Non-aqueous electrolyte and lithium-ion battery

Abstract

The present invention provides a non-aqueous electrolyte and a lithium-ion battery. The non-aqueous electrolyte includes a non-aqueous organic solvent, an electrolyte salt, and an additive, and the additive includes Compound A. The structural formula of Compound A is as shown in Structural Formula I, Structural Formula II, or Structural Formula III. In the non-aqueous electrolyte of the present invention, Compound A contains a connected cyclic sulfonimide and cyclic imide structure, and can form a stable interfacial film at the interface. First, this film has good lithium-ion transport channels and will not cause channel collapse during cycling, so the cycling and low-temperature performance are improved. Second, by forming a stable interfacial film, the positive electrode / electrolyte interface can be optimized, the surface activity of the positive electrode can be reduced, and the oxidative decomposition of the electrolyte can be inhibited, thereby improving the high and low temperature and cycling performance of the battery, especially for improving the high and low temperature and cycling performance of high-voltage (4.4 V) high-nickel ternary lithium-ion batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a non-aqueous electrolyte and a lithium-ion battery. Background Art

[0002] With the continuous increase in the requirements for the capacity of secondary batteries in pure electric vehicles, hybrid electric vehicles, portable energy storage devices, etc., it is expected to develop secondary batteries with higher energy density and power density to achieve energy storage and long-term endurance.

[0003] In addition to the improvement of existing materials and battery manufacturing processes, high-voltage (4.35 - 5V) ternary cathode materials are one of the popular research directions, which achieve high energy density of the battery by increasing the charging depth of the cathode active material. Among them, high-nickel ternary cathode materials (nickel content not less than 0.6) are relatively commonly used cathode materials due to their high capacity. However, high-nickel ternary materials are prone to irreversible phase transformation from H2 to H3 at high voltage and high temperature, resulting in the precipitation of oxygen, so the electrolyte and electrode interface are unstable, and the battery faces problems such as poor high-temperature storage and serious gas generation during cycling. At the same time, conventional carbonate electrolytes will oxidize and decompose on the surface of the battery cathode material at a high voltage of 4.4V, especially at high temperature, which will accelerate the oxidation and decomposition of the electrolyte, leading to deterioration of the cathode material.

[0004] Therefore, it is necessary to develop an electrolyte that can withstand a high voltage of 4.4V, so as to realize the excellent performance of lithium-ion batteries. Summary of the Invention

[0005] In view of the above problems, the purpose of the present invention is to provide a non-aqueous electrolyte and a lithium-ion battery. The additive in the non-aqueous electrolyte contains compound A, which can reduce the surface activity of the cathode material and thus inhibit the oxidation and decomposition of the electrolyte, so as to improve the high-temperature storage and cycling performance of high-voltage (4.4V) lithium-ion batteries (especially high-nickel ternary material systems).

[0006] To achieve the above purpose, the first aspect of the present invention provides a non-aqueous electrolyte, including a non-aqueous organic solvent, an electrolyte salt, and an additive, and the additive includes compound A. The structural formula of compound A is shown as structural formula I, structural formula II, or structural formula III.

[0007]

[0008] Wherein, R1 to R3 are each independently selected from hydrogen, halogen, substituted or unsubstituted C1 - C10 hydrocarbon groups, substituted or unsubstituted phosphonate groups, and R4 to R5 are each independently selected from hydrogen, substituted or unsubstituted C1 - C6 alkyl groups.

[0009] In the non-aqueous electrolyte of the present invention, compound A contains a connected cyclic sulfonimide and cyclic imide structure, which can form a stable interfacial film at the interface. First, this film has good lithium-ion transport channels and will not cause channel collapse during cycling, so the cycling and low-temperature performance are improved. Second, by forming a stable interfacial film, the positive electrode / electrolyte interface can be optimized, the surface activity of the positive electrode can be reduced, and the oxidation decomposition of the electrolyte can be inhibited, thereby improving the high and low temperature and cycling performance of the battery, especially for improving the high and low temperature and cycling performance of high-voltage (4.4V) high-nickel ternary lithium-ion batteries.

[0010] As a technical solution of the present invention, R1 to R3 are each independently selected from hydrogen, substituted or unsubstituted C1-C5 alkyl, substituted or unsubstituted C3-C6 cycloalkyl, substituted or unsubstituted phenyl, substituted or unsubstituted phosphonate group, and R4 to R5 are each independently selected from hydrogen, substituted or unsubstituted C1-C3 alkyl. Preferably, at least one of R1 to R3 is a phosphonate group. Introducing a phosphonate group can improve the stability of the SEI film. Elements such as P and O enrich the components of the electrode / electrolyte interfacial film, further improving the structural stability of the interfacial film, thereby improving the high-temperature storage performance of the lithium-ion battery.

[0011] Among them, P on the phosphonate group is connected to 3 O's, and its structural formula is as follows. R6 and R7 can be hydrogen or substituted or unsubstituted C1-C10 hydrocarbon groups.

[0012]

[0013] As a technical solution of the present invention, compound A is at least one of compound I to compound VI.

[0014]

[0015] As a technical solution of the present invention, compound A accounts for 0.1-5.0% of the total mass of the non-aqueous organic solvent, electrolyte salt, and additive. Preferably, compound A accounts for 0.1-2.0% of the total mass of the non-aqueous organic solvent, electrolyte salt, and additive. As an example, the proportion of compound A in the total mass of the non-aqueous organic solvent, electrolyte salt, and additive can be, but is not limited to, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%.

[0016] As a technical solution of the present invention, the electrolyte salt accounts for 6-15% of the sum of the masses of the non-aqueous organic solvent, the electrolyte salt, and the additive. Preferably, the proportion of the electrolyte salt is 8-15%. As an example, the proportion of the electrolyte salt can be but is not limited to 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%. The electrolyte salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethylsulfonyl)imide (LiN(CF3SO2)2), lithium bis(oxalato)borate (C4BLiO8), lithium difluoro(oxalato)borate (C2BF2LiO4), lithium difluorophosphate (LiPO2F2), lithium difluoro(bis(oxalato))phosphate (LiDFBP), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0017] As a technical solution of the present invention, the non-aqueous organic solvent is at least one of a chain carbonate, a cyclic carbonate, and a carboxylic acid ester. Preferably, the non-aqueous organic solvent is a mixture of a chain carbonate and a cyclic carbonate. As an example, the non-aqueous organic solvent is selected from at least one of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), n-butyl acetate (n-Ba), γ-butyrolactone (γ-Bt), n-propyl propionate (n-Pp), ethyl propionate (EP), and ethyl butyrate (Eb). The non-aqueous organic solvent accounts for ≥80% of the sum of the masses of the non-aqueous organic solvent, the electrolyte salt, and the additive, preferably ≥85%. As an example, the non-aqueous organic solvent accounts for the sum of the masses of the non-aqueous organic solvent, the electrolyte salt, and the additive can be but is not limited to ≥80%, ≥81%, ≥82%, ≥83%, ≥84%, ≥85%, ≥86%, ≥87%, ≥88%, ≥89%, ≥90%.

[0018] As a technical solution of the present invention, the additive further includes Compound B. Compound B is selected from at least one of vinylene carbonate (VC), ethylene vinylene carbonate (VEC), fluoroethylene carbonate (FEC), ethylene sulfite (ES), 1,3 - propanesultone (PS), tris(trimethylsilyl) phosphate (TMSP), and divinyl sulfate (DTD). Compound B accounts for 0.1 - 10.0% of the sum of the masses of the non - aqueous organic solvent, electrolyte salt, and additive. Preferably, Compound B accounts for 0.1 - 6.0% of the sum of the masses of the non - aqueous organic solvent, electrolyte salt, and additive. As an example, the proportion of Compound B in the sum of the masses of the non - aqueous organic solvent, electrolyte salt, and additive can be but is not limited to 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 6.0%, 7.0%, 8.0%, 9.0%, 10.0%.

[0019] The second aspect of the present invention provides a lithium - ion battery, comprising a positive electrode material, a negative electrode material, and a non - aqueous electrolyte. This lithium - ion battery has better cycle life and high - temperature storage performance, which is conducive to the further industrial development of lithium - ion batteries.

[0020] As a technical solution of the present invention, the positive electrode material is a nickel - cobalt - manganese oxide material. The chemical formula of the nickel - cobalt - manganese oxide material is LiNi x Co y Mn (1-x-y) M z O2, where 0.6 ≤ x ≤ 0.9, x + y < 1, 0 ≤ z < 0.08, and M is one of Al, Mg, Zr, and Ti. Preferably, x = 0.6, y = 0.2, M is Zr, z = 0.03, or x = 0.8, y = 0.1, M is Zr, z = 0.02.

[0021] As a technical solution of the present invention, the negative electrode material is selected from at least one of carbon - based negative electrode materials, titanium - based oxide negative electrode materials, and silicon - based negative electrode materials.

[0022] As a technical solution of the present invention, the negative electrode material can be selected from artificial graphite, natural graphite, hard carbon, soft carbon, lithium titanate, Si material, silicon - oxygen material, or silicon - carbon material (10 wt.% Si). Detailed Embodiments

[0023] To better illustrate the purpose, technical solution, and beneficial effects of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be noted that the methods described in the following embodiments are further explanatory descriptions of the present invention and should not be construed as limitations on the present invention.

[0024] Among them, for those without specific conditions noted in the examples, they can be carried out according to conventional conditions or the conditions recommended by the manufacturer. For the reagents or instruments without the production manufacturer noted, they are all conventional products that can be obtained through commercial channels.

[0025] Example 1

[0026] (1) Preparation of non-aqueous electrolyte: In an argon atmosphere, the electrolyte was prepared in a vacuum glove box with a water content < 1 ppm. In a dry argon atmosphere glove box, ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed according to a weight ratio of EC:DEC:EMC = 1:1:1. Then, Compound I was added, dissolved and stirred thoroughly, and then lithium hexafluorophosphate was added. After mixing evenly, the electrolyte was obtained.

[0027] (2) Preparation of the positive electrode: LiNi 0.6 Co 0.2 Mn 0.2 Zr 0.03 O2, binder PVDF, and conductive agent SuperP were mixed evenly according to a mass ratio of 97:1:2 to form a lithium-ion battery positive electrode slurry with a certain viscosity. After the mixed slurry was coated on both sides of the aluminum foil, it was dried and roll-pressed to obtain the positive electrode sheet.

[0028] (3) Preparation of the negative electrode: A slurry was prepared from a silicon-carbon negative electrode material (10 wt.% Si), conductive agent SuperP, thickener CMC, and binder SBR (styrene-butadiene rubber latex) according to a mass ratio of 96:1:1:2, mixed evenly, and the mixed slurry was coated on both sides of the copper foil. After drying and roll-pressing, the negative electrode sheet was obtained.

[0029] (4) Preparation of the lithium-ion battery: The positive electrode sheet, separator, and negative electrode sheet were made into a square battery cell in a stacked manner, packaged with a polymer, and filled with the non-aqueous electrolyte of the lithium-ion battery prepared above. After processes such as formation and grading, a lithium-ion battery with a capacity of 1400 mAh was made.

[0030] Among them, the electrolyte formulations of Examples 1 to 16 and Comparative Examples 1 to 7 are shown in Table 1. The steps for preparing the electrolyte and the battery in Examples 2 to 16 and Comparative Examples 1 to 7 are the same as those in Example 1.

[0031] Table 1 Electrolyte components of each example and comparative example

[0032]

[0033]

[0034]

[0035] The lithium-ion batteries prepared in Examples 1 to 16 and Comparative Examples 1 to 7 were respectively subjected to normal temperature cycle test, high temperature cycle test, high temperature storage test and low temperature discharge test. The specific test conditions are as follows, and the test results are shown in Table 2.

[0036] (1) Normal temperature cycle test

[0037] Under normal temperature (25°C) conditions, the lithium-ion battery was charged and discharged at 1.0C / 1.0C once (the battery discharge capacity is C0), the upper limit voltage was 4.4V, and then charged and discharged at 1.0C / 1.0C for 500 cycles under normal temperature conditions (the battery discharge capacity is C1).

[0038] Capacity retention rate = (C1 / C0) * 100%.

[0039] (2) High temperature cycle test of lithium-ion battery

[0040] Under high temperature (45°C) conditions, the lithium-ion battery was charged and discharged at 1.0C / 1.0C once (the battery discharge capacity is C0), the upper limit voltage was 4.4V, and then charged and discharged at 1.0C / 1.0C for 500 cycles under normal temperature conditions (the battery discharge capacity is C1).

[0041] Capacity retention rate = (C1 / C0) * 100%

[0042] (3) High temperature storage test

[0043] Under normal temperature (25°C) conditions, the lithium-ion battery was charged and discharged at 0.3C / 0.3C once (the battery discharge capacity is recorded as C0), the upper limit voltage was 4.4V. The battery was placed in an oven at 60°C for 15 days, taken out, placed in an environment at 25°C, and discharged at 0.3C. The discharge capacity was recorded as C1. Then the lithium-ion battery was charged and discharged at 0.3C / 0.3C once (the battery discharge capacity is recorded as C2).

[0044] Capacity retention rate = (C1 / C0) * 100%

[0045] Capacity recovery rate = (C2 / C0) * 100%

[0046] Low temperature discharge test

[0047] Under normal temperature (25°C) conditions, the lithium-ion battery was charged and discharged at 0.3C / 0.3C once (the battery discharge capacity is recorded as C0), the upper limit voltage was 4.4V. The battery was placed in an oven at -20°C for 4 hours, and then discharged at 0.3C. The discharge capacity was recorded as C1, and the cut-off voltage was 3.0V.

[0048] Discharge rate = (C1 / C0)*100%

[0049] Table 2 Lithium-ion battery performance test results

[0050]

[0051]

[0052] From the results in Table 2, it can be seen that the use of compound A of the present invention as an additive can greatly improve the cycle performance, high temperature storage and low temperature discharge performance of the battery. This is because compound A contains connected cyclic sulfoximine and cyclic imide structures, which can form a stable interface film with good lithium ion transmission channels at the interface.

[0053] Comparative Examples 1 to 6 show that when the content of compound A accounts for 0.1 to 2.0% of the sum of the mass of the non-aqueous organic solvent, the electrolyte salt and the additive, the cycle performance, high temperature storage and low temperature discharge performance of the lithium ion battery are better.

[0054] By comparing Examples 3 and 7 to 10, it can be seen that the battery obtained by introducing a phosphonate group into compound A has better high-temperature storage performance.

[0055] By comparing Example 3, Examples 12 to 16, and Comparative Examples 2 to 6, it can be seen that when compound B is introduced on the basis of compound A, especially when compound B contains VC and FEC at the same time, the performance of the lithium ion battery is the best. This may be due to the synergistic effect of VC, FEC and compound A: VC may form a polymerized organic layer, FEC forms an inorganic interface layer and a polymerized double-layer interface, and compound A forms an inorganic interface layer rich in S and N, which makes up for the inorganic SEI holes formed by FEC. The three work synergistically to form a complete and tough inorganic and organic double interface, thereby improving the electrochemical performance of the battery.

[0056] It can be seen from Examples 3, 7 to 10 and Comparative Example 7 that although the structure of Compound VI in Comparative Example 7 is similar to that of Compound A described in the present application, it is a cyclic sulfonic acid amide. Compared with the cyclic sulfoximine in the present application, since its sulfur-oxygen bond energy is greater than the sulfur-nitrogen bond energy, the structure shown in the present invention is more easily consumed to form an electrode electrolyte interface protective layer. In addition, the oxygen element in Compound VI in Comparative Example 7 is more active and is more likely to participate in the gas production at the battery interface, which has a negative impact on battery performance.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, it is not limited to the embodiments listed. Those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A non-aqueous electrolyte, comprising a non-aqueous organic solvent, an electrolyte salt, and an additive, characterized in that, The additive includes compound A, and the structural formula of the compound A is as shown in Structural Formula I, Structural Formula II or Structural Formula III. Among them, R1 to R3 are each independently selected from hydrogen, halogen, substituted or unsubstituted C1-C10 hydrocarbon groups, substituted or unsubstituted phosphonate groups, and R4 to R5 are each independently selected from hydrogen, substituted or unsubstituted C1-C6 alkyl groups.

2. The non-aqueous electrolyte according to claim 1, wherein R1 to R3 are each independently selected from hydrogen, substituted or unsubstituted C1-C5 alkyl groups, substituted or unsubstituted C3-C6 cycloalkyl groups, substituted or unsubstituted phenyl groups, substituted or unsubstituted phosphonate groups, and R4 to R5 are each independently selected from hydrogen, substituted or unsubstituted C1-C3 alkyl groups.

3. The non-aqueous electrolyte according to claim 1, wherein The compound A is at least one of Compound I to Compound V.

4. The non-aqueous electrolyte according to claim 1, wherein The compound A accounts for 0.1-5.0% of the sum of the masses of the non-aqueous organic solvent, the electrolyte salt and the additive.

5. The non-aqueous electrolyte according to claim 4, characterized in that, The compound A accounts for 0.1-2.0% of the sum of the masses of the non-aqueous organic solvent, the electrolyte salt and the additive.

6. The non-aqueous electrolyte according to claim 1, characterized in that, The electrolyte salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium difluorophosphate, lithium difluorobis(oxalato)phosphate, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

7. The non-aqueous electrolyte according to claim 1, characterized in that, The non-aqueous organic solvent is selected from at least one of linear carbonates, cyclic carbonates and carboxylic acid esters.

8. The non-aqueous electrolyte according to claim 1, wherein, The additive further includes compound B, and the compound B is selected from at least one of vinylene carbonate, ethylene ethylenecarbonate, fluorinated vinylene carbonate, ethylene sulfite, 1,3-propane sultone, tris(trimethylsilyl) phosphate and ethylene sulfate.

9. A lithium ion battery, comprising a positive electrode material, a negative electrode material and a non-aqueous electrolyte according to any one of claims 1-8.

10. The lithium-ion battery according to claim 9, characterized in that, The positive electrode material is a nickel cobalt manganese oxide material, and the chemical formula of the nickel cobalt manganese oxide material is LiNi x Co y Mn (1-x-y) M z O2, 0.6 ≤ x ≤ 0.9, x + y < 1, 0 ≤ z < 0.08, and M is one of Al, Mg, Zr, and Ti.

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