Internal protection insulating film structure, preparation method thereof and battery

Abstract

The invention relates to the technical field of batteries, and discloses an internal protection insulating film structure, a preparation method thereof and a battery. The inner protection insulating film structure is used for wrapping the core package to isolate the core package from the battery shell, the inner protection insulating film structure comprises an inner liquid absorption layer and an outer protection layer, the outer protection layer comprises an outer bottom film and outer side films, the outer side films comprise two first outer side films and two second outer side films which are connected with the outer bottom film, and the two first outer side films and the two second outer side films are connected with the inner liquid absorption layer. The two first outer side films are oppositely arranged and right face the two large faces in the thickness direction of the core bag, the two second outer side films are oppositely arranged and right face the two side faces in the width direction of the core bag, and a through hole is formed in the area, close to the outer bottom film, of at least one second outer side film. The method can improve the infiltration effect of the core package, reduces the phenomena of swelling and lithium precipitation at the lower part of the pole piece in the core package caused by deposition of free electrolyte at the bottom of the core package, and improves the safety and service life of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery, in particular to a core package inner protection insulation film structure, a preparation method thereof and a battery. BACKGROUND

[0002] The lithium ion battery generally comprises an aluminum shell, a core package arranged in the aluminum shell, and an electrolyte arranged in the aluminum shell. The electrolyte can conduct ions between the positive electrode and the negative electrode of the lithium ion battery, thereby realizing the charging and discharging function. The outer wall of the core package is coated with an insulation film to isolate the core package from the shell and prevent the shell from being electrochemically corroded.

[0003] The existing inner protection film is made of a single layer of insulation material (such as PET (Polyethylene Terephthalate), PI (Polyimide)), which wraps the core package. Although it can prevent the short circuit caused by the contact between the core package and the shell, it hinders the electrolyte from being soaked. Under the action of gravity, the free electrolyte is deposited at the bottom of the core package, which increases the gap at the bottom of the core package and causes the swelling and lithium precipitation at the bottom of the core package, thereby reducing the cycle life of the battery and even causing thermal runaway. SUMMARY

[0004] One of the purposes of the embodiments of the present application is to provide an inner protection insulation film structure and a preparation method thereof, which can improve the soaking effect of the core package and reduce the swelling and lithium precipitation at the bottom of the core package caused by the deposition of free electrolyte at the bottom of the core package.

[0005] The second purpose of the embodiments of the present application is to provide a battery with high safety and long service life.

[0006] To achieve the above-mentioned purposes, the present application adopts the following technical solutions:

[0007] On the one hand, an inner protection insulation film structure is provided for wrapping a core package to isolate the core package from a battery shell. The inner protection insulation film structure comprises an inner liquid absorption layer and an outer protection layer arranged on the outer surface of the inner liquid absorption layer. The outer protection layer comprises an outer bottom film and an outer side film. The outer side film comprises two first outer side films and two second outer side films connected to the outer bottom film. The two first outer side films are oppositely arranged and face two large surfaces in the thickness direction of the core package. The two second outer side films are oppositely arranged and face two side surfaces in the width direction of the core package. At least one of the second outer side films is provided with a plurality of through holes adjacent to the area of the outer bottom film.

[0008] As a further scheme of the inner protection insulation film structure, the inner protection insulation film structure is in the form of a bag with an open end. The density of the holes in the second outer side film gradually decreases from the outer bottom film towards the open end.

[0009] As a further solution of the inner protective insulation film structure, the inner protective insulation film structure is a bag-like structure provided with an open end, the second outer film has a first region adjacent to the outer bottom film and a second region adjacent to the open end, the hole density of the first region is greater than the hole density of the second region.

[0010] As a further solution of the inner protective insulation film structure, the hole density of the first region is 95-105 holes / mm 2 ; and / or,

[0011] the hole density of the second region is 25-35 holes / mm 2 ; and / or,

[0012] the area of the first region is 60-80% of the area of the second outer film.

[0013] As a further solution of the inner protective insulation film structure, the hole diameter of the through hole is 6-10 μm.

[0014] As a further solution of the inner protective insulation film structure, the inner protective insulation film structure has a bottom film, a side film and four edges corresponding to four side edges of two large faces of the core package, the inner absorbent layer includes an inner bottom film and an inner side film connected to the inner bottom film, the inner bottom film and the outer bottom film constitute the bottom film, the inner side film and the outer side film constitute the side film, and the thickness of the edge is greater than the thickness of the side film.

[0015] As a further solution of the inner protective insulation film structure, the thickness of the edge is 1.15-1.25 times the thickness of the side film.

[0016] As a further solution of the inner protective insulation film structure, the thickness of the outer protective layer is 30-50 μm, and the thickness of the inner absorbent layer is 20-30 μm.

[0017] As a further solution of the inner protective insulation film structure, the mechanical strength of the outer protective layer is greater than the mechanical strength of the inner absorbent layer, and the liquid absorption rate of the inner absorbent layer is greater than the liquid absorption rate of the outer protective layer.

[0018] As a further solution of the inner protective insulation film structure, the inner absorbent layer is a PP (Polypropylene) film impregnated with a nanocellulose solution; and / or,

[0019] The outer protective layer is selected from a PET film or a PI film.

[0020] In another aspect, a preparation method of the inner protective insulation film structure is provided, comprising the following steps:

[0021] S10, providing an outer protective film material and an inner liquid-absorbing film material, adhering the outer protective film material and the inner liquid-absorbing film material, and performing heat stretching treatment to form an insulation film bag composed of an outer protective layer and an inner liquid-absorbing layer and having an open end;

[0022] S20, performing hole punching treatment on a region of at least one second outer side film of the outer protective layer adjacent to an outer bottom film to form a plurality of through holes;

[0023] S30, performing heat setting and post-treatment on the insulation film bag after hole punching to obtain the inner protective insulation film structure.

[0024] As a further scheme of the preparation method of the inner protective insulation film structure, in step S10, the inner liquid-absorbing film material is prepared by impregnating a PP film in a nanocellulose solution and drying.

[0025] As a further scheme of the preparation method of the inner protective insulation film structure, the concentration of the nanocellulose solution is 0.05-0.5wt.%, the impregnation temperature is 50-70℃, and the impregnation time is 1-3h; the drying temperature is 90-110℃, and the drying time is 3-5min.

[0026] As a further scheme of the preparation method of the inner protective insulation film structure, the nanocellulose solution is prepared by dispersing nanocellulose in polyvinyl alcohol.

[0027] As a further scheme of the preparation method of the inner protective insulation film structure, the post-treatment in step S30 includes cooling and solidifying the insulation film bag after heat setting and edge thickening treatment, the edge thickening treatment includes spraying a PP suspension containing nanosilica on the edges of the insulation film bag and embedding the nanosilica into the insulation film bag by heat pressing to thicken the edges.

[0028] As a further scheme of the preparation method of the inner protective insulation film structure, the concentration of nanosilica in the PP suspension is 10-15wt.%, and / or the particle size D of the nanosilica is ≤50nm.

[0029] As a further scheme of the preparation method of the inner protective insulation film structure, cooling and solidifying the insulation film bag after heat setting means cooling the insulation film bag to 80-100℃ by air cooling, and then cooling the insulation film bag to room temperature by water cooling, and the cooling rate is not greater than 5℃ / s.

[0030] As a further solution of the preparation method of the inner protective insulation film structure, in step S30, the heat setting of the punched insulation film bag refers to heating the outer protective layer to 230-250℃, and blowing air into the insulation film bag through the opening end, so that the temperature of the inner liquid absorbing layer is maintained at 130-150℃, and the insulation is kept for 10-15s.

[0031] As a further solution of the preparation method of the inner protective insulation film structure, step S10 specifically includes the following steps:

[0032] S10a, providing the outer protective film material and the inner liquid absorbing film material, and connecting the outer protective film material and the inner liquid absorbing film material by heat pressing after lamination, and sealing the edges by heat melting to form an insulation film;

[0033] S10b, preheating and softening the insulation film and performing initial stretching positioning treatment, so that the insulation film is stretched in the transverse direction and the longitudinal direction respectively;

[0034] S10c, pouch-shaped bidirectional stretching of the insulation film after initial stretching positioning to form the insulation film bag.

[0035] As a further solution of the preparation method of the inner protective insulation film structure, step S10b includes:

[0036] preheating the insulation film to 100-120℃ for 30-90s, and then performing longitudinal stretching, so that the longitudinal stretching ratio is 3-5 times;

[0037] preheating the insulation film to 175-185℃ for 40-120s, and then performing transverse stretching, so that the transverse stretching ratio is 1.2-1.5 times.

[0038] As a further solution of the preparation method of the inner protective insulation film structure, in step S10c, the longitudinal stretching ratio of the insulation film bag is 4-6 times, the transverse stretching ratio is 5-8 times, and the total stretching ratio is 25-40 times.

[0039] In another aspect, a battery is provided, which includes a shell, a core package and an inner protective film, the inner protective film is the inner protective insulation film structure, the core package is located in the shell, and the inner protective film is wrapped outside the core package to isolate the core package and the shell.

[0040] Beneficial effects: in the present application, by compounding the inner liquid absorbing layer and the outer protective layer with through holes to form the inner protective insulation film structure, on the one hand, the mechanical strength and insulation performance of the inner protective insulation film structure can be improved; on the other hand, the electrolyte deposited at the bottom of the core package can quickly contact the inner liquid absorbing layer through the through hole adjacent to the outer bottom film area of the second outer side film, quickly absorb the electrolyte through the inner liquid absorbing layer and diffuse the electrolyte to the surface of the core package and penetrate between the pole pieces inside the core package, improve the core package infiltration effect, reduce the deposition of free electrolyte at the bottom of the core package, and cause the bottom of the pole piece in the core package to swell and lithium precipitation phenomenon, improve the battery safety and service life. BRIEF DESCRIPTION OF DRAWINGS

[0041] The present application will be further described in detail below according to the drawings and examples.

[0042] Figure 1 Structure diagram of the inner protective insulation film structure (the through hole is not shown) described in the embodiment of the present application;

[0043] Figure 2 Top view diagram of the inner protective insulation film structure described in the embodiment of the present application;

[0044] Figure 3 Local enlarged diagram of the second outer side film described in the embodiment of the present application;

[0045] Figure 4 Flow chart of the preparation method of the inner protective insulation film structure described in the embodiment of the present application.

[0046] In the drawings:

[0047] 100, inner liquid absorbing layer; 110, inner bottom film; 120, inner side film; 200, outer protective layer; 210, outer side film; 211, first outer side film; 212, second outer side film; 2101, first area; 2102, second area; 220, through hole; 300, opening end; 400, edge. DETAILED DESCRIPTION

[0048] In order to make the technical problems solved by the present application, the technical solutions adopted and the technical effects achieved more clear, the technical solutions of the embodiments of the present application will be further described in detail below with reference to the drawings. Obviously, the described embodiments are only part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0049] In the description of the present application, unless otherwise explicitly specified and limited, the terms "connected", "linked", "fixed" should be understood broadly, for example, can be fixedly connected, can be detachably connected, or integrated; can be mechanically connected, or electrically connected; can be directly connected, or indirectly connected through an intermediate medium, or the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0050] In the present application, unless otherwise explicitly specified and limited, "on" or "under" of the first feature to the second feature can include that the first feature and the second feature are in direct contact, or that the first feature and the second feature are not in direct contact but are in contact through another feature between them. Moreover, "on", "above" and "on" of the first feature to the second feature includes that the first feature is directly above and obliquely above the second feature, or only indicates that the horizontal height of the first feature is higher than that of the second feature. "Below", "under" and "under" of the first feature to the second feature includes that the first feature is directly below and obliquely below the second feature, or only indicates that the horizontal height of the first feature is less than that of the second feature.

[0051] In the description of the present embodiment, if the terms "up", "down", "left", "right" and other orientation or position relationship appear, they are based on the orientation or position relationship shown in the drawings, and are only for the convenience of description and simplification of operation, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore cannot be understood as a limitation on the present application. In addition, if the terms "first", "second" and the like appear, they are only used to distinguish in description, and have no special meaning.

[0052] As shown in Figures 1 to 3 The present embodiment provides an inner protective insulation film structure for wrapping the core package to isolate the core package from the battery case, which includes an inner liquid absorption layer 100 and an outer protective layer 200 arranged on the outer surface of the inner liquid absorption layer 100. The outer protective layer 200 includes an outer bottom film (not shown in the figure) and an outer side film 210. The outer side film 210 includes two first outer side films 211 and two second outer side films 212 connected with the outer bottom film. The two first outer side films 211 are oppositely arranged and face two large surfaces in the thickness direction of the core package. The two second outer side films 212 are oppositely arranged and face two side surfaces in the width direction of the core package. At least one second outer side film 212 is provided with a plurality of through holes 220 adjacent to the area of the outer bottom film.

[0053] In the embodiment, the outer protective layer 200 and the inner liquid-absorbing layer 100 both have insulation properties; the inner liquid-absorbing layer 100 and the outer protective layer 200 provided with the through holes 220 are combined to form the inner protective insulation film structure, which can improve the mechanical strength and insulation properties of the inner protective insulation film structure on the one hand; on the other hand, the electrolyte deposited at the bottom of the core package can quickly contact the inner liquid-absorbing layer 100 through the through holes 220 in the area adjacent to the outer bottom film of the second outer side film 212, quickly absorb the electrolyte through the inner liquid-absorbing layer 100 and diffuse the electrolyte to the surface of the core package and penetrate between the pole pieces inside the core package, improve the core package soaking effect, reduce the deposition of free electrolyte at the bottom of the core package, and prevent the swelling and lithium precipitation phenomenon at the bottom of the pole pieces in the core package, thereby improving the safety and service life of the battery.

[0054] In the embodiment, the "the area adjacent to the outer bottom film of the second outer side film 212 is provided with a plurality of through holes 220" means that the through holes 220 are not limited to being provided on only one second outer side film 212, and are not limited to being provided on only the area adjacent to the outer bottom film of the second outer side film 212, but can also be provided on both second outer side films 212 and on the entire second outer side film.

[0055] Preferably, both second outer side films 212 are provided with through holes 220. The electrolyte deposited at the bottom of the core package can quickly contact the inner liquid-absorbing layer 100 through the through holes 220 on the two second outer side films 212, which can further improve the core package soaking effect.

[0056] In the embodiment, the term "bottom of the core package" includes the area between the outer bottom of the core package and the shell and the area adjacent to the outer bottom of the core package on the outer side of the core package. In the prior art, the deposition of electrolyte at the bottom of the core package can cause the lower part of the pole piece in the core package to be soaked in the electrolyte, while the upper part of the pole piece is not sufficiently soaked in the electrolyte. The lower part of the pole piece is soaked in the electrolyte for a long time, which can cause swelling and lithium precipitation. The inner protective insulation film structure of the embodiment can effectively solve this technical problem.

[0057] In other embodiments, the through holes 220 are provided on the entire second outer side film 212, and the electrolyte that can contact the through holes can quickly contact the inner liquid-absorbing layer 100 through the through holes 220.

[0058] Further, the inner protective insulation film structure is a bag-like structure provided with an open end 300, and the hole density of the second outer side film 212 gradually decreases from the outer bottom film towards the open end 300. In other words, the hole density of the area adjacent to the outer bottom film of the second outer side film 212 is the largest, which can make the electrolyte at the bottom of the core package quickly diffuse to the inner liquid-absorbing layer 100 through the through holes 220 in this area, thereby preventing the deposition of free electrolyte at the bottom of the core package.

[0059] Further, the inner protective insulation film structure is a bag-like structure provided with an open end 300, and the second outer film 212 has a first region 2101 adjacent to the outer bottom film and a second region 2102 adjacent to the open end 300, the hole density of the first region 2101 being greater than that of the second region 2102.

[0060] It can be understood that the through holes 220 are distributed throughout the second outer film 212. In the embodiment, the region where the through holes 220 are densely distributed is designed in the region of the second outer film 212 adjacent to the outer bottom film, and the region where the through holes 220 are sparsely distributed is designed in the region of the second outer film 212 adjacent to the open end 300, which can promote the upward directional permeation of the electrolyte solution to avoid the deposition of free electrolyte solution at the bottom of the core package.

[0061] Further, the hole density of the first region 2101 is 95-105 holes / mm 2 .

[0062] In the embodiment, the hole density of the first region 2101 is limited to 95-105 holes / mm 2 , so that the electrolyte solution at the bottom of the core package can be quickly absorbed by the inner absorbent layer 100 through the outer protective layer 200. Specifically, the hole density of the first region 2101 can be 95 holes / mm 2 , 96 holes / mm 2 , 97 holes / mm 2 , 98 holes / mm 2 , 99 holes / mm 2 , 100 holes / mm 2 , 101 holes / mm 2 , 102 holes / mm 2 , 103 holes / mm 2 , 104 holes / mm 2 , or 105 holes / mm 2 .

[0063] Further, the hole density of the second region 2102 is 25-35 holes / mm 2 . In the embodiment, the hole density of the second region 2102 is limited to 25-35 holes / mm 2 , so that the electrolyte solution can be gradually absorbed by the inner absorbent layer 100 through the through holes 220 in the region. Specifically, the hole density of the second region 2102 can be 25 holes / mm 2 , 26 holes / mm 2 , 27 holes / mm 2 , 8 holes / mm 2 , 29 holes / mm 2 , 30 holes / mm 2 , 31 holes / mm 232 holes per mm 2 33 holes per mm 2 34 holes per mm 2 or 35 holes per mm 2 .

[0064] Further, the area of the first region 2101 is 60-80% of the area of the second outer film 212, for example, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 72%, 75%, 78%, or 80%, etc. By controlling the area of the first region 2101 to be within the range of 60-80% of the area of the second outer film 212, the embodiment can ensure that the electrolyte at the bottom of the core package automatically penetrates upward more optimally.

[0065] The aperture of the through hole 220 is 6-10 μm, which can enable the electrolyte at the bottom of the core package to automatically penetrate to the inner wicking layer 100. The principle is similar to the siphon effect, which will not be described in detail.

[0066] Alternatively, the aperture of the through hole 220 is 6 μm, 6.2 μm, 6.5 μm, 6.8 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, or 10 μm, etc.

[0067] Further, the inner protective insulation film structure has a bottom film, a side film, and four edges 400 corresponding to the four side edges of the two large faces of the core package, as shown in Figure 2 The inner wicking layer 100 includes an inner bottom film 110 and an inner side film 120 connected to the inner bottom film 110. The inner bottom film 110 and the outer bottom film constitute the bottom film, the inner side film 120 and the outer side film 210 constitute the side film, and the thickness of the edge 400 is greater than the thickness of the side film.

[0068] In the embodiment, the "side film" of the inner protective insulation film structure includes two side films corresponding to the two large faces in the thickness direction of the core package and two side films corresponding to the two side faces in the width direction of the core package. Similarly, the term "inner side film" includes two inner side films 120 corresponding to the two large faces in the thickness direction of the core package and two inner side films 120 corresponding to the two side faces in the width direction of the core package. The term "four side edges of the two large faces of the core package" refers to the four side edges formed by connecting the two large faces in the thickness direction of the core package and the two side faces in the width direction of the core package.

[0069] In the prior art, when entering the shell, the core package wrapped with the insulation film passes through the right-angle area of the shell, and the insulation film is bent, squeezed, and even scraped, which may cause the insulation film to be damaged, resulting in insulation failure between the core package and the shell. The embodiment thickens the edge 400 of the inner protective insulation film structure, which can effectively improve the bending resistance and thus improve the insulation effect of the inner protective insulation film structure.

[0070] Further, the thickness of the edge 400 is 1.15-1.25 times, for example, 1.15 times, 1.18 times, 1.2 times, 1.22 times or 1.25 times, etc. of the thickness of the side film. If the thickness of the edge 400 is less than 1.15 times of the thickness of the side film, the bending resistance is insufficient to resist the bending, extrusion and even scratching of the inner protective insulation film structure when the core is inserted into the shell; if the thickness of the edge 400 is greater than 1.25 times of the thickness of the side film, the inner protective insulation film structure is stuck at the opening of the shell when the core is inserted into the shell, which affects the efficiency of the core insertion into the shell.

[0071] The edge 400 is connected to the side film.

[0072] Since the mechanical strength of the outer protective layer 200 is greater than that of the inner liquid absorbing layer 100, the thickness of the outer protective layer 200 is designed to be 30-50 μm, and the thickness of the inner liquid absorbing layer 100 is designed to be 20-30 μm, which can improve the mechanical strength of the entire inner protective insulation film structure while not affecting the liquid absorbing effect of the inner protective insulation film structure.

[0073] Optionally, the thickness of the outer protective layer 200 is 30 μm, 31 μm, 32 μm, 34 μm, 35 μm, 38 μm, 40 μm, 42 μm, 45 μm, 48 μm or 50 μm, etc.; and the thickness of the inner liquid absorbing layer 100 is 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm or 30 μm, etc.

[0074] Further, the mechanical strength of the outer protective layer 200 is greater than that of the inner liquid absorbing layer 100, and the liquid absorbing rate of the inner liquid absorbing layer 100 is greater than that of the outer protective layer 200; after the outer protective layer 200 is combined with the inner liquid absorbing layer 100, the outer protective layer 200 can improve the mechanical stability of the inner protective insulation film structure, and at the same time, after the outer protective layer 200 is perforated, the good liquid absorbing rate of the inner liquid absorbing layer 100 can improve the liquid absorbing stability of the inner protective insulation film structure, thereby improving the core package immersion effect.

[0075] Further, the inner liquid absorbing layer 100 is a PP film impregnated with a nanocellulose solution, which can enhance the liquid affinity of the PP film after impregnation with the nanocellulose solution.

[0076] Further, the outer protective layer 200 is selected from a PET film or a PI film, which has good mechanical strength and can improve the mechanical strength and insulation of the inner protective insulation film structure.

[0077] The embodiment also provides a preparation method of the inner protective insulation film structure of any one of the above embodiments, which comprises the following steps:

[0078] S10, providing an outer protective film material and an inner liquid-absorbing film material, adhering the outer protective film material and the inner liquid-absorbing film material, and performing heat stretching treatment to form an insulation film bag composed of an outer protective layer 200 and an inner liquid-absorbing layer 100 and having an open end 300;

[0079] S20, performing hole punching treatment on an area of at least one second outer side film 212 of the outer protective layer 200 adjacent to the outer bottom film to form a plurality of through holes 220;

[0080] S30, performing heat setting and post-treatment on the insulation film bag after the hole punching to obtain a finished inner protective insulation film structure.

[0081] In the embodiment, after the outer protective film material and the inner liquid-absorbing film material are adhered and heat stretched to form the insulation film bag, the second outer side film 212 of the outer protective layer 200 of the insulation film bag is subjected to hole punching treatment. Compared with the pre-hole punching and then heat stretching, the hole edge deformation caused by high-temperature melting during the heat stretching can be prevented. The insulation film bag with the through holes 220 is subjected to setting and post-treatment, and an inner protective insulation film structure having both insulation protection and electrolyte directional permeation functions can be obtained. When the inner protective insulation film structure is applied to a battery, the safety and service life of the battery can be effectively improved.

[0082] In a specific example, after the stretching is completed, the second outer side film 212 is subjected to hole punching by laser to form micropores with a pore diameter of 8 μm, and the hole density of the second outer side film 212 adjacent to the outer bottom film area (the first area 2101) is 100 holes / mm 2 , and the hole density of the second outer side film 212 adjacent to the open end 300 area is 30 holes / mm 2 .

[0083] Further, in step S10, the inner liquid-absorbing film material is prepared by immersing a PP film in a nanocellulose solution and drying. In the embodiment, the PP film is immersed in the nanocellulose solution, which can enhance the liquid affinity of the PP film, and the formed inner liquid-absorbing film material can quickly absorb electrolyte and diffuse the electrolyte to the inside of the core bag.

[0084] Specifically, the nanocellulose solution is prepared by dispersing nanocellulose in polyvinyl alcohol. The polyvinyl alcohol has good film-forming property, and can form a uniform polyvinyl alcohol film with hydrophilicity on the surface of the PP film. The polyvinyl alcohol film can be bonded with the PP film, thereby stably adhering to the surface of the PP film and not easy to fall off. The chemical structure of nanocellulose is similar to that of polyvinyl alcohol, and the two have good compatibility, and can be tightly combined together and adhered to the surface of the PP film. The nanocellulose interlaces with each other in the polyvinyl alcohol matrix to form a highly interconnected porous three-dimensional network structure at the nanoscale, thereby generating strong capillary action to quickly and actively absorb the electrolyte into and transport to the entire wicking layer 100, and accelerate the efficiency of electrolyte infiltration into the core package.

[0085] Further, the concentration of the nanocellulose solution is 0.05-0.5wt.%, i.e. the dispersion concentration of nanocellulose in polyvinyl alcohol is 0.05-0.5wt.%, the impregnation temperature is 50-70℃, and the impregnation time is 1-3h; the drying temperature is 90-110℃, and the drying time is 3-5min. By controlling the appropriate concentration, impregnation temperature and impregnation time, and drying conditions, the wicking layer 100 can have good liquid absorption performance.

[0086] Exemplarily, the concentration of the nanocellulose solution can be 0.05wt.%, 0.08wt.%, 0.1wt.%, 0.12wt.%, 0.15wt.%, 0.18wt.%, 0.2wt.%, 0.25wt.%, 0.3wt.%, 0.35wt.%, 0.4wt.%, 0.45wt.% or 0.5wt.% etc.; the impregnation temperature, i.e. the temperature of the nanocellulose solution, can be 50℃, 52℃, 55℃, 58℃, 60℃, 62℃, 64℃, 66℃, 68℃ or 70℃ etc.; the impregnation time can be 1h, 1.2h, 1.5h, 1.8h, 2h, 2.5h or 3h etc.; the drying temperature is 90℃, 92℃, 93℃, 95℃, 97℃, 99℃, 100℃, 102℃, 104℃, 105℃, 107℃, 108℃ or 110℃ etc., and the drying time is 3min, 4min or 5min.

[0087] Further, the PP film is impregnated in the nanocellulose solution while ultrasonic dispersion is started, which can improve the uniformity of the dispersion of the nanocellulose solution on the PP film.

[0088] In a specific example, a PP film with a thickness of 25μm is placed in a nanocellulose solution with a temperature of 60℃ and a concentration of 0.3wt.%, and ultrasonic dispersion is assisted to enhance the wicking property.

[0089] The post-processing in step S30 includes cooling and curing the heat-set insulating film bag and thickening the edge 400. The edge 400 thickening process includes spraying a PP suspension containing nano-silica onto the edge 400 of the insulating film bag and embedding it into the insulating film bag by hot pressing, thereby thickening the edge 400.

[0090] In this embodiment, nano-silica particles are dispersed in a PP matrix to form a PP suspension. After being sprayed onto the edge 400 of an insulating film bag, it can be cured and embedded into the insulating film bag by hot pressing. The nano-silica particles, as rigid particles, are dispersed in the PP matrix and can effectively transfer and disperse stress, hindering the slippage of molecular chains, thereby significantly improving the tear resistance of the edge 400.

[0091] In this embodiment, for ease of operation, PP suspension is usually sprayed from the outside of the insulating film bag toward the edge 400. By thickening the edge 400 of the insulating film bag, the thickness of the edge 400 can be increased to 1.15-1.25 times.

[0092] Furthermore, the concentration of nano-silica in the PP suspension is 10-15 wt.%; the particle size of the nano-silica is D≤50 nm. By controlling the concentration of nano-silica within the range of 10-15 wt.% and the particle size of nano-silica within the range of 50 nm, the edge 400 of the insulating film bag has suitable bending resistance.

[0093] The cooling and curing of the heat-set insulating film bag refers to: cooling the insulating film bag to 80-100℃ by air cooling, specifically to 80℃, 82℃, 85℃, 88℃, 90℃, 92℃, 94℃, 95℃, 97℃, 98℃, 99℃ or 100℃, etc., to prevent the insulating film bag from becoming brittle due to sudden cooling; and then cooling the insulating film bag to room temperature by water cooling, with a cooling rate not exceeding 5℃ / s.

[0094] Understandably, after hot stretching, the temperature of the insulating film bag is very high, and the molecular chains are in a highly oriented but very active state. Air cooling lowers the temperature of the insulating film bag, eliminating most of the internal stress and preventing excessive shrinkage or deformation due to stress release during subsequent use. Water cooling after air cooling completely freezes the movement of the molecular chains within the insulating film bag, permanently fixing the orientation and crystalline structure formed during hot stretching.

[0095] Water cooling refers to the use of a cooling roller with internal cooling water in close contact with the insulating film bag to achieve cooling and solidification of the insulating film bag.

[0096] Further, in step S30, heat-setting the perforated insulating film bag refers to heating the outer protective layer 200 to 230-250°C, for example, by using an infrared radiation heater to heat the outer protective layer 200, causing the temperature of the outer protective layer 200 to rise rapidly to 230-250°C. Specifically, this temperature can be 230°C, 232°C, 235°C, 238°C, 240°C, 245°C, 246°C, 248°C, or 250°C; simultaneously, heat is applied to the insulating film bag through the open end 300. Air is blown inside the membrane bag (heat barrier) to maintain the temperature of the inner liquid-absorbing layer 100 at 130-150℃ (e.g., 130℃, 132℃, 135℃, 138℃, 140℃, 142℃, 144℃, 146℃, 148℃ or 150℃) for 10-15s (e.g., 10s, 11s, 12s, 13s, 14s or 15s) to lock the molecular orientation structure, eliminate internal stress, and improve the dimensional stability, mechanical strength and insulation of the insulating membrane bag.

[0097] Furthermore, step S10 specifically includes the following steps:

[0098] S10a. Provide an outer protective film and an inner liquid-absorbing film. After the outer protective film and the inner liquid-absorbing film are bonded together, they are hot-pressed together and the edges are hot-melted and sealed to form an insulating film.

[0099] S10b: Preheat and soften the insulating film and perform initial stretching and positioning treatment to stretch the insulating film in the transverse and longitudinal directions respectively;

[0100] S10c. The insulating film after initial stretching and positioning is subjected to bidirectional bag-shaped stretching to form an insulating film bag.

[0101] Specifically, in step S10b, the insulating film bag needs to be initially stretched longitudinally and laterally. Before both longitudinal and lateral stretching, the insulating film bag needs to be preheated. In step S10c, the bidirectional stretching of the bag involves stretching along the bag depth (longitudinal stretching) and stretching along the bag width (lateral stretching, consistent with the core package width direction). This embodiment combines initial stretching positioning with bidirectional stretching of the bag, which can avoid stress concentration leading to film breakage. After stretching, a bag-like structure with a closed bottom and an open top (open end 300) is ultimately formed, avoiding folded seams.

[0102] Further, step S10b includes:

[0103] Preheat the insulating film to 100-120℃ (e.g., 100℃, 102℃, 105℃, 108℃, 110℃, 112℃, 115℃, 118℃, or 120℃) and hold for 30-90 seconds (e.g., 30s, 35s, 40s, 45s, 50s, 55s, 60s, 65s, 70s, 75s, 80s, 85s, or 90s). Then, perform longitudinal stretching to achieve a longitudinal stretch ratio of 3-5 times (e.g., 3 times, 3.1 times, 3.2 times, 3.3 times, 3.4 times, 3.5 times, 3.6 times, 3.8 times, 4 times, 4.2 times, 4.5 times, 4.7 times, 4.8 times, 4.9 times, or 5 times).

[0104] Preheat the insulating film to 175-185℃ (e.g., 175℃, 176℃, 177℃, 178℃, 179℃, 180℃, 182℃, 184℃ or 185℃) and hold for 40-120s (e.g., 40s, 45s, 50s, 55s, 60s, 65s, 70s, 75s, 80s, 85s, 90s, 95s, 100s, 105s, 110s, 115s or 120s), then stretch it laterally to a ratio of 1.2-1.5 times (e.g., 1.2 times, 1.3 times, 1.4 times or 1.5 times).

[0105] In this process, longitudinal stretching can be performed first, followed by transverse stretching, or vice versa. During transverse stretching, a clamp is used to hold the edge of the insulating film as it enters the expansion chain clamp. This embodiment controls the preheating temperature appropriately by adjusting the required stretching ratio to prevent stress concentration and film breakage.

[0106] In a specific example, the preheating temperature before longitudinal stretching is 110℃ and held for 60 seconds; the preheating temperature before transverse stretching is 180℃ and held for 80 seconds.

[0107] In this embodiment, the equipment used in the hot pressing, initial stretching, bag-shaped biaxial stretching, heat setting, punching, and cooling processes are all conventional equipment in the field, and will not be described in detail here.

[0108] In step S10c, the longitudinal stretch ratio of the insulating film bag is 4-6 times (e.g., 4 times, 4.2 times, 4.5 times, 4.8 times, 5 times, 5.2 times, 5.4 times, 5.6 times, 5.8 times, or 6 times), the transverse stretch ratio is 5-8 times (e.g., 5 times, 5.2 times, 5.4 times, 5.6 times, 5.8 times, 6 times, 6.2 times, 6.4 times, 6.6 times, 7 times, 7.4 times, 7.8 times, or 8 times), and the total stretch ratio is 25-40 times (e.g., 25 times, 26 times, 27 times, 28 times, 29 times, 30 times, 31 times, 32 times, 33 times, 35 times, 37 times, 39 times, or 40 times) to further prevent stress concentration and film rupture.

[0109] It should be noted that after cooling and curing, the insulating film bag still needs to be cut and trimmed.

[0110] Exemplary, the method for preparing the inner protective insulating film structure in this embodiment is as follows: Figure 4 As shown, the process includes material preparation and pretreatment (preparing PET film (outer protective film) and PP film, and modifying the PP film to obtain inner liquid-absorbing film), preheating and softening, initial stretching and positioning, biaxial stretching of the bag, laser perforation, heat setting, cooling and curing, cutting and trimming, and edge thickening treatment, finally obtaining the inner protective insulating film structure, i.e. the finished insulating bag. The specific process steps are as described in the above embodiment and will not be repeated here.

[0111] This embodiment also provides a battery, including a casing, a core pack, and an inner protective film. The inner protective film is the inner protective insulating film structure of any of the above embodiments. The core pack is located inside the casing, and the inner protective film wraps around the core pack to isolate the core pack and the casing.

[0112] The battery in this embodiment is a square battery, which has the characteristics of high safety and long service life.

[0113] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. An inner protective insulating film structure for wrapping a core package to isolate the core package from the battery casing, characterized in that, The inner protective insulating film structure includes an inner liquid-absorbing layer and an outer protective layer disposed on the outer surface of the inner liquid-absorbing layer. The outer protective layer includes an outer bottom film and an outer side film. The outer side film includes two first outer side films and two second outer side films connected to the outer bottom film. The two first outer side films are disposed opposite to each other and face the two large surfaces in the thickness direction of the core package. The two second outer side films are disposed opposite to each other and face the two side surfaces in the width direction of the core package. At least one second outer side film has a plurality of through holes in the region adjacent to the outer bottom film.

2. The inner protective insulating film structure according to claim 1, characterized in that, The inner protective insulating film structure is a bag-shaped structure with an open end, and the pore density on the second outer film gradually decreases from the outer bottom film toward the open end.

3. The inner protective insulating film structure according to claim 1, characterized in that, The inner protective insulating film structure is a bag-shaped structure with an open end. The second outer film has a first region adjacent to the outer bottom film and a second region adjacent to the open end. The pore density of the first region is greater than the pore density of the second region.

4. The inner protective insulating film structure according to claim 3, characterized in that, The pore density in the first region is 95-105 pores / mm. 2 ; and / or, The pore density in the second region is 25-35 pores / mm. 2 ; and / or, The area of ​​the first region is 60-80% of the area of ​​the second outer membrane.

5. The inner protective insulating film structure according to any one of claims 1 to 4, characterized in that, The diameter of the through hole is 6-10 μm.

6. The inner protective insulating film structure according to any one of claims 1 to 4, characterized in that, The inner protective insulating film structure has a bottom film, a side film, and four edges that correspond one-to-one with the four side edges of the two large surfaces of the core package. The inner liquid-absorbing layer includes an inner bottom film and an inner side film connected to the inner bottom film. The inner bottom film and the outer bottom film constitute the bottom film, and the inner side film and the outer side film constitute the side film. The thickness of the edges is greater than the thickness of the side film.

7. The inner protective insulating film structure according to claim 6, characterized in that, The thickness of the edge is 1.15-1.25 times the thickness of the side membrane.

8. The inner protective insulating film structure according to any one of claims 1 to 4, characterized in that, The outer protective layer has a thickness of 30-50 μm, and the inner liquid-absorbing layer has a thickness of 20-30 μm.

9. The inner protective insulating film structure according to any one of claims 1 to 4, characterized in that, The mechanical strength of the outer protective layer is greater than that of the inner liquid-absorbing layer, and the liquid absorption rate of the inner liquid-absorbing layer is greater than that of the outer protective layer.

10. The inner protective insulating film structure according to any one of claims 1 to 4, characterized in that, The internal absorbent layer is a PP film impregnated with a nanocellulose solution; and / or... The outer protective layer is selected from PET film or PI film.

11. A method for preparing the inner protective insulating film structure according to any one of claims 1 to 10, characterized in that, Includes the following steps: S10. Provide an outer protective film and an inner liquid-absorbing film, and bond the outer protective film and the inner liquid-absorbing film together and perform a heat stretching treatment to form an insulating film bag consisting of an outer protective layer and an inner liquid-absorbing layer and having an open end. S20. Perforation is performed on at least one second outer membrane of the outer protective layer adjacent to the outer bottom membrane to form several through holes; S30. The perforated insulating film bag is heat-set and post-treated to obtain the inner protective insulating film structure.

12. The method for preparing the inner protective insulating film structure according to claim 11, characterized in that, In step S10, the internal liquid-absorbing membrane material is prepared by impregnating a PP membrane in a nanocellulose solution and then drying it.

13. The method for preparing the inner protective insulating film structure according to claim 12, characterized in that, The concentration of the nanocellulose solution is 0.05-0.5 wt.%, the impregnation temperature is 50-70℃, and the impregnation time is 1-3 h; the drying temperature is 90-110℃, and the drying time is 3-5 min.

14. The method for preparing the inner protective insulating film structure according to claim 13, characterized in that, The nanocellulose solution is prepared by dispersing nanocellulose in polyvinyl alcohol.

15. The method for preparing the inner protective insulating film structure according to claim 11, characterized in that, The post-processing in step S30 includes: cooling and curing the heat-set insulating film bag and thickening the edges; the edge thickening process includes: spraying a PP suspension containing nano-silica onto the edges of the insulating film bag and embedding it into the insulating film bag by hot pressing, thereby thickening the edges.

16. The method for preparing the inner protective insulating film structure according to claim 15, characterized in that, The concentration of nano-silica in the PP suspension is 10-15 wt.%; and / or, The particle size D of the nano-silica is ≤50nm.

17. The method for preparing the inner protective insulating film structure according to claim 15, characterized in that, Cooling and curing the heat-set insulating film bag means: cooling the insulating film bag to 80-100℃ by air cooling; and then cooling the insulating film bag to room temperature by water cooling, with a cooling rate of no more than 5℃ / s.

18. The method for preparing the inner protective insulating film structure according to claim 11, characterized in that, In step S30, heat setting of the perforated insulating film bag refers to heating the outer protective layer to 230-250°C, while blowing air into the insulating film bag through the open end to keep the temperature of the inner liquid-absorbing layer at 130-150°C for 10-15 seconds.

19. The method for preparing the inner protective insulating film structure according to claim 11, characterized in that, Step S10 specifically includes the following steps: S10a. Provide the outer protective film and the inner liquid-absorbing film, bond the outer protective film and the inner liquid-absorbing film together by hot pressing, and heat-seal the edges to form an insulating film; S10b: The insulating film is preheated, softened, and initially stretched and positioned to stretch the insulating film in the transverse and longitudinal directions, respectively. S10c. The insulating film after initial stretching and positioning is subjected to bidirectional bag-shaped stretching to form the insulating film bag.

20. The method for preparing the inner protective insulating film structure according to claim 19, characterized in that, Step S10b includes: The insulating film is preheated to 100-120℃ and held for 30-90 seconds, and then longitudinally stretched to achieve a longitudinal stretch ratio of 3-5 times. The insulating film is preheated to 175-185℃ and held for 40-120 seconds, and then stretched laterally to a ratio of 1.2-1.

5.

21. The method for preparing the inner protective insulating film structure according to claim 19, characterized in that, In step S10c, the longitudinal stretch ratio of the insulating film bag is 4-6 times, the transverse stretch ratio is 5-8 times, and the total stretch ratio is 25-40 times.

22. A battery, characterized in that, The device includes a shell, a core package, and an inner protective film. The inner protective film is an inner protective insulating film structure as described in any one of claims 1 to 10 or an inner protective insulating film structure prepared by the method described in any one of claims 11 to 21. The core package is located inside the shell, and the inner protective film wraps around the core package to isolate the core package from the shell.

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