Electrolyte and energy storage lithium ion battery

Abstract

The invention provides an electrolyte and an energy storage lithium ion battery, and belongs to the technical field of energy storage lithium ion batteries. The electrolyte comprises a non-aqueous solvent, a lithium salt, a first functional additive, a second functional additive and an auxiliary additive, wherein the chemical formula of the first functional additive is as shown in formula I; r1 is independently selected from one of hydrogen, C1-C6 alkyl, substituted carbonyl and substituted alkenyl; the chemical formula of the second functional additive is shown as a formula II; r1 and R2 are respectively and independently selected from one of C1-C5 alkyl groups and C2-C5 alkenyl groups; r1, R2, R3 are independently selected from one of C1-C5 alkyl groups, C2-C5 alkenyl groups and C2-C5 alkynyl groups; r1, R2, R3, R4 are independently selected from one of C1-C5 alkyl groups and C2-C5 alkenyl groups. Through the electrolyte additive combination, the chemical properties of the electrolyte and an electrode interface can be improved, and the problem of thermal runaway caused by overcharge of the high-nickel battery is effectively improved.

Description

TECHNICAL FIELD

[0001] The present disclosure belongs to the technical field of energy storage lithium ion batteries, and particularly relates to an electrolyte for improving overcharge and an energy storage lithium ion battery. BACKGROUND

[0002] Ternary lithium batteries have become the mainstream system of power batteries due to their high energy density, but the overcharge safety problem is still a key bottleneck restricting development. Under normal charging conditions, lithium ions are released from the positive electrode and then embedded into the negative electrode, which reduces the negative electrode potential and increases the positive electrode potential. When the potential difference between the positive electrode and the negative electrode reaches the highest voltage designed for lithium ion batteries, the charging is stopped, and at this time the battery is in a full charge state. However, when abnormal charging occurs, the lithium ion power battery may continue to charge after reaching the full charge state, resulting in overcharge. After overcharge occurs, the positive electrode material will collapse due to excessive delithiation, and the decomposition of the electrolyte and the oxidation of the separator will be intensified, resulting in a significant increase in the risk of thermal runaway. The lithium ion battery triggers thermal runaway, causing safety problems of the lithium battery. Although external circuit protection can partially alleviate this problem, the capacity difference of single batteries may still cause local overcharge, and external protection increases the complexity and cost of the system. Therefore, it is particularly important to develop an internal electrochemical protection mechanism, and electrolyte additives directly act on the reaction interface and become the focus of research. Developing additives with high oxidation potential, fast response and no effect on battery cycle is one of the core directions to improve the intrinsic safety of ternary batteries. SUMMARY

[0003] The present disclosure aims to at least solve one of the technical problems existing in the prior art, and provides an electrolyte and an energy storage lithium ion battery.

[0004] In one aspect of the present disclosure, an electrolyte is provided, comprising: a non-aqueous solvent, a lithium salt, a first functional additive, a second functional additive and an auxiliary additive; wherein, The chemical formula of the first functional additive is shown as formula I: Formula I; wherein R1 is independently selected from one of hydrogen, C1-C6 alkyl, substituted carbonyl and substituted alkenyl; The chemical formula of the second functional additive is shown as formula II: Formula II; wherein R2 is independently selected from one of C1-C5 alkyl and C2-C5 alkenyl; R3 is independently selected from one of C1-C5 alkyl, C2-C5 alkenyl and C2-C5 alkynyl; R4 is independently selected from one of C1-C5 alkyl and C2-C5 alkenyl. Optionally, R1 is selected from one of hydrogen, C1-C3 alkyl, carbonyl substituted with trimethylsilyl, and alkenyl substituted with trimethylsilyl.

[0005] Optionally, the first functional additive is selected from at least one of the following compounds: Formula I-1; Formula I-2; Formula I-3; Formula I-4; Formula I-5; Formula I-6.

[0006] Optionally, the second functional additive is selected from at least one of the following compounds: Formula II-1; Formula II-2; Formula II-3; Formula II-4; Formula II-5.

[0007] Optionally, the mass ratio of the first functional additive and the second functional additive is (0.5-1):(0.3-1). The content of the first functional additive can be preferably 0.5-1%, and the content of the second functional additive can be preferably 0.3-1%.

[0008] Optionally, the non-aqueous solvent includes a cyclic carbonate and a chain carbonate.

[0009] Optionally, the lithium salt is one or both of lithium hexafluorophosphate and lithium bisfluorosulfonylimide. The mass fraction of the lithium salt in the total mass of the electrolyte is 12%-15%.

[0010] Optionally, the auxiliary additive includes a sulfur-containing additive and a lithium salt additive; wherein, The mass fraction of the sulfur-containing additive in the total mass of the electrolyte is 0.5%-1.0%. The mass fraction of the lithium salt additive in the total mass of the electrolyte is 0.5%-1.0%.

[0011] Optionally, the sulfur-containing additive includes at least one of 1,3-propylene sulfite and ethylene sulfate. The lithium salt additive includes at least one of lithium difluorophosphate, lithium bisoxalate borate, and lithium tetrafluoroborate.

[0012] Another aspect of the present disclosure provides a lithium-ion battery for energy storage, which comprises a positive electrode sheet, a negative electrode sheet, a separator, and the electrolyte as described above.

[0013] The present disclosure provides an electrolyte and a lithium-ion battery for energy storage, wherein the electrolyte comprises a non-aqueous solvent, a lithium salt, a first functional additive, a second functional additive, and an auxiliary additive; wherein the first functional additive has the following formula I: Formula I; wherein in formula I, each R1 is independently selected from one of hydrogen, C1-C6 alkyl, substituted carbonyl, and substituted alkenyl; and the second functional additive has the following formula II: Formula II; wherein in formula II, each R2 is independently selected from one of C1-C5 alkyl and C2-C5 alkenyl; each R3 is independently selected from one of C1-C5 alkyl, C2-C5 alkenyl, and C2-C5 alkynyl; and each R4 is independently selected from one of C1-C5 alkyl and C2-C5 alkenyl. The present disclosure can improve the chemical properties of the electrolyte and the electrode interface by using the electrolyte additive combination, effectively improve the thermal runaway problem caused by overcharging of high-nickel batteries, and improve the safety performance of the battery. The additive combination has a broad application prospect. DETAILED DESCRIPTION

[0014] To enable those skilled in the art to better understand the technical solutions of the present disclosure, the present disclosure will be further described in detail below in combination with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present disclosure and are part of the embodiments of the present disclosure, but not all the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present disclosure.

[0015] In one aspect of the present disclosure, an electrolyte capable of improving overcharging is provided, which comprises a non-aqueous solvent, a lithium salt, a first functional additive, a second functional additive, and an auxiliary additive; wherein the first functional additive has the following formula I: Formula I; wherein in formula I, each R1 is independently selected from one of hydrogen, C1-C6 alkyl, substituted carbonyl, and substituted alkenyl; and the second functional additive has the following formula II: Formula II; wherein, in Formula II, each R2 is independently selected from one of C1-C5 alkyl, C2-C5 alkenyl; each R3 is independently selected from one of C1-C5 alkyl, C2-C5 alkenyl, C2-C5 alkynyl; each R4 is independently selected from one of C1-C5 alkyl, C2-C5 alkenyl. In the present embodiment, the first functional additive contains cyano group (-C≡N-) which electrochemically polymerizes at overcharge high voltage, forms a conductive polymer layer on the positive electrode surface, blocks the current, and the trimethylsilyl group provides steric hindrance effect, delays the side reaction of cyano group at normal working voltage, avoids the premature increase of battery internal resistance, thereby reducing the temperature rise during overcharge. The second functional additive contains unsaturated bond which undergoes free radical polymerization at higher voltage, forms an interpenetrating network structure with the polymer layer in the first functional additive, enhances the strength and ion conductivity of the film, in addition, the vinyl or alkynyl group polymerization consumes free radicals, reduces the generation of H2 / CO gas, and the phosphate group (P=O) preferentially adsorbs on the positive electrode surface, reduces the interface impedance, and provides active sites for polymerization. That is, the combination of electrolyte additives can improve the chemical properties of the electrolyte and electrode interface, effectively improve the thermal runaway problem of high-nickel batteries during overcharge, and improve the safety performance of the battery. The additive combination has broad application prospects.

[0016] In some preferred embodiments, R1 in the first functional additive is selected from one of hydrogen, C1-C3 alkyl, carbonyl substituted with trimethylsilyl, and alkenyl substituted with trimethylsilyl.

[0017] As a further preferred aspect, the first functional additive is selected from at least one of the following compounds: Formula I-1 (CAS: 725270-27-9); Formula I-2 (CAS: 107325-81-5); Formula I-3 (CAS: 866364-30-9); Formula I-4 (CAS: 100-47-0); Formula I-5 (p-methyl benzonitrile); Formula I-6 (p-ethyl benzonitrile).

[0018] In other preferred embodiments, the second functional additive is selected from at least one of the following compounds: Formula II-1 (CAS: 113419-25-3); Formula II-2 (CAS: 2401881-57-8); Formula II-3 (CAS: 2401882-41-3); Formula II-4 (CAS: 18192-98-8); Formula II-5 (CAS: 85197-28-0).

[0019] In some preferred embodiments, the mass ratio of the first functional additive to the second functional additive is (0.5-1):(0.3-1). That is, the mass fraction of the first functional additive in the total mass of the electrolyte is 0.5-1%, and the mass fraction of the second functional additive in the total mass of the electrolyte is 0.3-1%.

[0020] In some preferred embodiments, the lithium salt is one or both of lithium hexafluorophosphate (LiPF6) and lithium bisfluorosulfonylimide (LiFSi). In addition, the mass fraction of the lithium salt in the total mass of the electrolyte is 12%-15%.

[0021] In some preferred embodiments, the auxiliary additive includes a sulfur-containing additive and a lithium salt additive.

[0022] As a further preferred aspect, the sulfur-containing additive includes at least one of 1,3-propanesultone (PST) and vinyl sulfates (DTD). In addition, the mass fraction of the sulfur-containing additive in the total mass of the electrolyte is 0.5%-1.0%.

[0023] As a further preferred aspect, the lithium salt additive includes at least one of lithium difluorophosphate (LiPO2F2), lithium bis(oxalato)borate, and lithium tetrafluoroborate (LiBF4). In addition, the mass fraction of the lithium salt additive in the total mass of the electrolyte is 0.5%-1.0%.

[0024] In some preferred embodiments, the non-aqueous solvent is included in a remainder amount other than the first functional additive, the second functional additive, the lithium salt, and the auxiliary additive. That is, in the electrolyte, the total content of the non-aqueous solvent, the lithium salt, and the first functional additive, the second functional additive, and the auxiliary additive is 100%, and the non-aqueous solvent includes a cyclic carbonate and a chain carbonate.

[0025] As a further preferred solution, the cyclic carbonates include ethylene carbonate, propylene carbonate and fluoroethylene carbonate, the chain carbonates include dimethyl carbonate, methyl ethyl carbonate; it is noted that, for the non-aqueous solvent component, in the total mass of which is 100%, the cyclic carbonate component (ethylene carbonate, propylene carbonate and fluoroethylene carbonate) accounts for 20% to 25% in the total mass of the non-aqueous solvent, the dimethyl carbonate in the chain carbonate accounts for 55% to 65% in the total mass of the non-aqueous solvent, and the methyl ethyl carbonate in the chain carbonate accounts for 15% to 25% in the total mass of the non-aqueous solvent.

[0026] Further, the electrolyte of the embodiment is prepared by the following method: Under an argon atmosphere, the first functional additive and the second functional additive, the lithium salt, the sulfur-containing additive, and the lithium salt additive are added to the non-aqueous solvent, and stirred and mixed at a temperature of 8-12℃ for 2-4h to obtain the electrolyte.

[0027] In another aspect of the present disclosure, a kind of energy storage lithium ion battery is provided, which comprises a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte described above.The specific components of the electrolyte are described above and will not be repeated here.

[0028] The electrolyte additive combination described above is added to the electrolyte in the present disclosure, and the prepared electrolyte exhibits excellent performance when the battery is overcharged, improving the safety performance of the battery.The additive combination in the electrolyte can form a stable polymer layer to block the current during overcharging.These advantages make the electrolyte of the present application have a wide application prospect in the field of energy storage lithium ion batteries.

[0029] The electrolyte capable of improving overcharge and its additives will be further described below in conjunction with specific examples: Example 1 The present embodiment provides an electrolyte additive composition and electrolyte, which are as follows: According to the mass percentage of the components, the electrolyte formula used in the present embodiment is as follows: the first functional additive (such as formula I-1 ): 0.5%, the second functional additive (such as formula II-1 ): 0.3%, LiPO2F2: 0.5%, PST: 0.5%, LiPF6: 12.5%, the balance being non-aqueous solvent components, i.e., the content of non-aqueous solvents is 85.7%. Among them, the non-aqueous solvent components in the above electrolyte formula are composed of fluoroethylene carbonate, ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate, wherein the proportion of ethylene carbonate in the total mass of non-aqueous solvents is 15%, the proportion of propylene carbonate in the total mass of non-aqueous solvents is 5%, the proportion of fluoroethylene carbonate in the total mass of non-aqueous solvents is 3%, the proportion of dimethyl carbonate in the total mass of non-aqueous solvents is 55%, and the proportion of methyl ethyl carbonate in the total mass of non-aqueous solvents is 22%.

[0030] The above electrolyte is prepared by the following method: under an argon atmosphere, adding compounds represented by formula I-1, formula II-1, lithium difluorophosphate, 1,3-propylene sulfone, lithium hexafluorophosphate to the non-aqueous solvent formed by mixing methyl ethyl carbonate, ethylene carbonate, and dimethyl carbonate, propylene carbonate, and fluoroethylene carbonate, stirring and mixing at a temperature of 10°C for 3h to obtain the electrolyte.

[0031] Example 2 This example provides an electrolyte additive composition and an electrolyte, which are specifically as follows: The first functional additive is a compound represented by formula I-2 ( ), and the second functional additive is an additive represented by formula II-1 ( ), and the addition amount is 0.5%, and the others are the same as in Example 1.

[0032] Example 3 This example provides an electrolyte additive composition and an electrolyte, which are specifically as follows: The first functional additive is a compound represented by formula I-3 ( ), and the addition amount is 0.5%, and the second functional additive is an additive represented by formula II-1 ( ), and the addition amount is 0.5%, and the others are the same as in Example 1.

[0033] Example 4 This example provides an electrolyte additive composition and an electrolyte, taking the addition amount of the first functional additive as a variable, and the addition amount is 0.7%, and the others are the same as in Example 1.

[0034] Example 5 This example provides an electrolyte additive composition and an electrolyte, taking the addition amount of the first functional additive as a variable, and the addition amount is 1%, and the others are the same as in Example 1.

[0035] Example 6 This example provides an electrolyte additive composition and an electrolyte, which are specifically as follows: The first functional additive is a compound represented by Formula I-1 ), and the second functional additive is an additive represented by Formula II-2 ), and the other conditions are the same as in Example 1.

[0036] Example 7 This example provides an electrolyte additive composition and an electrolyte, which are as follows: The first functional additive is a compound represented by Formula I-2 ), and the second functional additive is an additive represented by Formula II-2 ), and the other conditions are the same as in Example 1.

[0037] Example 8 This example provides an electrolyte additive composition and an electrolyte, which are as follows: The first functional additive is a compound represented by Formula I-3 ), and the second functional additive is an additive represented by Formula II-2 ), and the other conditions are the same as in Example 1.

[0038] Example 9 This example provides an electrolyte additive composition and an electrolyte, which are as follows: The first functional additive is a compound represented by Formula I-1 ), and the second functional additive is an additive represented by Formula II-3 ), and the other conditions are the same as in Example 1.

[0039] Example 10 This example provides an electrolyte additive composition and an electrolyte, which are as follows: The first functional additive is a compound represented by Formula I-2 ), and the second functional additive is an additive represented by Formula II-3 ), and the other conditions are the same as in Example 1.

[0040] Example 11 This example provides an electrolyte additive composition and an electrolyte, which are as follows: The first functional additive is a compound represented by Formula I-3 ), and the second functional additive is an additive represented by Formula II-3 ), and the other conditions are the same as in Example 1.

[0041] Example 12 This example provides an electrolyte additive composition and electrolyte, as follows: With reference to the electrolyte formulation employed in Example 6, and with the amount of sulfur-containing additive included in the formulation as the variable, the difference from Example 1 is that the amount of PST is adjusted to 0.7%, and the other conditions are the same as in Example 6.

[0042] Example 13 This example provides an electrolyte additive composition and electrolyte, as follows: With reference to the electrolyte formulation employed in Example 6, and with the amount of sulfur-containing additive included in the formulation as the variable, the difference from Example 1 is that the amount of PST is adjusted to 1%, and the other conditions are the same as in Example 6.

[0043] Example 14 This example provides an electrolyte additive composition and electrolyte, as follows: With reference to the electrolyte formulation employed in Example 6, and with the amount of sulfur-containing additive included in the formulation as the variable, the difference from Example 1 is that the amount of PST is adjusted to 0.5%, and vinyl sulfonate (DTD) is added in an amount of 0.5%, and the other conditions are the same as in Example 6.

[0044] Example 15 This example takes the electrolyte formulation employed in Example 1 as the reference, and takes the type of lithium salt additive included in the formulation as the variable, the difference from Example 1 is that the amount of LiPO2F2 is 0.8%, and the other conditions are the same as in Example 1.

[0045] Example 16 This example takes the electrolyte formulation employed in Example 1 as the reference, and takes the type of lithium salt additive included in the formulation as the variable, the difference from Example 1 is that the amount of LiPO2F2 is 0.5%, and lithium tetrafluoroborate (LiBF4) is added in an amount of 0.2%, and the other conditions are the same as in Example 1.

[0046] Example 17 This example takes the electrolyte formulation employed in Example 1 as the reference, and takes the amount of lithium hexafluorophosphate included in the formulation as the variable, the difference from Example 1 is that the amount of lithium hexafluorophosphate is adjusted to 15%, and the amount of the non-aqueous solvent component is reduced or increased by the same mass, and the other conditions are the same as in Example 1.

[0047] Example 18 This example takes the electrolyte formulation used in Example 1 as a reference, and takes the lithium hexafluorophosphate content included in the formulation as a variable. The difference between this example and Example 1 is that the lithium hexafluorophosphate content is adjusted to 12%, lithium bisfluorosulfonylimide (LiFSi) is added in an amount of 3%, and the content of the non-aqueous solvent component used is reduced or increased in equal mass, and the rest is the same as Example 1.

[0048] Comparative Example 1 This comparative example provides an electrolyte which is different from Example 1 only in that the electrolyte functional additive is not contained in the comparative example, and the electrolyte functional additive in the electrolyte formulation of Example 1 is replaced with the non-aqueous solvent component used in equal mass, and the rest is the same as Example 1.

[0049] Comparative Example 2 This comparative example provides an electrolyte which is different from Example 1 only in that the first functional additive is not contained in Comparative Example 2, and the electrolyte functional additive in the electrolyte formulation of Example 1 is replaced with the non-aqueous solvent component used in equal mass, and the rest is the same as Example 1.

[0050] The electrolytes prepared in Examples 1-18 and Comparative Examples 1-2 are used to prepare batteries, wherein: Further, graphite is used as the negative active material, and the graphite, silicon-carbon, conductive agent, and binder are prepared into a negative electrode slurry in a mass percentage of 93.4:4:1.5:1.1, the negative electrode slurry is coated on a copper foil current collector, vacuum dried, and a negative electrode sheet is prepared; NCM811 is used as the positive active material, and the positive active material, conductive agent, and binder are prepared into a positive electrode slurry in a mass ratio of 97.0:1.5:2.0, the positive electrode slurry is coated on an aluminum foil current collector, vacuum dried, and a positive electrode sheet is prepared; The electrolytes prepared in Examples 1-18 and Comparative Examples 1-2 are respectively assembled into cylindrical batteries with the above-mentioned positive electrode sheet, negative electrode sheet, and separator, and the batteries are detected for initial room temperature cycle capacity retention rate and overcharge runaway SOC for 300 cycles, and the specific results are as follows: Table 1 Battery detection data

[0051] As shown in Table 1, the results of Comparative Examples 1-18 and Comparative Examples 1-2 show that the benzene nitrile additive has a higher overcharge SOC protection range, and the overcharge SOC protection range is further improved after the addition of the unsaturated silane-containing phosphate additive, which is mainly because the first functional additive and the second functional additive form a conductive polymer layer on the positive electrode surface, widening the overcharge protection window, thereby improving the overcharge performance of the battery.

[0052] The electrolyte and energy storage lithium ion battery have the following beneficial effects relative to the prior art: the electrolyte additive combination effectively improves the thermal runaway problem of high-nickel batteries during overcharging by improving the chemical properties of the electrolyte and the electrode interface, improves the safety performance of the battery, and has a broad application prospect.

[0053] It can be understood that the above embodiments are only exemplary embodiments adopted for illustrating the principles of the present disclosure, and the present disclosure is not limited thereto. Various modifications and improvements can be made by those of ordinary skill in the art without departing from the spirit and essence of the present disclosure, and these modifications and improvements are also considered within the protection scope of the present disclosure.

Claims

1. An electrolyte, characterized in that: include: Non-aqueous solvent, lithium salt, first functional additive, second functional additive and auxiliary additive; wherein, The chemical formula of the first functional additive is shown in Formula I below: Formula I; wherein R1 is independently selected from one of hydrogen, C1-C6 alkyl, substituted carbonyl and substituted alkenyl; The chemical formula of the second functional additive is shown in Formula II below: Formula II; Wherein, R2 is independently selected from one of C1-C5 alkyl and C2-C5 alkenyl; R3 is independently selected from one of C1-C5 alkyl, C2-C5 alkenyl, and C2-C5 alkynyl; R4 is independently selected from one of C1-C5 alkyl and C2-C5 alkenyl.

2. The electrolyte according to claim 1, characterized in that The R1 is selected from one of hydrogen, C1-C3 alkyl, carbonyl substituted by trimethylsilane, and alkenyl substituted by trimethylsilane.

3. The electrolyte according to claim 2, characterized in that The first functional additive is selected from at least one of the following compounds: Formula I-1; Formula I-2; Formula I-3; Formula I-4; Formula I-5; Formula I-6.

4. The electrolyte according to claim 1, characterized in that The second functional additive is selected from at least one of the following compounds: Formula II-1; Formula II-2; Formula II-3; Formula II-4; Formula II-5.

5. The electrolyte according to any one of claims 1 to 4, characterized in that The mass ratio of the first functional additive to the second functional additive is (0.5-1):(0.3-1).

6. The electrolyte according to any one of claims 1 to 4, characterized in that The non-aqueous solvent includes cyclic carbonate and chain carbonate.

7. The electrolyte according to any one of claims 1 to 4, characterized in that The lithium salt is one or both of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide; The mass fraction of the lithium salt in the total mass of the electrolyte is 12% to 15%.

8. The electrolyte according to any one of claims 1 to 4, characterized in that The auxiliary additives include sulfur-containing additives and lithium salt additives; wherein, The mass fraction of the sulfur-containing additive in the total mass of the electrolyte is 0.5% to 1.0%; The mass fraction of the lithium salt additive in the total mass of the electrolyte is 0.5% to 1.0%.

9. The electrolyte according to claim 8, characterized in that The sulfur-containing additive includes at least one of 1,3-propylene sultone and vinyl sulfate; The lithium salt additive includes at least one of lithium difluorophosphate, lithium bis(oxalatoborate), and lithium tetrafluoroborate.

10. An energy storage lithium-ion battery, characterized in that: The energy storage lithium-ion battery comprises a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte according to any one of claims 1 to 9.

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