Electrolytes and their electrochemical devices and electronic devices

Abstract

The present invention provides an electrolyte solution and an electrochemical device and an electronic device thereof. The electrolyte solution of the present invention includes a compound represented by formula (I), in which R1, R3, and R4 are each independently hydrogen, a cyano group, or a substituted or unsubstituted C 1-12 Hydrocarbon radicals, substituted or unsubstituted C 1-12 Carboxy group, substituted or unsubstituted C 6‐26 Aryl groups, substituted or unsubstituted C 2-12 Amide group, substituted or unsubstituted C 0-12 Phosphate group, substituted or unsubstituted C 0-12 Sulfonyl group, substituted or unsubstituted C 0-12 Siloxy group or substituted or unsubstituted C 0-12 When the boronate group is substituted, the substituents include halogen atoms. The electrolyte of the present invention can improve the high temperature and room temperature cycle performance of the electrochemical device while reducing the internal resistance of the electrochemical device. [Formula 1] JPEG2024505315000024.jpg2557

Description

[Technical Field]

[0001] The embodiments of the present invention relate to the technical field of electrolytes, and for example, to electrolytes and their electrochemical devices and electronic devices. [Background technology]

[0002] Lithium-ion batteries possess significant advantages such as high voltage and large capacity, and their long cycle life and superior safety performance make them promising for a wide range of applications in many fields, including portable electronic devices, electric vehicles, aerospace technology, and the defense industry.

[0003] The electrolyte is the "blood" of a lithium battery, one of the four essential raw materials, and plays a vital role in ion transport within the battery. It facilitates the conduction of lithium ions between the positive and negative electrodes, and significantly impacts the energy density, specific capacity, operating temperature range, cycle life, and safety performance of the lithium battery.

[0004] However, commonly used negative electrode film-forming additives such as VC have the characteristic of exhibiting a protective effect while having high internal resistance, making it difficult to achieve both high-temperature and room-temperature cycle performance and low resistance. [Overview of the project] [Means for solving the problem]

[0005] The following is a summary of the contents described in detail herein. This summary is not intended to limit the scope of protection of the claims.

[0006] The embodiments of the present invention provide an electrolyte, an electrochemical device therefor, and an electronic device. The electrochemical device made from the electrolyte of the present invention exhibits excellent high-temperature and room-temperature cycling performance, while simultaneously having low internal resistance.

[0007] In a first embodiment, the present invention provides an electrolyte. The present invention employs the following technical solution. An electrolytic solution containing a compound represented by formula (I). [Chemical formula] In formula (I), R1, R3, and R4 are each independently hydrogen, a cyano group, a substituted or unsubstituted C 1-12 hydrocarbon group, a substituted or unsubstituted C 1-12 carboxy group, a substituted or unsubstituted C 6‐26 aryl group, a substituted or unsubstituted C 2-12 amide group, a substituted or unsubstituted C 0-12 phosphate group, a substituted or unsubstituted C 0-12 sulfonyl group, a substituted or unsubstituted C 0-12 siloxy group or a substituted or unsubstituted C 0-12 boronate group, and when substituted, the substituent contains a halogen atom; R2 is a substituted or unsubstituted C 1-12 hydrocarbon group, a substituted or unsubstituted C 1-12 carboxy group, a substituted or unsubstituted C 6‐26 aryl group, a substituted or unsubstituted C 2-12 amide group, a substituted or unsubstituted C 0-12 phosphate group, a substituted or unsubstituted C 0-12 sulfonyl group, a substituted or unsubstituted C 0-12 siloxy group or a substituted or unsubstituted C 0-12 boronate group, and when substituted, the substituent contains a halogen atom. Note that the C 1-12 hydrocarbon group means a hydrocarbon group having 1 to 12 carbon atoms.

[0008] By adding the compound represented by formula (I), the electrolytic solution of the present invention can improve the negative electrode film forming property, reduce the usage amount of the negative electrode film forming additive, and achieve the effect of improving the internal resistance. The electrochemical device composed of the electrolytic solution of the present invention has excellent high temperature and room temperature cycle performance, and at the same time has a low internal resistance.

[0009] In the present invention, with respect to the mass of the electrolytic solution, the mass content of the compound represented by the formula (I) is 0.1% to 5%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, 3.1%, 3.2%, 3.3%, 3.4%, 3.5%, 3.6%, 3.7%, 3.8%, 3.9%, 4%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9% or 5%, etc. When the usage amount of the compound represented by the formula (I) is less than 0.1% and too small, the film-forming effect becomes unclear, and when the usage amount of the compound represented by the formula (I) exceeds 5% and is too much, the impedance increases dramatically.

[0010] In a preferred form, with respect to the mass of the electrolytic solution, the mass content of the compound represented by the formula (I) is from 0.3% to 3%.

[0011] In the present invention, the carboxy group contains any one of an ether group, an ester group and a carbonyl group.

[0012] In a preferred form of the present invention, R1, R3, and R4 are each independently hydrogen, a substituted or unsubstituted C 1-12 selected from hydrocarbon groups, and in a preferred embodiment, R2 is selected from substituted or unsubstituted hydrocarbon groups of C <~ 1-12

[0013] In a preferred form, the compound represented by the formula (I) is dimethyl fumarate

Chemical formula

Chemical formula

[0014] In the present invention, the electrolyte is converted to produce HF under conditions of a temperature of 45°C and a hot press pressure of 0.1 MPa, and the mass content of the generated HF relative to the mass of the electrolyte after conversion is 20 ppm to 800 ppm, for example, the mass content of HF is 20 ppm, 30 ppm, 40 ppm, 50 ppm, 60 ppm, 70 ppm, 80 ppm, 90 ppm, 10 ppm These include 0 ppm, 110 ppm, 120 ppm, 130 ppm, 140 ppm, 150 ppm, 160 ppm, 170 ppm, 180 ppm, 190 ppm, 200 ppm, 250 ppm, 300 ppm, 350 ppm, 400 ppm, 450 ppm, 500 ppm, 550 ppm, 600 ppm, 650 ppm, 700 ppm, 750 ppm, and 800 ppm. A small amount of HF is used as a reaction initiator, but if the amount of HF exceeds 800 ppm, the cycle performance of the electrochemical device will decrease and the impedance will increase. Therefore, the compound represented by formula (I) can suppress the acidification of the electrolyte after film formation and can improve the cycle performance of the electrochemical device.

[0015] In a second embodiment, the present invention provides an electrochemical device comprising a negative electrode, a positive electrode, and the electrolyte described in the first embodiment.

[0016] The electrochemical devices of the present invention include any device that causes an electrochemical reaction, and specific embodiments include all of the following: primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery, including lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries, or lithium ion polymer secondary batteries.

[0017] In some embodiments, the electrochemical device of the present invention comprises a positive electrode having a positive electrode active material capable of adsorbing and releasing metal ions, and a negative electrode having a negative electrode active material capable of adsorbing and releasing metal ions.

[0018] The negative electrode comprises a negative electrode active material and a current collector, and the negative electrode active material comprises graphite or silicon carbon negative electrode active material.

[0019] The silicon carbon anode active material is selected from one or more of silicon, silicon oxide compounds, and silicon alloys.

[0020] The negative electrode further comprises a carbon material, the carbon material being selected from one or more of acetylene black, conductive carbon black, carbon fibers, carbon nanotubes, and Ketjenblack.

[0021] In the present invention, the porosity of the negative electrode is 20% to 40%, for example, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, etc. If the porosity of the negative electrode is too low, below 20%, the impedance will increase, affecting the cycle performance. If the porosity of the negative electrode is too high, above 40%, the electrode will become thicker, leading to more side reactions, affecting the cycle and capacity retention performance.

[0022] The porosity of the negative electrode or positive electrode as described herein refers to the porosity of the negative electrode sheet or positive electrode sheet. The formula for calculating the porosity of the electrode sheet is: porosity = 1 - (compressed density / true density).

[0023] The positive electrode comprises a positive electrode active material, which is selected from one or more of lithium iron phosphate, lithium nickel transition metal composite oxide, and lithium nickel manganese composite oxide.

[0024] The electrochemical device further includes a positive electrode, the porosity of which is 20% to 35%, for example, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, etc. If the porosity of the positive electrode is too low, below 20%, the impedance will increase, affecting the cycle performance. If the porosity of the positive electrode is too high, above 35%, the electrode will become thicker, leading to more side reactions, affecting the cycle and capacity retention performance.

[0025] The lithium iron phosphate is either nanolithium iron phosphate or lithium iron phosphate secondary spheres.

[0026] The Dv50 particle size of the aforementioned nanolithium iron phosphate is 0.8 μm to 2.5 μm, for example, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, etc. Dv50 is the particle size corresponding to when the cumulative volume fraction of the positive electrode active material reaches 50%. The Dv50 of the positive electrode active material can be measured with a Malvern 3000 laser particle size analyzer, and the measurement result is obtained by taking the average of three measurements.

[0027] The Dv50 particle size of the lithium iron phosphate secondary spheres is 7 μm to 11 μm, for example, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, etc.

[0028] The general formula for the lithium nickel transition metal composite oxide is Li 1+a Ni x Co y Mn z M b O 2-e X ewherein, in the general formula, -0.2 < a < 0.2, 0.3 ≤ x ≤ 0.95, 0.05 ≤ y ≤ 0.3, 0.03 ≤ z ≤ 0.4, 0 ≤ b ≤ 0.05, 0 ≤ e ≤ 0.1, M is selected from any one or a combination of two or more of Al, Ti, Zr, Nb, Sr, Sc, Sb, Y, Ba, Co, Mn, and X is selected from F and / or Cl. Note that the general formula of the above chemical formula of the lithium nickel transition metal composite oxide is the chemical formula when the SOC (State of Charge) of the battery is 0%.

[0029] As a third aspect, an embodiment of the present invention provides an electronic device including the electrochemical device described in the second aspect.

[0030] The electronic device includes, for example, a notebook computer, a pen-input computer, a mobile computer, an e-book player, a mobile phone, a portable fax machine, a portable copier, a portable printer, stereo headphones, a video recorder, a liquid crystal TV, a portable cleaner, a portable CD player, a mini disk, a transceiver, an electronic notebook, a calculator, a memory card, a portable recorder, a radio, a backup power source, a motor, an automobile, a motorcycle, an assist bicycle, a bicycle, a lighting fixture, a toy, a game machine, a clock, a power tool, a flashlight, a camera, a large household battery, or a lithium ion capacitor, etc., but is not limited thereto.

Advantages of the Invention

[0031] Compared with the related art, the beneficial effects of the embodiments of the present invention are as follows. The electrolyte of the embodiments of the present invention can improve the high-temperature and room-temperature cycle performance of the electrochemical device and can simultaneously reduce the internal resistance of the electrochemical device by adding the compound represented by the formula (I).

[0032] Other aspects of the present invention will become apparent from the following detailed description.

Modes for Carrying Out the Invention

[0033] The technical aspects of the present invention will be further illustrated by the following specific examples. Unless otherwise specified, each of the raw materials of the present invention can be purchased commercially or prepared based on methods common in the art.

[0034] The electrolyte of the present invention contains a compound represented by formula (I). [ka] In formula (I), R1, R3, and R4 are each independently hydrogen, a cyano group, or a substituted or unsubstituted carbon. 1-12 Hydrocarbon groups, substituted or unsubstituted C 1-12 Carboxy group, substituted or unsubstituted C 6‐26 Aryl group, substituted or unsubstituted C 2-12 Amide group, substituted or unsubstituted C 0-12 Phosphate group, substituted or unsubstituted C 0-12 Sulfonyl group, substituted or unsubstituted C 0-12 Siloxy group or substituted or unsubstituted C 0-12 If selected from boronate groups and substituted, the substituents include halogen atoms; R2 is a substituted or unsubstituted C 1-12 Hydrocarbon groups, substituted or unsubstituted C 1-12 Carboxy group, substituted or unsubstituted C 6‐26 Aryl group, substituted or unsubstituted C 2-12 Amide group, substituted or unsubstituted C 0-12 Phosphate group, substituted or unsubstituted C 0-12 Sulfonyl group, substituted or unsubstituted C 0-12 Siloxy group or substituted or unsubstituted C 0-12 If selected from boronate groups and substituted, the substituents include halogen atoms.

[0035] In the present invention, the electrochemical device is a lithium-ion battery, and the lithium-ion battery is a lithium primary battery or a lithium secondary battery, and includes a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and an electrolyte.

[0036] The method for manufacturing the lithium secondary battery of the present invention is as follows.

[0037] (1) Fabrication of LFP (LiFePO4) cathode The positive electrode active material (LiFePO4), polyvinylidene fluoride as a binder, and Super P as a conductive agent were mixed in a weight ratio of 97:2:1. Then, N-methylpyrrolidone (NMP) was added, and the mixture was stirred under the action of a vacuum mixer until it became a uniform, transparent substance to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto aluminum foil. After drying the aluminum foil at room temperature, it was transferred to an oven for further drying, then cold-pressed and cut to obtain a positive electrode (electrode sheet).

[0038] (2)811(LiNi 0.8 Co 0.1 Mn 0.1 O2) Fabrication of the positive electrode Cathode active material (LiNi 0.8 Co 0.1 Mn 0.1 O2), polyvinylidene fluoride as a binder, and Super P as a conductive agent were mixed in a weight ratio of 98:1:1. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under the action of a vacuum mixer until the whole mixture became uniformly transparent to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto aluminum foil. After drying the aluminum foil at room temperature, it was transferred to an oven for drying, then cold-pressed and cut to obtain a positive electrode (electrode sheet).

[0039] (3) Fabrication of graphite anode Synthetic graphite was used as the negative electrode active material, Super P as the conductive agent, sodium carboxymethylcellulose (CMC-Na) as the thickener, and styrene-butadiene rubber (SBR) as the binder. These were mixed in a mass ratio of 96:1:1:2, deionized water was added, and a negative electrode slurry was obtained under the action of a vacuum mixer. The negative electrode slurry was uniformly coated onto the copper foil of the negative electrode current collector. After drying the copper foil at room temperature, it was transferred to an oven for further drying, then cold-pressed and cut to obtain the negative electrode (electrode sheet).

[0040] (4) Preparation of silicon oxide anode Silica and synthetic graphite were mixed in a mass ratio of 1:9 to form the negative electrode active material. This was then mixed with SWCNTs as a conductive agent and polyacrylic acid (PAA) as a binder in a mass ratio of 96:0.2:3.8. Deionized water was added, and a negative electrode slurry was obtained under the action of a vacuum mixer. The negative electrode slurry was uniformly coated onto the copper foil of the negative electrode current collector. After drying the copper foil at room temperature, it was transferred to an oven for further drying, then cold-pressed and cut to obtain the negative electrode (electrode sheet).

[0041] (5) Preparation of the electrolyte In a glove box under an argon atmosphere with a water content of less than 10 ppm, battery-grade ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 3:7 to form an organic solvent. Based on the electrolyte composition shown in the table below, other components were quantitatively added and homogeneously mixed to obtain the electrolyte. In the table, the content of each component is a weight percentage calculated based on the total weight of the electrolyte.

[0042] (6) Fabrication of insulating film A polypropylene film was used as the separator.

[0043] (7) Manufacturing of secondary batteries A 12 μm thick polypropylene film (PP) was used as a separator. The positive electrode, separator, and negative electrode prepared above were sequentially stacked, with the separator placed between the positive and negative electrodes to provide isolation. The assembly was then wrapped in aluminum plastic film, transferred to a vacuum oven, and dried at 120°C. After injecting 3.0 g / Ah of the electrolyte prepared above, the assembly was sealed and allowed to deconstitute, ultimately yielding a 1 Ah soft pack battery (i.e., a lithium-ion battery).

[0044] The chemical conversion conditions for the electrolyte in the ternary battery and lithium iron battery according to the present invention are as follows:

[0045] The process for the formation of the electrolyte in the ternary battery is as follows: After injecting the electrolyte, a hot-press environment of 0.1 MPa was maintained, and the battery was charged to 3.05 V at 0.02 C at 45°C in a static state. After 30 minutes, it was charged to 3.4 V at 0.05 C, and after another 30 minutes, it was charged to 3.75 V at 0.1 C. Then, the airbag was cut off, the battery was vacuum-sealed, and it was left at room temperature for 48 hours to complete the formation of the electrolyte.

[0046] The process for the formation of the electrolyte in the lithium iron battery is specifically as follows: After injecting the electrolyte, a hot-press environment of 0.1 MPa was maintained, and the battery was charged at 0.02C for 17 minutes at 45°C in a static state. After letting it stand for 5 minutes, it was charged to 0.3Ah at 0.02C. Then, the airbag was cut off, the battery was vacuum-sealed, and it was left at room temperature for 48 hours to complete the formation of the electrolyte.

[0047] In the embodiments of the present invention, the following five compounds are used as compounds represented by formula (I): Compound 1 is methyl methacrylate, Compound 2 is dimethyl fumarate, Compound 3 is dimethyl maleate, Compound 4 is 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, and Compound 5 is vinyl methacrylate.

[0048] The secondary battery of the present invention can be tested by the following method.

[0049] 1. Secondary battery cycle test The battery is repeatedly charged and discharged at a current of 1C within a specified potential range in an oven at a specified temperature (room temperature 25°C or high temperature 45°C). The discharge capacity of each cycle is recorded, and the test is terminated when the battery capacity reaches 80% of the capacity of the first cycle.

[0050] 2. DC Resistance (DCR) Test of Rechargeable Batteries At a specified temperature, when the battery is discharged to 50% SOC (state of charge reflecting the battery's remaining capacity) with a current of 1C, the current is increased to 4C and maintained for 30 seconds. The difference between the updated stable voltage and the original voltage is detected, and the ratio of this value to the 3C current value represents the battery's DC resistance. The DCR test result performed after the battery is first fully charged is the battery's initial DCR.

[0051] 3. High-temperature storage capacity retention rate test of secondary batteries After fully charging the secondary batteries, they were left in a constant temperature bath at 60°C. After 30 days, they were removed, cooled to room temperature, and then discharged at a rate of 0.33C until the cutoff voltage was reached. The percentage of the discharged capacity relative to the initial discharge capacity was then compared. Specifically, the cutoff voltages for charging and discharging were as follows: LFP-graphite: 2.5V~3.65V, 811-graphite: 2.8V~4.2V, and 811-silica: 2.8V~4.25V.

[0052] Table 1-1 shows the electrolyte compositions of Examples 1-7 and Comparative Example 1 of the present invention. Lithium-ion batteries were fabricated using the above method and their performance was tested. The test results are shown in Table 1-2.

[0053] [Table 1-1]

[0054] [Table 1-2]

[0055] As can be seen from the data in Table 1-2, when lithium iron phosphate is used as the positive electrode and graphite is used as the negative electrode, the electrolyte with the compound represented by formula (I) of the present invention added, compared to Comparative Example 1 which did not have the compound represented by formula (I) added, showed that when the amount of addition was 0.1 to 5%, the number of 80% cycles at room temperature for Examples 1 to 7 was 1021 to 2023, the number of 80% cycles at high temperature was 887 to 1810, the initial DCR was 98 to 109 mOhm (milliohms), and the storage capacity retention rate at 60°C for 30 days was 91 to 98%. All of these test results, to varying degrees, were superior to those of Comparative Example 1. In particular, when the amount of compound represented by formula (I) added was 0.3 to 4%, the number of 80% cycles at room temperature in Examples 2 to 5 was 1250 to 2023, the number of 80% cycles at high temperature was 1119 to 1810, the initial DCR was 98 mOhm to 105 mOhm, and the storage capacity retention rate at 60°C for 30 days was 95% to 98%. The test results were significantly better than those of Comparative Example 1, which did not contain the compound, indicating an improvement in the electrochemical properties of the electrolyte. This is thought to be because the addition of the compound represented by formula (I) improves the film formation properties of the negative electrode surface and optimizes the internal resistance. Furthermore, it is presumed that the addition of the compound represented by formula (I) creates a synergistic effect with the electrode sheet, thereby improving the high-temperature, room-temperature cycle performance, and high-temperature storage performance of the lithium battery, and enabling the achievement of lower internal resistance.

[0056] The electrolyte compositions of Examples 8 to 10 of the present invention are shown in Table 2-1. Lithium-ion batteries were fabricated using the above method and their performance was tested. The test results are shown in Table 2-2.

[0057] [Table 2-1]

[0058] [Table 2-2]

[0059] As can be seen from the data in Table 2-2, even when the combination of compounds represented by formula (I) added to the electrolyte was different, the electrochemical devices all exhibited excellent high-temperature, room-temperature cycling performance, and high-temperature storage performance, while simultaneously exhibiting low internal resistance.

[0060] Example 11 The lithium iron phosphate cathode material in both this embodiment and Example 3 is lithium iron phosphate secondary spheres. The only difference from Example 3 is that the Dv50 particle size of the lithium iron phosphate secondary spheres in this embodiment is 7 μm, while the Dv50 particle size of the lithium iron phosphate secondary spheres in Example 3 is 9 μm. The electrolyte composition and other compositions are the same as in Example 3.

[0061] Example 12 The lithium iron phosphate cathode material in both this embodiment and Example 3 is lithium iron phosphate secondary spheres. The only difference from Example 3 is that the Dv50 particle size of the lithium iron phosphate secondary spheres in this embodiment is 11 μm, while the Dv50 particle size of the lithium iron phosphate secondary spheres in Example 3 is 9 μm. The electrolyte composition and other compositions are the same as in Example 3.

[0062] Performance tests were conducted on the lithium-ion batteries fabricated in Examples 11 and 12, and the test results are shown in Table 3-1.

[0063] [Table 3-1]

[0064] As can be seen from the data in Table 3-1, the negative electrode of the present invention uses graphite, and the positive electrode uses lithium iron phosphate secondary spheres, with a Dv50 particle size of 7 μm to 11 μm. As a result, the synergistic effect between the compound in the electrolyte and the electrode sheet was further improved, resulting in better high-temperature, room-temperature cycle performance and high-temperature storage performance of the fabricated battery, and further lowering of the internal resistance.

[0065] Example 13 The difference between this embodiment and Example 3 is that nanolithium iron phosphate is used as the positive electrode, and the Dv50 particle size of the nanolithium iron phosphate is 0.8 μm, while the electrolyte composition and other compositions are the same as in Example 3.

[0066] Example 14 The difference between this embodiment and Example 3 is that nanolithium iron phosphate is used as the positive electrode, and the Dv50 particle size of the nanolithium iron phosphate is 1.6 μm, while the electrolyte composition and other compositions are the same as in Example 3.

[0067] Example 15 The difference between this embodiment and Example 3 is that nanolithium iron phosphate is used as the positive electrode, and the Dv50 particle size of the nanolithium iron phosphate is 2.5 μm, while the electrolyte composition and other compositions are the same as in Example 3.

[0068] Performance tests were conducted on the lithium-ion batteries prepared in Examples 13-15, and the test results are shown in Table 3-2.

[0069] [Table 3-2]

[0070] As can be seen from the data in Table 3-2, the negative electrode of the present invention uses graphite, and the positive electrode uses nanolithium iron phosphate, with a Dv50 particle size of 0.8 μm to 2.5 μm. This further improved the synergistic effect between the compound in the electrolyte and the electrode sheet, resulting in better high-temperature, room-temperature cycle performance and high-temperature storage performance of the lithium battery, and further lowering the internal resistance.

[0071] Example 16 The negative electrode material in both this embodiment and Example 3 is graphite. The only difference between this embodiment and Example 3 is that the porosity of the graphite in this embodiment is 20%, while the porosity of the graphite in Example 3 is 30%. The positive electrode, electrolyte composition, and other compositions are the same as in Example 3.

[0072] Example 17 The negative electrode material in both this embodiment and Example 3 is graphite. The only difference from Example 3 is that the porosity of the graphite in this embodiment is 40%, while the positive electrode, electrolyte composition, and other compositions are the same as in Example 3.

[0073] Performance tests were conducted on the lithium-ion batteries fabricated in Examples 16-17, and the test results are shown in Table 4.

[0074] [Table 4]

[0075] As can be seen from the data in Table 4, the negative electrode of the present invention uses graphite. When the porosity of the graphite material is 20% to 40%, the number of 80% cycles at room temperature is 1033 to 1826, the number of 80% cycles at high temperature is 989 to 1607, the initial DCR is 99 mOhm to 113 mOhm, and the storage capacity retention rate at 60°C for 30 days is 92% to 96%. In particular, when the porosity of the graphite material is 30% to 40%, the number of 80% cycles at room temperature is 1749 to 1826, and the number of 80% cycles at high temperature is 1449 to 1607. As can be seen from the above, by adding the compound represented by formula (I) to the electrolyte and controlling the porosity of the graphite material, the synergistic effect between the compound in the electrolyte and the electrode sheet is further improved, resulting in better high-temperature, room-temperature cycle performance and high-temperature storage performance of the lithium battery, and further lowering the internal resistance.

[0076] The electrolyte compositions of Examples 18-19 and Comparative Examples 2-3 are shown in Table 5-1. Lithium-ion batteries were fabricated using the above method, and their performance was tested. The test results are shown in Table 5-2.

[0077] [Table 5-1]

[0078] [Table 5-2]

[0079] As can be seen from the data in Table 5-2, compared to Comparative Example 3, which did not contain the compound represented by formula (I), the electrolytes of Examples 18 and 19 of the present invention showed improved copolymerization of the negative electrode film-forming additive, improved protection of the negative electrode, and improved internal resistance due to the addition of the compound represented by formula (I). The electrochemical devices fabricated from the electrolyte of the present invention exhibited excellent high-temperature and room-temperature cycling performance, while simultaneously having low internal resistance.

[0080] Example 20 The difference between this embodiment and Example 18 is the porosity of the cathode material; the porosity of 811 in this embodiment is 20%, while the porosity of 811 in Example 18 is 28%. Otherwise, it is the same as Example 18.

[0081] Example 21 The difference between this embodiment and Example 18 is the porosity of the cathode material; the porosity of 811 in this embodiment is 35%, while the porosity of 811 in Example 18 is 28%. Otherwise, it is the same as Example 18.

[0082] Performance tests were conducted on the lithium-ion batteries fabricated in Examples 20-21, and the test results are shown in Table 6.

[0083] [Table 6]

[0084] As can be seen from the data in Table 6, the positive electrode of the present invention employs 811, and by controlling the porosity of the positive electrode to 20% to 35%, the synergistic effect between the compound in the electrolyte and the electrode sheet is further improved, resulting in better high-temperature, room-temperature cycle performance and high-temperature storage performance of the lithium battery, and further lowering of the internal resistance. More preferably, the controlled porosity of the positive electrode is 20% to 28%.

[0085] The electrolyte compositions for Example 22, Comparative Example 4, and Examples 23-24 are shown in Table 7-1. Lithium-ion batteries were fabricated using the above method, and their performance was tested. The test results are shown in Table 7-2.

[0086] [Table 7-1]

[0087] [Table 7-2]

[0088] As can be seen from the data in Table 7-2, compared to Comparative Example 4, which uses 811 for the positive electrode and carbon silicon for the negative electrode and does not add the compound represented by formula (I), the electrolytes of Examples 23 and 24 of the present invention, by adding the compound represented by formula (I), can copolymerize with the negative electrode film-forming additive, improving negative electrode film formation and achieving the effect of improving internal resistance. The electrochemical devices fabricated using this electrolyte exhibited good high-temperature and room-temperature cycling performance, while simultaneously having low internal resistance.

[0089] In contrast to Example 18, which used graphite as the negative electrode, Examples 22-24 used a carbon silicon-based negative electrode and, due to the synergistic effect of adding the compound represented by formula (I), were able to improve the battery's capacity performance, further improving energy density and proving more effective in meeting the room temperature and high-temperature cycle requirements of the battery.

[0090] Example 25 The difference between this example and Example 24 is the SiO in silicon carbon. x The difference lies in the SiO content in the carbon silicon of Example 25. x The content is 1%, SiO in carbon silicon of Example 24 x The content is 10%, and the rest is the same as in Example 24.

[0091] Example 26 The difference between this example and Example 24 is the SiO in carbon silicon.x The content is 5%, and otherwise it is the same as in Example 24.

[0092] Example 27 The difference between this example and Example 24 is the SiO in carbon silicon. x The content is 15%, and otherwise it is the same as in Example 24.

[0093] Example 28 The difference between this example and Example 24 is the SiO in carbon silicon. x The content is 20%, and otherwise it is the same as in Example 24.

[0094] The lithium-ion batteries produced using the above-described methods in Examples 24-28 were tested for battery performance. The test results are shown in Table 8.

[0095] [Table 8]

[0096] As can be seen from the data in Table 8, carbon silicon is used for the negative electrode, SiO x By having a content of 1-20%, the synergistic effect between the compound in the electrolyte and the electrode sheet is further enhanced, significantly increasing the energy density of the lithium battery. At the same time, it maintains better high-temperature, room-temperature cycle performance and high-temperature storage performance, meeting the needs of applications requiring high energy density and low cycles.

[0097] Comparative Example 5 The only difference between Comparative Example 5 and Example 3 is the HF content; Comparative Example 5 has an HF content of 5000 ppm, while Example 3 has an HF content of 100 ppm.

[0098] In Comparative Example 5, a lithium-ion battery was fabricated using the above method, and its performance was tested. The test results are shown in Table 9.

[0099] [Table 9]

[0100] As can be seen from the data in Table 9, in Comparative Example 5, where the HF content in the electrolyte was too high, the number of 80% cycles at room temperature decreased from 1826 in Example 3 to 431, the number of 80% cycles at high temperature decreased from 1607 in Example 3 to 266, the initial DCR changed from 99 mOhm in Example 3 to 122 mOhm, and the 30-day storage capacity retention rate at 60°C decreased from 96% in Example 3 to 53%, resulting in a significant decrease in the overall performance of the battery.

[0101] While the present invention has been described in detail by the above examples, the present invention is not limited to the above detailed technical settings and processes, that is, it is not the case that the present invention can only be implemented based on the above detailed technical settings and processes. It will be apparent to those skilled in the art that any improvements to the present invention, equivalent substitutions of each raw material in the product of the present invention, addition of auxiliary components, selection of specific methods, etc., are all within the scope of protection and disclosure of the present invention.

[0102] Although preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical proposal of the present invention, and all of these simple modifications fall within the scope of protection of the present invention.

[0103] Furthermore, the specific technical features described in the above-mentioned specific embodiments can be combined as appropriate, as long as they do not contradict each other. To avoid unnecessary redundancy, the possible combinations of the present invention will not be specifically described.

[0104] Furthermore, various embodiments of the present invention can be combined in any way as long as they do not contradict the spirit of the invention, and such combinations should also be considered as part of the disclosures of the present invention.

Claims

1. An electrolyte comprising a mixture of methyl methacrylate and 1,1,1,3,3,3-hexafluoroisopropyl methacrylate, wherein the mass content of the mixture is 1% to 5% of the mass of the electrolyte.

2. The electrolyte according to claim 1, wherein the mass content of the mixture is 1% to 3% relative to the mass of the electrolyte.

3. The electrolyte according to claim 1 or 2, wherein the electrolyte is converted to produce HF under conditions of a temperature of 45°C and a hot press pressure of 0.1 MPa, and the mass content of the produced HF is 20 to 800 ppm relative to the mass of the electrolyte after conversion.

4. An electrochemical device comprising a negative electrode, a positive electrode, and an electrolyte according to any one of claims 1 to 3.

5. The negative electrode includes a negative electrode active material and a current collector. The negative electrode active material includes graphite or silicon carbon negative electrode active material. The electrochemical device according to claim 4, wherein the silicon carbon anode active material is selected from one or more of silicon, silicon oxide compounds, and silicon alloys.

6. The electrochemical device according to claim 5, wherein the porosity of the negative electrode is 20% to 40%.

7. The positive electrode includes a positive electrode active material, The electrochemical device according to any one of claims 4 to 6, wherein the positive electrode active material is selected from one or more of lithium iron phosphate, lithium nickel transition metal composite oxide, and lithium nickel manganese composite oxide having a spinel structure.

8. The electrochemical device according to claim 7, wherein the porosity of the positive electrode is 20% to 35%.

9. The positive electrode active material is lithium iron phosphate, and the lithium iron phosphate is nanolithium iron phosphate or lithium iron phosphate secondary spheres. The Dv50 particle size of the aforementioned lithium iron phosphate nanoparticles is 0.8 to 2.5 μm. The electrochemical device according to claim 8, wherein the Dv50 particle size of the lithium iron phosphate secondary sphere is 7 to 11 μm.

10. An electronic device comprising an electrochemical device according to any one of claims 4 to 9.

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