KR20180081009A - Method for detecting a low voltage defective secondary battery - Google Patents

Abstract

The present invention provides a method for detecting a low voltage defect of a secondary battery, capable of remarkably improving a detection ability on a low voltage defect caused by metal. The method for detecting a low voltage defect of a secondary battery includes a pre-aging step of manufacturing a battery by injecting an electrolyte after accommodating an electrode assembly in a battery container, and sealing the battery container; a formation step of charging the pre-aged battery at an initial stage under a voltage condition of 3.6 V or less; a primary aging step of aging the battery passing through the formation step at 60-70°C under 3.4 V to 3.6 V; a charging and discharging step of charging and discharging the primarily aged battery three times or more under 3.6 to 4.2 V; and a step of measuring a change in a voltage value while secondarily aging the charged and discharged battery.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a secondary battery low voltage defective secondary battery,

The present invention relates to a secondary battery low voltage fault detection method, and more particularly, to a secondary battery low voltage fault detection method in which a low voltage fault detection force is remarkably improved.

A phenomenon in which a battery that has been manufactured shows a voltage drop behavior over a self discharge rate is called a low voltage.

Among these low voltages, "metal induced low voltage deficiency" is a phenomenon in which metal foreign matter (Fe, Cu, etc.) in the anode is oxidized by the voltage during charge and discharge and grows as a dendrite in the cathode, resulting in internal short circuit ought.

This step of expression of "metal induced low voltage deficiency" is as follows.

The oxidation of the metal ions in the second step is carried out from the anode to the cathode through the electrolytic solution in the first step, , The reduction and growth of the metal ions as a result of the charge on the surface of the anode as the third step, and the shorting of the anode / cathode in the case where the metal grown to the last step is connected to the anode.

On the other hand, research on the detection method of undervoltage failure, which is detected by the voltage drop ratio during the activation process, is known as "failure due to metal induced low voltage" It is still required.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a method for detecting a secondary battery undervoltage failure in which the detection power against metal induced low voltage failure is remarkably improved.

However, the objects of the present invention are not limited to the above-mentioned objects, and other objects not mentioned can be clearly understood by those skilled in the art from the following description.

According to an aspect of the present invention, there is provided a method for detecting a secondary battery low voltage fault in the following embodiments.

The first embodiment includes a pre-aging step of accommodating an electrode assembly in a battery container, injecting an electrolyte solution and sealing the battery container to manufacture a battery;

Initially charging the pre-aged battery under a voltage condition of 3.6 V or less;

First aging the formed cell at a voltage of 3.4 V to 3.6 V and at 50 캜 to 70 캜;

Charging and discharging the primary-aged battery three or more times at a voltage of 3.6V to 4.2V; And

And measuring a change in a voltage value while the secondary battery is being charged / discharged, and a method of detecting a secondary battery undervoltage failure.

The second embodiment, in the first embodiment,

And the charging / discharging step is performed at 20 캜 to 40 캜.

The third embodiment is, in the first embodiment or the second embodiment,

Wherein the charging and discharging step supplies a current density of 0.5 C or more to accelerate the growth of the dendrite.

The fourth embodiment is, in any one of the first to third embodiments,

And the secondary aging step is performed at 20 캜 to 30 캜.

The fifth embodiment is, in any one of the first through fourth embodiments,

Measuring the voltage value at the start point of the secondary aging and measuring the voltage value at the end point of the secondary aging to determine whether the difference between the voltage value at the start point and the end point satisfies the reference value range And a method of detecting a secondary battery undervoltage failure.

The sixth embodiment is, in the fifth embodiment,

And determining that the difference between the voltage values is normal when the difference between the voltage values is less than or equal to the reference value range and determines that the difference is less than the reference value range.

According to the embodiment of the present invention, by promoting the dendrite growth of the metal foreign object through the charge / discharge cycle, it is possible to detect the type of defect which can not be detected by the rate of voltage drop during the normal activation process during the low voltage defect, Can be remarkably improved.

FIG. 1 is a schematic diagram showing a voltage change in steps of a method of detecting a low-voltage fault in a secondary battery according to an embodiment of the present invention.
FIG. 2 is a graph showing the results of measurement of the dOCV values of 20 secondary batteries (normal secondary batteries) and 20 secondary batteries (secondary charged secondary batteries) measured in the experiments of Examples 1 and 2 and Comparative Examples 1 and 2 Fig.

The present invention can be variously modified and may have various embodiments, and specific embodiments will be described in detail with reference to the drawings. It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Terms including ordinals, such as first, second, etc., may be used to describe various elements, but the elements are not limited to these terms. The terms are used only for the purpose of distinguishing one component from another.

Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the meaning in the context of the relevant art and are to be construed as ideal or overly formal in meaning unless explicitly defined in the present application Do not.

According to an aspect of the present invention, there is provided a method of detecting a low-

A pre-aging step of storing the electrode assembly in a battery container, injecting an electrolyte solution and sealing the battery container to manufacture a battery;

Initially charging the pre-aged battery under a voltage condition of 3.6 V or less;

First aging the formed cell at a voltage of 3.4 V to 3.6 V and at 50 캜 to 70 캜;

Charging and discharging the primary-aged battery three or more times at a voltage of 3.6V to 4.2V; And

And measuring a change in the voltage value while the secondary battery is being charged and discharged.

First, in the pre-aging step, the electrode assembly is prepared by interposing a separator between the anode and the cathode.

Specifically, an electrode assembly including an electrode active material and a binder is coated on an electrode current collector to prepare positive and negative electrodes, respectively, and then an electrode assembly is prepared between the positive and negative electrodes with a separator interposed therebetween.

After the prepared electrode assembly is housed in a battery container, an electrolyte is injected, and the battery container is sealed to manufacture a battery.

The step of producing such a battery is not particularly limited and can be carried out according to a known method.

The electrode assembly is not particularly limited as long as it includes a cathode, a cathode, and a separator interposed between the anode and the cathode. For example, the electrode assembly may be a jelly-roll type, a stack type or a stack / have.

The battery container is not particularly limited as long as it is used as a casing for packaging a battery, and a cylindrical, square or pouch type may be used.

The electrolyte includes an organic solvent and a lithium salt, and may further include an additive.

The organic solvent may be, for example, a cyclic carbonate, a linear carbonate, an ester, an ether, or a ketone, as long as the organic solvent can minimize decomposition due to an oxidation reaction or the like during the charge and discharge of the battery. These may be used alone or in combination of two or more.

Examples of the cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate (BC), and linear carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC) and ethyl propyl carbonate (EPC).

Wherein the lithium salt is selected from the group consisting of LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiBF ₄ , LiBF ₆ , LiSbF ₆ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiAlO ₄ , LiAlCl ₄ , LiSO ₃ CF ₃ , LiClO ₄ , and the like can be used without limitation, and they can be used singly or in combination of two or more.

In addition, the electrolyte solution may further contain an additive. For example, the additive may be vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, cyclic sulfite, saturated sulphone, But are not limited to, any one selected from the group consisting of unsaturated sulphones, unsaturated sulphones, noncyclic sulphones, lithium oxalyl difluoroborate (LiODFB), and derivatives thereof, or a mixture of two or more thereof.

Examples of the cyclic sulfite include ethylene sulfite, methyl ethylene sulfite, ethyl ethylene sulfite, 4,5-dimethylethylene sulfite, 4,5-diethyl ethylene sulfite, propylene sulfite, Diethyl propyl sulfite, 4,6-diethyl propyl sulfite, and 1,3-butylene glycol sulfite. The saturated sulphone includes, for example, 1,3-propane sultone, and 1,4-butane sultone. Examples of the unsaturated sultone include ethene sultone, 1,3-propene sultone, 1,4-butene sultone, Phenolsaltone, and the like. Examples of the non-cyclic sulfone include divinyl sulfone, dimethyl sulfone, diethyl sulfone, methyl ethyl sulfone, and methyl vinyl sulfone.

These additives are added to the electrolyte to improve the low-temperature power characteristics by forming a solid SEI film on the cathode, and to prevent decomposition of the anode surface, which may occur during high-temperature cycle operation, and to prevent oxidation reaction of the electrolyte.

When the battery case is pouch-shaped, an aluminum laminated pouch including an aluminum layer may be used. After the electrolytic solution is injected, the opened portion of the aluminum laminated pouch can be sealed by heat welding or heat sealing.

The cell is impregnated with the electrolytic solution injected in the pre-aging step.

More specifically, when the secondary battery is charged, the electrons move to the cathode through the lead wire and are charged. In order to achieve charge neutrality, the lithium ions are intercalated into the cathode. At this time, the lithium ion can be occluded at the site impregnated with the electrolyte, that is, at the wetting area where the movement path of the ions is maintained, but the occlusion is relatively difficult at the non-wetting area of the electrolyte.

Accordingly, the battery can be stored at room temperature and atmospheric pressure for 0.5 to 72 hours so that the electrolyte can penetrate the positive electrode and the negative electrode through the pre-aging step. For example, the pre-aging step may be performed at a temperature of, for example, 20 ° C to 30 ° C, specifically 22 ° C to 28 ° C, more specifically 23 ° C to 27 ° C, .

Next, the pre-aged battery is initially filled with a voltage of 3.6 V or less and formulated.

The charging-time voltage condition may be, for example, 3.4V to 3.6V.

The initial charging conditions at the posing step can be performed according to conditions known in the art, and can be performed by supplying a low current at a relatively low charging condition. Specifically, it can be performed by charging with a low-rate charging method and / or a low-rate charging method.

The forming step forms an SEI (solid electrolyte interface) layer, and sets the battery charge voltage within 3.6 V, which is the oxidation potential of a metal foreign substance in the anode, particularly a Fe-based metal foreign matter.

According to an embodiment of the present invention, when the additive is contained in the electrolyte solution as described above, it is possible to form a solid SEI layer on the surface of the electrode in the phase of the battery including the electrolyte additive for improving lifetime, It can be used to recover some damaged SEI layer in the charge / discharge step, thereby prolonging the lifetime.

The properties of the SEI layer depend on the type of the solvent contained in the electrolyte, the characteristics of the additives, etc., and are known to be one of the main factors affecting the performance of the battery by affecting ion and charge transfer.

According to one embodiment of the present invention, the initial charging in the forming step is performed by charging the battery such that the charging amount of the battery is, for example, about 30% to 70% of the design capacity at a current density of 0.1C to 0.5C can do.

Also, for example, the forming step may be carried out at a temperature of from 20 캜 to 30 캜, specifically from 22 캜 to 28 캜, more specifically from 23 캜 to 27 캜, and still more specifically from 25 캜 to 27 캜 .

Thereafter, the formed battery is subjected to primary aging at a voltage of 3.4 V to 3.6 V and at 50 캜 to 70 캜.

In the primary aging step, the SEI layer formed in the formation step can be further stabilized.

Particularly, in the present invention, such a first aging step is carried out at a high temperature of 50 캜 to 70 캜, specifically, 52 캜 to 68 캜, more specifically 55 캜 to 65 캜, Thereby increasing the possibility of growing the dendrite from the negative electrode in the subsequent charge / discharge step.

Next, the primary-aged battery is charged and discharged three times or more at a voltage of 3.6V to 4.2V.

In this charging and discharging step, it is possible to promote denitric growth through the supply of a constant high current density, for example, 0.5 C or more, or a current density of 1 C or more. As the current density increases, the amount of charge on the negative electrode increases, so that metal ions migrate to the negative electrode and precipitate into dendrites.

The charging and discharging step may be carried out at a temperature of from 20 to 40 캜, specifically from 22 to 38 캜, more specifically from 23 to 37 캜, and still more specifically from 25 to 35 캜. When the step of charging and discharging is performed at a low temperature, the metal ions mainly move in the direction of the cathode closest to the anode and do not diffuse in the other direction, which can be advantageous for dense dendrite growth.

That is, the charging / discharging cycle of three times or more allows the battery to be repeatedly charged and discharged three times or more in a voltage range of 3.6V to 4.2V to finally perform charging / discharging before secondary aging, which is the final aging step.

At each charge-discharge cycle, the battery can be charged with a constant current / constant voltage (CC-CV charging) until the battery reaches a preset voltage value. Here, CC-CV charging is a method of performing charging (CC charging) at a constant current value until reaching a predetermined voltage value, and then performing charging (CV charging) while maintaining the voltage value to be.

At this time, when the CC-CV is charged at a current density of 0.5 C or more in the charging process, the generation of dendrites due to locally lowering of the potential at the negative electrode can be promoted.

Next, the discharging step is a step of discharging the battery through the charging step. In the discharging step, discharge (CC discharging) at a constant current value can be performed until the battery reaches a predetermined voltage value.

Such charging and discharging processes are repeated three times or more, for example, three times to five times, or three times, so that the generation of dentrite can be repeatedly accelerated.

Next, the step of measuring the change of the voltage value while the secondary battery is charged and discharged. At this time, the change of the voltage value means a change value of OCV (open circuit voltage) over a predetermined time after the end of charge / discharge of the battery.

The secondary aging step is a step of further stabilizing the battery by maintaining the battery at a constant temperature and humidity before shipment charging.

The secondary aging step may be carried out at a temperature of, for example, 20 캜 to 30 캜, specifically 22 캜 to 28 캜, more specifically 23 캜 to 27 캜, and still more specifically, 25 캜 to 27 캜, The period may be suitably adjusted and may be, for example, 5 days or more, or 5 days to 10 days.

And the low voltage fault is detected through the step of measuring the change of the voltage value.

According to one embodiment of the present invention, the voltage value is measured at the start point of the secondary aging, and the voltage value at the end point where the secondary aging is completed is measured, and the change of the voltage value can be confirmed.

It may be judged whether or not the difference between the voltage values of the starting point and the ending point of the secondary aging satisfies a preset reference value range.

If the difference between the voltage values is less than or equal to the reference value range, the produced battery is determined to be normal, and if the difference between the voltage values is greater than the reference value range, the produced battery may be determined as defective.

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

Production Example 1 - Preparation of a secondary rechargeable battery (normal secondary battery)

96.7 parts by weight of Li [Ni _0.6 Mn _0.2 Co _0.2 ] O ₂ serving as a cathode active material, 1.3 parts by weight of graphite serving as a conductive agent and 2.0 parts by weight of polyvinylidene fluoride (PVdF) serving as a binder were mixed, To prepare a cathode mixture. The resulting cathode mixture was dispersed in 1-methyl-2-pyrrolidone serving as a solvent to prepare a cathode mixture slurry. The slurry was coated on both sides of an aluminum foil having a thickness of 20 mu m, dried, and pressed to prepare a positive electrode.

97.6 parts by weight of artificial graphite serving as a negative electrode active material and natural graphite (weight ratio: 90:10), 1.2 parts by weight of styrene-butadiene rubber (SBR) serving as a binder and 1.2 parts by weight of carboxymethyl cellulose (CMC) , An anode mix was prepared. This anode mix was dispersed in ion-exchange water functioning as a solvent to prepare an anode mix slurry. The slurry was coated on both sides of a copper foil having a thickness of 20 탆, dried and compressed to prepare a negative electrode.

LiPF ₆ was dissolved in an organic solvent mixed with ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) at a ratio of 3: 3: 4 (volume ratio) so as to have a concentration of 1.0 M to prepare a nonaqueous electrolytic solution .

A lithium secondary battery was prepared by stacking a separator of porous polyethylene interposed between the positive electrode and the negative electrode prepared above and storing the same in a pouch, and then injecting the electrolyte solution.

Production Example 2 - Production of foreign matter secondary battery

A lithium secondary battery was produced in the same manner as in Production Example 1, except that one foreign substance was charged in such a manner that one purity 99% Cu powder having a diameter of 100 占 퐉 was placed on the anode before injecting the electrolyte solution.

Example 1

Twenty batteries were prepared for each of the normal secondary battery of Production Example 1 and the foreign matter input secondary battery of Production Example 2 and the detection test of the secondary battery low voltage failure was conducted using these secondary batteries in accordance with the conditions shown in Fig. And,

Specifically, in the experiment for detecting the low-voltage fault, the pre-aging step and the forming step were carried out at 25 DEG C, and at this time, the forming step was charged to 3.6 V, then the first aging was performed at 60 DEG C, At a voltage of 3.6 V to 4.2 V at a current density of 0.5 C at 25 캜, and secondary aging was performed at 25 캜, which is the same temperature condition after completion of charging and discharging. At this time, the OCV (open circuit voltage) of the secondary battery and the OCV of the secondary battery after 7.5 days from the end of charging and discharging were measured at the elapsed time of 0.5 days after the completion of charging and discharging, and the dOCV values were compared.

Example 2

Discharge test was carried out in the same manner as in Example 1, except that the charge-discharge step was carried out three times at 25 DEG C and at a current density of 1C.

Comparative Example 1

Discharge test was carried out in the same manner as in Example 1, except that the charge-discharge step was carried out once at a current density of 1 C at 25 캜.

Comparative Example 2

A test for detecting a low-voltage fault was carried out in the same manner as in Example 1, except that primary aging was performed at 25 占 폚.

Evaluation of low voltage fault detection accuracy

The dOCV values of 20 secondary batteries (normal secondary batteries) measured in the experiments of Examples 1 and 2 and Comparative Examples 1 and 2 and 20 secondary batteries (secondary charged secondary batteries) were measured and shown in FIG. 2 .

Referring to FIG. 2, the left side portion (indicated by a black dot) and the right side portion (indicated by a red dot) are divided in each of Embodiments 1 and 2 and Comparative Examples 1 and 2, (DOCV), and the right part shows the measurement result of the voltage value change (dOCV) of 20 foreign-body-charged secondary batteries.

It was judged that a low voltage failure was caused when the dOCV value of 20 foreign substance-introducing secondary batteries of Production Example 2 exceeded the maximum dOCV value among 20 normal secondary batteries of Production Example 1. [

At this time, the detection accuracy of the undervoltage failure was calculated by the following formula, and the results are shown in Table 1 below.

Undervoltage Defect Detection Accuracy ( % ) = (The number of secondary batteries judged to be low voltage defective in the foreign matter input secondary battery) / (the total number of the foreign matter input secondary batteries (20)) X 100

Undervoltage Defect Detection Accuracy (%) Example 1 100 Example 2 100 Comparative Example 1 74 Comparative Example 2 94

Referring to Table 1, in the case of the method for detecting a secondary battery undervoltage failure according to Examples 1 and 2, the forming battery is first aged at a voltage of 3.4 V to 3.6 V and at 50 캜 to 70 캜, The first aged battery was charged and discharged at a voltage of 3.6 V to 4.2 V three times or more. As a result, it was found that the detection accuracy of the low voltage failure was remarkably higher than that of Comparative Examples 1 and 2.

As described above, preferred embodiments of the present invention have been disclosed in the present specification and drawings, and although specific terms have been used, they have been used only in a general sense to easily describe the technical contents of the present invention and to facilitate understanding of the invention , And are not intended to limit the scope of the present invention. It is to be understood by those skilled in the art that other modifications based on the technical idea of the present invention are possible in addition to the embodiments disclosed herein.

Claims (6)

A pre-aging step of storing the electrode assembly in a battery container, injecting an electrolyte solution and sealing the battery container to manufacture a battery;
Initially charging the pre-aged battery under a voltage condition of 3.6 V or less;
First aging the formed cell at a voltage of 3.4 V to 3.6 V and at 50 캜 to 70 캜;
Charging and discharging the primary-aged battery three or more times at a voltage of 3.6V to 4.2V; And
And measuring a change in a voltage value while the secondary battery is being charged / discharged. The method according to claim 1,
Wherein the step of charging and discharging is carried out at 20 캜 to 40 캜. The method according to claim 1,
Wherein the charging and discharging step supplies a current density of 0.5 C or more to promote dendrite growth. The method according to claim 1,
Wherein the secondary aging step is performed at 20 캜 to 30 캜. The method according to claim 1,
Measuring the voltage value at the start point of the secondary aging and measuring the voltage value at the end point of the secondary aging to determine whether the difference between the voltage values at the start point and the end point satisfies the reference value range And detecting a voltage drop in the secondary battery. 6. The method of claim 5,
And determining that the difference between the voltage values is normal when the difference between the voltage values is less than or equal to the reference value range and determines that the difference is not good when the difference between the voltage values is over the reference value range.

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