KR20250042660A - Negative Electrode Active Material for Secondary Battery - Google Patents

Abstract

A secondary battery negative electrode material according to the present invention is a particle-shaped material including a base material containing silicon (Si) based on elemental components and a surface layer containing carbon (C) positioned on the base material, and having a curvature ratio AR defined by (1-Con)/Con 100 of 1.00 or less, wherein Con is a curvature obtained by dividing the perimeter of a convex outer surface of a negative electrode particle (convex perimeter) by the actual perimeter (perimeter) of the negative electrode particle.

Description

Negative Electrode Active Material for Secondary Battery}

The present invention relates to a negative electrode material for a secondary battery, and more specifically, to a silicon-based negative electrode material for a lithium secondary battery.

Demand for long-life, high-energy-density, and high-power-density secondary batteries continues to grow across a variety of industries, including electronics, electric/hybrid vehicles, and aerospace/drones.

The most representative commercially used negative electrode material is graphite, but the theoretical maximum capacity of graphite is only 372 mAh/g. Accordingly, in order to implement high-energy density secondary batteries, research is continuously being conducted to use chalcogens such as sulfur (maximum capacity 1675 mAh/g), silicon such as silicon (maximum capacity 4200 mAh/g) or silicon oxide (maximum capacity 1500 mAh/g), and transition metal oxides as secondary battery negative electrode materials, and among various materials, silicon-based negative electrode materials are receiving the most attention.

However, in the case of silicon-based negative electrode materials, there is a problem that battery characteristics rapidly deteriorate due to insulation, particle detachment, and increased contact resistance as large volume changes occur with repeated charge/discharge cycling, and there is a problem that lithium is lost due to irreversible products such as lithium silicate or lithium oxide, and the initial charge/discharge efficiency rapidly decreases.

To solve the problems of these silicon-based cathode materials, technologies have been proposed, such as nano-forming silicon into wires and composites with carbon materials, doping silicon oxide with a different metal to form a composite oxide phase, or pre-lithiating silicon oxide.

However, while the development of technology related to silicon-based cathode materials is mainly focused on nano-fabrication, composites, and composition control, there has been little research on the influence of the morphology of silicon-based cathode materials on their physical properties.

U.S. Patent Publication No. 2020-0176758

According to one embodiment of the present invention, a negative electrode material for a secondary battery having improved capacity retention characteristics is provided.

The tasks of the present invention are not limited to the above-described contents. Those with ordinary knowledge in the technical field to which the present invention belongs will have no difficulty in understanding additional tasks of the present invention from the overall contents of this specification.

According to one embodiment of the present invention, a negative electrode material for a secondary battery is a particle-shaped material including a base material containing silicon (Si) based on elemental components and a surface layer located on the base material and containing carbon (C), and has a bending ratio of 1.00 or less calculated by the following equation 1.

(Formula 1)

In Equation 1, AR is the curvature ratio, and Con is the curvature calculated by dividing the perimeter of the convex outer surface of the negative electrode particle (convex perimeter) by the actual perimeter of the negative electrode particle (perimeter).

In one specific example, the bending ratio may be 0.55 or less.

In one specific example, the cathode material may satisfy one or more of the following I) to II).

I) Standard deviation value of the above curvature ≤ 0.050

II) The proportion of particles having a curvature of 0.9×Con or higher is 90% or more.

In one specific example, the sphericity of the negative electrode material may be 0.55 or more.

In one specific example, the cathode material may have an angular shape.

In one specific example, the average particle diameter (D ₅₀ ) of the negative electrode material may be 1 ㎛ to 30 ㎛.

In one specific example, the surface layer may include an amorphous carbon layer.

In one specific example, the thickness of the surface layer may be 1 to 50 nm.

According to another embodiment of the present invention, a secondary battery negative electrode material is a particulate silicon-based negative electrode material, and satisfies Equation 2 during a charge/discharge test under the following charge/discharge cycle conditions using a half-cell in which a counter electrode is a metal lithium foil.

Charge/discharge cycle conditions: CC/CV, cut-off voltage 0.005V~1.000V, 0.5C-rate

(Formula 2)

95 % < C _j /C ₁ *100

In Equation 2, C ₁ is the discharge capacity (mAh/g) in the first charge/discharge cycle, C _j is the discharge capacity in the jth charge/discharge cycle, and j is an arbitrary natural number greater than or equal to 10 and less than or equal to 80.

In one specific example of the negative electrode material for the secondary battery described above, the base material may include silicon, silicon oxide, silicon nitride, silicon sulfide, silicon carbide, silicon alloy, a mixture thereof, or a composite thereof.

In one specific example of the negative electrode material for the secondary battery described above, the base material may further contain a doping element (D) selected from the group consisting of alkali metals, alkaline earth metals, and transition metals.

In one specific example of the negative electrode material for the secondary battery described above, the base material may include, based on elemental components, a matrix containing silicon (Si), a doping element (D), and oxygen (O); and silicon nanoparticles dispersed and incorporated in the matrix.

A negative electrode for a secondary battery according to one embodiment of the present invention contains the negative electrode material for a secondary battery described above.

A secondary battery according to one embodiment of the present invention includes the negative electrode described above.

The cathode material according to the invention is a particulate cathode material including a silicon-based matrix and a carbon surface layer, and may have improved electrochemical properties due to its morphology.

The various advantageous and beneficial advantages and effects of the present invention are not limited to the above-described contents, and will be more easily understood in the process of explaining specific embodiments of the present invention.

Figure 1 is a scanning electron microscope photograph observing the negative electrode material manufactured in the example.
Figure 2 is a transmission electron microscope photograph of the surface layer of the negative electrode material manufactured in the example.
Figure 3 is a diagram showing the capacity retention rate according to the charge/discharge cycle of the negative electrode materials manufactured in the examples and comparative examples.

Hereinafter, preferred embodiments of the present invention will be described with reference to the attached drawings. However, the embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

Furthermore, the embodiments of the present invention are provided to more completely explain the present invention to a person having average knowledge in the art.

In describing the embodiments of the present invention, if it is determined that a detailed description of a known technology related to the present invention may unnecessarily obscure the gist of the present invention, the detailed description will be omitted. In addition, the terms described below are terms defined in consideration of their functions in the present invention, and these may vary depending on the intention or custom of the user or operator. Therefore, the definitions should be made based on the contents throughout this specification. The terms used in the detailed description are only for the purpose of describing the embodiments of the present invention, and should never be limited. Unless clearly used otherwise, the singular form includes the plural meaning.

In this description, expressions such as "including" or "having" are intended to refer to certain features, numbers, steps, operations, elements, portions or combinations thereof, and should not be construed to exclude the presence or possibility of one or more other features, numbers, steps, operations, elements, portions or combinations thereof other than those described.

Unless otherwise specifically stated in the specification of the present invention, the % unit means weight %.

Throughout the specification, when we say that a part is 'connected' to another part, this includes not only cases where it is 'directly connected', but also cases where it is 'indirectly connected' with other elements in between.

Below, the present invention will be described in detail through each embodiment or example of the present invention. It should be noted that each embodiment or example described in this specification is not limited to only one embodiment or example, and combinations with other embodiments or examples are also possible. Therefore, the citation of a claim in the scope of the patent claims is only an example of an embodiment, and the technical idea of the present invention should not be interpreted only as a combination with the cited claim, and the combination with various claims is also included in the scope of the technical idea of the present invention.

The present applicant has confirmed that in a particulate silicon-based negative electrode material, the electrochemical properties of the negative electrode material are very sensitive and greatly affected by the morphology of the particle, especially the degree of curvature itself. Based on this, the applicant has intensified the research and established a morphology that can greatly improve the electrochemical properties of the negative electrode material, thereby completing the present invention.

According to one aspect (Aspect I) of the present disclosure, a negative electrode material for a secondary battery is a particle-shaped material including a base material containing silicon (Si) based on elemental components and a surface layer containing carbon (C) positioned on the base material, and has a bending ratio of 1.00 or less calculated by the following Equation 1.

(Formula 1)

In Equation 1, AR is the tortuosity, and Con is the tortuosity, which is the ratio of the perimeter of the convex outer surface of the cathode particle (convex perimeter, L _CP ) to the actual perimeter of the cathode particle (perimeter, L _P ) (L _CP /L _P ).

As is known, the convex perimeter of the convex surface is defined as the length of an elastic band that surrounds the outline of the particle in a 2D image captured by a 3D particle to be measured, assuming that the elastic band is a virtual elastic band that stretches, and the actual perimeter means the perimeter length of the actual particle in the 2D image captured by the 2D image. In this case, it goes without saying that the captured image used to calculate the convex perimeter of the convex surface and the captured image used to calculate the actual perimeter may be the same image.

The value of the tortuosity can be a real number between 0 and 1, and the closer the tortuosity value is to 0, the more unevenness and/or the particle contour has a large step difference between the unevenness. The tortuosity is a value defined by the tortuosity according to Equation 1, and means the ratio of the difference between the actual circumference and the circumference of the convex outer surface of the particle-shaped negative electrode material to the circumference of the convex outer surface. Accordingly, the closer the actual circumference and the circumference of the convex outer surface are to each other, the closer the tortuosity value is to 0, and the larger the difference between the actual circumference and the circumference of the convex outer surface is, the larger the tortuosity value is.

The curvature (including the average value and distribution) of the particulate negative electrode material may differ from the curvature (including the average value and distribution) of the parent material itself, and even in the curvature of the same parent material, the negative electrode material may have a wide range of curvatures (see the comparative examples and examples described below). In this case, the curvature of the parent material itself means the average curvature of the powder material used as the parent material before the surface layer is formed.

The cathode material may be an aggregate of particles (hereinafter, also simply referred to as 'particles') including a base material and a surface layer.

An aggregate of particles may mean a 'group' of particles, and at this time, the 'group' means that it has a size that the electrochemical characteristics of the aggregate are not significantly changed by at least the number of particles forming the 'group'. In terms of implementing constant and stable electrochemical characteristics, an aggregate of particles may mean a group of particles having a weight of at least 1 g or more, specifically 10 g or more, more specifically 50 g or more, and even more specifically at least 100 g or more.

In experimental terms, a collection of particles can mean a 'group' of particles, and a 'group' of particles can mean a group of particles that is of a size that allows reliable measurements (such as average size, curvature values) to be obtained, i.e., a size that does not significantly change the measurements depending on the number of particles forming the 'group'.

The value of the curvature (Con in Equation 1) may be a statistical average value obtained by securing the curvature of each of at least 100 particles, typically 500 particles, and practically 1000 particles or more, and averaging the secured curvature values.

Experimentally, the curvature can be measured using commercial instruments commonly used for measuring curvature. An example of a commercial instrument is the morphologi 4 from Malvern Panalytical.

In the negative electrode material for secondary batteries, the flexure ratio is 1.00 or less. When the negative electrode material has a flexure ratio of 1.00 or less, the negative electrode material can exhibit excellent electrochemical properties, specifically excellent capacity retention properties.

Through preliminary experiments, it was confirmed that even if the negative electrode material has substantially the same composition and substantially the same microstructure, the capacity retention characteristics change significantly even with a small change in the bending ratio value.

For example, even when the negative electrode material has substantially the same composition and substantially the same microstructure and has a curvature ratio of 0.8 and 1.2, and the difference in the curvature ratios is only 0.4, the negative electrode material having a curvature ratio of 1.2 exhibits poor electrochemical characteristics, such as a discharge capacity retention ratio of less than 50% at the 100th charge/discharge cycle. On the other hand, the negative electrode material having a curvature ratio of 0.8 can exhibit an improved discharge capacity retention ratio of more than 80% at the 100th charge/discharge cycle.

As described above, the flexure ratio of the negative electrode material may be 1.00 or less, and specifically, 0.90 or less, 0.80 or less, 0.70 or less, 0.65 or less, 0.60 or less, 0.55 or less, 0.50 or less, 0.45 or less, 0.40 or less, or 0.35 or less. In practice, the flexure ratio of the negative electrode material may be 0.10 or more, more substantially 0.15 or more, and even more substantially 0.20 or more.

In an advantageous example, the flexure ratio of the negative electrode material may be 0.55 or less. A negative electrode material having a flexure ratio of 0.55 or less may exhibit a discharge capacity retention rate of 95% or more at the 50th charge/discharge cycle.

In a more advantageous example, the flexure ratio of the negative electrode material may be 0.35 or less. A negative electrode material having a flexure ratio of 0.35 or less may exhibit a discharge capacity retention ratio of 95% or more, specifically 98% or more, more specifically 100% or more, and even more specifically more than 100% at the 100th charge/discharge cycle.

In one specific example, the negative electrode material may satisfy one or more of the following conditions I) to II). The following conditions I) and II) are related to the tortuosity distribution of the negative electrode material, and the tortuosity distribution may correspond to a distribution diagram that has the tortuosity as a variable (x-axis) and represents the ratio (%) of the number of particles having the corresponding tortuosity among all particles (y-axis).

Condition I) Standard deviation value of curvature ≤ 0.050

Condition II) The proportion of particles with a curvature greater than or equal to 0.90× curvature (Con) is 90% or more.

The standard deviation value of the curvature (Con) can be less than 0.050. When the standard deviation of the curvature is small as described above, the fraction of particles with low curvature decreases, and a significant influence by particles with low curvature can be excluded.

In order to prevent adverse effects by particles having a small degree of curvature (high degree of curvature), the standard deviation value of the degree of curvature (Con) may be 0.050 or less, 0.040 or less, 0.035 or less, 0.030 or less, 0.025 or less, 0.020 or less, or 0.015 or less. The standard deviation value of the degree of curvature may be substantially 0.001 or more, or 0.005 or more, but is not limited thereto.

Condition II) In addition, it is a condition that can prevent the adverse effects caused by particles with small curvature. If Condition II) is satisfied, even if particles with small curvature exist, it is possible to prevent particles with small curvature from having a significant effect on the overall electrochemical characteristics of the negative electrode material.

Specifically, the negative electrode material may have a proportion of particles having a curvature of 0.90× the curvature (Con) or greater, more specifically, particles having a curvature of 0.91× the curvature (Con) or greater, 0.92× the curvature (Con) or greater, 0.93× the curvature (Con) or greater, 0.94× the curvature (Con) or greater, 0.95× the curvature (Con) or greater, 0.96× the curvature (Con) or greater, or 0.97× the curvature (Con) or greater of 90% or greater.

The cathode material can satisfy condition I), condition II), or both condition I) and II).

Furthermore, when a negative electrode material having a bending ratio of 0.55 or less satisfies condition I) and/or condition II), the discharge capacity retention characteristics can be improved to the extent that the negative electrode material can exhibit a discharge capacity greater than the discharge capacity (C1) in the first charge/discharge cycle in the 50th charge/discharge cycle, and together with or independently of this, the negative electrode material can exhibit a discharge capacity greater than the discharge capacity (C1) in the first charge/discharge cycle in the 20th charge/discharge cycle.

In addition, when a cathode material having a flexure ratio of 0.35 or less satisfies at least Condition I) and/or Condition II), it can exhibit a discharge capacity greater than the discharge capacity (C1) in the first charge/discharge cycle in the 10th to 80th charge/discharge cycle range (entire range).

By virtue of the morphological characteristics based on the bending rate, the negative electrode material can exhibit significantly improved charge/discharge cycle characteristics.

In terms of electrochemical properties, the negative electrode material for a secondary battery according to another aspect (Aspect II) of the present disclosure is a particulate silicon-based negative electrode material, which satisfies Equation 2 during a charge/discharge test under the following charge/discharge cycle conditions using a half-cell having a counter electrode of a metal lithium foil. At this time, the particulate silicon-based negative electrode material may mean a particle including a base material containing silicon (Si) based on elemental components and a surface layer located on the base material and containing carbon (C).

Charge/discharge cycle conditions: CC/CV, cut-off voltage 0.005V~1.000V, 0.05C-rate

(Formula 2)

95 % < Cj/C1*100

In Equation 2, C1 is the discharge capacity (mAh/g) in the first charge/discharge cycle, Cj is the discharge capacity in the jth charge/discharge cycle, and j is any natural number greater than or equal to 10 and less than or equal to 80. Since j is any natural number greater than or equal to 10 and less than or equal to 80, Equation 2 means that the discharge capacity in the 10th to 80th charge/discharge cycle range is greater than 95% of the initial discharge capacity C1.

Specifically, j can be any natural number greater than or equal to 10 and less than or equal to 90, more specifically, j can be any natural number greater than or equal to 10 and less than or equal to 100. This means that the battery can exhibit a large discharge capacity of 95% or greater than or equal to the initial discharge capacity C1 in the charge/discharge cycle range from the 10th to the 90th, more specifically from the 10th to the 100th. More specifically, Cj/C1*100 can be 98% or greater, more specifically, Cj/C1*100 can be 100% or greater, and can be substantially 120% or less, and even more substantially 110% or less.

A half-cell for examining the electrochemical characteristics of a negative electrode material may be a half-cell in which a formation process has been performed. The half-cell may be a cell equipped with: an anode including a negative electrode collector and a negative electrode active material layer positioned on at least one surface of the current collector and including the negative electrode material according to one embodiment; a counter electrode being a metal lithium foil; a separator interposed between the negative electrode and the counter electrode; and an electrolyte in which LiPF ₆ is dissolved at a concentration of 1 M in a mixed solvent in which ethylene carbonate and diethyl carbonate are mixed at a volume ratio of 1:1. The electrochemical characteristics of the half-cell may be measured at room temperature. The chemical reaction process may include a first process in which charge and discharge are performed under the conditions of CC/CV, cut-off voltage of 0.005 V to 1,500 V, and 0.1 C-rate, and a second process in which charge and discharge are performed under the conditions of CC/CV, cut-off voltage of 0.005 V to 1,000 V, and 0.1 C-rate. However, it should be understood that the present invention is not limited by the chemical reaction process conditions of a test cell (half cell), and a chemical reaction process that is typically performed in a cell used to test the electrochemical properties of a conventional negative electrode material is sufficient. More detailed configurations of half cells and measurement conditions, etc. are provided in the examples.

Hereinafter, unless specifically limited to one aspect, the following description applies to all aspects described above.

In one specific example, the cathode material may be a particle having an edge, i.e., an angular shape. In such angular particles, the electrochemical properties may be sensitively changed by the bending rate.

The angular shape may be a shape in which at least two surfaces contact each other and form a corner when observing the shape of the negative electrode material using a scanning electron microscope. The two surfaces forming the corner may be independently flat or curved. Although not particularly limited, in the angular shape, at least one of the two surfaces forming the corner within the particle may be a curved surface. The curved surface may be concave, convex, or a surface having both concave and convex regions. In addition, the curved surface may have micro-roughnesses such as a hill and valley structure or a step structure, and the curvature of the surface may be formed by these micro-roughnesses. The other of the two surfaces forming the corner may be a curved surface or a flat surface. When observing the shape of the negative electrode material, the magnification of the scanning electron microscope may be 3000 to 8000 times, but is not limited thereto.

In terms of the manufacturing method, the angular-shaped particles may be particles obtained by crushing, and at least one of the two faces forming the edge may be a fracture surface.

Even if the curvature of an angular shape and the curvature of a non-angular shape have the same curvature value, their effects on electrochemical characteristics may be different. For example, when forming an anode active material layer with an anode material, even if the particles have the same curvature value, the space-filling structure, the degree of contact with adjacent elements, and the surface area per unit volume may be different due to the shape difference between a spherical shape and an angular shape.

In order for the electrochemical properties to be strongly improved by the above-described bending rate, the bending rate may be a bending rate of particles having an angular shape.

In one specific example, the average particle diameter (D ₅₀ ) of the negative electrode material may be 1 ㎛ to 30 ㎛. The average particle diameter may correspond to a median diameter (D ₅₀ ) based on a cumulative volume. The cumulative volume-based D ₅₀ refers to a particle diameter at a point where the cumulative volume % is 50 vol % in a distribution curve (cumulative distribution curve) accumulated in order of particle diameters. Experimentally, a cumulative distribution curve including D ₅₀ can be obtained by a conventional particle size analyzer using a laser diffraction method or a dynamic light scattering method.

The _D50 of the negative electrode material may be 1 ㎛ to 30 ㎛, specifically 2 ㎛ to 20 ㎛, 2 ㎛ to 15 ㎛, 2 ㎛ to 10 ㎛, or 3 ㎛ to 8 ㎛. When the negative electrode material having the above-described bending rate has such a _D50 value, stable electrical conductivity is secured when the negative electrode active material layer is formed, while reducing the diffusion time of metal ions (e.g., lithium ions) involved in charge and discharge, thereby exhibiting more improved and stable charge and discharge cycle characteristics.

In one specific example, the negative electrode material may be a primary particle, a secondary particle, or a mixture thereof. That is, the negative electrode material may be primary particles, secondary particles, or particles in which primary particles and secondary particles are mixed. The primary particle may mean a single particle, and the secondary particle may mean an aggregate in which two or more particles are aggregated. A case where two or more parent materials forming the aggregate are in direct contact with each other to form an interface, or a case where a carbon component of a surface layer exists between two or more parent materials forming the aggregate, as described below, may be classified as an aggregate.

In one specific example, the sphericity of the negative electrode material may be 0.55 or more, specifically 0.55 to 0.95, more specifically 0.70 to 0.93, and even more specifically 0.80 to 0.90. The sphericity may be defined as a ratio of a circumference of a circle having the same area as a projected image (2D image) of the negative electrode material, which is a three-dimensional particle, divided by the perimeter (perimeter length) of the projected image. A negative electrode material having a high sphericity is advantageous for high densification, enables stable and homogeneous contact with the electrolyte, prevents stress caused by volume change accompanying a battery charge/discharge reaction from being locally concentrated, and exhibits improved durability.

In one specific embodiment, a surface layer containing carbon (C) may be positioned on the substrate, and the surface layer may cover part or all of the substrate surface. In practice, the surface layer may completely surround the substrate so that the substrate surface is not exposed to the surface of the cathode material (particle). At this time, the surface layer may surround one or more substrates. When the surface layer surrounds one substrate, the particle may be considered a primary particle, and when the surface layer surrounds two or more substrates, the particle may be considered a secondary particle.

The surface layer containing carbon may include a carbon layer. The parent material may be wrapped by the carbon layer, and at this time, the parent material and the carbon layer may be in contact with each other. The carbon layer may include an amorphous carbon layer, a crystalline carbon layer, or a composite layer in which amorphous carbon and crystalline carbon are mixed. The surface layer may include a single carbon layer or a carbon multilayer having a multilayer structure in which carbon layers having different physical properties are laminated.

For example, the carbon layer may be an amorphous carbon layer. In order to stably wrap the surface of the parent material while minimizing the resistance component due to the amorphous carbon layer, the thickness of the amorphous carbon layer may be 1 to 50 nm, specifically 1 to 40 nm, and more specifically 4 to 30 nm. Experimentally, the thickness of the amorphous carbon layer may be obtained by randomly measuring the thickness of the carbon layer at 10 or more locations, or practically 10 to 20 locations, using an image obtained through a microstructure observation device such as a transmission electron microscope (TEM) or a scanning transmission electron microscope (STEM), and taking the average value.

In one specific example, the surface layer may be derived from a liquid (room temperature liquid) carbon precursor. Specifically, the surface layer may be derived from a liquid carbon precursor having a surface tension of 20 to 60 dyne/cm, specifically, a surface tension of 25 to 50 dyne/cm. A liquid having such a surface tension is advantageous in that it can stably wrap the parent material with a decrease in surface energy as a driving force. As described above, by forming a surface layer on the parent material by mixing the liquid carbon precursor and the particulate parent material, a surface layer that completely wraps the parent material can be easily formed. In addition, during heat treatment for carbonization, the degree of curvature of the negative electrode material can be controlled through the density of the mixture including the liquid carbon precursor and the parent material.

Examples of liquid carbon precursors having a surface tension of 20 to 60 dyne/cm include coal tar, pyrolyzed fuel oil (PFO), etc., and coal tar is practically the example. However, the liquid carbon precursor is not limited to a liquid carbon precursor having a surface tension of 20 to 60 dyne/cm, and may be a liquid substance commonly used to form a carbon surface layer on a conventional silicon-based negative electrode active material.

The content of the surface layer contained in the negative electrode material may be 0.10 to 3.00 wt%, specifically 0.15 to 2.00 wt%, and more specifically 0.15 to 1.70 wt%, based on the total weight of the negative electrode material.

In one specific example, the parent material may be a parent material containing silicon based on elemental composition, or alternatively, a silicon-based parent material.

The silicon-based matrix may include silicon, silicon oxide, a composite oxide between silicon and a heterogeneous element (also called silicon composite oxide), silicon nitride, silicon sulfide, silicon carbide, a silicon alloy, a mixture thereof, or a composite thereof. At this time, specific examples of the composite include a composite between silicon and silicon oxide, a composite between silicon, silicon oxide, and silicon composite oxide, a composite between silicon carbide and silicon, etc. The silicon alloy may include an alloy (including an intermetallic compound) between silicon and a heterogeneous metal (for example, at least one selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, and Mg). The silicon composite oxide, which is a composite oxide between silicon and a heterogeneous element, may include a composite oxide between silicon and at least one metal selected from the group consisting of an alkali metal, an alkaline earth metal, and a post-transition metal. At this time, when the silicon-based matrix is a composite, it should not be interpreted as being limited to a composite between only materials containing silicon. For example, when the parent material is a composite, the composite may include a silicon-carbon composite, and the silicon-carbon composite may include a composite between metal silicon and a carbon component selected from the group consisting of graphitic carbon, non-graphitic carbon, and carbon nanostructures such as graphene or carbon nanotubes.

In one specific embodiment, the parent material (silicon-based parent material) may contain a doping element (D) selected from the group consisting of silicon, oxygen, alkali metals, alkaline earth metals, and post-transition metals, based on the elemental components. The silicon may include a silicon component in an elemental silicon state and a silicon component in an oxide state, and the silicon component in an oxide state may include an oxide state of silicon alone, a composite oxide state of silicon and the doping element, or all of them. The doping element may include a doping element component in an oxide state, and the doping element in an oxide state may include an oxide state of the doping element alone, a composite oxide state of silicon and the doping element, or all of them.

Based on the compound composition, the parent material (silicon-based parent material) may contain silicon oxide, a composite oxide of a doping element and silicon, or a mixture thereof, and may also contain elemental (metallic) silicon (Si).

The silicon oxide can satisfy SiO _x (x is a real number from 0.1 to 2, specifically, a real number from 0.5 to 2), and can include a first silicon oxide and a second silicon oxide having different x. For example, the silicon oxide contained in the base material can include a first silicon oxide of SiO _x1 (x1 is a real number from 1.8 to 2) and a second silicon oxide of SiO _x2 (x2 is a real number from 0.8 to 1.2).

The complex oxide can satisfy D _l Si _m O _n (D is a doping element, l is a real number from 1 to 6, m is a real number from 0.5 to 2, and n is a real number satisfying the charge neutrality according to the oxidation numbers of D and Si, respectively, and l and m).

The doping element (D) may be selected from at least one of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), aluminum (Al), gallium (Ga), indium (In), tin (Sn), and bismuth (Bi). Accordingly, the composite oxide may be an oxide between silicon (Si); and at least one element selected from lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), aluminum (Al), gallium (Ga), indium (In), tin (Sn), and bismuth (Bi). Specifically, the doping element may be at least one element selected from the group of alkali metals and alkaline earth metals, more specifically, lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba), and even more specifically, at least one element selected from magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). As a related example, when D is Mg, the composite oxide may include at least one oxide selected from MgSiO ₃ and Mg ₂ SiO ₄ , but the doping element and the composite oxide in the present invention are not necessarily limited to oxides between Mg and Mg-Si.

Based on the microstructure, the parent material (silicon-based parent material) may contain a matrix containing silicon oxide; a composite oxide of silicon and a doping element selected from the group consisting of an alkali metal, an alkaline earth metal, and a post-transition metal; or a mixture thereof; and a dispersed phase including silicon nanoparticles. The dispersed phase may be uniformly dispersed and incorporated into the matrix. The matrix may mean a solid medium in which silicon in the form of nanoparticles is dispersed in the parent material, and may mean material(s) excluding metallic silicon (Si), which is the dispersed phase.

In one specific embodiment, the matrix may contain both silicon oxide and a composite oxide, and the matrix may satisfy A/B of 2 to 50, 2 to 40, 2 to 30, or 2 to 20, when A is the weight part of the composite oxide based on 100 parts by weight of silicon oxide and B is the concentration of the doping element based on weight % in the cathode material.

In one specific embodiment, the silicon nanoparticles can be crystalline, amorphous, or a composite of crystalline and amorphous, and can be substantially crystalline. The average diameter of the silicon nanoparticles can be on the order of 100 nanometers to the order of 10 ¹ nanometers, specifically, but not limited to, 1 to 50 nm, 2 to 40 nm, 2 to 35 nm, 2 to 30 nm, 2 to 20 nm, or 2 to 15 nm.

In one specific embodiment, the matrix can be crystalline, amorphous, or a composite phase in which crystalline and amorphous are mixed. In particular, the matrix can be crystalline or a composite phase in which crystalline and amorphous are mixed. Specifically, the matrix can include amorphous, crystalline, or a composite oxide of silicon oxide and crystalline oxide in which amorphous and crystalline are mixed.

In one specific embodiment, the parent material (silicon-based parent material) may contain 15 to 50 wt% of nanoparticle silicon and the remainder of a matrix.

In one specific example, the negative electrode material may be a negative electrode material for a secondary battery, and in this case, the secondary battery may include a lithium secondary battery. The lithium secondary battery may be a lithium ion battery, a lithium ion polymer battery, or a lithium polymer battery based on the type of separator and electrolyte, and may be cylindrical, square, coin-shaped, or pouch-shaped, but is not limited thereto.

However, the negative electrode material according to one specific example of the present invention is not necessarily limited to the negative electrode material for a lithium secondary battery. The negative electrode material according to one specific example can be utilized as an active material for secondary batteries such as a sodium battery, an aluminum battery, a magnesium battery, a calcium battery, a zinc battery, etc., and can also be utilized in other energy storage/generation devices such as a super capacitor, a dye-sensitized solar cell, a fuel cell, etc., in which conventional silicon-based materials are used.

The present disclosure includes a method for manufacturing a negative electrode material for a secondary battery. When describing the manufacturing method, the negative electrode material manufactured is similar to or identical to the negative electrode material for a secondary battery described above. Accordingly, the method for manufacturing a negative electrode material for a secondary battery includes all of the contents described above in the negative electrode material.

A method for manufacturing a negative electrode material for a secondary battery according to one specific example comprises the steps of: heating a raw material mixed with silicon (Si) and silicon oxide (SiO ₂ ) to a temperature of 1,350 to 1,750°C under a vacuum of 0.1 torr or less to vaporize and condensing (condensing vaporized gas) on a collecting plate at 350 to 450°C to obtain a collected product; heat-treating the obtained collected product under an inert atmosphere at a temperature of 850 to 950°C, specifically, a temperature of 880 to 920°C, for 10 to 20 hours, specifically, 13 to 18 hours to obtain a heat-treated product; and pulverizing the obtained heat-treated product to obtain a pulverized product. A method of manufacturing a negative electrode material includes a step of manufacturing a negative electrode material by carbonizing a mixture of a pulverized material and a carbon precursor under conditions of a density (packing density) of 0.70 g/cm ³ or less at a temperature of 850 to 950° C., specifically, a temperature of 880 to 920° C., for 1 to 5 hours, specifically, 1 to 3 hours, in an inert atmosphere. At this time, through the carbonization treatment, an negative electrode material can be manufactured in a particle form including a base material containing silicon (Si) based on an elemental component and a surface layer located on the base material containing carbon (C), and having a curvature ratio of 1.00 or less calculated by the above-described Equation 1.

The raw material may further include an oxide of a doping element (D) together with silicon and silicon oxide. In the oxide of the doping element, the doping element may be similar to or identical to that described above in the above-described negative electrode material. Specifically, the oxide of the doping element may be an oxide of a doping element selected from the group consisting of alkali metals, alkaline earth metals and post-transition metals, and more specifically, may be an oxide of a doping element selected from lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), aluminum (Al), gallium (Ga), indium (In), tin (Sn) and bismuth (Bi).

The molar ratio of silicon contained in the raw material: silicon oxide may be 1:0.60 to 0.90, more specifically 1:0.70 to 0.80. When the raw material is a mixture of silicon, silicon oxide, and oxide of a doping element, the molar ratio of silicon contained in the raw material: oxide of a doping element may be 1:0.10 to 0.40, more specifically 1:0.15 to 0.30, but is not necessarily limited thereto.

After vaporization and capture of the raw material, the captured material is heat-treated, and the heat-treated material obtained can be mechanically pulverized. The obtained heat-treated material can be granulated into particles having an average size of 1 ㎛ to 30 ㎛ by pulverization.

The pulverized material can be mixed with a carbon precursor and subjected to carbonization. The carbon precursor can be a liquid carbon precursor that is liquid at room temperature, and advantageously, can be a liquid carbon precursor having a surface tension of 20 to 60 dyne/cm. As a specific example, the carbon precursor can be coal tar, pyrolyzed fuel oil (PFO), etc., but is not necessarily limited thereto.

In the carbonization treatment, the mixture of the pulverized material and the carbon precursor, or advantageously the pulverized material and the liquid carbon precursor, can be carbonized under an inert atmosphere while satisfying the condition of a density (packing density) of 0.70 g/cm ³ or less. Specifically, the mixture of the pulverized material and the liquid carbon precursor can be carbonized under an inert atmosphere while satisfying a packing density of 0.40 to 0.70 g/cc, advantageously 0.45 to 0.70 g/cc, more advantageously 0.45 to 0.60 g/cc, and even more advantageously 0.50 to 0.60 g/cc. At this time, the inert atmosphere can be argon, nitrogen, helium, neon, or a mixed gas thereof.

The invention includes a cathode containing the cathode material described above.

The present invention includes a negative electrode containing a negative electrode material manufactured by the above-described manufacturing method.

Specifically, the negative electrode may be an negative electrode for a secondary battery, specifically, an negative electrode for a lithium secondary battery. The negative electrode may include a current collector; a negative electrode active material layer located on at least one surface of the current collector and containing the above-described negative electrode material, and the negative electrode active material layer may further include a binder and a conductive material commonly used in a secondary battery negative electrode together with the above-described negative electrode material, if necessary, and may further include a non-silicon-based negative electrode active material (an example of a lithium secondary battery is graphite, etc.) if necessary.

The present invention includes a secondary battery including the above-described negative electrode. The secondary battery may include a positive electrode including a positive electrode collector and a positive electrode active material layer positioned on at least one surface of the positive electrode collector; the above-described negative electrode; a separator interposed between the positive electrode and the negative electrode; and an electrolyte that conducts active ions (for example, lithium ions) involved in charging and discharging of the battery. The positive electrode collector, the negative electrode collector, the positive electrode active material or composition of the positive electrode active material layer, the solvent of the separator and the electrolyte or the electrolyte salt or the concentration of the electrolyte salt may be any material or composition commonly adopted for each specific secondary battery or in the relevant secondary battery.

The present invention includes a power supply source that generates power by a secondary battery including a cathode material according to one specific example. Examples of the power supply source include, but are not limited to, a battery module, a battery pack, or an ESS (Energy Storage System).

The present invention includes a device that is supplied with power by a power supply source equipped with a secondary battery including a cathode material according to one specific example. Examples of such devices include, but are not limited to, automobiles (hybrid automobiles, electric automobiles, etc.), portable electronic communication devices (wireless terminals, laptops, etc.).

(Manufacturing example)

Si, SiO ₂ , and MgO powders were placed in a powder mixer at a molar ratio of 6 (Si): 4.5 (SiO ₂ ): 1.5 (MgO), respectively, and then homogeneously mixed to prepare raw materials.

The above raw material was placed in a crucible (26 kg) in a vacuum chamber at 0.1 torr or less, heated to 1,400°C to vaporize, and then condensed on a collecting plate at 400°C to obtain a collected product (magnesium-doped silicon oxide).

The obtained capture material was heat-treated at 900°C for 15 hours in an Ar atmosphere to produce a heat-treated product (bulk base material), and the heat-treated product was pulverized to particle size (D ₅₀ = 6.5 μm). Then, a liquid carbon precursor having a surface tension of 20 to 60 dyne/cm was mixed with the pulverized product, and carbonization was performed to produce a cathode material. Specifically, coal tar (specific gravity = 1.1-1.3 g/cc, carbonization yield about 25% when carbonized at 900°C) in a room temperature liquid state, which is generated during the dry distillation of raw coal in a steel mill, was used as the liquid carbon precursor. When mixing, 100 parts by weight of the pulverized product prepared by pulverizing the heat-treated product and 12 parts by weight of coal tar were mixed, and the mixture was placed in an alumina boat for carbonization and heat-treated at 900°C for 120 minutes in a 1-atm nitrogen atmosphere. At this time, the mixture of the pulverized material and coal tar was charged into the alumina boat, and the number of tappings was adjusted from 10 to 300 times using a tapping machine (Quanta chrom, Dual-tap) to control the packing density. In Example 1, the packing density of the mixture of the pulverized material and coal tar was 0.67 g/cc, in Example 2, the packing density of the mixture of the pulverized material and coal tar was 0.58 g/cc, in Example 3, the packing density of the mixture of the pulverized material and coal tar was 0.51 g/cc, and in the comparative example, the packing density of the mixture of the pulverized material and coal tar was 0.85 g/cc.

The properties of the negative electrode material manufactured in the examples, the detailed description, and the properties described in the claims were measured according to the following 'Analysis and Measurement Method'.

(Analysis and Measurement Methods)

D ₅₀

0.01 g of the target substance was suspended in ethanol, and the prepared suspension was sonicated for 1 minute. Then, the cumulative volume diameter distribution was measured using a conventional laser diffraction particle size distribution measuring device (Microtrac S3500). The median diameter D ₅₀ of the target substance refers to the diameter at the position where the cumulative volume is 50% in the cumulative volume diameter distribution.

Spherical shape

Sphericity was measured using an analyzer (Flowcam 8100, Fluid Imaging Technologies) commonly used for particle shape analysis after ultrasonically dispersing 0.01 g of the analyte in 5 mL of ethanol. The sphericity of a substance refers to the average value of the sphericity, and the average value of the sphericity is a statistical average value obtained by securing the sphericity of each of at least 500 or more, typically 1,000 or more particles and averaging the secured sphericity values.

Curvature

The tortuosity was measured using a particle shape analyzer (morphologi 4, Malvern Panalytical) after ultrasonically dispersing 0.01 g of the analyte in 5 mL of ethanol. The tortuosity (Con) of a substance means the average of the tortuosity(s) of each particle, and the average of the tortuosity is a statistical average value obtained by securing the tortuosity of each particle of at least 500 or more, typically 1,000 or more, and averaging the secured tortuosity values. The standard deviation value of the tortuosity of a substance and the ratio of particles in a substance having a tortuosity value of at least tortuosity (Con) × 0.9 (ratio based on the number of particles) can be calculated by a conventional program equipped with a particle shape analyzer as a data processing and analysis program based on the tortuosity data of each particle used to calculate the tortuosity (statistical average value) of a substance.

The bending rate, standard deviation of bending degree, and particle ratio belonging to bending degree (Con) x 0.9 or higher of the negative electrode materials manufactured in the examples and comparative examples were measured, and the results are summarized in Table 1 below.

(Table 1)

As can be seen from the curvature ratio in Table 1, even when a surface layer is formed using the same carbon precursor on a particulate matrix having the same composition and structure, the curvature ratio of the manufactured negative electrode material and the particle ratio (%) belonging to the curvature (Con) x 0.9 or higher can be seen to differ depending on the packing density of the mixture in which the particulate matrix and the carbon precursor are mixed during the carbonization treatment.

Figure 1 is a scanning electron microscope photograph of the negative electrode material manufactured in Example 3. The negative electrode materials manufactured in Examples 1, 2, and 3 and the comparative example had substantially similar average sizes (D ₅₀ ), and the average sizes (D ₅₀ ) of the negative electrode materials manufactured in Examples 1, 2, and 3 and the comparative example were on the order of 6.1 to 6.9 ㎛.

In addition, since the cathode material is manufactured by forming a surface layer on a pulverized product that has been pulverized into particles by pulverizing the bulk, as can be seen in Fig. 1, it can be seen that it has an angular shape with an edge due to the fracture surface caused by the pulverization.

The sphericity of the negative electrode materials manufactured in Examples 1, 2, and 3 and the Comparative Example was also substantially similar to that of D ₅₀ , and the sphericity of the negative electrode materials manufactured in Examples 1, 2, and 3 and the Comparative Example was at the level of 0.8 to 0.9.

Fig. 2 is a transmission electron microscope photograph showing an amorphous carbon layer coated on a base material in a cathode material manufactured in Example 3. As shown in the transmission electron microscope observation results of Fig. 2, it was confirmed that the surface of the base material was covered with amorphous carbon having a thickness of 4 to 30 nm.

In each of the examples and comparative examples, the manufactured negative electrode materials were used as active materials, and the active material:conductive material (carbon black):CMC (Carboxymethyl cellulose):SBR (Styrene Butadiene Rubber) were mixed in a weight ratio of 8:1:0.5:0.5 and applied to a 17 ㎛ thick copper foil, and then dried at 90°C for 40 minutes. After drying, a CR2032 coin-type half-cell was manufactured by stamping out a diameter of 14 mm, using metallic lithium with a diameter of 16 mm as a counter electrode, interposing a separator with a diameter of 18 mm and filling the electrolyte. The electrolyte was prepared by dissolving 1 M LiPF ₆ in a solvent containing EC (Ethylene carbonate)/DEC (Diethyl carbonate) in a volume ratio of 1:1, and using 3 wt% FEC (fluoroethylene carbonate) as an additive. The Martian process was performed by charging (lithiating) the manufactured battery to 0.005 V with a constant current of 0.1 C, charging at a constant voltage of 0.005 V until it reached 0.01 C, discharging (delithiating) to 1.5 V with a constant current of 0.1 C (first charring step), charging (lithiating) again to 0.005 V with a constant current of 0.1 C, charging at a constant voltage of 0.005 V until it reached 0.01 C, and discharging (delithiating) to 1.0 V with a constant current of 0.1 C (second charring step).

The half-cell on which the formation process was performed was charged (lithiated) to 0.005 V with a constant current of 0.5 C, charged at a constant voltage of 0.005 V until it reached 0.05 C, and then discharged (delithiated) to 1.0 V with a constant current of 0.5 C to evaluate the charge/discharge cycle characteristics, and the discharge capacity retention rate according to the charge/discharge cycle is shown in Fig. 3.

As can be seen in FIG. 3, the negative electrode materials manufactured in the examples and comparative examples have substantially the same surface layer as the base material having substantially the same composition and microstructure, but it can be seen that the discharge capacity retention rate significantly differs depending on the spherical morphology of the negative electrode material, and it can be seen that the negative electrode materials of Examples 1 to 3 having a small bending rate exhibit significantly superior discharge capacity retention rate.

Although the present invention has been described with reference to specific matters, limited examples, and drawings, these have been provided only to help a more general understanding of the present invention, and the present invention is not limited to the above examples, and those skilled in the art will appreciate that various modifications and variations may be made from these descriptions.

Therefore, the idea of the present invention should not be limited to the described embodiments, and all things that are equivalent or equivalent to the claims described below as well as the claims are included in the scope of the idea of the present invention.

Claims (13)

A particle-like material including a base material containing silicon (Si) based on elemental composition and a surface layer located on the base material and containing carbon (C).
A negative electrode material for a secondary battery having a bending ratio of 1.00 or less, calculated by the following equation 1.
(Formula 1)

(In Equation 1, AR is the curvature ratio, and Con is the curvature obtained by dividing the perimeter of the convex outer surface of the negative electrode particle (convex perimeter) by the actual perimeter of the negative electrode particle (perimeter).) In paragraph 1,
A negative electrode material for a secondary battery having a bending ratio of 0.55 or less. In paragraph 1,
The above negative electrode material is a negative electrode material for a secondary battery, satisfying at least one of the following I) to II).
I) Standard deviation value of the above curvature ≤ 0.050
II) The proportion of particles having a curvature of 0.9×Con or higher is 90% or more. In paragraph 1,
A negative electrode material for a secondary battery, wherein the sphericity of the above negative electrode material is 0.55 or more. In paragraph 1,
The above negative electrode material is a negative electrode material for a secondary battery having an angular shape. In paragraph 1,
A negative electrode material for a secondary battery having an average particle diameter (D ₅₀ ) of 1 ㎛ to 30 ㎛. In paragraph 1,
The above surface layer is a negative electrode material for a secondary battery including an amorphous carbon layer. In Article 7,
A negative electrode material for a secondary battery having a thickness of the surface layer of 1 to 50 nm. A secondary battery negative electrode material that satisfies Equation 2 when subjected to a charge-discharge test according to the following charge-discharge cycle conditions using a half-cell having a particulate silicon-based negative electrode material and a counter electrode made of metal lithium foil.
Charge/discharge cycle conditions: CC/CV, cut-off voltage 0.005V~1.000V, 0.5C-rate
(Formula 2)
95 % < C _j /C ₁ *100
(In Equation 2, C ₁ is the discharge capacity (mAh/g) in the first charge/discharge cycle, C _j is the discharge capacity in the jth charge/discharge cycle, and j is an arbitrary natural number greater than or equal to 10 and less than or equal to 80.) In any one of claims 1 to 9,
The above-mentioned parent material is a negative electrode material for a secondary battery including silicon, silicon oxide, silicon nitride, silicon sulfide, silicon carbide, silicon alloy, a mixture thereof, or a composite thereof. In any one of claims 1 to 9,
The above-mentioned parent material is a negative electrode material for a secondary battery, which further contains a doping element (D) selected from the group consisting of alkali metals, alkaline earth metals, and transition metals. In any one of claims 1 to 9,
The above-mentioned parent material is a secondary battery negative electrode material including a matrix containing silicon (Si), a doping element (D), and oxygen (O) based on elemental composition; and silicon nanoparticles dispersed and incorporated in the matrix. A secondary battery negative electrode containing a secondary battery negative electrode material according to any one of claims 1 to 9.