KR101208250B1 - Method of comparing the overcharge protection efficiency of additives for a rechargeable battery - Google Patents

Abstract

The present invention relates to a method for measuring the overcharge protection performance of a secondary battery and a method for comparing the overcharge protection performance of an additive for a secondary battery using the same.
Specifically, the present invention provides a method for measuring the overcharge protection performance of a secondary battery that can measure the overcharge prevention performance of the secondary battery simply by measuring the impedance of the film formed on the electrode for the secondary battery without completely manufacturing the secondary battery. It relates to a method of comparing the overcharge protection performance of the additive for secondary batteries using the same.

Description

Method of comparing the overcharge protection efficiency of additives for a rechargeable battery

The present invention relates to a method of comparing the overcharge prevention performance of the additive for secondary batteries.

Specifically, the present invention relates to a comparison method capable of comparing the overcharge prevention performance of the additive for secondary batteries simply by measuring the impedance of the film formed on the electrode for secondary batteries without completely manufacturing the secondary battery.

Recently, interest in energy storage technology is increasing. As the field of application extends to the energy of mobile phones, camcorders and notebook PCs, and even electric vehicles, efforts for research and development of electrochemical devices are becoming more concrete. Electrochemical devices are in the field of attention in this respect, and among them, lithium ion batteries developed in the early 1990's have operating voltages compared to conventional batteries such as Ni-MH, Ni-Cd, and sulfuric acid-lead batteries using an aqueous solution electrolyte. This high energy density is extremely popular due to its advantages.

However, such lithium ion batteries have safety problems such as ignition and explosion due to the use of nonaqueous electrolyte, and these problems become more serious as the capacity density of the battery increases. In the non-aqueous electrolyte secondary battery, ignition and explosion due to thermal runaway occur in the battery due to a series of exothermic reaction during overcharging.

Many solutions have been proposed to control the ignition or explosion caused by the temperature rise inside the battery as described above, and as an example, a method using a nonaqueous electrolyte additive is known. However, when the overcharge prevention performance is tested in the process of developing a preferred non-aqueous electrolyte additive or an overcharge preventing electrolyte, it is difficult to predict the actual performance simply because the variation of the overcharge result is large for each manufactured battery. Therefore, the performance of the additive is determined by manufacturing and testing a large number of batteries. Accordingly, there is a problem in that it is difficult to test a variety of additives, various electrolytes, or battery structures due to the high cost and time required for battery manufacture.

An object of the present invention is to provide a method for easily comparing the overcharge protection performance of various secondary battery additives without the production of secondary batteries.

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In order to achieve the above object, the present invention comprises the steps of adding an additive for a secondary battery in the electrolyte; Forming a passivation film on the electrode immersed in the electrolyte; Measuring an impedance of the passivation film; And comparing the value of the impedance, and determining that the additive exhibiting a relatively high impedance value can form a stable passivation film so as to form a stable secondary battery. Provides a comparison method.

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According to the measuring method of the overcharge protection performance according to the present invention, since the overcharge protection performance of the secondary battery can be measured only by measuring the impedance after forming the passivation film on the electrode, there is no need to manufacture the battery completely, and Even when the overcharge protection performance of the electrolyte or additive is to be measured, the overcharge protection performance can be easily measured by simply replacing the electrolyte and the additive.

In addition, according to the comparison method of the overcharge prevention performance of the additive for secondary batteries according to the present invention, the overcharge prevention performance can be easily compared by simply replacing various additives while using one test apparatus. Therefore, it is easy to find an additive that exhibits relatively good overcharge prevention performance.

FIG. 1 is a ten consecutive cyclic voltammetry curves obtained from an electrolyte prepared according to Example 1. FIG.
FIG. 2 is a ten consecutive cyclic voltammetry curves obtained from an electrolyte prepared according to Example 2. FIG.
FIG. 3 is a cyclic continuous cyclic voltammetry curve obtained from an electrolyte prepared according to Example 3. FIG.
FIG. 4 is a cyclic continuous cyclic voltammetry curve obtained from an electrolyte prepared according to Example 4. FIG.
FIG. 5 is a cyclic continuous cyclic voltammetry curve obtained from an electrolyte prepared according to Example 5. FIG.
Figure 6 shows the voltage in the electrolyte solution according to (a) Example 4, (b) Example 1, (c) Example 2, (d) Example 3, (e) Example 5 from 3 V to 5.5 V Impedance curve obtained at 5.0 V after applying successive cyclic voltages.
FIG. 7 shows voltages of 3 V to 5.5 V in the electrolyte according to (a) Example 4, (b) Example 1, (c) Example 2, and (d) Example 3 and (e) Example 5. The total resistance (Z _tot ) of the impedance curves obtained at 4.2 V, 4.6 V, 5.0 V, and 5.3 V after applying a series of cyclic voltages is shown.

Hereinafter, the present invention will be described more specifically.

Method for measuring the overcharge protection performance according to the present invention, forming a passivation layer (Passivation layer) on the electrode; And a method for measuring the impedance of the passivation film.

The electrode may be any electrode that can be used in the secondary battery, and may be, for example, at least one selected from the group consisting of carbon materials, metals, metal oxides, metalloids, and metalloid-containing alloys.

The passivation film is also referred to as a solid electrolyte interface (SEI) formed in the negative electrode active material, and as the charge and discharge proceed, the film becomes thicker and interferes with the movement of Li +.

The present invention proposes a method which can predict the overcharge prevention performance of an additive using such a passivation film without actually manufacturing a battery. That is, in an overcharge situation, the additive is oxidized to cause a polymerization reaction, and as a result, a passivation film is formed on the electrode surface.

Assuming this process, the passivation layer may be electrochemically formed in the electrode in the electrolyte, and the impedance of the passivation layer may be measured to determine that the passivation layer has a high resistance. That is, since the electrolyte or additive capable of forming a stable oxide film forms a high passivation film, the overcharge prevention performance of the secondary battery may be measured only by measuring the impedance after forming the passivation film. Therefore, by measuring the impedance by different additives under the same conditions, and comparing them, it is also possible to easily compare the relative overcharge protection performance of the various additives. In particular, when the battery is manufactured individually to measure the overcharge protection performance of the battery, it is possible to reduce the deviation that may occur according to the manufacture of the battery, it is possible to more accurately measure the overcharge protection effect of the battery, more excellent electrolyte or additive Development is easy.

The passivation film may be formed according to a method known in the art, and according to an embodiment of the present invention, the passivation film may be formed by a cyclic voltammetry, a constant voltage method, or a current method.

The electrode used in the present invention may be any negative electrode in the secondary battery.

An electrode is formed by apply | coating the active material slurry obtained by mixing and disperse | distributing an electrode active material, a binder, etc. to a solvent in the electrode collector, and drying and rolling it.

The negative electrode current collector may be a punching metal, an ex punching metal, a gold foil, a foamed metal, a reticulated metal fiber sintered body, a nickel foil, a copper foil, or the like.

The negative electrode active material is preferably capable of reversibly occluding and desorbing lithium ions, and a carbon-based material may be exemplified as the negative electrode active material. In addition, a material capable of alloying with lithium, and a composite material in which the metal material and the carbon-based material are mixed may also be exemplified as a negative electrode active material. Examples of the metal capable of alloying with lithium may include Al, Si, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, and Ge. These metals may be used alone or in combination or alloying.

Examples of the carbon-based material include natural graphite, artificial graphite, graphitized carbon fiber, graphitized mesocarbomicrobead (MCMB), graphitized mesoface pitch-based carbon fiber (MPCFF), fullerene, amorphous carbon, and the like. Can be.

As the solvent, a non-aqueous solvent or an aqueous solvent is used, and as the non-aqueous solvent, propylene carbonate, N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N, N-dimethylaminopropylamine, Ethylene oxide, tetrahydrofuran and the like can be used.

The method for measuring and comparing the overcharge prevention performance according to an embodiment of the present invention may be performed in a nonaqueous electrolyte containing (i) lithium salt, (ii) solvent, and (iii) additive at the same time. The lithium salt of the anion is ^{F -, Cl -, Br -} , I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF 4 -, ( ^{_{CF 3) 3 PF 3 -,}} (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 -, (FSO 2 _{^{) 2 N -, (CF 3}} SO 2) 2 N -, (CF 3 CF 2 SO 2) 2 N -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, (CF 3 SO 2 _{^{) 3 C -, CF 3 CO}} 2 -, CH 3 CO 2 - or SCN ^- a. The solvent is propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, ethyl propyl carbonate, methyl propyl carbonate, butylene carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane , Tetrahydrofuran, N-methyl-2-pyrrolidone, gamma butyrolactone or mixtures thereof.

The additive may be applied to any one used in a secondary battery for preventing overcharge.

In one embodiment of the present invention, the additive includes the compound represented by the following Formula 1 and Formula 2.

Formula 1

(In Formula 1, R1 to R8 are each independently, an alkyl group of -H, -F, -Cl, -Br, -I, -OH, -CN, -PO ₃ H ₂ , -NO ₂ , C1-C12 , C1-C12 aminoalkyl group, C1-C12 hydroxyalkyl group, C1-C12 haloalkyl group, C2-C12 alkenyl group, C1-C12 alkoxy group, C1-C12 alkylamino group, C1-C12 dialkyl Amino group, C6-C18 aryl group, C6-C18 aminoaryl group, C6-C18 hydroxyaryl group, C6-C18 haloaryl group, or C3-C8 cycloalkyl group.)

(2)

(In Formula 2, R9 to R12 are each independently, an alkyl group of -H, -F, -Cl, -Br, -I, -OH, -CN, -PO ₃ H ₂ , -NO ₂ , C1 ~ C12 , C1-C12 aminoalkyl group, C1-C12 hydroxyalkyl group, C1-C12 haloalkyl group, C2-C12 alkenyl group, C1-C12 alkoxy group, C1-C12 alkylamino group, C1-C12 dialkyl Amino group, C6-C18 aryl group, C6-C18 aminoaryl group, C6-C18 hydroxyaryl group, C6-C18 haloaryl group, or C3-C8 cycloalkyl group.)

In addition, R1 to R8 of Formula 1 are each independently a structure of the same formula (2).

The biphenyl or biphenyl derivative to be added to the electrolyte of the present invention is a compound which is oxidized above the operating voltage of the positive electrode, and the oxidation voltage (vs. Li / Li ⁺ ) is preferably 4.4 V or more, and more preferably 4.5 to 4.7. V range. Non-limiting examples of such biphenyl derivatives are biphenyl, o -terphenyl, p -terphenyl, biphenyl fluoride, biphenyl chloride, cyclohexylbiphenyl, methoxybiphenyl and the like. The content of the biphenyl derivative is not particularly limited, but is preferably in the range of 0.1 to 10 parts by weight per 100 parts by weight of the electrolyte. When the content of the biphenyl derivative is less than 0.1 parts by weight, the desired overcharge prevention effect is insignificant, and when it exceeds 10 parts by weight, battery performance may be deteriorated.

The oxidation voltage of the cyclohexylbenzene or benzene derivative to be added to the electrolyte of the present invention is preferably in the range of 4.6 to 5.0 V (vs. Li / Li ⁺ ) higher than that of the biphenyl derivative and lower than the oxidation voltage of the electrolyte. Non-limiting examples of the benzene derivatives include benzene, toluene, toluene fluoride, butylbenzene, amylbenzene, xylene, dibutylbenzene, trimethylbenzene, methoxybenzene, dimethoxybenzene, trimethoxybenzene, fluorodimethoxybenzene , Difluorodimethoxybenzene, bromodimethoxybenzene, dibromodimethoxybenzene, and the like. Compounds which can be oxidized in the aforementioned range to achieve similar mechanisms of action are also within the scope of the present invention. The content of the benzene derivative is not particularly limited, but is preferably in the range of 0.1 to 10 parts by weight per 100 parts by weight of the electrolyte. If the content of the benzene derivative is less than 0.1 parts by weight, the desired effect is insignificant, and if it exceeds 10 parts by weight, battery performance may be degraded.

The present invention will be described in more detail with reference to the following examples. However, the examples are only for illustrating the present invention and not for limiting the present invention.

Passivation  Confirmation of formation

<Example 1> Preparation electrolyte (0.15 M biphenyl and cyclohexylbenzene 0.05 M)

An electrolyte solution was prepared such that biphenyl 0.15 M and cyclohexylbenzene 0.05 M were added to the solution of 1 M LiClO ₄ dissolved in propylene carbonate. The glass carbon was used as the working electrode, and the passivation layer was formed by applying a cyclic voltage of 50 mV / sec from 3.0 V to 5.5 V using EG & G Princeton Applied Research model 273A Potentiostat instrument operated by M270 software. At this time, the formation of the passivation film can be seen from the cyclic voltammogram shown in FIG. Then, the impedance was measured at 4.2 V, 4.6 V, 5.0 V, 5.3 V using the Solartron SI 1255 HF frequency response analyzer operated with EG & G M398 EIS software. At this time, the AC amplitude was ± 5 mV (peak-to-peak), and the experiment was performed so that 10 points were recorded per decade between 100 kHz and 1 Hz. Impedance results were analyzed using EG & G ZSimpWin software, from which impedance values were obtained. Impedance measurement data is shown in FIGS. 6 and 7.

<Example 2> Preparation electrolyte (0.10 M biphenyl and cyclohexylbenzene 0.10 M)

Except that the electrolyte was prepared so that the biphenyl 0.10 M and cyclohexyl benzene 0.10 M as an additive, the same procedure as in Example 1 was carried out, the results are shown in Figures 2, 6 and 7.

<Example 3> Preparation electrolyte (0.05 M biphenyl and cyclohexylbenzene 0.15 M)

The same procedure as in Example 1 was performed except that an electrolyte solution was prepared such that the biphenyl was 0.05 M and the cyclohexylbenzene 0.15 M. The results are shown in FIGS. 3, 6 and 7.

<Example 4> Preparation electrolyte (biphenyl 0.20M)

The same procedure as in Example 1 was performed except that an electrolyte solution was prepared so that the biphenyl was 0.20M as an additive. The results are shown in FIGS. 4, 6 and 7.

<Example 5> Preparation electrolyte (cyclohexylbenzene 0.20 M)

The same procedure as in Example 1 was performed except that the electrolyte was prepared so that cyclohexylbenzene was 0.20 M as an additive. The results are shown in FIGS. 5, 6 and 7.

Passivation  Formation confirmation

4 and 5 show cyclic voltammetry curves when biphenyl and cyclohexylbenzene are used alone. Biphenyls begin to oxidize around 4.5 V and cyclohexylbenzenes oxidize around 4.7 V. As the voltage cycle is repeated, the peak current decreases in all cases, which means that the resistance of the film formed from the oxidative polymerization is gradually increased. Thus, it can be seen that a passivation film is formed at a voltage at which the peak current decreases.

1, 2, and 3 are cyclic voltammetry curves for an additive in which biphenyl and cyclohexylbenzene are mixed. In this case, the oxidative polymerization of biphenyl occurs first, followed by the oxidative polymerization of cyclohexylbenzene, which can be clearly seen from the fact that two peaks appear in FIG. 3. In this case, too, it can be seen that the peak current decreases as the voltage cycle is repeated, and the resistance of the film formed from the oxidation polymerization increases. Thus, it can be seen that the passivation film is formed.

Impedance Measurement and Battery Stability Evaluation

Experimental Example  One

Impedance experiments were performed on the passivation film made by cyclic voltammetry according to Examples 1 to 5.

In the electrolyte prepared according to Examples 1 to 5, each impedance obtained at 5.0 V after applying 10 consecutive cyclic voltages from 3 V to 5.5 V is shown in the graph of FIG. 6.

Experimental Example  2

In the electrolyte according to Examples 1 to 5, the voltage was applied 10 times from 3 V to 5.5 V, and then impedance was measured at 4.2 V, 4.6 V, 5.0 V, and 5.3 V, and the total resistance of the impedance curve ( Ztot) is shown graphically in FIG.

Referring to FIG. 7, impedance results are semi-circular or semi-elliptic, and Z _tot is obtained by intercepting the Zre axis from extrapolation of this curve. 6 and 7 show that the total resistance (Z _tot ) of the passivation film made from each additive varies depending on the voltage. Overall, the passivation film made of cyclohexylbenzene shows higher resistance than the passivation film made of biphenyl. Able to know. By the way, it can be seen that the maximum resistance is shown when the biphenyl 0.05 M and cyclohexyl benzene 0.15 M of Example 3 as an additive. That is, it can be seen from FIG. 6 and FIG. 7 that biphenyl and cyclohexyl benzene are used together as an additive at a higher ratio of 1: 3 than biphenyl or cyclohexyl benzene alone.

Therefore, it can be predicted from the results that the additive combination of Example 3 can constitute the safest cell. It was confirmed by configuring the actual battery as described below whether the prediction is correct.

Manufacture of batteries

<Example 6> Preparation of the battery (0.05 M biphenyl and cyclohexylbenzene 0.15 M)

A pouch cell of 760 mAh capacity consisting of a polyethylene film of about 25 mm mesocarbon microbead graphite, a cathode of about 10 mm LiCoO ₂ and a separator was prepared. Here, an electrolyte solution of Example 1 was prepared such that biphenyl 0.05 M and cyclohexylbenzene 0.15 M were used as additives. After charging and discharging from 3V to 4.2V, charging was carried out to 12V.

<Reference Example 1> Preparation of the battery (cyclohexylbenzene 0.20 M)

The same procedure as in Example 6 was performed except that the electrolyte solution was prepared so that cyclohexylbenzene was 0.20 M as an additive.

The cell using the additive combination of [biphenyl + cyclohexylbenzene], which was evaluated as the safest in Example 6, did not explode in the 12 V overcharge test, but showed a lower resistance in Reference Example 1, which is expected to be relatively unsafe. Cells using cyclohexylbenzene as an additive exploded in the 12 V overcharge test. That is, when the biphenyl and cyclohexyl benzene is used in combination of 1: 3 than when used alone, the overcharge prevention performance can be expected to be higher, and the same results can be obtained when the actual battery is manufactured and tested. It was.

It can be seen that the safety of the battery can be predicted simply by measuring the impedance according to the present invention. Therefore, it can be seen that the method for forming the passivation film and measuring the impedance of the passivation film according to the present invention is a method for measuring the overcharge prevention performance of the battery simply and effectively. Therefore, according to the present invention, it is possible to easily measure the overcharge protection performance without completely manufacturing the battery, and also can be measured by different additives only under the same conditions, so that the deviation of the measured value is less, more accurately the relative overcharge protection performance The value can be measured.

Therefore, the effect of easily comparing the overcharge prevention performance between the additives can also be obtained.

Claims (5)

Adding an additive for a secondary battery to the electrolyte;
Forming a passivation film on the electrode immersed in the electrolyte;
Measuring an impedance of the passivation film; And
Comparing the value of the impedance, the additive showing a relatively high impedance value is determined to form a stable passivation film to form a stable secondary battery; characterized in that the overcharge protection performance of the secondary battery additive Comparison method. The method of claim 1,
The passivation film is formed by a method selected from the group consisting of a cyclic voltammetry, a constant voltage method, and a constant current method. delete The method of claim 1,
Comparative method of the secondary battery additive overcharge prevention performance, characterized in that the additive for the secondary battery comprises a biphenyl derivative and a benzene derivative at the same time. delete

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