Patent Description:
Much progress has been made in optimizing the electrochemical performance and cycle life of metal hydride batteries through optimization of the electrodes. The electrolyte of metal hydride batteries is presently <NUM>% by weight aqueous KOH. The aqueous KOH electrolyte is corrosive to some electrode materials. Aqueous electrolyte is also limited by the hydrogen and oxygen evolution potential of water. The present invention is focused on improved electrolytes.

<CIT> discloses nickel metal hydride batteries. In claim <NUM> of said document, a positive electrode is disclosed for use in alkaline rechargeable electrochemical cells particularly comprising: a material comprising a compositionally and structurally disordered multiphase nickel hydroxide host matrix which includes at least one modifier chosen from a group of specific elements.

<CIT> particularly relates to a metal secondary battery comprising a positive electrode active material layer, a negative electrode active material layer, and an electrolyte layer formed between the positive electrode active material layer and the negative electrode active material layer, wherein the negative electrode active material layer contains MgH<NUM>, wherein the electrolyte layer is composed of an electrolytic solution containing an ionic liquid.

This invention was made with government support under <CIT> awarded by Advanced Research Projects Agency-Energy. The government has certain rights in the invention.

The present invention relates to a metal hydride battery (cell) comprising at least one negative electrode, at least one positive electrode, a casing having said electrodes positioned therein and an electrolyte composition, where the electrolyte composition comprises.

Preferably, the positive electrode comprises one or more cathode active materials selected from the group consisting of.

Preferably, the metal hydride battery (cell) exhibits a nominal open-circuit voltage of > <NUM> V (volts) and up to about <NUM> V, for example from about <NUM> to about <NUM> V, from about <NUM> to about <NUM> V, from about <NUM> to about <NUM> V or from about <NUM> to about <NUM> V.

Generally, a metal hydride battery comprises at least one negative electrode, at least one positive electrode, a casing having said electrodes positioned therein and an electrolyte composition in contact with the electrodes.

The electrolyte composition is useful in an electrochemical cell such as a metal hydride battery (metal hydride cell). According to the present invention, the active material of the negative electrode (anode material) comprises an ABx type alloy capable of reversibly adsorbing and desorbing hydrogen with A being a hydride forming element, B being a weak or non-hydride forming element and x being from <NUM> to <NUM>. A is in general a larger metallic atom with <NUM> or less valence electrons and B is in general a smaller metallic atom with <NUM> or more valence electrons. The alloys are capable of reversibly absorbing (charging) and desorbing (discharging) hydrogen. For example, the MH alloys are capable of reversibly absorbing and desorbing hydrogen electrochemically at ambient conditions (<NUM> and <NUM> atm).

ABx type alloys are for example of the categories (with simple examples), AB (HfNi, TiFe, TiNi, ZrNi), AB<NUM> (ZrMn<NUM>, TiFe<NUM>, ZrV<NUM>, TiMn<NUM>), A<NUM>B (Hf<NUM>Fe, Mg<NUM>Ni, Ti<NUM>Ni), AB<NUM> (NdCo<NUM>, GdFe<NUM>, CeNi<NUM>, YFe<NUM>), A<NUM>B<NUM> (Pr<NUM>Ni<NUM>, Ce<NUM>Co<NUM>, Y<NUM>Ni<NUM>, Th<NUM>Fe<NUM>), AB<NUM> (LaNi<NUM>, CeNi<NUM>) and A<NUM>B<NUM> (Y<NUM>Fe<NUM>).

Metal hydride alloys include alloys containing Ti, V and Mn (Ti-V-Mn alloys) and alloys containing Ti, V and Fe. For instance alloys containing from about <NUM> to about <NUM> atomic percent Ti, from about <NUM> to about <NUM> atomic percent V and from about <NUM> to about <NUM> atomic percent Mn and/or Fe. Suitable alloys are taught for instance in <CIT>.

Metal hydride alloys include alloys of formula ABx where A comprises from about <NUM> to below <NUM> atomic percent Ti and the remainder is Zr and/or Hf and B comprises from about <NUM> to below <NUM> atomic percent of Ni and the remainder is one or more elements selected from Cr, V, Nb, Ta, Mo, Fe, Co, Mn, Cu and rare earths and x is from about <NUM> to about <NUM>. These alloys are taught for example in <CIT>.

Metal hydride alloys include alloys of formula (TiV<NUM>-xNix)<NUM>-yMy where x is from about <NUM> to about <NUM> and M is Al and/or Zr; alloys of formula Ti<NUM>-xZrxV<NUM>-yNiy where x is from <NUM> to about <NUM> and y is from about <NUM> to about <NUM>; and alloys of formula Ti<NUM>-xCrxV<NUM>-yNiy where x is from <NUM> to about <NUM> and y is from about <NUM> to about <NUM>. These alloys are disclosed for example in <CIT>.

Metal hydride alloys for example comprise one or more elements selected from the group consisting of Mg, Ti, V, Zr, Nb, La, Si, Ca, Sc and Y and one or more elements selected from the group consisting of Cu, Mn, Fe, Ni, Al, Mo, W, Ti, Re and Co. For instance, MH alloys may comprise one or more elements selected from Ti, Mg and V and comprise Ni. Advantageously, MH alloys comprise Ti and Ni, for instance in an atomic range of from about <NUM>:<NUM> to about <NUM>:<NUM>. Advantageously, MH alloys comprise Mg and Ni, for instance in an atomic range of from about <NUM>:<NUM> to about <NUM>:<NUM>. Suitable alloys are disclosed for example in <CIT>.

MH alloys include those of formula (Ti<NUM>-xZrxV<NUM>-yNiy)<NUM>-zCrz where x is from <NUM> to about <NUM>, y is from about <NUM> to about <NUM> and z is ≤ <NUM>. These alloys are taught for instance in <CIT>.

Metal hydride alloys for instance comprise V, Ti, Zr and Ni (Ti-V-Zr-Ni alloys) or V, Ti, Zr, Ni and Cr. For instance, MH alloys comprise Ti, V and Ni and one or more elements selected from Cr, Zr and Al. For example, MH alloys include V<NUM>Ti<NUM>Zr<NUM>Ni<NUM>Cr<NUM>, (V<NUM>Ti<NUM>Zr<NUM>N<NUM>Cr<NUM>)<NUM>Al<NUM>, (V<NUM>Ti<NUM>Zr<NUM>N<NUM>Cr<NUM>)<NUM>Mn<NUM>, (V<NUM>Ti<NUM>Zr<NUM>N<NUM>Cr<NUM>)<NUM>Mo<NUM>, (V<NUM>Ti<NUM>Zr<NUM>N<NUM>Cr<NUM>)<NUM>Cu<NUM>, (V<NUM>Ti<NUM>Zr<NUM>N<NUM>Cr<NUM>)<NUM>W<NUM>, (V<NUM>Ti<NUM>Zr<NUM>N<NUM>Cr<NUM>)<NUM>Fe<NUM>, (V<NUM>Ti<NUM>Zr<NUM>N<NUM>Cr<NUM>)<NUM>Co<NUM>, V<NUM>Ti<NUM>Zr<NUM>N<NUM>Cr<NUM>Co<NUM>, V<NUM>Ti<NUM>Zr<NUM>N<NUM>Cr<NUM>Co<NUM>Mn<NUM>Al<NUM> and V<NUM>Ti<NUM>Zr<NUM>N<NUM>Cr<NUM>Co<NUM>Mn<NUM>Al<NUM> alloys. For instance, MH alloys include alloys of formula (Vy'-yNiyTix'-xZrxCrz)aMb where y' is from about <NUM> to about <NUM>, y is from about <NUM> to about <NUM>, x' is from about <NUM> to about <NUM>, x is from <NUM> to about <NUM>, z is from <NUM> to about <NUM>, a is from about <NUM> to about <NUM>, b is from <NUM> to about <NUM> and M is one or more elements selected from the group consisting of Al, Mn, Mo, Cu, W, Fe and Co. Values are atomic percent (at%). Suitable MH alloys are taught for instance in <CIT>.

MH alloys include those of formula (metal alloy)aCobMncFedSne where (metal alloy) comprises from about <NUM> to about <NUM> at% Ti, from about <NUM> to about <NUM> at% Zr, from <NUM> to about <NUM> at% V, from about <NUM> to about <NUM> at% Ni and from <NUM> to about <NUM> at% Cr; b is <NUM> to about <NUM> at%, c is from about <NUM> to about <NUM> at%, d is from <NUM> to about <NUM> at% and e is from <NUM> to about <NUM> at%, where a+b+c+d+e = <NUM> at%. Suitable MH alloys are taught for example in <CIT>.

Metal hydride alloys include LaNi<NUM> type alloys, alloys containing Ti and Ni and alloys containing Mg and Ni. Ti and Ni containing alloys may further contain one or more of Zr, V, Cr, Co, Mn, Al, Fe, Mo, La or Mm (mischmetal). Mg and Ni containing alloys may further contain one or more elements selected from Co, Mn, Al, Fe, Cu, Mo, W, Cr, V, Ti, Zr, Sn, Th, Si, Zn, Li, Cd, Na, Pb, La, Mm, Pd, Pt and Ca. Suitable alloys are taught for instance in <CIT>.

Metal hydride alloys include LaNi<NUM> or TiNi based alloys. For example, MH alloys include one or more hydride forming elements selected from the group consisting of Ti, V and Zr and one or more elements selected from the group consisting of Ni, Cr, Co, Mn, Mo, Nb, Fe, Al, Mg, Cu, Sn, Ag, Zn and Pd. For example, MH alloys comprise one or more hydride forming elements selected from the group consisting of Sc, Y, La, Ce, Pr, Nd, Sm and Mm and one or more elements selected from the group consisting of Ni, Cr, Co, Mn, Fe, Cu, Sn, Al, Si, B, Mo, V, Nb, Ta, Zn, Zr, Ti, Hf and W. MH alloys may include one or more elements selected from the group consisting of Al, B, C, Si, P, S, Bi, In and Sb.

MH alloys include (MgxNi<NUM>-x)aMb alloys where M is one or more elements selected from the group consisting of Ni, Co, Mn, Al, Fe, Cu, Mo, W, Cr, V, Ti, Zr, Sn, Th, Si, Zn, Li, Cd, Na, Pb, La, Mm, Pd, Pt and Ca; b is from <NUM> to about <NUM> atomic percent, a+b = <NUM> atomic percent and x is from about <NUM> to about <NUM>.

The MH alloys also include alloys of formula ZrModNie where d is from about <NUM> to about <NUM> and e is from about <NUM> to about <NUM>.

MH alloys include alloys of formula ZrMnwVxMyNiz where M is Fe or Co and w is from about <NUM> to about <NUM> at%, x is from about <NUM> to about <NUM> at%, y is from <NUM> to about <NUM> at%, z is from about <NUM> to about <NUM> at% and w+x+y+z is from about <NUM> to about <NUM> at%.

MH alloys include alloys of formula LaNi<NUM> where La or Ni is substituted by one or more metals selected from periodic groups la, II, III, IV and Va other than lanthanides, in an atomic percent from about <NUM> to about <NUM>.

MH alloys include those of formula TiV<NUM>-xNix where x is from about <NUM> to about <NUM>.

MH alloys also include alloys of formula TiaZrbNicCrdMx where M is one or more elements selected from the group consisting of Al, Si, V, Mn, Fe, Co, Cu, Nb, Ag and Pd, a is from about <NUM> to about <NUM>, b is from about <NUM> to about <NUM>, c is from about <NUM> to about <NUM>, d is from about <NUM> to about <NUM>, x is from <NUM> to about <NUM> and a+b+c+d = about <NUM>.

MH alloys include alloys of formula Ti<NUM>-xZrxMn<NUM>-y-zCryVz where x is from about <NUM> to about <NUM>, y is from <NUM> to about <NUM> and z is from <NUM> to about <NUM>.

MH alloys also include those of formula LnM<NUM> where Ln is one or more lanthanides and M is Ni and/or Co.

MH alloys for example comprise from about <NUM> to about <NUM> weight percent of one or more elements selected from periodic groups II, IV and V and one or more metals selected from the group consisting of Ni, Cu, Ag, Fe and Cr-Ni steel.

MH alloys may also comprise a main texture Mm-Ni system as taught for instance in <CIT>.

Metal hydride alloys for instance comprise V, Ti, Zr, Ni, Cr and Mn. For instance, MH alloys comprise V, Ti, Zr, Ni, Cr, Mn and Al; V, Ti, Zr, Ni, Cr, Mn and Sn; V, Ti, Zr, Ni, Cr, Mn and Co; V, Ti, Zr, Ni, Cr, Mn, Al, Sn and Co; or comprise V, Ti, Zr, Ni, Cr, Mn, Al, Sn, Co and Fe. MH alloys include alloys of formula (metal alloy)aCobFecAldSne where (metal alloy) comprises from about <NUM> to about <NUM> at% Ti, from about <NUM> to about <NUM> at% Zr, from <NUM> to about <NUM> at% V, from about <NUM> to about <NUM> at% Ni, from about <NUM> to about <NUM> at% Mn and from <NUM> to <NUM> at% Cr, b is from about <NUM> to about <NUM> at%, c is from <NUM> to about <NUM> at%, d is from about <NUM> to <NUM> at%, e is from about <NUM> to about <NUM> at% and a+b+c+d+e=<NUM> at%. Suitable MH alloys are taught for example in <CIT>.

Metal hydride alloys include one or more alloys selected from the group consisting of AB, AB<NUM>, AB<NUM> and A<NUM>B type alloys where A and B may be transition metals, rare earths or combinations thereof where component A generally has a stronger tendency to form hydrides than component B. In AB hydrogen storage alloys, A for instance comprises one or more elements selected from the group consisting of Ti, Zr and V and B comprises one or more elements selected from the group consisting of Ni, V, Cr, Co, Mn, Mo, Nb, Al, Mg, Ag, Zn and Pd. AB type alloys include ZrNi, ZrCo, TiNi, TiCo and modified forms thereof. A<NUM>B type alloys include Mg<NUM>Ni and modified forms thereof according to Ovshinsky principles where either or both of Mg and Ni are wholly or partially replaced by a multi-orbital modifier. AB<NUM> type alloys are Laves phase compounds and include alloys where A comprises one or more elements selected from the group consisting of Zr and Ti and B comprises one or more elements selected from the group consisting of Ni, V, Cr, Mn, Co, Mo, Ta and Nb. AB<NUM> type alloys include alloys modified according to the Ovshinsky principles. AB<NUM> metal hydride alloys include those where A comprises one or more elements selected from the group consisting of lanthanides and B comprises one or more transition metals. Included are LaNi<NUM> and LaNi<NUM> where Ni is partially replaced by one or more elements selected from the group consisting of Mn, Co, Al, Cr, Ag, Pd, Rh, Sb, V and Pt and/or where La is partially replaced by one or more elements selected from the group consisting of Ce, Pr, Nd, other rare earths and Mm. Included also are AB<NUM> type alloys modified according to the Ovshinsky principles. Such alloys are taught for instance in <CIT>.

MH alloys include TiMn<NUM> type alloys. For instance metal hydride alloys comprise Zr, Ti, V, Cr, and Mn where Zr is from about <NUM> to about <NUM> at%, Ti is from about <NUM> to about <NUM> at%, V is from about <NUM> to about <NUM> at%, Cr is from about <NUM> to about <NUM> at% and Mn is from about <NUM> to about <NUM> at%. These alloys may further include one or more elements selected from the group consisting of Ni, Fe and Al, for instance from about <NUM> to about <NUM> at% Ni, from about <NUM> to about <NUM> at% Fe and from about <NUM> to about <NUM> at% Al. These alloys may also contain up to about <NUM> at% Mm. Suitable alloys include Zr<NUM>Ti<NUM>V<NUM>. <NUM>Cr<NUM>. <NUM>Mn<NUM>. <NUM>Ni<NUM>. <NUM>Fe<NUM>. <NUM>Al<NUM>. <NUM>Mm<NUM>. <NUM>; Zr<NUM>. <NUM>Ti<NUM>. <NUM>V<NUM>. <NUM>Cr<NUM>. <NUM>Mn<NUM>. <NUM>Ni<NUM>. <NUM>Fe<NUM>. <NUM>Al<NUM>; Zr<NUM>. <NUM>Ti<NUM>. <NUM>V<NUM>. <NUM>Cr<NUM>. <NUM>Mn<NUM>. <NUM>Ni<NUM>. <NUM>Fe<NUM>. <NUM>Al<NUM>. <NUM> and Zr<NUM>Ti<NUM>V<NUM>. <NUM>Cr<NUM>Mn<NUM>Fe<NUM>. <NUM>Al<NUM>. Suitable alloys are taught for example in <CIT>.

Metal hydride alloys may comprise <NUM> at% or more of A<NUM>B<NUM> type structures of formula LaaR<NUM>-a-bMgbNic-d-e where <NUM> ≤ a ≤ <NUM> at%, <NUM> ≤ b ≤ <NUM> at%, <NUM> ≤ c ≤ <NUM> at%, <NUM> ≤ d ≤ <NUM> and <NUM> ≤ d ≤ <NUM>. Suitable alloys are taught for instance in <CIT>.

The MH alloys of this invention may be in the form of hydrogen-absorbing alloy particles containing at least Ni and a rare earth. The particles may have a surface layer and an interior where the surface layer has a nickel content greater than that of the interior and nickel particles having a size of from about <NUM> to about <NUM> are present in the surface layer. Metal hydride alloys may be of formula Ln<NUM>-xMgxNia-b-cAlbZc, where Ln is one or more rare earth elements, Z is one or more of Zr, V, Bn, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P and B, <NUM> ≤ x ≤ <NUM> at%, <NUM> ≤ a ≤ <NUM> at%, <NUM> ≤ b ≤ <NUM> at% and <NUM> ≤ c ≤ <NUM>. Suitable alloys are taught for example in <CIT>.

The MH alloys of this invention may comprise a crystalline structure having multiple phases containing at least an A<NUM>B<NUM> type structure and an A<NUM>B<NUM> type structure and a surface layer having a nickel content greater than that of the bulk. Metal hydride alloys include alloys of formula Ln<NUM>-xMgxNiy-a-bAlaMb, where Ln is one or more rare earths including Y, M is one or more of Co, Mn and Zn, where <NUM> ≤ x ≤ <NUM> at%, <NUM> ≤ y ≤ <NUM> at%, <NUM> ≤ a ≤ <NUM> at% and <NUM> ≤ b ≤ <NUM>. Suitable alloys are disclosed for example in <CIT>.

Metal hydride alloys may be of formula Ln<NUM>-xMgx(Ni<NUM>-yTy)z where Ln is one or more elements selected from lanthanide elements, Ca, Sr, Sc, Y, Ti, Zr and Hf, T is one or more elements selected from V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Al, Ga, Zn, Sn, In, Cu, Si, P and B and where <NUM> < x ≤ <NUM> at%, <NUM> ≤ y ≤ <NUM> at%, and <NUM> ≤ z ≤ <NUM> at%. Suitable alloys are taught for instance in <CIT>.

The MH alloys of this invention may comprise La, Nd, Mg, Ni and Al; La, Nd, Mg, Ni, Al and Co; La, Pr, Nd, Mg, Ni and Al or La, Ce, Pr, Nd, Ni, Al, Co and Mn as taught in <CIT>.

Metal hydride alloys may be of formula TiAZrB-YYXVCNiDME where A, B, C and D are each greater than <NUM> and less than or equal to <NUM> at%, X is greater than <NUM> and less than or equal to <NUM> at%, M is one or more metals selected from Co, Cr, Sn, Al and Mn and E is from <NUM> to <NUM> at%. Suitable alloys are taught for example in <CIT>.

The MH alloys of this invention include A<NUM>B<NUM> type hydrogen storage alloys. For instance, the MH alloys may be AxBy alloys where A includes at least one rare earth element and also includes Mg; B includes at least Ni and the atomic ratio x to y is from about <NUM>:<NUM> to about <NUM>:<NUM>, for instance about <NUM>:<NUM> to about <NUM>:<NUM>. MH alloys may further comprise one or more elements selected from the group consisting of B, Co, Cu, Fe, Cr and Mn. The atomic ratio of Ni to the further elements may be from about <NUM>:<NUM> to about <NUM>:<NUM>. The rare earths include La, Ce, Nd, Pr and Mm. The atomic ratio of rare earths to Mg may be from about <NUM>:<NUM> to about <NUM>:<NUM>. The B elements may further include Al where the atomic ratio of Ni to Al may be from about <NUM>:<NUM> to about <NUM>:<NUM>.

Metal hydride alloys include ABx high capacity hydrogen storage alloys where x is from about <NUM> to about <NUM> and which has a discharge capacity of ≥ <NUM> mAh/g, ≥ <NUM> mAh/g, ≥ <NUM> mAh/g or ≥ <NUM> mAh/g.

Metal hydride alloys include high capacity MH alloys containing magnesium (Mg), for example an AB, AB<NUM> or A<NUM>B type alloy containing Mg and Ni. For instance, MH alloys include MgNi, MgNi<NUM> and Mg<NUM>Ni. Such Mg and Ni containing alloys may further comprise one or more elements selected from the group consisting of rare earth elements and transition metals. For instance, alloys containing Mg and Ni may further comprise one or more 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.

For instance, MH alloys comprise Mg and Ni and optionally one or more 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.

Mm is "mischmetal". Mischmetal is a mixture of rare earth elements. For instance, Mm is a mixture containing La, Nd and Pr, for instance containing Ce, La, Nd and Pr.

For example, MH alloys include MgNi, Mg<NUM>Ti<NUM>Ni, Mg<NUM>Ti<NUM>Ni, Mg<NUM>Ti<NUM>Ni, Mg<NUM>Zr<NUM>Ni, Mg<NUM>Ti<NUM>La<NUM>Ni, Mg<NUM>Al<NUM>Ni, Mg<NUM>Ti<NUM>Ni, Mg<NUM>Ti<NUM>NiAl<NUM>, Mg<NUM>Pd<NUM>Ni, Mg<NUM>Ti<NUM>NiAl<NUM>, Mg<NUM>Ti<NUM>NiAl<NUM>Pd<NUM>, Mg<NUM>Ni<NUM>Pd<NUM>, Mg<NUM>Ti<NUM>Ni<NUM>, Mg<NUM>. <NUM>Ni<NUM>, Mg<NUM>Ni, Mg<NUM>Ni<NUM>Co<NUM>, Mg<NUM>Ni<NUM>Mn<NUM>, Mg<NUM>Ni<NUM>Cu<NUM>, Mg<NUM>La<NUM>Ni, Mg<NUM>Co<NUM>Ni, Mg<NUM>Cr<NUM>Ni, Mg<NUM>Nb<NUM>Ni, Mg<NUM>Ti<NUM>Ni, Mg<NUM>. 0V<NUM>Ni, Mg<NUM>Al<NUM>Ni, Mg<NUM>Ti<NUM>Ni, Mg<NUM>Ti<NUM>Zr<NUM>Al<NUM>Ni, Mg<NUM>Al<NUM>Ni and (MgAl)<NUM>Ni, Mg<NUM>Al<NUM>Ni.

For example, MH alloys include alloys of Mg and Ni in an atomic ratio of from about <NUM>:<NUM> to about <NUM>:<NUM> further comprising one or more 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. The further element or elements may be present from about <NUM> to about <NUM> atomic percent (at%) or from about <NUM> to about <NUM> at% or from about <NUM>, about <NUM>, about <NUM>, about <NUM>, about <NUM> or about <NUM> at% to about <NUM> at%, based on the total alloy. The atomic ratio of Mg to Ni is for instance about <NUM>:<NUM>. Thus, Mg and Ni together may be present from about <NUM> at% to about <NUM> at% based on the total alloy. Mg-Ni MH alloys may be free of further elements where Mg and Ni together are present at <NUM> at%.

Metal hydride alloys may comprise Mg and Ni in an atomic ratio of from about <NUM>:<NUM> to about <NUM>:<NUM> where Mg and Ni together are present at a level of ≥ <NUM> at%, based on the total alloy.

Metal hydride alloys may comprise ≥ <NUM> at% Mg.

Metal hydride alloys may comprise Mg and Ni in an atomic ratio of from about <NUM>:<NUM> to about <NUM>:<NUM> and further comprise Co and/or Mn. The alloys of this invention include Mg<NUM>Ni<NUM>Co<NUM>Mn<NUM> and Mg<NUM>Ni<NUM>Co<NUM>Mn<NUM>.

Metal hydride alloys may contain ≥ <NUM> weight % Mg and one or more additional elements. The one or more additional elements may be selected from the group consisting of Ni, Mm, Al, Y and Si. These alloys may contain for example from about <NUM> to about <NUM> weight % Ni and about <NUM> to about <NUM> weight % Mm. These alloys may also contain from about <NUM> to about <NUM> weight % Al and/or from about <NUM> to about <NUM> weight % Y and/or from about <NUM> to about <NUM> weight % Si.

Suitable high capacity MH alloys are disclosed for example in <CIT>, <CIT> and <CIT>.

The MH alloys of this invention for instance may be capable of storing at least <NUM> weight % hydrogen and/or absorbing at least <NUM>% of the full storage capacity of hydrogen in under <NUM> minutes at <NUM>; or may be capable of storing at least <NUM> weight % of hydrogen and/or absorbing <NUM>% of the full storage capacity of hydrogen in under <NUM> minutes at <NUM>; or may be capable of storing at least <NUM> weight % of hydrogen and/or capable of absorbing <NUM>% of the full storage capacity of hydrogen in under <NUM> minutes at <NUM>.

Metal hydride alloys include alloys of formula TiaZrb-xYxVcNidMe where each of a, b, c and d are greater than <NUM> and less than or equal to <NUM> at%, x is greater than <NUM> and less than or equal to <NUM> at%, M is one or more metals selected from the group consisting of Co, Cr, Sn, Al and Mn and e is from <NUM> to about <NUM> at%. These alloys are disclosed for example in <CIT>.

The active materials of the positive electrode (cathode materials) participate in the charge/discharge reactions. The active materials are for instance nickel hydroxide active materials, i.e. nickel hydroxide or modified nickel hydroxide.

The cathode materials may comprise a multi-phase disordered nickel hydroxide material having at least one modifier. The at least one modifier is for instance a metal, a metallic oxide, a metallic oxide alloy, a metal hydride and/or a metal hydride alloy. For example, the modifier is one or more components selected from the group consisting of Al, Ba, Ca, F, K, Li, Mg, Na, Sr, Bi, Co, Cr, Cu, Fe, In, LaH<NUM>, Mn, Ru, Sb, Sn, TiH<NUM>, TiO, and Zn. Such materials are taught in <CIT>.

Suitable cathode materials may comprise a disordered multi-phase nickel hydroxide matrix including at least one modifier, for example <NUM> modifiers, chosen from F, Li, Na, K, Mg, Ba, Ln, Se, Nd, Pr, Y, Co, Zn, Al, Cr, Mn, Fe, Cu, Zn, Sc, Sn, Sb, Te, Bi, Ru and Pb. Suitable cathode materials are taught for example in <CIT>.

Cathode materials may comprise nickel hydroxide modified with one or more group II elements and Co in a solid solution state. Such materials are taught in <CIT>.

The cathode active materials may comprise nickel hydroxide and one or more components selected from the group consisting of cobalt, cobalt hydroxide and cobalt oxide and a carbon powder. The cathode materials may further comprise a compound of Ca, Sr, Ba, Cu, Ag or Y, for example Ca(OH)<NUM>, CaO, CaF<NUM>, CaS, CaSO<NUM>, CaSi<NUM>O<NUM>, CaC<NUM>O<NUM>, CaWO<NUM>, SrCO<NUM>, Sr(OH)<NUM>, BaO, Cu<NUM>O, Ag<NUM>O, Y<NUM>(CO<NUM>)<NUM> or Y<NUM>O<NUM>. Suitable cathode materials are taught for instance in <CIT>.

Cathode active materials may comprise a metal oxide and one or more of Co, Ca, Ag, Mn, Zn, V, Sb, Cd, Y, Sr, Ba and oxides of Ca, Sr, Ba, Sb, Y or Zn. The metal oxide is for example nickel oxide and or manganese oxide. Such active materials are taught in <CIT>.

The cathode materials may contain nickel hydroxide and a further component selected from the group consisting of Y, In, Sb, Ba and Be and Co and/or Ca. Such materials are disclosed in <CIT>.

Cathode materials may be prepared by reacting nickel sulfate and ammonium hydroxide to form a nickel ammonium complex; the complex is then reacted with sodium hydroxide to form nickel hydroxide. The method may provide nickel hydroxide comprising one or more of Co, Zn and Cd. These materials are taught in <CIT>.

Cathode active materials may comprise nickel hydroxide and cobalt oxyhydroxide as taught in <CIT>.

Cathode materials may comprise nickel hydroxide, cobalt monoxide and elemental zinc as taught in <CIT>.

The cathode materials may comprise nickel hydroxide, nickel powder, a second powder and at least one of cobalt, cobalt hydroxide and cobalt oxide. The second powder contains one or more of Ca, Sr, Ba, Cu, Ag and Y. Such materials are taught in <CIT>.

The cathode active materials may comprise particles of nickel hydroxide or manganese hydroxide having at least partially embedded therein a conductive material. The conductive material may be for instance nickel, nickel alloys, copper, copper alloys; metal oxides, nitrides, carbides, silicides or borides; or carbon (graphite). These materials are disclosed in <CIT>.

The cathode materials may comprise nickel hydroxide particles containing at least three modifiers selected from the group consisting of Al, Bi, Ca, Co, Cr, Cu, Fe, In, La, rare earths, Mg, Mn, Ru, Sb, Sn, Ti, Ba, Si, Sr and Zn. For example, nickel hydroxide particles may contain at least four modifiers, for instance, Ca, Co, Mg and Zn. Such materials are disclosed in <CIT>.

The active cathode material for instance comprises nickel hydroxide and a carbon material such as graphite. The active material may also comprise a polymeric binder. The polymeric binder is for example a thermoplastic organic polymer, for instance selected from the group consisting of polyvinyl alcohol (PVA), polyethylene oxide, polypropylene oxide, polybutylene oxide, methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropylmethyl cellulose, polyethylene, polypropylene, polyisobutylene, polyvinyl chloride, polyvinyliden chloride, polyvinyliden fluoride, polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), perfluroalkoxy (PFA), polyvinylacetate, polyvinyl isobutylether, polyacrylonitrile, polymethacrylonitrile, polymethylmethacrylate, polymethylacrylate, polyethylmethacrylate, allyl acetate, polystyrene, polybutadiene, polyisoprene, polyoxymethylene, polyoxyethylene, polycyclic thioether, polydimethylsiloxane, polyesters such as polyethylene terephthalate, polycarbonate and polyamide. Blends and copolymers of the above are also suitable. The polymeric binder may also be an elastomer or rubber such as styrene-butadiene copolymer, styrene-butadienestyrene block copolymer, styrene-isoprene block copolymer, styrene-isoprene-styrene block copolymer, styrene-ethylene-styrene-butadiene block copolymer, styrene-ethylene-butadienestyrene block copolymer or styrene-acrylonitrile-butadiene-methyl acrylate copolymer. Suitable active materials are taught for instance in <CIT>.

The cathode active material may contain nickel hydroxide and nickel oxyhydroxide as taught in <CIT>.

Generally, cathode active material particles are formed in a sintered or pasted electrode. The pasted electrode may be made by mixing the material with various additives and/or binders and applying the paste to a conductive support. Preferably, one or more cobalt additives are added to the pasted electrode. The cobalt additives may include Co and/or CoO to enhance conductivity, improve utilization and reduce electrical resistance of the positive electrode.

In general, cathode active materials are nickel hydroxide or modified nickel hydroxide. Modified nickel hydroxide may contain one or more modifiers such as Co, Cd, Ag, V, Sb, Ca, Mg, Al, Bi, Cr, Cu, Fe, In, rare earths, Mn, Ru, Sn, Ti, Ba, Si, Sr or Zn. A suitable modified nickel hydroxide is (Ni,Co,Zn)(OH)<NUM>, for instance in the form of a spherical powder. In modified nickel hydroxides, nickel generally is present at a level of ≥ <NUM> atomic percent, for instance ≥ <NUM> atomic percent, based on the metals.

For example, the metal hydride (MH) battery according to the present invention comprises at least one negative electrode which comprises an ABx type alloy capable of reversibly storing hydrogen and comprises as least one positive electrode comprising nickel hydroxide or modified nickel hydroxide active materials.

A separator may be present which separates the negative electrodes from the positive electrodes. The separator is for instance a nonwoven web of natural or synthetic fibers. Natural fibers include cotton. Synthetic fibers include polyamide, polyester, polypropylene (PP), polyethylene (PE), PP/PE copolymer, polytetrafluoroethlene (PTFE), polyvinylchloride and glass.

Ionic liquids are ionic compounds that exhibit a melting point of ≤ <NUM>.

Cations of ionic liquids include ammonium and phosphonium ions.

For instance, ionic liquids may contain a cation selected from the group consisting of formulae (a)-(h).

Examples of ammonium ions include protic ions such as NH<NUM>+ (ammonium), methylammonium, ethylammonium, dimethylammonium, diethylammonium, trimethylammonium (NMe<NUM>H+), triethylammonium, tributylammonium, diethylmethylammonium, hydroxyethylammonium, methoxymethylammonium, dibutylammonium, methylbutylammonium, anilinium, pyridinium, <NUM>-methylpyridinium, imidazolium, <NUM>-methylimidazolium, <NUM>,<NUM>-dimethylimidazolium, imidazolinium, <NUM>-ethylimidazolium, <NUM>-(<NUM>-sulfobutyl)-<NUM>-methylimidazolium, <NUM>-allylimidazolium, quinolinium, isoquinolinium, pyrrolinium, pyrrolininium and pyrrolidinium.

Examples of ammonium ions also include aprotic ions such as <NUM>-butyl-<NUM>-methylpyrrolidinium, tetramethylammonium, tetraethylammonium, tetra-n-butylammonium, n-butyl-tri-ethylammonium, benzyl-tri-methylammonium, tri-n-butylmethylammonium, benzyl-triethylammonium, <NUM>-methylpyridinium, <NUM>-butyl-<NUM>,<NUM>-dimethylpyridinium, <NUM>,<NUM>,<NUM>-trimethylpyrazolium, trimethylhydroxyethylammonium (choline), tri-(hydroxyethyl)methylammonium, dimethyl-di(polyoxyethylene)ammonium, <NUM>,<NUM>,<NUM>-trimethylimidazolium, <NUM>-butyl-<NUM>-methylimidazolium, <NUM>-ethyl-<NUM>,<NUM>-dimethylimidazolium, <NUM>-allyl-<NUM>-methylimidazolium, <NUM>-hydroxyethyl-<NUM>-methylimidazolium, <NUM>,<NUM>-dimethylimidazolium, <NUM>-ethyl-<NUM>-methylpiperidinium, <NUM>-ethyl-<NUM>-methylmorpholinium, <NUM>-(cyanomethyl)-<NUM>-methylimidazolium, <NUM>-(<NUM>-cyanopropyl)pyridinium, <NUM>,<NUM>-bis(cyanomethyl)imidazolium, <NUM>-hexyl-<NUM>-methylimidazolium and <NUM>-ethyl-<NUM>-methylimidazolium.

Pyrrolinium is the ammonium of pyrrole, pyrrolininium is the ammonium of pyrroline and pyrrolidinium is the ammonium of pyrrolidine. Pyrroline may be <NUM>-, <NUM>- or <NUM>-pyrroline, thus the ammonium cation of <NUM>-, <NUM>- or <NUM>-pyrroline is included.

Examples of phosphonium ions include methyltriphenylphosphonium, tetraphenylphosphonium, tetrabutylphosphonium, tributylmethylphosphonium, triethylmethylphosphonium, trihexyltetradecylphosphonium, triphenylpropylphosphonium and tetrakis(hydroxymethyl)phosphonium.

For instance, suitable cations of ionic liquids include <NUM>-ethyl-<NUM>-methylimidazolium, <NUM>-hexyl-<NUM>-methylimidazolium, <NUM>-butyl-<NUM>-methylpyrrolidinium and trihexyl(tetradecyl)phosphonium.

Anions of ionic liquids include carboxylates, imides, methides, nitrate, bifluoride, halides, borates, phosphates, phosphinates, phosphonates, sulfonates, sulfates, carbonates and aluminates.

The ionic liquids may contain an anion selected from the group consisting of.

[N(C(O)-CmF<NUM>+<NUM>)(S(O)<NUM>-CmF<NUM>+<NUM>)]-,.

[N(S(O)<NUM>-CmF<NUM>+<NUM>)(S(O)<NUM>F)]-,.

The anions of ionic liquids may include F<NUM>P(C<NUM>F<NUM>)<NUM>-, F<NUM>P(C<NUM>F<NUM>)<NUM>-, F<NUM>P(C<NUM>F<NUM>)<NUM>-, F<NUM>P(C<NUM>F<NUM>)<NUM>-, F<NUM>P(C<NUM>F<NUM>)<NUM>-, F<NUM>P(C<NUM>F<NUM>)<NUM>-, F<NUM>P(C<NUM>F<NUM>)<NUM>-, F<NUM>P(C<NUM>F<NUM>)<NUM>-, F<NUM>P(C<NUM>F<NUM>)<NUM>-, perfluoroalkylcarboxylate, perfluoroalkylsulfonate, bis(perfluoroalkylsulfonyl)imide, (perfluoroalkylsulfonyl)(perfluoroalkylcarboxyl)imide, tris(perfluoroalkylsulfonyl)methide, trifluoroacetate, trifluoromethanesulfonate (triflate), bis(trifluoromethylsulfonyl)imide, tris(trifluoromethylsulfonyl)methide, tetrafluoroborate, spiro-oxo borates and spiro-oxo phosphates, for example bisoxalatoborate (BOB), difluorooxalatoborate (dFOB), di(trifluoroacetato)oxalatoborate (d(Ac)OB), trisoxalatophosphate, tetrafluorooxalatophosphate and di(trifluoroacetato)oxalatoaluminate.

Carboxylate anions include those of formula RCOO- where R is hydrogen or hydrocarbyl and include formate, acetate (ethanoate), propanoate, n-butanoate, i-butanoate, n-pentanoate, i-pentanoate, octanoate, decanoate, benzoate, salicylate, thiosalicylate, <NUM>-, <NUM>- or <NUM>-nitrobenzoate; citrate, oxalate, tartrate, glycolate, gluconate, malate, mandelate, a carboxylate of nitrilotriacetic acid, a carboxylate of N-(<NUM>-hydroxyethyl)-ethylenediaminetriacetic acid, a carboxylate of ethylenediaminetetraacetic acid, a carboxylate of diethylenetriaminepentaacetic acid and haloalkylcarboxylates such as fluoroacetate, difluoroacetate, trifluoroacetate, chloroacetate, dichloroacetate and trichloroacetate.

Imide anions include dicyanamide, N(SO<NUM>F)<NUM>- ((bisfluorosulfonyl)imide), bis(perfluoroalkylsulfonyl)imides such as [N(SO<NUM>CF<NUM>)<NUM>]- (bistriflimide), bis(pentafluoroethylsulfonyl)imide and N(CF<NUM>SO<NUM>)(CF<NUM>(CF<NUM>)<NUM>SO<NUM>)- and (perfluoroalkylsulfonyl)(perfluoroalkylcarboxyl)imides.

Methides include tris(perfluoroalkylsulfonyl)methides such as tris(trifluoromethylsulfonyl)methide, C(CF<NUM>SO<NUM>)<NUM>-.

Halide is chloride, bromide, iodide or fluoride.

Borates include orthoborate, tetrahydroxyborate, tetraborate, tetraphenylborate, [B(<NUM>,<NUM>-(CF<NUM>)<NUM>C<NUM>H<NUM>)<NUM>]- (BARF), B(C<NUM>O<NUM>)<NUM>- (bis(oxalato)borate) (BOB), difluoro(oxalato)borate (dFOB), di(trifluoroacetato)oxalatoborate (D(Ac)OB), B(C<NUM>F<NUM>)<NUM>- and BF<NUM>- (tetrafluoroborate).

Phosphates include dihydrogen phosphate, hydrogen phosphate, alkyl phosphate, dialkyl phosphate, phosphate, PF<NUM>- (hexafluorophosphate), HPO<NUM>F- (fluorohydrogen phosphate), trisoxalatophosphate (TOP), tetrafluorooxalatophosphate (TFOP) and fluoro(perfluoroalkyl)phosphates such as F<NUM>P(C<NUM>F<NUM>)<NUM>-, F<NUM>P(C<NUM>F<NUM>)<NUM>-(tris(pentafluoroethyl)trifluorophosphate or FAP), F<NUM>P(C<NUM>F<NUM>)<NUM>-, F<NUM>P(C<NUM>F<NUM>)<NUM>-, F<NUM>P(C<NUM>F<NUM>)<NUM>-, F<NUM>P(C<NUM>F<NUM>)<NUM>-, F<NUM>P(C<NUM>F<NUM>)<NUM>-, F<NUM>P(C<NUM>F<NUM>)<NUM>- and F<NUM>P(C<NUM>F<NUM>)<NUM>-.

Sulfonates include alkylsulfonates, arylsulfonates and perfluoroalkylsulfonates, for instance trifluoromethanesulfonate (triflate), p-toluenesulfonate (tosylate) or methanesulfonate (mesylate).

Sulfates include hydrogensulfate, sulfate, thiosulfate and alkylsulfates such as methylsulfate and ethylsulfate.

Carbonate anions are for instance carbonate, hydrogencarbonate or an alkylcarbonate such as methylcarbonate, ethylcarbonate or butylcarbonate.

Aluminates include Al(OC(CF<NUM>)<NUM>)<NUM>-, di(trifluoroacetato)oxalatoaluminate (d(Ac)OAl), tetrachloroaluminate, tetrafluoroaluminate, tetraiodoaluminate and tetrabromoaluminate.

Ionic liquids include protic compounds such as diethylmethylammonium trifluoromethanesulfonate (DEMA TfO), ethylammonium nitrate, triethylammonium methanesulfonate, <NUM>-methylpyridinium trifluoromethanesulfonate, ammonium fluoride, methylammonium nitrate, hydroxyethylammonium nitrate, ethylammonium nitrate, dimethylammonium nitrate, <NUM>-methylimidazolium nitrate, <NUM>-ethylimidazolium nitrate, t-butylammonium tetrafluoroborate, hydroxyethylammonium tetrafluoroborate, methylbutylammonium tetrafluoroborate, triethylammonium tetrafluoroborate, imidazolium tetrafluoroborate, <NUM>-methylimidazolium tetrafluoroborate, <NUM>,<NUM>-dimethylimidazolium tetrafluoroborate, t-butylammonium triflate, <NUM>-fluoropyridinium triflate, hydroxyethylammonium triflate, <NUM>,<NUM>-dimethylimidazolium triflate, imidazolium triflate, <NUM>-methylimidazolium hydrogensulfate, <NUM>-methylimidazolium chloride, <NUM>-methylimidazolium triflate, hydronium triflate, methylammonium mesylate, ethylammonium mesylate, butylammonium mesylate, methoxyethylammonium mesylate, dimethylammonium mesylate, dibutylammonium mesylate, triethylammonium mesylate, dimethylethylammonium mesylate, hydronium hydrogensulfate, ammonium hydrogensulfate, methylammonium hydrogensulfate, ethylammonium hydrogensulfate, propylammonium hydrogensulfate, n-butylammonium hydrogensulfate, t-butylammonium hydrogensulfate, dimethylammonium hydrogensulfate, diethylammonium hydrogensulfate, di-n-butylammonium hydrogensulfate, methylbutylammonium hydrogensulfate, ethylbutylammonium hydrogensulfate, trimethylammonium hydrogensulfate, triethylammonium hydrogensulfate, tributylammonium hydrogensulfate, dimethylethylammonium hydrogensulfate, dibutylammonium fluorohydrogen phosphate, triethylammonium fluorohydrogen phosphate, tributylammonium fluorohydrogen phosphate, hydronium dihydrogen phosphate, methylammonium dihydrogen phosphate, ethylammonium dihydrogen phosphate, propylammonium dihydrogen phosphate, n-butylammonum dihydrogen phosphate, methoxyethylammonium dihydrogen phosphate, dimethylammonium dihydrogen phosphate, dibutylammonium dihydrogen phosphate, methylbutylammonium dihydrogen phosphate, ammonium bifluoride, methylammonium bifluoride, ethylammonium bifluoride or dimethylammonium bifluoride.

Ionic liquids include aprotic compounds such as <NUM>-ethyl-<NUM>-methylimidazolium trifluoromethanesulfonate (EMIM TfO), <NUM>-ethyl-<NUM>-methylimidazolium tetrafluoroborate (EMIM BF<NUM>), <NUM>-ethyl-<NUM>-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM TFSI), <NUM>-ethyl-<NUM>-methylimidazolium acetate (EMIM Ac), <NUM>-butyl-<NUM>-methylimidazolium trifluoromethanesulfonate (BMIM TfO), <NUM>-butyl-<NUM>-methylimidazolium acetate (BMIM Ac), <NUM>-butyl-<NUM>-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIM TFSI), tri-n-butylmethylammonium methylsulfate, <NUM>-ethyl-<NUM>,<NUM>-dimethylimidazolium ethylsulfate, <NUM>-butyl-<NUM>-methylimidazolium thiocyanate, <NUM>-butyl-<NUM>-methylimidazolium tetrachloroaluminate, <NUM>-butyl-<NUM>-methylimidazolium methylsulfate, <NUM>-butyl-<NUM>-methylimidazolium methanesulfonate, <NUM>-butyl-<NUM>-methylimidazolium hydrogencarbonate, <NUM>-butyl-<NUM>-methylimidazolium hydrogensulfate, <NUM>-butyl-<NUM>-methylimidazolium chloride, <NUM>,<NUM>,<NUM>-trimethylimidazolium methylsulfate, tris-(hydroxyethyl)methylammonium methylsulfate, <NUM>,<NUM>,<NUM>-trimethylpyrazolium methylsulfate, <NUM>,<NUM>-dimethylimdiazolium hydrogencarbonate, <NUM>-ethyl-<NUM>-methylimidazolium hydrogencarbonate, <NUM>-ethyl-<NUM>-methylimidazolium chloride, <NUM>-ethyl-<NUM>-methylimidazolium tetrachloroaluminate, <NUM>-ethyl-<NUM>-methylimidazolium thiocyanate, <NUM>-ethyl-<NUM>-methylimidazolium methanesulfonate, <NUM>-ethyl-<NUM>-methylimidazolium hydrogensulfate, <NUM>-ethyl-<NUM>-methylimidazolium ethylsulfate, <NUM>-ethyl-<NUM>-methylimidazolium nitrate, <NUM>-butylpyridinium chloride, <NUM>-ethyl-<NUM>-methylimidazolium dicyanamide, <NUM>-ethyl-<NUM>-methylimidazolium hexafluorophosphate, <NUM>-butyl-<NUM>,<NUM>-dimethylpyridinium bromide, <NUM>-ethyl-<NUM>-methylimidazolium bis(pentafluoroethylsulfonyl)imide, <NUM>-ethyl-<NUM>,<NUM>-dimethylimidazolium methylcarbonate, carboxymethyl-tributylphosphonium bis(trifluoromethylsulfonyl)imide, N-carboxyethyl-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, N-carboxymethyl-trimethylammonium bis(trifluoromethylsulfonyl)imide, N-carboxymethyl-methylpyridinium bis(trifluoromethylsulfonyl)imide, hexyltrimethylammonium bis(trifluromethylsulfonyl)imide, tetrabutylphosphonium methanesulfonate, triethylmethylammonium methylcarbonate, <NUM>-ethyl-<NUM>-methylpiperidinium methylcarbonate, <NUM>-ethyl-<NUM>-methylmorpholinium methylcarbonate, <NUM>-butyl-<NUM>-methylpyrrolidinium methylcarbonate, triethylmethylammonium dibutylphosphate, tributylmethylphosphonium dibutylphosphate, triethylmethylphosphonium dibutylphosphate, tetrabutylphosphonium tetrafluoroborate, tetrabutylphosphonium p-toluenesulfonate, tributylmethylphosphonium methylcarbonate, <NUM>-ethyl-<NUM>-methylimidazolium hydrogencarbonate, tributylmethylammonium methylcarbonate, tributylmethylammonium dibutylphosphate, <NUM>-ethyl-<NUM>-methylimidazolium dibutylphosphate, <NUM>-butyl-<NUM>-methylimidazolium dibutylphosphate, <NUM>-(cyanomethyl)-<NUM>-methylimidazolium chloride, <NUM>-(<NUM>-cyanopropyl)-<NUM>-methylimidazolium chloride, <NUM>-(<NUM>-cyanopropyl)-<NUM>-methylimidazolium bis(trifluoromethylsulfonyl)imide, <NUM>-(<NUM>-cyanopropyl)-<NUM>-methylimidazolium dicyanamide, <NUM>-(<NUM>-cyanopropyl)pyridinium chloride, <NUM>-(<NUM>-cyanopropyl)pyridinium bis(trifluoromethylsulfonyl)imide, <NUM>,<NUM>-bis(cyanomethyl)imidazolium chloride, <NUM>,<NUM>-bis(cyanomethyl)imidazolium bis(trifluoromethylsulfonyl)imide, <NUM>,<NUM>-bis(cyanopropyl)imidazolium chloride, <NUM>,<NUM>-bis(<NUM>-cyanopropyl)imidazolium bis(trifluoromethylsulfonyl)imide, <NUM>-butyl-<NUM>-methylimidazolium hexafluorophosphate, <NUM>-butyl-<NUM>-methylimidazolium tetrafluoroborate, <NUM>-ethyl-<NUM>-methylimidazolium tetrafluoroborate, <NUM>-ethyl-<NUM>-methylimidazolium chloride, <NUM>-ethyl-<NUM>-methylimidazolium bromide, <NUM>-butyl-<NUM>-methylimidazolium bromide, <NUM>-hexyl-<NUM>-methylimidazolium chloride, tributylmethylphosphonium methylsulfate, triethylmethylphosphonium dibutylphosphate, trihexyltetradecylphosphonium bis(trifluromethylsulfonyl)imide, trihexyltetradecylphosphonium bis(<NUM>,<NUM>,<NUM>-trimethylphenyl)phosphinate, trihexyltetradecylphosphonium bromide, trihexyltetradecylphosphonium chloride, trihexyltetradecylphosphonium decanoate, trihexyltetradecylphosphonium dicyanamide, <NUM>-(triphenylphosphonio)propane-<NUM>-sulfonate or <NUM>-(triphenylphosphonio)propane-<NUM>-sulfonic acid tosylate.

Hydrocarbyl is for instance alkyl, alkenyl, cycloalkyl, cycloalkenyl, aryl or aralkyl, each of which may be substituted by one or more groups selected from the group consisting of halogen, hydroxy, C<NUM>-C<NUM>alkoxy, thio, C<NUM>-C<NUM>alkylthio, amino, C<NUM>-C<NUM>alkylamino, di-C<NUM>-C<NUM>alkylamino, nitro, cyano, -COOH and -COO-. Hydrocarbyl may also be interrupted by one or more groups selected from the group consisting of -O-, -S-, -NH- and -N(C<NUM>-C<NUM>alkyl)-. Hydrocarbyl may be both substituted by one or more of said groups and interrupted by one or more of said groups. For instance alkyl, alkenyl, cycloalkyl, cycloalkenyl, aryl or aralkyl may be substituted by one to three groups selected from the group consisting of chloro, hydroxy, methoxy, ethoxy, propoxy, butoxy, thio, methylthio, methylamino, ethylamino, propylamino, butylamino, dimethylamino, diethylamino, dipropylamino, dibutylamino, -COOH, -COO-, cyano and nitro and/or may be interrupted by one to three groups selected from the group consisting of -O-, -S-, -NH- and -N(C<NUM>-C<NUM>alkyl)-.

Alkyl is for instance from <NUM> to <NUM> carbon atoms, is branched or unbranched and includes methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, isobutyl, tert-butyl, <NUM>-ethylbutyl, n-pentyl, isopentyl, <NUM>-methylpentyl, <NUM>,<NUM>-dimethylbutyl, n-hexyl, <NUM>-methylhexyl, n-heptyl, isoheptyl, <NUM>,<NUM>,<NUM>,<NUM>-tetramethylbutyl, <NUM>-methylheptyl, <NUM>-methylheptyl, n-octyl, <NUM>-ethylhexyl, <NUM>,<NUM>,<NUM>-trimethylhexyl, <NUM>,<NUM>,<NUM>,<NUM>-tetramethylpentyl, nonyl, decyl, undecyl, <NUM>-methylundecyl, dodecyl, <NUM>,<NUM>,<NUM>,<NUM>,<NUM>,<NUM>-hexamethylhexyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, icosyl and docosyl.

Partly or fully fluorinated means replacement of one, more than one or all of the hydrogens of the alkyl with fluoro. Perfluoroalkyl means all hydrogens of an alkyl are replaced with fluoro (fully fluorinated).

Alkenyl is an unsaturated version of alkyl, for instance allyl.

Cycloalkyl includes cyclopentyl, methylcyclopentyl, dimethylcyclopentyl, cyclohexyl, methylcyclohexyl, dimethylcyclohexyl, trimethylcyclohexyl, tert-butylcyclohexyl, cycloheptyl or cyclooctyl.

Cycloalkenyl is an unsaturated version of cycloalkyl.

Aryl includes phenyl, o-, m- or p-methylphenyl, <NUM>,<NUM>-dimethylphenyl, <NUM>,<NUM>-dimethylphenyl, <NUM>,<NUM>-dimethylphenyl, <NUM>,<NUM>-dimethylphenyl, <NUM>,<NUM>-dimethylphenyl, <NUM>,<NUM>-dimethylphenyl, <NUM>-methyl-<NUM>-ethylphenyl, <NUM>-tert-butylphenyl, <NUM>-ethylphenyl or <NUM>,<NUM>-diethylphenyl.

Aralkyl includes benzyl, α-methylbenzyl, α,α-dimethylbenzyl and <NUM>-phenylethyl.

Suitable ionic liquids are also described for example in <CIT> and <CIT>.

Protic acids, also called Bronsted acids, for instance have a pKa of less than or equal to about <NUM>.

Protic acids include inorganic acids such as hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, boric acid, hydrofluoric acid, hydrobromic acid, hydroiodic acid, perchloric acid and periodic acid.

Protic acids also include bisulfates such as sodium bisulfate, potassium bisulfate and ammonium bisulfate.

Protic acids also include HAsF<NUM>, HBF<NUM>, H(OEt<NUM>)BF<NUM>, HPF<NUM>, ,H[N(SO<NUM>CF<NUM>)<NUM>] or H[N(SO<NUM>CF<NUM>CF<NUM>)<NUM>].

Protic acids include organic acids. Organic acids include carboxylic acids of formula RCOOH where R is hydrogen or hydrocarbyl.

Carboxylic acids include formic acid, acetic acid, acrylic acid, fluoroacetic acid, difluoroacetic acid, trifluoroacetic acid, chloroacetic acid, dichloroacetic acid, trichloroacetic acid, propanoic acid, butyric acid, <NUM>-methylbutanoic acid, valeric acid, hexanoic acid, heptanoic acid, caprylic acid, nonanoic acid, benzoic acid, salicylic acid, <NUM>-, <NUM>- or <NUM>-nitrobenzoic acid; citric acid, oxalic acid, tartaric acid, glycolic acid, gluconic acid, malic acid, mandelic acid, nitrilotriacetic acid, N-(<NUM>-hydroxyethyl)-ethylenediaminetriacetic acid, ethylenediaminetetraacetic acid and diethyleneaminepentaacetic acid.

Organic acids also include sulfonic acids of formula RSO<NUM>H where R is alkyl or aryl or alkyl or aryl substituted by one to three halogens, such as p-toluenesulfonic acid, phenylsulfonic acid, methanesulfonic acid and trifluoromethanesulfonic acid.

The protic acid may also be an oxonium ion of a highly non-coordinating ion such as Brookhart's acid (BARF acid), [H(OEt<NUM>)<NUM>][B[<NUM>,<NUM>-(CF<NUM>)<NUM>C<NUM>H<NUM>]<NUM>]. Other examples include [H(OEt<NUM>)<NUM>][B(C<NUM>F<NUM>)<NUM>] (oxonium acid) and [H(OEt<NUM>)<NUM>][Al(OC(CF<NUM>)<NUM>)<NUM>]. In these cases the cation is protonated diethyl ether (diethyl ether oxonium). Alternatively, the cation may be other protonated ethers, for instance protonated tetrahydrofuran (THF).

Suitable organic solvents are for instance selected from the group consisting of organic carbonates, ethers, glymes, ortho esters, polyalkylene glycols, esters, lactones, glycols, formates, sulfones, sulfoxides, amides, alcohols, ketones, nitro solvents, nitrile solvents and combinations thereof.

Organic carbonates are cyclic or acyclic and include ethylene carbonate (EC), propylene carbonate (PC), trimethylene carbonate, <NUM>,<NUM>-butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), vinylene carbonate, difluoroethylene carbonate and monofluoroethylene carbonate.

Ethers and glymes include dimethoxymethane (DMM), diethoxymethane, <NUM>,<NUM>-dimethoxyethane (DME or ethyleneglycol dimethylether or glyme), diglyme, triglyme, tetraglyme, ethyleneglycol diethylether (DEE), ethyleneglycol dibutylether, diethyleneglycol diethylether, tetrahydrofuran (THF), <NUM>-methyltetrahydrofuran (<NUM>-MeTHF), <NUM>,<NUM>-dioxane, <NUM>,<NUM>-dioxolane (DIOX), <NUM>-methyl-<NUM>,<NUM>-dioxolane (<NUM>-MeDIOX), <NUM>-methyl-<NUM>,<NUM>-dioxolane (<NUM>-MeDIOX), <NUM>,<NUM>-dioxane, dimethylether, ethylmethylether, diethylether, di-n-butylether, di-t-butylether, di-isopropylether, methyl-t-butylether, ethyl-t-butylether and t-amyl-methylether.

Ortho esters include trimethoxymethane, triethoxymethane, <NUM>,<NUM>-dimethyl-<NUM>,<NUM>,<NUM>-trioxabicyclo[<NUM>. <NUM>]octane and <NUM>-ethyl-<NUM>-methyl-<NUM>,<NUM>,<NUM>-trioxabicyclo[<NUM>. <NUM>]octane.

Polyalkylene glycols are homo- or cooligomers or homo- or copolymers of C<NUM>-C<NUM>alkylene glycols. For instance, polyethylene glycol (PEG) or monomethyl, dimethyl or diethyl (endcapped) polyethylene glycol. Weight average molecular weights (Mw) of polyalkylene glycols are for example from about <NUM> to about <NUM>/mol, from about <NUM> to about <NUM>/mol, from about <NUM> to about <NUM>/mol, from about <NUM> to about <NUM>/mol or from about <NUM> to about <NUM>/mol. Included are oligomers of <NUM> monomers and more, for instance tetraethylene glycol, fluorinated tetraethylene glycol and tetrapropylene glycol. For instance PEG <NUM>, PEG <NUM>, PEG <NUM>, PEG <NUM>, PEG <NUM>, PEG <NUM>, PEG <NUM>, PEG <NUM> or PEG <NUM>.

Esters and lactones include γ-butyrolactone (GBL), γ-valerolactone, δ-valerolactone, ethyl acetate (EA), <NUM>-methoxyethyl acetate, <NUM>-ethoxyethyl acetate, <NUM>-butoxyethyl acetate, <NUM>-(<NUM>-butoxyethoxy)ethyl acetate (diethylene glycol butyl ether acetate, DBA), ethylene glycol diacetate (EGDA), <NUM>-ethoxy ethyl propionate (EEP), methyl butyrate (MB), n-amyl acetate (NAAC), propylene glycol methyl ether acetate (PMA), ethyl butryate (EB), diethyl malonate, dimethyl malonate and dibasic ester mixture (DBE).

Dibasic ester mixture includes for instance methyl esters of adipic, glutaric and succinic acids.

Glycols include ethylene glycol, propylene glycol, <NUM>-methoxyethanol, <NUM>-ethoxyethanol, <NUM>-propoxyethanol, <NUM>-isopropoxyethanol, <NUM>-butoxyethanol (ethylene glycol butyl ether, EB), <NUM>-phenoxyethanol, <NUM>-benzyloxyethanol, <NUM>-(<NUM>-methoxyethoxy)ethanol, <NUM>-(<NUM>-ethoxyethoxy)ethanol, <NUM>-(<NUM>-butoxyethoxy)ethanol (diethylene glycol butyl ether, DB), propylene glycol butyl ether (PB), propylene glycol methyl ether (PM), triethylene glycol (TEG), dipropylene glycol methyl ether (DPM), diethylene glycol methyl ether, <NUM>,<NUM>-butanediol, <NUM>,<NUM>-butanediol, <NUM>,<NUM>-pentanediol, perfluoro-<NUM>,<NUM>-butanediol, perfluoro-<NUM>,<NUM>-butanediol, fluorinated diethylene glycol methyl ether, fluorinated triethylene glycol, fluorinated triethylene glycol methyl ether and fluorinated diethylene glycol butyl ether.

Formates include methyl formate, ethyl formate, isobutyl formate and tert-butyl formate.

Sulfones and sulfoxides include methylsulfonylmethane (MSM or dimethylsulfone), ethylmethylsulfone, sulfolane and dimethylsulfoxide (DMSO).

Amides include dimethylformamide (DMF), dimethylacetamide (DMA), N-methylpyrrolidone (NMP), <NUM>-pyrrolidone, <NUM>,<NUM>-dimethyl-<NUM>-imidazolidinone (DMI), hexamethylphosphoramide (HMPA) and N,N'-dimethyl-N,N'-trimethyleneurea (<NUM>,<NUM>-dimethyl-<NUM>,<NUM>,<NUM>,<NUM>-tetrahydro-<NUM>(<NUM>)-pyrimidinone (DMPU)).

Alcohols include for example benzylalcohol (BA), ethanol, trifluoroethanol (<NUM>,<NUM>,<NUM>-trifluoroethanol), methanol, isopropanol, t-butanol and n-butanol.

Ketones include for example methylethylketone (MEK) and methyl-isoamyl ketone (MIAK).

Nitro solvents include nitrobenzene, nitromethane and nitroethane.

Nitrile solvents include acetonitrile, propionitrile, butyronitrile and adiponitrile.

Advantageously, a mixture of solvents is employed, for instance a mixture of organic carbonates or a mixture of one or more organic carbonates and one or more ether or glyme.

Other organic solvents may be employed, for instance common non-polar organic solvents including toluene, hexane, heptane and the like.

Advantageously, present electrolyte compositions comprise.

The present electrolyte compositions are advantageously anhydrous, that is containing little or no water. The electrolyte compositions may typically contain ≤ <NUM> ppm water, for instance ≤ <NUM>, ≤ <NUM>, ≤ <NUM>, ≤ <NUM>, ≤ <NUM> or ≤ <NUM> ppm water by weight, based on the total weight of the electrolyte composition.

In accordance with the above, it is preferred that the electrolyte composition comprises a protic acid. The weight/weight ratio of the ionic liquids to the protic acids is for instance from about <NUM>/<NUM> to about <NUM>/<NUM>, from about <NUM>/<NUM> to about <NUM>/<NUM>, from about <NUM>/<NUM> to about <NUM>/<NUM>, from about <NUM>/<NUM> to about <NUM>/<NUM>, from about <NUM>/<NUM> to about <NUM>/<NUM>, from about <NUM>/<NUM> to about <NUM>/<NUM> or from about <NUM>/<NUM> to about <NUM>/<NUM>.

In accordance with the above, it is preferred that the electrolyte composition comprises an organic solvent. The weight/weight ratio of the ionic liquids to the organic solvents is for instance from about <NUM>/<NUM> to about <NUM>/<NUM>, from about <NUM>/<NUM> to about <NUM>/<NUM>, from about <NUM>/<NUM> to about <NUM>/<NUM>, from about <NUM>/<NUM> to about <NUM>/<NUM>, from about <NUM>/<NUM> to about <NUM>/<NUM>, from about <NUM>/<NUM> to about <NUM>/<NUM> or from about <NUM>/<NUM> to about <NUM>/<NUM>.

Additives may be incorporated in the electrolyte compositions of the invention.

Additives are for instance selected from the group consisting of corrosion inhibitors, solid electrolyte interface (SEI) improvers, proton evolution improvers, self-discharge inhibitors, anti-gassing agents, viscosity adjusting agents, cathode protection agents, salt stabilizers, conductivity improvers and solvating agents.

Corrosion inhibitors are for example fluorinated oil, sodium stannate, sodium citrate or polyacrylic acids.

Solid electrolyte interface improvers are for instance fluoride sources intended to fluorinate the surface of the metal hydride. Fluoride sources are for instance HF or KF. SEI improvers also include oxides or hydroxides of rare earths such as Y, which inhibit the formation of a thick oxide on the negative electrode. SEI improvers also include metal porphines which serve to reduce oxidation of the alloy surface. For example Ni or Fe porphine. SEI improvers may also incude vinylene carbonate, vinylethylene carbonate, methylene ethylene carbonate and fluoro-ethylene carbonate.

Self-discharge inhibitors include surfactants such as polyglycols, polyglycol alkyl ethers, polyglycol alkyl phosphate esters and polysorbates. Included are polyethylene glycol (PEG), polypropylene glycol, polysorbate <NUM>, polysorbate <NUM> and polysorbate <NUM>. Advantageously, a mixture of PEG <NUM> and polysorbate <NUM> are employed together or a mixture of PEG <NUM> and ZnO are employed together.

Anti-gassing additives include phosphate ester-based surfactants, propane sultone and fluoropropane sultone.

Viscosity adjusting agents include for instance DMSO.

Additives are for example employed at a level of from about <NUM>% to about <NUM>% by weight, based on the total weight of the electrolyte composition.

The present electrolyte compositions will not be limited by the hydrogen and oxygen evolution potential of water. Thus, the metal hydride batteries disclosed may exhibit a nominal open-circuit voltage of > <NUM> V (volts). The present MH batteries may supply a nominal open-circuit voltage up to about <NUM> V. For instance, present MH batteries may exhibit a nominal open-circuit voltage of from about <NUM> to about <NUM> V, from about <NUM> to about <NUM> V, from about <NUM> to about <NUM> V or from about <NUM> to about <NUM> V. For instance, present MH batteries may exhibit a nominal open-circuit voltage of about <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or about <NUM> V.

As the electrochemical window is enlarged beyond that of water, further cathode active materials are possible. Further cathode active materials include transition metals and their oxides, hydroxides and fluorides. For example, further cathode active materials include Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Lu, Hf, Ta, W, Re, Os, Ir, Pt and Au and their oxides, hydroxides, oxide/hydroxides and fluorides.

In further cathode active materials selected from the group consisting of transition metal oxides, transition metal hydroxides and transition metal oxide/hydroxides, nickel may be present at a level of ≤ <NUM>, ≤ <NUM>, ≤ <NUM>, ≤ <NUM>, ≤ <NUM>, ≤ <NUM>, ≤ <NUM>, ≤ <NUM>, ≤ <NUM>, ≤ <NUM>, ≤ <NUM>, ≤ <NUM>, ≤ <NUM>, ≤ <NUM>, ≤ <NUM>, ≤ <NUM> or ≤ <NUM> atomic percent, for instance ≤ <NUM> atomic percent, based on the total metals of the transition metal oxides, transition metal hydroxides and transition metal oxide/hydroxides.

By way of example, "an ionic liquid" means one ionic liquid or more than one ionic liquid.

The terms "substantially" and "about" used throughout this specification are used to describe and account for small fluctuations. For example, they can refer to less than or equal to ±<NUM>%, such as less than or equal to ±<NUM>%, less than or equal to ±<NUM>%, less than or equal to ±<NUM>%, less than or equal to ±<NUM>%, less than or equal to ±<NUM>% or less than or equal to ±<NUM>%. All numeric values herein are modified by the term "about," whether or not explicitly indicated. A value modified by the term "about" of course includes the specific value. For instance, "about <NUM>" must include <NUM>.

In the following examples, all measurements are performed at ambient conditions of <NUM> and <NUM> atm, unless specified otherwise.

Electrolyte compositions are prepared by mixing ionic liquids with acetic acid (AA). Acetic acid concentration is reported in mol/L (M) in the ionic liquid. Conductivity of each composition is measured and reported in mS/cm at <NUM>. Results are below.

It is seen that the presence of acetic acid in an ionic liquid leads to increased conductivity.

The electrolyte compositions are employed in a SWAGELOK cell assembly. A smaller anode is employed and therefore limits the capacity. Specific capacity is calculated based on the weight of the anode active material. The anode contains an AB<NUM> rare earth/nickel based metal hydride active material. The cathode contains Ni(OH)<NUM> active material and the separator is a conventional non-woven material.

Pure ionic liquids exhibit poor cell performance. Electrolyte compositions comprising an ionic liquid and <NUM> acetic acid show improved cell performance. The compositions containing BMIM Ac especially show very good performance in terms of charge/discharge overpotentials and cycle stability.

A <NUM>:<NUM> volume mixture of <NUM>-ethyl-<NUM>-methylimidazolium acetate (EMIM Ac) and methanol is prepared and tested in a cell as an electrolyte as in Example <NUM>. A discharge capacity of <NUM> mAh/g is obtained for a charge capacity of <NUM> mAh/g.

Electrolyte compositions of <NUM> H<NUM>PO<NUM> in EMIM TFSI, EMIM TfO and DEMA TfO are prepared. The electrolytes are tested in a cell as in Example <NUM>. The cells exhibit good charge/discharge characteristics. The example is repeated replacing phosphoric acid with each of citric acid, acrylic acid, methanesulfonic acid and oxalic acid.

A charge/discharge test is performed employing <NUM> acetic acid/EMIM Ac electrolyte composition in a cell as in Example <NUM>. The NiMH cell is charged to <NUM> mAh/g and discharged until a cutoff voltage of <NUM> V. Several cycles are required to activate the cell. Charge voltage drops and specific capacity increases dramatically over the first <NUM> cycles. Coulombic efficiency reaches <NUM>% at <NUM> cycles. The cell starts to degrade slightly after <NUM> cycles; after <NUM> cycles coulombic efficiency drops to <NUM>%. The AB<NUM> anode exhibits a specific capacity of <NUM> mAh/g when the cell is charged with a capacity of <NUM> mAh/g.

Cyclic voltammetry is performed for an AB<NUM> anode with a <NUM> acetic acid/EMIM Ac electrolyte and with a <NUM> weight percent (wt%) aqueous KOH electrolyte at variable scan rates after activation. The electrode potential is scanned from <NUM> V to -<NUM> V vs. a Hg/HgO reference for KOH and from <NUM> V to -<NUM> V vs. a commercial leak-free reference electrode for <NUM> acetic acid/EMIM Ac electrolyte.

At a scan rate of <NUM> mV/s, the hydrogen adsorption peak for <NUM> wt% KOH is observed at about -<NUM> V. For the acetic acid/EMIM Ac electrolyte, a hydrogen adsorption peak is observed at -<NUM> V and a further peak is observed at -<NUM> V. There is an extra <NUM> V voltage window for the present acetic acid/EMIM Ac electrolyte.

Solutions of EMIM Ac and propylene carbonate (PC) are prepared and tested for conductivity. EMIM Ac levels are reported in volume % based on the EMIM Ac/PC mixture. Conductivity of each composition is measured and reported in mS/cm at <NUM>. Results are below.

It is seen that a <NUM>:<NUM> volume mixture of an ionic liquid and PC is highly conductive.

Mixtures of acetic acid and <NUM>-ethyl-<NUM>-methylimidazolium acetate (EMIM Ac) are prepared and tested for conductivity. The highest conductivity achieved is about <NUM>/cm for <NUM>:<NUM> weight mixture.

Electrolyte compositions are prepared by mixing acetic acid with <NUM>:<NUM> volume mixtures of EMIM Ac and propylene carbonate (PC). Acetic acid concentration is wt% based on the total mixture. Conductivity is measured and is reported below.

Electrolyte compositions are prepared by mixing methanesulfonic acid with <NUM>:<NUM> volume mixtures of EMIM Ac/PC. Methanesulfonic acid concentration is wt% based on the total mixture. Conductivity is measured and is reported below.

Electrolyte compositions are prepared by mixing acrylic acid with <NUM>:<NUM> volume mixtures of EMIM Ac/PC. Acrylic acid concentration is wt% based on the total mixture. Conductivity is measured and is reported below.

It is seen that ternary electrolyte compositions containing ionic liquid, solvent and protic acid exhibit excellent conductivity.

The electrolyte composition of <NUM> wt% acetic acid in <NUM>:<NUM> volume mixture of EMIM Ac/PC is tested in a cell as in Example <NUM>. At the first cycle, the ternary electrolyte exhibits a reduced charge/discharge overpotential vs. <NUM> acetic acid in EMIM Ac. The ternary system exhibits a <NUM> V drop in charge voltage and increased discharge voltage plateau. The ternary system also has an an increased coloumbic efficiency of <NUM>% (<NUM>/<NUM> mAh/g) vs. <NUM>% <NUM>/<NUM> mAh/g) for the binary system.

Example <NUM> is repeated, replacing methanol with each of ethylene carbonate (EC), propylene carbonate (PC), <NUM>,<NUM>-dimethyoxyethane (DME), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), N, N-dimethylacetamide (DMA) and acetonitrile (AN).

Claim 1:
A metal hydride battery comprising at least one negative electrode, at least one positive electrode, a casing having said electrodes positioned therein and an electrolyte composition, which electrolyte composition comprises a) an ionic liquid and b) a protic acid and/or an organic solvent, wherein the active material of the negative electrode comprises an ABx type alloy capable of reversibly adsorbing and desorbing hydrogen with A being a hydride forming element, B being a weak or non-hydride forming element and x being from <NUM> to <NUM>.