[Battery materials] Vol.1 Lithium-ion batteries and fluoromaterials
Takanori Suzuki
Suzuki Material Technology and Consulting Co., Ltd.
【Serial column : Battery materials】
Vol.01 Lithium-ion batteries and fluoromaterials1. History of lithium-ion batteries
2. Trends in lithium-ion battery development
Figure.1 History of lithium-ion batteries
2-1. Cathode
The development of cathodes pursues greater battery capacities by increasing the amount of lithium contained in the active material and by increasing the voltage. At the same time, the design process pursues cost reduction and stable material supply with the reduced use of cobalt and nickel, which are rare metals, and with the use of easy-to-get materials only.2-2. Electrolyte
Studies on electrolytes have been conducted in combination with the improvement of withstand voltage to accommodate the cathode’s voltage, which has grown higher, as well as the development and selection of additives for the stable operation of the anode and the selection of solvents. Lithium-ion batteries are burdened with the big problem that they can burn, and this is attributable to the combustible organic solvent used as the electrolyte. Making electrolytes noncombustible is an enormous theme; and the solution coming up as an extension of this theme is solid-state batteries, which use a solid electrolyte.2-3. Separator
The separator is very important material to ensure safety. Yet, it does not contribute to the role of storing electricity. Therefore, there is always a demand to make it as thin as possible while ensuring safety. It can be said that the successful development of a separator depends on meeting both these safety and thinness requirements. As another requirement, the separator needs to resist the cathode’s voltage, which has grown higher.2-4. Anode
In order to gain higher capacity, the manufacturers of anodes are developing various methods, such as adding metal oxides like silicon, tin, and using the lithium metal itself as the anode.2-5. Binder
Polyvinylidene fluoride (PVDF) materials have long been used for cathode binders since the advent of lithium-ion batteries. Although some improvements, including the introduction of high polymerization and functional groups, have been added, the use of PVDF materials as principal materials has still remained the same.2-6. Conductive agent
As conductive agents, carbon black materials have been used for many years. However, against the background of recent years’ cost reductions, a multi-wall or single-wall CNT are now being released onto the market. A vapor deposition carbon existed in the past as well, but it seems to be a big breakthrough that we are now seeing some utilized as general conductive agents. CNTs are often supplied as dispersions.3. Material development by Daikin
Figure.2 Daikin's battery materials
3-1. Relationship between fluorochemicals and lithium-ion batteries
Fluorine compounds and fluoropolymers are generally known for their high chemical stability, and many of these fluorine materials are used in lithium-ion batteries. Fluorine was a behind-the-scenes key player so indispensable that lithium-ion battery materials - especially electrolytes and binders - would not have helped to realize high-performance batteries if it had not been used. Lithium-ion batteries can reach up to 4.6 V. This is due to the cathode, whose potential is very high. What other materials are there that could keep a stable performance under such an oxidizing condition? There are few except for fluorine compounds. Especially, electrolytes and binders, which lie in the cathode and are exposed to a strong oxidizing condition, must have extremely high stability.3-2. Binder
Daikin’s product lineup includes NEOFLON VT-475, which is a new binder additive improved from PVDF thanks to Daikin’s own technology to impart functionalities, including improved electrode flexibility, higher density, and gelation prevention of slurry. In addition, other binders such as for solid state electrolytes and for those dry process are under development.3-3. CNT dispersion
Daikin is proceeding with the development of NEOFLON VTD-475N, which is a binder-containing conductive agent dispersion combining a single-wall CNT and a binder elaborated based on Daikin’s binder. The market has high hopes for it as a product that can impart excellent conductivity to electrodes and also bring the binder performance of Daikin to batteries.3-4. Electrolyte (additive)
Daikin is also developing a fluorine electrolyte additive designed to be used in electrolytes in order to assist their functionalities. This is another excellent fluorine material that maintains both controlled reactivity and stability when in a battery and thereby contributes to enhancing battery performance.3-5. Gasket material
Gaskets are used as the seals around the terminals of prismatic lithium-ion batteries. Cylindrical cells also use gaskets to insulate and seal the cathode terminal and the can. These gaskets, which serve as terminal-can insulators and come into direct contact with the organic electrolyte in the can, are required to be chemically stable and resist pressing creep at the same time.
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