09 mg / cm 2 .

[0089] Verification result analysis:

[0090] Table 1 Coulombic efficiency of the first cycle of the batteries in Example 1 and Example 2

[0091]

[0092] First, we compared the Coulombic efficiency, first-cycle discharge capacity, and first-cycle charge capacity of the batteries pre-lithiated by infiltration with molten liquid metallic lithium prepared by the preparation method of the present invention in Example 1 and Example 2, the batteries pre-lithiated with metallic lithium sheets, and the batteries without pre-lithiation, as shown in Figure 3 , Figure 4 and Table 1. It can be seen from Figure 3 and Figure 4 that for the lithium-ion batteries without pre-lithiation (G-NCM group, G&SiO-NCM group), in the G-NCM group, the first-cycle charge capacity is 2.41 Ah, the first discharge capacity is 2.11 Ah, and the capacity loss is 0.3 Ah; in the G&SiO-NCM group, the first-cycle charge capacity is 2.42 Ah, the first discharge capacity is 1.89 Ah, and the capacity loss is 0.53 Ah. By pre-lithiation, the first discharge capacity of the lithium-ion battery can be improved, and the pre-lithiation method of the present invention can more significantly improve the first charge-discharge efficiency of the lithium-ion battery than the traditional method of using metallic lithium sheets for pre-lithiation, which can also be verified from Figure 4 . Further, it can be seen from Table 1 that in Example 1, the Coulombic efficiency of the battery obtained by the pre-lithiation method of the present invention in the first cycle is 2.3% higher than that of the battery obtained by the pre-lithiation method using metallic lithium sheets; in Example 2, the Coulombic efficiency of the battery obtained by the pre-lithiation method of the present invention in the first cycle is 2.3% higher than that of the battery obtained by the pre-lithiation method using metallic lithium sheets. It can be seen that the pre-lithiation method of the present invention, which obtains a uniformly coated pre-lithiated layer on the negative electrode, is more beneficial to improving the first charge-discharge efficiency of the battery than the traditional lithium sheet pre-lithiation method.

[0093] We use the preparation method of the present invention for prelithiation. During the prelithiation process, the key lies in how to uniformly and precisely controllably embed molten metallic lithium into the lithiophilic coating. We believe that the thickness of the lithiophilic coating, the solid content of the slurry during the coating of the lithiophilic coating, the pressure of the second rolling, and the infiltration time are all factors affecting the lithium loading capacity of the lithiophilic coating.

[0094] We further studied the influence of each factor on the lithium intercalation of the lithiophilic coating, as shown in Examples 3 - 12:

[0095] Table 2 Influence of the thickness of the lithiophilic coating on lithium intercalation

[0096] — Example 3 Example 4 Example 5 Example 6 — Thickness 5μm Thickness 10μm Thickness 15μm Thickness 20μm Complete wetting time 6s 10s 15s 25s Lithium loading per unit area <![CDATA[0.08mg / cm 2 > <![CDATA[0.16mg / cm 2 > <![CDATA[0.24mg / cm 2 > <![CDATA[0.31mg / cm 2 >

[0097] We first studied the influence of the thickness of the lithiophilic coating on lithium intercalation, as shown in Table 2. The lithiophilic material of the lithiophilic coating we used is porous carbon. On the basis of the solid content of the lithiophilic coating slurry being 20% and the pressure of the second rolling of the lithiophilic coating being 0 ton, we studied the influence of the thickness of the lithiophilic coating on the time for molten metallic lithium to completely infiltrate the lithiophilic coating and the lithium loading per unit area of the lithiophilic coating. We found from Table 2 that as the thickness of the lithiophilic coating increases, the time required for molten metallic lithium to completely infiltrate the lithiophilic coating also increases, and the change ratio of the lithium loading per unit area of the lithiophilic coating is consistent with the thickness change. We believe that when the thickness of the lithiophilic coating increases, it is beneficial to increase the lithium loading capacity of the lithiophilic coating, and the infiltration time needs to be correspondingly increased. In addition, we can calculate the thickness of the lithiophilic coating that should be controlled based on the lithium loading capacity test of the lithiophilic coating under certain conditions and the amount of lithium to be compensated per unit area, so as to achieve precise lithium intercalation.

[0098] Table 3 Influence of the solid content of the slurry of the lithiophilic coating on lithium intercalation of the lithiophilic coating

[0099] — Example 7 Example 8 Example 4 Example 9 — Solid content 10% Solid content 15% Solid content 20% Solid content 30% Complete wetting time — 7s 10s — Lithium loading per unit area — <![CDATA[0.17mg / cm 2 > <![CDATA[0.16mg / cm 2 > — Coating condition Difficult to coat normally Normal coating Normal coating Difficult to coat normally

[0100] We also further studied the effect of the solid content of the slurry during the coating of the lithiumophilic coating on lithium intercalation, as shown in Table 3. The lithiumophilic material of the lithiumophilic coating we used is porous carbon. Based on the lithiumophilic coating thickness of 10 μm and the second rolling pressure of the lithiumophilic coating being 0 tons, we studied the effect of the solid content of the slurry during the coating of the lithiumophilic coating on the time for molten metal lithium to completely infiltrate the lithiumophilic coating and the lithium loading per unit area of the lithiumophilic coating. We found from Table 3 that as the solid content of the slurry during the coating of the lithiumophilic coating increases, the time required for molten metal lithium to completely infiltrate the lithiumophilic coating also increases. We believe that the increase in the solid content in the lithiumophilic coating will increase the difficulty of lithium metal intercalation, and the lithium loading per unit area of the lithiumophilic coating will decrease slightly. In addition, when the solid content of the slurry during coating is less than 10%, it is difficult to coat normally due to the too low viscosity of the slurry; when the solid content of the slurry during coating is higher than 30%, it is also difficult to coat normally due to the too high viscosity of the slurry. Therefore, when coating the lithiumophilic coating, it is necessary to pay attention to controlling the solid content range and consistency of the coating slurry. We further preferably select the mass ratio of the solid content of the lithiumophilic coating slurry to be 15%-25%.

[0101] Table 4 Effect of the pressure of the second rolling of the lithiumophilic coating on lithium intercalation

[0102]

[0103] Finally, we studied the effect of the pressure of the second rolling of the lithiumophilic coating on lithium intercalation, as shown in Table 4. The lithiumophilic material of the lithiumophilic coating we used is porous carbon. Based on the lithiumophilic coating thickness of 10 μm and the solid content of the lithiumophilic coating slurry being 20%, we studied the effect of the pressure of the second rolling of the lithiumophilic coating on the time for molten metal lithium to completely infiltrate the lithiumophilic coating and the lithium loading per unit area of the lithiumophilic coating. We found from Table 4 that as the pressure of the second rolling of the lithiumophilic coating increases, it will cause the lithiumophilic coating to be more compact, so the infiltration difficulty of molten metal lithium will increase, resulting in an increase in the infiltration time and a certain degree of reduction in the lithium loading per unit area. In addition, when the lithiumophilic coating is coated, if the second rolling is not carried out, the coating sometimes shows slight powder shedding, and the powder shedding situation of the electrode sheet after the second rolling will be improved. Based on the above, we further preferably select the pressure of the second rolling of the lithiumophilic coating to be 1 ton - 3 tons.

[0104] In summary, through the method of using molten metal lithium to infiltrate the lithiumophilic coating on the electrode sheet of the present invention, we can achieve uniform contact between the compensated lithium metal and the active material. The amount of the compensated lithium metal can be precisely controlled by adjusting the thickness of the lithiumophilic coating, the solid content of the coating slurry, the pressure of the second rolling, and the infiltration time, thereby achieving an excellent prelithiation effect and further realizing the effect of significantly improving the first efficiency and energy density of the battery.

[0105] It should be noted that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a uniform and controllable prelithiated electrode, characterized in that, the preparation method includes, in an inert environment, immersing the electrode with a lithiophilic coating after the second rolling into a heating tank (22) containing molten liquid lithium metal. After the lithiophilic coating is completely immersed, surface extrusion is carried out through the roller shaft (23) of the pressure roller, and then the third curing is carried out through the cold air box (24); the mass ratio of the solid content of the slurry of the lithiophilic coating is 15%-25%; the thickness of the lithiophilic coating is 5µm-30µm; the immersion time is 6s-50s; the preparation method further includes: S1: Coating the negative electrode slurry on both sides of the current collector, performing the first curing and the first rolling to obtain an electrode with an active material coating; S2: Coating a lithiophilic material on the electrode with an active material layer, performing the second curing and the second rolling to obtain an electrode with an active material coating and a lithiophilic coating; the temperature of the first curing is 60°C-80°C, and the time of the first curing is 5min-7min; the temperature of the second curing is 50°C-70°C, and the time of the second curing is 1min-2min; the thickness of the current collector is 6µm-10µm; the thickness of the active material coating is 100µm-200µm; the pressure of the second rolling is 1 ton-3 tons; the lithiophilic coating includes a lithiophilic material, and the lithiophilic material is porous carbon.

2. A method for preparing a uniform and controllable prelithiated electrode according to claim 1, characterized in that, the pressure of the surface extrusion is 0 kg-100 kg.

3. A method for preparing a uniform and controllable prelithiated electrode according to claim 1, characterized in that, the thickness of the lithiophilic coating is 10µm-20µm; the immersion time of the molten liquid lithium metal is 10s-25s.

4. A method for preparing a uniform and controllable prelithiated electrode according to claim 1, characterized in that, the condition of the third curing is cold air.

5. A method for preparing a uniform and controllable prelithiated electrode according to claim 1, characterized in that, the pressure of the first rolling is 9 tons-11 tons.

6. A method for preparing a uniform and controllable prelithiated electrode according to claim 1, characterized in that, the current collector is copper foil.

7. A method for preparing a uniform and controllable prelithiated electrode according to claim 1, characterized in that, the active material layer includes a negative electrode active material.

8. A method for preparing a uniform and controllable prelithiated electrode according to claim 7, characterized in that, the negative electrode active material includes one or more of graphite, hard carbon, silicon monoxide, and silicon-carbon composite materials.

Images