Lithium ion battery electrolyte and secondary lithium battery

Abstract

The present application relates to a kind of lithium ion battery electrolyte and secondary lithium battery.For improving the cycle performance at room temperature and high temperature cycle performance of high-voltage secondary lithium battery, the present application provides a kind of lithium ion battery electrolyte, it includes base electrolyte and additive, base electrolyte includes organic solvent and lithium salt, organic solvent includes carbonate solvent and fluorinated carbonate solvent, and the mass ratio of carbonate solvent and fluorinated carbonate solvent is 1 :(1-3), additive includes potassium salt additive.The present application improves the cycle performance of conventional base electrode liquid under high voltage by adding special potassium salt additive, the present application further further with the appropriate amount of special film-forming additive is used with the appropriate amount of potassium salt additive, prevents the further decomposition of electrolyte, also can keep better cycle performance under the high voltage of 5V, improved lithium ion battery electrolyte can be applied to high-voltage spinel lithium nickel manganese oxide secondary lithium battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a lithium-ion battery electrolyte and a secondary lithium battery. Background Technology

[0002] With the rapid advancements in electric vehicle technology, the development of lithium-ion battery technology is becoming increasingly important. Electrolytes, as a key component of battery technology, have received significant attention. With the widespread application of batteries, the market demand for high energy density and low cost is urgent. Spinel nickel manganese oxide (LiMO) offers better energy density due to its higher voltage platform, and it eliminates the need for cobalt, reducing costs. However, increasing voltage poses a severe challenge to battery electrolyte solvents. Traditional electrolyte solvents, due to their chemical window, are easily decomposed by the electrodes at higher operating voltages, accelerating electrolyte consumption and reducing battery performance. Solvents suitable for high voltages also present problems such as poor conductivity, high viscosity, and incompatibility with the negative electrode, most directly resulting in a significant decrease in battery cycle performance at high voltages. Summary of the Invention

[0003] The purpose of this invention is to provide an electrolyte that can improve the room temperature and high temperature cycle performance of high-voltage secondary lithium batteries.

[0004] Another object of the present invention is to provide a secondary lithium battery using the above-described electrolyte.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] The first aspect of the present invention provides a lithium-ion battery electrolyte, the lithium-ion battery electrolyte comprising a base electrolyte and additives, the base electrolyte comprising an organic solvent and a lithium salt, the organic solvent comprising a carbonate solvent and a fluorinated carbonate solvent, wherein the mass ratio of the carbonate solvent to the fluorinated carbonate solvent is 1:(1-3), and the additives comprising potassium salt additives.

[0007] Preferably, the potassium salt additive includes one or more of KPF6, KFSI, KTFSI, KBF4, KClO4, KCH3SO3, KSCN, KNO3, KO3SCF2CF3, KAsF6, and KAlCl4.

[0008] More preferably, the potassium salt additive is one or more of KPF6, KTFSI, and KNO3.

[0009] More preferably, the potassium salt additive is KPF6 or KTFSI.

[0010] Preferably, the amount of potassium salt additive is 0.5% to 2% of the mass of the base electrolyte, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%.

[0011] Preferably, the additive further includes a film-forming additive, which includes one or more of lithium bis(trimethylsilyl)phosphate, lithium bis(oxalato)borate, lithium difluorooxalato)borate, vinyl sulfate, and vinylene carbonate. The amount of the film-forming additive is 0.5% to 2% of the mass of the base electrolyte, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, or 2%.

[0012] More preferably, the film-forming additive is one or more of lithium bis(trimethylsilyl)phosphate, lithium bis(oxalate-borate), and lithium difluorooxalate-borate.

[0013] More preferably, the film-forming additive is lithium bis(trimethylsilyl)phosphate.

[0014] More preferably, the mass ratio of the potassium salt additive to the film-forming additive is (0.5-3):1, for example, 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, 2.6:1, 2.7:1, 2.8:1, 2.9:1, or 3:1.

[0015] More preferably, the mass ratio of the potassium salt additive to the film-forming additive is (1-2):1.

[0016] Preferably, the lithium salt includes one or more of LiPF6, LiTFSI, LiBF4, LiClO4, LiCH3SO3, LiSCN, LiNO3, LiO3SCF2CF3, LiAsF6, and LiAlCl4.

[0017] Preferably, the amount of lithium salt used is 10% to 15% of the mass of the base electrolyte, for example, 10%, 11%, 12%, 13%, 14%, or 15%.

[0018] Preferably, the carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and propylene carbonate.

[0019] Preferably, the fluorocarbonate solvent includes one or more of fluoroethylene carbonate, difluoroethylene carbonate, methyl ethyl fluorocarbonate, dimethyl fluorocarbonate, diethyl fluorocarbonate, and methyl propyl fluorocarbonate.

[0020] According to some specific embodiments of the present invention, the organic solvent includes fluoroethylene carbonate, methyl ethyl carbonate and trifluoroethyl methyl carbonate, wherein the mass ratio of fluoroethylene carbonate, methyl ethyl carbonate and trifluoroethyl methyl carbonate is 1:(1-1.5):(1-1.5).

[0021] More preferably, the mass ratio of the fluoroethylene carbonate, methyl ethyl carbonate and trifluoroethyl methyl carbonate is 1:(1.2-1.4):(1.3-1.5).

[0022] A second aspect of the present invention provides a lithium secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the electrolyte is the lithium-ion battery electrolyte described above.

[0023] Preferably, the active material of the positive electrode is spinel lithium nickel manganese oxide.

[0024] Preferably, the active material of the negative electrode is lithium metal, natural graphite, artificial graphite, hard carbon, soft carbon, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, tin-based composite material, spinel-structured lithiated TiO2, or Li4Ti5O. 12 One or more of the following: Li-Al alloy, silicon, Li-Si alloy, Li-Si-O alloy, silicon-based composite material, and tin-silicon composite material.

[0025] Preferably, the diaphragm comprises a substrate and a coating, wherein the substrate is made of polyethylene and / or polypropylene, and the coating is an organic material and / or a metal oxide.

[0026] The voltage of the lithium secondary battery of the present invention is 4.5 to 5V.

[0027] Due to the application of the above-mentioned technical solution, the present invention has the following advantages compared with the prior art:

[0028] This invention improves the cycle performance of traditional basic electrode solutions at high voltages by adding special potassium salt additives. Furthermore, by combining appropriate amounts of potassium salt additives with appropriate amounts of special film-forming additives, further decomposition of the electrolyte is prevented, and better cycle performance can be maintained even at a high voltage of 5V. The improved lithium-ion battery electrolyte is suitable for high-voltage spinel nickel manganese lithium secondary lithium batteries. Detailed Implementation

[0029] To improve the room temperature and high temperature cycling performance of high-voltage secondary lithium batteries, the inventors of this application have improved the cycling performance of traditional basic electrolytes at high voltages by adding special potassium salt additives. Furthermore, by combining appropriate amounts of potassium salt additives with appropriate amounts of special film-forming additives, the cycle gas generation can be reduced to protect the negative electrode, inhibit dendrite formation, inhibit the dissolution of metal ions, and generate dense and stable positive and negative electrode films to prevent further decomposition of the electrolyte. Even at a high voltage of 5V, it can maintain better cycle performance. The improved lithium-ion battery electrolyte is suitable for high-voltage spinel nickel-manganese lithium secondary lithium batteries.

[0030] The present invention will be further described below with reference to embodiments. However, the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific applications, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0031] Unless otherwise specified, the raw materials used in the following examples and comparative examples are all commercially available products.

[0032] Examples 1-12 and Comparative Examples 1-2

[0033] The lithium-ion battery electrolyte was prepared according to the component dosages in Table 1. Lithium salt LiPF6 was dissolved in a mixed solvent of FEC / EMC / FEMC to form a basic electrolyte. Additives were added to the basic electrolyte and mixed evenly to obtain the lithium-ion battery electrolyte.

[0034] Table 1

[0035]

[0036]

[0037] In Table 1: FEC: fluoroethylene carbonate; EMC: methyl ethyl carbonate; FEMC: trifluoroethyl methyl carbonate; LiPF6: lithium hexafluorophosphate; LiTMSP: lithium bis(trimethylsilyl)phosphate; KPF6: potassium hexafluorophosphate; KTFSI: potassium bis(trifluoromethanesulfonyl)imide; KNO3: potassium nitrate.

[0038] Preparation of high-voltage secondary lithium batteries:

[0039] LiNi 0.5 Mn 1.5O4 (lithium nickel manganese spinel oxide LNMO): conductive additive (SuperP): binder (PVDF) are mixed evenly in N-methylpyrrolidone (NMP) at a mass ratio of 90:5:5. The mixture is then coated onto an aluminum foil current collector with a coating surface density of 360 g / m². 2 A positive electrode is prepared; a 12 μm polyethylene (PE) base film is coated with an alumina coating (2 μm) on both sides of the base film as a separator; artificial graphite is used as a negative electrode; and a high-voltage secondary lithium battery is assembled with the electrolyte prepared above. The battery assembly is a conventional method in the field and will not be described in detail here.

[0040] The room temperature cycling performance of the high-voltage secondary lithium batteries in Examples 1-12 and Comparative Examples 1-2 was tested. The test method was as follows: After formation, the high-voltage secondary lithium batteries were charged to 5V at 0.5C at 25°C, then left to stand for 5 minutes. The batteries were then discharged to 3V at 0.5C, left to stand for 5 minutes, and this process was repeated 300 times. The room temperature cycle retention rate (%) after 300 cycles was calculated as: (Discharge capacity of the 300th cycle / Discharge capacity of the first cycle) × 100%. The discharge capacity was tested using a Shenzhen Xinwei Battery Tester.

[0041] The high-temperature cycle performance of the high-voltage secondary lithium batteries in Examples 1-12 and Comparative Examples 1-2 was tested. The test method was as follows: After formation, the high-voltage secondary lithium batteries were charged to 5V at 0.5C at 60°C, then left to stand for 5 minutes. The batteries were then discharged to 3V at 0.5C, left to stand for 5 minutes, and this process was repeated 300 times. The high-temperature cycle retention rate (%) after 300 cycles was calculated as: (Discharge capacity of the 300th cycle / Discharge capacity of the first cycle) × 100%. The discharge capacity was tested using a Shenzhen Xinwei Battery Tester.

[0042] The room temperature cycling performance and high temperature cycling performance test results of the high voltage secondary lithium batteries of Examples 1-12 and Comparative Examples 1-2 are shown in Table 2.

[0043] Table 2

[0044]

[0045]

[0046] According to Tables 1 and 2, the traditional base electrolyte exhibits poor cycle performance in high-voltage secondary lithium batteries. Adding a small amount of LiTMSP improves cycle performance somewhat, but the improvement is not significant. Adding small amounts of potassium salt additives (KPF6, KTFSI, KNO3) significantly improves cycle performance, with a noticeable better effect than LiTMSP on improving cycle performance in high-voltage secondary lithium batteries. When LiTMSP is used in combination with potassium salt additives, cycle performance is further enhanced, with the combination of LiTMSP and KTFSI showing the best improvement in cycle performance for high-voltage secondary lithium batteries.

[0047] The present invention has been described in detail above, with the aim of enabling those skilled in the art to understand and implement the invention. However, this description should not be construed as limiting the scope of protection of the invention. All equivalent changes or modifications made in accordance with the spirit and essence of the invention should be included within the scope of protection of the invention.

Claims

1. A lithium-ion battery electrolyte, characterized in that, The lithium-ion battery electrolyte includes a base electrolyte and additives. The base electrolyte includes an organic solvent and a lithium salt. The organic solvent includes a carbonate solvent and a fluorocarbonate solvent, and the mass ratio of the carbonate solvent to the fluorocarbonate solvent is 1:(1-3). The additives include potassium salt additives.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that, The potassium salt additive includes one or more of KPF6, KFSI, KTFSI, KBF4, KClO4, KCH3SO3, KSCN, KNO3, KO3SCF2CF3, KAsF6, and KAlCl4; And / or, the amount of the potassium salt additive is 0.5% to 2% of the mass of the base electrolyte.

3. The lithium-ion battery electrolyte according to claim 1, characterized in that, The additives also include film-forming additives, which include one or more of lithium bis(trimethylsilyl)phosphate, lithium bis(oxalato)borate, lithium difluorooxalato)borate, vinyl sulfate, and vinylene carbonate. The amount of the film-forming additives used is 0.5% to 2% of the mass of the base electrolyte.

4. The lithium-ion battery electrolyte according to claim 3, characterized in that, The mass ratio of the potassium salt additive to the film-forming additive is (0.5-3):

1.

5. The lithium-ion battery electrolyte according to claim 1, characterized in that, The lithium salt includes one or more of LiPF6, LiTFSI, LiBF4, LiClO4, LiCH3SO3, LiSCN, LiNO3, LiO3SCF2CF3, LiAsF6, and LiAlCl4; And / or, the amount of lithium salt used is 10% to 15% of the mass of the base electrolyte.

6. The lithium-ion battery electrolyte according to claim 1, characterized in that, The carbonate solvent includes one or more of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and propylene carbonate. And / or, the fluorocarbonate solvent includes one or more of fluoroethylene carbonate, difluoroethylene carbonate, methyl ethyl fluorocarbonate, dimethyl fluorocarbonate, diethyl fluorocarbonate, and methyl propyl fluorocarbonate.

7. The lithium-ion battery electrolyte according to claim 6, characterized in that, The organic solvent includes fluoroethylene carbonate, methyl ethyl carbonate and trifluoroethyl methyl carbonate, wherein the mass ratio of fluoroethylene carbonate, methyl ethyl carbonate and trifluoroethyl methyl carbonate is 1:(1-1.5):(1-1.5).

8. A lithium secondary battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The electrolyte is the lithium-ion battery electrolyte according to any one of claims 1 to 7.

9. The lithium secondary battery according to claim 8, characterized in that, The active material of the positive electrode is spinel lithium nickel manganese oxide; and / or, the active material of the negative electrode is metallic lithium, natural graphite, artificial graphite, hard carbon, soft carbon, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, tin-based composite materials, spinel-structured lithiated TiO2, Li4Ti5O 12 One or more of the following: Li-Al alloy, silicon, Li-Si alloy, Li-Si-O alloy, silicon-based composite material, and tin-silicon composite material.

10. The lithium secondary battery according to claim 8, characterized in that, The diaphragm comprises a substrate and a coating, wherein the substrate is made of polyethylene and / or polypropylene, and the coating is an organic material and / or a metal oxide.

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