Nonaqueous electrolyte secondary battery anode material with a uniform metal-semiconductor alloy layer
The present invention relates to nonaqueous electrolyte secondary batteries and durable anode materials and anodes for use in nonaqueous electrolyte secondary batteries. The present invention also relates to methods for producing these anode materials. In the present invention, a metal-semiconductor alloy layer is formed on an anode material by contacting a portion of the anode material with a displacement solution. The displacement solution contains ions of the metal to be deposited and a dissolution component for dissolving a part of the semiconductor in the anode material. When the anode material is contacted with the displacement solution, the dissolution component dissolves a part of the semiconductor in the anode material thereby providing electrons to reduce the metal ions and deposit the metal on the anode material. After deposition, the anode material and metal are annealed to form a uniform metal-semiconductor alloy layer.
1. A composite anode for a secondary battery, the composite anode comprising a matrix comprising a binder and a particulate anode material bound together by the binder, the particulate anode material comprising a semiconductor material having a surface and a semiconductor alloy layer completely coating the semiconductor material surface, the semiconductor material comprising silicon, germanium, a III-V compound semiconductor or a II-VI compound semiconductor, the semiconductor alloy layer comprising an alloy of the semiconductor material and a metal selected from nickel, copper, cobalt, silver, gold, platinum, palladium and rhodium, the semiconductor alloy layer having a thickness of about 100 nanometers to about 3 micrometers and a thickness non-uniformity of less than about 25% wherein thickness non-uniformity is defined as the quantity of the maximum thickness minus the minimum thickness, divided by the average thickness.
2. The composite anode of claim 1 , wherein the metal is a noble metal.
3. The composite anode of claim 1 , wherein the metal is a base metal.
4. The composite anode of claim 3 , wherein the metal is nickel.
5. The composite anode of claim 1 , wherein the semiconductor is silicon.
6. The composite anode of claim 1 , wherein the metal is nickel and the semiconductor is silicon.
7. The composite anode of claim 1 , comprising a metal-semiconductor layer wherein the average thickness of the metal-semiconductor alloy layer is between about 100 nanometers and 3 micrometers.
8. The composite anode of claim 1 , comprising a metal-semiconductor layer wherein the thickness non-uniformity of the metal-semiconductor alloy layer is less than about 25%.
9. The composite anode of claim 1 wherein the semiconductor material contains silicon and the semiconductor alloy layer comprises an alloy of nickel or copper.
10. The composite anode of claim 9 wherein the semiconductor material contains silicon and the semiconductor alloy layer is a nickel silicide layer having a resistivity of 10-60 pa/cm.
11. The composite anode of claim 9 wherein the semiconductor alloy layer is a nickel silicide layer and the nickel silicide layer is formed by a process comprising the step of selectively etching the nickel silicide layer to remove excess nickel without etching the nickel silicide layer.