KR102171853B1 - A lithium ion secondary battery with enhanced high speed charging performance - Google Patents

Abstract

The present invention relates to a high-loading lithium ion secondary battery having improved fast charging characteristics. The secondary battery according to the present invention has excellent rapid charging characteristics due to low resistance in a high-loading battery, particularly an interface resistance of a negative electrode and a high depth of charge, by controlling the viscosity and ionic conductivity of an electrolyte in a predetermined range. In addition, there is an effect of minimizing lithium plating on the surface of the negative electrode even during high C-rate charging due to low resistance.

Description

A lithium ion secondary battery with enhanced high speed charging performance

The present invention relates to a lithium ion secondary battery. In more detail, it relates to a high-loading lithium ion secondary battery having improved fast charging characteristics.

As portable electronic devices such as mobile phones and notebook computers are developed, the demand for secondary batteries as an energy source is rapidly increasing. In recent years, the use of secondary batteries as a power source for hybrid electric vehicles (HEV) and electric vehicles (EV) has been realized. Accordingly, many studies are being conducted on secondary batteries that can meet various needs, and in particular, demand for lithium secondary batteries having high energy density, high discharge voltage, and output is increasing.

Lithium secondary batteries used in electric vehicles should have high energy density and high output in a short time, and can be used for more than 10 years under severe conditions in which charging and discharging by high current is repeated in a short time. It is inevitably required to have superior output characteristics and long life characteristics compared to lithium secondary batteries.

In particular, fast charging tends to depend in particular on the properties of the negative electrode. Therefore, it is necessary to prevent the negative electrode from overcharging, reduce the resistance of the negative electrode, and increase the depth of charge to prevent precipitation of lithium metal occurring on the surface of the negative electrode. As described above, development of an electrolyte solution is required to prevent negative electrode characteristics from deteriorating in a rapid charging environment and to promote diffusion of lithium ions in an active material.

In particular, in the case of a lithium secondary battery, as the name implies, it is a battery using Li, which has a high energy density and is light, but has a disadvantage in that it is dangerous because dendrites can be easily formed. Specifically, electricity is stored through a process in which Li ions from the positive electrode enter the negative electrode during charging. In this process, Li ions from the positive electrode at the beginning of charging enter the negative electrode through the electrolyte, and polarization occurs at the interface between the substances, leading to overvoltage. At this time, if ions that can move relative to the amount of current flowing are insufficient, lithium ions are precipitated due to overvoltage. The lithium precipitation occurs not only by the movement of lithium ions but also by electrical resistance, and in the case of the movement of ions, it is closely related to the porosity of the electrode. The higher the permeability, the greater the mobility of Li ions, but since the electrical contact surface is lowered, it is necessary to properly control it, but it is very difficult. In particular, high permeability naturally has a problem that leads to a low energy density. Accordingly, the first attempted commercialization of the secondary battery using Li-metal as a negative electrode failed due to safety issues.

In addition, more by-products are accumulated by side reactions around the once precipitated lithium metal, deteriorating cycle performance, and in severe cases, passing through the separator and causing a fine short, may lead to explosion, etc.

Accordingly, many researchers have devised a method for suppressing such lithium plating, but in the present situation, which increasingly demands higher energy density, satisfactory results have not yet been achieved.

Accordingly, the problem to be solved by the present invention is to reduce the interface resistance of the negative electrode with respect to lithium ions and increase the charging depth in a lithium ion secondary battery, particularly a high-loading secondary battery, thereby improving the rapid charging characteristics of the battery. In addition, the present invention is to provide a lithium ion secondary battery capable of smoothly conducting ion conduction against a large current during rapid charging of the battery and thus minimizing lithium plating on the surface of a negative electrode. Other objects and advantages of the present invention will be understood by the following description. On the other hand, it will be easily understood that the objects and advantages of the present invention can be realized by means or methods described in the claims, and combinations thereof.

The present invention relates to a lithium ion secondary battery for solving the above technical problem.

A first aspect of the present invention relates to a lithium ion battery, comprising: an electrode assembly including at least one negative electrode, a positive electrode, and a separator, respectively; And an electrolyte solution, wherein the negative electrode and the positive electrode are electrically insulated by a separator, and the negative electrode includes a negative electrode active material, a negative electrode binder resin, and a negative electrode conductive material, wherein the negative electrode conductive material includes carbon black, and , The carbon black includes an aggregate in which primary particles having a particle diameter (D ₅₀ ) of 10 to 100 nm are aggregated, and the aggregate has a particle diameter (D ₅₀ ) of 100 to 1000 nm.

In addition, the second aspect of the present invention is that the particle diameter (D ₅₀ ) of the aggregate in the first aspect is 300 to 600 nm.

In the third aspect of the present invention, in the first or second aspect, the aggregate is 80% by weight or more relative to 100% by weight of the conductive material.

A fourth aspect of the present invention is that, in any one of the first to third aspects, the conductive material further includes a linear conductive material such as carbon fiber and/or carbon nanotube.

The fifth aspect of the present invention is according to any one of the first to fourth aspects, wherein the negative electrode is a negative electrode active material such as crystalline graphite, amorphous carbon material, natural graphite, artificial graphite, expanded graphite, carbon fiber, graphitizable carbon, and It is one or more selected from the group consisting of graphitizable carbon, carbon black, carbon nanotube, fullerene, and activated carbon.

In a sixth aspect of the present invention, in any one of the first to fifth aspects, in the negative electrode, the negative electrode conductive material is contained in an amount of 0.1 parts by weight to 10 parts by weight based on 100 parts by weight of the negative electrode mixture.

In a seventh aspect of the present invention, in any one of the first to sixth aspects, the negative electrode has a pore having a long diameter of 0.5 μm to 3 μm, which is 20% or more of 100% of the total volume of pores in the negative electrode.

In an eighth aspect of the present invention, in any one of the first to seventh aspects, the carbon black is at least one selected from the group consisting of acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black. will be.

In a ninth aspect of the present invention, in any one of the first to eighth aspects, the time required for the battery to reach 70% SOC when charged in a constant current/constant voltage method of 1.5C is within 30 minutes.

A tenth aspect of the present invention is that in any one of the first to ninth aspects, the operating voltage is 2.2V to 4.5V.

In an eleventh aspect of the present invention, in any one of the first to tenth aspects, the positive electrode has a loading amount of an electrode active material of 3.0 mAh/cm ² based on a unit electrode area. To It is 4.8mAh/cm ² , and the N/P ratio of the positive electrode and the negative electrode is 105 to 120.

In a twelfth aspect of the present invention, in any one of the first to eleventh aspects, the electrolyte has a viscosity of 3.0cp to 4.5cp at 25.

A thirteenth aspect of the present invention is that in any one of the first to twelfth aspects, the electrolyte has a viscosity of 25 and an ionic conductivity of 8.0 to 9.0 mS/cm.

In any one of the first to thirteenth aspects of the present invention, a lithium salt is contained in a concentration of 1.0M to 2M in the electrolyte.

A fifteenth aspect of the present invention, according to any one of the first to fourteenth aspects, wherein the organic solvent is propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl Methyl carbonate (EMC), methyl propylene carbonate, dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma butyrolactone, propylene sulfite and tetrahydro It includes at least one selected from the group consisting of furan, fluoroethylene carbonate, lactone, ether, ester, acetonitrile, lactam, ketone, propane sultone, and ethylene sulfate.

A sixteenth aspect of the present invention, according to any one of the first to fifteenth aspects, wherein the separator is a porous substrate; And an organic/inorganic composite porous layer formed on at least one surface of the porous substrate, wherein the porous substrate includes a polymer nonwoven fabric and/or a porous polymer film, and the organic/inorganic composite porous layer comprises inorganic particles and It includes a mixture of a binder polymer, wherein the inorganic particles are connected and fixed to each other by the binder polymer, and pores derived from an interstitial volume between the inorganic particles are included.

In a seventeenth aspect of the present invention, in the sixteenth aspect, the binder polymer contains a particulate polymer.

In addition, the eighteenth aspect of the present invention is a battery module including the secondary battery according to any one of the first to seventeenth aspects of the present invention, and the 19th aspect is a device including the battery module, wherein the device is It is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a power storage system.

The secondary battery according to the present invention has excellent rapid charging characteristics due to low resistance in a high-loading battery, particularly an interface resistance of a negative electrode and a high depth of charge, by controlling the viscosity and ionic conductivity of an electrolyte in a predetermined range. In addition, there is an effect of minimizing lithium plating on the surface of the negative electrode even during high C-rate charging due to low resistance.

The accompanying drawings illustrate preferred embodiments of the present invention, and explain the principles of the present invention together with the detailed description, and the scope of the invention is not limited thereto. Meanwhile, the shape, size, scale, or ratio of elements in the drawings included in the present specification may be exaggerated to emphasize a clearer description.
1 shows a comparison of the depth of charge according to the C-rate change in the battery according to the embodiment and the comparative example of the present invention.
2 is a comparison of Nyquist plots through EIS experiments in cells according to Examples and Comparative Examples of the present invention.
3 shows a comparison of negative electrode profiles of batteries according to Examples and Comparative Examples.

The terms or words used in this specification and claims should not be construed as being limited to their usual or dictionary meanings, and the inventor shall appropriately define the concept of terms in order to describe his own invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of the present invention based on the principle that it can be. Accordingly, the embodiments described in the present specification and the configurations shown in the drawings are only the most preferred embodiment of the present invention, and do not represent all the technical spirit of the present invention, and thus various alternatives that can be substituted for them at the time of application It should be understood that there may be equivalents and variations.

The present invention relates to a lithium ion secondary battery. The lithium ion secondary battery is characterized in that it contains an electrolyte solution that falls within a specific viscosity and ionic conductivity range, and has improved resistance characteristics of a negative electrode and a high depth of charge.

The lithium ion secondary battery according to the present invention includes an electrode assembly including a negative electrode, a positive electrode, and a separator; and an electrolyte.

Each of the electrode assemblies may include at least one cathode, an anode, and a separator, and the cathode and the anode are electrically insulated by the separator.

Meanwhile, the negative electrode includes carbon black as a conductive material, and the carbon black includes an aggregate in which primary particles having a particle diameter (D ₅₀ ) of 10 to 100 nm are aggregated, and the aggregate has a particle diameter (D ₅₀ ) of 100 to 1000 nm It is characterized by being.

Hereinafter, the present invention will be described in detail.

1. Electrode assembly

The electrode assembly according to the present invention includes a cathode, an anode, and a separator interposed between the cathode and the anode.

1.2 cathode

The negative electrode includes a current collector and a negative electrode mixture coated on at least one side of the current collector, and the negative electrode mixture includes a negative electrode active material, a negative electrode conductive material, and a negative electrode binder resin.

In a specific embodiment of the present invention, the negative active material includes a carbon material. Both low crystalline carbon and high crystalline carbon may be used as the carbon material. Typical low crystalline carbons include soft carbon and hard carbon, and high crystalline carbons include natural graphite, artificial graphite, kish graphite, pyrolytic carbon, and liquid crystal pitch. High-temperature calcined carbon such as mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches, and petroleum or coal tar pitch derived cokes are typical.

In a specific embodiment of the present invention, the negative electrode conductive material includes carbon black. The carbon black includes an aggregate in which primary particles having a particle diameter (D ₅₀ ) of 10 to 100 nm are aggregated, and the aggregate has a particle diameter (D ₅₀ ) of 100 to 1000 nm.

When the particle diameter (D ₅₀ ) of the aggregate is in the range of 100 to 1000 nm, the dispersion degree of the conductive material in the negative electrode is improved to promote the movement of lithium ions, and thus the overvoltage of the negative electrode is eliminated, thereby preventing lithium plating.

The negative electrode conductive material is added to the electrode mixture to improve the conductivity of the negative electrode. However, since the conductive material is a material having hydrophobic properties, it has low wettability and has a large cohesiveness that is well agglomerated between conductive material particles, and thus it is difficult to uniformly disperse and mix with the active material or the binder polymer. In addition, since it cannot penetrate into the inside of the binder polymer, which is an insulator, there is a limit to improving the electrical conductivity. In accordance with the demand for high-capacity/low-resistance electrochemical devices that have recently increased in the electrochemical device market, the need for atomization of conductive materials is increasing. Due to the need for atomization of the conductive material, as the size of the conductive material becomes smaller in nanometer units, the aggregation property of the conductive material further increases, making it difficult to achieve uniform dispersion with the electrode active material and the binder polymer.

Therefore, in order for the conductive material to exhibit a uniform dispersed phase in the electrode mixture, the electrode slurry can be prepared in the following manner:

1) First high shear mixing of an electrode binder and a solvent to prepare a slurry

2) adding a conductive material to the slurry and performing secondary high shear mixing; And

3) adding and dispersing an electrode active material to the obtained slurry to obtain an electrode mixture slurry.

The first high shear mixing and the second high shear mixing are each independently beads mil, clear mixer, microfludizer, fill mixer, or planetary dispersive. This can be done by means of a planetary dispersive mixer.

The first high shear mixing and the second high shear mixing may each independently be performed in the range of 20,000 to 40,000 rpm, and the slurry after the second high shear mixing process has an absolute zeta potential in the range of 20 mV to 100 mV. I can.

According to an aspect of the present invention, a low resistance of the negative electrode is possible as the conductive material is uniformly dispersed between the active materials. In addition, when a high-capacity active material is used as the negative active material, an electrochemical device having low resistance and high capacity characteristics can be obtained.

Further, in a specific embodiment of the present invention, the negative electrode may have a pore having a long diameter of 0.5 μm to 3 μm, 20% or more or 27% or more of 100% of the total volume of pores in the negative electrode. The distribution of the negative electrode pores in the above-described range can increase the negative electrode permeability of lithium ions, thereby contributing to maximizing the aforementioned effect.

1.2 anode

The positive electrode is a metal current collector; And a positive active material layer formed on at least one surface of the current collector. The positive electrode active material layer may include a positive electrode active material, a conductive material, and an electrode binder resin.

In a specific embodiment of the present invention, the positive electrode may include a lithium-containing transition metal oxide. The lithium-containing transition metal oxide is, for example, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li(Ni _a Co _b Mn _C )O ₂(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 (O=y=1), Li(Ni _a Mn _b Co _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 ₄Any one selected from the group consisting of (O<z<2), LiCoPO ₄ and LiFePO ₄ , or a mixture of two or more of them may be used. In addition, in addition to these oxides, sulfide, selenide, and halide may also be used.

Meanwhile, according to a specific embodiment of the present invention, the positive electrode has a loading amount of 3.0mAh/cm ² based on a unit electrode area. To It is 4.8mAh/cm ² , and at this time, the N/P ratio of the positive electrode and the negative electrode is 105 to 120.

Meanwhile, the conductive material included in the positive electrode may refer to the contents of the negative conductive material.

1.3 Separator

In the present invention, the separator is a porous membrane that is capable of providing a path for lithium ions to move while preventing a short circuit by electrically insulating the cathode and the anode, and can be used without particular limitation as long as it can be used as a separator material for an electrochemical device. It is possible.

The separator may include a porous film and/or a nonwoven fabric including a polymer resin as a base material for the separator, and the polymer resin is high density polyethylene, low density polyethylene, linear low density polyethylene, ultra high molecular weight polyethylene, polypropylene, polyethylene terephthalate, polybutyl Polymer compounds such as lenterephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, etc. are each alone or 2 It may be a mixture of more than one species.

In addition, in a specific embodiment of the present invention, a heat-resistant ceramic layer may be formed on at least one surface of the separator. In the present invention, the heat-resistant ceramic layer includes a mixture of inorganic particles and a polymer binder resin, and is connected and fixed to each other by the polymer binder. As the surface of the separator is coated with inorganic particles, heat resistance of the separator is improved, while the air permeability of the separator is prevented from deteriorating due to micropores released from the interstitial volume between the inorganic particles.

In the present invention, the inorganic particles included in the heat-resistant ceramic layer are not particularly limited as long as the oxidation and/or reduction reaction does not occur in the operating voltage range of the electrochemical device (eg, 0 to 5V based on Li/Li+). As the inorganic particles, for example, BaTiO ₃ , Pb(Zr,Ti)O ₃ (PZT), Pb _{1 - x} La _x Zr _{1 - y} Ti _y O ₃ (PLZT, where 0 <x <1, 0 < y <1), Pb(Mg _1/3 Nb _2/3 )O ₃ -PbTiO ₃ (PMN-PT), hafnia (HfO ₂ ), SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, ZnO, ZrO ₂ , Y ₂ O ₃ , Al ₂ O ₃ , SiC, TiO ₂ and the like may be used alone or in combination of two or more, but are not particularly limited thereto.

The binder polymer is a component capable of binding between inorganic particles and/or between inorganic particles and a separator, and any one can be used as long as it is electrochemically stable at the driving voltage of the electrochemical device.

Meanwhile, in a specific embodiment of the present invention, the binder polymer may include a particulate polymer in order to improve the air permeability of the separator.

2. Electrolyte

2.1 Viscosity and ionic conductivity

In a specific embodiment of the present invention, the electrolyte solution includes an organic solvent and a lithium salt, and the electrolyte solution has a viscosity of 2.5cp to 5.0cp, or 3.0cp to 4.5cp at 25°C. In addition, the electrolyte is characterized in that the ionic conductivity is 7.0 to 10.0 mS/cm or 8.0 to 9.0 mS/cm/cm.

The separator of the secondary battery must be sufficiently immersed in the electrolyte to be charged and discharged by movement of ions. Typically, the separator is a polyolefin-based porous film or a nonwoven fabric. In particular, the porous film has a very fine pore size at the nanometer level, and thus a low electrolyte viscosity is required to increase its impregnation property. However, when an organic solvent having a low viscosity is used, leakage is easy and the volatility is very strong, and there is a fear of evaporation. On the other hand, when the viscosity of the electrolyte solution is lowered by using a low-viscosity solvent, the dielectric constant of the electrolyte solution decreases, making it difficult to dissociate the lithium salt, which may cause a problem in that ionic conductivity decreases.

In particular, when the ionic conductivity of a secondary battery that requires rapid charging is deteriorated, ions are insufficient compared to the amount of current flowing, resulting in an overvoltage at the negative electrode, which may deteriorate lithium plating on the surface of the negative electrode.

In the present invention, by controlling the viscosity and ionic conductivity of the electrolyte within the above-described ranges, the impregnating properties of the electrolyte solution to the electrode and the separator are improved, and the ion conductivity is maintained at an appropriate level. In particular, lithium plating is minimized during rapid charging by reducing the overvoltage of the negative electrode and promoting the diffusion of lithium ions in the active material to improve the charging depth.

2.2 organic solvent

In the present invention, the electrolyte solution contains an organic solvent. As the organic solvent, those commonly used may be used without limitation as long as it can represent the viscosity and ionic conductivity range of the above-described electrolyte. Specifically, the organic solvent is propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propylene carbonate, dipropyl carbonate (DPC), dimethyl Sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma butyrolactone, propylene sulfite and tetrahydrofuran, fluoroethylene carbonate, lactone, ether, ester, acetonitrile, lactam, It may include at least one selected from the group consisting of ketone, propane sultone, and ethylene sulfate, but is not particularly limited thereto. In particular, among the organic solvents, ethylene carbonate, fluoroethylene carbonate, and propylene carbonate, which are cyclic carbonates, have high dielectric constants and thus dissociate lithium salts well in the electrolyte, and thus may be preferably used. In addition, it is possible to adjust the ionic conductivity by mixing a linear carbonate having a low viscosity and low dielectric constant such as dimethyl carbonate and diethyl carbonate in an appropriate ratio in the cyclic carbonate solvent. The organic solvent is contained in an amount of 10 to 90% by weight of the total electrolyte solution content.

On the other hand, the organic solvent may further include an ionic liquid to exhibit a desired degree of viscosity and ionic conductivity, and the ionic liquid is an imidazolium-based ionic liquid, ammonium-based ionic liquid, and pyrrolidium It is at least one selected from the group consisting of ionic liquids, pyridinium ionic liquids, and phosphonium ionic liquids.

2.3 Lithium salt

Specifically, in the electrolytic solution of the present invention, the ionizable lithium salt may be used, without limitation, those which are commonly used in a lithium secondary battery electrolyte, for example as the lithium salt anion F ^-, Cl ^-, Br ^{-, _{I -, NO 3 -, N}} (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CH 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 -, (FO 2) 2 N - _{, CF 3 CF 2 (CF 3} ) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 6) 3 C -, (CF 3 SO 2) 3 C -, CF 3 (CF 2) 7 SO 3 ^- , CH ₃ CO ₂ ^- , SCN ^- and (CF ₃ CF ₂ SO ₂ ) ₂ N ^- may include any one selected from the group consisting of.

In a specific embodiment of the present invention, the lithium salt is contained in a concentration of 1.0 to 2.0M, or 1.1M to 1.5M based on 100% by weight of the electrolyte. As the amount of lithium salt added increases, the viscosity tends to increase, and the ionic conductivity increases and then decreases. The electrolyte according to the present invention has an excellent ionic conductivity in the above-described range of lithium salt content, and accordingly, an effect of reducing resistance and improving rapid charging characteristics can be expected.

3. Lithium ion secondary battery

In the present invention, the lithium ion secondary battery has an improved fast charging characteristic. In the present specification, fast charging refers to a method of charging a battery having a driving voltage of 2.2V to 4.5V, or 2.5V to 4.25V with a high current of 1C-rate or higher or 1.5C-rate or higher. In one embodiment of the present invention, when the battery is charged in a constant current/constant voltage method of 1.5C at a driving voltage of 4.25V, the time it takes to reach 70% state of charge (SOC) is within 30 minutes. In addition, in the present invention, lithium plating is suppressed by about 7% when the battery is charged at a high speed according to the above conditions.

The point at which lithium plating occurs can be confirmed by analyzing the negative electrode profile during rapid charging. By separately extracting the negative electrode profile during charging through the three-electrode system and then differentiating the graph expressed as the potential value for SOC, a section in which the slope changes rapidly can be found, and the SOC value at this time is the point at which lithium plating begins. 3 is a comparison of the negative electrode profiles of the batteries according to Examples and Comparative Examples, and shows that the battery of the Example according to the present invention has an effect of suppressing lithium plating because the depth of charge is about 7% deeper than that of the battery of Comparative Example. Able to know.

In addition, the present invention provides a battery module including the secondary battery according to the present invention and a device including the battery module. In a specific embodiment of the present invention, the device may be an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a power storage system.

Meanwhile, in the description of the electrode assembly and the electrolyte in the present invention, a conventional method used in the technical field to which the present invention pertains may be applied to contents not described in the present specification.

Hereinafter, examples will be described in detail to illustrate the present invention in detail. However, the embodiments according to the present invention may be modified in various forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. Embodiments of the present invention are provided to more completely describe the present invention to those of ordinary skill in the art.

Example

Example

1. Manufacture of battery

Artificial graphite, carbon black, CMC, and SBR were mixed with N-methylpyrrolidone in a weight ratio of 95.8:1:1.2:2 to prepare a negative electrode slurry. The negative electrode slurry was coated on a copper foil (Cu-foil) with a thickness of 14 μm to form a thin electrode plate, dried at 135° C. for 3 hours or more, and then pressed to prepare a negative electrode. The carbon black had a primary particle diameter of 35 nm and an aggregate particle diameter of 100 to 300 nm. In addition, the negative electrode had a volume of 28% of pores having a long pore diameter of 0.5 μm to 3 μm.

LiNi _{0 . 5} Mn _{0 . 3} Co _{0 . 2} O ₂ , polyvinylidene fluoride and carbon black were mixed with N-methylpyrrolidone in a weight ratio of 96:2:2 to prepare a positive electrode slurry. The positive electrode slurry was coated on an aluminum thin film to a thickness of 60 μm to form a thin electrode plate, dried at 135° C. for 3 hours or more, and then rolled to prepare a positive electrode. At this time, the loading amount of the positive electrode was 3.3mAh/cm ² and the NP ratio was 108.

The electrolyte was mixed with ethylene carbonate and ethyl methyl carbonate in a vol% ratio of 3:7, and LiPF ₆ was added thereto at a concentration of 1.3M. In addition, vinylene carbonate, propane sultone, and ethylene sulfate were added in an amount of 0.2% by weight, respectively, based on the total amount of the electrolyte. The electrolytic solution had an ionic conductivity of 8.98 mS/cm and a viscosity of 4.25 cp. A battery having a capacity of 1100mAh was manufactured using the negative electrode, positive electrode and electrolyte prepared above. Celgard2320 was used as a separator.

Comparative example

As an electrolyte, ethylene carbonate and ethyl methyl carbonate were mixed in a vol% ratio of 3:7 and LiPF ₆ was added at a concentration of 0.8M, and the ion conductivity was 8.2mS/cm and the viscosity was 2.4cp. , A battery was manufactured in the same manner as in Example, except that the carbon black had a particle diameter of 1.2 μm to 1.5 μm.

2. Experiment result

1) charging speed comparison

4.25V was used as the charging end voltage and charged in the CC mode at the c-rate shown in Table 1 below.

Example C-rate One 1.5 2 2.2 3 2.5 4 3.0 5 3.2

1 shows a comparison of the depth of charge according to the C-rate change in the battery according to the embodiment and the comparative example of the present invention. According to this, it was confirmed that in each C-rate charging, the battery of Example reached the same SOC within a short time compared to the battery of Comparative Example.

2) Impedance measurement

After charging the batteries prepared in Examples and Comparative Examples to 4.25V, a small voltage (10mV) was applied from a frequency of 3kHz to 100mHz, and a current response was measured, and compared with a Nyquist plot. Referring to FIG. 2 as a graph showing a Nyquist plot. Referring to this, it was confirmed that the battery of Example had an impedance decrease compared to the battery of Comparative Example due to the improvement of ionic conductivity of the electrolyte.

3) Lithium plating inhibitory effect

3 is an analysis of negative electrode profiles for cells of Examples and Comparative Examples. The negative electrode profile was confirmed by separately extracting the negative electrode profile (1.5C charge) at the time of charging through a three-electrode system, and then dividing the graph expressed as a potential value for SOC. In FIG. 3, A is an example battery, and B is a point at which the slope is changed in the comparative example battery, and the battery according to the example has a depth of charge of 7% higher than that of the battery according to the comparative example, thereby suppressing lithium plating. You can see that there is.

As a result, the battery according to the present invention is effective in suppressing lithium plating and exhibits an effect of improving fast charging characteristics.

Claims (19)

An electrode assembly each including at least one cathode, an anode, and a separator; And an electrolyte solution;
The cathode and anode are electrically insulated by a separator,
The negative electrode includes a negative electrode active material, a negative electrode binder resin, and a negative electrode conductive material, wherein the negative electrode conductive material includes carbon black, and the carbon black is an aggregate in which primary particles having a particle diameter (D ₅₀ ) of 10 to 100 nm are aggregated Including, the aggregate has a particle diameter (D ₅₀ ) of 100 to 1,000 nm,
The aggregate is 80% by weight or more based on 100% by weight of the conductive material, and the negative electrode has a pore having a long diameter of 0.5 μm to 3 μm, 20% or more compared to 100% of the total volume of pores in the negative electrode
The positive electrode has a loading amount of an electrode active material of 3.0mAh/cm ² based on a unit electrode area 4.8mAh/cm ² , and the N/P ratio between the positive and negative electrodes is 105 to 120,
The electrolyte contains an organic solvent and a lithium salt, has a viscosity of 4.25 cp to 4.5 cp at 25° C. and an ionic conductivity of 7.0 mS/cm to 10.0 mS/cm,
The organic solvent is propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propylene carbonate, dipropyl carbonate (DPC), dimethyl sulfoxide , Acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma butyrolactone, propylene sulfite and tetrahydrofuran, fluoroethylene carbonate, lactone, ether, ester, acetonitrile, lactam, ketone, A lithium ion secondary battery comprising at least one selected from the group consisting of propane sultone and ethylene sulfate.
The method of claim 1,
The aggregate is a lithium ion secondary battery having a particle diameter (D ₅₀ ) of 300 nm to 600 nm.
delete The method of claim 1,
The conductive material further comprises a linear conductive material such as carbon fiber and/or carbon nanotubes, a lithium ion secondary battery.
The method of claim 1,
The negative electrode is an anode active material, 1 selected from the group consisting of crystalline graphite, amorphous carbon material, natural graphite, artificial graphite, expanded graphite, carbon fiber, graphitizable carbon, non-graphitizable carbon, carbon black, carbon nanotubes, fullerene, activated carbon A lithium ion secondary battery of more than one species.
The method of claim 1,
The negative electrode is a lithium ion secondary battery in which the negative electrode conductive material is contained in an amount of 0.1 parts by weight to 10 parts by weight based on 100 parts by weight of the negative electrode mixture.
delete The method of claim 1,
The carbon black is at least one selected from the group consisting of acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black.
The method of claim 1,
When the battery is charged in a constant current/constant voltage method of 1.5C, it takes less than 30 minutes to reach SOC 70%.
The method of claim 1,
The battery is a lithium ion secondary battery that has an operating voltage of 2.2V to 4.5V.
delete delete delete The method of claim 1,
The lithium ion secondary battery in which the lithium salt is contained in a concentration of 1.0M to 2M in the electrolyte.
delete The method of claim 1,
The separator is a porous substrate; And an organic/inorganic composite porous layer formed on at least one surface of the porous substrate,
Here, the porous substrate includes a polymer nonwoven fabric and/or a porous polymer film,
The organic/inorganic composite porous layer includes a mixture of inorganic particles and a binder polymer, and the inorganic particles are connected and fixed to each other by the binder polymer, and originated from an interstitial volume between the inorganic particles. The lithium-ion secondary battery comprising pores.
The method of claim 16,
The binder polymer is a lithium ion secondary battery comprising a particulate polymer polymer.
Secondary according to any one of paragraphs 1, 2, 4, 5, 6, 8, 9, 10, 14, 16 and 17 A battery module including a battery.
A device comprising the battery module according to claim 18, wherein the device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a power storage system.

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