Title of Invention: Anode for secondary battery and secondary battery comprising same
technical field
[One]
Cross-Citation with Related Application(s)
[2]
This application claims the benefit of priority based on Korean Patent Application No. 10-2020-0093964 dated July 28, 2020, and all contents disclosed in the literature of the Korean patent application are incorporated as a part of this specification.
[3]
The present invention relates to a negative electrode for a secondary battery, and more particularly, to a negative electrode for a secondary battery that improves cell performance.
background
[4]
As technology development and demand for mobile devices increase, the demand for secondary batteries as an energy source is rapidly increasing. Among such secondary batteries, lithium secondary batteries with high energy density and voltage, long cycle life, and low self-discharge rate has been used and is widely used.
[5]
In particular, secondary batteries are of great interest not only as mobile devices such as mobile phones, digital cameras, notebooks, and wearable devices, but also as energy sources for power devices such as electric bicycles, electric vehicles, and hybrid electric vehicles.
[6]
In addition, as interest in environmental problems grows, research on electric vehicles and hybrid electric vehicles that can replace vehicles using fossil fuels such as gasoline vehicles and diesel vehicles, which are one of the main causes of air pollution, is being conducted. have. Although nickel-metal hydride secondary batteries are mainly used as power sources for such electric vehicles and hybrid electric vehicles, research using lithium secondary batteries with high energy density and discharge voltage is being actively conducted, and some are in the commercialization stage.
[7]
A carbon material is mainly used as an anode active material of such a lithium secondary battery, and natural graphite or artificial graphite is mainly used. In the case of artificial graphite, although the output characteristics and lifespan characteristics are excellent, the adhesive force is relatively low, so there is a problem in that the electrode detachment occurs during the electrode coating, drying, and rolling processes. In the case of natural graphite, although the adhesion is excellent, there is a problem in that there are many side reactions with the electrolyte because of the large number of internal pores. Accordingly, in recent years, natural graphite and artificial graphite are mixed in a certain ratio, and an electrode applied as a single layer on a current collector has been manufactured. The expansion rate is also high, which is still disadvantageous to cell performance.
[8]
Accordingly, the need for developing an anode having improved both electrode adhesion and cell performance is increasing.
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[9]
An object of the present invention is to provide a secondary battery negative electrode for improving the cell performance of a secondary battery and a secondary battery including the same.
[10]
The problem to be solved by the present invention is not limited to the above-mentioned problems, and the problems not mentioned will be clearly understood by those of ordinary skill in the art to which the present invention belongs from the present specification and the accompanying drawings. .
means of solving the problem
[11]
A negative electrode for a secondary battery according to an embodiment of the present invention includes a negative electrode current collector; a first active material layer coated with a first negative electrode slurry including a first negative active material on the negative electrode current collector; and a second active material layer coated with a second anode slurry including a second anode active material on the first active material layer, wherein the first anode active material has an internal pore volume of 0.6*10 -3 cm 3 /g or more 2.5*10 -3 cm 3 /g or less of natural graphite, and the second anode active material includes artificial graphite.
[12]
The first negative active material may include natural graphite having an average particle diameter (D50) of 17 μm or more and 25 μm or less.
[13]
The first negative active material may be made of the natural graphite.
[14]
The adhesive force between the first active material layer and the negative electrode current collector may be greater than or equal to 21 gf/cm and less than or equal to 40 gf/cm.
[15]
The second anode active material may include artificial graphite having an average particle diameter (D50) of 10 μm or more and 30 μm or less.
[16]
The second anode active material may be made of the artificial graphite.
[17]
The content of the second negative active material included in the second active material layer may be greater than the content of the first negative active material included in the active material layer of the first active material layer.
[18]
The content of the first negative active material and the second negative active material is a negative electrode for a secondary battery included in a ratio of 10 to 40 parts by weight: 60 to 90 parts by weight.
[19]
The secondary battery according to another embodiment of the present invention may include the negative electrode for the secondary battery.
[20]
In a state of charge of the secondary battery, a thickness swelling ratio may be 24% or less.
Effects of the Invention
[21]
According to an embodiment of the present invention, the cell performance of the secondary battery may be improved.
[22]
Effects of the present invention are not limited to the above-described effects, and effects not mentioned will be clearly understood by those of ordinary skill in the art to which the present invention belongs from the present specification and accompanying drawings.
Modes for carrying out the invention
[23]
Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.
[24]
Hereinafter, a negative electrode for a secondary battery according to an embodiment of the present invention and a secondary battery including the same will be described.
[25]
A negative electrode for a secondary battery according to an embodiment of the present invention includes a negative electrode current collector, a first active material layer, and a second active material layer. More specifically, the first active material layer and the second active material layer may be disposed on one side or both sides of the negative electrode current collector. The first active material layer is located on the negative electrode current collector, and the second active material layer is located on the first active material layer. That is, the first active material layer is positioned between the negative electrode current collector and the second active material layer.
[26]
Accordingly, the first active material layer containing natural graphite having excellent adhesion is in contact with the anode current collector, so that the anode for a secondary battery of the present invention may have improved electrode adhesion.
[27]
The first active material layer is formed by applying a first negative electrode slurry containing the first negative active material.
[28]
The first negative active material is natural graphite having an internal pore volume of 0.6*10 -3 cm 3 /g or more and 2.5*10 -3 cm 3 /g or less.
[29]
The first negative active material may have an internal pore volume of 0.6*10 -3 cm 3 /g or more and 2.5*10 -3 cm 3 /g or less , unlike general natural graphite . Accordingly, in the negative electrode for a secondary battery of the present invention, internal pores may be reduced, and side reactions with the electrolyte may be reduced as compared to general natural graphite. In addition, the first negative active material has reduced internal pores, so that cycle durability and expansion performance may be improved as compared to a negative electrode including general natural graphite. Accordingly, cell performance of the negative electrode for a secondary battery according to an embodiment of the present invention may be improved.
[30]
Here, the internal pore (mesopore) may be measured by a Brunauer-Emmett-Teller (BET method). More specifically, when measuring BET, the pore distribution can be confirmed through the BJH plot, and the pore volume corresponding to the mesopore size of the internal pore volume is calculated as the dVp/DDp sum value (cm 3 / g) can be measured.
[31]
In order to reduce the side reaction with the electrolyte, natural graphite is preferable as the internal pores are reduced. However, general natural graphite has a particle diameter of 9 μm or more and 17 μm or less, while having an internal pore volume in the range of 2.9*10 -3 cm 3 /g to 4.2*10 -3 cm 3 /g. In particular, in the case of general natural graphite, there are many internal pores compared to the particle size, and thus, the internal pore volume is increased in general natural graphite having a larger particle size than normal natural graphite having a small particle size. In order to reduce the internal pore volume, general natural graphite having a small particle size may be used, but in general, the smaller the particle size, the larger the specific surface area, and the larger the specific surface area, the more side reactions with the electrolyte proceed.
[32]
Alternatively, the first negative active material may be natural graphite having an average particle diameter (D50) and an average particle diameter (D50) of 15 μm or more and 30 μm or less. More preferably, the first negative active material may be natural graphite having an average particle diameter (D50) and an average particle diameter (D50) of 17 μm or more and 25 μm or less. For example, the first anode active material may be natural graphite having an average particle diameter (D50) and an average particle diameter (D50) of 18 μm or more and 20 μm or less. Accordingly, in the negative electrode for a secondary battery of the present invention, the particle size of natural graphite is larger than that of a general natural negative electrode, and side reactions with the electrolyte due to the specific surface area may be reduced. However, if the size of the first anode active material is too large, the specific surface area may be excessively reduced, thereby reducing adhesive strength.
[33]
In addition, the first negative active material of the present invention may be natural graphite having an internal pore volume of 0.6*10 -3 cm 3 /g or more and 2.5*10 -3 cm 3 /g or less. More preferably, the first negative active material of the present invention may be natural graphite having an internal pore volume of 1.0*10 -3 cm 3 /g or more and 2.0*10 -3 cm 3 /g or less. For example, the first negative active material of the present invention may be natural graphite having an internal pore volume of 1.6*10 -3 cm 3 /g or more and 1.8*10 -3 cm 3 /g or less. Accordingly, the negative electrode for a secondary battery of the present invention has an internal pore volume lower than that of general natural graphite, and side reactions with the electrolyte due to the internal pore volume can be reduced.
[34]
On the other hand, when the internal pore volume of the first negative active material of the present invention is excessively large, such as in the case of exceeding 2.5*10 -3 cm 3 /g, side reactions between the first negative active material and the electrolyte may increase, and thus Accordingly, there is a problem in that cell capacity and cell durability such as negative electrode expansion are deteriorated.
[35]
On the other hand, when the internal pore volume of the first negative active material of the present invention is too small, such as less than 0.6*10 -3 cm 3 /g, the electrolyte permeability of the first negative active material is inferior, and the first negative active material in the electrode impregnation uniformity may also be lowered. In addition, charge transfer resistance may be increased, and thus fast charging performance may be deteriorated.
[36]
Here, the adhesive force between the first active material layer and the negative electrode current collector may be 20 gf/cm or more and 40 gf/cm or less. Accordingly, the first active material layer has excellent adhesion to the negative electrode current collector, thereby preventing electrode detachment from occurring during electrode coating, drying, and rolling processes.
[37]
In addition, the shape of the natural graphite included in the first negative active material is not limited, and may be flake graphite, grain graphite, or amorphous graphite. Preferably, it may be earth graphite having a large contact area between particles to improve adhesion.
[38]
The second active material layer is formed by applying a second negative electrode slurry containing the second negative active material.
[39]
The second anode active material may be artificial graphite having an average particle diameter (D50) of 10 μm or more and 30 μm or less. More preferably, the second negative active material may be artificial graphite having an average particle diameter (D50) of 15 μm or more and 22 μm or less. When the size of the second anode active material is smaller than 10 μm, a specific surface area is greatly increased, so that a side reaction with the electrolyte is more proceeded, and thus cell performance may be deteriorated. When the size of the second anode active material is greater than 30 μm, a specific surface area may decrease, thereby reducing adhesion, and rapid charging performance may be deteriorated due to an increase in particle size.
[40]
In addition, the shape of the artificial graphite included in the second anode active material is not limited, and may be in the form of powder, flake, block, plate, or rod. Preferably, in order to have the best lifespan characteristics and output characteristics, the lithium ions may be in a flake shape or a plate shape with a short movement distance.
[41]
In addition, in the negative electrode according to an embodiment of the present invention, the content of the first negative active material included in the first active material layer and the second negative active material included in the second active material layer is the first negative active material: the second negative active material =10 to 40 parts by weight: may be included in a ratio of 60 to 90 parts by weight. More preferably, the content of the first negative active material included in the first active material layer and the second negative active material included in the second active material layer is: first negative active material: second negative active material = 20 to 30 parts by weight: 70 It may be included in a ratio of 80 parts by weight to 80 parts by weight.
[42]
When the content of the first anode active material is less than the above-mentioned range, the content of natural graphite may be relatively small, so that the adhesion of the entire active material layer may be reduced, and electrode detachment may occur during electrode coating, drying, and rolling processes. can still occur. In addition, when the content of the first anode active material is greater than the above-described range, the content of artificial graphite is relatively small, and the lifespan characteristics of the entire active material layer may be reduced, so that the overall cell performance may be reduced. have.
[43]
Each of the first active material layer and the second active material layer may further include a binder and a conductive material in addition to the first negative active material or the second active material.
[44]
The conductive material is used to impart conductivity to the electrode, and in the configured battery, it can be used without any particular limitation as long as it does not cause chemical change and has electronic conductivity. Specific examples include carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; graphite such as natural graphite and artificial graphite; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or a conductive polymer such as a polyphenylene derivative, and the like, and one or a mixture of two or more thereof may be used. The conductive material may be included in an amount of 1 wt% to 30 wt% based on the total weight of the negative electrode.
[45]
The binder serves to improve adhesion between the anode active material particles and adhesion between the anode active material and the 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, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any one of them or a mixture of two or more thereof may be used. The binder may be included in an amount of 1% to 30% by weight based on the total weight of the negative electrode.
[46]
The anode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface. Carbon, nickel, titanium, one surface-treated with silver, an aluminum-cadmium alloy, etc. may be used. In addition, the negative electrode current collector may have a thickness of typically 3 μm to 500 μm, and similarly to the positive electrode current collector, fine irregularities may be formed on the surface of the current collector to strengthen the bonding force of the negative 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 nonwoven body.
[47]
The secondary battery according to another embodiment of the present invention may include the negative electrode for the secondary battery. More specifically, the secondary battery may include an electrode assembly including the secondary battery negative electrode, the positive electrode, and a separator interposed between the secondary battery negative electrode and the positive electrode, and the electrolyte.
[48]
The positive electrode may be manufactured by applying a positive electrode slurry including a positive electrode active material, a binder, a conductive material, and the like to a positive electrode current collector, like the negative electrode for a secondary battery.
[49]
The positive electrode may also be prepared in a form in which a positive electrode slurry including a positive electrode active material is applied on a positive electrode current collector, and the positive electrode slurry may further include a conductive material and a binder as described above along with the positive electrode active material. have.
[50]
The positive active material may include, 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 oxides such as Formula Li 1+x Mn 2-x O 4 (wherein x is 0 or more and 0.33 or less), LiMnO 3 , LiMn 2 O 3 , and LiMnO 2 ; lithium copper oxide (Li 2 CuO 2 ); LiV 3 O 8 , LiFe 3 O 4 , V 2 O 5 , Cu 2 V 2 O vanadium oxide such as 7 ; Ni site-type lithium nickel oxide represented by the formula LiNi 1-x M x O 2 (wherein M is Co, Mn, Al, Cu, Fe, Mg, B, or Ga, and x is 0.01 or more and 0.3 or less); Formula LiMn 2-x M x O 2 (wherein M is Co, Ni, Fe, Cr, Zn, or Ta, and x is 0.01 or more and 0.1 or less) or Li 2 Mn 3 MO 8 (where M is Fe, lithium manganese composite oxide represented by Co, Ni, Cu, or Zn; LiNi x Mn 2-x O 4 A lithium manganese composite oxide having a spinel structure; LiMn 2 O 4 in which a part of the formula Li is substituted with an alkaline earth metal ion ; disulfide compounds; Fe 2(MoO 4 ) 3 and the like, but are not limited thereto.
[51]
The positive electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, fired carbon, or carbon, nickel, titanium on the surface of aluminum or stainless steel. , silver or the like surface-treated may be used. In addition, the positive electrode current collector may have a thickness of 3 μm to 500 μm, and fine irregularities may be formed on the surface of the current collector to increase 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 nonwoven body.
[52]
The separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move, and can be used without any particular limitation as long as it is normally used as a separator in a lithium secondary battery. Excellent is preferred. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene/butene copolymer, an ethylene/hexene copolymer, and an ethylene/methacrylate copolymer, or these A laminate structure of two or more layers of may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, or the like may be used. In addition, a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure.
[53]
In addition, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries, and are limited to these. it's not going to be
[54]
Specifically, the electrolyte may include an organic solvent and a lithium salt.
[55]
The organic solvent may be used without any particular limitation as long as it can serve as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, as the organic solvent, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone; ether-based solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon-based solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), propylene carbonate, carbonate-based solvents such as PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, which may include a double bond aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; Or sulfolanes and the like may be used. Among these, carbonate-based solvents are preferable, and cyclic carbonates (eg, A mixture of ethylene carbonate or propylene carbonate) and a low-viscosity linear carbonate-based compound (eg, ethylmethyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferable. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte may be excellent.
[56]
The lithium salt may be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the lithium salt is LiPF 6 , LiClO 4 , LiAsF 6 , LiBF 4 , LiSbF 6 , LiAl0 4 , LiAlCl 4 , LiCF 3 SO 3 , LiC4F 9 SO 3 , LiN(C 2 F 5 SO 3 ) 2 , LiN (C 2 F 5 SO 2 ) 2 , LiN(CF 3 SO 2 ) 2 . LiCl, LiI, or LiB(C 2 O 4 ) 2 and the like may be used. The concentration of the lithium salt is preferably used within the range of 0.1M to 2.0M. When the concentration of the lithium salt is included in the above range, since the electrolyte has an appropriate conductivity and viscosity, excellent electrolyte performance may be exhibited, and lithium ions may move effectively.
[57]
In addition to the above components, the electrolyte includes, for example, haloalkylene carbonate-based compounds such as difluoroethylene carbonate, pyridine, triethyl, for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. Phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidinone, N,N-substituted imidazoli One or more additives such as din, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride may be further included. In this case, the additive may be included in an amount of 0.1 wt% to 5 wt% based on the total weight of the electrolyte.
[58]
[59]
Hereinafter, the contents of the present invention will be described by way of examples, but the following examples are for illustrative purposes only, and the scope of the present invention is not limited thereto.
[60]

[61]
Natural graphite with an internal mesopore volume of 1.6*10 -3 cm 3 /g and an average particle diameter (D50) of 20 μm as the first negative active material, SBR as a binder, CMC as a thickener, and carbon black as a conductive material. After measuring to have a ratio of :SBR:CMC:carbon black=96.6:1.3:1.1:1.0, distilled water was added and mixed to prepare a first negative electrode slurry.
[62]
Artificial graphite with an average particle diameter (D50) of 22 μm as the second negative active material, SBR as a binder, CMC as a thickener, and carbon black as a conductive material in a ratio of natural graphite:SBR:CMC:carbon black=95.6:2.3:1.1:1.0 After weighing to have it, distilled water was added and mixed to prepare a second negative electrode slurry.
[63]
The prepared first negative electrode slurry was coated on a copper foil electrode current collector to form a first active material layer, and the prepared second negative electrode slurry was coated on the first active material layer to form a second active material layer to prepare a negative electrode. In this case, the negative electrode includes natural graphite included in the first active material layer and artificial graphite included in the second active material layer in a ratio of 30 parts by weight: 70 parts by weight.
[64]
[65]

[66]
Unlike Example 1, natural graphite having an internal mesopore volume of 1.7*10 -3 cm 3 /g and an average particle diameter (D50) of 18 μm of the first negative active material was used, and the first active material layer was The included natural graphite and the artificial graphite included in the second active material layer are included in a ratio of 20 parts by weight: 80 parts by weight. Except for this point, an anode was prepared in the same manner as in Example 1.
[67]
[68]

[69]
Unlike Example 1, natural graphite having an internal mesopore volume of 1.7*10 -3 cm 3 /g and an average particle diameter (D50) of 18 μm of the first negative active material was used. Except for this point, an anode was prepared in the same manner as in Example 1.
[70]
[71]

[72]
Unlike Example 1, natural graphite having an internal mesopore volume of 3.2*10 -3 cm 3 /g and an average particle diameter (D50) of 11 μm of the first negative active material was used, and the first active material layer was The included natural graphite and the artificial graphite included in the second active material layer are included in a ratio of 20 parts by weight: 80 parts by weight. Except for this point, an anode was prepared in the same manner as in Example 1.
[73]
[74]

[75]
Unlike Example 1, natural graphite having an internal mesopore volume of 4.2*10 -3 cm 3 /g and an average particle diameter (D50) of 9 μm of the first negative active material was used. Except for this point, an anode was prepared in the same manner as in Example 1.
[76]
[77]

[78]
Unlike Example 1, natural graphite having an internal mesopore volume of 3.2*10 -3 cm 3 /g and an average particle diameter (D50) of 11 μm of the first negative active material was used, and the first active material layer was The included natural graphite and the artificial graphite included in the second active material layer are included in a ratio of 80 parts by weight: 20 parts by weight. Except for this point, an anode was prepared in the same manner as in Example 1.
[79]
[80]

[81]
Unlike Example 1, natural graphite having an internal pore volume of 4.2*10 -3 cm 3 /g and an average particle diameter (D50) of 9 μm of the first negative active material was used, and the first active material layer was The included natural graphite and the artificial graphite included in the second active material layer are included in a ratio of 70 parts by weight: 30 parts by weight. Except for this point, an anode was prepared in the same manner as in Example 1.
[82]
[83]

[84]
Unlike Example 1, natural graphite having an internal mesopore volume of 2.9*10 -3 cm 3 /g and an average particle diameter (D50) of 17 μm of the first negative active material was used, and the first active material layer was The included natural graphite and the artificial graphite included in the second active material layer are included in a ratio of 20 parts by weight: 80 parts by weight. Except for this point, an anode was prepared in the same manner as in Example 1.
[85]
[86]

[87]
For the positive electrode, LCO (LiCoO 2 ) is used as the positive electrode active material, and mixed with carbon black and PVDF, but the positive electrode active material: carbon black: PVDF = 97.68 parts by weight: 1.2 parts by weight: 1.12 parts by weight Put in NMP to have a ratio of 1.12 parts by weight and mix (mixing) to prepare a positive electrode slurry, which was coated on an aluminum foil current collector so as to have a loading amount of 19.5 mg/cm 2 to prepare a positive electrode.
[88]
Prepare the prepared positive electrode and the negative electrode prepared in Examples 1 to 3 and Comparative Examples 1 to 5, a PE separator is interposed between the positive electrode and the negative electrode, and 1M LiPF6 and 0.5 in a solvent having EC:EMC=2:8 Coin full cells were prepared using an electrolyte containing wt% of VC additive.
[89]
The charging range of each coin full cell is set from SOC0 to SOC95, the first cycle is charged and discharged at 0.1C, the second cycle is charged and discharged at 0.2C, and from the third cycle to the 30th cycle is 0.5 After charging and discharging in C, the thickness change during charging and discharging was measured, and the cycle expansion performance (Swelling ratio) was converted to the rate of change of the thickness of the charged state, and the results are shown in Table 1.
[90]
[Table 1]
Swelling ratio@30 th cycle(charge) Electrode adhesion (gf/cm)
Example 1 22 26
Example 2 21 23
Example 3 21 23
Comparative Example 1 25 17
Comparative Example 2 25 17
Comparative Example 3 27 19
Comparative Example 4 26 19
Comparative Example 5 26 17
[91]
Hereinafter, Experimental Example 1 and Table 1 will be described together.
[92]
First, referring to Examples 1 to 3 and Comparative Examples 1, 2, and 5 in which the content ratio of the first anode active material and the second anode active material in the first active material layer and the second active material layer is similar throughout the anode, the present invention and the internal pore volume When this 0.6*10 -3 cm 3 /g or more and 2.5*10 -3 cm 3 /g or less of natural graphite is included in the first active material layer, natural graphite having an internal pore volume of 2.9*10 -3 cm 3 /g or more As compared to Comparative Examples 1, 2, and 5 included in the first active material layer, it can be confirmed that overall more improved cell expansion performance and excellent electrode adhesion are exhibited. This is because the internal pore volume of the natural graphite contained in the first active material layer of Examples 1 to 3 is 0.6*10 -3 cm 3 /g or more and 2.5*10 -3 cm 3 /g or less, so that the natural graphite has a large particle size. In spite of this, it can be seen that the cell expansion performance is improved due to the internal pores.
[93]
In addition, when comparing Comparative Examples 1 and 3, and Comparative Examples 2 and 4 having the same configuration but different content ratios of the first active material layer and the second active material layer, the natural graphite contained in the first active material layer When the content is greater than the content of artificial graphite included in the second active material layer, it can be seen that the electrode adhesion is increased. However, with respect to the cell expansion performance, when the content of natural graphite included in the first active material layer is greater than the content of artificial graphite included in the second active material layer, it can be seen that the cell expansion performance is deteriorated.
[94]
Through this, it can be confirmed that natural graphite included in the first active material layer has excellent adhesion, but has poor cycle durability and high thickness expansion rate due to a large internal pore volume compared to artificial graphite, which is disadvantageous in cell expansion performance. Accordingly, it can be confirmed that the natural graphite included in the first active material layer and the artificial graphite included in the second active material layer need to be included in an appropriate content ratio as in Examples 1 to 3.
[95]
Although the preferred embodiment of the present invention has been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims are also presented. It is within the scope of the invention.
[96]
Claims
[Claim 1]
negative electrode current collector; a first active material layer coated with a first negative electrode slurry including a first negative active material on the negative electrode current collector; and a second active material layer coated with a second anode slurry including a second anode active material on the first active material layer, wherein the first anode active material has an internal pore volume of 0.6*10 -3 cm 3 /g or more 2.5*10 -3 cm 3 /g or less containing natural graphite, the second negative active material is a negative electrode for a secondary battery containing artificial graphite.
[Claim 2]
The negative electrode of claim 1 , wherein the first negative active material includes natural graphite having an average particle diameter (D50) of 17 μm or more and 25 μm or less.
[Claim 3]
The negative electrode of claim 2 , wherein the first negative active material is made of the natural graphite.
[Claim 4]
The negative electrode for a secondary battery of claim 1, wherein the adhesive force between the first active material layer and the negative electrode current collector is greater than or equal to 21 gf/cm and less than or equal to 40 gf/cm.
[Claim 5]
The negative electrode of claim 1 , wherein the second negative active material includes artificial graphite having an average particle diameter (D50) of 10 μm or more and 30 μm or less.
[Claim 6]
The negative electrode of claim 5 , wherein the second negative active material is made of the artificial graphite.
[Claim 7]
The negative electrode for a secondary battery of claim 1 , wherein the content of the second negative active material included in the second active material layer is greater than that of the first negative active material included in the first active material layer.
[Claim 8]
The negative electrode of claim 1, wherein the first negative active material and the second negative active material are included in a ratio of 10 to 40 parts by weight: 60 to 90 parts by weight.
[Claim 9]
A secondary battery comprising the negative electrode for a secondary battery of claim 1 .
[Claim 10]
The secondary battery of claim 9 , wherein a thickness swelling ratio of the secondary battery in a charged state is 24% or less.