Lithium-ion battery electrodes with shape-memory-alloy current collecting substrates

Abstract

Lithium-ion battery electrode constructions use an array of nanowires (or of other long thin shapes) of active electrode material anchored at one end to a surface of a metal current collector sheet in an electrode assembly or construction. This form of active electrode material permits good contact with a liquid lithium-ion containing electrolyte that infiltrates the closely-spaced thin shapes. Stresses arising from volume changes in the long shapes with lithiation and de-lithiation of the active material is mitigated by strategic placement of shape memory apply forms between attachment surfaces of the active electrode material and other members of the electrode assembly.

Description

TECHNICAL FIELD[0001]This invention pertains to electrode materials and structures for the cells of lithium-ion batteries in which lithium atoms are repeatedly inserted into and removed from small, wire-like shapes of negative electrode active material during charging and discharging of the battery. More specifically, this invention pertains to the formation of such shapes of electrode materials, anchored in an elastic shape memory alloy substrate, to enable longer and more effective cycling of such electrode materials.BACKGROUND OF THE INVENTION[0002]Lithium-ion batteries are used as electric storage systems for powering electric and hybrid electric vehicles. These batteries comprise a plurality of suitably interconnected electrochemical cells arranged to provide a predetermined electrical current at a specified electrical potential. In each such cell, lithium is transported as lithium ions from a negative electrode through a non-aqueous, lithium-containing, electrolyte solution to...

AI Technical Summary

Benefits of technology

[0011]In accordance with embodiments of the invention, vulnerable thin sections of electrode material nanometer shapes are grown on, or embedded in a shape memory alloy (SMA) material. This SMA material in the electrode structure is placed and formed so as to accommodate growth and shrinkage of the thin shapes of active electrode material during cell operation, and to prevent them from breaking at critical locations and reducing the energy capacity of the cell. A nickel-titanium alloy, composed of 53 atomic percent titanium, is an example of a shape memory alloy that that displays superelastic properties. Nickel-titanium alloy (sometimes NiTi in this specification) is commercially available. NiTi and like superelastic metal alloys are used in practices of this invention to provide a stress buffer between the base ends of the many negative electrode material nanowires or other material shapes and the metal current collector bodies to which they are anchored. As will be described in more detail, the shape memory alloy buffer material displays large reversible deformation in response to the changing size of the ends of the nanowires and reduces the stress on them.

Problems solved by technology

While graphitic carbon is a durable and useful lithium-intercalating, negative electrode material for lithium-ion cells, it has a relatively low capacity for such lithium insertion.

However, the volume change of up to 300 volume percent for silicon during lithiation and de-lithiation processes leads to fracture of the active silicon material and / or loss of electrical contact with the conductive additives or the current collectors.

And tin has the same problem of a large volume expansion upon lithiation, leading to rapid capacity degradation.

Both problems shorten the effective cycling capacity of a battery.

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