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

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.

(II) Application and future development of lithium battery packaging film

Aluminum-plastic film can effectively protect the internal structure of lithium batteries and ensure their safety and stability. In addition to its application in lithium battery packaging, it is widely used in the field of pharmaceutical packaging due to its excellent barrier properties and mechanical properties, which can effectively prevent drug deterioration and bacterial growth. In addition, aluminum-plastic film has good transparency and barrier properties, which can maintain the freshness and taste of food, so it has broad application prospects in the field of food packaging. Aluminum-plastic composite film can also be used in electronic components, optical instruments and other fields. Aluminum-plastic film has excellent properties, and with the continuous advancement of science and technology and the improvement of people's environmental awareness, the market demand for aluminum-plastic film will further expand. In the future, with the continuous innovation of technology and the reduction of costs, the application field of aluminum-plastic film will be broader.

The main aluminum-plastic film manufacturers in my country include Xinlun Technology, Shanghai Zijiang Group, Zhejiang Daoming Optoelectronics, Mingguan New Materials, Hangzhou Foster, etc., which match different types of soft-pack lithium batteries, and each manufacturer has its own strengths. Overall, the market size of my country's aluminum-plastic film industry is on an upward trend. It is expected to grow rapidly in the future driven by downstream lithium battery demand. According to data, the market size of my country's aluminum-plastic film will grow at an average annual compound growth rate of 16.09% from 2021 to 2025, and its market size is expected to further reach 13.32 billion yuan in 2025.

With the popularity of new energy vehicles, smart phones and other electronic products and the growing market demand, the market size of soft-pack lithium batteries, as core components, continues to expand. As one of the key materials for soft-pack lithium batteries, the market demand for aluminum-plastic film is also growing. The compound annual growth rate (CAGR) is expected to be 15.6% in the next few years.

Lithium battery diaphragm

Performance determines battery quality

1. Characteristics and functions

As one of the key internal components of lithium batteries, lithium battery separator plays a vital role in the battery. It can separate the positive and negative electrodes of the battery to prevent the two electrodes from contacting and short-circuiting, and it also has the function of allowing electrolyte ions to pass through. The performance of the separator directly determines the battery's capacity, cycle and safety performance.

There are mainly the following types of lithium battery separators on the market:

1. Polyolefin separators: including PP/PE/PP multi-layer composite microporous membranes, PP or PE single-layer microporous membranes, etc. This type of separator is resistant to high and low temperatures, has low density, stable chemical structure, excellent mechanical strength, and good electrochemical stability. It is widely used in various types of lithium batteries.

2. Coated polyester film: Made of polyethylene terephthalate, it is made into thick sheets by extrusion and then biaxially stretched. It is relatively expensive and generally 0.012mm thick. It is widely used in fiberglass, building materials, printing, medicine and health industries.

3. Cellulose membrane: It has high strength, fast filtration speed, can capture coarse particles, and can also collect gel-like sediments, with low resistance and low impurity content.

4. Polyimide membrane: It has excellent heat resistance and oxidation stability, but due to the harsh synthesis and membrane making conditions and high cost, it is hindered from further application in membrane separation technology.

5. Polyamide membrane: From the perspective of hydrophilicity and hydrophobicity theory, polyamide should be a better reverse osmosis membrane material.

6. Spandex or aramid film: resistant to high temperatures, with the characteristics of low-temperature output, long charging cycle life, and moderate mechanical strength.

In addition, according to the structure and composition, lithium battery separators can also be divided into porous polymer membranes, non-woven membranes and inorganic composite membranes. Porous polymer membranes are membranes with uniform pore distribution prepared by various methods; non-woven membranes are composed of oriented or random fibers, usually compounded with organic matter or ceramic gel; inorganic composite membranes are obtained by compounding inorganic nanoparticles with high polymers.

Different types of separators have different characteristics and application scopes. For example, polyolefin separators have advantages in cost and stability, and are suitable for most consumer electronic product batteries; while new separators such as polyimide membranes, spandex or aramid membranes have potential application value in the field of high temperature resistant and high performance batteries.

2. Development Status and Challenges

Lithium battery diaphragm materials are developing rapidly at home and abroad, showing a trend of diversification. In China, with the rapid development of the new energy vehicle market, the demand for lithium battery diaphragms continues to grow. Leading companies such as Enjie Co., Ltd. are globally competitive in terms of production capacity, product quality, cost efficiency, and technology research and development. In recent years, the company has developed rapidly, with a substantial increase in production capacity and revenue, and its diaphragm production capacity and shipments rank first in the world.

At the same time, the thinning of diaphragms has become an important trend in the development of the industry. The thinner the diaphragm, the more conducive it is to reducing the internal resistance of the battery and improving the energy density and endurance of the battery. For example, the mainstream dry-process diaphragm in the power industry is a 12-14μm three-layer co-extruded diaphragm, and the conventional product thickness of the wet-process base film is 5-9μm. At present, some companies can produce 4μm thick lithium battery diaphragms. However, the ultra-thin diaphragm also brings a series of technical challenges. First of all, in the process of thinning the diaphragm, how to ensure its puncture resistance, mechanical strength and isolation properties to ensure product safety is a major technical challenge. Secondly, whether it is a dry or wet process, the preparation of ultra-thin diaphragms puts higher requirements on process accuracy and stability. In addition, the production of ultra-thin diaphragms requires advanced production equipment to ensure accuracy and stability, and domestic companies still need to make continuous efforts in equipment research and development and manufacturing. At the recent 13th Battery and Thin Film Industry Chain Development Summit Forum held in 2024, the outlook for diaphragm technology and market trends became one of the core topics hotly discussed by participants. Senior executives and technical personnel from related companies also shared a lot of innovative design ideas, future development trends, etc. at this meeting.

Despite many challenges, the lithium battery separator industry still has broad prospects for development. With the continuous advancement and innovation of technology, more breakthroughs are expected in separator materials, processes and equipment in the future to further solve the technical challenges brought by ultra-thinness. At the same time, driven by the continuous demand for thinner and lighter electronic products and improved lithium battery performance, the market demand for ultra-thin battery separators will continue to grow.

Battery blue film

The guardian of lithium batteries

1. Performance and advantages

The blue film of the battery cell is a protective film on the surface of the square aluminum shell of the power battery. The mainstream material is PET film. It has many properties and advantages and plays an important role in power batteries. First of all, it has excellent wear resistance and can effectively resist the friction that may be suffered during transportation and use, protecting the surface of the battery cell. At the same time, it has excellent puncture resistance and reduces the risk of short circuit caused by external sharp objects. The excellent mechanical strength enables it to withstand certain external force impacts and ensure the structural integrity of the battery cell.

In a long-term environment of humidity, heat and temperature changes, the blue film of the battery cell can still remain stable and adapt to various complex working conditions. It can also meet the 15-year service life requirement, providing reliable protection for the long-term use of the battery. In addition, the characteristics of puncture resistance, corrosion resistance and high pressure resistance enable it to operate safely in different chemical environments and high voltage conditions. The characteristic of no residual glue after peeling facilitates the maintenance and replacement of the battery. Finally, the excellent explosion-proof and flame-retardant effect can effectively reduce safety risks in unexpected situations.

2. Applications and Challenges

The blue film of battery cells is widely used in lithium batteries. On the one hand, it plays an insulating and protective role for single batteries, preventing a single battery cell from having adverse effects on other battery components due to various faults. It can prevent the battery from surface scratches and leakage during subsequent transportation and assembly, and can also play a waterproof and dustproof role to better protect the battery.

In the integrated coating inspection machine, the blue film of the battery cell also has an important development trend. With the large-scale expansion of power battery production capacity, battery companies have higher and higher requirements for product safety, performance, and quality control. As an insulating material, the quality inspection of blue film is extremely important. Since the blue film is a highly reflective material with a thickness of only 0.015mm-0.20mm, there are many types of defects and samples of some types of defects are difficult to collect. The over-kill rate and missed detection rate of traditional algorithms are extremely high. To address this problem, companies have introduced standardized solutions. For example, Huahan Weiye uses 2D+2.5D+3D+AI in combination to achieve image-level feature fusion, meet the online and precise detection of subtle and low-contrast defects, and effectively improve battery quality control and yield.

In addition, as the endurance and charging speed of new energy vehicles increase, power batteries are gradually developing in the direction of lightweight, high efficiency and high voltage, and the market has put forward higher requirements on the insulation capacity and voltage resistance level of battery materials. Traditional blue film insulation solutions may face the risk of being replaced by UV coated insulation materials, powder coatings, etc. However, blue film is currently one of the main application solutions for power battery electrical insulation due to its high cost performance. In 2023, the cumulative sales volume of power batteries in my country will be 616.3GWh, a year-on-year increase of 32.4%; the cumulative exports of power batteries will be 127.4GWh, a year-on-year increase of 87.1%. The expansion of the scale of the power battery industry has provided a broad demand space for the blue film industry.

All three are indispensable components of lithium batteries, and together they guarantee the performance and safety of lithium batteries. Lithium battery packaging film and battery cell blue film protect the battery cell from the outside and surface, while lithium battery separators ensure the isolation of positive and negative electrodes and the normal transmission of ions inside. Together they play an important role in the development and application of lithium batteries.

(Source: Baijucheng R&D Center)

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