With the wide application of mobile electronic equipment, electric vehicles and energy storage systems, lithium battery technology is continuously refined to meet different environments and performance requirements. High polymer lithium battery and special low temperature cell are important branches in the field of lithium battery. Due to their unique material system and technological characteristics, they are outstanding in terms of safety, energy density and low temperature performance. This paper focuses on the analysis of the structural characteristics, material selection and technology of high polymer lithium battery and special low temperature cell, and discusses its technical points and application background.

I. Overview of high polymer lithium batteries

high Polymer Lithium Battery (Polymer Lithium-ion Battery, referred to as PLB) is a Lithium ion Battery that uses Polymer as electrolyte carrier. Its core is different from traditional liquid electrolyte lithium battery. It adopts solid or gel polymer electrolyte membrane, which has higher safety and flexibility.

1. Structure and composition characteristics

high polymer lithium battery mainly consists of positive electrode material, negative electrode material, polymer electrolyte membrane and separator. Polymer electrolyte generally adopts polyethylene oxide (PEO), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA) and other polymer materials, through solution casting or hot pressing film forming, forming ion conductive channels. Compared with liquid electrolyte, high polymer electrolyte has no leakage risk, and can realize ultra-thin design to meet more shape requirements.

2. Material advantages

• high security: High polymer electrolyte is not easy to burn, reducing the risk of thermal runaway of the battery.
• Flexible design: High polymer electrolyte can be made into flexible film, suitable for wearable devices and flexible electronic products.
• High energy density: high capacity and cycle life can be achieved by optimizing the ion conductivity of high polymer electrolyte and matching of electrode materials.

3. Process control technology

the manufacturing process of high polymer lithium battery is different from that of traditional lithium battery. The key lies in the preparation process of electrolyte membrane and the composite process with electrode plate.

• Electrolyte membrane preparation: to ensure the uniformity and ionic conductivity of the film, solution casting is usually adopted to control the concentration, drying temperature and time of the solution to ensure uniform film thickness and no defects.
• Interface optimization: the tight contact density between polymer electrolyte and electrode interface directly affects the internal resistance and cycle performance of the battery. Through surface treatment, electrode coating optimization and hot pressing process, the interfacial binding force is improved.
• Encapsulation Technology: due to the characteristics of polymer electrolyte, battery packaging should be moisture-proof and oxidation-proof, and high barrier packaging materials should be adopted to prolong battery life.

II. Special low temperature cellTechnology

the performance attenuation of lithium battery in low temperature environment is obvious, the capacity decreases, the internal resistance increases and even cannot work normally, which limits its promotion in cold areas and special applications. Special low-temperature cell significantly improves the low-temperature performance of lithium batteries through optimization of materials and processes.

1. Factors affecting low temperature performance

• electrolyte conductivity decreases: the viscosity of traditional organic liquid electrolyte increases at low temperature, and the ion migration is blocked, which leads to the increase of internal resistance of the battery.
• Electrode reaction kinetics slows down: The low temperature environment affects the lithium ion embedding/stripping rate at the electrode interface, reducing the capacity release efficiency.
• Risk Plus-sized of lithium metal branches: Low-temperature charging easily leads to uneven lithium ion deposition, forming branches, affecting safety.

2. Material selection and design

• low temperature electrolyte formula: use electrolyte system with low viscosity and high ionic conductivity, such as adding carbonate solvent, polyol additive or using lithium salt to optimize the formula to improve ion conduction at low temperature.
• Modification of cathode material: improve the lithium ion diffusion rate and reaction activity of the cathode material at low temperature by means of doping and surface coating.
• : Select graphite, hard carbon and other negative electrode materials with excellent low temperature performance to improve the lithium ion embedding efficiency and reduce the formation of branches.

3. Process technology control

• electrolyte injection and packaging: low temperature cell requires higher electrolyte purity and injection process. Impurities should be prevented from affecting electrolyte conductivity to ensure sealing to prevent moisture from entering.
• Process adjustment: Step-by-step charging and low current slow charging strategy are adopted in the formation phase to promote the uniform formation of SEI film in low temperature environment and improve battery stability.
• Temperature control system: design a heating device or heat preservation structure at the battery pack level to assist the battery to maintain the working temperature and ensure stable performance in low temperature environment.

III. Performance comparison between high polymer lithium battery and special low temperature cell

IV. Application scenarios and process priorities

• high polymer lithium battery

• Special low temperature cell it is widely used in the environment of electric vehicles, aerospace, military equipment and so on in cold areas. The process focuses on the optimization of electrolyte formula and the adjustment of formation process to ensure the high capacity output and cycle stability of the battery at low temperature.