Non-aqueous electrolyte additive, and non-aqueous electrolyte for lithium secondary battery comprising the same and lithium secondary battery

Abstract

The present invention relates to a non-aqueous electrolyte additive, and a non-aqueous electrolyte for a lithium secondary battery including the same and a lithium secondary battery, and particularly, to a non-aqueous electrolyte additive having a nitrile group and a propargyl group, and a non-aqueous electrolyte for a lithium secondary battery and a lithium secondary battery, which include the non-aqueous electrolyte additive so that capacity and cycle lifespan characteristics at high temperature can be improved.

Claims

1. A non-aqueous electrolyte additive comprising at least one compound selected from the group consisting of compounds represented by Formula I and Formula II below: ##STR00015## wherein R.sub.1 is a C.sub.1 to C.sub.5 linear or nonlinear alkylene group substituted or unsubstituted with at least one nitrile group, or a C.sub.6 to C.sub.8 aromatic group substituted or unsubstituted with at least one nitrile group, R.sub.2 is a C.sub.1 to C.sub.5 linear or nonlinear alkylene group substituted or unsubstituted with at least one nitrile group, a C.sub.6 to C.sub.8 aromatic group substituted or unsubstituted with at least one nitrile group, a C.sub.6 to C.sub.8 heteroaromatic group substituted or unsubstituted with at least one nitrile group, a C.sub.2 to C.sub.5 linear or nonlinear alkenyl group, or C(O)R.sub.9, wherein R.sub.9 is a C.sub.1 to C.sub.3 linear or nonlinear alkylene group substituted with at least one nitrile group, R.sub.3 is hydrogen or a C.sub.1 to C.sub.5 linear or nonlinear unsubstituted alkyl group when m is 0, and a C.sub.1 to C.sub.5 linear or nonlinear alkylene group when m is 1, R.sub.4 is a C.sub.1 to C.sub.3 alkylene group or R.sub.10C(O), wherein R.sub.10 is a C.sub.1 to C.sub.3 alkylene group, and n and m each independently are an integer of 0 or 1, ##STR00016## wherein R.sub.5 is hydrogen or a C.sub.1 to C.sub.5 linear or nonlinear alkyl group substituted or unsubstituted with at least one nitrile group, wherein R.sub.6 is a C.sub.1 to C.sub.5 linear or nonlinear alkylene group, and wherein R.sub.7 to R.sub.8 each independently are a C.sub.1, C.sub.3, C.sub.4, or C.sub.5 linear or nonlinear alkylene group.

2. The non-aqueous electrolyte additive of claim 1, wherein the non-aqueous electrolyte additive comprises at least one compound selected from the group consisting of compounds represented by Formulae I-1 to I-9 and I-11 to I-23, and I-25 to I-39 below: ##STR00017## ##STR00018## ##STR00019## ##STR00020##

3. The non-aqueous electrolyte additive of claim 1, wherein the non-aqueous electrolyte additive comprises at least one compound selected from the group consisting of compounds represented by Formula II-1 to Formula II 3 below: ##STR00021##

4. A non-aqueous electrolyte for a lithium secondary battery comprising: an ionizable lithium salt; an organic solvent; and a non-aqueous electrolyte additive, wherein the non-aqueous electrolyte additive includes at least one compound selected from the group consisting of compounds represented by Formula I and Formula II below: ##STR00022## wherein R.sub.1 is a C.sub.1 to C.sub.5 linear or nonlinear alkylene group substituted or unsubstituted with at least one nitrile group, or a C.sub.6 to C.sub.8 aromatic group substituted or unsubstituted with at least one nitrile group, R.sub.2 is a C.sub.1 to C.sub.5 linear or nonlinear alkylene group substituted or unsubstituted with at least one nitrile group, a C.sub.6 to C.sub.8 aromatic group substituted or unsubstituted with at least one nitrile group, a C.sub.6 to C.sub.8 heteroaromatic group substituted or unsubstituted with at least one nitrile group, a C.sub.2 to C.sub.5 linear or nonlinear alkenyl group, or C(O)R.sub.9, wherein R.sub.9 is a C.sub.1 to C3 linear or nonlinear alkylene group substituted with at least one nitrile group, R.sub.3 is hydrogen or a C.sub.1 to C.sub.5 linear or nonlinear unsubstituted alkyl group when m is 0, and a C.sub.1 to C.sub.5 linear or nonlinear alkylene group when m is 1, R.sub.4 is a C.sub.1 to C.sub.3 alkylene group or R.sub.10C(O), wherein R.sub.10 is a C.sub.1 to C.sub.3 alkylene group, and n and m each independently are an integer of 0 or 1, ##STR00023## wherein R.sub.5 is hydrogen or a C.sub.1 to C.sub.5 linear or nonlinear alkyl group substituted or unsubstituted with at least one nitrile group, wherein R.sub.6 is a C.sub.1 to C.sub.5 linear or nonlinear alkylene group, and wherein R.sub.7 to R.sub.8 each independently are a C.sub.1, C.sub.3, C.sub.4, or C.sub.5 linear or nonlinear alkylene group.

5. The non-aqueous electrolyte of claim 4, wherein the non-aqueous electrolyte additive is included at 0.5 wt % to 5 wt % based on a total content of the non-aqueous electrolyte.

6. The non-aqueous electrolyte of claim 5, wherein the non-aqueous electrolyte additive is included at 1 wt % to 5 wt % based on a total content of the non-aqueous electrolyte.

7. The non-aqueous electrolyte of claim 4, wherein the lithium salt includes Li.sup.+ as a cation and any one selected from the group consisting of F.sup.-, Cl.sup.-, Br.sup.-, I.sup.-, NO.sub.3.sup.-, N(CN).sub.2.sup.-, BF.sub.4.sup.-,ClO.sub.4.sup.-, AlO.sub.4.sup.-, AlCl.sub.4.sup.-, PF.sub.6.sup.-, SbF.sub.6.sup.-, AsF.sub.6.sup.-, BF.sub.2C.sub.2O.sub.4.sup.-, BC.sub.4O.sub.8.sup.-, (CF.sub.3).sub.2PF.sub.4.sup.-, (CF.sub.3).sub.3PF.sub.3.sup.-, (CF.sub.3).sub.4PF.sub.2.sup.-, (CF.sub.3).sub.5PF.sup.-, (CF.sub.3).sub.6P.sup.-, CF.sub.3SO.sub.3.sup.-, C.sub.4F.sub.9SO.sub.3.sup.-, CF.sub.3CF.sub.2SO.sub.3.sup.-, (CF.sub.3SO.sub.2).sub.2N.sup.-, (F.sub.2SO.sub.2).sub.2N.sup.-, CF.sub.3CF.sub.2(CF.sub.3).sub.2CO.sup.-, (CF.sub.3SO.sub.2).sub.2CH.sup.-, CF.sub.3(CF.sub.2).sub.7SO.sub.3.sup.-, CF.sub.3CO.sub.2.sup.-, CH.sub.3CO.sub.2.sup.-, SCN.sup.-, and (CF.sub.3CF.sub.2SO.sub.2).sub.2N.sup.-as an anion.

8. The non-aqueous electrolyte of claim 4, wherein the organic solvent includes a mixture of at least one selected from the group consisting of an ether, an ester, an amide, a linear carbonate, and a cyclic carbonate.

9. A lithium secondary battery comprising a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and a non-aqueous electrolyte, wherein the non-aqueous electrolyte is the non-aqueous electrolyte for a lithium secondary battery according to claim 4.

Description

EXAMPLES

Example 1

(1) (Preparation of Non-Aqueous Electrolyte)

(2) 1 M LiPF.sub.6 was dissolved in a mixed organic solvent in which ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) were mixed (20:10:70 vol %), and then a compound of Formula I-1 was added at a content listed in Table 1 below to prepare a non-aqueous electrolyte.

(3) (Manufacture of Positive Electrode)

(4) A lithium cobalt composite oxide (LiCO.sub.2) as a positive electrode active material particle, carbon black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were added in a weight ratio of 90:5:5 (wt %) to N-methyl-2-pyrrolidone (NMP) as a solvent in a weight ratio of 100:40 to prepare a positive electrode active material slurry. The positive electrode active material slurry was applied on a positive electrode current collector (Al thin film) having a thickness of 100 m, dried, and roll-pressed to manufacture a positive electrode.

(5) (Manufacture of Negative Electrode)

(6) Natural graphite as a negative electrode active material, PVDF as a binder, and carbon black as a conductive material were added in a weight ratio of 95:2:3 (wt %) to NMP as a solvent in a weight ratio of 100:100 to prepare a negative electrode active material slurry. The negative electrode active material slurry was applied on a negative electrode current collector (Cu thin film) having a thickness of 90 m, dried, and roll-pressed to manufacture a negative electrode.

(7) (Manufacture of Secondary Battery)

(8) The positive electrode and the negative electrode manufactured by the above-described methods were laminated together with a porous polyethylene film to manufacture an electrode assembly. Afterward, the electrode assembly thus manufactured was put into a battery case, and the above-prepared non-aqueous electrolyte was injected into the battery case and sealed to manufacture a lithium secondary battery.

Examples 2 to 28

(9) Each of non-aqueous electrolytes and secondary batteries including the same according to Examples 2 to 28 was manufactured in the same manner as in Example 1 except that each additive was included at a content listed in Table 1 below when a non-aqueous electrolyte was prepared in Example 1.

Example 29

(10) (Preparation of Non-Aqueous Electrolyte)

(11) 1 M LiPF.sub.6 was dissolved in a mixed organic solvent in which ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) were mixed (20:10:70 vol%), and then a compound of Formula I-1 was added at a content listed in Table 2 below to prepare a non-aqueous electrolyte.

(12) (Manufacture of Positive Electrode)

(13) A lithium cobalt composite oxide (LiCO.sub.2) as a positive electrode active material particle, carbon black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were added in a weight ratio of 90:5:5 (wt %) to N-methyl-2-pyrrolidone (NMP) as a solvent in a weight ratio of 100:40 to prepare a positive electrode active material slurry. The positive electrode active material slurry was applied on a positive electrode current collector (Al thin film) having a thickness of 100 m, dried, and roll-pressed to manufacture a positive electrode.

(14) (Manufacture of Secondary Battery)

(15) The positive electrode thus manufactured was punched to be used for a coin-type battery, and three iron (Fe) powders having an average particle size (D50) of about 200 pm were fixed on a surface of the positive electrode. Afterward, the non-aqueous electrolyte was injected to manufacture a coin-type half-secondary battery.

Examples 30 to 56

(16) Each of non-aqueous electrolytes and secondary batteries including the same according to Examples 30 to 56 was manufactured in the same manner as in Example 29 except that each additive was included at a content listed in Table 2 below when a non-aqueous electrolyte was prepared in Example 29.

Comparative Example 1

(17) A non-aqueous electrolyte and a secondary battery including the same were manufactured in the same manner as in Example 1 except that an additive was not included when a non-aqueous electrolyte was prepared in Example 1.

Comparative Example 2

(18) As shown in Table 1 below, a non-aqueous electrolyte and a secondary battery including the same were manufactured in the same manner as in Example 1 except that 0.3 g of a compound of Formula a below was included instead of a compound of Formula I-1 when a non-aqueous electrolyte was prepared in Example 1.

(19) ##STR00011##

Comparative Example 3

(20) As shown in Table 1 below, a non-aqueous electrolyte and a secondary battery including the same were manufactured in the same manner as in Comparative Example 2 except that 0.5 g of a compound of Formula a was included when a non-aqueous electrolyte was prepared in Comparative Example 2.

Comparative Example 4

(21) As shown in Table 1 below, a non-aqueous electrolyte and a secondary battery including the same were manufactured in the same manner as in Comparative Example 2 except that 7 g of a compound of Formula a was included when a non-aqueous electrolyte was prepared in Comparative Example 2.

Comparative Example 5

(22) As shown in Table 1 below, a non-aqueous electrolyte and a secondary battery including the same were manufactured in the same manner as in Comparative Example 2 except that 0.5 g of a compound of Formula b below was included when a non-aqueous electrolyte was prepared in Comparative Example 2.

(23) ##STR00012##

Comparative Example 6

(24) As shown in Table 1 below, a non-aqueous electrolyte and a secondary battery including the same were manufactured in the same manner as in Comparative Example 2 except that 0.3 g of a compound of Formula c below was included when a non-aqueous electrolyte was prepared in Comparative Example 2.

(25) ##STR00013##

Comparative Example 7

(26) As shown in Table 1 below, a non-aqueous electrolyte and a secondary battery including the same were manufactured in the same manner as in Comparative Example 2 except that 0.5 g of a compound of Formula c was included when a non-aqueous electrolyte was prepared in Comparative Example 2.

Comparative Example 8

(27) As shown in Table 1 below, a non-aqueous electrolyte and a secondary battery including the same were manufactured in the same manner as in Comparative Example 2 except that 7 g of a compound of Formula c was included when a non-aqueous electrolyte was prepared in Comparative Example 2.

Comparative Example 9

(28) As shown in Table 1 below, a non-aqueous electrolyte and a secondary battery including the same were manufactured in the same manner as in Comparative

(29) Example 2 except that 0.5 g of a compound of Formula d below was included when a non-aqueous electrolyte was prepared in Comparative Example 2.

(30) ##STR00014##

Comparative Example 10

(31) A non-aqueous electrolyte and a coin-type half-secondary battery including the same were manufactured in the same manner as in Example 29 except that an additive was not included when a non-aqueous electrolyte was prepared in Example 29.

Comparative Example 11

(32) As shown in Table 2 below, a non-aqueous electrolyte and a coin-type half-secondary battery including the same were manufactured in the same manner as in Comparative Example 10 except that 0.3 g of a compound of Formula a was included when a non-aqueous electrolyte was prepared in Comparative Example 10.

Comparative Example 12

(33) As shown in Table 2 below, a non-aqueous electrolyte and a coin-type half-secondary battery including the same were manufactured in the same manner as in Comparative Example 10 except that 0.5 g of a compound of Formula a was included when a non-aqueous electrolyte was prepared in Comparative Example 10.

Comparative Example 13

(34) As shown in Table 2 below, a non-aqueous electrolyte and a coin-type half-secondary battery including the same were manufactured in the same manner as in Comparative Example 10 except that 7 g of a compound of Formula a was included when a non-aqueous electrolyte was prepared in Comparative Example 10.

Comparative Example 14

(35) As shown in Table 2 below, a non-aqueous electrolyte and a coin-type half-secondary battery including the same were manufactured in the same manner as in Comparative Example 10 except that 0.5 g of a compound of Formula b was included when a non-aqueous electrolyte was prepared in Comparative Example 10.

Comparative Example 15

(36) As shown in Table 2 below, a non-aqueous electrolyte and a coin-type half-secondary battery including the same were manufactured in the same manner as in Comparative Example 10 except that 0.3 g of a compound of Formula c was included when a non-aqueous electrolyte was prepared in Comparative Example 10.

Comparative Example 16

(37) As shown in Table 2 below, a non-aqueous electrolyte and a coin-type half-secondary battery including the same were manufactured in the same manner as in Comparative Example 10 except that 0.5 g of a compound of Formula c was included when a non-aqueous electrolyte was prepared in Comparative Example 10.

Comparative Example 17

(38) As shown in Table 2 below, a non-aqueous electrolyte and a coin-type half-secondary battery including the same were manufactured in the same manner as in Comparative Example 10 except that 7 g of a compound of Formula c was included.

Comparative Example 18

(39) As shown in Table 2 below, a non-aqueous electrolyte and a coin-type half-secondary battery including the same were manufactured in the same manner as in Comparative Example 10 except that 0.5 g of a compound of Formula d was included.

EXPERIMENTAL EXAMPLES

Experimental Example 1

(40) Each of the secondary batteries according to Examples 1 to 28 and Comparative Examples 1 to 9 was charged at a rate of 0.8 C until 4.35V under constant current(CC)/constant voltage(CV) conditions, cut off at 0.05 C, and discharged at 0.5 C until 3.0V (initial discharge capacity). Subsequently, the secondary battery was charged at a rate of 0.8 C until 4.35V under CC/CV conditions, cut off at 0.05 C, and then stored at 60 C. for 2 weeks. Afterward, the secondary battery was discharged at 0.5 C until 3.0V at room temperature, and then discharge capacity thereof was measured (residual discharge capacity). The secondary battery was charged again at a rate of 0.8 C until 4.35V under CC/CV conditions, cut off at 0.05 C, and then discharged at 0.5 C until 3.0V. Afterward, discharge capacity thereof was measured (recovery discharge capacity).

(41) The residual discharge capacity and recovery discharge capacity with respect to initial discharge capacity were calculated as a percentage, and these are shown in Table 1 below.

Experimental Example 2

(42) Each of the secondary batteries according to Examples 1 to 28 and Comparative Examples 1 to 9 was charged at a rate of 0.8 C until 4.35V under constant current(CC)/constant voltage(CV) conditions, cut off at 0.05 C, and discharged at 0.5 C until 3.0V. Subsequently, the secondary battery was charged at a rate of 0.8 C until 4.35V under CC/CV conditions, cut off at 0.05 C, and discharged at 0.5 C until 3.0V at room temperature. This process was determined as one cycle and repeated for 200 cycles. Afterward, cycle capacity retention with respect to one cycle capacity was calculated as a percentage, and these are shown in Table 1 below.

(43) TABLE-US-00001 TABLE 1 Content of non-aqueous Residual Recovery Cycle organic Additive discharge discharge capacity Example solvent (g) Formula Content (g) capacity (%) capacity (%) retention (%) Example 1 99.5 I-1 0.5 85 95 91 Example 2 99.5 I-2 0.5 83 96 90 Example 3 99.5 I-3 0.5 80 94 88 Example 4 99.5 I-5 0.5 87 93 90 Example 5 99.5 I-6 0.5 85 94 93 Example 6 99.5 I-9 0.5 83 95 89 Example 7 99.5 I-10 0.5 81 95 90 Example 8 99.5 I-12 0.5 84 93 91 Example 9 99.5 I-13 0.5 85 96 92 Example 10 99.5 I-14 0.5 83 94 88 Example 11 99.5 I-15 0.5 85 94 93 Example 12 99.5 I-16 0.5 81 92 93 Example 13 99.5 I-37 0.5 82 93 89 Example 14 99.5 I-39 0.5 82 95 87 Example 15 99 I-5 1 90 96 93 Example 16 95 I-5 5 89 94 88 Example 17 99.5 I-24 0.5 84 93 89 Example 18 99.5 I-25 0.5 81 95 91 Example 19 99.5 I-26 0.5 80 93 89 Example 20 99.5 I-28 0.5 85 93 92 Example 21 99.5 I-29 0.5 85 95 94 Example 22 99.5 II-1.sup. 0.5 81 92 90 Example 23 99.5 II-3.sup. 0.5 82 92 92 Example 24 99.5 II-4.sup. 0.5 84 95 93 Example 25 99.5 I-35 0.5 82 92 92 Example 26 99.5 I-36 0.5 84 93 90 Example 27 95 I-24 5 91 97 95 Example 28 99 I-24 1 88 95 92 Comparative 100 X X 64 80 60 Example 1 Comparative 99.7 a 0.3 80 87 65 Example 2 Comparative 99.5 a 0.5 70 80 65 Example 3 Comparative 93 a 7 76 85 70 Example 4 Comparative 99.5 b 0.5 72 83 70 Example 5 Comparative 99.7 c 0.3 69 84 71 Example 6 Comparative 99.5 c 0.5 73 84 69 Example 7 Comparative 93 c 7 76 85 70 Example 8 Comparative 99.5 d 0.5 67 82 64 Example 9

(44) As shown in Table 1, it can be seen that the secondary batteries according to Examples 1 to 28, in which the non-aqueous electrolyte including a compound containing a nitrile group and a propargyl group as an additive according to the present invention was included, had a residual discharge capacity of about 80% or more, a recovery discharge capacity of about 92% or more, and a cycle capacity retention of about 87% or more when stored at high temperature, all of which are excellent.

(45) On the other hand, it can be confirmed that the secondary battery according to Comparative Example 1, in which an additive was not used, had a residual discharge capacity of about 64%, a recovery discharge capacity of about 80%, and a cycle capacity retention of about 60% when stored at high temperature, which indicates that performance in various aspects was degraded compared to the secondary batteries according to Examples 1 to 28.

(46) In addition, it can be confirmed that the secondary batteries according to Comparative Examples 2 to 9, in which compounds of Formulas a to d were included as a non-aqueous electrolyte additive, had a residual discharge capacity of about 80% or less, a recovery discharge capacity of about 87% or less, and a cycle capacity retention of about 70% or less when stored at high temperature, all of which are less than those of the secondary batteries according to Examples 1 to 28.

Experimental Example 3

(47) Each of the coin-type half-secondary batteries according to Examples 29 to 56 and Comparative Examples 10 to 18 was charged at a rate of 0.8 C until 4.35V under CC/CV conditions, cut off at 0.05 C, and discharged at 0.5 C until 3.0V. In each example, five batteries were manufactured, and the number of batteries capable of charging and discharging was counted, the results of which are shown in Table 2 below.

(48) In addition, the batteries capable of charging and discharging were charged at a rate of 0.8 C until 4.35V under CC/CV conditions, and then stored at 45 C. for 6 days. After storage, voltage was measured at 45 C., the results of which are shown in Table 2 below.

(49) TABLE-US-00002 TABLE 2 Content Number of Voltage of non- battery capable after aqueous of charging and storage organic Additive discharging at high solvent Content (Possibility/ temperature (g) Formula (g) Manufacture) (V) Example 29 99.5 I-1 0.5 4/5 4.13 Example 30 99.5 I-2 0.5 4/5 4.05 Example 31 99.5 I-3 0.5 4/5 4.10 Example 32 99.5 I-5 0.5 4/5 4.12 Example 33 99.5 I-6 0.5 3/5 4.16 Example 34 99.5 I-9 0.5 3/5 4.02 Example 35 99.5 I-10 0.5 4/5 4.08 Example 36 99.5 I-12 0.5 4/5 4.10 Example 37 99.5 I-13 0.5 4/5 4.01 Example 38 99.5 I-14 0.5 4/5 4.05 Example 39 99.5 I-15 0.5 4/5 4.03 Example 40 99.5 I-16 0.5 5/5 4.09 Example 41 99.5 I-37 0.5 5/5 4.22 Example 42 99.5 I-39 0.5 5/5 4.17 Example 43 99 I-5 1 5/5 4.19 Example 44 95 I-5 5 5/5 4.26 Example 45 99.5 I-24 0.5 5/5 4.20 Example 46 99.5 I-25 0.5 4/5 4.02 Example 47 99.5 I-26 0.5 4/5 4.11 Example 48 99.5 I-28 0.5 4/5 4.16 Example 49 99.5 I-29 0.5 3/5 4.10 Example 50 99.5 II-1 0.5 5/5 4.18 Example 51 99.5 II-3 0.5 4/5 4.06 Example 52 99.5 II-4 0.5 4/5 4.10 Example 53 99.5 I-35 0.5 4/5 4.04 Example 54 99.5 I-36 0.5 4/5 4.01 Example 55 95 I-24 5 4/5 4.02 Example 56 99 I-24 1 5/5 4.15 Comparative 100 X X 0/5 2.65 Example 10 Comparative 99.7 a 0.3 1/5 3.45 Example 11 Comparative 99.5 a 0.5 3/5 3.67 Example 12 Comparative 93 a 7 5/5 3.93 Example 13 Comparative 99.5 b 0.5 3/5 3.55 Example 14 Comparative 99.7 c 0.3 1/5 3.55 Example 15 Comparative 99.5 c 0.5 3/5 3.87 Example 16 Comparative 93 c 7 5/5 3.93 Example 17 Comparative 99.5 d 0.5 1/5 3.34 Example 18

(50) As shown in Table 2, it can be seen that the secondary batteries according to Examples 29 to 56 were capable of charging and discharging in most cases, and maintained a voltage of about 4.01V or more even when stored at high temperature because a compound containing a nitrile group and a propargyl group included as an additive formed a complex through combination with Fe impurities to suppress elution of metal ions.

(51) On the other hand, it can be seen that the secondary battery according to Comparative Example 10, in which an additive was not used, was not capable of charging and discharging in most cases, and voltage after storage at high temperature was also reduced to 2.65 V.

(52) In addition, it can be confirmed that the secondary batteries according to Comparative Examples 11, 12, 14, 15, 16, and 18, in which compounds of Formulas a to d were included as a non-aqueous electrolyte additive, were capable of charging and discharging in some cases, but voltage after storage at high temperature was reduced to less than 3.7 V.

(53) Meanwhile, it can be confirmed that the secondary batteries according to Comparative Examples 13 and 17 exhibited a higher number of batteries capable of charging and discharging and a higher voltage after storage at high temperature than the secondary batteries according to Comparative Examples 11, 12, 14, 15, 16, and 18 because an excessive amount of an additive capable of suppressing elution of metal ions was included, but voltage after storage at high temperature was lower than that of the secondary batteries according to Examples 29 to 56 due to an increase in resistance.