Negative electrode active material, negative electrode containing the same, and lithium secondary battery

Abstract

The present invention provides a high-capacity negative electrode active material with excellent conductivity that is free from the problem of electrical short circuits within the electrode, a negative electrode for a lithium secondary battery that includes the negative electrode active material, and a lithium secondary battery that includes the negative electrode. [Solution] The present invention provides a negative electrode active material comprising: an active material core capable of absorbing and releasing lithium ions; a plurality of conductive materials located on the surface of the active material core; a plurality of organic linkers each including a hydrophobic group and a polar functional group bonded to the hydrophobic group; and an elastic unit; wherein the elastic unit comprises an elastic portion having two or more bonding sites and a functional group bonded to the bonding site of the elastic portion and capable of reacting with the polar functional group of the organic linker; at least one of the plurality of organic linkers is linked to the conductive material via the hydrophobic group of the organic linker, and the polar functional group of the organic linker is bonded to a functional group on the surface of the active material core or to a functional group of the elastic unit.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority based on Korean Patent Application No. 10-2018-0158018, filed December 10, 2018, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to an anode active material, an anode including the same, and a lithium secondary battery, and more particularly to an anode active material having a conductive material stably attached to a surface thereof via an organic linker, and an anode and a lithium secondary battery including the same. [Background technology]

[0003] The rapid increase in the use of fossil fuels has led to an increasing demand for alternative and clean energy, and as part of this, the most actively researched field is the field of power generation and storage using electrochemical reactions.

[0004] Currently, a representative example of an electrochemical element that uses electrochemical energy is a secondary battery, and its range of use is expanding. Recently, with the development of technology and increasing demand for portable devices such as portable computers, portable phones, and cameras, the demand for secondary batteries as energy sources has increased dramatically. Among such secondary batteries, much research has been conducted on high-energy density, i.e., high-capacity lithium secondary batteries, which have been commercialized and widely used.

[0005] Generally, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. The positive electrode active material of a lithium secondary battery is a metal oxide such as LiCoO2, LiMnO2, LiMn2O4, or LiCrO2, and the negative electrode active material is a carbon-based material such as metallic lithium, graphite, or activated carbon, or silicon oxide (SiO2).x ) have been used. Among the negative electrode active materials, metallic lithium was primarily used in the early days, but as charge and discharge cycles progress, lithium atoms grow on the surface of the metallic lithium, damaging the separator and causing damage to the battery. Therefore, carbon-based materials have recently become more common. However, carbon-based materials have the disadvantage of having a low theoretical capacity of only about 400 mAh / g. Therefore, various research efforts are underway to replace the carbon-based materials with high-capacity materials such as silicon (Si), which has a high theoretical capacity (4,200 mAh / g) as the negative electrode active material.

[0006] However, high-capacity materials have problems such as excessive volume change during charging and discharging, which can cause electrical short circuits within the electrode and the growth of a thick and unstable solid electrolyte interface (SEI), resulting in poor battery performance.

[0007] In the past, attempts have been made to solve these problems by forming a carbon coating layer on the surface of silicon-based particles or by using an additional conductive material.

[0008] However, the method of forming a carbon coating layer requires a process of applying heat during the formation of the carbon coating layer, which can lead to cracks in the silicon-based particles or a reduction in pores, resulting in a decrease in efficiency. Furthermore, the method of using an additional conductive material can lead to agglomeration of the conductive material as the content of the conductive material increases.

[0009] For this reason, as disclosed in Korean Patent Publication No. 10-2016-0149862, attempts have been made to further control volume change by disposing an additional polymer composite on the carbon coating layer. However, even if an additional polymer composite is formed, it is difficult to control volume change, and instead, problems can arise such as a decrease in the conductivity of the active material, an increase in resistance, and a decrease in battery capacity retention. Another problem is that excessive coating of silicon-based particles makes it difficult to absorb lithium ions, resulting in a decrease in capacity.

[0010] Therefore, there is a need to develop a new technology that can solve problems such as electrical short circuits and performance degradation within the electrode due to volume changes in high-capacity negative electrode active materials. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Korean Patent Publication No. 10-2016-0149862 Summary of the Invention [Problem to be solved by the invention]

[0012] The problem to be solved by the present invention is to provide a high-capacity negative electrode active material that is excellent in conductivity and does not cause the problem of electrical short circuits within the electrode.

[0013] Another object of the present invention is to provide a negative electrode for a lithium secondary battery, which includes the negative electrode active material.

[0014] Another object of the present invention is to provide a lithium secondary battery including the negative electrode. [Means for solving the problem]

[0015] To achieve this, the present invention provides a negative electrode active material comprising: an active material core capable of absorbing and releasing lithium ions; a plurality of conductive materials located on the surface of the active material core; a plurality of organic linkers, each including a hydrophobic group and a polar functional group bound to the hydrophobic group; and an elastic unit; wherein the elastic unit comprises an elastic portion having two or more binding sites and a functional group bound to the binding site of the elastic portion and capable of reacting with the polar functional group of the organic linker; at least one of the plurality of organic linkers is linked to the conductive material via the hydrophobic group of the organic linker, and the polar functional group of the organic linker is bound to a functional group on the surface of the active material core or to a functional group of the elastic unit.

[0016] In order to achieve the above-mentioned other object, the present invention provides a negative electrode including: a negative electrode current collector; and a negative electrode active material layer formed on the negative electrode current collector and including a negative electrode material, wherein the negative electrode material includes the above-mentioned negative electrode active material.

[0017] In order to achieve the above and other objects, the present invention provides a lithium secondary battery including the above-mentioned negative electrode; a positive electrode facing the negative electrode; a separator interposed between the negative electrode and the positive electrode; and an electrolyte. [Effects of the Invention]

[0018] The negative electrode active material according to the present invention includes a conductive material located on the surface of an active material core capable of absorbing and releasing lithium ions and having one or more organic linkers bound thereto. The organic linkers are connected to the surface of the active material core or to elastic units, so that the conductive material is tightly bound to the surface of the negative electrode active material. Furthermore, the conductive materials are connected to each other, so that the conductive material can provide sustained electrical conductivity even when the volume of the negative electrode active material changes due to charging and discharging, thereby exhibiting improved life characteristics. [Brief explanation of the drawings]

[0019] [Figure 1] 1A to 1C are diagrams for schematically illustrating a method for producing a negative electrode active material according to the present invention. [Figure 2] 1A to 1C are diagrams for schematically illustrating a method for producing a negative electrode active material according to the present invention. [Figure 3] 1A to 1C are diagrams for schematically illustrating a method for producing a negative electrode active material according to the present invention. [Figure 4] 1A to 1C are diagrams for schematically illustrating a method for producing a negative electrode active material according to the present invention. [Figure 5] 1A to 1C are diagrams for schematically illustrating a method for producing a negative electrode active material according to the present invention. [Figure 6] 1 is a graph showing an evaluation of the capacity retention rate with cycles in Examples 1 to 3, Comparative Example 1, and Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0020] The present invention will now be described in more detail to aid in understanding the invention.

[0021] The terms and words used in the description of the present invention and the claims should not be interpreted limited to their ordinary and dictionary meanings, but should be interpreted as meanings and concepts that are consistent with the technical idea of the present invention, in accordance with the principle that an inventor may appropriately define the concepts of terms in order to best describe his or her invention.

[0022] The term "polycyclic ring group" as used herein, unless otherwise specified, refers to a fused ring or fused nucleus, which is a ring in which two or more rings are bonded together by sharing two or more atoms.

[0023] The term "alkyl", as used herein, unless otherwise specified, means a straight-chain, cyclic or branched hydrocarbon residue.

[0024] The term "linear conductive material" as used in this specification means, unless otherwise specified, a conductive material having a fibrous structure such as a cylindrical type or a tube type, "planar conductive material" means, unless otherwise specified, a conductive material having a planar, sheet or flake shape, and "dot-like conductive material" means a commonly used conductive material having an approximately spherical particle shape.

[0025] <Negative electrode active material> The present invention relates to a negative electrode active material, particularly to a negative electrode active material for a lithium secondary battery.

[0026] The negative electrode active material according to the present invention includes an active material core capable of occluding and releasing lithium ions; a plurality of conductive materials located on the surface of the active material core; a plurality of organic linkers including hydrophobic groups and polar functional groups bonded to the hydrophobic groups; and an elastic unit. The elastic unit includes an elastic portion having two or more binding sites, and a functional group bonded to the binding sites of the elastic portion and capable of reacting with the polar functional groups of the organic linkers. One or more of the plurality of organic linkers are connected to the conductive material through the hydrophobic groups of the organic linkers, and the polar functional groups of the organic linkers are bonded to the functional groups on the surface of the active material core or the functional groups of the elastic unit.

[0027] According to the present invention, in the negative electrode active material, the conductive material may be firmly bonded to the core surface of the active material by the organic linker, and the conductive materials may be connected to each other by the elastic unit. Therefore, even when the volume expands / contracts due to charge / discharge of the negative electrode active material, the conductive material can continuously provide electrical conductivity between the active materials, and thus can exhibit improved stability.

[0028] The active material core is not particularly limited as long as it is a material capable of occluding and releasing lithium ions. However, the effect of including the organic linker, the elastic unit, and the plurality of conductive materials connected to the active material core or to each other according to the present invention can be more preferably exhibited in the case of a material having a large volume change during charge / discharge while having a high capacity. Such an active material core capable of occluding and releasing lithium ions may be one or more selected from the group consisting of Si, SiO x (0 < x < 2), Sn, SnO2, and Si-metal alloys. Examples of the metal capable of forming the Si-metal alloy include Al, Sn, Ag, Fe, Bi, Mg, Mn, Zn, In, Ge, Pb, and Ti, and examples of the metal oxide include SnO2, TiO2, Co3O4, Fe3O4, and Mn3O4.

[0029] The average particle diameter (D) of the active material core 50The average particle size (D) of the active material cores may be 0.01 to 30 μm, specifically 0.5 to 30 μm, and more specifically 1 to 20 μm. 50 ) satisfies the above range, the negative electrode can exhibit an appropriate density and have an appropriate capacity per volume, and the thickness of the negative electrode can be prevented from becoming too thick due to the volume expansion of the negative electrode active material.

[0030] In the present invention, the average particle size (D 50 ) can be defined as the particle size at 50% of the particle size distribution. The average particle size is not particularly limited, and can be measured, for example, using a laser diffraction method or a scanning electron microscope (SEM) photograph. The laser diffraction method generally enables measurement of particle sizes from the submicron range to several mm, and can provide results with high reproducibility and high resolution.

[0031] The active material core may be included in the negative electrode active material in an amount of 30 wt % to 99 wt %, preferably 60 wt % to 97 wt %, and more preferably 70 wt % to 80 wt %, in order to ensure sufficient capacity characteristics while smoothly achieving the effect of improving life characteristics due to the conductive network described below.

[0032] The conductive material may be a plurality of conductive materials located on the surface of the active material core. As described below, the conductive materials may be connected to the surface of the active material core by one or more organic linkers via hydrophobic groups of the organic linkers, and two or more of the conductive materials may be connected to each other by the elastic unit to form a conductive network.

[0033] The conductive material may include at least one of a linear conductive material and a planar conductive material, and two or more of the plurality of conductive materials may be connected to each other via the elastic unit.

[0034] The linear conductive material may form a fibrous structure and may be one or more selected from the group consisting of carbon fiber, carbon nanofiber (CNF), metal fiber, carbon nanotube (CNT) and conductive whisker, specifically carbon fiber, more specifically carbon nanotube (CNT).

[0035] The sheet-shaped conductive material may be in the form of a plane, a sheet, or a flake, and may be one or more selected from the group consisting of graphene, a metal thin film, and mxene.

[0036] Preferably, the conductive material may include a linear conductive material. In this case, since the conductive material has a linear structure, a conductive network that improves the electrical connectivity of the active material can be stably formed.

[0037] The conductive material may be contained in the negative electrode active material in an amount of 0.05 to 15 parts by weight, preferably 0.3 to 12 parts by weight, and more preferably 0.5 to 5 parts by weight, based on 100 parts by weight of the active material core. This range is preferable because it can prevent a decrease in the initial efficiency and capacity of the active material due to the addition of an excessive amount of conductive material, while allowing for sufficient formation of an electrical network within the active material.

[0038] The conductive material may be contained in the negative electrode active material in an amount of 0.05 wt % to 5 wt %, preferably 0.3 wt % to 3.5 wt %, and more preferably 0.5 wt % to 2 wt %. This range is preferable because it can prevent a decrease in the initial efficiency and capacity of the active material due to the addition of an excessive amount of conductive material, while allowing a sufficient electrical network to be formed within the active material.

[0039] The organic linkers may be plural and may include a hydrophobic group and a polar functional group bound to the hydrophobic group. As described below, one or more of the organic linkers may be linked to the conductive material via the hydrophobic group of the organic linker. In addition, the polar functional group of the organic linker may be bonded to a functional group (e.g., a hydroxy group) on the surface of the active material core or to a functional group of an elastic unit, which will be described below. As a result, the organic linker may firmly bind the conductive material to the surface of the active material core while simultaneously linking two or more of the conductive materials to each other.

[0040] Specifically, conductive materials are generally difficult to disperse in solvents. When attempting to introduce them onto the surface of a negative electrode active material or into the negative electrode, they are difficult to introduce in a uniformly dispersed form due to aggregation caused by the attractive forces between the conductive materials. Therefore, when using linear or planar conductive materials, dispersants are typically used. However, most dispersants rely on weak inter-substance attractive forces, making it difficult to bind the linear or planar conductive materials to the negative electrode active material to form a stable electrical network. Furthermore, when the volume of the negative electrode active material changes during charging and discharging, the conductive materials may detach from the surface of the negative electrode active material. In this case, despite the introduction of linear or planar conductive materials to maintain appropriate conductivity in response to volume changes of the negative electrode active material, it is difficult to avoid deterioration of battery performance.

[0041] To solve the above problems, the negative electrode active material of the present invention introduces an organic linker, which is a compound containing a hydrophobic group and a polar functional group. The organic linker firmly attaches a conductive material to the surface of the active material core. Furthermore, two or more conductive materials can be connected to each other via the organic linker. This allows the conductive material to provide stable electrical conductivity even when the volume of the negative electrode active material changes.

[0042] The conductive material may be connected to the surface of the active material core via one or more organic linkers. When the conductive material is a linear conductive material, it may be in linear contact or attached to the active material core. When the conductive material is a planar conductive material, it may be in face-to-face contact with the active material core, forming a stable electrical connection. The conductive material may be positioned across two or more active materials, thereby increasing electrical contact between the negative electrode active materials. This minimizes the disruption of the electrical network due to changes in the volume, position, or shape of the negative electrode active materials, thereby preventing an increase in negative electrode resistance due to the disruption of the electrical network.

[0043] The organic linker is a compound that can provide a bonding force between the conductive material and the surface of the active material and that contains a hydrophobic group and a polar functional group in its molecular structure, and at least one of the organic linkers is linked to the conductive material via the hydrophobic group of the organic linker.

[0044] The hydrophobic group may include at least one selected from the group consisting of a ring group having a π-electron conjugate structure and an alkyl group having 3 to 20 carbon atoms.

[0045] Specifically, the hydrophobic structure of the organic linker interacts with and bonds to the conductive material through van der Waals attraction. Specifically, conjugated π electrons of a π electron conjugated ring may form van der Waals bonds with π electrons included in the conductive material, or electrons of an alkyl group may form van der Waals bonds with electrons of the conductive material.

[0046] The ring group of the π-electron conjugated structure means an aromatic ring having the number of electrons satisfying the rule of "4n+2", and specifically may be a ring in which two or more rings are bonded, more specifically, a ring in which two or more rings have a fused ring structure. The ring group of the π-electron conjugated structure may include, for example, one or more selected from the group consisting of benzene, pyrene, naphthalene, anthracene, benzopyrene, phenanthrene, fluoranthene, chrysene, perylene, benz[a]anthracene, acenaphthylene, coronene, triphenylene, and tetracene.

[0047] In one embodiment of the present invention, the cyclic group having a π-electron conjugated structure may be a polycyclic group having four or more rings bonded thereto. The polycyclic group having four or more rings bonded thereto includes a group containing four or more rings therein, and may include, for example, one or more selected from the group consisting of pyrene, benzopyrene, fluoranthene, chrysene, perylene, benz[a]anthracene, coronene, triphenylene, and tetracene.

[0048] The alkyl group may be an alkyl group having 3 to 20 carbon atoms.

[0049] The polar functional group of the organic linker is bonded to a functional group on the surface of the active material core or to a functional group of an elastic unit, which will be described later.

[0050] The polar functional group may be bonded to or substituted on a π-electron conjugated ring group or alkyl group of the organic linker, which may improve dispersibility in a solvent. The polar functional group may bond to a functional group located on the surface of the active material core, allowing the conductive material bonded to the organic linker to adhere to the surface of the active material core, or may be bonded to an elastic unit.

[0051] In addition, the polar functional group has excellent affinity with the solvent, which allows the organic linker to be effectively dispersed in the solvent, and therefore the linear conductive material bound to the organic linker can be effectively dispersed in the solvent without agglomeration (debundling).

[0052] The polar functional group may be linked or bonded to the surface of the active material core via a bond with a functional group, specifically a functional group containing -OH, located on the surface of the active material core. The functional group containing -OH located on the surface of the active material core may be formed by oxidation of the surface of the active material core by oxygen in the air. Because the bond between the polar functional group and the functional group containing -OH is a chemical bond, the organic linker and the linear conductive material may be strongly attached to the active material core, allowing stable electrical conductivity to be maintained even when the volume of the active material core changes.

[0053] In a negative electrode active material according to an embodiment of the present invention, when the hydrophobic group of the organic linker is linked to the conductive material and the polar functional group is linked to the surface of the active material core, the bonding structure of the active material core, the organic linker, and the conductive material can be expressed as "active material core: chemical bond between the polar functional group and the -OH group: organic linker: π-π interaction: conductive material."

[0054] In addition, the polar functional group may be bonded to a functional group of the elastic unit. The bond between the polar functional group and the functional group of the elastic unit is a chemical bond, and the conductive materials connected to the organic linkers may be connected to each other via the elastic unit to form a conductive material network. The elastic unit includes an elastic portion having elasticity, so that the conductive material network can appropriately change its size in response to a change in volume during charge and discharge of the active material core, while still stably contacting the active material core.

[0055] The polar functional group may be one or more selected from the group consisting of a carboxylic acid group, a phosphonic acid group, a sulfonic acid group, and an alkyl group having 1 to 8 carbon atoms substituted with a carboxylic acid group, a phosphonic acid group, or a sulfonic acid group. The polar functional group may be linked via a chemical bond to a functional group containing —OH located on the surface of the active material core, and may also be linked via a chemical bond to the functional group portion of the elastic unit. Preferably, the polar functional group may be at least one selected from a carboxylic acid group and an alkyl group having 1 to 8 carbon atoms substituted with a carboxylic acid group, in view of excellent bonding with the polar functional group in the active material core.

[0056] The organic linker may be at least one selected from the group consisting of 1-pyreneacetic acid, 1-pyrenecarboxylic acid, 1-pyrenebutyric acid, dodecylsulfonic acid, and dodecylbenzenesulfonic acid. Preferably, the organic linker is 1-pyrenebutyric acid. In this case, the organic linker contains a carboxyl group, which provides excellent bonding strength with polar functional groups on the surface of the active material. The organic linker contains an appropriate amount of linear alkylene groups, which improves the flexibility of the conductive material and allows for the formation of a flexible conductive network between the negative electrode active materials, thereby improving battery life characteristics. When the organic linker and the conductive material are mixed in the preparation of the negative electrode active material, the excellent polarity of the carboxylate group in the organic linker improves the dispersibility of the conductive material, allowing for uniform distribution of the conductive material on the surface of the negative electrode active material.

[0057] The organic linker may include two different organic linkers, specifically a first organic linker and a second organic linker.

[0058] The first organic linker may be a compound including a ring group having a π-electron conjugated structure and a polar functional group, and the second organic linker may be a compound including an alkyl group having 3 to 20 carbon atoms and a polar functional group, a compound including a ring group having a π-electron conjugated structure, an alkyl group having 3 to 20 carbon atoms and a polar functional group, or a mixture thereof.

[0059] When the organic linker includes a first organic linker and a second organic linker, the conductive material may be more effectively dispersed in a solvent during the preparation of the negative electrode active material, and thus the conductive material may be more effectively dispersed and attached to the surface of the active material core, and thus may be more uniformly located.

[0060] The first organic linker may be one or more selected from the group consisting of 1-pyreneacetic acid, 1-pyrenecarboxylic acid, and 1-pyrenebutyric acid, and the second organic linker may be one or more selected from the group consisting of dodecyl sulfonic acid and dodecyl benzene sulfonic acid.

[0061] The organic linker may include the first organic linker and the second organic linker in a weight ratio of 1:99 to 99:1, specifically a weight ratio of 5:95 to 95:5, more specifically a weight ratio of 10:90 to 90:10. When the first organic linker and the second organic linker satisfy this weight ratio, the conductive material may be more effectively dispersed and more effectively attached to the active material core.

[0062] The organic linker may be included in the negative electrode active material in an amount of 0.005 wt % to 40 wt %, preferably 1 wt % to 35 wt %, and more preferably 3 wt % to 10 wt %, which is preferable in that it can effectively link the conductive material to the surface of the active material and / or the elastic unit.

[0063] The elastic unit comprises an elastic moiety having two or more binding sites and a functional group attached to the binding site of the elastic moiety that is reactive with the polar functional group of the organic linker.

[0064] The elastic unit may connect two or more of the plurality of conductive materials to each other. The elastic unit has elasticity and connects two or more conductive materials to each other, thereby providing a persistent conductive network in the active material core even when the volume of the active material core expands. The plurality of conductive materials connected by the elastic unit may form a conductive network with a network structure, and the conductive network with a network structure that is elastic and can adjust its size to accommodate the volume expansion of the active material core, providing a persistent conductive network. Furthermore, the conductive network formed by the elastic unit has a small area covering the active material core, thereby preventing the elastic unit from acting as a resistance when lithium ions are absorbed and released into and from the active material core.

[0065] The elastic portion has flexibility or stretchability, and has two or more binding sites to which functional groups capable of reacting with the polar functional groups of the organic linker are bound.

[0066] The elastic portion may be at least one of a linear polymer and a multi-arm polymer, specifically at least one of a linear polymer and a multi-arm polymer to which two or more functional groups are bonded. When the elastic portion is a polymer to which two or more functional groups are bonded, the two or more functional groups may be bonded to polar functional groups of organic linkers that are bonded to different conductive materials to link the different conductive materials, and the linked conductive materials may form a network structure.

[0067] The elastic portion may include at least one selected from the group consisting of alkylene units and alkyleneoxy units, specifically, at least one unit selected from the group consisting of -(CH)-, -(CHCHO)-, and -(CHCH(CH)O)-. The number of the at least one unit selected from -(CH)-, -(CHCHO)-, and -(CHCH(CH)O)- included in the elastic portion may be an integer of 10 to 1,000, specifically, an integer of 40 to 500.

[0068] The functional group of the elastic unit may include one or more selected from the group consisting of a cyanate group, an isocyanate group (OCN), an alcohol group, and an amino group (-NH). When the functional group of the elastic unit includes one or more selected from the group consisting of a cyanate group, an isocyanate group (OCN), an alcohol group, and an amino group (-NH), these functional groups can be appropriately linked to the polar functional group of the organic linker via a chemical bond. Specifically, when the functional group of the elastic unit is a cyanate group, an isocyanate group (OCN), and / or an amino group (-NH), and the polar functional group of the organic linker is a carboxylic acid group, an amide bond (-CO-NH-) can be formed by the reaction thereof. Furthermore, when the functional group of the elastic unit is an alcohol group, and the polar functional group of the organic linker is a carboxylic acid group, an ester bond (-COO-) can be formed by the reaction thereof.

[0069] The elastic unit may be one or more selected from poly(hexamethylene diisocyanate) and toluene 2,4-diisocyanate terminated (TDI) poly(propylene glycol).

[0070] The elastic units may be included in the negative electrode active material in an amount of 1 wt % to 70 wt %, preferably 5 wt % to 65 wt %, and more preferably 10 wt % to 20 wt %, which is preferred in that the conductive network formed by the elastic units can be easily maintained when the volume of the active material changes.

[0071] <Method of manufacturing negative electrode active material> The present invention also provides a method for producing the above-mentioned negative electrode active material.

[0072] Specifically, the method for preparing the negative electrode active material according to the present invention includes the steps of dispersing a conductive material and an organic linker in a solvent; adding an active material core to the solvent and mixing the mixture; and adding an elastic unit to the solvent and mixing the mixture.

[0073] Hereinafter, a method for manufacturing a negative electrode active material according to the present invention will be described in detail with reference to the drawings. When assigning reference numerals to components in each drawing, the same components may be assigned the same numerals as much as possible even if they are shown in different drawings. Furthermore, when describing the present invention, if it is determined that a detailed description of related known structures or functions may obscure the gist of the present invention, the detailed description may be omitted.

[0074] 1 to 5 are diagrams for schematically illustrating the method for producing a negative electrode active material of the present invention.

[0075] 1, a conductive material 10 and an organic linker 20 are dispersed in a solvent. The conductive material 10 and the organic linker 20 may be the same as the conductive material and organic linker described above.

[0076] 1, by dispersing the conductive material 10 and the organic linker 20 in a solvent first, the organic linker 20 can be effectively dispersed in the solvent, and at the same time, the conductive material 10 can be effectively dispersed in the solvent without agglomeration (debundling), allowing the hydrophobic groups in the conductive material 10 and the organic linker 20 to bond with each other through van der Waals attraction. If the conductive material is not dispersed first together with the organic linker and then mixed with the active material core, elastic unit, etc. (described below), the conductive material will agglomerate more, making it difficult to bond with the organic linker through van der Waals attraction. This may prevent the formation of bonds between the conductive material and the active material core, or between the conductive materials themselves through the elastic unit.

[0077] When the conductive material 10 and the organic linker 20 are dispersed first, the solvent may be a polar solvent. Dispersing the organic linker and conductive material in a polar solvent facilitates dispersion of the organic linker and allows the polar functional group of the organic linker to have a strong polarity. This allows the polar functional group to react with hydroxyl groups on the surface of the active material core or with functional groups of the elastic units, thereby linking the conductive material to the surface of the active material core through the organic linker, or linking different conductive materials to each other through the elastic units. The polar solvent may be N-methylpyrrolidone and / or an aqueous NaOH solution, preferably N-methylpyrrolidone, which allows the elastic units to be easily mixed and dispersed in the solvent without phase separation. If the solvent is not polar, the organic linker may not disperse in the solution, and the polar functional group of the organic linker may not react with the surface of the active material core and / or the elastic units, making it difficult to form the anode active material of the present invention.

[0078] 2 and 3, the active material core 30 is added to the solvent and mixed. The active material core 30 has been described above.

[0079] 2, functional groups 35 such as hydroxyl groups (OH groups) may be present on the active material core 30. The functional groups 35 are bonded to the surface of the active material core via binding sites (*), and may be formed by oxidation of the surface of the active material core 30 by oxygen in the air.

[0080] 3, functional groups 35 on the surface of active material core 30 may react with a portion of organic linker 20 to form active material core / organic linker / conductive material combination 25. Conductive material 10 and the surface of active material core 30 may be connected to each other through active material core / organic linker / conductive material combination 25.

[0081] 4 and 5, the elastic unit 40 is added to the solvent and mixed. The elastic unit 40 may be the same as the elastic unit described above.

[0082] 4 and 5, the elastic unit 40 includes, at two or more terminal locations, functional groups such as isocyanate groups that can react with polar functional groups of the organic linkers. As a result, some of the organic linkers 20 may react with the functional groups of the elastic unit 40 to form a conductive material / organic linker / elastic unit / organic linker / conductive material bond 45. As a result, two or more conductive materials 10 may be connected to each other via the elastic unit 40.

[0083] In this regard, the process of dispersing the organic linker and the conductive material in the solvent, the process of mixing the elastic unit, and the process of mixing the active material core may be carried out by a conventional mixing method, for example, a milling method such as ultrasonic sonification, a ball mill, a bead mill, or a basket mill, or a method using a mixing device such as a homogenizer, a bead mill, a ball mill, a basket mill, an attrition mill, a universal mixer, a clear mixer, or a TK mixer.

[0084] Through this process, the surface of the active material core 30 and the conductive material 10 are connected to each other via the organic linker 20, and two or more conductive materials are connected to each other via the organic linker 20 and the elastic unit 40, forming a conductive network. The conductive network formed as described above allows the conductive material to provide sustained electrical conductivity even when the volume changes due to charging and discharging of the negative active material, thereby exhibiting improved life characteristics.

[0085] <Negative electrode for lithium secondary battery and lithium secondary battery> The present invention also provides a negative electrode and a lithium secondary battery including the above-described negative electrode active material.

[0086] Specifically, the negative electrode includes a negative electrode current collector; and a negative electrode active material layer formed on the negative electrode current collector and including a negative electrode material, the negative electrode material including the above-described negative electrode active material.

[0087] The negative electrode current collector is not particularly limited as long as it has high conductivity and does not induce chemical changes in the battery. Specifically, the negative electrode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, or an aluminum-cadmium alloy.

[0088] The negative electrode current collector may typically have a thickness of 3 to 100 μm.

[0089] The negative electrode current collector may have a surface with fine irregularities to enhance the bonding strength of the negative electrode active material. For example, the negative electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous material, a foam, or a nonwoven fabric.

[0090] The negative electrode active material layer is formed on the negative electrode current collector and includes a negative electrode material containing the above-described negative electrode active material.

[0091] The negative electrode material may further include a carbon-based active material in addition to the negative electrode active material described above. The carbon-based active material can impart excellent cycle characteristics or battery life performance to the negative electrode or secondary battery of the present invention.

[0092] Specifically, the carbon-based active material may include at least one selected from the group consisting of graphite, artificial graphite, natural graphite, hard carbon, soft carbon, carbon black, acetylene black, Ketjen black, Super P, graphene, and fibrous carbon, and preferably includes at least one selected from the group consisting of graphite, artificial graphite, and natural graphite.

[0093] The negative electrode material may be contained in the negative electrode active material layer in an amount of 60 to 99% by weight, preferably 65 to 90% by weight.

[0094] The negative electrode active material layer includes a binder, which may include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polyacrylamide, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and materials in which hydrogen is substituted with Li, Na, K, or the like, or may include various copolymers thereof.

[0095] The binder may be contained in the negative electrode active material layer in an amount of 0.5 to 30% by weight, preferably 5 to 25% by weight.

[0096] The negative electrode active material layer may further include an additional conductive material.

[0097] The additional conductive material is not particularly limited as long as it is conductive without inducing a chemical change in the battery, and for example, at least one selected from the group consisting of graphite such as natural graphite and artificial graphite; carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives, preferably at least one selected from the group consisting of graphite such as natural graphite and artificial graphite; and carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black.

[0098] The additional conductive material may be included in the negative electrode active material layer in an amount of 0.5% to 25% by weight, preferably 3% to 20% by weight.

[0099] The thickness of the negative electrode active material layer may be 10 μm to 200 μm, preferably 20 μm to 150 μm.

[0100] The negative electrode may be manufactured by coating a negative electrode slurry containing a negative electrode material, a binder, and a conductive material and / or a solvent for forming the negative electrode slurry on the negative electrode current collector, followed by drying and rolling.

[0101] The solvent for forming the negative electrode slurry is an organic solvent such as NMP (N-methylpyrrolidone), DMF (dimethylformamide), acetone, dimethylacetamide, or water, and these solvents may be used alone or in combination of two or more.

[0102] The present invention also provides a lithium secondary battery including the above-described negative electrode; a positive electrode facing the negative electrode; a separator interposed between the negative electrode and the positive electrode for the lithium secondary battery; and an electrolyte.

[0103] The negative electrode has been described above.

[0104] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including the positive electrode active material.

[0105] The positive electrode current collector in the positive electrode is not particularly limited as long as it is conductive and does not induce chemical changes in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. The positive electrode current collector typically has a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to enhance adhesion of the positive electrode active material. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric.

[0106] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may be lithium cobalt oxide (LiCoO), lithium nickel oxide (LiNiO), Li[Ni x Co y Mn z Mv]O2 (wherein M is any one or more elements selected from the group consisting of Al, Ga, and In; 0.3≦x<1.0, 0≦y, z≦0.5, 0≦v≦0.1, and x+y+z+v=1), Li (Li a M b-a-b’ M' b’ )O 2-c A c(wherein 0≦a≦0.2, 0.6≦b≦1, 0≦b'≦0.2, 0≦c≦0.2; M includes Mn and one or more elements selected from the group consisting of Ni, Co, Fe, Cr, V, Cu, Zn, and Ti; M' is one or more elements selected from the group consisting of Al, Mg, and B; and A is one or more elements selected from the group consisting of P, F, S, and N); layered compounds and compounds substituted with one or more transition metals, such as compounds of the formula Li 1+y Mn 2-y Lithium manganese oxides such as LiMnO4 (where y is 0 to 0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, LiFe3O4, V2O5, and Cu2V2O7; and the chemical formula LiNi 1-y M y Ni-site lithium nickel oxide represented by the chemical formula LiMnO2 (where M=Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and y is 0.01 to 0.3); 2-y M y Examples of the lithium manganese composite oxides include, but are not limited to, lithium manganese composite oxides represented by LiMnO2 (where M=Co, Ni, Fe, Cr, Zn, or Ta, and y is 0.01 to 0.1) or Li2Mn3MO8 (where M=Fe, Co, Ni, Cu, or Zn); LiMn2O4 in which part of the Li in the chemical formula is substituted with an alkaline earth metal ion; disulfide compounds; and Fe2(MoO4)3. The positive electrode may be Li-metal.

[0107] The positive electrode active material layer may include a positive electrode conductive material and a positive electrode binder in addition to the positive electrode active material described above.

[0108] In this case, the positive electrode conductive material is used to impart conductivity to the electrode, and can be used without any particular limitation as long as it has electrical conductivity without causing chemical changes in the battery that is constructed. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. These may be used alone or in combination of two or more.

[0109] The positive electrode binder serves to improve adhesion between particles of the positive electrode active material and between the positive electrode active material and the positive electrode current collector. Specific examples of the positive electrode binder include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used singly or in combination.

[0110] The separator separates the negative electrode and the positive electrode and provides a path for lithium ions to move. Any separator typically used in secondary batteries can be used without particular limitation. In particular, a separator having low resistance to ion migration and excellent humidifying ability for the electrolyte is preferred. Specifically, a porous polymer film, such as a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof, may be used. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may also be used. Furthermore, a coated separator containing a ceramic component or a polymeric material to ensure heat resistance or mechanical strength may be used, and may be selectively used in a single-layer or multi-layer structure.

[0111] Examples of the electrolyte include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in manufacturing lithium secondary batteries, but are not limited to these.

[0112] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0113] Examples of the non-aqueous organic solvent that can be used include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran (franc), 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0114] In particular, among the carbonate-based organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate are preferably used because they are high-viscosity organic solvents with high dielectric constants and can dissociate lithium salts well. When such cyclic carbonates are mixed with linear carbonates having low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, an electrolyte having high electrical conductivity can be produced, and therefore, such cyclic carbonates are more preferably used.

[0115] The metal salt may be a lithium salt, which is a substance that is easily dissolved in the non-aqueous electrolyte solution. For example, the anion of the lithium salt may be F - , Cl - , I - , NO3 - , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3- , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - One or more selected from the group consisting of may be used.

[0116] In addition to the constituent components of the electrolyte, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing a decrease in the capacity of the battery, improving the discharge capacity of the battery, etc.

[0117] According to another embodiment of the present invention, there is provided a battery module including the secondary battery as a unit cell, and a battery pack including the same. The battery module and the battery pack include the secondary battery having high capacity, high rate characteristics, and high cycle characteristics, and may be used as a power source for medium to large devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0118] In the following, preferred embodiments will be presented to aid in understanding the present invention. However, the above embodiments are merely illustrative of the present description, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of the present description and technical ideas. Naturally, such changes and modifications fall within the scope of the claims.

[0119] Example Example 1: Si / PBA / SWCNT 1%-crosslinked 0.1 g of 1-pyrenebutyric acid (PBA) was dissolved in 100 g of N-methylpyrrolidone solvent. 0.01 g of single-walled carbon nanotubes (SWCNTs) was added to the prepared solution and subjected to probe-type sonication for 30 minutes. 1 g of Si powder was then added to the prepared solution and subjected to ultrasonic dispersion for 30 minutes, followed by stirring for 1 hour. 0.2 g of 2,4-diisocyanate toluene-terminated poly(propylene glycol), an elastic unit, was added to the prepared dispersion solution and stirred at 80°C for 24 hours.

[0120] In the solution, the carboxylate groups of 1-pyrenebutyric acid reacted with and bonded to hydroxy groups on the surface of the active material core, and the hydrophobic groups (pyrene groups) of 1-pyrenebutyric acid bonded to the conductive material through van der Waals attraction, connecting the conductive material to the surface of the active material. Furthermore, the carboxylate groups of 1-pyrenebutyric acid that had not reacted with the hydroxy groups of the active material core reacted with the isocyanate groups of the elastic units to form amide bonds, thereby connecting two or more conductive materials to each other via the elastic units to form a conductive network.

[0121] The reaction solution was filtered, washed, and dried to prepare the negative active material (Si / PBA / SWCNT 1%-crosslinked) of Example 1. The "SWCNT 1%" means that the content of SWCNT relative to the active material core (Si) was 1 wt%.

[0122] A negative electrode for evaluating battery performance using the negative electrode active material was prepared as follows: Si / PBA / SWCNT 1%-crosslinked: Super-C: polyacrylic acid (PAA) was mixed with distilled water in a weight ratio of 70:20:10 to prepare a slurry, which was then coated on copper foil and pre-dried at approximately 60°C for 6 hours. The slurry was then completely dried in a vacuum oven at 130°C for 12 hours to prepare a negative electrode.

[0123] Example 2: Si / PBA / SWCNT 0.1%-crosslinked An anode active material of Example 2 (Si / PBA / SWCNT 0.1%-crosslinked) was prepared in the same manner as in Example 1, except that 0.01 g of PBA was added instead of 0.1 g, 0.001 g of SWCNT was added instead of 0.01 g, and 0.02 g of 2,4-diisocyanate toluene-terminated poly(propylene glycol) was added instead of 0.2 g. The term "0.1% SWCNT" refers to a SWCNT content of 0.1 wt % relative to the active material core (Si).

[0124] A negative electrode was prepared in the same manner as in Example 1, except that the negative electrode active material prepared above was used.

[0125] Example 3: Si / PBA / SWCNT 10%-crosslinked An anode active material of Example 3 (Si / PBA / SWCNT 10%-crosslinked) was prepared in the same manner as in Example 1, except that 1 g of PBA was added instead of 0.1 g, 0.1 g of SWCNT was added instead of 0.01 g, and 2 g of 2,4-diisocyanatotoluene-terminated poly(propylene glycol) was added instead of 0.2 g. The term "SWCNT 10%" refers to a SWCNT content of 10 wt% relative to the active material core (Si).

[0126] A negative electrode was prepared in the same manner as in Example 1, except that the negative electrode active material prepared above was used.

[0127] Comparative Example 1: In Example 1, 0.1 g of 1-pyrenebutyric acid (PBA) was dissolved in 100 g of N-methylpyrrolidone solvent. 0.01 g of single-walled carbon nanotubes (SWCNTs) was added to the resulting solution and subjected to probe-type sonication for 30 minutes. Then, 1 g of Si powder was added to the resulting solution and subjected to ultrasonic dispersion for 30 minutes, followed by stirring for 1 hour. The resulting dispersion was filtered and washed by adding water several times. The resulting material was dried in a vacuum oven at 130°C for 12 hours to obtain a negative electrode active material (Si / PBA / SWCNT 1%) according to Comparative Example 1. The "SWCNT 1%" indicates that the SWCNT content relative to the active material core (Si) was 1 wt%.

[0128] A negative electrode was prepared in the same manner as in Example 1, except that the negative electrode active material obtained above was used.

[0129] Comparative Example 2: Anode slurry was prepared by adding Si:SWCNT:2,4-diisocyanate toluene-terminated poly(propylene glycol):Super-C:PAA to water in a weight ratio of 70:1:10:10:9:10 and stirring. The slurry was applied to copper foil, pre-dried at approximately 60°C for 6 hours, and then completely dried in a vacuum oven at 130°C for 12 hours to prepare an anode.

[0130] In the case of Comparative Example 2, the organic binder PBA was not added, so the bonding between the conductive material according to the present invention and the surface of the active material core and the formation of a conductive network by the elastic units were not achieved.

[0131] Experimental Example Coin-type half cells were fabricated using the negative electrodes prepared in Examples 1 to 3 and Comparative Examples 1 and 2. Metallic lithium foil was used as the positive electrode, and a polyethylene separator was interposed between the negative and positive electrodes to fabricate an electrode assembly.

[0132] The electrode assembly was placed in a battery case, and an electrolyte solution containing 1M LiPF6 in a non-aqueous solvent mixed with ethylene carbonate and diethyl carbonate in a volume ratio of 1:2 was injected to fabricate a coin-type half battery.

[0133] Experimental Example 1: Evaluation of initial discharge capacity and initial efficiency The charge-discharge characteristics of coin-type half cells fabricated using the negative electrodes fabricated in Examples 1 to 3 and Comparative Examples 1 and 2 were evaluated.

[0134] The first charge / discharge was performed at a current density of 0.1C / 0.1C, and subsequent cycles were performed at a current density of 0.5C / 0.5C. The detailed conditions are as follows: When charging, the battery was charged in CC mode at a predetermined current density up to 50% of the discharge capacity at 1C, and when discharging, the battery was discharged in CC mode up to 1V at a predetermined current density.

[0135] The initial discharge capacity and initial efficiency (initial discharge capacity / initial charge capacity×100) at the first charge / discharge of the examples and comparative examples are shown in Table 1 below.

[0136] [Table 1]

[0137] Referring to Table 1, it can be seen that the secondary batteries of Examples 1 to 3 have superior initial efficiency compared to the comparative example.

[0138] Experimental Example 2: Evaluation of cycle capacity retention rate The charge-discharge characteristics of coin-type half cells fabricated using the negative electrodes fabricated in Examples 1 to 3 and Comparative Examples 1 and 2 were evaluated.

[0139] The first charge / discharge was performed at a current density of 0.1C / 0.1C, and subsequent cycles were performed at a current density of 0.5C / 0.5C. The detailed conditions are as follows: During charging, the battery was charged in CC mode at a specified current density up to 50% of the discharge capacity at 1C, and during discharge, the battery was discharged to 1V in CC mode at a specified current density. The capacity retention rate over the cycles is shown in Figure 6.

[0140] Referring to FIG. 6, it can be seen that the cycle life characteristics of Examples 1 to 3 are significantly improved compared to Comparative Examples 1 and 2.

[0141] In the case of Comparative Example 1, the negative active material used did not have connections between conductive materials by elastic units, and therefore it is believed that the cycle capacity retention rate decreased because it was difficult to provide sustained and elastic conductivity due to changes in the volume of the active material core.

[0142] In the case of Comparative Example 2, since the organic linker component itself was not used, a conductive network formed by connections between the conductive material and the active material core, and between the conductive materials, could not be formed, resulting in a significant decrease in cycle life performance. [Explanation of symbols]

[0143] 10 Conductive materials 20 organic linkages 25 Active material core / organic linker / conductive material combination 30 Active material core 35 Functional groups on the surface of the active material core 40 Elastic Units 45 Conductive material / organic linkage / elastic unit / organic linkage / conductive material bond

Claims

1. an active material core in which lithium ions can be absorbed and released; a plurality of conductive materials located on a surface of the active material core; a plurality of organic linkers comprising hydrophobic groups and polar functional groups bonded to the hydrophobic groups; and an elastic unit; the elastic unit comprises an elastic moiety having two or more binding sites and a functional group attached to a binding site of the elastic moiety that is reactive with a polar functional group of the organic linker; At least one of the plurality of organic linkers is connected to the conductive material via a hydrophobic group of the organic linker; the polar functional group of the organic linker is bonded to a functional group on the surface of the active material core or to a functional group of the elastic unit; the elastic unit connects two or more of the plurality of conductive materials to each other, the elastic unit is a diisocyanate compound, a negative electrode active material, wherein the polar functional group of the organic linker is at least one selected from the group consisting of a carboxylic acid group and an alkyl group having 1 to 8 carbon atoms substituted with a carboxylic acid group;

2. the conductive material includes at least one of a linear conductive material and a planar conductive material; The negative electrode active material according to claim 1 , wherein two or more conductive materials among the plurality of conductive materials are connected to each other via the elastic unit.

3. the linear conductive material is at least one selected from the group consisting of carbon fiber, carbon nanofiber (CNF), metal fiber, metal nanotube, carbon nanotube (CNT) and conductive whisker; The negative electrode active material of claim 2 , wherein the planar conductive material is at least one selected from the group consisting of graphene, a metal thin film, and mxene.

4. The negative electrode active material according to claim 1 , wherein the hydrophobic group of the organic linker includes at least one of a π-electron conjugated ring group and an alkyl group having 3 to 20 carbon atoms.

5. 5. The negative electrode active material according to claim 4, wherein the ring group having the π-electron conjugated structure includes at least one selected from the group consisting of benzene, pyrene, naphthalene, anthracene, benzopyrene, phenanthrene, fluoranthene, chrysene, perylene, benz[a]anthracene, acenaphthylene, coronene, triphenylene, and tetracene.

6. The negative electrode active material according to claim 4 , wherein the cyclic group having a π-electron conjugated structure is a polycyclic cyclic group having four or more rings bonded thereto.

7. The negative electrode active material according to claim 1 , wherein the polar functional group of the organic linker is a carboxylic acid group.

8. 8. The negative electrode active material according to claim 1, wherein the elastic portion is at least one selected from the group consisting of a linear polymer and a multi-arm polymer.

9. The negative electrode active material according to claim 1 , wherein the elastic portion includes at least one of an alkylene unit and an alkyleneoxy unit.

10. 10. The negative electrode active material according to claim 1, wherein the elastic unit is at least one selected from the group consisting of poly(hexamethylene diisocyanate) and 2,4-diisocyanate toluene-terminated poly(propylene glycol).

11. a negative electrode current collector; and a negative electrode active material layer formed on the negative electrode current collector and including a negative electrode material; The negative electrode material comprises the negative electrode active material according to claim 1 .

12. The negative electrode according to claim 11 ; a positive electrode facing the negative electrode; a separator interposed between the negative electrode and the positive electrode; and an electrolyte.

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