KR20160079508A - Lithium secondary battery - Google Patents

Abstract

The present invention relates to a lithium secondary battery comprising: a negative electrode; a positive electrode; a separator interposed between the negative electrode and the positive electrode; and an electrolyte. A porosity ratio between the positive electrode and the negative electrode is in a range of 0.75 to 1.45, and when defining a product of the volume (cc) of a porosity of the positive electrode and the negative electrode and the density (g/cc) of the electrolyte as A, the amount (g) of the electrolyte exceeding the A as B, and a value derived by multiplying B/A and 100 as an excess factor (%) of an electrolyte, the excess factor (%) of the electrolyte is in a range of 5.5 to 45%. According to the present invention, by optimizing a porosity ratio of a positive electrode and a negative electrode, which is in a specific range, and an excess factor of an electrolyte, it is possible to improve not only high temperature lifespan characteristic but also low temperature and room temperature output characteristic.

Description

[0001] Lithium secondary battery [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery in which a porosity ratio between an anode and a cathode and an amount of an electrolyte are optimized.

As technology development and demand for mobile devices increase, the demand for secondary batteries that can be recharged and can be miniaturized and increased in capacity is rapidly increasing. In addition, among secondary batteries, lithium secondary batteries having high energy density and voltage are commercialized and widely used.

Among these, nickel-hydrogen (Ni-MH) batteries, lithium (Li) ion batteries and lithium ion (Li-ion) polymer batteries have been developed and used.

In these secondary batteries, most of the bare cells contain an electrode assembly made of an anode, a cathode and a separator in a can made of aluminum or an aluminum alloy, a can is finished with a cap assembly, an electrolyte is injected into the can .

 In the lithium secondary battery, the electrode is often formed by applying a slurry containing an electrode active material to a surface of a current collector made of a metal foil or a metal mesh. The slurry is usually formed by mixing a solvent, a conductive material, an electrode active material, a binder, and the like.

 The electrode of the lithium secondary battery is manufactured by mixing such an active material and a binder component and dispersing the active material in a solvent to form a slurry and applying the slurry to the collector surface to form a mixture layer after drying. However, due to the volume change caused by the reaction with lithium during charging and discharging, the active material is removed from the current collector during continuous charging and discharging, or the resistance increases due to the change of the contact interface between the active materials, And the cycle life is shortened.

In addition, the output characteristics of the secondary battery may deteriorate due to differences in ion conductivity and rate characteristics between the positive electrode and the negative electrode, and there is a limit in overcoming such a problem.

Therefore, in order to manifest the performance characteristics of the best secondary battery, there is a demand for development of the secondary battery by improving the performance of the secondary battery by adjusting and optimizing the electrochemical design factors by various methods.

Therefore, a problem to be solved by the present invention is to provide a lithium secondary battery capable of simultaneously improving high-temperature lifetime characteristics and output characteristics.

According to an aspect of the present invention, anode; A separator interposed between the cathode and the anode; Wherein a porosity ratio between the positive electrode and the negative electrode is 0.75 to 1.45, and a volume (cc) of the voids of the positive electrode and the negative electrode and a density (g / cc) of the electrolyte (%) Of the electrolytic solution when the product A of the electrolytic solution is defined as A, the amount (g) of the electrolytic solution exceeding the A as B, and the product of B / A multiplied by 100 is defined as an excess factor of the electrolytic solution. ) Is in the range of 5.5% to 45%.

The excess ratio (%) of the electrolytic solution may be 10% to 30%.

The porosity of the anode may be between 26% and 42%.

The porosity of the cathode may be 25% to 30%.

The density of the electrolytic solution may be 1.10 to 1.25 g / cc.

The N / P ratio of the cathode and the anode per unit area may be in the range of 115 to 120.

The anode may include first active material particles and second active material particles having different particle diameters.

The average particle diameter (D ₅₀ ) of the first active material particles may be in the range of 10 탆 to 15 탆.

The average particle diameter (D ₅₀ ) of the second active material particles may be in the range of 1 탆 to 5 탆.

The weight ratio of the first active material particles to the second active material particles may be 55:45 to 95: 5.

Wherein the first active material particle and the second active material particle are made of LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ (where 0 <a <1 , 0 <b <1, 0 <c <1, a + b + c = 1), LiNi 1 - Y Co Y O 2, LiCo 1 - Y Mn Y O 2, LiNi 1 - Y Mn Y O 2 ( here in, 0 = Y <1), Li (Ni a Co b Mn c) O 4 (0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2), LiMn 2 _{- z Ni z O 4, LiMn} 2 -z Co z O 4 ( where, 0 <z <2), Li (Li a M b -a- b 'M' b ') O 2-c a c ( here M = Mn, and Ni, Co, Fe, Cr, V, Cu, Zn, and Ti, where 0 = a = 0.2, 0.6 = b = 1, 0 = b '= 0.2 and 0 = M is at least one element selected from the group consisting of Mg, Sr, Ba, Cd, Zn, Al, Ti, Fe, V and Li; A is at least one selected from the group consisting of P, F, S and N), and Li _x FePO ₄ (0.5 &lt; x &lt; 1.3), or a mixed active material of two or more thereof.

The loading amount of the anode may be 0.3 to 0.6 g / cm &lt; ² &gt;.

The loading amount of the negative electrode may be 5.5 to 7.0 g / cm &lt; ² &gt;.

According to the present invention, by optimizing the specific porosity ratio of the positive electrode and the negative electrode and the excessive ratio of the electrolyte, it is possible to further improve the low temperature and room temperature output characteristics as well as the high temperature lifetime characteristics.

FIG. 1 is a graph comparing the capacity retention rate and the resistance increase rate according to the number of cycles at room temperature in order to examine changes in capacity and resistance characteristics according to the porosity change of the anode.
2 is a graph comparing the capacity retention rate and the resistance increase rate with respect to the number of cycles at a high temperature of 45 캜 in order to examine changes in capacitance and resistance characteristics according to the porosity change of the anode.

Hereinafter, the terms and words used in the present specification and claims should not be construed to be limited to ordinary or dictionary terms, and the inventor should appropriately define the concept of the term in order to describe its own invention in the best way. It should be construed as meaning and concept consistent with the technical idea of the present invention.

A lithium secondary battery according to an embodiment of the present invention includes a cathode; anode; A separator interposed between the cathode and the anode; Wherein a porosity ratio between the positive electrode and the negative electrode is 0.75 to 1.45 and a product of a volume (cc) of a gap of the positive electrode and the negative electrode and a density (g / cc) of the electrolyte is A, (%) Of the electrolytic solution is 5.5% when the amount (g) of the electrolytic solution exceeding A is defined as B and the value obtained by multiplying B / A by 100 is defined as an excess factor of the electrolytic solution. To 45%.

According to an embodiment of the present invention, not only the high-temperature lifetime characteristics but also the low-temperature and normal-temperature output characteristics can be further improved by optimizing the specific porosity ratio of the anode and cathode and the excess ratio of the electrolyte.

In the lithium secondary battery according to an embodiment of the present invention, the porosity ratio between the positive electrode and the negative electrode may be 0.75 to 1.45, specifically 0.90 to 1.32.

In the lithium secondary battery according to an embodiment of the present invention, when the porosity ratio between the positive electrode and the negative electrode is within the above range, the difference in ion conductivity and rate characteristics between the positive electrode and the negative electrode can be reduced. The output characteristic can be further improved.

When the porosity ratio between the positive electrode and the negative electrode is less than 0.75, the rate-limiting characteristic of the anode is lowered, and an overvoltage is formed on the surface, thereby causing a side reaction (cathode deterioration). On the other hand, if the porosity ratio exceeds 1.45, it may be difficult to reduce the side reaction with the electrolyte due to the excessively wide porosity of the anode.

The porosity of each of the positive electrode and the negative electrode is not particularly limited within a range that satisfies the porosity ratio in the above range. Specifically, the loaded amount of the positive electrode may be 0.3 to 0.6 g / cm ² , May be 5.5 to 7.0 g / cm &lt; ² &gt;, and porosity may be determined by controlling the thickness of the anode and the cathode.

That is, the porosity between the positive electrode and the negative electrode can be controlled according to the degree of pressing during the production of the positive electrode and the negative electrode.

The lithium secondary battery according to an embodiment of the present invention is characterized by having a porosity ratio between the anode and the cathode and an excess factor of an electrolyte in a specific range.

In general, in the case of a lithium secondary battery of high energy density or high voltage, the amount of electrolyte is adjusted to provide complete wettability of the electrode and the separator, and an excessive amount of undesirable electrolyte may nevertheless reduce performance in terms of capacity or output . Therefore, it may be desirable to ensure the amount of electrolyte optimized by taking into consideration the individual components included in the secondary battery.

Wherein an excess ratio of the electrolytic solution is obtained by multiplying the volume (cc) of the voids of the anode and the cathode by the density (g / cc) of the electrolyte and the amount (g) Can be defined as a value multiplied by 100.

A, which is the product of the volume (cc) of the pores of the anode and the cathode and the density (g / cc) of the electrolyte, can mean the amount (g) of the electrolyte that can be completely impregnated to ensure wetting of the electrode and the separator. In addition, B may mean the amount (g) of the electrolytic solution exceeding the amount of the electrolyte which can be completely impregnated to ensure wetting of the electrode and the separator. Therefore, the excess ratio of the electrolytic solution is a value converted into a percentage with respect to the A, that is, Equation 1 below.

[Equation 1]

Excess ratio of electrolyte (%) = B / A X 100

The excess ratio of the electrolytic solution for improving the low temperature and normal temperature output characteristics of the lithium secondary battery may be in the range of 5.5% to 45%, specifically 10% to 30%.

If the excess ratio of the electrolyte is less than 5.5%, there may be a problem of deterioration of lifetime characteristics. If it exceeds 45%, there may occur a problem of migration of lithium ions due to penetration of excess electrolyte between the electrode and the electrode. It may be a factor that deteriorates the performance.

Specifically, in Equation (1), A is a product of the volume cc of the gap and the density (g / cc) of the electrolyte, and can be influenced by the porosity of the positive electrode and the negative electrode and the density of the electrolyte.

According to an embodiment of the present invention, the porosity of the anode may be 26% to 42%, and the porosity of the cathode may be 25% to 30%.

The porosity of the positive electrode and the negative electrode can be defined as follows:

Porosity = volume of pores per unit mass formed inside the electrode / (specific volume + pore volume per unit mass)

The porosity can be measured by BELSORP (BET equipment) manufactured by BEL JAPAN using an adsorbing gas such as nitrogen according to an embodiment of the present invention.

Also, the density of the electrolytic solution may be, for example, 1.10 to 1.25 g / cc, specifically 1.12 to 1.23 g / cc.

According to an embodiment of the present invention, the active material used for the anode may be used without limitation as long as it satisfies the porosity of the anode in the above range. However, it may contain different kinds of active materials including, for example, large particles and small particles in order to satisfy the optimum conditions desired in the present invention. That is, the first active material particle and the second active material particle may have different particle diameters.

The first active material particle may have a mean particle size (D ₅₀ ) in the range of 10 탆 to 15 탆, and the second active material particle has a mean particle size (D ₅₀ ) in the range of 1 탆 to 5 탆 Lt; / RTI &gt;

The average particle diameter (D ₅₀ ) of the particles can be defined as a particle diameter at a reference of 50% of the particle diameter distribution of the particles. The average particle diameter (D ₅₀ ) of the particles according to an embodiment of the present invention can be measured using, for example, a laser diffraction method. The laser diffraction method generally enables measurement of a particle diameter of several millimeters from a submicron region, resulting in high reproducibility and high degradability.

The weight ratio of the first active material particles to the second active material particles may be 55:45 to 95: 5, preferably 55:45 to 80:20.

The first active material particle and the second active material particle may be selected from a variety of materials, individually or in combination, so long as the porosity of the positive electrode within the range and the impregnation property of the electrolyte are easily satisfied. Specifically, the types of the first active material particles and the second active material particles may be independently selected from the group consisting of LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ And LiNi _{1 - Y} Mn _{Y 2} , LiNi _{1 - Y} Mn _Y , and LiNi _{1 - Y} Co _{Y 2} O ₃ , O ₂ (here, 0 = Y <1), Li (Ni a Co b Mn c) O 4 (0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2 _{), LiMn 2 - z Ni z} O 4, LiMn 2 -z Co z O 4 ( where, 0 <Z <2), Li (Li a M b -a-b 'M' b ') O 2-c A c Wherein M is at least one element selected from the group consisting of Mn, Ni, Co, Fe, Cr, V, Cu, Zn and Ti (where 0 = a = 0.2, 0.6 = b = M is at least one element selected from the group consisting of Mg, Sr, Ba, Cd, Zn, Al, Ti, Fe, V and Li, A is at least one element selected from the group consisting of P, F, S and N) and Li _x FePO ₄ (0.5 &lt; x &lt; 1.3), or a mixed active material of at least two selected from the group consisting of Li _x FePO ₄ .

Also, the negative electrode active material may include a carbon-based, Si-based negative active material, or a mixed active material thereof.

Specifically, when the negative electrode active material is carbon-based, it may include at least one selected from the group consisting of natural graphite, artificial graphite, mesocarbon microbeads (MCMB), carbon fibers, and carbon black. When the negative electrode active material is a Si-based material, for example, it may be any one selected from the group consisting of SiOx (where x is not more than 2), porous Si-based particles and Si nanostructures, or a mixture of two or more thereof have.

The capacity ratio of the negative electrode N and the positive electrode P per unit area (hereinafter referred to as N / P ratio) may be from 115 to 120.

The N / P ratio used in the present invention can be calculated as (ratio of the capacity per unit area of the negative electrode) / (capacity per unit area of the positive electrode) X 100 as the ratio of the capacity per unit area of the negative electrode to the capacity of the positive electrode (opposing N / P).

In this specification, the capacity per unit area of the electrode used for the N / P ratio may be a value obtained by dividing the discharge capacity (mAh) of the battery by the electrode area (cm ² ).

The lithium secondary battery according to an embodiment of the present invention can be manufactured so as to prevent the deterioration of lifetime characteristics and the stability of the cell to the highest level by controlling the capacity ratio of the cathode and the anode to 115 to 120 per unit area.

If the battery capacity per unit area of the anode is out of the above range, that is, when the N / P ratio is lower than 115, life deterioration occurs, and when N / P is reversed, the reversible capacity of the cathode is utilized 100% If excessive lithium is deposited on the cathode, the safety of the cell is seriously threatened. Also, when the N / P ratio exceeds 120, degradation of the cell characteristics may be caused by excessive lifetime deterioration.

For example, in the lithium secondary battery of the present invention, the capacity per unit area of the negative electrode may be 2.8 to 3.2 mAh / cm 2, specifically 2.9 to 3.1 mAh / cm 2. Depending on the capacity per unit area of the negative electrode, / P ratio can be adjusted.

The N / P ratio can be satisfied by adjusting the area ratio, thickness ratio, and specific surface area (BET) of each active material layer.

A method of manufacturing a lithium secondary battery according to an embodiment of the present invention may be manufactured as follows.

The negative electrode is prepared, for example, by coating a negative electrode current collector with a mixture of a negative electrode active material, a conductive material and a binder, and drying the negative electrode current collector. The negative electrode may be manufactured by a manufacturing method commonly used in the art. For example, a negative electrode may be manufactured by preparing a slurry by mixing and stirring a binder and a solvent, if necessary, a conductive material and a dispersant in an anode active material according to an embodiment of the present invention, applying the slurry to a current collector, . At this time, it is possible to control the porosity ratio between the anode and the cathode according to the present invention.

Examples of the binder include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, Polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, styrene butylene rubber (SBR) , Various copolymers, and the like can be used.

As the solvent, N-methylpyrrolidone, acetone, water and the like can be used.

The conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, and examples thereof include graphite such as natural graphite and artificial graphite; Carbon black such as carbon black, acetylene black, Ketjen black, channel black, panes black, lamp black, and thermal black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as fluorocarbon, aluminum and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The cathode active material, the conductive material, the binder and the solvent are mixed to prepare a slurry, and the slurry is directly coated on the metal current collector or cast on a separate support, and the cathode active material film, which is separated from the support, The positive electrode can be manufactured by lamination to the current collector. The conductive material, the binder and the solvent used for the anode may be used in the same manner as that used in the anode.

The separator is a conventional porous polymer film used as a conventional separator, for example, 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 The prepared porous polymer film can be used singly or in a laminated form. Further, an insulating thin film having high ion permeability and mechanical strength can be used. The separator may include a safety reinforced separator (SRS) on the surface of which a ceramic material is thinly coated. In addition, nonwoven fabrics made of conventional porous nonwoven fabrics such as high melting point glass fibers, polyethylene terephthalate fibers and the like can be used, but the present invention is not limited thereto.

In the electrolyte solution used in the embodiment of the present invention, the lithium salt that can be included as the electrolyte may be used without limitation as long as it is commonly used in an electrolyte for a secondary battery. Examples of the anion of the lithium salt include F ^{- _{Cl -, I -, NO 3}} -, N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF 4 -, (CF 3) 3 PF 3 -, (CF 3 ^{_{) 4 PF 2 -, (CF}} 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (CF 3 SO 2) 2 N -, (FSO 2) _{^{2 N -, CF 3 CF 2}} (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2) 3 C -, CF 3 (CF 2) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- can be used.

In the electrolyte solution used in the embodiment of the present invention, the organic solvent contained in the electrolytic solution may be any of those conventionally used, and examples thereof include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl Selected from the group consisting of carbonate, methyl propyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma-butyrolactone, propylene sulfite and tetrahydrofuran May be used.

In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates in the carbonate-based organic solvent, can be preferably used because they have high permittivity as a high viscosity organic solvent and dissociate the lithium salt in the electrolyte well. To such a cyclic carbonate, dimethyl carbonate and diethyl When a low viscosity, low dielectric constant linear carbonate such as carbonate is mixed in an appropriate ratio, an electrolyte having a high electric conductivity can be prepared, and thus it can be more preferably used.

Alternatively, the electrolytic solution stored in accordance with the present invention may further include an additive such as an overcharge inhibitor or the like contained in an ordinary electrolytic solution.

A lithium secondary battery according to an embodiment of the present invention includes a separator disposed between a cathode and an anode to form an electrode assembly, and the electrode assembly is inserted into, for example, a pouch, a cylindrical battery case or a rectangular battery case, The secondary battery can be completed. Alternatively, the electrode assembly may be laminated, impregnated with the electrolytic solution, and the resultant may be sealed in a battery case to complete the lithium secondary battery.

According to an embodiment of the present invention, the lithium secondary battery may be a stacked type, a wound type, a stacked and folded type, or a cable type.

The lithium secondary battery according to the present invention can be used not only in a battery cell used as a power source of a small device but also as a unit cell in a middle- or large-sized battery module including a plurality of battery cells. Preferred examples of the middle- or large-sized device include an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, a power storage system, and the like, and particularly to a hybrid electric vehicle and a battery for storing a renewable energy Lt; / RTI &gt;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to the following examples. However, the embodiments according to the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the following embodiments. Embodiments of the invention are provided to more fully describe the present invention to those skilled in the art.

Example  One

A lithium secondary battery in which the porosity ratio of the anode / cathode was 1.3 and the excess factor (%) of the electrolyte was 24% was prepared.

&Lt; Preparation of negative electrode &

(PVdF) as a binder and carbon black as a conductive material in an amount of 96 wt%, 3 wt% and 10 wt%, respectively, in the ratio of 97: 3 by weight of natural graphite and Li ₄ Ti ₅ O ₁₂ as an anode active material, To 1 wt% of H ₂ O as a solvent to prepare a negative electrode active material slurry. The negative electrode active material slurry was applied to a copper (Cu) thin film as an anode current collector having a thickness of 10 mu m and dried to produce a negative electrode, followed by roll pressing to produce a negative electrode.

At this time, the porosity of the negative electrode is 27.0%.

&Lt; Preparation of positive electrode &

96% by weight of a mixed cathode active material mixed with Li (Ni _0.6 Mn _0.2 Co _0.2 ) O ₂ having an average particle diameter of 12 탆 and an average particle diameter of the second active material of 4 탆 in a ratio of 7: 3, and 2 wt% of polyvinylidene fluoride (PVdF) as a binder were mixed to prepare a positive electrode active material slurry. The prepared slurry was coated on one side of the aluminum current collector, dried and rolled, and punched to a predetermined size to prepare a positive electrode.

At this time, the porosity of the anode is 35.1%.

&Lt; Production of lithium secondary battery >

Aqueous electrolyte was prepared by adding an organic solvent having a composition of ethylene carbonate (EC): propylene carbonate (PC): diethyl carbonate (DEC) = 3: 2: 5 (volume ratio) and 1.0M of LiPF ₆ . At this time, the excess ratio (%) of the electrolytic solution was 24%.

The excess ratio of the electrolytic solution was calculated according to the following equation (1).

[Equation 1]

Excess ratio of electrolyte (%) = B / A X 100

In this formula,

A: Volume (cc) of the pores of the anode and the cathode X Density (g / cc) of the electrolyte solution

B: Amount of electrolyte exceeding A

After the polyolefin separator was interposed between the positive electrode and the negative electrode, the electrolyte solution was injected to prepare a lithium secondary battery.

Comparative Example  One

A lithium secondary battery was produced in the same manner as in Example 1 except that the excess factor (%) of the electrolytic solution was 55%.

Comparative Example  2 to 4

Except that the degree of rolling of the positive electrode and the negative electrode was controlled and the excess amount of the electrolyte was adjusted to vary the porosity of the positive electrode and the negative electrode and the excess factor (%) of the electrolyte described in Table 1 below, A lithium secondary battery was produced.

Experimental Example  1: Resistance at room temperature

The lithium secondary batteries manufactured in Example 1 and Comparative Examples 1 to 4 were discharged in a SOC50 at a constant current of 5 C for 10 seconds to calculate a voltage difference.

Experimental Example  2: Low temperature output characteristic

The low temperature output (CP) was calculated by the voltage difference generated by discharging the lithium secondary battery manufactured in Example 1 and Comparative Examples 1 to 4 at 0.5 C for 10 seconds in an environment of -30 캜 at SOC (charge depth). The process of discharging at SOC12 for 2 seconds and then waiting for 21 seconds in SOC12 under the environment of -30 deg. C was repeated 5 times and then extrapolated to the final discharge voltage (lower limit 2 V) to perform cold cranking, CC) output was calculated. The results are shown in Table 1 below.

Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Anode / cathode porosity ratio 1.3 1.3 0.7 1.5 1.5 Porosity of anode (%) 35.1 35.1 26.2 40.3 40.3 Excess ratio of electrolyte (%) 24 55 55 55 5 Resistance (mohm) 1.35 1.37 1.36 1.72 1.69 Low temperature output (W) CP 369 359 354 300 300 CC 109 104 101 81 84

As shown in Table 1, when the porosity ratio between the positive electrode and the negative electrode is between 0.75 and 1.45, which is the range of the present invention, and the excess ratio of the electrolyte is between 5.5% and 45% as in Example 1 of the present invention, As compared with Comparative Examples 1 to 4 which do not satisfy the above conditions.

In the case of the low temperature output characteristic at -30 占 폚, it can be seen that the static power (CP) in Example 1 was 369 W, which was remarkably improved by about 18% or more as compared with Comparative Examples.

Also, it can be seen that Example 1 has a cold cranking (CC) output of 109 W which is remarkably improved to about 20% or more as compared with Comparative Examples.

On the other hand, as in Example 1 and Comparative Example 1, even when the porosity of the positive electrode was 35.1%, it was confirmed that the resistance and the low-temperature output characteristics at room temperature were varied by changing the excess ratio of the electrolytic solution.

Experimental Example  3: anode In porosity  Measure resistance at room temperature

Meanwhile, in order to investigate the capacity characteristics and the resistance characteristics at room temperature and high temperature characteristics according to the porosity of the anode, the anode was manufactured in the same manner as in Example 1, and the porosity of the anode was 26% and 24% A positive electrode was fabricated to fabricate a mono cell. The resistance at room temperature was measured, and the resistance measurement conditions were performed in the same manner as in Experimental Example 1. The results are shown in Table 2 below.

Monocell Comparative Example 5 Comparative Example 6 Porosity of anode (%) 26 24 Room temperature resistance (mohm) 1.47 1.45

As can be seen from Table 2, there was a difference in the resistance value according to the porosity of the anode, and the resistance value at room temperature of Comparative Example 6 in which the porosity of the anode was low is lower.

Experimental Example  4: anode In porosity  Capacitance and Resistance Characteristics at Room Temperature and High Temperature

The monocells of Comparative Examples 5 and 6 were subjected to constant current (1 C) at 25 ° C. and 45 ° C. under constant current (CC) conditions in order to examine the capacity characteristics and resistance characteristics of the monocells of Comparative Examples 5 and 6 according to charging / (CC) condition After charging to 4.15V, charging was continued until the current reached 0.05C under the constant voltage condition (CV). After discharging to 2.5V under 1C constant current (CC) condition, The dose was measured . This was repeated with 1 to 200 cycles. The results are shown in Figs. 1 and 2.

As can be seen from FIGS. 1 and 2, the capacity retention ratio is superior to that of Comparative Example 5 in which the porosity is 24% at 25 ° C and 26% in Comparative Example 6 where the porosity is 24%.

However, as shown in FIG. 2, in Comparative Example 6 in which the porosity is as low as 24% at a high temperature of 45 ° C, the resistance increase rate rapidly increases by about 10% or more after 100 cycles, and the capacity retention ratio is remarkably decreased by about 7% Able to know.

Therefore, when the porosity of the anode is too low, it can be seen that the high-temperature lifetime characteristics and the resistance characteristics are rather lowered.

Claims (13)

cathode; anode; A separator interposed between the cathode and the anode; And a lithium secondary battery comprising an electrolyte,
A porosity ratio of the positive electrode and the negative electrode is 0.75 to 1.45,
A is a product of the volume (cc) of the voids of the positive electrode and the negative electrode and the density (g / cc) of the electrolyte and B is the amount of the electrolyte solution exceeding the A, and B / A is multiplied by 100 Wherein an excess ratio (%) of the electrolyte is defined as 5.5% to 45% when defined as an excess factor (%) of the electrolyte. The method according to claim 1,
Wherein an excess ratio (%) of the electrolytic solution is 10% to 30%. The method according to claim 1,
And the porosity of the positive electrode is 26% to 42%. The method according to claim 1,
And the porosity of the negative electrode is 25% to 30%. The method according to claim 1,
And the density of the electrolyte is 1.10 to 1.25 g / cc. The method according to claim 1,
Wherein a ratio of N / P ratio of the negative electrode to the positive electrode per unit area is from 115 to 120. The method according to claim 1,
Wherein the positive electrode comprises first active material particles and second active material particles having different particle diameters. 8. The method of claim 7,
Wherein the average particle diameter (D ₅₀ ) of the first active material particles is in the range of 10 탆 to 15 탆. 8. The method of claim 7,
And the average particle size (D ₅₀ ) of the second active material particles is in the range of 1 탆 to 5 탆. 8. The method of claim 7,
Wherein the weight ratio of the first active material particles to the second active material particles is 55:45 to 95: 5. 8. The method of claim 7,
Wherein the first active material particle and the second active material particle are made of LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ (where 0 <a <1 , 0 <b <1, 0 <c <1, a + b + c = 1), LiNi 1 - Y Co Y O 2, LiCo 1 - Y Mn Y O 2, LiNi 1 - Y Mn Y O 2 ( here in, 0 = Y <1), Li (Ni a Co b Mn c) O 4 (0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2), LiMn 2 _{- z Ni z O 4, LiMn} 2 -z Co z O 4 ( where, 0 <z <2), Li (Li a M b -a- b 'M' b ') O 2-c A c ( here M = Mn, and Ni, Co, Fe, Cr, V, Cu, Zn, and Ti, where 0 = a = 0.2, 0.6 = b = 1, 0 = b '= 0.2 and 0 = M is at least one element selected from the group consisting of Mg, Sr, Ba, Cd, Zn, Al, Ti, Fe, V and Li; A is at least one selected from the group consisting of P, F, S and N) and Li _x FePO ₄ (0.5 &lt; x &lt; 1.3), or a mixed active material of at least two selected from the group consisting of Li _x FePO ₄ Lithium secondary battery. The method according to claim 1,
And the loading amount of the positive electrode is 0.3 to 0.6 g / cm &lt; ² &gt;. The method according to claim 1,
And the loading amount of the negative electrode is 5.5 to 7.0 g / cm &lt; ² &gt;.

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