Silicon alloy-based negative electrode active material, negative electrode, and lithium secondary battery comprising same

Abstract

An embodiment of the present invention provides a silicon-based negative electrode active material comprising: a silicon single phase; and a matrix positioned around the silicon single phase, wherein the matrix includes elemental Si, a lanthanide, and an element M, the element M includes one or more selected from the group consisting of Al, Fe, Ti, and Mn, the content of the lanthanide is 2-9 wt% with respect to 100 wt% of the total negative electrode active material, and the silicon single phase is refined to have an average diameter of less than 30 nm due to the inclusion of the lanthanide in the matrix.

Description

Silicon alloy-based negative electrode active material, negative electrode, and lithium secondary battery including the same

[0001] The present invention relates to a silicon alloy-based negative electrode active material, a negative electrode, and a lithium secondary battery including the same. More specifically, the invention relates to a negative electrode active material, a negative electrode, and a lithium secondary battery including the same, which have excellent energy density and durability through the composition and structure of a Si (silicon)-based alloy containing a Group La element.

[0002] Silicon-based anode materials are attracting attention to realize high energy density in lithium-ion batteries, but silicon undergoes significant volume changes during charging and discharging, which leads to structural collapse of the electrode and a shortened lifespan.

[0003] To address this, alloys with various added metal elements have been studied. In conventional technology, alloys containing elements such as Ti and Mn provided limited improvements in durability, but they had limitations in that they did not sufficiently resolve the impact of the size of the precipitated silicon phase on the performance and lifespan of the electrode.

[0004]

[0005] The present invention can provide a silicon alloy-based negative electrode active material that can significantly improve the performance and lifespan of the electrode by adding a Group La element to refine the size of the silicon phase.

[0006] In particular, by optimizing the composition and role of group La elements, the size of the silicon phase can be reduced to up to 7 nm even at low content, thereby mitigating the problem of volume change of the electrode and ensuring electrochemical stability.

[0007]

[0008] (Patent Document 1) Republic of Korea Registered Patent No. 10-2323025

[0009]

[0010] The technical problem that the present invention aims to solve is to provide a silicon alloy-based negative electrode active material that can significantly improve the performance and lifespan of the electrode by adding a Group La element to refine the size of the silicon phase.

[0011]

[0012] The technical problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned technical problems will be clearly understood by those skilled in the art to which the present invention belongs from the description below.

[0013] To achieve the above technical problem, one embodiment of the present invention provides a silicon-based negative electrode active material.

[0014]

[0015] The silicon-based negative electrode active material according to one embodiment of the present invention is,

[0016] A silicon single phase; and a matrix located around the silicon single phase; wherein the matrix comprises a Si element, a La group element, and an element M, and the element M comprises one or more selected from the group consisting of Al, Fe, Ti, and Mn.

[0017] The silicon-based negative electrode active material may be characterized in that the content of the group La element is 2 wt% to 9 wt% for 100 wt% of the total negative electrode active material, and the average diameter of the silicon single phase is reduced to less than 30 nm by including the group La element.

[0018]

[0019] In addition, according to one embodiment of the present invention, there may be a silicon-based negative electrode active material characterized in that the content of the element M is 35 wt% to 46 wt% with respect to 100 wt% of the total negative electrode active material.

[0020]

[0021] In addition, according to one embodiment of the present invention, there may be a silicon-based negative electrode active material characterized in that the content of Si (silicon) element is 45 wt% to 63 wt% with respect to 100 wt% of the total negative electrode active material.

[0022]

[0023] In addition, according to one embodiment of the present invention, there may be a silicon-based negative electrode active material characterized in that the La group element comprises one or more selected from the group consisting of La, Ce, and Nd.

[0024]

[0025] In addition, according to one embodiment of the present invention, the average diameter of the silicon phase precipitated by including the La group element is,

[0026] There may be a silicon-based negative electrode active material characterized by having an average diameter in the range of 65% to 25% compared to the case where the above-mentioned La group elements are not included.

[0027]

[0028] In addition, according to one embodiment of the present invention, there may be a silicon-based negative electrode active material characterized in that the average diameter of the precipitated silicon phase is 7 nm to 20 nm.

[0029]

[0030] In addition, according to one embodiment of the present invention, the negative electrode active material may be a silicon-based negative electrode active material characterized by having an initial capacity of 1000 mAh / g or more.

[0031]

[0032] In addition, according to one embodiment of the present invention, the negative electrode active material may be a silicon-based negative electrode active material characterized by having a capacity retention of 70% or more even after repeating 500 charge / discharge cycles.

[0033]

[0034] To achieve the above technical problem, another embodiment of the present invention provides a negative electrode for a lithium secondary battery.

[0035] According to one embodiment of the present invention, the negative electrode for a lithium secondary battery comprises a current collector and a negative electrode material formed on at least one surface of the current collector, wherein the negative electrode of the lithium secondary battery comprises:

[0036] The above-mentioned negative electrode material may be a negative electrode for a lithium secondary battery characterized by including the aforementioned silicon-based negative electrode active material.

[0037]

[0038] To achieve the above technical problem, another embodiment of the present invention provides a lithium secondary battery.

[0039] According to one embodiment of the present invention, the lithium secondary battery comprises a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, wherein

[0040] The above-mentioned negative electrode may be a lithium secondary battery characterized by being a negative electrode for a lithium secondary battery comprising the aforementioned silicon-based negative electrode active material.

[0041]

[0042] According to one embodiment of the present invention, a silicon alloy-based negative electrode active material can be provided that can significantly improve the performance and lifespan of an electrode by adding a group La element to refine the size of the silicon phase.

[0043] According to one embodiment of the present invention, by adding a group La element to a silicon alloy in an appropriate content range, the effect of refining the precipitated silicon phase while maintaining a high negative electrode active material capacity can be obtained.

[0044]

[0045] The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the configuration of the invention described in the detailed description of the invention or the claims.

[0046] Figure 1 is a graph illustrating the trend of change in Si phase size according to Si content in silicon alloy-based cathode active materials through various experimental data.

[0047] Figure 2 is a graph showing the trend of capacity change according to the size of the Si phase of a silicon alloy-based anode active material through various experimental data. The size of the Si phase is the result calculated by substituting the FWHM (full width at half maximum) value of the Si (111) peak from the XRD (X-ray diffraction) analysis results of the silicon alloy-based anode active material into the Scherrer formula.

[0048] Figure 3 is a graph illustrating the trend of capacity retention rate change according to the size of the Si phase of silicon alloy-based cathode active materials through various experimental data.

[0049] FIG. 4 is an SEM image showing the surface structure of a negative electrode ribbon according to the La content of a silicon alloy-based negative electrode active material according to one embodiment of the present invention.

[0050] The present invention will be described below with reference to the attached drawings. However, the present invention can be implemented in various different forms and is not limited to the embodiments described herein, and should be understood to include all modifications, equivalents, and substitutions that fall within the spirit and scope of the invention.

[0051] In addition, to clearly explain the invention in the drawings, parts unrelated to the explanation have been omitted, and similar parts throughout the specification have been given similar reference numerals.

[0052] Throughout the specification, when it is stated that a part is "connected (connected, in contact, joined)" to another part, this includes not only cases where they are "directly connected," but also cases where they are "indirectly connected" with other members in between.

[0053] Furthermore, when a part such as a layer, film, region, or plate is described as being “on” another part, this includes not only cases where it is “immediately above” the other part, but also cases where there is another part in between. Additionally, in this specification, when a part such as a layer, film, region, or plate is described as being formed “on” another part, the direction in which it is formed is not limited to the upward direction only, but includes cases where it is formed in the lateral or downward direction. Conversely, when a part such as a layer, film, region, or plate is described as being “below” another part, this includes not only cases where it is “immediately below” the other part, but also cases where there is another part in between.

[0054] In this specification, "upper surface" and "lower surface" are used as relative concepts to facilitate understanding of the technical concept of the present invention. Accordingly, "upper surface" and "lower surface" do not refer to specific directions, locations, or components, but are interchangeable.

[0055] For example, 'upper surface' may be interpreted as 'lower surface,' and 'lower surface' may be interpreted as 'upper surface.' Therefore, 'upper surface' may be expressed as 'No. 1' and 'lower surface' as 'No. 2,' or 'lower surface' may be expressed as 'No. 1' and 'upper surface' as 'No. 2.' However, within a single embodiment, 'upper surface' and 'lower surface' are not used interchangeably.

[0056] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as generally understood by those skilled in the art to which the present invention pertains. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and should not be interpreted in an ideal or overly formal sense unless explicitly defined in this application.

[0057] Furthermore, when it is stated that a part "includes" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but rather allows for the inclusion of additional components.

[0058] The terms used herein are merely for describing specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as “comprising” or “having” are intended to indicate the presence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0059]

[0060] Embodiments of the present invention will be described in detail below with reference to the attached drawings.

[0061] A silicon alloy-based cathode active material according to one embodiment of the present invention is described.

[0062]

[0063] Silicon is converted into lithium ions (Li) during the charging process. +When combined with ), volume expansion of up to 300% occurs, which can lead to electrode cracking and separator damage, resulting in reduced battery performance and shortened lifespan.

[0064] In the present invention, when the silicon phase is refined by adding a Group La element, the absolute value of volume expansion per particle is reduced and the stress generated inside the particle is reduced, thereby mitigating structural damage to the electrode.

[0065] As a result, this has the effect of improving electrode durability and cycle life.

[0066]

[0067] In addition, as the size of the silicon phase increases, the distance lithium ions diffuse into the interior of the particle becomes longer, which leads to a problem where the charge / discharge reaction rate decreases.

[0068] As in the above embodiment of the present invention, in the case of a silicon alloy in which a group La element is introduced, the diffusion distance of lithium ions can be shortened by reducing the size of the precipitated silicon phase as described above.

[0069] This enables rapid insertion and extraction of lithium ions, resulting in improved charge / discharge speeds and enhanced high power and rapid charging characteristics.

[0070]

[0071] As an example of the above embodiment, the method comprises a silicon single phase; and a matrix located around the silicon single phase; wherein the matrix comprises a Si element, a La group element, and an element M, and the element M comprises one or more selected from the group consisting of Al, Fe, Ti, and Mn.

[0072] There may be a silicon-based negative electrode active material characterized in that the content of the group La element is 2 wt% to 9 wt% for 100 wt% of the total negative electrode active material, and the average diameter of the silicon single phase is reduced to less than 30 nm by including the group La element.

[0073]

[0074] At this time, the content of the element M may be characterized as being 35 wt% to 46 wt% with respect to 100 wt% of the total negative electrode active material, and

[0075] In addition, the content of Si (silicon) element included in 100 wt% of the total negative electrode active material can be characterized as being 45 wt% to 63 wt%.

[0076]

[0077] More specifically, as an example of the above embodiment, with respect to 100 wt% of the total negative electrode active material,

[0078] Comprising 10 wt% to 12 wt% Ti, 15 wt% to 20 wt% Fe, 8 wt% to 10 wt% Al, 2 wt% to 4 wt% Mn, 2 wt% to 9 wt% Group La elements, and the remainder being Si and other unavoidable impurities,

[0079] There may be a silicon-based negative electrode active material characterized by reducing the average diameter of the precipitated silicon phase by including the above-mentioned La group element.

[0080]

[0081] At this time, since the above Si constitutes the remainder, it may be included in a mass percentage of 45 wt% to 63 wt%, and

[0082] The above La group element may be any one selected from the group consisting of La, Ce, and Nd, or may include two or more.

[0083] The aforementioned other unavoidable impurities mainly refer to trace components naturally incorporated during raw materials and manufacturing processes, and may include, for example, oxygen, carbon, iron, and sulfur.

[0084]

[0085] As in the above example, when a group La element is included in the silicon alloy,

[0086] The above-mentioned La group element acts as a nucleation site for Si, thereby enabling the refinement of the precipitated Si phase.

[0087] However, it is important that the above-mentioned La group elements are included in an appropriate amount,

[0088] If the above silicon alloy contains too little of the above group La element, less than 2 wt%, there is a problem that the effect of refining the Si phase cannot be sufficiently obtained, and

[0089] Conversely, if the silicon alloy contains more than 9 wt% of the above-mentioned La group element, there is a problem of the price increasing as a result, and a problem of the capacity of the silicon alloy-based negative electrode active material decreasing due to the heavy La group element.

[0090]

[0091] In the above embodiment of the present invention, the content of the La group element is formed in the range of 2 wt% to 9 wt%, thereby enabling the effect of refining the precipitated silicon phase while maintaining a high cathode active material capacity.

[0092]

[0093] When the silicon phase is refined as described above, as previously mentioned,

[0094] Effects such as reduced electrode damage, improved cycle life, and increased charge / discharge speed can be achieved.

[0095]

[0096] If we look at it in more detail,

[0097] Generally, the capacity of silicon alloy-based negative electrode active materials tends to be proportional to the size of the silicon phase precipitated within the alloy.

[0098] A large size of the precipitated silicon phase implies a high silicon content per unit volume within the alloy, which can lead to an increase in lithium-ion storage capacity.

[0099] However, if the size of the precipitated silicon phase becomes excessive, the volume expansion and contraction occurring during the charging and discharging process intensify, leading to increased internal stress. This degrades the structural stability of the electrode, causing physical damage such as cracking or separation, which can consequently result in a shortened electrode lifespan and performance degradation.

[0100]

[0101] Therefore, miniaturizing the silicon phase to an appropriate size is a critical factor in improving the performance and stability of the cathode active material.

[0102]

[0103] If the silicon alloy contains the same amount of silicon,

[0104] When the silicon phase is dispersed and precipitated as small clumps, the active surface area per unit volume or unit mass increases, and

[0105] This provides more pathways for lithium ions to be inserted into silicon, allowing electrochemical reactions to occur more efficiently.

[0106]

[0107] In other words, if it is possible to reduce the size of the precipitated silicon phase while increasing only the silicon content contained within the silicon alloy, it is not only desirable in terms of capacity, but also

[0108] It has the advantage of also being able to solve the aforementioned problem of shortened cycle life.

[0109]

[0110] However, generally, since the capacity of the silicon alloy-based negative electrode active material and the size of the silicon phase precipitated within the silicon alloy-based negative electrode active material are proportional,

[0111] There is a need for a method to increase only the silicon content contained within the silicon alloy while reducing the size of the precipitated silicon phase.

[0112]

[0113] In this regard, in the above embodiment of the present invention, by adding a group La element in an appropriate content range to the silicon alloy, the effect of refining the precipitated silicon phase while maintaining a high negative electrode active material capacity is obtained.

[0114]

[0115] In other words, since the average diameter of the precipitated silicon phase can be reduced while maintaining a high negative electrode active material capacity, it is possible to obtain the effect of having a high negative electrode active material capacity and a high capacity retention rate.

[0116]

[0117] More preferably, the silicon alloy may be characterized by containing the La group element in a mass percentage of 3 wt% to 6 wt%.

[0118] Most preferably, the silicon alloy may be characterized by containing the La group element in a mass percentage of 3 wt% to 5 wt%.

[0119] Regarding the scope of the above preferred embodiment, critical significance can be confirmed through the experimental examples described below.

[0120]

[0121] Through this, it can be confirmed that the content ratio of the above-mentioned Group La elements corresponds to the core composition of the technical concept of the present invention.

[0122]

[0123] However, even if Group La elements are added in the same amount, different physical properties may be obtained depending on the content range of other elements.

[0124] As it is an alloy containing various metallic elements, it is natural that the content ratio of metallic elements other than Group La elements also affects the physical properties of the entire alloy, and

[0125] Accordingly, physical properties such as the size of the precipitated Si phase, the capacity of the cathode active material, and the capacity retention rate may vary,

[0126] Not only the content ratio of the above-mentioned Group La elements, but also the content ratio of other metal elements is important.

[0127]

[0128] For example, as the content of the above Si increases or decreases, it may result in an increase or decrease in the diameter of the precipitated Si phase, and

[0129] In the case of the above element M,

[0130] Depending on Ti and Fe, not only can various amorphous matrices be formed, but Mn can also contribute to the refinement of the matrix and Si phases.

[0131] In addition, since Al is a low-density alloying element that does not form mutual compounds with Si, it can effectively increase the volume of the alloy matrix even in small amounts; therefore, even if volume expansion of Si occurs, the overall volume expansion rate of the alloy can be reduced, thereby improving structural stability.

[0132]

[0133] As described above, the average diameter of the silicon phase precipitated by including a group La element in a silicon alloy containing Si and M elements in appropriate amounts is,

[0134] It may correspond to a range of 65% to 25% of the average diameter when not containing the above La group elements.

[0135]

[0136] That is, the average diameter is reduced by as little as 35% to as much as 75% compared to the case where group La elements are not included, and a refinement effect can be obtained.

[0137]

[0138] As described below in the experimental examples, referring to Table 1 below,

[0139] When the above Group La element is included in an amount of 2 wt% to 9 wt%,

[0140] It can be confirmed that the average diameter of the precipitated silicon phase is in the range of 65% to 25% compared to the average diameter when the above-mentioned La group elements are not included.

[0141]

[0142] More preferably, the average diameter of the silicon phase precipitated by including the group La element in a mass percentage of 3 wt% to 6 wt% is,

[0143] There may be a silicon alloy negative electrode active material characterized by having an average diameter of 40% or less compared to the case where the above-mentioned La group elements are not included.

[0144]

[0145] Likewise, referring to Table 1 below, when the above Group La element is included in a mass percentage of 3 wt% to 6 wt%,

[0146] It can be confirmed that the average diameter of the precipitated silicon phase is in the range of 40% to 35% compared to the average diameter when the above-mentioned La group elements are not included.

[0147]

[0148] As a result of the silicon phase precipitated as described above being refined,

[0149] The average diameter of the precipitated silicon phase may be characterized as being 7 nm to 30 nm, and

[0150]

[0151] More preferably, there may be a silicon alloy-based negative electrode active material characterized in that the average diameter of the precipitated silicon phase is 7 nm to 16 nm, and

[0152] Most preferably, there may be a silicon alloy-based negative electrode active material characterized in that the average diameter of the precipitated silicon phase is 10 nm to 15 nm.

[0153] The above diameter range can be verified through Table 1 below.

[0154]

[0155] As an example of the above embodiment, the negative electrode active material may be a silicon alloy-based negative electrode active material characterized by having an initial capacity of 1000 mAh / g or more.

[0156] In addition, as an example of the above embodiment, there may be a silicon alloy-based negative electrode active material characterized by having a capacity retention rate of 70% or more even after repeating 500 charge / discharge cycles.

[0157]

[0158] As described above, in the case of the present invention, since the average diameter of the precipitated silicon phase can be refined while maintaining a high negative electrode active material capacity,

[0159] The core of the technical concept is to achieve the effect of having a high cathode active material capacity while simultaneously maintaining a high capacity retention rate.

[0160] That is, in the above embodiment, when the La group element is included in the silicon alloy in a mass percentage of 2 wt% to 9 wt%, the negative electrode active material may be characterized by having an initial capacity of 1000 mAh / g or more, and at the same time having a capacity retention rate of 70% or more even after repeating 500 charge / discharge cycles.

[0161]

[0162] More preferably, when the silicon alloy contains the La group element in a mass percentage of 3 wt% to 6 wt%, the negative electrode active material may be characterized by having an initial capacity of 1190 mAh / g or more, and at the same time having a capacity retention rate of 70% or more even after repeating 500 charge / discharge cycles.

[0163]

[0164] Most preferably, when the silicon alloy contains the group La element in a mass percentage of 3 wt% to 5 wt%, the negative electrode active material may be characterized by having an initial capacity of 1280 mAh / g or more, and at the same time having a capacity retention rate of 70% or more even after repeating 500 charge / discharge cycles.

[0165]

[0166] As in the above embodiment of the present invention, when a Group La element is added to a silicon alloy, the effect of lowering the melting point of the alloy can also be obtained.

[0167] In the case of the above embodiment, there may be a silicon alloy-based negative electrode active material characterized by having a melting point of about 1240°C to 1270°C.

[0168]

[0169] As mentioned above, the silicon alloy according to the above embodiment has the advantage of being excellent in terms of mass production of the alloy due to its low melting point, and is also easier to form ribbons.

[0170] Therefore, an excellent effect can be obtained in forming a ribbon, which can be formed into a flatter and more uniform thin film.

[0171]

[0172] Referring to Figure 4 below, it can be confirmed that as the content of group La elements increases, the surface roughness of the cathode active material gradually decreases, resulting in the formation of a flatter and more uniform thin film.

[0173]

[0174] As shown in the above example, lowering the surface roughness of the negative electrode active material and forming it into a flat and uniform thin film can improve electrochemical performance, stability, and process efficiency, which is a particularly important factor in the design of high-energy-density and long-life lithium secondary batteries.

[0175]

[0176]

[0177] A negative electrode for a lithium secondary battery according to another embodiment of the present invention is described.

[0178]

[0179] As an example of the above embodiment, in a negative electrode of a lithium secondary battery comprising a current collector and a negative electrode material formed on at least one surface of the current collector,

[0180] The above-mentioned negative electrode may be a negative electrode for a lithium secondary battery characterized by including the aforementioned silicon-based negative electrode active material.

[0181]

[0182] Since the above-mentioned negative electrode for a lithium secondary battery retains the core of the technical concept of the aforementioned silicon-based negative electrode active material,

[0183] The above description of the silicon-based negative electrode active material can be applied as is to the negative electrode for the lithium secondary battery.

[0184]

[0185] A lithium secondary battery according to another embodiment of the present invention is described.

[0186]

[0187] As an example of the above embodiment, in a lithium secondary battery comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode,

[0188] There may be a lithium secondary battery characterized in that the above-mentioned negative electrode is a negative electrode for a lithium secondary battery comprising the aforementioned silicon-based negative electrode active material.

[0189]

[0190] Since the above-mentioned lithium secondary battery retains the core of the technical concept of the aforementioned silicon-based negative electrode active material,

[0191] The above description of the silicon-based negative electrode active material can be applied as is to the above lithium secondary battery.

[0192]

[0193] Examples 1–12 and Comparative Examples 1–3

[0194] <Manufacturing of Silicon Alloy-Based Cathode Active Material>

[0195]

[0196] The Si alloy-based active material was prepared by mixing metal raw materials in wt% as described in each example in Tables 1 and 2 below, and then melting them at a high temperature of 1,200°C or higher using an arc melting method or a vacuum induction melting method to achieve a uniform alloy state. Subsequently, the molten material was sprayed onto a copper wheel rotating at high speed with a cooling temperature controlled to 20°C or lower to apply a single-roll rapid solidification method. During this process, the linear velocity of the cooling wheel was maintained at 36 m / s to produce a fine ribbon shape. The process conditions were continuously optimized to ensure a uniform thickness and uniform composition of the produced ribbon.

[0197]

[0198] However, the method for manufacturing the active material of the present invention is not limited thereto, and it is specified that various fine powder manufacturing techniques applicable as long as a sufficient rapid cooling rate can be obtained, such as gas atomizer method, centrifugal gas atomizer method, plasma atomizer method, rotary electrode method, mechanical alloying method, ultra-high pressure water jet atomizer method, etc., may be applied in addition to the single-roll rapid cooling solidification method.

[0199]

[0200] Ribbons produced by the rapid solidification method were subjected to grinding and classification, thereby enabling the formation of powders with arbitrary particle sizes. Various grinding methods, such as wet grinding and dry grinding, can be applied.

[0201]

[0202] The present invention provides a lithium-ion secondary battery comprising a Si-based alloy negative electrode active material according to one embodiment of the present invention described above.

[0203] According to the present invention, a lithium secondary battery can be manufactured by housing an electrode assembly comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and an electrolyte in a rectangular or cylindrical can or a polymer pouch.

[0204] In the present invention, the cathode may include the aforementioned cathode active material, conductive material, and binder. Examples of conductive materials in the present invention include carbon, metal, metal nitride, metal carbide, metal silicide, and metal boride, but are not limited thereto.

[0205] For example, commercial powders such as Super P and Super S, or carbon black, acetylene black, furnace black, lamp black, graphite, carbon fiber, or a combination thereof may be used as conductive materials.

[0206] In the present invention, the anode may include a lithiated intercalation compound, and may also include inorganic sulfur (S8, elemental sulfur) and a sulfur compound.

[0207] The above sulfur compounds include Li2Sn (n≥1), Li2Sn (n≥1) dissolved in catholyte, organic sulfur compounds, or carbon-sulfur polymers ((C2S f ) n : f=2.5 to 50, n≥2) etc. may be included.

[0208] The type of electrolyte included in the lithium secondary battery of the present invention is also not particularly limited, and general means known in the field may be employed. In one example of the present invention, the electrolyte may include a non-aqueous organic solvent and a lithium salt.

[0209]

[0210]

[0211]

[0212]

[0213]

[0214]

[0215] Experimental Example 1. Data analysis according to lanthanum content.

[0216]

[0217] The experimental example above will be explained below with reference to FIGS. 1 to 4 together with Tables 1 and 2.

[0218]

[0219] Figure 1 is a graph illustrating the trend of change in Si phase size according to Si content in silicon alloy-based cathode active materials through various experimental data.

[0220] Referring to Fig. 1, it can be seen that, generally, as the silicon content increases, the diameter of the precipitated silicon phase also increases proportionally.

[0221]

[0222] Figure 2 is a graph illustrating the trend of capacity change according to the size of the Si phase of a silicon alloy-based cathode active material through various experimental data.

[0223] Referring to Figure 2 above, it can be confirmed that as the size of the generally deposited silicon phase increases, the capacity of the negative electrode active material also tends to increase in proportion.

[0224] This is because the large size of the precipitated silicon phases essentially implies a high silicon content per unit volume within the alloy, which increases the active surface area capable of storing lithium ions within the alloy.

[0225]

[0226] Figure 3 is a graph illustrating the trend of capacity retention rate change according to the size of the Si phase in silicon alloy-based negative electrode active materials through various experimental data. The capacity retention rate is the result of performing a 500-cycle charge-discharge test under 1C charge / 1C discharge conditions in the range of 3.0V to 4.2V on fabricated pouch full cells. NCM622 cathode material was used for the anode with a current density of 3mA / cm² 2 A silicon alloy-based cathode active material was mixed with graphite at the blending ratio specified in the table, and a cathode containing a binder (SBR+CMC=4%) and a conductive agent (single-walled carbon nanotubes 0.25%) was fabricated.

[0227] Referring to Fig. 3, it can be seen that as the size of the generally deposited silicon phase increases, the capacity retention rate of the negative electrode active material decreases inversely.

[0228]

[0229] This is because as the size of the precipitated silicon phase increases, the stress caused by volume expansion increases, leading to structural damage to the electrode and resulting in a shortened cycle life.

[0230]

[0231] Therefore, miniaturizing the silicon phase to an appropriate size is a critical factor in improving the performance and stability of the cathode active material.

[0232]

[0233] Through the above Figures 1 to 3, if the silicon alloy contains the same amount of silicon,

[0234] When the silicon phase is dispersed and precipitated as small clumps, the active surface area per unit volume or unit mass increases, and

[0235] This confirms that it provides more pathways for lithium ions to be inserted into silicon, allowing electrochemical reactions to occur more efficiently.

[0236]

[0237] In other words, it is most desirable to increase only the silicon content contained within the silicon alloy while reducing the size of the precipitated silicon phase.

[0238]

[0239] Referring to Tables 1 and 2 above, it can be seen that as the content of Group La elements included in the silicon alloy increases little by little, the diameter of the precipitated silicon phase gradually decreases.

[0240] More specifically, referring to Table 1, the average diameter of the precipitated silicon phase when group La elements are not included is 25.7 nm, and

[0241] When Group La elements are added gradually, when the included Group La element is 1.96 wt%, the average diameter of the precipitated silicon phase is 16 nm,

[0242] It corresponds to approximately 62% of the above 25.7nm.

[0243]

[0244] As the content of group La elements increases, the average diameter of the precipitated silicon phase decreases, and

[0245] When the above Group La element is 9.09 wt%, the average diameter of the precipitated silicon phase is 7 nm,

[0246] It corresponds to approximately 27% of the above 25.7nm.

[0247]

[0248] However, as can be seen in Table 1 above,

[0249] It can be confirmed that when the content of Group La elements is less than 3 wt%, the capacity retention rate of the negative electrode active material decreases rapidly, and

[0250] It can be confirmed that when the content of Group La elements exceeds 9 wt%, the capacity of the negative electrode active material decreases to less than 1000 mAh / g.

[0251] It is more preferable to include the above-mentioned La group element in a mass percentage of 3 wt% to 6 wt% so that the average diameter of the precipitated silicon phase is in the range of 40% to 35% compared to the average diameter when the above-mentioned La group element is not included.

[0252]

[0253] FIG. 4 is an SEM image showing the surface structure of a negative electrode active material ribbon according to the La content of a silicon alloy-based negative electrode active material according to one embodiment of the present invention.

[0254] Figures 4a to 4g above are SEM images corresponding to each sample (Comparative Example 2 and Examples 8 to 13) of Table 2 above, in order.

[0255] Referring to FIG. 4, it can be seen that as the content of group La elements in the silicon alloy increases, the uneven parts of the surface of the negative electrode active material gradually disappear, and a uniform and flat surface is formed.

[0256]

[0257] The foregoing description of the present invention is for illustrative purposes only, and those skilled in the art will understand that other specific forms can be easily modified without altering the technical spirit or essential features of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single unit may be implemented in a distributed manner, and components described as distributed may likewise be implemented in a combined form.

[0258] The scope of the present invention is defined by the claims set forth below, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts thereof should be interpreted as being included within the scope of the present invention.

Claims

Silicon single phase; and A matrix located around the above silicon single phase; comprising, The above matrix includes Si elements, La group elements, and element M, and The above element M comprises one or more selected from the group consisting of Al, Fe, Ti, and Mn, and The content of the above Group La element is 2 wt% to 9 wt% for 100 wt% of the total negative electrode active material, and A silicon-based negative electrode active material characterized by the inclusion of the above-mentioned La group element, wherein the average diameter of the silicon single phase is refined to less than 30 nm. In paragraph 1, A silicon-based negative electrode active material characterized in that the content of the element M is 35 wt% to 46 wt% with respect to 100 wt% of the total negative electrode active material. In paragraph 1, A silicon-based negative electrode active material characterized by having a Si element content of 45 wt% to 63 wt% for 100 wt% of the total negative electrode active material. A silicon-based negative electrode active material according to claim 1, characterized in that the above La group element comprises one or more selected from the group consisting of La, Ce, and Nd. In claim 1, the average diameter of the silicon phase precipitated by including the above-mentioned La group element is, A silicon-based negative electrode active material characterized by having an average diameter in the range of 65% to 25% compared to the case where the above-mentioned La group element is not included. A silicon-based negative electrode active material according to claim 1, characterized in that the average diameter of the precipitated silicon phase is 7 nm to 30 nm. A silicon-based negative electrode active material according to claim 1, characterized in that the negative electrode active material has an initial capacity of 1000 mAh / g or more. A silicon-based negative electrode active material according to claim 1, characterized in that the negative electrode active material has a capacity retention of 70% or more even after 500 charge / discharge cycles. A negative electrode of a lithium secondary battery comprising a current collector and a negative electrode material formed on at least one surface of the current collector, A negative electrode for a lithium secondary battery, characterized in that the above negative electrode material comprises the negative electrode active material of claim 1. A lithium secondary battery comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, A lithium secondary battery characterized in that the above-mentioned negative electrode is a negative electrode according to claim 9.

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