A Review on Inorganic Nanoparticles Modified Composite Membranes for Lithium-Ion Batteries

What is it about?

The main focus of the study here is the separator, which separates the anode and cathode electrode inside the lithium-ion battery to protect it from an internal short circuit and provide better safety. Some a prominent attribute of the separator should be that it must be physically and mechanically strong without any reaction with electrolyte, be responsible to keep lithium ions movement continuous without shrinkage or structure damage, high porosity, and interconnected well-groomed porous structure which provide a smooth exchange of ions from anode to cathode, hydrophilic nature of the separator material for containment of the liquid electrolyte thoroughly and quickly, high ion conduction, fast and smooth charging and discharging and maintaining the long cycling capacity. The abovementioned attributes somehow can be achieved by a single component microporous separator such as PE, PP, PP/PE/PP. They are mechanically fit but still inappropriate electrochemically for future batteries. Other developed single polymeric membranes such as PVDF, PVP, cellulose and its copolymer and Polyimide, Membranes 2019, 9, 78 22 of 37 and so forth, are made by phase inversion method, casting technique and electrospinning using a different pore-forming agent (e.g., glycerol, DBP and PEG). These polymers having a hydrophilic nature, sheet forming capability and solubility into an organic solvent, make them applicable for the lithium-ion battery but the mechanical aspect still needs to be improved. To remove the fatal flaws from the separator, researchers’ approach is to add ceramic inorganic nanoparticles to enhance the electrochemical and physical characteristics of the lithium-ion battery. The common inorganic nanoparticles are alumina, titania and silica, which have the ability to disperse into an organic solvent, have a high surface area, hydrophilic nature and thermal characterization. They provide polymer membrane mechanical strength, improve their electrolyte uptake, provide electrochemical stability and enhance the long cycling capacity. The common categories for modification of membrane are coating them on separator surface, inorganic-filled composite and inorganic-filled nonwoven separator. The coating method further includes dip coating, sol-gel method, plasma treatment and grafting, other substrate use and particle surface modification. The dip coating method is common and more practical because of its easy method but it contains some organic solvent involvement which enhances the cost. Sol-gel is another technique in which we somehow reduce the cost of the coating by eliminating the solvent. To remove the substrate hydrophobicity, Polydopamine can be applied on the surface before or after inorganic particles coating to enhance the hydrophilicity of the separator substrate or coating. Plasma technique is applicable for grafting the nanoparticles onto the surface to enhance the strength of the coating and attain uniformity throughout the coating. Sometimes the inorganic particles are modified to enhance their hydrophilicity or cross-linking before application for coating. The inorganic nanoparticles coating is applied on the electrospun separator to reduce the cost of the coating substrate. These methods are widely applied to coat the nanoparticles on the surface of separators, which enhance the thermal stability and performance of the lithium-ion batteries but increase the interfacial resistance due to an increase in the thickness and there are chances of the detachment of the nanoparticles during working of a lithium-ion battery due to binder swelling in the electrolyte. The inorganic nanoparticles blended with polymer composites and non-woven separators can remove the above-mentioned coating problem and enhance the battery performance as they contain high porosity, mechanical strength and electrochemical stability as well as stability for long cycling (Table 1). However, some flaws are still present in these inorganic modified separators like organic electrolyte use, which are volatile in nature and could cause shut down of batteries easily, particles detachments from polymers, which could block the pores and cease the lithium transfer and low mechanical strength due to high porosity which could enhance the chance of structural collapse during assembly. These drawbacks could be minimized by enhancing the polymer and particles aunity towards each other and towards electrolyte for better capacity. To minimize the cost and solve the mechanical stability problem, the solid electrolyte separator could be used because they reduce the components of the lithium-ion batteries by excluding usage of the flammable organic electrolyte and enhance the safety of the batteries without minimizing the performance.

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Photo by Tinh Khuong on Unsplash

Photo by Tinh Khuong on Unsplash

Why is it important?

this article provides a good opportunity for the broad readership of the research community to develop and enhance knowledge about the battery separator. The article includes recent progress in membranes made or modified with inorganic particle use.

Perspectives