LMFP cathode materials with improved electrochemical performance
Particulate LMFP cathode materials having high manganese contents and small amounts of dopant metals are disclosed. These cathode materials are made by milling a mixture of precursor materials in a wet or dry milling process. Preferably, off-stoichiometric amounts of starting materials are used to make the cathode materials. Unlike other high manganese LMFP materials, these cathode materials provide high specific capacities, very good cycle life and high energies even at high discharge rates.
1. A particulate cathode material comprising an electroactive material having the empirical formula Li a Mn b Fe c D d PO 4 , wherein
a is a number from 1.04 to 1.08;
b is from 0.73 to 0.79;
c is from 0.15 to 0.24;
d is from 0.003 to 0.053;
2.96≤(a+2b+2c+dV)≤3.086 and 1.92≤(2b+2c+dV)≤2.01, wherein V is the valence of D, and D is a metal ion selected from cobalt or a mixture of magnesium and cobalt, and further wherein at least a portion of the electroactive material has an olivine structure.
2. A nanocomposite containing at least 70% by weight of a particulate cathode material of claim 1 with up to 30% by weight of a graphite, carbon black and/or other conductive carbon.
3. A battery cathode comprising the nanocomposite of claim 2 .
4. A lithium battery comprising an anode, a battery cathode of claim 3 , a separator disposed between the anode and cathode, and an electrolyte solution containing at least one lithium salt.
5. A method for making an olivine lithium manganese transition metal phosphate cathode material, comprising
a) forming a mixture of at least one lithium precursor, at least one iron precursor, at least one manganese precursor, at least one dopant metal precursor selected from a magnesium precursor, a cobalt precursor or a mixture of magnesium and cobalt precursors and at least one precursor of H x PO 4 ions where x is 0, 1 or 2, wherein the precursors are present in amounts such that:
the mole ratio of lithium ions to H x PO 4 ions is 1.04 to 1.08;
the mole ratio of manganese ions to H x PO 4 ions is 0.73 to 0.79;
the mole ratio of iron ions to H x PO 4 ions is 0.15 to 0.24;
the mole ratio of dopant metal ions to H x PO 4 ions is 0.003 to 0.053; and
the mole ratio of lithium, manganese, iron and dopant metal ions combined to H x PO 4 ions is such that (2.96×Moles H x PO 4 )≤[moles Li+(2×Moles Mn)+(2×Moles Fe)+(2×Moles Dopant Metal)]≤(3.086×Moles H x PO 4 ) and (1.92×Moles H x PO 4 )≤[(2×Moles Mn)+(2×Moles Fe)+(2×Moles Dopant Metal)]≤(2.006×Moles H x PO 4 );
b) milling the mixture and then;
c) calcining the milled mixture to form the olivine lithium manganese iron phosphate cathode material.