A lithium ion battery electrolyte and a lithium ion battery containing the same

Abstract

The present invention provides a lithium ion battery electrolyte and a lithium ion battery containing the same. The electrolyte includes a flame retardant additive, and the flame retardant additive includes bis (2,2,2-trifluoroethyl) methyl phosphate and vinyl-tris-(2-methoxyethoxy) silane. The present invention greatly improves the flame retardant effect of the electrolyte by using the flame retardant additive, solves the problem of thermal diffusion of soft-pack batteries, and does not affect the stability of electrochemical performance.

Description

Technical Field

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

[0002] This year, there have been many reports of fires and explosions caused by lithium-ion batteries, and the safety of lithium batteries has become an important focus in the field of lithium-ion batteries. Carbonate-based organic solvents are commonly used in lithium-ion batteries, but carbonate-based organic solvents have a low flash point and are prone to causing combustion of the electrolyte, resulting in fires and explosions. Therefore, adding flame retardants to carbonate-based electrolytes is an effective means of preventing thermal runaway.

[0003] CN108183259A discloses a flame retardant electrolyte for lithium ion batteries and a preparation method thereof, wherein the electrolyte includes adiponitrile, dimethylacetamide, lithium diacetate borate, sodium sulfite, propylene carbonate, trimethyl phosphite, lithium salt, film former, and flame retardant. Among them, the flame retardant is at least one of tris(2,2,2-trifluoroethyl)phosphite, di(2,2,2-trifluoroethyl)methyl phosphate, trichloroalkyl phosphate, trimethylphosphite, and triethoxyphosphite. However, the coordinated use of flame retardants has not been explored, which may easily lead to the flame retardant failing to achieve a good flame retardant effect.

[0004] CN106450442A discloses a flame retardant gel electrolyte for lithium ion batteries and a preparation method thereof, and a preparation method of lithium ion batteries, including a flame retardant gel electrolyte, and a flame retardant including trimethyl phosphate, triethyl phosphate, tributyl phosphate, triphenyl phosphate, tricresyl phosphate, tri-(2,2,2-trifluoroethyl) phosphate, di-(2,2,2-trifluoroethyl)-methyl phosphate, (2,2,2-trifluoroethyl) diethyl phosphate, tri-(2,2,2-trifluoroethyl) phosphite, hexamethylphosphoramide, or a mixture of two thereof. However, the use of flame retardants has not been further explored, and the best flame retardant effect cannot be achieved.

[0005] Therefore, how to prepare lithium-ion battery electrolyte with good flame retardant effect and excellent electrochemical performance is an important research direction in this field. Summary of the invention

[0006] In view of the shortcomings of the prior art, the object of the present invention is to provide a lithium ion battery electrolyte and a lithium ion battery containing the same.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] One of the purposes of the present invention is to provide a lithium ion battery electrolyte, the electrolyte comprising a flame retardant additive, the flame retardant additive comprising bis(2,2,2-trifluoroethyl)methyl phosphate and vinyl-tris-(2-methoxyethoxy)silane.

[0009] The present invention significantly improves the flame retardant effect of the electrolyte by adding flame retardants bis(2,2,2-trifluoroethyl)methyl phosphate and vinyl-tris-(2-methoxyethoxy)silane into the electrolyte, thereby solving the problem of thermal diffusion of the soft-pack battery core without affecting the stability of the electrochemical performance.

[0010] As a preferred technical solution of the present invention, the mass ratio of bis(2,2,2-trifluoroethyl)methyl phosphate and vinyl-tris-(2-methoxyethoxy)silane is (1.6-1.8):(0.7-0.9), wherein the mass ratio can be 1.6:0.7, 1.6:0.8, 1.6:0.9, 1.7:0.7, 1.7:0.8, 1.7:0.9, 1.8:0.7, 1.8:0.8 or 1.8:0.9, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0011] The mass ratio of the two flame retardant additives of the present invention is within a preferred range, which can maximize the flame retardant effect and improve the electrochemical performance of the battery containing the flame retardant additive.

[0012] As a preferred technical solution of the present invention, the mass fraction of the flame retardant additive in the electrolyte is 2.3-2.7%, calculated by mass fraction, wherein the mass fraction can be 2.3%, 2.4%, 2.5%, 2.6% or 2.7%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0013] As a preferred technical solution of the present invention, the electrolyte further includes lithium salt, organic solvent and additives.

[0014] Preferably, the lithium salt comprises any one of LiPO2F2, LiFSI, LiODFB, LiTFSI or LiODFP, or a combination of at least two thereof, wherein typical but non-limiting examples of the combination include: a combination of LiPO2F2 and LiFSI, a combination of LiFSI and LiODFB, a combination of LiODFB and LiTFSI, or a combination of LiTFSI and LiODFP, etc.

[0015] Preferably, the mass fraction of the lithium salt in the electrolyte is 50%, wherein the mass fraction can be 35%, 40%, 45%, 50%, 55%, 60%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0016] As a preferred technical solution of the present invention, the organic solvent includes a carbonate solvent.

[0017] As a preferred technical solution of the present invention, the carbonate solvent includes any one of vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate or diethyl carbonate, or a combination of at least two of them, wherein typical but non-limiting examples of the combination include: a combination of vinylene carbonate and dimethyl carbonate, a combination of dimethyl carbonate and ethyl methyl carbonate, a combination of ethyl methyl carbonate and propylene carbonate, or a combination of propylene carbonate and diethyl carbonate, etc.

[0018] Preferably, calculated by mass fraction, the organic solvent accounts for 30% of the mass fraction of the electrolyte, wherein the mass fraction can be 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34% or 35%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0019] As a preferred technical solution of the present invention, the additive includes any one of vinylene carbonate, vinyl ethylene carbonate, 1,3-propylene sultone or vinyl sulfate, or a combination of at least two of them, wherein typical but non-limiting examples of the combination include: a combination of vinylene carbonate and vinyl ethylene carbonate, a combination of vinyl ethylene carbonate and 1,3-propylene sultone, or a combination of 1,3-propylene sultone and vinyl sulfate, etc.

[0020] Preferably, calculated by mass fraction, the additive accounts for 15 to 25% of the electrolyte, wherein the mass fraction can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24% or 25%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0021] A second object of the present invention is to provide a lithium ion battery, the lithium ion battery comprising the lithium ion battery electrolyte as described in the first object;

[0022] The lithium-ion battery also includes a positive electrode and a negative electrode.

[0023] As a preferred technical solution of the present invention, the active material of the positive electrode includes any one of lithium iron phosphate, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide, or a combination of at least two of them, wherein typical but non-limiting examples of the combination include: a combination of lithium iron phosphate and lithium cobalt oxide, a combination of lithium cobalt oxide and lithium nickel oxide, a combination of lithium nickel oxide and lithium manganese oxide, a combination of lithium nickel manganese oxide and lithium nickel cobalt manganese oxide, or a combination of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide, etc.

[0024] As a preferred technical solution of the present invention, the active material of the negative electrode includes any one of soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxide compounds, silicon carbon compounds or lithium titanate, or a combination of at least two of them, wherein typical but non-limiting examples of the combination include: a combination of soft carbon and hard carbon, a combination of hard carbon and artificial graphite, a combination of natural graphite and silicon, a combination of silicon and silicon oxide compounds, or a combination of silicon carbon compounds and lithium titanate, etc.

[0025] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The electrolyte prepared by the present invention has a high capacity retention rate, which can reach a capacity retention rate of more than 97.60% at 1C for 300 cycles; the electrolyte prepared by the present invention has good thermal stability and chemical stability; the electrolyte prepared by the present invention has good compatibility. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further illustrated below through specific implementation methods.

[0029] Example 1

[0030] This embodiment provides a lithium ion battery electrolyte:

[0031] The electrolyte includes 50 wt % LiPO2F2, 30.5 wt % ethylene carbonate, 17 wt % vinylene carbonate, 1.7 wt % bis(2,2,2-trifluoroethyl)methyl phosphate and 0.8 wt % vinyl-tris-(2-methoxyethoxy)silane.

[0032] Example 2

[0033] This embodiment provides a lithium ion battery electrolyte:

[0034] The electrolyte includes 50 wt % LiFSI, 30.7 wt % dimethyl carbonate, 17 wt % vinyl ethylene carbonate, 1.6 wt % bis(2,2,2-trifluoroethyl)methyl phosphate, and 0.7 wt % vinyl-tris-(2-methoxyethoxy)silane.

[0035] Example 3

[0036] This embodiment provides a lithium ion battery electrolyte:

[0037] The electrolyte includes 50 wt % LiODFP, 30.3 wt % ethyl methyl carbonate, 17 wt % 1,3-propylene sultone, 1.8 wt % bis(2,2,2-trifluoroethyl)methyl phosphate, and 0.9 wt % vinyl-tris-(2-methoxyethoxy)silane.

[0038] Example 4

[0039] In this comparative example, except that 1.7wt% of bis(2,2,2-trifluoroethyl)methyl phosphate and 0.8wt% of vinyl-tris-(2-methoxyethoxy)silane are replaced by 2.3wt% of bis(2,2,2-trifluoroethyl)methyl phosphate and 0.2wt% of vinyl-tris-(2-methoxyethoxy)silane, other conditions are the same as those in Example 1.

[0040] Example 5

[0041] In this comparative example, except that 1.7wt% of bis(2,2,2-trifluoroethyl)methyl phosphate and 0.8wt% of vinyl-tris-(2-methoxyethoxy)silane are replaced by 2wt% of bis(2,2,2-trifluoroethyl)methyl phosphate and 0.5wt% of vinyl-tris-(2-methoxyethoxy)silane, other conditions are the same as those in Example 1.

[0042] Example 6

[0043] In this comparative example, except that 1.7wt% of bis(2,2,2-trifluoroethyl)methyl phosphate and 0.8wt% of vinyl-tris-(2-methoxyethoxy)silane are replaced by 1.5wt% of bis(2,2,2-trifluoroethyl)methyl phosphate and 1.0wt% of vinyl-tris-(2-methoxyethoxy)silane, other conditions are the same as those in Example 1.

[0044] Comparative Example 1

[0045] In this comparative example, except that 1.7wt% of bis(2,2,2-trifluoroethyl)methyl phosphate and 0.8wt% of vinyl-tris-(2-methoxyethoxy)silane were replaced by 2.5wt% of bis(2,2,2-trifluoroethyl)methyl phosphate, other conditions were the same as those in Example 1.

[0046] Comparative Example 2

[0047] In this comparative example, except that bis(2,2,2-trifluoroethyl)methyl phosphate and vinyl-tris-(2-methoxyethoxy)silane were not added, other conditions were the same as those in Example 1.

[0048] Comparative Example 3

[0049] In this comparative example, except that bis(2,2,2-trifluoroethyl)methyl phosphate was replaced by trimethylphosphite, other conditions were the same as those in Example 1.

[0050] Comparative Example 4

[0051] In this comparative example, except that vinyl-tris-(2-methoxyethoxy)silane was replaced by trimethylphosphite, other conditions were the same as those in Example 1.

[0052] Comparative Example 5

[0053] In this comparative example, except that 1.7 wt % of bis(2,2,2-trifluoroethyl)methyl phosphate and 0.8 wt % of vinyl-tris-(2-methoxyethoxy)silane are replaced by 1.7 wt % of hexamethylphosphoramide and 0.8 wt % of triphenyl phosphate, other conditions are the same as those in Example 1.

[0054] The electrolytes in Examples 1-6 of the present invention and Comparative Examples 1-5 were assembled into batteries, with ternary 613 single crystal material as the positive electrode and a graphite system as the negative electrode. The battery was tested for 300 cycles of capacity retention, ACR and DCR under 1C charge and discharge conditions, and the test results are shown in Table 1.

[0055] The method for flame retardancy evaluation is: using a cone calorimeter: low peak heat release rate and total heat release are optimal.

[0056] Table 1

[0057]

[0058] It can be seen from the above table that the mass ratio of the flame retardant additives in Examples 1-3 is within the preferred range of the present invention, and the thermal stability and chemical stability of the battery are good. The mass ratio of the two flame retardant additives in Examples 4-6 is not within the preferred mass ratio of the present invention of (1.6-1.8): (0.7-0.9). In Example 4, the mass ratio of bis(2,2,2-trifluoroethyl)methyl phosphate and vinyl-tri-(2-methoxyethoxy) silane is above 2.3:0.2, and the flame retardant effect of the battery is good. In Example 5, the amount of vinyl-tri-(2-methoxyethoxy) silane is increased, and the flame retardant effect of the battery becomes excellent, but the capacity retention rate of the battery is still worse than that of Example 1. Compared with Example 1, Example 6 also has the problem of low capacity retention rate of the battery, and the thermal stability and chemical properties of the battery are reduced compared with Example 1. Comparative Example 1 only adds bis(2,2,2-trifluoroethyl)methyl phosphate, and the flame retardant effect of the battery is good. Comparative Example 2 does not add flame retardant additives, and it can be observed that the flame retardant effect of the battery is general. Comparative Examples 3-5 replaced the flame retardant in the present invention, the capacity retention rate of the battery decreased, while the ACR and DCR increased, and the flame retardant effect also deteriorated. Therefore, the flame retardant in the present application is selected and used in combination within the preferred range to achieve excellent flame retardant effect and high capacity retention rate, low ACR and low DCR.

[0059] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A lithium ion battery electrolyte, characterized in that: The electrolyte comprises a flame retardant additive and an organic solvent, wherein the flame retardant additive comprises bis(2,2,2-trifluoroethyl)methyl phosphate and vinyl-tris-(2-methoxyethoxy)silane; The mass ratio of the bis(2,2,2-trifluoroethyl)methyl phosphate to vinyl-tris-(2-methoxyethoxy)silane is (1.6-1.8):(0.7-0.9); The mass fraction of the flame retardant additive in the electrolyte is 2.3-2.7%; The organic solvent includes a carbonate solvent.

2. The electrolyte according to claim 1, characterized in that The electrolyte also includes a lithium salt and an additive.

3. The electrolyte according to claim 2, characterized in that The lithium salt includes any one of LiPO2F2, LiFSI, LiODFB, LiTFSI or LiODFP, or a combination of at least two thereof.

4. The electrolyte according to claim 2, characterized in that The mass fraction of the lithium salt in the electrolyte is 50%.

5. The electrolyte according to claim 1, characterized in that The carbonate solvent includes any one of vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate or diethyl carbonate, or a combination of at least two thereof.

6. The electrolyte according to claim 1, characterized in that Calculated by mass fraction, the mass fraction of the organic solvent in the electrolyte is 25-35%.

7. The electrolyte according to claim 2, characterized in that The additive includes any one of vinylene carbonate, vinyl ethylene carbonate, 1,3-propylene sultone or vinyl sulfate, or a combination of at least two thereof.

8. The electrolyte according to claim 2, characterized in that In terms of mass fraction, the additive accounts for 15-25% of the mass fraction of the electrolyte.

9. A lithium ion battery, characterized in that: The lithium-ion battery comprises the lithium-ion battery electrolyte as claimed in any one of claims 1 to 8; the lithium-ion battery further comprises a positive electrode and a negative electrode.

10. The lithium ion battery according to claim 9, characterized in that: The active material of the positive electrode includes any one of lithium iron phosphate, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide, or a combination of at least two thereof.

11. The lithium ion battery according to claim 9, characterized in that: The active material of the negative electrode includes any one of soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxide, silicon carbon compound or lithium titanate, or a combination of at least two thereof.

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