Title of invention: electrode assembly
technical field
[One]
This application claims the benefit of priority based on Korean Patent Application No. 10-2019-0020424 dated February 21, 2019, and all contents disclosed in the literature of the Korean patent application are incorporated as a part of this specification.
[2]
The present invention relates to an electrode assembly configured by repeatedly stacking a cathode, a separator, and an anode, and more particularly, to an electrode assembly capable of preventing ignition from occurring due to thermal runaway.
[3]
background
[4]
A battery for storing electrical energy may be generally divided into a primary battery and a secondary battery. A primary battery is a disposable consumable battery, whereas a secondary battery is a rechargeable battery manufactured using a material in which oxidation and reduction processes between an electric current and a substance are repeatable. That is, when the reduction reaction of the material is performed by the electric current, the power is charged, and when the oxidation reaction is performed on the material, the power is discharged. Such charge-discharge can be repeatedly performed.
[5]
Among various types of secondary batteries, lithium secondary batteries are generally manufactured by mounting an electrode assembly in which a positive electrode, a separator, and an anode are stacked in a case, and lithium ions are produced from the lithium metal oxide of the positive electrode to the negative electrode. As the process of intercalation and deintercalation is repeated, charging and discharging of the lithium secondary battery proceeds.
[6]
The electrode assembly is manufactured such that the positive electrode 1 / separator 3 / negative electrode 2 are repeatedly stacked, and the electrode assembly is accommodated in a case such as a cylindrical can or a square pouch. As shown in Fig. 1a showing a side view of the electrode assembly, the positive electrode 1 of the electrode assembly is a positive electrode current collector 1a on both sides of the positive electrode active material 1b, and the negative electrode 2 is a negative electrode collector ( 2a) has a structure in which a negative electrode active material 2b is coated on both sides, and in the negative electrode 2 and the positive electrode 1, respectively, in the negative electrode current collector 2a and the positive electrode current collector 1a (active material is not applied) A negative electrode tab (not shown) and a positive electrode tab (not shown) each protrude, and current flows through the negative electrode tab and the positive electrode tab.
[7]
Meanwhile, as the demand for secondary batteries increases in fields such as ESS (Energy Storage System) and electric vehicles, research and development is being conducted to increase the capacity to volume ratio of secondary batteries.
[8]
As a part of this, secondary batteries using NCM (nickel (Ni), cobalt (Co), manganese (Mn))-based cathode active materials are being developed. However, the NCM-based secondary battery has a problem in that when the nickel content is relatively high, the capacity is increased, but the thermal stability is lowered and the ignition possibility is also increased.
[9]
FIG. 1B is a graph showing temperature and voltage changes over time when thermal runaway proceeds in a conventional electrode assembly. In this experiment, the positive electrode stacked on the electrode assembly was coated with a positive electrode active material with a composition ratio of nickel, cobalt, and manganese of 8:1:1, and the experimental conditions were changes in temperature and voltage versus time (horizontal axis) during which heat was applied at a constant rate (horizontal axis). (vertical axis) was measured.
[10]
As shown in the graph, when heat is applied above a specific temperature (approximately 150° C. in the graph), thermal runaway occurs in the electrode assembly and ignition (the point where the voltage becomes 0: 100 minutes) can be confirmed. That is, at about 100 minutes of the graph, ignition occurred, the voltage dropped to 0V, and the temperature instantly rose to 900°C or higher.
[11]
In addition, it is known that the use of a positive electrode active material having a relatively higher nickel content tends to ignite at a lower temperature (it is known that the higher the nickel content, the lower the thermal stability).
[12]
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[13]
Accordingly, the main object of the present invention is to provide an electrode assembly capable of preventing ignition due to thermal runaway even when a positive electrode active material having a high nickel content (eg, NCM811 active material) is used.
[14]
means of solving the problem
[15]
The present invention for achieving the object as described above, in the electrode assembly in which the positive electrode, the separator, and the negative electrode are repeatedly laminated, the shrink film is made of a material having a greater thermal contraction rate than the separator and shrinks in area above a certain temperature Including; at least one place between the positive electrode and the negative electrode, the shrink film is laminated instead of the separator, and when the shrink film is contracted by a temperature increase, the adjacent positive electrode and the negative electrode with the shrink film interposed therebetween It is characterized in that the parts come into contact with each other and a microcurrent is generated. This flow of microcurrent can improve stability by lowering the state of charge (state of charge) of the electrode assembly.
[16]
The shrink film may be manufactured to restore its original area when the temperature is lowered below a specific temperature. Conversely, the shrink film may be manufactured not to be restored even if the temperature is lowered below a specific temperature. This may be determined according to the design of the electrode assembly. When the shrink film is restored to its original area according to the temperature drop after shrinkage (if it is wider than the contracted area, even if it is not the original area), the flow of microcurrent is blocked or minimized so that the electrode assembly can be placed in a stable state and It is possible to prevent a short circuit by flowing a large current.
[17]
The shrink film according to the present invention is prepared to contain a material that shrinks from the crystal structure. For example, the material that shrinks from the crystal structure may be zirconium tungstate (ZrW 2 O 8 ).
[18]
Meanwhile, the positive electrode is coated with an NCM positive electrode active material containing nickel, cobalt, and manganese on the surface of the positive electrode current collector. The NCM cathode active material has a higher weight ratio of nickel than cobalt and manganese. For example, the NCM cathode active material may be NCM811 having a nickel, cobalt, and manganese content (composition ratio) of 8:1:1 or NCM622 having 6:2:2.
[19]
And, in the present invention, a single-sided positive electrode coated with a positive electrode active material on only one surface of the positive electrode current collector is disposed on the outermost layer, and the shrink film is laminated so as to contact the single-sided positive electrode located in the outermost layer. At this time, the single-sided positive electrode located in the outermost layer is laminated so that the positive electrode current collector faces outward, and the positive electrode active material faces the shrink film.
[20]
At this time, the shrink film may be laminated only at the position in contact with the single-sided positive electrode, and at the position in contact with the single-sided positive electrode and in addition to the positive electrode active material on both sides of the positive electrode current collector, the negative electrode active material is applied on both sides of the negative electrode current collector It can also be laminated in one or more places between the double-sided cathodes. Alternatively, the shrink film is not laminated at the outermost position, but may be laminated at one or more places between the double-sided positive electrode coated with the positive electrode active material on both sides of the positive electrode current collector and the double-sided negative electrode coated with the negative electrode active material on both sides of the negative electrode current collector have.
[21]
Accordingly, in the present invention, it is possible to additionally provide a secondary battery in which the above electrode assembly is built into the case.
[22]
Effects of the Invention
[23]
The present invention having the above technical characteristics can increase thermal stability by lowering the charging rate of the electrode assembly by allowing the flow of microcurrent when high heat is generated by thermal runaway of the positive electrode material or by external factors (reducing the possibility of ignition can).
[24]
Since the shrink film according to the present invention contains a material that causes shrinkage from the crystal structure, shrinkage can occur uniformly as a whole.
[25]
In the present invention, a single-sided positive electrode coated with a positive electrode active material on only one surface of the positive electrode current collector is disposed on the outermost layer to prevent lithium precipitation.
[26]
Brief description of the drawing
[27]
1A is a side view of a conventional electrode assembly in which an anode, a separator, and a cathode are repeatedly stacked;
[28]
1B is a graph showing changes in temperature and voltage over time when thermal runaway proceeds in a conventional electrode assembly;
[29]
2 is a side view of an electrode assembly in which a positive electrode, a separator, and a negative electrode are repeatedly stacked according to the present invention, and a shrink film is stacked instead of the separator at one or more places where the separator is stacked.
[30]
FIG. 3 is a view showing a state before (left figure) and after (right figure) occurrence of contact between the anode and the cathode when the shrinkage film is contracted in the electrode assembly of FIG. 2;
[31]
4 is a side view showing a state in which a shrink film is additionally laminated in addition to a position in contact with the outermost anode according to a second embodiment of the present invention;
[32]
5 is a graph showing the temperature and voltage changes over time as a state in which the temperature falls before thermal runaway proceeds in the electrode assembly according to the present invention.
[33]
Modes for carrying out the invention
[34]
Hereinafter, based on the accompanying drawings, the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. However, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.
[35]
In order to clearly explain the present invention, parts irrelevant to the description are omitted, and the same reference numerals are assigned to the same or similar elements throughout the specification.
[36]
In addition, the terms or words used in the present specification and claims should not be construed as being limited to conventional or dictionary meanings, and the inventor appropriately defines the concept of the term in order to best describe his invention. It should be interpreted as meaning and concept consistent with the technical idea of ​​the present invention based on the principle that it can be done.
[37]
The present invention relates to an electrode assembly in which a positive electrode, a separator, and a negative electrode are repeatedly stacked, characterized in that ignition due to thermal runaway can be suppressed by using a shrink film whose area shrinks when heat is applied. Embodiments according to the present invention will be described in more detail with reference to the drawings.
[38]
[39]
first embodiment
[40]
[41]
As described above, the electrode assembly according to the present invention includes a shrink film 31 whose area is contracted at a specific temperature or higher, and in this embodiment, the shrink film 31 is the first of the positions at which the separator 30 is disposed. It is disposed in place of the separation membrane 30 at each of the upper and lower sides.
[42]
As shown in FIG. 2 , a side view of an electrode assembly in which a shrink film 31 is disposed in place of the separators at the top and bottom respectively among the positions where the separators 30 are disposed is shown in FIG. 2 , in the present invention, the anode 10 ) and at least one place between the negative electrode 20 is configured such that the shrink film 31 is stacked instead of the separator 30 , and the shrink film 31 is disposed at the stacking position of the separators disposed on the outermost side.
[43]
The shrink film 31 may be configured to separate the positive electrode 10 and the negative electrode 20 in the same manner as the separator 30 in a normal temperature range, but allow the conduction of lithium ions, and the separator ( 30), it can even block the conduction of lithium ions. In addition, the shrink film 31 is manufactured to contain a material that shrinks from the crystal structure and shrinks when heated to a specific temperature or higher.
[44]
However, since the separator 30 also has a structure in which a coating layer is applied to the surface of the polymer substrate, it may have heat shrinkability according to the molecular bonding structure of the polymer substrate and/or the coating layer. However, here, the thermal contraction rate of the separator 30 is considered to be sufficiently small to not permit contact between the negative electrode and the positive electrode. Therefore, in the present specification, the separator 30 does not allow contact between the negative electrode and the positive electrode even when heat is applied, whereas the shrink film 31 allows the negative electrode and the positive electrode to contact when heat is applied above a certain temperature. .
[45]
Accordingly, when the thermal runaway phenomenon starts in the anode 10 and the temperature starts to rise, the shrinkage film 31 is contracted. Accordingly, when the shrinkage of the shrinkage film 31 occurs, the shrinkage film 31 is interposed between the shrinkage film 31 as shown in FIG. The positive electrode 10 and the negative electrode 20 adjacent to each other are in contact with each other. For reference, in the drawing, the positive electrode active material 10a of the positive electrode 10 and the negative electrode active material 20a of the negative electrode 20 are drawn so that they can contact, but in reality, the active material 10b, 20b is not applied to the electrode tab (not shown). ), the positive electrode current collector 10a and the negative electrode current collector 20a may come into contact with the active materials 10b and 20b of opposite polarity at the position where they are formed.
[46]
At this time, since the area in which the negative electrode 20 and the positive electrode 10 come into contact due to the contraction of the shrink film 31 is very small compared to the total area of ​​the negative electrode 20 and the positive electrode 10, the microcurrent in the contact portion (Micro current means a current that flows in a small area compared to the electrode area, and does not mean a current with an absolutely small value. Therefore, the meaning of microcurrent here is a relatively small short circuit. (Soft short) It can be said that it is clear in the meaning of current).
[47]
As this microcurrent flows, the state of charge (state of charge [SOC]) of the entire electrode assembly is gradually lowered, and thermal runaway caused by overcharge or external factors is calmed before ignition occurs.
[48]
Meanwhile, in this embodiment, the material that shrinks from the crystal structure may be zirconium tungstate (ZrW 2 O 8 ). Since the zirconium tungstate has a very low natural vibration frequency generated inside the material, it is known that the atoms are attracted to each other when the temperature rises, thereby reducing the overall size, and research and development are being conducted to utilize it in various fields.
[49]
The shrink film 31 containing zirconium tungstate having the above characteristics may be restored to its original area when thermal runaway is calmed down and falls below a specific temperature, depending on the content and manufacturing method of zirconium tungstate, It may be manufactured to maintain a contracted state, which may be determined according to the design of the electrode assembly.
[50]
For reference, the shrink film 31 will have to be manufactured so that the maximum amount of shrinkage and the range of shrinkage are limited in order to prevent a short circuit through which a large current flows. And, even if the shrinkage film 31 is not restored to its original area after the temperature drop (since the filling amount is continuously reduced), there will be no problem in terms of lowering the possibility of ignition, but the original area according to the temperature drop after shrinkage If it is restored to the original area or is wider than the contracted area even if it is not the original area, the flow of microcurrent will be blocked, thereby further reducing the possibility of a short circuit through which a large current flows.
[51]
Meanwhile, in this embodiment, the positive electrode 10 is coated with an NCM positive electrode active material 10b containing nickel, cobalt, and manganese on the surface of the positive electrode current collector 10a. The NCM positive electrode active material 10b has a higher weight ratio of nickel than cobalt and manganese. For example, the NCM cathode active material may be NCM811 having a nickel, cobalt, and manganese content (composition ratio) of 8:1:1 or NCM622 having 6:2:2.
[52]
And, as shown in FIGS. 2 and 3 , in the present invention, a single-sided positive electrode 10 ′ coated with a positive electrode active material 10b on only one surface of the positive electrode current collector 10a is disposed on the outermost layer exposed to the outside. In addition, the shrink film 31 is laminated so as to be in contact with the single-sided anode 10 ′ located in the outermost layer. At this time, the single-sided positive electrode 10 ′ located in the outermost layer is stacked such that the positive electrode current collector 10a faces outward, and the positive electrode active material 10b faces the shrink film 31 .
[53]
The reason that the single-sided positive electrode 10 ′ is disposed on the outermost layer as described above is that when the double-sided positive electrode 10 is disposed on the outermost layer, lithium precipitation may occur between the inner wall surface of the case in which the electrode assembly is built and the positive electrode active material placed on the outermost layer. This is because (that is, when a double-sided positive electrode is disposed on the outermost shell, lithium ions desorbed from the positive electrode active material placed on the outermost shell are not accommodated in the negative electrode and are precipitated).
[54]
[55]
second embodiment
[56]
[57]
As described in the first embodiment, in the present invention, the shrink film 31 may be laminated only at the position in contact with the single-sided positive electrode 10', and in addition to the position in contact with the single-sided positive electrode 10', the positive electrode current collector 10a It can also be laminated in one or more places between the double-sided positive electrode 10 coated with the positive electrode active material 10b on both sides of the negative electrode current collector 20a and the double-sided negative electrode 20 coated with the negative electrode active material 20b on both sides of the negative electrode current collector 20a. Alternatively, it may be stacked only between the double-sided positive electrode 10 and the double-sided negative electrode 20 except for a position in contact with the single-sided positive electrode 10 ′.
[58]
Referring to FIG. 4 in which an additional shrink film 31 is laminated in addition to the position in contact with the outermost cross-sectional anode 10 ′ according to the second embodiment of the present invention, the shrink film 31 is the outermost cross-section. In addition to the position in contact with the anode 10 ′, it may be additionally disposed between the double-sided anode 10 and the double-sided cathode 20 .
[59]
The electrode assembly in which the positive electrode 10, the separator 30, and the negative electrode 20 are repeatedly stacked has a higher temperature in the inner (middle layer) portion than the outer side close to the outside, because heat dissipation is difficult in the inner (middle layer) portion. . Accordingly, for faster shrinkage of the shrinkable film 31, the shrinkable film 31 may be additionally disposed or selectively disposed in the intermediate layer of the electrode assembly generating relatively higher heat generation.
[60]
That is, in this embodiment, by adjusting the lamination position and the number of laminations of the shrink film 31, the timing at which the amount of charge starts to decrease by the microcurrent can be tuned.
[61]
[62]
As shown in FIG. 5 , which shows a graph showing changes in temperature and voltage over time as a state in which the temperature falls before thermal runaway proceeds in the electrode assembly according to the present invention, as shown in FIG. 5 , the electrode assembly according to the present invention undergoes thermal runaway When the temperature rises due to the shrinkage of the shrink film 31, a flow of micro-current occurs (the point where the voltage drops sharply in the vicinity of 90 minutes), so that the amount of charge is lowered and ignition can be blocked.
[63]
In addition, in the present invention, it is possible to additionally provide a secondary battery in which the above electrode assembly is built into the case.
[64]
According to the present invention having the above technical characteristics, when high heat is generated by thermal runaway of the positive electrode 10 or by external factors, the possibility of ignition can be lowered by allowing the flow of microcurrent to lower the charge rate of the electrode assembly.
[65]
Since the shrink film 31 according to the present invention contains a material that shrinks from the crystal structure, shrinkage can occur uniformly as a whole.
[66]
In the present invention, a single-sided positive electrode 10 ′ coated with a positive electrode active material on only one surface of the positive electrode current collector is disposed on the outermost layer to prevent lithium precipitation.
[67]
In the above, although the present invention has been described with reference to limited embodiments and drawings, the present invention is not limited thereto, and it is described below with the technical idea of ​​the present invention by those of ordinary skill in the art to which the present invention pertains. Various implementations are possible within the scope of equivalents of the claims to be made.
Claims
[Claim 1]
In an electrode assembly in which a positive electrode, a separator, and a negative electrode are repeatedly stacked, a shrink film made of a material having a greater thermal contraction rate than the separator and shrinking in area at a specific temperature or higher; including, at least one place between the positive electrode and the negative electrode The shrink film is laminated instead of the separator, and when the shrink film is contracted due to a rise in temperature, the anode and the cathode adjacent to each other with the shrink film interposed therebetween, causing a microcurrent to be generated. electrode assembly.
[Claim 2]
The electrode assembly according to claim 1, wherein the shrink film contains a material that shrinks from a crystal structure.
[Claim 3]
The electrode assembly according to claim 2, wherein the material that shrinks from the crystal structure contained in the shrink film is zirconium tungstate (ZrW 2 O 8 ).
[Claim 4]
The electrode assembly according to claim 1, wherein the positive electrode is coated with an NCM positive electrode active material containing nickel, cobalt, and manganese on the surface of the positive electrode current collector.
[Claim 5]
The electrode assembly according to claim 4, wherein the NCM cathode active material has a greater weight ratio of nickel than cobalt and manganese.
[Claim 6]
The electrode assembly according to claim 1, wherein a single-sided positive electrode coated with a positive electrode active material is disposed on only one surface of the positive electrode current collector on the outermost layer, and the shrink film is laminated so as to contact the single-sided positive electrode located in the outermost layer.
[Claim 7]
The electrode assembly according to claim 6, wherein the single-sided positive electrode located in the outermost layer has the positive electrode current collector facing outward and the positive electrode active material is laminated to face the shrink film.
[Claim 8]
The electrode assembly according to claim 7, wherein the shrink film is laminated only at a position in contact with the single-sided anode.
[Claim 9]
The electrode assembly according to claim 7, wherein the shrink film is laminated at one or more places between the double-sided positive electrode coated with the positive electrode active material on both sides of the positive electrode current collector and the double-sided negative electrode coated with the negative electrode active material on both sides of the negative electrode current collector. .
[Claim 10]
The electrode assembly according to claim 1, wherein the shrink film is restored to its original area when the temperature is lowered below a specific temperature.
[Claim 11]
A secondary battery in which the electrode assembly of any one of claims 1 to 10 is built in a case.