Nickel hydroxide positive electrode for alkaline rechargeable battery
Certain nickel hydroxide active cathode materials for use in alkaline rechargeable batteries are capable of transferring >1.3 electrons per Ni atom under reversible electrochemical conditions. The specific capacity of the nickel hydroxide active materials is for example ≧325 mAh/g. The cathode active materials exhibit an additional discharge plateau near 0.8 V vs. a metal hydride (MH) anode. Ni in an oxidation state of less than 2, such as Ni 1+ , is able to participate in electrochemical reactions when using the present cathode active materials. It is possible that up to 2.3 electrons, up to 2.5 electrons or more may be transferred per Ni atom under electrochemical conditions.
1. A nickel hydroxide cathode active material for use in an alkaline rechargeable electrochemical cell, the cathode active material comprising an alpha-Ni(OH) 2 phase with an oxidation state on the Ni of +1 or lower, and where an electrochemical cell using the cathode active material in a positive electrode exhibits a discharge plateau near 0.8 V vs. a metal hydride anode during charge/discharge cycling.
2. A cathode active material according to claim 1 , which is capable of transferring >1.67 electrons per Ni atom.
3. A cathode active material according to claim 1 , where the specific capacity of the material is ≧330 mAh/g.
4. A cathode active material according to claim 1 , where Ni reaches an oxidation state of less than + 2 during charge/discharge cycling of an alkaline rechargeable cell.
5. A cathode active material according to claim 1 , which also exhibits a discharge plateau near 1.2 V and a discharge plateau at >1.2 V and <1.3 V.
6. A cathode active material according to claim 1 comprising one or more modifiers selected from the group consisting of Al, Ba, Bi, Ca, Co, Cr, Cu, F, Fe, In, La, Li, Mg, Mn, Na, Nd, Pb, Pr, Ru, Sb, Sc, Se, Sn, Sr, Te, Ti, Y and Zn.
7. A cathode active material according to claim 1 comprising one or more modifiers selected from the group consisting of Co, Zn and Al.
8. A cathode active material according to claim 1 selected from the group consisting of (Ni,Co,Zn)(OH) 2 , (Ni,Co)(OH) 2 ,(Ni Co,Al)(OH) 2 and (Ni,Co,Zn,Al)(OH) 2 .
9. A cathode active material according to claim 8 selected from the group consisting of (Ni,Co)(OH) 2 nickel hydroxides where Ni is present from about 89 atomic percent (at %) to about 99 at % and Co is present from about 1 at % to about 11 at %, based on 100at % total of Ni and Co combined.
10. A cathode active material according to claim 8 selected from the group consisting of (Ni,Co,Al)(OH) 2 nickel hydroxides where Ni is present from about 80 at % to about 90 at % and Co and Al together are from about 10 to about 20 at %, based on 100 at % total of Ni, Co and Al combined.
11. A cathode active material according to claim 10 where the atomic ratio of Co to Al is from about 1:1 to about 1:5.
12. A cathode active material according to claim 8 selected from the group consisting of (Ni,Co,Zn,Al)(OH) 2 nickel hydroxides where Ni is present from about 64 to about 74 at % and Co, Zn and Al together are present from about 26 to about 36 at %, based on 100 at % total of Ni, Co, Zn and Al combined.
13. A cathode active material according to claim 12 where the atomic ratio of Co to Al is from about 1:1 to about 1:5 or from about 1:2 to about 1:4.
14. A cathode active material according to claim 12 where the atomic ratio of Co to Zn is from about 1:2 to about 2:1.
15. A cathode active material according to claim 12 where the atomic ratio of Zn to Al is from about 1:1 to about 1:5.
16. A cathode active material according to claim 8 selected from the group consisting of Ni 0.94 Co 0.06 (OH) 2 , Ni 0.85 Co 0.05 Al 0.10 (OH) 2 and Ni 0.69 Co 0.05 Zn 0.06 Al 0.2 (OH) 2 .
17. A positive electrode for use in an alkaline rechargeable electrochemical cell, the electrode comprising a cathode active material according to claim 1 , a conductive substrate and optionally one or more components selected from binders and additives.