TECHNICAL FIELD
The present invention relates to a method for making lithium metal phosphates.
BACKGROUND ART
[0001] Lithium metal phosphates, such as lithium iron phosphate, are widely used in the
manufacture of lithium ion batteries due to its high energy density good stability, ability to
withstand a large number of charge/discharge cycles and relatively low-cost.
[0002] It will be clearly understood that, if a prior art publication is referred to herein, this
reference does not constitute an admission that the publication forms part of the common general
knowledge in the art in Australia or in any other country.
SUMMARY OF INVENTION
[0003] In one aspect, the present invention is directed to a method for making a material of
formula LixMI-zDzP04, where M is one or more transition metals, D represents one or more
elements selected from the group consisting of Mg, Ca, Sr, Ba, Ti, Zn, B, AI, Ga, In, Si, Ge, Sc,
Y, and rare earth elements, 0.8:Sx:Sl.2 and 0:Sz:S0.2, the method comprising the steps of:
a) forming a mixture comprising a source of the one or more transition metals, a source of
phosphorus, a source of lithium and a surfactant, and optionally a source of D, the mixture,
wherein (i) a ratio of Li:P04:(M+D) relative to the stoichiometry required to form the material is
within the range of 1.04-1.10:1.00-1.05:1, or (ii) a ratio of (Li+P04):(M+D) relative to the
stoichiometry required to form the material is greater than 2.05;
b) drying the mixture from step (a) to form particles or a powder; and
c) thermally treating the particles or powder from step (b) to form the material.
[0004] In one embodiment, M is one or more transition metals selected from Fe, Mn, Ni,
Co, Cr or V. In one embodiment, M is Fe. In one embodiment, M comprises Fe and one or more
of Mn, Ni, Co, Cr or V. In one embodiment, M comprises 2 or more of Fe, Mn, Ni, Co, Cr or V.
[0005] In one embodiment, the process further comprises the steps of:
wo 2021/248181 PCT/AU2021/050572
2
d) mixing the material from step (c) with a liquid containing a carbon precursor,
e) spray drying the mixture from step (d) to form particles of the material coated with the carbon
precursor, and
f) converting the carbon precursor to carbon.
[0006] In one embodiment, the mixture formed in step (a) includes a liquid. In one
embodiment, the liquid comprises water. In one embodiment, the liquid comprises demineralised
water or deionised water.
[0007] In one embodiment, the mixture formed in step (a) comprises a solution in which the
source of one or more transition metals, the source of phosphorus and the source of lithium are
dissolved, and the source of D, if present, are dissolved.
[0008] In another embodiment, the mixture formed in step (a) comprises a slurry in which
one or more of the source of one or more transition metals, the source of phosphorus or the
source of lithium, or the source of D, if present, is present as particulate material. In one
embodiment, the source of one or more transition metals is present as particulate material. In this
embodiment, the particulate material remains as or persists as particulate material during the
mixing and drying step. In one embodiment, the source of one or more transition metals is a
source of iron and the source of iron is present as particulate material in the mixture. Prior art
methods known to the present inventors for forming lithium metal phosphates typically involve
forming a solution in which all precursor compounds are dissolved. Some of the precursor
compounds can be difficult to dissolve and/or forming the solution may require additional
reactants or additional processing steps. As a result, the present inventors believe that processes
in accordance with the present invention in which the mixture of step (a) comprises a slurry are
particularly advantageous as they can result in one or more of reduced processing steps, less
reactants or simple processing.
[0009] In embodiments where one or more of the source of one or more transition metals,
the source of phosphorus or the source of lithium, or the source of D, if present, is present as
particulate material, the particulate material or the slurry may be milled prior to drying. In one
embodiment, the particulate material or slurry is milled in a bead mill or a rotating mill. Other
milling processes may be used. The milling step may reduce the size of the particulate material
and intimately and homogeneously mix the particulate material with the other components of the
slurry.
wo 2021/248181 PCT/AU2021/050572
3
[0010] In one embodiment, the source of one or more transition metals comprises a source
of one or more of Fe, Mn, Ni, Co, Cr or V. In one embodiment, the source of one or more
transition metals comprises one or more compounds containing the transition metal(s). This may
include M+2 salts, such as chloride and sulphate salts, M+3 salts, such as chloride salts, nitrate
salts, sulphate salts, organic M salts, such as M-oxalate, M-citrate, M-phosphates, M-oxides,
metallic M or other M-containing compounds.
[0011] In one embodiment, the source of one or more transition metals comprises a source
of iron. In this embodiment, the source of iron may comprise an iron containing compound. Any
suitable iron containing compound can be used, although it is desirable that the iron containing
compound has iron in the form of iron (II). Iron (II) oxalate dihydrate is one example of a
suitable iron containing compound. The source of iron can be mineral Fe+2 salts (e.g. FeCh,
FeS04 etc), mineral Fe+3 salts (e.g. FeCb, Fe(N03)3, Fe2(S04)3 etc), organic Fe salts (e.g. Fe
oxalate, Fe citrate etc), Fe phosphates (e.g. FeP04, Fe3(P04)2), Fe oxides (e.g. magnetite,
haematite etc), metallic Fe or other Fe containing compounds.
[0012] In one embodiment, the source of phosphorus comprises a phosphorus containing
compound or a phosphorus containing acid. In one embodiment, the source of phosphorus
comprises phosphoric acid. The source of phosphorus may be phosphoric acid, lithium
containing phosphates (e.g. LbP04, LhHP04, LiH2P04), organic phosphates (e.g. (NH4)3P04,
(NH4)2HP04, NH4H2P04) or other phosphate containing compounds.
[0013] The source of lithium may be carbonates (e.g. LhC03, LiHC03), phosphates (e.g.
LbP04, LhHP04, LiH2P04), hydroxides (e.g. LiOH), mineral lithium salts (e.g. LiCl, LiN03,
LhS04 etc), organic mineral salts (e.g. Li acetates, lithium oxalates etc), metallic Li or other
lithium containing compounds. In one embodiment, the source of lithium comprises lithium
carbonate.
[0014] In one embodiment, the source of D may comprise one or more water soluble
compounds containing D or one or more water insoluble compounds (including oxides)
containing D, or mixtures thereof.
[0015] The inventors have surprisingly found that better performing material, such as
LiMP04, is obtained where the amount of Li is greater than a stoichiometric amount, the amount
of P04 is greater than a stoichiometric amount but less than the amount of Li, where Li and P04
quantities are stated relative to the amount of M or M+D. In other words, the ratio of each of Li,
P04 and M or M+D in the mixture, when expressed as a ratio of the stoichiometric amount is
wo 2021/248181 PCT/AU2021/050572
4
such that the input ratios are Li>P04>M (or M+D). For example, Li may be present as about
1.04 - 1.10 of the stoichiometric amount, P04 may be present as about 1.00 - 1.05 of the
stoichiometric amount and M (or M and D) may be present as about 1.00 the stoichiometric
amount. P04 in this context also refers to P04 precursors. In one embodiment, the ratio of each
of Li, P04 and M (or M and D) in the mixture, when expressed as a ratio of the stoichoimetric
amount, is such that the input ratios are Li> P04> M, or Li is present as about 1.05 the
stoichiometric amount, P04 is present as about 1.02 the stoichiometric amount and M (or M and
N) is present as about 1.00 the stoichiometric amount.
[0016] In one embodiment, the ratio of Li:P04:(M+D) relative to the stoichiometry required
to form the material is within the range of 1.05-1.09:1.00-1.04:1. In one embodiment, the ratio of
each of Li, P04 and M (or M and D) in the mixture, when expressed as a ratio of the
stoichiometric amount, is such that the input ratios are Li> P04> M, or Li is present as about 1.07
the stoichiometric amount, P04 is present as about 1.02 the stoichiometric amount and M (or M
and D) is present as about 1.00 the stoichiometric amount. In one embodiment, the ratio of each
of Li, P04 and M (or M and D) in the mixture, when expressed as a ratio of the stoichiometric
amount, is such that the input ratios are Li> P04> M, or Li is present as about 1.05 the
stoichiometric amount, P04 is present as about 1.02 the stoichiometric amount and M (or M and
D) is present as about 1.00 the stoichiometric amount.
[0017] In other embodiments, a ratio of (Li+P04):(M+D) relative to the stoichiometry required to
form the material is greater than 2.05, or even preferably in the range of from 2.07- 2.13.
[0018] In one embodiment, the present invention comprises a method for making lithium
metal phosphate of formula LiMP04, where M is one or more transition metals comprising the
steps of:
a) forming a mixture comprising water, a source of the one or more transition metals, a
source of phosphorus, a source of lithium and a surfactant, wherein the mixture formed in step
(a) comprises a slurry in which one or more of the source of one or more transition metals, the
source of phosphorus or the source of lithium is present as particulate material, and wherein the
mixture has an amount of Li greater than a stoichiometric amount, an amount of P04 greater than
a stoichiometric amount but less than the amount of Li, where Li and P04 quantities are stated
relative to the amount of M;
b) spray drying the mixture from step (a) to form particles or a powder; and
c) thermally treating the particles or powder from step (b) to form lithium metal
wo 2021/248181
phosphate.
5
PCT/AU2021/050572
[0019] In one embodiment, the mixture of step (a) comprises a solution and the step of
forming the solution comprises mixing a solvent or a reactant with water and particles of one or
more of the source of iron, the source of phosphorus or the source of lithium to thereby dissolve
the particles of one or more of the source of iron, the source of phosphorus or the source of
lithium. In one embodiment, one or more of the source of iron, the source of phosphorus source
of lithium is only sparingly soluble water. In one embodiment, the source of iron is only
sparingly soluble in water and the solvent or reactant dissolves or reacts with the source of iron
to thereby place iron into solution.
[0020] In one embodiment, the mixture formed in step (a) further includes oxalic acid and
the mixture of step (a) comprises a solution formed by mixing water and oxalic acid and the
source of iron with a solvent or reactant that dissolves or reacts with the oxalic acid and the
source of iron to thereby solubilise the oxalic acid and the source of iron, adding the source of
phosphorus and then adding the source of lithium to thereby form the solution. The surfactant
may then be added to the solution to form the mixture of step (a) in liquid form.
[0021] In one embodiment, the mixture of step (a) comprises water present in amount from
25% to 75% by weight of the total weight of the mixture.
[0022] In one embodiment, the surfactant is present in an amount of from 0.05% to 10% by
weight of the mixture, or from 1% to 4% by weight of the total mixture, or from about 1.4% to
2.8%.
[0023] In one embodiment, the source of one or more transition metals may comprise from
5% to 40% by weight of the mixture, or from 10% to 35% by weight of the mixture, or from
15% to 30% by weight of the mixture.
[0024] In one embodiment, the source of phosphorus is present in an amount of from 5% to
30% by weight of the mixture, or from 5% to 25% by weight of the mixture, or from 9% to 20%
by weight of the mixture.
[0025] In one embodiment, the source of lithium is present in an amount of from 2% to 21%
by weight of the mixture, or from 2% to 10% by weight of the mixture, or from 2.5% to 8% by
weight of the mixture, or from about 3% to 7% by weight of the mixture.
[0026] If Dis present, the source of D will typically be present in an amount commensurate
wo 2021/248181 PCT/AU2021/050572
6
with the requirements for the final composition of the material.
[0027] In embodiments where the mixture contains other ingredients, such as solvents
and/or other reactants or other materials, the other ingredients may be present in an amount of
from 15% to 35% by weight of the mixture, or from 17% to 30% by weight, or from 20% to 30%
by weight of the mixture.
[0028] In one embodiment, the mixture of step (a) comprises a solution that has had water,
iron (II) oxalate dihydrate, oxalic acid dihydrate, hydrogen peroxide, phosphoric acid and lithium
carbonate added to it, and the surfactant added.
[0029] In one embodiment, the mixture of step (a) comprises a slurry containing particulate
material. In one embodiment, the slurry comprises particles of iron (II) oxalate dihydrate,
phosphoric acid, lithium carbonate, water and surfactant. In one embodiment, phosphoric acid is
added to water and then lithium carbonate is added, which reacts/dissolves. Iron oxalate is then
added to form the slurry and the slurry is then subjected to milling. Surfactant is added during or
after milling. In one embodiment, the surfactant is added after milling. In another embodiment,
the slurry may be made by mixing particles of iron (II) oxalate dihydrate with water in a grinding
mill and milling, and adding lithium carbonate and phosphoric acid to the grinding mill to form a
slurry, and then mixing the slurry with the surfactant to form the mixture.
[0030] The surfactant may comprise a non-ionic surfactant, an anionic surfactant or a
cationic surfactant. In one embodiment, the surfactant comprises a non-ionic surfactant. In one
embodiment, the surfactant comprises an ethoxylate surfactant or an alkoxylate surfactant. In one
embodiment, the surfactant comprises an alcohol ethoxylate, or an ethoxylated lauryl alcohol
surfactant. Other surfactants that could be used include Polyoxyethylene(4)lauryl ether,
Octylphenol Ethoxylate and block copolymers based on ethylene/propylene oxide. Other
surfactants may also be used, such as lipids.
[0031] Step (b) of the present invention involves drying the mixture from step (a). In one
embodiment, step (b) comprises spray drying.
[0032] In one embodiment, the surfactant is added to form the mixture of step (a) in a tank
prior to the dryer or spray dryer.
[0033] The spray dryer may be any spray dryer known to be suitable to a person skilled in
the art. In one embodiment, the spray dryer comprises a rotating disk spray dryer or a disk
atomiser.
wo 2021/248181 PCT/AU2021/050572
7
[0034] In one embodiment, the inlet gas temperature to the dryer has a temperature of from
150 °C to 500 °C, or from 175 °C to 350°C, and the dryer outlet gas has a temperature of from 50
°C to 150 °C, or from 80 °C to 120 °C.
[0035] The spray drying step produces a dry, free-flowing powder at high product recovery.
The present inventors have found that including surfactant in the mixture that is spray dried in
step (b) is essential as tests conducted without the surfactant produced a moist powder having
poor product recovery due to accumulation of sticky powder in the drying chamber of the spray
dryer. The present inventors have also used polyethylene glycol instead of surfactant and these
tests produced unsatisfactory results.
[0036] In other embodiments, the dryer may comprise a fluidised bed dryer, a rotary dryer, a
rolling bed dryer, a conduction dryer, a convection dryer, a toroidal bed dryer, a vacuum dryer or
a dispersion dryer.
[0037] In some embodiments, the mixture of step (a) is dried in step (b) and the dried
product may need to be broken up into smaller particles or a powder, such as by milling or
vibrating.
[0038] The powder produced in step (b) is a precursor powder or precursor particulate
material. This precursor powder/particulate material is then thermally treated to produce particles
of the material. The material is represented by the formula LixMI-zDzP04, wherein x and z are as
stated above in this specification. The thermal treatment of step (c) is suitably conducted in an
oxygen free atmosphere, for example, in a nitrogen atmosphere or in an inert atmosphere. In
some embodiments, step (c) may comprise passing the powder/particulate material from step (b)
into an environment having a temperature of from 400 to 600°C, or from 450 to 500°C, or from
450 to 480°C. The powder/particulate material may be heated for sufficiently long to ensure
essentially complete conversion to the material. In some embodiments, the powder/particulate
material may be treated in a reactor or furnace for a period of from 5 minutes to 6 hours, or from
10 minutes to 3 hours, or from 20 minutes to 2 hours, or from 30 minutes to 1 hour, or for about
45 minutes.
[0039] In embodiments where one or more of the source of one or more transition metals,
the source of phosphorus or the source of lithium, or the source of D, if present, is present as
particulate material, the particulate material remains as particulate material after the drying or
spray drying step and the particulate material then takes part in the reaction(s) that form the
lithium metal phosphate.
wo 2021/248181 PCT/AU2021/050572
8
[0040] The raw powder of the material formed in step (c) may comprise particles that are
formed as agglomerates of crystallites. The crystallites may have a particle size in the range from
10 to 200nm, or from 20 to 1 OOnm.
[0041] Preliminary testing conducted by the inventors has shown that the crystallites which
form in step (c) may have a particle size distribution having a primary particle (or crystallite)
size in the range from 10 to 200nm, or from 20 to lOOnm and the agglomerates which form in
step (c) have a particle size distribution having dw of from 1-10 f.lm, dso of from 5-50 f.lm and dgo
of from 10-100 f.lm.
[0042] In one embodiment, the present invention provides a method for making a material
of formula LixMI-zDzP04, where M is one or more transition metals comprising the steps of:
a) forming a mixture comprising a source of the one or more transition metals, a source of
phosphorus, a source of lithium, optionally a source of D, and a surfactant, the mixture
comprising a slurry and one or more of the source of one or more transition metals, the source of
phosphorus or the source of lithium or the source of D, if present, is present as particulate
material, wherein (i) a ratio of Li:P04:(M+D) relative to the stoichiometry required to form the
material is within the range of 1.04-1.10:1.00-1.05:1, or (ii) a ratio of (Li+P04):(M+D) relative
to the stoichiometry required to form the material is greater than 2.05;
b) drying the mixture from step (a) to form a powder; and
c) thermally treating the powder from step (b) to form the material.

CLAIMS
1. A method for making a material of formula LixMI-zDzP04, where M is one or more transition
metals, D represents one or more elements selected from the group consisting of Mg, Ca, Sr,
Ba, Ti, Zn, B, Al, Ga, In, Si, Ge, Sc, Y, and rare earth elements, 0.8:Sx:Sl.2 and 0:Sz:S0.2, the
method comprising the steps of:
a) forming a mixture comprising a source of the one or more transition metals, a source
of phosphorus, a source of lithium and a surfactant, and optionally a source of D,
wherein (i) a ratio of Li:P04:(M+D) relative to the stoichiometry required to form the
material is within the range of 1.04-1.10:1.00-1.05:1, or (ii) a ratio of
(Li+P04):(M+D) relative to the stoichiometry required to form the material is greater
than 2.05;
b) drying the mixture from step (a) to form particles or a powder; and
c) thermally treating the particles or powder from step (b) to form the material.
2. A method as claimed in claim 1 wherein M is one or more transition metals selected from Fe,
Mn, Ni, Co, Cr or V, or M is Fe, or M comprises Fe and one or more of Mn, Ni, Co, Cr or V,
or M comprises two or more of Fe, Mn, Ni, Co, Cr or V.
3. A method as claimed in claim 1 or claim 2 wherein the process further comprises the steps
of:
d) mixing the material from step (c) with a liquid containing a carbon precursor,
e) spray drying the mixture from step (d) to form particles of the material coated with the
carbon precursor, and
f) converting the carbon precursor to carbon.
4. A method as claimed in any one of the preceding claim wherein the mixture formed in step
(a) includes a liquid.
5. A method as claimed in claim 4 wherein the liquid comprises water.
6. A method as claimed in any one of the preceding claim wherein the mixture formed in step
(a) comprises a solution in which the source of one or more transition metals, the source of
phosphorus and the source of lithium, and the source of D, if present, are dissolved.
7. A method as claimed in any one of claim 1 to 5 wherein the mixture formed in step (a)
wo 2021/248181 PCT/AU2021/050572
42
comprises a slurry in which one or more of the source of one or more transition metals, the
source of phosphorus or the source of lithium, or the source of D, if present, is present as
particulate material.
8. A method as claimed in claim 7 wherein the source of one or more transition metals is
present as particulate material.
9. A method as claimed in claim 7 or claim 8 wherein the particulate material or the slurry is
milled prior to drying.
10. A method as claimed in any one of the preceding claim wherein the source of one or more
transition metals comprises a source of one or more of Fe, Mn, Ni, Co, Cr or V.
11. A method as claimed in any one of the preceding claims wherein the source of one or more
transition metals comprises one or more compounds containing the transition metal(s).
12. A method as claimed in any one of the preceding claims wherein the source of one or more
transition metals comprises a source of iron or an iron containing compound.
13. A method as claimed in any one of the preceding claims wherein the source of phosphorus
comprises a phosphorus containing compound or a phosphorus containing acid, or
phosphoric acid, or lithium containing phosphates, or organic phosphates or other phosphate
containing compounds.
14. A method as claimed in any one of the preceding claims wherein the source oflithium
comprises one or more of lithium-containing carbonates, lithium-containing phosphates,
lithium-containing hydroxides, mineral lithium salts, organic mineral salts containing
lithium, or metallic lithium or other lithium containing compounds.
15. A method as claimed in any one of the preceding claims wherein the source of D may
comprise one or more water soluble compounds containing D or one or more water insoluble
compounds (including oxides) containing D, or mixtures thereof.
16. A method as claimed in any one of the preceding claims wherein the ratio of (Li+P04):(M
+D) relative to the stoichiometry required to form the material is in the range of from 2.07-
2.13.
17. A method as claimed in any one of the preceding claims wherein the mixture of step (a)
comprises water present in amount from 25% to 75% by weight of the total weight of the
wo 2021/248181 PCT/AU2021/050572
43
mixture.
18. A method as claimed in any one of the preceding claims wherein the surfactant is present in
an amount of from 0.05% to 10% by weight of the mixture, or from 1% to 4% by weight of
the total mixture, or from about 1.4% to 2.8%.
19. A method as claimed in any one of the preceding claims wherein the source of one or more
transition metals may comprise from 5% to 40% by weight of the mixture, or from 10% to
35% by weight of the mixture, or from 15% to 30% by weight of the mixture.
20. A method as claimed in any one of the preceding claims wherein the source of phosphorus is
present in an amount of from 5% to 30% by weight of the mixture, or from 5% to 25% by
weight of the mixture, or from 9% to 20% by weight of the mixture.
21. A method as claimed in any one of the preceding claims wherein the source of lithium is
present in an amount of from 2% to 21% by weight of the mixture, or from 2% to 10% by
weight of the mixture, or from 2.5% to 8% by weight of the mixture, or from about 3% to 7%
by weight of the mixture.
22. A method as claimed in any one of the preceding claims wherein the mixture contains other
ingredients, such as solvents and/or other reactants or other materials, the other ingredients
being present in an amount of from 15% to 35% by weight of the mixture, or from 17% to
30% by weight, or from 20% to 30% by weight of the mixture.
23. A method as claimed in claim 1 wherein the mixture of step (a) comprises a solution that has
had water, iron (II) oxalate dihydrate, oxalic acid dihydrate, hydrogen peroxide, phosphoric
acid and lithium carbonate added to it, and the surfactant added.
24. A method as claimed in claim 1 wherein the mixture of step (a) comprises a slurry containing
particulate material.
25. A method as claimed in any one of the preceding claims wherein the surfactant comprises a
non-ionic surfactant, an anionic surfactant or a cationic surfactant.
26. A method as claimed in any one of the preceding claims wherein step (b) comprises spray
drying.
27. A method as claimed in claim 26 wherein step (b) is conducted using a spray dryer and an
inlet gas temperature to the dryer has a temperature of from 150 °C to 500 °C, or from 175 °C
wo 2021/248181 PCT/AU2021/050572
44
to 350°C, and a dryer outlet gas has a temperature of from 50 °C to 150 °C, or from 80 °C to
120 °C.
28. A method as claimed in any one of the preceding claims wherein a powder produced in step
(b) is a precursor powder or precursor particulate material and the precursor powder or
precursor particulate material is thermally treated to produce particles of the material.
29. A method as claimed in claim 28 wherein the thermal treatment of step (c) is conducted in an
oxygen free atmosphere, or in a nitrogen atmosphere or in an inert atmosphere.
30. A method as claimed in any one of the preceding claims wherein step (c) comprises passing
the powder/particulate material from step (b) into an environment having a temperature of
from 400 to 600°C, or from 450 to 500°C, or from 450 to 480°C for a period of from 5
minutes to 6 hours, or from 10 minutes to 3 hours, or from 20 minutes to 2 hours, or from 30
minutes to 1 hour, or for about 45 minutes.
31. A method as claimed in any one of the preceding claims wherein the material formed in step
(c) comprises particles that are formed as agglomerates of crystallites and the crystallites
have a particle size in the range from 10 to 200nm, or from 20 to 1 OOnm.
32. A method as claimed in any one of the preceding claims wherein the material formed in step
(c) comprises particles that are formed as agglomerates of crystallites having a particle size
distribution having dw of from 1-10 f.lm, dso of from 5-50 f.lm and dgo of from 10-100 f.lm.
33. A method as claimed in any one of the preceding claims wherein the material produced in
step (c) is (d) mixed with a liquid containing a carbon precursor and (e) that mixture is then
spray dried to form particles of lithium metal phosphate coated with the carbon precursor,
following which (f) the particles are treated to convert the carbon precursor to carbon.
34. A method as claimed in claim 33 wherein step (d) comprises mixing the material from step
(c) with a liquid containing a carbon precursor.
35. A method as claimed in claim 34 wherein the liquid containing a carbon precursor contains a
solvent containing a dissolved carbon precursor, or the liquid containing a carbon precursor
comprises an aqueous solution containing a dissolved carbon precursor
36. A method as claimed in claim 33 or claim 34 wherein the material produced in step (c) is
milled in the liquid containing the carbon precursor in order to break up any large
agglomerates and densify the material, whilst also coating the particles of the material with
wo 2021/248181 PCT/AU2021/050572
45
the carbon precursor.
37. A method as claimed in claim 36 wherein the milling step takes place by milling a slurry
containing from 5 to 50% by weight solids, or from 10 to 30% by weight solids, or from 15
to 25% by weight solids, to reduce the particle size to a dso of from 200nm to 400nm, or from
250 to 350nm.
38. A method as claimed in any one of claims 33 to 37 wherein once the particles of the material
have been coated with the carbon precursor, it is then spray dried to form agglomerates
having a mean particle size of less than 10 f.lm, or from 2.5 f.lm to less than 10 f.lm, or from 5
to 8 f.lm, or from 6 to 7 f.lm and the particles or agglomerates formed in this step have a
particle size distribution in which dw is from 2 to 4 f.lm, dso is from 5 to 10 f.lm and dgo is
from 10 to 20 f.lm.
39. A method as claimed in any one of claims 33 to 38 wherein the carbon precursor coating on
the agglomerates is then converted to carbon in step (f) by drying and then heating under a
non-reactive or an inert atmosphere to carbonise the carbon precursor.
40. A method as claimed in claim 39 wherein the agglomerates are placed in a furnace operated
at a temperature of from 500°C to 1000°C, or from 600°C to 900°C, from 700° to 800°C, or
at about 750°C, and the agglomerates are held at the elevated temperature for a period of
from 30 minutes to 6 hours, or from 45 minutes to 5 hours, or from 1 hour to 4 hours, or from
1.5 hours to 3 hours, or for about 2 hours.