Battery active materials and methods for synthesis
View Patent ↗Active materials for rechargeable batteries have a general formula A a (MO) b M′ c XO 4 where A represents an alkali metal or mixture of alkali metals, a is greater than about 0.1 and less than or equal to about 2; MO is an ion containing a transition metal M not in its highest oxidation state, M′ represents a metal, or mixture of metals, and b is greater than 0 and less than or equal to about 1, c is less than 1 wherein a, b and c are selected so as to maintain the electroneutrality of the compound, and X is phosphorus, arsenic, or sulfur, or mixtures thereof. Preferred active materials are alkali metal vanadyl metal phosphates of general formula A a (VO) b M′ c PO 4 where a and b are both greater than 0 and c may be zero or greater. New synthetic routes are provided to alkali metal mixed metal phosphates where at least one of the starting materials is a metal-oxo group (MO) 3+ , where M represents a metal in a +5 oxidation state. Reductive methods are provided for reacting a metal-oxo phosphate with an alkali metal compound in the presence of reducing carbon. The carbothermal reduction step can for example result in the reduction of a +5 metal to a +4 state or lower.
1. A method for synthesizing active materials of general formula
A a (MO) b M′ c XO 4
wherein X is selected from the group consisting of phosphorous, sulfur, arsenic and combinations thereof, A is an alkali metal or mixture of alkali metals, M is a transition metal or mixture of transition metals at least one of which is not in its highest oxidation state, M′ comprises a metal, 0<b≦1 and 0<a<2, and 0≦c<1 where a, b, and c are selected to maintain the electroneutrality of the compound, the method comprising the steps of
combining starting materials to form a mixture, wherein the starting materials comprise
a metal compound of formula (MO) b M′ c XO 4 , wherein M and M′ are the same elements as in the formula above for the active material, but wherein at least one of M and M′ has a higher oxidation state than in the above formula for the active material,
a source of reducing carbon, and
a source of alkali metal A; and
heating the mixture at a temperature about greater than 400° C. and for a time sufficient to form a reaction product wherein at least one of M or M′ is reduced in oxidation state without full reduction to elemental state.
2. A method according to claim 1 , wherein M comprises vanadium and M′ comprises at least one element selected from the group consisting of chromium, iron, cobalt, nickel, molybdenum, manganese and vanadium.
3. A method according to claim 1 , wherein A comprises sodium, lithium, or a mixture of lithium and sodium.
4. A method according to claim 1 , wherein the material has general formula
Li a (VO) b M′ c PO 4
wherein M′ is selected from the group consisting of chromium, iron, cobalt, nickel, molybdenum, manganese and vanadium.
5. A method according to claim 1 , wherein the reducing carbon is selected from the group consisting of elemental carbon, carbohydrates and sucrose.
6. A method according to claim 1 , wherein the reducing carbon comprises an organic precursor material that decomposes during the heating step to form a carbonaceous material containing carbon in a form capable of acting as a reductant.
7. A method according to claim 1 , wherein X comprises phosphorous.
8. A method according to claim 7 , wherein the starting material metal compound has general formula
(MO) b M′ 1-b PO 4
and is prepared by a process comprising:
reacting a source of phosphate with an M 5+ oxide and a source of M′ in a chemical precipitation or reflux preparation route to form a reaction product.