Method of preparing lithium secondary battery
The present invention relates to a method of preparing a lithium secondary battery which may improve productivity and performance of the lithium secondary battery by visually measuring an actual electrolyte solution impregnation time for an electrode active material, setting an estimated impregnation time of the electrolyte solution for a battery based on a measured result, and reflecting the estimated impregnation time in a production process.
1. A method comprising:
preparing an electrode active material slurry (S1);
preparing a non-aqueous electrolyte solution (S2);
pressure-molding the electrode active material slurry into a form of a pellet having a thickness of less than 1,000 μm, a porosity of 18 vol % to 30 vol %, and a density of 1 g/cc to 4.5 g/cc (S3);
calculating an electrolyte solution impregnation rate by measuring a time at which the non-aqueous electrolyte solution passes through the pellet (S4); and
setting an estimated electrolyte solution impregnation time of a measurement target unit cell by using the electrolyte solution impregnation rate (S5).
2. The method of claim 1 , wherein the electrode active material slurry comprises an electrode active material; a solvent; and at least one additive of a binder, a conductive agent, and a filler.
3. The method of claim 2 , wherein the electrode active material is a negative electrode active material or a positive electrode active material.
4. The method of claim 3 , wherein, in a case in which the electrode active material slurry comprises the negative electrode active material,
the pellet has a porosity of 20 vol % to 30 vol % and a density of 1.3 g/cc to 1.8 g/cc.
5. The method of claim 3 , wherein, in a case in which the electrode active material slurry comprises the positive electrode active material,
the pellet has a porosity of 18 vol % to 30 vol % and a density of 3.4 g/cc to 4.2 g/cc.
6. The method of claim 1 , wherein the pellet has a diameter of a bottom surface of 5 mm to 20 mm and a thickness of 400 μm to 1,000 μm.
7. The method of claim 6 , wherein the thickness of the pellet is in a range of 400 μm to 800 μm.
8. The method of claim 1 , wherein th electrode active material slurry is a pressure-molded at a pressure of 10 MPa to 100 MPa in a temperature range of 0° C. to 120° C.
9. The method of claim 1 , wherein the calculating of the electrolyte solution impregnation rate comprises:
dispensing 1 μL to 10 μL of the non-aqueous electrolyte solution on a top surface of the pellet, and
calculating the electrolyte solution impregnation rate by measuring an electrolyte solution passing time from a time of dispensing the non-aqueous electrolyte solution until a time at which the dispensed non-aqueous electrolyte solution passes through the pellet and appears on a bottom surface.
10. The method of claim 9 , wherein a method of measuring the electrolyte solution passing time is performed by visual confirmation or is performed by indirect confirmation through a medium between an object and an observer.
11. The method of claim 1 , wherein the electrolyte solution impregnation rate is calculated using Equation 1:
Impregnation rate(μm/sec)=pellet thickness(μm)/time(sec) from a time of dispensing the electrolyte solution to a time of reaching a bottom surface [Equation 1].
12. The method of claim 1 , wherein the estimated electrolyte solution impregnation time of the measurement target unit cell is set by using Equation 2:
Estimated
unit
cell
impregnation
time
(
hr
)
=
0.077
(
hr
/
sec
·
mm
2
)
×
electrode
thickness
(
µm
)
×
(
electrode
area
(
mm
2
)
)
2
electrolyte
solution
impregnation
rate
(
µm
/
sec
)
[
Equation
2
]
wherein, in Equation 2,
the estimated unit cell impregnation time denotes the estimated electrolyte solution impregnation time of the unit cell, and the electrode is a positive electrode or a negative electrode.
13. The method of claim 1 , wherein the method further comprises:
preparing the measurement target unit cell;
preparing a lithium secondary battery including the measurement target unit cell (S6);
injecting the non-aqueous electrolyte solution into the secondary battery (S7); and
performing an electrolyte solution impregnation process during the set estimated electrolyte solution impregnation time of the unit cell (S8).