Secondary battery internal pressure measurement method

In order to more accurately measure internal pressure of a secondary battery, the present disclosure provides a measurement method including (a) interposing the secondary battery between an upper plate and a lower plate, (b) increasing internal pressure of the secondary battery by injecting a gas into the inside of the secondary battery, (c) monitoring surface pressure of the secondary battery at a measuring member which is in contact with the lower plate, and (d) measuring a value of the surface pressure from the measuring member at a point in time when at least one sealing portion of the secondary battery is vented.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority under 35 U.S.C. § 119(a) to Korean patent application number 10-2022-0072167 filed on Jun. 14, 2022, in the Korean Intellectual Property Office, the entire disclosure of which is incorporated by reference herein.

BACKGROUND

1. Technical Field

The present disclosure relates to a method of measuring internal pressure of a secondary battery that is able to more accurately measure the internal pressure of the secondary battery.

2. Related Art

Secondary batteries are rechargeable batteries and are used in mobile phones, laptops, digital cameras, electric vehicles, etc. Lithium secondary batteries, which are the most used among secondary batteries, have the advantages of high operating voltage and large energy density.

However, the lithium secondary batteries have heat generation issues caused by internal short circuit, overcharge and overdischarge, etc. In addition, the lithium secondary batteries have various issues that threaten stability such as electrolyte decomposition, thermal runaway, etc.

In particular, explosion of the lithium secondary battery may occur due to decomposition of electrolyte and an increase in gas pressure inside the secondary battery. Specifically, during repeated charging and discharging of the lithium secondary battery, gas is generated due to the electrochemical reaction between the electrolyte and an electrode active material. The generated gas increases the internal pressure of the lithium secondary battery, causing issues such as electrode deformation, internal short circuit, explosion, etc.

In order to solve the stability issues of the lithium secondary batteries, it is required to measure the internal pressure that an external material accommodating the electrode assembly can withstand. Currently, as a method of measuring the internal pressure, after continuously injecting a gas inside the external material, the maximum pressure of the injected gas at the time when a sealing portion of the external material is vented is determined as the internal pressure of the secondary battery.

However, in the process of measuring the internal pressure of the secondary battery, an issue may occur in which the pressure of the injected gas is lost by a minute leak or the like. Due to this, there was a limitation in the method of indirectly measuring the internal pressure of the secondary battery through the pressure of the injected gas.

Therefore, in order to solve the stability issues of the lithium secondary battery, a method that is able to measure the internal pressure of the secondary battery more precisely is required.

SUMMARY

Embodiments provide a method of measuring internal pressure of a secondary battery in which a measuring member capable of measuring surface pressure of the secondary battery is introduced in order to more accurately measure the internal pressure of the secondary battery.

In accordance with an aspect of the present disclosure, there is provided a measurement method including (a) interposing a secondary battery between an upper plate and a lower plate, (b) increasing internal pressure of the secondary battery by injecting a gas into the inside of the secondary battery, (c) monitoring surface pressure of the secondary battery at a measuring member which is in contact with the lower plate, and (d) measuring a value of the surface pressure from the measuring member at a time in time when at least one sealing portion of the secondary battery is vented.

In accordance with an embodiment, the secondary battery may include an electrode assembly and an external material for accommodating the electrode assembly.

In accordance with an embodiment, the external material may include a first area for accommodating the electrode assembly and a second area including a space in which the gas is injected.

In accordance with an embodiment, the upper plate and the lower plate in step (a) may fix the first area.

In accordance with an embodiment, the gas in step (b) may be injected at a predetermined time interval.

In accordance with an embodiment, the gas in step (b) may be injected through a hole formed in the second area.

In accordance with an embodiment, the internal pressure in step (b) may be pressure of the gas injected into the secondary battery.

In accordance with an embodiment, the internal pressure in step (b) may be increased using a regulator.

In accordance with an embodiment, step (b) may further include monitoring the internal pressure of the secondary battery.

In accordance with an embodiment, the measuring member in step (c) may be in contact with a bottom surface of the lower plate.

In accordance with an embodiment, the measuring member in step (c) may be a load cell.

In accordance with an embodiment, the surface pressure in step (c) may be a value monitored in a pressure display unit indicating pressure applied to the measuring member.

In accordance with an embodiment, step (c) may further include comparing a value of the internal pressure of the secondary battery and a value of the surface pressure of the secondary battery.

In accordance with an embodiment, the sealing portion in step (d) may be formed on an outer periphery where an electrode tab is present.

In accordance with an embodiment, step (d) may further include calculating the value of the surface pressure as a value of the maximum internal pressure of the secondary battery

A measurement method according to the present disclosure introduces a measuring member capable of measuring the surface pressure of the secondary battery, thereby having an effect of directly measuring the internal pressure of the secondary battery.

In addition, the measurement method according to the present disclosure directly measures the internal pressure of the secondary battery, thereby having an effect of accurately measuring the internal pressure of the secondary battery.

In addition, the measurement method according to the present disclosure measures the pressure of the gas injected into the secondary battery and at the same time measures the surface pressure of the secondary battery, thereby having the effect of accurately measuring the internal pressure of the secondary battery even if a pressure loss of the gas injected into the secondary battery occurs.

In addition, the measurement method according to the present disclosure compares the pressure of the gas injected into the secondary battery with the surface pressure of the secondary battery in real time, thereby having the effect of predicting the error range of the internal pressure measurement result of the secondary battery generated according to the pressure of the gas.

DETAILED DESCRIPTION

The specific structural or functional description disclosed herein is merely illustrative for the purpose of describing embodiments according to the concept of the present disclosure. The embodiments according to the concept of the present disclosure can be implemented in various forms in addition to the embodiments disclosed in this specification or application. In addition, the technical idea of the present disclosure is not construed as limited to the embodiments disclosed in this specification or application.

A measurement method according to the present disclosure includes (a) interposing a secondary battery between an upper plate and a lower plate, (b) increasing internal pressure of the secondary battery by injecting a gas into the inside of the secondary battery, (c) monitoring surface pressure of the secondary battery at a measuring member which is in contact with the lower plate, and (d) measuring a value of the surface pressure from the measuring member at a point in time when at least one sealing portion of the secondary battery is vented.

FIG.1schematically illustrates a flowchart for a method of measuring internal pressure of a secondary battery in accordance with an embodiment of the present disclosure, andFIG.2schematically illustrates a secondary battery structure interposed between an upper plate and a lower plate.

Referring toFIGS.1and2, the method of measuring the internal pressure of the secondary battery includes step S10of interposing the secondary battery. In step S10, a secondary battery100is interposed between an upper plate200and a lower plate300. The upper plate200and the lower plate300may have a disk shape with a specific thickness. The upper plate200may be in contact with one surface of the secondary battery100. The lower plate300may be in contact with the other surface of the secondary battery100. The secondary battery100seated on the lower plate300may be in the form that the upper plate200covers its other surface. The width of the upper plate200and the lower plate300may be the same as or different from the width of the secondary battery100in contact therewith, and the secondary battery100may be altered to different sizes as long as the secondary battery100does not depart or significantly deviate from the placement in which the secondary battery100was originally interposed. The upper plate200and the lower plate300may be fixed by a fastening means, but is not limited thereto.

The secondary battery100may include an electrode assembly10and an external material20for accommodating the electrode assembly10.

The electrode assembly10may include a structure in which a cathode, an anode, and a separator interposed between the cathode and the anode are stacked. The cathode may include a cathode active material into which Lithium (Li) ions can be inserted and detached, and the anode may include an anode active material into which Lithium (Li) ions can be absorbed and detached. In addition, the cathode and the anode may further include binders and conductive materials in each of the cathode and anode active materials for improving mechanical stability and electrical conductivity. A separator may be configured to prevent electrical short circuits between the cathode and the anode and to generate the flow of ions. The type of the separator is not particularly limited, but may include a porous polymer film. The electrode assembly10may be manufactured by a stacking or zigzag stacking method by alternately stacking a plurality of cathodes and anodes and interposing separators between cathodes and anodes.

An external material20serves to protect the electrode assembly10from the external environment. The external material20may include a water-resistant resin and may be in the form of a film in which a polyolefin-based resin, a metal, a nylon resin and a polyterephthalate resin are laminated.

The external material20may include a first area21for accommodating the electrode assembly10and a second area22including a space in which a gas is injected. In addition, the upper plate200and the lower plate300may fix the first area21. The upper plate200and the lower plate300may compress so that the first area21accommodating the electrode assembly10does not inflate by the injection of the gas. As the first area21is compressed, the second area22is inflated by the injection of the gas, and the internal pressure of the secondary battery100increases as the injection amount of the gas increases, thereby the sealing portion of the secondary battery100may be vented.

FIG.3schematically illustrates a form in which the internal pressure of the secondary battery is increased by injecting the gas into the inside of the secondary battery.

Referring toFIGS.1and3, the method of measuring the internal pressure of the secondary battery includes step S20of increasing the internal pressure of the secondary battery. In step S20, the gas is injected into the inside of the secondary battery100, thereby increasing internal pressure p of the secondary battery100. The type of the gas injected into the inside of the secondary battery100is not particularly limited. In addition to the gas generated by the electrochemical reaction between the electrolyte and the electrode active material during repeated charging and discharging of the secondary battery100, carbon monoxide, carbon dioxide, hydrogen, dry air, nitrogen, and the like may be used to measure the internal pressure of the secondary battery. The gas may be injected through holes22-3formed in the second area22. The second area22may include a gas pocket area22-1capable of accommodating the gas injected through the hole22-3and other areas22-2, and the hole22-3may be formed using a needle on the gas pocket area22-1.

The internal pressure p of the secondary battery100may be the pressure of the gas injected into the secondary battery. The internal pressure p of the secondary battery100may be increased using a regulator T2. In addition, the gas may be injected into the inside of the secondary battery100using the regulator T2at a predetermined time interval. The regulator T2is in communication with a gas injection unit T1and a gas exhaust unit T3, so that the internal pressure p of the secondary battery100may be constantly increased to a desired level. The gas regulated by the regulator T2may be injected into the inside of the secondary battery100through a gas injection pathway h communicating with the gas exhaust unit T3and the hole22-3.

In step S20, the internal pressure p of the secondary battery100may be monitored. The internal pressure p of the secondary battery100may be indirectly monitored through the pressure of the gas injected into the inside of the secondary battery100. The pressure of the gas injected into the inside of the secondary battery100may be monitored using the regulator T2. By monitoring the internal pressure p of the secondary battery100in real time, a value of the internal pressure at the point in time when at least one sealing portion of the secondary battery100is vented may be indirectly measured.

FIG.4schematically illustrates a structure of a measuring member for monitoring the surface pressure of the secondary battery.

Referring toFIGS.1,3and4, a method of measuring the internal pressure of the secondary battery includes step S30of monitoring the surface pressure of the secondary battery. In step S30, the surface pressure q of the secondary battery100is monitored at the measuring member400which is in contact with the lower plate300. The measuring member400may be in contact with the bottom surface310of the lower plate. The internal pressure p of the secondary battery100may be transmitted to the measuring member400through the lower plate300, and the surface pressure q of the secondary battery100may be measured at the measuring member400, to monitor a change in the internal pressure p of the secondary battery100in real time.

The surface pressure q of the secondary battery100may be a value monitored by the pressure display unit indicating the pressure applied to the measuring member400. The measuring member400is not particularly limited as long as it is a device for measuring the surface pressure q of the secondary battery100, but may preferably be a load cell. The load cell may measure the value of the surface pressure q of the secondary battery100generated as the secondary battery100is inflated by the injection of the gas, and may output the value as an electrical signal at the pressure display.

In step S30, the value of the internal pressure p of the secondary battery100and the value of the surface pressure q of the secondary battery100may be compared. The value of the internal pressure p of the secondary battery100may be measured through the pressure display unit of the regulator T2, and the value of the surface pressure q of the secondary battery100may be measured through the pressure display unit of the load cell400. By comparing the value of the internal pressure p of the secondary battery100and the value of the surface pressure q of the secondary battery100in real time, the error value between the value of the internal pressure p of the secondary battery100generated by the pressure of the gas injected into the secondary battery100and the value of the surface pressure q of the secondary battery100may be quantified, and the error range between the value of the internal pressure p of the secondary battery100and the value of the surface pressure q of the secondary battery100may be predicted.

FIG.5schematically illustrates a structure of the sealing portion of the secondary battery and a structure of the measuring member for measuring the value of the surface pressure at the point in time when the sealing portion is vented.

Referring toFIGS.1,2and5, a sealing portion600may be formed on the outer periphery where an electrode tab500is present, and may be formed by thermal bonding to one another along the outer periphery of an upper case and a lower case. The electrode tab500may be electrically connected to the electrode assembly10. The electrode tap500may extend to the outside of the external material20accommodating the electrode assembly10to become an electrode terminal. For example, an electrode tab which is electrically connected to a plurality of cathodes may be a cathode terminal, and an electrode tab which is electrically connected to a plurality of anodes may be an anode terminal. The method of measuring the internal pressure of the secondary battery includes step S40of measuring the surface pressure at the point in time when the sealing portion of the secondary battery is vented. In step S40, a value of the surface pressure q′ is measured from the measuring member400at the point in time when at least one sealing portion600of the secondary battery100is vented.

The measuring member400measures the value of the surface pressure q′ at the point in time when at least one sealing portion600of the secondary battery100is vented, and the time when the sealing portion600is vented means a time when the gas injected into the inside of the secondary battery100is ejected to the outside through the sealing portion600. In step S40, the value of the surface pressure q′ at the point in time when at least one sealing portion600of the secondary battery100is vented may be calculated as the value of the maximum internal pressure of the secondary battery100. The value of the maximum internal pressure of the secondary battery100means a critical pressure at which the sealing portion600of the secondary battery100is not vented. The maximum internal pressure at the point in time when the sealing portion600of the secondary battery100is vented may be transmitted to the measuring member400through the lower plate300, and the measuring member400may measure the value of the surface pressure q′ of the secondary battery generated at the point in time when the sealing portion600of the secondary battery100is vented, thereby calculating as the value of the maximum internal pressure of the secondary battery100.

By measuring the value of the surface pressure q′ at the point in time when at least one sealing portion600of the secondary battery100is vented by the measuring member400, the internal pressure of the secondary battery may be more accurately measured in comparison to indirectly measuring the pressure of the gas injected into the secondary battery as the value of the internal pressure p of the secondary battery100.

In the above-described embodiments, all steps may be selectively performed or part of the steps and may be omitted. In each embodiment, the steps are not necessarily performed in accordance with the described order and may be rearranged. The embodiments disclosed in this specification and drawings are only examples to facilitate an understanding of the present disclosure, and the present disclosure is not limited thereto. That is, it should be apparent to those skilled in the art that various modifications can be made on the basis of the technological scope of the present disclosure.