Tuesday, June 29, 2010

Nanotek Graphene Platelets Provide Improved Anode Compositions for Rechargeable Lithium Batteries

Nanotek Instruments, Inc. (Dayton, OH) received U.S. Patent 7,745,047 for nano graphene platelet-base composite anode compositions for lithium ion batteries.  

Inventors Aruna Zhamu and Bor Z. Jang provides a nano-scaled graphene platelet-based composite material composition for use as an electrode, particularly as an anode of a lithium ion battery. The composition comprises: (a) micron- or nanometer-scaled particles or coating which are capable of absorbing and desorbing lithium ions; and (b) a plurality of nano-scaled graphene platelets (NGPs), wherein a platelet comprises a graphene sheet or a stack of graphene sheets having a platelet thickness less than 100 nm.

At least one of the particles or coating is physically attached or chemically bonded to at least one of the graphene platelets and the amount of platelets is in the range of 2% to 90% by weight and the amount of particles or coating in the range of 98% to 10% by weight. Also provided is a lithium secondary battery comprising such a negative electrode (anode). The battery exhibits an exceptional specific capacity, an excellent reversible capacity, and a long cycle life.

FIG. 2 is a TEM micrograph of NGPs (several NGPs overlapping each other. 

The invention provides a negative electrode (anode) composite material composition for use in a lithium secondary battery. The composition comprises an electrochemically active material admixed with nano-scaled graphene platelets (NGPs), characterized in that both the active material and the NGPs are capable of absorbing and desorbing lithium ions. The electrochemically active material is in a fine powder form (smaller than 500 .mu.m, preferably smaller than 200 .mu.m, and most preferably smaller than 1 .mu.m) and/or thin film (coating) form (preferably smaller than 100 nm in thickness), in contact with or attached to graphene platelets.

An NGP is essentially composed of a sheet of graphene plane or multiple sheets of graphene plane stacked and bonded together through van der Waals forces. Each graphene plane, also referred to as a graphene sheet or basal plane, comprises a two-dimensional hexagonal structure of carbon atoms. Each plate has a length and a width parallel to the graphite plane and a thickness orthogonal to the graphite plane. By definition, the thickness of an NGP is 100 nanometers (nm) or smaller, with a single-sheet NGP being as thin as 0.34 nm.

The length and width of a NGP are typically between 1 .mu.m and 20 .mu.m, but could be longer or shorter. The NGPs form a myriad of electron transport paths for improving the electrical conductivity or reducing the internal resistance of the anode. The flexibility and strength of NGPs make them ideal materials to absorb or buffer the volume expansion or contraction of the electrochemically active material particles or coating. NGPs themselves are also capable of absorbing and extracting lithium (explained in a later section). 

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