Note: Descriptions are shown in the official language in which they were submitted.
CA 022~i998~i 1999-01-07
"LiPF6 ~ 11~ ~_I~;n
Description
This invention relates to a process of producing LiPF6. This
compound is used in particular as electrolyte in batteries
and as catalyst.
It is known that LiPF6 can be produced from LiF and PF5 at an
elevated pressure and an elevated temperature. However, this
reaction takes place with a low yield and is therefore uneco-
nomic. The yield can be increased by using reactive LiF,
which is obtained during the thermal decomposition of LiHF2,
but the production of the reactive LiF is technically complex
and involves considerable costs. In addition, the gaseous PF5
is not available on the market as raw material, but must be
produced directly before the synthesis of LiPF6. Moreover,
PF5 can only be handled with difficulty due to its toxicity
and reactivity.
LiPF6 can also be produced from red phosphorus and LiF in the
presence of HF at 200~C in a closed reactor under pressure.
Due to the corrosive properties of HF, this process can tech-
nically be realized only with difficulty, and the purifica-
tion of the LiPF6 thus obtained is expensive. The LiPF6 can
furthermore be produced by reacting PF5 with LiF in anhydrous
HF at 25~C in a closed reactor under pressure. With this
process, too, the product yield is too low, and the process
CA 022~998~ 1999-01-07
requires a great effort for purifying the product, as in par-
ticular the quantitative separation of HF and other by-
products is very difficult.
US-PS 3,607,020 furthermore proposes a process of producing
LiPF6, wherein LiF is reacted with PFs in an inert organic
solvent, where suitable solvents include in particular lower,
saturated alkyl ethers and lower alkyl esters of aliphatic
saturated monocarboxylic acids- The PFs is easily soluble in
these solvents, and the process can be performed at tempera-
tures between 0 and 50~C. However, it involves the disadvan-
tage that directly before the execution of the process PF5
must be synthesized, as this raw material is not available on
the market.
From US-PS 3,907,977 there is also known a process of produc-
ing LiPF6. In this process, LiF is reacted with PF5 in aceto-
nitrile as solvent at -40 to 80~C- The PFs is introduced into
the LiF-acetonitrile suspension at low temperatures, and the
reaction mixture is then heated to 60 to 80~C and filtered.
The filtered solution is cooled to 0~C, so that the complex
compound Li(CH3CN)4PF6 is precipitated- This complex can be
liberated from acetonitrile by heating the same to 80OC in a
vacuum, and can be converted to LipF6. As raw material, this
process also utilizes PFs, which can be handled only with
difficulty.
From JP-OS 60-251 109 there is finally known a process of
producing LiPF6, where PCls is reacted with LiF in liquid HF
at -78 to 0~C. Due to the use of liquid HF as solvent it is
necessary to purify the end product from HF, which causes
certain problems. Moreover, anhydrous HF is very toxic. This
known process employs inexpensive raw materials, but requires
an expensive low-temperature technology.
CA 022~998~ l999-0l-07
-- 3 --
Since the compound LiPF6 is only of interest as industrial
raw material when it can be produced in the purest possible
form from inexpensive raw materials by means of a simple
technically controllable process, it is the object underlying
the invention to create a process of producing the aforemen-
tioned compound, which employs generally available inexpen-
sive raw materials, supplies process products of high purity,
and can be performed under most simple process conditions,
where the use and the formation of corrosive and toxic sub-
stances should possibly be avoided.
The object underlying the invention is solved by a process of
producing LiPF6, wherein LiF iS reacted with PC15 or POCl3 to
form LiPF6 at a reaction temperature of -20 to 300OC for a
reaction time of 0.1 to 10 hours corresponding to the chemi-
cal equations
a) PCl5 + 6LiF - > 5LiCl + LiPF6
b) 4POCl3 + 18LiF - > 12LiCl + Li3Po4 + 3LiPF6
and wherein the LiPF6 is isolated from the reaction mixture
in the form of a solution, where ethers, nitriles, esters,
sulfones, carbonates, halogenated hydrocarbons and/or terti-
ary amines are used as solvent.
This process employs raw materials which are offered on the
market as inexpensive products, and which are mostly avail-
able in a very pure form- The use of pure LiF is very advan-
tageous, but it is also possible to use LiF contaminated with
minor amounts of other alkali and alkaline earth fluorides.
The chemical reactions utilized for the inventive process
supply the end product LiPF6 in a high yield, where the other
reaction products can easily be separated and recovered. The
solvents required for performing the process in accordance
with the invention, which solvents must be acid-free and
aprotic, are available in a high purity and can be recovered
CA 022~998~ 1999-01-07
.
and purified by means of simple methods. The required reac-
tion times and reaction temperatures are easy to control on a
technical scale even in the presence of the raw materials re-
quired for the execution of the process, as corresponding re-
actors are nowadays provided by the process technology. It is
possible to also use PBrs and POBr3 instead of PC15 and POCl3
for performing the inventive process, but it turned out that
these bromium compounds are very expensive and hardly avail-
able on the market. Therefore, PBrs and POBr3 are not suited
for performing the inventive process on a technical scale.
In the process in accordance with the invention diethyl ether
is preferably used as solvent, as LiPF6 is particularly eas-
ily soluble in diethyl ether.
In the process in accordance with the invention, the reaction
times are shortened and/or the yields are increased, when an
excess of 0.1 to 2 mol LiF, based on 1 mol PC15 and POCl3, is
present.
The process in accordance with the invention can on the one
hand be performed such that the reaction is first of all ef-
fected for 0.1 to 5 hours at 150 to 300~C and subsequently
for 0.1 to 5 hours at 60 to 120~C, and that the LiPF6 is then
extracted from the solid reaction mixture by means of the
solvent at 0 to 80~C. This procedure is performed in a closed
reactor under the pressure caused by the starting substances
and the reaction temperature. At 150 to 300~C PF5 is probably
formed in situ and subsequently reacts with LiF to form the
end product at 60 to 120~C. During the extraction of the
cooled, solid reaction mixture by means of a solvent, the end
product goes into solution and can be filtered off the solid
reaction residue. The residue consists of LiCl, LiF and pos-
sibly lithium phosphate, which can be processed according to
known methods. The solvent used for extraction can be puri-
fied by distillation or again be utilized for extraction.
.
CA 022~998~ 1999-01-07
To be able to utilize the inexpensive raw material PCl3 for
the inventive process, it is provided in accordance with the
invention that PCls and POC13 are produced in situ from PC13
during the reaction stage taking place at 150 to 300~C corre-
sponding to the chemical equations
c) PC13 + Cl2 - > PCl5
d) 2PC13 + ~2 - > 2POC13.
It is quite obvious for the man skilled in that art that the
execution of the inventive process corresponding to the gas-
solids reaction is not impaired by the presence of chlorine
and oxygen.
The process in accordance with the invention can on the other
hand be performed such that the reaction is effected for 0.1
to 5 hours at -20 to 100~C in the presence of the solvent,
and that the solution containing LiPF6 is filtered off the
insoluble reaction products.
What is particularly advantageous in this alternative proce-
dure is the fact that relatively low reaction temperatures
can be employed, where reaction temperatures of 0 to 80~C are
preferred in accordance with the invention. Moreover, the re-
action in the solvent takes place with a good yield, the
LiPF6 is easily soluble in the solvent, and the other reac-
tion products can be separated in solid form by means of fil-
tration. The PCls can advantageously be reacted with LiF in
the solvents diethyl ether as well as dimethyl, ethylene and
propylene carbonate, whereas the solvents acetonitrile, tet-
rahydrofuran and methyltetrahydrofuran turned out to be par-
ticularly useful for reacting POC13 with LiF.
In accordance with the invention it is provided that before
or during the reaction taking place in the solvent the PCl5
CA 022~998~ 1999-01-07
is produced by chlorinating PC13 in the presence of the sol-
vent at -20 to 100~C according to the equation
e) PCl3 + Cl2 -> PCl5.
In this way, the inexpensive raw material PC13 is also avail-
able for the variant of the inventive process which is per-
formed at -20 to 100~C in the presence of a solvent. The
chlorination of PC13 is highly exothermal (~H = 125kJ/mol).
The economy of the inventive process can be improved in that
the solvent contains 5 to 50 wt-% liquid, aliphatic or aro-
matic hydrocarbons. This measure does not negatively influ-
ence the solubility of the process product LiPF6; however,
the use of inexpensive, liquid hydrocarbons leads to a reduc-
tion of the process costs.
Finally, it is provided in accordance with the invention that
the LiPF6 is obtained from the solution containing LiPF6 in
crystalline form by evaporating the solvent. The separation
of the solvent from the process product by distillation is
advantageously promoted by an inert gas stream and/or by
means of a distillation under a reduced pressure. It was
noted that the used organic solvents can be removed from the
process product much easier and with less residues than HF.
When performing the inventive process it should of course be
made sure that no water is present in the individual reac-
tions. The used solvents should almost be anhydrous. It has
turned out that the raw materials provided for the execution
of the inventive process are in any case easier to handle
than gaseous PFs. The LiF is used in a finely crystalline
form. In the gas-solids reactions belonging to the inventive
process and in the reactions taking place in a liquid phase,
very little or no PFs was identified in the reaction mixtures
upon completion of the reaction; it is, however, assumed that
.
CA 022~998~ 1999-01-07
PF5 is formed in situ in the individual reactions and is then
decomposed immediately. The reaction time of the inventive
reactions can be shortened by stirring or grindingly stir-
ring. The reaction of LiF with POC13 performed in a solvent
should take place in a closed, pressure-tight reactor, in or-
der to avoid that the POF3 formed intermediately escapes from
the reactor uncontrolled. The relatively low pressures occur-
ring here are easy to control.
The processing of the residue obtained in the individual re-
actions, which contains LiCl or LiCl and Li3Po4 as well as
excess LiF, iS effected such that the residue is treated with
water. LiF and Li3P04 are obtained in insoluble form. If PCl5
is used as raw material, the insoluble residue exclusively
consisting of LiF can again be used as raw material for the
inventive process upon filtering and drying the same. When
treated with water, LiCl goes into solution and can be recov-
ered from the aqueous solution and be reused in some other
way.
It is known that the process product LiPF6 forms addition
products with water, so that the suitability of this sub-
stance, in particular as electrolyte for batteries, is re-
stricted. For removing residual traces of water, which get
into the reaction system in particular by the used raw mate-
rials, it is provided that the solutions of LiPF6 produced in
accordance with the inventive process are reacted with or-
ganolithium compounds, in particular methyllithium or butyl-
lithium, or with lithium hydride, before further processing
the same. Together with water, these compounds form lithium
hydroxide as well as hydrocarbons such as methane or butane
and hydrogen. The lithium hydroxide can be filtered off,
whereas the hydrocarbons or the hydrogen escape from the so-
lution as gases. However, the water content of the product
solutions is small in any case, as LiCl, which is formed in
the inventive process, is hygroscopic and therefore already
.
CA 022~998~ 1999-01-07
largely binds the water contained in the solutions. The dry-
ing effect of the LiCl provides for the use of solvents which
need not be anhydrous quantitatively, which advantageously
reduces the costs for the dehydration of the solvent.
Purifying the LiPF6 may be effected by recrystallizing in the
solvent, as the product is easily soluble in the solvent at
an elevated temperature and less easily soluble at a lower
temperature. Diethyl ether is particularly useful as solvent
and suited for recrystallizing the LiPF6, where the LiPF6 is
dissolved at 30 to 40~C and recrystallized at 0 to 10~C. The
product produced in accordance with the inventive process in
any case has a purity > 99.0 % and in general even a purity
> 99.8 %. The product is virtually anhydrous; the product-
containing solutions obtained after the extraction or filtra-
tion still have a water content < 10 ppm (determined accord-
ing to K. Fischer). The process product is marketed either in
the form of solutions or in solid form.
In the gas-solids reactions, the product yield generally is
80 to 95 % after the extraction, and in the reactions per-
formed in a solvent the yield is 90 to 96 % after the filtra-
tion.
The subject-matter of the invention will subsequently be ex-
plained in detail with reference to embodiments.
Example 1
500 g (2.4 mol~ PCls (purity 99 %) and 448 g (17.3 mol) dried
LiF were filled into a stainless steel autoclave and heated
to 300~C within one hour by stirring. This temperature was
maintained for about one hour- There was achieved an autoge-
nous pressure of 55 bar. Then, the temperature was decreased
to about 80~C, and stirring was effected at this temperature
. .
- CA 022~998~ 1999-01-07
for 3 hours. Upon cooling to room temperature, a final pres-
sure of about 5 bar was achieved.
The gaseous reaction products were absorbed in sodium hydrox-
ide solution. They contained about 1 % of the used phosphorus
as volatile halogen compounds- The white, finely powdered
residue was filled into a glass apparatus under an inert gas,
mixed with 1500 ml diethyl ether and stirred for about 30
minutes. The insoluble constituents (573.4 g, consisting of a
mixture of LiCl and LiF) were filtered off via a fritted-
glass filter (G3) and rinsed three times with about 200 ml
diethyl ether. The water content in the combined filtrates
was < 10 ppm (Karl Fischer titration). A lP-NMR spectrum ex-
clusively revealed a signal at -143.5 ppm (septet) for the
formed PF6. Upon separation of the diethyl ether 335 g (yield
91.9 %) finely powdered LiPF6 were left. The product con-
tained 0.2 % chloride and had a purity of about 99.8 %.
Example 2
To 8.04 g (0.31 mol) dried LiF, suspended in 80 ml commer-
cially available propylene carbonate (purity 99 %) 8.97 g
(0.043 mol) PCls were added within about 15 minutes. The tem-
perature of the reaction mixture increased from 20 to about
32~C. After stirring for one hour at room temperature, the
reaction was completed ( P-NMR spectrum only revealed a sig-
nal at -143.5 ppm). The filtered solution (90.8 g) had a wa-
ter content < 10 ppm and contained 6.2 g LiPF6 (yield 86.1
%). By rinsing the precipitate with propylene carbonate the
yield could be increased to 90 %.
Example 3
In a double-walled reactor 117.5 g (0,56 mol) PCls were added
to a suspension of 96.7 g (3.73 mol) LiF in 480 ml diethyl
ether at a reaction temperature of 20OC within about 30 min-
CA 022~998~ 1999-01-07
-- 10 --
utes. By means of cooling, the temperature was maintained at
22~C. Subsequently, stirring was effected for about one hour
at 20~C, and the reaction solution was liberated from insolu-
ble constituents (127.1 g, mixture of LiCl and LiF) by fil-
tering the same. The filtration residue was rinsed three
times with 50 ml diethyl ether each- The solvent was con-
densed off the combined filtrates, and the residue was dried
in a vacuum until the weight remained constant. There were
left 82.0 g (yield 95.7 %) pure LiPF6.
Example 4
27.7 g (0.2 mol) PC13 were dissolved in 99 g methylene chlo-
ride. Into this solution, dried chlorine was introduced at 20
to 30~C by cooling the same- The chlorination of PC13 took
place exothermally and was terminated when no further reac-
tion heat was observed. The PCls formed was contained in
methylene chloride partly in dissolved form and partly in
suspended form. Excess chlorine was washed out of the suspen-
sion with a dried stream of nitrogen. Subsequently, the sus-
pension was diluted with 105.5 g diethyl ether and then
charged with 37.4 g (1.44 mol) LiF for a period of 50 min-
utes. The exothermal reaction of PCls with LiF started imme-
diately and was maintained at 20 to 28~C by means of cooling.
When the entire amount of LiF had been introduced into the
suspension, stirring was continued for two hours. Then, the
solids were filtered off, the solvent was distilled off the
filtrate, and the remaining LiPF6 was purified by recrystal-
lizing the same in diethyl ether- The yield was 83 %, based
on PCl3.
Example 5
In an autoclave, 8.65 g POC13 (65.4 mmol) and 9.8 g (370
mmol) finely divided, dry LiF were mixed with 50 ml tetrahy-
drofuran. The mixture was grindingly stirred for 9 hours at
.__
CA 022~998~ 1999-01-07
25~C, where an excess pressure of about 0.1 bar was produced.
Upon cooling, the autoclave was relieved, and the reaction
mixture was filtered- In the filtrate, no POC13 could be de-
tected. The tetrahydrofuran was filtered off the filtrate in
a vacuum, and the LiPF6 was left as product, which was puri-
fied by recrystallizing the same with diethyl ether.
