A battery and a method for preparing the same

Abstract

The present invention relates to the technical field of battery processing, and provides a battery, which includes an electrode core and a packaging body. A sealing area is provided at the edge of at least one side of the packaging body to seal and wrap the electrode core therein. The packaging body includes a protective layer, a metal layer, and a heat-sealing layer that are stacked in sequence. Among them, in the sealing area, the side of the heat-sealing layer away from the electrode core is the outer sealing side, and the side close to the electrode core is the inner sealing side. The crystallinity of the outer sealing side is greater than that of the inner sealing side. This battery contains a packaging body with high packaging strength and strong bending resistance, which can more effectively block water vapor from entering the battery, and at the same time improve the safety performance and service life of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of battery processing, and particularly relates to a battery and a preparation method thereof. Background Art

[0002] The aluminum-plastic film of a soft-pack battery is a composite film composed of an outer protective layer, an intermediate metal layer, and an inner heat-sealing layer, and an adhesive is used to bond between the composite layers. The encapsulation of the aluminum-plastic film of a soft-pack lithium-ion battery is mainly after the aluminum-plastic film wraps the bare battery cell, and the heat-sealing layer in the encapsulation area is fused by the high temperature and high pressure of the sealing head, so as to form a sealed space. As the outer shell material of the soft-pack battery, the aluminum-plastic film plays a role in isolating air and moisture and protecting the battery core.

[0003] Nowadays, with the soft-pack battery cells entering the field of power battery cells, the requirements for the encapsulation of the aluminum-plastic film are further improved. For example, power battery cells require higher encapsulation strength and bending resistance at the encapsulation part of the aluminum-plastic film. At present, the heat-sealing layer in the encapsulation area is fused by the high temperature and high pressure of the sealing head, resulting in a relatively large overall crystallinity of the heat-sealing layer, which has problems such as poor bending resistance, high hardness and easy fracture leading to liquid leakage.

[0004] Therefore, it is of great significance to develop a battery containing an aluminum-plastic film with high encapsulation strength and strong bending resistance. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above problems existing in the prior art, and provide a battery and a preparation method thereof. The battery contains an encapsulation body (such as an aluminum-plastic composite film) with high encapsulation strength and strong bending resistance, which can more effectively block water vapor from entering the battery, and at the same time improve the safety performance and service life of the battery.

[0006] The inventor of the present invention found that after the heat-sealing layer of the encapsulation body (aluminum-plastic composite film) in the battery is fused to form a sealing area, heat treatment is carried out by arranging an electromagnetic induction heating device at the edge of the sealing area, so that the temperature of the heat-sealing layer shows a downward trend along the direction from the outer sealing side to the inner sealing side. Furthermore, the crystallinity of the heat-sealing layer also shows a downward trend. The crystallinity of the inner sealing side close to the battery cell is low and the elasticity is good, which can ensure that the inner sealing side is not easy to break during folding; the crystallinity of the outer sealing side far from the battery cell is high, the strength is high, and the tensile resistance performance is high, which improves the sealing strength and can effectively block water vapor.

[0007] To achieve the above purpose, the first aspect of the present invention provides a battery, including a battery cell body and an encapsulation body. At least one side edge of the encapsulation body is provided with a sealing area to seal and wrap the battery cell body therein. The encapsulation body includes a protective layer, a metal layer, and a heat-sealing layer that are stacked in sequence; wherein, in the sealing area, the side of the heat-sealing layer away from the battery cell body is the outer sealing side, and the side close to the battery cell body is the inner sealing side, and the crystallinity of the outer sealing side is greater than that of the inner sealing side.

[0008] In a second aspect of the present invention, a method for preparing the battery described in the first aspect of the present invention is provided, including the following steps:

[0009] An electromagnetic induction heating device is applied to the edge of the sealing area of the encapsulation body, so that the temperature of the heat-sealing layer shows a downward trend along the direction from the outer sealing side to the inner sealing side, thereby making the crystallinity of the outer sealing side greater than that of the inner sealing side.

[0010] The present invention adopts the above technical solutions and has the following beneficial effects:

[0011] The battery provided by the present invention contains an encapsulation body with high encapsulation strength and strong bending resistance, which can more effectively block water vapor from entering the battery, and at the same time improve the safety performance and service life of the battery.

[0012] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values and individual point values of each range, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein. Description of the Drawings

[0013] Figure 1 The cross-sectional structural schematic diagram of the battery in an example of the present invention is shown.

[0014] Figure 2 The picture of the polypropylene heat-sealing layer in an example of the present invention is shown.

[0015] Figure 3 The cross-sectional structural schematic diagram of the aluminum-plastic composite film in an example of the present invention is shown.

[0016] Figure 4 The schematic diagram of non-contact heat source heating the aluminum-plastic composite film in an example of the present invention is shown.

[0017] Figure 5 The cross-sectional schematic diagram of the battery cell in an example of the present invention is shown.

[0018] Description of the Reference Numerals

[0019] 1. Battery cell; 2. Sealing area; 21. Inner sealing area; 22. Outer sealing area; 23. First sealing area; 24. Second sealing area; 3. Tab. Detailed Embodiments

[0020] The following provides a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0021] Unless otherwise defined, all scientific and technical terms used in the present invention have the same meaning as commonly understood by those skilled in the technical field to which the present invention pertains.

[0022] A first aspect of the present invention provides a battery, comprising an electrode core and a packaging body. A sealing area is provided at the edge of at least one side of the packaging body to seal and wrap the electrode core body therein. The packaging body comprises a protective layer, a metal layer, and a heat-sealing layer which are stacked in sequence; wherein, in the sealing area, the side of the heat-sealing layer away from the electrode core body is the outer sealing side, and the side close to the electrode core body is the inner sealing side, and the crystallinity of the outer sealing side is greater than that of the inner sealing side.

[0023] In the present invention, the "electrode core body" and the "electrode core" have the same meaning.

[0024] In one example, the packaging body is an aluminum-plastic composite film. The following will take the aluminum-plastic composite film as the packaging body as an example for illustration.

[0025] In the present invention, the crystallinity of the inner sealing side close to the electrode core is low and the elasticity is good, which can ensure that the inner sealing side is not easily broken when folding the edge; the crystallinity of the outer sealing side away from the electrode core is high, the strength is high, and the tensile resistance performance is high, which improves the sealing strength and can effectively block water vapor.

[0026] In one example, the sealing area is divided along the center line in its length direction. The area from the center line to the side close to the electrode core is the inner sealing area, and the area from the center line to the side away from the electrode core is the outer sealing area.

[0027] In one example, as Figure 1 shown, the battery comprises an electrode core 1 and a packaging body that seals and wraps the electrode core. The sealing area 2 in the packaging body is divided into an inner sealing area 21 and an outer sealing area 22 along the center line in its length direction. Along the direction from the outer sealing area 22 to the inner sealing area 21, the crystallinity of the heat-sealing layer shows a downward trend.

[0028] In one example, the electrode core is a soft-pack electrode core, comprising a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte. There are no specific limitations on the selection of the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte, which can be selected in the art according to needs. The assembly method of the electrode core is carried out in a conventional manner in the art.

[0029] In one example, the packaging body comprises a protective layer, a metal layer, and a heat-sealing layer that are stacked in sequence along the direction close to the electrode core.

[0030] Exemplarily, the protective layer is selected from at least one of nylon, polyethylene terephthalate, polybutylene terephthalate, polyvinylidene fluoride, polytetrafluoroethylene, polypropylene, polyamide, and polyimide.

[0031] Exemplarily, the metal layer includes at least one of aluminum foil, aluminum alloy foil, copper foil, copper alloy foil, iron foil, iron alloy foil, nickel foil, and nickel alloy foil.

[0032] In order to better enable the encapsulation body to have higher encapsulation strength and stronger bending resistance, one or more technical features can be further optimized.

[0033] In one example, along the direction from the outer sealing side to the inner sealing side, the crystallinity of the heat-sealing layer shows a downward trend.

[0034] Crystallinity (Xe) is the mass fraction or volume fraction of the crystalline region in a polymer. It is one of the important parameters characterizing semi-crystalline polymers and has a direct relationship with many important properties of the polymer. Generally, the greater the crystallinity, the greater the density, strength, hardness, and stiffness of the material, and the better the dimensional stability, heat resistance, and chemical resistance. However, elasticity, elongation at break, impact strength, and light transmittance decrease.

[0035] In one example, the DSC test method is used to test the crystallinity of the mass fractions on the inner sealing side and the outer sealing side. The test principle is that the heat absorbed by the crystalline phase in the same type of polymer during its melting process (the melting heat enthalpy ΔH of the sample 实际 ) is proportional to its crystallinity. The formula is Xe = ΔH 实际 / ΔH (100％结晶 度) .

[0036] In one example, calculated by mass fraction, the difference in crystallinity between the outer sealing side and the inner sealing side is 0.5% - 50%, preferably 1% - 20%.

[0037] In one example, the XRD test method is used to test the crystallinity of the volume fractions on the inner sealing side and the outer sealing side. The test principle is that the sample is composed of two significantly different phases. Since the electron density of the crystalline region is greater than that of the amorphous region, corresponding crystalline region diffraction peaks and amorphous region diffuse peaks are generated. After peak separation processing, the ratio of the intensity of the crystalline region diffraction peak to the total intensity of all peaks is calculated as the crystallinity of the sample. The formula is Xe = Ic / (Ic + Ia), (where Ic is the intensity of the crystalline diffraction peak and Ia is the intensity of the non-crystalline diffraction peak).

[0038] In one example, calculated by volume fraction, the difference in crystallinity between the outer sealing side and the inner sealing side is 8% - 50%, preferably 10% - 30%.

[0039] In the present invention, the minimum value within the range of crystallinity difference refers to the difference measured by sampling at the position closest to the center line in the outer sealing area and the inner sealing area, and the maximum value refers to the difference measured by sampling at the position farthest from the center line in the outer sealing area and the inner sealing area, wherein the width of the test sampling is 1 mm and the length is 20 mm.

[0040] In one example, the width of the sealing area is 2 mm - 8 mm.

[0041] Exemplarily, the width of the sealing area is 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, and 8 mm.

[0042] Preferably, the width of the sealing area is 3 - 5 mm.

[0043] In one example, the material of the heat-sealing layer is selected from polymers with a crystallinity of 30 - 80%, preferably polymers with a crystallinity of 40 - 60%.

[0044] In one example, the polymer is selected from at least one of polyolefins, halogenated polyolefins, and modified polyolefins.

[0045] Exemplarily, the polyolefin is selected from at least one of polypropylene, polyethylene, poly-1-butene, poly-4-methyl-1-pentene, ethylene-vinyl acetate copolymer, and ethylene-acrylic acid copolymer.

[0046] Exemplarily, the halogenated polyolefin is selected from at least one of fluorinated polypropylene, chlorinated polypropylene, fluorinated polyethylene, fluorinated poly-1-butene, and fluorinated ethylene-acrylic acid copolymer.

[0047] Exemplarily, the modified polyolefin can be one or more of physical modification and chemical modification. Specifically, the physical modification can be one or more of filling modification, blending modification, and nucleating agent modification; the chemical modification can be one or more of block modification and graft modification.

[0048] Preferably, the material of the heat-sealing layer is polypropylene with a crystallinity of 30 - 80%.

[0049] In one example, as Figure 3 shown, taking the aluminum-plastic composite film laminated in sequence with nylon (protective layer), aluminum layer (metal layer), and polypropylene (heat-sealing layer) as an example, the present invention also provides a method for obtaining a heat-sealing layer with a sealing area, including the following steps:

[0050] (1) Cut off the aluminum-plastic composite film containing a partial sealing area with scissors;

[0051] (2) Mix 40% hydrofluoric acid with warm water in a ratio of 1:4, and then put the cut aluminum-plastic composite film into the prepared hydrofluoric acid, and let it react and stand for 2 h to completely dissolve the aluminum layer in the hydrofluoric acid;

[0052] (3) Take out the remaining film, wash off the excess hydrofluoric acid with clean water, and peel off the nylon layer to obtain the polypropylene film as shown in Figure 2 .

[0053] In one example, as shown in Figure 2 , the sealing area 2 in the polypropylene film (heat-sealing layer) is divided into an inner sealing area 21 and an outer sealing area 22 along the center line in its length direction.

[0054] In one example, as shown in Figure 3 , the sealing area is divided along the center line in its length direction. The area from the center line to the side close to the battery cell is the inner sealing area, and the area from the center line to the side far from the battery cell is the outer sealing area. The light and dark colors respectively represent the high and low crystallinity (dark color represents high crystallinity, and light color represents low crystallinity), that is, along the direction from the outer sealing area to the inner sealing area, the crystallinity of the heat-sealing layer shows a downward trend.

[0055] In one example, the present invention also provides a method for preparing the sealing area, including the following steps:

[0056] Apply an electromagnetic induction heating device at the edge of the sealing area to make the temperature of the heat-sealing layer show a downward trend along the direction from the outer sealing side to the inner sealing side, so that the crystallinity of the outer sealing side is greater than that of the inner sealing side.

[0057] During the processing of the battery, after wrapping the battery cell with an aluminum-plastic composite film, press the aluminum-plastic composite film tightly at the edge where the battery cell contacts the aluminum-plastic composite film by the pressure of the sealing head, so that the heat-sealing layers (such as PP) of the upper and lower layers of the aluminum-plastic composite film are closely attached. After the above steps are completed, set an electromagnetic induction heating device (such as a high-frequency electromagnetic induction coil) at the edge of the area to be sealed for heat treatment. Under the action of the high-frequency magnetic field, an alternating current is generated and heat is generated at the place where the aluminum layer of the aluminum-plastic composite film is close to the coil, melting the PP. After stopping heating, the PP recrystallizes and forms a seal. The outer sealing side is close to the heat source, so the temperature is higher, and the temperature shows a downward trend along the direction from the outer sealing side to the inner sealing side. The crystallinity of the heat-sealing layer material decreases with the decrease of temperature. Therefore, along the direction from the outer sealing side to the inner sealing side, the crystallinity of the heat-sealing layer shows a downward trend.

[0058] In one example, the minimum distance between the electromagnetic induction heating device and the edge of the sealing area is 0.5 mm - 10 mm, preferably 1 mm - 3 mm. Among them, the edge of the sealing area refers to the edge far from the battery cell side.

[0059] In one example, the electromagnetic induction heating device is a high-frequency electromagnetic induction coil.

[0060] In one example, the exciting current of the electromagnetic induction coil is 8 - 20 A, and the alternating frequency is 100 kHz - 600 kHz.

[0061] The principle of electromagnetic induction heating is that the alternating current generated by the induction heating power supply passes through the inductor (i.e., the coil) to generate an alternating magnetic field. A ferromagnetic object is placed therein to cut the alternating magnetic force lines, thereby generating an alternating current (i.e., eddy current) inside the object. The eddy current causes the free electrons inside the object to move at high speed in a directional manner. The directional movement of the electrons is affected by the metal resistance, thus achieving the effect of heating the object.

[0062] As Figure 4 shown, in electromagnetic induction heating, the coil is close to the sealing area of the aluminum-plastic composite film for heating.

[0063] In one example, the battery cell body further includes tabs. The sealing area includes a first sealing area for sealing the tabs and second sealing areas on both sides of the first sealing area. The cross-sectional width of the first sealing area is greater than the cross-sectional width of the second sealing area.

[0064] As Figure 5 shown, the battery cell body has tabs 3. There are two tabs 3, namely a positive tab and a negative tab. Along the arrangement direction of the tabs 3, the sealing area 2 is divided into a first sealing area 23 for sealing the tabs 3 and second sealing areas 24 on both sides of the first sealing area 23. There are two first sealing areas 23 and three second sealing areas 24. At least part of the sealing area in the first sealing area 23 is adhered to the tabs 3 to seal the tabs 3. In some embodiments, the length of the first sealing area 23 is not less than the width of the tabs 3 (the arrangement direction of the tabs 3 is the same as the length direction of the sealing area 2, which is also the width direction of the tabs 3). At the same time, the sealing cross-section, i.e., the cross-sectional width, of the first sealing area 23 is greater than the cross-sectional width of the second sealing area 24.

[0065] The battery cell provided by the present invention, while ensuring the length of the first sealing area, increases the width of the first sealing area, so that the sealing area at the tabs is increased, the adhesion strength and adhesion area between the encapsulation body and the tabs are enhanced, the encapsulation strength at the tab position is improved, ensuring the encapsulation at the tab position is tight and firm, significantly reducing or completely avoiding the problem of virtual sealing, and being able to effectively avoid the risk that the sealing area at the tabs is extremely easy to break when the battery cell generates gas, collides or drops; improves the encapsulation quality of the battery cell, solves the hidden trouble factors causing battery cell failure due to poor encapsulation, more effectively guarantees the safe use of the battery cell, and ensures the safe and effective service life of the battery cell. The battery cell with this encapsulation structure has stable performance and high safety.

[0066] In one example, the cross-section of the first sealing area includes a central block, and a first protruding block and a second protruding block protruding outward from both sides of the central block.

[0067] As Figure 5 shown, the cross-section of the second sealing area 24 is strip-shaped. In one embodiment, the cross-section of the first sealing area 23 can be divided into a central block, a first protruding block, and a second protruding block. The width of the central block is the same as the width of the second sealing area 24. The first protruding block is located on one side in the width direction of the central block, and the second protruding area is located on the other side in the width direction of the central block. The first protruding block and the second protruding block are formed by protruding outward from both sides of the central block. That is, compared with the second sealing area 24, the first sealing area 23 has widened blocks protruding on both sides in the width direction, in the direction close to the tab 3 and in the direction close to the bottom of the battery cell body.

[0068] The cross-sectional width of the first sealing area is greater than the cross-sectional width of the second sealing area, and there is an increase on both the upper and lower sides in the width direction. The increased area is the effective sealing area for adhesion to the tab, which can significantly enhance the adhesion area and adhesion strength between the encapsulation body and the tab, ensuring a tight and firm encapsulation.

[0069] In one example, in the length direction of the sealing area, one side edge of the first sealing area extends beyond the same-side edge of the tab by 1 - 20 mm; and / or, the other side edge of the first sealing area extends beyond the same-side edge of the tab by 1 - 20 mm.

[0070] The second aspect of the present invention provides a method for manufacturing the battery according to the first aspect of the present invention, including the following steps:

[0071] Apply an electromagnetic induction heating device to the edge of the sealing area of the encapsulation body, so that the temperature of the heat-sealing layer shows a downward trend from the outer sealing side to the inner sealing side, and further make the crystallinity of the outer sealing side greater than the crystallinity of the inner sealing side.

[0072] The inventor of the present invention found that when a high-frequency magnetic field is applied to the edge of the area to be sealed, an alternating current will be generated in the edge of the aluminum-plastic film by the magnetic field and heat will be generated. The heat diffuses from the edge to the inside, making the temperature of the heat-sealing layer show a downward trend from the outer sealing side to the inner sealing side, and further making the crystallinity of the outer sealing side greater than the crystallinity of the inner sealing side.

[0073] In one example, the minimum distance between the electromagnetic induction heating device and the edge of the sealing area is 0.5 mm - 3 mm, preferably 1 mm - 3 mm.

[0074] In one example, the electromagnetic induction heating device is a high-frequency electromagnetic induction coil.

[0075] In one example, the excitation current of the electromagnetic induction coil is 8 - 20 A, and the alternating frequency is 100 kHz - 600 kHz.

[0076] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0077] The materials, reagents, etc. used in the following embodiments can be obtained from commercial channels without special instructions.

[0078] The present invention will be described in detail below in combination with specific embodiments, and these embodiments are for understanding rather than limiting the present invention.

[0079] Embodiment 1

[0080] Prepare a battery cell (conventional structure, soft-pack battery cell, including a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte) and an aluminum-plastic composite film for wrapping the battery cell. The aluminum-plastic composite film includes a nylon (protective layer), an aluminum layer (metal layer), and a polypropylene (PP with a crystallinity of 50%, heat-sealing layer) laminated in sequence. Plan a sealing area with a width of 3 mm at the edges to be sealed on three sides, and use a high-pressure sealing head and an electromagnetic induction coil to perform hot pressing to form a sealing area to tightly wrap the battery cell, as Figure 1 shown;

[0081] Process the above-mentioned sealing area, including the following steps:

[0082] Use the pressure of the sealing head to press the aluminum-plastic film in the area to be sealed, so that the PP layers of the upper and lower aluminum-plastic films are closely attached. After the above steps are completed, apply a high-frequency magnetic field at a position 1 mm away from the edge of the sealing area. The induction coil excites a current of 12 A and an alternating frequency of 200 kHz. Under the action of the high-frequency magnetic field, an alternating current is generated in the aluminum layer of the aluminum-plastic film near the coil and generates heat, melting the PP. After stopping heating, the PP recrystallizes and forms a seal. The outer seal side is close to the heat source, so the temperature is higher, and the temperature shows a downward trend along the direction from the outer seal side to the inner seal side. The crystallinity of the heat-sealing layer material decreases with the decrease in temperature. Therefore, along the direction from the outer seal side to the inner seal side, the crystallinity of the heat-sealing layer shows a downward trend, and further, the crystallinity of the outer seal side is greater than that of the inner seal side;

[0083] Take samples at positions 1 mm close to the edges of the outer seal side and the inner seal side (i.e., the side far from the center line) for crystallinity testing. The width of the sample is 1 mm and the length is 20 mm. Use the DSC test method. The formula is Xe = ΔH 实际 / ΔH (100％结晶度) , and the melting enthalpy of PP (polypropylene) with 100% crystallinity is calculated as 165 J / g. It is measured that the crystallinity difference between the outer seal side and the inner seal side is 1%.

[0084] Embodiment 2

[0085] Use the same battery cell and aluminum-plastic composite film as in Example 1, and the width of the sealing area is 3 mm;

[0086] Process the above sealing area, including the following steps:

[0087] Use the pressure of the sealing head to press the aluminum-plastic film in the area to be sealed, so that the PP layers of the upper and lower aluminum-plastic films are closely attached. After the above steps are completed, apply a high-frequency magnetic field at a distance of 2 mm from the edge of the sealing area. The exciting current of the induction coil is 10 A, and the alternating frequency is 300 kHz. Under the action of the high-frequency magnetic field, an alternating current is generated in the aluminum layer of the aluminum-plastic film near the coil and generates heat, melting the PP. After stopping heating, the PP recrystallizes and forms a seal, making the crystallinity of the outer seal side greater than that of the inner seal side;

[0088] Take samples at positions 1 mm from the edges of the outer seal side and the inner seal side respectively for crystallinity testing. The width of the sample is 1 mm and the length is 20 mm. Use the XRD testing method, and the formula is Xe = Ic / (Ic + Ia). It is measured that the crystallinity difference between the outer seal side and the inner seal side is 10%.

[0089] Example 3

[0090] Use the same battery cell and aluminum-plastic composite film as in Example 1, and the width of the sealing area is 2 mm;

[0091] Process the above sealing area. The difference from Example 1 is that a high-frequency magnetic field is applied at a distance of 2 mm from the edge of the sealing area; finally, it is measured that the crystallinity difference between the outer seal side and the inner seal side is 0.8%.

[0092] Example 4

[0093] Use the same battery cell and aluminum-plastic composite film as in Example 1, and the width of the sealing area is 7 mm;

[0094] Process the above sealing area. The difference from Example 1 is that a high-frequency magnetic field is applied at a distance of 0.8 mm from the edge of the sealing area; finally, it is measured that the crystallinity difference between the outer seal side and the inner seal side is 5%.

[0095] Example 5

[0096] Use the same battery cell and aluminum-plastic composite film as in Example 2, and the width of the sealing area is 2 mm;

[0097] Process the above sealing area. The difference from Example 1 is that a high-frequency magnetic field is applied at a distance of 2 mm from the edge of the sealing area; finally, it is measured that the crystallinity difference between the outer seal side and the inner seal side is 8%.

[0098] Example 6

[0099] The same battery cells and aluminum-plastic composite films as those in Example 2 are used, and the width of the sealing area is 7 mm;

[0100] The above sealing area is processed. The difference from Example 1 is that a high-frequency magnetic field is applied at a distance of 0.8 mm from the edge of the sealing area; finally, the crystallinity difference between the outer sealing side and the inner sealing side is measured to be 20%.

[0101] Comparative Example 1

[0102] It is carried out with reference to Example 1. The difference is that electromagnetic induction coils are not used for hot pressing treatment, and the crystallinity difference between the outer sealing side and the inner sealing side measured by the DSC test method is less than 0.3%.

[0103] Comparative Example 2

[0104] It is carried out with reference to Example 1. The difference is that electromagnetic induction coils are not used for hot pressing treatment, and the crystallinity difference between the outer sealing side and the inner sealing side measured by the XRD test method is less than 8%.

[0105] Test Example

[0106] (1) Conduct safety performance tests on the battery

[0107] Inflation and bursting experiment: Drill a round hole with a diameter of about 1 mm on the surface of the aluminum-plastic film of the completed packaged soft-pack battery. After the air injection hole is tightly pressed against the round hole, inflate the aluminum-plastic film package of the battery. First, fill the air pressure to 0.2 MPa. After the air pressure is stable, increase the air pressure by 0.01 MPa each time. After the air pressure is stable, continue to increase the pressure until the aluminum-plastic film package bursts or loses pressure after cracking along the seal, and record the maximum air pressure before the package fails. The obtained results are recorded in Table 1.

[0108] Table 1

[0109]

[0110]

[0111] (2) Conduct life tests on the battery

[0112] High-temperature and high-humidity environment storage:

[0113] 1. Measure the thickness, voltage, and internal resistance of the sample at 25°C ± 5°C;

[0114] 2. Discharge at 0.2C to 3V, let it stand for 10 min, charge at a constant current and constant voltage of 0.7C to the upper limit voltage, the cut-off current is 0.05C, let it stand for 10 min, and discharge at 0.2C to 3V (initial capacity);

[0115] 3. The battery is fully charged: Let it stand for 10 min, charge at a constant current and constant voltage of 0.7C to the upper limit voltage, and the cut-off current is 0.05C;

[0116] 4. Measure the voltage, internal resistance, and thickness in the fully charged state after leaving it for 2 h.

[0117] 5. Then place it in an environment of 60 ± 2 °C for storage for 14 days, and no test process data is required.

[0118] 6. Take it out after the storage is completed. After the sample returns to room temperature, measure the final voltage, internal resistance, and cold thickness.

[0119] 7. Discharge at 0.2C to the cut-off voltage of 3.0 V (residual capacity).

[0120] 8. Stand still for 10 min.

[0121] 9. Charge at 0.7C constant current and constant voltage to the upper limit voltage, with a cut-off current of 0.05C. Stand still for 10 min, and then discharge at 0.2C to 3 V (recovery capacity).

[0122] 10. Record the capacity retention rate (residual capacity / initial capacity), capacity recovery rate (recovery capacity / initial capacity), and thickness change rate. The results are shown in Table 2.

[0123] Table 2

[0124]

[0125]

[0126] (3) Conduct a water vapor barrier test on the battery

[0127] Water bath test: After charging the battery cell to full charge at 0.7C (cut-off current 0.025C), place it in a water bath at 60 °C for 90 days. Use PPG to measure the thickness of the battery every day. When the thickness change rate of the battery cell is greater than 20%, record it as NG, and count the number of days required for the battery to reach NG. Record the obtained results in Table 3.

[0128] Table 3

[0129] Water bath failure time / day Example 1 47 Example 2 44 Example 3 50 Example 4 45 Example 5 49 Example 6 42 Comparative Example 1 32 Comparative Example 2 35

[0130] It can be seen from the data in Table 1 - Table 3 above that the battery provided by the present invention contains an aluminum-plastic composite film with high encapsulation strength and strong bending resistance, which can more effectively block water vapor from entering the battery, and at the same time improve the safety performance and service life of the battery.

[0131] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A battery, comprising a battery cell body and a packaging body for packaging the battery cell body. A sealing area is provided at the edge of at least one side of the packaging body to seal and wrap the battery cell body therein. The packaging body comprises a protective layer, a metal layer and a heat-sealing layer stacked in sequence; Among them, In the sealing area, the side of the heat-sealing layer away from the battery cell body is the outer sealing side, and the side close to the battery cell body is the inner sealing side. Along the direction from the outer sealing side to the inner sealing side, the crystallinity of the heat-sealing layer shows a downward trend, and the crystallinity of the outer sealing side is greater than that of the inner sealing side; Using the DSC test method to test the crystallinity of the mass fractions of the inner sealing side and the outer sealing side. Calculated by mass fraction, the difference in crystallinity between the outer sealing side and the inner sealing side is 0.5% - 50%; Using the XRD test method to test the crystallinity of the volume fractions of the inner sealing side and the outer sealing side. Calculated by volume fraction, the difference in crystallinity between the outer sealing side and the inner sealing side is 8% - 50%.

2. The battery according to claim 1, wherein, The width of the sealing area is 2 mm - 8 mm.

3. The battery according to claim 2, wherein, The width of the sealing area is 3 mm - 5 mm.

4. The battery according to claim 1, wherein, The material of the heat-sealing layer is selected from polymers with a crystallinity of 30 - 80%.

5. The battery according to claim 4, wherein, The polymer is selected from at least one of polyolefins, halogenated polyolefins and modified polyolefins.

6. The battery according to any one of claims 1-5, wherein, The battery cell body comprises electrode tabs. The sealing area comprises a first sealing area for sealing the electrode tabs and second sealing areas located on both sides of the first sealing area. The cross-sectional width of the first sealing area is greater than that of the second sealing area.

7. The battery according to claim 6, wherein, The cross-section of the first sealing area comprises a central block, and first protruding blocks and second protruding blocks protruding outward from both sides of the central block.

8. The battery according to claim 6, wherein In the length direction of the sealing area, one side edge of the first sealing area extends beyond the same-side edge of the electrode tab by 1 - 20 millimeters; and / or, The other side edge of the first sealing area extends beyond the same-side edge of the electrode tab by 1 - 20 millimeters.

9. A method for preparing the battery according to any one of claims 1-8, characterized in that, Comprising the following steps: An electromagnetic induction heating device is arranged at the edge of the sealing area of the packaging body, so that the temperature of the heat-sealing layer shows a downward trend along the direction from the outer sealing side to the inner sealing side, thereby making the crystallinity of the outer sealing side greater than that of the inner sealing side.

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