Specification
Title of Invention: Secondary Battery and Device Containing Same
technical field
[One]
Cross-Citation with Related Application(s)
[2]
This application claims the benefit of priority based on Korean Patent Application No. 10-2019-0165769 dated December 12, 2019, and all contents disclosed in the literature of the Korean patent application are incorporated as a part of this specification.
[3]
The present invention relates to a secondary battery and a device including the same, and more particularly, to a secondary battery including an electrode assembly having a jelly roll structure and a device including the same.
background
[4]
Recently, an increase in the price of energy sources due to the depletion of fossil fuels, interest in environmental pollution is amplified, and the demand for an eco-friendly alternative energy source is becoming an indispensable factor for future life. Accordingly, research on various power production technologies such as nuclear power, solar power, wind power, and tidal power is continuing, and power storage devices for using the generated energy more efficiently are also of great interest.
[5]
In particular, as technology development and demand for mobile devices increase, the demand for batteries as an energy source is rapidly increasing, and accordingly, many studies on batteries capable of meeting various needs are being conducted.
[6]
Typically, there is a high demand for lithium secondary batteries, such as lithium ion batteries and lithium ion polymer batteries, which have advantages such as high energy density, discharge voltage, and output stability.
[7]
In addition, depending on the shape of the battery case, the secondary battery consists of a cylindrical battery and a prismatic battery in which the electrode assembly is embedded in a cylindrical or prismatic metal can, and a pouch-type battery in which the electrode assembly is embedded in a pouch-type case of an aluminum laminate sheet. classified.
[8]
In addition, secondary batteries are classified according to the structure of the electrode assembly in which a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode are stacked.
[9]
Typically, a jelly roll (winding type) electrode assembly having a structure in which long sheet-shaped anodes and cathodes are wound in a state in which a separator is interposed, and a plurality of cathodes and anodes cut into units of a predetermined size are interposed with a separator and stack-type (stacked-type) electrode assemblies that are sequentially stacked in one state.
[10]
Recently, in order to solve the problems of the jelly roll type electrode assembly and the stack type electrode assembly, as a mixed form of the jelly roll type and the stack type, unit cells in which positive and negative electrodes of a predetermined unit are stacked with a separator interposed therebetween. A stack/folding type electrode assembly having a structure in which it is sequentially wound in a state placed on a separation film has been developed.
[11]
On the other hand, in the case of a lithium secondary battery, a “swelling phenomenon” in which the volume of the electrode assembly expands as the electrode thickens during repeated charging and discharging may occur. When the swelling phenomenon intensifies, the performance of the secondary battery may be deteriorated, and the external shape thereof may be changed to adversely affect structural stability.
[12]
In particular, in the case of a lithium secondary battery using pure lithium metal as an anode, the charging mechanism is different from that of a general graphite anode, so that the thickness expansion of the anode leads to swelling of the secondary battery, which may cause serious problems.
[13]
In the graphite negative electrode, intercalation occurs in which lithium moved from the positive electrode is inserted into the layered graphite, but in the lithium metal negative electrode, the negative electrode deposited from the positive electrode is laminated as it is, so the thickness change of the secondary battery is more serious. do.
[14]
For example, when a positive electrode loading of 4.0 mAh/cm 2 is applied, a lithium metal negative electrode of 20 μm can be stretched by 10 μm based on both sides, and when a Cu current collector is used, a lithium metal negative electrode of 50 μm can be stretched to 90 μm. In particular, considering that the lithium metal negative electrode is porous and that dendrite growth of lithium occurs, the thickness change of the secondary battery may be more serious.
[15]
Therefore, it is necessary to develop a secondary battery capable of effectively controlling the volume expansion occurring during charging and discharging.
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[16]
Embodiments of the present invention are proposed to solve the above problems of the previously proposed methods, and the purpose of the present invention is to provide a secondary battery capable of effectively controlling volume expansion occurring during charging and discharging, and a device including the same. do it with
[17]
However, the problems to be solved by the embodiments of the present invention are not limited to the above problems and may be variously expanded within the scope of the technical idea included in the present invention.
means of solving the problem
[18]
A secondary battery according to an embodiment of the present invention includes an electrode assembly having a jelly roll structure including a positive electrode sheet, a negative electrode sheet, and a separator; a cylindrical case in which the electrode assembly is embedded; and a flat spiral spring positioned between the outer circumferential surface of the electrode assembly and the inner wall of the cylindrical case.
[19]
The spiral leaf spring may have one end in contact with the electrode assembly and the other end in contact with the inner wall of the cylindrical case, and may wrap the electrode assembly at least once.
[20]
A positive electrode tab attached to the positive electrode sheet may extend upward from the electrode assembly, and a negative electrode tab attached to the negative electrode sheet may extend downward from the electrode assembly.
[21]
The one end of the spiral leaf spring may coincide with at least one of the positive electrode tab and the negative electrode tab in a radial direction of the electrode assembly.
[22]
The thickness of the spiral leaf spring may increase from the other end to the one end.
[23]
The helical plate spring may include first and second helical plate springs respectively located at both ends of the electrode assembly in a height direction of the electrode assembly.
[24]
The spiral leaf spring may include a third spiral leaf spring positioned between the first and second spiral leaf springs.
[25]
The first and second helical leaf springs may have a greater spring constant than the third helical plate spring or may have a greater number of times to wrap the electrode assembly.
[26]
A positive electrode tab attached to the positive electrode sheet may extend upward from the electrode assembly, and a negative electrode tab attached to the negative electrode sheet may extend downward from the electrode assembly.
[27]
The first and second helical leaf springs may surround portions corresponding to portions to which the positive electrode tab and the negative electrode tab are attached among the outer peripheral surfaces of the electrode assembly, respectively.
[28]
A negative active material is coated on the negative electrode sheet, and the negative active material may include at least one of Li, Si, SiO 2 and Sn.
Effects of the Invention
[29]
According to embodiments of the present invention, by disposing a flat spiral spring between the electrode assembly having a jelly roll structure and a cylindrical case, the position of the electrode assembly is stably fixed as well as generated during charging and discharging. Reversible charging and discharging may be enabled by suppressing volume expansion of the electrode assembly.
Brief description of the drawing
[30]
1 is an exploded perspective view of an electrode assembly according to an embodiment of the present invention.
[31]
FIG. 2 is a perspective view illustrating a state in which the electrode assembly of FIG. 1 is wound and then wrapped in a spiral leaf spring.
[32]
3 is a cross-sectional perspective view of a secondary battery including the electrode assembly of FIG. 2 and a helical leaf spring;
[33]
Fig. 4 is a schematic horizontal cross-sectional view taken along line A-A' in Fig. 3 .
[34]
5 is a perspective view illustrating an electrode assembly wrapped in first to third spiral leaf springs.
Modes for carrying out the invention
[35]
Hereinafter, with reference to the accompanying drawings, various embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily carry out the present invention. The present invention may be embodied in many different forms and is not limited to the embodiments described herein.
[36]
In order to clearly describe 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.
[37]
In addition, since the size and thickness of each component shown in the drawings are arbitrarily indicated for convenience of description, the present invention is not necessarily limited to the illustrated bar. In order to clearly express various layers and regions in the drawings, the thicknesses are enlarged. And in the drawings, for convenience of description, the thickness of some layers and regions are exaggerated.
[38]
Also, when a part of a layer, film, region, plate, etc. is said to be “on” or “on” another part, this includes not only cases where it is “directly on” another part, but also cases where another part is in between. . Conversely, when we say that a part is "just above" another part, we mean that there is no other part in the middle. In addition, to be "on" or "on" the reference part means to be located above or below the reference part, and it means to be located "on" or "on" the direction opposite to gravity. not.
[39]
In addition, throughout the specification, when a part "includes" a certain component, this means that other components may be further included rather than excluding other components unless otherwise stated.
[40]
In addition, throughout the specification, when referring to "planar view", it means when the target part is viewed from above, and "cross-sectional view" means when viewed from the side when a cross-section of the target part is vertically cut.
[41]
1 is an exploded perspective view of an electrode assembly 100 according to an embodiment of the present invention, and FIG. 2 is a perspective view showing a state in which the electrode assembly 100 of FIG. 1 is wound and then wrapped in a spiral leaf spring 500. , FIG. 3 is a cross-sectional perspective view of the secondary battery 10 including the electrode assembly 100 and the spiral plate spring 500 of FIG. 2 .
[42]
1 to 3 , a secondary battery 10 according to an embodiment of the present invention is an electrode assembly 100 having a jelly roll structure including a positive electrode sheet 200 , a negative electrode sheet 300 , and a separator 400 . ), a cylindrical case 600 in which the electrode assembly 100 is embedded, and a spiral plate spring located between the outer circumferential surface 101 of the electrode assembly 100 and the inner wall of the cylindrical case 600 (Flat spiral spring 500). do.
[43]
The electrode assembly 100 having a jelly roll structure is formed by winding the positive electrode sheet 200 , the negative electrode sheet 300 and the separator 400 together, and the separator 400 is between the positive electrode sheet 200 and the negative electrode sheet 300 . may be interposed in In addition, in order to prevent the positive electrode sheet 200 and the negative electrode sheet 300 from contacting each other when wound in the form of a jelly roll, a separator 400 may be additionally disposed under the negative electrode sheet 300 .
[44]
The positive electrode active material is applied on the positive electrode sheet 200 to form the positive electrode active material layer 220 , and the positive electrode tab 210 is bonded to the positive electrode uncoated region 230 in which the positive electrode active material layer 220 is not formed by welding or the like. can be
[45]
Similarly, the negative electrode active material is applied on the negative electrode sheet 300 to form the negative electrode active material layer 320, and the negative electrode tab 310 is applied to the negative electrode uncoated region 330 in which the negative electrode active material layer 320 is not formed by welding, etc. can be joined by
[46]
At this time, although the positive electrode uncoated region 230 and the negative electrode uncoated region 330 are formed at one end of the positive electrode sheet 200 and the negative electrode sheet 300, respectively, in FIG. 1 , this is an example, and the positive electrode sheet 200 and one end of the negative electrode sheet 300 may be spaced apart from each other and formed in the middle.
[47]
Meanwhile, as shown in FIG. 1 , the extending directions of the positive electrode tab 210 and the negative electrode tab 310 are preferably opposite to each other. Accordingly, when the electrode assembly 100 is wound, as shown in FIG. 2 , the positive electrode tab 210 extends upward (Z-axis direction) from the electrode assembly 100 , and the negative electrode tab 310 is the electrode assembly. It may extend downward (in the direction opposite to the z-axis) from (100).
[48]
Fig. 4 is a schematic horizontal cross-sectional view taken along line A-A' in Fig. 3 .
[49]
Referring to FIG. 4 together with FIGS. 1 to 3 , the spiral leaf spring 500 positioned between the outer circumferential surface 101 of the electrode assembly 100 and the inner wall of the cylindrical case 600, one end 501 has an electrode In contact with the assembly 100 , the other end 502 may contact the inner wall of the cylindrical case 600 .
[50]
In addition, the spiral leaf spring 500 may wrap the electrode assembly 100 one or more times in order to effectively press the electrode assembly 100 .
[51]
As described above, a swelling phenomenon in which the volume of the electrode assembly 100 expands may occur during repeated charging and discharging of the secondary battery 10 . When this swelling phenomenon intensifies, the performance of the secondary battery 10 may be deteriorated, and the external shape thereof may be changed to adversely affect structural stability.
[52]
Accordingly, according to the present embodiment, the spiral plate spring 500 positioned between the outer circumferential surface 101 of the electrode assembly 100 and the inner wall of the cylindrical case 600 stabilizes the electrode assembly 100 inside the cylindrical case 600 . In addition to being able to fix the electrode assembly 100, volume expansion of the electrode assembly 100 can be effectively suppressed.
[53]
If the volume expansion of the electrode assembly 100 cannot be suppressed, the distance between the positive electrode sheet 200 and the negative electrode sheet 300 increases due to the volume expansion, thereby increasing resistance, and eventually reversible discharge may not be achieved. At this time, since the spiral leaf spring 500 according to the present embodiment can effectively suppress the volume expansion of the electrode assembly 100 , reversible charging and discharging of the secondary battery 10 is possible.
[54]
In addition, since it is a spiral-shaped spring, an even pressure can be applied to the entire outer circumferential surface 101 of the electrode assembly 100 . That is, it is possible to evenly take the effect of suppressing volume expansion over the entire outer peripheral surface 101 .
[55]
In addition, although exaggerated for explanation in FIG. 4 , since the spiral leaf spring 500 is a spring wound in a spiral shape, it occupies a large volume between the inside of the cylindrical case 600 and the cylindrical jelly roll electrode assembly 100 . It can be placed without That is, the space utilization is improved, which has an advantage in improving the battery capacity.
[56]
In particular, since the electrode assembly 100 has a relatively small volume in the discharge state, the spiral plate spring 500 is disposed on the outer circumferential surface of the electrode assembly 100 in the discharged state, and then it can be inserted into the cylindrical case 600 . have.
[57]
After charging is made and the electrode assembly 100 expands, as described above, the spiral leaf spring 500 may apply uniform pressure to the entire outer circumferential surface of the electrode assembly 100 .
[58]
Meanwhile, one end 501 of the spiral leaf spring 500 may coincide with at least one of the positive electrode tab 210 and the negative electrode tab 310 in a radial direction of the electrode assembly 100 .
[59]
Here, the radial direction means a direction corresponding to a radius with respect to the center of the electrode assembly 100 when the wound electrode assembly 100 is viewed from above.
[60]
In FIG. 4 , only the radial direction of the one end 501 and the positive electrode tab 210 coincides, but the negative electrode tab 310 may also coincide with the one end 501 in the radial direction.
[61]
The wound electrode assembly 100 inevitably has an asymmetric shape when viewed from above due to the positive electrode tab 210 and the negative electrode tab 310 respectively attached to the positive electrode sheet 200 and the negative electrode sheet 300 . When the electrode assembly 100 expands due to charging and discharging, this asymmetrical shape may be further deepened and a problem of distortion of the shape may occur.
[62]
Accordingly, by disposing one end 501 of the spiral leaf spring 500 so that at least one of the positive electrode tab 210 and the negative electrode tab 310 and the radial direction of the electrode assembly 100 coincide with each other, the distortion of the shape is greatest. It is possible to apply the highest pressure to the part where it can occur. Through this, it is possible to minimize distortion of the shape of the electrode assembly 100 due to the positive electrode tab 210 or the negative electrode tab 310 during volume expansion.
[63]
Furthermore, although not specifically illustrated, the thickness of the spiral leaf spring 500 may increase from the other end 502 to the one end 501 .
[64]
By forming a thickness gradient in the spiral leaf spring 500 in this way, one end 501 of the spiral leaf spring 500 positioned to correspond to the positive electrode tab 210 or the negative electrode tab 310 applies a stronger elastic force. can be designed Through this, it is possible to minimize distortion of the shape of the electrode assembly 100 due to the positive electrode tab 210 or the negative electrode tab 310 during volume expansion.
[65]
Meanwhile, referring again to FIG. 2 , the spiral leaf spring 500 according to the present embodiment may surround the entire outer circumferential surface 101 of the electrode assembly 100 . This is to apply an even pressure to the entire outer circumferential surface 101 of the electrode assembly 100 .
[66]
5 is a perspective view illustrating a state in which the electrode assembly 100 is wrapped around the first to third spiral leaf springs 510 , 520 , and 530 as a modified embodiment of the present invention.
[67]
Referring to FIG. 5 , as described above, the positive electrode tab 210 extends upward from the electrode assembly 100 (in the Z-axis direction), and the negative electrode tab 310 extends downwardly from the electrode assembly 100 (opposite to the z-axis). direction) can be
[68]
The spiral leaf spring 500a according to the present embodiment includes first and second spiral leaf springs ( 510 and 520). In particular, the first and second helical leaf springs 510 and 520 may wrap portions corresponding to the portions to which the positive electrode tab 210 and the negative electrode tab 310 are attached among the outer circumferential surfaces 101 of the electrode assembly 100 , respectively. have.
[69]
In addition, the spiral leaf spring 500a may include a third spiral leaf spring 530 positioned between the first and second spiral leaf springs 510 and 520 .
[70]
Although divided into first to third spiral leaf springs 510, 520, and 530, in order to apply an even pressure to the entire outer circumferential surface 101 of the electrode assembly 100, the first to third spiral leaf springs 510, 520 and 530 may surround the entire outer circumferential surface 101 of the electrode assembly 100 .
[71]
In this case, the first and second helical leaf springs 510 and 520 may have a higher spring constant than the third helical leaf spring 530 , or the number of wraps around the electrode assembly may be greater. That is, the pressure applied by the first and second spiral leaf springs 510 and 520 may be greater than the pressure applied by the third spiral leaf spring 530 .
[72]
Both ends of the electrode assembly 100 in the height direction (a direction parallel to the z-axis) of the electrode assembly 100 correspond to portions to which the positive electrode tab 210 and the negative electrode tab 310 are attached, respectively. As mentioned above, the wound electrode assembly 100 inevitably has an asymmetric shape when viewed from above due to the positive electrode tab 210 and the negative electrode tab 310 , and the electrode assembly 100 may expand due to charging and discharging. In this case, the asymmetric shape may be further deepened and a problem of distortion of the shape may occur.
[73]
Accordingly, the spring constant or the number of wraps of the first and second spiral leaf springs 510 and 520 is greater than that of the third spiral leaf spring 530 , so that the shape distortion of the electrode assembly 100 in the height direction is the largest. A higher pressure was applied to the part where it could occur.
[74]
In FIG. 5 , only one positive electrode tab 210 and one negative electrode tab 310 are illustrated, respectively, but this is an example, and the plurality of positive electrode tabs 210 extend upward, and the plurality of negative electrode tabs 310 extend downward. can be In this way, when the positive electrode tab 210 and the negative electrode tab 310 are each configured in plurality, shape distortion may be more problematic during volume expansion, so the first and second spiral leaf springs 510 and 520 according to the present embodiment. This could be more effective.
[75]
Referring back to FIG. 1 , an anode active material is applied on the anode sheet 300 to form a cathode active material layer 320 , and the anode active material may include at least one of Li, Si, SiO 2 and Sn.
[76]
When the negative active material includes the above materials, greater volume expansion is induced in the electrode assembly 100 including the negative electrode sheet 300 . Accordingly, the effect of suppressing volume expansion in the present invention through the spiral leaf springs 500 and 500a may be more pronounced when the anode active material includes at least one of Li, Si, SiO 2 and Sn.
[77]
The negative active material, more specifically, carbon, such as non-graphitizable carbon, graphite-based carbon; Li x Fe 2 O 3 (0≤x≤1), Li x WO 2 (0≤x≤1), Sn x Me 1-x Me' y O z (Me: Mn, Fe, Pb, Ge; Me' : metal composite oxides such as Al, B, P, Si, elements of Groups 1, 2, and 3 of the periodic table, halogen elements; 0