Multi-layer polymeric electrolytes for electrochemical devices

Composite layered solid or semi-solid state polymeric electrolytes which contain at least a first layer which is a tough, mechanically strong adhesive layer which is non-reactive with alkali metal and preferably polyalkylene oxide based such as PEO, which is applied to an anode, and a second layer applied to a cathode which is a moist, adhesive layer which may be reactive with alkali metal, is loaded with aprotic liquids and alkali metal salts which activates the first layer and maintains the cell integrity.

BACKGROUND OF THE INVENTION 
Field of the Invention 
A composite solid, or semi-solid state polymer electrolyte for 
electrochemical devices which is preferably comprised of two layers, with 
the first layer being a tough, mechanically strong adhesive layer that is 
non-reactive with alkali metals such as lithium, and the second layer 
being an adhesive layer containing aprotic liquids and alkali metal salts 
which migrate into the first layer, but do not destroy the first layer, 
and do not substantially react with alkali metals. 
DESCRIPTION OF THE PRIOR ART 
In the prior art, various solid state electrolytes have been proposed for 
use in electrochemical devices, such as alkali and alkaline earth metal 
batteries. Among the problems associated with many electrolytes is that 
they may exhibit poor adherence to the electrodes, and are susceptible to 
shorting after several cycles due to the low mechanical strength of the 
commonly used polyethylene oxide (PEO) based plasticized electrolytes, and 
especially with PC (propylene carbonate). In other electrolytes such as 
polyacrylonitrile (PAN) and other polymer based electrolytes or their 
alloys, bubbles are often trapped in the dense mix which creates pinholes 
which result in dendrite growth, or the electrolytes react with the alkali 
metal anode and create dendric dust in the anode interface, resulting in 
the subsequent failure of the device. Examples of various electrolytes are 
disclosed in the U.S. patents to Hope, et al U.S. Pat. No. 5,006,431; 
Abraham et al, U.S. Pat. No. 5,219,679; Chesire et al, U.S. Pat. No. 
5,001,023; Nakajima U.S. Pat. No. 5,017,444, Lee et al U.S. Pat. No. 
4,990,413 and Chua et al U.S. Pat. No. 5,240,790. 
The multi layer polymeric electrolytes of the invention do not suffer from 
the problems of prior art electrolytes and provide many positive 
advantages. 
SUMMARY OF THE INVENTION 
It has now been found that composite polymer electrolytes can be made by 
using at least two layers to form the electrolyte, which is highly ion 
conductive, inert to alkali or alkaline earth metal battery components, 
flexible and tough enough to resist dendrite formation, with increased 
electrochemical and temperature stability, and improved cycling 
characteristics. The first layer is tough, preferably polyalkylene oxide 
based, such as PEO, which is highly adhesive, mechanically strong, 
ionically permeable and substantially non-reactive with alkali metals, 
which acts to prevent dendrite formation and shorting of the device. The 
first polymeric layer is coated, preferably cold, onto at least one 
electrode at room temperature and is solidified by solvent evaporation or 
other means. The second layer which is moist, and adhesive, is applied as 
a hot melt, and is loaded with aprotic liquids and alkali metal salts 
which soak into and activate the first layer, but do not destroy it. The 
first layer is preferably formed on the anode, and the second layer 
preferably on the cathode, after which they are assembled to form the 
electrochemical device. The second layer is preferably solidified by 
cooling to room temperature or by other known methods, such as electron 
beam treatment or other radiation treatment, and may also be resistant to 
high temperatures after solidification, and the polymer component may be 
reactive with alkali metals, which also stops dendrite growth. The aprotic 
liquids in the second layer must be selected from a group which does not 
destroy the first polymeric layer, and do not substantially react with 
alkali metals. The same or similar additional polymeric layers may also be 
added or inserted as required. 
The principal object of the invention is to provide a composite, multilayer 
solid or semi-solid state polymer electrolyte for batteries and other 
electrochemical devices, that has excellent ionic conductivity, is 
flexible and tough, but easy to handle and produce. 
A further object of the invention is to provide an electrolyte of the 
character aforesaid that has excellent adherence and low shrinkage 
properties. 
A further object of the invention is to provide an electrolyte of the 
character aforesaid, that is resistant to dendrite formation and shorting. 
A further object of the invention is to provide an electrolyte of the 
character aforesaid which has improved electrochemical stability. 
A further object of the invention is to provide an electrolyte of the 
character aforesaid which has improved cycling characteristics. 
A further object of the invention is to provide an electrolyte of the 
character aforesaid which has improved temperature stability. 
A further object of the invention is to provide an electrolyte of the 
character aforesaid that is highly suitable for mass production. 
Other objects and advantageous features of the invention will be apparent 
from the description and claims. 
It should, of course, be understood that the description is merely 
illustrative and that various modifications, combinations and changes can 
be made in the structures disclosed without departing from the spirit of 
the invention. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
When referring to the preferred embodiments, certain terminology will be 
utilized for the sake of clarity. Use of such terminology is intended to 
encompass not only the described embodiment, but also technical 
equivalents which operate and function in substantially the same way to 
bring about the same result. 
Electrochemical devices such as alkali metal batteries, and for example 
lithium polymer batteries, consist of at least an anode layer, a polymer 
electrolyte layer, and a cathode layer. Such batteries may be of virtually 
any desired size and configuration, and usually include additional layers 
such as current conducting backing layers, insulating layers and electrode 
connection layers. 
The polymer dielectric composite layered electrolyte of the invention must 
be compatible with the component materials used to fabricate the batteries 
while possessing suitable ionic conductivity and mechanical strength. 
In the described battery, fabrication preferably takes place in an inert 
dry atmosphere. To construct the battery, an anode is provided which can 
be of lithium foil or lithium alloy foil such as described in U.S. Pat. 
No. 5,350,647. The anode is coated with the first layer of electrolyte, 
which electrolyte is at room temperature and contains solvent which is 
allowed to evaporate. The second layer of electrolyte is heated and coated 
while hot preferably onto the cathode, which may be a V.sub.6 O.sub.13 
based composite sheet, and the second electrolyte layer can optionally 
have had a woven or non-woven electrically non-conductive net inserted 
therein. If desired, the second layer of electrolyte may be formed as a 
film which is then applied to the cathode. To form the electrochemical 
device, the pre-coated anode layer is placed on top and facing the cathode 
layer, and the assembly is rolled together. Additional layers may then be 
added as required. The first layer is preferably polyalkylene oxide based 
such as PEO, which is tough, highly adhesive, mechanically strong, 
ionically permeable and substantially non-reactive with lithium, which 
acts to prevent dendrite formation and shorting of the device. The first 
polymeric layer is coated, preferably onto at least one electrode at room 
temperature, and solidified by solvent evaporation. The second layer which 
is soft, moist, and adhesive, is applied as a hot melt, and is loaded with 
aprotic liquids and alkali metal salts which soak into and activate the 
first layer, but do not destroy it, and do not substantially react with 
alkali metals. The first layer is preferably formed on the anode, and the 
second layer on the cathode, after which they are assembled to form the 
electrochemical device. The second layer is preferably solidified by 
cooling to room temperature or other known method such as electron beam 
treatment or other radiation treatment, may also be resistant to high 
temperature after solidification, and the polymer component may be 
reactive with alkali metals which also stops dendrite growth. The aprotic 
liquids in the second layer must be selected from a group which does not 
destroy the first polymeric layer, and do not substantially react with 
alkali metals. 
The first layer contains a mixture of an ether such as THF and an ester 
such as EC, a polymer such as PEO, and at least one alkali metal salt such 
as lithium triflate. The first layer may also contain only PEO and an 
alkali metal salt. The second layer contains a mixture of a plurality of 
esters, or an ether and at least one ester with an alkali metal salt and 
preferably a PEO or a PVDF-PEO based alloy. The following examples were 
constructed in accordance with the invention and in a dry inert atmosphere 
.

EXAMPLE #1 
A. The first layer, which was a PEO based coating, was applied to an anode 
of metallic lithium alloy. The coating was prepared by mixing: 
______________________________________ 
1. 252 g THF (tetrahydrofuran) 
2. 63 g EC (Ethylene Carbonate) 
3. 15.6 g Li-Triflate 
(Lithium Triflate) 
4. 6 g (PEO) (Polyethylene Oxide) 
______________________________________ 
The mixture was heated to 60 degrees celsius while being mixed with a 
magnetic stirrer in a closed bottle to dissolve the PEO, and was then 
cooled to room temperature to minimize reactivity with the lithium. The 
anode of lithium foil, or lithium alloy foil as described in U.S. Pat. No. 
5,350,647 was dipped into the mixture to ensure uniform coating. The THF 
was allowed to substantially evaporate, and preferably for 1 hour, while 
the foil was suspended in dry air. The resulting tough coating or "skin" 
on the anode foil was approximately 2 mils thick. It should be noted that 
the mixture could also be coated on only one side of the anode foil, by 
any well-known means such as a doctor blade, or by extruding the coating 
through a slot similar to well-known hot melt coaters. The evaporation of 
the THF can be accelerated by blowing dry air or dry inert gas on the 
coated surface, and the THF solvent is preferably recovered by using a 
condenser. The anode which has been dip-coated on both sides may be used 
in constructing a bi-cell device which has two cathodes. 
The THF component determines the thickness of the layer and is varied as 
required. After exclusion of the THF, the EC component is useful in a 
range of 1% to 60% by percentage weight, the Li-triflate component is 
useful in a range of 1% to 50% by percentage weight, and the PEO component 
is useful in a range of 0.5% to 70% by percentage weight. 
B. The second (adhesive) layer was coated onto the cathode. This layer is 
PVDF-PEO alloy based, and was prepared by mixing: 
______________________________________ 
1. 27 g DMC (Dimethyl Carbonate) 
2. 13 g EC (Ethylene Carbonate) 
3. 5 g Li-perchlorate 
(Lithium Perchlorate) 
4. 6.5 g homopolymer PVDF 
(Polyvinyldienefluoride) 
5. 1 g PEO (Polyethylene Oxide) 
______________________________________ 
In the second layer, the DMC component is useful in a range of 0.1% to 90% 
by percentage weight, the PVDF component which is useful in a range of 
0.1% to 50% by percentage weight improves the temperature resistance of 
the alloy. The EC component is useful in a range of 0.1% to 60% by 
percentage weight, the Li-perchlorate component is useful in a range of 1% 
to 50% by percentage weight, and the PEO component which is useful in a 
range of 0.5% to 70% by percentage weight, improves the ionic conductivity 
and makes the alloy flexible. 
The mixture was heated to 90 degrees celsius to accelerate blending in the 
PVDF and PEO, while being mixed in a closed bottle with a magnetic 
stirrer, and the mixture is then applied to the cathode sheet by a doctor 
blade or by extrusion, which sheet is preferably V.sub.6 O.sub.3 based. A 
woven or non-woven electrically non-conducting and inert net, or mesh may 
be inserted into the layer while the layer is still hot and liquid, as 
described in U.S. Pat. No. 5,102,752 and patent application Ser. No. 
08/286,345 of Joseph B. Kejha. With the net enveloped and the adhesive 
layer at a thickness of two mils, the layer was cooled but while still 
tacky--the pre-coated anode was placed on top with the first layer facing 
the second layer, and the assembly was rolled together. The resultant cell 
provided 3.81 volts, and was rechargeable with several hundred cycles 
obtained. 
It should be noted that the homopolymer PVDF in the alloy may be replaced 
by a copolymer of PVDF/HFP (such as Elf-Atochem #2801 Kynar) 
(HFP=Hexafluoropropylene and the DMC may be replaced by THF, DME 
(Dimethoxty ethane) or other ethers, of the same percentage weight. For 
other alkali metal or alkaline earth metal based batteries (other than 
lithium based)--the lithium-perchlorate and lithium-triflate salts should 
be replaced by perchlorate and triflate salts matching the selected alkali 
or alkaline earth metal. 
EXAMPLE 2 
A. The first layer, which is a PEO based coat, was applied to an anode of 
metallic lithium alloy. The coating layer was prepared by mixing: 
______________________________________ 
1. 252 g THF (tetrahydrofuran) 
2. 63 g EC (Ethylene Carbonate) 
3. 15.6 g Li-Triflate 
(Lithium triflate) 
4. 6 g (PEO) (Polyethylene Oxide) 
______________________________________ 
The mixture was heated to 60 degrees celsius to accelerate blending in the 
PEO while being mixed with a magnetic stirrer in a closed bottle, and was 
then cooled to room temperature to minimize reactivity with the lithium. 
The anode of lithium foil, or lithium alloy foil as described in U.S. Pat. 
No. 5,350,647 was dipped into the mixture to ensure uniform coating. The 
THF was allowed to substantially evaporate, and preferably for 1 hour, 
while the foil was suspended in dry air. The resulting tough coating or 
"skin" on the anode foil was approximately 2 mils thick. It should be 
noted that the mixture could also be coated on only one side of the anode 
foil by any well-known means such as a doctor blade, or by extruding the 
coating through a slot similar to well-known hot melt coaters. The 
evaporation of the THF can be accelerated by blowing dry air or dry inert 
gas on the coated surface, and the THF solvent is preferably recovered by 
using a condenser. The anode which has been dip-coated on both sides may 
be used in constructing a bi-cell device which has two cathodes. 
The THF component determines the thickness of the layer and is varied as 
required. After exclusion of the THF, the EC component is useful in a 
range of 1% to 60% by percentage weight, the lithium-triflate component is 
useful in a range of 1% to 50% by percentage weight, and the PEO component 
is useful in a range of 0.5% to 70% by percentage weight. 
B. The second (adhesive) layer was coated onto the cathode. This layer is 
also PEO based, and was prepared by mixing: 
______________________________________ 
1. 42 g DMC (Dimethyl Carbonate) 
2. 21 g EC (Ethylene Carbonate) 
3. 7.8 g Li-triflate 
(Lithium triflate) 
4. 2 g PEO (Polyethylene Oxide) 
______________________________________ 
The DMC component is useful in a range of 0.1% to 90% by percentage weight, 
the EC component is useful in a range of 0.1% to 60% by percentage weight, 
the lithiumi-triflate component is useful in a range of 1% to 50% by 
percentage weight, and the PEO component is useful in a range of 0.5% to 
70% by percentage weight. 
The mixture was heated to 90 degrees celsius while being mixed in a closed 
bottle with a magnetic stirrer to accelerate blending in the PEO, and then 
applied to the cathode sheet by a doctor blade or extrusion, which sheet 
is preferably V.sub.6 O.sub.13 based. A woven or non-woven electrically 
non-conducting and inert net, or mesh may be inserted into the layer while 
the layer is still hot and liquid, as described in U.S. Pat. No. 
5,102,752, and the pending patent application Ser. No. 08/286,345 of 
Joseph B. Kejha et al. With the net enveloped and the adhesive layer at a 
thickness of two mils, the layer was cooled, but while still tacky--the 
pre-coated anode was placed on top with the first layer facing the second 
layer and the assembly was rolled together. The resultant cell provided 
3.81 volts, and was rechargeable with several hundred cycles obtained. 
It should be noted that for low temperature device operation, the DMC may 
be replaced by DEC (Diethyl Carbonate) or other esters or ethers which do 
not destroy the PEO in the first layer, of the same percentage weight 
range. For other alkali metal or alkaline earth metal based batteries 
(other than lithium-based)--the lithium-triflate salt should be replaced 
by a triflate salt matching the selected metal. Because both layers in the 
example are PEO based, the layers may also be reversed. 
EXAMPLE #3 
A. The first layer, a PEO-PVDF alloy-based mixture was prepared by mixing: 
______________________________________ 
1. 245 g THF (tetrahydrofuran) 
2. 32.5 g DMC (Dimethyl Carbonate) 
3. 16 g EC (Ethylene Carbonate) 
4. 6 g Li-triflate (Lithium triflate) 
5. 2.5 g homopolymer PVDF 
(Polyvinyldienefluoride) 
6. 6 g PEO (Polyethylene Oxide) 
______________________________________ 
The mixture was heated to 60 degrees celsius to accelerate blending in the 
PEO while being mixed with a magnetic stirrer in a closed bottle, and the 
mixture was then cooled to room temperature to minimize reactivity with 
the lithium. The anode of lithium foil, or lithium alloy foil as described 
in U.S. Pat. No. 5,350,647 was dipped into the mixture to ensure uniform 
coating. The THF was allowed to substantially evaporate, and preferably 
for 1 hour, while the foil was suspended in dry air. The resulting tough 
coating or "skin" on the anode foil was approximately 2 mils thick. It 
should be noted that the mixture could also be coated on only one side of 
the anode foil by any well-known means such as a doctor blade, or by 
extruding the coating through a slot similar to well-known hot melt 
coaters. The evaporation of the THF can be accelerated by blowing dry air 
or dry inert gas on the coated surface, and the THF solvent is preferably 
recovered by using a condenser. The anode which has been dip-coated on 
both sides may be used in constructing a bi-cell device which has two 
cathodes. The THF component determines the thickness of the layer and is 
varied as required. 
After exclusion of the THF, the DMC component is useful in a range of 0.1% 
to 90% by percentage weight, the EC component is useful in a range of 0.1% 
to 60% by percentage weight, the Li-triflate component is useful in a 
range of 1% to 50% by percentage weight, the PVDF component is useful in a 
range of 0.1 to 70% by percentage weight, and the PEO component which is 
useful in a range of 0.5% to 70% by percentage weight, improves ionic 
conductivity and makes the alloy flexible. It should be noted that the 
PVDF homopolymer in the alloy may be replaced by a PVDF/HFP copolymer of 
the same percentage weight. For other alkali metal devices, the lithium 
salts should be replaced by salts matching the selected alkali metal. 
B. The second (adhesive) layer was the same as described in Example #1B 
(PVDF-PEO alloy based) and the second layer was also constructed as 
described in example #2B (PEO based), or as will be described in example 
#4B (PVDF-PEO alloy based). The layers were applied as described above in 
Example #1 and provided 3.75 volts and several hundred cycles. 
EXAMPLE 4 
A. The first layer was a PEO-based coat applied to a metallic lithium 
alloy. It was prepared by mixing; 
______________________________________ 
1. 252 g THF (tetrahydrofuran) 
2. 63 g EC (Ethylene Carbonate) 
3. 15.6 g Li-triflate 
(Lithium triflate) 
4. 6 g PEO (Polyethylene Oxide) 
______________________________________ 
The mixture was heated to 60 degrees celsius to accelerate blending in the 
PEO while being mixed with a magnetic stirrer in a closed bottle, and was 
then cooled to room temperature to minimize reactivity with the lithium. 
The anode of lithium foil, or lithium alloy foil as described in U.S. Pat. 
No. 5,350,647 was dipped into the mixture to ensure uniform coating. The 
THF was allowed to substantially evaporate, and preferably for 1 hour, 
while the foil was suspended in dry air. The resulting tough coating or 
"skin" on the anode foil was approximately 2 mils thick. It should be 
noted that the mixture could also be coated on only one side of the anode 
foil, by any well-known means such as a doctor blade, or by extruding the 
coating through a slot similar to well-known hot melt coaters. The 
evaporation of the THF can be accelerated by blowing dry air or dry inert 
gas on the coated surface, and the THF solvent is preferably recovered by 
using a condenser. The anode which has been dip-coated on both sides may 
be used in constructing a bi-cell device which has two cathodes. 
The THF component determines the thickness of the layer and is varied as 
required. After exclusion of THF, the EC component is useful in a range of 
1% to 60% by percentage weight, the Li-triflate component is useful in a 
range of 1% to 50% by percentage weight, and the PEO component is useful 
in a range of 0.5% to 70% by percentage weight. 
B. The second (adhesive) layer was coated on the cathode. This layer was a 
PVDF/HFP-PEO based alloy which was prepared by mixing: 
______________________________________ 
1. 40 g DMC (Dimethyl Carbonate) 
2. 20 g EC (Ethylene Carbonate) 
3. 6.9 g Li-triflate 
(Lithium triflate) 
4. 8.8 g PVDF/HFP copolymer 
(Polyvinyldienefluoride/Hexafluoro- 
propylene) 
6. 1.76 g PEO (Polyethylene Oxide) 
______________________________________ 
In the second layer, the DMC component is useful in a range of 0.1% to 90% 
by percentage weight, the EC component is useful in a range of 0.1% to 60% 
by percentage weight, the Li-triflate component is useful in a range of 1% 
to 50% by percentage weight, the PVDF/HFP component is useful in a range 
of 0.1% to 70% by percentage weight, and improves the temperature 
resistance of the alloy, and the PEO component is useful in a range of 
0.5% to 70% by percentage weight and improves the ionic conductivity and 
makes the alloy flexible. 
The mixture was heated to 90 degrees celsius to accelerate blending in the 
PVDF/HFP and PEO while being mixed in a closed bottle with a magnetic 
stirrer, and the mixture was then applied to the cathode sheet by a doctor 
blade or by extrusion, which sheet is preferably V.sub.6 O.sub.13 based. A 
woven or non-woven electrically non-conducting and inert net, or mesh may 
be inserted into the layer while the layer is still hot and liquid, as 
described in U.S. Pat. No. 5,102,752 and patent application Ser. No. 
08/286,345 of Joseph B. Kejha. With the net enveloped and the adhesive 
layer at a thickness of two mils, the layer was cooled, but while still 
tacky--the pre-coated anode was placed on top with the first layer facing 
the second layer, and the assembly was rolled together. The resultant cell 
provided 3.81 volts, and was rechargeable with several hundred cycles 
obtained. 
It should be noted that the copolymer PVDF/HFP in the alloy may be replaced 
by a homopolymer of PVDF (such as Kynar #711, Elf Atochem) and the DMC may 
be replaced by THF, DME (Dimethoxty ethane) or other ethers, of the same 
percentage weight. For other alkali metal or alkaline earth metal based 
batteries (other than lithium based)--the lithium-perchlorate and 
lithium-triflate salts should be replaced by perchlorate and triflate 
salts matching the selected alkali or alkaline earth metal. 
EXAMPLE 5 
A. The first layer (PEO Based) was prepared by mixing: 
______________________________________ 
1. 200 g THF (tetrahydrofuran) 
2. 16 g Li-Triflate 
(Lithium Triflate) 
3. 6 g (PEO) (Polyethylene Oxide) 
______________________________________ 
The mixture was heated to 60 degrees celsius to accelerate blending in the 
PEO, while being mixed with a magnetic stirrer in a closed bottle, and the 
mixture was then cooled to room temperature to minimize reactivity with 
the lithium. The anode of lithium foil, or lithium alloy foil as described 
in U.S. Pat. No.5,350,647 was dipped into the mixture to ensure uniform 
coating. The THF was allowed to substantially evaporate, and preferably 
for 1 hour, while the foil was suspended in dry air. The resulting tough 
coating or "skin" on the anode foil was approximately 2 mils thick. It 
should be noted that the mixture could also be coated on only one side of 
the anode foil, by any well-known means such as a doctor blade, or by 
extruding the coating through a slot similar to well-known hot melt 
coaters. The evaporation of the THF can be accelerated by blowing dry air 
or dry inert gas on the coated surface, and the THF solvent is preferably 
recovered by using a condenser. The anode which has been dip-coated on 
both sides may be used in constructing a bi-cell device which has two 
cathodes. 
The THF component determines the thickness of the layer and is varied as 
required. After exclusion of the THF, the EC component is useful in a 
range of 1% to 60% by percentage weight, the Li-triflate component is 
useful in a range of 1% to 90% by percentage weight, and the PEO component 
is useful in a range of 0.5% to 90% by percentage weight. 
B. The Second (adhesive) layer may be the same as described in example #1B, 
#2B or #4B. The application of the layers may be the same as described in 
example #1. 
It is apparent that the second layer facing the cathode may be of any 
polymer based material which is compatible with and does not destroy the 
first layer. In addition, in all cases described, additional layers of the 
same compositions as disclosed may be added to create a multilayer 
composite electrolyte, but the first non-reactive layer should always 
contact the anode. The described electrolytes solve the problem of alkali 
metal anode interface reactivity and provide long cycle life. The 
described electrolytes may also be useful in lithium-ion batteries or 
other alkali metal-ion batteries. 
It will thus be seen that multi-layer polymeric electrolytes for 
electrochemical devices have been described for which the objects of the 
invention were attained.