Electrolyte for lithium secondary battery and lithium secondary battery including same

Abstract

The present invention provides an electrolyte for a lithium secondary battery and a lithium secondary battery including the same, the electrolyte including a polymer, and one or more selected from the group consisting of an inorganic solid electrolyte particle and a ferrodielectric, wherein the polymer includes one or more selected from the group consisting of a polymer represented by Formula 1 and a polymer including a repeating unit represented by Formula 2.

Claims

1. An electrolyte for a lithium secondary battery, comprising: a polymer; and one or more selected from the group consisting of an inorganic solid electrolyte particle and a ferrodielectric, wherein the polymer includes one or more selected from the group consisting of a polymer represented by Formula 1 below and a polymer including a repeating unit represented by Formula 2 below: ##STR00009## in Formula 1 above, R.sub.1, R.sub.2, and R.sub.3 are each independently hydrogen or —CH.sub.2—CH═CH.sub.2, wherein at least one of the R.sub.1, R.sub.2, or R.sub.3 is —CH.sub.2—CH═CH.sub.2, and a, b, and c are each independently an integer of 1 to 10,000, ##STR00010## in Formula 2 above, R.sub.a to R.sub.d are each independently an element selected from the group consisting of H, F, Cl, Br, and I, R.sub.e to R.sub.h are each independently one selected from the group consisting of H, F, Cl, Br, and *—OR.sub.0SO.sub.3.sup.−M.sup.+, and at least one of the R.sub.e to R.sub.h is *—OR.sub.0SO.sub.3.sup.−M.sup.+, wherein R.sub.0 is —CH(CF.sub.3)CF.sub.2— or —CF(CF.sub.3) and M.sup.+ is one selected from the group consisting of H.sup.+, Li.sup.+, Na.sup.+, and K.sup.+, and m and n are each independently an integer of 1 to 10,000.

2. The electrolyte for a lithium secondary battery of claim 1, wherein the polymer represented by Formula 1 is at least one selected from the group consisting of polymers represented by Formulas 1a to 1c: ##STR00011## in Formula 1a above, a1, b1, and c1 are each independently an integer of 1 to 10,000, ##STR00012## in Formula 1b above, a2, b2, and c2 are each independently an integer of 1 to 10,000, ##STR00013## in Formula 1c above, a3, b3, and c3 are each independently an integer of 1 to 10,000.

3. The electrolyte for a lithium secondary battery of claim 1, wherein the repeating unit represented by Formula 2 is at least one selected from the group consisting of repeating units represented by Formula 2a and Formula 2b: ##STR00014## in Formula 2a above, m1 and n1 are each independently an integer of 1 to 10,000, and R.sub.0 is —CH(CF.sub.3)CF.sub.2— or —CF(CF.sub.3), ##STR00015## in Formula 2b above, m2 and n2 are each independently an integer of 1 to 10,000, and R.sub.0 is —CH(CF.sub.3)CF.sub.2— or —CF(CF.sub.3).

4. The electrolyte for a lithium secondary battery of claim 3, wherein in Formula 2a and Formula 2b, a molar ratio of m1:n1 and a molar ratio of m2:n2 are 1:1 to 10:1, respectively.

5. The electrolyte for a lithium secondary battery of claim 3, wherein in Formula 2a and Formula 2b, R.sub.0 is —CH(CF.sub.3)CF.sub.2.

6. The electrolyte for a lithium secondary battery of claim 1, wherein the polymer represented by Formula 1 is cross-linked using one or more curing agents selected from the group consisting of a photo-curing agent and a thermal curing agent.

7. The electrolyte for a lithium secondary battery of claim 1, wherein, in the repeating unit represented by Formula 2, R.sub.0 is CH(CF.sub.3)CF.sub.2.

8. The electrolyte for a lithium secondary battery of claim 1, wherein the electrolyte is a solid electrolyte or a gel electrolyte.

9. The electrolyte for a lithium secondary battery of claim 1, wherein the inorganic solid electrolyte particle comprises at least one element selected from the group consisting of Li, La, Zr, O, Ti, Al, Ge, P, W, Nb, Te, Ln, Si, Nd, N, S, Ba, Ga, In, F, Cl, Br, I, As, Se, Sb, Sn, and Ru.

10. The electrolyte for a lithium secondary battery of claim 1, wherein the ferrodielectric comprises at least one element selected from the group consisting of Li, La, O, Ti, Ge, P, Nb, Te, Ba, K, H, D, Ta, Bi, Pb, Rb and As.

11. The electrolyte for a lithium secondary battery of claim 1, wherein the one or more selected from the group consisting of the inorganic solid electrolyte particle and the ferrodielectric is included in an amount of 10 parts by weight to 900 parts by weight based on 100 parts by weight of the polymer.

12. A lithium secondary battery comprising the electrolyte for a lithium secondary battery according to claim 1.

13. The electrolyte for a lithium secondary battery of claim 1, wherein the polymer represented by Formula 1 has a weight molecular weight (Mw) of 1,000 g/mol to 1,000,000 g/mol.

14. The electrolyte for a lithium secondary battery of claim 1, wherein the polymer represented by Formula 2 has a weight molecular weight (Mw) of 5,000 g/mol to 2,000,000 g/mol.

15. The electrolyte for a lithium secondary battery of claim 1, wherein in Formula 2, a molar ratio of m:n is 1:1 to 10:1.

Description

MODE FOR CARRYING OUT THE INVENTION

(1) Hereinafter, the present invention will be described in more detail with reference to specific examples. However, the following examples are merely illustrative of the present invention and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art that various changes and modifications can be made without departing from the scope and spirit of the invention, and it is obvious that such variations and modifications are within the scope of the appended claims.

I. Solid Electrolyte for Lithium Secondary Battery and Lithium Secondary Battery

1. Example 1

(1) Manufacturing Electrode

(2) 94 wt % of a LiCoO.sub.2 compound of 4.2 V level as a positive electrode active material, 4 wt % of carbon black as a conductive material, and 2 wt % of polyvinylidene fluoride (PVDF) as a binder were added to N-methyl-2-pyrrolidone (hereinafter, NMP) which is a solvent to prepare a positive electrode active material slurry (solid content 90 wt %).

(3) The positive electrode active material slurry was applied on the surface of an aluminum (Al) thin film having a thickness of 20 μm, and then dried to prepare a positive electrode plate on which a positive electrode active material layer is formed.

(4) A lithium metal was applied on a Cu thin film, and then roll-pressed to prepare a negative electrode plate having a thickness of 20 μm.

(2) Preparing Solid Electrolyte for Lithium Secondary Battery

(5) To 90 g of an organic solvent (NMP), 4 g of a polymer represented by Formula 1b (weight average molecular weight (Mw)=50,000, a2=380, b2=380, c2=380), 6 g of an inorganic solid electrolyte particle (LLZO) were introduced, followed by further introducing 0.08 g of 2-hydroxy-2-methylpropiophenone (HMPP) as a photo-curing agent thereto and stirring to prepare a composition for an electrolyte for a lithium secondary battery. Thereafter, the composition for an electrolyte for a lithium secondary battery was applied on one surface of the negative electrode plate, dried to remove all the organic solvent (NMP), and cured by being exposed in a UV atmosphere for 2 minutes to form a solid electrolyte having a thickness of 50 μm on the negative electrode plate.

(3) Manufacturing Lithium Secondary Battery

(6) The manufactured positive electrode and the negative electrode on which a solid electrolyte is formed were sequentially laminated such that the solid electrolyte faces the positive electrode to manufacture an electrode assembly. Thereafter, the electrode assembly was received in a pouch-type battery case to manufacture a lithium secondary battery of a 4.2 V level.

2. Example 2

(7) A solid electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 1 except that when preparing the solid electrolyte for a lithium secondary battery, 6 g of LGPS (Li.sub.10GeP.sub.2S.sub.12) was introduced into the composition for an electrolyte for a lithium secondary battery instead of LLZO as an inorganic solid electrolyte particle.

3. Example 3

(8) A solid electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 1 except that when preparing the solid electrolyte for a lithium secondary battery, 6 g of BaTiO.sub.3 was introduced as a ferrodielectric into the composition for an electrolyte for a lithium secondary battery instead of an inorganic solid electrolyte particle (LLZO).

4. Example 4

(9) A solid electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 1 except that when preparing the solid electrolyte for a lithium secondary battery, 4 g of a polymer (weight average molecular weight (Mw)=100,000) represented by Formula 1c was introduced instead of the polymer represented by Formula 1b.

5. Example 5

(10) A solid electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 4 except that when preparing the solid electrolyte for a lithium secondary battery, 1 wt % of TEPi was further introduced as an oxygen inhibitor to the composition for an electrolyte for a lithium secondary battery.

6. Example 6

(11) When preparing the solid electrolyte for a lithium secondary battery, to 99 g of an organic solvent (NMP), 1 g of a polymer including a repeating unit represented by Formula 2a-2 (weight average molecular weight (Mw)=100,000, m12=600, n12=150, m12:n12=4:1) and 1.5 g of an inorganic solid electrolyte particle (LLZO) were introduced, followed stirring to prepare a composition for an electrolyte for a lithium secondary battery. Thereafter, the composition for an electrolyte for a lithium secondary battery was applied on one surface of the negative electrode plate, and all the organic solvent (NMP) was removed to form a solid electrolyte having a thickness of 30 μm on the negative electrode plate.

7. Example 7

(12) A solid electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 6 except that when preparing the solid electrolyte for a lithium secondary battery, 1.5 g of LGPS (Li.sub.10GeP.sub.2S.sub.12) was introduced into the composition for an electrolyte for a lithium secondary battery instead of LLZO as an inorganic solid electrolyte.

8. Example 8

(13) A solid electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 6 except that when preparing the solid electrolyte for a lithium secondary battery, 1.5 g of BaTiO.sub.3 was introduced as a ferrodielectric into the composition for an electrolyte for a lithium secondary battery instead of an inorganic solid electrolyte particle (LLZO).

9. Example 9

(14) A solid electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 6 except that 1 g of a polymer including a repeating unit represented by Formula 2a-3 (weight average molecular weight (Mw)=50,000, m13=320, n13=80, m13:n13=4:1) was introduced instead of the polymer including a repeating unit represented by 2a-2.

10. Example 10

(15) A solid electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 6 except that when preparing the solid electrolyte for a lithium secondary battery, 4 g of an inorganic solid electrolyte particle LLZO was introduced into the composition for an electrolyte for a lithium secondary battery.

11. Example 11

(16) A solid electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 6 except that when preparing the solid electrolyte for a lithium secondary battery, 4 g of an inorganic solid electrolyte particle LGPS was introduced into the composition for an electrolyte for a lithium secondary battery.

12. Example 12

(17) A solid electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 8 except that, when preparing the solid electrolyte for a lithium secondary battery, 4 g of a ferrodielectric BaTiO.sub.3 was introduced into the composition for an electrolyte for a lithium secondary battery.

13. Comparative Example 1

(18) A solid electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 1 except that 4 g of a linear polyethylene oxide copolymer (L-PEO, weight average molecular weight (Mw)=100,000) was used instead of the polymer represented by Formula 1b.

14. Comparative Example 2

(19) When preparing the solid electrolyte for a lithium secondary battery, to 90 g of an organic solvent (NMP), 10 g of a polymer represented by Formula 1b was introduced, followed by further introducing 0.08 g of 2-hydroxy-2-methylpropiophenone (HMPP) as a photo-curing agent thereto and stirring to prepare a composition for an electrolyte for a lithium secondary battery.

15. Comparative Example 3

(20) A solid electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 6 except that 1 g of a linear polyethylene glycol copolymer (L-PEO, weight average molecular weight (Mw)=100,000) was used instead of the polymer including a repeating unit represented by Formula 2a-2.

16. Comparative Example 4

(21) A solid electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 6 except that 1.5 g of an organic solid electrolyte particle LLZO was not introduced to the composition for an electrolyte for a lithium secondary battery.

II. Gel Electrolyte for Lithium Secondary Battery and Lithium Secondary Battery

1. Example 13

(1) Manufacturing Electrode

(22) 94 wt % of a LiCoO.sub.2 compound of 4.2 V level as a positive electrode active material, 4 wt % of carbon black as a conductive material, and 2 wt % of PvDF as a binder component were added to N-methyl-2-pyrrolidone (NMP) which is a solvent to prepare a positive electrode active material slurry (solid content 90 wt %).

(23) The positive electrode active material slurry was applied on the surface of an aluminum (Al) thin film having a thickness of 20 μm, and then dried to prepare a positive electrode plate on which a positive electrode active material layer is formed.

(24) A lithium metal was applied on a Cu thin film, and then roll-pressed to prepare a negative electrode plate having a thickness of 20 μm.

(2) Manufacturing Lithium Secondary Battery

(25) To 95 g of NMP, 2 g of a polymer represented by Formula 1b (weight average molecular weight (Mw)=50,000, a2=380, b2=380, c2=380), 3 g of an inorganic solid electrolyte particle (LLZO) were introduced, followed by further introducing 0.04 g of 2-hydroxy-2-methylpropiophenone (HMPP) as a photo-curing agent thereto and stirring to prepare a composition for an electrolyte for a lithium secondary battery. Thereafter, the composition for an electrolyte was applied on one surface of the negative electrode plate, dried to remove all the organic solvent (NMP), and cured by being exposed in a UV atmosphere for 2 minutes to form a solid electrolyte having a thickness of 1 μm on the negative electrode plate.

(26) The positive electrode/polyolefin-based separator (thickness: 20 μm)/negative electrode on which a solid electrolyte is formed were sequentially laminated to manufacture an electrode assembly. Thereafter, the electrode assembly was received in a pouch-type battery case.

(27) Thereafter, 500 μl of a non-aqueous organic solvent in which 1 M of LiPF.sub.6 is dissolved (FEC:EMC=3:7 vol %) was injected to manufacture a lithium secondary battery (full cell) of a 4.2 V level including a gel electrolyte for a lithium secondary battery formed by impregnating the solid electrolyte to the non-aqueous electrolyte solution.

2. Example 14

(28) A gel electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 13 except that 3 g of LGPS (Li.sub.10GeP.sub.2S.sub.12) was introduced into the composition for an electrolyte for a lithium secondary battery instead of LLZO as an inorganic solid electrolyte particle.

3. Example 15

(29) A gel electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 13 except that 3 g of BaTiO.sub.3 was introduced as a ferrodielectric into the composition for an electrolyte for a lithium secondary battery instead of an inorganic solid electrolyte particle (LLZO).

4. Example 16

(30) A gel electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 13 except that 2 g of a polymer (weight average molecular weight (Mw)=100,000) represented by Formula 1c was introduced instead of the polymer represented by Formula 1b.

5. Example 17

(31) A gel electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 13 except that 1 wt % of TEPi was further introduced as an oxygen inhibitor to the composition for an electrolyte for a lithium secondary battery.

6. Example 18

(32) A gel electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 13 except that 100 μl of an ionic liquid (Pyr13-FSI) was further introduced after the non-aqueous electrolyte solution was injected.

7. Example 19

(33) To 99 g of NMP, 1 g of a polymer including a repeating unit represented by Formula 2a-2 (weight average molecular weight (Mw)=100,000, m12=600, n12=150, m12:n12=4:1) and 1.5 g of an inorganic solid electrolyte particle (LLZO) were introduced, followed stirring to prepare a composition for an electrolyte for a lithium secondary battery. Thereafter, the composition for an electrolyte for a lithium secondary battery was applied on one surface of the negative electrode plate, and all the organic solvent (NMP) was removed to form a solid electrolyte having a thickness of 1.0 μm on the negative electrode plate.

(34) The manufactured positive electrode, negative electrode including a solid electrolyte, and polyolefin-based separator (thickness: 20 μm) were sequentially laminated to manufacture an electrode assembly. Thereafter, the electrode assembly was received in a pouch-type battery case.

(35) Thereafter, 700 μl of a non-aqueous organic solvent in which 1 M of LiPF.sub.6 is dissolved (FEC:EMC=3:7 vol %) was injected to manufacture a lithium secondary battery (full cell) of a 4.2 V level including a gel electrolyte for a lithium secondary battery formed by impregnating the solid electrolyte to the non-aqueous electrolyte solution.

8. Example 20

(36) A gel electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 19 except that 1.5 g of LGPS was introduced as an inorganic solid electrolyte particle instead of LLZO.

9. Example 21

(37) A gel electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 19 except that 1.5 g of BaTiO.sub.3 was introduced as a ferrodielectric into the composition for an electrolyte for a lithium secondary battery instead of 1.5 g of an inorganic solid electrolyte particle LLZO.

10. Example 22

(38) A gel electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 19 except that 1 g of a polymer including a repeating unit represented by Formula 2a-3 (weight average molecular weight (Mw)=50,000, m13=320, n13=80, m13:n13=4:1) was introduced instead of the polymer including a repeating unit represented by 2a-2 (weight average molecular weight (Mw)=100,000, m12=600, n12=150, m12:n12=4:1).

11. Example 23

(39) A gel electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 19 except that 4 g of an inorganic solid electrolyte particle LLZO was introduced to the composition for an electrolyte for a lithium secondary battery.

12. Example 24

(40) A gel electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 19 except that 4 g of an inorganic solid electrolyte particle LGPS was introduced to the composition for an electrolyte for a lithium secondary battery.

13. Example 25

(41) A gel electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 19 except that 4 g of BaTiO.sub.3 was introduced as a ferrodielectric to the composition for an electrolyte for a lithium secondary battery.

14. Example 26

(42) A gel electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 19 except that when manufacturing a lithium secondary battery in Example 19, 140 μl of an ionic liquid (Pyr13-FSI) was further introduced after the non-aqueous electrolyte solution was injected.

15. Comparative Example 5

(43) A gel electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 13 except that 2 g of a linear polyethylene oxide copolymer (L-PEO, weight average molecular weight (Mw)=100,000) was used for the composition for an electrolyte for a lithium secondary battery instead of the polymer represented by Formula 1b.

16. Comparative Example 6

(44) A gel electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 13 except that to 95 g of an organic solvent (NMP), 5 g of a polymer represented by Formula 1b was introduced (weight average molecular weight (Mw)=50,000, a2=380, b2=380, c2=380), followed by further introducing 0.04 g of 2-hydroxy-2-methylpropiophenone (HMPP) as a photo-curing agent thereto and stirring to prepare a composition for an electrolyte for a lithium secondary battery.

17. Comparative Example 7

(45) A gel electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 19 except that 1 g of a linear polyethylene glycol copolymer (L-PEO, weight average molecular weight (Mw)=100,000) was used for the composition for an electrolyte for a lithium secondary battery instead of the polymer including a repeating unit represented by Formula 2a-2.

18. Comparative Example 8

(46) A gel electrolyte for a lithium secondary battery and a lithium secondary battery including the same were manufactured in the same manner as in Example 19 except that 1.5 g of an inorganic solid electrolyte particle LLZO was not introduced to the composition for an electrolyte for a lithium secondary battery.

EXPERIMENTAL EXAMPLES

1. Experimental Example 1. Evaluation of Mechanical Strength of Solid Electrolyte for Lithium Secondary Battery

(47) The solid electrolyte for a lithium secondary battery prepared in each of Examples 1 to 12, and the solid electrolyte for a lithium secondary battery prepared in each of Comparative Examples 1 to 4 were subjected to a mechanical strength test through the measurement of tensile strength.

(48) At this time, electrolyte specimens were prepared using ASTM standard D638 (Type V specimens) and the tensile strength was measured at 25° C., at a rate of 5 mm per minute, and at a relative humidity of about 30% through Lloyd LR-10K. The results are shown in Table 1 below.

(49) TABLE-US-00001 TABLE 1 Tensile strength (MPa) Example 1 15.7 Example 2 13.8 Example 3 14.1 Example 4 18.9 Example 5 22.5 Example 6 12.9 Example 7 13.1 Example 8 10.2 Example 9 9.5 Example 10 10.6 Example 11 10.1 Example 12 8.2 Comparative Example 1 4.6 Comparative Example 2 9.8 Comparative Example 3 4.6 Comparative Example 4 2.8

(50) Referring to Table 1, the tensile strength of the solid electrolyte for a lithium secondary battery prepared according to each of Examples is higher than that of the solid electrolyte for a lithium secondary battery prepared according to each of Comparative Examples.

2. Experimental Example 2. Evaluation of Ion Conductivity of Electrolyte for Lithium Secondary Battery

(51) A gold (Au) electrode was coated in a circular form with a diameter of 1 mm using a sputtering method on an upper portion of the electrolytes prepared according to each of Examples and Comparative Examples, and ion conductivity was measured at 25° C. using an alternating current impedance measurement method. The ion conductivity was measured using a VMP3 measurement device and 4294A at a frequency band of 100 MHz to 0.1 Hz. The measurement results are shown in Table 2 below.

(52) TABLE-US-00002 TABLE 2 Ion conductivity (S/cm) Example 1 6.7 × 10.sup.−5 Example 2 7.7 × 10.sup.−5 Example 3 7.2 × 10.sup.−5 Example 4 4.9 × 10.sup.−5 Example 5 4.3 × 10.sup.−5 Example 6 8.9 × 10.sup.−5 Example 7 8.6 × 10.sup.−5 Example 8 7.1 × 10.sup.−5 Example 9 9.2 × 10.sup.−5 Example 10 9.6 × 10.sup.−5 Example 11 9.4 × 10.sup.−5 Example 12 7.1 × 10.sup.−5 Example 13 2.8 × 10.sup.−4 Example 14 3.2 × 10.sup.−4 Example 15 3.0 × 10.sup.−4 Example 16 2.8 × 10.sup.−4 Example 17 2.7 × 10.sup.−4 Example 18 2.9 × 10.sup.−4 Example 19 4.6 × 10.sup.−4 Example 20 5.1 × 10.sup.−4 Example 21 3.2 × 10.sup.−4 Example 22 4.8 × 10.sup.−4 Example 23 5.2 × 10.sup.−4 Example 24 5.3 × 10.sup.−4 Example 25 3.5 × 10.sup.−4 Example 26 4.1 × 10.sup.−4 Comparative Example 1 1.8 × 10.sup.−6 Comparative Example 2 2.9 × 10.sup.−5 Comparative Example 3 3.5 × 10.sup.−6 Comparative Example 4 1.8 × 10.sup.−6 Comparative Example 5 1.4 × 10.sup.−4 Comparative Example 6 1.7 × 10.sup.−4 Comparative Example 7 8.6 × 10.sup.−5 Comparative Example 8 7.7 × 10.sup.−5

(53) Referring to Table 2, the electrolyte according to each of Examples 1 to 5 has a higher ion conductivity than the electrolyte according to each of Comparative Examples 1 and 2, and the electrolyte according to each of Examples 13 to 18 has a higher ion conductivity than the electrolyte according to each of Comparative Examples 4 and 5. Meanwhile, the electrolyte according to each of Examples 6 to 10 has a higher ion conductivity than the electrolyte according to each of Comparative Examples 3 and 4, and the electrolyte according to each of Examples 19 to 26 has a higher ion conductivity than the electrolyte according to each of Comparative Examples 7 and 8.

3. Experimental Example 3. Evaluation of Capacity Retention Rate of Lithium Secondary Battery at Room Temperature

(54) The lithium secondary battery manufactured according to each of Examples and Comparative Examples was subjected to formation, and charged/discharged once at a charge/discharge rate of 0.2 C/0.5 C under a temperature condition of room temperature (25° C.), respectively. At this time, the first charge/discharge state was defined as the initial charge, and the number of cycles (n) at the time when the capacity retention rate with respect to the initial capacity was maintained at 80% was measured. The values are respectively shown in Table 3 below.

(55) TABLE-US-00003 TABLE 3 Number of cycles (n) Example 1 48 Example 2 39 Example 3 45 Example 4 52 Example 5 56 Example 6 56 Example 7 54 Example 8 48 Example 9 62 Example 10 59 Example 11 59 Example 12 44 Example 13 124 Example 14 120 Example 15 107 Example 16 116 Example 17 119 Example 18 106 Example 19 92 Example 20 85 Example 21 82 Example 22 95 Example 23 80 Example 24 81 Example 25 80 Example 26 87 Comparative Example 1 10 Comparative Example 2 22 Comparative Example 3 22 Comparative Example 4 20 Comparative Example 5 35 Comparative Example 6 41 Comparative Example 7 45 Comparative Example 8 40

(56) Referring to Table 3, the lithium secondary battery according to each of Examples 1 to 5 has a higher cycle number than the lithium secondary battery according to each of Comparative Examples 1 and 2, and the lithium secondary battery according to each of Examples 13 to 18 has a higher cycle number than the lithium secondary battery according to each of Comparative Examples 4 and 5. Meanwhile, the lithium secondary battery according to each of Examples 6 to 1 has a higher cycle number than the lithium secondary battery according to each of Comparative Examples 3 and 4, and the lithium secondary battery according to each of Examples 19 to 26 has a higher cycle number than the lithium secondary battery according to each of Comparative Examples 7 and 8.

4. Experimental Example 4. Evaluation of High Temperature (45° C.) Capacity Retention Rate of Lithium Secondary Battery

(57) The lithium secondary battery manufactured according to each of Examples and Comparative Examples was subjected to formation, and charged/discharged once at a charge/discharge rate of 0.2 C/0.5 C at 45° C., respectively. At this time, the first charge/discharge state was defined as the initial charge, and the number of cycles (n) at the time when the capacity retention rate with respect to the initial capacity was maintained at 80% was measured. The values are respectively shown in Table 4 below.

(58) TABLE-US-00004 TABLE 4 Number of cycles (n) Example 1 71 Example 2 60 Example 3 65 Example 4 75 Example 5 67 Example 6 63 Example 7 60 Example 8 60 Example 9 67 Example 10 77 Example 11 74 Example 12 70 Example 13 138 Example 14 129 Example 15 116 Example 16 121 Example 17 140 Example 18 138 Example 19 121 Example 20 118 Example 21 107 Example 22 122 Example 23 106 Example 24 102 Example 25 97 Example 26 116 Comparative Example 1 16 Comparative Example 2 20 Comparative Example 3 20 Comparative Example 4 16 Comparative Example 5 12 Comparative Example 6 18 Comparative Example 7 15 Comparative Example 8 12

(59) Referring to Table 4, the lithium secondary battery according to each of Examples has a higher cycle number than the lithium secondary battery according to each of Comparative Examples under high temperature conditions.

5. Experimental Example 5: High-Temperature Electrochemical Stability Test

(60) The lithium secondary battery manufactured in each of Examples 6 to 12 and Comparative Examples 3 and 4 were measured for oxidation starting voltage at a high temperature (60° C.) using a linear sweep voltammetry (LSV) method or a cyclic voltammetry method up to 8 V.

(61) The results are shown in Table 5 below.

(62) TABLE-US-00005 TABLE 5 High-temperature oxidation stability (V) @ 60° C. Example 6 5.5 Example 7 5.4 Example 8 5.7 Example 9 5.2 Example 10 6.2 Example 11 5.9 Example 12 6.7 Comparative Example 3 4.9 Comparative Example 4 4.6

(63) As shown in Table 5, all of the lithium secondary batteries manufactured in Examples 6 to 12 exhibited an oxidation starting voltage at about 5.0 V or higher, so that it can be confirmed that the electrochemical (oxidation) safety thereof at high temperatures is high. On the contrary, in the case of the lithium secondary batteries manufactured in Comparative Examples 3 and 4, the oxidation starting voltage thereof was all lower than 5.0 V, so that it can be confirmed that the electrochemical (oxidation) safety thereof at high temperatures is lower than that of the lithium secondary batteries according to Examples.