KR102074376B1 - Method of Charging Secondary Battery by Changing Fully Charged Voltage Depending on Impedance - Google Patents

Abstract

The present invention provides a method of charging a secondary battery by changing a full charge voltage, the method comprising: (a) charging a secondary battery based on a first full charge voltage value stored in a memory; (b) measuring the impedance of the secondary battery after charging; (c) deriving a second full charge voltage value to be applied at the next charging based on the measured impedance; And (d) storing the second full charge voltage value in a memory.

Description

How to charge the secondary battery by changing the full charge voltage according to the impedance {Method of Charging Secondary Battery by Changing Fully Charged Voltage Depending on Impedance}

The present invention relates to a method for charging a secondary battery by changing the full charge voltage according to the impedance and a battery module having a variable full charge voltage.

Due to the rapid increase in the use of fossil fuels, the demand for the use of alternative energy or clean energy is increasing. As a part of this, the most actively researched fields are power generation and storage using electrochemistry.

A representative example of an electrochemical device using such electrochemical energy is a secondary battery, and its use area is gradually increasing.

Among these secondary batteries, lithium secondary batteries are used as power sources for various electronic devices with high voltage and high energy density.

As the performance of electronic devices such as smart phones is improved and miniaturized, demand for secondary batteries with high energy density is increasing. In addition, as the use cycle of electronic devices becomes longer, the need for a secondary battery having a high energy density and improved life characteristics is increasing.

As such, in order to develop a secondary battery having high energy density and improved life characteristics, many studies have been conducted on materials of secondary batteries such as a positive electrode active material, a negative electrode active material, or a binder, and in some studies, energy density and life characteristics are somewhat different. An improved secondary battery was also developed.

However, there is a limit in that sufficient energy density and lifespan characteristics may not be secured through the method of improving the material characteristics of the secondary battery.

Therefore, there is a high need for a technology capable of improving the life characteristics of the secondary battery while maintaining the existing energy density through other methods than improving the material of the secondary battery.

The present invention aims to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

The inventors of the present application, after repeated in-depth research and various experiments, as described later, a method of charging the secondary battery by changing the full charge voltage, the process of measuring the impedance of the secondary battery after charging and measured impedance Based on the derivation of the second full charge voltage value to be applied at the next charge, it was confirmed that the life characteristics can be significantly improved while maintaining the energy density of the secondary battery, and thus the present invention has been completed. .

Therefore, the method of charging the secondary battery by changing the full charge voltage according to the present invention,

(a) charging the secondary battery based on the first full charge voltage value stored in the memory;

(b) measuring the impedance of the secondary battery after charging;

(c) deriving a second full charge voltage value to be applied at the next charging based on the measured impedance; And

(d) storing the second full charge voltage value in a memory;

Characterized in that it comprises a.

The energy density of the secondary battery may vary depending on the full charge voltage, and specifically, increases as the full charge voltage increases within an acceptable range. However, as the energy density is maintained higher, the life characteristics in the trade off can be rapidly decreased. In particular, the tendency for the life characteristics to decrease is accelerated as the secondary battery is used for a long time.

In light of this, by using the rechargeable battery for a long time, it is possible to increase the life characteristics of the secondary battery by reducing the full charge voltage. However, even in the method of reducing the full charge voltage of the secondary battery, the amount of the full charge voltage and the time point of the decrease may greatly affect the life characteristics of the secondary battery.

For simplicity, a configuration of reducing the full charge voltage may be considered as the number of charge / discharge cycles of the secondary battery increases. In this case, even when the secondary battery is charged and discharged, the charge capacity and the discharge capacity may be different for each cycle, and thus, there is a problem that it is difficult to accurately reflect the state of the secondary battery at the time of charging.

According to the present invention, it is most preferable to adjust the full charge voltage to accurately reflect the state of the secondary battery at the time of charging, and to accurately reflect the state of the secondary battery when the full charge voltage is adjusted based on the impedance of the secondary battery after charging. And, through this, it is possible to significantly improve the life characteristics of the secondary battery.

In the process (a), the charging method of the secondary battery is not particularly limited, and in one specific example, the secondary battery may be charged by a constant current charging method and / or a constant voltage charging method.

In one specific example, in the process (c), the second full charge voltage value may be equal to or less than the first full charge voltage value. As such, the full charge voltage may be reduced according to the increase in the impedance of the secondary battery to further increase the life characteristics of the secondary battery.

In addition, in the process (c), the second full charge voltage value may be derived based on the increase of the measured impedance with respect to the initial impedance of the secondary battery.

In this case, the initial impedance may be an impedance value measured after initially charging a commercialized secondary battery according to a rated voltage, or may be a value input during a manufacturing process of a secondary battery, statistically or theoretically predicted.

Since the second full charge voltage value is derived based on the increase in the impedance measured with respect to the initial impedance, when the impedance measured due to a temporary error or the like in the impedance measurement is measured lower than the initial impedance, the first full charge voltage value is satisfied. Charging and discharging can be carried out without error by applying the full voltage as it is.

In one specific example, the second full charge voltage value may be derived stepwise and / or continuously based on the measured increase amount of the impedance with respect to the initial impedance of the secondary battery.

In one example, the second full charge voltage value may be derived in stages based on the measured increase amount of the impedance with respect to the initial impedance of the secondary battery.

In detail, the second full charge voltage value may be derived, including the voltage section of steps 3 to 10.

More specifically, the voltage section may include at least three steps to derive a second full charge voltage value:

When (ZZ ₀ ) / Z ₀ <a, V = V ₀

When a ≤ (ZZ ₀ ) / Z ₀ <b, V = V _a

when b ≤ (ZZ ₀ ) / Z ₀ , V = V _b

Wherein Z ₀ is the initial impedance, Z is the measured impedance, V ₀ is the initial full charge voltage value, V is the second full charge voltage value, a and b are constant, 0 <a <b <0.3, 4.2 Volts <V _b <V _a <V ₀

As described above, when the second full charge voltage value is derived in steps based on the measured increase in the impedance, the process of deriving the second full charge voltage value is simplified, thereby minimizing an error that may occur in the calculation process. can do.

In addition, each voltage section may be subdivided to further change the second full charge voltage.

In another example, the second full charge voltage value may be continuously derived based on the measured increase in the impedance with respect to the initial impedance of the secondary battery.

Specifically, the second full charge voltage value can be derived continuously according to the following equation (1):

V = V ₀ (1-kexp (1-Z ₀ / Z)) (1)

In the above formula, Z ₀ is the initial impedance, Z is the measured impedance, V ₀ is the initial full charge voltage value, V is the second full charge voltage value, and k is a constant where 0 <k ≤ 0.1.

As such, when continuously deriving the second full charge voltage value based on the measured increase in the impedance, the second full charge may be derived and applied to the state at the time of charging of the secondary battery. The voltage can be changed at the finest level, and thus the life characteristics of the secondary battery can be remarkably improved.

Meanwhile, in another example, the second full charge voltage value may be derived stepwise and continuously based on the measured increase amount of the impedance with respect to the initial impedance of the secondary battery.

In detail, a voltage section includes steps 3 to 10, and at least one step of the voltage section may continuously derive the second full charge voltage value based on the measured increase in impedance.

The full charge voltage value of the secondary battery may be changed depending on the material characteristics of the secondary battery such as the active material and the measured impedance of the secondary battery. However, in one specific example, the full charge voltage value of the secondary battery may be 4.2 volts to It can be determined in the range of 4.6 volts.

The impedance during full charge of the secondary battery may also vary depending on the capacity and material of the secondary battery to be manufactured.

The present invention also provides a battery module having a variable full charge voltage.

The battery module, the secondary battery; A memory for storing a first full charge voltage value; A charging voltage adjusting unit adjusting a charging voltage based on a first full charging voltage value stored in the memory during charging; an impedance measuring unit measuring an impedance of the secondary battery after charging; And a controller configured to derive a second full charge voltage value to be applied at the next charge based on the measured impedance, and store the second full charge voltage value in a memory.

In one specific example, the secondary battery may be a lithium secondary battery.

Hereinafter, other components of the secondary battery will be described.

The secondary battery includes a positive electrode, a negative electrode, and a separator, and the positive electrode may be manufactured by, for example, applying a positive electrode mixture including a positive electrode active material, a conductive material, and a binder to a positive electrode current collector. Filler may be further added to the positive electrode mixture.

The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, carbon, nickel on the surface of stainless steel, aluminum, nickel, titanium, and aluminum or stainless steel may be used. , One selected from surface treated with titanium or silver may be used, and in detail, aluminum may be used. The current collector may form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and may be in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The positive electrode active material may include, for example, a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as 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 , LiV ₃ O ₄ , V ₂ O ₅ , Cu ₂ V ₂ O _7, and the like; Ni-site type lithium nickel oxide represented by the formula LiNi _1-x M _x O ₂ , wherein M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3; Formula LiMn _2-x M _x O ₂ , wherein M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1, or Li ₂ Mn ₃ MO ₈ , where M = Fe, Co, Lithium manganese composite oxide represented by Ni, Cu, or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with alkaline earth metal ions; Disulfide compounds; Fe ₂ (MoO ₄ ) ₃ and the like, but are not limited to these.

The total content of the conductive material may be added in 0.1 to 3.0% by weight based on the total weight of the positive electrode mixture.

The binder included in the positive electrode is a component that assists in bonding the active material and the conductive material to the current collector, and is generally added in an amount of 0.1 to 3.0 wt% based on the total weight of the mixture including the positive electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, 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 inhibiting expansion of the positive electrode, and is not particularly limited as long as it is a fibrous material without causing chemical change in the battery. Examples of the filler include olefinic polymers such as polyethylene and polypropylene; Fibrous materials, such as glass fiber and carbon fiber, are used.

On the other hand, the negative electrode may be manufactured by applying a negative electrode mixture including a negative electrode active material, a conductive material, and a binder to the negative electrode current collector, and may further include a filler and the like.

The negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, the negative electrode current collector may be formed on the surface of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper, or stainless steel. Surface-treated with carbon, nickel, titanium, silver and the like, aluminum-cadmium alloy and the like can be used. In addition, like the positive electrode current collector, fine concavities and convexities may be formed on the surface to enhance the bonding strength of the negative electrode active material, and may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

In the present invention, the thicknesses of the negative electrode current collectors may all be the same, but in some cases, may have different values.

The negative electrode active material may be, for example, carbon such as hardly 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 ≦ 1; 1 ≦ y ≦ 3; 1 ≦ z ≦ 8); Lithium metal; Lithium alloys; Silicon-based alloys; Tin-based alloys; 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 metal oxides such as Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

In one specific example, the porous substrate may be a polyolefin-based separation film commonly used in the art, for example, high density polyethylene, low density polyethylene, linear low density polyethylene, ultra high molecular weight polyethylene, polypropylene, polyethylene terephthalate (polyethyleneterephthalate), polybutyleneterephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone It may be a sheet consisting of one or more selected from the group consisting of polyethersulfone, polyphenyleneoxide, polyphenylenesulfidro, polyethylenenaphthalene, and mixtures thereof.

Pore size and porosity of the porous substrate is not particularly limited, porosity is in the range of 10 to 95%, pore size (diameter) may be 0.1 to 50 ㎛. When the pore size and porosity are less than 0.1 μm and 10%, respectively, it acts as a resistive layer, and when the pore size and porosity exceeds 50 μm and 95%, it is difficult to maintain mechanical properties.

The electrolyte may be a lithium salt-containing non-aqueous electrolyte, the lithium salt-containing non-aqueous electrolyte is composed of a non-aqueous electrolyte and a lithium salt, the non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte and the like are used, but these It is not limited only.

As the non-aqueous organic solvent, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma Butyl lactone, 1,2-dimethoxy ethane, tetrahydroxyfuran, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolon, formamide, dimethylformamide, dioxolon, acetonitrile Nitromethane, methyl formate, methyl acetate, triester phosphate, trimethoxy methane, dioxoron derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, Aprotic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyroionate and ethyl propionate can be used.

As the organic solid electrolyte, for example, a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, a polyedgetion lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, an ion Polymerizers containing a sex dissociation group and the like can be used.

Examples of the inorganic solid electrolytes 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, sulfates and the like of Li, such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , and the like, may be used.

The lithium salt is a good material to dissolve in the nonaqueous 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 lithium carbonate, lithium tetraphenylborate, imide and the like can be used.

In addition, nonaqueous electrolytes include pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, for the purpose of improving charge and discharge characteristics, flame retardancy, and the like. Nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxy ethanol, aluminum trichloride and the like may be added. have. In some cases, in order to impart nonflammability, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high temperature storage characteristics, and FEC (Fluoro-Ethylene) may be further included. Carbonate), PRS (Propene sultone) may be further included.

In one specific example, lithium salts such as LiPF ₆ , LiClO ₄ , LiBF ₄ , LiN (SO ₂ CF ₃ ) _2, and the like, may be formed of a cyclic carbonate of EC or PC, which is a highly dielectric solvent, and DEC, DMC, or EMC, which are low viscosity solvents. The lithium salt-containing nonaqueous electrolyte can be prepared by adding it to a mixed solvent of linear carbonates.

The present invention also provides a battery pack including at least one such battery module as a unit module, and a device including the battery pack as a power source.

The device may be, for example, a laptop computer, a netbook, a tablet PC, a mobile phone, an MP3, a wearable electronic device, a power tool, an electric vehicle (EV), or a hybrid electric vehicle (HEV). , Plug-in hybrid electric vehicles (PHEVs), electric bikes (E-bikes), electric scooters (E-scooters), electric golf carts, or power storage systems However, of course, it is not limited only to these.

Since the structure and fabrication method of such a device are known in the art, detailed description thereof will be omitted herein.

As described above, the method for charging the secondary battery by changing the full charge voltage according to the present invention includes measuring the impedance of the secondary battery after charging and the second full charge voltage to be applied at the next charge based on the measured impedance. Including the process of deriving a value, it is possible to significantly improve the life characteristics while maintaining the energy density of the secondary battery.

1 is a flowchart illustrating a method of charging a secondary battery according to an embodiment of the present invention;
2 is a schematic view showing a battery module according to an embodiment of the present invention.

Hereinafter, although described with reference to the drawings according to an embodiment of the present invention, this is for easier understanding of the present invention, the scope of the present invention is not limited thereto.

1 is a flowchart illustrating a method of charging a secondary battery according to an embodiment of the present invention.

Referring to FIG. 1, a secondary battery is charged based on a first full charge voltage value stored in a memory, and after charging, an impedance of the secondary battery is measured (111).

Next, the process 111 determines whether the measured impedance of the initial impedance is increased (112).

When the measured impedance with respect to the initial impedance in step 112 increases, a second full charge voltage value is derived 113 step by step and / or continuously based on the impedance increase amount.

In operation 113, the second full charge voltage value derived based on the impedance increase amount is stored in the memory (114).

Meanwhile, when the measured impedance with respect to the initial impedance in step 112 does not increase, the first full charge voltage value stored in the memory is maintained in the same manner as before (115).

2 is a schematic diagram showing a battery module according to an embodiment of the present invention.

Referring to FIG. 2, the battery module 200 includes a secondary battery 210, a charging voltage adjusting unit 220, an impedance measuring unit 230, a controller 240, and a memory 250.

In detail, the first full charge voltage value is stored in the memory 250, and the controller 240 controls the charging voltage adjuster 220 based on the first full charge voltage value stored in the memory 250. The secondary battery 210 is charged by adjusting.

After the secondary battery 210 is charged, the impedance of the secondary battery 210 is measured using the impedance measuring unit 230.

The controller 240 derives the second full charge voltage value to be applied at the next charging based on the measured impedance, and controls to store the second full charge voltage value in the memory 250. In this case, when the measured impedance does not increase, the first full charge voltage value is maintained in the memory as it is and is controlled to be charged to the first full charge voltage value at the next charge.

On the other hand, when the control unit 240 derives the second full charge voltage value step by step, even if the measured impedance increases compared to the initial impedance, the second full charge voltage value and the first full charge voltage value are the same, The first full charge voltage value may be maintained in the memory 250 as it is.

Although described above with reference to the drawings according to an embodiment of the present invention, those skilled in the art will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

Claims (16)

As a method of charging the secondary battery by changing the full charge voltage,
(a) charging the secondary battery based on the first full charge voltage value stored in the memory;
(b) measuring the impedance of the secondary battery after charging;
(c) deriving a second full charge voltage value to be applied at the next charging based on the measured impedance; And
(d) storing the second full charge voltage value in a memory;
Method comprising a. The method of claim 1, wherein in the step (a), the secondary battery is charged by a constant current charging method and / or a constant voltage charging method. The method of claim 1, wherein in step (c), the second full charge voltage value is less than or equal to the first full charge voltage value. The method of claim 1, wherein in the step (c), a second full charge voltage value is derived based on an increase amount of the measured impedance with respect to the initial impedance of the secondary battery. The method of claim 4, wherein the second full charge voltage value is derived in stages based on the measured increase in the impedance of the secondary battery. delete delete The method of claim 4, wherein the second full charge voltage value is continuously derived based on the measured increase in the impedance with respect to the initial impedance of the secondary battery. 9. The method of claim 8, wherein the second full charge voltage value is derived continuously according to Equation 1 below:
V = V ₀ (1-kexp (1-Z ₀ / Z)) (1)
In the above formula, Z ₀ is the initial impedance, Z is the measured impedance, V ₀ is the initial full charge voltage value, V is the second full charge voltage value, and k is a constant where 0 <k ≤ 0.1. The method of claim 4, wherein the second full charge voltage value is derived stepwise and continuously based on the measured increase in the impedance with respect to the initial impedance of the secondary battery. delete The method of claim 1, wherein the full charge voltage value of the secondary battery is determined in the range of 4.2 volts to 4.6 volts. A battery module with a variable full charge voltage,
Secondary battery;
A memory for storing a first full charge voltage value;
A charging voltage controller configured to adjust the charging voltage based on a first full charge voltage value stored in the memory during charging;
An impedance measuring unit measuring an impedance of the secondary battery after charging; And
A controller configured to derive a second full charge voltage value to be applied at a next charge based on the measured impedance and to store the second full charge voltage value in a memory;
Battery module comprising a. The battery module of claim 13, wherein the secondary battery is a lithium secondary battery. A battery pack comprising at least one battery module according to claim 13 as a unit module. A device comprising the battery pack according to claim 15 as a power source.

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