Synthesis of lithium-metal-phosphates under hydrothermal conditions

1. A process for preparing a compound of general formula (I)

Li a-b M 1 b Q 1-c M 2 c P d-e M 3 e O x   (I),

wherein Q has the oxidation state +2 and M 1 , M 2 , M 3 , a, b, c, d, e and x are:

Q: Fe, Mn, Co, Ni,

M 1 : Na, K, Rb and/or Cs,

M 2 : Mg, Al, Ca, Ti, Co, Ni, Cr, V, Fe, Mn, wherein Q and M 2 are different from each other,

M 3 : Si, S, F

a: 0.8-1.9,

b: 0-0.3,

c: 0-0.9,

d: 0.8-1.9,

e: 0-0.5,

x: 1.0-8, depending on the amount and oxidation state of Li, M 1 , M 2 , P, M 3 , wherein compounds of general formula (I) are neutrally charged,

comprising

(A) providing an essentially aqueous mixture comprising at least one lithium-comprising compound, at least one Q-comprising compound, in which Q has at least partially an oxidation state higher than +2, and at least one M 1 -comprising compound, if present, and/or at least one M 2 -comprising compound, if present, and/or at least one M 3 -comprising compound, if present, and at least one carbon-free reducing agent which is oxidized to a compound comprising at least one phosphorous atom in oxidation state +5, and

(B) heating the mixture obtained in (A) at a temperature of 100 to 500° C. and at an autogeneous pressure to reduce Q to oxidation state +2.

2. The process according to claim 1 , wherein the mixture in (A) further comprises at least one compound comprising at least one phosphorous atom in oxidation state +5.

3. The process according to claim 2 , wherein the at least one compound comprising at least one phosphorous atom in oxidation state +5 is selected from the group consisting of H 3 PO 4 , (NH 4 )H 2 PO 4 , (NR 4 ) 2 HPO 4 , (NH 4 ) 3 PO 4 , Li 3 PO 4 , LiH 2 PO 4 , Li 2 HPO 4 , and mixtures thereof.

4. The process according to claim 2 , wherein the heating in (B) is conducted at a temperature of 180 to 350° C.

5. The process according to claim 1 , wherein the at least one carbon-free reducing agent is selected from the group consisting of H 3 PO 3 , (NH 4 ) 2 HPO 3 , (NH 4 ) 2 HPO 3 , H 3 PO 2 , (NH 4 )H 2 PO 2 , LiH 2 PO 3 , Li 2 HPO 3 , Li 2 PO 2 and mixtures thereof.

6. The process according to claim 1 , further comprising:

(C) separating the compound of general formula (I) from the mixture obtained in (B).

7. The process according to claim 1 , wherein (B) is conducted in an autoclave.

8. A process for preparing a mixture comprising at least one compound of general formula (I) of claim 1 and at least one electrically conducting material, comprising:

(E) providing an essentially aqueous mixture comprising at least one electrically conducting material or at least one precursor of an electrically conducting material, at least one lithium-comprising compound, at least one Q-comprising compound, in which Q has at least partially an oxidation state higher than +2, and at least one M 1 -comprising compound, if present, and/or at least one M 2 -comprising compound, if present, and/or at least one M 3 -comprising compound, if present, and at least one carbon-free reducing agent which is oxidized to a compound comprising at least one phosphorous atom in oxidation state +5; and

(F) heating the mixture obtained in (E) at a temperature of 100 to 500° C. and at an autogeneous pressure to reduce Q to oxidation state +2.

9. The process according to claim 8 , wherein the mixture in (E) further comprises at least one compound comprising at least one phosphorous atom in oxidation state +5.

10. The process according to claim 8 , wherein the at least one carbon-free reducing agent is selected from the group consisting of H 3 PO 3 , (NH 4 )H 2 PO 3 , (NH 4 ) 2 HPO 3 , H 3 PO 2 , (NH 4 )H 2 PO 2 , LiH 2 PO 3 , Li 2 HPO 3 , LiH 2 PO 2 and mixtures thereof.

11. The process according to claim 8 , wherein the electrically conducting material is selected from the group consisting of carbon black, graphite, carbon fibres, carbon nanofibres, carbon nanotubes, electrically conducting polymers,and mixtures thereof.