KR20170063270A - A lithium ion secondary battery with enhanced high speed charging performance - Google Patents

Abstract

The present invention relates to a rechargeable lithium ion secondary battery having improved fast charge characteristics. The secondary battery according to the present invention has excellent resistance to rapid charging because the resistance of the reloading cell, particularly the interface resistance of the negative electrode, and the depth of charge are high, by controlling the viscosity and ionic conductivity of the electrolyte solution to a predetermined range. In addition, since the resistance is low, lithium plating on the surface of the negative electrode is minimized even when high C-rate is charged.

Description

[0001] The present invention relates to a lithium ion secondary battery having a fast charging characteristic,

The present invention relates to a lithium ion secondary battery. More particularly, the present invention relates to a rechargeable lithium ion secondary battery having improved fast charge characteristics.

BACKGROUND ART Portable electronic devices such as portable telephones and notebook computers have been developed, and the demand for secondary batteries as their energy sources is rapidly increasing. In recent years, the use of a secondary battery as a power source for a hybrid electric vehicle (HEV) and an electric vehicle (EV) has been realized. Accordingly, a lot of research has been conducted on a secondary battery that can meet various demands, and in particular, there is a trend of increasing demand for a lithium secondary battery having a high energy density, a high discharge voltage, and an output.

A lithium secondary battery used in an electric vehicle and the like must have high energy density and characteristics capable of exhibiting high output in a short time, and must be used for more than 10 years under severe conditions in which charging and discharging by a large current are repeated in a short time, It is inevitably required an output characteristic and a long-term service life characteristic that are far superior to those of a lithium secondary battery.

Particularly rapid charging tends to depend on the characteristics of the cathode in particular. Therefore, it is necessary to prevent overcharge of the negative electrode, decrease the resistance of the negative electrode and raise the depth of charge to prevent precipitation of lithium metal on the surface of the negative electrode. Thus, development of an electrolyte solution is required to prevent deterioration of the negative electrode characteristics in the rapid charging environment and accelerate diffusion of lithium ions in the active material.

In particular, in the case of a lithium secondary battery, as the name suggests, a battery using Li is disadvantageous in that it has a high energy density and is light, but can easily form a dendrite. Specifically, electricity is stored through the process of Li ions from the anode entering the cathode during charging. In this process, Li ions from the initial charging electrode enter the cathode through the electrolyte, causing polarization at the interface between the materials, leading to overvoltage. At this time, if the amount of movable ions is insufficient relative to the amount of current flowing, lithium ions are precipitated by overvoltage. The lithium precipitation is caused not only by the movement of lithium ions but also by the electrical resistance. In the case of ion migration, the lithium precipitation is also closely related to the porosity of the electrode. The higher the permeability, the greater the mobility of Li ions, but the lower the electrical contact surface, so it is necessary to control it appropriately, but it is very difficult. Especially, high permeability naturally leads to low energy density. Therefore, Li-metal secondary battery failed as a cathode for commercialization.

In addition, more byproducts are accumulated due to the side reaction around the once-deposited lithium metal, and the cycle performance may deteriorate due to the shortage of the electrolyte.

Many researchers have devised a method to suppress such lithium plating, but have not yet achieved satisfactory results in the current state of demanding higher energy densities.

Accordingly, a problem to be solved by the present invention is to reduce the interfacial resistance of a negative electrode to lithium ion in a lithium ion secondary battery, particularly a rechargeable secondary battery, and improve the rapid charging characteristic of the battery by increasing the charging depth. Another object of the present invention is to provide a lithium ion secondary battery capable of minimizing lithium plating on the surface of a negative electrode by facilitating ion conduction with respect to a large current during rapid charging of a battery. Other objects and advantages of the present invention will become apparent from the following description. On the contrary, it is to be understood that the objects and advantages of the present invention can be realized by the means or method described in the claims, and the combination thereof.

The present invention is directed to a lithium ion secondary battery for solving the above technical problems. A first aspect of the present invention is directed to a lithium ion battery comprising: an electrode assembly comprising at least one negative electrode, a positive electrode and a separator, respectively; And an electrolyte solution, wherein the cathode and the anode are electrically insulated by a separation membrane, the electrolyte solution includes an organic solvent and a lithium salt, the electrolyte has a viscosity of 2.5 cp to 5.0 cp at 25 ° C, Is 7.0 to 10.0 mS / cm.

The second aspect of the present invention is the battery according to the first aspect, wherein the electrolytic solution has a viscosity of 3.0 cp to 4.5 cp at 25 캜.

The third aspect of the present invention is the electrolyte according to the first or second aspect, wherein the electrolyte has a viscosity at 25 캜 and an ion conductivity of 8.0 to 9.0 mS / cm.

A fourth aspect of the present invention resides in a battery according to any one of the first to third aspects, wherein the battery is charged at a constant current / constant voltage of 1.5 C at a charging time of less than 30 minutes to reach a state of charge (SOC) of 70% .

A fifth aspect of the present invention is the lithium ion secondary battery according to any one of the first to fourth aspects, wherein the driving voltage is 2.2 V to 4.5 V.

In a sixth aspect of the present invention, in any one of the first to fifth aspects, the loading amount of the electrode active material in the anode is 3.0 mAh / cm ² To 4.8 mAh / cm ² , and the ratio of the positive electrode to the negative electrode (N / P ratio) is 105 to 120.

In a seventh aspect of the present invention, in any one of the first to sixth aspects, the lithium salt is contained in the electrolyte solution at a concentration of 1.0M to 2M.

In an eighth aspect of the present invention, in any one of the first to seventh aspects, a lithium salt is contained in the electrolytic solution at a concentration of 1.1M to 1.5M.

A ninth aspect of the present invention resides in the electrochemical device according to any one of the first to eighth aspects, wherein the organic solvent is at least one selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate Examples of the solvent include methyl carbonate (EMC), methylpropylene carbonate, dipropyl carbonate (DPC), dimethylsulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma butyrolactone, propylene sulfite and tetrahydrofuran At least one member selected from the group consisting of furan, fluoroethylene carbonate, lactone, ether, ester, acetonitrile, lactam, ketone, propane sultone and ethylene sulfate.

In a tenth aspect of the present invention, in any one of the first to ninth aspects, the organic solvent is an imidazolium ionic liquid, an ammonium ionic liquid, a pyrrolidinium ionic liquid, a pyridinium ionic liquid And at least one selected from the group consisting of a liquid and a phosphonium ionic liquid.

11th aspect of the invention, the first to the 10 process according to any one of the aspects, the lithium salt of the 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 ^- .

A twelfth aspect of the present invention is directed to any one of the first to eleventh aspects, wherein the separation membrane comprises: a separation membrane substrate; And a heat-resistant ceramic layer formed on at least one surface of the porous substrate, wherein the separator substrate includes a polymer nonwoven fabric and / or a porous polymer film, and the heat-resistant ceramic layer includes a mixture of inorganic particles and a polymeric polymer And the inorganic particles are connected and fixed to each other by the binder polymer and include micropores derived from an interstitial volume between the inorganic particles.

A thirteenth aspect of the present invention is the twelfth aspect, wherein the binder polymer comprises a particulate polymer.

In a fourteenth aspect of the present invention, in any one of the first through thirteenth aspects, the negative electrode includes a negative electrode mixture, and the negative electrode mixture is a mixture including a negative electrode active material, an anode binder resin, and a negative electrode conductive material.

In a fifteenth aspect of the present invention, in the fourteenth aspect, the negative electrode active material includes natural graphite and / or artificial graphite.

In a sixteenth aspect of the present invention, in the fourteenth aspect of the present invention, the negative electrode conductive material includes carbon black, and the carbon black includes an agglomerated aggregate of primary particles having a particle size (D ₅₀ ) dl of 10 to 100 nm, The aggregate has a particle diameter (D ₅₀ ) of 100 to 1000 nm.

A seventeenth aspect of the present invention resides in the first to the sixteenth aspects of the present invention, wherein the cathode has a pore size of 0.5 to 3 mu m in pore diameter of 20% or more of 100% of the total volume of pores in the anode.

An eighteenth aspect of the present invention is a battery module including the secondary battery according to any one of the first aspect to the seventeenth aspect of the present invention, wherein the nineteenth aspect is a device including the battery module, An electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or a system for electric power storage.

The secondary battery according to the present invention has excellent resistance to rapid charging because the resistance of the reloading cell, particularly the interface resistance of the negative electrode, and the depth of charge are high, by controlling the viscosity and ionic conductivity of the electrolyte solution to a predetermined range. In addition, since the resistance is low, lithium plating on the surface of the negative electrode is minimized even when high C-rate is charged.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. On the other hand, the shape, size, scale or ratio of the elements in the drawings incorporated herein can be exaggerated to emphasize a clearer description.
FIG. 1 is a graph comparing the depths of charge according to C-rate changes in batteries according to Examples and Comparative Examples of the present invention.
FIG. 2 is a graph comparing Nyquist plots through EIS experiments in batteries according to Examples and Comparative Examples of the present invention.
3 is a graph comparing the cathode profiles of the batteries according to Examples and Comparative Examples.

The terms or words used in the present specification and claims should not be construed to be limited to ordinary or dictionary terms and the inventor shall properly define the concept of the term in order to best explain its invention The present invention should be construed in accordance with the meaning and concept consistent with the technical idea of the present invention. Therefore, the embodiments described in this specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention. Therefore, It is to be understood that equivalents and modifications are possible.

The present invention relates to a lithium ion secondary battery. The lithium ion secondary battery includes an electrolyte having a specific viscosity and an ion conductivity range. The lithium ion secondary battery is characterized in that the resistance characteristic of the negative electrode is improved and the filling depth is high.

A lithium ion secondary battery according to the present invention includes an electrode assembly including a cathode, an anode, and a separator, and an electrolyte.

The electrode assembly may include at least one negative electrode, a positive electrode and a separator, respectively, and the negative electrode and the positive electrode are electrically insulated by a separator.

The electrolytic solution includes an organic solvent and a lithium salt, and has a viscosity of 2.5 cp to 5.0 cp at 25 ° C and an ion conductivity of 7.0 to 10.0 mS / cm.

Hereinafter, the present invention will be described in detail.

1. electrolyte

1.1 Viscosity and ionic conductivity

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

The separation membrane of the secondary battery must be sufficiently impregnated with the electrolytic solution to enable charging and discharging by the action of ions. In general, a polyolefin-based porous film or a nonwoven fabric is used as the separation membrane. Particularly, since the pore size of the porous film is very minute to the nanometer level, a low electrolyte viscosity is required to enhance its impregnation property. However, when an organic solvent having a low viscosity is used, leakage is easy and volatility is very strong, which may cause evaporation. On the other hand, when the viscosity of the electrolyte is lowered by using a solvent having a low viscosity, the dielectric constant of the electrolyte is lowered and the dissociation of the lithium salt is difficult, so that the ion conductivity may be lowered.

Particularly, when the ion conductivity of a secondary battery requiring rapid charging is decreased, an overvoltage is generated at the cathode due to a shortage of ions in relation to the amount of current flowing, which may lead to deterioration of lithium plating on the surface of the cathode.

The present invention improves the electrolyte impregnation property of the electrode and the separator by controlling the viscosity and the ion conductivity of the electrolyte solution within the above range, and maintains the ion conductivity at an appropriate level. In particular, it reduces the overvoltage of the cathode and promotes diffusion of lithium ions in the active material to improve the depth of charge, thereby minimizing lithium plating during rapid charging.

1.2 Organic solvent

In the present invention, the electrolytic solution includes an organic solvent. The organic solvent may be any of those conventionally used as long as it can exhibit the viscosity and the ion conductivity of the electrolyte. Examples of the organic solvent include propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropylene carbonate, dipropyl carbonate Ethers, esters, acetonitriles, lactams, ethers, sulfates, sulfoxides, sulfoxides, sulfoxides, sulfoxides, acetonitriles, dimethoxy ethanes, diethoxy ethanes, vinylene carbonates, sulfolanes, gamma butyrolactones, propylene sulfites and tetrahydrofurans, fluoroethylene carbonates, Ketone, propane sultone, and ethylene sulfate, but the present invention is not limited thereto. In particular, ethylene carbonate, fluoroethylene carbonate, and propylene carbonate, which are cyclic carbonates in the organic solvent, can be preferably used since they have a high dielectric constant and dissociate the lithium salt well in the electrolyte. It is also possible to control ionic conductivity by mixing linear carbonate having a low viscosity and a low dielectric constant such as dimethyl carbonate and diethyl carbonate in the cyclic carbonate solvent at an appropriate ratio. The organic solvent is contained in an amount of 10 to 90% by weight of the total electrolyte solution.

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 may be an imidazolium ionic liquid, an ammonium ionic liquid, Based ionic liquid, a pyridinium-based ionic liquid, and a phosphonium-based ionic liquid.

1.3 Lithium salt

Specifically, in the electrolytic solution of the present invention, the ionizable lithium salt can be used without limitation as those conventionally used in an electrolyte for a lithium secondary battery, and examples of the anion of the lithium salt include 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 ^- .

In one embodiment of the present invention, the lithium salt is contained at a concentration of 1.0 to 2.0 M, or a concentration of 1.1 to 1.5 M based on 100% by weight of the electrolytic solution. As the amount of lithium salt 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 at the lithium salt content within the above-mentioned range, and accordingly, the effect of reducing the resistance and improving the rapid charging property can be expected.

2. Electrode assembly

The electrode assembly according to the present invention includes a negative electrode, a positive electrode, and a separator interposed between the negative electrode and the positive electrode.

2.1 Anode

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

In one specific embodiment of the present invention, the anode may include a lithium-containing transition metal oxide. Examples of the lithium-containing transition metal oxide include 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 ₄ (O <z <2), LiCoPO may be any one or two or more kinds of them, and ₄ is selected from the group consisting of LiFePO ₄ is used for the mixture. In addition to these oxides, sulfide, selenide and halide may also be used.

Meanwhile, according to a specific embodiment of the present invention, the loading amount of the anode is 3.0 mAh / cm ² To 4.8 mAh / cm &lt; ² &gt;, wherein the ratio of the positive electrode to the negative electrode (N / P ratio) is 105 to 120.

On the other hand, the conductive material contained in the anode can refer to the contents of the anode conductive material.

2.2 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 one specific embodiment of the present invention, the negative electrode active material comprises a carbonaceous material. As the carbonaceous material, both low-crystalline carbon and high-crystalline carbon may be used. Examples of low crystalline carbon include soft carbon and hard carbon. Examples of highly crystalline carbon include natural graphite, artificial graphite, kish graphite, pyrolytic carbon, High-temperature sintered carbon such as mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch derived cokes.

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

When the particle size (D ₅₀ ) of the agglomerate falls within the range of 100 to 1000 nm, the dispersibility of the conductive material in the anode is improved and the movement of lithium ions is promoted. Thus, the overvoltage of the cathode is dissolved to prevent 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 hydrophobic material, the wettability is low, and the cohesive property of cohesion between the conductive material particles is large, so that it is difficult to uniformly disperse the conductive material and the binder polymer. In addition, since it can not penetrate into the interior of the binder polymer, which is an insulator, there is a limit in improving the electrical conductivity. In accordance with the demand for a high-capacity / low-resistance electrochemical device, which has been increasing in the electrochemical device market, needs for atomization of the conductive material are increasing. As the size of the conductive material becomes smaller in terms of nanometer unit due to the need for atomization of the conductive material, the cohesion property of the conductive material further increases and it becomes difficult to achieve uniform dispersion with the electrode active material and the binder polymer.

Thus, an electrode slurry can be prepared in the following manner to ensure that the conductive material exhibits a uniformly dispersed phase in the electrode mix:

1) preparing a slurry by first high-shear mixing of an electrode binder and a solvent

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

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

The first high shear mix and the second high shear mix may each independently be mixed with a beads mill, a clear mixer, a microfludizer, an Fill mixer or a planetary disperser And may be carried out by a planetary dispersive mixer.

The first high shear mixing and the second high shear mixing can 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 .

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

In one embodiment of the present invention, the cathode may have a pore size of 0.5 to 3 m in the long diameter of the pore, 20% or more, or 27% or more of 100% of the total pore size of the anode. The distribution of the cathode pores within the above-mentioned range can increase the anode permeability of the lithium ion, thereby contributing to maximization of the above-mentioned effect.

2.3 Membrane

In the present invention, the separation membrane is a porous membrane that can electrically insulate the cathode and the anode to prevent short-circuiting, while providing a path for lithium ion migration. The separation membrane is not particularly limited as long as it can be used as a separation membrane material of an electrochemical device. It is possible.

The separation membrane may include a porous film and / or a nonwoven fabric including a polymer resin as a separation membrane substrate, and the polymer resin may be selected from the group consisting of high density polyethylene, low density polyethylene, linear low density polyethylene, ultra high molecular weight polyethylene, polypropylene, polyethylene terephthalate, Polymeric compounds such as polyethylene terephthalate, polyethylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, polyethylene naphthalene, More than one species may be mixed.

Further, in one specific embodiment of the present invention, the separation membrane may have a heat-resistant ceramic layer formed on at least one surface thereof. In the present invention, the heat-resistant ceramic layer includes a mixture of inorganic particles and a polymeric binder resin, and is connected and fixed to each other by the polymeric binder. The surface of the separation membrane is coated with the inorganic particles to improve the heat resistance of the separation membrane while the micropores liberated from the interstitial volume between the inorganic particles prevent the decrease in the permeability of the separation membrane.

In the present invention, the inorganic particles contained in the heat resistant ceramic layer are not particularly limited as long as oxidation and / or reduction reaction does not occur in the operating voltage range of the electrochemical device (for example, 0 to 5 V 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 _{Im), 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, and TiO ₂ may be used alone or in combination of two or more, but the present invention is not limited thereto.

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

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

3. Lithium ion secondary battery

In the present invention, the lithium ion secondary battery has a feature of improving the fast charging characteristic. In the present specification, fast charging refers to charging a battery having a driving voltage of 2.2 V to 4.5 V, or 2.5 V to 4.25 V with a current of 1 C-rate or more or 1.5 C-rate or more. In one embodiment of the present invention, the battery has a constant current / voltage of 1.5 C at a drive voltage of 4.25 V, and the time required for reaching the state of charge (SOC) of 70% is 30 minutes or less. Further, in the present invention, the lithium battery is suppressed by about 7% at the time of fast charging according to the above conditions. The point at which lithium plating occurs can be confirmed by analyzing the negative electrode profile at the time of rapid charging. When the cathode profile is separately extracted through the three-electrode system, and the graph represented by the potential value for SOC is differentiated, a region where the slope changes rapidly can be found. The SOC value at this time is the point where the lithium plating starts. FIG. 3 is a graph comparing the cathode profiles of the batteries according to the examples and the comparative examples. Compared with the battery of the comparative example, the battery according to the present invention has a deepening depth of charge of about 7% Able to know.

The present invention also provides a battery module including the secondary battery according to the present invention and a device including the battery module. In one 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 system for power storage.

Meanwhile, in the present invention, the conventional methods used in the technical field to which the present invention belongs can be applied to the contents not described in the description of the electrode assembly and the electrolytic solution.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to 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 embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example

Example

1. Manufacture of batteries

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 an anode slurry. The negative electrode slurry was coated on Cu foil to a thickness of 14 μm to form a thin electrode plate, dried at 135 ° C for 3 hours or more, and then pressed to manufacture 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 pores having a pore diameter of 0.5 mu m to 3 mu m of 28%.

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 foil to a thickness of 60 μm to form a thin electrode plate, dried at 135 ° C. for 3 hours or more, and rolled to prepare a positive electrode. At this time, the loading amount of the anode was 3.3 mAh / cm ² , and the NP ratio was 108.

Electrolyte solution is ethylene carbonate and ethyl methyl carbonate 3: LiPF ₆ was added thereto and mixed in a ratio of 7 vol% to 1.3M concentration. In addition, vinylene carbonate, propane sultone, and ethylene sulfate were added in an amount of 0.2 wt% based on the total amount of the electrolytic solution. The ionic conductivity of the electrolytic solution was 8.98 mS / cm and the viscosity was 4.25 cp. A battery having a capacity of 1100 mAh was manufactured using the negative electrode, positive electrode and electrolyte prepared above. As the separation membrane, celgard2320 was used.

Comparative Example

As the electrolytic solution, ethylene carbonate and ethylmethyl carbonate were mixed at a volume ratio of 3: 7 vol.%, LiPF ₆ was added at a concentration of 0.8 M, the ion conductivity was 8.2 mS / cm and the viscosity was 2.4 cp , And carbon black had a particle diameter of 1.2 탆 to 1.5 탆.

2. Experimental results

1) Comparison of charging speed

4.25 V was charged to the end-of-charge voltage and charged to 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

FIG. 1 is a graph comparing the depths of charge according to C-rate changes in batteries according to Examples and Comparative Examples of the present invention. According to this, it was confirmed that the cells of the Examples reached the same SOC within a short time as compared with the cells of the Comparative Example at each C-rate charging.

2) Impedance measurement

The cells prepared in the above Examples and Comparative Examples were charged up to 4.25 V and then a small voltage (10 mV) was applied from a frequency of 3 kHz to 100 mHz, and the current response was measured and compared with a Nyquist plot. Referring to FIG. 2, the graph of the Nyquist plot shows that the battery of the present embodiment has reduced impedance compared to the battery of the comparative example by improving the ionic conductivity of the electrolyte.

3) Effect of inhibiting lithium plating

3 is an analysis of the cathode profiles for the cells of the Examples and Comparative Examples. The negative electrode profile was obtained by separately extracting the negative electrode profile (1.5 C charge) at the time of charging through the three electrode system and then differentiating the graph represented by the potential value for SOC. In FIG. 3, A is a cell in Example and B is a cell in which a slope is changed in a comparative cell. Compared with the battery according to the comparative example, the battery according to the embodiment has a deepening depth of charge of about 7% .

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

Claims (19)

An electrode assembly comprising at least one cathode, an anode and a separator, respectively; And an electrolytic solution,
Wherein the cathode and the anode are electrically insulated by a separator,
Wherein the electrolytic solution comprises an organic solvent and a lithium salt,
Wherein the electrolyte has a viscosity of 2.5 cp to 5.0 cp at 25 占 폚 and an ion conductivity of 7.0 to 10.0 mS / cm.
The method according to claim 1,
Wherein the electrolyte has a viscosity of 3.0 cp to 4.5 cp at 25 占 폚.
The method according to claim 1,
Wherein the electrolyte has a viscosity at 25 캜 and an ion conductivity of 8.0 to 9.0 mS / cm.
The method according to claim 1,
Wherein the battery has a time to reach 70% of SOC (state of charge) during charging by a constant current / constant voltage method at 1.5 C within 30 minutes.
The method according to claim 1,
Wherein the battery has a driving voltage of 2.2V to 4.5V.
The method according to claim 1,
The amount of loading of the electrode active material in the positive electrode was 3.0 mAh / cm &lt; ² &gt; To 4.8 mAh / cm &lt; ² &gt;, and the ratio of the positive electrode to the negative electrode (N / P ratio) is 105 to 120. [
The method according to claim 1,
Wherein a lithium salt is contained in the electrolyte solution at a concentration of 1.0M to 2M.
The method according to claim 1,
And a lithium salt in the electrolyte solution is contained at a concentration of 1.1M to 1.5M.
The method according to claim 1,
The organic solvent may be at least one selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methylpropylene carbonate, dipropyl carbonate Ethers, esters, acetonitriles, lactams, ketones, ketones, and the like, such as acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane, gamma butyrolactone, propylene sulfite and tetrahydrofuran, fluoroethylene carbonate, Propane sultone, and ethylene sulfate. The lithium ion secondary battery according to claim 1,
The method according to claim 1,
The organic solvent includes at least one selected from the group consisting of an imidazolium ionic liquid, an ammonium ionic liquid, a pyrrolidium ionic liquid, a pyridinium ionic liquid, and a phosphonium ionic liquid , &Lt; / RTI &gt; lithium ion secondary battery.
The method according to claim 1,
The lithium salt has an anion such as 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 ^{- _{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 - is, lithium is at least one member selected from the group comprising Ion secondary battery.
The method according to claim 1,
Wherein the separation membrane comprises a separation membrane substrate; And a heat-resistant ceramic layer formed on at least one surface of the porous substrate,
Here, the separator substrate includes a polymer nonwoven fabric and / or a porous polymer film,
Wherein the heat-resistant ceramic layer comprises a mixture of inorganic particles and a polymeric polymer, wherein the inorganic particles are connected and fixed to each other by the binder polymer, and the micropores derived from the interstitial volume between the inorganic particles And a lithium ion secondary battery.
13. The method of claim 12,
Wherein the binder polymer comprises a particulate high molecular polymer.
The method according to claim 1,
Wherein the negative electrode includes a negative electrode mixture, and the negative electrode mixture is a mixture including a negative electrode active material, a negative electrode binder resin, and a negative electrode conductive material.
The method according to claim 14,
Wherein the negative electrode active material comprises natural graphite and / or artificial graphite.
15. The method of claim 14,
Wherein the negative electrode conductive material comprises carbon black, and the carbon black includes aggregated aggregated primary particles having a particle diameter (D ₅₀ ) dl of 10 to 100 nm, and the aggregate has a particle diameter (D ₅₀ ) of 100 to 1000 nm Lithium ion secondary battery.
The method according to claim 1,
Wherein the negative electrode has a pore diameter of 0.5 to 3 mu m in pore diameter of 20% or more of 100% of the total volume of pores in the negative electrode.
17. A battery module comprising the lithium ion secondary battery according to any one of claims 1 to 17.
A device comprising a battery module according to claim 18, characterized in that the device is an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle or a system for power storage.

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