KR20210080086A - Method of preparing negative electrode for lithium secondary battery, negative electrode prepared by the method, and lithium secondary battery comprising the negative electrode - Google Patents

Abstract

The present embodiments relate to a method for manufacturing a negative electrode for a lithium secondary battery, a negative electrode and a lithium secondary battery manufactured by the method, and a negative electrode plate for a pre-lithiation process. The method for manufacturing a negative electrode for a lithium secondary battery according to an embodiment includes the steps of: (a) coating an organic material on a part or all of the uncoated area of the negative electrode plate to form an organic material layer, and applying a negative electrode active material to a holding unit of the negative electrode plate to form a negative electrode active material layer; (b) pre-lithiating the negative electrode plate manufactured in step (a) using an electrodeposition process; and (c) removing the organic layer from the negative electrode plate manufactured in step (b).

Description

A method for manufacturing a negative electrode for a lithium secondary battery, an anode manufactured thereby, and a lithium secondary battery including the same

The present embodiments relate to a method of manufacturing a negative electrode for a lithium secondary battery, an anode manufactured according to the method, and a lithium secondary battery including the same.

As the demand for high-energy-density lithium secondary batteries increases, the use of silicon-based and silicon-oxide-based materials having an effective capacity 10 times or more than that of carbon-based materials is increasing as a negative active material. When silicon-based and silicon-oxide-based materials are used as negative active materials for lithium secondary batteries, the initial irreversible phenomenon is severe during the initial charging process after battery assembly, and as a result, the initial columb efficiency (ICE) is 70 to 80%. with very low problems.

Therefore, in order to use high-capacity silicon-based and silicon-oxide-based materials as negative electrode materials for lithium secondary batteries, it is essential to compensate for the loss of lithium occurring during the initial charging process in advance. call it

As one of various prelithiation methods, a negative electrode for a lithium secondary battery containing a high-capacity negative active material such as silicon-based and silicon-oxide-based material is immersed in an electrolyte in which lithium salt is dissolved, and then an electric current is applied to prelithiate the negative electrode. method has been developed. However, according to this prelithiation method, a side-reactant film is formed due to the electrochemical reaction of the electrolyte on the uncoated portion of the negative electrode plate on which the negative electrode active material is not coated, and as a result, the weldability between the uncoated portion of the negative electrode plate and the negative electrode lead is lowered. There is a problem that manufacturing becomes difficult.

As a method for solving the above problems, there is a technique for preventing the formation of side reactants by forming an inorganic layer on the uncoated area of the negative electrode before the prelithiation process (Korean Patent Registration No. 10-1783447). However, in this method, the inorganic layer is still maintained on the uncoated area surface of the electrode even during the battery assembly stage after the prelithiation process, and accordingly, the performance and safety deteriorated due to the insertion of foreign substances in the battery, and the friction of inorganic particles during ultrasonic welding of the ultra-thin electrode There are problems such as damage to the electrode due to an increase in the electrode weight and a decrease in battery energy density due to an increase in electrode weight.

The present embodiment aims to provide a method for improving the weldability of a negative electrode uncoated region and a negative electrode lead by preventing the formation of a side-reactant film on the negative electrode uncoated region during the prelithiation process, and a negative electrode plate used therefor. In addition, an object of the present invention is to provide an anode that is easy to manufacture while realizing a high energy density and secures performance reliability and stability, and a lithium secondary battery including the same.

In one embodiment, (a) coating an organic material on a part or all of the uncoated portion of the negative electrode plate to form an organic material layer, and applying the negative electrode active material to the holding portion of the negative electrode plate to form the negative electrode active material layer, (b) the step (a) Pre-lithiation of the negative plate prepared in step (pre-lithiation) using an electrodeposition process, and (c) removing the organic layer from the negative plate prepared in step (b) of a negative electrode for a lithium secondary battery comprising the steps of A manufacturing method is provided.

In another embodiment, an anode for a lithium secondary battery manufactured by the above manufacturing method is provided, and an electrode assembly including the anode, the cathode, and a separator positioned between the anode and the cathode is provided.

In another embodiment, there is provided a lithium secondary battery including at least two electrode assemblies according to an embodiment, wherein the negative electrode uncoated portion of each electrode assembly is welded to the negative electrode lead.

According to the present embodiments, high energy density can be realized through the all-lithiation process, and at the same time, the reliability of the battery performance even when the conventional battery manufacturing process is applied by solving the existing problem of poor electrode weldability by the all-lithiation process. and safety.

1 is a diagram schematically showing a portion of the negative electrode plate manufactured in step (a) according to an embodiment.
FIG. 2 is a photograph showing a state in which 30 uncoated region samples of the negative electrode plate prepared in Example 1 are laminated and welded according to Evaluation Example 1.
FIG. 3 is a photograph showing a state in which 30 samples of the uncoated region of the negative electrode plate prepared in Example 1 are laminated, and the stacked uncoated regions and the negative electrode lead are welded according to Evaluation Example 1. Referring to FIG.
4 is a photograph showing a state in which 30 samples of the uncoated region of the negative electrode plate prepared in Comparative Example 1 are laminated, and the stacked uncoated regions and the negative electrode lead are welded according to Evaluation Example 1. Referring to FIG.
FIG. 5 is a photograph when 30 sheets of uncoated negative electrode plate samples prepared in Comparative Example 1 and negative electrode leads were welded according to Evaluation Example 1 by increasing the ultrasonic welding pressure.

The terminology used herein is for the purpose of referring to specific embodiments only, and is not intended to limit the invention. As used herein, the singular forms also include the plural forms unless the phrases clearly indicate the opposite. The meaning of "comprising," as used herein, specifies a particular characteristic, region, integer, step, operation, element and/or component, and includes the presence or absence of another characteristic, region, integer, step, operation, element and/or component. It does not exclude additions.

All terms including technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs. In addition, unless otherwise specified, % means % by weight.

Hereinafter, embodiments of the present invention will be described in detail. However, this is provided as an example, and the present invention is not limited thereto, and the present invention is only defined by the scope of the claims to be described later.

In the method for manufacturing a negative electrode for a lithium secondary battery according to an embodiment of the present invention, (a) coating an organic material on a part or all of the uncoated area of the negative electrode plate to form an organic material layer, and applying the negative electrode active material to the holding part of the negative electrode plate to form a negative electrode active material layer forming, (b) pre-lithiation of the negative electrode plate prepared in step (a) using an electrodeposition process, and (c) the organic layer in the negative electrode plate prepared in step (b) including the step of removing

According to the method, the formation of a side-reactant film on the uncoated region of the negative electrode plate in the prelithiation step (b) is effectively prevented, and the weldability between the uncoated region and the negative electrode lead is greatly improved after the step (c). Accordingly, it is possible to provide a lithium secondary battery that facilitates the manufacture of electrodes and batteries, realizes high energy density, and secures performance reliability and safety at the same time.

1 is a diagram schematically showing a portion of the negative electrode plate manufactured in step (a). Referring to FIG. 1 , the holding part 11 refers to a portion of the electrode plate 10 to which the active material 20 is applied, or a portion to which the active material is to be applied, and the uncoated portion 12 is the electrode plate to which the active material is not applied. It refers to a part, or a part where the active material is not to be applied. The uncoated part may be one end or both ends of the electrode plate. For example, the uncoated portion may be a portion corresponding to several mm or several tens of mm from one or both ends of the electrode plate. Usually, a part of the uncoated region becomes the tab part, and the part where the tab part and the electrode lead are welded is called a welding part. The organic layer 30 may be formed on the entire uncoated area or only on a part of the uncoated area. For example, the organic material layer may be formed only on the portion corresponding to the tab portion in the uncoated portion or may be formed only on the portion corresponding to the welding portion.

For reference, in the present invention, although reference numeral 10 in FIG. 1 is expressed as a pole plate, it may also be referred to as a base material of the pole plate. In addition, the shape including the reference numerals 10, 20, and/or 30 of FIG. 1 is also referred to as a pole plate. That is, a state in which an active material layer and/or an organic material layer is formed on a base material of an electrode plate such as a copper thin plate may also be referred to as an electrode plate.

Also, on the other hand, in the method of manufacturing a negative electrode for a lithium secondary battery according to an embodiment, before the step (a), (a') of determining the holding part to which the negative electrode active material is to be applied and the uncoated area to which the negative electrode active material is not to be applied in the negative electrode plate It may include more.

In the method of manufacturing the negative electrode for a lithium secondary battery, the organic material is a material capable of blocking contact between the uncoated region of the negative electrode and the electrolyte without being dissolved in the electrolyte during the prelithiation process. For example, the organic material is a material having chemical resistance to a carbonate-based organic solvent or an ether-based organic solvent, which is a major component of the electrolyte.

Specifically, the organic material is polypropylene, polyethylene, polyacrylonitrile, polyvinyl chloride, polyvinyl acetate, polyethylene oxide, polypropylene oxide, polydimethylsiloxane, poly (meth) acrylate, polymethyl methacrylate, polyvinyl Leadene fluoride, polyvinyl chloride, polyethyleneimine, polyphenylene terephthalamide, polyethylene terephthalate, polystyrene, polytetrafluoroethylene, polysiloxane, polyimide, polystyrene butadiene rubber, polybutadiene, polyurethane, polyester, polyphenylene sulfide, polycyanoacrylate, polyvinyl alcohol, It may include at least one selected from the group consisting of copolymers thereof, and combinations thereof.

The thickness of the organic layer may be 0.1 μm to 1 mm. If the thickness of the organic material layer is too thin, it is difficult to remove the organic material layer in step (c), and the weldability of the electrode may be deteriorated due to a part of the organic material layer remaining. The thicker the organic layer, the easier it is to remove the organic layer, but if it is thicker than 1 mm, some peeling of the organic layer occurs before step (c), so that the electrolyte solution during the pre-lithiation process of step (b) is In contact with the electrode uncoated region, a side-reactant film is formed when a current is applied, and thus the weldability of the electrode may be deteriorated. The thickness of the organic layer may be, for example, 0.5 μm or more, 1 μm or more, 10 μm or more, 50 μm or more, or 100 μm or more, and also 800 μm or less, 600 μm or less, 500 μm or less, 400 μm or less, or It may be 300 μm or less. When the thickness range is satisfied, the organic layer is not peeled off in the prelithiation process of step (b) and is easily removed in step (c).

As a method of forming the organic material layer on the uncoated portion of the negative electrode plate, any general organic material coating method may be applied, and for example, a method such as screen printing, tape casting, or spraying may be used.

The negative active material may be a high-capacity negative electrode material such as a silicon-based negative electrode material, as well as a carbon-based negative electrode material such as graphite used in a typical lithium secondary battery. In an embodiment, the negative active material may include silicon (Si), an alloy of silicon, SiO _x (x=0.5 to 1.2), LiSiO, or a combination thereof. In this case, the effect of improving the initial irreversibility of the prelithiation process can be maximized, and a high energy density anode and battery can be realized. For example, the negative active material may include a combination of a carbon-based material and a silicon-based material, or a combination of a carbon-based material and a silicon oxide-based material.

The base material of the negative electrode plate may be applied regardless of a general current collector material, and may be, for example, a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, or a polymer substrate coated with a conductive metal.

Applying the negative active material to the holding part of the negative electrode plate may be to prepare an active material composition by mixing the negative electrode active material, a conductive material, a binder, etc. in a solvent, and then applying the composition to the negative electrode plate, such a method is in the art. Since the content is widely known, detailed description thereof will be omitted.

The prelithiation of step (b) is a process of pre-compensating for loss of lithium occurring during the initial charging process of the battery. In an embodiment, the prelithiation may be performed by immersing the negative electrode in an electrolyte in which a lithium salt is dissolved and applying an electric current. Specifically, the prelithiation may be performed by immersing a lithium source such as a negative electrode plate and a lithium metal plate in an electrolyte in which a lithium salt is dissolved, and then applying an electric current.

The electrolyte may include a carbonate-based solvent, an ether-based solvent, or a combination thereof. For example, the electrolyte may be a solvent such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, methyl cionate, or ethyl propionate.

The lithium salt may be, for example, LiCl, LiBr, LiI, _{LiCO 3} , LiNO ₃ , LiFSI, LiTFSI, LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiClO ₄ , LiN(SO ₂ CF ₃ ) ₂ , LiBOB, and the like.

The method of applying the current may be, for example, applying so that the average current density is in the range of 0.1 mA/cm 2 to 100 mA/cm 2 based on the electrode area.

Removing the organic layer in step (c) is applicable regardless of any method. The organic layer can be easily removed by hand. For example, by attaching a general adhesive tape on the organic layer and then peeling the organic layer together with the adhesive tape, the organic layer can be easily removed.

According to an embodiment, in the negative electrode plate from which the organic layer is removed in step (c), there is no side reaction film due to the pre-lithiation process in the uncoated part, and there is no other coating layer or particles such as an organic layer, so that foreign substances in the battery are not present. There is no problem of deterioration in performance and safety due to insertion, and it is possible to prevent the electrode from being damaged due to residual particles when welding the negative lead to the uncoated area, and to reduce the energy density of the battery due to the increase in the electrode weight. can prevent the problem.

In the negative electrode plate finally manufactured in step (c), the negative electrode active material layer supplemented with lithium ions is formed in the holding portion, and no coating layer or particles such as the negative electrode active material layer or organic material layer are formed in the uncoated portion. That is, the negative plate prepared in step (c) includes a holding part including a negative electrode active material layer supplemented with lithium ions, a negative electrode active material is not applied, and an organic material layer is not formed (or an organic material layer is removed) It can be said that it includes the ignorance.

In another embodiment of the present invention, there is provided a negative electrode for a lithium secondary battery manufactured according to the above-described method for manufacturing a negative electrode for a lithium secondary battery. Such a negative electrode for a lithium secondary battery includes a negative plate including a holding portion including a negative active material layer supplemented with lithium ions and an uncoated portion on which an anode active material is not applied and an organic material layer is not formed.

Another embodiment of the present invention provides an electrode assembly including a negative electrode manufactured by the above method, a positive electrode, and a separator positioned between the negative electrode and the positive electrode.

Such an electrode assembly may be wound or folded to be accommodated in a battery container, and an electrolyte may be injected into the battery container and sealed to complete a lithium secondary battery. In this case, the battery container may have various shapes such as a cylindrical shape, a square shape, a pouch shape, and a coin shape.

The positive electrode may include a positive electrode active material layer and a positive electrode current collector.

The positive active material layer may include, for example, at least one of Ni, Co, Mn, Al, Cr, Fe, Mg, Sr, V, La, Ce and O, F, S, P, and combinations thereof. Li compound including at least one non-metal element selected from may be included. The positive active material layer may include active material particles having a size of about 0.01 μm to 200 μm, and may be appropriately selected according to the required characteristics of the battery.

In some cases, a conductive material may be added to the positive electrode active material layer. The conductive material may be, for example, carbon black, ultrafine graphite particles, fine carbon such as acetylene black, or nano metal particle paste, but is not limited thereto.

The positive electrode current collector serves to support the positive electrode active material layer. As the positive electrode current collector, for example, a thin aluminum plate (Foil), a thin nickel plate, or a combination thereof may be used, but the present invention is not limited thereto.

The separator separates the positive electrode and the negative electrode and provides a passage for lithium ions to move, and any one commonly used in lithium secondary batteries may be used. That is, one having low resistance to ion movement of the electrolyte and excellent moisture content of the electrolyte may be used. The separator may be, for example, selected from glass fiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene, or a combination thereof, and may be in the form of a nonwoven fabric or a woven fabric. Meanwhile, when a solid electrolyte is used as the electrolyte, the solid electrolyte may also serve as a separator.

Another embodiment of the present invention provides a lithium secondary battery including at least two or more of the electrode assembly.

That is, two or more electrode assemblies are stacked, and the uncoated region of each negative electrode and the negative electrode lead are welded in the stacked electrode assembly to be electrically connected to the electrode terminal.

In this case, there may be one negative lead, or the same number as the uncoated part of the negative electrode. Since the negative electrode manufactured as in the embodiment of the present invention does not have a side-reactant film by the prelithiation process on the uncoated area, and there is no other coating layer or particle such as an organic material layer, the negative electrode lead can be welded very easily and , there is no bad case of electrode and lead falling off after welding, and there may be no problem of tearing of the welded part. Accordingly, it is possible to provide an anode having a high capacity and securing performance reliability and safety, an electrode assembly including the same, and a lithium secondary battery. Any method may be used to weld the uncoated region and the negative electrode lead, and ultrasonic welding may be used as an example.

As the electrolyte charged in the lithium secondary battery, a non-aqueous electrolyte or a solid electrolyte may be used.

The non-aqueous electrolyte may include, for example, a lithium salt such as lithium hexafluorophosphate and lithium perchlorate and a solvent such as ethylene carbonate, propylene carbonate, or butylene carbonate. Further, as the solid electrolyte, for example, a gel polymer electrolyte obtained by impregnating an electrolyte solution in a polymer electrolyte such as polyethylene oxide or polyacrylonitrile, or an inorganic solid electrolyte such as _{LiI or Li 3 N may be used.}

Hereinafter, embodiments of the present invention will be described in detail. However, this is provided as an example, and the present invention is not limited thereto, and the present invention is only defined by the scope of the claims to be described later.

[Example 1]

Step (a): A roll-shaped copper foil (Cu foil) having a width of 140 mm and a thickness of 10 μm was used as the electrode base material, and 20 mm portions of both ends in the width direction of the thin copper plate were determined as uncoated areas. An organic layer was coated on the uncoated region of the copper thin plate by a spray method so that the thickness was in the range of 100 um to 300 um. Here, as the organic material, a vinyl chloride/vinyl acetate copolymer was used and mixed with solvents such as acetone and toluene. A solid organic layer was obtained by volatilizing the solvent through drying for a certain period of time after spray coating.

In addition, a composite negative electrode material having a capacity of 700 mAh/g composed of a silicon oxide-based material having a weight ratio of 30% and graphite having a weight ratio of 70% was applied to both surfaces of the thin copper plate by 70 μm on both sides of the copper thin plate except for the uncoated part of the copper plate.

Step (b): The negative electrode plate prepared in step (a) was immersed in an electrolyte in which lithium salt was dissolved, and then the negative electrode plate was prelithiated by applying an electric current. The electrolyte used for prelithiation was prepared by dissolving _{1M concentration of LiPF 6} in a solvent of EC/EMC=30/70. As a lithium source, a lithium metal plate having a purity of 99.9% and a thickness of 500 μm was used by pressing it onto a copper current collector plate having a size of 20 cm in width and 20 cm in length. Then, using the power supply, a current of 2 mA/cm 2 was flowed for 1 hour using the lithium metal electrode and the negative plate of step (a) as (+) and (-) electrodes, respectively, corresponding to 2.0 mAh/cm 2 lithium was inserted into the anode active material layer.

Step (c): From the negative plate prepared in step (b), the organic material layer coated on the uncoated area was removed using an adhesive tape. Thereafter, the negative plate was washed and dried, and only the uncoated region was cut to collect a sample.

[Comparative Example 1]

A negative electrode was prepared in the same manner as in Example 1, except that the organic material layer was not coated on the negative electrode uncoated area in step (a) of Example 1, and a sample was collected from the uncoated area.

[Evaluation Example 1: Weldability Evaluation]

For evaluation of uncoated area weldability of the negative electrode plates prepared in Example 1 and Comparative Example 1, an ultrasonic welding machine (Ecosonic, model name: ECM35-50) currently applied to the production of lithium secondary batteries and welding conditions (Amplitue: 70%, Welding) time: 0.3 s, Hold time: 0.2 s, pressure: 0.18 MPa) was used. Weldability was evaluated by laminating 30 uncoated region samples of the negative electrode plate and welding together with the negative electrode lead.

2 is a photograph of a state in which 30 sheets of uncoated region samples of the negative electrode plate prepared in Example 1 are laminated and welded. 3 is a photograph showing the front and back sides of the negative electrode plate prepared in Example 1 in a state in which 30 uncoated region samples are laminated and welded together with the negative electrode lead.

2 and 3, in the case of Example 1, welding between the negative electrodes and ultrasonic welding between the negative electrode plates and the negative electrode lead were performed very well even using conventional ultrasonic welding equipment and welding conditions, and welding defects were found. It didn't happen. This is because the organic layer of the present invention effectively prevented the electrochemical side reaction of the electrolyte from occurring on the surface of the negative electrode uncoated region in the prelithiation step of step (b) during the manufacturing process of the negative electrode according to an embodiment of the present invention. . Accordingly, it is possible to improve the weldability of the electrode and the electrode lead, to facilitate the manufacture of the battery, and to secure battery performance reliability and safety while realizing a battery having a high capacity and high energy density.

4 is a photograph of a state in which 30 uncoated samples of the negative electrode plate prepared in Comparative Example 1 are stacked and welded together with the negative electrode lead. Referring to FIG. 4 , in the case of Comparative Example 1, a side reaction film formed during the prelithiation process was formed on the uncoated region of the negative electrode, and as a result, fusion between the negative electrode plate and the negative electrode plate, and between the negative electrode plates and the negative electrode lead did not occur properly, so that most of the welding part was separated. became

5 is a photograph of 30 sheets of uncoated negative electrode plate samples and negative electrode leads by increasing the pressure condition among ultrasonic welding conditions to 0.25 MPa in order to improve the welding bonding strength of the sample prepared in Comparative Example 1. Referring to FIG. Referring to FIG. 5 , it can be confirmed that, in Comparative Example 1, when the ultrasonic welding pressure is increased to improve welding bonding strength, a problem in which the joint between the negative electrode plates and the negative electrode lead is torn occurs.

The present invention is not limited to the above embodiments, but can be manufactured in a variety of different forms, and those of ordinary skill in the art to which the present invention pertains can take other specific forms without changing the technical spirit or essential features of the present invention. It will be understood that it can be implemented as Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.

10: electrode plate
11: maintenance department
12: Muzibu
20: active material layer
30: organic layer

Claims (8)

(a) forming an organic material layer by coating part or all of the uncoated portion of the negative electrode plate, and coating the negative electrode active material on the holding portion of the negative electrode plate to form a negative electrode active material layer;
(b) pre-lithiation of the negative plate prepared in step (a) using an electrodeposition process, and
(c) a method of manufacturing a negative electrode for a lithium secondary battery comprising the step of removing the organic material layer from the negative electrode plate prepared in step (b). According to claim 1,
The organic material is polypropylene, polyethylene, polyacrylonitrile, polyvinyl chloride, polyvinyl acetate, polyethylene oxide, polypropylene oxide, polydimethylsiloxane, poly (meth) acrylate, polymethyl methacrylate, polyvinylidene fluoride , polyvinyl chloride, polyethyleneimine, polyphenylene terephthalamide, polyethylene terephthalate, polystyrene, polytetrafluoroethylene, polysiloxane, polyimide, polystyrenebutadiene rubber, polybutadiene, polyurethane, polyester, polyphenylenesulfide, polish Anoacrylate, polyvinyl alcohol, A method of manufacturing a negative electrode for a lithium secondary battery comprising at least one selected from the group consisting of copolymers thereof, and combinations thereof. According to claim 1,
The thickness of the organic material layer is 0.1 um to 1 mm method of manufacturing a negative electrode for a lithium secondary battery. According to claim 1,
The negative active material is a method of manufacturing a negative electrode for a lithium secondary battery comprising silicon (Si), an alloy of silicon, SiO _x (x = 0.5 to 1.2), LiSiO, or a combination thereof. According to claim 1,
The pre-lithiation is a method of manufacturing a negative electrode for a lithium secondary battery that is performed by immersing the negative electrode plate in an electrolyte solution in which lithium salt is dissolved and applying an electric current. A negative electrode for a lithium secondary battery prepared according to any one of claims 1 to 5. The negative electrode of claim 6;
anode; And
An electrode assembly comprising a separator positioned between the cathode and the anode. It comprises two or more of the electrode assembly of claim 7,
A lithium secondary battery wherein the negative electrode uncoated portion of each electrode assembly is welded to the negative electrode lead.

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