KR20230106498A - Negative electrode including silicon based negative active material and secondary battery including the same - Google Patents

Abstract

The present invention relates to a negative electrode including a silicon-based negative active material and a secondary battery including the same. According to an embodiment of the present invention, a current collector and a negative electrode disposed on the current collector and including a plurality of silicon-based active material particles A negative electrode for a secondary battery including an active material layer and satisfying the following relational expression 1 may be provided.
[Relationship 1] 0.01 ≤ AB ≤ 0.81
In the relational expression 1, A is the average value of the Raman spectrum peak intensity ratio Ia/Ib for 50 randomly selected silicon-based active material particles in the negative electrode active material layer, and B is each value for each of the 50 silicon-based active material particles. With respect to the Raman spectrum peak intensity ratio Ia/Ib value, the average value of the remaining values excluding the top 10 values and the bottom 10 values, Ia is the peak intensity at 515±15cm ^-1 , and the Ib is 470±30cm ^-1 is the peak intensity at

Description

Negative electrode containing silicon-based negative electrode active material and secondary battery including the same

The present disclosure relates to a negative electrode including a silicon-based negative electrode active material and a secondary battery including the negative electrode.

Recently, as a response to the issue of global warming, the demand for eco-friendly technologies is rapidly increasing. In particular, as the technical demand for electric vehicles and ESS (energy storage systems) increases, the demand for lithium secondary batteries, which are in the spotlight as energy storage devices, is also explosively increasing. Therefore, studies to improve the energy density of lithium secondary batteries are being conducted.

Existing commercial lithium secondary batteries generally use graphite active materials such as natural graphite and artificial graphite. However, due to the low theoretical capacity of graphite (372 mAh/g), there is a limit to the low energy density of the battery. Because of these limitations, researches are being conducted to develop new anode materials to improve energy density.

Silicon-based anodes are emerging as a solution due to their high theoretical capacity (3580 mAh/g). However, a silicon-based negative electrode forms a crystalline Si phase and an amorphous Si phase during the manufacturing process, and these are known to have different degrees of expansion and contraction during charging and discharging of the battery. In addition, if the size distribution of crystalline Si is not uniform during electrode manufacturing, deterioration is initiated during charge/discharge cycles from particles containing some enlarged crystalline Si, which may cause non-uniform deterioration in the entire electrode and local electrode deterioration. there is. As a result of this, there is a possibility that the life characteristics of the battery may be deteriorated.

Korean Patent Publication No. 10-2005-0032464 (published on April 7, 2005)

The present disclosure is to improve the lifespan characteristics of a battery by providing an electrode active material layer having uniform crystallinity of silicon-based active material particles and an electrode including the same when manufacturing an electrode to which a silicon-based active material is applied.

As one means for achieving the above object, according to one embodiment of the present disclosure, the current collector; and a negative active material layer disposed on the current collector and including a plurality of silicon-based active material particles,

A negative electrode for a secondary battery that satisfies the following relational expression 1 can be provided.

[Relationship 1] 0.01 ≤ A-B ≤ 0.81

In the relational expression 1, A is the average value of the Raman spectrum peak intensity ratio Ia/Ib for 50 randomly selected silicon-based active material particles in the negative electrode active material layer, and B is each value for each of the 50 silicon-based active material particles. With respect to the Raman spectrum peak intensity ratio Ia/Ib value, the average value of the remaining values excluding the top 10 values and the bottom 10 values, Ia is the peak intensity at 515±15cm ^-1 , and the Ib is 470±30cm ^-1 is the peak intensity at

According to one embodiment, the silicon-based active material may be at least one selected from the group consisting of silicon, silicon oxide (SiO _x , 0<x≤2), silicon alloy, and silicon/carbon composite.

According to one embodiment, the silicon-based active material may include metal pre-treated silicon oxide.

According to one embodiment, the metal pretreated silicon oxide is silicon oxide (SiO _x , 0<x≤2); and a metal silicate (M _a Si _b O _c , M is Li or Mg) located on at least a part of the silicon oxide , and 1≤a≤6, 1≤b<3, 0<c≤7); may include.

According to one embodiment, the metal pretreated silicon oxide may include 40 to 95% by weight of metal silicate based on the total weight.

A negative electrode for a secondary battery according to an embodiment may further satisfy the following relational expression 2.

[Relationship 2] 0.01 ≤ A-C ≤ 0.65

In the relational expression 2, A is the average value of the Raman spectrum peak intensity ratio Ia/Ib for 50 randomly selected silicon-based active material particles in the negative electrode active material layer, and C is the average value for each of the 50 silicon-based active material particles. With respect to the Raman spectrum peak intensity ratio Ia/Ib value, the average value of the remaining values excluding the top 5 values and the bottom 5 values, wherein Ia is the peak intensity at 515±15cm ^-1 , and the Ib is 470±30cm ^-1 is the peak intensity at

A negative electrode for a secondary battery according to an embodiment may satisfy at least one selected from the following relational expressions 3a, 3b, and 3c.

[Relationship 3a] 0.3 ≤ A ≤ 8.50

[Relationship 3b] 0.3 ≤ B ≤ 7.71

[Relationship 3c] 0.3 ≤ C ≤ 7.91

In the relations 3a, 3b, and 3c, A is the average value of the Raman spectrum peak intensity ratio Ia/Ib for 50 randomly selected silicon-based active material particles in the negative electrode active material layer, and B is the average value of the 50 silicon-based active material particles For each Raman spectrum peak intensity ratio Ia / Ib value for , the average value of the remaining values excluding the top 10 values and the bottom 10 values, C is the peak intensity of each Raman spectrum for the 50 silicon-based active material particles For the ratio Ia/Ib value, it is the average value of the remaining values excluding the top 5 values and the bottom 5 values.

According to one embodiment, the negative active material layer may include 10% by weight or more of the silicon-based active material particles based on the total weight of the negative active material.

In addition, as another means for achieving the above object, according to an embodiment of the present disclosure, a) a process of mixing silicon compound particles and a metal precursor at 200 to 800 rpm, b) the product of step a) A process for preparing a negative electrode for a secondary battery, including a step of pre-heating at 100 ° C. or more and less than 500 ° C., and c) a step of heat-treating the product of step b) at 500 to 800 ° C.

According to an embodiment, the silicon compound particles may be prepared by further including p1) mixing Si powder and SiO ₂ powder and heat-treating the mixture at less than 900° C. before step a).

According to one embodiment, prior to step a), p1) mixing Si powder and SiO ₂ powder and heat-treating the mixture at less than 900°C, and p2) heat-treating the product of step p1) at less than 800°C in the presence of hydrocarbon gas. The silicon compound particles may be prepared by further including.

In addition, as another means for achieving the above object, a secondary battery including the negative electrode of the above-described embodiment may be provided.

According to the present disclosure, a uniform size distribution of crystalline Si (c-Si) can be secured by controlling manufacturing conditions for manufacturing a silicon-based negative electrode active material under specific conditions and performing a preliminary heat treatment process prior to a high-temperature metal pretreatment process. .

According to the present disclosure, uniform crystallinity and size distribution of silicon-based active material particles in the negative electrode active material layer are secured by controlling the Raman spectrum peak intensity ratio for 50 randomly selected silicon-based active material particles in the negative electrode active material layer under specific conditions. can do.

Advantages and features of the present disclosure, and methods of achieving them, will become apparent with reference to the detailed implementation examples taken in conjunction with the accompanying drawings. However, the present disclosure is not limited to the implementations disclosed below and will be implemented in a variety of different forms, only the present disclosures make the present disclosure complete, and those skilled in the art to which the present disclosure belongs It is provided to fully inform you of the scope of the disclosure, and the disclosure is only defined by the scope of the claims. Specific details for the practice of the present disclosure will be described in detail with reference to the accompanying drawings below. Like reference numbers refer to like elements, regardless of drawing, and "and/or" includes each and every combination of one or more of the recited items.

Unless otherwise defined, all terms (including technical and scientific terms) used in this specification may be used in a meaning commonly understood by those of ordinary skill in the art to which this disclosure belongs. When it is said that a certain part "includes" a component throughout the specification, this means that it may further include other components, not excluding other components unless otherwise stated. In addition, singular forms also include plural forms unless specifically stated in the text.

In this specification, when a part such as a layer, film, region, plate, etc. is said to be “on” or “on” another part, this includes not only the case where it is “directly on” the other part, but also the case where there is another part in the middle. do.

One embodiment provides a negative electrode for a secondary battery. The negative electrode is a current collector; and a negative active material layer disposed on the current collector and including a plurality of silicon-based active material particles.

In this embodiment, the distribution of crystalline Si (c-Si) in a plurality of silicon-based compound particles by performing a metal pretreatment process of a silicon-based compound under specific conditions and a preliminary heat treatment process prior to a high-temperature metal pretreatment process. There is a technical feature in improving the non-uniformity of, for example, the non-uniformity of the size distribution of c-Si.

According to the present embodiment, by controlling the Raman spectrum peak intensity ratio of 50 randomly selected silicon-based active material particles in the negative electrode active material layer as follows, uniform crystallinity and size distribution of all silicon-based active material particles in the negative electrode active material layer can be obtained.

According to one embodiment, it may be characterized in that the following relational expression 1 is satisfied.

[Relationship 1] 0.01 ≤ A-B ≤ 0.81

In the relational expression 1, A is the average value of the Raman spectrum peak intensity ratio Ia/Ib for 50 randomly selected silicon-based active material particles in the negative electrode active material layer, and B is each value for each of the 50 silicon-based active material particles. With respect to the Raman spectrum peak intensity ratio Ia/Ib value, the average value of the remaining values excluding the top 10 values and the bottom 10 values, Ia is the peak intensity at 515±15cm ^-1 , and the Ib is 470±30cm ^-1 is the peak intensity at Alternatively, specifically, the Ib may be a peak intensity at 480±20 cm ⁻¹ .

The measurement of the Raman spectrum peak intensity ratio may be performed on a plurality of silicon-based active material particles in the negative electrode active material layer of a previously prepared or freshly prepared negative electrode. Since the variability of the Raman spectrum peak intensity ratio due to charge/discharge cycles is expected to be very low, a negative electrode subjected to several charge/discharge cycles may be used as a target. For example, the negative electrode may have been subjected to less than 10 charge/discharge cycles. Considering that charging and discharging cycles are generally performed approximately 2 to 3 times when manufacturing a negative electrode, it is okay to perform the negative electrode extracted by disassembling a secondary battery sold in the market.

The Raman spectrum peak intensity ratio Ia / Ib means the formation ratio of the crystalline Si phase and the amorphous Si phase, the Ia peak intensity is an index indicating the formation of c-Si (crystalline Si phase), and the Ib peak intensity is It may be an indicator of the formation of a-Si (amorphous Si phase).

The smaller the value of A-B, which is the difference between the average value of the peak intensity ratio A and the average value of the peak intensity ratio B, means that the crystallinity of the plurality of silicon-based active material particles distributed in the negative active material layer is uniform. By satisfying the above-described relational expression 1, the present embodiment can maintain overall electrode expansion and contraction uniformly in the thickness direction and width direction of the electrode, and can improve the lifespan characteristics of the electrode. Meanwhile, the numerical range A-B of the present embodiment means that the composition of one silicon-based active material particle is close to the overall average value of a plurality of particles.

Specifically, when 0.01 ≤ A-B ≤ 0.73, or more specifically 0.01 ≤ A-B ≤ 0.5, or even more specifically 0.01 ≤ A-B ≤ 0.17, the plurality of silicon-based active material particles distributed in the negative active material layer have more uniform crystallinity. that can mean

In addition, the fact that the silicon-based active material particle is crystalline means that the shape of the single Si located inside the particle is crystalline, and the amorphous means that the shape of the single Si located inside the particle is amorphous or Scherrer's equation in XRD analysis It may mean that it is a particle so small that it is difficult to measure the size through it.

The negative electrode of this embodiment may further satisfy the following relational expression 2.

[Relationship 2] 0.01 ≤ A-C ≤ 0.65

In the relational expression 2, A is the average value of the Raman spectrum peak intensity ratio Ia/Ib for 50 randomly selected silicon-based active material particles in the negative electrode active material layer, and C is the average value for each of the 50 silicon-based active material particles. With respect to the Raman spectrum peak intensity ratio Ia/Ib value, the average value of the remaining values excluding the top 5 values and the bottom 5 values, wherein Ia is the peak intensity at 515±15cm ^-1 , and the Ib is 470±30cm ^-1 is the peak intensity at Alternatively, specifically, the Ib may be a peak intensity at 480±20 cm ⁻¹ .

Specifically, when 0.01 ≤ A-C ≤ 0.59, or more specifically 0.01 ≤ A-C ≤ 0.54, or even more specifically 0.01 ≤ A-C ≤ 0.48, the plurality of silicon-based particles distributed in the negative active material layer have more uniform crystallinity. that can mean

The cathode of this embodiment may satisfy at least one selected from the following Relational Expressions 3a, 3b, and 3c.

[Relationship 3a] 0.3 ≤ A ≤ 8.50

[Relationship 3b] 0.3 ≤ B ≤ 7.71

[Relationship 3c] 0.3 ≤ C ≤ 7.91

In the relations 3a, 3b, and 3c, A is the average value of the Raman spectrum peak intensity ratio Ia/Ib for 50 randomly selected silicon-based active material particles in the negative electrode active material layer, and B is the average value of the 50 silicon-based active material particles For each Raman spectrum peak intensity ratio Ia / Ib value for , the average value of the remaining values excluding the top 10 values and the bottom 10 values, C is the peak intensity of each Raman spectrum for the 50 silicon-based active material particles For the ratio Ia/Ib value, it is the average value of the remaining values excluding the top 5 values and the bottom 5 values.

The A may satisfy one of the above relations, and may be, but is not limited to, 0.3 to 8.5, or 0.3 to 7.5, or 0.3 to 2.9, or 0.3 to 2.5, or 0.3 to 1.5, or 0.3 to 0.8. there is.

The B may satisfy one of the above relations, and may be 0.3 to 7.7, or 0.3 to 6.7, or 0.3 to 2.8, or 0.3 to 2.5, or 0.3 to 0.7 for non-limiting examples.

The C may satisfy one of the above relations, and may be, but is not limited to, 0.3 to 8.0, or 0.3 to 7.0, or 0.3 to 3.0, or 0.3 to 2.5, or 0.3 to 2.1, or 0.3 to 0.7. there is.

Hereinafter, the current collector and the negative electrode active material layer, each component of the negative electrode, will be described in detail.

As the current collector, one selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, conductive metal-coated polymer substrate, and combinations thereof may be used. It is not limited.

The negative active material layer includes a silicon-based active material, and may further include a binder and a conductive material. The anode active material layer may further include, in addition to the silicon-based active material, a material capable of selectively reversibly intercalating/deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide. there is. Examples of the material capable of reversibly intercalating/deintercalating lithium ions include carbon materials, that is, carbon-based negative electrode active materials generally used in lithium secondary batteries. Representative examples of the carbon-based negative electrode active material may include crystalline carbon, amorphous carbon, or a combination thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-shaped, flake-shaped, spherical or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon or hard carbon. carbon), mesophase pitch carbide, calcined coke, and the like. The lithium metal alloy is a group consisting of lithium and Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn. An alloy of a metal selected from may be used.

The silicon-based active material includes silicon (Si), silicon oxide (SiO _x , 0<x≤2), silicon alloy (Si-Q, Q is an alkali metal, an alkaline earth metal, a group 13 element, a group 14 element, a group 15 element, It is an element selected from the group consisting of Group 16 elements, transition metals, rare earth elements, and combinations thereof, except for Si), and may be at least one selected from the group consisting of silicon/carbon composites.

Specifically, the silicon-based active material may include metal pre-treated silicon oxide. In general, silicon oxide shows excellent lifespan characteristics due to a lower volume expansion rate than silicon, but exhibits a unique low initial efficiency by forming an irreversible phase during initial charging and discharging. It is possible to improve the initial efficiency decrease problem by forming the metal silicate in advance through the metal pretreatment. Specifically, the metal pretreated silicon oxide may be lithium or magnesium pretreated silicon oxide, silicon oxide (SiOx, 0<x≤2); and a metal silicate (M _a Si _b O located on at least a part of the silicon oxide) _c , M is Li or Mg, and 1≤a≤6, 1≤b<3, 0<c≤7); may include an active material particle. The metal silicate may be Li ₂ SiO ₃ , Li ₂ Si ₂ O ₅ , Li ₄ SiO ₄ or a combination thereof when the metal is Mg, MgSiO ₃ , MgSi ₂ O ₅ , Mg ₂ SiO ₄ when the metal is Mg. Or it may be a combination thereof, but is not limited thereto. On the other hand, it is more preferable that the metal pretreated silicon oxide does not substantially include Li ₄ SiO ₄ or Mg ₂ SiO ₄ . The Li ₄ SiO ₄ or Mg ₂ SiO ₄ phase has irreversible characteristics with respect to M ions (Li, Mg ions) and is vulnerable to moisture, making it undesirable to use as an active material for an anode using a water-based binder. In order to prepare a stable slurry, It is preferred that the content of the Li ₄ SiO ₄ or Mg ₂ SiO ₄ phase is less than 35% by weight, preferably less than 5% by weight, better still substantially free, based on the total weight of the silicon oxide. Accordingly, the water resistance of the negative electrode active material can be improved.

The metal pretreated silicon oxide may contain 40 to 95% by weight of metal silicate based on the total weight, preferably 45 to 90% by weight, or 50 to 90% by weight, more preferably 40 to 85% by weight, or 50 to 85% by weight, but is not particularly limited. Conventionally, during the pretreatment of the silicon-based active material, the content of the metal silicate is locally increased due to the non-uniform temperature gradient of the silicon-based active material and the non-uniform mixing state of the silicon-based active material and the Li source, and at the same time, a partial non-uniformization reaction is initiated. . As a result, there is a problem in that the generation of c-Si seeds is locally increased or aggregated, further accelerating a phenomenon in which c-Si size distribution becomes non-uniform. That is, in the conventional synthesis method, c-Si growth could not be uniformly controlled during pretreatment to secure a high content of metal silicate, resulting in deterioration of the electrode. On the other hand, in this embodiment, it is possible to form a high content of metal silicate while maintaining the shape of a fine c-Si seed by performing a metal pretreatment process under specific conditions to be described later. This result is analyzed because c-Si growth can be suppressed by uniformly distributing fine c-Si to a plurality of SiOx particles.

The silicon-based active material particles may have an average particle size of greater than 2 μm and less than 30 μm, preferably greater than 6 μm and less than 10 μm, and in this case, during metal pretreatment, they are uniformly mixed with several micro-sized metal precursors surrounding the SiOx particles. Since this is possible, as the uniform reaction (prelithiation) proceeds in all directions of the SiOx particles during subsequent heat treatment, the Li-pretreated _SiO particles having uniform crystallinity can be recovered.

The average particle size of the silicon-based active material particles may mean D50, and the D50 means a particle diameter when the cumulative volume becomes 50% from a small particle size in particle size distribution measurement by a laser scattering method. Here, D50 may take a sample according to KS A ISO 13320-1 standard for the manufactured carbonaceous material and measure the particle size distribution using Malvern's Mastersizer3000. Specifically, after dispersing using ethanol as a solvent and using an ultrasonic disperser if necessary, the volume density can be measured.

The silicon-based active material may be included in an amount of 10 wt% or more, preferably 20 wt% or more, 30 wt% or more, and more preferably 40 wt% or more or 50 wt% or more, based on the total weight of the anode active material included in the anode active material layer. , is not particularly limited. According to one example, the silicon-based active material may be included in an amount of 100% by weight based on the total weight of the negative electrode active material. Conventionally, when only silicon-based active materials are used as the negative electrode active material, excellent lifespan characteristics cannot be implemented due to electrode volume expansion, so graphite-based active materials that can alleviate contraction / expansion of active material particles have been used in a mixture of more than half, but this implementation In the example, it is possible to manufacture a negative electrode having improved high-capacity characteristics and long-term cycle characteristics by improving local deterioration of the electrode due to non-uniform volume expansion.

The binder serves to well attach the anode active material particles to each other and to well attach the anode active material to the current collector, and may be preferably an aqueous binder. The aqueous binder includes polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoro ethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, various copolymers thereof, and the like. As such, the binder may include a binder made of carboxyl methyl cellulose (CMC), styrene-butadiene rubber (SBR), and a mixture thereof.

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

The content of the binder and the conductive material in the negative electrode active material layer may be 1 to 10% by weight, preferably 1 to 5% by weight, based on the total weight of the negative electrode active material layer, but is not limited thereto.

Another embodiment provides a method for manufacturing a negative electrode for a secondary battery. According to an example, the manufacturing method may include: a) mixing silicon compound particles and a metal precursor; b) preliminarily heat-treating the product of step a); and c) heat-treating the product of step b) to prepare an anode active material.

According to an example, the manufacturing method may further include p1) mixing and heat-treating Si powder and SiO ₂ powder to prepare the silicon compound particles. The process is to mix the raw material powder and heat-treat it. The mixing of the raw material powder may be performed by appropriately adjusting the mixing ratio of the Si powder and the SiO ₂ powder to form the Si and O molar ratio of the desired silicon compound particles (SiO _x , 0<x≤2). there is. Then, the mixed raw material powder is placed in a furnace with an inert atmosphere and heated under reduced pressure at a temperature of less than 900°C, preferably less than 800°C, or a temperature of 500 to 700°C, more preferably 500 to 650°C. It may be heat treated for 1 to 12 hours or 1 to 8 hours. Conventionally, heat treatment was performed at a high temperature of 900 to 1600 ° C. to produce silicon compound particles, but for SiO _x material or SiO material, c-Si seeds grow at a heat treatment temperature of 800 ° C or higher, and at about 900 ° C. crystallites grow. Therefore, in the present embodiment, the formation of c-Si seeds and the growth of c-Si are suppressed during the production of silicon compound particles to prepare an amorphous or microcrystalline silicon-based compound, uniformly distributing the crystallinity of Si, and crystallization at the same time Particles can be controlled to be small. In a low temperature range that suppresses the growth of c-Si, the seed form may be maintained or finely grown c-Si may be uniformly distributed. However, in the high temperature range, since the disproportionation reaction is accelerated rather than additional seed generation and c-Si is controlled in the direction of local growth, c-Si growth of coarse and non-uniform size can be confirmed.

Subsequently, the prepared silicon compound is extracted, and pulverized and powdered to produce silicon compound particles.

In addition, according to an example, the silicon compound particles may be prepared by further including, in addition to the process p1), a process of optionally p2) heat-treating the product of the process p1) in the presence of a hydrocarbon gas.

In step p2), a carbon layer may be further formed on the surfaces of the prepared silicon compound particles. According to an example, a carbon layer may be formed by introducing a hydrocarbon gas into a furnace and raising the temperature to a temperature lower than the heat treatment temperature in preparing the silicon compound. Specifically, it may be heat treatment for 1 to 12 hours or 1 to 8 hours at a temperature of less than 800 ° C or 500 to 700 ° C, more preferably 500 to 650 ° C under reduced pressure or an inert atmosphere. Conventionally, heat treatment was performed at a relatively high temperature of 800 to 1200 ° C or 800 to 950 ° C to coat the surface of silicon compound particles with a carbon material. It is divided into SiO _x (0<x≤2) or SiO ₂ region, and the silicon compound material is analyzed to promote the growth of c-Si at a temperature of 800 ° C or higher and increase the size of Si crystallites. In this embodiment, c-Si growth can be extremely suppressed by controlling the size of Si crystallites to be small enough to be unmeasurable. In the case of using the amorphous or microcrystalline silicon-based compound of the present embodiment compared to the conventional silicon-based compound in which the above crystallites are grown, the growth of c-Si can be suppressed to a high level even if Li pretreatment is performed under the same conditions.

Therefore, in order to maintain the uniformity of crystallinity during the carbon layer coating, wet coating using a polymer must be performed or controlled below the synthesis temperature of the silicon compound. For uniform coating at low temperature, care must be taken in selecting the carbon layer coating precursor or adjusting the pressure and selecting the type of the carrier gas during wet coating. Amorphous or microcrystalline silicon compounds can be synthesized when c-Si growth is effectively suppressed in the carbon layer coating process to ensure electrical conductivity of silicon compounds, which is a very important base material to be checked during pretreatment of negative electrode active materials with uniform crystalline characteristics. can be said to be a characteristic of

As the hydrocarbon gas, when a hydrocarbon gas having 3 or less carbon atoms is used, it is preferable to reduce manufacturing costs and form a good coating layer, but is not limited thereto.

Subsequently, a metal pretreatment process is performed.

a) The mixing process may be mixing the silicon compound particles and the metal precursor, specifically, mixing at 200 to 800 rpm, 250 to 600 rpm, or 300 to 500 rpm for 30 to 120 minutes. If the mixing speed is less than 200 rpm, uniform mixing is difficult even when mixing is performed for a long time, and it is not preferable in terms of process simplification. On the other hand, when the mixing speed exceeds 800 rpm, a chemical reaction by kinetic energy occurs, causing local chemical transformation of the metal precursor, and it may be difficult to control a uniform metal pretreatment reaction.

In the mixing, the M/Si molar ratio between the silicon compound particles and the metal (M) precursor is greater than 0.3 and less than or equal to 1.0, or greater than 0.3 and less than or equal to 0.8, preferably 0.4 to 1.0 or 0.4 to 0.8, more preferably 0.5 to 1.0, or 0.5 to 0.8 is preferable when mixing.

The silicon compound particles are the same as those described above.

As the metal precursor, at least one Li precursor selected from LiOH, Li, LiH, Li ₂ O and Li ₂ CO ₃ , or at least one selected from Mg(OH) ₂ , Mg, MgH ₂ , MgO and MgCO ₃ One or more types of Mg precursors may be used, and any compound capable of being decomposed during heat treatment is not particularly limited.

The mixing process may be performed in a mixer, and as long as a physical mixing process is possible, it is not particularly limited to the structure and principle of the device. For example, there are mixers in which blades rotate in one direction, rotary ball mills in one direction or two directions, and mixers or milling machines capable of two or three axis motion. On the other hand, in the case of raw materials that are concerned about the possibility of deterioration in air or moisture, atmospheric conditions may need to be adjusted, such as in a dry room or glove box form.

b) The preliminary heat treatment process may be a preliminary heat treatment of a mixture of silicon compound particles and metal precursors uniformly mixed as a product of process a) at a low temperature. The metal pretreatment process is a high-temperature heat treatment. Due to the high activity of the Li source under rapid temperature change conditions, the temperature of the central and surface parts of the furnace may be non-uniform, and accordingly, the generation and growth of c-Si seeds inside the furnace Depending on the gradient, there is a risk of having non-uniform crystallinity due to heavy load in the local area.

According to the present embodiment, by placing an intermediate process of preliminary heat treatment before high-temperature heat treatment, volatile side reaction materials that may react with the Li source can be removed in advance, and a uniform reaction can be induced by relieving the temperature gradient. In addition, some of the metal precursors in a reaction-activated state during the preliminary heat treatment tend to move to a place where the concentration of the pre-treated metal is low among the silicon-based compound particles and react first. Using this, the preliminary heat treatment process can solve the fact that the metal precursor is non-uniformly mixed and partially excessively present around the SiO _x particle before the high-temperature heat treatment for the subsequent metal pretreatment. Therefore, it is possible to precisely control the aggregation and growth of c-Si in the subsequent c) heat treatment process through the preliminary heat treatment process b).

b) preliminary heat treatment process according to an example may include preliminary heat treatment at 100 ° C. to less than 500 ° C., 150 ° C. to less than 500 ° C., 200 to 450 ° C., or 250 to 400 ° C. for 30 to 120 minutes in an inert atmosphere. If the preliminary heat treatment temperature is 150° C. or less or the heat treatment time is 30 minutes or less, there is a concern that the effect for securing by the preliminary heat treatment may not be sufficient. On the other hand, if the temperature of the preliminary heat treatment is 500° C. or higher, the reaction between the precursor metal and the silicon compound is started by the preliminary heat treatment, and it is difficult to control the reaction in the subsequent heat treatment process, for example, the prelithiation reaction.

c) In the heat treatment process, the mixture of the preheated silicon compound particles and the metal precursor as a product of the process b) may be heat treated at a high temperature. According to this embodiment, it is possible to manufacture amorphous or microcrystalline silicon oxide particles by suppressing c-Si growth through c) heat treatment process, and a uniform characteristic distribution of the particles can be expected.

For example, c) heat treatment may be heat treatment at 500 to 800 °C, 550 to 750 °C or 600 to 750 °C for 1 to 12 hours under an inert atmosphere. If the heat treatment temperature is less than 500 ° C., too few c-Si seeds are generated, and local aggregation and growth occur in the small c-Si seeds, so that the c-Si size distribution may become non-uniform. On the other hand, when the heat treatment temperature exceeds 800 ° C., growth of c-Si is promoted rather than additional generation of c-Si seeds, and as a result, the size of some c-Si increases rapidly, resulting in non-uniform c-Si size distribution. There is a risk of breaking down.

Meanwhile, as the inert atmosphere, a known method of creating an inert atmosphere by purging the inside of the reaction unit with an inert gas may be applied, and the inert gas may be selected from Ne, Ar, Kr, and N ₂ , and preferably Ar. Alternatively, N ₂ may be used, but is not limited thereto.

Subsequently, the anode active material including final anode active material particles may be prepared by recovering and pulverizing the heat treatment product, but is not limited thereto. The crushing process may apply a known crushing method, but is not limited thereto.

Another embodiment provides a secondary battery including the negative electrode. The cathode is the same as described above.

According to an example, the secondary battery may include the negative electrode; anode; a separator positioned between the cathode and anode; And an electrolyte solution; may include.

The cathode may include a current collector and a cathode active material layer formed by applying a cathode slurry containing a cathode active material on the current collector.

The current collector may use the above-described negative electrode current collector, and when a material known in the art is used, it may be used, but is not limited thereto.

The positive electrode active material layer includes a positive electrode active material, and may optionally further include a binder and a conductive material. The cathode active material may be used when a known cathode active material in the art is used, and for example, a composite oxide of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof is used, but is limited thereto It is not.

As the binder and the conductive material, the above-described negative electrode binder and negative electrode conductive material may be used, and materials known in the art may be used, but are not limited thereto.

The separator may be selected from, for example, glass fiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene, or a combination thereof, and may be in the form of a nonwoven fabric or a woven fabric. For example, a polyolefin-based polymer separator such as polyethylene or polypropylene may be mainly used in a lithium secondary battery, and a separator coated with a composition containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength. It may be used in a single-layer or multi-layer structure, and when using a separator known in the art, it may be used, but is not limited thereto.

The electrolyte solution includes an organic solvent and a lithium salt.

The organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move, and for example, carbonate-based, ester-based, ether-based, ketone-based, alcohol-based or aprotic solvents may be used, The organic solvents may be used alone or in combination of two or more, and when two or more organic solvents are used in combination, the mixing ratio may be appropriately adjusted according to the desired battery performance. On the other hand, in the case of using an organic solvent known in the art, it may be used, but is not limited thereto.

The lithium salt is a material that dissolves in an organic solvent and acts as a source of lithium ions in the battery to enable basic operation of the lithium secondary battery and promotes the movement of lithium ions between the positive electrode and the negative electrode. Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiN(SO ₃ C ₂ F ₅ ) ₂ , LiN(CF ₃ SO ₂ ) ₂ , LiC ₄ F ₉ SO ₃ , LiClO ₄ , LiAlO ₂ , LiAlCl ₄ , LiN(C _x F _2x+1 SO ₂ )(C _y F _2y+1 SO ₂ ) (x and y are natural numbers), LiCl, LiI, LiB(C ₂ O ₄ ) ₂ or combinations thereof. It may include, but is not limited thereto.

The concentration of the lithium salt may be used within the range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, since the electrolyte solution has appropriate conductivity and viscosity, excellent performance of the electrolyte solution can be exhibited, and lithium ions can move effectively.

In addition, the electrolyte solution is pyridine, triethyl phosphate, triethanolamine, cyclic ether, ethylene diamine, n-glyme (glyme), hexaphosphoric acid triamide, nitrobenzene derivatives to improve charge and discharge characteristics, flame retardancy characteristics, etc. as needed , sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxy ethanol, aluminum trichloride, and the like may further be included. . In some cases, halogen-containing solvents such as carbon tetrachloride and trifluoroethylene may be further included to impart incombustibility, and FEC (fluoro-ethylene carbonate), PRS (propane sultone), FPC ( fluoro-propylene carbonate) and the like may be further included.

In the method for manufacturing a secondary battery according to the present embodiment for achieving the above object, an electrode assembly is formed by sequentially stacking a negative electrode, a separator, and a positive electrode, and the manufactured electrode assembly is a cylindrical battery case or a prismatic battery case Then, a battery can be manufactured by injecting an electrolyte solution. Alternatively, it may be manufactured by laminating the electrode assembly, impregnating it with an electrolyte, and sealing the obtained result by putting it in a battery case.

As the battery case used in the present disclosure, those commonly used in the field may be adopted, and there is no limitation on the external appearance according to the purpose of the battery, for example, a cylindrical shape using a can, a prismatic shape, a pouch shape, or a coin ( coin) type, etc.

The lithium secondary battery according to the present disclosure can be used not only as a battery cell used as a power source for a small device, but also can be preferably used as a unit cell in a medium or large battery module including a plurality of battery cells. Preferred examples of the medium or large-sized device include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, power storage systems, and the like.

Hereinafter, preferred examples and comparative examples of this embodiment will be described. However, the following examples are only preferred examples of this embodiment and are not limited thereto.

Example

(Examples 1 to 16 and Comparative Examples 1 to 7)

1. Manufacture of silicon-based active material

a) Silicon-based compound particles prepared in advance (LiH) containing SiO _x (0<x≤2) and lithium were put into a sealed container and thoroughly mixed in a mixer. Silicon-based compound particles and LiH were added at a Li / Si molar ratio of 0.5 to 1.0, and a shaker capable of biaxial motion was used as a mixer with a ball, and the mixing speed and mixing time at this time are shown in Table 1 below.

b) Subsequently, the mixed powder was filtered using a 25-500 μm sieve, and then placed in an alumina crucible. An aluminum crucible was subjected to preliminary heat treatment in a furnace under a nitrogen gas atmosphere. Preliminary heat treatment temperature and time are shown in Table 1 below.

c) Subsequently, the temperature of the furnace was raised and heat treatment was performed for 1 to 12 hours. Heat treatment temperatures are shown in Table 1 below. Thereafter, the heat-treated powder was recovered and pulverized in a mortar to prepare a silicon-based active material including silicon oxide (SiO _x ) and lithium silicate (Li ₂ Si ₂ O ₅ , Li ₂ SiO _{3 ,} etc.).

2. Cathode fabrication

23% by weight of the silicon-based active material, 71.5% by weight of artificial graphite, 0.5% by weight of conductive material (CNT), 2% by weight of carboxymethyl cellulose, and 3% by weight of styrene butadiene rubber (SBR) in distilled water was mixed to prepare a slurry, coated on a Cu foil, and vacuum dried at 80 to 160° C. for 1 to 24 hours to prepare a negative electrode.

3. Half-cell manufacturing

A coin cell (CR2016) was assembled by using the manufactured negative electrode and lithium metal as a counter electrode, interposing a PE separator between the negative electrode and the counter electrode, and then injecting an electrolyte solution. A half-cell was manufactured by resting the assembled coin cell at room temperature for 3 to 24 hours. At this time, the electrolyte solution was a mixture of lithium salt 1.0M LiPF ₆ in an organic solvent (EC:EMC = 3:7 Vol%) and an electrolyte additive FEC 2 Vol%.

a) mixing process b) preliminary heat treatment process c) heat treatment process mixing speed
[rpm] mixing time
[min] heat treatment temperature
[℃] heat treatment time
[min] heat treatment temperature
[℃] Example 1 500 120 400 120 750 Example 2 500 30 400 60 750 Example 3 300 60 400 120 600 Example 4 300 60 400 60 600 Example 5 300 60 400 30 600 Example 6 500 80 300 120 750 Example 7 500 30 300 120 750 Example 8 300 120 300 30 600 Example 9 300 120 300 120 600 Example 10 300 80 300 60 600 Example 11 300 80 300 120 600 Example 12 500 120 150 30 750 Example 13 500 60 150 60 750 Example 14 300 30 150 30 750 Example 15 300 30 150 60 750 Example 16 300 120 150 120 600 Comparative Example 1 500 60 400 30 900 Comparative Example 2 900 60 400 30 900 Comparative Example 3 100 120 150 30 600 Comparative Example 4 100 120 400 120 600 Comparative Example 5 900 60 400 120 750 Comparative Example 6 500 120 500 30 750 Comparative Example 7 900 120 500 120 900

evaluation example

(Assessment Methods)

* Structural analysis of negative electrode active material particles through Raman spectrum analysis

Raman spectrum analysis was performed on the fabricated cathode using an Invia confocal Raman microscope manufactured by Renishaw (UK). The laser wavelength was 532 nm, the lens magnification was 50 times, and the particle surface was measured 8 times in the range of 67 to 1800 cm ^-1 in static mode, and the average value was applied.

The Raman spectrum peak intensity ratio 'Ia/Ib' in Table 2 is '2. The negative electrode prepared for the initial efficiency evaluation in 'manufacture of negative electrode' was measured as a target, and a plurality of silicon-based active material particles in the negative electrode active material layer were measured as a target. Here, Ia is the peak intensity of 515±15cm ^-1 in the Raman spectrum, and Ib is the peak intensity of 470±30cm ^-1 in the Raman spectrum.

In Table 2, 'A', 'B', and 'C' were measured for each of the prepared negative electrodes. 'A' is the average value of the Raman spectrum peak intensity ratio Ia/Ib for 50 randomly selected silicon-based active material particles in the negative electrode active material layer. 'B' is the average value of the remaining values excluding the top 10 values and the bottom 10 values for each Raman spectrum peak intensity ratio Ia/Ib value for the 50 silicon-based active material particles, and 'C' is the average value of the 50 For each Raman spectrum peak intensity ratio Ia/Ib value for the silicon-based active material particles, it is an average value of the remaining values excluding the top 5 values and the bottom 5 values.

* Electrochemical characteristics evaluation (life characteristics)

In order to evaluate the electrochemical characteristics of the negative electrode, half-cells were prepared and life characteristics were measured. The prepared half-cell was charged with a constant current at room temperature (25°C) at a current of 0.1C rate until the voltage reached 0.01V (vs. Li/Li ⁺ ), followed by constant current charging while maintaining 0.01V in constant voltage mode. It was cut-off at a current of and charged with a constant voltage. It was discharged with a constant current of 0.1C rate until the voltage reached 1.5V (vs.Li/Li ⁺ ). The charging and discharging were performed as one cycle, and then, in order to check the life characteristics, 50 cycles were performed by changing the applied current to 0.5C during charging and discharging, and a 10-minute rest period was placed between the cycles. To confirm the life characteristics, the life characteristics were measured using the 50 cycle discharge capacity as the capacity retention rate (%) for the 2 cycle discharge capacity, and the results are summarized in Table 2 below.

Ia/Ib Deviation capacity retention rate
[%, @50 cycle] A C B A-C A-B Example 1 4.58 4.38 4.40 0.20 0.18 73 Example 2 3.09 2.85 2.86 0.24 0.23 71 Example 3 1.24 0.96 0.62 0.28 0.62 83 Example 4 1.00 0.68 0.61 0.32 0.39 86 Example 5 0.94 0.54 0.44 0.40 0.50 94 Example 6 2.42 2.22 2.18 0.20 0.24 80 Example 7 2.14 2.06 2.05 0.08 0.09 82 Example 8 0.78 0.66 0.61 0.12 0.17 91 Example 9 0.61 0.51 0.49 0.10 0.12 92 Example 10 0.59 0.48 0.43 0.11 0.16 95 Example 11 0.41 0.38 0.38 0.03 0.03 97 Example 12 2.90 2.78 2.79 0.12 0.11 74 Example 13 2.5 2.47 2.47 0.03 0.03 90 Example 14 1.80 1.15 0.99 0.65 0.81 77 Example 15 1.41 1.05 0.87 0.36 0.54 90 Example 16 1.30 0.83 0.58 0.48 0.73 90 Comparative Example 1 8.99 7.55 7.01 1.44 1.98 48 Comparative Example 2 9.12 8.61 6.40 0.51 2.72 47 Comparative Example 3 7.18 6.44 6.05 0.74 1.13 53 Comparative Example 4 7.64 7.12 5.49 0.52 2.15 57 Comparative Example 5 7.89 6.52 5.70 1.37 2.19 58 Comparative Example 6 8.78 7.33 5.22 1.45 3.56 45 Comparative Example 7 13.02 9.48 8.26 3.54 4.76 36

From Tables 1 and 2, it can be seen that the examples of this embodiment have very excellent life characteristics compared to the comparative examples.

Referring to Comparative Examples 1 and 2, when the heat treatment was performed at a high temperature of 900 ° C. or higher, the crystal size increased and excessively grown rather than additionally generated c-Si seeds, so that a uniform all-lithium reaction did not appear.

From Comparative Examples 3 and 4, when the mixing speed is too low and substantially sufficient mixing is not performed, uniform mixing is difficult even after mixing for a long time, and it can be seen that a non-uniform mixture is produced even if pretreatment (preliminary heat treatment) is performed thereafter. there was. On the other hand, in Comparative Examples 5 and 7, the mixing speed (900 rpm) was relatively high, so a chemical reaction occurred due to kinetic energy, making it difficult to control the uniform lithium reaction.

Referring to Comparative Examples 6 and 7, when the pretreatment (preliminary heat treatment) temperature is excessive at 500 ° C or more, the reaction between Li and SiO _x has already started during the preliminary heat treatment, making it difficult to control the entire lithium reaction, and as the preliminary heat treatment time increases, (more than 120 minutes) It was found that a uniform reaction was difficult.

In summary, the heat treatment temperature is preferably 800° C. or lower to improve phase uniformity. In addition, under harsh conditions (increase in mixing speed, increase in mixing time, increase in pretreatment temperature, increase in pretreatment time, increase in heat treatment temperature), the crystallinity of the silicon-based active material increases and the initial efficiency may be slightly improved, but the uniformity of the crystalline silicon-based active material particles Failure to ensure size distribution leads to rapid life deterioration.

Although the embodiments of this embodiment have been described above, this embodiment is not limited to the above embodiments and can be manufactured in a variety of different forms, and those skilled in the art to which this disclosure belongs are essential to this embodiment. It will be appreciated that it may be embodied in other specific forms without changing its characteristics. Therefore, the embodiments described above should be understood as illustrative in all respects and not limiting.

Claims (12)

current collector; and a negative active material layer disposed on the current collector and including a plurality of silicon-based active material particles,
A negative electrode for a secondary battery satisfying the following relational expression 1:
[Relationship 1] 0.01 ≤ AB ≤ 0.81
In the relational expression 1, A is the average value of the Raman spectrum peak intensity ratio Ia/Ib for 50 randomly selected silicon-based active material particles in the negative electrode active material layer, and B is each value for each of the 50 silicon-based active material particles. With respect to the Raman spectrum peak intensity ratio Ia/Ib value, the average value of the remaining values excluding the top 10 values and the bottom 10 values, Ia is the peak intensity at 515±15cm ^-1 , and the Ib is 470±30cm ^-1 is the peak intensity at According to claim 1,
The silicon-based active material is at least one selected from the group consisting of silicon, silicon oxide (SiO _x , 0<x≤2), silicon alloy, and silicon / carbon composite negative electrode for a secondary battery. According to claim 1,
The silicon-based active material is a negative electrode for a secondary battery comprising a metal pre-treated silicon oxide. According to claim 3,
The metal pretreated silicon oxide is silicon oxide (SiO _x , 0<x≤2); and a metal silicate (M _a Si _b O _c , M is Li or Mg, and 1≤a located on at least a part of the silicon oxide) ≤6, 1≤b<3, 0<c≤7); a negative electrode for a secondary battery comprising a. According to claim 3,
The metal pretreated silicon oxide is a negative electrode for a secondary battery comprising 40 to 95% by weight of a metal silicate based on the total weight. According to claim 1,
A negative electrode for a secondary battery further satisfying the following relational expression 2:
[Relationship 2] 0.01 ≤ AC ≤ 0.65
In the relational expression 2, A is the average value of the Raman spectrum peak intensity ratio Ia/Ib for 50 randomly selected silicon-based active material particles in the negative electrode active material layer, and C is the average value for each of the 50 silicon-based active material particles. With respect to the Raman spectrum peak intensity ratio Ia/Ib value, the average value of the remaining values excluding the top 5 values and the bottom 5 values, wherein Ia is the peak intensity at 515±15cm ^-1 , and the Ib is 470±30cm ^-1 is the peak intensity at According to claim 6,
A negative electrode for a secondary battery that satisfies at least one selected from the following relations 3a, 3b and 3c:
[Relationship 3a] 0.3 ≤ A ≤ 8.50
[Relationship 3b] 0.3 ≤ B ≤ 7.71
[Relationship 3c] 0.3 ≤ C ≤ 7.91
In the relations 3a, 3b, and 3c, A is the average value of the Raman spectrum peak intensity ratio Ia/Ib for 50 randomly selected silicon-based active material particles in the negative electrode active material layer, and B is the average value of the 50 silicon-based active material particles For each Raman spectrum peak intensity ratio Ia / Ib value for , the average value of the remaining values excluding the top 10 values and the bottom 10 values, C is the peak intensity of each Raman spectrum for the 50 silicon-based active material particles For the ratio Ia/Ib value, it is the average value of the remaining values excluding the top 5 values and the bottom 5 values. According to claim 1,
The negative electrode active material layer includes 10% by weight or more of the silicon-based active material particles based on the total weight of the negative electrode active material. a) mixing the silicon compound particles and the metal precursor at 200 to 800 rpm;
b) preliminarily heat-treating the product of step a) at 100° C. or more and less than 500° C.; and
c) a step of heat-treating the product of step b) at 500 to 800 ° C; to prepare a negative electrode active material, including a method for producing a negative electrode for a secondary battery. According to claim 9,
Before step a) above
p1) a step of mixing Si powder and SiO ₂ powder and heat-treating the powder at less than 900° C.; further comprising preparing the silicon compound particles, a method for manufacturing a negative electrode for a secondary battery. According to claim 9,
Before step a) above
p1) mixing Si powder and SiO ₂ powder and heat-treating at less than 900°C; and
p2) heat-treating the product of step p1) at less than 800° C. in the presence of a hydrocarbon gas; the method of manufacturing a negative electrode for a secondary battery, further comprising preparing the silicon compound particles. A secondary battery comprising the negative electrode of any one of claims 1 to 8.