Analysis of Lithium Battery Injection Process

The role of lithium battery electrolyte is to conduct ions between the positive and negative electrodes and act as a medium for charging and discharging, just like blood in the human body. How to make the electrolyte fully and evenly infiltrate the interior of the lithium battery has become an important issue. Therefore, the injection process is a very important process that directly affects the performance of the battery.

The "Three Musketeers" of Lithium Batteries: Lithium Battery Packaging Film, Lithium Battery Separator and Battery Cell Blue Film

Lithium battery packaging film

The patron saint of electronic products

1. Structure and characteristics of lithium battery packaging film

Lithium battery packaging film usually consists of three layers of aluminum foil (nylon layer) ON/Al/CPP or four layers (nylon layer) ON/Al/PA/CPP. The outer nylon layer mainly plays a protective role to prevent the aluminum foil layer from being scratched. The outer material is required to be puncture-resistant and impact-resistant. The middle aluminum foil layer, as a base material, plays a waterproof and barrier role to prevent moisture from invading and block oxygen to protect the contents of the battery. The main function of the inner heat-sealing layer (CPP) is heat sealing. Based on the multi-layer structure, it has the functions of corrosion resistance, puncture resistance, aging resistance, insulation, and moisture resistance. It is an ideal packaging material for electronic products. The industry also calls it "aluminum-plastic film". In addition to the above properties, the recyclable characteristics of battery separator film, combined with the concept of green environmental protection, adapt to the trend of the times.

Negative electrode binder performance requirements, test methods and failure mechanisms!

Binders have a low mass ratio in the electrode and do not participate in the electrochemical reaction. Their main function is to adhere the active material and the conductive agent to the current collector to keep the electrode intact . Binders affect the formation of the solid electrolyte interface (SEI) , the charge transfer inside the electrode and between the electrode - electrolyte interface , the wetting behavior of the electrode, and the cycle performance and cost of the battery .

Battery Cell Section: Introduction to the Manufacturing Process of Lithium-ion Battery Pouch Cells

Introduction

Soft-pack battery cells, referring to cells using aluminum-plastic composite film as packaging material, have seen widespread application in the lithium-ion battery field due to their high energy density, enhanced safety, and flexible design. Below, I will provide a detailed introduction to the manufacturing process of soft-pack battery cells, covering material preparation, critical steps, and post-processing aspects.

1. Cell Design

Cell design refers to the process of assembling the cathode material, anode material, electrolyte, separator, and current collectors for the positive and negative electrodes in specific proportions and processes to meet particular electrical performance requirements. This process requires designers to understand the characteristics of various materials, possess extensive electrochemical knowledge, and have the ability to think logically and comprehensively.

1.1 Clarify Design Requirements

It's important to clarify the usage scenarios for the cell, such as whether it is for consumer batteries, energy storage batteries, or power batteries, and the application conditions, like drones, mining trucks, cars, ships, etc.

Determine the basic parameters of the cell, such as capacity, cycle performance, rate capability, high and low-temperature performance, energy density, safety, etc.

1.2 Select Materials

• Cathode Material: Determines the energy density of the cell. Commonly used cathode materials are lithium cobalt oxide (for consumer batteries), ternary materials (such as NCM, for power batteries), and lithium iron phosphate (for power batteries, which is cost-effective and has good safety).
• Anode Material: Common anode materials include artificial graphite, which can be mixed with silicon or use lithium titanate, hard carbon, etc. The choice of anode material will affect the cell's energy density, cycle life, and fast-charging capability.
• Electrolyte: Acts as ionic conductor and electronic insulator between the battery's cathode and anode. The nature of the electrolyte has a significant impact on the battery's cycle life, operating temperature range, charge-discharge efficiency, battery safety, and power density.
• Separator: Used to isolate the cathode and anode to prevent internal short circuits within the battery.
• Current Collectors: Carry active material and collect the current generated by electrode active materials for output. Commonly used current collector materials include copper, aluminum, nickel, and stainless steel.

1.3 Design Structure

Design the cell structure, such as winding or stacking, based on the characteristics of materials and the cell's needs.

Determine the cell's size and shape to meet the requirements of the usage scenario.

1.4 Optimize Performance

Improve the energy density, cycle life, and safety of the cell by adjusting material ratios and optimizing process parameters.Conduct simulation analysis and testing verification on the cell to ensure its performance meets design requirements.

1.5 Key Parameters of Cell Design

• Energy Density: The amount of energy a cell can store per unit volume or unit weight. Increasing energy density is one of the key goals in cell design.
• Cycle Life: The number of times a cell can be charged and discharged under specific conditions. The length of cycle life directly influences the battery's lifespan and cost.
• Safety: The stability and reliability of the cell under various conditions. Safety is one of the primary considerations in cell design.

2. Electrode Manufacturing

2.1 Slurry Mixing

The active materials of the cathode/anode, conductive agents, and binders are uniformly dispersed in a solvent and stirred to form a stable slurry with a certain viscosity.

The uniformity of slurry mixing has a significant effect on subsequent coating and cell performance.

2.2 Electrode Coating

Apply the uniformly mixed slurry onto a copper/aluminum foil current collector.

The coating process includes two methods: traditional wet coating and dry coating.

• Wet Coating: The slurry is coated onto the current collector and then sent into a drying chamber to evaporate the solvent, with the solvent being recovered.
• Dry Coating: Active particles and conductive agents are dry-mixed uniformly before adding a binder. A self-supporting film is formed under the fibrillation action of the binder, which is then roll-pressed onto the surface of the current collector.
• Coating Uniformity: Ensure that the slurry is evenly distributed on the current collector to avoid issues such as uneven coating or missing spots.
• Coating Precision: Control the thickness and width of the coating to meet the cell design requirements.

2.3 Electrode Roll Pressing

• Place the coated electrodes under the twin rollers of a roll press machine. By compressing the electrodes, achieve the desired thickness and interfacial uniformity.
• The rolling process can increase the compaction density of the electrodes, thereby improving the energy density of the cell.
• Roll Pressing Pressure: Select the appropriate roll pressing pressure to ensure the electrodes achieve the desired thickness and compaction density.
• Roll Pressing Speed: Control the roll pressing speed to avoid overheating, deformation, or damage to the electrodes.

2.4 Electrode Slitting

• Cut the wide electrodes, after roll pressing, into narrow strips.
• The slitting process has strict requirements for the consistency of electrode width, the size of burrs on the cut edges, and the morphological characteristics, all of which can affect the quality of cell winding or stacking.

• Slitting Precision: Ensure the width consistency of the electrodes and that the size of burrs on the cut edges meets requirements.
• Slitting Speed: Match the speed to the material's ductility to prevent material damage.

2.5 Process Optimization Directions

• Improve Coating Uniformity: Use advanced coating equipment and techniques to enhance coating uniformity and reduce cell performance fluctuations.
• Reduce Roll Pressing Costs: Optimize the roll pressing process and equipment to improve pressing efficiency and lower costs.
• Enhance Slitting Quality: Use high-precision slitting equipment and techniques to improve slitting quality, ensuring consistency and safety of the cells.
• Promote Process Innovation: Continuously explore and try new electrode processes and technologies, such as dry process methods, to reduce cost, improve energy density, and enhance safety.

3. Cell Assembly

3.1 Stacking & Winding

• Stacking Process: Arrange battery separators, cathodes, and anodes in a specific order and method to form the cell structure. This process is mainly used for the production of pouch batteries, offering advantages such as high energy density, easier control of dimensions and structure, and flexible manufacturing processes. During stacking, it is essential to strictly control the alignment of electrodes and separators, the number of layers, and the stacking pressure parameters to ensure the uniformity and stability of the cell's internal structure. There are various stacking methods, such as Z-folding and integrated cutting-stacking machines, with different stacking equipment having unique methods and characteristics.
• Winding Process: Roll the cathode, anode, and separator into cylindrical or prismatic cell structures in a specific sequence, controlling winding speed and tension. This process is mainly used for large batteries, like those for electric vehicles, and offers benefits such as high production efficiency and low costs.

Comparison of Stacking & Winding:

• Energy Density: The stacking process has higher energy density as it can make full use of the battery's corner space, while the winding process has relatively lower energy density due to space waste during winding.
• Structural Stability: The stacking process offers better structural stability and does not have "C-corner" issues, leading to longer cycle life. In contrast, the winding process is less stable as electrodes and separators may bend during winding.
• Safety: The stacking process provides higher safety due to efficient heat dissipation and stable internal structure. The winding process is relatively less safe because the "C-corner" in wound cells is prone to deformation and twisting.
• Production Efficiency: The stacking process has relatively lower production efficiency because it requires precise control during stacking, whereas the winding process has higher production efficiency as winding can be performed quickly.
• Cost: The stacking process generally has higher costs due to the complexity of stacking equipment and techniques; the winding process tends to be cheaper because its equipment and procedures are simpler.

3.2 Tab Welding

In this process, the positive and negative electrode sheets of the cell are connected to tabs through welding to ensure the conduction of internal currents and stability of the battery structure. This process significantly impacts the performance, safety, and lifespan of the battery.

• 
• Cleaning Treatment: Thoroughly clean the tabs and welding areas of pouch cells to remove oil, moisture, and impurities, ensuring a clean and dry welding surface. This helps reduce defects during the welding process and improves welding quality.
• Tab Positioning: Precisely position the tabs on the stacks according to design requirements, ensuring the gaps between tabs are appropriate. Avoid excessively large or small gaps that could impact welding effectiveness.
• Welding Method: Choose an appropriate welding method, such as laser welding or ultrasonic welding, and prepare corresponding fixtures, molds, and protective sheets as auxiliary tools.
• Laser Welding: Laser welding is a high-precision, high-efficiency welding method suitable for welding tabs on pouch cells. During welding, the laser beam focuses on the tab welding area, generating high temperatures to melt and connect the tab materials. Laser welding offers advantages like concentrated energy, fast welding speed, and a high depth-to-width ratio of the weld, enabling high-quality welding.
• Ultrasonic Welding: Ultrasonic welding utilizes energy generated by high-frequency vibrations to melt tab materials and achieve connection. During welding, the welding head rapidly approaches and contacts the outer aluminum plastic film and tabs of the pouch cell under preset parameters. By generating local high temperatures and pressure through high-frequency vibration, the materials soften and fuse. Ultrasonic welding provides high welding strength, good sealing, and safe operation, making it suitable for welding tabs of pouch cells with different specifications and materials.

4. Packaging

4.1 Aluminum Plastic Film Forming

Pouch cells can be designed into various sizes according to customer requirements. Once the dimensions are determined, corresponding molds are needed to form the aluminum plastic film. The forming process, also known as "punching pits," involves using forming molds under heated conditions to punch a pit in the aluminum plastic film that can accommodate a rolled cell. Once the aluminum plastic film is punched and cut to shape, it is typically referred to as a pocket bag.

When the cell is relatively thin, choose to punch a single pit. For thicker cells, use double pits because excessive deformation on one side can exceed the deformation limit of the aluminum plastic film, leading to rupture. Sometimes, depending on design needs, a small pit is punched in the position of the gas bag to increase its volume.

4.2 Top and Side Sealing

First, place the welded electrode sheets into the punched pit and fold the packaging film along the dotted line. Next, after placing the rolled cell into the pit, the entire aluminum plastic film can be placed into a fixture for top and side sealing in the top-side sealing machine. The machine typically has multiple fixtures; the left workstation is for top sealing, and the right is for side sealing. Two yellow metal pieces work as the upper sealing heads, with a lower sealing head beneath them. During sealing, both sealing heads are heated (usually about 180°C) and pressed onto the aluminum plastic film, melting the PP layer of the film, which adheres together—completing the sealing.

In this process, the top seal must encompass the tabs, which are metal (aluminum for the positive and nickel for the negative). The sealing relies on a small component on the tab known as tab adhesive. During sealing, the PP in the tab adhesive melts and bonds with the PP layer of the aluminum plastic film, forming an effective sealed structure.

4.3 Gas Bag Reservation

During packaging, additional material is left in the aluminum plastic film, known as the gas bag. This is because during cell formation, a large amount of gas is generated. This reserve will be used to remove the gas in subsequent processes.

5. Formation and Aging

• Liquid Injection: Inject electrolyte into the packaged cell. The electrolyte serves as a medium to facilitate ion transport within the battery.
• Formation: Perform the first battery charge to activate the new battery. The electrolyte reacts on the electrode surface, generating gas and forming a dense solid electrolyte interface (SEI) film. The quality of the formation process directly affects the battery quality.
• Aging: Also known as curing, it's a resting process for the battery after formation, during which the battery's performance gradually stabilizes.

6. Exhaust and Second Sealing

• Exhaust: The gas generated during formation can affect battery performance, so post-formation, the battery needs to undergo exhaust treatment. During exhaust, the gas bag is pierced and the gas along with a small portion of the electrolyte is extracted.
• Second Sealing: After exhaust, the cell undergoes a second sealing to ensure its airtightness. The principle of second sealing is similar to the top and side sealing, where the PP layer of the aluminum plastic film is melted to form the seal.

7. Subsequent Processing

• Trimming and Folding: Trim and fold the edges from the first and second sealing to suitable widths to ensure the cell's dimensions remain within specifications.
• Capacity Testing: Conduct capacity testing on the cell to ensure its capacity meets the specified minimum value. Ideally, all cells must undergo capacity testing before leaving the factory.
• Appearance Inspection and Labeling: Inspect the cell’s appearance to ensure it's flawless, then apply labels.
• Packaging and Shipping: Properly package the tested cells to ensure their safety during transportation and storage before shipping.

——End——

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Tsinghua University’s Kang Feiyu Team Reports in Nature Communications: Homogeneous Polymer-Ion Solvent Electrolyte with Weak Dipole-Dipole Interactions Enables High-Performance Lithium Metal Pouch Cells

Lithium metal batteries have attracted significant attention due to their high energy density. However, their development has been hindered by issues such as uncontrollable dendrite growth of lithium metal anodes, unstable solid electrolyte interphase (SEI), and poor cycling stability. Solid-state electrolytes (SSEs) are attractive due to their inherent safety, with polymer solid-state electrolytes (SPEs) receiving particular attention for their processability, cost-effectiveness, and good contact with electrodes. However, traditional SPEs (such as poly(ethylene oxide) (PEO)-based electrolytes) have low ionic conductivity (typically <10⁻⁵ S cm⁻¹ at room temperature), limiting their application at room temperature.

Recently, Kang Feiyu, Lu Wei, Liu Ming, and He Yanbing’s team from Tsinghua University’s Shenzhen International Graduate School proposed a 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) diluent to significantly modulate dipole-dipole interactions in polymer ionic solvate electrolytes (TPISEs). TTE can encapsulate ionic solvents, reducing dipole-dipole interactions between ionic solvents and the polymer matrix, thereby promoting their uniform distribution and forming a continuous ionic percolation network within the polymer matrix. As a result, the ionic conductivity of TPISEs was enhanced to 1.27×10⁻³ S cm⁻¹ at 25°C. Meanwhile, TTE induces ionic solvents to transform from contact ion pairs to aggregates, which helps form a stable Li/electrolyte interface, with an exchange current density 190 times higher than without TTE. The Li||LiNi₀.₈Co₀.₁Mn₀.₁O₂ (NCM811) full cell exhibits good cycling stability across a temperature range of 30°C to 60°C. The practical pouch cell, using a 50 μm thick lithium metal foil and high areal capacity cathode (3.58 mAh cm⁻²), achieved a high specific energy of 354.4 Wh kg⁻¹ and maintained 78.1% capacity after 450 cycles at 25°C and 54 mA g⁻¹. This study provides a design strategy for polymer electrolytes to overcome the ionic conductivity bottleneck in practical solid-state batteries.

This achievement was published in “Nature Communications” under the title “Homogeneous polymer ionic solvate electrolyte with weak dipole-dipole interaction enabling long cycling pouch lithium metal battery,” with first authors Chen Likun, Gu Tian, and Mi Jinshuo.

【Key Points of the Work】

This study significantly enhances the ionic conductivity and interface stability of polymer-ionic solvate electrolytes (TPISEs) by introducing 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) to modulate dipole-dipole interactions.

Mechanism of Ionic Conductivity Enhancement

Construction of Weak Dipole-Dipole Interactions: TTE can encapsulate ionic solvents, reducing dipole-dipole interactions between ionic solvents and the polymer matrix. This weak interaction promotes uniform distribution of ionic solvents in the polymer matrix, forming a continuous ionic percolation network. Compared with traditional polymer electrolytes, this uniform distribution allows lithium ions (Li⁺) to move more freely in the polymer matrix, significantly improving ionic conductivity. At 25°C, the ionic conductivity of TPISEs reaches 1.27×10⁻³ S cm⁻¹, far exceeding traditional polymer electrolytes (such as PEO-based electrolytes, typically <10⁻⁵ S cm⁻¹ at room temperature).

Optimization of Ionic Transport Pathways: The introduction of TTE transforms ionic solvents from contact ion pairs (CIPs) to aggregates (AGGs), which facilitates rapid lithium ion transport. In traditional polymer electrolytes, lithium ions mainly transport through coordination with polymer chain movement, while strong ion-dipole interactions limit the migration rate of lithium ions. In TPISEs, the TTE-encapsulated ionic solvents reduce interactions with polymer chains, allowing lithium ions to migrate more quickly in the polymer matrix, achieving efficient ion transport.

Interface Stability

Formation of Stable Solid Electrolyte Interface (SEI): TTE induces ionic solvents to transform from CIPs to AGGs, helping form an SEI layer rich in lithium fluoride (LiF). This SEI layer has high mechanical modulus and uniformity, effectively suppressing lithium dendrite growth. Experiments show that the average Derjaguin-Müller-Toporov (DMT) modulus of the SEI layer formed by TPISEs is 9.46 GPa, 8 times that of the SEI layer formed by traditional polymer electrolytes (1.18 GPa). This high-modulus SEI layer not only physically blocks lithium dendrite penetration but also reduces side reactions of the lithium metal anode, significantly improving battery cycling stability and Coulombic efficiency.

Formation of High-Quality Cathode-Electrolyte Interface (CEI): The introduction of TTE also optimizes the chemical composition and structure of the cathode-electrolyte interface (CEI). In TPISEs, preferentially oxidized FSI⁻ anions in the CEI layer produce more LiF, reducing side reactions between the electrolyte and cathode material. This high-quality CEI layer not only effectively prevents electrolyte decomposition but also promotes rapid lithium ion migration in the cathode material, improving battery charging-discharging efficiency and cycling stability.

Battery Performance

Wide Temperature Range Cycling Stability: Due to the high ionic conductivity and stable interface characteristics of TPISEs, Li||NCM811 full cells exhibit good cycling stability across a wide temperature range of 30°C to 60°C. At low temperatures, TPISEs maintain high ionic conductivity to ensure normal battery discharge; at high temperatures, stable SEI and CEI layers effectively suppress electrolyte decomposition and side reactions, extending battery life.

High Specific Energy and Long Cycle Life: Pouch cells using TPISEs perform excellently in practical applications. Using a 50 μm thick lithium metal foil and high areal capacity cathode (3.58 mAh cm⁻²), the battery achieves a high specific energy of 354.4 Wh kg⁻¹ and maintains 78.1% capacity after 450 cycles at 25°C and 54 mA g⁻¹. This high performance is attributed to the significant advantages of TPISEs in ionic transport and interface stability, meeting the practical application requirements of high-energy-density lithium metal batteries.

Figure 1 | Design principle of TPISEs for high-performance, high-safety lithium metal batteries

• Illustrates the restricted ion transport pathways and ion solvent structure dominated by contact ion pairs (CIPs) in PISEs.
• Illustrates the rapid ion transport pathways achieved through uniformly distributed ion solvents and the structure of TPISEs dominated by aggregates (AGGs).
• Illustrates the ion solvent structure dominated by solvent-separated ion pairs (SSIPs) and lithium ion transport pathways in PISEs using traditional solvents.

Figure 2 | Properties and solvation structure of electrolytes based on PISEs

• HAADF image of PISEs and corresponding elemental distribution map of electron energy loss spectrum.
• HAADF image of TPISEs and corresponding elemental distribution map of electron energy loss spectrum.
• Arrhenius plot of PISEs and TPISEs.
• 2D ¹H¹⁹F heteronuclear correlation spectrum of PISEs.
• 2D ¹H¹⁹F heteronuclear correlation spectrum of TPISEs.
• Schematic diagram of TPISEs solvation structure.
• Lithium ion self-diffusion coefficient and corresponding diffusion mode derived from MD simulation mean square displacement.
• Raman spectra of PISEs and TPISEs.
• PDOS curve of HCEs.
• PDOS curve of PISEs.
• PDOS curve of TPISEs.

Figure 3 | Lithium reversibility and SEI microstructure

• Coulombic efficiency of Li||Cu batteries using HCEs, PISEs, and TPISEs at 0.1 mA cm⁻² and 0.2 mAh cm⁻² for lithium deposition/stripping.
• Modified Aurbach Coulombic efficiency test of Li||Cu batteries using HCEs, PISEs, and TPISEs.
• Tafel plots of lithium symmetric cells using PISEs and TPISEs.
• Galvanostatic charge-discharge curves of lithium symmetric cells using HCEs, PISEs, and TPISEs at 0.5 mA cm⁻² and 0.5 mAh cm⁻², with inset showing scanning electron microscopy images of lithium metal anodes after 100 hours of cycling.
• Galvanostatic charge-discharge curves of lithium symmetric cells using HCEs, PISEs, and TPISEs at 1 mA cm⁻² and 1 mAh cm⁻².
• Atomic force microscopy images of lithium metal anodes after cycling using PISEs (top) and TPISEs (bottom).
• Three-dimensional views of LiF and C₂H₆O in the sputtered volume of SEI formed using HCEs, PISEs, and TPISEs as characterized by TOFSIMS.
• Atomic ratio of F element in SEI formed using HCEs, PISEs, and TPISEs as characterized by XPS.

Figure 4 | Cycle stability of Li||NCM811 full cells and cathode structure characterization

• Rate performance of Li||NCM811 full cells using PISEs and TPISEs.
• Long-term cycle stability of Li||NCM811 full cells using PISEs and TPISEs at 25°C (cathode mass loading = 2 mg cm⁻², lithium metal thickness = 450 μm).
• Long-term cycle stability of Li||NCM811 full cells using PISEs and TPISEs at 30°C (cathode mass loading = 2 mg cm⁻², lithium metal thickness = 450 μm).
• Long-term cycle stability of Li||NCM811 full cells using PISEs and TPISEs at 60°C (cathode mass loading = 2 mg cm⁻², lithium metal thickness = 450 μm).
• Insitu XRD characterization of NCM811 cathode using TPISEs during initial charge-discharge cycles.
• HAADF-STEM image of NCM811 particles after cycling with PISEs.
• HAADF-STEM image of NCM811 particles after cycling with TPISEs.

Figure 5 | Cycle stability and safety tests of pouch cells

• Long-term cycle stability of Li||NCM811 pouch cells using PISEs and TPISEs at 25°C (cathode mass loading = 2 mg cm⁻², lithium metal thickness = 50 μm).
• Charge-discharge curves of Li||NCM811 pouch cells using TPISEs at different cycle numbers.
• Long-term cycle stability of high-energy Li||NCM811 pouch cells using TPISEs at 25°C (cathode mass loading = 20 mg cm⁻², lithium metal thickness = 50 μm). Inset shows the Li|TPISE|NCM811-based pouch cell for abuse testing.
• Charge-discharge curves of high-energy Li||NCM811 pouch cells using TPISEs at different cycle numbers.
• Infrared thermal imaging photos of Li|TPISE|NCM811 pouch cells under abuse conditions.

[Conclusion]

In this work, we designed a homogeneous polymer-ion solvent electrolyte (TPISEs) with weak dipole-dipole interactions, achieving a high ionic conductivity of 1.27×10⁻³ S cm⁻¹ at 25°C. The TTE-induced aggregate-dominated ion-solvent structure helps form stable LiF-rich SEI and CEI, stabilizing both the lithium metal anode and NCM811 cathode interfaces simultaneously. Notably, the exchange current density at the Li/TPISEs interface is 190 times higher than without TTE addition. As a result, solid-state Li|TPISE|NCM811 batteries exhibit excellent cycling stability over a wide temperature range from -30°C to 60°C. Excitingly, practical lithium metal pouch cells using TPISEs achieve 78.1% capacity retention after 450 cycles at a specific energy of 354.4 Wh kg⁻¹.

——End——

Canrd Brief Introduce：Canrd use high battery R&D technology(core members are from CATL) and strong Chinese supply chain to help many foreign companies with fast R&D. 

We provide lab materials, electrodes, custom dry cells, material evaluation, perfomance and test, coin/pouch/cylindrical cell equipment line, and other R&D services.

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Square, Cylindrical, Soft Pack: Analysis of Manufacturing Processes for Different Lithium Battery Packaging Form

In the new energy era, lithium batteries, as the core power and storage units, are of undeniable importance. Among the many characteristics of lithium batteries, the packaging shape, though an external manifestation, actually contains complex technological considerations and technical logic. The three mainstream packaging shapes—square, cylindrical, and soft pack—each correspond to unique manufacturing processes, akin to three keys that open the doors to different application scenarios. This article delves into the technical routes and manufacturing mysteries behind these three lithium battery packaging shapes.

1. Square Lithium Battery: Craftsmanship Behind Solidity

(1) Structural and Design Advantages

The square lithium battery is known for its regular shape, which offers significant advantages in space utilization. Its flat structure can be tightly arranged, making it suitable for scenarios with high space layout requirements, such as battery modules for electric vehicles. Structurally, the square casing provides stable support for internal components like electrodes and separators, helping improve the battery’s overall strength and stability.

(2) Manufacturing Process

Shell Manufacturing: The outer casing of square lithium batteries is typically made from metal materials, such as aluminum alloys or stainless steel. The manufacturing process involves stamping and stretching operations, where metal sheets are processed into casings of specific shapes and sizes through molds. The precision of molds is critical to ensure the consistency and surface smoothness of the casing, which is essential for assembling internal battery components. The stretching process further shapes the shell’s depth and form, allowing it to house the battery core.

Cell Assembly: The core of square lithium batteries is meticulously complex in its assembly. Positively and negatively charged layers and separators are stacked or wound into the cell and then carefully placed into the formed casing. The stacking process can enhance the battery’s energy density and charge/discharge performance because it minimizes the internal resistance and mechanical stress within the cell. The winding process is more suited for large-scale production, providing high efficiency. After cell assembly, electrolyte injection takes place, where the injection quantity and uniformity directly affect the battery’s performance and lifespan.

Sealing and Welding: To ensure the battery’s tightness and safety, processes like laser welding or resistance welding are used to seal the shell and top cover. Laser welding has the advantages of high energy density, fast welding speed, and narrow and attractive weld seams, effectively preventing electrolyte leakage and external air ingress. Parameter control during welding is crucial, such as laser power, welding speed, and pulse frequency; any deviation could lead to welding quality issues affecting the battery’s overall performance.

(3) Application Scenarios and Challenges

Square lithium batteries find extensive applications in electric vehicles and energy storage systems. In electric vehicles, their compact structure can better fit the vehicle’s chassis space, enhancing vehicle range and handling performance. However, the manufacturing process for square lithium batteries is relatively complex, with higher costs and stringent requirements for production equipment and process control. Additionally, square batteries face certain challenges in heat dissipation, requiring efficient thermal management systems to ensure stable performance under different operating conditions.

2. Cylindrical Lithium Battery: Efficiency Under a Round Form

(1) Unique Structural Features

Cylindrical lithium batteries stand out with their rounded shape. Common cylindrical battery types, such as 18650 and 21700, have standardized dimensions. This standardized design facilitates large-scale production and interchangeability, offering innate advantages in consumer electronics. The cylindrical structure leads to more uniform internal heat dissipation paths, promoting battery safety and stability during charge and discharge.

(2) Manufacturing Process Analysis

Shell Forming: The cylindrical battery case is usually made from metallic materials, often utilizing seamless steel tube stretching techniques. By stretching metal tubes in specific molds, a shell with defined wall thickness and length is formed. During stretching, careful control over material properties, stretching speed, and mold lubrication conditions is necessary to ensure shell dimensional accuracy and surface quality. Compared to square battery casings, cylindrical casing manufacturing is relatively straightforward, with higher production efficiency.

Cell Winding: Cylindrical battery cells commonly adopt winding techniques. Positive and negative layers and separators are alternately stacked and wound into a cylindrical cell. Controlling winding tension is critical because tension that is too high or too low will impact the cell’s internal structure and performance. Additionally, winding speed and precision directly relate to battery consistency and yield.

Sealing and Assembly: After cell winding, sealing and assembly processes follow. In sealing, resistance welding is typically used to connect the top cover and casing tightly. Resistance welding applies high current momentarily, causing high temperatures at the welding site to achieve metal fusion. The assembly process includes installing components like cell, electrolyte, and protection circuits into the casing, forming a complete battery.

(3) Application Scenarios and Limitations

Cylindrical lithium batteries dominate consumer electronics like laptops and portable power supplies. Their standardized dimensions and excellent heat dissipation make product design and manufacturing more convenient. However, in electric vehicle applications, cylindrical lithium batteries face challenges. Due to the relatively small capacity of a single cylindrical cell, meeting electric vehicle’s high energy demands requires many cells to be connected in series and parallel, increasing the complexity and cost of battery management systems. Moreover, space utilization efficiency is relatively low within battery modules, somewhat affecting the energy density of the entire battery system.

3. Soft Pack Lithium Battery: Innovation and Breakthrough of a Flexible Form

(1) The Charm of Flexible Structure

Soft pack lithium batteries differentiate themselves from square and cylindrical batteries with their unique soft packaging structure. Their casing uses aluminum-plastic composite film, a material that combines the barrier properties of metal with the flexibility of plastic. The soft package structure allows the battery to be custom-designed for different application needs, such as ultra-thin or irregular shapes, meeting stringent requirements for battery shape in some specialized scenarios. Additionally, soft pack batteries have intrinsic safety advantages; when the internal pressure is excessively high, the aluminum-plastic composite film will bulge and rupture to release pressure, avoiding serious accidents like explosions.

(2) Detailed Manufacturing Process

Aluminum-Plastic Composite Film Preparation: The aluminum-plastic composite film is a critical material for soft pack lithium batteries, with a complex preparation process. Typically, aluminum foil and plastic film are laminated with adhesives, followed by surface coating to enhance film barrier properties, heat sealability, and resistance to electrolyte corrosion. The coating material formulation and coating process significantly affect the composite film’s performance, directly related to battery lifespan and safety.

Cell Stacking: Soft pack lithium batteries often use stacking techniques to prepare cells. Unlike the winding process of cylindrical cells, stacking involves placing positive and negative sheets and separators in sequence to form the cell. This technique can increase battery energy density because the stacked structure minimizes internal voids, leading to more adequate contact between electrode materials and electrolyte. Also, the stacking process aids in improving battery charge/discharge performance and cycle life.

Heat-Sealing and Packaging: Upon completing cell stacking, cells are placed into aluminum-plastic composite films and sealed using heat sealing techniques. Heat sealing temperature, pressure, and duration are key parameters, requiring precise control to ensure good sealing effects, preventing electrolyte leakage. After packaging, post-processes such as electrolyte injection and forming are conducted to achieve stable electrochemical properties for the battery.

(3) Application Scenarios and Development Bottlenecks

Soft pack lithium batteries have widespread applications in consumer electronics, wearable devices, and some high-end electric vehicles. In wearable devices, their lightweight, flexible characteristics allow them to better conform to the human body, providing a comfortable wearing experience. In electric vehicles, the high energy density and custom design capability of soft pack batteries offer possibilities for vehicle lightweight design and space optimization. However, manufacturing processes for soft pack batteries demand high environmental humidity and cleanliness, making production quality control difficult. Moreover, the cost of aluminum-plastic composite film is relatively high, limiting the cost advantages of soft pack batteries in large-scale applications.

4. Comparison of Technical Routes and Future Prospects of Three Packaging Shapes

(1) Technical Route Comparison

From a manufacturing complexity standpoint, square lithium batteries, with their structural design and sealing process requirements, have the most complex manufacturing processes and relatively high costs; cylindrical lithium batteries have simpler manufacturing processes and high standardization, suitable for large-scale production; soft pack lithium batteries, although cell stacking is relatively simple, demands stringent requirements for aluminum-plastic composite film preparation and heat-sealing techniques, posing considerable overall process difficulty.

In terms of energy density, soft pack lithium batteries, due to their stacking process and relatively compact structure, have higher energy density under equal conditions; optimized stacking processes and structural designs allow square lithium batteries to reach high energy density; cylindrical lithium batteries, given their internal structural characteristics, have relatively lower energy density but continuously improve it through electrode material and process advances.

Regarding safety, soft pack lithium batteries have inherent advantages in pressure release; square lithium batteries ensure high safety with perfect thermal management systems and fail-proof safety designs; cylindrical lithium batteries benefit from heat dissipation advantages to improve safety, yet require enhanced protection in extreme scenarios like overcharge and short circuit.

(2) Future Prospects

With the continuous development of new energy technologies, all three lithium battery packaging shapes will keep innovating in their respective advantage fields. Square lithium batteries will further optimize their processes in electric and energy storage fields, aiming to enhance energy density and safety while reducing costs; cylindrical batteries are expected to expand their application in electric vehicles with technological advancements while consolidating their position in consumer electronics; soft pack lithium batteries, benefiting from their flexible and customizable strengths, will achieve greater breakthroughs in wearable devices and high-end electronics, along with parts of niche electric vehicle segments.

In the future, technical development routes for lithium battery packaging shapes will closely revolve around enhancing energy density, security, reducing costs, and adapting to varied application scenarios. Different lithium battery packaging shapes will compete and complement each other, jointly driving the new energy industry to new heights. In this game of shape and technology, the ultimate beneficiaries will be the whole new energy ecosystem and the vast consumer base.

 

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Battery Technology | Button Cell Battery Manufacturing Process (Includes Practical Testing Tutorial)

Introduction:

Button cells are one of the commonly used battery types in laboratories, widely applied in material development, electrochemical performance testing, and other fields. This article provides a detailed introduction to the complete process of button cell electrode preparation and battery assembly, including required materials, equipment, steps, and precautions, offering comprehensive guidance for relevant researchers.