Sodium reference electrode sheet

Preparation method of sodium tablets

Before conducting electrochemical performance tests of materials, the experimental battery is first assembled. In order to avoid the influence of multiple factors, a two-electrode half-cell is usually assembled for measurement, and a metal sodium sheet is generally used as the reference electrode and the pair electrode. The preparation process of sodium anode in button batteries is to cut sodium blocks, roll sodium blocks, and flush sodium tablets.

Traditional preparation methods have many limitations, mainly reflected in the following aspects:

1. The operation is cumbersome, four steps, which increases the preparation time of deduction power.

2. Due to manual operation, the consistency of different batches or even the same batch cannot be guaranteed, and the surface state of size, thickness and surface will be different.

3. The surface is uneven, which is easy to produce dendrites, break through the diaphragm, affect the performance and even short circuit.

4. After preparing sodium tablets, there will be residual debris, which is not easy to handle.

The emergence of commercial sodium tablets avoids most of the problems of traditional preparation and provides more convenient and high-quality consumables for scientific research and development.

Polymer vs Li-IonBatteries: The Key Differences You Can’t AffordtoIgnore

Lithium Battery Basics

A polymer battery refers to a lithium-ion battery that uses polymer as the electrolyte. Specifically, it is further divided into two types: “semi-polymer” and “full-polymer”.The “semi-polymer” type means coating a layer of polymer (usually PVDF) on the separator, which makes the bonding force of the cell stronger and the battery can be made harder. Its electrolyte is still liquid electrolyte. The “full-polymer” type refers to using polymer to form a gel network inside the cell, and then injecting electrolyte to form the electrolyte. Although the “full-polymer” battery still needs to use liquid electrolyte, the amount is much less, which greatly improves the safety performance of the lithium-ion battery. As far as the author knows, currently only SONY is mass-producing “full-polymer” lithium-ion batteries. From another perspective, a polymer battery refers to a lithium-ion battery that uses an aluminum-plastic packaging film as the outer packaging, also commonly known as a soft-pack battery. This packaging film is composed of three layers, namely the PP layer, the Al layer, and the nylon layer. Because PP and nylon are polymers, this type of cell is called a polymer battery.

Differences between lithium polymer batteries and ordinary lithium - ion batteries:

1. Different Raw Materials​

Lithium-ion batteries use liquid or colloidal electrolytes as raw materials.​

lithium polymer batteries adopt electrolytes including solid or gel-state polymer electrolytes and organic electrolytes.​

Supplementary note: The polymer electrolyte enables better flexibility in structural design, while organic electrolytes in polymer batteries still maintain ion conductivity similar to traditional lithium-ion batteries.​

2. Varying Safety Performance​

Lithium-ion batteries are prone to explosion under high-temperature or high-pressure conditions due to their liquid electrolyte and rigid casing.​

Polymer lithium batteries use aluminum-plastic films as casings. Even when using organic electrolytes, they will not explode even if the internal temperature rises, as the flexible casing can relieve pressure without causing violent rupture.​

Supplementary note: The aluminum-plastic film casing also reduces the risk of electrolyte leakage compared to metal casings in lithium-ion batteries.​

3. Diverse Shaping Capabilities​

Polymer batteries can achieve thin-form, large-area, and arbitrary shape designs because their electrolytes exist in solid or gel states (instead of liquid), eliminating the need for a rigid container.​

Lithium-ion batteries use liquid electrolytes, requiring a sturdy casing as secondary packaging to contain the electrolyte, which limits their shape flexibility.​

Supplementary note: This characteristic makes polymer batteries ideal for thin electronic devices (e.g., foldable phones), while lithium-ion batteries are more commonly used in cylindrical or prismatic formats for electric vehicles.​

4. Different Cell Voltages​

Polymer batteries can achieve high voltage through multi-layer combinations within the cell due to their polymer materials, with typical nominal voltages ranging from 3.7V to 4.35V (depending on cathode materials).​

Lithium-ion batteries have a nominal cell voltage of 3.6V (e.g., NCM/NCA cells). To achieve high voltage in practical applications, multiple cells must be connected in series to form a sufficient high-voltage working platform.​

Supplementary note: Series connection of lithium-ion cells increases system complexity, while polymer batteries can simplify circuit design through internal voltage stacking.​

5. Distinct Manufacturing Processes​

Polymer batteries are easier to produce in thinner formats, while lithium-ion batteries are more efficiently manufactured in thicker structures, allowing lithium-ion batteries to expand into more application fields (e.g., large-scale energy storage systems).​

Supplementary note: The thin-film manufacturing process of polymer batteries requires precise control of electrolyte viscosity, whereas lithium-ion battery production benefits from mature winding or stacking processes for thick electrodes.​

6. Capacity Differences​

The capacity of polymer batteries has not been effectively improved; in fact, it is slightly lower than that of standard-capacity lithium-ion batteries under the same volume.​

Supplementary note: This is mainly due to the lower energy density of polymer electrolytes compared to liquid electrolytes, though advancements in high-capacity cathode materials (e.g., NCM811) are gradually narrowing this gap.

Advantages and Disadvantages of Polymer Lithium Batteries

Advantages of Polymer Lithium Batteries

1. Excellent Safety Performance

Polymer lithium batteries adopt an aluminum-plastic soft package structure, differing from the metal casing of liquid cells. In case of safety hazards, liquid lithium-ion cells are prone to explosion, while polymer cells only swell or burn at most, significantly reducing the risk of explosion.

2. Ultra-thin Design with Minimal Thickness

Extreme Thinness: The thickness can be reduced to less than 1mm, allowing integration into credit cards or other ultra-thin devices.

Technical Limitations of Traditional Batteries: Conventional liquid lithium batteries face technical bottlenecks in reducing thickness below 3.6mm, and 18650 batteries are constrained by their standardized volume.

3. Lightweight and High Capacity

Weight Advantage: Batteries with polymer electrolytes eliminate the need for metal casings as protective outer packaging. When having the same capacity, they are 40% lighter than steel-cased lithium batteries and 20% lighter than aluminum-cased batteries.

Capacity Advantage: For the same volume, polymer batteries have approximately 30% higher capacity, demonstrating superior energy density.

4. Customizable Shape

The thickness of polymer battery cells can be adjusted according to practical needs. For example, a new laptop model from a renowned brand uses a trapezoidal polymer battery to fully utilize the internal space, optimizing structural design flexibility.

Disadvantages of Polymer Lithium Batteries

1. Higher Costs

Custom designs tailored to client needs add to research and development expenses. Moreover, the wide variety of shapes and sizes means production relies on non-standard fixtures and tools, which further pushes up manufacturing costs—unlike standardized options such as 18650 batteries that benefit from mass production efficiencies.

2. Poor Universality

The flexibility in design comes with a downside: even a 1mm difference in thickness often requires a completely new custom cell. This lack of standardization means polymer batteries have little cross-device compatibility, making them less versatile than more uniform battery types.

3. Fragility and Reliance on Protection Systems

A single fault typically renders the entire battery unusable, as there are no replaceable components. Additionally, overcharging or over-discharging can permanently damage the internal chemical structure, severely shortening lifespan. This makes strict oversight by a Battery Management System (BMS) essential.

4. Shorter Lifespan and Inferior High-Current Performance

Polymer batteries usually offer 300–500 charge-discharge cycles, which is shorter than the 500–1000 cycles of 18650 batteries. They also perform less effectively under high-current discharge—such as in power tools or drones—due to electrolyte limitations, trailing behind the cylindrical 18650s in these scenarios.

——End——

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Elaborate the Lithium-ion Battery Manufacturing Process 5 - Winding/Stacking

 Winding Process

1. Principle and Process

• Principle: The winding process involves the use of a fixed winding needle to wind and compress the pre-processed anode sheets, separator, and cathode sheets in sequence to form a cylindrical or elliptical shape.
• Process: The raw materials are stacked in the sequence of anode, separator, cathode, separator. Then, they are wound into cylindrical or elliptical shapes and placed into metal casings, either square or cylindrical. Specific steps include the unwinding of the anode and cathode sheets and separators, automatic alignment, automatic tension detection and control. The anode and cathode sheets are fed into the winding section by a clamp feeding mechanism, which, together with the separator, undergoes automatic winding according to specified process requirements. After the winding is completed, the machine automatically switches workstations, cuts the separator, attaches the end seal tape, and the finished bare cell is automatically discharged. After pre-pressing, the cell is transported to the discharge outlet by a pull belt.
• Application Scenario: The winding process is mostly used in square and cylindrical batteries.

2. Key Parameter Control

• Tension Parameters: Tension is crucial for ensuring the formation of the wound cell and the interface of the electrodes after the formation process. If the tension is too low, the cell may be loose, and the electrodes may shift during transportation. If the tension is too high, the cell will be tightly wound, which may lead to wrinkles in the electrodes.
• Separator Cutter Temperature: The separator cutter temperature is determined by experimental comparison of cutting effects at different temperatures. After determining the type and thickness of the separator, the separator chamber provides an approximate heat resistance temperature. This temperature acts as the upper limit for the hot-pressing and drying temperatures. Exceeding this limit will cause increased shrinkage of the separator, affecting the coating dimensions and potentially leading to closed pores.
• Winding Needle Circumference: The standard for the winding needle circumference comes from the design process. Theoretically, the circumference of the winding needle equals (cell width - cell thickness) × 2. However, after the cell undergoes hot-pressing, the corners of the cell are not semi-circular but more trapezoidal in shape. Additionally, to accommodate fluctuations in material thickness, the Teflon adjustment results in the winding needle circumference being slightly smaller than the theoretical value.
• Anode Cutter Lifespan: The anode cutter's lifespan is primarily determined by customer requirements. Even if there are burrs at the cutting position, since the negative electrode is wrapped around the positive electrode at the beginning and end of the wound cell, any burrs that puncture the separator will still overlap with the negative electrode. Therefore, burr control may not be necessary.
• Separator Free Revolution Numbers at Winding Head and Tail: The current design specifies 1.5 revolutions for the winding head and 1.25 revolutions for the winding tail, based on design drawings. Adjustments to the winding head revolutions need to mainly verify the impact on core extraction and the thickness of the cell. The number of revolutions at the winding tail is primarily considered with respect to the sealing glue, cell QR code position, and scanning effects, which are closely related to the assembly and welding methods.

3. Equipment and Technical Requirements

• Automation Equipment: The winding process is typically completed using automated equipment to ensure uniformity and consistency in the winding. These devices are usually characterized by high precision, high speed, and high reliability.
• CCD Inspection Device: During the winding process, a CCD inspection device is used to monitor alignment in real-time, ensuring that the anode and cathode sheets are uniformly and tightly bonded with the separator, and that the wrapping is appropriately done.
• Strict Control of Process Parameters: Several key parameters must be strictly controlled during the winding process, including tension, separator cutter temperature, and the circumference of the winding needle, to ensure the quality and performance of the cell.

4. Quality Inspection and Testing

After the winding process is completed, a series of quality inspections and tests are required to ensure that the cell meets the design specifications and quality standards. These checks and tests typically include appearance inspection, electrical performance testing, and safety performance testing.

Stacking Process

1. Principle and Process

• Principle: The coated anode and cathode layers are first cut into predetermined sizes, and then the anode layer, separator, and cathode layer are sequentially bonded together. Multiple "sandwich" structure layers are then stacked in parallel to form a cell core that can be packaged. The continuity of the stacking process relies on the "Z" shaped bending of the separator, which sequentially stacks the anode and cathode onto the separator, with the separator "zig-zagging" through them to separate the electrodes. Finally, the stack is enclosed in an outer casing for packaging.
• Process: The anode and cathode sheets are fed into the stacking machine via an automatic conveyor line, with material boxes for automatic loading and returning. The separator is unwound automatically and is guided through tension control and alignment mechanisms before being introduced into the stacking station. The stacking station moves the separator back and forth to place the electrodes. Two sets of robotic arms with suction cups pick up the anode and cathode sheets from their respective material boxes and, after precise positioning by the pre-positioning system, place them onto the stacking station. After stacking, the robotic arms move the cell to the end-winding and glue application station, where the tail is automatically wound. The separator is cut, and glue is applied to the sides of the cell. Meanwhile, the automatic stacking of the next cell begins. The completed cells, with applied glue, are automatically transferred to the cell transport line's following fixture and then moved to the next process.

• Application Scenario: This process is commonly used for square and soft-pack batteries, and it is especially suited for the production of high-rate batteries, large-size batteries, and custom-shaped batteries.

2. Core Equipment of the Stacking Process

The stacking machine is one of the key pieces of equipment in lithium battery production and is typically composed of the following components.

• Feeding Mechanism: Used to place the anode, cathode sheets, and separator.
• Electrode Sheet Material Box: Used to store and transport the anode and cathode sheets.
• Electrode Positioning Mechanism: Ensures the accurate placement of the electrode sheets during the stacking process.
• Feeding Mechanism: Picks up the electrode sheets from the material boxes and conveys them to the stacking station.
• Stacking Station: Used to support and stack the anode and cathode sheets along with the separator.
• Glue Application Mechanism: Applies protective glue to the finished cells.
• Discharge Mechanism: Removes the finished stack of the cells from the stacking station.

3. Advantages of the Stacking Process

• Improved Battery Performance: The stacking process can significantly enhance the energy density, safety, and cycle life of the battery. Compared to wound batteries, stacked batteries have a higher volumetric energy density limit, more stable internal structures, and longer cycle life.
• High Adaptability: The stacking process is more suited for producing high-rate batteries, large-sized batteries, and custom-shaped batteries, meeting the diverse performance requirements across different fields.
• Higher Material Utilization: In the stacking process, material waste is minimized, as only single sheets need to be removed. In contrast, the winding process often results in waste of entire sheets, or even both the anode and cathode sheets. Therefore, the stacking process offers higher material utilization.

——End——

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The Influence of Polymerization Temperature on the Volume Expansion of Battery Cells Analysis

Preface

Formation is a critical step in the production process of lithium-ion batteries. The primary purpose of formation is to generate a solid electrolyte interphase (SEI) on the surface of the anode, which serves to isolate electrons while allowing ion conduction. The quality of the SEI formation directly affects the subsequent cycling performance of the battery. Therefore, controlling appropriate formation conditions (such as formation temperature, charging rate, applied pressure, etc.) is a crucial production step. The SEI formation process is accompanied by an increase in the volume of the battery. This increase is attributable to two main factors: the gaseous byproducts generated during the film formation reaction and the expansion of the anode structure as lithium ions are extracted from the cathode and intercalate into the anode.

 

In this study, in-situ volume monitoring instruments (GVM) are employed to conduct in-situ volume testing of NCM523/graphite cells (theoretical capacity of 2400 mAh) at different formation temperatures, thereby analyzing the impact of formation temperature.

1. Experimental Equipment and Testing Methods

1.1 Experimental Equipment

Model GVM2200 (IEST Yuan Energy Technology) was used for the testing, with a temperature range of 20°C to 85°C. It supports dual-channel (2 cells) simultaneous testing. The appearance of the equipment is shown in Figure 2

1.2 Testing Information

NCM523/Graphite cell system, charged at 0.5C constant current (CC) to 4.2V, with a theoretical capacity of 2400 mAh.

 1.3 Testing Method

Initially, weigh the battery cell (m₀) and place the cell to be tested into the corresponding channel of the equipment. Launch the MISG software and set the corresponding cell identification numbers and sampling frequency parameters for each channel. The software will automatically read the volume change, testing temperature, current, voltage, capacity, and other data.

 2. In-Situ Volume Expansion Analysis of Battery Cells

Five parallel samples were subjected to formation at temperatures of 25°C, 45°C, 55°C, 65°C, and 85°C according to the process shown in Figure 4(a). The resulting volume expansion curves and differential capacity curves are presented in Figures 4(b) and (c). As the formation temperature increases, the corresponding gas generation rate also gradually rises. When the battery is charged to around 3.7V, the volume curve of the battery reaches a relatively stable maximum value, followed by a slight volume contraction during the constant voltage phase. From the enlarged volume expansion curves and differential capacity curves, it can be observed that the increase in formation temperature causes the volume expansion to occur earlier, with the peak positions of each phase transition shifting to the left. This indicates that the polarization of the battery is continuously decreasing. However, when the temperature exceeds 55°C, the first phase transition reaction peak becomes sharper, which may be related to the intensified SEI formation reactions at elevated temperatures.

During formation, a solid electrolyte interphase (SEI) forms on the surface of the graphite electrode to prevent solvent co-intercalation. The physical and chemical properties of the interface significantly affect the polarization potential and lifespan of lithium-ion batteries. An ideal SEI layer requires high ionic conductivity, good electronic insulation, and excellent thermal and electrochemical stability to ensure rapid lithium ion transport while effectively isolating electrons to reduce side effects. The main components of the SEI include electrolyte salts, LiF, Li₂CO₃, RCO₂Li, carbonates, etc. Only with successful formation of a stable SEI can lithium ions intercalate and de-intercalate stably with graphite. The capacity retention and storage lifespan of lithium-ion batteries are also directly dependent on the stability of the SEI.

The formation of the SEI involves two reverse processes: growth (increase) and dissolution (decrease) of the SEI. Research indicates that SEI growth is associated with the electrochemical reduction process of the electrolyte solvent and is not overly sensitive to temperature. In contrast, an increase in temperature significantly accelerates the dissolution of the initially formed SEI into the electrolyte. Therefore, the SEI interfaces formed at different temperatures exhibit distinct characteristics.

At high temperatures, both the solvent molecules and the electrode's activity are relatively high, making the electrochemical performance at the electrode/electrolyte interface more complex. The organic components of the SEI dissolve more easily in organic electrolytes than inorganic components, leading to collapse of the SEI film. Consequently, at high temperatures, inorganic components become the primary constituents of the SEI film, significantly reducing the electrode's capacity to withstand volume changes. High temperatures can also trigger severe side reactions and produce more gas; moreover, the increased speed of lithium ion transport at elevated temperatures generates greater electrochemical stress at the interface, contributing to instability.

At low temperatures, the formed SEI tends to be denser, resulting in lower ionic conductivity and restricting rapid lithium transport. Furthermore, excessively low temperatures, due to high polarization, can lead to direct deposition of metallic lithium. Hence, only within an optimal temperature range can the formed interfacial film possess the best ionic conductivity and stability.

In conclusion, the formation temperature affects the viscosity and conductivity of the electrolyte as well as the ionic diffusion rate of the electrode materials, thereby influencing the formation results. Generally, higher formation temperatures result in lower electrolyte viscosity, higher electrolyte conductivity, and faster ionic diffusion rates in the electrode materials. Consequently, higher temperatures lead to smaller battery polarization and better formation effects. However, excessively high formation temperatures can damage the already formed SEI structure, increase side reactions, and accelerate the volatilization of low-boiling components in the electrolyte, which is detrimental to the formation effects. Therefore, the commonly selected formation temperature in the industry is typically between 45°C and 70°C.

3.Conclusion

This study employs a controllable dual-channel in-situ gas volume monitoring instrument to conduct in-situ volume expansion tests under different formation temperature conditions. It was found that the higher the temperature, the earlier and larger the volume expansion of the battery cells. By quantitatively characterizing the volume of the battery cells, this approach can assist battery researchers in determining optimal formation conditions.

——End——

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