Negative electrode material for li secondary battery

Abstract

A negative electrode material for a Li secondary battery, according to one disclosure, comprises: a core comprising natural graphite; and a carbon-containing surface layer that covers the core. A nitrogen adsorption isotherm and a nitrogen desorption isotherm are different in a nitrogen relative pressure region of at least 0.20 to 0.95, and physical properties 1 and 2 are satisfied. Physical property 1: In PSD (DS), which is a pore volume distribution graph obtained by a nitrogen desorption isotherm, two peaks are positioned in a pore size range from 2 nm to 5 nm. Physical property 2: In PSD (AS), which is a pore volume distribution graph obtained by a nitrogen adsorption isotherm, pore size increases and pore volume increases in a pore size range from 10 nm to 100 nm.

Description

Anode materials for lithium secondary batteries

[0001] The present disclosure relates to an anode material for a lithium secondary battery, and more particularly, to a natural graphite-based anode material for a lithium secondary battery.

[0002] Among the components that make up a lithium secondary battery, the anode material stores lithium ions during charging and plays a crucial role in determining factors such as charging speed and battery capacity. Carbon-based active materials are representative examples of commercially used anode materials.

[0003] Among carbon-based active materials, natural graphite is highly price competitive and has a higher capacity than artificial graphite, but it has problems such as a large irreversible reaction due to the exposed edge surface, a limited lithium ion diffusion path due to the uniaxial orientation of the graphene layer plane, poor high-rate output characteristics, and low electrode density due to the ease of plane orientation on the current collector.

[0004] To solve these problems, a technology is being developed to process natural graphite into a spherical shape and form a carbon coating layer on the surface of the spherical natural graphite to prevent deterioration of properties due to side reactions at the edges of the natural graphite.

[0005] However, to date, only the shape of natural graphite particles has been processed to be as close to a sphere as possible by applying mechanical force, and then a carbon coating layer has been formed to completely surround the edges of the natural graphite. However, a pore structure that is advantageous for improving high-rate characteristics in a cathode material based on spherical natural graphite has not yet been established.

[0006] According to one embodiment of the present invention, a negative electrode material for a lithium secondary battery capable of exhibiting improved high-rate characteristics can be provided.

[0007] The objectives of the present invention are not limited to the above-described scope. Those skilled in the art will have no difficulty understanding the additional objectives of the present invention from the overall content of this specification.

[0008] A negative electrode material for a lithium secondary battery according to the present invention comprises a core including natural graphite and a carbon-containing surface layer covering the core, wherein the nitrogen adsorption isotherm and the nitrogen desorption isotherm are different in a nitrogen relative pressure range of at least 0.20 to 0.95, and the negative electrode material satisfies the following physical properties 1 and 2:

[0009] Property 1: In the PSD(DS), which is a pore volume distribution graph obtained by nitrogen desorption isotherm, two peaks are located in the pore size range from 2 nm to 5 nm.

[0010] Property 2: In the PSD(AS), which is a pore volume distribution graph obtained by a nitrogen adsorption isotherm, the graph shows that the pore size increases and the pore volume increases in the pore size range from 10 nm to 100 nm.

[0011] In one specific example, the cathode material may further satisfy the following property 3:

[0012] Property 3: The ratio (PV2 / PV1) of the maximum value PV2 of the second peak having a larger peak center size among the two peaks of Property 1 divided by the maximum value PV1 of the first peak having a smaller peak center size is 0.8 or more.

[0013] In one specific example, the negative electrode material further satisfies the following property 4, and can satisfy the following property 4: separation distance A < separation distance B < separation distance C:

[0014] Property 4: In the range of nitrogen relative pressure (P / P0) from 0.25 to 0.30, the separation distance A between the nitrogen desorption isotherm and the nitrogen adsorption isotherm is 0.1 cm. 3 / g STP or higher, and in the nitrogen relative pressure region of 0.90 to 0.95, the separation distance B between the nitrogen desorption isotherm and the nitrogen adsorption isotherm is 0.4 cm. 3 / g STP or higher, and in the nitrogen relative pressure region of 0.97 to 0.98, the separation distance C between the nitrogen desorption isotherm and the nitrogen adsorption isotherm is 0.9 cm. 3 / g STP or higher.

[0015] In one specific example, the specific surface area S by pore size from 2 nm to 5 nm based on nitrogen adsorption isotherm 2-5 (AS) is 0.5 to 1.2 m 2 / g may be.

[0016] In one specific example, in Property 2, when the pore size increases from 10 nm to 100 nm, the increase in pore volume in PSD(AS) is 0.010 cm 3 g -1 nm -1 It could be strange.

[0017] In one specific example, the specific surface area S by pore size from 5 nm to 100 nm based on nitrogen adsorption isotherm 5-100 (AS) Specific surface area S by pore size from 2 nm to 5 nm based on nitrogen adsorption isotherm 2-5 (AS) divided by (S) 5-100 (AS) / S 2-5 (AS)) can be between 1.0 and 2.5.

[0018] In one specific example, the linseed oil absorption amount of the negative electrode material may be 35 to 45 ml / 100 g.

[0019] In one specific example, the median diameter (D50) of the cathode material may be 8 to 25 μm.

[0020] In one specific example, the BET specific surface area of ​​the cathode material is 3.0 to 4.5 m 2 / g may be.

[0021] In one specific example, the span of the cathode material may be 0.7 to 1.0.

[0022] In one specific example, the tap density of the negative electrode material is 0.90 to 1.20 g / cm 3 It could be.

[0023] In one specific example, the surface layer may include amorphous carbon.

[0024] In one specific example, the thickness of the surface layer may be 5 nm to 20 nm.

[0025] In one specific example, the core may be spherical natural graphite.

[0026] The present invention includes a negative electrode for a lithium secondary battery containing the above-described negative electrode material.

[0027] The cathode material according to one specific example may have improved high-rate output characteristics.

[0028] The various advantageous and beneficial effects of the present invention are not limited to the above-described contents, and will be more easily understood in the course of explaining specific embodiments of the present invention.

[0029] Hereinafter, preferred embodiments of the present invention will be described. However, the embodiments of the present invention may be modified in various other forms, and the scope of the present invention is not limited to the embodiments described below.

[0030] In addition, the embodiments of the present invention are provided to more completely explain the present invention to a person having average knowledge in the relevant technical field.

[0031] In describing the embodiments of the present invention, if a detailed description of a known technology related to the present invention is judged to unnecessarily obscure the gist of the present invention, such detailed description will be omitted. In addition, the terms described below are terms defined in consideration of their functions in the present invention, and these may vary depending on the intention or custom of the user or operator. Therefore, the definitions should be made based on the contents throughout this specification. The terminology used in the detailed description is only for the purpose of describing the embodiments of the present invention and should in no way be limiting. Unless clearly defined otherwise, expressions in the singular form include plural meanings.

[0032] In this description, expressions such as "including" or "having" are intended to indicate certain features, numbers, steps, operations, elements, portions or combinations thereof, and should not be construed to exclude the presence or possibility of one or more other features, numbers, steps, operations, elements, portions or combinations thereof other than those described.

[0033] Unless otherwise specified in the specification of the present invention, the % unit means weight %.

[0034] Throughout the specification, when we say that a part is 'connected' to another part, this includes not only cases where it is 'directly connected', but also cases where it is 'indirectly connected' with other elements in between.

[0035] In this specification and the appended claims, pore size classifications are defined by the International Union of Pure and Applied Chemistry (IUPAC). Specifically, according to the IUPAC definition, micropores refer to pores with a diameter of 2 nm or less, mesopores refer to pores with a diameter of 2 nm to 50 nm, and macropores refer to pores with a diameter of 50 nm or more.

[0036] Below, the present invention will be described in detail through each embodiment or example of the present invention. It should be noted that each embodiment or example described in this specification is not limited to a single embodiment or example, but may be combined with other embodiments or examples. Therefore, the citation of a claim in the patent claims is only an example of an embodiment, and the technical concept of the present invention should not be interpreted solely as a combination of the cited claim, and combinations with various claims also fall within the scope of the technical concept of the present invention.

[0037] A negative electrode material for a lithium secondary battery according to the invention comprises a core including natural graphite and a carbon-containing surface layer covering the core, wherein the nitrogen adsorption isotherm and the nitrogen desorption isotherm are different in a nitrogen relative pressure range of at least 0.20 to 0.95, and the negative electrode material satisfies the following physical properties 1 and 2:

[0038] Property 1: In the PSD(DS), which is a pore volume distribution graph obtained by nitrogen desorption isotherm, two peaks are located in the pore size range from 2 nm to 5 nm.

[0039] Property 2: In the PSD(AS), which is a pore volume distribution graph obtained by a nitrogen adsorption isotherm, a graph in which the pore size increases and the pore volume increases in the pore size range from at least 10 nm to 100 nm.

[0040] A cathode material may have different nitrogen (N2) adsorption isotherms and nitrogen (N2) desorption isotherms. In this case, the nitrogen adsorption isotherm refers to the isotherm during the nitrogen adsorption process of the cathode material, and the nitrogen desorption isotherm refers to the isotherm during the nitrogen desorption process of the cathode material.

[0041] The fact that the nitrogen adsorption isotherm and the nitrogen desorption isotherm are different may mean that the nitrogen adsorption isotherm and the nitrogen desorption isotherm have a form that is spaced apart from each other in at least some nitrogen relative pressure (P / P0) ranges based on the nitrogen adsorption-desorption isotherm in which the nitrogen adsorption isotherm and the nitrogen desorption isotherm are compiled. Specifically, the nitrogen adsorption isotherm and the nitrogen desorption isotherm may have a form that is spaced apart from each other in the nitrogen relative pressure (P / P0) range of at least 0.20 to 0.95, specifically in the nitrogen relative pressure range of at least 0.10 to 0.98. In other words, the negative electrode material according to one specific example may have hysteresis in the nitrogen adsorption-desorption isotherm of the negative electrode material in the nitrogen relative pressure (P / P0) range of at least 0.20 to 0.95, specifically in the nitrogen relative pressure (P / P0) range of at least 0.10 to 0.98.

[0042] In a negative electrode material comprising a core including natural graphite and a carbon-containing surface layer covering the core, the hysteresis described above may be derived from the connection structure of pores and interstitial spaces in the form of slits and / or wedges toward the basal plane of the natural graphite.

[0043] The hysteresis appearing in a very wide nitrogen relative pressure range of at least 0.20 to 0.95, and specifically at least 0.10 to 0.98, may indicate the presence of well-developed slit and / or wedge-shaped pores in a wide pore size range of mesopores and macropores in the negative electrode material. The coarse pores of the mesopores and macropores can be easily impregnated with the electrolyte, and the coarse-sized slit and / or wedge-shaped pores are advantageous in that they enable smooth and rapid lithium ion diffusion into the graphite through the pores.

[0044] At nitrogen relative pressures of 0.20 to 0.95, specifically 0.10 to 0.98, the separation between nitrogen desorption isotherms and nitrogen adsorption isotherms can increase as the nitrogen relative pressure increases.

[0045] In detail, the cathode material has a separation distance between the nitrogen desorption isotherm and the nitrogen adsorption isotherm in the nitrogen relative pressure range of 0.25 to 0.30 (the difference obtained by subtracting the nitrogen adsorption isotherm value from the nitrogen desorption isotherm value in the corresponding range, hereinafter, separation distance A) of 0.1 cm. 3 / g STP or higher, specifically 0.1 to 0.4 cm 3 / g STP, more specifically 0.1 to 0.3 cm 3 / g may be STP.

[0046] In addition, the cathode material has a separation distance between the nitrogen desorption isotherm and the nitrogen adsorption isotherm (hereinafter, separation distance B) of 0.4 cm in the nitrogen adsorption-desorption isotherm in the nitrogen relative pressure range of 0.90 to 0.95. 3 / g STP or higher, specifically 0.4 to 1.0 cm 3 / g STP, more specifically 0.5 to 0.7 cm 3 / g may be STP.

[0047] Furthermore, the cathode material has a separation distance (hereinafter, separation distance C) of 0.9 cm between the nitrogen desorption isotherm and the nitrogen adsorption isotherm in the nitrogen relative pressure range of 0.97 to 0.98 in the nitrogen adsorption-desorption isotherm. 3 / g STP or higher, specifically 0.9 to 2.0 cm 3 / g STP, more specifically 1.1 to 1.6 cm 3 / g may be STP.

[0048] In addition, at a nitrogen relative pressure of 0.20 to 0.95, specifically 0.10 to 0.98, the separation distance A < separation distance B < separation distance C can be satisfied. That is, at a nitrogen relative pressure of 0.20 to 0.95, specifically 0.10 to 0.98, the separation distance between the nitrogen desorption isotherm and the nitrogen adsorption isotherm can increase as the nitrogen relative pressure increases. Such a nitrogen adsorption / desorption isotherm of the negative electrode material may mean that coarser pores in the shape of a slit and / or a wedge are better developed in the negative electrode material.

[0049] With the hysteresis described above, the negative electrode material can satisfy property 1, in which two peaks are located in the pore size range from 2 nm to 5 nm in the PSD(DS), which is a pore volume distribution graph obtained by a nitrogen desorption isotherm, and property 2, in which the PSD(AS), which is a pore volume distribution graph obtained by a nitrogen adsorption isotherm, is a graph in which the pore size increases and the pore volume increases in the pore size range from 5 nm to 80 nm.

[0050] In Property 1 and Property 2, PSD(DS) may be a pore volume distribution graph obtained from a nitrogen desorption isotherm of the negative electrode material by the Barrett-Joyner-Halenda (BJH) method based on the Harkins-Jura equation, and PSD(AS) may be a pore volume distribution graph obtained from a nitrogen adsorption isotherm of the negative electrode material by the BJH method based on the Harkins-Jura equation.

[0051] As is well known, the nitrogen adsorption / desorption isotherm represents the relationship between the nitrogen partial pressure and the amount of nitrogen adsorbed, and the adsorption amount (cm) according to the relative nitrogen pressure (P / P0) 3 / g STP) values. By the BJH method based on the Harkins-Jura equation, the relative pressure of nitrogen (P / P0) of the adsorption or desorption isotherm is expressed as pore diameter (nm), and the nitrogen adsorption amount (cm 3By converting the pore volume (cm3 / g) to the pore volume (cm3 / g), a pore volume distribution (PSD) graph based on the adsorption isotherm or based on the desorption isotherm can be obtained. In detail, the pore volume distribution graph is plotted on the x-axis of the pore diameter (w, nm) in logarithmic scale in pore volume (V) and pore diameter (w), and on the x-axis of the pore volume (dVdlog(w), cm 3 g -1 nm -1 ) may be a semi-log scale graph having a y-axis of the first derivative of the pore volume (V) with respect to the logarithm of the pore diameter (w) (dV / dlog(w)). That is, the pore volume distribution graph may be a semi-log graph having a y-axis of the first derivative of the pore volume (V) with respect to the logarithm of the pore diameter (w) (dV / dlog(w)) and an x-axis of the log scale of the pore diameter. The first pore volume distribution graph may be a semi-log scale pore volume distribution graph (PSD(AS)) obtained by the BJH method based on the Harkins-Jura equation from a nitrogen adsorption isotherm obtained by nitrogen adsorption. The second pore volume distribution graph may be a semi-log scale pore volume distribution graph (PSD(DS)) obtained by the BJH method based on the Harkins-Jura equation from a nitrogen desorption isotherm obtained by nitrogen desorption. A superimposed graph may mean a graph in a semi-log scale in which a first pore volume distribution graph and a second pore volume distribution graph are drawn together.

[0052] Property 1, in which two peaks are located in the pore size range of 2 nm to 5 nm in PSD(DS), means that fine slit- and / or wedge-shaped pores in the pore size range of 2 nm to 5 nm are also developed in the negative electrode material. These fine pores can have a major influence on the insertion and deintercalation reaction of lithium ions. Specifically, the fine slit- and / or wedge-shaped pores in the pore size range of 2 nm to 5 nm can substantially act similarly to an increase in the area of ​​the edge surface through which lithium ions can penetrate, thereby improving the high-rate output characteristics of the negative electrode material.

[0053] In a favorable example, among the two peaks located in the pore size range of 2 nm to 5 nm of property 1, the peak with a relatively large center size is designated as the second peak, and the peak with a relatively small center size is designated as the first peak, and the maximum value of the second peak (peak maximum, cm 3 g -1 nm -1 ) PV2 / PV1, which is the ratio of PV2 divided by the maximum value PV1 of the first peak, may be 0.8 or more (Property 3). Specifically, PV2 / PV1 may be 0.8 to 1.5, more specifically 0.9 to 1.4, and even more specifically 1.0 to 1.3.

[0054] As described above, the ratio PV2 / PV1, which is the maximum value PV2 of the second peak having a larger peak center size among the two peaks of Property 1, divided by the maximum value PV1 of the first peak having a smaller peak center size, may be 0.8 or more (Property 3). The specific surface area in the pore size range of 2 nm to 5 nm, specifically the specific surface area based on the nitrogen adsorption isotherm, is a value determined only by how many pores having the corresponding size are formed, and the value does not significantly change depending on the shape of the pores having the corresponding size. Property 3 based on the nitrogen desorption isotherm indicates that slit-shaped and / or wedge-shaped pores or a pore structure in which these pores are connected, which affect the insertion / deinsertion reaction of lithium ions, are well developed over the entire pore size range of 2 nm to 5 nm.

[0055] Specific surface area by pore size from 2 nm to 5 nm based on nitrogen adsorption isotherm (Surface area by pore size of 2-5 nm) 2-5 (AS) may be a specific surface area related to the area where lithium ions can be inserted and deintercalated, and at the same time, the area where the electrolyte decomposition reaction can actively occur. Accordingly, S 2-5 When (AS) is excessively small, PSD (DS) has two peaks according to property 1, and even if slit-shaped and / or wedge-shaped pores or pore structures connected to these pores are well developed in various sizes in the negative electrode material, there is a risk that the specific surface area provided by these pores itself will be small, resulting in minimal improvement in high-rate characteristics. In addition, S 2-5 If (AS) is excessively large, there is a risk of initial efficiency decrease or increased gas generation because excessive decomposition of the electrolyte cannot be suppressed. Therefore, in order to fully realize the high-rate characteristic improvement by property 1 while suppressing excessive decomposition reaction of the electrolyte, S 2-5 (AS) is 0.5 to 1.2 m 2 / g, more specifically 0.6 to 1.1 m 2 / g, more specifically 0.7 to 1.0 m 2 / g, more specifically 0.8 to 0.9 m 2 / g is advantageous.

[0056] As described above, property 1 may be a property mainly involved in the insertion / deintercalation reaction of lithium ions into natural graphite, and property 2, which is a graph of PSD(AS) in which the pore size increases and the pore volume increases in the pore size range from 10 nm to 100 nm, may be a property mainly involved in the supply (movement) of lithium ions into the negative electrode material.

[0057] In the pore size range of 10 to 100 nm, the pore size (nm) increases and the pore volume (cm 3 g -1 nm -1 ) By increasing the PSD(AS) in the form of electrolyte, lithium ions can be supplied (moved) smoothly and quickly from the electrolyte to the negative electrode material and from the negative electrode material to the electrolyte.

[0058] The aforementioned 'increasing form' is characterized by an increase in pore size (nm) and pore volume (cm) over the entire pore size range of at least 10 nm to 100 nm, specifically 5 to 100 nm. 3 g -1 nm -1 ) may be in the form of increasing. In other words, the slope of the PSD(AS) graph may be a positive value in the entire region of the pore size range of at least 10 nm to 100 nm, specifically, the pore size range of 5 to 100 nm.

[0059] Specifically, in the 'increasing form', the slope of the PSD(AS) graph can be represented by the slope between two points, 10 nm and 100 nm. In detail, in Property 2, when the pore size increases from 10 nm to 100 nm, the increase in pore volume in PSD(AS) is 0.010 cm3 g -1 nm -1 Above, specifically 0.010 to 0.025 cm 3 g -1 nm -1 , more specifically 0.013 to 0.025 cm 3 g -1 nm -1 , more specifically 0.015 to 0.023 cm 3 g -1 nm -1 , more specifically 0.017 to 0.023 cm 3 g -1 nm -1 This high slope indicates that a very wide range of coarse pores, from mesopores to macropores, are developed in the negative electrode material, and the larger the pore size from mesopores to macropores, the better the pore development. This mesopore to macropore pore structure is advantageous in that it facilitates the cyclic insertion and deintercalation of lithium ions, enables smooth and rapid lithium ion transfer and electron conduction, and improves the electrolyte impregnation efficiency.

[0060] Specific surface area by pore size from 5 nm to 100 nm based on nitrogen adsorption isotherm (Surface area by pore size 5-100 nm) 5-100 (AS) to S 2-5 (AS) divided by (S) 5-100 (AS) / S 2-5 (AS)) may be 1.0 to 2.5, specifically 1.3 to 2.3, more specifically 1.5 to 2.1, and even more specifically 1.6 to 2.0. S 5-100 (AS) / S 2-5 By having the ratio described above, both activity (rapid lithium ion insertion / deinsertion reaction) and transport (ion transfer and electron conduction), which have a major influence on the high-rate characteristics of the negative electrode material, can be improved. As a practical example, S 5-100(AS) satisfies the above-mentioned ratio and is 1.0 to 2.0 m 2 / g, specifically 1.2 to 1.8 m 2 / g, more specifically 1.4 to 1.7 m 2 / g may be.

[0061] In one specific example, the BET surface area of ​​the cathode material is 3.0 to 4.5 m 2 / g, specifically 3.2 to 4.3 m 2 / g. At this time, the BET specific surface area may be the specific surface area based on the nitrogen adsorption isotherm. 3.0 to 4.5 m 2 The BET surface area of ​​ / g level is a surface area that is advantageous for the all-round penetration of lithium ions in the particulate negative electrode material due to its high surface area, while also appropriately suppressing the electrolyte decomposition reaction.

[0062] In one specific example, the linseed oil absorption of the negative electrode material may be 35 to 45 ml / 100g, specifically 37 to 44 ml / 100g. The linseed oil absorption of the negative electrode material is a property that indicates the reactive area of ​​the negative electrode material, the liquid diffusion of the electrolyte, and other rheological behavioral characteristics. If the linseed oil absorption is excessively high, the dispersibility of the negative electrode material may be poor, causing it to easily precipitate in the slurry, and the transfer resistance may increase during lithium ion diffusion. In addition, if the linseed oil absorption is excessively low, there is a risk that the negative electrode material may be damaged during the rolling process due to its low density, and there is also a risk that side reactions within the electrode may increase. An absorption amount of 35 to 45 ml / 100 g of linseed oil is advantageous in that it can achieve stable dispersion in the slurry, lower the impedance of mass transfer, prevent unwanted distortion such as stripe formation during application and / or drying of the slurry containing the negative electrode material, and suppress damage to the negative electrode material due to rolling.

[0063] In one specific example, the median diameter (D50) of the negative electrode material may be 8 to 25 μm, specifically 10 to 20 μm, more specifically 13 to 18 μm, and even more specifically 14 to 17 μm. The size of the negative electrode material is advantageous for increasing the density of the negative electrode, and is a size that allows a stable open pore structure to be formed within the active material layer, a flat electrode surface to be formed, spring back to be suppressed, and the viscosity of the slurry to be prevented from being excessively increased during the electrode manufacturing process.

[0064] Span is a value related to the particle size distribution of the negative electrode material, and in one specific example, the span value of the negative electrode material may be 0.7 to 1.0, specifically 0.7 to 0.9. A span value of 0.7 to 1.0 can suppress an increase in specific surface area due to fine powder, a decrease in initial charge / discharge efficiency, and an increase in slurry viscosity, and can have an appropriate porosity for the negative electrode active material layer to be wetted by the electrolyte, and is a span value that can be densified with an improved tap density.

[0065] In one specific example, the negative electrode material is 0.90 g / cm 3 Above, specifically 0.95 g / cm 3 Above, more specifically 1.00g / cm 3 The anode material can have a high tap density. A high tap density is advantageous because it can increase the electrode packing density. However, an excessively high tap density significantly increases the time and energy required for manufacturing the anode material, thereby hindering productivity. In addition, it can cause a large number of defects in the natural graphite contained in the anode material, thereby reducing the life characteristics of the battery. Accordingly, the tap density of the anode material is practically 1.20 g / cm. 3 It could be as follows:

[0066] In one specific example, the negative electrode material may have a core-shell structure, with the particle comprising natural graphite representing the core and the surface layer comprising carbon representing the shell. In terms of the manufacturing method, the surface layer may represent a coating layer covering the surface of the core comprising natural graphite.

[0067] The surface layer can cover at least the edges of graphite crystals exposed to the surface in the natural graphite contained in the core. As a practical example, the negative electrode material can include a core comprising spherical natural graphite and a surface layer containing carbon surrounding the core. Since the spherical natural graphite is covered by the surface layer containing carbon, the edges of the natural graphite contained in the spherical natural graphite can be prevented from being directly exposed to the surface, side reactions caused by the electrolyte can be suppressed, and irreversible reactions can be reduced.

[0068] The surface layer may be a carbon layer, and the carbon layer may be a low-crystalline (disordered) carbon layer. In this case, the low-crystalline carbon includes amorphous carbon. Specifically, the low-crystalline carbon layer may include soft carbon, hard carbon, or a mixture thereof. The thickness of the surface layer may be, but is not limited to, 5 to 200 nm, specifically 5 to 150 nm, and more specifically 5 to 20 nm.

[0069] The natural graphite contained in the core may be spherical natural graphite. For example, the spherical natural graphite may be natural graphite particles assembled by forming natural graphite fragments in a cabbage shape or randomly. In the spherical natural graphite, a spherical shape means that when the natural graphite is observed planarly (two-dimensionally) using a conventional image observation device such as a scanning electron microscope, the shape of the natural graphite may be considered spherical if the circumference of the natural graphite is within 120% of the circumference of a circle with the same area.

[0070] In terms of manufacturing method, spherical natural graphite may be natural graphite particles (spherical assembled natural graphite particles) formed by mechanically processing natural graphite fragments into pieces, folds, and / or assembles. In this case, the mechanical processing may include a process that applies mechanical force, such as impact compression, friction, and / or shear force, to the raw natural graphite particles. A representative example of mechanical processing includes, but is not necessarily limited to, rotary processing using airflow.

[0071] Mechanical processing can be performed by a spheroidization method using mechanical processing commonly known in the secondary battery field. Representative examples of mechanical processing include Air Classifying milling, Spheronizing milling, Grinding milling, Mechanofusion milling, Planetary milling, Hybridization milling, Shape milling, and High speed milling. Spheroidization of natural graphite can be performed at a rotation speed of 500 to 4000 rpm and a processing time of 5 to 60 minutes, but is not limited thereto. After spheroidization, a step of forming a surface layer containing carbon on the surface of a core including spherical natural graphite can be performed, so that an anode material can be manufactured.

[0072] The present invention includes a method for manufacturing the above-described negative electrode material.

[0073] A method for manufacturing a negative electrode material for a lithium secondary battery according to the invention comprises a selection step of selecting spherical natural graphite satisfying the following conditions 1, 2, 3, 4 and 5 as a core; and a median diameter (D) of the spherical natural graphite. 50 )in D 50Based on (SNG), 0.4 D 50 (SNG) to 0.6 D 50 A coating step is included in which a surface layer containing carbon is formed on a core using a solid carbon precursor including at least a first carbon precursor having an average diameter of (SNG).

[0074] Condition 1: Hysteresis exists in the nitrogen adsorption / desorption isotherm in the nitrogen relative pressure range of 0.20 to 0.95.

[0075] Condition 2: In the pore volume distribution graph obtained by the nitrogen desorption isotherm of spherical natural graphite, two peaks are located in the pore size range from 2 nm to 5 nm, and the ratio of the maximum value of the peak having a larger peak center size among the two peaks divided by the maximum value of the peak having a smaller peak center size is 1.0 to 2.5.

[0076] Condition 3: In the pore volume distribution graph obtained by the nitrogen adsorption isotherm of spherical natural graphite, when the pore size increases from 10 nm to 100 nm, the pore volume increase in the pore volume distribution graph is 0.015 to 0.025 cm 3 g -1 nm -1

[0077] Condition 4: The ratio of the specific surface area by pore size from 5 nm to 100 nm based on the nitrogen adsorption isotherm of spherical natural graphite divided by the specific surface area by pore size from 2 nm to 5 nm based on the same nitrogen adsorption isotherm is 0.7 to 1.5.

[0078] Condition 5: The BET surface area of ​​spherical natural graphite is 6 to 8 m 2 / g

[0079] The selection step may be performed on commercially available spherical natural graphite(s), or, together with or independently of this, on spherical natural graphite manufactured by mechanically processing flaky natural graphite by varying the rpm, processing time, hammer shape, etc. during processing.

[0080] Spherical natural graphite satisfying the above conditions 1, 2, 3, 4 and 5 is used as a core, and at least, D 50 (SNG) When a carbon coating layer is formed using a carbon precursor including at least a first carbon precursor having a relatively large size as a reference, a negative electrode material having a desired pore structure can be manufactured.

[0081] In detail, a coating step can be performed in which spherical natural graphite satisfying the above-mentioned conditions 1, 2, 3, 4 and 5 is mixed with a carbon precursor and heat-treated to form a surface layer containing carbon.

[0082] In the coating step, the pore structure of the spherical natural graphite may vary during the formation of the surface layer depending on the particle size distribution of the solid carbon precursor. In order to manufacture the negative electrode material without excessively damaging the pore structure of the core in the range of 2 to 5 nm, at least, 0.4 D 50 (SNG) to 0.6 D 50 A carbon precursor comprising a first carbon precursor having an average diameter of (SNG) may be used.

[0083] Advantageously, it is advantageous to use a solid carbon precursor having a bi-modal particle size distribution so that the pore structure of the core in the 2 to 5 nm range is not excessively damaged, the pore structure in the appropriate meso to macro range (5-100 nm) is maintained, and at least, a surface layer that stably covers the graphite edge of the spherical natural graphite can be formed. Specifically, the median diameter (D) of the spherical natural graphite 50 )in D 50Based on (SNG), the solid carbon precursor is 0.1 D 50 (SNG) to 0.3 D 50 A second carbon precursor with an average diameter of (SNG) and 0.4 D 50 (SNG) to 0.6 D 50 (SNG) may be a mixture of first carbon precursors having an average diameter of 1:1 to 1.5. At this time, it is advantageous that the weight ratio of the second carbon precursor to the first carbon precursor is 1:1 to 1.5.

[0084] The solid carbon precursor may be at least one selected from the group consisting of petroleum pitch, coal pitch, mesophase pitch, organic synthetic pitch, polyvinyl alcohol (PVA), polyvinyl chloride (PVC), sucrose, phenol resin, furan resin, furfuryl alcohol, polyacrylonitrile, cellulose, styrene, polyimide, epoxy resin, and glucose. Advantageously, the solid carbon precursor may be a pitch comprising petroleum pitch, coal pitch, mesophase pitch, organic synthetic pitch, or a mixture thereof, and more advantageously, may be petroleum pitch, coal pitch, or a mixture thereof.

[0085] The mixing ratio of the carbon precursor mixed with the core may be any amount that allows the formation of a surface layer that stably covers the surface of the natural graphite contained in the core. As a specific example, the weight ratio of the core:carbon precursor may be 100:0.1 to 20, specifically 100:1 to 15, and more specifically 3 to 10, but is not limited thereto.

[0086] After mixing is performed, a heat treatment for carbonizing the carbon precursor may be performed. The heat treatment for carbonization may be performed in an atmosphere of hydrogen, nitrogen, argon, or a mixed gas thereof at a temperature of 600 to 1500°C, specifically 800 to 1300°C, and more specifically 1000 to 1300°C for 1 to 5 hours, but is not limited thereto.

[0087] The present invention includes a negative electrode material manufactured by the above-described manufacturing method.

[0088] The present invention includes a negative electrode for a secondary battery containing a negative electrode material manufactured by the above-described manufacturing method.

[0089] The present invention includes a negative electrode for a secondary battery containing the above-described negative electrode material.

[0090] The negative electrode according to the invention is a negative electrode for a secondary battery, and includes a current collector and a negative electrode active material layer located on at least one surface of the current collector and containing the above-described negative electrode material.

[0091] The negative electrode active material layer may include 95 to 99 wt% of the negative electrode material based on the total weight of the negative electrode active material layer.

[0092] The negative electrode active material layer may further include an additive including an organic binder together with the negative electrode material, and if necessary, the additive may further include a conductive material. In order to ensure stable fixation between the negative electrode materials and between the negative electrode material and the current collector by the organic binder and not to damage the conductivity and open pore structure within the negative electrode active material layer, the negative electrode active material layer may contain 1 to 5 wt% of the organic binder, and substantially 1 to 3 wt% of the organic binder. In addition, when the negative electrode active material layer further contains a conductive material, the negative electrode active material layer may contain 0.5 to 3 wt% of the conductive material, and substantially 0.5 to 2 wt% of the conductive material, but is not limited thereto.

[0093] The organic binder may be a polymer binder commonly used in the secondary battery field to bind particulate negative electrode materials to each other and to bind the negative electrode materials to a current collector. Practical examples of the organic binder include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, or mixtures thereof.

[0094] The conductive agent may be any conductive additive commonly used to improve the conductivity of anodes in the secondary battery field. Specifically, the conductive agent may include a dot-shaped conductive agent, a linear conductive agent, a planar conductive agent, or a mixture thereof. Examples of dot-shaped conductive agents include conductive carbon materials such as carbon black, acetylene black, Ketjen black, channel black, paneth black, lamp black, thermal black, etc.; metal particles such as copper, nickel, aluminum, and silver; conductive polymer particles; core-shell particles with a non-conductive core and a conductive shell; and examples of linear conductive agents include carbon nanotubes, conductive carbon fibers, metal fibers, and conductive polymer fibers. Examples of planar conductive agents include, but are not limited to, graphene or reduced graphene oxide. As a practical example, the conductive agent may include carbon black, and as another practical example, the conductive agent may include carbon black and carbon nanotubes.

[0095] The cathode density (electrode density) of the cathode is 1.20 to 1.90 g / cm 3 Level, specifically 1.50 to 1.90 g / cm 3 , more specifically 1.70 to 1.90 g / cm 3 It may be, but is not limited to,

[0096] The current collector can be any conductive material commonly used in secondary battery applications to ensure smooth current flow to the anode active material layer. The current collector may be, but is not limited to, a foil, a porous foil, a foam, a mesh, a non-woven fabric, a non-conductive material with a conductive coating layer, or a combination thereof. The current collector material may be any material that has high conductivity and does not induce chemical changes within the battery. For example, the current collector may be, but is not limited to, copper, stainless steel, aluminum, nickel, titanium, or alloys thereof. The current collector may have a conventional thickness, for example, but is not limited to, a thickness of 3 to 500 μm.

[0097] The negative electrode can be manufactured using a method commonly used for manufacturing negative electrodes in the secondary battery field. For example, the negative electrode can be manufactured by applying a slurry containing the negative electrode material, a binder, a solvent, and, if necessary, a conductive material to at least one surface of a current collector, followed by drying and rolling, but is not limited thereto.

[0098] In the secondary battery field, any solvent commonly used in slurry formation for negative electrode manufacturing may be sufficient. Examples of solvents include, but are not limited to, dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, dimethylformamide (DMF), water, or mixtures thereof.

[0099] The slurry may be applied using any method commonly used to form an active material layer using slurry in the secondary battery field. For example, the slurry may be applied using slot die coating, Meyer bar coating, gravure coating, comma coating, roll coating, blade coating, bar coating, or dipping coating.

[0100] Drying is the T of the solvent of the slurry, specifically the aqueous solvent. bTemperature above (boiling point under 1 atm, ℃), for example T b +10℃ to T b It can be performed by vacuum drying at a temperature of +50℃ for 5 to 12 hours, but is not limited thereto. Rolling can be performed using two rollers facing each other, but is not limited thereto.

[0101] The present invention includes a secondary battery including the above-described negative electrode.

[0102] A secondary battery according to the present invention may include the above-described negative electrode, positive electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte. Specifically, the secondary battery may include a positive electrode including a positive electrode current collector and a positive electrode active material layer positioned on at least one surface of the positive electrode current collector, the above-described negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte that conducts active ions (for example, lithium ions) involved in charging and discharging of the battery. The positive electrode current collector, the positive electrode active material or composition of the positive electrode active material layer, the solvent or electrolyte salt of the separator and the electrolyte, or the concentration of the electrolyte salt, may be any material or composition typically adopted for each specific secondary battery. In addition, the secondary battery may further include an electrode assembly including a positive electrode, a negative electrode, and a separator, and a sealable battery container in which an electrolyte is stored inside.

[0103] The secondary battery may be a lithium secondary battery. The lithium secondary battery may be a lithium ion battery, a lithium ion polymer battery, or a lithium polymer battery based on the type of separator and electrolyte, and may be cylindrical, square, coin-shaped, or pouch-shaped, but is not limited thereto.

[0104] Hereinafter, specific examples of a positive electrode, a separator, and an electrolyte are described based on a lithium secondary battery, which is a representative secondary battery, but the present invention is not limited to the configuration of the positive electrode, the separator, and the electrolyte.

[0105] The positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and the positive electrode active material layer may include a positive electrode active material. The positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and 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. In addition, the positive electrode current collector may typically have a thickness of 3 to 500 ㎛, and fine unevenness may be formed on the surface of the positive electrode current collector to increase the adhesion of the positive electrode active material. For example, it may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0106] A compound capable of reversibly intercalating and deintercalating lithium (a lithiated intercalation compound) can be used as the cathode active material. Specifically, one or more composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof can be used. A specific example of such a compound is a compound represented by one of the following chemical formulas:

[0107] Li a A 1-b B b D2 (in the above formula, 0.90 ≤ a ≤ 1.8, and 0 ≤ b ≤ 0.5); Li a E 1-b B b O 2-c D c (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); LiE 2-b B b O 4-c D c (In the above formula, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a Ni 1-b-c Co b B c Dα (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li a Ni 1-b-c Co b B c O 2-α T α (In the above equation, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Co b B c O 2-α T2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Mn b B c D α (In the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α ≤ 2); Li a Ni 1-b-c Mn b B c O 2-α T α (In the above equation, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni 1-b-c Mn b B c O 2-α T2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, 0 < α < 2); Li a Ni b E c G d O2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0.001 ≤ d ≤ 0.1); Li a Ni b Co c Mn dGeO2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0.001 ≤ e ≤ 0.1); Li a NiG b O2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a CoG b O2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a MnG b O2 (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn2G b O4 (in the above formula, 0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); QO2; QS2; LiQS2; V2O5; LiV2O5; LiIO2; LiNiVO4; Li (3-f) J2(PO4)3(0 ≤ f ≤ 2); Li (3-f) Fe2(PO4)3(0 ≤ f ≤ 2); and LiFePO4. In the above chemical formula, A is Ni, Co, Mn or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof; D is O, F, S, P or a combination thereof; E is Co, Mn or a combination thereof; T is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; Q is Ti, Mo, Mn or a combination thereof; I is Cr, V, Fe, Sc, Y or a combination thereof; and J may be V, Cr, Mn, Co, Ni, Cu or a combination thereof.

[0108] A compound having a coating layer on the surface of the above-mentioned compound or a mixture of the above-mentioned compound and a compound having a coating layer may be used as a cathode active material.

[0109] The coating layer may include at least one coating element compound selected from the group consisting of an oxide of a coating element, a hydroxide of a coating element, an oxyhydroxide of a coating element, an oxycarbonate of a coating element, and a hydroxycarbonate of a coating element. The compounds forming these coating layers may be amorphous or crystalline. The coating elements included in the coating layer may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. The coating layer forming process may use any coating method as long as it can coat the compound with these elements by a method (e.g., spray coating, dipping, etc.) that does not adversely affect the physical properties of the positive electrode active material. Since this is well understood by those working in the relevant field, a detailed description thereof will be omitted.

[0110] The positive electrode active material layer may further include a binder (positive electrode binder) and / or a conductive material (positive electrode conductive material) in addition to the positive electrode active material described above.

[0111] The positive electrode binder serves to improve the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, styrene butadiene rubber (SBR), fluoroelastomer, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof, but is not limited thereto. The positive electrode binder may be included in an amount of 1 to 30 wt% based on the total weight of the positive electrode active material layer.

[0112] The cathode conductive material is used to provide conductivity to the electrode, and in the battery to be formed, as long as it does not cause a chemical change and has electronic conductivity, it can be used without any special restrictions. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One type alone or a mixture of two or more types may be used among these, but the present invention is not limited thereto. The cathode conductive material may typically be included in an amount of 1 to 30 wt% based on the total weight of the cathode active material layer.

[0113] The positive electrode can be manufactured according to a conventional positive electrode manufacturing method. Specifically, the positive electrode can be manufactured by applying a composition for forming a positive electrode active material layer, including a positive electrode active material and optionally a positive electrode binder, a positive electrode conductive material, and / or a solvent, onto a positive electrode current collector, followed by drying and rolling. At this time, the types and contents of the positive electrode active material, positive electrode binder, and positive electrode conductive material are as described above.

[0114] In the composition for forming a positive electrode active material layer, the solvent may be a solvent generally used in the relevant technical field, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, dimethylformamide (DMF), or water. One of these may be used alone or a mixture of two or more thereof may be used. The amount of solvent used is sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity when applied thereafter for manufacturing the positive electrode.

[0115] Alternatively, the positive electrode may be manufactured by casting a composition for forming a positive electrode active material layer on a separate support, then peeling the resulting film from the support and laminating it on a positive electrode current collector.

[0116] A separator separates the positive and negative electrodes and provides a passage for lithium ions. Any separator commonly used in lithium secondary batteries can be used without any particular restrictions. However, a separator having low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity is preferred. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous non-woven fabric, for example, a non-woven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may also be used. In addition, a coated separator containing a ceramic component or polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0117] Electrolytes that can be used in the manufacture of lithium secondary batteries include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes.

[0118] As a specific example, the organic liquid electrolyte may include an organic solvent and a lithium salt.

[0119] Any organic solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move may be used without particular restrictions. Specifically, organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (wherein R is a C2 to C20 linear, branched, or cyclic hydrocarbon group, and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant that can improve the charge / discharge performance of the battery and a linear carbonate compound having low viscosity (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable.In this case, the performance of the electrolyte may be improved when the cyclic carbonate and the chain carbonate are mixed and used in a volume ratio of about 1:1 to about 1:9.

[0120] Lithium salts can be used without any special restrictions as long as they are compounds that can provide lithium ions used in lithium secondary batteries. Specifically, lithium salts include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2. LiCl, LiI, or LiB(C2O4)2. It is recommended that the concentration of the lithium salt be within the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above-mentioned range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively.

[0121] In addition to the aforementioned electrolyte components, the electrolyte may further include one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexamethylphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine 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 battery capacity decline, and improving the discharge capacity of the battery. At this time, the additives may be included in an amount of 0.1 to 5 wt% based on the total weight of the electrolyte.

[0122] A lithium secondary battery may be placed within a battery case. The shape of the battery case may be one or more selected from the group consisting of a cylindrical shape using a can, a square shape, a pouch shape, and a coin shape. However, the shape of the battery case is not limited to this, and may have various shapes used in the relevant industry.

[0123] The present invention includes a battery module in which the secondary battery described above is used as a unit cell, and a plurality of unit cells are connected in series and / or in parallel.

[0124] The present invention includes a battery pack including a plurality of the above-described battery modules.

[0125] The present invention encompasses devices powered by the secondary battery, battery module, or battery pack described above. Representative examples of such devices include electronic and communication devices such as mobile phones, laptops, and PCs, as well as electric vehicles.

[0126] Hereinafter, the present invention will be described in detail through examples. However, it should be noted that the examples described below are intended only to illustrate and concretize the present invention and are not intended to limit the scope of the invention. This is because the scope of the invention is determined by the matters set forth in the patent claims and matters reasonably inferred therefrom.

[0127] The physical and electrochemical properties described in the detailed description and patent claims were analyzed and measured according to the methods specified in the ‘Analysis and Measurement Methods’ below.

[0128] Analysis and Measurement Methods

[0129] Cumulative volume diameter distribution (D 10 , D 50 , D 90 )

[0130] Cumulative volume diameter distribution was measured by suspending 0.01 g of the analyte in an aqueous solution containing 0.2 wt% of a nonionic surfactant, ultrasonicating the prepared suspension for 1 minute, and then using a laser diffraction particle size distribution measuring device (Microtrac S3500). D 90 , D 10 , D 50 is the diameter at the points where the cumulative volume is 90%, 10%, and 50% in the cumulative volume diameter distribution, and the span is (D 90 -D 10 ) / D 50 It was produced as follows.

[0131] Nitrogen adsorption-desorption isotherm

[0132] The target material was dried for 12 hours at 150°C under a vacuum of 0.1 Torr or less, and then the nitrogen adsorption / desorption isotherm was measured. The nitrogen adsorption / desorption isotherm was measured using a surface area measuring device (Tristar Ⅱ 3020, Micromeritics, USA) at a temperature of 77 K and a relative pressure (P / P0) measurement precision of 0.05 using nitrogen as adsorbed gas and liquid nitrogen.

[0133] Using the BJH method, the relative pressure of nitrogen (P / P0) in the nitrogen adsorption isotherm or nitrogen desorption isotherm was converted to pore size (nm) and nitrogen adsorption amount (cm 3 / g STP) to cumulative pore volume (cm 3 / g) or cumulative pore area (m 2 / g) to obtain the pore volume distribution or pore area distribution. At this time, when converting the relative pressure to the pore size, a correction was performed using the Harkins-Jura thickness curve. In addition, the Faas correction, which is a standard BJH correction, was performed together with the Harkins-Jura thickness curve. In both the adsorption and desorption isotherms, the conversion from pore size to pore volume (or pore area) was performed in the pore size range of 1.7 to 300 nm. In addition, the BET specific surface area (m) was obtained from the nitrogen adsorption isotherm using the BET method. 2 / g) was produced.

[0134] Spherical shape

[0135] The sphericity of the analyte was measured using a particle shape analyzer (Flowcam 8100, Fluid Imaging Technologies) commonly used for particle shape analysis after ultrasonically dispersing 0.01 g of the cathode material in 5 mL of ethanol. The sphericity of the analyte refers to the average value of the sphericity. In this case, the sphericity is the circumference (C) of a circle having the same area as the projected image (2D image) of the analyte, which is a three-dimensional particle. ir ) is the perimeter of the projected image (P rj ) divided by the ratio (C) ir / P rj ) can be defined as follows.

[0136] Absorption amount

[0137] The linseed oil absorption of the analyte was measured using a conventional absorption meter (S-500, ASAHI SOUKEN) in accordance with JIS K 6217-4. 30 g of the analyte powder was loaded into the absorption meter, and linseed oil was added dropwise. The oil and the analyte were mixed with a mixer, and the torque applied to the mixer was recorded. The amount of linseed oil added at 70% of the maximum torque was read, and the absorption (mL / 100 g) was calculated based on this. The linseed oil absorption was determined using the average of three measurements.

[0138] Tap density

[0139] Tap density of the target substance (g / cm) 3 ) was measured using a tap density measuring device (Autotap, Quantachrome). Specifically, the tap density was measured by placing 15 g of the analyte into a 25 mL container and tapping 3000 times with a stroke length of 1.2 cm (tapping speed = 284 times / min) based on ASTM B527.

[0140] Manufacturing of half-cells

[0141] Negative electrode material manufactured in the examples or comparative examples: Styrene butadiene rubber (SBR): Carboxymethyl cellulose (CMC): Carbon black (CB) was prepared in a weight ratio of 97: 1: 1: 1 to prepare an aqueous slurry, and then the prepared slurry was applied to a copper (Cu) foil, and then dried and rolled to form a negative electrode (loading amount 3.6 mAh / cm 2 ) was manufactured.

[0142] A coin-type 2032 half-cell was fabricated using lithium foil as the counter electrode. A porous polypropylene film was used as the separator, and the electrolyte was a solution containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 2:8, vinylene carbonate (VC) at 0.5 wt%, and 1 M LiPF6 dissolved therein.

[0143] The manufactured cathodes and half-cells are also collectively referred to by the same numbers as the examples or comparative examples of the cathode material. For example, a half-cell manufactured using the cathode material manufactured in Example 1 is collectively referred to as the half-cell of Example 1.

[0144] Electrochemical property evaluation

[0145] After manufacturing the half-cell, it was aged at 25°C for 48 hours, and a formation process was performed in which it was charged and discharged three times under the conditions of a potential range of 0.005 V / 1.5 V and a current density of 0.36 mA / cm2 at 25°C, and then the electrochemical characteristics of the cell were measured.

[0146] For high-rate output evaluation, the manufactured half-cells were tested for CC / CV, cut-off voltage 0.005 V to 1.5 V, and discharge capacity (C) at 0.1 C-rate. 0.1 ) was measured, and the discharge capacity (C7) at CC / CV, cut-off voltage 0.005 V to 1.5 V, 7 C-rate was measured, and the ratio of the discharge capacity at 7 C divided by the discharge capacity at 0.1 C (C7 / C 0.1 *100, %) was calculated as a high-rate characteristic.

[0147] For life evaluation, the manufactured half-cells were repeatedly charged and discharged at CC / CV, cut-off voltage 0.005 V to 1.5 V, 1 C-rate, and the discharge capacity (C) at the 50th cycle was compared with the discharge capacity (C1) at the first cycle. 50 ) ratio (C 50 / C1*100, %) was calculated as the lifespan characteristic.

[0148] (Example 1)

[0149] Natural graphite, which satisfies the following properties and has been sphericalized by mechanical processing, was selected as a core, and used as a carbon precursor as described below. The carbon precursor was mixed so that 7 parts by weight was used based on 100 parts by weight of the core, and then heat-treated at 1200°C for 5 hours under an argon atmosphere to manufacture a negative electrode material.

[0150] Properties of spheroidized natural graphite: 1) Hysteresis in the nitrogen relative pressure range of 0.20 to 0.95 in the nitrogen adsorption-desorption isotherm, 2) Two peaks (peak centers 2.3 nm and 4.1 nm) are located in the pore size range of 2 nm to 5 nm in the pore volume distribution graph obtained by the nitrogen desorption isotherm, 3) The ratio of the maximum value of the peak located at 4.1 nm to the maximum value of the peak located at 2.3 nm is 1.51, 4) The increase in pore volume of 0.20 cm in the pore volume distribution graph obtained by the nitrogen adsorption isotherm when the pore size increases from 10 nm to 100 nm 3 g -1 nm -1 , 5) The ratio of the specific surface area by pore size from 5 nm to 100 nm based on nitrogen adsorption isotherm to the specific surface area by pore size from 2 nm to 5 nm based on the same nitrogen adsorption isotherm is 0.78, 6) BET specific surface area 6.2701 m 2 / g, 7) D 50 15.13 ㎛ and 8) sphericity 0.90

[0151] Carbon precursor: D of 2.5 ㎛ 50 First petroleum pitch (softening point 250℃) with D of 8 ㎛ 50 A mixture in which a second petroleum-based pitch (softening point 250°C) having a first petroleum-based pitch: a second petroleum-based pitch is mixed in a weight ratio of 1:1.2.

[0152] (Example 2)

[0153] D of 7 ㎛ 50 A negative electrode material was manufactured in the same manner as in Example 1, except that only petroleum pitch (softening point 250°C) having .

[0154] (Comparative Example 1)

[0155] D of 2.5 ㎛ 50A negative electrode material was manufactured in the same manner as in Example 1, except that only petroleum pitch (softening point 250°C) having .

[0156] (Comparative Example 2)

[0157] A commercial product made of amorphous carbon coated on mechanically spherical natural graphite as a cathode material (D 50 16.1 ㎛) was used.

[0158] The negative electrode materials of Examples 1 to 2 and Comparative Examples 1 to 2 all had hysteresis in the range of nitrogen relative pressure 0.2 to 0.95. The pore characteristics of the negative electrode materials of Examples 1 to 2 and Comparative Examples 1 to 2 based on nitrogen adsorption / desorption isotherms are summarized in Table 1. Specifically, in Table 1, N is the number of peaks located in the pore size range of 2 to 5 nm in the PSD (DS) based on the nitrogen desorption isotherm of the negative electrode materials. In Table 1, PV2 / PV1 is the value of the ratio (PV2 / PV1) obtained by dividing the maximum value PV2 of the second peak having a larger peak center size among the two peaks by the maximum value PV1 of the first peak having a smaller peak center size when the number of peaks (N) is 2. In Table 1, shape is a graph of PSD(AS) based on the nitrogen adsorption isotherm of the cathode material, and in PSD(AS), when the pore volume increases as the pore size increases across the pore size range from 10 nm to 100 nm, it is indicated as 'increase', and when the pore volume decreases, it is indicated as 'decrease'. In Table 1, Δ 10-100 (cm 3 g -1 nm -1 ) is the change in pore volume in PSD(AS) when the pore size increases from 10 nm to 100 nm in PSD(AS), which is the difference obtained by subtracting the PSD(AS) value at 10 nm from the PSD(AS) value at 100 nm. In Table 1, S 2-5 (AS)(m 2 / g) is the specific surface area by pore size from 2 nm to 5 nm based on nitrogen adsorption isotherm. In Table 1, S 5-100 (AS) / S2-5 (AS) is the specific surface area S for pore sizes from 5 nm to 100 nm based on nitrogen adsorption isotherms. 5-100 (AS) to S 2-5 (AS) is the ratio divided by . In Table 1, BET(m 2 / g) is the BET specific surface area based on the nitrogen adsorption isotherm.

[0159] Example 1 Example 2 Comparative Example 1 Comparative Example 2 N2202PV2 / PV11.040.39-1.37 shape increase increase increase decrease Δ 10-100 (cm 3 g -1 nm -1 )+0.0174+0.0159+0.0191-0.0001S 2-5 (AS) (m 2 / g)0.8750.9730.4911.408S 5-100 (AS) / S 2-5 (AS)1.711.802.910.47BET (m 2 / g)3.713.973.442.41

[0160] In addition, when examining the separation distance between the nitrogen desorption isotherm and the nitrogen adsorption isotherm of the negative electrode material manufactured in Example 1, the minimum separation distance A in the nitrogen relative pressure range of 0.25 to 0.30 is 0.1724 cm 3 / g STP, and the minimum separation distance B in the nitrogen relative pressure region of 0.90 to 0.95 was 0.5457 cm 3 / g STP, and the minimum separation distance C in the nitrogen relative pressure region of 0.97 to 0.98 was 1.3372 cm 3 / g was STP.

[0161] As shown in Table 1, it can be seen that the micropore structure of the cathode material manufactured with the same core varies depending on the size of the solid carbon precursor used for the amorphous carbon coating.

[0162] In detail, as in Comparative Example 1, when a solid carbon precursor in a relatively fine particle form is used compared to spherical natural graphite, the specific surface area of ​​fine pores in the pore size range of 2-5 nm is greatly reduced, while the specific surface area value of relatively coarse pores in the pore size range of 5-100 nm is large, resulting in a remarkably high S of up to 2.91. 5-100 (AS) / S 2-5 (AS) ratio. In addition, no peak was observed in the pore size range of 2-5 nm in the PSD (DS) of Comparative Example 1, which can be interpreted as meaning that the slit and / or wedge-shaped pores belonging to the pore size range of 2-5 nm were filled by amorphous carbon or did not function as open pores by amorphous carbon.

[0163] As in Example 2, when a relatively coarse particle-shaped solid carbon precursor is used compared to spherical natural graphite, it can be seen that the specific surface area value of the relatively coarse pores in the 5-100 nm pore size range decreases more significantly than the specific surface area of ​​the fine pores in the 2-5 nm pore size range, and it can be seen that an anode material having two peaks in the 2-5 nm pore size range in PSD (DS) is produced.

[0164] As in Example 1, when a solid carbon precursor having a bimodal distribution of relatively fine particles and relatively coarse particles compared to spherical natural graphite is used, it can be seen that a negative electrode material having appropriate specific surface areas for both pores of 2-5 nm size and pores of 5-100 nm size is produced without damaging the pore structure formed in the 2-5 nm size range.

[0165] In the case of Comparative Example 2, two peaks were located in the pore size region of 2-5 nm, and the ratio of PV2 / PV1 was up to 1.37. However, in the meso- to macro-pore region of 10 nm to 100 nm, the graph showed that PSD(AS) decreased as the pore size increased, indicating that most of the specific surface area was formed by micro-pores of 5 nm or less.

[0166] Table 2 shows the tap density (g / cm) of the negative electrode materials according to Examples 1 and 2 and Comparative Examples 1 and 2. 3 ), absorption (ml / 100g), D 50 (㎛) and span values ​​are summarized in this table.

[0167] Example 1 Example 2 Comparative Example 1 Comparative Example 2 Tap density (g / cm 3 )1.031.041.041.07Absorption (ml / 100g)40.543.945.039.1D 50 (㎛)15.6115.2215.3617.1span0.850.820.830.80

[0168] Through Table 2, the negative electrode materials of Examples 1 to 2 and Comparative Examples 1 to 2 have similar tap densities, D 50 And it can be seen that the cathode materials of Example 1 and Comparative Example 2 and the cathode materials of Example 2 and Comparative Example 1 have similar absorption amounts.

[0169] Table 3 summarizes the electrochemical characteristics of half cells equipped with negative electrode materials according to Examples 1 and 2 and Comparative Examples 1 and 2.

[0170] Example 1 Example 2 Comparative Example 1 Comparative Example 2 High-rate characteristics (%) 88.8 87.5 87.1 86.3 Life characteristics (%) 84.7 84.2 83.9 84.4

[0171] Tap density, D 50, it can be seen that the negative electrode material of the embodiment having a unique pore structure according to one specific example has significantly improved high-rate characteristics compared to the conventional negative electrode material, even though the span value and absorption amount are similar to each other, and it can be seen that in addition to the improved high-rate characteristics, it exhibits life characteristics similar to or better than the conventional negative electrode material.

[0172] The present invention is not limited to the embodiments described herein, but can be manufactured in a variety of different forms. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. A negative electrode material for a lithium secondary battery comprising a core including natural graphite and a carbon-containing surface layer covering the core, wherein the nitrogen adsorption isotherm and the nitrogen desorption isotherm are different in a nitrogen relative pressure range of at least 0.20 to 0.95, and the negative electrode material satisfies the following physical properties 1 and 2: Property 1: In the PSD(DS), which is a pore volume distribution graph obtained by nitrogen desorption isotherm, two peaks are located in the pore size range from 2 nm to 5 nm. Property 2: In the PSD(AS), which is a pore volume distribution graph obtained by a nitrogen adsorption isotherm, the graph shows that the pore size increases and the pore volume increases in the pore size range from 10 nm to 100 nm.

2. In paragraph 1, A negative electrode material for lithium secondary batteries that satisfies the following physical properties 3: Property 3: The ratio (PV2 / PV1) of the maximum value PV2 of the second peak having a larger peak center size among the two peaks of Property 1 divided by the maximum value PV1 of the first peak having a smaller peak center size is 0.8 or more.

3. In paragraph 1, A negative electrode material for a lithium secondary battery that satisfies the following property 4 and satisfies the spacing distance A < spacing distance B < spacing distance C in property 4: Property 4: In the range of nitrogen relative pressure (P / P0) from 0.25 to 0.30, the separation distance A between the nitrogen desorption isotherm and the nitrogen adsorption isotherm is 0.1 cm. 3 / g STP or higher, and in the nitrogen relative pressure region of 0.90 to 0.95, the separation distance B between the nitrogen desorption isotherm and the nitrogen adsorption isotherm is 0.4 cm. 3 / g STP or higher, and in the nitrogen relative pressure region of 0.97 to 0.98, the separation distance C between the nitrogen desorption isotherm and the nitrogen adsorption isotherm is 0.9 cm. 3 / g STP or higher.

4. In paragraph 1, Specific surface area S for pore sizes from 2 nm to 5 nm based on nitrogen adsorption isotherms 2-5 (AS) is 0.5 to 1.2 m 2 / g, negative electrode material for lithium secondary batteries.

5. In paragraph 2, In the above property 2, when the pore size increases from 10 nm to 100 nm, the increase in pore volume in PSD(AS) is 0.010 cm 3 g -1 nm -1 Ideal, negative electrode material for lithium secondary batteries.

6. In paragraph 1, Specific surface area S for pore sizes from 5 nm to 100 nm based on nitrogen adsorption isotherms 5-100 (AS) Specific surface area S by pore size from 2 nm to 5 nm based on nitrogen adsorption isotherm 2-5 (AS) divided by (S) 5-100 (AS) / S 2-5 (AS)) is a negative electrode material for a lithium secondary battery having an index of 1.0 to 2.

5.

7. In paragraph 1, A negative electrode material for a lithium secondary battery, wherein the linseed oil absorption amount of the above negative electrode material is 35 to 45 ml / 100 g.

8. In any one of paragraphs 1 to 7, The median diameter (D) of the above cathode material 50 ) is a negative electrode material for a lithium secondary battery, having a diameter of 8 to 25 μm.

9. In any one of paragraphs 1 to 7, The BET specific surface area of ​​the above cathode material is 3.0 to 4.5 m 2 / g, negative electrode material for lithium secondary batteries.

10. In any one of paragraphs 1 to 7, A negative electrode material for a lithium secondary battery, wherein the span of the negative electrode material is 0.7 to 1.

0.

11. In any one of paragraphs 1 to 7, The tap density of the above negative electrode material is 0.90 to 1.20 g / cm 3 In, a negative electrode material for lithium secondary batteries.

12. In any one of paragraphs 1 to 7, A negative electrode material for a lithium secondary battery, wherein the surface layer comprises amorphous carbon.

13. In any one of paragraphs 1 to 7, A negative electrode material for a lithium secondary battery, wherein the thickness of the surface layer is 5 nm to 20 nm.

14. In any one of paragraphs 1 to 7, The above core is a spherical natural graphite, a negative electrode material for lithium secondary batteries.

15. A negative electrode for a lithium secondary battery containing a negative electrode material according to any one of claims 1 to 7.