Electrolytes and metal hydride batteries
Metal hydride batteries comprising an electrolyte composition which comprises an aqueous solution comprising potassium hydroxide (KOH) and one or more halide and/or oxyacid salts exhibit reduced degradation of the anode material during operation. The salts are for instance alkali metal salts. Anode materials exhibit for instance <100 % of the degradation of the same anode material in the same battery when replacing the electrolyte composition with 30 weight percent (wt %) aqueous KOH and the conductivity of the electrolyte composition is for instance ≥85 % of 30 wt % aqueous KOH. Anode materials are for example ABx high capacity hydrogen storage alloys comprising Mg where x is from about 0.5 to about 5 and which has a discharge capacity of ≥400 mAh/g.
1. A metal hydride battery comprising at least one negative electrode comprising an active anode material, at least one positive electrode comprising an active cathode material, a casing having said electrodes positioned therein and an electrolyte composition;
wherein the anode material comprises an alloy comprising Mg and Ni in an atomic ratio of from about 1:2 to about 2:1 and one or more modifying elements selected from the group consisting of Co, Mn, Al, Fe, Cu, Mo, W, Cr, V, Ti, Zr, Sn, Th, Si, Zn, Li, Cd, Na, Pb, La, Ce, Pr, Nd, Mm, Pd, Pt, Nb, Sc and Ca, wherein Mg and Ni together are present at a level of ≥70 at % and the one or more modifying elements are present from about 0.1 at % to about 30 at %, based on the total alloy;
wherein the electrolyte composition comprises an aqueous solution comprising from about 3 M to about 8 M KOH and from 0.4 M to 2.0 M one or more salts selected from the group consisting of NaCl, KCI and RbCl; and
wherein the degradation of the anode material in the battery is <100 percent of the degradation of the same anode material in the same battery when replacing the electrolyte composition with 30 weight percent aqueous KOH and wherein the conductivity of the electrolyte composition is ≥85 percent of that of 30 weight percent aqueous KOH.
2. A battery according to claim 1 where the anode material comprises an alloy selected from the group consisting of Mg 0.8 Ti 0.2 Ni, Mg 0.7 Ti 0.3 Ni, Mg 0.9 Ti 0.1 Ni, Mg 0.8 Zr 0.2 Ni, Mg 0.7 Ti 0.225 La 0.075 Ni, Mg 0.8 Al 0.2 Ni, Mg 0.9 Ti 0.1 Ni, Mg 0.9 Ti 0.1 NiAl 0.05 , Mg 0.08 Pd 0.2 Ni, Mg 0.09 Ti 0.1 NiAl 0.05 , Mg 0.09 Ti 0.1 NiAl 0.05 Pd 0.1 , Mg 50 Ni 45 Pd 5 , Mg 0.85 Ti 0.15 Ni 1.0 , Mg 0.95 Ti 0.15 Ni 0.9 , and Mg 2.0 Ni 0.6 Co 0.4 .
3. A battery according to claim 1 where the anode material comprises Mg 2 Ni 0.6 Mn 0.4 , Mg 2 Ni 0.7 Cu 0.3 , Mg 0.8 La 0.2 Ni, Mg 2.0 Co 0.1 Ni, Mg 2.1 Cr 0.1 Ni, Mg 2.0 Nb 0.1 Ni, Mg 2.0 Ti 0.1 Ni, Mg 2.0 V 0.1 Ni, Mg 1.3 Al 0.7 Ni, Mg 1.5 Ti 0.5 Ni, Mg 1.5 Ti 0.3 Zr 0.1 Al 0.1 Ni, Mg 1.75 Al 0.25 Ni, (MgAl) 2 Ni, or Mg 1.70 Al 0.3 Ni.
4. A battery according to claim 1 where the anode material has a discharge capacity of ≥400 mAh/g.
5. A battery according to claim 1 where the anode material has a discharge capacity of ≥450 mAh/g.
6. A battery according to claim 1 where the anode material comprises an alloy selected from the group consisting of Mg 52 Ni 39 Co 6 Mn 3 and Mg 52 Ni 39 Co 3 Mn 6 .
7. A battery according to claim 1 , wherein the degradation of the anode material in the battery is ≤95 percent of the degradation of the same anode material in the same battery when replacing the electrolyte composition with 30 wt percent aqueous KOH and wherein the conductivity of the electrolyte composition is ≥87 percent of that of 30 wt percent aqueous KOH.
8. A battery according to claim 1 , wherein the one or more modifying elements are Co and/or Mn.