U.S. patent application number 10/731166 was filed with the patent office on 2004-06-24 for isolation of lithium.
Invention is credited to Dietz, Christian, Huber, Gunther, Schierle-Arndt, Kerstin, Weppner, Werner.
Application Number | 20040118700 10/731166 |
Document ID | / |
Family ID | 32336409 |
Filed Date | 2004-06-24 |
United States Patent
Application |
20040118700 |
Kind Code |
A1 |
Schierle-Arndt, Kerstin ; et
al. |
June 24, 2004 |
Isolation of lithium
Abstract
Lithium is isolated from lithium amalgam by electrolysis over a
solid lithium ion conductor having the composition
Li.sub.4-xSi.sub.1-xP.sub.xO- .sub.4, where x is at least 0.3 and
not more than 0.7.
Inventors: |
Schierle-Arndt, Kerstin;
(Zwingenberg, DE) ; Huber, Gunther; (Ludwigshafen,
DE) ; Weppner, Werner; (Heikendorf, DE) ;
Dietz, Christian; (Kiel, GB) |
Correspondence
Address: |
Herbert B. Keil
KEIL & WEINKAUF
1350 Connecticut Ave., N.W.
Washington
DC
20036
US
|
Family ID: |
32336409 |
Appl. No.: |
10/731166 |
Filed: |
December 10, 2003 |
Current U.S.
Class: |
205/407 |
Current CPC
Class: |
C25C 7/04 20130101; C22B
26/12 20130101; C25C 3/02 20130101 |
Class at
Publication: |
205/407 |
International
Class: |
C25C 003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 16, 2002 |
GB |
10259020.6 |
Claims
We claim:
1. A process for isolating lithium from lithium amalgam by
electrolysis over a solid lithium ion conductor, wherein a lithium
ion conductor used has the composition
Li.sub.4-xSi.sub.1-xP.sub.xO.sub.4 where x is at least 0.3 and not
more than 0.7.
2. A process as claimed in claim 1, wherein the lithium ion
conductor used has the composition
Li.sub.4-xSi.sub.1-xP.sub.xO.sub.4, where x is at least 0.4 and not
more than 0.6.
3. A process as claimed in claim 2, wherein the lithium ion
conductor used has the composition
Li.sub.4-xSi.sub.1-xP.sub.xO.sub.4, where x is about 0.5.
4. A process as claimed in one of claims 1, 2 or 3, wherein the
lithium ion conductor used is prepared by shaping and calcining
Li.sub.4-xSi.sub.1-xP.sub.xO.sub.4, where x is at least 0.3 and not
more than 0.7, and/or compounds which are converted into this
during calcination, where the Li.sub.4-xSi.sub.1-xP.sub.xO.sub.4
and/or the compounds is/are used in the form of powder having a
mean particle size of not more than 5 microns.
5. A process as claimed in claim 4, wherein the
Li.sub.4-xSi.sub.1-xP.sub.- xO.sub.4 and/or the compounds is/are
used in the form of powder having a mean particle size of not more
than 3 microns.
Description
[0001] The present invention relates to a process for producing
lithium. In particular, the invention relates to a process for
isolating lithium from lithium amalgam by electrolysis over a solid
electrolyte which conducts lithium ions. It also relates to a
process for preparing this electrolyte.
[0002] Lithium is an important basic inorganic chemical and is
required in a variety of industrial applications. For example,
lithium is used for producing organolithium compounds which in turn
serve as strong bases or starting materials for specific syntheses,
as alloying additives or in lithium batteries. Ullmann's
Encyclopedia of Industrial Chemistry, 6th edition, 2000 Electronic
Release, keyword "Lithium and Lithium Compounds", in particular
sections 5.1 "Production of Lithium Metal" and 5.2 "Uses of Lithium
Metal", gives an overview of the prior art relating to the
production and use of lithium. The usual industrial method of
producing lithium is melt electrolysis of a eutectic mixture of
lithium chloride with potassium chloride at from 400 to 460.degree.
C. This process requires a comparatively large quantity of energy
(28-32 kWh/kg of lithium) and, in addition, only anhydrous lithium
chloride can be used. Since lithium chloride is hygroscopic, the
necessity of drying has an additional adverse effect on the
economics of this process.
[0003] DE 199 14 221 A1 (US equivalent: U.S. Pat. No. 6,287,448)
discloses a comparatively economical process for preparing lithium
from aqueous solutions, in which a lithium amalgam is firstly
produced from an aqueous lithium salt solution and, in a second
step, lithium is isolated from this amalgam by connecting the
amalgam as anode in an electrolysis cell having a solid electrolyte
which conducts lithium ions and a lithium cathode. The solid
electrolyte, viz. a ceramic material or a glass, separates the
anode and cathode spaces in a "helium-type" manner but is permeable
to lithium ions. A number of types of suitable solid electrolytes
which conduct lithium ions are mentioned, namely a)
Li-.beta."-Al.sub.2O.sub.3 or Li-.beta.-Al.sub.2O.sub.3, b) lithium
analogues of NASICON ceramics having a particular structure and
composition, c) LISICONS having a particular structure and
composition, d) lithium ion conductors having a perovskite
structure and a particular composition and e) sulfidic glasses.
[0004] Another class of known lithium ion conductors is derived
from lithium silicate in which silicon is partly replaced by
aluminum, phosphorus and/or sulfur. For example, U.S. Pat. No.
4,042,482 discloses monoclinic compounds of the formula
Li.sub.4+w-x-ySi.sub.1-w-x-yAl.sub.wP- .sub.xS.sub.yO.sub.4, where
w is from 0 to 0.45, x is from 0 to 0.5 and y is from 0 to 0.35 and
at least one of the two values w and (x+2y) is 0.1 or more. R. A.
Huggins, Electrochimica Acta 22 (1977) 773-781 teaches the
preparation of solid solutions of LiSiO.sub.4 and Li.sub.3PO.sub.4
by hot pressing a stoichiometric mixture of lithium hydroxide,
silicon dioxide and ammonium dihydrogen phosphate. In Mat. Res.
Bull. 11 (1976) 1227-1230 and in J. Electrochem. Soc. 124 (1977)
1240-1242, Y.-W Hu, I. D. Raistrick and R. A. Huggins disclose
processes for preparing such compounds by hot pressing a mixture of
lithium phosphate and lithium silicate. R. D. Shannon, B. E.
Taylor, A. D. English and T. Berzins, Electrochimica Acta 22 (1977)
783-796, teach the preparation of such compounds by mixing lithium
hydroxide, silicon dioxide and aluminum hydroxide at 850.degree. C.
Although these disclosures mention the possibility of using these
compounds as ion conductors in lithium batteries, they have not
been employed in practice for this purpose.
[0005] DE 199 48 548 A1 discloses paste-like compositions for
electrochemical components, which comprise nanocrystalline
materials and a matrix, including
Li.sub.0.5Si.sub.0.5P.sub.0.5O.sub.4 which at particle sizes below
10 microns is paste-like even without a matrix.
[0006] Ion conductors for the preparation of lithium have to
satisfy a number of requirements in order to be suitable. Apart
from suitable electrochemical properties (for example good
conductivity for lithium ions under the process conditions
employed, stability to liquid lithium and lithium amalgam and a
negligibly low electron conductivity), they should also be simple
and inexpensive to produce, be stable on storage and easy to handle
and have a very high stability and thus a long life. A particular
problem is the formation of microcracks which form under
electrochemical stress or grow larger and lead to leakages of
mercury into the lithium produced. The ion conductors known for the
isolation of lithium do not fulfill all these requirements in a
fully satisfactory manner. For example, Li-.beta."-Al.sub.2O.sub.3,
Li-.beta.-Al.sub.2O.sub.- 3 or lithium analogues of NASICON
ceramics, which are preferred from the point of view of their
electrochemical properties, are comparatively expensive and, owing
to their hygroscopic nature, special precautions have to be taken
when handling and storing them to ensure that their performance in
the process is not impaired.
[0007] It is an object of the present invention to find an improved
process for the isolation of lithium and, in particular, further
lithium ion conductors which can be used in this process and
satisfy the abovementioned requirements. A further object is to
find a process for preparing such ion conductors.
[0008] We have found that this object is achieved by a process for
isolating lithium from lithium amalgam by electrolysis over a solid
lithium ion conductor which has the composition
Li.sub.4-xSi.sub.1-xP.sub- .xO.sub.4, where x is at least 0.3 and
not more than 0.7. We have also found a process for preparing a
lithium ion conductor having the composition
Li.sub.4-xSi.sub.1-xP.sub.xO.sub.4, where x is at least 0.3 and not
more than 0.7, by shaping and calcining Li.sub.4-xSi.sub.1-xP.sub-
.xO.sub.4, where x is at least 0.3 and not more than 0.7 and/or
compounds which are converted into this during calcination, wherein
the Li.sub.4-xSi.sub.1-xP.sub.xO.sub.4 and/or the compounds is/are
used in the form of powder having a mean particle size of not more
than 5 microns.
[0009] The invention is firstly based on the recognition that the
lithium phosphate silicates to be used according to the present
invention are good lithium ion conductors for the recovery of
lithium from lithium amalgam. Secondly, it is based on the
recognition that the use of comparatively finely divided lithium
salts makes it possible to produce particularly impermeable lithium
phosphate silicates which are particularly resistant to crack
formation and are therefore impermeable and very stable.
[0010] The process of the present invention for isolating lithium
from lithium amalgam by electrolysis over a solid lithium ion
conductor is carried out in an electrolysis cell whose anode and
cathode spaces are separated by a solid electrolyte which conducts
lithium ions and has the composition
Li.sub.4-xSi.sub.1-xP.sub.xO.sub.4, where x is generally at least
0.3 and preferably at least 0.4 and is generally not more than 0.7
and preferably not more than 0.6. A preferred solid electrolyte is
Li.sub.4-xSi.sub.1-xP.sub.xO.sub.4 in which x is about 0.5, and a
particularly preferred solid electrolyte is
Li.sub.4-xSi.sub.1-xP.sub.xO.- sub.4 in which x is 0.5.
[0011] Processes for isolating lithium from lithium amalgam by
electrolysis over a solid lithium ion conductor which separates the
anode and cathode spaces of an electrolysis cell are known. The
process of the present invention is carried out like the known
processes except that the lithium ion conductor
Li.sub.4-xSi.sub.1-xP.sub.xO.sub.4 to be used according to the
present invention, in which x is in the range from 0.3 to 0.7, is
used as wall ("membrane") separating cathode and anode spaces. In
particular, the process of the present invention for isolating
lithium from lithium amalgam is carried out precisely like the
process known from DE 199 14 221 A1 (or from its equivalents EP 1
041 177 and U.S. Pat. No. 6,287,448), except that the lithium ion
conductor Li.sub.4-xSi.sub.1-xP.s- ub.xO.sub.4 to be used here
according to the present invention, in which x is in the range from
0.3 to 0.7, is employed as wall ("membrane") separating the cathode
and anode spaces of the electrolysis cell. Its teachings are hereby
expressly incorporated by reference.
[0012] The lithium amalgam used in the process of the present
invention for the isolation of lithium is a solution of lithium in
mercury which is liquid at the reaction temperature employed. It
generally contains at least 0.02% by weight of lithium (about 0.5
atom %) and preferably contains at least 0.04% by weight of lithium
(about 1 atom %) and generally not more than 0.19% by weight of
lithium (5 atom %) and preferably not more than 0.1% by weight of
lithium (about 3 atom %), balance mercury. It can be prepared in
any way, for example from an aqueous lithium salt solution in an
electrolysis cell by the amalgam process. For this purpose, a
lithium chloride solution having a lithium chloride content of from
220 to 350 g/l is fed in and lithium amalgam is produced at the
cathode and chlorine is produced at the anode, completely analogous
to the known amalgam process for chloralkali electrolysis by means
of which chlorine and sodium amalgam, for example, are produced
worldwide on a large scale. The sodium amalgam is often decomposed
by means of water to produce sodium hydroxide. It is likewise
possible to use other sources of lithium, for instance lithium
waste from batteries and reaction solutions like the lithium salt
solutions formed in the reaction of organolithium compounds with
halogen-substituted compounds and subsequent aqueous work-up. This
usually gives aqueous lithium chloride solutions, but it is also
possible to use other lithium halides and other lithium salts such
as lithium sulphate, lithium sulphonates or lithium salts of
organic acids. If lithium chloride is used, chlorine is produced
anodically in the preparation of lithium amalgam and this is
processed further in a customary fashion; if other lithium salts
are used, other process engineering measures may have to be
employed (the use of lithium sulphate results, for example, in
formation of oxygen at the anode and a pH of the liquor of
generally from 2 to 4 has to be set and maintained by addition of
lithium-containing bases.) These measures are known.
[0013] To isolate metallic lithium from lithium amalgam, the
lithium amalgam is used as liquid anode which is preferably kept in
motion in an electrolysis cell. The lithium amalgam anode is
separated from the cathode space in which liquor lithium is present
by a dividing wall which conducts lithium ions and is otherwise
very impermeable. During electrolysis in such a cell, the lithium
is conveyed from the amalgam in the form of lithium ions through
the membrane which conducts lithium ions into the cathode space and
is there reduced to the metal. The anode potential is set so that
virtually no metals which are more noble than lithium are oxidized,
in particular no mercury is oxidized to mercury ions. The lithium
metal obtained is taken off from the cathode space and processed
further in a customary fashion. Fresh liquid amalgam is fed into
the anode space and lithium-depleted amalgam or mercury is taken
off from this space. The mercury or the depleted amalgam is
recirculated to the lithium amalgam synthesis. The process is
carried out at a temperature at which both lithium amalgam and
lithium are liquid and the conductivity for lithium ions of the
dividing wall which conducts lithium ions is sufficiently high. The
reaction temperature is typically at least 150.degree. C.,
preferably at least 180.degree. C. and particularly preferably at
least 200.degree. C. and generally not more than 450.degree. C.,
preferably not more than 400.degree. C. and particularly preferably
not more 350.degree. C. A pressure which is slightly above that on
the anode side is preferably applied on the cathode side to prevent
leakages of mercury into the lithium obtained. This overpressure is
generally at least 0.1 bar, preferably at least 0.5 bar, and
generally not more than 5 bar and preferably not more than 1
bar.
[0014] The dividing wall which conducts lithium ions (also referred
to simply as "membrane", "ion conductor" or "solid electrolyte")
separates the anode space and cathode space from one another. The
seal is made "helium-tight" so that no substances apart from
lithium in ionic form are exchanged between anode space and cathode
space.
[0015] The shape chosen for the dividing wall depends on the shape
of the electrolysis cell. An advantageous and frequently used shape
of the dividing wall which conducts lithium ions is that of a tube
which is closed at one end and has a circular or other cross s
ction and at whose open end there is an electrically insulating
seal, for instance an electrically insulating ring with a
helium-tight, electrically insulating glass solder connection. Such
constructions are known, for example from GB 2 207 5645 A, EP 482
785 A1. The thickness of the dividing wall is chosen so that
sufficient mechanical strength (stability and pressure resistance)
and impermeability are achieved but migration of the lithium ions
through the dividing wall is not made unnecessarily difficult. It
is in general at least 0.3 mm and preferably at least 1 mm and
generally not more than 5 mm, preferably not more than 3 mm and
particularly preferably not more than 2 mm.
[0016] The impermeability of the dividing wall has to meet high
standards in order to avoid leakage of metallic mercury into the
lithium which has been obtained. "Helium-tight" dividing walls
which have leakage rates of less than 10.sup.-9 mbar per liter and
second in a helium leakage test are desirable. The other seals in
the system should also be liquid-tight and gastight in order to
prevent diffusion of mercury vapor into the environment or into the
lithium obtained.
[0017] To produce dividing walls which conduct lithium ions and are
to be used according to the present invention,
Li.sub.4-xSi.sub.1-xP.sub.xO.sub- .4 where x is at least 0.3 and
not more than 0.7, is brought to the desired shape of the dividing
wall. This can be carried out in any conceivable way, for example
by shaping an Li.sub.4-xSi.sub.1-xP.sub.xO.s- ub.4 powder or by
synthesis of the compound in the desired shape. A simple and
preferred method is shaping a compound or a mixture of compounds
which finally react to give Li.sub.4-xSi.sub.1-xP.sub.xO.sub.4 in
powder form and in the desired stoichiometry and subsequently
reacting the powder or powder mixture in the shaped part to form
Li.sub.4-xSi.sub.1-xP.sub.xO.sub.4, where x is at least 0.3 and not
more than 0.7.
[0018] In principle, it is possible to use all compounds and
mixtures of compounds which during the preparation of the ion
conductor react to give Li.sub.4-xSi.sub.1-xP.sub.xO.sub.4 as final
product. It is convenient and preferred to use lithium phosphate
and lithium silicate as anhydrous ortho compounds Li.sub.3PO.sub.4
and Li.sub.4SiO.sub.4. However, it is likewise possible to use
compounds which are converted into these substances during the
course of the preparation of the ion conductor. It is likewise
possible to use compounds containing water of crystallization or
hydrates such as Li.sub.3O.sub.4. 1/2 H.sub.2O, meta compounds such
as Li.sub.2SiO.sub.3 or LiPO.sub.3 or hydrogen salts such as
Li.sub.2HPO.sub.4 or LiH.sub.2PO.sub.4. The stoichiometry can also
be adjusted by addition of phosphorus oxides such as P.sub.2O.sub.5
or P.sub.2O.sub.3, silicon dioxide, including silicon hydroxide in
hydrated or partly hydrated form ("silica gel"), lithium oxide
and/or lithium hydroxide.
[0019] Preference is given to using pulverulent starting materials
which have a particular mean particle size. The mean particle size
(often also referred to as "d50") is such that 50% by weight of the
powder is present in the form of particles having a particle size
of not more than this mean particle size. In the case of relatively
coarse particles, the mean particle size is measured by means of
sieves, while in the case of finer particles in the size range of
only a few microns, use is genrally made of laser light scattering
(in accordance with the ISO/DIS standard 13320 "Particle Size
Analysis Guide to Laser Diffraction). In the case of spherical
particles, the particle size measured corresponds to the sphere
diameter, while in the case of nonspherical particles, the
measurement method necessarily gives an effective diameter of the
particles which corresponds to the diameter of spherical particles
having the same volume. Analogously, the powders have d90 values,
at which 90% by weight of the powder is present in the form of
particles having an effective diameter of not more than this
value.
[0020] The mean particle size of the pulverulent starting materials
used is generally not more than 5 microns. It is preferably not
more than 3 microns and particularly preferably not more than 1
micron.
[0021] It is not absolutely necessary but is preferred for the
powder used to contain few or no comparatively coarse particles. In
other words, the d90 is preferably not very much higher than the
d50. The d90 is preferably not more than five times the d50 and
particularly preferably not more than three times the d50.
[0022] If the powder used does not have this particle size, it is
brought to this particle size prior to shaping. This can be carried
out using any known comminution process. Particularly useful
apparatuses for this purpose are ball mills or attritor mills into
which the powder is usually introduced as a suspension in an inert
suspension medium (for example water, alcohols, ethers or
hydrocarbons). Preference is given to using alcohols, in particular
C.sub.1-C.sub.4-alcohols (methanol, ethanol, propanol, isopropanol,
butanol, sec-butanol, isobutanol, tert-butanol) as suspension
medium. Attritor mills can achieve d50 values of about 0.5 microns.
The most important parameter when using ball or attritor mills is
the milling time. Milling is always continued until the desired
fineness has been reached. If a mixture of compounds is used, joint
milling can conveniently at the same time effect the intensive
mixing necessary before shaping.
[0023] Shaping of the ion conductor or a mixture of substances from
which it is prepared to produce the desired shape is carried out
using known shaping methods, for example cold isostatic pressing,
hot isostatic pressing, slip casting or tape casting. For this
purpose, the powder is, if necessary after milling and if necessary
after removal of suspension medium, subjected to the appropriate
process. A preferred shaping process is cold isostatic pressing.
For this purpose, the powder is pressed in a mold under a pressure
of generally at least 1000 bar, preferably at least 2000 bar and
particularly preferably at least 3000 bar.
[0024] Subsequent to shaping or at the same time as shaping (for
instance in the case of hot isostatic pressing), the ion conductor
is fired to full density by heating ("heat treatment",
"calcination" or "sintering") so as to produce the finished
dividing wall of the electrolysis cell. If shaping has not been
carried out using Li.sub.4-xSi.sub.1-xP.sub.xO.sub.4 in which x is
at least 0.3 and not more than 0.7 itself, this ion conductor is
also produced from the powder mixture used during sintering.
Sintering is carried out by heating the shaped bodies to a
temperature of generally at least 700.degree. C., preferably at
least 800.degree. C. and particularly preferably at least
900.degree. C. Sintering is continued until an ion conductor of the
desired density is obtained at the temperature set. In general, the
sintering temperature is held for at least 15 minutes, preferably
at least 30 minutes and particularly preferably at least 1 hour.
Sintering is generally complete after no more than 10 hours;
sintering is preferably carried out for not more than 6 hours and
particularly preferably for not more than 4 hours. On heating and
cooling the shaped bodies to or from the sintering temperature,
care has to be taken to ensure that temperature stresses do not
cause cracks. The heating or cooling rate is therefore generally
not more than 20.degree. C./min, preferably not more than
10.degree. C./min and particularly preferably not more than
5.degree. C./min.
[0025] Lithium ion conductors which have a high density and
cracking resistance and are very suitable for lithium production
can be produced in this way.
EXAMPLES
Example 1
[0026] Preparation of a Lithium Ion Conductor Having the
Composition Li.sub.4-xSi.sub.1-xP.sub.xO.sub.4, x=0.5
[0027] 15.0 g (0.125 mol) of LiSiO.sub.4 and 14.49 g (0.125 mol) of
Li.sub.3PO.sub.4 were placed in a zirconium dioxide container and
slurried in 20 ml of isopropanol. Three spherical milling media
having diameters of 0.5 and 2 cm were in each case placed in the
container. The closed container was left on a ball mill for 12
hours. The isopropanol was subsequently removed by evaporation and
the powder which remained was pressed through a sieve. The powder
was shaped into a crucible shape by cold isostatic pressing at a
pressure of 3500 bar, heated at a heating rate of 1.degree. C./min
to 1000.degree. C., sintered at this temperature for 2 hours and
subsequently cooled at a cooling rate of 1.degree. C./min.
Example 2
[0028] Preparation of a Lithium Ion Conductor Having the
Composition Li.sub.4-xSi.sub.1-xP.sub.xO.sub.4, x=0.5
[0029] 15.0 g (0.125 mol) of LiSiO.sub.4 and 14.49 g (0.125 mol) of
Li.sub.3PO.sub.4 were placed in a zirconium dioxide container and
slurried in 20 ml of isopropanol. Three spherical milling media
having diameters of 0.5 and 2 cm were in each case placed in the
container. The closed container was left on a ball mill for 1 hour,
and the slurry was subsequently milled in an attritor mill (1.5 kg
of spherical ZrO.sub.2 milling m dia having a diameter of 2 mm) for
another 30 minutes. The isopropanol was removed by evaporation and
the powder which remained was pressed through a sieve. The powder
was shaped into a crucible shape by cold isostatic pressing at a
pressure of 3500 bar, heated at a heating rate of 1.degree. C./min
to 1000.degree. C., sintered at this temperature for 2 hours and
subsequently cooled at a cooling rate of 1.degree. C./min.
Example 3
[0030] Lithium Ion Conduction in a Model System
[0031] The ceramic produced in example 1 was subjected to a
transport measurement in the model system lithium-lithium at
195.degree. C. This corresponds to the procedure in the
electrolysis of lithium amalgam, but liquid lithium is used on both
sides of the dividing wall. The polarity of the electrodes was set
so that transport occurred from the exterior into the interior of
the lithium ion conductor crucible. A current of 1 mA was applied
for a period of 70 hours. The current yield achieved was
quantitative within the measurement accuracy. Cracks in the ion
conductor were not observed.
* * * * *