Soft package battery aluminum plastic film structure with transparent observation window and preparation method of soft package battery aluminum plastic film structure

Abstract

The invention relates to the technical field of lithium ion battery manufacturing, and discloses a soft package battery aluminum-plastic film structure with a transparent observation window and a preparation method of the soft package battery aluminum-plastic film structure. Through the design that the observation window is locally formed and the transparent polymer film is designed, on the premise that the advantages of the soft package battery aluminum plastic film are completely reserved, in-situ lossless real-time observation of the infiltration dynamic state of electrolyte in the battery, the gas generation behavior and the gas path evolution is achieved, and a direct visual basis is provided for research and development verification, process optimization and safety design; the transparent window and the aluminum plastic film are in homogeneous or high-compatibility sealing connection, so that the key packaging performance is not influenced; the scheme is highly compatible with an existing manufacturing process, subversive equipment transformation is not needed, second-level nondestructive quality inspection and fault diagnosis of a synchronous enabling production line are achieved, and transparent observation and packaging performance are achieved at the same time.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery manufacturing technology, specifically to a soft-pack battery aluminum-plastic film structure with a transparent observation window and its preparation method. Background Technology

[0002] Due to their advantages such as high energy density, good safety, flexible shape design, and good economy, soft-pack lithium batteries are widely used in consumer electronics, power batteries, energy storage, and experimental testing.

[0003] Currently, the mainstream packaging material, aluminum-plastic film, is typically composed of an outer layer (nylon or PET), a barrier layer (aluminum foil), and an inner layer (heat-sealing layer, such as modified polypropylene CPP or PP). While this composite structure provides excellent barrier properties (water and oxygen), mechanical strength, and heat-sealing performance, its overall opacity presents a significant technical bottleneck.

[0004] The electrolyte wetting process cannot be observed in real time: During the electrolyte injection and settling (aging) stages, it is impossible to visually determine whether the electrolyte has uniformly and fully wetted the pores of the electrodes and separator. Poor wetting can lead to increased battery internal resistance, decreased capacity, shortened cycle life, and even lithium plating, posing safety hazards. Currently, inspection mainly relies on experience or destructive disassembly, which is inefficient and cannot monitor the process effect in real time.

[0005] The dynamics of gas generation are difficult to capture: During battery formation, aging, cycling, or overcharging / over-discharging, gases may be generated internally (such as SEI film formation and electrolyte decomposition). Existing aluminum-plastic films cannot directly observe the specific location, rate, morphology (bubble size and distribution), and formation and evolution of gas pathways (gas escape channels) of gas generation. This is crucial for studying battery side reaction mechanisms, assessing safety risks, and optimizing formation processes.

[0006] Hinders real-time monitoring and process optimization of internal reactions: Due to the lack of direct visual feedback, researchers and engineers find it difficult to correlate the physicochemical changes occurring inside the battery (such as lithium plating, dendrite growth, separator shrinkage / deformation, and interface reactions) with external test data (voltage, current, temperature, and internal resistance) in real time, which greatly limits the efficiency and accuracy of optimizing cell design, electrolyte formulation, and manufacturing processes (liquid injection, formation, and aging).

[0007] Existing patented solutions, such as those using fully transparent resin (rigid) shells (CN215955367U), often sacrifice the inherent advantages of pouch batteries, such as lightweight, flexibility, and high energy density, or suffer from high costs, insufficient barrier properties, poor mechanical strength, and difficulties in heat sealing. Using fully transparent polymer (soft) shells (CN104143642A), such as TPT encapsulation films or ETFE encapsulation films, makes it difficult to guarantee the sealing and structural strength of the pouch battery. Therefore, there is an urgent need to develop a novel encapsulation structure that can maintain the core advantages of pouch batteries while enabling visualization of their internal state. To this end, a pouch battery aluminum-plastic film structure with a transparent observation window and its preparation method are proposed. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a soft-pack battery aluminum-plastic film structure with a transparent observation window and its preparation method, thereby solving the problems in the background technology.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] In a first aspect, a soft-pack battery aluminum-plastic film structure with a transparent observation window includes:

[0011] The aluminum-plastic film consists of a nylon outer layer, an aluminum foil barrier layer, and a heat-sealed inner layer, with an observation window that penetrates through the nylon outer layer, the aluminum foil barrier layer, and the heat-sealed inner layer.

[0012] A transparent polymer film is used to fill and seal the observation window, and is heat-sealed or glue-sealed to form a connection with the aluminum-plastic film.

[0013] The aluminum-plastic film is configured such that after being folded along the centerline, it is combined with a transparent polymer film to seal the observation window, forming a sealed cavity that accommodates the battery core and electrolyte.

[0014] Preferably, the transparent polymer film is one of transparent polypropylene (PP) film, transparent polyimide (CPI) film, cyclic olefin polymer (COP) film, or coated reinforced PET film, and the heat-sealed inner layer is polypropylene (PP) or modified polypropylene (CPP), and the two are connected by heat sealing or adhesive sealing.

[0015] Preferably, the observation window is located on the aluminum-plastic film in the area corresponding to the large surface of the soft-pack battery core, and is offset from the electrode area and the tab-side sealing area of ​​the battery core.

[0016] Preferably, the number of observation windows is one or two.

[0017] In a second aspect, a method for preparing a soft-pack battery aluminum-plastic film with a transparent observation window is provided, for preparing the soft-pack battery aluminum-plastic film structure with a transparent observation window described in the first aspect, comprising:

[0018] Step 1: Based on the size of the battery core, cut aluminum-plastic film to the matching size;

[0019] Step 2: Cut an observation window in the designated area of ​​the aluminum-plastic film. The observation window extends through the nylon outer layer, aluminum foil barrier layer, and heat-sealed inner layer of the aluminum-plastic film.

[0020] Step 3: Based on the dimensions of the observation window, cut the matching transparent polymer film. The length and width of the transparent polymer film are larger than the length and width of the observation window.

[0021] Step 4: Cover the inside of the aluminum-plastic film with the transparent polymer film, completely covering the observation window, and seal it with the aluminum-plastic film by heat sealing or adhesive sealing;

[0022] Step 5: Place the large side of the battery core flat on the transparent polymer film. The negative and positive electrode tabs of the battery core extend beyond the aluminum-plastic film. At this time, fold the aluminum-plastic film along the center line, heat-seal or glue-seal the three sides of the aluminum-plastic film, and inject the electrolyte. The transparent polymer film inside the aluminum-plastic film blocks the observation window, forming a sealed cavity to accommodate the battery core and electrolyte.

[0023] Preferably, when the transparent polymer film is a transparent polypropylene (PP) film, step 4 adopts a heat sealing process with a heat sealing temperature of 160℃–200℃.

[0024] Preferably, if there is one observation window on the aluminum-plastic film, the folded aluminum-plastic film folds a transparent polymer film at the same time; if there are two observation windows, the folded aluminum-plastic film places the two transparent polymer films in parallel.

[0025] Preferably, when the transparent polymer film is a transparent polyimide (CPI) film, a cyclic olefin polymer (COP) film, or a coated reinforced polyethylene terephthalate (PET) film, step 4 employs an adhesive sealing process.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] This invention, through its innovative design of partial window opening and transparent material sealing, enables, for the first time, in-situ, real-time, and non-destructive direct observation of the electrolyte wetting distribution, gas generation dynamics (position, rate, and morphology), and gas path evolution process inside the battery (especially in large areas) while maintaining the basic packaging structure of the soft-pack battery and the core advantages of the aluminum-plastic film. This provides unprecedented direct visual evidence for research and development, process optimization, and quality control.

[0028] The transparent observation window material of this invention achieves a highly reliable seal with the inner layer of the aluminum-plastic film through a homogeneous or compatible connection method (heat sealing or adhesive sealing), effectively preventing electrolyte leakage and external environmental intrusion; the partial window design retains the excellent barrier properties, mechanical strength and flexibility of the aluminum-plastic film body to the greatest extent, and the overall encapsulation performance meets the requirements of battery use.

[0029] The key steps used in this invention, such as opening windows and connecting transparent windows (heat sealing or glue sealing), are highly compatible with existing core processes and equipment for manufacturing soft-pack batteries, without the need to introduce complex and expensive new equipment or disruptive processes; the transparent materials have a wide range of choices and are relatively inexpensive, making industrialization easier and reducing incremental costs.

[0030] This invention allows for real-time monitoring of the electrolyte wetting process through a transparent observation window, enabling rapid assessment of the impact of different injection processes, settling conditions, electrolyte formulations, and diaphragm / electrode materials on the wetting effect. This significantly shortens the R&D cycle and improves product yield.

[0031] This invention allows for direct observation of the generation, accumulation, migration, and exhaust processes of internal gases in batteries under formation, cycling, or abuse conditions through a transparent observation window. This provides intuitive and crucial data for a deeper understanding of side reaction mechanisms, optimization of formation / aging regimes, and design of safer and more efficient exhaust structures (gas paths), significantly improving the level of battery safety assessment and design.

[0032] This invention, through a transparent observation window, allows for the rapid and accurate assessment of critical internal states of batteries (such as whether electrolyte wetting is complete and whether abnormal gas generation exists) on production lines or in laboratory environments, assisting in root cause analysis of faults and improving the efficiency and level of production quality control.

[0033] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the overall structure of the window opening at the center of the front and rear large surfaces of the present invention;

[0035] Figure 2 This is a schematic diagram of the unfolded structure of the aluminum-plastic film with windows at the center of the front and rear large surfaces of the present invention;

[0036] Figure 3 This is a schematic diagram of the window structure on the left (right) side of the front and rear surfaces of the present invention;

[0037] Figure 4 This is a schematic diagram of the unfolded structure of the aluminum-plastic film with windows on the left (right) side of the front and rear surfaces of the present invention.

[0038] In the diagram: 1. Aluminum-plastic film; 2. Observation window; 3. Transparent polymer film. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0040] Please see Figure 1-4 This invention discloses a soft-pack battery aluminum-plastic film structure with a transparent observation window and its preparation method. By opening a through-hole observation window in a specific area of ​​the aluminum-plastic film and sealing it with a transparent polymer film, in-situ, real-time, and non-destructive visualization observation of the electrolyte wetting state, gas generation dynamics, and gas path evolution process inside the battery is achieved. At the same time, the barrier properties, mechanical strength, and heat sealing reliability of the aluminum-plastic film are completely preserved, providing key technical support for the research and development verification, process optimization, and failure analysis of soft-pack batteries.

[0041] Example 1:

[0042] Preparation steps:

[0043] 1. Cutting aluminum-plastic film

[0044] Operation: According to the cell size (50×70×5mm), cut the composite aluminum-plastic film (25μm nylon outer layer / 40μm aluminum foil barrier layer / 50μm heat-sealing inner layer of modified polypropylene (CPP)) into 140×80mm rectangular pieces.

[0045] Positioning: On the inner surface of the heat-sealed aluminum-plastic film 1, use laser to mark the folding center line (70mm along the length direction) and the position of the observation window 2. The center of the observation window 2 is located at the midpoint of the folding center line.

[0046] 2. Open observation window 2

[0047] Procedure: Fix the aluminum-plastic film 1 on the vacuum adsorption platform, and use an ultraviolet laser (wavelength 355nm, power 20W) to cut an 80×40mm rectangular window along the markings, as shown below. Figure 3 Figure 4 As shown, it extends through the outer nylon layer, the aluminum foil barrier layer, and the heat-sealed inner layer.

[0048] Post-processing: Clean the window edges with argon plasma (100W power, 30s time).

[0049] 3. Transparent polymer film treatment

[0050] Cutting: Cut the transparent polypropylene (PP) film (100μm thick) into 85×45mm pieces (length and width greater than the observation window 2) to form a transparent polymer film 3.

[0051] Activation: Corona treatment is applied to the bonding area of ​​the three-layer transparent polymer film (power 2kW, speed 5m / min) to enhance surface adhesion.

[0052] 4. Heat-sealed observation window 2

[0053] operate:

[0054] A transparent polymer film 3 is placed over the heat-sealed inner layer of the aluminum-plastic film 1 to completely block the observation window 2;

[0055] A heat-sealing blade (5mm wide) is used to press along the edge of the transparent polymer film 3 with parameters of 180℃, 0.5MPa, and 3s to achieve a heat-sealing between the transparent polymer film 3 and the aluminum-plastic film 1.

[0056] The transparent polymer film 3 made of polypropylene (PP) and the heat-sealing inner layer of modified polypropylene (CPP) are made of the same material. After melting, the molecular chains dissolve to form a metallurgical-grade sealing interface, preventing electrolyte penetration.

[0057] 5. Cell Packaging

[0058] Placing the battery cell: The large surface of the battery core is flatly attached to the transparent polymer film 3, with the ends of the negative electrode tab and the positive electrode tab extending to the outside of the unsealed side of the aluminum-plastic film 1;

[0059] Folding: Fold the aluminum-plastic film 1 along the marked center line, so that the transparent polymer film 3 follows the fold and wraps around both sides of the battery core, so that the interior can be seen from both sides;

[0060] Three-sided sealing: The three sides (long side × 1 + short side × 2) of the aluminum-plastic film 1 are sealed using a heat sealing machine with parameters of 190℃ / 0.3MPa / 2s, and one short side is reserved as an injection port.

[0061] 6. Liquid Injection and Observation Experiment

[0062] Vacuum electrolyte injection: Electrolyte is injected through the injection port (volume = core pore size × 1.1);

[0063] Injection port sealing: Immediately after injection, heat seal the injection port (parameters are the same as for the three-sided sealing).

[0064] Example 2:

[0065] Preparation steps:

[0066] 1. Pretreatment of aluminum-plastic film:

[0067] Cut the aluminum-plastic film to 140×80mm and mark the positions of the two observation windows (symmetrically distributed on both sides of the fold center line, each 20mm from the center line).

[0068] Two 50×60mm observation windows are laser-cut, as shown below. Figure 1 Figure 2 As shown, the edge of observation window 2 is ≥15mm from the boundary of the aluminum-plastic film.

[0069] 2. Transparent polymer film 3. Sealing:

[0070] Cutting the film: Cut the transparent polyimide (CPI) film (50μm) into two pieces of 55×65mm to form a transparent polymer film 3;

[0071] Coating: Apply acid-modified polyisobutylene + epoxy resin composite adhesive (adhesive line width 2mm, thickness 0.1mm) to the edge of transparent polymer film 3;

[0072] Lamination: The two transparent polymer films 3 are evenly bonded to the inside of the aluminum-plastic film 1, and the two observation windows 2 are blocked respectively. The roller applies pressure (1MPa) to remove air bubbles.

[0073] Curing: Cur in an 80℃ oven for 30 minutes.

[0074] Polyimide (CPI) films are resistant to electrolyte corrosion but cannot be thermally melted; adhesives provide chemical bonding and sealing, and withstand internal battery stress.

[0075] 4. Double-sided packaging:

[0076] Battery core placement: The battery core is placed on one of the transparent polymer films 3;

[0077] Folding: Fold the aluminum-plastic film 1 along the center line so that another transparent polymer film 3 covers the large surface of one side of the battery core. The contents can be seen through both transparent polymer films 3.

[0078] Edge sealing: Heat seal three open edges (with reserved injection ports). The transparent polymer film 3 on both sides is located on the large surface of the battery core. After the electrolyte is injected, the injection port is sealed.

[0079] Comparative Example 1:

[0080] Preparation steps:

[0081] 1. Shell preparation:

[0082] Ethylene-tetrafluoroethylene copolymer (ETFE) film is used.

[0083] Cut into 140×80mm rectangular pieces, with no window openings (completely transparent).

[0084] 2. Cell packaging:

[0085] Place the battery core on the ETFE membrane, fold it along the center line to wrap the battery core, and seal the three sides of the ETFE membrane with UV-curable adhesive (Loctite 352) (adhesive line width 3mm, 365nm UV irradiation for 60s) (leave a liquid injection port).

[0086] 3. Liquid injection and sealing:

[0087] Mechanical strength test: Apply 5N lateral pressure to the encapsulated battery, and the ETFE film will rupture (ultimate compressive strength <8MPa, traditional aluminum-plastic film >50MPa).

[0088] Heat sealing compatibility: When attempting heat sealing (180°C), the ETFE membrane melts and adheres, causing blockage of the injection port.

[0089] Comparative Example 2:

[0090] Preparation steps:

[0091] 1. Shell preparation:

[0092] Injection-molded polycarbonate (PC) top cover (1.2 mm thick) and acrylonitrile-butadiene-styrene (ABS) bottom shell (1.5 mm thick).

[0093] The shell dimensions are 52×72×6mm (internal volume = core volume × 1.3).

[0094] 2. Cell assembly:

[0095] Place the battery core into the bottom shell, and let the positive / negative terminals protrude through the pre-drilled holes in the shell.

[0096] Apply silicone sealant (0.5mm thick) to bond the top cover to the bottom shell.

[0097] Cur at 80℃ for 1 hour.

[0098] 4. Liquid injection and sealing:

[0099] Electrolyte was injected into the drilled hole, and the injection hole was sealed with epoxy resin.

[0100] Energy density decreases: the shell mass accounts for 38% (traditional soft-pack <5%), and the volumetric energy density is only 280Wh / L (soft-pack >400Wh / L).

[0101] Difficulty in heat sealing: After sealing the injection hole, the electrolyte evaporation rate is 0.15 g / day (soft pack standard <0.001 g / day).

[0102] Safety risk: The shell melts and deforms during thermal runaway testing (150°C).

[0103] Flexibility test: The shell cracks when the bending radius is greater than 50cm.

[0104] Effect verification experiment:

[0105] Experiment 1: Optimization of Electrolyte Wetting Process

[0106] Sample preparation:

[0107] Control group: Traditional opaque aluminum-plastic film batteries (n=10)

[0108] Experimental Group 1: Example 1

[0109] Experimental Group 2: Example 2

[0110] Variable settings:

[0111] Injection process: Atmospheric pressure injection vs. vacuum injection (-90kPa)

[0112] Standing temperature: 25℃ vs. 45℃

[0113] Electrolyte formulation: High viscosity EC / DMC (4.5 cP) vs. Low viscosity EC / DEC (2.1 cP)

[0114] Observation method:

[0115] A high-speed camera (100fps) recorded the expansion process of the infiltration front, and the infiltration area percentage was quantified (ImageJ software analysis).

[0116] Results analysis:

[0117] Vacuum injection optimization: Experimental group 1 showed an unwetted area (area 12%) at the bottom of the electrode, which was eliminated after adjusting the vacuum to -95kPa.

[0118] Temperature effect: When placed at 45℃, experimental group 2 showed that the top of the electrode was wetted 30 minutes faster than the bottom. After optimization, the temperature difference was reduced to 5 minutes.

[0119] Formulation screening: The high-viscosity electrolyte was soaked in experimental group 1 for 7 hours.

[0120] Experiment 2: Gas Behavior and Safety Monitoring

[0121] Test conditions:

[0122] Overcharge test: 0.5C charging to 5V (safety limit 4.2V)

[0123] Cyclic testing: 500 cycles of 1C charge / discharge (25℃)

[0124] Observation system:

[0125] Synchronously trigger a high-speed camera (1000fps) and an electrochemical workstation to correlate voltage / current surges with bubble dynamics.

[0126] Overcharge process (Experimental group 1):

[0127] At 4.6V, the bubble generation rate at the positive electrode interface reaches 150 bubbles / min, while that at the negative electrode it is only 20 bubbles / min.

[0128] Bubbles aggregate to form a gas path (0.5 mm wide), which migrates along the diaphragm toward the tab (velocity 1.2 mm / s).

[0129] Cyclic aging (experimental group 2):

[0130] After the 300th cycle, local lithium plating (dendritic length > 50 μm) was observed in the negative electrode observation window, accompanied by the generation of microbubbles (diameter < 10 μm).

[0131] Safety design optimization: Based on the gas path migration path, an exhaust microchannel (0.3mm wide) is added to the tab side, improving gas escape efficiency by 70%.

[0132] Experiment 3: Online Diagnosis of Production Quality

[0133] System setup:

[0134] The structure of Example 1 (n=1000) was implanted in the formation and capacity testing line.

[0135] Develop an AI visual inspection module: infrared light source (850nm) + industrial camera (5MP) + algorithm platform.

[0136] Testing process:

[0137] Step 1: After injection, let stand for 30 minutes, then irradiate the observation window with infrared light;

[0138] Step 2: The camera captures the reflected image (the fully wetted area appears as a uniform bright spot, and the unwetted area appears as a dark spot);

[0139] Step 3: The algorithm calculates the percentage of dark spots (threshold > 5% is judged as defective).

[0140] Using observation window 2, defective batteries can be quickly identified, improving the screening rate of poorly wetted batteries and preventing defective products from entering the market.

[0141] Based on the verification of Examples 1 and 2, this invention achieves in-situ non-destructive observation of electrolyte wetting and gas behavior inside the soft-pack battery by partially opening an observation window 2 in the aluminum-plastic film 1 and sealing it with a transparent polymer 3 (Experiment 1: Optimized electrolyte injection process shortens wetting time by 40%; Experiment 2: Capturing overcharge bubbles to guide gas path design). Compared with the fully transparent ETFE soft shell (Comparative Example 1: Seal failure causes electrolyte leakage, mechanical strength <8MPa) and PC hard shell (Comparative Example 2: Energy density decreases by 32%, bending cracks), this invention retains the lightweight and high barrier properties of the aluminum-plastic film (water and oxygen permeability ≤0.05g / m³). 2 While enabling online diagnostics of production quality (Experiment 3: AI vision detected 100% of wetting defects in 2 seconds, improving yield by 8.3%), it achieves a balance between transparent observation and packaging performance.

Claims

1. A soft-pack battery aluminum-plastic film structure with a transparent observation window, characterized in that, include: The aluminum-plastic film (1) is composed of a nylon outer layer, an aluminum foil barrier layer and a heat-sealed inner layer, and has an observation window (2) that penetrates through the nylon outer layer, the aluminum foil barrier layer and the heat-sealed inner layer; A transparent polymer film (3) is filled and sealed over the observation window (2) and heat-sealed or glue-sealed to form a connection with the aluminum-plastic film (1); The aluminum-plastic film (1) is configured such that after being folded along the centerline, it is combined with a transparent polymer film (3) to seal the observation window (2) to form a sealed cavity that accommodates the battery core and electrolyte.

2. The aluminum-plastic film structure of a soft-pack battery with a transparent observation window according to claim 1, characterized in that, The transparent polymer film (3) is one of transparent polypropylene (PP) film, transparent polyimide (CPI) film, cyclic olefin polymer (COP) film or coated reinforced PET film, and the heat-sealed inner layer is polypropylene (PP) or modified polypropylene (CPP), and the two are connected by heat sealing or adhesive sealing.

3. The aluminum-plastic film structure of a soft-pack battery with a transparent observation window according to claim 1, characterized in that, The observation window (2) is located on the aluminum-plastic film (1) in the area corresponding to the large surface of the soft-pack battery core, and is misaligned with the electrode area and the tab side sealing area of ​​the battery core.

4. The aluminum-plastic film structure of a soft-pack battery with a transparent observation window according to claim 1, characterized in that, The number of observation windows (2) is one or two.

5. A method for preparing an aluminum-plastic film for a soft-pack battery with a transparent observation window, characterized in that, The method for preparing the aluminum-plastic film structure with a transparent observation window for a soft-pack battery as described in any one of claims 1-4 includes: Step 1: Based on the size of the battery core, cut aluminum-plastic film of matching size (1); Step 2: Cut an observation window (2) in a designated area of ​​the aluminum-plastic film (1). The observation window (2) penetrates the nylon outer layer, aluminum foil barrier layer and heat-sealed inner layer of the aluminum-plastic film (1). Step 3: Based on the dimensions of the observation window (2), cut the matching transparent polymer film (3), the length and width of the transparent polymer film (3) being larger than the length and width of the observation window (2); Step 4: Cover the inside of the aluminum-plastic film (1) with the transparent polymer film (3) and completely cover the observation window (2), and seal it with the aluminum-plastic film (1) by heat sealing or glue sealing; Step 5: Place the large surface of the battery core flat on the transparent polymer film (3). The negative electrode tab and positive electrode tab of the battery core extend to the outside of the aluminum-plastic film (1). At this time, fold the aluminum-plastic film (1) along the center line, heat seal or glue seal the three sides of the aluminum-plastic film (1) and inject electrolyte. The transparent polymer film (3) inside the aluminum-plastic film (1) blocks the observation window (2) to form a sealed cavity for containing the battery core and electrolyte.

6. The method for preparing a soft-pack battery aluminum-plastic film with a transparent observation window according to claim 6, characterized in that, When the transparent polymer film (3) is a transparent polypropylene (PP) film, step 4 adopts a heat sealing process with a heat sealing temperature of 160℃–200℃.

7. The method for preparing a soft-pack battery aluminum-plastic film with a transparent observation window according to claim 6, characterized in that, If there is one observation window (2) on the aluminum-plastic film (1), the folded aluminum-plastic film (1) will fold a transparent polymer film (3) at the same time. If there are two observation windows (2), the folded aluminum-plastic film (1) will place the two transparent polymer films (3) in parallel.

8. The method for preparing a soft-pack battery aluminum-plastic film with a transparent observation window according to claim 6, characterized in that, When the transparent polymer film (3) is a transparent polyimide (CPI) film, a cyclic olefin polymer (COP) film, or a coated reinforced polyethylene terephthalate (PET) film, step 4 adopts an adhesive sealing process.

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