Additive for electrolyte of lithium ion battery, electrolyte and lithium ion battery

Abstract

The present invention provides an additive for lithium-ion battery electrolyte, an electrolyte, and a lithium-ion battery. The additive comprises a compound having a structure of Formula (1), wherein R is a substituted or unsubstituted straight-chain C1-6 hydrocarbon group. The additive for lithium-ion battery electrolyte, the electrolyte, and the lithium-ion battery of the present invention can provide improved cycle performance and cycle impedance. (1).

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, and more specifically, to an additive for a lithium-ion battery electrolyte, an electrolyte, and a lithium-ion battery. Background Technology

[0002] In recent years, with the continuous development of electronic technology, the demand for battery devices to support the energy supply of electronic devices has been increasing. Currently, there is a need for batteries capable of storing more electricity and outputting higher power. Traditional lead-acid and nickel-metal hydride batteries can no longer meet the needs of new electronic products such as mobile devices like smartphones and stationary devices such as energy storage systems. Therefore, lithium-ion batteries have attracted widespread attention. In the development of lithium-ion batteries, their capacity and performance have been significantly improved.

[0003] Lithium-ion batteries consist of a positive electrode, a negative electrode, and an electrolyte. Additives in the electrolyte of lithium-ion batteries have a significant impact on the overall battery performance. Research has been conducted on electrolyte additives for lithium-ion batteries. The use of additives in the electrolyte of lithium-ion batteries may improve battery capacity or cycle performance, but it may also lead to an increase in battery impedance.

[0004] Therefore, it remains necessary to develop electrolyte additives, electrolytes, and lithium-ion batteries with improved cycle performance and cycle resistance.

[0005] Furthermore, there are no existing reports on the use of alkyldiaminetetraacetic dianhydride and its derivatives as electrolyte additives. For example, Japanese Patent JP3977970B2 mentions that ethylenediaminetetraacetic dianhydride (EDTAA) can be directly coated onto the current collector surface as a negative electrode additive, which can effectively suppress gas generation in the battery. However, in this patent, it can be seen that after adding EDTAA additive, the coulombic efficiency of the battery CV process is not as close to 100% as the inventors expected, and even shows worse performance than the standard sample. Moreover, the patent does not mention the improvement of actual battery performance by EDTAA. Summary of the Invention

[0006] The main objective of this invention is to provide an additive for lithium-ion battery electrolyte, an electrolyte, and a lithium-ion battery, so as to solve the problems of poor cycle performance and cycle impedance of lithium-ion batteries in the prior art.

[0007] To achieve the above objectives, the present invention provides an additive for lithium-ion battery electrolytes, comprising a compound having the structure of formula (1).

[0008] (1)

[0009] Wherein, R is a substituted or unsubstituted straight-chain or branched C1-6 hydrocarbon group.

[0010] Furthermore, in formula (1), R is an unsubstituted straight-chain or branched C1-6 alkyl group.

[0011] Further, compounds having the structure of formula (1) are methyldiaminetetraacetic dianhydride, ethylenediaminetetraacetic dianhydride, propylenediaminetetraacetic dianhydride, butyldiaminetetraacetic dianhydride, pentanediaminetetraacetic dianhydride, hexanediaminetetraacetic dianhydride, 4,4'-(propane-1,2-diyl)bis(morpholin-2,6-dione), 4,4'-(butane-1,2-diyl)bis(morpholin-2,6-dione), 4,4'-(pentane-1,2-diyl)bis(morpholin-2,6-dione), 4,4'-(hexane-1,2-diyl)bis(morpholin-2,6-dione), 4,4'-(butane-2,3-diyl)bis(morpholin-2,6-dione) or 4,4'-(hexane-3,4-diyl)bis(morpholin-2,6-dione).

[0012] To achieve the above objectives, another aspect of the present invention provides an electrolyte for lithium-ion batteries, comprising the additives, organic solvents and lithium salts described above.

[0013] Furthermore, based on the total mass of the electrolyte, the amount of additive is 0.005wt%-0.5wt%.

[0014] Furthermore, the organic solvent includes cyclic carbonates, linear carbonates, or any combination thereof.

[0015] Furthermore, the lithium salt is selected from the group consisting of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium di(oxalate-borate), lithium di(fluorooxalate-borate), lithium perchlorate, or combinations thereof.

[0016] Another aspect of the present invention provides a lithium-ion secondary battery, comprising: a positive electrode, a negative electrode, a separator, and an electrolyte as described above.

[0017] Furthermore, the cathode material comprises ternary or lithium cobalt oxide cathode material.

[0018] Furthermore, the negative electrode sheet contains graphite or silicon-carbon negative electrode materials.

[0019] By applying the technical solution of this invention, the compound of formula (1) is used as an electrolyte additive for lithium-ion batteries, which can protect the positive electrode during battery cycling, improve the first-cycle and cycle discharge capacity, suppress the rise in battery impedance, and improve the discharge platform. In the compound of formula (1), the anhydride structure can form a stable CEI film on the surface of the positive electrode, removing the negative impact of H2O and HF generated by the electrolyte during cycling on the positive electrode; the alkyl diaminetetraacetic acid dianhydride and its derivatives with chain structure are added to the electrolyte as electrolyte additives, which can effectively suppress the rise in battery impedance, and the battery can exhibit better cycle performance, better cycle capacity and capacity retention rate, and exhibit lower impedance after cycling, and can also discharge higher capacity at high rate after cycling. Attached Figure Description

[0020] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0021] Figure 1 This is a graph showing the cycle capacity of lithium-ion batteries prepared using EDTAA as an electrolyte additive and lithium-ion batteries prepared using the base electrolyte, as illustrated in the examples.

[0022] Figure 2 The figures show the charging and discharging curves of lithium-ion batteries prepared using EDTAA as an electrolyte additive and lithium-ion batteries prepared using the base electrolyte, as illustrated in the examples.

[0023] Figure 3 The graph shows the cycle impedance of lithium-ion batteries prepared using EDTAA as an electrolyte additive and lithium-ion batteries prepared using the base electrolyte.

[0024] Figure 4 This is a graph showing the capacity and temperature changes during cycling of a lithium-ion battery prepared using EDTAA as an electrolyte additive and a lithium-ion battery prepared using a basic electrolyte.

[0025] Figure 5 This is a schematic diagram illustrating the mechanism by which the additive compound of the present invention removes H2O and HF generated in the electrolyte during the cycling process. Detailed Implementation

[0026] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0027] As described in the background section, existing lithium-ion batteries suffer from poor cycle performance and cycle impedance. To address these issues, this application provides an additive for lithium-ion battery electrolytes, comprising a compound having the structure of formula (1).

[0028] (1)

[0029] Wherein, R is a substituted or unsubstituted straight-chain C1-6 hydrocarbon group.

[0030] Using the compound of formula (1) as an electrolyte additive for lithium-ion batteries can protect the positive electrode during battery cycling, thereby improving the first-cycle and cycle discharge capacity, suppressing the rise in battery impedance, and enhancing the discharge platform. In the compound of formula (1), the anhydride structure can form a stable CEI film on the surface of the positive electrode, removing the negative impact of H2O and HF generated by the electrolyte during cycling on the positive electrode; the alkyl diaminetetraacetic anhydride and its derivatives with chain structure are added to the electrolyte as electrolyte additives, which can effectively suppress the rise in battery impedance, and the battery can exhibit better cycle performance, better cycle capacity and capacity retention rate, and exhibit lower impedance after cycling, and can also discharge higher capacity at high rate after cycling.

[0031] The mechanism by which the compound of formula (1) removes H2O and HF is as follows: Figure 5 As shown (taking ethylenediaminetetraacetic anhydride as an example), its tetraacetic anhydride portion can react with H2O and HF to adsorb H2O and HF generated by the electrolyte during cycling, thus preventing H2O from corroding the battery electrolyte, reducing electrolyte degradation and decomposition, and ultimately forming HF. Furthermore, similar to the above mechanism, the compound of formula (1) can undergo a ring-opening reaction after oxidation during cycling, forming a CEI film on the positive electrode surface. It forms a film on the electrode surface preferentially over the electrolyte, preventing continuous oxidation and reduction of the electrolyte on the electrode surface, thus protecting the electrode during battery cycling, increasing the battery's first-cycle and cycle discharge capacity, suppressing the rise in battery impedance, and improving the discharge plateau. Therefore, the additive of the present invention has the advantages of forming lower impedance CEI and SEI films while ensuring battery usability is not affected, improving battery cycle performance, and extending battery life.

[0032] The choice of the R group in the compound of formula (1) can affect its performance as an additive. If the carbon chain of the R group is too long, the molecule will be too large when CEI is formed on the positive electrode surface, the reaction sites will be reduced, the CEI film formed will not be uniform enough, and it will not be conducive to lithium ion insertion and extraction.

[0033] Preferably, in formula (1), R is an unsubstituted straight-chain or branched C1-6 alkyl group.

[0034] Preferably, the compound having the structure of formula (1) is methyldiaminetetraacetic dianhydride, ethylenediaminetetraacetic dianhydride, propylenediaminetetraacetic dianhydride, butyldiaminetetraacetic dianhydride, pentanediaminetetraacetic dianhydride, hexanediaminetetraacetic dianhydride, 4,4'-(propane-1,2-diyl)bis(morpholin-2,6-dione), 4,4'-(butane-1,2-diyl)bis(morpholin-2,6-dione), 4,4'-(pentane-1,2-diyl)bis(morpholin-2,6-dione), 4,4'-(hexane-1,2-diyl)bis(morpholin-2,6-dione). (6-dione), 4,4'-(but-2,3-diyl)bis(morpholin-2,6-dione) or 4,4'-(hex-3,4-diyl)bis(morpholin-2,6-dione), more preferably methyldiaminetetraacetic anhydride, ethylenediaminetetraacetic anhydride, propylenediaminetetraacetic anhydride, 4,4'-(propane-1,2-diyl)bis(morpholin-2,6-dione), 4,4'-(but-1,2-diyl)bis(morpholin-2,6-dione), 4,4'-(but-2,3-diyl)bis(morpholin-2,6-dione).

[0035] The chemical formulas of 4,4'-(propyl-1,2-diyl)bis(morpholin-2,6-dione), 4,4'-(but-1,2-diyl)bis(morpholin-2,6-dione), 4,4'-(pentan-1,2-diyl)bis(morpholin-2,6-dione), 4,4'-(hexane-1,2-diyl)bis(morpholin-2,6-dione), 4,4'-(but-2,3-diyl)bis(morpholin-2,6-dione), and 4,4'-(hexane-3,4-diyl)bis(morpholin-2,6-dione) are as follows:

[0036] , , , , , .

[0037] Preferably, the compound having the structure of formula (1) is ethylenediaminetetraacetic dianhydride, methyldiaminetetraacetic dianhydride, propylenediaminetetraacetic dianhydride, 4,4'-(propane-1,2-diyl)bis(morpholin-2,6-dione), 4,4'-(butane-1,2-diyl)bis(morpholin-2,6-dione), or 4,4'-(butane-2,3-diyl)bis(morpholin-2,6-dione).

[0038] The specific compounds mentioned above are beneficial for further improving the cycle performance and cycle impedance of lithium-ion batteries.

[0039] According to another aspect of the invention, an electrolyte is provided comprising an organic solvent, a lithium salt, and the additives described in the invention.

[0040] The electrolyte of this invention contains the electrolyte additives described herein. Using the compound of formula (1) as an electrolyte additive for lithium-ion batteries can protect the positive electrode during battery cycling, thereby improving the first-cycle and cycle discharge capacity, suppressing the rise in battery impedance, and improving the discharge platform. In the compound of formula (1), the anhydride structure can form a stable CEI film on the surface of the positive electrode, removing the negative impact of H2O and HF generated by the electrolyte during cycling on the positive electrode; the alkyl diaminetetraacetic anhydride and its derivatives with chain structure are added to the electrolyte as electrolyte additives, which can effectively suppress the rise in battery impedance, and the battery can exhibit better cycle performance, better cycle capacity and capacity retention rate, and exhibit lower impedance after cycling, and can also discharge higher capacity at high rate after cycling.

[0041] Preferably, based on the total mass of the electrolyte, the amount of additive is 0.005wt%-0.5wt%, or 0.005wt%-0.4wt%, or 0.005wt%-0.3wt%, or 0.005wt%-0.2wt%, or 0.005wt%-0.1wt%.

[0042] Using additives within the above-mentioned range is beneficial for further improving the cycle performance and cycle impedance of lithium-ion batteries.

[0043] Preferably, the organic solvent includes cyclic carbonates, linear carbonates, or any combination thereof.

[0044] Preferably, the organic solvent is selected from one or more of ethylene carbonate, propylene carbonate, butyl carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dihexyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, and propyl propionate. The above are merely examples of the organic solvents used in this invention, and are not intended to limit the invention. Those skilled in the art can select suitable organic solvents according to actual needs. In a preferred embodiment, at least one carbonate is used as the organic solvent of the electrolyte of this invention. In a preferred embodiment, at least one linear carbonate and at least one cyclic carbonate are used together as the organic solvent of the electrolyte of this invention.

[0045] Preferably, the lithium salt is selected from the group consisting of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium di(oxalate)borate, lithium di(fluorooxalate)borate, lithium perchlorate, or combinations thereof.

[0046] When the electrolyte contains linear carbonates, cyclic carbonates or any combination thereof, lithium salts, and additives of the present invention, it is beneficial to improve the cycle performance and cycle impedance of lithium-ion secondary batteries.

[0047] According to another aspect of the present invention, a lithium-ion secondary battery is provided, comprising: a positive electrode, a negative electrode, a separator, and the electrolyte described above.

[0048] Preferably, the positive electrode sheet contains ternary or lithium cobalt oxide positive electrode material.

[0049] Preferably, the negative electrode sheet contains graphite or silicon-carbon negative electrode material.

[0050] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0051] Example

[0052] Preparation of positive electrode sheet

[0053] 95.5g of lithium nickel cobalt aluminum oxide (NCA) (LiNiCoAlO2), 2.5g of conductive carbon black, 1.9g of polyvinylidene fluoride (PVDF), and 0.1g of dispersant polyvinylpyrrolidone (PVP) were mixed to obtain a positive electrode mixture. This mixture was then dispersed in N-methylpyrrolidone to obtain a positive electrode slurry. Subsequently, the positive electrode slurry was uniformly coated onto aluminum foil to obtain a positive current collector. The positive current collector was dried and then formed into a positive electrode sheet using a stamping process.

[0054] Preparation of negative electrode sheet

[0055] A negative electrode slurry was prepared by stirring 95.85 g of a 9:1 mixture of silicon suboxide and graphite powder, 1 g of Super P, 3.15 g of a 1:1 mixture of carboxymethyl cellulose (CMC) and styrene-butadiene latex (SBR) binder, and an appropriate amount of water. The obtained negative electrode slurry was then uniformly coated onto copper foil to obtain a negative electrode current collector. The negative electrode current collector was dried and then formed into a negative electrode sheet using a stamping process.

[0056] Preparation of basic electrolyte

[0057] A basic electrolyte was prepared by mixing 20.75 g of ethylene carbonate, 56.75 g of dimethyl carbonate, 3.5 g of ethyl methyl carbonate, 0.4 g of lithium tetrafluoroborate, and 18.6 g of lithium hexafluorophosphate. The mixture was stirred until homogeneous and then set aside.

[0058] Preparation of electrolytes in Examples 1-56

[0059] Add electrolyte additives to the base electrolyte, mix well and set aside. The types and amounts of additives are shown in Table 1 below.

[0060] Preparation of electrolyte in Comparative Example 1

[0061] Same as the base electrolyte, no additives are added.

[0062] Battery assembly

[0063] CR2016 coin cells were assembled in a dry laboratory. The positive electrode sheet prepared in the above steps was used as the positive electrode, the negative electrode sheet as the negative electrode, and the electrolyte prepared in the examples and comparative examples was used as the electrolyte. The positive electrode, negative electrode, separator, and coin cell casing were assembled, and the electrolyte was injected. After assembly, the cells were allowed to stand for 12 hours to age, thus obtaining the coin cell.

[0064] Battery performance testing

[0065] At room temperature, the button batteries of the examples and comparative examples were subjected to initial charge-discharge tests and impedance tests at voltages between 2.0V and 4.2V. Charge-discharge cycle tests and impedance tests were also performed on the button batteries of the examples and comparative examples at voltages between 2.5V and 4.2V. The batteries of the examples and comparative examples were first subjected to one 0.1C charge-discharge cycle test at 23°C, then 100 cycles of 0.5C charge and 5C discharge at 60°C to determine the battery's cycle retention rate. Finally, one 0.5C charge test was performed at 60°C to determine the battery's impedance value.

[0066] Capacity retention rate after 100 cycles [%] = (Discharge capacity after 100 cycles / Initial discharge capacity (first cycle)) × 100%.

[0067] The cycle performance test results of the batteries of Examples 1-85 and Comparative Example 1 are shown in Table 1 below.

[0068] Furthermore, the cycle capacity, charge and discharge curves, and cycle impedance of the lithium-ion batteries prepared in Examples 1-9 and Comparative Document 1 are... Figure 1-3 As shown in [the image]. Among them, in [the image]... Figure 1 In the curve, the peak is obtained by performing a small-scale 0.1C capacity recovery after every 25 cycles.

[0069] Table 1

[0070]

[0071] Table 1 (continued)

[0072]

[0073] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0074] By comparing Examples 1-85 with Comparative Example 1, and referring to Figure 1-3 It can be seen that the electrolyte additive of the present invention can improve the cycle performance and / or cycle impedance of lithium-ion secondary batteries. It should be understood that, depending on the actual product used, different performance requirements will be placed on batteries in different application scenarios: long-cycle batteries require higher cycle life, so slightly higher impedance is acceptable if the impact on cycle performance is not significant; power batteries, on the other hand, have higher impedance requirements, and slightly lower cycle life is acceptable. Therefore, even if the additive of the present invention achieves only an improvement in either cycle performance or cycle impedance compared to additive-free batteries in some cases, it still provides an advantage in specific battery applications.

[0075] By comparing Examples 1-28, 44-61, 72-80 with Comparative Example 1, and referring to Figure 1-3 It can be seen that when the electrolyte additives of the present invention are methyldiaminetetraacetic dianhydride, ethylenediaminetetraacetic dianhydride, propylenediaminetetraacetic dianhydride, 4,4'-(propane-1,2-diyl)bis(morpholin-2,6-dione), 4,4'-(butane-1,2-diyl)bis(morpholin-2,6-dione), or 4,4'-(butane-2,3-diyl)bis(morpholin-2,6-dione), the improvement on the cycle performance and cycle impedance of lithium-ion secondary batteries is more significant.

[0076] Comparing Examples 1-10, it can be seen that, based on the total mass of the electrolyte, when the amount of the additive of the present invention is 0.005wt%-0.5wt%, it is beneficial to further improve the cycle performance and cycle impedance of the lithium-ion secondary battery.

[0077] In addition, through Figure 2 and 3 It can be seen that the batteries of Examples 1-9 have comparable or better capacity and shorter constant voltage plateau, as well as lower cycle impedance compared with Comparative Example 1, thus exhibiting superior battery performance.

[0078] In addition, 1Ah-level pouch cells were assembled using the electrolytes of Example 9 and Comparative Example 1, and charge-discharge tests were performed on these cells (test conditions: 23°C, 11A discharge, cutoff voltage 2.5V). During the tests, the cells were insulated, and temperature data was monitored using thermocouples attached to the cells. Capacity data was simultaneously obtained using the charge-discharge equipment. Specifically, three cells were assembled using each of the electrolytes from Example 9 and Comparative Example 1, and each cell was tested twice. Figure 4 The graph shows the changes in capacity and temperature during battery cycling, comparing the increase in battery capacity with the increase in temperature under high current. Δcapacity represents the capacity released during battery discharge, and Δtemperature represents the temperature change during discharge. The 99% in the legend refers to the possible range covered by the data in the graph.

[0079] pass Figure 4 It can be seen that when the battery is discharged at a high rate in a 1Ah-level battery, the battery capacity of Examples 1-9 is greater than that of Comparative Example 1, while the temperature rise is less than that of Comparative Example 1, which proves that the electrolyte additive of the present invention can improve the cycle performance and cycle impedance of the battery.

[0080] It should be noted that the terms "first," "second," etc., used in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such terms can be used interchangeably where appropriate so that the embodiments of this application described herein can be implemented, for example, in a sequence other than those described herein.

[0081] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An additive for lithium-ion battery electrolytes, characterized in that, The additive comprises a compound having the structure of formula (1). （1） Wherein, R is a substituted or unsubstituted straight-chain or branched C1-6 hydrocarbon group.

2. The additive according to claim 1, characterized in that, In formula (1), R is an unsubstituted straight-chain or branched C1-6 alkyl group.

3. The additive according to claim 1 or 2, characterized in that, The compound having the structure of formula (1) is methyldiaminetetraacetic dianhydride, ethylenediaminetetraacetic dianhydride, propylenediaminetetraacetic dianhydride, butyldiaminetetraacetic dianhydride, pentanediaminetetraacetic dianhydride, hexanediaminetetraacetic dianhydride, 4,4'-(propane-1,2-diyl)bis(morpholin-2,6-dione), 4,4'-(butane-1,2-diyl)bis(morpholin-2,6-dione), 4,4'-(pentane-1,2-diyl)bis(morpholin-2,6-dione), 4,4'-(hexane-1,2-diyl)bis(morpholin-2,6-dione), 4,4'-(butane-2,3-diyl)bis(morpholin-2,6-dione) or 4,4'-(hexane-3,4-diyl)bis(morpholin-2,6-dione).

4. An electrolyte for lithium-ion batteries, characterized in that, The electrolyte comprises the additive, organic solvent, and lithium salt as described in any one of claims 1-3.

5. The electrolyte according to claim 4, characterized in that, The amount of the additive is 0.005wt%-0.5wt% based on the total mass of the electrolyte.

6. The electrolyte according to claim 4, characterized in that, The organic solvent includes cyclic carbonates, linear carbonates, or any combination thereof.

7. The electrolyte according to claim 4, characterized in that, The lithium salt is selected from the group consisting of lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium di(oxalate)borate, lithium di(fluorooxalate)borate, lithium perchlorate, or combinations thereof.

8. A lithium-ion secondary battery, characterized in that, include: Positive electrode plate, Negative electrode plate, Diaphragm, and The electrolyte according to any one of claims 4 to 7.

9. The lithium-ion secondary battery according to claim 8, characterized in that, The positive electrode sheet contains ternary or lithium cobalt oxide positive electrode materials.

10. The lithium-ion secondary battery according to claim 8 or 9, characterized in that, The negative electrode sheet contains graphite or silicon-carbon negative electrode material.

Images