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Producing Process of Li-Po Battery I

Intro

Lithium-polymer (LiPo) batteries have become an integral part of our daily lives, powering everything from smartphones and laptops to electric vehicles and drones. However, the production process of these batteries is not widely known, and it involves several complex steps. The manufacturing of LiPo batteries is a highly specialized process that requires strict adherence to safety protocols and quality control measures. The process involves the use of various chemicals and materials, including lithium cobalt oxide, graphite, and electrolytes. These components are assembled in a controlled environment to ensure that the battery meets the required specifications and performs optimally.

In this article, we will explore the production process of LiPo batteries in detail, from the preparation of the raw materials to the final assembly of the battery. We will also examine the various challenges and safety concerns associated with the manufacturing process and how they are addressed. Overall, this article aims to provide a comprehensive overview of the LiPo battery production process, shedding light on the intricate science behind this ubiquitous technology.

STEP 1–Mixed Pulping

The preparation of slurry is a key process in the production of lithium batteries, and the uniformity of slurry mixing is directly related to the preparation process and battery performance of subsequent processes. The traditional method of homogenizing the positive electrode of lithium-ion batteries, first stir the solvent and the binder for 2 to 4 hours, then add the conductive agent and stir for 1 to 3 hours, and then add the active substance and stir for 2 to 4 hours to prepare a positive electrode slurry. During the homogenization process, the binder will have fine clumps of particles that are not completely dissolved, and the conductive agent is easy to agglomerate, difficult to disperse, and poor dispersion effect.

This homogenization process has the following disadvantages:

(1) The uniformity of the slurry is not good;

(2) The stability of the slurry is not good, and the slurry is easy to layer after being placed for a period of time.

Therefore, a Li-Po battery positive electrode slurry has been developed and applied to polymer lithium-ion batteries to improve the uniformity and stability of the slurry, and to improve the cycle performance, magnification charge and discharge performance and overcharge safety performance of polymer lithium-ion batteries, which is of great significance to the development of the polymer lithium-ion battery preparation industry.

STEP 2–Dry li-Po battery’s pole sheet wet coating

The drying process and coating process of lipo battery poles are independent and interconnected. The nature of the coating affects the design and operation of the drying process. The coating speed and the thickness of the coating determine the drying length. During the drying process, the coating has a leveling process, which will affect the uniformity of the coating. Therefore, whether the coating can accurately use the best coating and drying processes in the design process, balance the relationship between the two, and ultimately affect the comprehensive technical performance of the coating.

There are roughly the following ways to dry polar tablets´╝Ü

(1) Drying by far-infrared radiation.

Use a far-infrared emitter to radiate heat energy to the surface of a dry object, evaporate and vaporize the liquid for drying.

Features: Its drying speed mainly depends on the radiation temperature, the temperature is high, and the drying speed is fast. The advantage is that the equipment is relatively simple, so it is used in relatively low-gear coating machines. The disadvantage is that the drying efficiency is low, the drying is uneven, and it is prone to drying ills.

(2) Double-sided air supply floats and dries.

Floating drying is to set up a specially designed air nozzle on both sides of the drying foil to send a high-speed jet of air. Under the action of the wall effect of the air flow, it acts vertically on the drying foil. Under the action of the air flow, the dry sheet is in a floating state for drying.

(3) Conventional convection hot air drying.

Convection drying is a more traditional drying technique. The heated dry air is fed into the drying channel, and the heat energy in the dry air is transmitted to the dried object through the convection of the air, causing the liquid to evaporate and vaporize for drying. Its advantage is that the equipment is simple, and its disadvantage is that the drying efficiency is low, which is gradually replaced by efficient hot air impact drying in modern drying equipment.

(4) Circulating hot air shocks and dries.

Efficient drying technology developed using the principles of air jet fluid mechanics. The dry air is sprayed onto the surface of the dried object at high speed through a specially designed air nozzle, which prevents the dry still air layer on the surface of the dried object from being destroyed under the impact, thereby speeding up the drying process and greatly improving the drying efficiency. The characteristics of circulating hot air impact drying are: the drying speed is related to temperature, and it is related to the drying air volume. The air supply of partially circulating dry air can be increased to increase the air volume and increase the drying speed, which greatly improves the heat utilization of the dry air. Therefore, the impact drying of circulating hot air has the characteristics of high efficiency and energy saving. In addition, by increasing the air supply volume to increase the drying speed, the ills of cracking and drying that may arise from the use of high temperature drying can be avoided.

(5) Superheated water vapor dries.

Superheated vapor is the vapor obtained by heating the liquid to a saturated vapor that evaporates all of it, and then continuing to heat it.Superheated steam drying is an emerging drying method in which the drying medium is in direct contact with the wet coating, and its heat is mainly passed into the material by convection, and the dried precipitated solvent is taken away by the drying medium.During the drying process, superheated steam passes through the surface of the material as the drying medium, and the heat is transmitted to the wet coating. The free solvent on the surface of the coating is heated and vaporized, resulting in a difference in the moisture concentration between the surface of the material and the interior. Under this difference, the internal moisture content diffuses from the liquid or gaseous form to the surface, and the gasified water vapor is taken away by the superheated steam air flow.The advantage is that the latent heat of steam can be used, the thermal efficiency is high, and the effect of energy saving can be achieved. The heat transfer coefficient of superheated steam drying is larger than that of hot air drying.

(6) Microwave drying.

Microwave drying is a method of using microwave energy with a frequency of 915~2450MHZ to heat up the material, thereby evaporating the water for drying. Microwave drying is different from traditional drying methods, and the direction of heat conduction is the same as the direction of moisture diffusion.

Compared with traditional drying methods, microwave drying has the advantages of fast drying rate, energy saving and environmental protection, high production efficiency, clean production, excellent drying effect, easy to realize automated operation and control, and can improve product quality.

STEP 3–Rolling the Pole Sheet

Pole sheet rolling is generally done by a double-roller press, which is composed of two cast steel compaction rollers, a motor and a drive shaft. When the roller press is not in working condition, it should be coated with a thin layer of oil to prevent it from rusting. Wipe the oil layer with absolute ethanol before use, and clean up the retracting and unwinding mechanism, the automatic correction mechanism, the roller, and other places that may be contaminated with impurities in contact with the pole piece.

After the coated pole piece is fixed to the unwinding mechanism, the pole piece is correctly passed through the double-roller gap and connected to the winding system. After turning on the rolling mode, the motor drives the upper and lower rollers to rotate at the same time, and the pole piece pulled by the winding mechanism will steadily pass through the rolling gap, and finally be pressed to the desired compaction density.

The ultimate goal of rolling is to obtain a pole piece that meets the design requirements. What is in line with the design requirements? It is to require the relevant parameters of the pole piece: what is the surface density, what is the compaction density, how is the adhesion, particle integrity, warping size, etc. to meet the design requirements of the battery cell. The necessity of rolling: After the electrode sheet is coated and dried, the peel strength of the living substance and the collector foil is very low. At this time, it should be rolled to strengthen the bonding strength of the living substance and the foil to prevent it from peeling off during the immersion of the electrolyte and the use of the battery.

STEP 4–Cut Pole Sheet into strips to Make Pole Pieces

After the lithium-ion battery electrode sheet is coated with slurry, dried and rolled, a three-layer composite structure with fluid collection and coating on both sides is formed.Then according to the battery design structure and specifications, we need to cut the pole piece again.Generally, for winding batteries, the pole pieces are slotted according to the design width; for laminated batteries, the pole pieces are cut into pieces accordingly.

At present, the li-po battery pole sheet cutting process mainly adopts the following three types:

(1) disc cutting and slitting

(2) mold punching

(3) laser cutting.

STEP 5–Pile Up Electrode Sheet

In the die-cutting process, the traditional winding adopts bilateral die-cutting, with unequal spacing between the die-cutting pole ears, and there are perforations at the punching position for positioning: while the laminated piece adopts unilateral die-cutting, the pole ears are the same spacing, and the equal spacing will be cut off.In the pole-forming workshop, the negative electrode sheet is continuously wound, and the negative electrode sheet is a sheet-like material. With the same number of layers, compared with the winding battery, the number of laminated batteries is twice as large. At the same time, the tension of the film is almost flat to zero, and the hole accuracy is consistent with the raw material.At present, there are four main mainstream laminator equipment routes on the market: Z-shaped laminating machine, cutting and stacking all-in-one machine, thermal laminating machine and winding all-in-one machine. Among them, Z-type laminating is currently the most widely used in China. The technology of thermal laminating machine is more difficult, and the rolling and stacking all-in-one machine involves Japanese and Korean patents, and there are fewer domestic applications.

Advantage of laminated battery

Compared with winding batteries, laminated batteries have certain advantages:
1) a higher upper limit of volumetric energy density: In the case of battery design of the same volume, the energy density of laminated batteries is about 5% higher.
2) a more stable internal structure and higher safety: there is no problem of uneven stress in the corners, and the expansion force of each layer is close, so the interface can be kept flat and the internal structure is more stable. At the same time, the force at the corners is uniform, and the risk of fracture is reduced.
3)longer cycle life: the number of pole ears is twice that of the winding battery, the internal resistance is reduced by more than 10% accordingly, and the cycle life is about 10% higher than that of the winding.
4)more suitable for high magnification, large size and special-shaped batteries.However, there are also disadvantages such as low production efficiency, low yield, large equipment investment, and high process difficulty in film inspection, which are the main factors that previously restricted mass production.

In next article, we will continue to talk about left producing process of lipo battery.

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