KR20170094720A - Electrode with improved safety and method of making the same - Google Patents

Abstract

The present invention relates to an electrode with enhanced safety, and a production method thereof. According to the present invention, the electrode contains linearly dispersed polyethylene particles capable of being molten at a specific temperature range. In addition, resistance in the electrode can rapidly increase when abnormal heat emission takes place in batteries, and reduction in energy density of the battery and an increase in initial resistance can be minimized since a small amount of the polyethylene particles is used.

Description

TECHNICAL FIELD [0001] The present invention relates to an electrode having improved safety,

The present invention relates to an electrode having improved safety and a manufacturing method thereof.

As technology development and demand for mobile devices have increased, there has been a rapid increase in demand for secondary batteries as energy sources. Among such secondary batteries, lithium secondary batteries, which exhibit high energy density and operational potential, long cycle life, Batteries have been commercialized and widely used.

Generally, a lithium secondary battery has a structure in which a lithium electrolyte is impregnated into an electrode assembly composed of a positive electrode including a lithium transition metal oxide as an electrode active material, a negative electrode including a carbonaceous active material, and a separator interposed between the positive electrode and the negative electrode have. The secondary battery has a non-aqueous composition. The electrode is generally manufactured by coating a current collector made of metal with an electrode material mixture. The electrode material includes an electrode active material for storing energy, a conductive material for imparting electrical conductivity, (N-methyl pyrrolidone) or the like in an organic solvent composed of a binder polymer for attachment to the whole.

However, when such a lithium secondary battery is exposed to a high temperature or a large current flows in a short time due to overcharge, external short circuit, nail penetration, local crush, etc., the battery is heated by IR heat, There is a risk of this happening. That is, when the temperature of the battery rises, the reaction between the electrolyte and the electrode is promoted. As a result, a reaction heat is generated and the temperature of the battery further rises, which again accelerates the reaction between the electrolyte and the electrode. As a result, the temperature of the battery rapidly rises, which again accelerates the reaction between the electrolyte and the electrode. Such a vicious circle causes a thermal runaway phenomenon in which the temperature of the battery rises sharply, and when the temperature rises to a certain level or higher, the battery may ignite. Further, as a result of the reaction between the electrolyte and the electrode, gas is generated and the internal pressure of the battery is increased, and the lithium secondary battery explodes at a certain pressure or higher. Thus, the risk of explosion is the most fatal disadvantage of lithium secondary batteries.

Therefore, it is necessary to secure safety for the development of lithium secondary batteries. As an effort to secure such safety, there are a method of mounting an element on the outside of the cell and a method of using a material inside the cell. PTC devices, CID devices, protection circuits for controlling voltage and current, safety vents using changes in the internal pressure of the battery, and the like are used for the change of temperature, voltage, and current inside the battery. (PTC) characteristics by physical, chemical, and electrochemical changes according to the temperature of the substrate.

The present invention provides an electrode capable of exhibiting a PTC effect in a specific temperature range, while minimizing side effects such as lowering of energy density and initial resistance of the battery, and a method of manufacturing the electrode.

According to one aspect of the present invention, there is provided an electrode comprising an electrode active material, a conductive material, a binder polymer, and polyethylene particles, wherein the polyethylene particles are linearly dispersed in an electrode.

The polyethylene particles may be low density polyethylene (LDPE), high density polyethylene (HDPE), or a mixture thereof.

The polyethylene particles may have an average particle diameter of 1 to 100 mu m.

The polyethylene particles may be included in the electrode mixture at an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the active material.

The distribution of the polyethylene particles may have a standard deviation of less than 4 depending on the position of the electrodes.

According to another aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: (s1) mixing an electrode material slurry formed by adding an electrode active material, a conductive material, a binder polymer, and polyethylene particles to a solvent; And (s2) milling the electrode mixture slurry so that the polyethylene particles are linearly dispersed. Wherein the milling in (s2) is performed by using a spike mill, a beads mill, a shear mix, or a combination thereof. do.

The milling in (s2) may be performed at 500 to 3000 rpm.

According to still another aspect of the present invention, there is provided an electrode for a secondary battery including the electrode.

The electrode for a secondary battery according to the present invention contains polyethylene particles which can be melted in a specific temperature range in a linearly dispersed state, so that the resistance in the electrode can be drastically increased upon abnormal heat generation of the battery.

Further, since a small amount of polyethylene particles can be used, there is an advantageous effect that the energy density reduction and initial resistance increase of the battery can be minimized.

1A schematically shows an electrode in which polyethylene particles are dispersed in a conventional manner, and Fig. 1B is a SEM photograph of such an electrode.
Figure 2a schematically illustrates an electrode in which polyethylene particles are linearly dispersed according to an embodiment of the invention, and Figure 2b is a SEM image of such an electrode.
FIG. 3A schematically illustrates the state before an abnormal heat generation of the electrode according to an embodiment of the present invention, and FIG. 3B schematically illustrates an embodiment after abnormal heat generation of the electrode according to an embodiment of the present invention.
FIG. 4 is a graph showing the particle diameter distribution of the polyethylene particles (before the electrode mixture is introduced) usable in the present invention and the particle diameter distribution of the polyethylene particles in the electrode of the embodiment.
FIGS. 5A and 5B are cross sectional photographs of the electrode obtained in each of the comparative example and the example, in which the width and height of the cross-sectional areas are divided into three equal parts, and are divided into nine areas.

According to one aspect of the present invention, there is provided an electrode comprising an electrode active material, a conductive material, a binder polymer, and polyethylene particles, wherein the polyethylene particles are linearly dispersed in the electrode.

The polyethylene particles may be low density polyethylene (LDPE), high density polyethylene (HDPE), or a mixture thereof, as long as the polyethylene particles can be melted when the battery is abnormally heated to lower the electrical conductivity of the electrode.

The polyethylene particle may be, for example, a particle having a spherical shape.

It is also preferable that the polyethylene particles have an average particle diameter as small as possible. The polyethylene particles may have an average particle size in the range of 1 to 100 [mu] m non-limitingly. When the polyethylene particles have an average particle diameter in the above numerical range, aggregation in the electrode mixture can be suppressed and better linear dispersibility can be obtained.

The polyethylene particles usable in the present invention can be obtained by a known method. For example, a method of pulverizing polyethylene to obtain polyethylene particles; A method of obtaining polyethylene particles by directly polymerizing an ethylene monomer using an ethylene polymerization catalyst in a fine particulate shape controlled in shape; A method of drying an aqueous dispersion of the polyethylene particles prepared by the emulsification method to obtain polyethylene particles, and the like.

The polyethylene particles may be included in the electrode mixture at an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the active material. If the content of the polyethylene particles is less than the lower limit value, it is difficult for the battery to undergo an abrupt resistance increase upon abnormal heat generation, and if it is higher than the upper limit value, the initial resistance of the battery and the energy density are lowered.

The term " linear dispersion " as used herein can be more easily understood from the comparison of FIGS. 1A and 1B.

1A and 1B illustrate an electrode in which an active material layer 200 containing polyethylene particles 230 together with an active material 210 and having no polyethylene particles 230 dispersed therein is applied to a current collector 100 2A and 2B schematically show the active material layer 200 in which the polyethylene particles 230 are contained together with the active material 210 and the polyethylene particles 230 are dispersed in a linear dispersion state, And schematically showing the electrode formed by coating the whole body 100. As shown in Fig.

In comparison between FIG. 1B and FIG. 2B, it can be confirmed that the polyethylene particles are agglomerated in a circle marked in red in FIG. 1B, but in FIG. 2B, the polyethylene particles are uniformly dispersed around the active material particles, It can be confirmed that it is linearly dispersed.

3A, an electrode active material layer 200 including an active material 210, a conductive material 220, and polyethylene particles 230 and having the polyethylene particles 230 linearly dispersed therein is disposed on the current collector 100 (See FIG. 3A). The polyethylene particles 230 of the electrode active material layer are melted at a temperature of 130 to 140 ° C or more during abnormal heat generation of the battery to form a gap between the active material 210 and the active material 210 or a conductive material 220 and the active material 210, the same effect as the PTC can be obtained.

The uniform linear dispersion of the polyethylene according to the present invention can also be confirmed from FIG. According to Fig. 4, the polyethylene particle size distribution in the electrode produced according to the present invention does not show a large difference as compared with the polyethylene particle size distribution before being added to the electrode mixture. Therefore, it can be predicted that the polyethylene forms a linear dispersion state in the electrode manufactured according to the present invention.

The electrode according to one aspect of the present invention may have a standard deviation of less than 4, preferably from 0 to 2.5, depending on the position of the electrode.

In the present specification, the term 'standard deviation' refers to a standard deviation obtained by dividing the electrode cross-sectional area into three successive regions by dividing the cross-sectional area into three regions, that is, the width and the height, . For example, in Figs. 5A and 5B, the cross-sectional area of the electrode made up of 25 mu m in width and 50 mu m in height is regarded as one region.

The electrode may be a cathode including a cathode active material or a cathode including a cathode active material.

The positive electrode for a secondary battery is prepared by coating a positive electrode mixture containing a positive electrode active material, a conductive material and a binder polymer on a positive electrode current collector, followed by drying and pressing. If necessary, a filler may be further added to the positive electrode mixture.

The cathode current collector generally has a thickness of 3 to 500 mu m. The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the positive electrode current collector may be made of stainless steel, aluminum, nickel, titanium, sintered carbon or a surface of aluminum or stainless steel Treated with carbon, nickel, titanium, silver or the like may be used. The current collector may have fine irregularities on the surface thereof to increase the adhesive force of the cathode active material, and various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric are possible.

The cathode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + x} Mn _{2 -x} O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ and the like; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ and Cu ₂ V ₂ O ₇ ; Formula _{LiNi 1 - x M x O 2} ( where, the M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, x = 0.01 ~ 0.3 Im) Ni site type lithium nickel oxide which is represented by; Formula _{LiMn 2 - x M x O 2} ( where, M = Co, Ni, Fe , Cr, and Zn, or Ta, x = 0.01 ~ 0.1 Im) or Li ₂ Mn ₃ MO ₈ (where, M = Fe, Co, Ni, Cu, or Zn); A lithium manganese composite oxide having a spinel structure represented by LiNi _x Mn _2-x O ₄ ; LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with an alkaline earth metal ion; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ , and the like. However, the present invention is not limited to these.

The conductive material is usually added in an amount of 1 to 50% by weight based on the total weight of the mixture including the cathode active material.

Such a conductive material is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, for example, graphite such as natural graphite or artificial graphite; Carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fiber and metal fiber; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey 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 binder polymer is a component that assists in bonding between the active material and the conductive material and bonding to the current collector, and is usually added in an amount of 1 to 50 wt% based on the total weight of the mixture containing the cathode active material. Examples of such a binder polymer include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, Polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluorine rubber, various copolymers and the like.

The filler is optionally used as a component for suppressing expansion of the anode, and is not particularly limited as long as it is a fibrous material without causing a chemical change in the battery, and examples thereof include olefin polymers such as polyethylene and polypropylene; Fibrous materials such as glass fibers and carbon fibers are used.

The solvent is not particularly limited in its kind, and examples thereof include N-methyl-2-pyrrolidone (NMP) and methyl ethyl ketone (MEK).

On the other hand, the negative electrode is manufactured by applying, drying and pressing an anode active material on an anode current collector, and may optionally further include a conductive material, a binder polymer, a filler, and a solvent as described above.

The negative electrode current collector is generally made to have a thickness of 3 to 500 mu m. Such an anode current collector is not particularly limited as long as it has electrical conductivity without causing chemical changes in the battery, and examples of the anode current collector include copper, stainless steel, aluminum, nickel, titanium, sintered carbon, a surface of copper or stainless steel A surface treated with carbon, nickel, titanium, silver or the like, an aluminum-cadmium alloy, or the like can be used. In addition, like the positive electrode collector, fine unevenness can be formed on the surface to enhance the bonding force of the negative electrode active material, and it can be used in various forms such as films, sheets, foils, nets, porous bodies, foams and nonwoven fabrics.

The negative electrode active material may include, for example, carbon such as non-graphitized carbon or graphite carbon; _{Li x Fe 2 O 3 (0≤x≤1} ), Li x WO 2 (0≤x≤1), Sn x Me 1 - x Me 'y O z (Me: Mn, Fe, Pb, Ge; Me' : Metal complex oxides such as Al, B, P, Si, Group 1, Group 2, Group 3 elements of the periodic table, Halogen, 0 < x < Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, And Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials; Titanium oxide; Lithium titanium oxide and the like can be used.

In one embodiment, lithium-titanium oxide (LTO) having a small average particle size may be used as the negative electrode active material. In this case, the spinel lithium manganese composite oxide of LiNi _x Mn _{2 - x} O _{4 having} a relatively high potential due to the high potential of LTO can be used as the cathode active material.

According to another aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising: (s1) adding an electrode active material, a conductive material, a binder polymer, and a polyethylene particle to a solvent and mixing; And (s2) milling the polyethylene particles to be linearly dispersed; The method for manufacturing an electrode material mixture according to the present invention is characterized by comprising the steps of:

As for the polyethylene particles, the electrode active material, the conductive material, the binder polymer and the solvent, the above-mentioned contents are referred to.

The mixing performed in (s1) may be carried out in a conventional manner in the art.

On the other hand, the milling for linear dispersion of the polyethylene particles, which is carried out in (s2), can be carried out by using a spike mill, a beads mill, a shear mix or a combination thereof . The milling speed may be 500 to 3000 rpm.

The electrode may be an anode, a cathode, or both an anode and a cathode.

The present invention provides a secondary battery having a structure in which a lithium salt-containing electrolyte is impregnated in an electrode assembly having a structure in which a separator is interposed between the positive electrode and the negative electrode.

The separator is interposed between the positive electrode and the negative electrode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the separator is generally 0.01 to 10 mu m and the thickness is generally 5 to 300 mu m. As such a separator, for example, an olefin-based polymer such as polypropylene having chemical resistance and hydrophobicity; A sheet or nonwoven fabric made of glass fiber, polyethylene or the like is used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The electrolyte solution containing the lithium salt is composed of an electrolyte solution and a lithium salt. The electrolyte solution may be a non-aqueous organic solvent, an organic solid electrolyte, or an inorganic solid electrolyte, but is not limited thereto.

Examples of the non-aqueous organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma -Butyrolactone, 1,2-dimethoxyethane, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, formic acid And examples thereof include methyl, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, Ethers, methyl pyrophonate, ethyl propionate and the like can be used.

Examples of the organic solid electrolyte include a polymer electrolyte such as a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymer containing an ionic dissociation group and the like may be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides and sulfates of Li such as Li ₄ SiO ₄ -LiI-LiOH and Li ₃ PO ₄ -Li ₂ S-SiS ₂ can be used.

The lithium salt is a material that is readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF _{6, LiSbF 6, LiAlCl 4,} CH 3 SO 3 Li, (CF 3 SO 2) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide.

For the purpose of improving the charge / discharge characteristics and the flame retardancy, the electrolytic solution is preferably mixed with an organic solvent such as pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, glyme, Benzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, . In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further added to impart nonflammability. In order to improve the high-temperature storage characteristics, carbon dioxide gas may be further added. FEC (Fluoro-Ethylene Carbonate, PRS (Propene sultone), and the like.

In a preferred _{embodiment, LiPF 6, LiClO 4, LiBF} 4, LiN (SO 2 CF 3) 2 , such as a lithium salt, a highly dielectric solvent of DEC, DMC or EMC Fig solvent cyclic carbonate and a low viscosity of the EC or PC of And then adding it to a mixed solvent of linear carbonate to prepare a lithium salt-containing non-aqueous electrolyte.

The present invention also provides a battery module including the secondary battery as a unit cell, and a battery pack including the battery module.

The battery pack can be used as a power source for a medium and large-sized device requiring high temperature stability, long cycle characteristics, and high rate characteristics.

Preferred examples of the above medium to large devices include a power tool that is powered by an electric motor and moves; An electric vehicle including an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like; An electric motorcycle including an electric bike (E-bike) and an electric scooter (E-scooter); An electric golf cart; And a power storage system, but the present invention is not limited thereto.

<Examples>

A negative electrode active material composed of lithium titanium oxide, 5 wt% of super-P (conductive material), 5 wt% of PVdF (binder) and 5 wt% of polyethylene particles were added to NMP and mixed, followed by spike milling. , Beads mill or shear mixer under the conditions of 500 to 3000 rpm to prepare an anode mixture.

<Comparative Example>

An anode mixture was prepared in the same manner as in Example 1, except that the polyethylene particles were used in an amount of 2% by weight.

&Lt; Evaluation example &

SEM photographs were taken of the cross-sectional areas of the electrodes obtained in the comparative examples and the examples. Subsequently, the SEM image is divided into nine regions so as to have a width of 25 mu m and a height of 50 mu m. The uppermost region is defined as A1, A2, A3 from the left, the middle region is defined as B1, B2 and B3 from the left, And the lower end region is defined as C1, C2, and C3 from the left.

The ratio of the area occupied by polyethylene in the total area excluding the active material area, that is, the area of each of polyethylene, conductive material and void, in each of the above areas was obtained.

As a result, the results shown in Table 1 and Table 2 were obtained from the comparative example and the example, respectively.

One 2 3 A 36.13 25.55 26.05 B 24.37 20.84 25.07 C 22.37 25.83 26.34 Average: 25.8%
Standard deviation: 4.3

One 2 3 A 25.95 25.59 26.99 B 21.88 27.79 26.92 C 20.96 22.73 23.31 Average: 24.7%
Standard deviation: 2.5

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (8)

An electrode active material, a conductive material, a binder polymer, and polyethylene particles,
Wherein the polyethylene particles are linearly dispersed in the electrode.
The method according to claim 1,
Wherein the polyethylene particles are low density polyethylene (LDPE), high density polyethylene (HDPE), or mixtures thereof.
The method according to claim 1,
Wherein said polyethylene particles have an average particle size of from 1 to 100 mu m.
The method according to claim 1,
Wherein the polyethylene particles are included in the electrode mixture in an amount of 0.1 to 10 parts by weight based on 100 parts by weight of the active material.
The method according to claim 1,
Wherein the distribution of the polyethylene particles has a standard deviation of less than 4 depending on the position of the electrode.
(s1) mixing an electrode mixture slurry formed by adding an electrode active material, a conductive material, a binder polymer, and polyethylene particles to a solvent; And (s2) milling the electrode mixture slurry so that the polyethylene particles are linearly dispersed. Lt; / RTI &gt;
Wherein the milling in (s2) is carried out by use of a spike mill, a beads mill, a shear mix or a combination thereof.
The method according to claim 6,
Wherein the milling at (s2) is performed at 500 to 3000 rpm.
An electrode for a secondary battery comprising an electrode according to any one of claims 1 to 5.

Images