Metal hydride alloys with improved rate performance
Methods of preparing improved metal hydride alloy materials are provided. The alloys include a mixture of at least four of vanadium, titanium, nickel, chromium, and iron. The alloy is processed by at least one of thermal and physical treatment to generate a refined microstructure exhibiting improved kinetics when used as electrodes in MH batteries (e.g., higher discharge current). The thermal treatment includes rapid cooling of the alloy at greater than 10 4 K/s. The physical treatment includes mechanical pulverization of the alloy after cooling. The microstructure is a single phase (body centered cubic) with a heterogeneous composition including a plurality of primary regions having a lattice parameter selected from the range of 3.02 Å to 3.22 Å and a plurality of secondary regions having a lattice parameter selected from the range of 3.00 Å to 3.22 Å and at least one physical dimension having a maximum average value less than 1 μm.
1. A method of fabricating a metal alloy, said method comprising at least one of the steps of:
rapidly cooling an alloy precursor; and
ball milling the alloy precursor;
wherein the alloy precursor comprises titanium (Ti), vanadium (V), nickel (Ni), and at least one of chromium (Cr) and iron (Fe);
thereby generating said metal alloy characterized by a heterogeneous microstructure having a body centered cubic (BCC) crystal structure, said heterogeneous microstructure comprising:
a plurality of primary regions characterized by a lattice parameter selected from the range of 3.02 Å to 3.22 Å; and
a plurality of secondary regions characterized by a lattice parameter selected from the range of 3.00 Å to 3.22 Å and having at least one physical dimension with a maximum average value less than 1 μm;
wherein said at least one of rapidly cooling and ball milling said alloy precursor provides for said heterogeneous microstructure being characterized by a maximum average distance between a center of a primary region and a nearest secondary region of less than 1.5 μm.
2. The method of claim 1 , wherein the alloy is capable of sorbing at least 1.3 wt. % hydrogen at a pressure less than 2 atm.
3. The method of claim 1 , wherein the maximum average value of the at least one physical dimension is less than 0.5 μm.
4. The method of claim 1 , wherein the secondary region is mixed within a matrix of the primary region.
5. The method of claim 1 , wherein:
the plurality of primary regions are further characterized by an amount of vanadium greater than 54 at. % and an amount of nickel less than 9 at. %; and
the plurality of secondary regions are further characterized by an amount of vanadium less than 40 at. % and an amount of nickel greater than 15 at %.
6. The method of claim 1 , wherein:
the plurality of primary regions are further characterized by an amount of titanium less than 31 at. %; and
the plurality of secondary regions are further characterized by an amount of titanium greater than 30 at. %.
7. The method of claim 1 , wherein the heterogeneous microstructure further comprises a plurality of boundary regions extending between the plurality of primary regions and the plurality of secondary regions, said plurality of boundary regions characterized by a lattice parameter selected from the range of 3.00 Å to 3.22 Å.
8. The method of claim 1 , wherein the composition of the primary region comprises:
18 at. % to 31 at. % Ti;
54 at. % to 72 at. % V;
3 at. % to 9 at. % Ni; and at least one of:
6 at. % to 13 at. % Cr; and
2 at. % to 12 at. % Fe.
9. The method of claim 1 , wherein the composition of the secondary region comprises:
30 at. % to 50 at. % Ti;
8 at. % to 40 at. % V;
15 at. % to 42 at. % Ni; and at least one of:
2 at. % to 5 at. % Cr; and
5 at. % to 18 at. % Fe.
10. The method of claim 1 , wherein said providing step comprises:
mixing titanium (Ti), vanadium (V), nickel (Ni), and at least one of chromium (Cr) and iron (Fe) to form a mixture;
melting the mixture to generate a first melt; and
cooling the first melt to generate an ingot of the alloy precursor comprising the mixture of the titanium (Ti), vanadium (V), nickel (Ni), and at least one of chromium (Cr) and iron (Fe).
11. The method of claim 1 , said step of rapidly cooling comprising:
cooling a melt of said alloy precursor at a rate selected from the range of greater than 10 4 K/s to less than 10 8 K/s.
12. The method of claim 11 , wherein said cooling is performed by at least one of suction casting, liquid quenching, air quenching, gas atomization and melt spinning.
13. The method of claim 1 , further comprising pulverizing the alloy precursor to a powder having a particle size selected from the range of 0.1 μm to 75 μm.
14. The method of claim 13 , wherein said pulverizing comprises at least one of hydrogen activation, mechanical crushing, grinding, and ball milling.
15. The method of claim 1 , wherein:
the metal alloy composition is characterized by Ti a V b Ni c Cr d Fe e ;
a is greater than 0 and less than or equal to 97 at. %;
b is greater than 0 and less than 100 at. %;
c is selected from the range of 3 to 20 at. %; and wherein:
d is greater than 0 and less than or equal to 20 at. % and e is selected from the range of 0 to 20 at. %; or d is selected from the range of 0 to 20 at. % and e is greater than 0 and less than or equal to 20 at. %.
16. A method of forming a metal hydride electrode, comprising:
providing an active material comprising the metal alloy fabricated according to claim 1 ;
mixing a powder of the active material with a binder; and
compressing the mixture of powdered active material and the binder into a desired electrode shape.
17. The method of claim 16 , wherein the active material is treated by a hydriding/dehydriding operation for 5 cycles under a pressure from the range between 8 bar to 50 bar prior to mixing with the binder.
18. The method of claim 16 , wherein the binder is selected from at least one of nickel, copper, and carbon.
19. The method of claim 16 , wherein the powdered active material and the binder are mixed in a ratio selected from the range of 95:5 and 25:75.
20. The method of claim 16 , wherein the metal hydride electrode is capable of electrochemical discharge capacity of at least 350 mAh/g at currents of at least 10 mA/g.
21. A metal alloy, comprising:
a composition comprising titanium (Ti), vanadium (V), nickel (Ni), and at least one of chromium (Cr) and iron (Fe);
the alloy further being characterized by a heterogeneous, single phase microstructure having a body centered cubic (BCC) crystal structure, said heterogeneous microstructure comprising:
a plurality of primary regions characterized by a lattice parameter selected from the range of 3.02 Å to 3.22 Å; and
a plurality of secondary regions characterized by a lattice parameter selected from the range of 3.00 Å to 3.22 Å and having at least one physical dimension with a maximum average value less than 1 μm;
wherein said heterogeneous microstructure is characterized by a maximum average distance between a center of a primary region and a nearest secondary region of less than 1.5 μm.
22. The metal alloy of claim 21 , wherein the metal alloy is capable of sorbing at least 1.3 wt. % hydrogen at a pressure less than 2 atm.
23. The metal alloy of claim 21 , wherein the maximum average value of the at least one physical dimension is less than 0.5 μm.
24. The metal alloy of claim 21 , wherein the secondary region is mixed within a matrix of the primary region.
25. The metal alloy of claim 21 , wherein:
the plurality of primary regions are further characterized by an amount of vanadium greater than 54 at. % and an amount of nickel less than 9 at. %; and
the plurality of secondary regions are further characterized by an amount of vanadium less than 40 at. % and an amount of nickel greater than 15 at. %.
26. The metal alloy of claim 21 , wherein:
the plurality of primary regions are further characterized by an amount of titanium less than 31 at. %; and
the plurality of secondary regions are further characterized by an amount of titanium greater than 30 at. %.
27. The metal alloy of claim 21 , wherein the heterogeneous microstructure further comprises a plurality of boundary regions extending between the plurality of primary regions and the plurality of secondary regions, said plurality of boundary regions characterized by a lattice parameter selected from the range of 3.00 Å to 3.22 Å.
28. The metal alloy of claim 21 , wherein the composition of the primary region comprises:
18 at. % to 31 at. % Ti;
54 at. % to 72 at. % V;
3 at. % to 9 at. % Ni; and at least one of:
6 at. % to 13 at. % Cr; and
2 at. % to 12 at. % Fe.
29. The metal alloy of claim 21 , wherein the composition of the secondary region comprises:
30 at. % to 50 at. % Ti;
8 at. % to 40 at. % V;
15 at. % to 42 at. % Ni; and at least one of:
2 at. % to 5 at. % Cr; and
5 at. % to 18 at. % Fe.
30. The metal alloy of claim 21 , wherein:
the metal alloy composition is characterized by Ti a V b Ni c Cr d Fe e ;
a is greater than 0 and less than or equal to 97 at. %;
b is greater than 0 and less than 100 at. %;
c is selected from the range of 3 to 20 at. %; and wherein:
d is greater than 0 and less than or equal to 20 at. % and e is selected from the range of 0 to 20 at. %; or d is selected from the range of 0 to 20 at. % and e is greater than 0 and less than or equal to 20 at. %.
31. The metal alloy of claim 21 , wherein metal alloy is characterized bar Ti 29 V 56 Cr 6 Ni 9 , Ti 29 V 53 Cr 9 Ni 9 , or Ti 29 V 50 Cr 12 Ni 9 .
32. The metal alloy of claim 30 , wherein the composition is characterized by Ti a V 2.1-b Ni c Fe d and wherein the ratio of Fe/(V+Fe) is selected from the range of 0 to 0.4.
33. A metal hydride electrode comprising:
an active material comprising the metal alloy of claim 21 ; and
a binder.
34. The metal hydride electrode of claim 33 , wherein the metal hydride electrode is capable of electrochemical discharge capacity of at least 350 mAh/g at currents of at least 10 mA/g.
35. The metal hydride electrode of claim 33 , wherein the metal hydride electrode is capable of discharging at least 65% of a total capacity of the electrode at 167 mA/g for at least 100 cycles.
36. The metal hydride electrode of claim 33 , wherein an exchange current density of the metal hydride electrode is greater by a factor of at least 10% compared to that of a metal hydride electrode having the same composition and not characterized by said heterogeneous microstructure.
37. The metal hydride electrode of claim 33 , wherein a limiting current density of the metal hydride electrode is greater by a factor of at least 10% compared to that of a metal hydride electrode having the same composition and not characterized by said heterogeneous microstructure.
38. A metal alloy, comprising:
a composition comprising titanium (Ti), vanadium (V), nickel (Ni), and at least one of chromium (Cr) and iron (Fe); and
a heterogeneous, single phase microstructure having a body centered cubic (BCC) crystal structure, said heterogeneous microstructure comprising a mixture of a plurality of secondary regions in a matrix of a plurality of primary regions, wherein:
said plurality of primary regions characterized by a lattice parameter selected from the range of 3.02 Å to 3.22 Å;
said plurality of secondary regions characterized by a lattice parameter selected from the range of 3.00 Å to 3.22 Å and having at least one physical dimension with a maximum average value less than 1 μm; and
said heterogeneous microstructure is characterized by a maximum average distance between a center of a primary region and a nearest secondary region of less than 1.5 μm;
wherein said heterogeneous microstructure is formed via at least one of rapid cooling and ball milling of an alloy precursor comprising the titanium (Ti), vanadium (V), nickel (Ni), and at least one of chromium (Cr) and iron (Fe).
39. The metal alloy of claim 38 , wherein the alloy is capable of sorbing at least 1.3 wt. % hydrogen at a pressure less than 2 atm.
40. The metal alloy of claim 38 , wherein the maximum average value of the at least one physical dimension is less than 0.5 μm.
41. The metal alloy of claim 38 , wherein:
the plurality of primary regions are further characterized by an amount of vanadium greater than 54 at. % and an amount of nickel less than 9 at. %; and
the plurality of secondary regions are further characterized by an amount of vanadium less than 40 at. % and an amount of nickel greater than 15 at %.
42. The metal alloy of claim 38 , wherein:
the plurality of primary regions are further characterized by an amount of titanium less than 31 at. %; and
the plurality of secondary regions are further characterized by an amount of titanium greater than 30 at. %.
43. The metal alloy of claim 38 , wherein said rapid cooling comprises cooling a melt of said alloy precursor at a rate selected within the range of greater than 10 4 K/s to less than 10 8 K/s.
44. A metal hydride electrode, comprising:
an active material comprising the metal alloy of claim 38 ; and
a binder.
45. The metal hydride electrode of claim 44 , wherein the metal hydride electrode is capable of electrochemical discharge capacity of at least 350 mAh/g at currents of at least 10 mA/g.
46. The metal hydride electrode of claim 44 , wherein the metal hydride electrode is capable of discharging at least 65% of a total capacity of the electrode at 167 mA/g for at least 100 cycles.
47. The metal hydride electrode of claim 44 , wherein an exchange current density of the metal hydride electrode is greater by a factor of at least 10% compared to that of a metal hydride electrode having the same composition and not characterized by said heterogeneous microstructure.
48. The metal hydride electrode of claim 44 , wherein a limiting current density of the metal hydride electrode is greater by a factor of at least 10% compared to that of a metal hydride electrode having the same composition and not characterized by said heterogeneous microstructure.
49. The metal hydride electrode of claim 33 , wherein a high rate dischargeability (HRD) of said metal hydride electrode is greater by an absolute value that is at least 10% compared to a metal hydride electrode having the same composition and not characterized by said heterogeneous microstructure, for discharge cycles selected from the range of 5 to 10.
50. The metal hydride electrode of claim 33 , wherein a high rate dischargeability (HRD) of said metal hydride electrode is greater by an absolute value that is at least 6% compared to a metal hydride electrode having the same composition and not characterized by said heterogeneous microstructure, when a discharge current density is 250 mA/g.
51. The metal hydride electrode of claim 44 , wherein a high rate dischargeability (HRD) of said metal hydride electrode is greater by an absolute value that is at least 10% compared to a metal hydride electrode having the same composition and not characterized by said heterogeneous microstructure, for discharge cycles selected from the range of 5 to 10.
52. The metal hydride electrode of claim 44 , wherein a high rate dischargeability (HRD) of said metal hydride electrode is greater by an absolute value that is at least 6% compared to a metal hydride electrode having the same composition and not characterized by said heterogeneous microstructure, when a discharge current density is 250 mA/g.
53. The method of claim 1 , said method comprising ball milling the alloy precursor; wherein at least said ball milling said alloy precursor provides for said heterogeneous microstructure being characterized by a maximum average distance between a center of a primary region and a nearest secondary region of less than 1.5 μm.
54. The method of claim 1 , said method comprising a combination of steps of rapidly cooling the alloy precursor and ball milling the alloy precursor; wherein said combination of rapidly cooling and ball milling said alloy precursor provides for said heterogeneous microstructure being characterized by a maximum average distance between a center of a primary region and a nearest secondary region of less than 1.5 μm.
55. The metal alloy of claim 38 , wherein said heterogeneous microstructure is formed via at least ball milling of said alloy precursor.
56. The metal alloy of claim 38 , wherein said heterogeneous microstructure is formed via a combination of rapid cooling and ball milling of said alloy precursor.
57. The method of claim 1 , wherein said alloy precursor is a mixture comprising said titanium (Ti), vanadium (V), nickel (Ni), and at least one of chromium (Cr) and iron (Fe).
58. The metal alloy of claim 38 , wherein said alloy precursor is a mixture comprising said titanium (Ti), vanadium (V), nickel (Ni), and at least one of chromium (Cr) and iron (Fe).