KR20240085850A - Negative electrode active material, manufacturing method of negative electrode active material, negative electrode composition, negative electrode for lithium secondary battery comprising same, and lithium secondary battery comprising negative electrode - Google Patents

Abstract

This application relates to a negative electrode active material, a method of manufacturing the negative electrode active material, a negative electrode composition, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the negative electrode.

Description

Negative electrode active material, method of producing negative electrode active material, negative electrode composition, negative electrode for lithium secondary battery including same, and lithium secondary battery including negative electrode BATTERY COMPRISING SAME, AND LITHIUM SECONDARY BATTERY COMPRISING NEGATIVE ELECTRODE}

This application claims the benefit of the filing date of Korean Patent Application No. 10-2022-0170486 filed with the Korea Intellectual Property Office on December 8, 2023, the entire contents of which are incorporated into this specification.

This application relates to a negative electrode active material, a method of manufacturing the negative electrode active material, a negative electrode composition, a negative electrode for a lithium secondary battery including the same, and a lithium secondary battery including the negative electrode.

Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative or clean energy is increasing, and as part of this, the most actively researched fields are power generation and storage using electrochemical reactions.

Currently, secondary batteries are a representative example of electrochemical devices that use such electrochemical energy, and their use area is gradually expanding.

As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among these secondary batteries, lithium secondary batteries with high energy density and voltage, long cycle life, and low self-discharge rate have been commercialized and are widely used. In addition, as an electrode for such a high-capacity lithium secondary battery, research is being actively conducted on methods for manufacturing a high-density electrode with a higher energy density per unit volume.

Generally, a secondary battery consists of an anode, a cathode, an electrolyte, and a separator. The negative electrode includes a negative electrode active material that inserts and desorbs lithium ions from the positive electrode, and silicon-based particles with a large discharge capacity may be used as the negative electrode active material.

In particular, in response to the recent demand for high-density energy batteries, research is being actively conducted on ways to increase capacity by using silicon-based compounds such as Si/C or SiOx, which have a capacity more than 10 times greater than graphite-based materials, as anode active materials. However, in the case of silicon-based compounds, which are high-capacity materials, the capacity is large compared to conventionally used graphite, but there is a problem in that the volume expands rapidly during the charging process and the conductive path is cut off, deteriorating battery characteristics.

Accordingly, in order to solve the problem of using a silicon-based compound as a negative electrode active material, the volume expansion itself is suppressed, such as a method of controlling the driving potential, a method of additionally coating a thin film on the active material layer, and a method of controlling the particle size of the silicon-based compound. Various methods are being discussed to prevent the conductive path from being disconnected or to prevent the conductive path from being disconnected, but these methods have limitations in application because they can reduce battery performance, so the negative electrode battery still has a high content of silicon-based compounds. There are limits to commercialization of manufacturing.

Therefore, even when using a silicon-based active material as a negative electrode active material to improve capacity performance, research is needed on the silicon-based active material itself, which can alleviate the phenomenon of silicon cracking due to insertion and detachment of lithium during charging and discharging.

Japanese Patent Publication No. 2009-080971

When the distribution and sphericity of crystal planes within the silicon-based active material are adjusted by adjusting the plate shape of the silicon-based active material according to the silicon processing method, the reaction occurs uniformly during the insertion/desorption reaction of lithium and the stress on the silicon-based active material is reduced. Confirmed. In particular, it was confirmed through research that the plate shape of the silicon-based active material itself can be specifically controlled when the milling temperature, pressure, and time are specifically set in the processing method, and through this, insertion and desorption of lithium ions are achieved uniformly. Confirmed.

Accordingly, the present application relates to a negative electrode active material that can solve the above-mentioned problems, a method of manufacturing the negative electrode active material, a negative electrode composition, a negative electrode for a lithium secondary battery containing the same, and a lithium secondary battery including the negative electrode.

One embodiment of the present specification is a negative electrode active material containing a silicon-based active material that satisfies the plate shape of Equation 1 below, wherein the silicon-based active material is selected from the group consisting of SiOx (x=0) and SiOx (0<x<2) It provides a negative electrode active material containing at least 1 and at least 70 parts by weight of SiOx (x=0) based on 100 parts by weight of the silicon-based active material.

[Equation 1]

45 ≤ (A/B) x 100

In equation 1 above,

A refers to the length of the short axis of the silicon-based active material,

B refers to the length of the long axis of the silicon-based active material.

In another embodiment, preparing metal silicon; and pulverizing the metal silicon to form a silicon-based active material, wherein the silicon-based active material satisfies the plate shape of Equation 1 above.

In another exemplary embodiment, a negative electrode active material according to the present application; cathode conductive material; and a negative electrode binder.

In another embodiment, a negative electrode current collector layer; and a negative electrode active material layer provided on one or both sides of the negative electrode current collector layer, wherein the negative electrode active material layer includes the negative electrode composition or a cured product thereof according to the present application.

Finally, the anode; A negative electrode for a lithium secondary battery according to the present application; A separator provided between the anode and the cathode; It provides a lithium secondary battery including; and an electrolyte.

The negative electrode active material of the present invention is a silicon-based active material and includes at least one selected from the group consisting of SiOx (x=0) and SiOx (0<x<2), and based on 100 parts by weight of the silicon-based active material, the SiOx (x=0) It contains 70 parts by weight or more, that is, it is produced by controlling the grinding conditions by improving the existing processing method while having a Pure Si active material, and thus includes a silicon-based active material that satisfies certain physical properties. When using the silicon-based active material manufactured in this way, it is possible to react uniformly during the insertion and desorption reaction of lithium during charging and discharging, and by reducing the stress on the silicon-based active material, cracking of particles can be alleviated, thereby increasing the lifespan of the electrode. Retention rate can be improved.

In particular, the present application is characterized by controlling the plate shape that satisfies the range of Equation 1 above when manufacturing a silicon-based active material as described above. That is, when the plate shape satisfies the range of Equation 1 above, the silicon-based active material contains a larger proportion of 220 crystal planes than before, so lithium enters and exits uniformly during the lithium insertion/desorption reaction, resulting in silicon cracking on the electrode surface. It can alleviate the phenomenon and thus has the feature of strengthening the lifespan characteristics of the electrode.

Figure 1 is a diagram showing a stacked structure of a negative electrode for a lithium secondary battery according to an exemplary embodiment of the present application.
Figure 2 is a diagram showing a stacked structure of a lithium secondary battery according to an exemplary embodiment of the present application.
Figure 3 is a diagram showing a method for calculating grain size.
Figure 4 is a diagram showing the unit structure of the silicon-based active material according to the present application.
Figure 5 is a diagram showing sides 220 and 111 of the silicon-based active material according to the present application.
Figure 6 is a diagram comparing the density of the 220 side and the 111 side of the silicon-based active material.

Before explaining the present invention, some terms are first defined.

In this specification, when a part “includes” a certain element, this means that it may further include other elements rather than excluding other elements, unless specifically stated to the contrary.

In this specification, 'p to q' means a range of 'p to q or less.'

In this specification, “specific surface area” is measured by the BET method, and is specifically calculated from the amount of nitrogen gas adsorption under liquid nitrogen temperature (77K) using BELSORP-mino II from BEL Japan. That is, in the present application, the BET specific surface area may mean the specific surface area measured by the above measurement method.

In this specification, “Dn” refers to particle size distribution and refers to the particle size at the n% point of the cumulative distribution of particle numbers according to particle size. In other words, D50 is the particle size (average particle diameter) at 50% of the cumulative distribution of particle numbers according to particle size, D90 is the particle size at 90% of the cumulative distribution of particle numbers according to particle size, and D10 is the cumulative particle number according to particle size. This is the particle size at 10% of the distribution. Meanwhile, the average particle diameter can be measured using a laser diffraction method. Specifically, after dispersing the powder to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (for example, Microtrac S3500), and the difference in diffraction patterns according to particle size is measured when the particles pass through the laser beam, thereby distributing the particle size. Calculate .

In an exemplary embodiment of the present application, the particle size or particle size may mean the average diameter or representative diameter of each grain forming the metal powder.

In this specification, the fact that a polymer contains a certain monomer as a monomer unit means that the monomer participates in a polymerization reaction and is included as a repeating unit in the polymer. In this specification, when it is said that a polymer contains a monomer, this is interpreted the same as saying that the polymer contains a monomer as a monomer unit.

In this specification, the term 'polymer' is understood to be used in a broad sense including copolymers, unless specified as 'homopolymer'.

In this specification, the weight average molecular weight (Mw) and number average molecular weight (Mn) are determined by using monodisperse polystyrene polymers (standard samples) of various degrees of polymerization commercially available for molecular weight measurement as standard materials, and using gel permeation chromatography (Gel Permeation). Polystyrene equivalent molecular weight measured by chromatography (GPC). In this specification, molecular weight means weight average molecular weight unless otherwise specified.

Hereinafter, the present invention will be described in detail with reference to the drawings so that those skilled in the art can easily practice the present invention. However, the present invention may be implemented in various different forms and is not limited to the following description.

One embodiment of the present specification is a negative electrode active material containing a silicon-based active material that satisfies the plate shape of Equation 1 below, wherein the silicon-based active material is selected from the group consisting of SiOx (x=0) and SiOx (0<x<2) It provides a negative electrode active material containing at least 1 and at least 70 parts by weight of SiOx (x=0) based on 100 parts by weight of the silicon-based active material.

[Equation 1]

45 ≤ (A/B) x 100

In equation 1 above,

A refers to the length of the short axis of the silicon-based active material,

B refers to the length of the long axis of the silicon-based active material.

This application is characterized by controlling the plate shape that satisfies the range of Equation 1 above when manufacturing a silicon-based active material. That is, when the plate shape satisfies the range of Equation 1 above, the silicon-based active material contains a larger proportion of 220 crystal planes than before, so lithium enters and exits uniformly during the lithium insertion/desorption reaction, resulting in silicon cracking on the electrode surface. It can alleviate the phenomenon and thus has the feature of strengthening the lifespan characteristics of the electrode.

In an exemplary embodiment of the present application, A refers to the length of the short axis of the silicon-based active material, and B refers to the length of the long axis of the silicon-based active material. To measure the long axis and short axis, the ratio of the long axis and short axis of the silicon-based active material can be measured by taking an SEM image of the cross-section of the electrode containing the silicon-based negative active material and then analyzing the cross-sectional image of each particle through an image processing program.

At this time, the length of the long axis of the silicon-based active material can refer to the length of the longest axis of the silicon-based active material particle by confirming individual particles through the above-described SEM image capture and image processing program, and the length of the minor axis can be the length of the shortest axis. It can mean.

In an exemplary embodiment of the present application, Equation 1 is 45 ≤ (A / B) x 100, preferably 46 ≤ (A / B) x 100, more preferably 47 ≤ (A / B) x 100. The range may be satisfied, and (A / B) x 100 ≤ 100, preferably (A / B) x 100 ≤ 90, more preferably (A / B) x 100 ≤ 88.

In the present application, the silicon-based active material satisfies the range of the plate shape (Equation 1), and through the control of the particle shape as described above, the surface with high lithium mobility in the active material can be relatively widely distributed within the particles, allowing It has the feature of easy insertion and removal of lithium. In other words, it has the feature of improving the lifespan performance of a battery containing a silicon-based active material by alleviating the phenomenon of particle cracking at the top of the electrode by improving the uniformity between active materials in the electrode in the insertion/desorption of lithium.

In the present application, the silicon-based active material that satisfies the plate shape of Equation 1 can be adjusted by a manufacturing method described later, the details of which will be described later.

One embodiment of the present specification provides a negative electrode active material in which the silicon-based active material includes 220 crystal planes and 111 crystal planes, and the silicon-based active material satisfies the following equation 2.

[Equation 2]

37 ≤ (X/Y) x 100

In equation 2 above,

Y refers to the ratio of 111 crystal planes in the silicon-based active material,

X refers to the ratio of 220 crystal planes in the silicon-based active material.

This application is characterized by controlling the grain direction distribution that satisfies the plate shape of Equation 1 and the range of Equation 2 when manufacturing a silicon-based active material. In other words, when a relatively large proportion of 111 crystal planes is formed as before, the 111 crystal plane has lower lithium mobility than the 220 crystal plane, so lithium does not enter and exit evenly during the insertion/desorption reaction of lithium. However, the silicon-based active material according to the present application contains a larger proportion of 220 crystal planes than before, allowing lithium to enter and exit uniformly during the insertion/desorption reaction of lithium, thereby mitigating the phenomenon of silicon cracking on the electrode surface. It has features that enhance its lifespan characteristics.

Figure 4 shows the monomer structure of the silicon-based active material according to the present application. It includes a grain surface, and specifically, surfaces 220 and 111 of the silicon-based active material can be seen in Figure 5. Figure 6 corresponds to a diagram comparing the density of the 220 side and the 111 side of the silicon-based active material. As can be seen specifically, when checking the density and direction of the 220 side and the 110 side, the 220 side has a lower particle density within the same area, so when Li moves, the 220 side with a smaller particle density is more advantageous. there was.

In an exemplary embodiment of the present application, may satisfy 35 to 60, more preferably 35 to 55.

In an exemplary embodiment of the present application, Y refers to the ratio of 111 crystal planes in the silicon-based active material, which means the ratio based on the entire surface of the silicon-based active material, and Y is 50 to 80, preferably may satisfy 55 to 80, more preferably 55 to 75.

In an exemplary embodiment of the present application, the silicon-based active material may further include various crystal planes.

In an exemplary embodiment of the present application, the silicon-based active material includes one or more selected from the group consisting of SiOx (x=0) and SiOx (0<x<2), and the SiOx (based on 100 parts by weight of the silicon-based active material) x=0) may be included in an amount of 70 parts by weight or more.

In an exemplary embodiment of the present application, the silicon-based active material includes SiOx (x=0), and may include 70 parts by weight or more of SiOx (x=0) based on 100 parts by weight of the silicon-based active material.

In another embodiment, based on 100 parts by weight of the silicon-based active material, the SiOx (x=0) may include 70 parts by weight or more, preferably 80 parts by weight or more, and more preferably 90 parts by weight or more, It may contain 100 parts by weight or less, preferably 99 parts by weight or less, and more preferably 95 parts by weight or less.

In an exemplary embodiment of the present application, the silicon-based active material may be used as a silicon-based active material, especially one containing pure silicon (Si) particles. Using pure silicon (Si) particles as a silicon-based active material means that pure Si particles (SiOx (x=0)) that are not combined with other particles or elements are used based on a total of 100 parts by weight of the silicon-based active material as described above. It may mean included in the scope.

In an exemplary embodiment of the present application, the silicon-based active material may be composed of silicon-based particles having 100 parts by weight of SiOx (x=0) based on 100 parts by weight of the silicon-based active material.

In an exemplary embodiment of the present application, the silicon-based active material may contain metal impurities. In this case, the impurity is a metal that can generally be included in the silicon-based active material, and may specifically include 0.1 part by weight or less based on 100 parts by weight of the silicon-based active material. there is.

In the case of silicon-based active materials, compared to existing graphite-based active materials, the capacity is significantly higher, so attempts to apply them are increasing. However, due to the high volume expansion rate during the charging and discharging process, it is limited to cases where trace amounts are mixed with graphite-based active materials. there is.

Therefore, in the case of the present invention, only the silicon-based active material is used as the negative electrode active material to improve capacity performance, but in order to solve the above problems, the crystal grain size or surface area of the silicon-based active material itself is adjusted rather than the composition of the conductive material and binder. Through this, the existing problems were solved.

In an exemplary embodiment of the present application, the crystal grain size of the silicon-based active material may be 500 nm or less.

In another embodiment, the crystal grain size of the silicon-based active material is 500 nm or less, preferably 400 nm or less, more preferably 200 nm or less, even more preferably 100 nm or less, specifically 95 nm or less, more specifically It may be 91 nm or less. The crystal grain size of the silicon-based active material may be in the range of 10 nm or more, preferably 15 nm or more.

The silicon-based active material has the above-mentioned grain size, and the grain size of the silicon-based active material can be adjusted by changing the process conditions during the manufacturing process. At this time, the grain boundaries are distributed widely by satisfying the above range, so that when lithium ions are inserted, they enter uniformly, thereby reducing the stress applied when lithium ions are inserted into silicon particles, thereby alleviating particle cracking. can do. As a result, it has characteristics that can improve the lifetime stability of the cathode. If the grain size exceeds the above range, the grain boundaries within the grain are narrowly distributed. In this case, lithium ions within the grain are inserted unevenly, and the stress due to ion insertion increases, resulting in grain breakage.

In an exemplary embodiment of the present application, the silicon-based active material includes a crystal structure having a grain distribution of 1 nm or more and 200 nm or less, and the area ratio of the crystal structure is 5% or less based on the total area of the silicon-based active material. provides.

In another embodiment, the area ratio of the crystal structure based on the total area of the silicon-based active material may be 5% or less, 3% or less, and may be 0.1% or more.

That is, the silicon-based active material according to the present application has a crystal grain size of 200 nm or less, so that the size of one crystal structure is small and can satisfy the above area ratio. Accordingly, the distribution of grain boundaries may be broadened, and thus the above-mentioned effect may appear.

In an exemplary embodiment of the present application, a negative electrode active material is provided in which the number of crystal structures included in the silicon-based active material is 20 or more.

In another embodiment, the number of crystal structures included in the silicon-based active material may be 20 or more, 30 or more, or 35 or more, and may satisfy the range of 60 or less and 50 or less.

In other words, as described above, if the crystal grain size of the silicon-based active material satisfies the above range and the number of crystal structures satisfies the above range, the strength of the silicon-based active material itself has an appropriate range and can provide flexibility when included in the electrode. It also has the characteristic of efficiently suppressing volume expansion.

In the present application, a crystal grain refers to a crystal particle that is a collection of irregular shapes of microscopic size in a metal or material, and the grain size may refer to the diameter of the observed crystal grain particle. That is, in the present application, the crystal grain size refers to the size of a domain sharing the same crystal direction within the particle, and has a different concept from the size of the particle size or particle diameter, which expresses the size of the material.

In an exemplary embodiment of the present application, the grain size can be calculated as a FWHM (Full Width at Half Maximum) value through XRD analysis. Specifically, in Figure 6 you can see how to calculate the grain size. In FIG. 6, the remaining values except L are measured through XRD analysis of the silicon-based active material, and the grain size can be measured through the Debey-Scherrer equation, which shows that FWHM and grain size are inversely proportional. At this time, the Debey-Scherrer equation is as shown in Equation 1-1 below.

[Equation 1-1]

FWHM=Kλ/LCosθ

In Equation 1-1 above,

L is the grain size, K is a constant, θ is the bragg angle, and λ is the wavelength of the X-ray.

In addition, the shape of the crystal grains can be measured three-dimensionally as they vary, and the size of the grains can generally be measured by the commonly used circle method and diameter measurement method, but is not limited thereto.

The diameter measurement method can be measured by drawing 5-10 balanced lines with a length of L mm on a microscope photo of the target particle, counting the number of grains z on the lines, and averaging them. At this time, only what goes in is counted and what is put on is excluded. If the number of lines is P and the magnification is V, the average particle diameter can be calculated using the following equation 1-2.

[Equation 1-2]

Dm = (L*P*10 ³ )/(zV) (um)

In addition, the circle method is a method of drawing a circle of a certain diameter on a microscopic photo of a target particle and then calculating the average area of the crystal grains based on the number of crystal grains inside the circle and the number of crystal grains on the boundary line, calculated using the following equation 1-3. It can be.

[Equation 1-3]

Fm = (Fk * 10 ⁶ ) /((0.67n + z) V ² )(um ² )

In Equation 1-3, Fm is the average particle area, Fk is the measured area on the photograph, z is the number of particles entering the circle, n is the number of particles caught in the arc, and V is the magnification of the microscope.

In an exemplary embodiment of the present application, the negative electrode active material may include a silicon-based active material with a surface area of 0.25 m ² /g or more.

In another embodiment, the silicon-based active material has a surface area of 0.25 m ² /g or more, preferably 0.28 m ² /g or more, more preferably 0.30 m ² /g or more, specifically 0.31 m ² /g. It may be more than, more specifically, 0.32 m ² /g or more. The silicon-based active material may have a surface area of 3 m ² /g or less, preferably 2.5 m ² /g or less, and more preferably 2.2 m ² /g or less. The surface area can be measured according to DIN 66131 (using nitrogen).

The silicon-based active material has the above-mentioned surface area, and the size of the surface area of the silicon-based active material can be adjusted by changing the process conditions in the manufacturing process and the growth conditions of the silicon-based active material, which will be described later. That is, when the anode active material is manufactured using the manufacturing method according to the present application, the rough surface results in a larger surface area compared to particles with the same particle size. In this case, the above range is satisfied and the bonding strength with the binder increases, so the charge and discharge cycle is repeated. It has features that can alleviate cracks in the electrode.

In addition, when lithium ions are inserted, they are inserted uniformly, thereby reducing the stress applied when lithium ions are inserted into silicon particles, thereby alleviating breakage of particles. As a result, it has characteristics that can improve the lifetime stability of the cathode. If the surface area size is less than the above range, even if it has the same particle size, the surface is formed smoothly, the bonding force with the binder decreases, and electrode cracks occur. In this case, lithium ions in the particles are inserted unevenly, resulting in ion insertion. If the stress is large, particle breakage occurs.

In an exemplary embodiment of the present application, the silicon-based active material provides a negative electrode active material that satisfies the range of Equation 2-1 below.

[Equation 2-1]

X1/Y1 ≤ 0.960

In Equation 2-1 above,

X1 is the actual area of the silicon-based active material,

Y1 refers to the area of a spherical particle with the same circumference of the silicon-based active material.

The measurement of Equation 2-1 above can be performed using a particle analyzer. Specifically, the silicon-based active material according to the present application can be scattered on a glass plate through air injection, and then the shape of 10,000 silicon-based active material particles in the photo can be measured by taking a shadow image of the scattered silicon-based active material particles. At this time, Equation 2-1 is a value expressing the average of 10,000 particles. Equation 2-1 according to the present application can be measured from the above image, and Equation 2-1 can be expressed as the circularity of the silicon-based active material. The degree of sphericity can also be expressed by the equation [4π*actual area of silicon-based active material/(boundary) ² ].

In an exemplary embodiment of the present application, the sphericity degree of the silicon-based active material may be, for example, 0.960 or less, for example, 0.957 or less. The sphericity degree of the silicon-based active material may be 0.8 or higher, for example, 0.9 or higher, specifically 0.93 or higher, more specifically 0.94 or higher, for example, 0.941 or higher.

In an exemplary embodiment of the present application, the silicon-based active material provides a negative electrode active material that satisfies the range of Equation 2-2 below.

[Equation 2-2]

X2/Y2 ≤ 0.995

In Equation 2-2 above,

Y2 is the actual perimeter of the silicon-based active material

X2 is the perimeter of the circumscribed shape of the silicon-based active material.

The measurement of Equation 2-2 above can be performed using a particle analyzer. Specifically, the silicon-based active material according to the present application can be scattered on a glass plate through air injection, and then the shape of 10,000 silicon-based active material particles in the photo can be measured by taking a shadow image of the scattered silicon-based active material particles. At this time, Equation 2-2 is a value expressing the average of 10,000 particles. Equation 2-2 according to the present application can be measured from the above image, and Equation 2-2 can be expressed as the convexity of the silicon-based active material.

In an exemplary embodiment of the present application, the range of X2/Y2 ≤ 0.996, preferably X2/Y2 ≤ 0.995, may be satisfied, and 0.8≤ X2/Y2, preferably 0.9≤ ≤ X2/Y2, specifically, the range of 0.98≤ X2/Y2 can be satisfied.

The smaller the value of Equation 2-1 or Equation 2-2, the greater the roughness of the silicon-based active material. As the silicon-based active material with the above range is used, the bonding strength with the binder increases. It has the characteristic of alleviating cracks in the electrode due to repeated charge and discharge cycles.

In an exemplary embodiment of the present application, the silicon-based active material may include silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less.

That the silicon-based active material includes silicon-based particles having a particle size distribution of 0.01 μm or more and 30 μm or less means that it contains a large number of individual silicon-based particles having a particle size within the above range, and the number of silicon-based particles included is not limited. .

If the silicon-based particle is spherical, the particle size may be expressed as its diameter, but even if it has a shape other than a sphere, the particle size can be measured compared to the spherical case, and is generally measured individually in the art. The particle size of silicon-based particles can be measured.

Meanwhile, the average particle diameter (D50 particle size) of the silicon-based active material of the present invention may be 3㎛ to 10㎛, specifically 5.5㎛ to 8㎛, and more specifically 6㎛ to 7㎛. When the average particle diameter is within the above range, the specific surface area of the particles is within an appropriate range, and the viscosity of the anode slurry is within an appropriate range. Accordingly, dispersion of the particles constituting the cathode slurry becomes smooth. In addition, since the size of the silicon-based active material is greater than the above lower limit, the contact area between the silicon particles and the conductive material is excellent due to the composite of the conductive material and the binder in the negative electrode slurry, and the possibility of the conductive network being maintained increases, increasing the capacity. Retention rate increases. Meanwhile, when the average particle diameter satisfies the above range, excessively large silicon particles are excluded to form a smooth surface of the cathode, thereby preventing current density unevenness during charging and discharging.

In one embodiment of the present application, the silicon-based active material generally has a characteristic BET surface area. The BET surface area of the silicon-based active material is preferably 0.01 to 150.0 m ² /g, more preferably 0.1 to 100.0 m ² /g, particularly preferably 0.2 to 80.0 m ² /g, most preferably 0.2 to 18.0 m ² It is /g. BET surface area is measured according to DIN 66131 (using nitrogen).

In an exemplary embodiment of the present application, a negative electrode active material is provided containing 80 parts by weight or more and 100 parts by weight or less of a silicon-based active material that satisfies the plate shape of Equation 1, based on 100 parts by weight of the negative electrode active material.

In another embodiment, based on 100 parts by weight of the negative electrode active material, the amount of the silicon-based active material satisfying the plate shape of Equation 1 is 80 parts by weight or more and 100 parts by weight or less, preferably 85 parts by weight or more and 99 parts by weight or less, and further. Preferably, it may contain 90 parts by weight or more and 99 parts by weight or less.

That is, the negative electrode active material according to the present application includes a silicon-based active material that satisfies the range of Equation 1 described above, and at the same time may further include a silicon-based active material or a carbon-based active material that can be generally included.

In an exemplary embodiment of the present application, the negative electrode active material; cathode conductive material; and a negative electrode binder.

In an exemplary embodiment of the present application, a negative electrode composition is provided in which the negative electrode active material is 60 parts by weight or more based on 100 parts by weight of the negative electrode composition.

In an exemplary embodiment of the present application, a negative electrode composition is provided in which the silicon-based active material is contained in an amount of 60 parts by weight or more based on 100 parts by weight of the negative electrode composition.

In another embodiment, the silicon-based active material may contain at least 60 parts by weight, preferably at least 65 parts by weight, more preferably at least 70 parts by weight, based on 100 parts by weight of the negative electrode composition, and not more than 95 parts by weight. , preferably 90 parts by weight or less, more preferably 85 parts by weight or less.

The negative electrode composition according to the present application uses a negative electrode active material that satisfies a specific grain size that can control the volume expansion rate during the charging and discharging process even if a silicon-based active material with a significantly high capacity is used within the above range, and even if the negative electrode composition includes the above range, the negative electrode composition It does not degrade performance and has excellent output characteristics during charging and discharging.

In the past, it was common to use only graphite-based active materials as negative electrode active materials, but recently, as demand for high-capacity batteries increases, attempts to use silicon-based active materials mixed to increase capacity are increasing. However, in the case of silicon-based active materials, even if the characteristics of the silicon-based active material itself are adjusted as described above, some problems may arise in which the volume expands rapidly during the charging/discharging process, damaging the conductive path formed in the negative electrode active material layer.

Therefore, in an exemplary embodiment of the present application, the negative conductive material may include one or more selected from the group consisting of a point-shaped conductive material, a planar conductive material, and a linear conductive material.

In an exemplary embodiment of the present application, the point-shaped conductive material refers to a point-shaped or spherical conductive material that can be used to improve conductivity in the cathode and has conductivity without causing chemical change. Specifically, the dot-shaped conductive material is natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, channel black, Parness black, lamp black, thermal black, conductive fiber, fluorocarbon, aluminum powder, nickel powder, zinc oxide, It may be at least one selected from the group consisting of potassium titanate, titanium oxide, and polyphenylene derivatives, and preferably may include carbon black in terms of realizing high conductivity and excellent dispersibility.

In an exemplary embodiment of the present application, the point-shaped conductive material may have a BET specific surface area of 40 m ² /g or more and 70 m ² /g or less, preferably 45 m ² /g or more and 65 m ² /g or less, more preferably 50 m ^{2 /g.} It may be more than /g and less than 60m ² /g.

In an exemplary embodiment of the present application, the point-shaped conductive material may satisfy a functional group content (Volatile matter) of 0.01% or more and 1% or less, preferably 0.01% or more and 0.3% or less, and more preferably 0.01% or more and 0.1% or less. there is.

In particular, when the functional group content of the dot-shaped conductive material satisfies the above range, functional groups exist on the surface of the dot-shaped conductive material, so that when water is used as a solvent, the dot-shaped conductive material can be smoothly dispersed in the solvent. In particular, in the present invention, by using a specific silicon-based active material, the functional group content of the point-shaped conductive material can be lowered, which has an excellent effect in improving dispersibility.

In an exemplary embodiment of the present application, it is characterized in that it includes a point-type conductive material having a functional group content in the above range along with a silicon-based active material, and the content of the functional group can be adjusted according to the degree of heat treatment of the point-type conductive material. there is.

In an exemplary embodiment of the present application, the particle diameter of the point-shaped conductive material may be 10 nm to 100 nm, preferably 20 nm to 90 nm, and more preferably 20 nm to 60 nm.

In an exemplary embodiment of the present application, the conductive material may include a planar conductive material.

The planar conductive material may serve to improve conductivity by increasing surface contact between silicon particles within the cathode and at the same time suppress disconnection of the conductive path due to volume expansion. The planar conductive material may be expressed as a plate-shaped conductive material or a bulk-type conductive material.

In an exemplary embodiment of the present application, the planar conductive material may include at least one selected from the group consisting of plate-shaped graphite, graphene, graphene oxide, and graphite flakes, and may preferably be plate-shaped graphite.

In an exemplary embodiment of the present application, the average particle diameter (D50) of the planar conductive material may be 2㎛ to 7㎛, specifically 3㎛ to 6㎛, and more specifically 3.5㎛ to 5㎛. . When the above range is satisfied, dispersion is easy without causing an excessive increase in viscosity of the anode slurry due to the sufficient particle size. Therefore, the dispersion effect is excellent when dispersed using the same equipment and time.

In one embodiment of the present application, the planar conductive material has a D10 of 0.5 μm or more and 2.0 μm or less, a D50 of 2.5 μm or more and 3.5 μm or less, and a D90 of 6.5 μm or more and 15.0 μm or less. It provides a negative electrode composition.

In an exemplary embodiment of the present application, the planar conductive material is a high specific surface area planar conductive material having a high BET specific surface area; Alternatively, a low specific surface area planar conductive material can be used.

In an exemplary embodiment of the present application, the planar conductive material includes a high specific surface area planar conductive material; Alternatively, a planar conductive material with a low specific surface area can be used without limitation, but in particular, the planar conductive material according to the present application can be affected to some extent by dispersion on electrode performance, so it is possible to use a planar conductive material with a low specific surface area that does not cause problems with dispersion. This may be particularly desirable.

In an exemplary embodiment of the present application, the planar conductive material may have a BET specific surface area of 1 m ² /g or more.

In another embodiment, the planar conductive material may have a BET specific surface area of 1 m ² /g or more and 500 m ² /g or less, preferably 5 m ² /g or more and 300 m ² /g or less, more preferably 5 m ² /g or more. It may be more than g and less than 250m ² /g.

The planar conductive material according to the present application includes a high specific surface area planar conductive material; Alternatively, a low specific surface area planar conductive material can be used.

In another embodiment, the planar conductive material is a high specific surface area planar conductive material, and has a BET specific surface area of 50 m ² /g or more and 500 m ² /g or less, preferably 80 m ² /g or more and 300 m ² /g or less, more preferably In other words, it can satisfy the range of 100m ² /g or more and 300m ² /g or less.

In another embodiment, the planar conductive material is a low specific surface area planar conductive material, and the BET specific surface area is 1 m ² /g or more and 40 m ² /g or less, preferably 5 m ² /g or more and 30 m ² /g or less, more preferably In other words, it can satisfy the range of 5m ² /g or more and 25m ² /g or less.

Other conductive materials may include linear conductive materials such as carbon nanotubes. The carbon nanotubes may be bundled carbon nanotubes. The bundled carbon nanotubes may include a plurality of carbon nanotube units. Specifically, the 'bundle type' herein means, unless otherwise stated, a bundle in which a plurality of carbon nanotube units are arranged side by side or entangled with the longitudinal axis of the carbon nanotube units in substantially the same orientation. It refers to a secondary shape in the form of a bundle or rope. The carbon nanotube unit has a graphite sheet in the shape of a cylinder with a nano-sized diameter and an sp2 bond structure. At this time, the characteristics of a conductor or semiconductor can be displayed depending on the angle and structure at which the graphite surface is rolled. Compared to entangled type carbon nanotubes, the bundled carbon nanotubes can be uniformly dispersed when manufacturing a cathode, and can smoothly form a conductive network within the cathode, improving the conductivity of the cathode.

In an exemplary embodiment of the present application, a negative electrode composition is provided in which the negative electrode conductive material is in an amount of 10 parts by weight or more and 40 parts by weight or less based on 100 parts by weight of the negative electrode composition.

In another embodiment, the anode conductive material is present in an amount of 0.1 to 40 parts by weight, preferably 0.2 to 30 parts by weight, more preferably 0.4 to 25 parts by weight, based on 100 parts by weight of the anode composition. parts or less, most preferably 0.4 parts by weight or more and 10 parts by weight or less.

In an exemplary embodiment of the present application, the negative electrode conductive material is a planar conductive material; and a linear conductive material.

In an exemplary embodiment of the present application, the negative electrode conductive material is 80 parts by weight or more and 99.9 parts by weight or less of the planar conductive material based on 100 parts by weight of the negative electrode conductive material; and 0.1 to 20 parts by weight of the linear conductive material.

In another embodiment, the negative electrode conductive material is present in an amount of 80 parts by weight or more and 99.9 parts by weight or less, preferably 85 parts by weight or more and 99.9 parts by weight or less, more preferably, based on 100 parts by weight of the negative electrode conductive material. It may contain 95 parts by weight or more and 98 parts by weight or less.

In another embodiment, the anode conductive material is 0.1 part by weight or more and 20 parts by weight or less, preferably 0.1 part by weight or more and 15 parts by weight or less, more preferably 0.2 parts by weight, based on 100 parts by weight of the anode conductive material. It may contain more than 5 parts by weight and less than 5 parts by weight.

In an exemplary embodiment of the present application, since the negative conductive material includes a planar conductive material and a linear conductive material and satisfies the above composition and ratio, it does not significantly affect the lifespan characteristics of the existing lithium secondary battery, especially the planar conductive material. When ash and linear conductive materials are included, the number of possible charging and discharging points increases, resulting in excellent output characteristics at high C-rates and reduced high-temperature gas generation.

In an exemplary embodiment of the present application, the negative electrode conductive material may be made of a linear conductive material.

In particular, when a linear conductive material is used alone, the electrode tortuosity, which is a problem of silicon-based anodes, can be simplified, the electrode structure can be improved, and the movement resistance of lithium ions in the electrode can be reduced accordingly. do.

In an exemplary embodiment of the present application, when the negative electrode conductive material includes a linear conductive material alone, the negative electrode conductive material is 0.1 part by weight or more and 5 parts by weight or less, preferably 0.2 parts by weight or more, based on 100 parts by weight of the negative electrode composition. It may contain less than or equal to 0.4 parts by weight and less than or equal to 1 part by weight.

The cathode conductive material according to the present application has a completely separate configuration from the anode conductive material applied to the anode. In other words, in the case of the anode conductive material according to the present application, it serves to hold the contact point between silicon-based active materials whose volume expansion of the electrode is very large due to charging and discharging. The anode conductive material acts as a buffer when rolled and retains some conductivity. It has a role in providing , and its composition and role are completely different from the cathode conductive material of the present invention.

In addition, the negative electrode conductive material according to the present application is applied to a silicon-based active material and has a completely different structure from the conductive material applied to the graphite-based active material. In other words, the conductive material used in the electrode having a graphite-based active material simply has smaller particles compared to the active material, so it has the property of improving output characteristics and providing some conductivity, and is different from the anode conductive material applied together with the silicon-based active material as in the present invention. The composition and roles are completely different.

In an exemplary embodiment of the present application, the planar conductive material used as the above-described negative electrode conductive material has a different structure and role from the carbon-based active material generally used as the negative electrode active material. Specifically, the carbon-based active material used as a negative electrode active material may be artificial graphite or natural graphite, and refers to a material that is processed into a spherical or dot-shaped shape to facilitate storage and release of lithium ions.

On the other hand, the planar conductive material used as a negative electrode conductive material is a material that has a plane or plate shape and can be expressed as plate-shaped graphite. In other words, it is a material included to maintain a conductive path within the negative electrode active material layer, and refers to a material that does not play a role in storing and releasing lithium, but rather secures a conductive path in a planar shape inside the negative electrode active material layer.

That is, in this application, the use of plate-shaped graphite as a conductive material means that it is processed into a planar or plate-shaped shape and used as a material that secures a conductive path rather than storing or releasing lithium. At this time, the negative electrode active material included has high capacity characteristics for storing and releasing lithium, and plays a role in storing and releasing all lithium ions transferred from the positive electrode.

On the other hand, in the present application, the use of a carbon-based active material as an active material means that it is processed into a point-shaped or spherical shape and used as a material that plays a role in storing or releasing lithium.

That is, in one embodiment of the present application, artificial graphite or natural graphite, which is a carbon-based active material, is in the form of points and can satisfy a BET specific surface area of 0.1 m ² /g or more and 4.5 m ² /g or less. In addition, plate-shaped graphite, which is a planar conductive material, is in the form of a planar surface and may have a BET specific surface area of 5 m ² /g or more.

In an exemplary embodiment of the present application, the negative electrode binder is polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidenefluoride, polyacrylonitrile, Polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene. -Selected from the group consisting of propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, poly acrylic acid, and materials whose hydrogen is replaced with Li, Na, or Ca, etc. It may include at least one of the following, and may also include various copolymers thereof.

The negative electrode binder according to an exemplary embodiment of the present application plays a role in holding the active material and the conductive material to prevent distortion and structural deformation of the negative electrode structure in the volume expansion and relaxation of the silicon-based active material. If the above role is satisfied, the negative electrode binder serves as a general Any binder can be applied, specifically, a water-based binder can be used, and more specifically, a PAM-based binder can be used.

In an exemplary embodiment of the present application, the negative electrode binder may be 30 parts by weight or less, preferably 25 parts by weight or less, more preferably 20 parts by weight or less, and 5 or more parts by weight, 10 parts by weight, based on 100 parts by weight of the negative electrode composition. It can be more than wealth.

In one embodiment of the present application, preparing metal silicon; and pulverizing the metal silicon to form a silicon-based active material, wherein the silicon-based active material satisfies the plate shape of Equation 1 above.

In the present application, the step of preparing the metal silicon includes forming a pulverized metal silicon; Or, it provides a method for producing a negative electrode active material comprising a silane deposition-type silicon metal formation step.

That is, the metal silicon can be formed by physically pulverizing a general silicon lump (unprocessed silicon) or chemically by silane deposition, but is not limited thereto.

In an exemplary embodiment of the present application, the pulverizing metal silicon forming step provides a method of manufacturing a negative electrode active material including the step of pulverizing unprocessed silicon (silicon lump) to form the metal silicon.

The pulverizing metal silicon forming step may correspond to pulverizing unprocessed silicon (silicon lump) through physical force.

In an exemplary embodiment of the present application, the silane deposition-type metal silicon forming step includes depositing a metal silicon-based active material on a substrate by chemically reacting silane gas; and obtaining a metal silicon-based active material deposited on the substrate.

The silane deposition-type silicon metal formation step corresponds to a chemical method. That is, metal silicon can be formed by depositing a metal silicon-based active material on a substrate or wafer through a chemical reaction with silane gas, and then scraping the deposited metal silicon-based active material to obtain a metal silicon-based active material.

At this time, when forming silicon metal through silane deposition (chemical method), it is formed in bulk and is larger in size than when forming silicon metal through existing grinding methods, and accordingly, through the grinding (milling) process described later. It can be manufactured to satisfy the plate shape of Equation 1.

According to one example, the silane gas may include one or more gases selected from monosilane, dichlorosilane, and trichlorosilane, and may specifically be trichlorosilane gas.

In an exemplary embodiment of the present application, the step of depositing a metal silicon-based active material on a substrate by chemically reacting the silane gas may be performed under pressure conditions of 10 Pa to 150 Pa. Due to this low pressure, the silicon growth rate is reduced, which can lead to the formation of small crystal grains. The step may be performed at a temperature of 100°C or higher, specifically 500°C or higher, preferably 800°C or higher, more preferably 800°C to 1300°C, 800°C to 2200°C. This is a lower temperature than the existing gas atomizing method, which heats above 1600°C to melt Si.

In an exemplary embodiment of the present application, the metal silicon-based active material may further include a step of growing through crystal nucleation, and the step of growing the metal silicon-based active material through crystal nucleation is 800° C. or higher, preferably 800° C. It can be performed under temperature conditions of ℃ to 1300℃. This is a lower temperature than the existing gas atomizing method, which heats above 1600°C to melt Si. Additionally, the step of growing the silicon-based active material through crystal nucleation may be performed under a pressure of 100 Pa to 150 Pa. Due to this low pressure, the silicon growth rate is reduced, which can lead to the formation of small grains and a specific surface area.

In an exemplary embodiment of the present application, the method further includes depositing a metal silicon-based active material on a substrate by chemically reacting silane gas; thereafter, growing the metal silicon-based active material through crystal nucleation, wherein the metal silicon-based active material It provides a method of producing a negative electrode active material, wherein the step of growing through crystal nucleation includes generating crystal nuclei at a temperature of 800° C. or higher for 1 hour to 24 hours.

That is, a metal silicon-based active material can be formed by the above-described method, and then the silicon-based active material can be manufactured through the step of pulverizing the metal silicon to form a silicon-based active material.

In an exemplary embodiment of the present application, the step of forming a silicon-based active material by pulverizing the metal silicon includes milling for 12 hours or more and 48 hours or less under a pulverizing pressure condition of 3 bar or more and 10 bar or less. Manufacture of a negative electrode active material. Provides a method.

In an exemplary embodiment of the present application, the step of pulverizing the metal silicon to form a silicon-based active material is performed under pulverizing pressure conditions of 3 bar or more and 10 bar or less, preferably 3.5 bar or more and 9 bar or less, more preferably 4 bar or more. A range of 8 bar or less can be satisfied.

In an exemplary embodiment of the present application, the step of pulverizing the metal silicon to form a silicon-based active material may include milling under the pulverizing pressure conditions for 12 hours or more and 48 hours or less, and specifically, 12 hours or more and 30 hours. Hereinafter, more specifically, 12 hours or more and 24 hours or less may be satisfied.

By changing the pressure, time, and process conditions as described above, a silicon-based active material that satisfies the range of Equation 1 described above can be formed. That is, in the process of crushing metal silicon using physical force to generate particle breakage, the difference in particle shape was controlled by adjusting the crushing pressure and time, and thus the above conditions that satisfied the range of Equation 1 were found.

In an exemplary embodiment of the present application, the milling step may include any process that can cause particle breakage through physical force, and specifically, a jet mill, disk mill, or ball mill. It may include processes such as (ball mill).

In an exemplary embodiment of the present application, a negative electrode current collector layer; and a negative electrode active material layer comprising the negative electrode composition or a cured product thereof according to the present application formed on one or both sides of the negative electrode current collector layer.

Figure 1 is a diagram showing a stacked structure of a negative electrode for a lithium secondary battery according to an exemplary embodiment of the present application. Specifically, it can be seen that the negative electrode 100 for a lithium secondary battery includes a negative electrode active material layer 20 on one side of the negative electrode current collector layer 10, and Figure 1 shows that the negative electrode active material layer is formed on one side, but the negative electrode collector layer 10 has a negative electrode active material layer 20 on one side. It can be included on both sides of the entire floor.

In an exemplary embodiment of the present application, the negative electrode for a lithium secondary battery may be formed by applying and drying a negative electrode slurry containing the negative electrode composition on one or both sides of a negative electrode current collector layer.

At this time, the cathode slurry includes the cathode composition described above; and a slurry solvent.

In an exemplary embodiment of the present application, the solid content of the anode slurry may satisfy 5% or more and 40% or less.

In another embodiment, the solid content of the anode slurry may be within the range of 5% to 40%, preferably 7% to 35%, and more preferably 10% to 30%.

The solid content of the negative electrode slurry may mean the content of the negative electrode composition contained in the negative electrode slurry, and may mean the content of the negative electrode composition based on 100 parts by weight of the negative electrode slurry.

When the solid content of the negative electrode slurry satisfies the above range, the viscosity is appropriate when forming the negative electrode active material layer, thereby minimizing particle agglomeration of the negative electrode composition, thereby enabling efficient formation of the negative electrode active material layer.

In an exemplary embodiment of the present application, the slurry solvent can be used without limitation as long as it can dissolve the negative electrode composition, and specifically, water or NMP can be used.

In an exemplary embodiment of the present application, the negative electrode current collector layer generally has a thickness of 1 μm to 100 μm. This negative electrode current collector layer is not particularly limited as long as it has high conductivity without causing chemical changes in the battery, for example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, copper or stainless steel. Surface treatment of carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc. can be used. In addition, the bonding power of the negative electrode active material can be strengthened by forming fine irregularities on the surface, and it can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven fabrics.

In one embodiment of the present application, a negative electrode for a lithium secondary battery is provided, wherein the negative electrode current collector layer has a thickness of 1 μm or more and 100 μm or less, and the negative electrode active material layer has a thickness of 20 μm or more and 500 μm or less.

However, the thickness may vary depending on the type and purpose of the cathode used and is not limited to this.

In an exemplary embodiment of the present application, the porosity of the negative electrode active material layer may satisfy a range of 10% to 60%.

In another embodiment, the porosity of the negative electrode active material layer may be within the range of 10% to 60%, preferably 20% to 50%, and more preferably 30% to 45%.

The porosity includes the silicon-based active material included in the negative electrode active material layer; conductive material; and varies depending on the composition and content of the binder, especially the silicon-based active material according to the present application; and a conductive material of a specific composition and content satisfies the above range, and thus the electrode is characterized by having an appropriate range of electrical conductivity and resistance.

In an exemplary embodiment of the present application, an anode; A negative electrode for a lithium secondary battery according to the present application; A separator provided between the anode and the cathode; It provides a lithium secondary battery including; and an electrolyte.

Figure 2 is a diagram showing a stacked structure of a lithium secondary battery according to an exemplary embodiment of the present application. Specifically, a negative electrode 100 for a lithium secondary battery including a negative electrode active material layer 20 can be confirmed on one side of the negative electrode current collector layer 10, and a positive electrode active material layer 40 on one side of the positive electrode current collector layer 50. A positive electrode 200 for a lithium secondary battery can be confirmed, indicating that the negative electrode 100 for a lithium secondary battery and the positive electrode 200 for a lithium secondary battery are formed in a stacked structure with a separator 30 in between.

The secondary battery according to an exemplary embodiment of the present specification may particularly include the above-described negative electrode for a lithium secondary battery. Specifically, the secondary battery may include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, and the negative electrode is the same as the negative electrode described above. Since the cathode has been described above, detailed description will be omitted.

The positive electrode is formed on the positive electrode current collector and the positive electrode current collector, and may include a positive electrode active material layer containing the positive electrode active material.

In the positive electrode, the positive electrode current collector is not particularly limited as long as it is conductive without causing chemical changes in the battery, for example, stainless steel, aluminum, nickel, titanium, fired carbon, or carbon on the surface of aluminum or stainless steel. , surface treated with nickel, titanium, silver, etc. can be used. In addition, the positive electrode current collector may typically have a thickness of 3 to 500㎛, and fine irregularities may be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, it can be used in various forms such as films, sheets, foils, nets, porous materials, foams, and non-woven materials.

The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material is a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium iron oxide such as LiFe ₃ O ₄ ; Lithium manganese oxide with the formula Li _1+c1 Mn _2-c1 O ₄ (0≤c1≤0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ , etc.; lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , V ₂ O ₅ , and Cu ₂ V ₂ O ₇ ; Chemical formula LiNi _1-c2 M _c2 O ₂ (where M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B and Ga, and satisfies 0.01≤c2≤0.3). Ni site-type lithium nickel oxide; Chemical formula LiMn _2-c3 M _c3 O ₂ (where M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn and Ta, and satisfies 0.01≤c3≤0.1) or Li ₂ Mn ₃ MO lithium manganese composite oxide represented by ₈ (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu and Zn); Examples include LiMn ₂ O ₄ in which part of Li in the chemical formula is replaced with an alkaline earth metal ion, but it is not limited to these. The anode may be Li-metal.

The positive electrode active material layer may include the positive electrode active material described above, a positive conductive material, and a positive electrode binder.

At this time, the anode conductive material is used to provide conductivity to the electrode, and can be used without particular restrictions in the battery being constructed as long as it does not cause chemical change and has electronic conductivity. Specific examples include graphite such as natural graphite and artificial graphite; Carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; Metal powders or metal fibers such as copper, nickel, aluminum, and silver; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Alternatively, conductive polymers such as polyphenylene derivatives may be used, and one of these may be used alone or a mixture of two or more may be used.

Additionally, the positive electrode binder serves to improve adhesion between positive electrode active material particles and adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, and carboxymethyl cellulose (CMC). ), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber. (SBR), fluororubber, or various copolymers thereof, and one type of these may be used alone or a mixture of two or more types may be used.

The separator separates the cathode from the anode and provides a passage for lithium ions. It can be used without particular restrictions as long as it is normally used as a separator in secondary batteries. In particular, it has low resistance to ion movement in the electrolyte and has an electrolyte moisture capacity. Excellent is desirable. Specifically, porous polymer films, for example, porous polymer films made of polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, and ethylene/methacrylate copolymer, or these. A laminated structure of two or more layers may be used. In addition, conventional porous non-woven fabrics, for example, non-woven fabrics made of high melting point glass fibers, polyethylene terephthalate fibers, etc., may be used. In addition, a coated separator containing ceramic components or polymer materials may be used to ensure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.

The electrolytes include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butylo lactone, and 1,2-dimethyl. Toxy ethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxoran, formamide, dimethylformamide, dioxoran, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid. Triesters, trimethoxy methane, dioxoran derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl pyropionate, propionic acid. Aprotic organic solvents such as ethyl may be used.

In particular, among the carbonate-based organic solvents, ethylene carbonate and propylene carbonate, which are cyclic carbonates, are high-viscosity organic solvents and have a high dielectric constant, so they can be preferably used because they easily dissociate lithium salts. These cyclic carbonates include dimethyl carbonate and diethyl carbonate. If linear carbonates of the same low viscosity and low dielectric constant are mixed and used in an appropriate ratio, an electrolyte with high electrical conductivity can be made and can be used more preferably.

The metal salt may be a lithium salt, and the lithium salt is a material that is easily soluble in the non-aqueous electrolyte. For example, anions of the lithium salt include F ^- , Cl ^- , I ^- , NO ₃ ^- , N(CN ) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , PF ₆ ^- , (CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , CF ₃ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- , CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- At least one selected from the group consisting of can be used.

In addition to the electrolyte components, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, and trifluoroethylene for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. Ethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexanoic acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N, N-substituted imida. One or more additives such as zolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, or aluminum trichloride may be further included.

One embodiment of the present invention provides a battery module including the secondary battery as a unit cell and a battery pack including the same. Since the battery module and battery pack include the secondary battery with high capacity, high rate characteristics, and cycle characteristics, they are medium-to-large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems. It can be used as a power source.

Hereinafter, preferred embodiments are presented to aid understanding of the present invention. However, the above examples are merely illustrative of the present description, and it is clear to those skilled in the art that various changes and modifications are possible within the scope and technical spirit of the present description, It is natural that such variations and modifications fall within the scope of the attached patent claims.

<Manufacturing example>

<Manufacture of first metal silicon-based active material>

After the silicon lump was gasified with silane, a metal silicon-based active material was formed through chemical reaction and deposition on a substrate. At this time, the crystal nucleus growth time was 1 h to 30 h, and accordingly, the crystal grain size was 58.4 nm and the particle size (D50) was 5.94 μm.

<Manufacture of second metal silicon-based active material>

Unprocessed silicon (silicon chunks) was pulverized using physical force to produce an unprocessed silicon-based active material.

<Manufacture of silicone-based composite of Comparative Example 2>

Particles (A1) containing Si with an average particle diameter dAV of the primary particles of 5 nm to 95 nm, particles (A2) consisting of a material containing graphite, and carbonaceous material (A3) formed on the surface of the particles (A1). A silicon-based composite containing a composite (A) was prepared.

The metal silicon-based active material or the silicon-based composite of Comparative Example 2 was prepared in the same manner as above, and then the silicon-based active material was prepared by changing the grinding pressure and grinding time in Table 1 below.

Grinding method crushing pressure grinding time plate shape
(Equation 1) I(220)/I(110) x100
(Equation 2) Comparative Example 1 Jet mill 2bar 12h 44.4 36.42 Comparative Example 2 Jet mill 2bar 12h 42.3 31.03 Example 1 Jet mill 4bar 12h 47.1 37.67 Example 2 Jet mill 4bar 15h 48.1 38.42 Example 3 Jet mill 4bar 24h 48 38.87 Example 4 Jet mill 5bar 12h 50.5 39 Example 5 Jet mill 5bar 15h 52.4 41.81 Example 6 Jet mill 5bar 24h 53.3 40.15 Example 7 Jet mill 6bar 12h 56.6 39.52 Example 8 Jet mill 6bar 15h 61.8 39.54 Example 9 Jet mill 6bar 24h 65.4 43.08 Example 10 Jet mill 10bar 12h 74.9 43.32 Example 11 Jet mill 10bar 15h 81.4 44.27 Example 12 Jet mill 10bar 24h 87.7 45.00 Example 13 Jet mill 10bar 48h 93.7 40.24

<Manufacture of cathode>

A negative electrode slurry was prepared by adding the negative electrode active material containing the silicon-based active material, the first conductive material, the second conductive material, and polyacrylamide as a binder to distilled water as a solvent for forming the negative electrode slurry at a weight ratio of 80:9.6:0.4:10. (solid concentration 25% by weight).

Specifically, the first conductive material was plate-shaped graphite (specific surface area: 17 m ² /g, average particle diameter (D50): 3.5 μm), and the second conductive material was SWCNT.

As a specific mixing method, the first conductive material, the second conductive material, the binder, and water were dispersed at 2500 rpm for 30 min using a homomixer, then the silicon-based active material was added and dispersed at 2500 rpm for 30 min to produce a negative electrode slurry. did.

As a negative electrode current collector layer, the negative electrode slurry was coated at a loading amount of 85 mg/25 cm ² on both sides of a copper current collector (thickness: 8㎛), rolled, and dried in a vacuum oven at 130°C for 10 hours. A negative electrode active material layer (thickness: 33 μm) was formed and used as a negative electrode (negative electrode thickness: 41 μm, negative electrode porosity 40.0%).

<Manufacture of secondary batteries>

LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (average particle diameter (D50): 15㎛) as the positive electrode active material, carbon black (product name: Super C65, manufacturer: Timcal) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder. A positive electrode slurry was prepared by adding N-methyl-2-pyrrolidone (NMP) as a solvent for forming positive electrode slurry at a weight ratio of :1.5:1.5 (solid concentration: 78% by weight).

As a positive electrode current collector, the positive electrode slurry was coated at a loading amount of 537 mg/25 cm ² on both sides of an aluminum current collector (thickness: 12㎛), rolled, and dried in a vacuum oven at 130°C for 10 hours to form a positive electrode. An active material layer (thickness: 65㎛) was formed to prepare a positive electrode (anode thickness: 77㎛, porosity 26%).

A lithium secondary battery was manufactured by interposing a polyethylene separator between the positive electrode and the negative electrode of the examples and comparative examples and injecting electrolyte.

The electrolyte is made by adding 3% by weight of vinylene carbonate based on the total weight of the electrolyte to an organic solvent mixed with fluoroethylene carbonate (FEC) and diethyl carbonate (DMC) at a volume ratio of 10:90, and LiPF as a lithium salt. ₆ was added at a concentration of 1M.

Experimental Example 1: Monocell lifespan evaluation

The lifespan of the secondary battery containing the negative electrode manufactured in the above Examples and Comparative Examples was evaluated using an electrochemical charger and discharger, and the capacity maintenance rate was evaluated. In-situ cycle testing was conducted on the secondary battery at 4.2-3.0V 1C/0.5C, and the capacity maintenance rate was maintained by charging/discharging (4.2-3.0V) at 0.33C/0.33C every 50 cycles during the test. Measurements were made and the results are listed in Table 2.

Life maintenance rate (%) = {(discharge capacity in Nth cycle)/(discharge capacity in first cycle)} Х 100

life maintenance rate
(after 200cycle) Comparative Example 1 81 Comparative Example 2 78.7 Example 1 81.3 Example 2 82.1 Example 3 83.4 Example 4 82.7 Example 5 85.4 Example 6 83 Example 7 83 Example 8 84 Example 9 85.4 Example 10 85.6 Example 11 86 Example 12 86.7 Example 13 81.7

Experimental Example 2: @SOC50 2.5C discharge resistance increase rate (after 200cycle) evaluation

In the test in Experimental Example 1, the capacity maintenance rate was measured by charging/discharging (4.2-3.0V) at 0.33C/0.33C every 50 cycles, and then the resistance increase rate was measured by discharging at 2.5C pulse at SOC50. A comparative analysis was conducted.

For the evaluation of the resistance increase rate, data from 200 cycles were calculated, and the results are shown in Table 3 below.

2.5C discharge resistance increase rate
(1C/0.5C, after 200cycle) Comparative Example 1 40 Comparative Example 2 51 Example 1 38 Example 2 37 Example 3 36 Example 4 37 Example 5 32 Example 6 34 Example 7 34 Example 8 33 Example 9 32 Example 10 31 Example 11 27 Example 12 23 Example 13 39

As can be seen in Tables 2 and 3 above, in the case of Examples 1 to 9 in which the plate shape according to the present application was adjusted, it was confirmed that the life evaluation and resistance increase rate were superior to Comparative Example 1.

This is to control the plate shape that satisfies the range of Equation 1 above. That is, when a relatively large proportion of 111 crystal planes is formed as before, the 111 crystal plane has lower lithium mobility compared to the 220 crystal plane, leading to insertion and desorption of lithium. During the reaction, lithium cannot enter and exit evenly. However, the silicon-based active material according to the present application contains a larger proportion of 220 crystal planes than before, allowing lithium to enter and exit uniformly during the insertion/desorption reaction of lithium, thereby mitigating the phenomenon of silicon cracking on the electrode surface. It was confirmed that it had features that strengthened its lifespan characteristics.

In the case of Comparative Example 2, the range of Equations 1 and 2 was not satisfied due to an increase in the ratio of 111 due to sintering of the silicon formed internally by high temperature heating (over 1500°C) for graphitization of Si/C, and accordingly, the lifespan It was confirmed that the performance was deteriorated and the resistance increase rate was evaluated as high.

For reference, it can be seen that the plate shape (Equation 1) increases from Example 1 to Example 13. Generally, in this case, it can be seen that the lifespan performance tends to increase as the sizes of the major and minor axes become similar. However, in Example 13, the sizes of the major and minor axes were most similar, but as too strong a force was applied for this, the target level of D50 was not satisfied, and the lifespan was confirmed to be lower than that of other examples.

10: Negative current collector layer
20: Negative active material layer
30: Separator
40: positive electrode active material layer
50: Anode current collector layer
100: Negative electrode for lithium secondary battery
200: Anode for lithium secondary battery

Claims (15)

A negative electrode active material containing a silicon-based active material that satisfies the plate shape of Equation 1 below,
The silicon-based active material includes one or more selected from the group consisting of SiOx (x=0) and SiOx (0<x<2), and the SiOx (x=0) is contained in an amount of 70 parts by weight or more based on 100 parts by weight of the silicon-based active material. A negative electrode active material comprising:
[Equation 1]
45 ≤ (A/B) x 100
In equation 1 above,
A refers to the length of the short axis of the silicon-based active material,
B refers to the length of the long axis of the silicon-based active material. In claim 1,
The silicon-based active material includes 220 crystal planes and 111 crystal planes,
The silicon-based active material is a negative electrode active material that satisfies the following equation 2:
[Equation 2]
37 ≤ (X/Y) x 100
In equation 2 above,
Y refers to the ratio of 111 crystal planes in the silicon-based active material,
X refers to the ratio of 220 crystal planes in the silicon-based active material. In claim 1,
A negative electrode active material wherein the silicon-based active material has a D50 particle size of 3 μm or more and 10 μm or less. In claim 1,
A negative electrode active material wherein the crystal grain size of the silicon-based active material is 500 nm or less. In claim 1,
A negative electrode active material containing 80 parts by weight or more and 100 parts by weight or less of a silicon-based active material that satisfies the plate shape of Equation 1, based on 100 parts by weight of the negative electrode active material. Preparing metal silicon; and
Forming a silicon-based active material by pulverizing the metal silicon;
A method for producing a negative electrode active material comprising,
The silicon-based active material satisfies the plate shape of Equation 1 below:
[Equation 1]
45 ≤ (A/B) x 100
In equation 1 above,
A refers to the length of the short axis of the silicon-based active material,
B refers to the length of the long axis of the silicon-based active material. In claim 6,
The step of preparing the metal silicon includes forming a pulverized metal silicon; Or a silane deposition method of forming silicon metal. In claim 7,
The pulverizing metal silicon forming step includes forming the metal silicon by pulverizing unprocessed silicon. In claim 7,
The silane deposition-based metal silicon forming step includes depositing a metal silicon-based active material on a substrate by chemically reacting silane gas; and
Obtaining a metal silicon-based active material deposited on the substrate;
A method for producing a negative electrode active material comprising. In claim 6,
The step of forming a silicon-based active material by grinding the metal silicon includes milling for 12 hours or more and 48 hours or less under a grinding pressure condition of 3 bar or more and 10 bar or less. A negative electrode active material according to any one of claims 1 to 5; cathode conductive material; and a cathode binder. In claim 11,
The negative electrode active material is 60 parts by weight or more based on 100 parts by weight of the negative electrode composition. Negative current collector layer; and a negative electrode active material layer provided on one or both sides of the negative electrode current collector layer,
A negative electrode for a lithium secondary battery, wherein the negative electrode active material layer includes the negative electrode composition according to claim 11 or a cured product thereof. In claim 13,
The thickness of the negative electrode current collector layer is 1 μm or more and 100 μm or less,
A negative electrode for a lithium secondary battery, wherein the thickness of the negative electrode active material layer is 20 μm or more and 500 μm or less. anode;
A negative electrode for a lithium secondary battery according to claim 13;
A separator provided between the anode and the cathode; and
A lithium secondary battery containing an electrolyte.