TECHNICAL FIELD
[0001] This application claims priority from Korean Patent
Application No. 10-2021-0016331, filed on February 04, 2021,
the disclosures of which are incorporated herein.
10 [0002] The present invention relates to a composition for
preparing a solid electrolyte, and a solid electrolyte and a
lithium secondary battery using the same.
BACKGROUND ART
[0003] A lithium secondary battery may be miniaturized, and
15 has high energy density and working voltage, thereby being
applied in various fields including mobile devices, electronic
products, electric vehicles, and the like. As the field of
application of a lithium secondary battery becomes diverse,
required physical properties conditions of the lithium
20 secondary battery are also increasing, and particularly, there
is a demand for the development of a lithium secondary battery
which may be stably driven in various environments.
[0004] In general, a secondary battery is manufactured by
mounting an electrode assembly composed of a negative electrode,
25 a positive electrode, and a separator inside a case in the
2
form of a cylinder, prism, or pouch having a certain space,
and injecting an electrolyte into the electrode assembly.
[0005] Typically, as an electrolyte for an electrochemical
device, a liquid electrolyte prepared by dissolving a salt in
5 a non-aqueous organic solvent has been mainly used. However,
such a liquid electrolyte causes the deterioration of electrode
materials and there is a high possibility of the volatilization
of an organic solvent, and also, combustion due to temperature
rise occurs, and there is a risk of leakage, so that it
10 difficult to implement various types of electrochemical
devices which require safety.
[0006] A solid electrolyte has an advantage in that it has
higher electrochemical stability than a liquid electrolyte.
However, the ion conductivity of a solid electrolyte at room
15 temperature is significantly lower than that of a liquid
electrolyte, and although research is actively being conducted
to solve the problem, there are still limitations in that when
the ion conductivity is increased, the electrochemical window
is reduced, and the like.
20 DISCLOSURE OF THE INVENTION
TECHNICAL PROBLEM
[0007] An aspect of the present invention provides a solid
electrolyte having increased flexibility through the crosslinking
of a supramolecular material.
25 [0008] Another aspect of the present invention provides a
3
lithium secondary battery having improved stability and ion
conductivity by including the solid electrolyte.
TECHNICAL SOLUTION
[0009] According to an aspect of the present invention, there
5 is provided a composition for preparing a solid electrolyte
including a polyrotaxane compound, a cross-linking agent, a
lithium salt, and an organic solvent, wherein the cross-linking
agent includes a compound represented by Formula 1 below and
a compound represented by Formula 2.
10 [0010] [Formula 1]
[0011] In Formula 1 above, L1 is a C1 to C10 alkylene group,
and
[0012] [Formula 2]
15
[0013] in Formula 2 above, L2 is a C1 to C5 alkylene group.
[0014] According to another aspect of the present invention,
there is provided a method for preparing a solid electrolyte
for a lithium secondary battery including thermal-curing the
20 composition for preparing a solid electrolyte.
[0015] According to another aspect of the present invention,
there is provided a solid electrolyte for a lithium secondary
battery comprising a thermo-cured product of the composition
for preparing a solid electrolyte.
4
[0016] According to another aspect of the present invention,
there is provided a lithium secondary battery including a
positive electrode having a positive electrode active material,
a negative electrode having a negative electrode active
5 material, and the solid electrolyte for a lithium secondary
battery interposed between the positive electrode and the
negative electrode.
ADVANTAGEOUS EFFECTS
[0017] The present invention may provide a solid electrolyte
10 having excellent flexibility, tensile strength, and ion
conductivity.
[0018] In addition, the present invention may provide a
lithium ion battery having improved stability and ion
conductivity by including the solid electrolyte.
15 BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a view showing the molecular structure of
polyrotaxane;
[0020] FIG. 2 is a view showing a molecular structure (a) of
a linear polymer Pullulan used in Comparative Example 3 herein
20 and a molecular structure (b) of a ring polymer PCD used in
Comparative Example 4 herein;
[0021] FIG. 3 is a schematic view showing a cross-linking
network formed by a polyrotaxane compound through a crosslinking
agent in a solid electrolyte according to the present
25 invention;
5
[0022] FIG. 4 is a view showing changes in ion conductivity
according to the temperatures of a solid electrolyte prepared
in Example 1 of the present invention;
[0023] FIG. 5 shows measurement results of the tensile
5 physical properties of solid electrolytes prepared in Example
1 and Comparative Examples 1 to 4 of the present invention;
and
[0024] FIG. 6 is a view showing CV curves of a battery to
which the solid electrolyte prepared in Example 1 of the
10 present invention is applied.
BEST MODE FOR CARRYING OUT THE INVENTION
[0025] Hereinafter, the present invention will be described
in more detail.
15 [0026] A polymer most commonly used in a solid polymer
electrolyte is poly(ethylene oxide) (PEO), and despite being
a solid, PEO has the ability to conduct lithium ions, but has
low flexibility due to high crystallinity, and cannot
dissociate a large amount of lithium ions due to a low
20 dielectric constant, and thus, has low ion conductivity at
room temperature, so that it is difficult to apply PEO to a
lithium secondary battery. Therefore, there have been a number
of studies conducted to increase ion conductivity through
modification such as blending a PEO-based polymer or
25 synthesizing the PEO-based polymer into a block copolymer.

CLAIMS
1. A composition for preparing a solid electrolyte,
comprising:
5 a polyrotaxane compound, a cross-linking agent, a lithium
salt, and an organic solvent,
wherein the cross-linking agent includes a compound
represented by Formula 1 and a compound represented by Formula
2 below:
10 [Formula 1]
wherein in Formula 1,
L1 is a C1 to C10 alkylene group,
[Formula 2]
15
wherein in Formula 2,
L2 is a C1 to C5 alkylene group.
2. The composition of claim 1, wherein the polyrotaxane
20 compound comprises 10 to 90 α-cyclodextrin molecules.
3. The composition of claim 1, wherein the weight average
molecular weight of the polyrotaxane compound is 10,000 g/mol
to 100,000 g/mol.
42
4. The composition of claim 1, wherein the content of the
polyrotaxane compound is 5 wt% 20 wt% based on the total weight
of the composition.
5
5. The composition of claim 1, wherein the weight ratio of
the compound represented by Formula 1 and the compound
represented by Formula 2 is 1:1 to 10:1.
10 6. The composition of claim 1, wherein the content of the
cross-linking agent is 0.5 wt% 5 wt% based on the total weight
of the composition.
7. The composition of claim 1, wherein the lithium salt is
15 one or more selected from LiNO3 and LiClO4.
8. The composition of claim 1, wherein the concentration of
lithium salt in the composition is 0.05 M to 3.0 M.
20 9. The composition of claim 1, further comprising one or
more polymers selected from the group consisting of
polyethylene oxide, polyvinylidene fluoride, and cellulose.
10. A method for preparing a solid electrolyte for a lithium
25 secondary battery, the method comprising thermal-curing the
43
composition of claim 1.
11. The method of claim 10, wherein the thermal-curing is
performed at a temperature from 50°C to 90°C.
5
12. A solid electrolyte for a lithium secondary battery, the
solid electrolyte comprising a thermo-cured product of the
composition of claim 1.
10 13. A lithium secondary battery comprising:
a positive electrode including a positive electrode
active material;
a negative electrode including a negative electrode
active material; and
15 the solid electrolyte of claim 12 interposed between the
positive electrode and the negative electrode.