Non-aqueous electrolyte for lithium-ion battery and lithium-ion battery using non-aqueous electrolyte

Abstract

The present disclosure provides a non-aqueous electrolyte for a lithium-ion battery and a lithium-ion battery using the non-aqueous electrolyte. The non-aqueous electrolyte includes (a) a lithium, (b) a non-aqueous organic solvent, and (c) at least one compound represented by formula 1; ##STR00001## where the non-aqueous electrolyte further includes at least one of the following components (d) and (e): (d) a nitrile compound including at least one of 1,3,6-hexane trinitrile, glycerol trinitrile, and 3-methoxypropionitrile, and (e) vinyl sulfate. Through the synergy effect between them, the positive electrode is protected and meanwhile the negative electrode is also be protected to a certain extent, and an impedance of a film is lowered. The battery has an excellent high temperature storage performance, high temperature cycle performance and low temperature charge and discharge performance.

Claims

1. A non-aqueous electrolyte, comprising: (a) a lithium, (b) a non-aqueous organic solvent, and (c) at least one compound represented by formula 1; wherein the non-aqueous electrolyte further comprises at least one of the following components (d) and (e): (d) a nitrile compound including at least one of 1,3,6-hexane trinitrile, glycerol trinitrile, and 3-methoxypropionitrile, and (e) vinyl sulfate; ##STR00004## wherein R.sub.1 and R.sub.2 are the same or different, and are each independently selected from hydrogen, halogen, a halogen-substituted or unsubstituted C.sub.1-C.sub.6 alkyl group, a halogen-substituted or unsubstituted C.sub.2-C.sub.5 alkenyl group, or a halogen-substituted or unsubstituted C.sub.2-C.sub.5 alkynyl group.

2. The non-aqueous electrolyte according to claim 1, wherein the compound represented by formula 1 is selected from at least one of the following compounds A1 to A5: ##STR00005##

3. The non-aqueous electrolyte according to claim 1, wherein the nitrile compound is selected from at least one of 1,3,6-hexanetrinitrile, glycerol trinitrile, and 3-methoxypropionitrile.

4. The non-aqueous electrolyte according to claim 1, wherein a content of the compound represented by formula 1 is 0.1-10 wt % of a total mass of the non-aqueous electrolyte.

5. The non-aqueous electrolyte according to claim 1, wherein a content of the nitrile compound is 0-8 wt % of the total mass of the non-aqueous electrolyte.

6. The non-aqueous electrolyte according to claim 1, wherein a content of the vinyl sulfate is 0-2 wt % of the total mass of the non-aqueous electrolyte.

7. A lithium-ion battery, comprising the non-aqueous electrolyte according to claim 1.

8. The lithium-ion battery according to claim 7, wherein the lithium-ion battery further comprises a positive electrode sheet containing a positive electrode active material, a negative electrode sheet containing a negative electrode active material and a lithium-ion diaphragm.

9. The lithium-ion battery according to claim 8, wherein the positive electrode active material is selected from one or more of a layered lithium transition metal composite oxide, a lithium manganate and a lithium cobalt oxide mixed ternary material; a chemical formula of the layered lithium transition metal composite oxide is Li.sub.1+xNi.sub.y Co.sub.zM.sub.(1−y−z)Q.sub.2, wherein −0.1≤x≤1, 0≤y≤1, 0≤z≤1, and 0≤y+z≤1; wherein M is one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo and Zr; Q is one or more of O, F, P and S: the negative electrode active material is selected from one or more of a carbon material, a silicon-based material, a tin-based material or their corresponding alloy materials.

10. The lithium-ion battery according to claim 7, wherein an operating voltage range of the lithium-ion battery is 4.25V and more.

11. The lithium-ion battery according to claim 8, wherein an operating voltage range of the lithium-ion battery is 4.25V and more.

12. The lithium-ion battery according to claim 9, wherein an operating voltage range of the lithium-ion battery is 4.25V and more.

Description

DESCRIPTION OF EMBODIMENTS

(1) Hereinafter, the present disclosure will be further described in detail in conjunction with specific embodiments. It should be understood that the following embodiments are only to exemplarily illustrate and explain the present disclosure, and should not be construed as limiting protection scope of the present disclosure. All technical solution implemented based on the foregoing contents of the present disclosure are covered within the scope intended to be protected by the present disclosure.

(2) The experimental methods used in the following examples are conventional methods unless otherwise specially stated: the reagents and materials used in the following examples can be obtained from commercial sources unless otherwise specially stated.

Comparative Example 1 □

(3) (1) Preparation of a Positive Electrode Sheet

(4) 4.4V lithium cobalt oxide (LCO) as a positive active material, polyvinylidene fluoride (PVDF) as a binder, and acetylene black as a conductive agent are mixed in a weight ratio of 97:1.5:1.5, and N-methylpyrrolidone (NMP) is added, stirring under an action of a vacuum mixer until a mixed system becomes a positive electrode slurry with uniform fluidity; the positive electrode slurry is uniformly coated on an aluminum foil with a thickness of 12 μm; after the above-mentioned well-coated aluminum foil is baked in an oven with five different temperature gradients, then it is dried in an oven at 120° C. for 8 hours, and then is rolled and slit, to obtain a desired positive electrode sheet.

(5) (2) Preparation of a Negative Electrode Sheet

(6) Graphite as a negative active material, sodium car boxy methyl cellulose (CMC-Na) as a thickener, styrene butadiene rubber as a binder, acetylene black as a conductive agent are mixed in a weight ratio of 97:1:1:1, and a deionized water is added. A negative electrode slurry is obtained under an action of a vacuum mixer; the negative electrode slurry is evenly coated on a copper foil with a thickness of 8 μm; the copper foil is dried at room temperature and then is transferred to an oven to dry at 80° C. for 10 hours, and then is cold pressed and slit, to obtain the negative electrode sheet.

(7) (3) Preparation of an Electrolyte

(8) In a glove box filled with argon gas and with qualified water and oxygen contents, ethylene carbonate, propylene carbonate, diethyl carbonate, n-propyl propionate, and fluoroethylene carbonate are mixed evenly in a mass ratio of 13.5:13.5:13.5:51:8.5 (solvents and additives need to be normalized together), then 14.3 wt % of fully dried lithium hexafluorophosphate (LiPF.sub.6) is quickly add to it, and is dissolved in the organic solvents, stirring well, and after passing moisture and free acid tests, an electrolyte of Comparative Example 1 is obtained.

(9) (4) Preparation of a Diaphragm

(10) 8 μm thick polyethylene is selected as the diaphragm (provided by Asahi Kasei).

(11) (5) Preparation of a Lithium-Ion Battery

(12) The positive electrode sheet, the diaphragm, and the negative electrode sheet, as prepared above, are laid in order, to ensure that the diaphragm is located between the positive and negative electrode sheets and plays a role of isolation, and then a bare battery core without liquid injection is got by winding: the bare battery core is placed in an outer packaging foil, the electrolyte prepared above is injected into a dried bare battery core, going through processes of vacuum packaging, standing, forming, shaping, and sorting etc., to obtain a required lithium-ion battery.

(13) (6) Low Temperature Cycle Experiment at 5° C.

(14) Before a test, a thickness D.sub.0 of a fully charged battery core is tested. The battery is placed in an environment of 5±2° C. and left to stand for 3 hours. When the battery core body reaches 5±2° C., the battery is charged to 4.4V at 0.3 C, then is charged at a constant voltage of 4.4V until a cut-off current is 0.05 C, then is discharged to 3V at 0.5 C, and an initial capacity Q.sub.0 is recorded. When a required number of cycles is reached or a capacity attenuation rate is less than 70% or the thickness exceeds the thickness required by the test, the previous discharge capacity is used as the battery's capacity Q.sub.1, and a capacity retention rate (%) is calculated, then the battery is fully charged, and the battery core is taken out, then left at room temperature for 3 hours, and the thickness D.sub.1 at full charge is tested, and a thickness change rate (%) is calculated. Recorded results are shown in Table 2. Where calculation formulas used are as follows:
The thickness change rate (%)=(D.sub.1−D.sub.0)/D.sub.0×100%; and the capacity retention rate (%)=Q.sub.1/Q.sub.0×100%.

(15) (7) Room Temperature Cycle Experiment at 25° C.

(16) Before the test, the thickness D.sub.0 of the fully charged battery core is tested. The battery is placed in an environment of 25±3° C. and left to stand for 3 hours. When the battery core body reaches 25±3° C., the battery is charged to 4.4V at 1 C, then is charged to 4.4V at 0.7 C, then is charged at a constant voltage of 4.4V until a cut-off current is 0.05 C, then is discharged to 3V at 0.5 C, and an initial capacity Q.sub.0 is recorded. When the required number of cycles is reached or the capacity attenuation rate is less than 70% or the thickness exceeds the thickness required by the test, the previous discharge capacity is used as the battery's capacity Q.sub.2, and the capacity retention rate (%) is calculated, then the battery is fully charged, and the battery core is taken out, then left at room temperature for 3 hours, and the thickness D.sub.2 at full charge is tested, and the thickness change rate (%) is calculated. Recorded results are shown in Table 2. Where the calculation formulas used are as follows:
The thickness change rate (%)=(D.sub.2−D.sub.0)/D.sub.0×100%; and the capacity-retention rate (%)=Q.sub.2/Q.sub.0×100%.

(17) (8) High Temperature Cycle Experiment at 45° C.

(18) Before the test, the thickness D.sub.0 of the fully charged battery core is tested. The battery is placed in an environment of 45±3° C. and left to stand for 3 hours. When the battery core body reaches 45±3° C., the battery is charged to 4.4V at a constant current of 0.7 C, then is charged at a constant voltage of 4.4V until a cut-off current is 0.05 C, then is discharged at 0.5 C, and an initial capacity Q.sub.0 is recorded. The cycle is repeated. When required number of cycles is reached or the capacity attenuation rate is less than 70% or the thickness exceeds the thickness required by the test, the previous discharge capacity is used as the battery's capacity Q.sub.3, and then the capacity retention rate (%) is calculated, then the battery is fully charged, and the battery core is taken out, then left at room temperature for 3 hours, and the thickness D.sub.3 at full charge is tested, and the thickness change rate (%) is calculated. Recorded results are shown in Table 2. Where the calculation formulas used are as follows:
The thickness change rate (%)=(D.sub.3−D.sub.0/D.sub.0×100%; and the capacity retention rate (%)=Q.sub.3/Q.sub.0×100%.

(19) (9) High Temperature Storage Experiment at 60° C.

(20) At 25° C., the thickness D.sub.0 of the fully charged battery core is tested, the sorted battery is charged to 4.4V at 0.7 C, then is charged at a constant voltage of 4.4V until a cut-off current is 0.05 C, then is discharged to 3.0V at a constant current of 0.5 C, then is charged to 4.4V at 0.7 C, then is charged at a constant voltage of 4.4V until a cut-off current is 0.05 C, and it is placed in an environment at 60° C. for 14 days. The thickness D.sub.4 at full charge is tested, and the thickness change rate (%) is calculated. Recorded results are shown in Table 2. Where the calculation formula used is as follows.
The thickness change rate (%)=(D.sub.4−D.sub.0)/D.sub.0×100%.

(21) TABLE-US-00001 TABLE 1 Compositions and contents of electrolytes of Examples 1-13 and Comparative Examples 1-9 1,3,6- 3- hexane Glycerol methoxy Vinyl A1 A2 A4 Succinonitrile trinitrile trinitrile propionitrile sulfate Comparative Example 1 Comparative 0.5 Example 2 Comparative 0.5 Example 3 Comparative 0.5 Example 4 Comparative 1 Example 5 Comparative 1 Example 6 Comparative 1 Example 7 Comparative 1 Example 8 Comparative 0.5 1 Example 9 Example 1 0.5 1 Example 2 0.5 1 Example 3 0.5 1 Example 4 0.5 1 Example 5 0.5 1 Example 6 0.5 1 Example 7 0.5 1 1 Example 8 0.5 1 1 Example 9 0.5 1 1 Example 10 0.5 1 1 Example 11 0.5 1 1 Example 12 0.5 0.5 1 1 Example 13 0.5 1 1 1 Annotation: the unit of the content of each component is wt %

(22) TABLE-US-00002 TABLE 2 Comparisons of experimental results of batteries of Examples 1-13 and Comparative Examples 1-9 300 cycles at 5° C. 500 cycles at 25° C. 400 cycles at 45° C. 60° C./14 days Thickness Capacity Thickness Capacity Thickness Capacity Thickness change retention change retention change retention change rate rate rate rate rate rate rate Comparative 5.4% 99.5% 13.2% 79.1% 14.0% 70.5% 12.3% example 1 Comparative 6.3% 98.4% 9.4% 82.7% 9.7% 78.1% 9.4% example 2 Comparative 6.1% 98.7% 9.1% 81.7% 9.5% 78.5% 9.3% example 3 Comparative 6.7% 97.9% 9.3% 82.4% 9.3% 78.8% 9.1% example 4 Comparative 7.5% 98.2% 8.3% 83.1% 8.5% 79.4% 8.7% example 5 Comparative 6.5% 98.5% 8.6% 83.5% 8.9% 79.2% 8.9% example 6 Comparative 5.8% 99.0% 8.2% 84.3% 8.7% 79.7% 8.8% example 7 Comparative 6.0% 98.8% 8.9% 82.5% 9.1% 78.3% 9.5% example 8 Comparative 6.7% 98.3% 8.3% 83.1% 8.7% 79.3% 9.1% example 9 Example 1 6.4% 98.5% 8.0% 83.4% 8.3% 80.2% 8.5% Example 2 6.6% 98.7% 8.2% 83.8% 8.6% 80.5% 8.6% Example 3 6.9% 98.6% 8.0% 83.5% 9.1% 79.6% 8.4% Example 4 5.5% 99.2% 7.9% 84.7% 8.3% 80.3% 8.2% Example 5 5.9% 98.6% 8.5% 83.0% 8.6% 80.6% 8.9% Example 6 6.2% 98.3% 8.5% 82.8% 8.4% 80.3% 8.6% Example 7 6.0% 98.9% 7.6% 83.8% 7.9% 81.8% 8.1% Example 8 6.3% 98.7% 7.8% 84.3% 8.1% 81.6% 8.3% Example 9 5.3% 99.3% 7.5% 85.3% 8.0% 81.4% 7.9% Example 10 6.4% 99.1% 7.6% 83.9% 7.8% 81.8% 8.0% Example 11 6.6% 98.1% 7.7% 83.7% 7.9% 81.6% 8.2% Example 12 5.7% 99.4% 7.3% 84.8% 7.3% 82.6% 7.5% Example 13 6.2% 99.4% 7.3% 84.5% 7.2% 82.9% 7.3%

Examples 1-13 and Comparative Examples 2-9

(23) The preparation processes of Examples 1-13 and Comparative Examples 2-9 are the same as the preparation process of Comparative Example 1. The only difference lies in the components and contents of the electrolytes. The specifically added components and contents thereof are shown in Table 1 The test results are listed in Table 2.

(24) It can be seen from above Table 2 that the batteries prepared in the examples of the present application have achieved a better electrical performance. The specific analysis is as follows:

(25) Through comparisons of Comparative Example 1 and Comparative Examples 2-10, it can be found that on the basis of a blank electrolyte, the compound represented by formula 1, the nitrile compound and the vinyl sulfate can all improve the high-temperature cycle performance and high-temperature storage performance of the battery, but all of them will degrade low-temperature cycle performance.

(26) Through comparisons of Comparative Examples 2-10 and Examples 1-6, a combination of the compound represented by formula 1 and the nitrile compound including at least one of 1,3,6-hexane trinitrile, glycerol trinitrile, and 3-methoxypropionitrite, or a combination of the compound represented by formula 1 and the vinyl sulfate, can improve the high temperature cycle performance and high temperature storage performance of the battery, and take into account the low temperature cycle performance.

(27) Through Comparative Example 9 and Examples 1-2, 4, it can be found that compared with succinonitrile, the nitrile compounds, i.e., 1,3,6-hexane trinitrile, glycerol trinitrile and 3-methoxypropionitrile in the present disclosure have a better high-temperature cycle performance and high-temperature storage performance.

(28) Through comparisons of Examples 1 and 7, Examples 2 and 8, Examples 4 and 9, Examples 3 and 10, and Examples 6 and 11, it can be found that a combination of the compound represented by formula 1, the nitrile compound including at least one of 1,3,6-hexane trinitrile, glycerol trinitrile, and 3-methoxypropionitrile, and the vinyl sulfate can further improve the high-temperature cycle performance and high-temperature storage of the battery.

(29) Through comparisons of Examples 12 and 7, Examples 13 and 10, it can be found that a combination of multiple compounds represented by formula 1 or a combination of multiple nitrile compounds including at least one of 1,3,6-hexane trinitrile, glycerol trinitrile, and 3-methoxypropionitrile can further improve the high-temperature cycle performance and high-temperature storage performance of the battery.

(30) The embodiments of the present disclosure have been described above. However, the present disclosure is not limited to the above-mentioned embodiments. Any modifications, equivalent replacements, improvements, etc., made within the spirit and principle of the present disclosure should be included in the protection scope of the present disclosure.