Synthesis of nanoparticles of lithium metal phosphate positive material for lithium secondary battery
Novel process for the preparation of finely divided, nano-structured, olivine lithium metal phosphates (LiMPO 4 ) (where metal M is iron, cobalt, manganese, nickel, vanadium, copper, titanium and mix of them) materials have been developed. This so called Polyol” method consists of heating of suited precursor materials in a multivalent, high-boiling point multivalent alcohol like glycols with the general formula HO—(—C 2 H 4 O—), —H where n=1-10 or HO—(—C 3 H 6 O—) n —H where n=1-10, or other polyols with the general formula HOCH 2 —(—C 3 H 5 OH—) n —H where n=1-10, like for example the tridecane-1,4,7,10,13-pentaol. A novel method for implementing the resulting materials as cathode materials for Li.-ion batteries is also developed.
1. A process for the production of nanostructured olivine lithium metal phosphate particles comprising
(a) dissolving a metal salt in a multivalent alcohol solvent having a high-boiling point wherein the metal of the metal salt is iron, manganese, cobalt, nickel, vanadium, copper, titanium or a mixture thereof and the dissolving in said solvent is at a first temperature to form a solution with said metal salt dissolved in the solvent,
(b) subsequently adding a lithium salt, a phosphate salt, water and optionally a hydrolyzing agent to the solution such that a precipitate is formed,
(c) heating the solution and precipitate to a second temperature higher than the first temperature such that the solution is dehydrated and the precipitate is crystallized to form the nanostructured olivine lithium metal phosphate, and
(d) separating the lithium metal phosphate from the solvent.
2. The process according to claim 1 wherein the nanostructured olivine lithium metal phosphate particles have a particle size in the range 20-100 nm.
3. The process according to claim 2 wherein the particle size is in the range 20-50 nm.
4. The Process according to claim 1 further comprising drying the precipitate separated from the solvent.
5. The process according to claim 1 , wherein the solvent is a glycol.
6. The process according to claim 4 , wherein the first temperature is 100 to 150° C.
7. The process according to claim 1 , wherein the lithium salt and phosphate salt are dissolved first in distilled water and added as a solution in step (b).
8. The process according to claim 1 , wherein the second temperature is 160 to 210° C.
9. The process according to claim 6 , wherein the hydrolyzing agent is used for the hydrolysis of the polyol solution and hydrolyzing agent is an acidic solution.
10. The process according to claim 1 , wherein the molar ratio of the metal salts to multivalent alcohol is 0.01 to 0.15.
11. The process according to claim 4 , wherein the precipitate is dried at 80° C. for 24 h.
12. The process according to claim 4 further comprising calcining the dried powder at 350-500° C. for 30 minutes to 1 hour.