ELECTROLYTE ADDITIVE, BATTERY ELECTROLYTE INCLUDING ELECTROLYTE ADDITIVE, AND SECONDARY BATTERY INCLUDING BATTERY ELECTROLYTE

Abstract

The present invention relates to an electrolyte additive, a battery electrolyte including the electrolyte additive, and a secondary battery, and more particularly, to an electrolyte additive including a compound represented by Chemical Formula 1, an electrolyte including the electrolyte additive, and a secondary battery including the electrolyte. According to the present invention, due to low charging resistance, charging efficiency and output may be improved. In addition, the present invention has an effect of providing a secondary battery having a long lifespan and excellent capacity retention at high temperature.

Claims

1. An electrolyte additive, comprising a compound represented by Chemical Formula 1 below: ##STR00009## wherein G is —O—, —OR.sub.a—, —N(R.sub.b)— or —R.sub.c—N(R.sub.d)—R.sub.e—, —R.sub.f(NR.sub.gR.sub.h)—, or —R.sub.i—; R.sub.a, R.sub.e, R.sub.e, R.sub.f, and R.sub.i are each independently a linear or branched alkylene group having 1 to 10 carbon atoms; R.sub.b, R.sub.d, R.sub.g, and R.sub.h are each independently hydrogen or a linear or branched alkyl group having 1 to 10 carbon atoms; Q.sub.1 and Q.sub.2 are each independently phosphorus (P), sulfur (S), or arsenic (As); D.sub.1, D.sub.2, D.sub.3, D.sub.4, D.sub.5, and D.sub.6 are each independently oxygen (═O) or one or two unshared electron pairs; E.sub.1, E.sub.2, E.sub.3, or E.sub.4 is oxygen or carbon; when D.sub.2, D.sub.3, D.sub.5, or D.sub.6 is oxygen, E.sub.1, E.sub.2, E.sub.3, or E.sub.4 bonded thereto is carbon; R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6, R.sub.7, and R.sub.8 are each independently hydrogen, or a linear or branched alkyl group, an alkenyl group, an alkynyl group, an alkoxy group, an alkoxycarbonyl group or an alkoxyalkyl group having 1 to 10 carbon atoms; optionally, R.sub.3 and R.sub.4, or R.sub.7 and R.sub.8, are bonded to form a ring; n and k are each independently an integer of 0 to 5; m and l are each independently 0 or 1; and at least one of n and m, and at least one of k and l are not 0.

2. The electrolyte additive according to claim 1, wherein the compound represented by Chemical Formula 1 comprises one or more selected from the group consisting of compounds represented by Chemical Formulas 2 to 25 below: ##STR00010## In chemical Formula 2, A.sub.1 and A.sub.2 are each independently phosphorus or sulfur; R.sub.1′, R.sub.2′, R.sub.3′, and R.sub.4′ are each independently hydrogen, or a substituted or unsubstituted alkyl group having 1 to 10 carbon atoms; and m and n are each independently an integer of 1 to 5. ##STR00011## ##STR00012## ##STR00013## wherein, in Chemical Formulas 3 to 25, a line denotes a bond, a point where the lines meet without any element being marked denotes carbon, and hydrogens satisfying a valence of the carbon are omitted.

3. An electrolyte for batteries, comprising an organic solvent, a lithium salt, and an electrolyte additive, wherein the electrolyte additive comprises a compound represented by Chemical Formula 1 below: ##STR00014## in Chemical Formula 1, G is —O—, —OR.sub.a—, —N(R.sub.b)— or —R.sub.c—N(R.sub.d)—R.sub.e—, —R.sub.f(NR.sub.gR.sub.h)—, or —R.sub.i—; R.sub.a, R.sub.c, R.sub.e, R.sub.f, and R.sub.i are each independently an linear or branched alkylene group having 1 to 5 carbon atoms; R.sub.b, R.sub.d, R.sub.g, and R.sub.h are each independently oxygen or a linear or branched alkyl group having 1 to 5 carbon atoms; Q.sub.1 and Q.sub.2 are each independently phosphorus (P) or arsenic (As); D.sub.1, D.sub.2, D.sub.3, D.sub.4, D.sub.5, and D.sub.6 are each independently oxygen (═O) or one or two unshared electron pairs; E.sub.1, E.sub.2, E.sub.3, or E.sub.4 is oxygen or carbon; when D.sub.2, D.sub.3, D.sub.5, or D.sub.6 is oxygen, E.sub.1, E.sub.2, E.sub.3, or E.sub.4 bonded thereto is carbon; R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, R.sub.6, R.sub.7, and R.sub.8 are each independently hydrogen, or a linear or branched alkyl group, an alkenyl group, an alkynyl group, an alkoxy group, an alkoxycarbonyl group or an alkoxyalkyl group having 1 to 10 carbon atoms; optionally, R.sub.3 and R.sub.4 or R.sub.7 and R.sub.8 are bonded to form an aromatic ring; n and k are each independently an integer of 0 to 5; m and l are each independently 0 or 1; and at least one of n and m, and at least one of k and l are not 0.

4. The electrolyte according to claim 3, wherein, based on 100% by weight in total of the electrolyte, the compound represented by Chemical Formula 1 is comprised in an amount of 0.1 to 10% by weight.

5. The electrolyte according to claim 3, wherein the compound represented by Chemical Formula 1 has a symmetric structure by satisfying “m=n”.

6. The electrolyte according to claim 3, wherein the organic solvent comprises one or more selected from the group consisting of ethylene carbonate (EC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate (PC), dipropyl carbonate (DPC), butylene carbonate, methylpropyl carbonate, and ethylpropyl carbonate.

7. The electrolyte according to claim 3, wherein the lithium salt comprises one or more selected from the group consisting of LiPF.sub.6, LiF.sub.4, LiCl, LiBr, LiI, LiClO.sub.4, LiB.sub.10Cl.sub.10, LiCF.sub.3SO.sub.3, LiCF.sub.3CO.sub.2, LiAsF.sub.6, LiSbF.sub.6, LiAlCl.sub.4, CH.sub.3SO.sub.3Li, CF.sub.3SO.sub.3Li, and (CF.sub.3SO.sub.2).sub.2NLi.

8. The electrolyte according to claim 3, wherein the electrolyte comprises a metal phosphate-based compound.

9. The electrolyte according to claim 8, wherein the metal phosphate-based compound comprises one or more selected from the group consisting of lithium difluoro(bisoxalato) phosphate, lithium tetrafluoro oxalato phosphate, lithium difluorophosphate, and lithium trioxalato phosphate.

10. A secondary battery, comprising an anode, a cathode, a separator interposed between the anode and the cathode, and an electrolyte, wherein the electrolyte is the electrolyte according to claim 1.

11. The secondary battery according to claim 10, wherein the secondary battery has an HPPC charging resistance value of 500 mΩ or less at 25° C.

12. The secondary battery according to claim 10, wherein the secondary battery has a recovery capacity of 580 mAh or more at 45° C.

13. The secondary battery according to claim 10, wherein the secondary battery has a lifespan maintenance efficiency of 80% or more at 45° C.

14. The secondary battery according to claim 10, wherein the secondary battery is a battery for vehicles.

Description

SYNTHESIS EXAMPLE 1

Preparation of 1,3,2-dioxaphospholan-2-yl diethyl phosphite

[0071] 2.38 g (17.2 mmol) of diethyl phosphite was placed in a dried 50 ml three-necked flask, and 5 ml of benzene was added thereto dropwise. While stirring, 1.75 g (17.2 mmol) of triethylamine was slowly added to the flask dropwise. While maintaining reaction temperature at 0° C., 2.18 g (17.2 mmol) of ethylene chlorophosphite was slowly added to the flask for 30 minutes dropwise. Thereafter, stirring was performed at 0° C. for 30 minutes, and the resulting triethylamine salt was filtered. The filtrate was vacuum distilled to obtain 2.1 g (yield: 55%) of 1,3,2-dioxaphosphorane-2-yl diethyl phosphite, which was a desired product. The structure of the obtained product was confirmed by 1H NMR as follows.

[0072] 1H NMR (CDCl3, 400 MHz) δ=4.18 (m, 2H), 4.05 (m, 2H), 3.85 (m, 4H), 1.24 (m. 6H)

SYNTHESIS EXAMPLE 2

Preparation of 2-((trimethylsilyl)oxy)-1,3,2-dioxaphospholane

[0073] 5 g (55.4 mmol) of trimethylsilanol was placed in a dried 100 ml three-necked flask, and 50 ml of diethyl ether as a solvent and 6.1 g (60.0 mmol) of triethylamine were added thereto dropwise. While maintaining reaction temperature at −10° C., 5.8 g (46.1 mmol) of 2-chloro-1,3,2-dioxaphosphorane was slowly added to the flask dropwise. Reaction was performed by stirring for 10 hours. At room temperature, triethylamine salt was removed by filtration. The filtrate was vacuum distilled to obtain 4.9 g (yield: 60%) of 2-((trimethylsilyl)oxy)-1,3,2-dioxaphosphorane, which was a desired product. The structure of the obtained product was confirmed by 1H NMR as follows.

[0074] 1H NMR (CDCl3, 400 MHz) δ=4.12 (m, 2H), 3.92 (m, 2H), 0.18 (s. 9H)

EXAMPLE 1

[0075] When an electrolyte for batteries was prepared, a carbonate-based mixed solvent having a volume ratio of EC:EMC:CEC=3:4:3 was used as an organic solvent, and 0.5% by weight of an electrolyte additive represented by Chemical Formula 2a below was added to a 1.15 M solution containing LiPF6 as a lithium salt.

##STR00008##

[0076] (CAS number: 22063-07-6, Chemical name: bisethylene pyrophosphate)

EXAMPLE 2

[0077] When an electrolyte for batteries was prepared, a carbonate-based mixed solvent having a volume ratio of EC:EMC:CEC=3:4:3 was used as an organic solvent, and 1% by weight of LiDFOP and 0.5% by weight of the electrolyte additive represented by Chemical Formula 2a were added to a 1.15 M solution containing LiPF.sub.6 as a lithium salt.

EXAMPLE 3

[0078] The same procedure as in Example 2 was performed, except that 0.3% by weight of the electrolyte additive was used.

EXAMPLE 4

[0079] The same procedure as in Example 2 was performed, except that 0.8% by weight of the electrolyte additive was used.

EXAMPLE 5

[0080] The same procedure as in Example 2 was performed, except that 1.0% by weight of the electrolyte additive was used.

EXAMPLE 6

[0081] The same procedure as in Example 2 was performed, except that 2.0% by weight of the electrolyte additive was used.

EXAMPLES 7 to 8

[0082] The same procedure as in Example 1 was performed, except that the electrolyte additive of Example 1 was replaced by a compound of Synthesis Example 1 represented by Chemical Formula 16, and 0.5% by weight (Example 7) and 1% by weight (Example 8) of the compound were used.

EXAMPLES 9 to 10

[0083] The same procedure as in Example 1 was performed, except that the electrolyte additive of Example 1 was replaced by a compound of Synthesis Example 2 represented by Chemical Formula 25, and 0.5% by weight (Example 9) and 1% by weight (Example 10) of the compound were used.

COMPARATIVE EXAMPLE 1

[0084] The same procedure as in Example 2 was performed, except that the electrolyte additive of Example 2 represented by Chemical Formula 2a was not used.

COMPARATIVE EXAMPLE 2

[0085] The same procedure as in Example 1 was performed, except that the electrolyte additive of Example 1 represented by Chemical Formula 2a was replaced by cyclic ethylene phosphate (CAS number: 6711-47-3) having an asymmetric structure, and 0.5% by weight of cyclic ethylene phosphate was added.

[0086] Preparation of battery 92% by weight of Li(Ni.sub.0.5Co.sub.0.2Mn.sub.0.3)O.sub.2 as a cathode active material, 4% by weight of carbon black as a conductive agent, and 4% by weight of polyvinylidene fluoride (PVdF) as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent to prepare a cathode mixture slurry. The cathode mixture slurry was applied to an aluminum (Al) thin film that was a cathode current collector having a thickness of about 20 μm, followed by drying and roll pressing to prepare a cathode.

[0087] 96% by weight of carbon powder as an anode active material, 3% by weight of PVdF as a binder, and 1% by weight of carbon black as a conductive agent were added to NMP as a solvent to prepare an anode mixture slurry. The anode mixture slurry was applied to a copper (Cu) thin film that was an anode current collector having a thickness of about 10 μm, followed by drying and roll pressing to prepare an anode.

[0088] A pouch-type battery was manufactured in a conventional manner using the prepared cathode and anode and a separator consisting of three layers of polypropylene/polyethylene/polypropylene (PP/PE/PP), and then the electrolytes prepared in Examples 1 to 10 and Comparative Examples 1 and 2 were injected thereto to manufacture a lithium secondary battery.

Test Examples

[0089] The performance of the prepared secondary batteries was evaluated according to the following methods, and the results are shown in Table 1 below.

[0090] [Evaluation of HPPC Charging Resistance]

[0091] HPPC charging resistance was measured using a method specified in the document “Battery test manual for plug-in hybrid electric vehicles (2010, Department of Energy, Idaho National Laboratory for the U.S.)”.

[0092] A voltage value, a charge/discharge current value corresponding to C-rate, degree of current change (ΔI), degree of change in discharge voltage (ΔV), degree of change in charge voltage (ΔV), discharging resistance, and charging resistance were measured at high temperature (60° C.). A resistance value was calculated using a slope value obtained from the degree of change in current and voltage by briefly flowing charge/discharge current for each C-rate for a certain period of time.

[0093] [Evaluation of High-Temperature Recovery Capacity]

[0094] As charging conditions, charging was performed at a constant current of 1.0 C and a voltage of 4.2 V until charging current reaches 1/10 C. As discharging conditions, charging and discharging were performed by discharging up to 3.0 V at a constant current of 1.0 C, and then discharge capacity was measured.

[0095] After charging under the same charging and discharging conditions, the secondary batteries were stored in a constant temperature bath at 60° C. for 4 weeks. Then, the secondary batteries were discharged to a discharge voltage of 3 V at a high temperature of 60° C., and the residual capacity was measured. Thereafter, the above process was repeated three times under the same charging and discharging conditions, and the average value of the measured values was calculated.

[0096] [Evaluation of High Temperature Lifespan]

[0097] The secondary batteries were charged with a current of 1 C rate at 45° C. in a constant current mode until voltage reached 4.20 V (vs. Li), and then cut-off was performed at a current of 0.05 C rate while maintaining 4.20 V in a constant voltage mode. Then, the secondary batteries were discharged at a constant current of 1 C rate until voltage reached 3.0 V (vs. Li) (1st cycle). The cycle was repeated 300 times, and the average value of the measured values was calculated.

TABLE-US-00001 TABLE 1 High- High- HPPC temperature temperature charging recovery lifespan resistance capacity efficiency Classification Additives (% by weight) (mΩ) (mAh) (%) Example 1 Chemical — 51.1 663.3 88.3 Formula 2a (0.5) Example 2 Chemical LiDFOP 52.1 661.1 88.5 Formula (1.0) 2a (0.5) Example 3 Chemical LiDFOP 51.8 666.3 88.1 Formula (1.0) 2a(0.3) Example 4 Chemical LiDFOP 51.3 659.6 88.8 Formula (1.0) 2a(0.8) Example 5 Chemical LiDFOP 52.8 656.5 87.9 Formula (1.0) 2a(1.0) Example 6 Chemical LiDFOP 52.1 661.8 88.1 Formula (1.0) 2a(2.0) Example 7 Chemical 50.0 685.5 89.0 Formula 16 (0.5) Example 8 Chemical 48.0 683.1 90.0 Formula 16 (1.0) Example 9 Chemical 48.2 693.2 90.0 Formula 25 (0.5) Example 10 Chemical 46.0 696.5 91.0 Formula 25 (1.0) Comparative — LiDFOP 113.7 598.1 71.2 Example 1 (1.0) Comparative Cyclic — 98.3 601.1 75.4 Example 2 ethylene phosphate (0.5)

[0098] As shown in Table 1, the secondary battery using the electrolyte additive of the present invention exhibited a charging resistance value of 51.1 to 52.8 mΩ. In contrast, in the case of Comparative Example 1 using only LiDFOP as a conventional electrolyte additive, a high charging resistance value was observed, showing a charging resistance value of 113.7 mΩ. In the case of Comparative Example 2 using only cyclic ethylene phosphate, which was an asymmetric phosphate, a high charging resistance value was observed, showing a charging resistance value of 98.3 mΩ. It was confirmed that the charging resistance value was reduced by up to 45% by using the electrolyte additive of the present invention. Accordingly, these results indicated that the output of the battery was improved by the electrolyte additive of the present invention.

[0099] In addition, as shown in Table 1, the secondary battery using the electrolyte additive of the present invention exhibited a high-temperature recovery capacity of 656.5 to 696.5 mAh. In contrast, Comparative Examples 1 and 2 exhibited a high-temperature recovery capacity of 598.1 and 601.1 mAh. That is, the high-temperature recovery capacity of Comparative Examples 1 and 2 was less than that of the example of the present invention, showing a difference of up to 98.4 mAh. These results showed that recovery capacity at a high temperature of 45° C. could be improved by using the electrolyte additive of the present invention. Accordingly, it was confirmed that the recovery capacity of a battery during long-term storage at high temperature was improved by the electrolyte additive of the present invention.

[0100] In addition, as a result of high-temperature lifespan efficiency evaluation, the secondary battery using the electrolyte additive of the present invention exhibited a high-temperature lifespan efficiency of 87.9 to 91.0%. In contrast, Comparative Examples 1 and 2 exhibited a high-temperature lifespan efficiency of 71.2% and 75.4%, which was at most 19.8%point lower than that of the example of the present invention. That is, compared to the case of using only the conventional electrolyte additive, by using the electrolyte additive of the present invention, the capacity retention of a battery was improved when the cycle was repeated 300 times at a high temperature. Accordingly, it can be seen that the cycle characteristics and lifespan efficiency of a battery may be improved in a high-temperature environment by using the electrolyte additive of the present invention.

[0101] Therefore, when the electrolyte additive according to embodiments of the present invention and the electrolyte including the electrolyte additive are applied to a secondary battery, charging resistance, output, recovery capacity, and lifespan efficiency are improved, and thus the secondary battery of the present invention is suitable for use as the secondary battery for vehicles.