A high-voltage lithium-ion battery electrolyte, preparation method and lithium-ion energy storage battery

Abstract

The present application discloses a high-voltage lithium-ion battery electrolyte, a preparation method and a lithium-ion energy storage battery, relating to the field of lithium-ion batteries. It includes an electrolyte lithium salt, an organic solvent and a silyl sulfate, and the dosage of the silyl sulfate is 0.1-0.3% of the total mass of the electrolyte lithium salt and the organic solvent. The present application has the effect of improving the cycle life of the lithium-ion energy storage battery.

Description

Technical Field

[0001] The present application relates to the field of lithium-ion batteries, and particularly to a high-voltage lithium-ion battery electrolyte, a preparation method thereof, and a lithium-ion energy storage battery. Background Art

[0002] Lithium-ion batteries (LIBs) have advantages such as high energy density, long cycle life, and environmental friendliness, and dominate the portable electrical energy storage technology in today's electronic device and electric vehicle markets. To achieve the goal of high-energy lithium-ion batteries, researchers have made many efforts, such as expanding the electrochemical window and increasing the specific capacity of electrode materials. Among many advanced cathode materials, high-nickel ternary cathode materials are considered to be one of the most remarkable and promising cathode materials due to their relatively high reversible capacity and low cost.

[0003] However, commercial carbonate-based electrolytes decompose severely on the surface of highly lithiated materials, and the accumulation of products causes an increase in interfacial impedance. Meanwhile, during charge and discharge, transition metal ions dissolve out in the layered high-nickel ternary materials, leading to an irreversible phase transition of the material from a layered structure to a spinel-like structure. As a result, when the voltage is higher than 4.3 V, the lithium-ion energy storage battery using the high-nickel ternary material as the cathode material will be accompanied by rapid capacity decay, resulting in a shortened cycle life. Summary of the Invention

[0004] In view of the deficiencies of the above-mentioned related technologies, the present application provides a high-voltage lithium-ion battery electrolyte, a preparation method thereof, and a lithium-ion energy storage battery. The high-voltage lithium-ion battery electrolyte adopted in the present application can improve the cycle life of the lithium-ion energy storage battery at a voltage of 4.5 V.

[0005] In the first aspect, a high-voltage lithium-ion battery electrolyte provided by the present application adopts the following technical solution:

[0006] A high-voltage lithium-ion battery electrolyte includes an electrolyte lithium salt, an organic solvent, and a silyl sulfate, and the dosage of the silyl sulfate is 0.1-0.3% of the total mass of the electrolyte lithium salt and the organic solvent.

[0007] Preferably, the silyl sulfate is bis(trimethylsilyl) sulfate.

[0008] Preferably, the organic solvent includes a cyclic carbonate and a linear carbonate in a weight ratio of 1:1-3.

[0009] Preferably, the organic solvent includes a cyclic carbonate and a linear carbonate in a weight ratio of 3:7.

[0010] Preferably, the cyclic carbonate includes one or more of ethylene carbonate, propylene carbonate, butylene carbonate, butyrolactone, and valerolactone; the linear carbonate includes one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, butyl acetate, methyl propionate, ethyl propionate, and propyl propionate.

[0011] Preferably, the linear carbonate includes ethyl methyl carbonate and diethyl carbonate in a weight ratio of 5:1-3.

[0012] Preferably, the linear carbonate includes ethyl methyl carbonate and diethyl carbonate in a weight ratio of 5:2.

[0013] Preferably, the electrolyte lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, and lithium difluoro(oxalato)borate.

[0014] Preferably, the concentration of the electrolyte lithium salt is 0.5-1.5 mol / L.

[0015] Preferably, the concentration of the electrolyte lithium salt is 1 mol / L.

[0016] In a second aspect, a preparation method of a high-voltage lithium-ion battery electrolyte provided by the present application adopts the following technical solution:

[0017] A preparation method of a high-voltage lithium-ion battery electrolyte includes the following steps: adding an electrolyte lithium salt to an organic solvent to dissolve and obtain a raw material electrolyte, and adding a silyl sulfate to the raw material electrolyte to dissolve to obtain the high-voltage lithium-ion battery electrolyte.

[0018] Preferably, the organic solvent is prepared by mixing a cyclic carbonate and a linear carbonate in proportion and then purifying by removing impurities and water.

[0019] In a third aspect, a lithium-ion energy storage battery provided by the present application adopts the following technical solution:

[0020] A lithium-ion energy storage battery includes a positive electrode, a negative electrode, a separator, and a high-voltage lithium-ion battery electrolyte.

[0021] Preferably, the positive electrode includes one or more positive electrode active materials such as NCM811, NCM622, LCO, and LNMO.

[0022] Preferably, the positive electrode includes one of NCM622, NCM811, and LCO as the positive electrode active material.

[0023] Preferably, the positive electrode includes NCM622 or NCM811 as the positive electrode active material.

[0024] Preferably, the positive electrode includes NCM622 as the positive electrode active material.

[0025] Preferably, the positive electrode further includes graphite microparticles, acetylene black, Ketjen black, and carbon nanofibers as conductive materials.

[0026] Preferably, the negative electrode includes one or more of natural graphite, artificial graphite, silicon, silicon-carbon composite, and lithium metal.

[0027] Preferably, the separator includes a polyethylene separator or a polypropylene separator.

[0028] In summary, the present application includes at least one of the following beneficial technical effects:

[0029] 1. By adding 0.1 - 0.3 parts of silyl sulfate, the voltage that the electrolyte of the high-voltage lithium-ion battery of the present application can act on is increased to 4.5V, and the cycle life of the lithium-ion energy storage battery when the voltage is above 4.3V is improved;

[0030] 2. When NCM622 is used as the positive electrode active material for the positive electrode, silyl sulfate can preferentially accumulate on the surface of NCM622 before other basic components in the system are oxidized, occupy the active sites, form a protective film before lithium ions are deintercalated / inserted from NCM622, inhibit the decomposition of other basic components in the electrolyte, protect other basic components in the electrolyte, and improve the cycle life and rate performance of the lithium-ion energy storage battery;

[0031] 3. By adding 0.1 - 0.3 parts of silyl sulfate, it is beneficial to inhibit the polarization of Li metal as the negative electrode, and is beneficial to improving the cycle life and safety of the lithium-ion energy storage battery. Description of the Drawings

[0032] Figure 1 A comparison chart of the cycle tests for the lithium-ion energy storage batteries of Example 2 and Comparative Example 1;

[0033] Figure 2 A comparison chart of the results after the cyclic voltammetry tests for the lithium-ion energy storage batteries of Example 2 and Comparative Example 1;

[0034] Figure 3 Results of the HOMO and LUMO theoretical calculations for EC, EMC, and DEC in the lithium-ion energy storage battery of Example 2;

[0035] Figure 4 A comparison chart of the rate performance tests for the lithium-ion energy storage batteries of Example 2 and Comparative Example 1;

[0036] Figure 5Impedance test comparison chart of the lithium-ion energy storage batteries of Example 2 and Comparative Example 1 after 3 cycles of cycling test;

[0037] Figure 6 Impedance test comparison chart of the lithium-ion energy storage batteries of Example 2 and Comparative Example 1 after 200 cycles of cycling test;

[0038] Figure 7 Comparison chart of TEM and SEM characterization results of the electrode sheets of the lithium-ion energy storage batteries of Example 2 and Comparative Example 1 after 200 cycles of cycling;

[0039] Figure 8 Comparison chart of ICP test results on the surface of the negative electrode of the lithium-ion energy storage batteries of Example 2 and Comparative Example 1 after 200 cycles of cycling.

[0040] Figure 9 Cycling performance chart of the lithium-lithium symmetric battery made from the high-voltage lithium-ion battery electrolyte obtained during the preparation of Example 2 and Comparative Example 1 after cycling test. Detailed implementation mode

[0041] The following further details the present application in conjunction with examples. The following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those conditions not specified in the following examples, they are carried out according to conventional conditions or conditions recommended by the manufacturer. The methods used, unless otherwise specified, are all conventional methods well known in the art. The consumables and reagents used, unless otherwise specified, are all commercially available. Unless otherwise stated, the professional and scientific terms used herein have the same meaning as those familiar to skilled personnel in the art. In addition, any method or material similar or equivalent to the described content can also be applied to the present invention.

[0042] The raw materials used in the examples and comparative examples can all be obtained commercially. Among them, bis(trimethylsilyl)sulfate, English name: Bis(trimethylsilyl)Sulfate, CAS No.: 18306-29-1, molecular formula: C6H18O4SSi2, molecular weight: 242.4400, also known as BTTS.

[0043] Example 1

[0044] Example 1 of the present application provides a lithium-ion energy storage battery, which is prepared by the following method:

[0045] Preparation of the positive electrode sheet: Put LiNi 0.6 Co 0.2 Mn 0.2(NCM622), polytetrafluoroethylene (PVDF), and acetylene black were dissolved in N-methylpyrrolidone (NMP) at a mass ratio of 8:1:1. The slurry was evenly coated on the current collector aluminum foil, first dried in an oven at 80 °C for 1 h, and then transferred to a vacuum dryer at 120 °C for 12 h, and then cut to obtain a positive electrode sheet with a diameter of 12 mm.

[0046] Preparation of high-voltage lithium-ion battery electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate were mixed in a mass ratio of 3:5:2, and purified and dehydrated (water content less than 10 ppm) using molecular sieves, calcium hydride, and lithium hydride to obtain an organic solvent; at room temperature, the conductive lithium salt LiPF6 was dissolved in the organic solvent and stirred evenly. The final concentration of LiPF6 was 1.0 mol / L to obtain a basic electrolyte; bis(trimethylsilyl) sulfate was added to the basic electrolyte, and the addition amount of bis(trimethylsilyl) sulfate was 0.1 wt.% of the basic electrolyte, and stirred evenly to obtain a high-voltage lithium-ion battery electrolyte.

[0047] The positive electrode sheet, high-voltage lithium-ion battery electrolyte, separator, and Li as the negative electrode sheet were assembled to obtain a lithium-ion energy storage battery.

[0048] In this example, the model of the separator is Celgard 2400, LiNi 0.6 Co 0.2 Mn 0.2 (NCM622) was used as the positive electrode active material, polytetrafluoroethylene (PVDF) as the binder, and acetylene black as the conductive material.

[0049] Example 2

[0050] Example 2 of this application provides a lithium-ion energy storage battery. The difference between Example 2 and Example 1 is that in the process of preparing the high-voltage lithium-ion battery electrolyte in Example 2, the addition amount of bis(trimethylsilyl) sulfate is 0.2 wt.% of the basic electrolyte.

[0051] Example 3

[0052] Example 3 of this application provides a lithium-ion energy storage battery. The difference between Example 3 and Example 1 is that in the process of preparing the high-voltage lithium-ion battery electrolyte in Example 3, the addition amount of bis(trimethylsilyl) sulfate is 0.3 wt.% of the basic electrolyte.

[0053] Example 4

[0054] Example 4 provides a lithium-ion energy storage battery. The difference between Example 4 and Example 2 is that in the process of preparing the positive electrode sheet in Example 4, NCM811 (LiNi 0.8 Co 0.1Mn 0.1 Replace NCM622 as the cathode active material.

[0055] Example 5

[0056] Example 5 provides a lithium-ion energy storage battery. The difference between Example 5 and Example 2 is that in the process of preparing the cathode electrode, LCO (lithium cobaltate) is used to replace NCM622 as the cathode active material.

[0057] Comparative Example 1

[0058] Comparative Example 1 provides a lithium-ion energy storage battery. The difference between Comparative Example 1 and Example 2 is that in the process of preparing the high-voltage lithium-ion battery electrolyte, bis(trimethylsilyl)sulfate is not added.

[0059] Comparative Example 2

[0060] Comparative Example 2 provides a lithium-ion energy storage battery. The difference between Comparative Example 2 and Example 2 is that in the process of preparing the high-voltage lithium-ion battery electrolyte, tris-thiopheneboric acid is used to replace bis(trimethylsilyl)sulfate and added to the base electrolyte.

[0061] Comparative Example 3

[0062] Comparative Example 3 provides a lithium-ion energy storage battery. The difference between Comparative Example 3 and Comparative Example 1 is that in the process of preparing the cathode electrode, NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 Replace NCM622 as the cathode active material.

[0063] Comparative Example 4

[0064] Comparative Example 4 provides a lithium-ion energy storage battery. The difference between Comparative Example 4 and Example 2 is that in the process of preparing the cathode electrode, LCO (lithium cobaltate) is used to replace NCM622 as the cathode active material.

[0065] Test and detection

[0066] (1) The lithium-ion energy storage batteries prepared in Examples 1-5 and Comparative Examples 1-4 were subjected to a cycle test, and the capacity retention rate after 200 cycles was obtained as shown in Table 1. The comparison of the cycle number-capacity retention rate between the lithium-ion energy storage batteries of Example 2 and Comparative Example 1 is Figure 1 as shown.

[0067] Table 1: Capacity retention rate of the lithium-ion energy storage batteries of Examples 1-5 and Comparative Examples 1-4

[0068]

[0069] (2) The cyclic voltammetry (CV) tests were performed on the lithium-ion energy storage batteries prepared in Example 2 and Comparative Example 1, and the results are as Figure 2 shown.

[0070] (3) The HOMO and LUMO of the high-voltage lithium-ion battery electrolyte during the preparation process of Example 2 were theoretically calculated, and the results are as Figure 3 shown.

[0071] (4) The cycle performance tests were carried out on the lithium-ion energy storage batteries prepared in Example 2 and Comparative Example 1 at different rates (0.3C, 1.0C, 3.0C, 7.0C, 0.3C, 10C, 15C), and the test results are as Figure 4 shown.

[0072] (5) The battery impedance tests were carried out on the lithium-ion energy storage batteries prepared in Example 2 and Comparative Example 1 after 3 cycles of cycle performance tests as Figure 5 shown, and the battery impedance tests were carried out after 200 cycles as Figure 6 shown

[0073] (6) The positive electrode plates of the lithium-ion energy storage batteries prepared in Example 2 and Comparative Example 1 after 200 cycles of cycle performance tests were imaged by transmission electron microscopy (TEM) and scanning electron microscopy (SEM), as Figure 7 shown.

[0074] (7) The ICP (inductively coupled plasma mass spectrometry) tests were carried out on the surface of the negative electrode of the lithium-ion energy storage batteries of Example 2 and Comparative Example 1 after 200 cycles, and the test results are as Figure 8 shown.

[0075] (8) The high-voltage lithium-ion battery electrolytes obtained during the preparation of Example 2 and Comparative Example 1 were made into lithium-lithium symmetric batteries, and then cycled at a current density of 1 mAcm -2 , and the cycle performance is as Figure 9 shown.

[0076] (9) The binding energies of Ni 2+ , Ni 4+ , Mn 4+ in the lithium-ion energy storage battery of Example 2 and each component in the electrolyte were calculated using DFT, and the calculation results are shown in Table 2.

[0077] Table 2: Calculation results of DFT binding energy

[0078]

[0079] Result analysis

[0080] The following combines Table 1-2 andFigures 1-9 The provided experimental data are used to elaborate on this application in detail.

[0081] From the capacity retention rates of the lithium-ion energy storage batteries after 200 cycles in Examples 1-5, it can be seen that the lithium-ion energy storage battery with 0.2 wt.% BTTS exhibits the best capacity retention rate of 81.3% under the condition that the charge-discharge cut-off voltage is 3.0 - 4.5 V, which improves the service life of the lithium-ion energy storage battery when the working voltage is above 4.3 V. When the BTTS concentration is 0.1 wt.%, the capacity retention rate is lower than that of the lithium-ion energy storage battery containing 0.2 wt.% BTTS, only 76.3%. The analysis is that the interfacial film formed by BTTS is not sufficient to completely cover the material surface; while when the BTTS concentration is 0.3 wt.%, the capacity retention rate after long cycling is 80.7%, slightly less than that of the lithium-ion energy storage battery with 0.2 wt.% BTTS. The analysis is that the increase in BTTS concentration will slightly increase the impedance of the battery and reduce the first-cycle efficiency.

[0082] From Examples 2 and Comparative Example 1, Examples 4 and Comparative Example 3, and Examples 5 and Comparative Example 4, it can be seen that the high-voltage lithium-ion battery electrolyte added with BTTS increases the capacity retention rate of the lithium-ion energy storage battery prepared using NCM622 as the positive electrode active material from 52.5% to 81.3%, the high-voltage lithium-ion battery electrolyte added with BTTS increases the capacity retention rate of the lithium-ion energy storage battery prepared using NCM811 as the positive electrode active material from 57.6% to 71.0%, and the high-voltage lithium-ion battery electrolyte added with BTTS increases the capacity retention rate of the lithium-ion energy storage battery prepared using LCO as the positive electrode active material from 44.5% to 53.3%. Therefore, the high-voltage lithium-ion battery electrolyte added with BTTS has a synergistic effect in increasing the capacity retention rate of the lithium-ion energy storage battery prepared using NCM622 as the positive electrode active material.

[0083] Referring to Comparative Examples 1-2 and Example 2, it can be seen that the capacity retention rate of the lithium-ion energy storage battery prepared by combining the high-voltage lithium-ion battery electrolyte added with tris-thiopheneboronic acid and using NCM622 as the positive electrode active material is not only much lower than that of the lithium-ion energy storage battery prepared by the high-voltage lithium-ion battery electrolyte added with BTTS and using NCM622 as the positive electrode active material, but even lower than that of the lithium-ion energy storage battery prepared by the basic electrolyte and using NCM622 as the positive electrode active material. This further illustrates that the high-voltage lithium-ion battery electrolyte added with BTTS has a synergistic effect in increasing the capacity retention rate of the lithium-ion energy storage battery prepared using NCM622 as the positive electrode active material.

[0084] And as Figure 1As shown, it can be seen that the lithium-ion energy storage battery of Comparative Example 1 shows obvious capacity attenuation, and the capacity retention rate after 200 cycles is only 52.5% of the initial value. For the lithium-ion energy storage battery of Example 2, the capacity retention rate is still 81.3% after 200 cycles of battery cycling, indicating that the use of a high-voltage lithium-ion battery electrolyte added with bis(trimethylsilyl)sulfate can significantly improve the cycling stability of the lithium-ion energy storage battery.

[0085] Referring to Example 2 and Comparative Example 1, in combination with Figures 2-7 , where by Figure 2 and Figure 3 , compared with the lithium-ion energy storage battery of Comparative Example 1, when the lithium-ion energy storage battery of Example 2 is subjected to cyclic voltammetry scanning, it can be clearly observed that an oxidation current appears prematurely between 3.4 V and 3.65 V in the battery. Figure 3 The results in Figure 4 also confirm this point. The theoretical calculation results of HOMO and LUMO show that BTTS undergoes an oxidation reaction prior to other components in the high-voltage lithium-ion battery electrolyte. From Figure 5 and Figure 6 , it can be seen that at high rates of 7.0 C and above, the capacity performance of the battery of Example 2 with BTTS added as a component of the high-voltage lithium-ion battery electrolyte is better than that of the lithium-ion energy storage battery of Comparative Example 1. This phenomenon is particularly obvious at a high rate of 15 C. In the lithium-ion energy storage battery of Comparative Example 1, the battery capacity can only reach 53.5% of the initial capacity, while the lithium-ion energy storage battery of Example 2 can reach 75.1% of the initial capacity. Referring to Figure 7, it was found by the results of TEM that the thickness of the interfacial film formed by the lithium-ion energy storage battery of Comparative Example 1 after cycling was distributed between 5 and 26 nm, with a low degree of uniformity. However, the thickness of the interfacial film formed by the lithium-ion energy storage battery of Example 2 after cycling was around 6.5 nm, indicating that the interfacial film formed by the participation of BTTS was thinner and more uniform, reducing the impedance of the battery. The test results of SEM were consistent with those of TEM. After the lithium-ion energy storage battery of Comparative Example 1 was cycled 200 times, cracks appeared on the surface of the bulk particles of the positive electrode sheet, indicating that the positive electrode sheet was severely damaged during long cycling. On the contrary, after the lithium-ion energy storage battery of Example 2 was cycled 200 times, the shape of the positive electrode sheet remained intact and there was no obvious change compared with the fresh electrode sheet (the positive electrode sheet of the lithium-ion energy storage battery of Example 2 before cycling 200 times). Figure 8 The ICP results further verified the stability of the interfacial film formed by the additive. By comparison, it was found that adding 0.2 wt.% BTTS could significantly inhibit the dissolution of transition metals in the positive electrode active material, thereby improving the capacity retention rate of the lithium-ion energy storage battery after long cycling.

[0086] Referring to Figure 9 , the high-voltage lithium-ion battery electrolytes obtained during the preparation of Example 2 and Comparative Example 1 were made into lithium-lithium symmetric batteries, and then cycled at a current density of 1 mA cm-2 respectively. For the lithium-ion energy storage battery of Example 2 using the high-voltage lithium-ion battery electrolyte added with 0.2 wt.% BTTS, compared with the lithium-ion energy storage battery of Comparative Example 1 using the basic electrolyte without BTTS, the cycling time of the lithium-lithium symmetric battery increased from 120 h to 325 h, indicating that the high-voltage lithium-ion battery electrolyte added with 0.2 wt.% BTTS could improve the cycling stability of the lithium-ion energy storage battery using lithium metal as the negative electrode. It was analyzed that the high-voltage lithium-ion battery electrolyte added with 0.2 wt.% BTTS reduced the polarization of lithium metal and inhibited the formation of lithium dendrites.

[0087] This specific embodiment is only an explanation of the present application and is not a limitation to the present application. Those skilled in the art can make modifications without creative contributions to this embodiment according to needs after reading this specification, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A lithium-ion energy storage battery, characterized in that: It includes a positive electrode, a negative electrode, a separator and a high-voltage lithium-ion battery electrolyte. The positive electrode uses NCM622 as the positive electrode active material. The high-voltage lithium-ion battery electrolyte includes an electrolyte lithium salt, an organic solvent and a silyl sulfate. The dosage of the silyl sulfate is 0.1-0.3% of the total mass of the electrolyte lithium salt and the organic solvent; The silyl sulfate is bis(trimethylsilyl) sulfate; the working voltage range of the lithium-ion energy storage battery is 3.0-4.5V.

2. The lithium-ion energy storage battery according to claim 1, characterized in that: The organic solvent includes a cyclic carbonate and a linear carbonate with a weight ratio of 1:1-3.

3. A lithium-ion energy storage battery according to claim 2, characterized in that: The cyclic carbonate includes one or more of ethylene carbonate, propylene carbonate, butylene carbonate, butyrolactone and valerolactone; the linear carbonate includes one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, butyl acetate, methyl propionate, ethyl propionate and propyl propionate.

4. The lithium-ion energy storage battery according to claim 3, wherein: The linear carbonate includes ethyl methyl carbonate and diethyl carbonate with a weight ratio of 5:1-3.

5. A lithium-ion energy storage battery according to claim 1, characterized in that: The electrolyte lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorooxalate borate, lithium bis(oxalato)borate and lithium difluorooxalate borate.

6. A lithium-ion energy storage battery according to claim 1, characterized in that: The preparation of the high-voltage lithium-ion battery electrolyte includes the following steps: adding the electrolyte lithium salt to the organic solvent to dissolve, obtaining a raw material electrolyte, and adding the silyl sulfate to the raw material electrolyte to dissolve, obtaining the high-voltage lithium-ion battery electrolyte.

7. A lithium-ion energy storage battery according to claim 6, characterized in that: The organic solvent is prepared by mixing a cyclic carbonate and a linear carbonate in proportion and then purifying by removing impurities and water.

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