KR20200053300A - Negative electrode for lithium secondary battery, method of preparing the saem, and lithium secondary battery using the same - Google Patents

Abstract

The present invention relates to a negative electrode for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery using the same. The negative electrode for a lithium secondary battery comprises a current collector and a negative electrode active material layer positioned on the current collector, wherein the negative electrode active material layer is uniformly pre-lithiated in a thickness direction.

Description

A cathode for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery using the same {NEGATIVE ELECTRODE FOR LITHIUM SECONDARY BATTERY, METHOD OF PREPARING THE SAEM, AND LITHIUM SECONDARY BATTERY USING THE SAME}

A negative electrode for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery using the same.

As the demand for high-energy-density lithium secondary batteries increases, the use of silicon-based and / or silicon oxide-based materials having an effective capacity of 10 times or more as carbon-based materials as the negative electrode active material is increasing.

The silicon-based material has an advantage of a very high capacity, but there is a problem of cracking and powdering due to volume expansion due to a large volume change during charging and discharging. . The silicon oxide-based material has a lower capacity than the silicon-based material, but the volume expansion coefficient is relatively small, so it is excellent in durability, and when used as a composite anode material, it is possible to increase the content of the silicon oxide-based material, thus increasing the effective capacity.

On the other hand, the lithium ion battery not only forms a solid electrolyte interface (SEI) at the negative electrode during the initial charging process, but also generates active lithium losses due to irreversible lithium plating and side reactions. A phenomenon in which the capacity is reduced appears, and this is called an initial irreversible phenomenon.

This initial irreversible phenomenon is prominent when a silicon-based material or a silicon oxide-based material is used as a negative electrode active material compared to a carbon-based negative electrode active material, and in particular, in the case of a silicon oxide-based material, as oxygen is present in the active material, Li ₂ O, Li ₄ SiO It is easy to generate irreversible materials such as the initial irreversible phenomenon more severe, and as a result, there is a problem that the initial coulomb efficiency (ICE, Initial Columb Efficiency) is very low at 70%.

Therefore, in order to use high-capacity silicon-based and silicon-oxide-based materials as negative electrode materials for lithium ion batteries, it is essential to compensate for the loss of lithium generated during the initial charging process in advance, and pre-lithiation of these processes I call it.

The pre-lithiation can be divided into the pre-lithiation of the positive electrode material and the pre-lithiation of the negative electrode material depending on the position to compensate for lithium. Cathode material pre-lithiation is the use of an over-lithiated cathode material or a high-capacity cathode material such as Li ₂ NiO ₂ as an additive, which has a simple process advantage, but the effect of capacity increase is limited, and lithium After compensating for, there is a problem of causing weight gain and side reaction with the electrolyte because it remains without decomposition. In addition, the positive electrode material additive has a problem in that a large amount of gas is generated through a gelation reaction or a decomposition process during slurry production.

On the other hand, the pre-lithiation of the anode material has been developed in more various ways than the pre-lithiation of the cathode material. For example, to compensate for lithium by adding stabilized lithium metal powder (SLMP) from the step of manufacturing the anode material or lithium silicon oxide (Li _x SiO), which has already been reacted with lithium in the raw material synthesis step. There is a way. However, the additive material used in this method is very expensive and there is a limitation in uniformly distributing it over the entire area in the negative electrode material.

The initial irreversible reaction occurring in the negative electrode material by directly contacting the lithium metal in a state of being immersed in an electrolyte before assembling the negative electrode material that has already been manufactured into a lithium ion battery or by supplying a lithium source to the negative electrode material externally through an electrochemical method There is a method that is completed before the battery assembly, so that irreversible reaction does not occur after the battery assembly. This method has a problem in that the negative electrode material must be separated and the electrolytic solution washed before battery assembly after pre-lithiation.

As described above, each has advantages and disadvantages depending on the location of pre-lithiation, the steps and methods of pre-lithiation, and the like. Nevertheless, as an essential element in the pre-lithiation process, an appropriate amount of lithium must be pre-lithiated, and uniformly pre-lithiated in all regions.

If the total amount of lithium is insufficiently quantified, the effect of initial irreversible prevention becomes insignificant, and if excessively pre-lithiated compared to quantitative, an excessive amount of lithium is plated on the negative electrode during operation, thereby causing safety problems such as overcharging. Since this problem can occur even in the local non-uniformity of pre-lithiation, quantitative and uniformity are very important requirements for pre-lithiation.

In KR 10-2013-0090181, the surface of the negative electrode was pre-lithiated by immersing the roll in which the negative electrode material and lithium metal were wound together in an electrolyte solution.

However, such a direct contact method has a disadvantage that it is impossible to accurately control the degree of pre-lithiation. In addition, there is a problem in that the degree of pre-lithiation is locally different because the contacting region is not uniform.

Accordingly, there is a need for an improved method of pre-lithiation.

In one embodiment of the present invention, in the pre-lithiation of a negative electrode material, especially a negative electrode material containing a silicon-based and / or silicon oxide-based material having an effective capacity of 10 times or more than a carbon-based material, the entire area over a commercially available size In order to propose a method for securing a negative electrode material in which not only lithium is uniformly compensated, but the amount of compensated lithium is accurately controlled.

In one embodiment of the present invention, the current collector; And a negative electrode active material layer positioned on the current collector, wherein the negative electrode active material layer is uniformly pre-lithiated in the thickness direction to provide a negative electrode for a lithium secondary battery.

The content of lithium at any point with respect to the entire thickness direction of the negative electrode active material may be a value within a range of a minimum and maximum value of lithium in 20% by length in the thickness direction from the surface portion of the negative electrode active material layer. More specifically, the distribution of lithium from the surface portion to the bottom of the current collector in the thickness direction of the negative electrode may be uniform. The detailed experimental basis for this will be described in more detail in the Examples to be described later.

A surface of the negative electrode active material layer may not have a lithium plating layer. More specifically, it is not carried out at a level in which the lithium plating layer is formed on the surface because the pre-lithiation proceeds excessively.

The negative electrode active material in the negative electrode active material layer may include a silicon-based compound, a silicon oxide-based compound, a carbon-based compound, or a combination thereof. Various types of composite silicon-based negative active materials known to date can be used.

The negative electrode may have a structure in which the negative electrode active material layer is located on both sides of the current collector.

The current collector is for electrical connection within the battery.

The current collector may have the form of a thin film (Foil), but is not limited thereto, for example, a mesh (mesh), foam (Foam), rod (rod), wire (wire), and wire (wire, It may have the form of a sheet (woven) of fibers.

As the material of the current collector, a material having electrical conductivity and having limited reaction with lithium may be used. As a material of the current collector, for example, a conductive layer is coated on copper, nickel, titanium, stainless steel, gold, platinum, silver, tantalum, ruthenium, and alloys thereof, carbon, conductive polymer, and non-conductive polymer. Any one or a combination of the composite fibers can be used.

If the thickness of the current collector is thick, the weight of the battery is increased and the energy density of the battery is lowered. If the thickness of the current collector is thin, there is a risk of overheat damage during high current operation and may be damaged by tension during the battery manufacturing process. Therefore, the thickness of the current collector may range from 1 μm to 50 μm.

The negative active material layer may have a thickness of 10 to 200 μm. When the negative electrode active material layer is too thick, it is difficult to see a sufficient charging effect compared to an increase in the thickness of the battery, and peeling problems may occur. If it is too thin, there is a fear that battery characteristics may deteriorate.

A film positioned on the surface of the negative electrode active material layer may be further included.

The coating is formed by a reaction between the electrodeposited lithium metal and the plating solution in the manufacturing process of the negative electrode, and the thickness and composition, characteristics, etc. of the coating can be controlled by controlling the composition of the plating solution used and the conditions of the electrodeposition process. .

The thickness of the coating may be, for example, 2 nm to 2 μm, more specifically 10 nm to 500 nm.

When the thickness of the coating located on the surface of the negative electrode is too thick, lithium ion conductivity is lowered and interface resistance is increased, so that charge / discharge characteristics may be deteriorated when the battery is applied. In addition, if the thickness of the coating is too thin, the coating may be easily lost in the process of applying the negative electrode according to the embodiment to the battery.

Therefore, it is preferable that the coating is formed to be uniform and dense on the entire surface of the cathode, with a thin thickness, in a range that satisfies the thickness range.

The coating may be a Li-N-C-H-O based ionic compound, a Li-P-C-H-O based ionic compound, LiF or a combination thereof. As described above, the composition of the film can be controlled by the additives of the electrolyte solution and the composition of the electrolyte solution.

For a specific example, the coating includes a Li-N-C-H-O-based ionic compound.

In this embodiment, in the process of pre-lithiating the negative electrode by an electrodeposition (Electroplating) process, by controlling the composition and content of the plating solution, a film containing the Li-N-C-H-O-based ionic compound can be formed.

The Li-N-C-H-O-based ionic compound may include Li-O, C-N, C-O, and C-H bonds.

More specifically, the Li-N-C-H-O-based ionic compound may include a compound represented by any one of the following Chemical Formulas 1 to 2.

[Formula 1]

In Formula 1, R ₁ and R ₂ are each CH _m F _{2 -m} (m = 0, one of 1, 2),

또는

이며,A ₁ is

or

And

n1 is an integer from 1 to 10.

[Formula 2]

In the formula (2), R ₃ and R ₄ are each CH _m F _{2 -m} (m = 0, one of 1, 2),

또는

이며,A ₂ is

or

And

n2 is an integer from 1 to 10.

More specifically, for example, lithium nitrate (Lithium nitrate, LiNO ₃ ) is used as a nitrogen-based compound, and the pre-lithiation process is performed using a plating solution in which an appropriate amount is added to an ether-based solvent (Solvent). When the negative electrode is pre-lithiated, a film containing the compound represented by Chemical Formula 1 or 2 may be formed on the surface of the negative electrode.

On the other hand, the coating may further include LiF in addition to the Li-N-C-H-O-based ionic compound.

More specifically, for example, in the case of using lithium bis fluorosulfonyl imide (LiN (FSO ₂ ) ₂ ) as the nitrogen-based compound included in the plating solution, the fluorine (F) component contained therein may cause The coating may further include LiF in addition to the Li-NCHO-based ionic compound.

Further, even when a fluorine-based compound such as fluoroethylene carbonate (FEC) is further included in the plating solution, the film 13 may include LiF together with a Li-N-C-H-O-based ionic compound.

As described above, when the film further includes LiF, the electrochemical performance of the film may be further improved by interaction with a Li-N-C-H-O-based ionic compound.

As in this embodiment, when a negative electrode including a film containing a Li-N-C-H-O-based ionic compound is applied to a lithium secondary battery, side reactions between the electrolyte and the pre-lithiated negative electrode can be blocked. In addition, charging and discharging life of the lithium secondary battery can be improved by uniformly desorbing and adhering lithium on the surface of the negative electrode to suppress dendritic growth.

In another embodiment of the present invention, the step of preparing a negative electrode and a lithium electrode opposed thereto, impregnated in the electrolyte solution; And applying a current to the negative electrode and the lithium electrode, thereby pre-lithiating the negative electrode; wherein the interval between the negative electrode and the lithium electrode is greater than 0 and less than 1,500 μm for a lithium secondary battery. Provided is a method of manufacturing a cathode.

1 is a schematic diagram of an apparatus for pre-lithiation according to an embodiment of the present invention.

In the pre-lithiation apparatus as shown in FIG. 1, a flat-type lithium electrode may be applied to maintain a constant distance between the surface of the negative electrode material and the lithium electrode (for example, a lithium metal electrode).

The smaller the gap between the surface of the anode material and the lithium electrode, the more uniform current application can be obtained. However, if the gap is too narrow to make direct contact, it causes a large difference in current flow between the direct contact area and the non-contact area. In addition to causing a difference in the degree of lithiation, pre-lithiation can occur only at the center of the surface of the anode material.

In order to prevent this, an additional separator may be additionally inserted between the negative electrode material and the lithium electrode to fundamentally prevent contact. Therefore, whether or not the separator is inserted can be freely selected according to the need.

More specifically, the interval between the negative electrode and the lithium electrode may be greater than 0 and 1,500 μm or less. More specifically, it may be 10 to 1,500㎛. More specifically, it may be 10 to 1,000㎛. The detailed experimental basis for this will be described in more detail in the Examples below.

The current density may be 0.1 to 100 mA / cm ² based on the area of the lithium electrode. As the current density increases, the total lithiation rate increases, so productivity increases, but the uniformity and the properties of the coating decrease, resulting in a decrease in the performance of the cathode. Therefore, it is preferable that the current density is within the above range. In addition, the correlation between the current density and the interval is replaced with the above description.

The area of the lithium electrode may be 25 to 1,000 cm ² .

A separator may be positioned between the negative electrode and the lithium electrode. As described above, in this case, the gap between the negative electrode and the lithium electrode can be uniformly maintained.

The separator separates two electrodes and provides a passage for lithium ions, and any of those commonly used in lithium secondary batteries can be used. That is, one having low resistance to ion migration of the electrolyte and having excellent electrolyte-moisturizing ability may be used. The separator may be, for example, glass fiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene, or a combination thereof, and may be in the form of nonwoven or woven fabric. On the other hand, when a solid electrolyte is used as the electrolyte, the solid electrolyte may also serve as a separator.

The electrolyte may be prepared by dissolving a lithium salt in a non-aqueous solvent.

More specifically, the lithium salt is LiCl, LiBr, LiI, LiCO ₃ , LiNO ₃ , LiFSI, LiTFSI, LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiClO ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiBOB, or It can be a combination of these. The concentration of the lithium salt may be 0.1 to 3.0M based on the total electrolyte solution.

More specifically, in this embodiment, the electrolyte solution is characterized in that it contains a nitrogen-based compound as at least one of the lithium salt and the non-aqueous solvent.

The nitrogen-based compound is, for example, lithium nitrate (Lithium nitrate), lithium bis fluorosulfonyl imide, Lithium bis trifluoromethane sulfonimide (Lithium bis trifluoromethane sulfonimide), caprolactam (e-Caprolactam), methyl caprolactam (N-methyl-e-caprolactam), triethylamine (Triethylamine) and may include one or more selected from the group consisting of tributylamine (Tributylamin).

Among the nitrogen-based compounds, at least one of lithium nitrate, lithium bis fluorosulfonyl imide, and lithium bis trifluoromethane sulfonimide is a lithium salt. Can be used.

Of the nitrogen-based compounds, at least one of caprolactam (e-Caprolactam), methyl caprolactam (N-methyl-e-caprolactam), triethylamine (Triethylamine) and tributylamine (Tributylamin) can be used as a non-aqueous solvent have.

Meanwhile, the electrolyte may be added with a general non-aqueous solvent as a solvent in consideration of viscosity of a plating solution and the like. This is because if the viscosity of the electrolyte is too high, the mobility of lithium ions decreases and the ionic conductivity of the electrolyte decreases, so the time required for the pre-lithiation process increases and productivity decreases.

The solvent is, for example, ethylene carbonate (Ethylene carbonate), propylene carbonate (Propylene carbonate), dimethyl carbonate (Dimethyl carbonate), ethyl methyl carbonate (Ethyl methyl carbonate), diethyl carbonate (Diethyl carbonate), 1 , 2-Dimethoxyethane, Diethylene glycol dimethyl ether, Tetraethylene glycol dimethyl ether, Tetrahydrofuran, 1,3-dioxane Contains one or more selected from the group consisting of solan (1,3-Dioxolane), 1,4-dioxane (1,4-Dioxane) and 1,3,5-trioxane (1,3,5-Trioxane) can do.

In another embodiment of the present invention, the anode; cathode; And an electrolyte positioned between the positive electrode and the negative electrode, wherein the negative electrode provides a lithium secondary battery that is a negative electrode according to one embodiment of the present invention described above.

The lithium secondary battery may have an initial coulomb efficiency of 90 to 110%. This can be achieved by the pre-lithiation process described above.

Description of the positive electrode, the negative electrode, and the electrolyte of the lithium secondary battery will be omitted since the configuration of the battery that is currently commonly used can be commonly used.

In one embodiment of the present invention, in the pre-lithiation of a negative electrode material, especially a negative electrode material containing a silicon-based and / or silicon oxide-based material having an effective capacity of 10 times or more than a carbon-based material, the entire area over a commercially available size In addition to being uniformly compensated for lithium, it is possible to provide a negative electrode material in which the amount of compensated lithium is accurately controlled.

1 is a schematic diagram of an apparatus for pre-lithiation according to an embodiment of the present invention.
2 is a schematic diagram of an electrode design for a pre-lithiation method performed in an embodiment of the present invention.
3 is an external surface state of a pre-lithiated anode material according to each Example and Comparative Example.
4A to 4D show the distribution of lithium in the thickness direction from the surface with respect to the pre-lithiated anode material according to each Example and Comparative Example using Secondary Ion mass Spectrometry (SIMS) equipment. .
5 is a result of conducting an evaluation of charging and discharging characteristics by manufacturing a coin cell using an all-lithiated anode material according to each example and comparative example.
In FIG. 6, the Coulombic efficiency calculated from the charge and discharge capacities during charge / discharge performance evaluation is shown.

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 thereby, and the present invention is only defined by the scope of claims to be described later.

As described above, the problems of the prior arts are when the current is passed through direct contact or resistance connection to the negative electrode material, which is the object of all lithiation, due to various reasons, each contact is uniformly distributed over the entire area or is uniform. It is that it is not easy to apply a current. In addition, there is a problem in that in the thickness direction, only the surface of the negative electrode material is pre-lithiated.

Therefore, it is very important that a constant amount of current is uniformly applied to the entire negative electrode material, so that lithium can be uniformly inserted not only in the area direction but also in the thickness direction.

To this end, the electrolyte must be able to penetrate the negative electrode material well, the distance between the lithium electrode and the negative electrode material must be constant, and the supply of electrons in the thickness direction of the negative electrode material must be uniform.

That is, the anode material roll should be exposed on both sides of the electrolyte, not in a wound state, and a uniform gap between the surface of the anode material and the lithium electrode should be maintained when a current is applied.

On the other hand, when the surface of the negative electrode material and the lithium electrode are in direct contact, electrons and lithium ions move directly from the lithium electrode to the surface of the negative electrode material, which results in a problem in which lithium is intensively inserted only on the surface of the negative electrode material. All surfaces are pre-lithiated. In addition, since the degree of lithiation in direct contact varies depending on the degree of contact, if it is not completely and uniformly contacted over the entire area, non-uniformity occurs in the degree of total lithiation.

In order to prevent this, it is necessary to keep the surface of the lithium metal and the negative electrode material in direct contact.

In addition, even if a uniform gap is maintained, if the gap is too large, local current non-uniformity may be generated due to the flow of the electrolyte, and a problem that the external shape of the negative electrode material is deformed due to lithium insertion due to the large space is expected.

Accordingly, in the present invention, a structure in which the gap is optimized while preventing the anode material from contacting the lithium electrode as a lithium source during the pre-lithiation process in which lithium is inserted by applying a current is applied. To this end, the lithium electrode maintains a constant distance from the surface of the negative electrode material by using a flat electrode. Through this process, the pre-lithiated anode material electrode is in a state in which lithium is uniformly inserted over the thickness direction.

Hereinafter, examples and comparative examples of the present invention will be described. However, the following examples are only examples of the present invention, and the present invention is not limited to the following examples.

Example  And Comparative example

( Example  1) Using electrochemical method Total lithiation  (Lithium Metal Cathode material  Spacing adjustment)

2 is a schematic diagram of an electrode design for a pre-lithiation method performed in an embodiment of the present invention. Using the electrochemical method as shown in Figure 2, the negative electrode material was pre-lithiated.

The electrolytic solution used for pre-lithiation was prepared by dissolving 1 M concentration of LiPF ₆ in a solvent of EC / EMC = 30/70, and additionally adding FEC and VC 1.5% to 2% by weight of the electrolyte solution to 2%. As a lithium source, a lithium metal plate having a purity of 99.9% and having a thickness of 500 µm was compressed and used on a copper plate, and the lithium metal electrode was 20 cm wide and 20 cm long, with a total area of 400 cm 2.

On the other hand, as the negative electrode material, a composite negative electrode material consisting of a silicon oxide-based material having a weight ratio of 30% and 70% graphite on a flat 10 μm thick copper foil was used, each of which was coated with 70 μm on both sides of the copper foil. . The capacity of the negative electrode material used was 700 mAh / g, and a lithium current corresponding to a capacity of 2.0 mAh / cm 2 was charged by passing a current of 2 mA / cm 2 for 1 hour for total lithiation of the negative electrode material.

The gap between the lithium metal electrode and the negative electrode material was intended to be maintained at 10 µm, and a separator having a thickness of 10 µm was inserted to prevent direct contact between the lithium metal and the negative electrode material over the entire area.

In this state, a current was applied to the lithium metal electrode and the current collector as a (+) and (-) electrode, respectively, using a power supply to separate lithium ions from the lithium metal to be inserted into the negative electrode material.

( Example  2) Using electrochemical method Total lithiation  (Lithium Metal Cathode material  Spacing adjustment)

Pre-lithiation was performed in the same manner as in Example 1. At this time, the gap between the lithium metal electrode and the negative electrode material was maintained at 1,000 μm, and a separate separator was not inserted in the middle.

( Example  3) Using electrochemical method Total lithiation  (Lithium Metal Cathode material  Spacing adjustment)

Pre-lithiation was performed in the same manner as in Example 1. At this time, the gap between the lithium metal electrode and the negative electrode material was maintained at 1,500 μm, and a separate separator was not inserted in the middle.

( Comparative example  1) Lithium Metal Cathode material  Gap influence (direct contact)

The same electrolyte, negative electrode material, and current collector as in Example 1 were used.

At this time, the lithium metal electrode and the negative electrode material were brought into direct contact without any gap. Therefore, a separator was not inserted between the lithium metal electrode and the negative electrode material.

On the other hand, in the case of direct contact, since a current flows directly between the lithium metal and the negative electrode material, a separate current was not applied, and the contact was maintained for 1 hour.

( Comparative example  2) Lithium Metal Cathode material  Spacing effect (gap expansion)

Pre-lithiation was performed in the same manner as in Example 1.

At this time, the gap between the lithium metal electrode and the negative electrode material was maintained at 2,000 μm, and a separate separator was not inserted in the middle.

Experimental Example

3 is an external surface state of a pre-lithiated anode material according to each Example and Comparative Example. In Examples 1 to 2, there was no trace of lithium plating on the surface, and the overall appearance of the negative electrode material was smooth. On the other hand, in Comparative Example 1 in which the lithium metal electrode and the negative electrode material were brought into direct contact, it can be seen that lithium is plated on the surface locally.

This is because excessive current is concentrated and flows through the local direct contact area, and due to this, lithium is plated on the surface rather than being inserted into the negative electrode material. On the other hand, in Comparative Example 2 in which the gap between the lithium metal electrode and the negative electrode material was excessively widened, when lithium was inserted on both sides of the negative electrode material, the outer surface of the negative electrode material was deformed due to the large space, resulting in bending on the surface.

4A to 4D show the distribution of lithium in the thickness direction from the surface with respect to the pre-lithiated anode material according to each Example and Comparative Example using Secondary Ion mass Spectrometry (SIMS) equipment. .

4A is Example 1, FIG. 4B is Example 2, FIG. 4C is Comparative Example 1, and FIG. 4D is Comparative Example 2.

In Examples 1 to 2, it is shown that the lithium content on the surface is maintained uniformly to a depth of 60 µm. That is, when the gap between the lithium metal electrode and the negative electrode material is optimized and maintained while the electrolyte is well exposed on both surfaces of the negative electrode material roll, it can be seen that a uniform current distribution is formed not only in the area direction but also in the depth direction.

From this, it is shown that not only uniform pre-lithiation is possible over a large area, but uniform lithium can be inserted from the surface to the base of the negative electrode material in the thickness direction of the negative electrode material.

On the other hand, Comparative Example 1 in direct contact shows that the distribution of lithium between the surface and the base was non-uniform. While the lithium content on the surface is high, the lithium content at the base is greatly reduced. It can be seen that this is consistent with the results for the surface appearance of the negative electrode material of Comparative Example 1 in FIG. 3 (c).

On the other hand, in Comparative Example 2, although the same current was applied, the amount of lithium inserted as a whole appears lower than Examples 1 and 2. In addition, it is shown that the lithium content rapidly decreases in the depth region after 40 μm. That is, similar to Comparative Example 1, it is shown that the lithium content of the surface is not maintained uniformly to the base, and thus, uniform pre-lithiation is not achieved.

From this fact, it can be seen that, in the case of performing pre-lithiation in a state where excessive spacing is maintained as in Comparative Example 2, it is not suitable not only in terms of efficient current use but also in terms of uniformity of pre-lithiation.

5 is a result of conducting an evaluation of charging and discharging characteristics by manufacturing a coin cell using an all-lithiated anode material according to each example and comparative example. The coin cell used in the evaluation has a size of 2032 type, and a material of Li _{1 + x} (Ni _y Mn _z Co _w ) _{1- x} O ₂ was used as a cathode material.

The charging condition was a constant current-constant voltage mixed mode, the constant current was 0.1C, the constant voltage was 4.2V, and the cutoff current was set to 0.05C.

Meanwhile, the discharge condition was a constant current mode, the constant current was 0.1C, and the cutoff voltage was set to 2.5V. In Examples 1 and 2, by showing a high charge and discharge capacity, the effect of the capacity increase according to the pre-lithiation of the negative electrode material is shown.

On the other hand, Comparative Example 1 showed unstable charging and discharging performance in the initial cycle process, and in Comparative Example 2, the capacity was significantly lower than that of the Example, and thus there was no effect of capacity increase due to pre-lithiation.

In FIG. 6, the Coulombic efficiency calculated from the charge and discharge capacities when evaluating charge and discharge performance is shown. Examples 1 and 2 show a high initial columb efficiency (ICE) of 92% level in the first cycle of the initial charge / discharge process.

This is because the reduction of active lithium due to the initial irreversible reaction was greatly alleviated by the effect of lithium previously compensated through pre-lithiation. On the other hand, in Comparative Examples 1 and 2, the initial coulomb efficiency was found to be 86% and 82%.

Considering that the initial coulomb efficiency is about 70% when a silicon oxide-based material that is not pre-lithiated is used as a negative electrode material, it can be seen that the effect of pre-lithiation is not sufficiently exhibited in the comparative example.

Accordingly, in an embodiment of the present invention, when an anode material, especially a cathode material containing silicon-based and silicon oxide-based materials having an effective capacity of at least 10 times greater than that of a carbon-based material is pre-lithiated, is uniform in the entire area of the anode material Not only can lithium be compensated, it is also possible to uniformly insert lithium from the surface to the base of the current collector in the thickness direction of the negative electrode material.

In addition, since pre-lithiation is performed using an electrochemical method, the amount of lithium to be compensated can be accurately controlled by controlling the applied current. As described above, when a lithium secondary battery is manufactured with an all-lithiated negative electrode material in which lithium is uniformly and quantitatively well compensated for all regions, as the initial irreversible problem is solved, high initial coulomb efficiency and high battery energy density can be obtained. In addition, excellent effects can be expected in terms of battery stability.

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

Claims (14)

Current collector; And a negative electrode active material layer positioned on the current collector.
The negative electrode active material layer is a lithium secondary battery negative electrode that is uniformly pre-lithiation (pre-lithiation) in the thickness direction.
According to claim 1,
The content of lithium at any point with respect to the overall thickness direction of the negative electrode active material,
The negative electrode for a lithium secondary battery, which is a value within a range of a minimum value and a maximum value of lithium content in 20 length% in the thickness direction from the surface portion of the negative electrode active material layer.
According to claim 1,
A negative electrode for a lithium secondary battery, wherein a surface of the negative electrode active material layer does not have a lithium plating layer.
According to claim 1,
The negative electrode active material in the negative electrode active material layer,
A negative electrode for a lithium secondary battery comprising a silicon-based compound, a silicon oxide-based compound, a carbon-based compound, or a combination thereof.
According to claim 1,
The cathode,
A negative electrode for a lithium secondary battery having a structure in which the negative electrode active material layer is located on both sides of the current collector.
According to claim 1,
The negative electrode active material layer has a thickness of 10 to 200㎛, the negative electrode for a lithium secondary battery.
According to claim 1,
A negative electrode for a lithium secondary battery, further comprising a film located on the surface of the negative electrode active material layer.
The method of claim 7,
The coating is a negative electrode for a lithium secondary battery, which is a Li-NCHO-based ionic compound, a Li-PCHO-based ionic compound, LiF or a combination thereof.
Preparing a negative electrode and a lithium electrode opposed thereto, impregnated in the electrolyte solution; And
Applying a current to the negative electrode and the lithium electrode, thereby pre-lithiating the negative electrode;
Including,
The gap between the negative electrode and the lithium electrode is a method of manufacturing a negative electrode for a lithium secondary battery, which is greater than 0 and less than 1,500 μm.
The method of claim 9,
The current density is 0.1 to 100 mA / cm ² based on the area of the lithium electrode.
The method of claim 9,
The area of the lithium electrode is 25 to 1,000cm ^{2 The} method of manufacturing a negative electrode for a lithium secondary battery.
The method of claim 9,
A method of manufacturing a negative electrode for a lithium secondary battery, wherein a separator is positioned between the negative electrode and the lithium electrode.
anode; cathode; And an electrolyte positioned between the positive electrode and the negative electrode,
The negative electrode is a lithium secondary battery that is the negative electrode according to claim 1.
The method of claim 13,
The lithium secondary battery is a lithium secondary battery having an initial Coulomb efficiency of 90 to 110%.

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