ELECTROLYTE SUITABLE FOR LITHIUM-ION BATTERY OF SILICON-CARBON SYSTEM AND LITHIUM-ION BATTERY

Abstract

Disclosed are an electrolyte suitable for a lithium-ion battery of a silicon-carbon system and a lithium-ion battery. The electrolyte provided in the present disclosure includes an organic solvent, an additive, and a lithium salt, where the additive includes lithium trifluoromethyl triethyl borate, prop-1-ene-1,3-sultone, and fluoroethylene carbonate. The combined use of the additive may significantly prolong the cycle life of a silicon-carbon battery, and enables the silicon-carbon battery to have both high-temperature/low-temperature performance and safety performance, so that the silicon-carbon battery is enabled to be more suitable for large-scale commercial production.

Claims

1. An electrolyte suitable for a lithium-ion battery of a silicon-carbon system, comprising an organic solvent, an additive, and a lithium salt, wherein the additive comprises lithium trifluoromethyl triethyl borate, prop-1-ene-1,3-sultone, and fluoroethylene carbonate.

2. The electrolyte according to claim 1, wherein a content of lithium trifluoromethyl triethyl borate accounts for 0.1 wt% to 2 wt% of a total mass of the electrolyte.

3. The electrolyte according to claim 2, wherein the content of lithium trifluoromethyl triethyl borate accounts for 0.2 wt% to 1.0 wt% of the total mass of the electrolyte.

4. The electrolyte according to claim 3, wherein the content of lithium trifluoromethyl triethyl borate accounts for 0.2 wt% to 0.5 wt% of the total mass of the electrolyte.

5. The electrolyte according to claim 1, wherein a content of prop-1-ene-1,3-sultone accounts for 0.2 wt% to 3.5 wt% of a total mass of the electrolyte.

6. The electrolyte according to claim 5, wherein the content of prop-1-ene-1,3-sultone accounts for 0.5 wt% to 2 wt% of the total mass of the electrolyte.

7. The electrolyte according to claim 1, wherein a content of fluoroethylene carbonate accounts for 8 wt% to 20 wt% of a total mass of the electrolyte.

8. The electrolyte according to claim 1, wherein the additive further comprises at least one of succinonitrile, adiponitrile, glycerol trinitrile, 1,3,6-hexanetricarbonitrile, and 1,2-bis (cyanoethoxy) ethane, and a content thereof accounts for 0 wt% to 10 wt% of a total mass of the electrolyte.

9. The electrolyte according to claim 1, wherein the additive further comprises at least one of succinonitrile, adiponitrile, glycerol trinitrile, 1,3,6-hexanetricarbonitrile, and 1,2-bis (cyanoethoxy) ethane, and a content thereof accounts for 1 wt% to 5 wt% of a total mass of the electrolyte.

10. The electrolyte according to claim 1, wherein the organic solvent is selected from at least one of a carbonic ester, a carboxylic ester, and a fluoroether.

11. The electrolyte according to claim 10, wherein the carbonic ester is selected from a combination of one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and methyl propyl carbonate.

12. The electrolyte according to claim 10, wherein the carboxylic ester is selected from a combination of one or both of ethyl propionate and propyl propionate.

13. The electrolyte according to claim 10, wherein the fluoroether is selected from 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether.

14. The electrolyte according to claim 1, wherein the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, or lithium bis(trifluoromethanesulphonyl)imide.

15. The electrolyte according to claim 14, wherein a content of the lithium salt accounts for 10 wt% to 20 wt% of a total mass of the electrolyte.

16. A lithium-ion battery, comprising an electrolyte, wherein the electrolyte comprises an organic solvent, an additive, and a lithium salt, and the additive comprises lithium trifluoromethyl triethyl borate, prop-1-ene-1,3-sultone, and fluoroethylene carbonate.

17. The lithium-ion battery according to claim 16, wherein the lithium-ion battery is a lithium-ion battery of a silicon-carbon system.

18. The lithium-ion battery according to claim 16, wherein the lithium-ion battery further comprises a negative electrode plate, the negative electrode plate comprises a negative electrode active material layer, the negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material is selected from a silicon-carbon negative electrode material composed of nano-silicon and/or SiO.sub.x (0.8 ≤ x ≤ 1.3) and graphite.

19. The lithium-ion battery according to claim 18, wherein one or more of the nano-silicon and SiO.sub.x account for 1 wt% to 55 wt% of a total mass of the silicon-carbon negative electrode material.

Description

DETAILED DESCRIPTIONS OF THE EMBODIMENTS

[0055] The following further describes the present disclosure in detail with reference to specific embodiments. It should be understood that the following examples are only intended to illustrate and explain the present disclosure, and shall not be construed as a limitation on the protection scope of the present disclosure. All technologies implemented based on the foregoing content of the present disclosure shall fall within the intended protection scope of the present disclosure.

[0056] Experimental methods used in the following examples are conventional methods unless otherwise specified. Reagents, materials, and the like that are used in the following examples may be all obtained from commercial sources unless otherwise specified.

[0057] Comparative Examples 1 to 6 and Examples 1 to 8

[0058] Lithium-ion batteries in Comparative Examples 1 to 6 and Examples 1 to 8 were all prepared according to the following preparation method, and the difference lies in selection and addition amounts of components in an electrolyte. For specific differences, refer to Table 1.

Preparation of a Positive Electrode Plate

[0059] Mixing a positive electrode active material LiCoO.sub.2, a binder polyvinylidene fluoride (PVDF), and a conductive agent acetylene black in a weight ratio of 96.5:2:1.5; adding N-methyl pyrrolidone (NMP) and stirring the mixture under the action of a vacuum blender until a mixed system becomes positive electrode slurry with uniform fluidity; uniformly applying the positive electrode slurry to aluminum foil with a thickness ranging from 9 .Math.m to 12 .Math.m; baking the foregoing well coated aluminum foil in an oven with five different temperature gradients; and drying the aluminum foil in the oven at 120° C. for 8 hours, followed by rolling and slitting, to obtain a required positive electrode plate.

Preparation of a Silicon-carbon Negative Electrode Plate

[0060] Preparing negative electrode slurry according to a wet process from a silicon-carbon negative electrode material (composed of SiO and graphite, where a mass percentage of SiO is 3%) with a mass percentage of 95.9%, a conductive agent single-walled carbon nanotubes (SWCNT) with a mass percentage of 0.1%, a conductive agent conductive carbon black (SP) with a mass percentage of 1%, a dispersing agent sodium carboxymethyl cellulose (CMC) with a mass percentage of 1%, and a binder styrene-butadiene rubber (SBR) with a mass percentage of 2%; uniformly applying the negative electrode slurry to copper foil with a thickness ranging from 9 .Math.m to 12 .Math.m; baking the foregoing well coated copper foil in an oven with five different temperature gradients; and drying the copper foil in the oven at 85° C. for 5 hours, followed by rolling and slitting, to obtain a required silicon-carbon negative electrode plate.

Preparation of an Electrolyte

[0061] Uniformly mixing ethylene carbonate, propylene carbonate, propyl propionate, and ethyl propionate in a mass ratio of 1:2:5:2 (the solvent needs to be normalized) in a glove box that is filled with argon gas and that has qualified water content and oxygen content; and quickly adding 1 mol/L (12.5 wt%) of fully dried lithium hexafluorophosphate (LiPF.sub.6), 3 wt% of mass percentage of 1,3,6-hexanetricarbonitrile, and other additive (including lithium trifluoromethyl triethyl borate, prop-1-ene-1,3-sultone, and fluoroethylene carbonate, where for specific content and selection, refer to Table 1) to the mixture, to obtain the electrolyte.

Preparation of a Separator

[0062] Using a polyethylene separator with a thickness ranging from 7 .Math.m to 9 .Math.m.

Preparation of a Lithium-ion Battery

[0063] Winding the positive electrode plate, the separator, and the negative electrode plate prepared above to obtain a bare cell that has not undergone injection; placing the bare cell into outer package foil; and injecting the prepared electrolyte into the dried bare cell, followed by processes such as vacuum packaging, standing, formation, shaping, and sorting, to obtain a required lithium-ion battery.

TABLE-US-00001 Composition and adding amounts of other additives in the electrolyte in step (3) in Comparative Examples 1 to 6 and Examples 1 to 8 Item Adding amount of lithium trifluoromethyl triethyl borate (wt%) Adding amount of prop-1-ene-1,3-sultone (wt%) Adding amount of fluoroethylene carbonate (wt%) Comparative Example 1 0.5 / / Comparative Example 2 / 0.5 / Comparative Example 3 / / 8.0 Comparative Example 4 0.5 0.5 / Comparative Example 5 0.5 / 8.0 Comparative Example 6 / 0.5 8.0 Example 1 0.5 0.5 8.0 Example 2 0.1 2.0 10.0 Example 3 1.0 1.5 12.0 Example 4 1.5 2.5 15.0 Example 5 2.0 0.2 9.0 Example 6 0.8 3.5 18.0 Example 7 1.2 3.0 20.0 Example 8 1.4 2.8 14.0

[0064] Electrochemical performance of batteries obtained in the foregoing comparative examples and examples was tested, and related descriptions are as follows:

45° C. Cyclic Experiment

[0065] The batteries obtained in the foregoing examples and comparative examples were placed in an environment of (45±2)°C, followed by standing for 2-3 hours; when battery bodies reached (45±2)°C, the batteries underwent 1 C constant-current charge with a cut-off current of 0.05 C until the batteries were fully charged, followed by standing for 5 minutes; and then the batteries underwent 0.7 C constant-current discharge with a cut-off voltage of 3.0 V, where the highest discharge capacity of the first three cycles was recorded as an initial capacity Q, an initial thickness T of each battery cell was recorded, and when the cycles reached a required quantity of times, a discharge capacity Q.sub.1 and a battery thickness T.sub.1 of each battery in the last cycle were recorded. The recorded results are shown in Table 2.

[0066] The following calculation formulas were used:

[00001]$\text{Capacity retention}\left(\%\right)={\text{Q}}_1/\text{Q}\times 100\%;\text{and}$

[00002]$\text{Thickness change rate}\left(\%\right)=\left({\text{T}}_1-\text{T}\right)/\text{T}\times 100\%.$

Experiment With 10-hour High-temperature Storage at 85° C.

[0067] The batteries obtained in the foregoing examples and comparative examples were placed at room temperature to perform three times of charge/discharge cycle tests at a charge/discharge rate of 0.5 C, and then charged at a rate of 0.5 C to a fully charged state, where the highest discharge capacity Q.sub.2 and a battery thickness T.sub.2 of each battery in the first three 0.5 C cycles were recorded respectively. The batteries were stored at 85° C. for 10 hours after being fully charged, and after the 10 hours, a battery thickness T.sub.3 and a 0.5 C discharge capacity Q.sub.3 were recorded. Experimental data, such as thickness change rate and capacity retention of the batteries stored at high temperature, were calculated, where recorded results are shown in Table 2.

[0068] The following calculation formulas were used:

[00003]$\text{Capacity retention}\left(\%\right)={\text{Q}}_3/{\text{Q}}_2\times 100\%;\text{and}$

[00004]$\text{Thickness change rate}\left(\%\right)=\left({\text{T}}_3-{\text{T}}_2\right)/{\text{T}}_2\times 100\%.$

130° C. Thermal Shock Experiment

[0069] The batteries obtained in the foregoing examples and comparative examples were heated according to a convection method or by using a circulating hot air box at an initial temperature of (25±3)°C with a temperature change rate of (5±2)°C/min; and when the temperature was raised to (130±2)°C, the experiment was ended after the temperature had been kept for 60 minutes. The state results of the batteries were recorded as in Table 2.

Low-temperature Discharge Experiment

[0070] The batteries obtained in the foregoing examples and comparative examples were placed in an environment with a temperature of (25±3)°C to first discharge to 3.0 V at 0.2 C, and then charged at 0.7 C after standing for 5 minutes; when a cell terminal voltage reached a limited charge voltage, charging was performed at a constant voltage; the charging was stopped when a charge current become less than or equal to a cut-off current, followed by standing for 5 minutes; the batteries were discharged to 3.0 V at 0.2 C; and a discharge capacity in this time was recorded as a room-temperature capacity Q.sub.4. Then, the cell is charged at 0.7 C; when the cell terminal voltage reached the limited charge voltage, charging was performed at a constant voltage; the charging was stopped when the charge current become less than or equal to the cut-off current; the fully charged batteries left to stand for 4 hours at (-10±2)°C, and were discharged with a current of 0.4 C to the cut-off voltage of 3.0 V; and a discharge capacity Q.sub.5 was recorded. A low-temperature discharge capacity retention may be calculated, and recorded results are shown in Table 2.

[0071] The following calculation formula was used: Low-temperature discharge capacity retention (%) = Q.sub.5/Q.sub.4 x 100% .

TABLE-US-00002 Performance test results of Comparative Examples 1 to 6 and Examples 1 to 8 Item 500 cycles for 1C at 45° C. 10-hour high-temperature storage at 85° C. 130° C. thermal shock for 60 minutes Capacity retention of 0.4 C discharge at -10° C. Capacity retention % Thickness change rate % Capacity retention % Thickness change rate % Fire (passes/ tests) Explosion (passes/tests) Comparative Example 1 55.45% 28.4% 62.44% 23.9% 0/5 0/5 79.41% Comparative Example 2 57.71% 23.1% 68.29% 16.7% ⅖ ⅖ 61.06% Comparative Example 3 65.47% 13.5% 53.45% 29.5% ⅕ ⅕ 63.49% Comparative Example 4 60.14% 19.4% 70.83% 15.5% ⅖ ⅖ 68.34% Comparative Example 5 67.12% 13.2% 55.39% 24.7% 0/5 0/5 66.15% Comparative Example 6 68.39% 12.2% 69.38% 15.0% ⅗ ⅘ 57.86% Example 1 73.62% 10.8% 74.32% 9.8% 5/5 5/5 74.94% Example 2 74.34% 9.6% 77.49% 8.3% 5/5 5/5 71.34% Example 3 75.10% 9.0% 75.10% 9.3% 5/5 5/5 74.56% Example 4 77.62% 8.5% 79.18% 7.5% 5/5 5/5 76.71% Example 5 73.54% 10.3% 70.31% 12.9% 5/5 5/5 79.89% Example 6 80.40% 7.5% 80.21% 5.9% 5/5 5/5 75.19% Example 7 82.58% 8.5% 79.36% 6.8% 5/5 5/5 77.12% Example 8 75.38% 10.5% 77.48% 7.3% 5/5 5/5 78.33%

[0072] The following can be learned from the results in Table 2.

[0073] In summary, the electrolyte suitable for a lithium-ion battery of a silicon-carbon system provided in the present disclosure contains an additive combination of lithium trifluoromethyl triethyl borate, prop-1-ene-1,3-sultone, and fluoroethylene carbonate. Due to a synergistic effect of the additives, a lithium-ion battery of a silicon-carbon system is enabled to have not only excellent high-temperature cycling performance, high-temperature storage performance, and low-temperature discharge performance, but also high safety performance.

[0074] The foregoing illustrates implementation of the present disclosure. However, the present disclosure is not limited to the foregoing implementation. Any modifications, equivalent replacements, improvements, or the like made without departing from the spirit and principle of the present disclosure shall fall within the protection scope of the present disclosure.