FIELD OF INVENTION
[0001] The subject matter of the present disclosure broadly relates to the field of
battery. Particularly, the present disclosure relates to a solid electrolyte film and a
process for preparing the solid electrolyte film.
5 BACKGROUND OF THE INVENTION
[0002] The rapid increase in the use of lithium-ion batteries in daily life has raised
concerns regarding safety and durability issues due to volatile nature and side
reactions between organic liquid electrolytes/electrodes in lithium-ion batteries
with liquid electrolytes. The replacement of organic liquid electrolytes with
10 inorganic solid electrolytes has attracted enormous attention, because they not only
offer a wide electrochemical stability window, but also make the batteries safer and
more durable, with a higher energy density and simple battery design as well.
[0003] Therefore, all-solid-state lithium batteries (ASSLBs) with solid electrolytes
are a promising candidate to support the demand for high energy density storage
15 systems. Generally, materials like ceramic oxides, chlorides, sulphides, or polymers
possessing higher ionic conductivity are used in electrolyte composition of
ASSLBs. Enhanced ionic conductivity of a solid electrolyte film is an important
feature for the better ionic conduction between the positive and the negative
electrodes. High ionic conductivity facilitates better Li+
ion movement across the
20 electrode-electrolyte interface in a lithium-ion battery. However, achieving a highly
ion-conducting dry solid electrolyte film becomes a challenge owing to the
presence of at least one insulating polymer,such as polytetrafluoroethylene (PTFE),
polyvinylidene fluoride (PVDF) etc. For achieving better ion conductivity in case
of dry solid electrolyte, one of the solutions can be reduction of the binder content
25 in the solid electrolyte film. In view of this, in order to retain good ionic
conductivity in a dry solid electrolyte film, the PTFE content used for the solid
electrolyte film should be as low as possible because the binder possesses an
inherent insulating property which can influence directly on the overall ionic
conductivity of the solid electrolyte thereby resulting in detrimental effects on the
30 electrochemical performance of the cell.
2
[0004] However, when the quantity of binder is reduced in an electrolyte film,
either the mechanical strength or the flexibility of the film gets badly affected. If
the solid electrolyte film obtained from the dry process is hard and brittle, it can
result in cracking of the electrolyte as well as electrodes which can eventually result
5 in circuit shorting while electrochemical cycling of the cell. Therefore, a good solid
electrolyte film should possess good flexibility in order to provide a physical barrier
between the positive and negative electrodes without breaking. In addition, highly
flexible and free-standing solid electrolyte films should retain their film nature and
quality upon twisting or bending so that it can be explored in various cell formats.
10 [0005] Further, it was understood that a solid electrolyte film with lesser porosity
and higher density produced better mechanical integrity and considerably higher
ionic conductivity. Hence there is a need in the art to develop a free-standing solid
electrolyte film having high flexibility, better ionic conductivity, good mechanical
strength and high density with less porosity.
15 SUMMARY OF THE INVENTION
[0006] In an aspect of the present disclosure, there is provided a solid electrolyte
film comprising: a. 98.8 to 99.5% by weight of an electrolyte material; and b. 0.5
to 1.2% by weight of a fibrillating binder; wherein the electrolyte material has a
particle size in a range of 0.8 to 5 micrometres; the fibrillating binder has a number
average molecular weight in a range of 1 × 106
to 3 × 106
20 g/mol.
[0007] In another aspect of the present disclosure, there is provided a process of
preparing the solid electrolyte film as disclosed herein, the process comprising:
mixing an electrolyte material with a fibrillating binder and calendering to obtain
the solid electrolyte film, wherein calendering involves pressing at a temperature in
25 a range of 70 to 130 ℃.
[0008] In yet another aspect of the present disclosure, there is provided an
electrochemical cell comprising: a. a cathode; an anode; and the solid electrolyte
film as disclosed herein.
[0009] In still another aspect of the present disclosure, there is provided a use of
30 the solid electrolyte film as disclosed herein, for manufacture of energy storage
devices.
3
[0010] These and other features, aspects, and advantages of the present subject
matter will be better understood with reference to the following description. This
summary is provided to introduce a selection of concepts in a simplified form. This
summary is not intended to identify key features or essential features of the claimed
5 subject matter, nor is it intended to be used to limit the scope of the claimed subject
matter.

I/We Claim:
1. A solid electrolyte film comprising:
a. 98.8 to 99.5% by weight of an electrolyte material; and
b. 0.5 to 1.2% by weight of a fibrillating binder;
5 wherein the electrolyte material has a particle size in a range of 0.8 to 5
µm; the fibrillating binder has a number average molecular weight in a
range of 1× 106
to 3 × 106
g/mol.
2. The solid electrolyte film as claimed in claim 1, wherein the electrolyte
material is lithium phosphorus sulfur chloride (LiPSCl) having a Formula
10 Li7-xPS6-xClx, wherein x is in a range of 1 to 2; and the fibrillating binder is
polytetrafluoroethylene.
3. The solid electrolyte film as claimed in claim 1, wherein the solid electrolyte
film exhibits an ionic conductivity in a range of 0.35 to 2 mS/cm.
4. The solid electrolyte film as claimed in claim 1, wherein the solid electrolyte
15 film has a thickness in a range of 50 to 130 µm and exhibits a tensile strength
in a range of 0.29 to 0.35 MPa.
5. A process of preparing the solid electrolyte film as claimed in claim 1, the
process comprising:
mixing an electrolyte material with a fibrillating binder and
20 calendering to obtain the solid electrolyte film,
wherein calendering involves pressing at a temperature in a range of
70 to 130 ℃.
6. The process as claimed in claim 5, wherein the mixing is carried out at a
speed in a range of 2000 to 3500 rpm at a temperature in a range of 25 to 90
25 ℃ and for a period in a range of 10 to 40 minutes.
7. The process as claimed in claim 5, wherein the fibrillating binder has a
particle size in a range of 400 to 800 µm and the electrolyte material has a
particle size in a range of 0.8 to 5µm.
8. An electrochemical cell comprising:
30 a. a cathode;
b. an anode; and
22
c. the solid electrolyte film as claimed in claim 1.
9. Use of the solid electrolyte film as claimed in claim 1 for manufacture of
energy storage devices.