Tin alloy sheets as negative electrodes for non-aqueous Li and Na-ion batteries
This invention relates to materials for the negative electrode in non-aqueous rechargeable alkali-ion batteries in free-standing form. In particular, this invention relates to the use of metal ribbon that is produced by melt spinning directly as a battery electrode. The invention also relates to a method producing a highly dispersed, multiphase composite material in a single step, as well as a way to generate porosity while maintaining the ‘binder-free’ and ‘additive-free’ characterization of the electrode.
1. A method of producing a battery electrode comprising:
a) spinning a metal ribbon on a melt spinning apparatus; to directly produce a ribbon of Sn alloy or composite material of Sn and at least one of Al and Cu between 20 and 45 micrometer thickness as the battery electrode without powder processing.
2. The method as claimed in claim 1 further comprising:
a) setting a spin speed between a surface velocity of between 20 to 50 m/s;
b) selecting a rotating copper wheel with a crucible;
c) selecting Sn and Cu or Sn and Al as metal in the crucible;
d) melting a mixture of c) in the crucible;
e) setting a gap between a bottom of the crucible and the copper rotating wheel between 0.1 and 0.5 mm when a molten material is ejected;
f) selecting an overpressure on top of the melt used to expel the molten material from the crucible onto the copper wheel between 0.2 and 0.4 atmospheres.
3. The method of claim 1 wherein a composite from a group comprising Sn—Al and Sn—Cu is produced.
4. The method as claimed in claim 1 followed by a cooling step to ambient temperatures.
5. The method as claimed in claim 1 further including dissolving Al in 1 M (aq) KOH solution resulting in a porous Sn structure.
6. The method as claimed in claim 1 wherein;
a) a spin speed is selected between a surface velocity of between of 28.27 to 42.4 m/s;
b) a gap between a bottom of the crucible and a copper rotating wheel is selected between 0.25 and 0.4 mm when a molten material is ejected; and
c) an overpressure on top of a melt used to expel the molten material from the crucible onto the copper wheel between 0.2 and 0.4 atmospheres.
7. The method as claimed in claim 2 comprising:
a) cold rolling a Sn—Al ribbon to densify the Sn—Al ribbon.
8. The method as claimed in claim 4 comprising
a) alkaline etching of the Al using potassium hydroxide solution to introduce pores into the Sn ribbon.
9. The method as claimed in claim 8 wherein the ribbon is used as a battery anode in the form of a sheet.
10. The method as claimed in claim 3 wherein the Sn—Al composite comprises Al inclusions of up to 50 atomic percentage.
11. The method as claimed as claim 1 free of binder and conductive additives.
12. The method as claimed in claim 2 comprising Sn with Cu6Sn5 inclusions less than 1 micron or Sn with Al inclusions less than 250 nano meters.