WO2024177366A1 - Secondary battery having anode current collector, which has anode aqueous binder to which sbr is added to improve adhesion and flexibility, and separator, which is elastically deformable to improve safety - Google Patents

Abstract

The present invention relates to a secondary battery comprising: a cathode current collector to which a cathode mixture including a cathode active material is applied; an anode current collector to which an anode mixture including an anode active material is applied; an electrolyte filled between the cathode current collector and the anode current collector; a separator provided in the electrolyte so that, between the cathode current collector and the anode current collector, ions are permitted to move and electrons are blocked from moving; and a deformation part provided in the separator so that the separator enters a low-density state in a first temperature range and the separator enters a high-density state in a second temperature range that is higher than the first temperature. Therefore, in a high temperature range due to a charging situation, the high-density state of the separator is induced to prevent separator penetration caused by dendrites, and thus safety is improved, and, in a low temperature range due to situations other than a charging situation, the low-density state of the separator is induced to facilitate movement of lithium ions through separator pores, and thus performance such as that of charge/discharge capacity and lifespan can be improved.

Description

A secondary battery having a negative electrode collector with a negative electrode aqueous binder to which SBR is added for improved adhesion and flexibility and a separator that is elastically deformable for improved safety

The present invention relates to a secondary battery having a positive electrode collector, a negative electrode collector, and a separator.

Lithium secondary batteries, which use lithium (Li) ions for electrical charging and discharging, have high energy density and discharge voltage compared to other secondary batteries, and thus have excellent charge and discharge capacity and long-term use. Due to these advantages, lithium secondary batteries are widely used in not only small portable devices such as mobile phones, but also large transportation such as electric vehicles.

As the charging and discharging in lithium secondary batteries are repeated, the metal crystals detached from the positive or negative current collectors tend to grow into irregular, needle-shaped dendrites. For example, dendrites detached from the negative current collector approach the separator as the volume of the negative electrode compound increases in the charging state of the secondary battery, and eventually cause a problem of penetrating the separator. If the separator is penetrated by dendrites, it can cause an electrical short circuit or even an explosion.

In order to prevent dendrites from penetrating the separator, attempts have been made to apply reinforcing agents such as ceramics to the separator. However, since the reinforcing agents block some or all of the pores of the separator, the movement of lithium ions through the pores of the separator is not smooth. The restriction of the movement of lithium ions reduces the charge/discharge capacity and shortens the life of the secondary battery.

Accordingly, there is an increasing demand for secondary batteries that not only ensure safety by preventing membrane penetration by dendrites, but also have superior performance, such as charge/discharge capacity and lifespan, by facilitating the movement of lithium ions through the membrane pores.

Therefore, the purpose of the present invention is to prevent membrane penetration by dendrites to ensure safety and to provide a secondary battery with excellent performance by facilitating the movement of lithium ions through membrane pores.

The above-described object of the present invention can be achieved by a secondary battery including: a positive electrode collector having a positive electrode mixture including a positive electrode active material applied thereto; a negative electrode collector having a negative electrode mixture including a negative electrode active material applied thereto; an electrolyte charged between the positive electrode collector and the negative electrode collector; a separator provided in the electrolyte to allow movement of ions and block movement of electrons between the positive electrode collector and the negative electrode collector; and a deformation member provided in the separator to cause the separator to be in a low-density state in a first temperature range and to be in a high-density state in a second temperature range higher than the first temperature.

Accordingly, in a high temperature range due to a charging situation, a high density state of the separator can be induced, thereby preventing the phenomenon of the separator being penetrated by dendrites, thereby improving safety, and in a low temperature range due to a situation other than a charging situation, such as a discharging situation, a low density state of the separator can be induced, thereby facilitating the movement of lithium ions through the pores of the separator, thereby improving performance such as charge/discharge capacity and lifespan.

The above-mentioned deformation portion is provided in the separator and includes a shape memory alloy powder layer that shrinks in the second temperature range to cause the separator to become a high-density state.

According to this, the high-density state of the membrane can be more easily induced in a high-temperature range, so safety can be further improved.

It includes a housing that accommodates the separator therein, and further includes a deformation recovery member that is interposed between both ends of the separator and the inner surface of the housing and elastically contracts so that the separator can be changed from the high-density state to the low-density state.

According to this, the high-density membrane can be easily restored to a low-density state in the first temperature range, so that the movement of ions can become faster and smoother.

The above-mentioned deformation portion includes a shape memory alloy chamber provided in the separator that shrinks in the second temperature range to cause the separator to become a high-density state.

According to this, the high-density state of the membrane can be more easily induced in the second temperature range, so safety can be further improved.

It further includes an expansion spring inserted into the shape memory alloy room.

According to this, the high-density state separation membrane can be easily restored to a low-density state in the first temperature range, and since it can be manufactured integrally with a shape memory alloy room, design efficiency can be improved.

According to the present invention, not only is safety ensured by preventing the phenomenon of membrane penetration by dendrites, but also the movement of lithium ions through the pores of the membrane is facilitated, thereby providing a secondary battery with excellent performance.

Figure 1 illustrates a cross-section of a secondary battery according to one embodiment of the present invention.

Figure 2 illustrates an example of a deformation portion that causes the state of the description in Figure 1 to be deformed.

Figure 3 illustrates an example of a deformation recovery section that allows the membrane of Figure 1 to elongate.

Figure 4 illustrates an example of a deformation portion according to another embodiment.

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the drawings. This is intended to describe in detail enough to enable a person having ordinary knowledge in the technical field to which the present invention belongs to to easily carry out the invention, and it is to be understood that the technical idea and scope of the present invention are not limited thereby.

FIG. 1 illustrates a cross-section of a secondary battery (1) according to one embodiment of the present invention, and FIG. 2 illustrates an example of a deformation portion (50) that causes the state of the separator (30) of FIG. 1 to be deformed.

Hereinafter, the structure of a secondary battery (1) according to one embodiment of the present invention will be described in detail with reference to FIG. 1.

The secondary battery (1) according to the present embodiment includes an electrode current collector (10, 20). The electrode current collector (10, 20) is a part where movement of ions (3) occurs in the electrochemical reaction of the active material, and has a positive electrode current collector (10) and a negative electrode current collector (20) depending on the type of electrode.

The positive electrode current collector (10) and the negative electrode current collector (20) are provided in the form of a plate or foil having a thickness of 300 to 500 μm, and can be implemented with a material having high conductivity without causing chemical changes in the secondary battery (1).

The positive electrode current collector (10) may be implemented as stainless steel, aluminum, nickel (Ni), titanium, calcined carbon, etc., or may be implemented as aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. The negative electrode current collector (20) may be implemented as copper, stainless steel, aluminum, nickel, titanium, calcined carbon, etc., or may be implemented as copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc.

When the secondary battery (1) is implemented as a lithium secondary battery, the positive electrode current collector (10) and the negative electrode current collector (20) can be implemented as aluminum and copper, respectively. When charging a lithium secondary battery, ions (3) on the positive electrode side move to the negative electrode side, and ions (3) on the negative electrode side move to the positive electrode side, thereby discharging.

A cathode current collector (10) is coated with a cathode composite (11) including a cathode active material. The cathode active material is a lithium transition metal oxide and includes two or more transition metals. For example, the cathode active material may be implemented as a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), etc. substituted with at least one transition metal, or may be implemented as lithium manganese oxide, lithium nickel cobalt manganese composite oxide, olivine-based lithium metal phosphate, etc. substituted with at least one transition metal, but is not limited thereto.

A negative electrode current collector (20) is coated with a negative electrode composite (21) containing a negative electrode active material. The negative electrode active material may be implemented as natural graphite, artificial graphite, expanded graphite, carbon fiber, non-graphitizable carbon, carbon black, carbon nanotubes, fullerene, activated carbon, or a metal such as aluminum, silicon, silver, magnesium, manganese, phosphorus, lead, titanium, etc. that can be alloyed with lithium, or a compound thereof, but is not limited thereto.

The positive electrode composite (11) and the negative electrode composite (12) include a conductive material. The conductive material can further improve the conductivity of the electrode active material (positive electrode active material and negative electrode active material). The conductive material can be implemented with a material having conductivity without causing a chemical change in the secondary battery (1). For example, the conductive material can be implemented with, but is not limited to, graphite such as natural graphite or artificial graphite, carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, conductive fibers such as carbon fibers or metal fibers, metal powders such as fluorinated carbon, aluminum, and nickel powder, conductive whiskey such as zinc oxide or potassium titanate, conductive metal oxides such as titanium oxide, and conductive materials such as polyphenylene derivatives.

The positive electrode composite (11) and the negative electrode composite (12) contain a binder. The binder allows the electrode active material to be firmly bonded to the conductive material and allows the electrode active material to be firmly adhered to the electrode current collector (10, 20). The positive electrode binder is applied to the bonding and adhesion of the positive electrode active material, and the negative electrode binder is applied to the bonding and adhesion of the negative electrode active material.

The positive electrode binder and the negative electrode binder may be implemented as a water-based binder such as polyvinylidene fluoride (PVdF), but are not limited thereto. For example, the water-based binder may include carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), etc. When CMC and SBR are used, the adhesion of the water-based binder to the electrode current collector (10, 20) is improved and the fluidity is increased. In addition, SBR is environmentally friendly and can improve the capacity and initial charge/discharge efficiency of the secondary battery (1) by reducing the binder usage content.

According to various embodiments, the binder can be implemented as a silane coupling agent having the following chemical formula.

R-(CH ₂ ) _n -Si-X _m

Here, R is a group including at least one reactive group capable of reacting with a polymer, X is a hydrolyzable group or an alcohol group, m is an integer from 1 to 3, and n is an integer from 0 to 10. In this way, the binder including the silane coupling agent allows the electrode active material to be more firmly adhered to the electrode current collector (10, 20) due to high adhesive strength.

The secondary battery (1) may include an electrolyte (40) charged between a positive electrode current collector (10) and a negative electrode current collector (20). An aprotic organic solvent may be used as the electrolyte (40). The aprotic organic solvent may include propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyrolactoneformamide, dimethylformamide, nitromethane, methyl formate, dioxolan derivatives, sulfolane, methyl sulfolane, propylene carbonate derivatives, tetrahydrofuran derivatives, ethyl propionate, and the like. However, the present invention is not limited thereto, and the electrolyte (40) may be implemented as an organic solid electrolyte, an inorganic solid electrolyte, and the like.

A secondary battery (1) has a separator (30) that is immersed in an electrolyte (40). The separator (30) can be interposed between a positive electrode current collector (10) and a negative electrode current collector (20) while being immersed in the electrolyte (40).

The separator (30) is formed as a thin film. The thickness of the separator (30) may be 5 to 300 ㎛, but is not limited thereto. The separator (30) may have insulation with high ion permeability and mechanical strength. For example, the separator (30) may include a polyolefin-based polymer resin having chemical resistance and hydrophobicity. The polyolefin-based polymer resin may include one selected from polyethylene, high-density polyethylene, linear low-density polyethylene, low-density polyethylene, ultra-high molecular weight polyethylene, polypropylene, polybutylene, polypentene, etc., or a combination of two or more of these.

The separator (30) has elasticity and can be elastically deformed. For example, the separator (30) can expand or contract in the X-axis direction or the Y-axis direction. When expanding, the separator (30) can be in a low-density state, and when contracting, the separator (30) can be in a high-density state.

For elastic deformation, the separator (30) may be implemented with a polymer resin in which an elastic material is uniformly dispersed. The elastic material may mean an elastic material that quickly returns to its original length when stretched to more than twice its original length or contracted to more than half its original length.

The elastic material may include an elastomer, natural rubber, artificial rubber, etc. The elastomer may include a polyolefin elastomer (POE), a styrenic block copolymer (SBC), a vinyl chloride elastomer, a chlorinated polyethylene elastomer (CPE), a urethane elastomer (TPU), a polyester elastomer (TPEE), a polyamide elastomer (TPAE), a fluorinated elastomer, and a silicone elastomer.

A plurality of pores (31) can be formed in the separation membrane (30). The pores (31) can be formed by a method of mixing the separation membrane (30) and the pore-forming agent at a high temperature, extruding and stretching, and then extracting the pore-forming agent, but the present invention is not limited thereto and can be formed by various methods.

The pores (31) can be passages for the movement of ions (3) in a charge/discharge situation. In other words, the pores (31) allow the movement of ions (3) but block the movement of electrons. For this purpose, the pores (31) can have a diameter of about 0.01 to 1 ㎛, but are not limited thereto.

When the membrane (30) has elasticity and elastically deforms, the diameter of the pore (31) may also be deformed. For example, in a high-density state of the membrane (30), the diameter of the pore (31) may be smaller than in a low-density state. However, even if the diameter of the pore (31) is small in a high-density state of the membrane (30), the diameter of the pore (31) may be large enough to ensure the movement of ions (3), and even if the diameter of the pore (31) is large in a low-density state of the membrane (30), it may be large enough to block the movement of electrons.

The secondary battery (1) may include a housing (2) that accommodates or encloses the electrode current collector (10, 20), separator (30), electrolyte (40), etc. The housing (2) may be implemented with an aluminum laminate film. The aluminum laminate film may be composed of a plastic layer such as PET or nylon, an aluminum layer, and an adhesive layer.

Below, the process of preventing the phenomenon of the secondary battery (1) according to the present embodiment from penetrating the separator by dendrites (2) is described in detail. For convenience of explanation, it is assumed that the dendrites (2) grow by detaching from the negative electrode current collector (20), but this is not limited to the process, and they may grow by detaching from the positive electrode current collector (10).

In a discharge state, one side of the negative electrode mixture (21) can be located at P1. Even in a discharge state, a small number of ions (3) can be accommodated in the negative electrode active material of the negative electrode mixture (21). When the discharge state is changed to a charge state, a large number of ions (3) are accommodated in the negative electrode active material, and as a result, the negative electrode mixture (21) undergoes a volume change, and one side of the negative electrode mixture (21) moves to P2.

According to related technology, when the negative electrode mixture approaches the separator in a charging situation, dendrites may protrude from the negative electrode mixture toward the separator and penetrate the separator. If the separator is penetrated by dendrites, it may cause an electrical short circuit or even an explosion.

Accordingly, the secondary battery (1) according to the present embodiment prevents the phenomenon of the separator being penetrated by dendrites (4) through the deformation portion (50). Specifically, the deformation portion (50) is provided in the separator (30), and causes the separator (30) to be in a low-density state in a first temperature range, and causes the separator (30) to be in a high-density state in a second temperature range higher than the first temperature.

Here, the first temperature range can be a low temperature range formed in a situation other than a charging situation, such as a discharging situation. However, for convenience of explanation, it is assumed below that the first temperature range is formed by a discharging situation.

Meanwhile, the second temperature range can be a high temperature range formed in a charging situation. Normally, the temperature of the electrolyte (40) rises more rapidly in a charging situation than in a discharging situation, so the second temperature range can be higher than the first temperature range. The first temperature range and the second temperature range can be determined in various ways depending on the design method and operating environment of the secondary battery (1).

Therefore, when changing from a discharge state to a charge state, the separator (30) changes from a low-density state to a high-density state by the deformation portion (50) as the temperature increases from the first temperature range to the second temperature range. As described above, even if the dendrite (4) comes into contact with the separator (30) due to the increase in the volume of the negative electrode mixture (21) in the charge state, the dendrite (4) is prevented from advancing by the separator (21) in the high-density state, so that the penetration of the separator by the dendrite (4) can be prevented. The separator (30) can have a strength sufficient to prevent the penetration of the dendrite (4) through the separator in the high-density state.

Even when the separator (30) is in a high-density state, the pores (31) have a diameter that can ensure the movement of ions (3), so that part or all of the pores (31) are not blocked. Accordingly, the charging capacity is not reduced in the high-density state of the separator (30), and the lifespan of the secondary battery (1) is not shortened.

Conversely, when changing from a charging state to a discharging state, the separator (30) can become a low-density state. In the discharging state, the dendrite (4) is separated from the separator (30) due to the decrease in the volume of the negative electrode mixture (21), so the concern about the dendrite (4) penetrating the separator is reduced. In particular, in the low-density state, the diameter of the pore (31) also increases, so that the ions (3) can move more smoothly through the pore (31). The change to the low-density state of the separator (30) will be described in more detail with reference to FIG. 3.

According to this embodiment, in a high temperature range due to a charging situation, the separator (30) is made to be in a high density state, thereby preventing the phenomenon of the separator penetrating by dendrites (4), thereby improving safety. In addition, in a low temperature range due to a discharging situation, the separator (30) is made to be in a low density state, thereby facilitating the movement of ions (3) through the pores (31), thereby improving performance such as charge/discharge capacity and lifespan.

Hereinafter, an example of a deformation portion (50) will be described in more detail with reference to FIG. 2. The deformation portion (50) is provided in the separator (30) and includes a shape memory alloy powder layer (50) that shrinks in a second temperature range to cause the separator (30) to become a high-density state.

The shape memory alloy powder layer (50) may be uniformly provided on the separator (30) by powdering the shape memory alloy or may be uniformly applied to the surface of the separator (30). When the separator (30) has a surface facing the positive electrode current collector (10) and a surface facing the negative electrode current collector (20), the shape memory alloy powder layer (50) may be applied to at least one of the surfaces.

Shape memory alloys become austenite when heated at a very high temperature higher than the shape recovery temperature for a certain period of time while in a state of a specific shape. Since shape memory alloys remember their shape in the austenite state, they maintain the remembered shape in a temperature range higher than the shape recovery temperature.

Shape memory alloys are in a martensite state at temperatures lower than their shape recovery temperature, and their shape can be changed by an external force in martensite. Shape memory alloys maintain their shape changed by an external force at temperatures lower than their shape recovery temperature, but when the temperature range is higher than their shape recovery temperature, the atoms of the shape memory alloy return to their original positions during the reverse transformation process to the austenite state, thereby recovering the state with the remembered shape.

The shape memory alloy may include a nickel (Ni)-titanium (Ti) shape memory alloy. Since the nickel-titanium shape memory alloy has superior restoring power compared to other shape memory alloys, it is possible to easily change the state of the shape memory alloy. In the case of the nickel-titanium shape memory alloy, the shape recovery temperature can be set in various ways by varying the temperature conditions when the shape memory alloy is heated to an ultra-high temperature higher than the shape recovery temperature when it initially has a specific shape, and the composition ratio between nickel and titanium.

According to the present embodiment, the shape memory alloy can be set to be in an expanded state at a first temperature range lower than the shape recovery temperature and to be in a contracted state at a second temperature range higher than the shape recovery temperature. When a shape memory alloy powder layer (50) in which the shape memory alloy set in this way is powdered is applied to the surface of the separator (30), the state of the separator (30) can also change in response to the state change of the shape memory alloy. Accordingly, the separator (30) expands in accordance with the expansion of the shape memory alloy powder layer (50) in the first temperature range and becomes a low-density state, and contracts in accordance with the contraction of the shape memory alloy powder layer (50) in the second temperature range and becomes a high-density state.

In this way, if the deformation portion (50) is implemented as a shape memory alloy powder layer (50) and provided in the separator (30), the high-density state of the separator (30) can be induced more easily in the second temperature range, so that safety can be further improved.

According to various embodiments, as in FIG. 2, a shape memory alloy powder layer (50) may be provided on both surfaces of the separator (30). The shape memory alloy of the shape memory alloy powder layer (50) provided on both surfaces may be set to have the same shape memory characteristics. That is, it may be set to be in an expanded state in a first temperature range lower than the shape recovery temperature and in a contracted state in a second temperature range higher than the shape recovery temperature.

In this way, when a shape memory alloy powder layer (50) is provided on both surfaces of the separator (30), the shrinkage force increases in the second temperature range, so the separator (30) can be brought into a high-density state more quickly at the second temperature, and thus safety can be further improved.

According to various embodiments, the shape memory alloy powder layer (50) may be provided along the inner surface of the pore (31). In this case, in the first temperature range, the shape memory alloy powder layer (50) is in an expanded state, so that the diameter of the pore (31) increases, but in the second temperature range, it is in a contracted state, so that the diameter of the pore (31) decreases.

Therefore, when a dendrite (4) tries to penetrate a pore (31) in the second temperature range, the diameter of the pore (31) can be made smaller to prevent penetration, thereby further improving safety.

According to various embodiments, the deformation member (50) may be implemented as a filter including a shape memory alloy. The shape memory alloy filter may be interposed between the negative electrode current collector (20) and the separator (30). However, it is not limited thereto, and may also be interposed between the positive electrode current collector (10) and the separator (30).

In this way, by applying the shape memory alloy filter, not only can the high-density state of the separator (30) be induced more easily in the second temperature range, but also, since the shape memory alloy filter only needs to be interposed between the negative electrode current collector (20) and the separator (30), the design efficiency can be improved compared to the case where the shape memory alloy powder layer (50) mentioned above is provided on the separator (30).

Figure 3 illustrates an example of a deformation recovery part (60) that allows the separator (30) of Figure 1 to expand.

As shown in Fig. 3, the secondary battery (1) includes a deformation recovery unit (60). The deformation recovery unit (60) is interposed between the two ends of the separator (30) and the inner surface of the housing (2). For example, the deformation recovery unit (60) may be provided as a pair at both ends of the separator (30) in the Y-axis direction, but is not limited thereto, and may be provided at only one of the two ends in the Y-axis direction.

The deformation recovery part (60) has elasticity. For example, the deformation recovery part (60) can be implemented with an elastic polymer, natural rubber, artificial rubber, etc. The description of the type of elastic polymer is omitted because it is the same as the elastic polymer described above in relation to the separator (30).

The separator (30) has a shape retention ability that maintains a high-density state in the second temperature range, but the shape retention ability decreases when the first temperature range is formed again. Eventually, when the elastic restoring force of the deformation recovery portion (60) overcomes the shape retention ability of the separator (30), the separator (30) is stretched by the elastic contraction of the deformation recovery portion (60) and restored to a low-density state.

Of course, if the low-density separator (30) changes to a high-density state in the second temperature range, the deformation recovery part (60) can elastically expand along the shrinking separator (30).

In this way, by using the deformation restoration unit (60), the high-density separation membrane (30) can be easily restored to a low-density state in the first temperature range, so that the movement of ions (3) can be made faster and smoother.

Figure 4 illustrates an example of a deformation portion (80) according to another embodiment.

The separation membrane (70) according to the present embodiment corresponds to the separation membrane (30) of Fig. 1. For example, a plurality of pores (71) corresponding to the pores (31) of Fig. 1 are formed in the separation membrane (70) according to the present embodiment. Hereinafter, descriptions overlapping with the embodiment of Fig. 1 will be omitted and descriptions will be made in detail focusing on different configurations.

As shown in Fig. 4, a deformation portion (80) is provided in the separator (70). The deformation portion (80) shrinks in the second temperature range to cause the separator (30) to become a high-density state. For this purpose, the deformation portion (80) may be provided as a shape memory alloy room. The shape memory alloy room may be provided singly or may be formed by twisting and combining multiple shape memory alloy rooms. The shape memory characteristics of the shape memory alloy room are as described with reference to Fig. 1, so they will be omitted.

The shape memory alloy chamber can be arranged to connect a pair of symmetrical angles in the separator (70). If the shape memory alloy chamber is arranged diagonally, the separator (70) can shrink in both the X-axis direction and the Y-axis direction when shrinking in the second temperature range, so that the density of the separator (70) can be further increased in a high-density state compared to, for example, shrinking only in the X-axis direction or only in the Y-axis direction.

According to various embodiments, the shape memory alloy may include an expansion spring. The expansion spring has the characteristic of storing elastic force when contracted by an external force and expanding to restore to its original state when the external force is removed.

As explained above, when the separator (70) becomes a high-density state in the second temperature range and then becomes a first temperature range again, the expansion spring elastically expands to expand the separator (70), thereby restoring the separator (70) to a low-density state.

Of course, if the low-density separator (70) changes to a high-density state in the second temperature range, the expansion spring can elastically contract along with the contracting separator (70).

By using an expansion spring in this way, not only can a high-density separator (70) be easily restored to a low-density state in the first temperature range, but design efficiency can also be improved because it can be manufactured as an integral part with the deformation part (80).

Although the present invention has been described in detail through the preferred embodiments above, the present invention is not limited thereto and can be implemented in various ways within the scope of the claims.

Claims (5)

In secondary batteries, A cathode current collector coated with a cathode composite containing a cathode active material; A negative electrode current collector coated with a negative electrode composite containing a negative electrode active material; An electrolyte charged between the positive electrode collector and the negative electrode collector; A separator provided in the electrolyte to allow movement of ions between the positive electrode collector and the negative electrode collector and block movement of electrons; and A secondary battery comprising a deformation member provided on the separator and causing the separator to have a low-density state in a first temperature range and causing the separator to have a high-density state in a second temperature range higher than the first temperature. In the first paragraph, A secondary battery including a shape memory alloy powder layer, wherein the above-mentioned deformation portion is provided in the separator and shrinks in the second temperature range to cause the separator to become a high-density state. In the first paragraph, It comprises a housing that accommodates the above-mentioned separator inside, A secondary battery further comprising a deformation recovery member interposed between both ends of the separator and the inner surface of the housing, the deformation recovery member elastically contracting to elongate the separator so that the separator changes from the high-density state to the low-density state. In the first paragraph, A secondary battery including a shape memory alloy room provided in the separator and shrinking in the second temperature range to cause the separator to become a high-density state. In paragraph 4, A secondary battery further comprising an expansion spring inserted into the shape memory alloy chamber.

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