Electrolyte additive, electrolyte containing electrolyte additive and lithium ion battery

Abstract

The invention provides an electrolyte additive, an electrolyte containing the electrolyte additive and a lithium ion battery. The electrolyte additive comprises one or more of Ba (TFSI) 2, Ca (TFSI) 2 and Sr (TFSI) 2. The electrolyte comprises the electrolyte additive, a lithium salt and a solvent. The electrolyte additive provided by the invention can form an SEI layer rich in BaF2, CaF2 and / or SrF2 on the surface of a negative electrode material in the charging and discharging process of the battery, the SEI layer is relatively compact and low in porosity, side reactions between an electrolyte and a silicon-based negative electrode active material in the storage (especially high SOC state storage) process of the silicon-containing lithium ion battery can be effectively reduced, and the service life of the battery is prolonged. Therefore, the storage life of the silicon-containing lithium ion battery is prolonged.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to an electrolyte additive and an electrolyte and a lithium ion battery containing the electrolyte additive. Background Art

[0002] At present, lithium-ion batteries have been widely used in 3C portable electronic devices, electric vehicles and other fields due to their advantages such as high reversible capacity, high energy density and long cycle life. With the rapid development of the electric vehicle industry, people are increasingly pursuing long driving range and high safety. Conventional lithium-ion batteries use graphite as the negative electrode active material, and its theoretical capacity is only 372mAh / g, which is difficult to meet the needs of practical applications.

[0003] Silicon-based materials can be alloyed with Li + The reaction contributes to the capacity, and has the advantage of high energy density. Its theoretical capacity can reach nearly 10 times the gram capacity of commercial graphite. However, there are still many problems in the practical application of existing silicon-based materials: due to its high surface activity and huge volume expansion / contraction effect during the battery charging and discharging process, the silicon-based material in the negative electrode will continue to react with the electrolyte during the battery storage process, consuming active lithium, which makes the storage life of lithium-ion batteries a great challenge, and its further commercial application is limited.

[0004] Therefore, how to reduce the side reactions between electrolyte and silicon-based materials and extend the storage life of silicon-containing lithium-ion batteries is an urgent problem to be solved in the practical application of silicon-based negative electrode materials. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention aims to provide an electrolyte additive and an electrolyte and a lithium ion battery containing the same. The additive can improve the properties of the SEI film (solid electrolyte membrane) of the negative electrode of the lithium ion battery, reduce the side reaction between the electrolyte and the silicon-based negative electrode active material, and thus extend the storage life of the silicon-containing lithium ion battery.

[0006] To achieve this object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides an electrolyte additive, wherein the electrolyte additive includes one or more of Ba(TFSI)2, Ca(TFSI)2 and Sr(TFSI)2.

[0008] The additive provided by the present invention can form a SEI layer rich in BaF2, CaF2 and / or SrF2 on the surface of the negative electrode material during the battery charging and discharging process. The SEI layer is relatively dense and has low porosity, which can effectively reduce the side reaction between the electrolyte and the silicon-based negative electrode active material during the storage of silicon-containing lithium-ion batteries (especially storage in a high SOC state), thereby extending the storage life of silicon-containing lithium-ion batteries.

[0009] In some embodiments of the present invention, the electrolyte additive is Ba(TFSI)2.

[0010] The present invention has found through research that the SEI layer containing BaF2 formed by Ba(TFSI)2 is more insoluble than the SEI layer containing CaF2 and the SEI layer containing SrF2 formed by Ca(TFSI)2 and Sr(TFSI)2, and the film layer is denser and has a lower porosity, which is more conducive to preventing the penetration of electrolyte and reducing the side reaction between electrolyte and silicon-based negative electrode active materials. Therefore, the electrolyte additive in the present invention is more preferably Ba(TFSI)2.

[0011] In a second aspect, the present invention provides an electrolyte, comprising the electrolyte additive as described in the first aspect, a lithium salt and a solvent.

[0012] In some embodiments of the present invention, the content of the electrolyte additive in the electrolyte is 0.5-3wt%; for example, it can be 0.5wt%, 0.6wt%, 0.8wt%, 1wt%, 1.2wt%, 1.3wt%, 1.5wt%, 1.6wt%, 1.8wt%, 2wt%, 2.2wt%, 2.3wt%, 2.5wt%, 2.6wt%, 2.8wt% or 3wt%, etc.

[0013] If the content of the electrolyte additive is too low, its corresponding effect will be weak; if the content of the electrolyte additive is too high, it will easily lead to a large internal resistance of the battery and poor dynamic performance.

[0014] In some embodiments of the present invention, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bis(oxalatoborate), lithium tetrafluoroborate and lithium bis(trifluoromethylsulfonylimide).

[0015] In some embodiments of the present invention, the concentration of the lithium salt in the electrolyte is 0.5-2 mol / L; for example, it can be 0.5 mol / L, 0.6 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.5 mol / L, 1.6 mol / L, 1.8 mol / L or 2 mol / L, etc.

[0016] In some embodiments of the present invention, the solvent is selected from one or more of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC) and fluoroethylene carbonate (FEC).

[0017] In a third aspect, the present invention provides a lithium ion battery, wherein the lithium ion battery comprises the electrolyte as described in the second aspect.

[0018] In some embodiments of the present invention, the negative electrode of the lithium-ion battery contains a silicon-based negative electrode active material.

[0019] The silicon-based negative electrode active material can be simple silicon, SiO x (0<x<2) etc.

[0020] In a fourth aspect, the present invention provides an electrical device comprising the lithium-ion battery as described in the third aspect.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The additive provided by the present invention can form a SEI layer rich in BaF2, CaF2 and / or SrF2 on the surface of the negative electrode material during the battery charging and discharging process. The SEI layer is relatively dense and has low porosity, which can effectively reduce the side reaction between the electrolyte and the silicon-based negative electrode active material during the storage of silicon-containing lithium-ion batteries (especially storage in a high SOC state), thereby extending the storage life of silicon-containing lithium-ion batteries. DETAILED DESCRIPTION

[0023] The technical solution of the present invention is further described below by means of specific implementation methods. It should be understood by those skilled in the art that the specific implementation methods are only used to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0024] Example 1

[0025] This embodiment provides an electrolyte, comprising the following components:

[0026]

[0027] Example 2

[0028] This embodiment provides an electrolyte, comprising the following components:

[0029]

[0030]

[0031] Example 3

[0032] This embodiment provides an electrolyte, comprising the following components:

[0033]

[0034] Example 4

[0035] This embodiment provides an electrolyte, comprising the following components:

[0036]

[0037] Example 5

[0038] This embodiment provides an electrolyte, comprising the following components:

[0039]

[0040] Example 6

[0041] This embodiment provides an electrolyte, comprising the following components:

[0042]

[0043] Example 7

[0044] This embodiment provides an electrolyte, which is different from the embodiment 3 only in that the additive is Ca(TFSI)2.

[0045] Example 8

[0046] This embodiment provides an electrolyte, which is different from the embodiment 3 only in that the additive is Sr(TFSI)2.

[0047] Example 9

[0048] This embodiment provides an electrolyte, which is different from the embodiment 3 only in that the content of Ba(TFSI)2 is 4 wt%.

[0049] Comparative Example 1

[0050] This comparative example provides an electrolyte, which differs from Example 1 only in that it does not contain Ba(TFSI)2.

[0051] Comparative Example 2

[0052] This comparative example provides an electrolyte, which differs from Example 2 only in that it does not contain Ba(TFSI)2.

[0053] Comparative Example 3

[0054] This comparative example provides an electrolyte, which differs from Example 4 only in that it does not contain Ca(TFSI)2.

[0055] Comparative Example 4

[0056] This comparative example provides an electrolyte, which differs from Example 5 only in that it does not contain Sr(TFSI)2.

[0057] Lithium-ion batteries were prepared using the electrolytes provided in the above examples and comparative examples, and their high-temperature storage performance was tested.

[0058] Preparation of lithium-ion batteries:

[0059] Positive electrode sheet: 9 series NCM ternary positive electrode material (LiNi 0.9 Co 0.05 Mn 0.05 O2) and conductive agent super P (conductive carbon black) and binder PVDF (polyvinylidene fluoride) are added to NMP (N-methylpyrrolidone) in a mass ratio of 96:2.5:1.5, and stirred evenly to form a positive electrode slurry. The positive electrode slurry is coated on an aluminum foil (thickness 12μm), and a positive electrode sheet (thickness 90μm) is obtained after drying, cutting and other steps;

[0060] Negative electrode sheet: Add negative electrode active material (95wt% graphite + 5wt% SiO), conductive agent super P (conductive carbon black), SBR (styrene-butadiene rubber) and CMC (carboxymethyl cellulose) to water in a mass ratio of 95:2:2:1, stir evenly to form negative electrode slurry, apply the negative electrode slurry on copper foil (thickness 6μm), and obtain negative electrode sheet (thickness 102μm) after drying and cutting.

[0061] A lithium-ion battery was assembled using the positive electrode sheet, negative electrode sheet, electrolyte provided in the embodiments and comparative examples, and a separator (Celgard 2325).

[0062] High temperature storage performance test:

[0063] The lithium-ion battery is charged to SOC (state of charge) = 100%, and discharged to the lower limit voltage (2.5V) at 0.33C at room temperature, and the discharge capacity is Q1; then the lithium-ion battery is charged to SOC = 100% and stored in an environment of 60°C for 90 days; then the lithium-ion battery is charged to SOC = 100%, and discharged to the lower limit voltage (2.5V) at 0.33C at room temperature, and the discharge capacity is recorded as Q2; then the storage capacity retention rate is Q2 / Q1, and the higher the storage capacity retention rate, the better the high temperature stability.

[0064] The results of the above tests are shown in Table 1 below.

[0065] Table 1

[0066]

[0067]

[0068] It should be noted that in the art, when the difference in the storage capacity retention rate reaches 1%, there is a significant difference.

[0069] By comparing the test results of Example 1 with Comparative Example 1, Examples 2-3 with Comparative Example 2, Example 4 with Comparative Example 3, and Example 5 with Comparative Example 4, it can be seen that since the electrolyte provided in the embodiment adds the additives described in the present invention, the negative electrode of the lithium ion battery can form an SEI layer rich in BaF2, CaF2 and / or SrF2, and the side reaction between the electrolyte and the silicon-based negative electrode active material is reduced. Therefore, the storage capacity retention rate of the lithium ion battery using the electrolyte provided in the embodiment is significantly higher, and the storage life is significantly improved.

[0070] Among them, by comparing the test results of Example 3, Example 7 and Example 8, it can be seen that Ba(TFSI)2 has a better effect of improving the storage life of lithium-ion batteries than Ca(TFSI)2 and Sr(TFSI)2. Compared with Example 3, Example 9 has a larger internal resistance and poorer kinetic performance of the lithium-ion battery due to the excessive addition of Ba(TFSI)2, which affects the capacity performance, so the storage capacity retention rate of the battery is reduced.

[0071] The above description is only a specific embodiment of the present disclosure, so that those skilled in the art can understand or implement the present disclosure. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure will not be limited to the embodiments described herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An electrolyte additive, characterized in that: The electrolyte additive includes one or more of Ba(TFSI)2, Ca(TFSI)2 and Sr(TFSI)2.

2. The electrolyte additive according to claim 1, characterized in that: The electrolyte additive is Ba(TFSI)2.

3. An electrolyte, characterized in that: The electrolyte comprises the electrolyte additive according to claim 1 or 2, a lithium salt and a solvent.

4. The electrolyte according to claim 3, characterized in that The content of the electrolyte additive in the electrolyte is 0.5-3 wt %.

5. The electrolyte according to claim 3 or 4, characterized in that The lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bis(oxalatoborate), lithium tetrafluoroborate and lithium bis(trifluoromethylsulfonylimide).

6. The electrolyte according to any one of claims 3 to 5, characterized in that: The concentration of the lithium salt in the electrolyte is 0.5-2 mol / L.

7. The electrolyte according to any one of claims 3 to 6, characterized in that: The solvent is selected from one or more of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate and fluoroethylene carbonate.

8. A lithium ion battery, characterized in that: The lithium-ion battery comprises the electrolyte according to any one of claims 3 to 7.

9. The lithium-ion battery according to claim 8, characterized in that: The negative electrode of the lithium-ion battery contains a silicon-based negative electrode active material.

10. An electrical device, characterized in that: Comprising a lithium ion battery as claimed in claim 8 or 9.

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