U.S. patent application number 15/026016 was filed with the patent office on 2016-08-18 for carbon coated electrochemically active powder.
The applicant listed for this patent is UMICORE. Invention is credited to DaeKwang Kim, KyungTae Lee, Jens PAULSEN, Xin XIA.
Application Number | 20160240856 15/026016 |
Document ID | / |
Family ID | 49303686 |
Filed Date | 2016-08-18 |
United States Patent
Application |
20160240856 |
Kind Code |
A1 |
PAULSEN; Jens ; et
al. |
August 18, 2016 |
Carbon Coated Electrochemically Active Powder
Abstract
The invention relates to an electrochemically active powder
comprising particles containing a compound represented by formula
A.sub.aM.sub.m(XO.sub.4).sub.n wherein A comprises an alkaline
metal; M comprises at least one transition metal and optionally at
least one non-transition metal; and X is chosen among S, P and Si;
wherein 0<a.ltoreq.3.2; 1.ltoreq.m.ltoreq.2; and
1.ltoreq.n.ltoreq.3; wherein said particles are at least partially
coated with a layer comprising a carbonaceous material, said
carbonaceous material comprising a highly ordered graphite, wherein
said highly ordered graphite has a ratio (I.sub.1360/I.sub.1580) of
a peak intensity (I.sub.1360) at 1360 cm.sup.-1 to a peak intensity
(I.sub.1360) at I.sub.1580 cm.sup.-1, obtained by Raman spectrum
analysis, of at most 3.05.
Inventors: |
PAULSEN; Jens; (Daejeon,
KR) ; XIA; Xin; (Cheonan, KR) ; Lee;
KyungTae; (Asan, KR) ; Kim; DaeKwang;
(Cheonan, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
UMICORE |
Brussels |
|
BE |
|
|
Family ID: |
49303686 |
Appl. No.: |
15/026016 |
Filed: |
September 17, 2014 |
PCT Filed: |
September 17, 2014 |
PCT NO: |
PCT/EP2014/069746 |
371 Date: |
March 30, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 10/052 20130101;
H01M 10/0525 20130101; H01M 4/625 20130101; Y02E 60/10 20130101;
H01M 4/1397 20130101; H01M 4/136 20130101; H01M 4/0471 20130101;
H01M 4/366 20130101; H01M 2004/028 20130101; H01M 4/5825
20130101 |
International
Class: |
H01M 4/62 20060101
H01M004/62; H01M 10/0525 20060101 H01M010/0525; H01M 4/1397
20060101 H01M004/1397; H01M 4/04 20060101 H01M004/04; H01M 4/58
20060101 H01M004/58; H01M 4/136 20060101 H01M004/136 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 2, 2013 |
EP |
13004760.8 |
Claims
1-17. (canceled)
18. An electrochemically active powder comprising particles which
contain a core which is provided with a coating layer, whereby the
core contains a compound represented by formula
Li.sub.aM.sub.m(XO.sub.4).sub.n wherein M comprises at least one
transition metal and optionally at least one non-transition metal;
and X is selected from the group consisting of S, P and Si; wherein
0<a.ltoreq.3.2; 1.ltoreq.m.ltoreq.2; and 1.ltoreq.n.ltoreq.3;
wherein said particles are at least partially coated by said
coating layer and whereby the coating layer comprises a
carbonaceous material, said carbonaceous material comprising a
highly ordered graphite, wherein said highly ordered graphite has a
ratio (I.sub.1360/I.sub.1580) of a peak intensity (I.sub.1360) at
1360 cm.sup.-1 to a peak intensity (I.sub.1580) at 1580 cm.sup.-1,
obtained by Raman spectrum analysis, of at least 1.5 and at most
3.05.
19. The powder of claim 18, wherein X is P.
20. The powder of claim 18, wherein M comprises a transition metal
comprising iron, manganese, vanadium, titanium, molybdenum,
niobium, tungsten, zinc and mixtures thereof.
21. The powder of claim 18, wherein the compound is characterized
by the formula LiMPO.sub.4, and where M comprises a metallic cation
belonging to the first line of transition metals.
22. The powder of claim 18, wherein the compound is characterized
by the formula Li.sub.aM.sub.1-yM'.sub.y(XO.sub.4).sub.n, in which
0.ltoreq.a.ltoreq.2; 0.ltoreq.y.ltoreq.0.6 and
1.ltoreq.n.ltoreq.1.5, wherein M comprises a transition metal or a
mixture of transition metals from the first line of the periodic
table; M' comprises an element with fixed valence selected from the
group consisting of Mg.sup.2+, Ca.sup.2+, Al.sup.3+, Zn.sup.2+ and
a combination of these same elements.
23. The powder of claim 18, wherein the compound is characterized
by the formula Li.sub.a(M,M')PO.sub.4, wherein 0.ltoreq.a.ltoreq.1,
M comprises one or more cations selected from the group consisting
of Mn, Fe, Co, Ni, and Cu, and M' comprises an optional
substitutional cation selected from the group consisting of Na, Mg,
Ca, Ti, Zr, V, Nb, Cr, Zn, B, Al, Ga, Ge, and Sn.
24. The powder of claim 18, wherein the compound is characterized
by the formula Li.sub.uM.sub.v(XO.sub.4).sub.w with u=1, 2 or 3;
v=1 or 2; w=1 or 3; M has a formula
Ti.sub.aV.sub.bCr.sub.cMn.sub.dFe.sub.eCo.sub.fNi.sub.gSc.sub.hNb.sub.i
with a+b+c+d+e+f+g+h+i=1 and X is P.sub.x-1S.sub.x with
0.ltoreq.x.ltoreq.1.
25. The powder of claim 18, wherein the compound is characterized
by the formula Li.sub.1+xM.sub.m(XO.sub.4).sub.n, wherein
0<x.ltoreq.0.2; m=1; and 1.ltoreq.n.ltoreq.1.05; and M comprises
a transition metal selected from the group consisting of iron,
manganese, vanadium, titanium, molybdenum, niobium, tungsten, zinc
and mixtures thereof.
26. The powder of claim 18, wherein I.sub.1360/I.sub.1580 is at
most 2.10.
27. The powder of claim 18, wherein the layer comprising the
carbonaceous material has a thickness of at least 2 nm.
28. The powder of claim 18, wherein said
Li.sub.aM.sub.m(XO.sub.4).sub.n has a crystal size, measured by
Rietveld refinement of XRD data, of at most 90 nm.
29. An electrochemically active powder comprising particles
containing a compound represented by formula Li.sub.1+xFePO.sub.4
wherein x is at least 0.01, said particles being at least partially
coated with a layer comprising a carbonaceous material and having a
thickness of at least 3 nm, said carbonaceous material comprising a
highly ordered graphite, wherein said highly ordered graphite has a
ratio (I.sub.1360/I.sub.1580) of a peak intensity (I.sub.1360) at
1360 cm.sup.-1 to a peak intensity (I.sub.1580) at 1580 cm.sup.-1,
obtained by Raman spectrum, of at most 3.00.
30. An electrode material comprising a composition containing the
electrochemically active powder of claim 18, and a binder.
31. An electrochemical cell containing at least two electrodes and
at least one electrolyte, wherein at least one of the electrodes is
the electrode of claim 30.
32. A battery and devices containing thereof, wherein said battery
contains at least one of the electrochemical cells of claim 31, and
wherein said devices are chosen from the group consisting of
portable electronic devices, portable computers, tablets, mobile
phones, electrically powered vehicles and energy storage
systems.
33. A method for making a carbon coated electrochemically active
powder, said powder comprising particles containing a compound
represented by formula Li.sub.aM.sub.m(XO.sub.4).sub.n wherein
0<a.ltoreq.3.2; 1.ltoreq.m.ltoreq.2; and 1.ltoreq.n.ltoreq.3; M
comprises at least one transition metal and optionally at least one
non-transition metal; and X is selected from the group consisting
of S, P and Si; said method comprising: i. providing a mixture of
the following precursors a. a source of Li; b. a source of an
element M; c. a source of an element X; and d. a source of carbon;
wherein the sources of elements A, M and X are introduced in whole
or in part in the form of compounds having the at least one source
element; ii. heating up said mixture in a sintering chamber to a
sintering temperature of at least 500.degree. C. and sintering said
mixture at said sintering temperature for a first period of time,
wherein a stream of inert gas is provided to said chamber; iii.
continuously injecting steam in said sintering chamber before or
during the heating up, and before or during the sintering the
mixture, for an injection time; thereby producing particles
containing said compound wherein the particles are at least
partially coated with a carbonaceous material containing a highly
graphitized carbon; and iv. cooling said powder.
34. A method according to claim 33, wherein X is P.
Description
[0001] The invention relates to an electrochemically active powder
comprising carbon-coated particles, said particles containing an
electrochemically active compound, the compound preferably having
an olivine or NASICON structure. The invention also relates to a
process for manufacturing said powder and to various products
containing said powder. In particular the invention relates to a
positive electrode comprising said powder and to a battery, in
particular lithium-ion battery, containing said electrode.
[0002] An electrochemically active powder is for instance known
from US 2009/0148771 A1 wherein a lithium (Li)-based powder is
disclosed. Said powder comprises lithium phosphate based particles,
which are known for their electrochemical activity. In particular,
said publication discloses a particulate LiM.sub.xPO.sub.4 compound
with M being among others manganese, iron, nickel and magnesium;
with 0.ltoreq.X.ltoreq.1; and having a mean particle diameter of
between 50 nm and 500 nm. Said particulate compound is used as
active material in a cathode, wherein it is mixed with a carbon
material, e.g. graphite, and with a binder.
[0003] A known limitation of the known electrochemically active
powders, e.g. powders based on lithium phosphates such as
LiFePO.sub.4, is their low conductivity, which in turn may restrict
a broad application thereof. In particular lithium-ion
battery-driven electrical devices requiring a high rate performance
of their battery may not perform up to the required intended use.
In order to improve the conductivity and achieve better
electrochemical performance of such materials, many approaches have
been applied, e.g. addition of carbon, carbon coating, metal
doping, particle size control, etc.
[0004] For example, US 2009/0148771 A1 discloses that the addition
of a particulate carbon material to a LiFePO.sub.4 powder improves
the performance of a positive battery electrode containing thereof.
Said publication further demonstrates that when said carbon
material contains an increased amount of graphite, better results
were achieved. To quantify the amount of graphite in the
particulate carbon material, the inventors in US 2009/0148771 A1
used a ratio (I.sub.1360/I.sub.1580) of a peak intensity
(I.sub.1360) at 1,360 cm.sup.-1 to a peak intensity (I.sub.1580) at
1,580 cm.sup.-1 obtained by Raman spectrum analysis. As explained
therein, the peak intensity I.sub.1580 is attributed to the
graphitized carbon, whereas the peak intensity I.sub.1360 is
attributed to the disordered carbon and for ratios as low as 0.25,
a very good performance was achieved.
[0005] However, another optimal way to improve the conductivity of
known electrochemically active powders and in particular of those
powders based on lithium phosphates such as LiFePO.sub.4, is to
cover the particles of the powders with a carbon coating.
[0006] Carbon coating is one of the most important techniques used
to improve the powders' performance, in particular their
conductivity, specific capacity, rate performance and cycling life.
Various research programs showed that an effective carbon coating
not only enhances the surface electronic conductivity of
particulate electrochemically active materials such as lithium
phosphates but it may also improve or simplify the preparation
thereof. For instance, carbon coated LiFePO.sub.4 can be readily
prepared by milling LiFePO.sub.4 particles with carbon powders or
by in situ carbonization of organic precursors previously deposited
on the surface of said LiFePO.sub.4 particles.
[0007] However, the structure of the carbon coating applied to
electrochemically active particulate materials such as the above
mentioned LiFePO.sub.4 particles, may significantly affect the
electrochemical performance thereof. Carbon coatings prepared at
high temperature (>800.degree. C.) have much higher electronic
conductivity than those prepared at lower temperatures
(<600.degree. C.). Supposedly, the cause of these benefices was
the increased graphitization of the carbon coating, i.e. the
presence of an increased amount of graphitized carbon in the
coating to the expense of non-graphitized carbon, e.g. disordered
carbon. The extent of graphitized carbon in a carbon based material
and its ratio to the disordered carbon can be characterized as
shown by US 2009/0148771 A1 by an ID/IG (disordered/graphite) peak
intensity ratio as determined by Raman spectroscopy. The lower the
ID/IG ratio, the higher the amount of graphitized carbon.
[0008] As a consequence of such insights, various attempts were
made to coat electrochemically active particulate materials such as
lithium phosphate based particles with graphitized carbon.
Methodologies such as a) coating particles with organic precursors
and using increased sintering temperatures (>800.degree. C.) to
carbonize said precursors; b) combining particles with materials
having an increased amount of graphitized carbon source, e.g.
carbon nanotubes, graphene, carbon nano-fibers; or c) using various
catalysts, e.g. ferrocene, during sintering to achieve a higher
graphitization of the carbon; were applied in attempts to enhance
the properties of the electrochemically active particulate
materials.
[0009] However, all the above enumerated approaches have
disadvantages and none succeeded in achieving an optimal product.
For instances, higher sintering temperatures not only that could
result in particle agglomeration of the electrochemically active
particulate materials such as lithium phosphate based particles but
usually lead to an oxidation of said materials which in turn may
strongly decrease their electrochemical activity. In other words,
although obtaining particles coated with an acceptably graphitized
carbon layer, during the sintering process, the electrochemically
activity of the obtained powders is reduced below an acceptable
level.
[0010] On the other hand, by reducing the sintering temperatures in
an attempt to avoid its deleterious effects on the electrochemical
activity of the active particulate materials, dissatisfactory
carbon layers with insufficient amounts of graphitized carbon are
achieved.
[0011] It may thus be an aim of the present invention to provide an
electrochemically active particulate material such as particles
containing a lithium phosphate based material, having acceptable
electrochemical properties and being coated with a highly
graphitized carbon layer. A further aim of the present invention is
to provide an electrode containing a carbon-coated
electrochemically active particulate material, said coating
comprising a high amount of graphitized carbon, said electrode
providing a battery containing thereof with optimal properties.
[0012] The invention provides an electrochemically active powder
comprising particles containing a compound represented by formula
A.sub.aM.sub.m(XO.sub.4).sub.n wherein A comprises an alkaline
metal; M comprises at least one transition metal and optionally at
least one non-transition metal; and X is chosen among S, P and Si;
wherein 0.ltoreq.a.ltoreq.3.2; 1.ltoreq.m.ltoreq.2; and
1.ltoreq.n.ltoreq.3; wherein said particles are at least partially
coated with a layer comprising a carbonaceous material, said
carbonaceous material comprising a highly ordered graphite, wherein
said highly ordered graphite has a ratio (I.sub.1360/I.sub.1580) of
a peak intensity (I.sub.1360) at 1360 cm.sup.-1 to a peak intensity
(I.sub.1580) at 1580 cm.sup.-1, obtained by Raman spectrum
analysis, of at most 3.05.
[0013] Hereinafter the figures are explained:
[0014] FIG. 1 shows the apparatus used to manufacture the powder of
the invention.
[0015] FIG. 2 shows a temperature profile, i.e. temperature vs.
time, used in a process to manufacture the powder of the
invention.
[0016] FIG. 3 shows pictographs of representative particles of the
powder of the invention and those of powders used for
comparison.
[0017] The present inventors surprisingly observed that the coating
layer of carbonaceous material contained by the active powders of
the invention had a high degree of graphitization and showed an
increased uniformity. These advantageous properties may lead to an
enhanced surface electronic conductivity of the active powders and
to electrodes containing thereof having optimal specific
capacities, enhanced rate performance and cycling life. Additional
benefits of having an optimized coating may be reduced polarization
effects during charge and discharge and high stability of the
active powder during charge and discharge.
[0018] In particular the present inventors obtained a
highly-graphitized and uniform carbon layer on the surface of
lithium iron phosphate particles without the need of an expensive
and complicated process. The process used to manufacture such
powders, utilized relatively low sintering temperature
(<800.degree. C.) and relatively short sintering times
(.ltoreq.2 h). The carbon layer seems to provide the lithium iron
phosphate with effective discharge capacity and rate
capability.
[0019] In the compound used as active materials according to the
present invention, preferably A is Li, Na or K. Preferably, M is a
transition metal comprising iron, manganese, vanadium, titanium,
molybdenum, niobium, tungsten, zinc and mixtures thereof, said
transition metals being preferably in the following oxidation
states: Fe.sup.2+, Mn.sup.2+, V.sup.2+, V.sup.3+, Cr.sup.3+,
Ti.sup.2+, Ti.sup.3+, Mo.sup.3+, Mo.sup.4+, Nb.sup.2+, Nb.sup.4+
and W.sup.4+. Preferably, the non-transition metal comprises
magnesium and aluminum.
[0020] In a first embodiment, the compound used in accordance with
the invention has the formula LiMPO.sub.4, said with compound
preferably having an olivine structure, where M is a metallic
cation belonging to the first line of transition metals, preferably
being selected from the group consisting of Mn, Fe, Co, and Ni.
Such compounds can be synthesized by using the precursors disclosed
for example by U.S. Pat. No. 5,910,382 included herein by
reference. Preferably, M is a combination of cations, at least one
of which is selected from the group consisting of Mn, Fe, Co and
Ni. More preferably M is Fe.sub.1-xMn.sub.x or Fe.sub.1-xTi.sub.x
with 0<x<1. Most preferably M is Fe.
[0021] In a second embodiment, the compound used in accordance with
the invention has the formula
Li.sub.xM.sub.1-yM'.sub.y(XO.sub.4).sub.n, in which
0.ltoreq.X.ltoreq.2; 0.ltoreq.y.ltoreq.0.6 and
1.ltoreq.n.ltoreq.1.5, wherein M is a transition metal or a mixture
of transition metals from the first line of the periodic table; M'
is an element with fixed valence selected among Mg.sup.2+,
Ca.sup.2+, Al.sup.3+, Zn.sup.2+ or a combination of these same
elements; and X is chosen from among S, P and Si, with P being
preferred. Such compounds can be synthesized by using the
precursors disclosed for example by US 2004/0033360 A1 included
herein by reference.
[0022] In a third embodiment of the invention, the compound has the
formula Li.sub.x(M,M')PO.sub.4, wherein 0.ltoreq.x.ltoreq.1, M is
one or more cations selected from the group consisting of Mn, Fe,
Co, Ni, and Cu, and M' is an optional substitutional cation
selected from the group consisting of Na, Mg, Ca, Ti, Zr, V, Nb,
Cr, Zn, B, Al, Ga, Ge, and Sn.
[0023] In a fourth preferred embodiment of the invention, the
compound has the formula Li.sub.uM.sub.v(XO.sub.4).sub.w with u=1,
2 or 3; v=1 or 2; w=1 or 3; M has a formula
Ti.sub.aV.sub.bCr.sub.cMn.sub.dFe.sub.eCo.sub.fNi.sub.gSc.sub.hNb.sub.i
with a+b+c+d+e+f+g+h+i=1 and X is P.sub.x-1S.sub.x with
0.ltoreq.x.ltoreq.1.
[0024] In a preferred embodiment, the compound is a Li-rich
compound represented by formula Li.sub.1+xM.sub.m(XO.sub.4).sub.n,
wherein 0<x.ltoreq.0.2; 0.ltoreq.m.ltoreq.1; and
1.ltoreq.n.ltoreq.1.05. Preferably 0<x.ltoreq.0.2;
0.ltoreq.m.ltoreq.1; and n=1. Preferably, M is a transition metal,
more preferably a transition metal chosen from the group consisting
of iron, manganese, vanadium, titanium, molybdenum, niobium,
tungsten, zinc and mixtures thereof. Alternatively M has the
formula M=Fe.sub.1-mM'.sub.m, with 0.ltoreq.m.ltoreq.0.025, wherein
M' is either one or more elements chosen from the group consisting
of alkaline earth metals and non-metals. Preferably M' is chosen
from the group consisting of Mg, Ca, Sr, Ba, and B. Most
preferably, M' is Mg or B. Preferably, X is chosen from among S, P
and Si, with P being preferred. The Li content of the compound of
this embodiment is non-stoichiometrically controlled meaning that
the molar ratio Li/M is more than 1.00 and in particular for
powders having a NASICON structure, preferably more than 1.5.
[0025] Preferably, the particles forming the inventive powder have
a mean diameter of at least 50 nm, more preferably at least 80 nm,
most preferably at least 150 nm. Preferably, said mean diameter is
at most 600 nm, more preferably at most 400 nm, most preferably at
most at most 200 nm. The mean particle diameter of said particles
is calculated from the mean value of measured longest diameters on
observed images obtained, e.g., from a scanning electron microscope
(SEM).
[0026] Preferably, the particles forming the inventive powder have
a particle size distribution with an average particle size d50 of
less than 500 nm, more preferably less than 200 nm; and preferably
of more than 30 nm. The particle size distribution is preferably
mono-modal. Preferably, the inventive powder is characterized by a
ratio (d90-d10)/d50 of at most 1.5, more preferably of at most 1.3,
most preferably at most 1.1.
[0027] In accordance to the invention, the particles forming the
powder of the invention are coated with a layer comprising a
carbonaceous material containing a highly ordered graphite. By
carbonaceous material is herein understood a material rich in
carbon, e.g. containing carbon in an amount based on the total
amount of carbonaceous material of from 60 to 100% molar, and
preferably having an electronic conductivity higher than 10.sup.-6
S/cm at room temperature, preferably higher than 10.sup.-4 S/cm.
Other elements that can be present in the carbonaceous material are
hydrogen, oxygen, nitrogen, as long as they do not interfere with
the chemical inertia of the carbon during the electrochemical
operation. By highly ordered graphite is herein understood a
graphite having a ratio (I.sub.1360/I.sub.1580) of a peak intensity
(I.sub.1360) at 1360 cm.sup.-1 to a peak intensity (I.sub.1580) at
1580 cm.sup.-1, obtained by Raman spectrum analysis, of at most 3.0
5. Preferably, the ratio I.sub.1360/I.sub.1580 is at most 2.80,
more preferably at most 2.60, even more preferably at most 2.40,
yet even more preferably at most 2.20, most preferably at most
2.10. Preferably, the ratio I.sub.1360/I.sub.1580 is at least 1.5,
more preferably at least 1.8, most preferably at least 2.0.
Preferably, the amount of highly ordered graphite contained by said
carbonaceous material is at least 22 wt % based on the total
content of carbonaceous material, more preferably at least 28 wt %,
most preferably at least 30 wt %. In a preferred embodiment, the
carbonaceous material essentially consists of highly ordered
graphite.
[0028] Preferably, said Li.sub.aM.sub.m(XO.sub.4).sub.n has a
crystal size of at most 90 nm and preferably at most 85 nm. This is
determined by Rietveld refinement of XRD data.
[0029] Thanks to the relatively low sintering temperatures and
periods used in the disclosed method, a small crystal size combined
with a relatively high degree of graphitization can be obtained,
whereas in prior art methods the crystal size will grow to around
100 nm or even above if a sintering temperature and period allowing
sufficient graphitization is chosen.
[0030] The layer comprising the carbonaceous material preferably
has a thickness of at least 2 nm, more preferably at least 5 nm,
most preferably at least 8 nm. Preferably, said layer has a
thickness of at most 20 nm, more preferably at most 15 nm, most
preferably at most 12 nm. Preferably, said layer has a thickness of
between 2 nm and 20 nm, more preferably of between 5 nm and 15 nm,
most preferably of between 8 nm and 12 nm. The thickness of said
layer can be determined using Transmission Electron Microscopy.
[0031] Preferably, the particles forming the powder of the
invention have a BET of at most 25 g/m.sup.2, more preferably at
most 20 g/m.sup.2, most preferably at most 18 g/m.sup.2.
Preferably, said BET is at least 10 g/m.sup.2, more preferably at
least 12 g/m.sup.2, most preferably at least 15 g/m.sup.2.
[0032] In a preferred embodiment, the invention relates to a carbon
coated powder comprising particles containing a compound
represented by formula Li.sub.1+xFePO.sub.4 wherein x is at least
0.01, more preferably x is at least 0.03, most preferably x is at
least 0.06; wherein said particles are at least partially coated
with a layer comprising a carbonaceous material; wherein said layer
has a thickness of at least 3 nm, more preferably at least 6 nm,
even more preferably at least 9 nm; wherein said carbonaceous
material comprises a highly ordered graphite, wherein said highly
ordered graphite has a ratio (I.sub.1360/I.sub.1580) of a peak
intensity (I.sub.1360) at 1360 cm.sup.-1 to a peak intensity
(11580) at 1580 cm.sup.-1, obtained by Raman spectrum, of at least
1.50 and at most 3.00, more preferably of between 1.80 and 2.40,
most preferably between 1.90 and 2.10. Most preferably said
carbonaceous material essentially consists of said highly ordered
graphite. Most preferably the thickness of said layer is between 8
nm and 12 nm.
[0033] The invention also relates to a composition comprising the
carbon-coated electrochemically active powder of the invention and
preferably a binder, said composition being preferably used as an
electrode material. Therefore, the invention also relates to an
electrode material comprising the composition of the invention. The
composition may further comprise a conductive agent, which is
preferably fibrous carbon. The binder is preferably a material
chosen from the group consisting of polyethers, polyesters,
polymers based on methyl methacrylate units, acrylonitrile-based
polymers, vinylidene fluorides and mixtures thereof. The invention
further relates to an electrode comprising the electrode material
of the invention.
[0034] The invention also relates to an electrochemical cell
containing at least two electrodes and at least one electrolyte,
wherein at least one of the electrodes, preferably the positive
electrode, is the electrode of the invention. Examples of cells may
include cylindrical cells and prismatic cells. Preferably, the
electrolyte is a polar liquid containing one or more metallic salts
in solution or a polymer, solvating or not, optionally plasticized
or gelled by said polar liquid. The electrolyte can also be a polar
liquid immobilized in a microporous separator, such as a
polyolefin, a polyester, nanoparticles of silica, alumina or
lithium aluminate LiAlO.sub.2. Examples of polar liquids include
cyclic or linear carbonates, alkyl formiates, oligoethylene
glycols, alkylethers, N-methylpyrolidinone, y-butyrolactone,
tetraalakylsulfamides and mixtures thereof.
[0035] The invention further relates to a battery containing at
least one of the electrochemical cells of the invention and to
various devices containing said batteries. Examples of devices may
be portable electronic devices, e.g. portable computers, tablets,
mobile phones; electrically powered vehicles; and energy storage
systems.
[0036] The invention also relates to a method for making a carbon
coated electrochemically active powder, said powder comprising
particles containing a compound represented by formula
A.sub.aM.sub.m(XO.sub.4).sub.n wherein 0<a.ltoreq.3.2;
1.ltoreq.m.ltoreq.2; and 1.ltoreq.n.ltoreq.3; A comprises an
alkaline metal; M comprises at least one transition metal and
optionally at least one non-transition metal; and X is chosen among
S, P and Si; preferably said powder being the inventive powder,
said method comprising the steps of: [0037] i. providing a mixture
of the following precursors: [0038] a. a source of an element A;
[0039] b. a source of an element M; [0040] c. a source of an
element X; and [0041] d. a source of carbon; [0042] wherein the
sources of elements A, M and X are introduced in whole or in part
in the form of compounds having the at least one source element;
[0043] ii. heating up said mixture in a sintering chamber to a
sintering temperature of at least 500.degree. C. and sintering said
mixture at said sintering temperature for a first period of time,
wherein a stream of inert gas is provided to said chamber; [0044]
iii. continuously injecting steam in said sintering chamber before,
during and/or after said heating up and/or said sintering of said
mixture, for an injection time; thereby producing particles
containing said compound wherein the particles are at least
partially coated with a carbonaceous material containing a highly
graphitized carbon; and [0045] iv. cooling said powder to
preferably room temperature.
[0046] The invention also relates to an apparatus for carrying out
the inventive method. With reference to FIG. 1, the inventive
apparatus (100) contains a furnace (101) having a sintering chamber
(102); an inlet (103) to introduce an inert gas in said sintering
chamber; a steam source (104) used to produce steam and means (105)
to transport the steam and inject it into the sintering chamber
(102). The furnace can also comprise an outlet (106) used to
evacuate the steam in excess.
[0047] In accordance with the invention, the sources of the
elements utilized therein are mixed together and said mixture is
subjected to further processing. Although it is also possible to
combine step i. with step ii. of the inventive method, e.g. mixing
said sources of elements during heating up, it is preferred that
said sources of elements are mixed before the commencing of step
ii. The mixture obtained at step i. of the inventive method is
preferably a homogeneous mixture, i.e. a mixture having an
essentially uniform composition throughout. Homogeneous mixtures
can be obtained for example by mixing said sources of elements in a
ball mill, or by using horizontal or vertical attritors,
rotor-stator machines, high-energy mills, planetary kneaders,
shaking apparatuses or shaking tables, ultrasonic apparatuses or
high shear mixers or combinations of the abovementioned
apparatuses. To achieve homogeneous mixtures, preferably the
precursors are in the form of powders, preferably having a
sub-micron size distribution, more preferably having a sub-micron
d50 size distribution.
[0048] In a preferred embodiment of the inventive method, A is
lithium and the source of lithium is preferably a compound selected
from the group consisting of lithium oxide, lithium hydroxide,
lithium carbonate, neutral phosphate Li.sub.3PO.sub.4, acid
phosphate LiH.sub.2PO.sub.4, lithium orthosilicates, lithium
metasilicates, lithium polysilicates, lithium sulfate, lithium
oxalate, lithium acetate, and mixtures thereof.
[0049] Preferably, the source of M is a compound comprising a
transition metal or mixture of transition metals selected from the
group consisting of iron, manganese, cobalt, nickel, vanadium,
titanium, chromium, and copper. In a preferred embodiment, the
source of M is a compound selected from the group consisting of
iron (III) oxide, magnetite, manganese dioxide, di-vanadimn
pentoxide, trivalent iron phosphate, trivalent iron nitrate,
trivalent iron sulfate, iron hydroxyphosphate, lithium
hydroxyphosphate, trivalent iron sulfate, trivalent iron nitrate,
and mixtures thereof. Preferably, the source of M is a mixture of
an iron-containing precursor and an M'-containing precursor.
Examples of suitable iron containing precursors include iron (II)
phosphate, iron (II) oxalate and iron (II) oxide. Examples of
suitable M'-containing precursors include at least one compound
containing Mg and B such as an oxide, hydroxide or organic
complex.
[0050] Preferably, the source of X is selected from the group
consisting of sulfuric acid, lithium sulfate, phosphoric acid,
phosphoric acid esters, neutral phosphate Li.sub.3PO.sub.4, acid
phosphate LiH.sub.2PO.sub.4, monoanunonium phosphate, diarmnonium
phosphate, trivalent iron phosphate, manganese and ammonium
phosphate (NH.sub.4MnPO.sub.4), silica, lithium silicates,
alkoxysilanes and partial hydrolysis products thereof, and mixtures
thereof. In a preferred embodiment, the source of X is a metal
sulfate, e.g. trivalent iron phosphate.
[0051] It is also possible in accordance with the invention that
the source of M is also the source of X, the source of A is also
the source of X; or when A is lithium, the source of lithium is
also the source of X, or the source of X is also the source of
lithium.
[0052] Preferably, the source of carbon is an organic precursor
material or a combination of organic precursor materials. In
general, any organic precursor material or combination of organic
precursor materials leading to the carbonaceous material with the
desired property is suitable for utilization in accordance with the
present invention. Preferably, said precursors do not affect the
stability of the particulate material.
[0053] Preferred precursors that can be suitably utilized as the
carbon source in accordance with the invention include, but are not
limited to: hydrocarbons and their derivatives, especially those
comprising polycyclic aromatic moieties, like pitch and tar
derivatives, perylene and its derivatives; polyhydric compounds
like sugars and carbon hydrates and their derivatives; and
polymers. Preferred examples of such polymers include polyolefins,
polybutadienes, polyvinylic alcohol, phenol condensation products,
including those from a reaction with an aldehyde, polymers derived
from furfurylic alcohol, polymers derivatives of styrene,
divinylbenzene, naphtalene, perylene, acrylonitrile, vinyl acetate;
cellulose, starch and their esters and ethers, and mixtures
thereof.
[0054] Further sources of carbon that can be used in accordance
with the invention are compounds of formula CY--CY wherein Y
represents a halogen or a pseudo-halogen. The term pseudo-halogen
means an organic or inorganic radical susceptible of existing in
the form of an ion Y.sup.- and which can form a corresponding
protonated compound HY. Examples of halogen and pseudo-halogen
include F, Cl, Br, I, CN, SCN, CNO, OH, N.sub.3, RCO.sub.2,
RSO.sub.3 wherein R is H or an organic radical. The formation by
reduction of CY bonds is preferably performed in the presence of
reducing elements such as hydrogen, zinc, magnesium, Ti.sup.3+
ions, T.sup.2+ ions, Sm.sup.2+ ions, Cr.sup.2+ ions, V.sup.2+ ions,
tetrakis(dialkylamino ethylene) or phosphines. These reagents can
eventually be obtained or regenerated electrochemically. Further,
It can also be advantageous to use catalysts increasing the
reduction kinetic. Palladium or nickel derivatives are particularly
efficient, particularly in the form of complexes with phosphorous
or nitrogen compounds like 2,2'-bipyridine. Similarly, these
compounds can be generated chemically in an active form in the
presence of reducing agents, such as those mentioned above, or
electrochemically. The carbonaceous material is in such instance
produced by reducing the carbon-halogen bonds according to the
equation:
CY--CY+2e.sup.-.fwdarw.--C.dbd.C--+2Y.sup.-
Compounds susceptible of generating carbon by reduction include
perhalocarbons, particularly in the form of polymers,
hexachlorobutadiene and hexachlorocyclopentadiene.
[0055] Another way to obtain a carbonaceous material comprises the
elimination of the hydrogenated compound HY, Y being as defined
above, according to the equation:
--CH--CY--+B.sup.-.fwdarw.--C.dbd.C--+BHY.sup.-
[0056] Compounds susceptible of generating carbon from reduction
include organic compounds comprising an even number of hydrogen
atoms and Y groups, such as hydrohalocarbons, in particular in the
form of polymers, such as vinylidene polyfluoride, polychloride or
polybromide, or carbon hydrates. The dehydro (pseudo) halogenation
can be obtained at low temperature, including room temperature, by
reacting a base with the HY compound to form a salt. Example of
suitable bases include tertiary basis, amines, amidines,
guanidines, imidazoles, inorganic bases such as alkaline
hydroxides, organometallic compounds behaving like strong bases,
such as A(N(Si(CH.sub.3).sub.3).sub.2,
LiN[CH(CH.sub.3).sub.2].sub.2, and butyl-lithium.
[0057] In a preferred embodiment, the following compounds are used
as sources to prepare a carbon-coated lithium-rich lithium iron
phosphate Li.sub.1+xFePO.sub.4 with 0<x.ltoreq.0.2:
Li.sub.3PO.sub.4 as the source for Li and P,
Fe.sub.3(PO.sub.4).sub.2.8H.sub.2O as the source for Fe and P, and
cellulose for carbon, wherein the Li: Fe molar ratio was 1.06:1 and
the weight ratio of carbon source was 5.85 wt % (defined as
m.sub.Cellulose/m.sub.Li3PO4+m.sub.Fe3(PO4)2.8H2O).
[0058] For convenience, the sources of the elements utilized in
accordance with the present invention are hereinafter called
precursors.
[0059] In accordance to the invention and with reference to FIG. 2
showing the temperature (201) profile in time (202), the mixture of
precursors, i.e. the mixture containing the sources of the elements
utilized in the present invention, is heated up with a heating rate
(203) to a temperature (204) where the sintering of the mixture
takes place. Said temperature which is herein referred to as the
sintering temperature is preferably at least 500.degree. C., more
preferably at least 550.degree. C., most preferably at least
600.degree. C. Preferably, the sintering temperature is at most
800.degree. C., more preferably at most 750.degree. C., most
preferably at most 700.degree. C. Preferably, the sintering
temperature is between 500.degree. C. and 800.degree. C., more
preferably between 550.degree. C. and 750.degree. C., most
preferably between 600.degree. C. and 700.degree. C. The sintering
temperature can be constant during the sintering process or it can
vary. In case the sintering temperature varies during the sintering
process, by sintering temperature in herein understood the average
of the variations. The sintering temperature is considered as the
temperature of the sintering chamber as measured with typical means
utilized to read such high temperatures.
[0060] Preferably, said mixture is heat up with a heating rate
(203) of at least 3.degree. C./min, more preferably of at least
5.degree. C./min, most preferably of at least 6.degree. C./min.
Preferably, said mixture is heat up with a heating rate of at most
15.degree. C./min, more preferably of at most 10.degree. C./min,
most preferably of at most 8.degree. C./min. Preferably, said
heating rate is between 3.degree. C./min and 15.degree. C./min,
more preferably between 5.degree. C./min and 10.degree. C./min,
most preferably between 6.degree. C./min and 8.degree. C./min.
[0061] The time used for sintering (206), hereinafter referred to
as the sintering time, is preferably at least 60 min, more
preferably at least 80 min, most preferably at least 100 min. Said
sintering time is preferably at most 600 min, more preferably at
most 300 min, most preferably at most 180 min. Said sintering time
is preferably between 60 and 600 min, more preferably between 80
and 300 min, most preferably between 100 and 180 min.
[0062] In accordance with the invention, steam is continuously
injected in the sintering chamber before, during and/or after said
heating up and/or said sintering of said mixture, for an injection
time. By continuous injection is herein understood that fresh steam
is continuously supplied to the sintering chamber throughout the
injection time. For example, in one embodiment, a first
steam-injection is carried out during the heating-up step for a
first injection time and a second steam-injection is carried out
during the sintering step for a second injection time. In another
embodiment, a steam-injection is commenced during the heating-up
step (207) and extended uninterruptedly to the sintering step
wherein said steam-injection during sintering is carried out for at
least part (208) of said sintering step. In FIG. 2, the time for
which steam is injected is shown by the shaded area (209). It is
also possible to commence the steam-injection before or during the
heating up, sintering and/or cooling step.
[0063] For convenience, when a temperature is mentioned, the unit
considered to express the temperature is always .degree. C., unless
otherwise expressly indicated.
[0064] In a first preferred embodiment of the inventive method, the
steam is continuously injected in the sintering chamber during
heating up said mixture of precursors to the sintering temperature.
Preferably the steam injection commences (204) during said heating
up when the temperature in the sintering chamber is at least a
fifth of the sintering temperature, more preferably at least a
third of the sintering temperature. In case a sintering temperature
of between 500.degree. C. and 800.degree. C. is used, the steam
injection preferably commences during said heating up when the
temperature in the sintering chamber is at least 150.degree. C.,
more preferably at least 200.degree. C., most preferably at least
250.degree. C.
[0065] In a second preferred embodiment, the steam injection
commences when the temperature in the sintering chamber is
substantially equal with the sintering temperature (202).
[0066] In a third preferred embodiment, the steam injection
commences (207) when the temperature in the sintering chamber is
below the sintering temperature but preferably at least a fifth of
said sintering temperature and the steam injection is extended
uninterruptedly to the sintering step; wherein said steam-injection
during sintering is carried out for least part of said sintering
step; wherein the steam injection during the sintering step is
carried out for an injection time of at most 1/4 of the total
sintering time, more preferably of at most 1/2 of the total
sintering time, most preferably of at most 1/4 of the total
sintering time. Preferably, the steam injection during the
sintering step is carried out for an injection time of at least
1/10, more preferably of at least 1/5 of the total sintering
time.
[0067] Preferably the steam injection is uninterruptedly carried
out during a total injection time of at least about 1/4 of the time
needed to both heat up and sinter said mixture of precursors, more
preferably of at least about 1/3, most preferably of at least about
1/2. Preferably, said steam injection is carried out
uninterruptedly during at least part of the heating up step and at
least part of the sintering step. Preferably, the steam injection
is extended to the sintering step, i.e. there is no discontinuity
in steam injection between the heating up step and sintering
step.
[0068] In accordance with the invention, the steam is injected into
the sintering chamber during an injection time, which can vary from
seconds to hours. For example, in a preferred embodiment, the
injection time during the heating up step is at least 25% of the
total time needed to heat up said mixture of precursors to the
sintering temperature, more preferably at least 50%, most
preferably at least 75%. In a further preferred embodiment, the
injection time during the sintering step is at least 10% of the
total sintering time, more preferably at least 15%, even more
preferably at least 20%, most preferably at least 75%. In a third
preferred embodiment, the injection time during the heating up step
is at least 25% of the total time needed to heat up said mixture of
precursors to the sintering temperature, more preferably at least
50%, most preferably at least 75% and the injection time during the
sintering step is at least 10% of the total sintering time, more
preferably at least 15%, even more preferably at least 20%, most
preferably at least 75% and there is no discontinuity in the steam
injection between the heating up step and sintering step.
[0069] In a preferred embodiment of the inventive method, steam is
injected in the sintering chamber during a part, preferably the
initial part, of the sintering step, the remaining part, preferably
the last part, of the sintering step being carried out in a
steam-free atmosphere.
[0070] The steam is preferably injected at atmospheric pressure in
the sintering chamber and is preferably water-based, i.e. water is
mainly used as the liquid medium used to produce the steam.
Preferably, when injected, the steam is at a temperature of at
least 150.degree. C., more preferably at least 200.degree. C., most
preferably at least 250.degree. C. The temperature of the steam can
be increased for example by mixing the water-based steam with
flammable gases and igniting said gases thereby transferring heat
to the steam. It is particularly advantageous to use a water-based
steam and allow water to react with the precursors since better
results are obtained. In particular it is preferred to adjust the
steam injection such that an amount of at least 1.5 L of water per
150 g of active material participate are reacted, more preferably
at least 2.0 L. most preferably at least 2.5 L. Preferably said
amount of reacted water is at most 1.5 L, more preferably at most
2.0 L, most preferably at most 2.5 L. The amount of reacted water
can be calculated from the difference between the amount of water
introduced as steam and the amount of water captured at the end of
the method of the invention.
[0071] The steam can be supplied to and injected in the sintering
chamber from a steam source via suitable piping for example. Any
conventional steam sources using conventional materials and
conventional steam producing methods can be used in accordance with
the invention. The steam can also be collected from the sintering
chamber and condensed to recover the liquid medium used to produce
said steam, e.g. water.
[0072] Preferably, the steam is injected with a flow rate of at
least 10 L/min, more preferably at least 20 L/min, most preferably
at least 25 L/min. Preferably, the steam is injected with a flow
rate of at most 50 L/min, more preferably at most 40 L/min, most
preferably at most 30 L/min.
[0073] By sintering chamber is herein understood the chamber
wherein the heating up and sintering of the mixture of precursors
takes place. By injecting steam in the sintering chamber is herein
understood that an atmosphere containing steam is provided in said
sintering chamber.
[0074] In accordance with the invention, the sintering chamber is
provided with a stream of an inert gas. Examples of such gases
include nitrogen, carbon dioxide, or noble gases such as helium or
argon, or mixtures thereof. Although called inert gas, said gas may
also contain small amounts of reactive gases, e.g. hydrogen. In a
preferred embodiment, the inert gas is a mixture containing a small
amount of a reactive gas, preferably hydrogen, and an inert gas
with a majority of said inert gas; preferably in a volume ratio
inert gas/H.sub.2 of 99 to 95:1 to 5 v/v, wherein the another inert
gas is preferably nitrogen. The inert gas is used to blanket the
reactive precursors used in accordance with the invention to
prevent unwanted reactions from taking place. Preferably, the
stream of inert gas is provided to the sintering chamber throughout
the entire process of preparing the powders of the invention.
[0075] After forming the inventive particles, the obtained powder
is cooled to preferably room temperature. The cooling rate (210) is
preferably at least 1.degree. C./min, more preferably of at least
2.degree. C./min, most preferably of at least 4.degree. C./min.
Preferably, said cooling rate of at most 10.degree. C./min, more
preferably of at most 7.degree. C./min, most preferably of at most
5.degree. C./min. Preferably, said cooling rate is between
1.degree. C./min and 10.degree. C./min, more preferably between
2.degree. C./min and 7.degree. C./min, most preferably between
4.degree. C./min and 5.degree. C./min.
[0076] It is to be recognized that different implementations of the
inventive method are possible, especially regarding the processing
conditions, the nature of the different precursors and their
sequence of blending.
[0077] It was observed that with the inventive method, relatively
short sintering times can be utilized to produce qualitative
electrochemically active powders. It was also surprisingly observed
that said method delivers qualitative powders in an energy saving
manner and at an economical cost.
[0078] The invention will be further explained with the help of the
following examples and comparative experiments, without being
however limited thereto.
Method for Measuring
[0079] Electrochemical performances are tested in CR2032 coin type
cells, with a Li foil as counter electrode in a lithium
hexafluorite (LiPF.sub.6) type electrolyte at 25.degree. C. The
active material loading is 4.75 (.+-.0.2) mg/cm.sup.2. Cells are
charged to 4.0V and discharged to 2.5V to measure rate performance
and capacity. The current density applied is calculated by that 1 C
discharge gets 140 mAh/g specific capacity of the active materials.
[0080] Electronic conductivity of a carbonaceous material can be
measured in accordance with the method disclosed in US2002/0195591.
[0081] Carbon structure of the samples was measured by Raman
Spectroscope using a JASCO NRS 3100 High Resolution Dispersive
Raman Microscope equipped with a solid state laser at a wavelength
of 532 nm. [0082] The microstructure characterization of the
samples is performed by Transmission Electron Microscopy (TEM)
using a JEOL3100F Field Emission TEM. [0083] The particle size
distribution can be determined following the methodology disclosed
in WO 2005/051840. [0084] The BET of particles can be determined by
N.sub.2 adsorption method developed by Brunauer, S., Emmett, P. H.,
and Teller, E., J. Am. Chem. Soc. 60: 309-319 (1938). [0085]
Crystal sizes were determined as follows: XRD patterns were
recorded on a Rigaku D/MAX 2200 PC X-ray diffractometer in the
17-144 2-theta range in a 0.02 degree scan step. Scan speed was set
to 1.0 degree per minute. A goniometer with theta/2theta Bragg
Brentano geometry was used having has a radius of 185 mm. A copper
target X-ray tube was operated at 40 KV and 40 mA. A diffracted
beam monochromator, based on a curved graphite crystal, was used to
remove KBeta Cu radiation. An incident beam optic setup was used
comprising a 10 mm divergent height limiting slit (DHLS), a
1-degree divergence slit (DS) and 5 degree vertical Soller slit.
The diffracted beam optic setup included a 1-degree anti-scatter
slit (SS), 5 degree vertical Soller slit and 0.3 mm reception slit
(RS). Crystal size was calculated by Bruker AXS Topas 3.0 software,
by using Rietveld refinement method as disclosed in H. M. Rietveld
(1969), J. Appl. Crystallography 2 (2): 65-71
EXAMPLE 1
[0086] A blend containing Fe.sub.3(PO4).sub.2.8H.sub.2O as the
source for Fe, Li.sub.3PO.sub.4 as the source for Li and PO.sub.4
and cellulose as the source for carbon, was dried in N.sub.2 at
240.degree. C. for 1 h. The Li:Fe ratio in the blend was 1.06:1.
The ratio M.sub.Cellulose/(M.sub.Li3PO4+M.sub.Fe3(PO4)2.8H2O) was
5.85 wt %.
[0087] After drying, the blend was transferred into a furnace
provided with an inlet for steam injection and provided with a
stream of an inert gas composed of N.sub.2/H.sub.2(99:1, v/v). The
blend was heated up to a sintering temperature of 600'C and
sintered at that temperature for 2 h. The heating up rate was
5.degree. C./min. Steam injection into the furnace commenced during
the heating up of said furnace when the temperature in the furnace
reached 250.degree. C. and it was extended uninterrupted to the
sintering step. The total steam injection time was 100 minutes. The
total sintering time in the presence of steam amounted to 0.5 h.
The temperature profile and an indication of when steam injection
is carried out are shown in FIG. 2.
[0088] After sintering the obtained powder was cooled to room
temperature with a cooling rate of 5.degree. C./min.
Comparative Experiment 1
[0089] The process of Example 1 was repeated without using steam
injection.
Comparative Experiment 2
[0090] Commercial carbon-coated LiFePO.sub.4 samples from Prayon
(Prayon FE100, CAS No: 15365-14-7, Product code: PR-038) were
investigated.
Powder Analysis
[0091] FIG. 3 shows Transmission Electron Microscopy (TEM)
pictographs of the powders of Ex. 1 (300) and C. Exp. 1 (400) and 2
(500), respectively. The powder of Ex 1 contains particles (301)
coated with a carbon coating layer (302) having a thickness of
around 10 nm, whereas the carbon coatings (402 and 502) on the
particles (401 and 501) forming the powders of the Comparative
Experiments have a thickness of maximum about 3 nm.
[0092] Table 1 further shows the peak-intensity ratio
I.sub.1360/I.sub.1580 as obtained by Raman Spectroscopy of the
obtained powders. As detailed above, the ratio
I.sub.1360/I.sub.1580 is an indication of the extent of carbon's
graphitization. The lower the ratio I.sub.1360/I.sub.1580, the
higher the extent of graphitization, i.e. the amount of highly
ordered graphite in the carbon layer. Example 1 shows the lowest
ratio I.sub.1360/I.sub.1580 indicating that the carbon layer has a
high amount of highly ordered graphite.
TABLE-US-00001 TABLE 1 sample I.sub.1360/I.sub.1580 Ratio Example1
27447/13378 2.05 C. Exp. 1 9448/2019 4.68 C. Exp. 2 83229/27088
3.07
Electrochemical Behavior
[0093] The electrochemical behavior of the powders obtained by the
processes of the Example and Comparative Experiments was studied in
so called coin cells. A slurry was prepared by mixing the obtained
powders with 10 wt % carbon black and 10 wt % PVDF into N-Methyl
Pyrrolidone (NMP) and deposited on an Al foil as current collector.
The obtained electrode containing 80 wt % active material was used
as the positive electrode in the manufacturing of the coin cells,
using a loading of 6 mg/cm.sup.2 active material. The negative
electrodes were made of metallic Li. The coin cells were cycled in
LiBF.sub.4 based electrolyte between 2.5 and 4 0 V at various
C-rates.
[0094] Table 2 shows the electrochemical performance of the coin
cells wherein the powders of the Example, Comparative Experiments 1
and 2, respectively, were used as the active material. It is
immediately observable that Example 1 shows the highest charge
capacity (CQ1), highest discharge capacity (DQ1) and best rate
capabilities in all C-rate tests even at a high rate as 20 C
TABLE-US-00002 TABLE 2 CQ1 DQ1 IRRQ1 Sample (mAh/g) (mAh/g) (%) 1 C
5 C 10 C 15 C 20 C DV1 DV6 Example1 159.5 157.2 1.4% 91.3% 80.3%
75.0% 72.6% 68.3% 3.383 3.057 C. Exp. 1 148.2 144.6 2.4% 90.6%
78.8% 72.2% 67.9% 64.3% 3.370 3.025 C. Exp. 2 154.0 152.9 0.7%
91.2% 76.4% 68.3% 63.2% 60.6% 3.371 3.008
Crystal Size
[0095] Table 3 shows the crystal sizes, obtained by the Rietveld
method, of the powders.
TABLE-US-00003 TABLE 3 Crystal sample Size (nm) Example 1 70.5
Comparative Example 1 78.6 Comparative Example 2 71.8
Obviously other lithium containing electrochemically active powders
may be prepared by analogous methods by using different starting
material. In particular, phosphates of other transition metals such
as Mn, Co, Ni. V, Cr, Ti, Mo, Nb, and W may be used instead of or
in addition to Fe.sub.3(PO.sub.4).sub.2.8H.sub.2O to prepare
Lithium metal phospates according to the invention with mixed metal
or with metals other than Fe.
* * * * *