The current collector is one of the indispensable components of lithium-ion batteries, which can not only carry the active material, but also converge and output the current generated by the electrode active material, which is conducive to lowering the internal resistance of lithium-ion batteries, and improving the battery's Coulombic efficiency, cycling stability, and multiplier performance.

Lithium-ion battery current collector

In principle, the ideal lithium-ion battery fluid collector should meet the following conditions: (1) high conductivity; (2) good chemical and electrochemical stability; (3) high mechanical strength; (4) good compatibility and bonding with the electrode active substance; (5) cheap and easy to obtain; (6) light weight.

Currently, the materials that can be used as lithium-ion battery collectors include metal conductor materials such as copper, aluminum, nickel and stainless steel, semiconductor materials such as carbon, and composite materials.

2.1 Copper collector

Copper is an excellent metal conductor with electrical conductivity second only to silver, and has many advantages such as abundant resources, cheap and easy to obtain, and good ductility. However, considering that copper is easy to be oxidized at higher potentials, it is often used as a collector for negatively active substances such as graphite, silicon, tin and cobalt-tin alloys. Common copper collectors include copper foils, copper foam and copper mesh, and three-dimensional copper nano-array collectors.

2.2 Aluminum Collector

Although the conductivity of the metal aluminum is lower than that of copper, the mass of the aluminum wire is only half that of the copper wire when delivering the same amount of power, and there is no doubt that the use of an aluminum collector contributes to an increase in the energy density of lithium-ion batteries. In addition, compared with copper, aluminum is more affordable. During the charging/discharging process of lithium-ion batteries, a dense oxide film is formed on the surface of the aluminum foil collector, which improves the corrosion resistance of the aluminum foil, and it is often used as the collector for the positive electrode in lithium-ion batteries.

2.3 Nickel collector

Comparatively speaking, nickel is a base metal, relatively inexpensive, has good electrical conductivity, and is more stable in acid and alkaline solutions, so nickel can be used as both positive and negative electrode collectors. It is matched with both positive active substances such as lithium iron phosphate and negative active substances such as nickel oxide, sulfur and carbon and silicon composites. The shape of nickel collector is usually of two types: nickel foam and nickel foil.

2.4 Stainless steel collector

Stainless steel is an alloy steel containing elements such as nickel, molybdenum, titanium, niobium, copper, iron, etc. It has good electrical conductivity and stability, and it can resist the chemical attack of weak corrosive mediums such as air, steam, water and strong corrosive mediums such as acid, alkali, salt, etc. The surface of stainless steel is also easy to form a passivation film to protect its surface from corrosion. Stainless steel surface is also easy to form a passivation film, which can protect its surface from corrosion, while stainless steel can be processed thinner than copper, with the advantages of low cost, simple process and mass production. Stainless steel can be used as a positive or negative electrode collector, common stainless steel collector has stainless steel mesh and porous stainless steel two types.

2.5 Carbon fluid collector

Carbon material as positive or negative electrode fluid collector can avoid the electrolyte corrosion of the metal collector, and it has the advantages of abundant resources, easy processing, low resistivity, no harm to the environment, low price and so on.

Carbon fiber cloth can be used as the fluid collector of flexible lithium-ion battery with its own good flexibility, conductivity and electrochemical stability. Carbon nanotubes are another form of carbon collector, compared to metal collectors, its obvious advantage is the lightweight and can significantly increase the energy density of the battery.

2.6 Composite fluid collector

In addition to the single collector such as copper collector, aluminum collector, nickel collector, stainless steel collector and carbon collector and so on have been widely concerned, in recent years, the composite collector has also aroused the research interest of scholars, such as the conductive resin, carbon coated aluminum foil and titanium-nickel shape memory alloy.

Collector is one of the indispensable and important parts of lithium-ion battery, which has the multiple functions of carrying electrode active material and collecting output current. Collectors prepared by different materials and production processes have different properties and have different effects on lithium-ion batteries.

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