CN116885101A - Negative electrode comprising graphite and silicon-based material having different diameters and lithium secondary battery comprising same - Google Patents
Negative electrode comprising graphite and silicon-based material having different diameters and lithium secondary battery comprising same Download PDFInfo
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- CN116885101A CN116885101A CN202311079497.6A CN202311079497A CN116885101A CN 116885101 A CN116885101 A CN 116885101A CN 202311079497 A CN202311079497 A CN 202311079497A CN 116885101 A CN116885101 A CN 116885101A
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- China
- Prior art keywords
- negative electrode
- graphite
- particle
- secondary battery
- lithium secondary
- Prior art date
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- 239000002210 silicon-based material Substances 0.000 title claims abstract description 64
- 229910052744 lithium Inorganic materials 0.000 title claims abstract description 47
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims abstract description 44
- 239000007770 graphite material Substances 0.000 title description 5
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- 239000010405 anode material Substances 0.000 claims description 12
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Abstract
The present application relates to a negative electrode for a lithium secondary battery and a lithium secondary battery including the same, wherein a negative electrode material layer is formed on at least one surface of a negative electrode current collector, and the negative electrode material layer includes large particle graphite, small particle silicon-based material, fine particle graphite, and carbon nanotubes, and satisfies the following conditions 1 to 3: [ condition 1 ]]Average diameter D50 of large particle graphite (D 1 ): 1 to 50 μm [ condition 2 ]]Average diameter D50 (D 2 )：0.155D 1 To 0.414D 1 [ condition 3 ]]Average diameter D50 of fine particle graphite (D 3 )：0.155D 1 To 0.414D 1 Or 0.155D 2 To 0.414D 2 。
Description
The application relates to a divisional application, the application number of the original application is 201980026545.0, the application date is 6 months and 26 days in 2019, and the application is named as a negative electrode comprising graphite and silicon-based materials with different diameters and a lithium secondary battery comprising the negative electrode.
Technical Field
Cross Reference to Related Applications
The present application claims priority from korean patent application No. 10-2018-0127786, which was filed 24 in 10 in 2018, and korean patent application No. 10-2019-007475, which was filed 18 in 6 in 2019, which is incorporated herein by reference in its entirety.
The present application relates to a negative electrode including graphite having different diameters and a silicon-based material, and a lithium secondary battery including the same. In particular, the present application relates to a negative electrode including large-particle graphite, small-particle silicon-based material, and fine-particle graphite satisfying specific particle size conditions, and further carbon nanotubes, and a lithium secondary battery including the same.
Background
The rapid increase in fossil fuel use accelerates the demand for alternative energy and clean energy, and studies on power generation and power storage using electrochemistry have been actively conducted.
A typical example of an electrochemical device using such electrochemical energy is a secondary battery, which has been increasingly used in various fields.
Recently, technical developments and demands related to portable devices such as portable computers, cellular phones, and cameras have increased, resulting in an increase in demand for secondary batteries as an energy source. Among these secondary batteries, lithium secondary batteries having high energy density and operating potential, long life, and low self-discharge rate have been actively studied, commercialized, and widely used.
In addition, there is an increasing concern about environmental problems, and a great deal of research is being conducted on electric vehicles or hybrid electric vehicles, etc. instead of vehicles using fossil fuel (e.g., gasoline vehicles and diesel vehicles). These electric vehicles and hybrid electric vehicles generally use a nickel-metal hydride secondary battery as a power source. However, the use of lithium secondary batteries having high energy density and discharge voltage is currently being studied, and some are being commercialized.
Materials containing graphite are widely used as negative electrode active materials for lithium secondary batteries. The average potential of the graphite-containing material upon release of lithium is about 0.2V (relative to Li/li+), and the potential change during discharge is relatively uniform. This has the advantage that the voltage of the battery is high and constant. Although the capacity per unit mass of graphite material is as low as 372mAh/g, the capacity of graphite material has been increased and is now approaching the theoretical capacity, and thus it is difficult to further increase the capacity.
For higher capacity of lithium secondary batteries, many negative electrode active materials are being studied. As a negative electrode active material having a high capacity, a material forming an intermetallic compound with lithium (for example, silicon or tin) is expected to be a promising negative electrode active material. In particular, silicon is an alloy type negative electrode active material whose theoretical capacity (4200 mAh/g) is at least about 10 times that of graphite, and is currently attracting attention as a negative electrode active material for lithium secondary batteries.
However, silicon-containing silicon-based materials cause large volume changes (300%) during charge and discharge, resulting in the physical contact between the materials breaking and flaking. As a result, ion conductivity, electron conductivity, and the like drastically decrease, and thus the actual initial lifetime characteristics tend to drastically decrease.
In order to improve the characteristics of silicon-based materials having a high theoretical capacity, various attempts have been made in a top-down manner, such as Si/carbon composites. However, it is not sufficient to commercialize it due to a complicated manufacturing process and low productivity.
Therefore, there is a need to develop a technology for improving initial life characteristics when a silicon-based material is used as an active material of a lithium secondary battery.
Disclosure of Invention
[ technical problem ]
The present application is directed to solving the above-mentioned problems and other technical problems that have yet to be resolved.
Specifically, the present application provides a negative electrode having improved initial life characteristics while containing a silicon-based material as an active material by including large-particle graphite, small-particle silicon-based material, and fine-particle graphite, and carbon nanotubes satisfying specific particle size conditions in a negative electrode material layer, and a lithium secondary battery including the negative electrode.
Technical scheme
According to an embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein a negative electrode material layer is formed on at least one surface of a negative electrode current collector, and
the anode material layer contains large particle graphite, small particle silicon-based material, fine particle graphite, and carbon nanotubes, and satisfies the following conditions 1 to 3:
[ condition 1 ]]Average diameter D50 of large particle graphite (D 1 ): 1 to 50 μm
[ condition 2 ]]Average diameter D50 (D 2 )：0.155D 1 To 0.414D 1
[ condition 3 ]]Average diameter D50 of fine particle graphite (D 3 )：0.155D 1 To 0.414D 1 Or 0.155D 2 To 0.414D 2 。
According to another embodiment of the present application, there is provided a lithium secondary battery including the negative electrode for a lithium secondary battery.
The lithium secondary battery including the above-described negative electrode has significantly improved initial life characteristics while containing a silicon-based material as an active material.
Hereinafter, the anode and the lithium secondary battery according to the embodiment of the present application will be described in detail.
Unless explicitly indicated, the terms are used solely to refer to a specific embodiment and are not intended to limit the application.
The singular expressions of the present application may include plural expressions unless the context indicates otherwise.
The terms "comprises" and "comprising," etc. are used in the present application to specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, and do not preclude the presence or addition of other features, regions, integers, steps, operations, elements, and/or components.
Detailed Description
According to an embodiment of the present application, there is provided a negative electrode for a lithium secondary battery, wherein a negative electrode material layer is formed on at least one surface of a negative electrode current collector, and
the anode material layer contains large particle graphite, small particle silicon-based material, fine particle graphite, and carbon nanotubes, and satisfies the following conditions 1 to 3:
[ condition 1 ]]Average diameter D50 of large particle graphite (D 1 ): 1 to 50 μm
[ condition 2 ]]Average diameter D50 (D 2 )：0.155D 1 To 0.414D 1
[ condition 3 ]]Average diameter D50 of fine particle graphite (D 3 )：0.155D 1 To 0.414D 1 Or 0.155D 2 To 0.414D 2 。
The average diameter (D50) is defined as the diameter at 50% of the particle size distribution obtained based on the volume of the particles. The average diameter (D50) of the particles can be measured using, for example, laser diffraction.
For example, each particle is dispersed in a solution of water/triton X-100 and introduced into a commercially available laser diffraction particle size analyzer (e.g., microtrac S3500). Thereafter, ultrasonic waves of about 28kHz were irradiated at an output of 60W for 1 minute, and the average diameter (D50) at 50% of the particle size distribution could be calculated from the measuring instrument.
The large particle graphite and the fine particle graphite may each be at least one selected from the group consisting of natural graphite and artificial graphite.
Natural graphite has excellent adhesion, and artificial graphite has excellent output characteristics and life characteristics. Therefore, the type and content ratio thereof can be appropriately selected.
It is not excluded that the above-mentioned large-particle graphite and fine-particle graphite are mixtures of natural graphite and artificial graphite. Thus, the large particle graphite and the fine particle graphite may be a mixture of natural graphite and artificial graphite. Alternatively, the large particle graphite may be artificial graphite and the fine particle graphite may be natural graphite, or vice versa.
When both natural graphite and artificial graphite are contained, it is preferable that the content ratio of natural graphite to artificial graphite is 5:95 to 95:5 in terms of the performance of the secondary battery.
The specific surface area (BET) of the natural graphite may be 2m 2 /g to 8m 2 /g, or 2.1m 2 /g to 4m 2 And/g. The specific surface area (BET) of the artificial graphite may be 0.5m 2 /g to 5m 2 /g, or 0.6m 2 /g to 4m 2 /g。
The specific surface area can be measured by the BET (Brunauer-Emmett-Teller) method. For example, it can be measured by a BET 6-point method according to a nitrogen adsorption-flow method using a porosity analyzer (Belsorp-II mini manufactured by Bell Japan Inc).
The specific surface area of natural graphite exhibiting excellent adhesion is preferably large. This is because, as the specific surface area becomes larger, the physical interlocking effect of the adhesion between particles by the binder can be sufficiently ensured.
The shape of the natural graphite is not limited, and may be flake graphite, pulse (vein) graphite, or amorphous graphite, particularly pulse graphite or amorphous graphite. More specifically, as the contact area between particles increases, the bonding area increases, and thus the adhesion improves. Therefore, the tap density or bulk density is preferably large. In addition, it is also preferable that the grain orientation of the natural graphite exhibits anisotropy, and thus the natural graphite may be amorphous graphite.
Meanwhile, the shape of the artificial graphite is not limited, and may be in the form of powder, flakes, blocks, plates, or rods. Specifically, in order to exhibit the best output characteristics, the shorter the movement distance of lithium ions is, the better. In order to shorten the moving distance to the electrode direction, it is preferable that the grain orientation of the artificial graphite exhibits isotropy, and therefore, the artificial graphite may be in the form of a sheet or a plate, more specifically, in the form of a sheet.
The tap density of natural graphite may be 0.9g/cc to 1.3g/cc, more specifically 0.92g/cc to 1.15g/cc, and the tap density of artificial graphite may be 0.7g/cc to 1.1g/cc, more specifically 0.8g/cc to 1.05g/cc.
Tap density was measured as follows: 50g of the precursor was added to a 100cc vibrating cylinder and then tapped 3000 times using a JV-1000 measuring device (manufactured by COPLEY) and a KYT-4000 measuring device (manufactured by SEISHIN).
When the tap density is too small to exceed the above range, the contact area between particles may be insufficient, and thus the adhesion may be deteriorated. When it is too large, the tortuosity (tortuosity) of the electrode and the wettability of the electrolyte may decrease, and thus the output characteristics during charge and discharge may deteriorate, which is not preferable.
Regardless of the type, the average diameter D50 (D 1 ) May be 1 μm to 50 μm, specifically 3 μm to 40 μm, more specifically 5 μm to 30 μm.
When the average diameter (D 1 ) When too small, the initial efficiency of the secondary battery may be lowered due to the increase of the specific surface area, and thus the battery performance may be deteriorated. When the average diameter (D 1 ) When too large, the rolling property of the electrode may decrease, the electrode density may become difficult to achieve, and the electrode surface layer may become uneven, resulting in a decrease in charge-discharge capacity.
Average diameter D50 of fine particle graphite (D 3 ) May be 0.155D 1 To 0.414D 1 Or relative to the average diameter D50 (D 2 ) May be 0.155D 2 To 0.414D 2 。
Fine particle graphite is required to satisfy either of the above two conditions in order to be properly located between large particle graphite and small particle silicon-based material to connect them, thereby improving electron conductivity and exhibiting capacity.
When the average particle diameter (D) 3 ) Too small, agglomeration may occur, and it is difficult to uniformly coat fine particle graphite onto the current collector when forming the anode material layer. When the average diameter (D 3 ) Too large, adhesion may deteriorate, and fine-particle graphite may not effectively penetrate between the large-particle graphite and the silicon-based material. That is, fine particle graphite may not sufficiently exert the function of connecting them, and thus, electron conductivity may be lowered, which may not effectively improve initial life characteristics.
More specifically, the average diameter (D 3 ) May be 0.2D 1 To 0.4D 1 Or 0.2D 2 To 0.4D 2 。
The small particle silicon-based material may be selected from the group consisting of Si/C composite, siO x (0<x<2) Metal doped SiO x (0<x<2) At least one of the group consisting of pure Si and Si alloys, in particular SiO x (0<x<2) Or metal doped SiO x (0<x<2)。
For example, the Si/C complex may have the following structure: a structure in which carbon material obtained by firing when carbon is combined with silicon or silicon oxide particles is coated on the particle surface, a structure in which carbon is dispersed in an atomic state inside silicon particles, or a structure such as a silicon/carbon composite of PCT international application WO 2005/01030 of the present inventors. The present application is not limited thereto as long as it is a composite of carbon and silicon materials.
The silicon oxide may be 0< x.ltoreq.1, and includes a structure of silicon oxide whose surface is treated with a carbon coating, and the like.
In addition, metal doped SiO x (0<x<2) May be doped with at least one metal selected from the group consisting of Li, mg, al, ca and Ti.
When doping is performed as described above, siO can be reduced by 2 Phase (this is for SiO) 2 The material is irreversible) or by converting it into an electrochemically inert metal-silicate phase x Initial efficiency of the material.
The Si alloy is an alloy of Si with at least one metal selected from the group consisting of Zn, al, mn, ti, fe and Sn, and may include solid solutions, intermetallic compounds, eutectic alloys therewith. But the present application is not limited thereto.
Average diameter D50 (D 2 ) May be 0.155D 1 To 0.414D 1 In particular 0.2D 1 To 0.4D 1 。
Although silicon-based materials have very high capacities, there are the following problems: poor conductivity compared to graphite and does not achieve initial capacity and efficiency well. However, when silicon-based materials are placed between large particle graphite particles, they are in good contact with graphite, thus properly forming conductive paths, resulting in stable capacity and efficiency.
At this time, when the average diameter (D 2 ) When the above range is satisfied, the silicon-based material is suitably located between large-particle graphite particles, and a conductive path is suitably formed, resulting in good capacity and efficiency.
When the average diameter (D 2 ) When too small to exceed the above range, the silicon-based material may agglomerate even if the silicon-based material is distributed among large-particle graphite particles, and many electrolyte side reactions may occur, resulting in a decrease in initial efficiency. When the average diameter (D 2 ) When too large, the silicon-based material cannot be distributed between large-particle graphite particles, and thus the capacity and efficiency of the anode may be insufficient, resulting in overall deterioration.
According to the present application, carbon nanotubes may be contained in the negative electrode material layer in addition to the above-described large particle graphite, small particle silicon-based material, and fine particle graphite.
The carbon nanotubes have a tubular three-dimensional structure, which is more advantageous in forming a network structure in the thickness direction of the electrode. Therefore, this is advantageous in ensuring an electron transfer path between the anode material layer and the anode current collector, and the intended effect of the present application can be further improved.
The carbon nanotubes may have an oriented or entangled structure. The carbon nanotubes of the present application may comprise any type, but preferably, the carbon nanotubes have an oriented structure.
Specifically, the oriented type carbon nanotubes and the entanglement type carbon nanotubes are classified according to particle size and shape, and they can be manufactured by changing the temperature in chemical vapor deposition to obtain a desired type of carbon nanotubes. Since the entangled carbon nanotubes have a bulk structure, which is similar to the intermediate form of the dot-type conductive material and the aligned carbon nanotubes, formation of a network structure is disadvantageous. On the other hand, the oriented structure transfers electrons more easily because carbon atoms are separated from each other by a certain distance and exist in a strand. Therefore, it is more preferable to use aligned carbon nanotubes.
In addition, in order to have the most preferable electron transfer path to improve conductivity, the average diameter of the carbon nanotube may be 0.1nm to 20nm and the average length may be 100nm to 5 μm.
Here, the diameter and length may be measured by AFM. When they are within the above-described range, it is more advantageous to form a three-dimensional network structure, which is more preferable in terms of ensuring electron conductivity.
When the diameter is too large to exceed the above range, crystallinity and conductivity may deteriorate, and when the diameter is too small, it may not be easy to apply the anode material to the anode current collector. When the length is too short, there may be a problem in forming a network structure, and when the length is too long exceeding 5 μm, it may be difficult to uniformly distribute, which is not preferable.
Specifically, the negative electrode material layer may include 30 to 98.995 wt% of the large particle graphite, 0.5 to 30 wt% of the small particle silicon-based material, 0.5 to 20 wt% of the fine particle graphite, and 0.005 to 20 wt% of the carbon nanotubes, based on the total weight of the large particle graphite, the small particle silicon-based material, the fine particle graphite, and the carbon nanotubes.
As described above, the present application includes a silicon-based material as an active material to ensure high capacity. In addition, the present application also includes large particle graphite and fine particle graphite to improve insufficient conductivity of the silicon-based material.
In this case, since the small particle silicon-based material is placed in the void formed by the large particle graphite, the silicon-based material and graphite are in contact with each other, and the conductive path of the silicon-based material is appropriately formed, resulting in stable capacity and efficiency.
As a result, it is preferable that the above-mentioned large particle graphite is the main substance and the silicon-based material is located therebetween so that the large particle graphite can occupy the largest weight percentage in the anode material layer.
Thus, the negative electrode material layer may comprise 30 to 98.5 wt%, specifically 40 to 97 wt%, more specifically 60 to 95.5 wt% of the large particle graphite, and 0.5 to 30 wt%, specifically 1 to 25 wt%, more specifically 1.5 to 20 wt% of the small particle silicon-based material, based on the total weight of the large particle graphite, the small particle silicon-based material, the fine particle graphite, and the carbon nanotubes.
Meanwhile, fine particle graphite, although affecting capacity and efficiency like large particle graphite, can also have an effect of improving electron conductivity by being located between and connecting particles of the above large particle graphite and small particle silicon-based material. The content of the fine particle graphite may be 0.5 to 20 wt%, specifically 1 to 20 wt%, more specifically 1.5 to 10 wt%, based on the total weight of the large particle graphite, the small particle silicon-based material, the fine particle graphite, and the carbon nanotubes.
As described above, the carbon nanotube is more advantageous in forming a mesh-like network structure in the thickness direction of the electrode, and thus it can be used as a conductive material for securing an electron transfer path between the anode material layer and the anode current collector.
Accordingly, the content of the carbon nanotubes may be 0.005 to 20 wt%, specifically 0.007 to 15 wt%, more specifically 0.01 to 10 wt%, based on the total weight of the large particle graphite, the small particle silicon-based material, the fine particle graphite, and the carbon nanotubes.
The anode material layer is not limited to the above materials, and may further include a conductive material and a binder.
The conductive material is not particularly limited as long as it is a conventionally known conductive material other than carbon nanotubes and has conductivity without causing chemical changes in the battery. Examples of conductive materials include: carbon blacks such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as fluorocarbon powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives, etc.
The binder aids in adhesion between the active material and the conductive material and with the current collector, examples of which include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluororubber, various copolymers thereof, and the like.
At this time, the contents of the conductive material and the binder other than the carbon nanotubes may be 0.1 to 30 wt%, specifically 0.5 to 10 wt%, more specifically 1 to 5 wt%, respectively, based on the total weight of the anode material layer.
Since carbon nanotubes can be used as the conductive material, the negative electrode material layer may be composed of large particle graphite, small particle silicon-based material, fine particle graphite, carbon nanotubes, and a binder.
The negative electrode material layer may include additional active materials in addition to the above materials. For example, carbon-based materials such as amorphous hard carbon, low crystalline soft carbon, carbon black, acetylene black, ketjen black, super P, graphene, and fibrous carbon; metal complex oxides, e.g. Li x Fe 2 O 3 (0≤x≤1)、Li x WO 2 (0≤x≤1)、Sn x Me 1-x Me’ y O z (Me: mn, fe, pb, ge; me' Al, B, P, si, an element of group 1, group 2 or group 3 of the periodic Table of the elements, halogen; 0)<x is less than or equal to 1; y is more than or equal to 1 and less than or equal to 3; z is more than or equal to 1 and less than or equal to 8); lithium metal; a lithium alloy; a tin alloy; metal oxides, e.g. SnO, snO 2 、PbO、PbO 2 、Pb 2 O 3 、Pb 3 O 4 、Sb 2 O 3 、Sb 2 O 4 、Sb 2 O 5 、GeO、GeO 2 、Bi 2 O 3 、Bi 2 O 4 And Bi (Bi) 2 O 5 The method comprises the steps of carrying out a first treatment on the surface of the Conductive polymers such as polyacetylene; li-Co-Ni based material; titanium oxide; and lithium titanium oxide, and the like.
In addition, the anode material layer may further include a filler or the like.
The filler is optionally used as a component for suppressing expansion of the positive electrode. The filler is not particularly limited as long as it is a fibrous material that does not cause chemical changes in the battery. For example, olefin-based polymers such as polyethylene and polypropylene; and fibrous materials such as glass fibers and carbon fibers.
The negative electrode current collector may be generally formed to have a thickness of 3 to 200 μm. The negative electrode current collector is not particularly restricted so long as it has conductivity without causing chemical changes in the battery. For example, it may be copper; stainless steel; aluminum; nickel; titanium; sintering carbon; copper or stainless steel surface treated with carbon, nickel, titanium or silver; or an aluminum-cadmium alloy, etc. Further, similar to the positive electrode current collector, the negative electrode current collector may form fine irregularities on the surface thereof to improve the adhesion of the negative electrode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam body, and a non-woven fabric body may be used.
According to another embodiment of the present application, there is provided a lithium secondary battery including the negative electrode for a lithium secondary battery.
The lithium secondary battery may have the following structure: an electrode assembly including a positive electrode and a separator, and a negative electrode is embedded in a battery case together with an electrolyte.
For example, the positive electrode may be prepared by coating a positive electrode material mixed with a positive electrode active material and a binder onto a positive electrode current collector, and if necessary, a conductive material and a filler may be further added as described in the negative electrode.
The positive electrode current collector may be generally formed to have a thickness of 3 to 200 μm. The positive electrode current collector is not particularly restricted so long as it has conductivity without causing chemical changes in the battery. For example, it may be stainless steel; aluminum; nickel; titanium; or aluminum or stainless steel surface-treated with carbon, nickel, titanium or silver, etc., and it may be preferably aluminum. The current collector may form fine irregularities on the surface thereof to improve the adhesion of the positive electrode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric body may be used.
The positive electrode active material may be, for example, a layered compound, such as lithium cobalt oxide (LiCoO) 2 ) Lithium nickel oxide (LiNiO) 2 ) Or a compound substituted with one or more transition metals; lithium manganese oxideFor example Li 1+x Mn 2-x O 4 (wherein x is 0 to 0.33), liMnO 3 、LiMn 2 O 3 And LiMnO 2 The method comprises the steps of carrying out a first treatment on the surface of the Lithium copper oxides, e.g. Li 2 CuO 2 The method comprises the steps of carrying out a first treatment on the surface of the Vanadium oxides, e.g. LiV 3 O 8 、LiV 3 O 4 、V 2 O 5 And Cu 2 V 2 O 7 The method comprises the steps of carrying out a first treatment on the surface of the Ni-site lithium nickel oxides, e.g. LiNi 1-x M x O 2 (wherein M is Co, mn, al, cu, fe, mg, B or Ga, x is 0.01 to 0.3); lithium manganese composite oxides, e.g. LiMn 2-x M x O 2 (wherein M is Co, ni, fe, cr, zn or Ta, x is 0.01 to 0.1), and Li 2 Mn 3 MO 8 (wherein M is Fe, co, ni, cu or Zn); liMn with a portion of Li replaced by alkaline earth metal ions 2 O 4 The method comprises the steps of carrying out a first treatment on the surface of the Disulfide; and Fe (Fe) 2 (MoO 4 ) 3 Etc. However, the present application is not limited thereto.
Examples of binders, conductive materials, and fillers are described in the negative electrode.
The separator may be made of the same material, but is not limited thereto. Depending on the safety, energy density and overall performance of the battery cell, it may be made of materials different from each other.
The pore diameter and the porosity of the separator are not particularly limited, but the porosity may be 10 to 95%, and the pore diameter (diameter) may be 0.1 to 50 μm. The separator may act as a resistive layer when the pore size and porosity are less than 0.1 μm and 10%, respectively. When the pore diameter and the porosity are greater than 50 μm and 95%, respectively, it is difficult to maintain mechanical properties.
The electrolyte may be a non-aqueous electrolyte containing a lithium salt. The nonaqueous electrolyte containing a lithium salt is composed of a nonaqueous electrolyte and a lithium salt, and examples of the nonaqueous electrolyte include a nonaqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, and the like, but are not limited thereto.
Examples of the nonaqueous organic solvent include aprotic organic solvents such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ -butyrolactone, 1, 2-dimethoxyethane, tetrahydroxy flange g, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1, 3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphotriester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1, 3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, ethyl propionate, and the like.
Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate polymers, polylysine, polyester sulfides, polyvinyl alcohol, polyvinylidene fluoride, polymers containing ion dissociating groups, and the like.
Examples of the inorganic solid electrolyte include nitrides, halides and sulfates of lithium (Li), such as Li 3 N、LiI、Li 5 NI 2 、Li 3 N-LiI-LiOH、LiSiO 4 、LiSiO 4 -LiI-LiOH、Li 2 SiS 3 、Li 4 SiO 4 、Li 4 SiO 4 -LiI-LiOH and Li 3 PO 4 -Li 2 S-SiS 2 Etc.
The lithium salt is a material readily soluble in a nonaqueous electrolyte, examples of which include LiCl, liBr, liI, liClO 4 、LiBF 4 、LiB 10 Cl 10 、LiPF 6 、LiCF 3 SO 3 、LiCF 3 CO 2 、LiAsF 6 、LiSbF 6 、LiAlCl 4 、CH 3 SO 3 Li、(CF 3 SO 2 ) 2 NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenyl borate, lithium imidizate, and the like.
In order to improve charge-discharge characteristics, flame retardancy, and the like, the nonaqueous electrolyte may include, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, N-glyme, hexaphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, or the like. In some cases, a halogen-containing solvent such as carbon tetrachloride and trifluoroethylene may be further added to provide incombustibility, or carbon dioxide gas may be further added to improve high-temperature storage characteristics. FEC (fluoroethylene carbonate), PRS (propenoic acid lactone) and the like may be further added thereto.
In one specific example, a lithium salt (e.g., liPF 6 、LiClO 4 、LiBF 4 And LiN (SO) 2 CF 3 ) 2 Etc.) are added to a mixed solvent of a cyclic carbonate (e.g., EC and PC) as a high dielectric solvent and a linear carbonate (e.g., DEC, DMC and EMC) as a low viscosity solvent to prepare a lithium salt-containing nonaqueous electrolyte.
The lithium secondary battery of the present application can be used as a power source in a device. The device may be, for example, a notebook computer, a netbook, a tablet PC, a cellular phone, MP3, a wearable electronic device, an electric tool, an Electric Vehicle (EV), a Hybrid Electric Vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), an electric bicycle (E-bike), an electric scooter (E-scoote), an electric golf cart, or an electric power storage system, but the present application is not limited thereto.
Hereinafter, the present application will be described in more detail by means of specific examples. However, these examples are for illustrative purposes only, and the present application is not intended to be limited by these examples.
<Example 1>(D 2 :0.4D 1 ,D 3 :0.23D 1 )
Large-particle natural graphite (spherical, D50:15 μm), a silicon-based material (SiO, D50:6 μm) and fine-particle artificial graphite (flake, D50:3.5 μm) were mixed at a negative electrode active material weight ratio of 88:7:5, and then the negative electrode active material mixture, carbon nanotubes (oriented CNT, average diameter: 10nm, length: 4.5 μm), CMC (carboxymethylcellulose) as a binder, and SBR (styrene butadiene rubber) were added to solvent distilled water at a weight ratio of 97.8:0.8:0.7:0.7 to prepare a negative electrode slurry.
The negative electrode slurry was coated on a copper foil having a thickness of 15 μm to a thickness of 150 μm. It was pressed to have a porosity of 25% and dried at 130 ℃ under vacuum for about 8 hours to prepare a negative electrode.
<Example 2>(D 2 :0.4D 1 ,D 3 :0.33D 2 )
A negative electrode was prepared in the same manner as in example 1, except that fine-grained artificial graphite having a D50 of 2 μm was used.
<Example 3>(D 2 :0.4D 1 ,D 3 :0.23D 1 )
A negative electrode was prepared in the same manner as in example 1, except that large-particle natural graphite (spherical, d50:15 μm), a silicon-based material (SiO, d50:6 μm) and fine-particle artificial graphite (flake, d50:3.5 μm) were mixed at a negative electrode active material weight ratio of 85:10:5.
<Example 4>(D 2 :0.3D 1 ,D 3 :0.3D 1 )
A negative electrode was prepared in the same manner as in example 1, except that large-particle natural graphite (spherical, D50:5 μm), a silicon-based material (SiO, D50:1.5 μm) and fine-particle artificial graphite (flake-form, D50:1.5 μm) were used.
<Example 5>(D 2 :0.25D 1 ,D 3 :0.16D 1 ,D 3 :0.4D 2 )
A negative electrode was prepared in the same manner as in example 1, except that large-particle natural graphite (spherical, D50:5 μm), a silicon-based material (SiO, D50:2 μm) and fine-particle artificial graphite (flake-form, D50:0.8 μm) were used.
<Example 6>(D 2 :0.24D 1 ,D 3 :0.2D 1 )
A negative electrode was prepared in the same manner as in example 1, except that large-particle natural graphite (spherical, D50:25 μm), a silicon-based material (SiO, D50:6 μm) and fine-particle artificial graphite (flake-form, D50:5 μm) were used.
<Example 7>(D 2 :0.25D 1 ,D 3 :0.33D 2 )
A negative electrode was prepared in the same manner as in example 1, except that large-particle natural graphite (spherical, D50:25 μm), a silicon-based material (SiO, D50:6 μm) and fine-particle artificial graphite (flake-form, D50:2 μm) were used.
Comparative example 1 ]
A negative electrode was prepared in the same manner as in example 1, except that carbon nanotubes were not used. Specifically, large-particle natural graphite (spherical, D50:15 μm), a silicon-based material (SiO, D50:6 μm), and fine-particle artificial graphite (flake, D50:3.5 μm) were mixed at a negative electrode active material weight ratio of 88:7:5, and then the negative electrode active material mixture, CMC (carboxymethylcellulose) as a binder, and SBR (styrene butadiene rubber) were added to solvent distilled water at a weight ratio of 98.6:0.7:0.7 to prepare a negative electrode slurry.
Comparative example 2 ]
A negative electrode was prepared in the same manner as in example 2, except that carbon nanotubes were not used. Specifically, large-particle natural graphite (spherical, D50:15 μm), a silicon-based material (SiO, D50:6 μm), and fine-particle artificial graphite (flake, D50:2 μm) were mixed at a negative electrode active material weight ratio of 88:7:5, and then the negative electrode active material mixture, CMC (carboxymethyl cellulose) as a binder, and SBR (styrene butadiene rubber) were added to solvent distilled water at a weight ratio of 98.6:0.7:0.7 to prepare a negative electrode slurry.
<Comparative example 3>(not meeting D 1 ,D 2 :0.27D 1 ,D 3 :0.18D 1 )
A negative electrode was prepared in the same manner as in example 1, except that large-particle natural graphite (spherical, d50:55 μm), a silicon-based material (SiO, d50:15 μm), and fine-particle artificial graphite (flake, d50:10 μm) were mixed at a negative electrode active material weight ratio of 88:7:5, and then the negative electrode active material mixture, carbon nanotubes (aligned CNT, average diameter 10nm, length: 4.5 μm), CMC (carboxymethyl cellulose) as a binder, and SBR (styrene butadiene rubber) were added to solvent distilled water at a weight ratio of 97.8:0.8:0.7:0.7 to prepare a negative electrode slurry.
<Comparative example 4>(D 2 :0.133D 1 ,D 3 :0.23D 1 )
A negative electrode was prepared in the same manner as in example 1, except that large-particle natural graphite (spherical, d50:15 μm), a silicon-based material (SiO, d50:2 μm), and fine-particle artificial graphite (flake, d50:3.5 μm) were mixed at a negative electrode active material weight ratio of 88:7:5, and then the negative electrode active material mixture, carbon nanotubes (aligned CNT, average diameter 10nm, length: 4.5 μm), CMC (carboxymethyl cellulose) as a binder, and SBR (styrene butadiene rubber) were added to solvent distilled water at a weight ratio of 97.8:0.8:0.7:0.7 to prepare a negative electrode slurry.
<Comparative example 5>(D 2 :0.66D 1 ,D 3 :0.23D 1 ,0.35D 2 )
A negative electrode was prepared in the same manner as in example 1, except that large-particle natural graphite (spherical, d50:15 μm), a silicon-based material (SiO, d50:10 μm), and fine-particle artificial graphite (flake, d50:3.5 μm) were mixed at a negative electrode active material weight ratio of 88:7:5, and then the negative electrode active material mixture, carbon nanotubes (aligned CNT, average diameter 10nm, length 4.5 μm), CMC (carboxymethyl cellulose) as a binder, and SBR (styrene butadiene rubber) were added to solvent distilled water at a weight ratio of 97.8:0.8:0.7:0.7 to prepare a negative electrode slurry.
<Comparative example 6>(D 2 :0.4D 1 ,D 3 :0.03D 1 ,0.083D 2 )
A negative electrode was prepared in the same manner as in example 1, except that large-particle natural graphite (spherical, d50:15 μm), a silicon-based material (SiO, d50:6 μm), and fine-particle artificial graphite (flake, d50:0.5 μm) were mixed at a negative electrode active material weight ratio of 88:7:5, and then the negative electrode active material mixture, carbon nanotubes (aligned CNT, average diameter 10nm, length: 4.5 μm), CMC (carboxymethyl cellulose) as a binder, and SBR (styrene butadiene rubber) were added to solvent distilled water at a weight ratio of 97.8:0.8:0.7:0.7 to prepare a negative electrode slurry.
<Comparative example 7>(D 2 :0.4D 1 ,D 3 :0.53D 1 ,1.33D 2 )
A negative electrode was prepared in the same manner as in example 1, except that large-particle natural graphite (spherical, d50:15 μm), a silicon-based material (SiO, d50:6 μm), and fine-particle artificial graphite (flake, d50:8 μm) were mixed at a negative electrode active material weight ratio of 88:7:5, and then the negative electrode active material mixture, carbon nanotubes (aligned CNT, average diameter 10nm, length: 4.5 μm), CMC (carboxymethyl cellulose) as a binder, and SBR (styrene butadiene rubber) were added to solvent distilled water at a weight ratio of 97.8:0.8:0.7:0.7 to prepare a negative electrode slurry.
<Comparative example 8>(D 2 :0.133D 1 ,D 3 :0.013D 1 ,0.1D 2 )
A negative electrode was prepared in the same manner as in example 1, except that large-particle natural graphite (spherical, d50:15 μm), a silicon-based material (SiO, d50:2 μm), and fine-particle artificial graphite (flake, d50:0.2 μm) were mixed at a negative electrode active material weight ratio of 88:7:5, and then the negative electrode active material mixture, carbon nanotubes (aligned CNT, average diameter 10nm, length: 4.5 μm), CMC (carboxymethyl cellulose) as a binder, and SBR (styrene butadiene rubber) were added to solvent distilled water at a weight ratio of 97.8:0.8:0.7:0.7 to prepare a negative electrode slurry.
<Comparative example 9>(D 2 :0.66D 1 ,D 3 :0.53D 1 ,0.8D 2 )
A negative electrode was prepared in the same manner as in example 1, except that large-particle natural graphite (spherical, d50:15 μm), a silicon-based material (SiO, d50:10 μm), and fine-particle artificial graphite (flake, d50:8 μm) were mixed at a negative electrode active material weight ratio of 88:7:5, and then the negative electrode active material mixture, carbon nanotubes (aligned CNT, average diameter 10nm, length: 4.5 μm), CMC (carboxymethyl cellulose) as a binder, and SBR (styrene butadiene rubber) were added to solvent distilled water at a weight ratio of 97.8:0.8:0.7:0.7 to prepare a negative electrode slurry.
Comparative example 10 ]
A negative electrode was prepared in the same manner as in example 1, except that large-particle natural graphite (spherical, d50:15 μm) and a silicon-based material (SiO, d50:6 μm) were mixed in a negative electrode active material weight ratio of 93:7, and then the negative electrode active material mixture, a dot-type conductive material (densa black), CMC (carboxymethylcellulose) as a binder, and SBR (styrene butadiene rubber) were added to solvent distilled water in a weight ratio of 97:1.6:0.7:0.7 to prepare a negative electrode slurry.
Experimental example 1 ]
96 wt% of positive electrode active material (LiNi in a weight ratio of 97:3 0.4 Mn 0.3 Co 0.3 O 2 And LiNiO 2 2.3 wt.% of Super-P (conductive material) and 1.7 wt.% of PVDF (binder) to NMP (N-methyl-2-pyrrolidone); solvent) to prepare a positive electrode slurry, and then coating the positive electrode slurry onto an aluminum foil having a thickness of 15 μm to a thickness of 150 μm. It was pressed to have a porosity of 23% and dried at 130 ℃ under vacuum for about 12 hours to prepare a positive electrode.
The negative electrode, positive electrode, polyethylene separator (Celgard, thickness: 20 μm) and liquid electrolyte (wherein vinylene carbonate (VC, additive) and 1M LiPF were used, which were 0.5 wt% based on the weight of the electrolyte solvent, were prepared in the above examples and comparative examples 6 Dissolved in a mixed solvent of ethylene carbonate and ethylene methyl carbonate in a volume ratio of 3:7).
These secondary batteries were charged and discharged 100 times at 1.0C in the voltage range of 2.5V to 4.2V, and the results are shown in table 1 below.
Watch (watch)
| 1 cycle | 100 cycles (%) | |
| Example 1 | 100％ | 87.05 |
| Example 2 | 100％ | 87.12 |
| Example 3 | 100％ | 85.43 |
| Example 4 | 100％ | 88.95 |
| Example 5 | 100％ | 89.01 |
| Example 6 | 100％ | 86.32 |
| Example 7 | 100％ | 86.45 |
| Comparative example 1 | 100％ | 78.00 |
| Comparative example 2 | 100％ | 78.21 |
| Comparative example 3 | 100％ | 81.00 |
| Comparative example 4 | 100％ | 80.49 |
| Comparative example 5 | 100％ | 81.21 |
| Comparative example 6 | 100％ | 80.55 |
| Comparative example 7 | 100％ | 80.78 |
| Comparative example 8 | 100％ | 81.07 |
| Comparative example 9 | 100％ | 80.95 |
| Comparative example 10 | 100％ | 77.89 |
Referring to table 1, it was confirmed that when all the conditions of the present application were satisfied, the life characteristics of 85% or more were exhibited after 100 cycles. It was also confirmed that sufficient lifetime characteristics could not be obtained even if one condition was not satisfied.
Those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the application as disclosed in the accompanying claims.
[ Industrial applicability ]
As described above, the anode of the present application has improved initial life characteristics while containing a silicon-based material as an active material by including large-particle graphite, small-particle silicon-based material, and fine-particle graphite satisfying specific particle size conditions, and further carbon nanotubes in the anode material layer.
Claims (13)
1. A negative electrode for a lithium secondary battery, wherein a negative electrode material layer is formed on at least one surface of a negative electrode current collector, and
the negative electrode material layer contains large particle graphite, small particle silicon-based material, fine particle graphite, and carbon nanotubes, and satisfies the following conditions 1 to 3:
[ condition 1 ]]Average diameter D50 of large-particle graphite, D 1 :1 to 50 μm
[ condition 2 ]]Average diameter D50 of small-particle silicon-based material, i.e. D 2 ：0.155D 1 To 0.414D 1
[ condition 3 ]]Average diameter D50 of fine-grained graphite, i.e. D 3 ：0.155D 1 To 0.414D 1 Or 0.155D 2 To 0.414D 2 。
2. The negative electrode for a lithium secondary battery according to claim 1,
wherein the large-particle graphite and the fine-particle graphite are at least one selected from the group consisting of natural graphite and artificial graphite, respectively.
3. The negative electrode for a lithium secondary battery according to claim 1,
wherein [ condition 1]Diameter D50 of large particle graphite, D 1 Is 5 to 30 mu m.
4. The negative electrode for a lithium secondary battery according to claim 1,
wherein [ condition 2]Diameter D50 of small particle silicon-based material, D 2 Is 0 to.2D 1 To 0.4D 1 。
5. The negative electrode for a lithium secondary battery according to claim 1,
wherein the negative electrode material layer comprises 0.01 to 10 wt% of carbon nanotubes based on the total weight of the large particle graphite, the small particle silicon-based material, the fine particle graphite, and the carbon nanotubes.
6. The negative electrode for a lithium secondary battery according to claim 1,
wherein the small particle silicon-based material is at least one selected from the group consisting of: si/C complex; siO (SiO) x Wherein 0 is<x<2; metal doped SiO x Wherein 0 is<x<2; pure Si; and Si alloys.
7. The negative electrode for a lithium secondary battery according to claim 6,
wherein the metal doped SiO x Doped with at least one metal selected from the group consisting of Li, mg, al, ca and Ti.
8. The negative electrode for a lithium secondary battery according to claim 1,
wherein the carbon nanotubes have an oriented or entangled structure.
9. The negative electrode for a lithium secondary battery according to claim 1,
wherein the average diameter of the carbon nanotubes is 0.1nm to 20nm and the average length is 100nm to 5 μm.
10. The negative electrode for a lithium secondary battery according to claim 1,
wherein the negative electrode material layer comprises 40 to 98.5 wt% of the large particle graphite, 0.5 to 30 wt% of the small particle silicon-based material, and 0.5 to 20 wt% of the fine particle graphite, based on the total weight of the large particle graphite, the small particle silicon-based material, the fine particle graphite, and the carbon nanotubes.
11. The negative electrode for a lithium secondary battery according to claim 1,
wherein the negative electrode material layer further comprises a conductive material and a binder.
12. The negative electrode for a lithium secondary battery according to claim 11,
wherein the contents of the conductive material and the binder are each 0.1 to 30 wt% based on the total weight of the anode material layer.
13. A lithium secondary battery comprising the negative electrode for a lithium secondary battery according to claim 1.
Applications Claiming Priority (6)
| Application Number | Priority Date | Filing Date | Title |
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| KR10-2018-0127486 | 2018-10-24 | ||
| KR20180127486 | 2018-10-24 | ||
| KR10-2019-0072305 | 2019-06-18 | ||
| KR1020190072305A KR102590425B1 (en) | 2018-10-24 | 2019-06-18 | Anode Comprising Graphite and Silicon-based material having the Different Diameter and Lithium Secondary Battery Comprising the Same |
| CN201980026545.0A CN112005407A (en) | 2018-10-24 | 2019-06-26 | Negative electrode comprising graphite and silicon-based material having different diameters and lithium secondary battery comprising same |
| PCT/KR2019/007740 WO2020085610A1 (en) | 2018-10-24 | 2019-06-26 | Anode comprising graphite and silicon-based material which have different diameters, and lithium secondary battery comprising same |
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| CN201980026545.0A Division CN112005407A (en) | 2018-10-24 | 2019-06-26 | Negative electrode comprising graphite and silicon-based material having different diameters and lithium secondary battery comprising same |
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| KR102114044B1 (en) * | 2013-11-29 | 2020-05-25 | 강원대학교산학협력단 | Negative active material for rechargeable lithium battery, method of preparing the same, and rechargeable lithium battery including the same |
| TWI668901B (en) * | 2014-01-09 | 2019-08-11 | 日商昭和電工股份有限公司 | Method of producing negative electrode active material for lithium ion secondary battery |
| JP2015164127A (en) * | 2014-01-31 | 2015-09-10 | 三菱化学株式会社 | Carbon material for nonaqueous secondary battery negative electrode, negative electrode for nonaqueous secondary battery and nonaqueous secondary battery |
| JP6599106B2 (en) * | 2014-02-12 | 2019-10-30 | 大阪瓦斯株式会社 | Negative electrode material for lithium secondary battery and method for producing the same, composition for negative electrode active material layer for lithium secondary battery using the negative electrode material, negative electrode for lithium secondary battery, and lithium secondary battery |
| KR102323428B1 (en) * | 2015-03-13 | 2021-11-09 | 삼성에스디아이 주식회사 | Negative electrode for rechargeable lithium battery, method of manufacturing the same, and rechargeable lithium battery including the same |
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