Electrolyte and battery using the same

Abstract

This application provides an electrolyte and a battery using the same. The electrolyte includes a lithium salt, an organic solvent, and a functional additive. The functional additive has the following structural formula: wherein, among R1, R2, R3, R4, and R5, at least one includes at least one of an oxygen-containing substituent, a cyano-containing substituent, an ester-containing substituent, and a nitrogen-containing heterocyclic substituent; R6, R7, R8, R9, and R... 10 R 11 R 12 R 13 The electrolyte contains at least one of oxygen-containing boron heterocyclic substituents and halogen substituents. This electrolyte facilitates the formation of a uniform and dense interfacial film on the positive and negative electrode surfaces, provides interfacial stability, reduces the degree of side reactions at the positive and negative electrode interfaces, and thus optimizes the overall performance of the battery, especially high-nickel ternary / silicon anode batteries.

Description

Technical Field

[0001] This application belongs to the field of lithium-ion battery technology, specifically relating to an electrolyte and a battery using the same. Background Technology

[0002] With the large-scale application of power batteries and energy storage battery systems, the development of a new generation of high-energy-density lithium-ion batteries has become a key focus in the battery industry. High-nickel cathode materials and silicon-carbon anode materials are the main cathode and anode material systems for the next generation of lithium-ion batteries.

[0003] On the one hand, the tetravalent nickel ions in high-nickel batteries have high catalytic activity and rapid oxidation and decomposition, which easily damages the electrolyte structure. Furthermore, during battery cycling, transition metals such as manganese and cobalt dissolve, which can damage the SEI film on the negative electrode. On the other hand, silicon-based negative electrodes, due to their high expansion characteristics, struggle to form a stable solid electrolyte interface film in the electrolyte (the electrode structure is damaged during battery cycling, and new solid electrolyte interface films continuously form on the exposed silicon surface), leading to corrosion of the negative electrode material and capacity decay, which is detrimental to the electrolyte's cycling and safety performance.

[0004] The electrolyte in a lithium-ion battery is a crucial medium for transferring lithium ions and connecting the positive and negative electrode materials, playing a vital role in maximizing battery capacity and improving cycle stability. Electrolyte additives are an important component of the electrolyte, a core element in the development of functional electrolytes, and one of the most economical and effective methods for improving the electrochemical performance of lithium-ion batteries.

[0005] Therefore, further research on electrolyte additives for high-nickel cathode and silicon-carbon anode systems to improve the performance of lithium-ion batteries with high-nickel cathode and silicon-carbon anode is of great significance to the current lithium-ion battery industry. Summary of the Invention

[0006] To address the problems and shortcomings of existing technologies, this application provides an electrolyte and a battery using the same. This electrolyte facilitates the formation of a uniform and dense interfacial film on the surfaces of the positive and negative electrodes, provides interfacial stability, reduces the degree of side reactions at the positive and negative electrode interfaces, and thereby optimizes the overall performance of the battery, especially high-nickel ternary / silicon anode batteries.

[0007] According to a first aspect of this application, an electrolyte is provided, comprising a lithium salt, an organic solvent, and a functional additive; the functional additive has the following structural formula:

[0008] Among them, R1, R2, R3, R4, and R5, at least one includes at least one of the following: an oxygen-containing substituent, a cyano-containing substituent, an ester-containing substituent, and a nitrogen-containing heterocyclic substituent; R6, R7, R8, R9, and R 10 R11 R 12 R 13 In this context, at least one of the following is included: an oxygen-containing boron heterocyclic substituent or a halogen substituent.

[0009] This application effectively improves the electrochemical performance of batteries, especially high-nickel ternary / silicon-carbon system batteries, by introducing functional additives with the above-mentioned structure, thereby improving the battery's room temperature, high temperature cycle performance, and rate performance. Specifically, the aforementioned functional additives, firstly, have a main structure containing a benzene ring or naphthalene ring, and also contain cyano substituents or alkynyl groups. This forms a large conjugated structure, which allows electrons to move relatively freely throughout the conjugated system, thereby increasing the charge transfer rate, reducing the transfer resistance, and thus improving the rate performance and cycle performance of the battery electrode material. Moreover, during the first charge and discharge of the battery, the additives containing the benzene ring conjugated structure can preferentially undergo oxidative decomposition before the electrolyte and deposit on the electrode surface, participating in the formation of the solid electrolyte interphase (SEI) film. In the early stages, they can promote the solvent decomposition of the electrolyte, resulting in an increase in the carbonate content in the SEI film due to solvent decomposition, which is beneficial to improving the cycle performance and rate performance of the battery electrode material. In addition, the presence of the benzene ring conjugated structure makes the formed SEI film more stable, dense, and with lower impedance. This high-quality SEI film can not only effectively prevent further reactions between the electrolyte and the electrode material, but also improve the migration efficiency of lithium ions at the electrode / electrolyte interface, further enhancing the battery performance. Secondly, cyano substituents, with lone pairs of electrons, can complex the positive electrode transition metal to prevent its dissolution. Alternatively, alkynyl substituents can polymerize on the positive and negative electrode surfaces during the first charge and discharge process to form a protective film, preventing the electrode material from contacting the electrolyte, preventing the positive electrode from reacting and generating a large amount of gas. Furthermore, the polymerized interface film is flexible, which can buffer the expansion of the silicon negative electrode, improve the stability of the silicon negative electrode, and thus optimize the battery cycle performance and rate performance.

[0010] Further, among R1, R2, R3, R4, and R5, at least one includes at least one of an oxygen-containing substituent, a cyano-containing substituent, an ester-containing substituent, and a nitrogen-containing heterocyclic substituent; R6, R7, R8, R9, and R 10 R 11 R 12 R 13The electrode material contains at least one of an oxygen-containing boron heterocyclic substituent and a halogen substituent. These substituents facilitate the formation of a stable interfacial film at the positive or negative electrode interface, improving interfacial stability and thus optimizing the stability of the positive and negative electrode materials during cycling, thereby improving the overall battery performance. Specifically, oxygen-containing substituents, cyano substituents, ester-containing substituents, nitrogen-containing heterocyclic substituents, oxygen-containing boron heterocyclic substituents, and halogen substituents can interact with some active materials on the electrode surface, participate in the formation of the interfacial film, or reduce structural changes and side reactions of the electrode material during charging and discharging. These factors contribute to maintaining the integrity and stability of the electrode material, reducing interfacial impedance, promoting lithium-ion transport, and thus optimizing the battery's charge-discharge efficiency and cycle performance.

[0011] Preferably, the halogen substituent includes F.

[0012] Preferably, at least one of R1, R2, R3, R4, and R5 includes an oxygen-containing substituent or a cyano-containing substituent; or at least one of R1, R2, R3, R4, and R5 includes an ester-containing substituent or a nitrogen-containing heterocyclic substituent; R6, R7, R8, R9, and R 10 R 11 R 12 R 13 In the presence of at least one oxygen-boron heterocyclic substituent, and at least one halogen substituent.

[0013] Preferably, at least one of R1, R2, R3, R4, and R5 includes an oxygen-containing substituent and a cyano-containing substituent; the oxygen-containing substituent is an ether-containing substituent.

[0014] Preferably, the structural formula of the functional additive includes

[0015] Preferably, the relative molecular weight of the functional additive is 120–700 g / mol. Controlling the relative molecular weight of the functional additive within this range is beneficial for balancing various performance aspects such as solubility, ion conduction, battery safety, and energy density, and is more conducive to improving the overall performance of the battery. A smaller relative molecular weight is beneficial for lithium-ion migration and improves conductivity. At the same time, a smaller relative molecular weight means a relatively larger amount of small molecule additives, which can provide more active sites to participate in the electrode reaction, helping to improve the specific capacity of the battery and thus improve the energy density of the battery. However, a smaller relative molecular weight usually means a lower flash point and boiling point. Under abnormal conditions such as high temperature or overcharging, it is more likely to volatilize and burn, which may increase the safety risk of the battery. In addition, a smaller relative molecular weight means a relatively larger amount of small molecule additives and too many active sites, which is not conducive to the overall stability of the electrolyte, and therefore not conducive to maintaining the stability of the electrode material structure, which is detrimental to the cycle life and charge-discharge efficiency of the battery.

[0016] Preferably, the relative molecular weight of the functional additive is 120–700 g / mol; the mass percentage of the functional additive in the electrolyte is 0.5–3 wt%.

[0017] Preferably, the relative molecular weight of the functional additive is 120–400 g / mol.

[0018] Preferably, the functional additive includes at least one of 2-(prop-2-yn-1-yloxy)benzonitrile, 2-(8-ethynyl-7-fluoronaphth-1-yl)-4,4,5,5-tetramethyl-1,3,2-dioxoboronylcyclopentane, and 1-Boc-4-(4-cyanophenyl)piperazine.

[0019] Preferably, when the functional additive includes 2-(prop-2-yne-1-yloxy)benzonitrile, the mass percentage of the functional additive in the electrolyte is 0.5 to 2 wt%.

[0020] Preferably, when the functional additive includes 2-(8-ethynyl-7-fluoronaphth-1-yl)-4,4,5,5-tetramethyl-1,3,2-dioxoborane, the mass percentage of the functional additive in the electrolyte is 0.8 to 3 wt%.

[0021] Preferably, when the functional additive includes 1-Boc-4-(4-cyanophenyl)piperazine, the mass percentage of the functional additive in the electrolyte is 0.8 to 2 wt%.

[0022] The amount of functional additives added has a certain impact on the overall performance of the electrolyte and battery. Too little additive will not help optimize the overall performance of the electrolyte and battery, while too much additive may lead to more side reactions that are detrimental to the stability of electrode materials, or may hinder the function of other components in the electrolyte, resulting in a decline in the overall performance of the electrolyte and battery.

[0023] It should be noted here that the structural formula of 2-(propan-2-yn-1-yloxy)benzonitrile is... The structural formula of 2-(8-ethynyl-7-fluoronaphth-1-yl)-4,4,5,5-tetramethyl-1,3,2-dioxoborhecyclopentane is: The structural formula of 1-Boc-4-(4-cyanophenyl)piperazine is:

[0024] Preferably, the electrolyte further includes film-forming additives, including phosphorus-based additives, specifically at least one selected from tris(trimethylsilane) phosphate, tris(triethylsilane) phosphate, tris(isopropylsilane) phosphate, trimethyl phosphate, triethyl phosphate, trimethyl phosphite, and diethyl phosphite. This application further adds phosphorus-based additives to the electrolyte, which can further interact with the aforementioned functional additives and other components in the electrolyte to further promote the uniformity, density, and stability of the electrode interface film, thereby further improving the stability of the electrode material during charge and discharge processes and optimizing the overall battery performance.

[0025] Preferably, the film-forming additive accounts for 0.2 to 1 wt% of the mass of the electrolyte.

[0026] Preferably, when the functional additive includes 2-(prop-2-yn-1-yloxy)benzonitrile, the film-forming additive includes at least one of tris(trimethylsilane) phosphate, tris(triethylsilane) phosphate, and tris(isopropylsilane) phosphate; when the functional additive includes 2-(8-ethynyl-7-fluoronaphth-1-yl)-4,4,5,5-tetramethyl-1,3,2-dioxoborane, the film-forming additive includes at least one of trimethyl phosphite and diethyl phosphite; when the functional additive includes 1-Boc-4-(4-cyanophenyl)piperazine, the film-forming additive includes at least one of trimethyl phosphate and triethyl phosphate.

[0027] Preferably, the lithium salt includes a first lithium salt and a second lithium salt; the first lithium salt includes lithium hexafluorophosphate; the second lithium salt includes at least one of lithium difluorophosphate (LiPOF), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). In addition to adding a relatively conventional lithium salt such as lithium hexafluorophosphate, this application also introduces the aforementioned low-resistance second lithium salt, which helps to reduce the impedance of the interface film, improve lithium-ion transport efficiency, and further optimize the cycle performance and rate performance of the battery.

[0028] Preferably, the concentration of the first lithium salt in the electrolyte is 1–1.5 mol / L; and the mass percentage of the second lithium salt in the electrolyte is 0.5–6 wt%.

[0029] Preferably, the second lithium salt comprises lithium difluorophosphate.

[0030] Preferably, when the second lithium salt includes lithium difluorophosphate, the mass percentage of lithium difluorophosphate in the electrolyte is 0.5 to 1 wt%.

[0031] Preferably, the organic solvent includes linear carbonates and cyclic carbonates.

[0032] Preferably, the volume ratio of linear carbonate to cyclic carbonate is 60-80:20-40. Preferably, the linear carbonate includes at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate; the cyclic carbonate includes at least one of ethylene carbonate, fluoroethylene carbonate, and propylene carbonate.

[0033] Preferably, the organic solvent includes diethyl carbonate, fluoroethylene carbonate, ethylene carbonate, and methyl ethyl carbonate. Preferably, the volume ratio of diethyl carbonate, fluoroethylene carbonate, ethylene carbonate, and methyl ethyl carbonate is 15–40:5–20:10–35:30–60.

[0034] Preferably, the volume ratio of diethyl carbonate, fluoroethylene carbonate, ethylene carbonate, and methyl ethyl carbonate is 25:10:20:45.

[0035] According to a second aspect of this application, a battery is provided, comprising the aforementioned electrolyte. The battery prepared using the aforementioned electrolyte exhibits a uniform, dense, and stable interfacial film at the interface between the electrode material and the electrolyte. In particular, the stability of the SEI film at the negative electrode interface is significantly improved, and the interfacial impedance is also low, ensuring lower impedance and further enhancing the lithium-ion transport efficiency. Therefore, the cycle performance and rate performance of the battery are effectively improved.

[0036] Preferably, the battery includes a positive electrode and a negative electrode; the positive electrode includes a high-nickel ternary material, wherein the molar percentage of nickel in the three components (nickel, cobalt, and manganese) is not less than 80%; the negative electrode includes at least one of silicon material and silicon-carbon material. For high-nickel ternary / silicon or silicon-carbon battery systems, the electrolyte provided in this application provides a more significant optimization of the electrochemical performance, such as cycle performance and rate performance, of this type of battery. Therefore, it is more suitable for high-nickel ternary / silicon or silicon-carbon battery systems and is of great significance for the research of electrolytes for this type of battery system. Detailed Implementation

[0037] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments.

[0038] Example 1

[0039] 1. Composition and preparation of electrolyte

[0040] The electrolyte in this embodiment includes lithium salt, organic solvent, film-forming additive, and functional additive.

[0041] The lithium salts include lithium hexafluorophosphate (LiPF6) and lithium difluorophosphate (LiPOF), with the concentration of lithium hexafluorophosphate in the electrolyte being 1 mol / L and the mass percentage of lithium difluorophosphate in the electrolyte being 0.8 wt%.

[0042] The functional additive is 2-(prop-2-yn-1-yloxy)benzonitrile, and its mass percentage in the electrolyte is 1.2 wt%.

[0043] The film-forming additive is (trimethylsilane) phosphate, and its mass percentage in the electrolyte is 0.6 wt%.

[0044] The organic solvents include diethyl carbonate (DEC), fluoroethylene carbonate (FEC), ethylene carbonate (EC), and methyl ethyl carbonate (EMC), with a volume ratio of 25:10:20:45. The electrolyte is prepared according to the following steps: Under an argon atmosphere, the above-mentioned lithium salt, functional additives, and film-forming additives are mixed uniformly in the organic solvent, with low-temperature stirring during the mixing process.

[0045] 2. Battery manufacturing

[0046] Preparation of lithium-ion batteries

[0047] (1) Preparation of positive electrode

[0048] Ternary material NCM (LiNi) 0.9 Co 0.05 Mn 0.05 O2) positive electrode active material, binder PVDF (polyvinylidene fluoride), and conductive agent SP (conductive carbon black Super-P) are mixed and stirred evenly at a mass ratio of 96:1.8:2.2 to obtain positive electrode slurry. Then, the positive electrode slurry is coated onto aluminum foil through a coating process, and after vacuum drying and cold pressing, a positive electrode sheet is obtained.

[0049] (2) Preparation of negative electrode

[0050] Silicon-carbon anode material (silicon content 40-60 wt%), conductive agent SP (Super-P conductive carbon black), SWCNT (single-walled carbon nanotubes), and binder PAA (polyacrylic acid) are mixed and stirred evenly in a mass ratio of 83.5:8:0.5:8 to obtain a negative electrode slurry. The solid content is controlled at 30%. The negative electrode slurry is then coated onto copper foil through a coating process. After vacuum drying and cold pressing, a negative electrode sheet is obtained.

[0051] (3) Selection of electrolyte

[0052] The electrolyte prepared using this embodiment.

[0053] (4) Selection of the separator

[0054] Polyethylene (PE) + ceramic was chosen as the separator for lithium-ion batteries.

[0055] (5) Preparation of lithium-ion batteries

[0056] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The bare cell is placed in the outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a soft-pack lithium-ion battery is obtained.

[0057] Example 2

[0058] The difference between this embodiment and Example 1 is that the functional additive in the prepared electrolyte is adjusted to 2-(8-ethynyl-7-fluoronaphth-1-yl)-4,4,5,5-tetramethyl-1,3,2-dioxoborane, and its mass percentage in the electrolyte is 1.9 wt%.

[0059] Example 3

[0060] The difference between this embodiment and Example 1 is that the functional additive in the prepared electrolyte is adjusted to 1-Boc-4-(4-cyanophenyl)piperazine, and its mass percentage in the electrolyte is 1.4 wt%.

[0061] Example 4

[0062] The difference between this embodiment and Example 1 is that the functional additive in the prepared electrolyte is adjusted to 2-propoxybenzonitrile, with the structural formula [structural formula missing]. The rest is the same as in Example 1.

[0063] Example 5

[0064] The difference between this embodiment and Example 2 is that the functional additive in the prepared electrolyte is adjusted to 2-(8-ethynylnaphth-1-yl)-4,4,5,5-tetramethyl-1,3,2-dioxoborane, with the structural formula [structure not provided]. The rest is the same as in Example 2.

[0065] Example 6

[0066] The difference between this embodiment and Example 3 is that the functional additive in the prepared electrolyte is adjusted to tert-butyl 2-(3-cyanophenyl)acetate, with the structural formula [structure not provided]. The rest is the same as in Example 3.

[0067] Example 7

[0068] The difference between this embodiment and Example 1 is that the content of the functional additive in the prepared electrolyte is adjusted to 0.4 wt%; the rest is the same as in Example 1.

[0069] Example 8

[0070] The difference between this embodiment and Example 3 is that the content of the functional additive in the prepared electrolyte is adjusted to 2.2 wt%; the rest is the same as in Example 3.

[0071] Example 9

[0072] The difference between this embodiment and Example 1 is that tris(trimethylsilane) phosphate is not added to the prepared electrolyte; otherwise, it is the same as Example 1.

[0073] Example 10

[0074] The difference between this embodiment and Example 1 is that the phosphorus additive in the prepared electrolyte is changed to trimethyl phosphate; the rest is the same as in Example 1.

[0075] Example 11

[0076] The difference between this embodiment and Example 2 is that the phosphorus additive in the prepared electrolyte is changed to trimethyl phosphite; the rest is the same as in Example 2.

[0077] Example 12

[0078] The difference between this embodiment and Example 3 is that the phosphorus additive in the prepared electrolyte is changed to triethyl phosphate; the rest is the same as in Example 3.

[0079] Example 13

[0080] The difference between this embodiment and Example 1 is that lithium difluorophosphate is not added to the prepared electrolyte, that is, the lithium salt only contains lithium hexafluorophosphate; the rest is the same as in Example 1.

[0081] Example 14

[0082] The difference between this embodiment and Example 1 is that the prepared electrolyte does not contain fluorinated ethylene carbonate in the organic solvent, and the volume ratio of diethyl carbonate, ethylene carbonate, and methyl ethyl carbonate is 25:20:45; the rest is the same as in Example 1.

[0083] Comparative Example 1

[0084] The difference between this comparative example and Example 1 is that the electrolyte prepared does not contain functional additives, i.e., it does not contain 2-(prop-2-yn-1-yloxy)benzonitrile; otherwise, it is the same as Example 1.

[0085] Comparative Example 2

[0086] The difference between this comparative example and Example 2 is that the electrolyte prepared does not contain functional additives, that is, it does not contain 2-(8-ethynyl-7-fluoronaphth-1-yl)-4,4,5,5-tetramethyl-1,3,2-dioxoborane; otherwise, it is the same as Example 2.

[0087] Comparative Example 3

[0088] The difference between this comparative example and Example 3 is that the electrolyte prepared does not contain functional additives, i.e., it does not contain 1-Boc-4-(4-cyanophenyl)piperazine; otherwise, it is the same as Example 3.

[0089] Comparative Example 4

[0090] The difference between this comparative example and Example 1 is that the functional additives in the prepared electrolyte are adjusted to... The rest is the same as in Example 1.

[0091] Comparative Example 5

[0092] The difference between this comparative example and Example 2 is that the functional additive in the prepared electrolyte is adjusted to 2-(8-ethyl-7-fluoronaphth-1-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborane, with the structural formula [structural formula missing]. The rest is the same as in Example 1.

[0093] Comparative Example 6

[0094] The difference between this embodiment and Example 1 is that the functional additive in the prepared electrolyte is adjusted to 2-propoxybenzonitrile, with the structural formula [structural formula missing]. The rest is the same as in Example 1.

[0095] Test case

[0096] 1. Experimental Construction Method

[0097] The batteries prepared in all the above embodiments and comparative examples were tested at room temperature (25°C) on the LAND battery testing system of Wuhan Jinno Electronics Co., Ltd., with the charge and discharge voltage limited to 2.5V to 4.2V. The specific test methods for performance such as first-efficiency, cycle life, and rate capability are as follows:

[0098] 1) First Coulomb efficiency

[0099] At 25°C, the battery was charged at a constant current and constant voltage of 0.33C to 4.2V, allowed to stand for 10 minutes, and then discharged at a constant current of 0.33C to 2.5V, allowed to stand for 10 minutes. The initial coulombic efficiency of the battery was then calculated.

[0100] Initial coulombic efficiency (%) = Total capacity of battery during initial discharge at 0.33C / Total capacity of battery during initial charge at 0.33C × 100%.

[0101] 2) Capacity retention rate after 1000 cycles at room temperature (1°C) / 1°C

[0102] At 25°C, the battery was charged at a constant current and constant voltage of 1C to 4.2V, with a cutoff current of 0.05C. After resting for 10 minutes, the battery was discharged at a constant current of 1C to 2.5V and then rested for 10 minutes. This constitutes one charge-discharge cycle. The battery was charged and discharged for 1000 cycles using the above method. The capacity retention rate after 1000 charge-discharge cycles at 1C / 1C was calculated.

[0103] The capacity retention rate (%) of a battery after N cycles = (discharge capacity of the Nth cycle / initial discharge capacity) × 100%, where N is the number of battery cycles.

[0104] 3) Capacity retention rate after 1000 cycles at 45℃ (1C / 1C)

[0105] At 45°C, the battery is charged at a constant current and constant voltage of 1C to 4.2V, with a cutoff current of 0.05C. After resting for 10 minutes, the battery is discharged at a constant current of 1C to 2.5V and then rested for 10 minutes. This constitutes one charge-discharge cycle. The battery is charged and discharged for 1000 cycles using the above method. The capacity retention rate after 1000 charge-discharge cycles at 1C / 1C is calculated.

[0106] The capacity retention rate (%) of a battery after N cycles = (discharge capacity of the Nth cycle / initial discharge capacity) × 100%, where N is the number of battery cycles.

[0107] 4) Room temperature 6C rate performance - constant current charge ratio

[0108] At 25℃, the battery was discharged at a constant current rate of 1C to 2.5V, left to stand for 10 minutes, and then charged at a constant current and constant voltage rate of 6C to 4.2V with a cutoff current of 0.05C. After standing for 10 minutes, the constant current charging capacity Q1 and the total constant current and constant voltage charging capacity Q2 were recorded. The constant current charging ratio at the 6C rate was calculated using the following formula: 6C rate charging constant current charging ratio = constant current charging capacity Q1 / total constant current and constant voltage charging capacity Q2 × 100%.

[0109] 2. Experimental Results

[0110] The performance test results of the batteries prepared in all the above embodiments and comparative examples are shown in Table 1.

[0111] Table 1. Performance test results of batteries prepared in the examples and comparative examples.

[0112]

[0113]

[0114] As shown in Table 1, the battery prepared using the electrolyte provided in this application has a high initial efficiency, high capacity retention rate at room temperature and high temperature, and a 6C constant current charge ratio. In particular, the capacity retention rate at room temperature and high temperature and the 6C constant current charge ratio are significantly improved, as detailed in Examples 1 to 14.

[0115] Comparative Examples 1, 2, and 3 all lacked functional additives, resulting in a significant decrease in battery capacity retention and 6C constant current charge ratio during both room temperature and high temperature cycling. This indicates that without functional additives, the performance of the electrolyte will significantly decrease, causing instability of the negative electrode SEI film and failing to effectively alleviate the volume expansion of the silicon-based negative electrode, greatly reducing the stability of the silicon-based negative electrode interface, thus leading to a significant deterioration in the relevant performance of the battery.

[0116] The functional additives in Comparative Examples 4, 5, and 6 lacked certain specific functional groups in their structural formulas, and the molecular weight of the functional additive in Comparative Example 6 was less than 120 g / mol, which caused a decrease in the performance of the electrolyte, and ultimately led to a significant decrease in the battery's capacity retention rate at room temperature and high temperature cycles as well as the 6C constant current charge ratio.

[0117] Further comparison of Examples 1-3 shows that when the functional additive is 2-(8-ethynyl-7-fluoronaphth-1-yl)-4,4,5,5-tetramethyl-1,3,2-dioxoborhexacyclopentane, the battery exhibits better performance. This indicates that when 2-(8-ethynyl-7-fluoronaphth-1-yl)-4,4,5,5-tetramethyl-1,3,2-dioxoborhexacyclopentane acts together with other electrolyte components, it is more beneficial to improve the overall performance of the electrolyte, thus more beneficial to improving the SEI film on the silicon anode and alleviating the volume expansion of the silicon anode, thereby improving the battery's performance.

[0118] Comparing Examples 1 and 4, Examples 2 and 5, Examples 3 and 6, there are some changes in the structural formula of the functional additives in Examples 4, 5 and 6, which have caused changes in the performance of the electrolyte in Examples 4, 5 and 6, ultimately leading to a decrease in the performance of the battery in various aspects.

[0119] Comparing Example 1 and Example 7, and comparing Example 3 and Example 8, the content of functional additives in Example 7 and Example 8 is lower and higher, respectively. This results in the functional additives having limited effect in the electrolyte or affecting the role of other components in the electrolyte, ultimately leading to a decrease in the performance of the batteries in Example 7 and Example 8.

[0120] Comparing Examples 1 and Examples 9-12, Examples 9-12 either did not contain phosphorus-based additives or the types of phosphorus-based additives varied, resulting in changes in various aspects of battery performance, either improving or worsening. This indicates that phosphorus-based additives have a certain effect on further optimizing electrolyte performance, and the selection of phosphorus-based additives also has a certain impact on electrolyte performance. Furthermore, combining different types of functional additives with different types of phosphorus-based additives is more conducive to maximizing the synergistic effect of the electrolyte, and further optimizes various aspects of battery performance.

[0121] Comparing Example 1 and Examples 13-14, Example 13 only contained lithium hexafluorophosphate as the lithium salt, and Example 14 did not contain FEC as the organic solvent. Both of these resulted in a decrease in the battery's constant current charge ratio at 6C. This indicates that the type of lithium salt and organic solvent also affects the overall performance of the electrolyte. Selecting appropriate lithium salt and organic solvent is more conducive to improving the overall performance of the electrolyte and further optimizing the rate performance of the battery.

[0122] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application, but such modifications or substitutions are all within the scope of protection of this application.

Claims

1. An electrolyte, characterized by: The lithium salt, the organic solvent, and the functional additive; The functional additive has a structural formula as shown in the following formula (I): , , or .

2. The electrolyte of claim 1, wherein: The functional additive has a relative molecular weight of 120-700 g / mol. The functional additive has a mass ratio of 0.5-3 wt% in the electrolyte.

3. The electrolyte of claim 1, wherein: The functional additive includes at least one of 2-(8-ethynyl-7-fluoropyren-1-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane and 1-Boc-4-(4-cyanophenyl)piperazine.

4. The electrolyte of claim 3, wherein: The functional additive includes the 2-(8-ethynyl-7-fluoropyren-1-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, and the functional additive has a mass ratio of 0.8-3 wt% in the electrolyte; or, The functional additive includes the 1-Boc-4-(4-cyanophenyl)piperazine, and the functional additive has a mass ratio of 0.8-2 wt% in the electrolyte.

5. The electrolyte of claim 1, wherein: The film-forming additive includes at least one of phosphorus-based additives including trimethylsilane phosphate, triethylsilane phosphate, triisopropylsilane phosphate, trimethyl phosphate, triethyl phosphate, trimethyl phosphite, and diethyl phosphite. The film-forming additive has a mass ratio of 0.2-1 wt% in the electrolyte.

6. The electrolyte of claim 5, wherein: The functional additive includes the 2-(8-ethynyl-7-fluoropyren-1-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, and the film-forming additive includes at least one of the trimethyl phosphate and the diethyl phosphite; or, The functional additive includes the 1-Boc-4-(4-cyanophenyl)piperazine, and the film-forming additive includes at least one of the trimethyl phosphate and the triethyl phosphate.

7. A battery, characterized by: The electrolyte includes the electrolyte according to any one of claims 1-6.

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