KR102405902B1 - Negavive electrode for lithium secondary battery, and lithium secondary battery comprising the same - Google Patents

Abstract

A negative electrode for a lithium secondary battery, and a lithium secondary battery comprising the same, comprising a silicon (Si)-based negative active material, a first carbon-based negative active material, and a second carbon-based negative active material having a lower hardness than the first carbon-based negative active material and a mixed negative active material comprising a, wherein the silicon-based negative active material is included in an amount of 45% by weight or less based on 100% by weight of the total amount of the mixed negative active material, and the weight ratio of the first carbon-based negative active material to the second carbon-based negative active material is 2: It is possible to provide an anode for a lithium secondary battery of 8 to 8:2, and a lithium secondary battery including the same.

Description

Anode for a lithium secondary battery, and a lithium secondary battery comprising the same

The present invention relates to a lithium secondary battery, and more particularly, to a negative electrode for a lithium secondary battery.

Recently, as the demand for electronic devices such as mobile devices increases, technology development for mobile devices is expanding. Demand for lithium secondary batteries, such as lithium batteries, lithium ion batteries, and lithium ion polymer batteries, as a driving power source for these electronic devices is greatly increasing. In addition, the growth of the electric vehicle market is accelerating as regulations on automobile fuel efficiency and exhaust gas are tightening around the world. Demand for batteries is expected to surge.

On the other hand, a carbon-based negative electrode material having excellent cycle characteristics and a theoretical capacity of 372 mAh/g was generally used as a negative electrode material for a secondary battery. However, as the high capacity of secondary batteries such as medium and large-sized secondary batteries is gradually required, silicon (Si), germanium (Ge), tin (Sn) or antimony having a capacity of 500 mAh/g or more that can replace the theoretical capacity of carbon-based anode materials Inorganic negative electrode materials such as (Sb) are attracting attention. Among these inorganic anode materials, the silicon-based anode material exhibits a very large amount of lithium bonding. However, silicon-based negative electrode material may cause pulverization by causing a large volume change during insertion/desorption of lithium, ie, charging and discharging of the battery. As a result, a phenomenon in which the pulverized particles are agglomerated may occur, and the anode active material may be electrically detached from the current collector, which may lead to a loss of reversible capacity under a long cycle. For this reason, the silicon-based negative electrode material and the secondary battery including the same have disadvantages of showing low cycle life characteristics and capacity retention despite the advantages of high charge capacity, which is a barrier to practical use.

In addition, in general, the negative electrode is prepared by mixing a negative electrode active material such as silicon, a conductive material, and a binder to prepare a negative electrode active material slurry, then applying the slurry to an electrode current collector such as copper foil, and drying, When the slurry is applied, the active material powder is pressed onto the current collector, and a pressing process is performed to uniform the thickness of the electrode.

At this time, as the active material powder is pressed during the rolling process, the space between the active materials is reduced, and penetration of the electrolyte becomes difficult, so that a lot of resistance is applied during charging and discharging.

This phenomenon is exacerbated when the electrode thickness is increased to achieve high capacity and high energy density, and as it becomes difficult to impregnate the electrolyte into the inside of the electrode, it is difficult to secure an ion movement path, which prevents smooth ion movement. the lifespan characteristics of

Accordingly, it is necessary to develop a technology capable of inhibiting the expansion of the silicon-based negative active material to improve adhesion to the electrode, and preventing the silicon-based negative active material from being crushed during manufacturing of the negative electrode, thereby preventing an increase in resistance during charging and discharging of the battery.

In one aspect of the present invention, it is possible to suppress the expansion of the silicon-based negative active material during charging and discharging of the lithium secondary battery, the adhesion between the negative electrode active material and the current collector can be improved, and even when a negative electrode of high capacity and high energy density is manufactured, the battery An object of the present invention is to provide a negative electrode for a lithium secondary battery in which the increase in resistance due to charging and discharging of the battery is suppressed and the lifespan characteristics of the battery can be improved.

One aspect of the present invention is to provide a lithium secondary battery including the negative electrode for a lithium secondary battery.

An aspect of the present invention includes a mixed negative active material comprising a silicon (Si)-based negative active material, a first carbon-based negative active material, and a second carbon-based negative active material having a lower hardness than the first carbon-based negative active material, The silicon-based negative active material is included in an amount of 45% by weight or less based on 100% by weight of the total amount of the mixed negative active material, and the weight ratio of the first carbon-based negative active material to the second carbon-based negative active material is 2:8 to 8:2, An anode for a lithium secondary battery is provided.

The first carbon-based negative active material may satisfy Equation 1 below, and the second carbon-based negative active material may satisfy Equation 2 below.

[Equation 1]

ΔH _A /H _A ≤ 0.1

[Equation 2]

ΔH _B /H _B ≥ 0.3

(In Equation 1, HA is the average particle size of the first carbon-based negative active material, _ΔHA is the average particle size change of the first carbon-based negative active material when a pressure of 30 MPa is applied for 5 seconds, and in Equation ₂ , H _B is the average particle diameter of the second carbon-based negative active material, and _ΔHB is the average particle diameter change of the second negative active material when a pressure of 30 MPa is applied for 5 seconds.)

The silicon-based negative active material may be Si, SiO _x (0<x<2), or SiC.

The first carbon-based negative active material may be artificial graphite, and the second carbon-based negative active material may be natural graphite.

The weight ratio of the first carbon-based negative active material to the second carbon-based negative active material may be 4:6 to 6:4.

One aspect of the present invention provides a lithium secondary battery including the negative electrode for a lithium secondary battery of the one aspect of the present invention.

In the negative electrode for a lithium secondary battery of an aspect of the present invention, the expansion of the silicon-based negative active material can be suppressed during charging and discharging of the lithium secondary battery, and the crushing of the silicon-based negative electrode active material due to rolling during the manufacturing of the negative electrode is minimized to reduce the permeability of the electrolyte it can be prevented Accordingly, the lifespan characteristics of the lithium secondary battery may be improved.

In addition, in addition to suppression of expansion of the silicon-based anode active material, additional adhesion is provided between the anode active material and the anode current collector, so that the adhesion between the anode active material and the anode current collector is greatly improved, thereby improving the lifespan characteristics of the lithium secondary battery.

In addition, it is possible to prevent an increase in resistance during charging and discharging of the battery even when a negative electrode having a high capacity and high energy density is manufactured. Accordingly, it is possible to manufacture a high-capacity and high-energy-density battery having excellent lifespan characteristics.

Unless otherwise defined, all terms (including technical and scientific terms) used in this specification may be used with meanings commonly understood by those of ordinary skill in the art to which the present invention belongs. In the entire specification, when a part "includes" a certain component, this means that other components may be further included, rather than excluding other components, unless otherwise stated. The singular also includes the plural, unless the phrase specifically states otherwise.

An aspect of the present invention includes a mixed negative active material comprising a silicon (Si)-based negative active material, a first carbon-based negative active material, and a second carbon-based negative active material having a lower hardness than the first carbon-based negative active material, The silicon-based negative active material is included in an amount of 45% by weight or less based on 100% by weight of the total amount of the mixed negative active material, and the weight ratio of the first carbon-based negative active material to the second carbon-based negative active material is 2:8 to 8:2, An anode for a lithium secondary battery is provided.

The negative electrode for a lithium secondary battery of one embodiment of the present invention includes two types of carbon-based negative active materials having different hardness together with a silicon-based negative active material.

In the negative active material, a silicon-based negative active material and a second carbon-based negative active material having a relatively small hardness are positioned in the gap between the first carbon-based negative active material having a relatively high hardness, and the silicon-based negative active material, the first carbon-based negative active material , and the second carbon-based negative active material may be in a form in which a void exists.

The carbon-based negative active material having a relatively high hardness serves as a support in the rolling process during the manufacturing of the negative electrode, thereby preventing the silicon-based negative active material from being excessively crushed. Accordingly, the negative electrode active material of the present invention may have the above-described form, and the size of the pores between particles of the silicon-based negative active material and the carbon-based negative active material may be excessively small, thereby preventing a decrease in the permeability of the electrolyte.

The carbon-based negative active material having a relatively small hardness may play a role in physically inhibiting expansion of the silicon-based negative active material due to charging and discharging of a lithium secondary battery and improving adhesion between the negative electrode active material and the current collector.

The negative electrode for a lithium secondary battery of an aspect of the present invention includes two types of carbon-based negative active materials having different hardnesses, so that the adhesion between the negative electrode active material and the current collector is improved, and the negative electrode according to charging and discharging by suppressing the volume expansion of the silicon-based negative active material can suppress the volume expansion of the anode, and the silicon-based anode active material is crushed in the rolling process during the manufacture of the anode, thereby reducing the permeability of the electrolyte and increasing the resistance of the battery, and the lifespan characteristics of the battery can be improved.

This is an effect that cannot be realized when a silicon-based negative active material and one type of carbon-based negative active material are mixed as in the examples to be described later. Density of the negative electrode can be made possible.

Accordingly, applicability to industries requiring large-capacity batteries, such as electric vehicles and energy storage systems, may be greatly increased.

In the negative electrode for a lithium secondary battery of one embodiment of the present invention, the weight ratio of the first and second carbon-based negative active materials having different hardnesses may need to be appropriately adjusted. Specifically, the weight ratio of the first carbon-based negative active material to the second carbon-based negative active material (first carbon-based negative active material: second carbon-based negative active material) may be 2:8 to 8:2.

In the above range, the adhesive strength between the negative electrode active material and the current collector is improved, the volume expansion of the silicon-based negative active material is suppressed, the volume expansion of the negative electrode is suppressed due to charging and discharging of the battery, and the silicon-based negative active material is crushed in the rolling process during the manufacturing of the negative electrode, so that the permeability of the electrolyte is reduced and the battery The effect of alleviating the problem of increasing the resistance of the battery and improving the lifespan characteristics of the battery can be realized.

Specifically, when the content of the second anode active material with low hardness is too large, the crushing phenomenon of the silicon-based anode active material in the rolling process during the manufacturing of the anode is not sufficiently suppressed, so that the electrolyte impregnation property is lowered, and as the battery resistance increases, the battery Lifespan characteristics may be deteriorated.

When the content of the first anode active material having a high hardness is too large, it is difficult to sufficiently suppress the volume expansion of the silicon-based anode active material, and the resistance of the battery may be increased, and thus the lifespan characteristics of the battery may be deteriorated.

The weight ratio of the first carbon-based negative active material to the second carbon-based negative active material may be more specifically 4:6 to 6:4, and in this range, the above-described effect may be further maximized.

In the negative electrode for a lithium secondary battery of one aspect of the present invention, the silicon-based negative active material may be included in an amount of 45% by weight or less based on 100% by weight of the total amount of the negative active material.

When the content of the silicon-based negative active material is too large, the volume expansion according to charging and discharging may increase, the adhesion between the negative active material and the electrode may decrease, the battery resistance may increase during charging and discharging, and the lifespan characteristics of the battery may be reduced.

The lower limit of the content of the silicon-based negative active material is not particularly limited, but may be greater than 0% by weight or 5% by weight or more. More specifically, 10% by weight or more may be good to realize high capacity characteristics of the silicon-based negative active material, but is not limited thereto.

For example, in the negative electrode for a lithium secondary battery of an aspect of the present invention, the carbon-based negative active material is 55 weight as the total amount of the silicon-based negative active material 10% by weight or more and 45% by weight or less, and the first carbon-based negative active material and the second carbon-based negative active material % or more and 90% by weight or less. However, the present invention is not limited thereto. A weight ratio of the first carbon-based negative active material to the second carbon-based negative active material may be the same as described above.

In the negative electrode for a lithium secondary battery of an aspect of the present invention, the first carbon-based negative active material may satisfy Equation 1 below, and the second carbon-based negative active material may satisfy Equation 2 below.

[Equation 1]

ΔH _A /H _A ≤ 0.1

[Equation 2]

ΔH _B /H _B ≥ 0.3

This is related to the hardness of the first and second carbon-based negative active materials, and the smaller the value of the formula, the greater the hardness.

In Equation 1, HA is the average particle size of the first carbon-based negative active material, _ΔHA is the average particle size change of the first carbon-based negative active material when a pressure of 30 MPa is applied for 5 seconds, and in Equation _{2, H B is} It is the average particle diameter of the second carbon-based negative active material, and _ΔHB is the average particle diameter change of the second negative electrode active material when a pressure of 30 MPa is applied for 5 seconds.

Throughout this specification, unless otherwise specified, the average particle diameter means a value measured as a volume average value D50 (ie, particle diameter when the cumulative volume becomes 50%) in particle size distribution measurement by laser light diffraction method. can do.

More specifically, the average particle size change of the first carbon-based negative active material ( _ΔHA ) and the average particle size change of the second carbon-based negative active material (ΔH _b ) are a plurality of sample particles using a tip or the like. One may be averaged by applying a pressure of 30 MPa for 5 seconds, and the plurality may be five or more sample grains.

The lower limit of Equation 1 is not particularly limited, but may be 0.03 or more.

The upper limit of Equation 2 is not particularly limited, but may be 0.8 or less, and more specifically, 0.6 or less.

The silicon-based negative active material may be Si, SiO _x (0<x<2), or SiC, but the present invention is not limited thereto.

The first carbon-based negative active material may be artificial graphite, and the second carbon-based negative active material may be natural graphite, but the present invention is not limited thereto.

In the negative electrode for a lithium secondary battery of one embodiment of the present invention, the average particle diameter of the first carbon-based negative active material and the second carbon-based negative active material is not particularly limited, but 500 nm or more and 100 μm or less, specifically 1 μm or more and 40 μm Hereinafter, more specifically, it may be 5 μm or more and 20 μm or less.

The average particle diameter of the silicon-based negative electrode active material in the negative electrode for a lithium secondary battery of one embodiment of the present invention is not particularly limited, but 500 nm or more and 100 μm or less, specifically 1 μm or more and 50 μm or less, more specifically 10 μm or more and 40 μm may be below.

The negative electrode for a lithium secondary battery of one embodiment of the present invention may include a current collector and a negative active material layer formed on the current collector, and the negative active material layer may include the negative active material of the above-described embodiment of the present invention. Since the description of the negative active material is the same as described above, it will be omitted.

The anode active material layer may also include an anode binder, and may optionally further include a conductive material.

Hereinafter, the current collector, the negative electrode binder, and the conductive material will be described in more detail. However, the present invention is not limited thereto.

The negative electrode binder serves to well adhere the negative active material particles to each other and also to adhere the negative active material to the current collector. As the binder, a water-insoluble binder, a water-soluble binder, or a combination thereof may be used.

Examples of the water-insoluble binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, and polyvinylidene fluoride. , polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

Examples of the water-soluble binder include styrene-butadiene rubber, acrylated styrene-butadiene rubber, polyvinyl alcohol, sodium polyacrylate, propylene and an olefin copolymer having 2 to 8 carbon atoms, (meth)acrylic acid and (meth)acrylic acid alkyl ester. copolymers, or combinations thereof.

When a water-soluble binder is used as the negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included. As the cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropylmethyl cellulose, methyl cellulose, or alkali metal salts thereof may be mixed and used. As the alkali metal, Na, K or Li may be used.

The conductive material is used to impart conductivity to the electrode, and in the battery configured, any electronic conductive material can be used as long as it does not cause chemical change, for example, natural graphite, artificial graphite, carbon black, acetylene black, ketjen carbon-based materials such as black and carbon fiber; Metal-based substances, such as metal powders, such as copper, nickel, aluminum, and silver, or metal fibers; conductive polymers such as polyphenylene derivatives; Alternatively, a conductive material including a mixture thereof may be used.

In addition, as the current collector, one selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with conductive metal, and combinations thereof may be used. can

One aspect of the present invention provides a lithium secondary battery including the negative electrode for a lithium secondary battery of the one aspect of the present invention described above.

As the lithium secondary battery of an aspect of the present invention includes the anode active material of the aspect of the present invention described above, adhesion between the anode active material and the current collector is improved, and volume expansion of the anode can be suppressed, When discharging, the resistance of the battery is small, and it may have a high capacity and a high energy density.

The lithium secondary battery of one embodiment of the present invention may include a positive electrode, a separator, and an electrolyte, and these components will be described in detail below. However, the present invention is not limited thereto.

The positive electrode may include a current collector and a positive active material layer disposed on the current collector. Al or Cu may be used as the current collector, but the present invention is not limited thereto.

As the cathode active material, a compound capable of reversible intercalation and deintercalation of lithium (a lithiated intercalation compound) may be used. Specifically, at least one of a complex oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used. As a more specific example, a compound represented by any one of the following formulas may be used.

Li _a A _{1 - b} X _b D ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5); Li _a A _{1 - b} X _b O _{2 - c} D _c (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤0.05); LiE _{1 - b} X _b O _{2 - c} D _c (0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); LiE _{2 - b} X _b O _{4 - c} D _c (0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li _a Ni _{1 -b- c} Co _b X _c D _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li _a Ni _{1 -b- c} Co _b X _c O _{2 -α T α ( 0.90} ≤ a ≤1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _{1 -b- c} Co _b X _c O _{2 - α} T ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _{1 -b- c} Mn _b X _c D _α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤2); Li _a Ni _{1 -b- c} Mn _b X _c O _{2 -α T α ( 0.90} ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _{1 -bc} Mn _b X _c O _2-α T ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α <2); Li _a Ni _b E _c G _d O ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1); Li _a Ni _b Co _c Mn _d G _e O ₂ (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤0.5, 0 ≤ d ≤0.5, 0.001 ≤ e ≤ 0.1); Li _a NiG _b O ₂ (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a CoG _b O ₂ (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a MnG _b O ₂ (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a Mn ₂ G _b O ₄ (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li _a MnG _b PO ₄ (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); QO ₂ ; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ;LiZO ₂ ; LiNiVO ₄ ; Li _(3-f) J ₂ (PO ₄ ) ₃ (0 ≤ f ≤ 2); Li _(3-f) Fe ₂ (PO ₄ ) ₃ (0 ≤ f ≤ 2); LiFePO ₄

In the above formula, A is selected from the group consisting of Ni, Co, Mn, and combinations thereof; X is selected from the group consisting of Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, and combinations thereof; D is selected from the group consisting of O, F, S, P, and combinations thereof; E is selected from the group consisting of Co, Mn, and combinations thereof; T is selected from the group consisting of F, S, P, and combinations thereof; G is selected from the group consisting of Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, and combinations thereof; Q is selected from the group consisting of Ti, Mo, Mn, and combinations thereof; Z is selected from the group consisting of Cr, V, Fe, Sc, Y, and combinations thereof; J is selected from the group consisting of V, Cr, Mn, Co, Ni, Cu, and combinations thereof.

Those having a coating layer on the surface of this compound may be used, or a mixture of the compound and a compound having a coating layer may be used. The coating layer may include at least one coating element compound selected from the group consisting of oxide and hydroxide of the coating element, oxyhydroxide of the coating element, oxycarbonate of the coating element, and hydroxycarbonate of the coating element. The compound constituting these coating layers may be amorphous or crystalline. As the coating element included in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof may be used. In the coating layer forming process, any coating method may be used as long as it can be coated by a method that does not adversely affect the physical properties of the positive electrode active material by using these elements in the compound (for example, spray coating, dipping, etc., for this Since it is a content that can be well understood by those engaged in the field, a detailed description will be omitted.

The positive electrode active material layer may also include a positive electrode binder and a conductive material.

The binder serves to adhere the positive active material particles well to each other and also to the positive active material to the current collector, and representative examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl. Chloride, carboxylated polyvinylchloride, polyvinylfluoride, polymers including ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene- Butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc. may be used, but the present invention is not limited thereto.

The conductive material is used to impart conductivity to the electrode, and in the battery configured, any electronic conductive material can be used as long as it does not cause chemical change, for example, natural graphite, artificial graphite, carbon black, acetylene black, ketjen Black, carbon fiber, copper, nickel, aluminum, metal powder, such as silver, metal fiber, etc. can be used, and also conductive material, such as polyphenylene derivative, can be used 1 type or in mixture of 1 type or more.

The lithium secondary battery may be a non-aqueous electrolyte secondary battery, and in this case, the non-aqueous electrolyte may include a non-aqueous organic solvent and a lithium salt.

The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.

As the non-aqueous organic solvent and lithium salt, materials commonly used in the field of lithium secondary battery technology may be employed, and the material is not limited to a specific material.

In addition, as mentioned above, a separator may be present between the positive electrode and the negative electrode. As the separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used, and a polyethylene/polypropylene two-layer separator, a polyethylene/polypropylene/polyethylene three-layer separator, and a polypropylene/polyethylene/poly It goes without saying that a mixed multilayer film such as a propylene three-layer separator may be used.

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

[Assessment Methods]

- Life characteristics

After all cells with a large capacity of 10Ah or more were manufactured using the same anode, the lifespan was evaluated (35℃) in a chamber maintained at a constant temperature set within the DOD90 range at 1C charge / 1C discharge c-rate. .

- volume expansion rate

Using lithium metal as a positive electrode, three coin cells were fabricated in the same manner, respectively, and then charged at 0.1C. After measuring the thickness of the electrode before and after charging with a micrometer, the average of three values was calculated.

- Adhesion

After attaching the 3M tape to the electrode, the strength of the force applied when the tape was peeled off at the same angle (vertical) and speed (360 rpm) was measured.

- Direct current internal resistance (DCIR)

For measurement of battery resistance, DC internal resistance was measured at 50% SOC while discharging the prepared cells of 10Ah or more at 1C and charging at 0.75C for 10 seconds, respectively. At this time, when the SOC 50% is 100% of the total charge capacity of the battery, it means a state in which the battery is charged so as to have a charge capacity of 50%.

[Example 1]

The negative electrode active material was prepared by mixing 1 g of SiO negative active material with an average particle diameter of 6 μm, 4.5 g of artificial graphite with an average particle diameter of 18 μm, and 4.5 g of natural graphite with an average particle diameter of 12 μm. As a binder, styrene-butadiene rubber as an aqueous binder (SBR): Carboxymethyl cellulose (CMC) was prepared by mixing 1:1, and carbon black was prepared as a conductive material.

After mixing the prepared negative electrode active material: binder: conductive material in a weight ratio of 96:2:2, it was dispersed in water to prepare a negative electrode slurry. This negative electrode slurry was coated on a copper thin film, dried in an oven at 80° C. for 2 hours, rolled at a pressure of 3.8 MPa, and further dried in a vacuum oven at 110° C. for 12 hours to prepare a negative electrode for a secondary battery.

For the positive electrode, a nickel-cobalt-manganese (NCM)-based positive electrode was prepared, and ethylene carbonate/ethylmethyl carbonate/diethyl carbonate containing 1M LiPF6 as an electrolyte solution was mixed in a volume ratio of 1/1/1. was used.

A CR2016 coin-type half cell was manufactured according to a commonly known manufacturing process.

[Examples 2 to 5, Comparative Examples 1 to 4]

A coin cell was manufactured in the same manner as in Example 1, except that an anode active material satisfying Table 1 was used. The total mixing amount of artificial graphite and natural graphite is 9 g, and Table 1 shows the mixing ratio (by weight) of artificial graphite and natural graphite.

SiO Artificial graphite: natural graphite ΔH _A /H _A ΔH _b /H _b Example 1 1 g 5:5 0.05 0.35 Example 2 1 g 4:6 0.05 0.35 Example 3 1 g 6:4 0.05 0.35 Example 4 1 g 2:8 0.05 0.35 Example 5 1 g 8:2 0.05 0.35 Comparative Example 1 1 g 1:9 0.05 0.35 Comparative Example 2 1 g 9:1 0.05 0.35 Comparative Example 3 1 g 0:10 - 0.35 Comparative Example 4 1 g 10:0 0.05 -

- In Table 1, ΔHA / HA is the average of the particle size change rate of each particle by applying a pressure of 30 Mpa to 5 artificial graphite particles using a tip for 5 seconds.

- In Table 1, ΔHb/Hb is an average of the particle size change rate of each of the 5 natural graphite particles by applying a pressure of 30 Mpa for 5 seconds using a tip.

Table 2 is the evaluation data of the above-described evaluation items for Examples 1 to 5, and Comparative Examples 1 to 4.

volume expansion coefficient ( volume% ) Adhesion (N) DC internal resistance during charging (mΩ) Life characteristics ( % )
@ 100 ^th Example One 48 0.39 6.24 95 Example 2 49 0.37 6.47 93 Example 3 50 0.35 6.52 90 Example 4 55 0.31 6.66 85 Example 5 59 0.29 6.89 78 comparative example One 62 0.21 7.12 60 comparative example 2 71 0.19 7.32 47 comparative example 3 77 0.18 7.68 42 comparative example 4 79 0.17 7.94 30

As shown in Table 2, in the case of Comparative Examples 3 and 4 in which only SiO and one type of graphite were mixed, compared to Examples 1 to 5, Comparative Example 1, and Comparative Example 2 in which two types of graphite having different hardness were mixed together The volume expansion rate of the negative electrode, the adhesion between the active material and the current collector, the battery resistance during charging and discharging, and the battery life characteristics were very poor.

In addition, in Examples 1 to 5, in which two types of graphite having different hardnesses were mixed at 2:8 to 8:2, the volume expansion rate of the negative electrode was small compared to Comparative Examples 1 and 2 outside the above range, and the adhesive strength between the active material and the current collector It can be confirmed that this is excellent, the battery resistance is low during charging and discharging, and the battery life characteristics are excellent. In particular, when Example 5 and Comparative Example 1 are compared, it can be seen that the adhesive force between the active material and the current collector and the lifespan characteristics of the battery are rapidly reduced.

In addition, when two types of graphite having different hardnesses were mixed in a ratio of 4:6 to 6:4, the volume expansion coefficient was 50% by volume or less, and the service life characteristics were 90% or more, showing high performance.

[Examples 6 to 9, Comparative Examples 5 and 6]

In order to investigate the effect of the ratio of total graphite including SiO to artificial graphite and natural graphite, a coin cell was manufactured in the same manner as in Example 1 while changing the amount of SiO mixed as shown in Table 3. The total mixing amount of SiO and all graphite was 10 g, and the ratio of artificial graphite: natural graphite was fixed to 5:5.

SiO Artificial graphite: natural graphite ΔH _A /H _A ΔH _b / H _b Example 6 1.5g 5:5 0.05 0.35 Example 7 2.5g 5:5 0.05 0.35 Example 8 3.5g 5:5 0.05 0.35 Example 9 4.5g 5:5 0.05 0.35 comparative example 5 5g 5:5 0.05 0.35 comparative example 6 5.5g 5:5 0.05 0.35

Table 4 is the evaluation data of the above-described evaluation items for Examples 6 to 9 and Comparative Examples 5 and 6.

volume expansion coefficient
( volume% ) adhesion
(N) DC internal resistance during charging (mΩ) Life characteristics (%) Example 6 49 0.39 6.27 94 Example 7 50 0.38 6.35 93 Example 8 49 0.35 6.44 91 Example 9 50 0.37 6.43 90 Comparative Example 5 70 0.21 7.65 78 Comparative Example 6 77 0.20 7.57 73

As shown in Table 4, when the content of SiO exceeds 45% (by weight), the volume expansion coefficient of the negative electrode increases, the adhesive force between the positive electrode active material and the current collector decreases, the resistance of the battery increases during charging and discharging, and the It can be seen that the lifespan characteristics are rapidly reduced.

This is considered to be due to an increase in the degree of volume expansion as the mixing amount of the silicon-based negative active material increases.

Claims (6)

A mixed negative active material of a silicon (Si)-based negative active material, a first carbon-based negative active material of artificial graphite, and a second carbon-based negative active material of natural graphite having a lower hardness than the first carbon-based negative active material,
The silicon-based negative active material is included in an amount of 45% by weight or less based on 100% by weight of the total amount of the mixed negative active material,
The weight ratio of the first carbon-based negative active material to the second carbon-based negative active material is 2:8 to 8:2,
The first carbon-based negative active material satisfies Formula 1, and the second carbon-based negative active material satisfies Formula 2 below.
[Equation 1]
ΔH _A /H _A ≤ 0.1
[Equation 2]
ΔH _B /H _B ≥ 0.3
(In Equation 1, HA is the average particle size of the first carbon-based negative active material, _ΔHA is the average particle size change of the first carbon-based negative active material when a pressure of 30 MPa is applied for 5 seconds, and in Equation ₂ , H _B is the average particle diameter of the second carbon-based negative active material, and _ΔHB is the average particle diameter change of the second negative active material when a pressure of 30 MPa is applied for 5 seconds.) delete In claim 1,
The silicon-based negative active material is Si, SiO _x (0 < x < 2), or SiC anode for a lithium secondary battery. delete In claim 1,
A negative electrode for a lithium secondary battery in which the weight ratio of the first carbon-based negative active material to the second carbon-based negative active material is 4:6 to 6:4. A lithium secondary battery comprising the negative electrode for a lithium secondary battery of any one of claims 1, 3 and 5.