Processes for the alkaliation or re-alkaliation of an electrode active material
Processes are described for the direct or indirect electrochemical alkaliation of an alkali metal deficient electrochemically active material. The processes include an electrolysis step either during the alkaliation of the alkali metal deficient electrochemically active material on an electrode current collector (direct) or during the regeneration of a reducing agent used for the alkaliation of the electrochemically active material (indirect).
1 . A process for the electrochemical alkaliation of an electrochemically active material, the process comprising the steps of:
(i) adding the electrochemically active material to a solution containing a reducing agent and an alkali metal salt in a solvent to produce an alkaliated electrochemically active material;
(ii) separating the alkaliated electrochemically active material and the solution; and
(iii) electrochemically treating the solution separated in step (ii) to regenerate the reducing agent in the solution;
the process optionally further comprising drying the alkaliated electrochemically active material.
2 . The process of claim 1 , wherein the electrochemically active material comprises a metal oxide, metal phosphate, metal silicate, metal sulfate, or a partially alkaliated metal oxide, metal phosphate, metal silicate, or metal sulfate.
3 . The process of claim 1 , wherein the reducing agent is the reducing member of a redox couple having a lower redox potential than that of the electrochemically active material to be reduced.
4 . The process of claim 3 , wherein the redox couple is Fe (II)/Fe (III) based.
5 . The process of claim 4 , wherein the redox couple is selected from
[
Fe
(
CN
)
6
]
3
-
/
[
Fe
(
CN
)
6
]
4
-
,
[Fe(nta)]/[Fe(nta)] − , [Fe(tdap)] 2− /[Fe(tdap)] 3− , [Fe(edta)] − /[Fe(edta)] 2− , [Fe(citrate)]/[Fe(citrate)] − , [Fe(TEOA)OH] − /[Fe(TEOA)OH] − , and [Fe(oxalate)] + /[Fe(oxalate)].
6 . The process of claim 1 , wherein:
step (i) further comprises a step of deoxygenating the solution; and/or
steps (i) and/or (iii) are carried out in the presence of a gas allowing to eliminate the presence of oxygen.
7 . The process of claim 1 , wherein the alkali metal salt is selected from an alkali metal sulfate and an alkali metal bicarbonate.
8 . The process of claim 1 , further comprising a step of adjusting the pH of the solution to a pH adapted to the electrochemically active material of step (i).
9 . The process of claim 8 , further comprising the electrochemically active material of step (a) is FePO 4 , and the pH is adjusted to between 6 and 7.5.
10 . The process of claim 1 , wherein the solvent is an aqueous solvent.
11 . The process of claim 1 , wherein the electrochemical treatment step (iii) is carried out in an electrolytic cell by passing a current between at least one cathode and at least one anode.
12 . The process of claim 11 , wherein the electrolytic cell comprises at least one ionic or non-ionic separator installed between the anode and the cathode to protect the regenerated reducing agent and/or the electrolytic cell further comprises a system for keeping the solution deoxygenated.
13 . The process of claim 12 , wherein the system comprises an oxygen-free gas such as carbon dioxide, nitrogen, or argon.
14 . The process of claim 1 , wherein:
the electrochemically active material is in the form of a suspension in the solution of step (i), and step (ii) is carried out by filtration, centrifugation, or decantation, optionally followed by a washing step; or
the electrochemically active material is comprised in an electrode material on a current collector, and step (ii) comprises removing the electrode from the solution, optionally followed by a washing step.
15 . The process of claim 14 , wherein the electrode material further comprises an electronically conductive material selected from the group consisting of carbon black, acetylene black, graphite, graphene, carbon fibers or nanofibers, carbon nanotubes, and a combination of at least two thereof.
16 . The process of claim 14 , wherein the electrode material further comprises a binder.
17 . The process of claim 1 , wherein the alkali metal salt is an alkali metal bicarbonate and step (i) is carried out in the presence of gaseous carbon dioxide.
18 . The process of claim 1 , wherein the alkali metal of the alkali metal salt is lithium.