Blending or copolymerization of polyethylene oxide solid polymer electrolyte and introducing side chains

Blending or copolymerization of polyethylene oxide solid polymer electrolyte and introducing side chains

Polyethylene oxide (PEO) is the earliest and most widely used solid polymer electrolyte matrix material. Professor Wright et al. discovered in 1973 that the blend of PEO and salt complex has ionic conductivity. In 1979, polymer electrolytes were applied to lithium batteries.

1. Blending or copolymerization

The blending or copolymerization of PEO with one or several other polymers can disrupt the order of the PEO molecular chain to a certain extent, increase the flexibility of the polymer chain, and reduce the crystallinity. At the same time, the advantages of the two substances can be combined to improve the electrochemical and mechanical properties of the polymer electrolyte. Inspired by the traditional Chinese Tai Chi culture, Qingdao Energy Storage Industry Technology Research Institute has learned from the idea of “hardness and flexibility” and obtained a composite solid polymer electrolyte with greatly improved electrochemical and mechanical properties through blending methods. “Rigid” refers to the use of rigid framework support materials, such as cellulose non-woven membranes, to provide mechanical support and safety; “flexible” refers to flexible polymer ion transport materials, which enable rapid transport of lithium ions and provide good interface compatibility; “Combination” means that two or more materials achieve complementary advantages and become natural, and then achieve a substantial improvement in the overall performance of the solid polymer electrolyte. The specific method is to dissolve PEO, polycyanoacrylate (PCA) and lithium dioxalate borate (LiBOB) in a solvent at a mass ratio of 10:2:1, and then coat them on a self-made cellulose substrate film. The cellulose substrate in the solid electrolyte film has excellent mechanical properties and provides a rigid skeleton for the solid polymer electrolyte, and the solid electrolyte composite (PCA-PEO) therein provides Li+ transport channels. The LiFePO4/Li battery assembled by using the solid polymer electrolyte exhibits excellent rate performance and stable cycle characteristics, and greatly improves the safety of the battery. Even at 160°C, the charge and discharge are still relatively stable, and the safety is extremely high.

In order to effectively reduce the crystallinity of PEO, improve its ionic conductivity. Tanaka et al. blended PEO and polyethyleneimine (PEI) to obtain a new solid polymer electrolyte system [PEO/PEI (8: 2) 10LiClO4 at 30°C with an ionic conductivity of 10-4S/cm. The ionic conductivity of the solid polymer electrolyte is the highest in the PEO-LiClO4 system without solvent and low molecular weight. This also shows that the blending of PEO and PE1 can reduce the crystallinity of each other and obtain a polymer electrolyte with better performance.

PEO has a low electrochemical stability window and is difficult to match with high-potential cathode materials, which limits its application in high-voltage lithium batteries. The ionic conductivity of the PAN-PEO-LiClO4 electrolyte obtained by the copolymerization of PEO and polyacrylonitrile (PAN) at 25°C is 6.79×10-4S/cm ([EO]/[Li]=10). And the polymer electrolyte The electrochemical performance has been greatly improved. In addition, the addition of PAN can also effectively inhibit the generation of lithium dendrites during the cycle. The literature also reported that the PAN-PEO cross-linked solid polymer electrolyte is expected to be suitable for high-voltage lithium battery systems (such as the use of high-voltage lithium cobalt oxide and lithium nickel manganate cathode materials).

2. Introduce the side chain

The introduction of side chains into the PEO main chain is another way to reduce the crystallinity of the PEO oxyethylene segment. For example, the introduction of short ether side chains can increase the ion transmission rate and obtain higher ion conductivity; the introduction of hydroxyethylamine can better solvate the lithium salt. Introducing 2-(2-methoxyethoxy) ethyl glycidyl ether (MEEGE) side chain into the PEO main chain to form a comb polymer, which can effectively reduce the crystallinity of the PEO segment and increase the ionic conductivity of the polymer electrolyte.

Polyethylene oxide (PEO) is the earliest and most widely used solid polymer electrolyte matrix material. Professor Wright et al. discovered in 1973 that the blend of PEO and salt complex has ionic conductivity. In 1979, polymer electrolytes were applied to lithium batteries.

1. Blending or copolymerization

The blending or copolymerization of PEO with one or several other polymers can disrupt the order of the PEO molecular chain to a certain extent, increase the flexibility of the polymer chain, and reduce the crystallinity. At the same time, the advantages of the two substances can be combined to improve the electrochemical and mechanical properties of the polymer electrolyte. Inspired by the traditional Chinese Tai Chi culture, Qingdao Energy Storage Industry Technology Research Institute has learned from the idea of “hardness and flexibility” and obtained a composite solid polymer electrolyte with greatly improved electrochemical and mechanical properties through blending methods. “Rigid” refers to the use of rigid framework support materials, such as cellulose non-woven membranes, to provide mechanical support and safety; “flexible” refers to flexible polymer ion transport materials, which enable rapid transport of lithium ions and provide good interface compatibility; “Combination” means that two or more materials achieve complementary advantages and become natural, and then achieve a substantial improvement in the overall performance of the solid polymer electrolyte. The specific method is to dissolve PEO, polycyanoacrylate (PCA) and lithium dioxalate borate (LiBOB) in a solvent at a mass ratio of 10:2:1, and then coat them on a self-made cellulose substrate film. The cellulose substrate in the solid electrolyte film has excellent mechanical properties and provides a rigid skeleton for the solid polymer electrolyte, and the solid electrolyte composite (PCA-PEO) therein provides Li+ transport channels. The LiFePO4/Li battery assembled by using the solid polymer electrolyte exhibits excellent rate performance and stable cycle characteristics, and greatly improves the safety of the battery. Even at 160°C, the charge and discharge are still relatively stable, and the safety is extremely high.

In order to effectively reduce the crystallinity of PEO, improve its ionic conductivity. Tanaka et al. blended PEO and polyethyleneimine (PEI) to obtain a new solid polymer electrolyte system [PEO/PEI (8: 2) 10LiClO4 at 30°C with an ionic conductivity of 10-4S/cm. The ionic conductivity of the solid polymer electrolyte is the highest in the PEO-LiClO4 system without solvent and low molecular weight. This also shows that the blending of PEO and PE1 can reduce the crystallinity of each other and obtain a polymer electrolyte with better performance.

PEO has a low electrochemical stability window and is difficult to match with high-potential cathode materials, which limits its application in high-voltage lithium batteries. The ionic conductivity of the PAN-PEO-LiClO4 electrolyte obtained by the copolymerization of PEO and polyacrylonitrile (PAN) at 25°C is 6.79×10-4S/cm ([EO]/[Li]=10). And the polymer electrolyte The electrochemical performance has been greatly improved. In addition, the addition of PAN can also effectively inhibit the generation of lithium dendrites during the cycle. The literature also reported that the PAN-PEO cross-linked solid polymer electrolyte is expected to be suitable for high-voltage lithium battery systems (such as the use of high-voltage lithium cobalt oxide and lithium nickel manganate cathode materials).

2. Introduce the side chain

The introduction of side chains into the PEO main chain is another way to reduce the crystallinity of the PEO oxyethylene segment. For example, the introduction of short ether side chains can increase the ion transmission rate and obtain higher ion conductivity; the introduction of hydroxyethylamine can better solvate the lithium salt. Introducing 2-(2-methoxyethoxy) ethyl glycidyl ether (MEEGE) side chain into the PEO main chain to form a comb polymer, which can effectively reduce the crystallinity of the PEO segment and increase the ionic conductivity of the polymer electrolyte.

Blending or copolymerization of polyethylene oxide solid polymer electrolyte and introducing side chains
Figure 1 – The structural formula of P (EO-MEEGE) and the relationship between the crystallinity and ionic conductivity of the electrolyte and the MEEGE content