KR102574500B1 - Method for detecting a low voltage defective secondary battery - Google Patents

Abstract

pre-aging to prepare a battery by housing the electrode assembly in a battery container, injecting an electrolyte solution and sealing the battery container; Formation by initially charging the pre-aged battery under a voltage condition of 3.6V or less; primary aging of the formed battery at a voltage of 3.4V to 3.6V and 60° C. to 70° C.; charging and discharging the primary aged battery three or more times at a voltage of 3.6V to 4.2V; and measuring a change in voltage value while performing secondary aging of the charged/discharged battery.

Description

Method for detecting a low voltage defective secondary battery {Method for detecting a low voltage defective secondary battery}

The present invention relates to a method for detecting a low-voltage defect in a secondary battery, and more particularly, to a method for detecting a low-voltage defect in a secondary battery with remarkably improved low-voltage defect detection capability.

A phenomenon in which a battery that has been manufactured exhibits a voltage drop behavior higher than the self-discharge rate is called low voltage.

Among these low voltages, "metal-caused low voltage defects" are known to be caused by metal foreign substances (Fe, Cu, etc.) in the anode being oxidized by the voltage during charging and discharging and growing into dendrites at the cathode, resulting in an internal short circuit. are losing

The stage of occurrence of such "metal-caused low-voltage defect" is as follows.

In the first step, metal foreign substances (Cu, Cu/Zn, Fe, Fe/Cr are mainly found) on the surface or inside of the anode are oxidized), and in the second step, the oxidized metal ions are transferred from the anode to the cathode through the electrolyte. In the third step, reduction and growth of metal ions as a result of receiving charge from the surface of the cathode, and finally, in the fourth step, when the grown metal continues to the anode, it is expressed by a short circuit inside the anode/cathode.

On the other hand, "metal-caused low-voltage defects" are detected by the voltage drop rate during the activation process, but there are still types of defects that cannot be detected during the process, so research on a method for detecting low-voltage defects with improved detection power is needed. It is still in demand.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and to provide a method for detecting a low voltage defect of a secondary battery with remarkably improved detection ability for a metal-caused low voltage defect.

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

In order to achieve the above object, according to an aspect of the present invention, a method for detecting a low voltage defect in a secondary battery according to the following embodiment is provided.

The first embodiment includes the steps of pre-aging to prepare a battery by housing the electrode assembly in a battery container, injecting an electrolyte solution and sealing the battery container;

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

primary aging of the formed battery at a voltage of 3.4V to 3.6V and 50° C. to 70° C.;

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

It relates to a method for detecting a low voltage defect of a secondary battery, comprising: measuring a change in voltage value while secondary aging the charged/discharged battery.

In the second embodiment, in the first embodiment,

A method for detecting a low voltage defect in a secondary battery in which the charging and discharging step is performed at 20° C. to 40° C.

In the third embodiment, in the first embodiment or the second embodiment,

A method for detecting a low voltage defect in a secondary battery in which the charging and discharging step promotes dendrite growth by supplying a current density of 0.5C or more.

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

A method for detecting a low voltage defect in a secondary battery in which the secondary aging is performed at 20° C. to 30° C.

In the fifth embodiment, in any one of the first to fourth embodiments,

The step of measuring the change in voltage value measures the voltage value at the start point of the secondary aging and measures the voltage value at the end point of the secondary aging, and determines whether the difference between the voltage values at the start point and the end point satisfies a reference value range. It relates to a method for detecting a secondary battery low voltage defect comprising the step of doing.

In the sixth embodiment, in the fifth embodiment,

A method for detecting a low voltage defect in a secondary battery is determined to be normal when the difference between the voltage values is less than or equal to a reference value range, and judged to be defective when the difference between the voltage values is greater than the reference value range.

According to an embodiment of the present invention, by promoting dendrite growth of metal foreign matter through charge and discharge cycles, it is possible to detect the type of defect that is not detected by the voltage drop rate during a general activation process among low voltage defects, resulting in metal-caused low voltage defects. detection ability can be significantly improved.

1 is a schematic diagram illustrating step-by-step voltage changes in a method for detecting a low voltage defect of a secondary battery according to an embodiment of the present invention.
2 is a result of measuring dOCV values of 20 secondary batteries (normal secondary batteries) of Preparation Example 1 and 20 secondary batteries (secondary batteries injected with foreign matter) of Preparation Example 2 measured in the experiments of Examples 1 and 2 and Comparative Examples 1 and 2 is a graph showing

Since the present invention can have various changes and various embodiments, it will be described in detail by exemplifying specific embodiments in the drawings. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents, or substitutes included in the spirit and technical scope of the present invention.

Terms including ordinal numbers, such as first and second, may be used to describe various components, but the components are not limited by the terms. These terms are only used for the purpose of distinguishing one component from another.

Unless defined otherwise, 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 the present invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related art, and unless explicitly defined in the present application, it should not be interpreted in an ideal or excessively formal meaning. don't

A method for detecting a low voltage defect of a secondary battery according to an aspect of the present invention,

pre-aging to prepare a battery by housing the electrode assembly in a battery container, injecting an electrolyte solution and sealing the battery container;

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

primary aging of the formed battery at a voltage of 3.4V to 3.6V and 50° C. to 70° C.;

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 voltage value while secondary aging the charged/discharged battery.

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

Specifically, an electrode mixture containing an electrode active material and a binder is applied to an electrode current collector to prepare a positive electrode and a negative electrode, respectively, and then an electrode assembly is prepared by interposing a separator between the positive electrode and the negative electrode.

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

A step of preparing such a battery is not particularly limited and can be performed according to a known method.

In addition, the electrode assembly is not particularly limited as long as it has a structure including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and may be, for example, a jelly-roll type, stacked, or stacked/folded structure. there is.

The battery container is not particularly limited as long as it is used as an exterior material for packaging a battery, and a cylindrical, prismatic or pouch type may be used.

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

The organic solvent is not limited as long as decomposition due to an oxidation reaction or the like can be minimized during the charge/discharge process of the battery, and may be, for example, a cyclic carbonate, a linear carbonate, an ester, an ether, or a ketone. These may be used alone, or two or more may be used in combination.

Among the organic solvents, carbonate-based organic solvents may be preferably used. Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate (BC), and examples of linear carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethylmethyl carbonate (EMC), methylpropyl carbonate (MPC) and ethylpropyl carbonate (EPC) are representative.

The lithium salt is 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 , Lithium salts commonly used in electrolytes of lithium secondary batteries, such as LiSO ₃ CF ₃ and LiClO ₄ , may be used without limitation, and these may be used alone or in combination of two or more.

In addition, the electrolyte solution may optionally further contain additives. For example, as the additives, in order to stably form an SEI film, vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, cyclic sulfite, saturated sultone, Any one selected from the group consisting of unsaturated sultone, acyclic sulfone, lithium oxalyldifluoroborate (LiODFB), and derivatives thereof, or a mixture of two or more thereof may be used, but is not limited thereto.

Examples of the cyclic sulfite include ethylene sulfite, methyl ethylene sulfite, ethyl ethylene sulfite, 4,5-dimethyl ethylene sulfite, 4,5-diethyl ethylene sulfite, propylene sulfite, and 4,5-dimethyl propylene sulfite. pyrite, 4,5-diethyl propylene sulfite, 4,6-dimethyl propylene sulfite, 4,6-diethyl propylene sulfite, 1,3-butylene glycol sulfite, and the like, and saturated sultones include 1,3-propane sultone, 1,4-butane sultone, and the like, and unsaturated sultones include ethene sultone, 1,3-propene sultone, 1,4-butene sultone, 1-methyl-1,3-propene sultone, phensultone and the like, and examples of the acyclic sulfone include divinyl sulfone, dimethyl sulfone, diethyl sulfone, methylethyl sulfone, methylvinyl sulfone and the like.

These additives are added to the electrolyte to improve low-temperature output characteristics by forming a robust SEI film on the negative electrode, as well as to suppress decomposition of the surface of the positive electrode that may occur during high-temperature cycle operation and to prevent oxidation of the electrolyte.

When the battery case is of a pouch type, an aluminum laminated pouch including an aluminum layer may be used. After the electrolyte solution is injected, the opened portion of the aluminum laminated pouch may be sealed by heat welding or heat fusion.

Wetting of the battery with the electrolyte solution injected in the pre-aging step is performed.

More specifically, when the secondary battery is charged by moving electrons along a wire to the negative electrode during charging, lithium ions are intercalated in the negative electrode to achieve charge neutrality. At this time, lithium ions can be occluded in an electrolyte-impregnated area, that is, in a wetting area where the ion movement path is maintained, but occlusion becomes relatively difficult in a non-wetting area.

Therefore, through the pre-aging step, the battery may be stored for 0.5 to 72 hours at room temperature and normal pressure so that the electrolyte can permeate well into the positive electrode and the negative electrode. For example, the pre-aging step is, for example, 20 ° C to 30 ° C, specifically 22 ° C to 28 ° C, more specifically 23 ° C to 27 ° C, still more specifically at 25 ° C to 27 ° C can be carried out.

Next, formation is performed by initially charging the pre-aged battery under a voltage condition of 3.6V or less.

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

Initial charging conditions in the forming step may be performed according to conditions known in the art, and may be performed by supplying a low current under relatively low charging conditions. Specifically, it may be performed by charging under low charging conditions of a slow charging method and/or a multi-step charging method.

The formation step forms a solid electrolyte interface (SEI) layer, and sets the battery charging voltage within 3.6V, which is the oxidation potential of metal foreign substances in the positive electrode, in particular, Fe-based metal foreign substances.

According to one embodiment of the present invention, as described above, when an additive is included in the electrolyte, in particular, a solid SEI layer is formed on the surface of the electrode in the formation step of the battery including the electrolyte additive for improving lifespan, or after repeated By being used to restore a part of the damaged SEI layer in the charge and discharge step, the effect of extending the lifespan can be shown.

The properties of the SEI layer vary depending on the type of solvent or additives contained in the electrolyte, and is known as one of the main factors that affect the movement of ions and charges, resulting in changes in battery performance.

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

Also, for example, the forming step may be carried out at 20 ° C to 30 ° C, specifically 22 ° C to 28 ° C, more specifically 23 ° C to 27 ° C, and even more specifically 25 ° C to 27 ° C. .

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

In the first aging step, the SEI layer formed in the formation step may be further stabilized.

In particular, in the present invention, the first aging step is performed at a high temperature of 50 ° C to 70 ° C, specifically 52 ° C to 68 ° C, more specifically 55 ° C to 65 ° C, such that Fe, Cu, etc. present in the anode It is possible to obtain an effect of increasing the possibility of growing dendrites in the negative electrode in the subsequent charging and discharging step by accelerating the oxidation of the metal foreign matter.

Next, a step of charging and discharging the primary aged battery three or more times at a voltage of 3.6V to 4.2V.

In this charge/discharge step, dendrite growth may be promoted by continuously supplying a high current density, for example, 0.5C or more, or 1C or more. The higher the current density, the greater the amount of charge on the negative electrode, so that metal ions can move to the negative electrode and be deposited as dendrites at the same time.

In addition, the charging and discharging step may be carried out at 20°C to 40°C, specifically 22°C to 38°C, more specifically 23°C to 37°C, and more specifically 25°C to 35°C. When the charging and discharging step is performed at a low temperature, metal ions mainly move toward the cathode closest to the anode and do not spread and diffuse in other directions, which may be advantageous for dense dendrite growth.

That is, in the three or more charge/discharge cycle steps, charging and discharging of the battery is repeated three or more times in a voltage range of 3.6V to 4.2V, so that charge/discharge can be finally performed before secondary aging, which is the final aging step.

In each charge/discharge cycle step, constant current/constant voltage charging (CC-CV charging) may be performed on the battery until the battery reaches a preset voltage value. Here, CC-CV charging is a method in which charging at a constant current value (CC charging) is performed until a predetermined voltage value is reached, and then charging (CV charging) is additionally performed while maintaining the voltage value. am.

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

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

By repeating the charging process and the discharging process three or more times, for example, three to five times, or three times, the generation of dentrite can be repeatedly accelerated.

Next, a step of measuring a change in voltage value while secondary aging the charged and discharged battery. At this time, the change in the voltage value means a change in OCV (open circuit voltage) for a predetermined time after the end of charging and discharging of the battery.

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

The secondary aging step may be carried out at, for example, 20 ° C to 30 ° C, specifically 22 ° C to 28 ° C, more specifically 23 ° C to 27 ° C, and even more specifically 25 ° C to 27 ° C, The period may be appropriately adjusted, and may be, for example, 5 days or more, or 5 to 10 days.

A low voltage defect is detected through the step of measuring the change in the voltage value.

According to an embodiment of the present invention, it is possible to check a change in the voltage value by measuring a voltage value at a starting point where the secondary aging starts and measuring a voltage value at an end point where the secondary aging is completed.

A step of determining whether the difference between the voltage values at the start point and the end point of the secondary aging satisfies a preset reference value range may be performed.

When the voltage difference is less than the reference value range, the produced battery may be determined to be normal, and when the voltage difference exceeds the reference value range, the produced battery may be determined to be defective.

Hereinafter, examples will be described in detail to aid understanding of the present invention. However, the embodiments according to the present invention can be modified in many different forms, and the scope of the present invention should not be construed as being limited to the following examples. Embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

Preparation Example 1 - Preparation of a secondary battery (normal secondary battery) without introduction of foreign substances

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

97.6 parts by weight of artificial graphite and natural graphite (weight ratio: 90:10) functioning as negative electrode active materials, 1.2 parts by weight of styrene-butadiene rubber (SBR) functioning as a binder, and 1.2 parts by weight of carboxymethyl cellulose (CMC) were mixed. , an anode mixture was prepared. An anode mixture slurry was prepared by dispersing the anode mixture in ion-exchanged water serving as a solvent. This slurry was coated on both sides of a copper foil having a thickness of 20 μm, dried, and pressed to prepare a negative electrode.

LiPF ₆ was dissolved in an organic solvent in which ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were mixed in a composition of 3:3:4 (volume ratio) to a concentration of 1.0 M to obtain a non-aqueous electrolyte solution. manufactured.

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

Preparation Example 2 - Preparation of secondary battery injected with foreign matter

A lithium secondary battery was manufactured in the same manner as in Preparation Example 1, except that a foreign material was added by placing one 99% pure Cu powder having a diameter of 100 μm on the cathode before injecting the electrolyte.

Example 1

20 normal secondary batteries of Production Example 1 and 20 secondary batteries injected with foreign substances of Production Example 2 were prepared, and under the conditions shown in FIG. 1, a secondary battery low-voltage defect detection experiment was conducted using these secondary batteries did,

Specifically, in the detection experiment of the low voltage defect, the pre-aging step and the formation step were performed at 25 ° C. At this time, the formation step was charged up to 3.6V, and then the primary aging was performed at 60 ° C., and the charge and discharge step It was performed three times at a voltage of 3.6V to 4.2V at a current density of 0.5C at 25°C, and after charging and discharging was completed, secondary aging was performed at the same temperature condition, 25°C. At this time, the dOCV values were compared by measuring the OCV (open circuit voltage) of the secondary battery at 0.5 days after the end of charging and discharging and the OCV of the secondary battery at 7.5 days after the end of charging and discharging.

Example 2

A low-voltage defect detection experiment was performed in the same manner as in Example 1, except that the charging and discharging steps were performed three times at a current density of 1 C at 25 ° C.

Comparative Example 1

A low voltage defect detection experiment was performed in the same manner as in Example 1, except that the charging and discharging step was performed once at 25° C. and a current density of 1 C.

Comparative Example 2

A low-voltage defect detection experiment was conducted in the same manner as in Example 1, except that the primary aging was performed at 25° C.

Evaluation of low voltage defect detection accuracy

In the experiments of Examples 1 and 2 and Comparative Examples 1 and 2, the dOCV values of 20 secondary batteries (normal secondary batteries) of Preparation Example 1 and 20 secondary batteries (secondary batteries injected with foreign substances) of Preparation Example 2 were measured and shown in FIG. was

Referring to FIG. 2, each of Examples 1 and 2 and Comparative Examples 1 and 2 is divided into a left part (indicated by a black dot) and a right part (indicated by a red dot), and the left part has a voltage value of 20 normal secondary batteries. The right part shows the measurement result of change (dOCV), and the right part shows the measurement result of voltage value change (dOCV) of 20 foreign matter injected secondary batteries.

When the dOCV values of 20 foreign substance-injected secondary batteries of Preparation Example 2 exceeded the maximum dOCV value among 20 normal secondary batteries of Preparation Example 1, it was judged as a low voltage defect.

At this time, the low voltage defect detection accuracy was calculated by the following formula, and the results are shown in Table 1 below.

Low voltage defect detection accuracy ( % ) = (Number of secondary batteries judged to be low-voltage defective among secondary batteries injected with foreign matter)/(Total number of secondary batteries injected with foreign matter (20)) X 100

Low voltage 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 secondary battery low voltage detection method according to Examples 1 and 2, the steps of primary aging the formed battery at a voltage of 3.4V to 3.6V and 50 ° C to 70 ° C. As a result of charging and discharging the primary aged battery three or more times at a voltage of 3.6V to 4.2V, it was found that the low voltage defect detection accuracy was remarkably high compared to 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 are only used in a general sense to easily explain the technical content of the present invention and help understanding of the present invention. However, it is not intended to limit the scope of the present invention. It is obvious to those skilled in the art that other modified examples based on the technical spirit of the present invention can be implemented in addition to the embodiments disclosed herein.

Claims (6)

pre-aging to prepare a battery by housing the electrode assembly in a battery container, injecting an electrolyte solution and sealing the battery container;
Formation by initially charging the pre-aged battery under a voltage condition of 3.6V or less;
primary aging of the formed battery at a voltage of 3.4V to 3.6V and 50° C. to 70° C.;
A step of charging and discharging the primary aged battery three or more times at a voltage of 3.6 V to 4.2 V, wherein the charging and discharging step is performed at 20 ° C to 40 ° C, and a current density of 0.5 C or more is supplied to grow dendrites charging and discharging to promote; and
While the charged and discharged battery is subjected to secondary aging at 20° C. to 30° C., a voltage value is measured at the start point of the secondary aging, and a voltage value is measured at the end point of the secondary aging, and the voltage value is measured at the start point and end point of the battery. Finding the difference between; and
When the difference between the voltage value at the start point and the end point of the battery is less than the reference value range, the battery is determined to be normal, and when the voltage difference between the start point and the end point of the battery exceeds the reference value range, the battery is judged to be defective. Step; including,
The reference value means the difference between the voltage value at the starting point and the ending point of the foreign matter injection battery,
The difference between the voltage values at the start and end points of the foreign matter injection battery,
A step of pre-aging to manufacture a foreign material injected battery by placing the electrode assembly in a battery container, injecting metal powder onto the positive electrode of the electrode assembly, injecting an electrolyte solution, and sealing the battery container;
Formation by initially charging the pre-aged foreign matter injected battery under a voltage condition of 3.6V or less;
primary aging of the formed foreign matter input battery at a voltage of 3.4V to 3.6V and 50° C. to 70° C.;
A step of charging and discharging the primary aged foreign matter injected battery three or more times at a voltage of 3.6 V to 4.2 V, wherein the charging and discharging step is performed at 20 ° C to 40 ° C, and a current density of 0.5 C or more is supplied to charging and discharging to promote dry matter growth; and
While the charged and discharged foreign matter injected battery is subjected to secondary aging at 20 ° C to 30 ° C, a voltage value is measured at the start point of the secondary aging, and a voltage value is measured at the end point of the secondary aging. A method of detecting a low voltage defect of a secondary battery obtained by a method comprising: obtaining a difference between voltage values of endpoints. delete delete delete delete delete