Electrochemical device and electric equipment

Abstract

The invention relates to an electrochemical device and electric equipment. The electrochemical device is characterized in that the electrochemical device comprises a positive electrode, a negative electrode and an electrolyte, the electrolyte comprises a first additive, a second additive, a third additive and an initiator, the first additive comprises fluoroethylene carbonate, the second additive comprises a fluorine-containing unsaturated chain compound, and the three additives comprise an acrylate compound containing a plurality of double bonds. After the electrochemical device is manufactured, the content of the cobalt element in the negative electrode active layer is X ppm; and the electrochemical device satisfies (A + B + C) / X > = 0.001, where 1 < = A < = 40, 0.5 < = B < = 5, 0.5 < = C < = 5, and 0 < X < = 2000. According to the scheme provided by the invention, the problems of electrolyte decomposition, silicon negative electrode pulverization and the like caused by the cobalt element can be reduced through the synergistic effect of multiple additives, and synchronous optimization of the high-temperature cycle life and the low-temperature discharge efficiency is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to an electrochemical device and a power utilization device. BACKGROUND

[0002] As a representative product of modern energy storage technology, lithium-ion batteries have dominated the field of portable electronic devices and new energy vehicles due to their significant energy density advantage, excellent self-discharge characteristics and reliable cycle life. In the battery system, the presence of cobalt element in the negative active material can affect the cycle stability of the battery through various chemical pathways. For example, 1. Under low temperature working conditions, cobalt ions have strong diffusion ability in the electrolyte, which can easily coordinate with organic solvents, causing a decrease in electrolyte flowability and a decrease in interfacial ion conduction efficiency. 2. Under high temperature conditions, cobalt elements can promote the oxidation reaction of ester-based electrolyte, leading to the accumulation of gas byproducts and the non-uniform growth of the solid electrolyte interface layer (SEI). 3. During the electrochemical cycle process, the dissolved cobalt ions will diffuse to the negative electrode side, affecting the structural integrity of the negative electrode material through lattice intercalation or surface precipitation.

[0003] In related technologies, the performance of the battery is improved by adding functional additives to the electrolyte. However, when the content of the functional additive is high, the viscosity of the electrolyte increases, leading to deterioration of the low-temperature rate performance and an increase in the amount of gas produced at high temperature. Therefore, a single functional additive has defects in terms of low-temperature ion conduction or high-temperature gas production, and cannot simultaneously optimize the high-temperature and low-temperature performance of the battery. SUMMARY

[0004] To solve or partially solve the problems in the related art, the present application provides an electrochemical device and a power utilization device, which can reduce the problems of electrolyte decomposition and silicon negative electrode pulverization caused by cobalt elements through the synergistic effect of multiple additives, and simultaneously optimize the high-temperature cycle life and low-temperature discharge efficiency.

[0005] The first aspect of the present application provides an electrochemical device, comprising a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte comprises a first additive, a second additive and a third additive, the first additive comprises fluoroethylene carbonate, and the mass percentage content of the first additive in the electrolyte is A%; the second additive comprises a fluorine-containing unsaturated chain compound, and the mass percentage content of the second additive in the electrolyte is B%; the third additive comprises a multi-double-bond-containing acrylate compound, and the mass percentage content of the third additive in the electrolyte is C%; the negative electrode comprises a negative electrode current collector and a negative electrode active layer coated on at least one side of the negative electrode current collector, after the completion of the preparation of the electrochemical device, the content of cobalt element in the negative electrode active layer is X ppm; and the electrochemical device satisfies the following relationship: (A+B+C) / X≥0.001 Where 1≤A≤40, 0.5≤B≤5, 0.5≤C≤5, and 0<X≤2000.

[0006] As an optional embodiment, the electrochemical device satisfies: (A+B+C) / X≥0.004.

[0007] As an optional embodiment, the electrochemical device also satisfies: 0.1 ≤ A / (B+C) ≤ 40.

[0008] As an optional embodiment, the electrochemical device also satisfies: 0.5 ≤ A / (B+C) ≤ 20.

[0009] As an optional embodiment, the fluorine-containing unsaturated chain compound includes at least one of compounds having the following structural formulas:

[0010] Structural Formula 1

[0011] Structural Formula 2 R1 is an alkane group containing 1 to 3 carbon atoms, or a fluorine atom or a hydrogen atom, and R2 and R3 are alkane groups containing 1 to 20 fluorine atoms.

[0012] As an optional embodiment, the fluorine-containing unsaturated chain compound includes at least one of the following compounds:

[0013] Compound 1

[0014] Compound 2

[0015] Compound 3

[0016] Compound 4

[0017] Compound 5

[0018] Compound 6

[0019] Compound 7

[0020] Compound 8

[0021] Compound 9.

[0022] As an optional embodiment, the acrylate compound containing multiple double bonds includes at least one of the following compounds:

[0023] compound a

[0024] Compound b

[0025] Compound C

[0026] compound d

[0027] compound e

[0028] compound f

[0029] compound g

[0030] compound h

[0031] Compound i.

[0032] As an optional embodiment, the electrochemical device also satisfies: 0.1 ≤ B / C ≤ 10.

[0033] As an optional embodiment, the electrochemical device also satisfies: 0.2 ≤ B / C ≤ 5.

[0034] As an optional embodiment, the positive electrode active material comprises a transition metal lithium oxide, wherein the chemical formula of the transition metal lithium oxide is Li. （1+x） Ni y Co z M (1-y-z)O2, wherein -0.1≤x≤1; 0≤y≤1, 0≤z≤1, and 0≤y+z≤1; wherein M is selected from one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr; and / or, the negative electrode active layer comprises a negative electrode active material, wherein the negative electrode active material comprises at least one of graphite and silicon carbide.

[0035] A second aspect of this application provides an electrical device, including the aforementioned electrochemical device.

[0036] The technical solution provided in this application may include the following beneficial results: This application limits (A+B+C) / X to ≥ 0.001, with 1 ≤ A ≤ 40, 0.5 ≤ B ≤ 5, 0.5 ≤ C ≤ 5, and 0 < X ​​≤ 2000. Based on the measured value of X and (A+B+C) / X ≥ 0.001, the values ​​of A, B, and C are adjusted accordingly. This allows the ternary additive system (fluoroethylene carbonate / fluorinated unsaturated chain compounds / acrylate compounds containing multiple double bonds) to synergistically construct a composite SEI interface: a rigid LiF phase enhances thermal stability, a gel network enables self-healing, and a cross-linked structure provides dual anchoring of cobalt ions. This design simultaneously solves the problems of low-temperature conduction and high-temperature gas generation, effectively suppressing electrolyte decomposition and silicon anode pulverization caused by cobalt ion migration, enabling the battery to maintain excellent cycle performance in a range from low temperatures (e.g., -20°C) to high temperatures.

[0037] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Detailed Implementation

[0038] The embodiments of this application will now be described in more detail. It should be understood that this application may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to make this application more thorough and complete, and to fully convey the scope of this application to those skilled in the art.

[0039] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0040] It should be understood that although the terms "first," "second," "third," etc., may be used in this application to describe various information, this information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0041] In silicon-based anode battery systems, the presence of cobalt in the anode active material affects the battery's cycle stability through various chemical pathways. For example: 1. At low temperatures, cobalt ions have strong diffusion capabilities in the electrolyte and easily coordinate with organic solvents, leading to decreased electrolyte fluidity and reduced interfacial ion conduction efficiency. 2. At high temperatures, cobalt promotes the oxidation reaction of ester-based electrolytes, resulting in the accumulation of gaseous byproducts and non-uniform growth of the solid electrolyte interphase (SEI). 3. During electrochemical cycling, dissolved cobalt ions diffuse towards the anode side, affecting the structural integrity of the silicon-based material through lattice embedding or surface deposition. Related technologies improve battery performance by adding functional additives to the electrolyte. However, higher levels of functional additives increase electrolyte viscosity, leading to deterioration in low-temperature rate performance and increased gas generation during high-temperature storage. Therefore, single functional additives have limitations in low-temperature ion conduction or high-temperature gas generation, and cannot simultaneously optimize both high-temperature and low-temperature battery performance.

[0042] To address the aforementioned issues, this application provides an electrochemical device that, through the synergistic effect of multiple additives, reduces problems such as electrolyte decomposition and silicon anode pulverization caused by cobalt, thereby achieving simultaneous optimization of high-temperature cycle life and low-temperature discharge efficiency.

[0043] This application provides an electrochemical device, including a positive electrode, a negative electrode, and an electrolyte. The electrolyte includes a first additive, a second additive, a third additive, and an initiator. The first additive includes fluoroethylene carbonate, and the mass percentage of the first additive in the electrolyte is A. The second additive includes a fluorinated unsaturated chain compound, and the mass percentage of the second additive in the electrolyte is B. The third additive includes an acrylate compound containing multiple double bonds, and the mass percentage of the third additive in the electrolyte is C. The negative electrode includes a negative electrode current collector and a negative electrode active layer coated on at least one side of the negative electrode current collector. After the electrochemical device is fabricated, the cobalt content in the negative electrode active layer is X%. The electrochemical device satisfies the following relationship: (A+B+C) / X≥0.001 Where 1≤A≤40, 0.5≤B≤5, 0.5≤C≤5, and 0<X≤2000.

[0044] In this embodiment, the raw materials for preparing the negative electrode active layer do not contain cobalt. After the electrochemical device is manufactured, the cobalt in the negative electrode active layer may be introduced from the positive electrode, separator, substrate, and manufacturing process. For example, during battery manufacturing, pre-cycle charging and discharging is performed during the formation stage. This stage causes cobalt in the positive electrode active material to dissolve into the negative electrode, increasing the cobalt content in the negative electrode active layer. Cobalt accelerates performance degradation in the battery system through multiple mechanisms: 1. At low temperatures, cobalt ions coordinate with the electrolyte, reducing fluidity; 2. At high temperatures, it catalyzes electrolyte oxidation, producing gaseous byproducts; 3. During cycling, dissolved cobalt migrates to the negative electrode, damaging the structure of the negative electrode material, such as silicon, through lattice insertion / surface precipitation, interfering with lithium ion insertion / extraction, and exacerbating volume expansion stress, leading to active material pulverization and SEI film failure. These cobalt degradation effects significantly increase the battery capacity decay rate under wide temperature range conditions.

[0045] The embodiments of this application utilize three additives to synergistically improve the cobalt degradation effect: The first additive includes fluoroethylene carbonate (FEC), which improves the battery performance of cobalt-containing negative electrode active layers through a triple mechanism: ① Fluorine atoms induce the formation of a LiF-rich inorganic SEI film, inhibiting cobalt dissolution and its catalytic reduction side reactions at the interface; ② F-Li bonds enhance the mechanical strength of the SEI, alleviating film rupture caused by the volume expansion of the silicon negative electrode; ③ The fluorinated layer reduces interfacial impedance and improves discharge efficiency at low temperatures, such as -20°C. However, a higher FEC content leads to increased electrolyte viscosity, resulting in increased gas generation during high-temperature storage.

[0046] In this embodiment of the application, 1≤A≤40.

[0047] When the content of the first additive in the electrolyte is less than 1%, insufficient LiF phase formation leads to SEI film defects, exacerbates cobalt catalytic side reactions, reduces low-temperature discharge efficiency, and accelerates cycle decay. Conversely, when the content of the first additive in the electrolyte exceeds 40%, the high viscosity of the electrolyte hinders ion migration, deteriorates low-temperature rate performance, and excessive FEC decomposes at high temperatures, generating CO / F2 gas, causing battery bulging and SEI structure damage. Furthermore, an excessively thick fluoride layer hinders lithium-ion transport, thus reducing high-temperature cycle stability. Therefore, the embodiments of this application limit the mass percentage of the first additive in the electrolyte to 1%~40%, achieving a balance between the construction of the LiF protective layer and the rheological properties of the electrolyte.

[0048] In this embodiment, the mass percentage of the first additive in the electrolyte is A%, and A can be 1, 5, 10, 20, 30, 40, or any value within the above-mentioned range. This application does not limit this value.

[0049] The second additive includes fluorinated unsaturated chain compounds. These compounds undergo electrochemical polymerization on the electrode surface via unsaturated bonds, such as carbon-carbon double bonds, under the action of an initiator, and crosslink with acrylate compounds containing multiple double bonds to form a three-dimensional gel network structure. The "self-healing" property of the three-dimensional gel network structure (enhanced polymer chain segment movement at increased temperature, automatically filling SEI film cracks) can improve the high-temperature storage performance of the battery. However, high fluorine content leads to an excessively thick interfacial layer, increasing the lithium-ion migration barrier. Simultaneously, gel network shrinkage restricts ion transport at low temperatures, resulting in a significant decrease in discharge efficiency at low temperatures, such as -20°C.

[0050] In this embodiment, 0.5 ≤ B ≤ 5.

[0051] When the content of the second additive in the electrolyte is less than 0.5%, the gel network coverage is insufficient, failing to effectively suppress SEI damage caused by high-temperature gas generation from the FEC, and the cobalt ion blocking ability is weakened, leading to a decline in high-temperature storage and cycling performance. Conversely, when the content of the second additive in the electrolyte exceeds 5%, the excessively high crosslinking density increases the electrolyte viscosity, hindering lithium ion migration; simultaneously, the excessively thick polymer interface layer increases ion transport resistance, exacerbating high-temperature polarization and worsening cycling performance. Therefore, the embodiments of this application limit the mass percentage of the second additive in the electrolyte to 0.5%~5%, achieving a balance between self-repair function and ion conduction efficiency.

[0052] In this embodiment, the mass percentage of the second additive in the electrolyte is B%, and B can be 0.5, 1, 2, 3, 4, 5, or any value within the above-mentioned range. This application does not limit this value.

[0053] The third additive includes acrylate compounds containing multiple double bonds, which can construct a three-dimensional cross-linked network SEI film at the electrode interface through free radical polymerization under the action of an initiator. The ester groups (-COOR) in the compound can chemically anchor electrolyte decomposition products, forming a dense and stable interfacial layer, thereby improving high-temperature cycle life. This structure inhibits cobalt dissolution through a triple mechanism: ① carbonyl oxygen forms a stable coordination with Co; ② the nanoscale network pore size physically blocks cobalt ion migration; ③ it reduces the probability of electron tunneling. However, the high cross-linking density of the three-dimensional cross-linked network structure increases the activation energy for lithium ion migration, leading to a decrease in discharge efficiency at low temperatures, such as -20°C.

[0054] In this embodiment, 0.5 ≤ C ≤ 5.

[0055] When the concentration of the third additive in the electrolyte is below 0.5%, insufficient cross-linking density leads to sparse cobalt anchoring points, which cannot effectively suppress cobalt catalytic side reactions. Furthermore, the excessively large network pores make it difficult to block cobalt diffusion, resulting in deterioration of high-temperature storage and cycling performance. Conversely, when the concentration of the third additive in the electrolyte exceeds 5%, excessive cross-linking increases the rigidity of the SEI film, blocks ion migration channels leading to intensified polarization, and stress concentration induces microcracks, which in turn form electrolyte permeation channels, accelerating interface degradation. Therefore, the embodiments of this application limit the mass percentage of the third additive in the electrolyte to 0.5%~5%, balancing chemical anchoring and ion transport to form a gradient buffered composite interface layer.

[0056] In the embodiments of this application, the mass percentage of the third additive in the electrolyte is C%, and C can be 0.5, 1, 2, 3, 4, 5, or any value within the above-defined range. This application does not limit this value.

[0057] Therefore, this application embodiment achieves synergistic optimization through the complementary functions and content limitation of three additives: the LiF-rich SEI film constructed by the first additive and the gel network formed by the second additive together constitute a "rigid-flexible" composite interface layer. The rigid LiF phase provides high-temperature stability, while the dynamic cross-linking characteristics of the gel network compensate for the high-temperature gas generation defect of FEC; the three-dimensional cross-linking network of the third additive further enhances the cobalt ion anchoring ability, and its nanoscale pore size synergistically blocks cobalt migration with the gel network. In terms of temperature adaptability, the improved low-temperature conductivity effect of the first additive offsets the ion migration barriers caused by the second and third additives, while the "self-healing" characteristics of the second additive and the chemical coordination of the third additive maintain the integrity of the high-temperature interface. The final synergistic effect of the three additives is as follows: the LiF phase, gel network, and three-dimensional cross-linking network together form a multi-level barrier, suppressing cobalt side reactions, significantly improving high-temperature performance, while maintaining high discharge efficiency at -20℃ by controlling the FEC content.

[0058] Furthermore, the inventors discovered that when the sum of the contents of the first, second, and third additives is too low relative to the cobalt content (i.e., (A+B+C) / X < 0.001), insufficient additive content leads to the failure of the composite SEI interface construction, triggering a cascade of destructive effects on cobalt ion migration. First, insufficient FEC content results in incomplete formation of the LiF rigid phase, failing to effectively suppress cobalt dissolution and its catalytic electrolyte decomposition side reactions. Second, the reduced coverage of the gel network formed by the polymerization of fluorinated unsaturated chain compounds weakens the self-healing ability at high temperatures and reduces the anchoring points of the fluorinated layer for cobalt ions, causing cobalt ions to penetrate the interface and diffuse towards the silicon anode. Simultaneously, insufficient density of the three-dimensional cross-linked network formed by acrylate compounds containing multiple double bonds weakens its triple cobalt barrier mechanism: reduced coordination sites cause chemical anchoring failure, increased pore size leads to decreased physical barrier ability, and increased electron tunneling probability exacerbates Co. 2+ Reduction deposition allows uninhibited cobalt ions to disrupt the integrity of the silicon structure through lattice insertion, catalyzing non-uniform SEI growth and inducing synergistic degradation of silicon particle pulverization and hindered lithium-ion insertion / extraction. This systemic failure manifests as increased gas generation at high temperatures, a surge in low-temperature impedance, and rapid decay of cycle capacity.

[0059] In this embodiment, 0 < X ​​≤ 2000.

[0060] X represents the cobalt content in the negative electrode active layer after the electrochemical device is fabricated. Different application scenarios and fabrication systems result in different measured values ​​of X for the fabricated batteries. This application embodiment, by setting 0 < X ​​≤ 2000, can simulate different application scenarios and fabrication systems for the battery, making the collaborative mechanism of this application embodiment applicable to a wider range of scenarios.

[0061] The method for testing the cobalt content in the negative electrode active layer is as follows: Take 5 mg of the negative electrode active layer from the completed battery, add 3 mL of concentrated sulfuric acid and 3 mL of concentrated nitric acid in sequence, heat to 180°C until the solution is clear and transparent, cool, add water to make up to 50 mL, send the sample for testing, and use an ICP (Inductively Coupled Plasma Emission Spectrometer) to test the cobalt content.

[0062] When the cobalt content exceeds 2000 ppm, its harmful mechanism in negative electrodes, such as silicon-based negative electrodes, is mainly manifested as: ① Cobalt ions (Co 2+ / Co 3+① Solid solution in the silicon lattice induces lattice distortion, blocking lithium-ion diffusion channels and exacerbating volumetric stress concentration; ② The multivalent redox properties of cobalt catalyze electrolyte decomposition, generating an insulating deposition layer containing Co-O bonds and a poorly conductive CoF2 / Li2O composite phase; ③ The d-orbital electrons of cobalt form hybrid states with the p-orbitals of silicon, leading to an imbalance in interfacial charge distribution and significantly increasing charge transfer impedance. More importantly, cobalt's catalytic activity is far higher than that of manganese, and its induced electrolyte oxidation reaction continuously consumes additives such as FEC, rendering the SEI repair mechanism ineffective. Even with the combined use of three types of additives, cobalt impurities still damage the polymer network through electron tunneling and accelerate the dissolution-deposition cycle of cobalt ions at high temperatures, ultimately leading to silicon particle pulverization and electrode structure collapse. Therefore, this application's embodiments limit the content of cobalt in the negative electrode active layer to 0 < X ​​≤ 2000, which can simulate electrochemical devices with multiple application scenarios and different fabrication systems, and also balance the cobalt degradation effect with the synergistic effect of the three types of additives.

[0063] In the embodiments of this application, X can be 1, 100, 200, 300, 400, 500, 1000, 1500, 2000, or any value within the above-mentioned range, and this application does not limit it in this regard.

[0064] In summary, this application proposes a battery technology to suppress cobalt degradation. By limiting (A+B+C) / X ≥ 0.001, and 1 ≤ A ≤ 40, 0.5 ≤ B ≤ 5, 0.5 ≤ C ≤ 5, and 0 < X ​​≤ 2000, the values ​​of A, B, and C can be adjusted based on (A+B+C) / X ≥ 0.001 using the actually measured X. This allows the ternary additive system (fluoroethylene carbonate / fluorinated unsaturated chain compounds / acrylate compounds containing multiple double bonds) to synergistically construct a composite SEI interface: the LiF rigid phase enhances thermal stability, the gel network achieves self-healing, and the cross-linked structure provides dual anchoring for cobalt ions. This design simultaneously solves the problems of low-temperature conduction and high-temperature gas generation, effectively suppressing electrolyte decomposition and silicon anode pulverization caused by cobalt ion migration, enabling the battery to maintain excellent cycle performance in the range from low temperatures (e.g., -20°C) to high temperatures.

[0065] As an optional embodiment, the electrochemical device satisfies: (A+B+C) / X≥0.004.

[0066] When the electrochemical device satisfies (A+B+C) / X≥0.004, the synergistic effect of the first additive, the second additive, and the third additive is better, which can improve the battery's high-temperature cycle and high-temperature storage performance as well as its low-temperature discharge performance.

[0067] As an optional embodiment, the electrochemical device also satisfies: 0.1 ≤ A / (B+C) ≤ 40.

[0068] In this embodiment, when A / (B+C) < 0.1, insufficient FEC leads to an excessively thin LiF substrate, allowing cobalt ions to penetrate the SEI catalytic electrolyte for chain oxidation, increasing high-temperature gas production. Simultaneously, the gel network collapses due to a lack of rigid support, resulting in decreased discharge efficiency at low temperatures, such as -20°C. When A / (B+C) > 40, excessive FEC causes a surge in electrolyte viscosity, hindering lithium ion migration and deteriorating low-temperature rate performance. Furthermore, its thermal decomposition products (CO / F2) increase high-temperature storage gas production and disrupt the chemical anchoring function of the acrylate crosslinking network.

[0069] Therefore, the embodiments of this application construct a gradient SEI interface through the synergistic effect of three components: FEC, fluorine-containing unsaturated chain compounds, and acrylate compounds with multiple double bonds. FEC forms a rigid LiF-rich substrate layer to inhibit cobalt dissolution; the gel network polymerized from fluorine-containing monomers provides self-healing capabilities; and the acrylate crosslinking structure achieves this through chemical coordination (-COOR with Co). 2+ Cobalt ions are captured through a dual mechanism of combination (B+C) and physical sieving. When the A / (B+C) ratio is between 0.1 and 40, the low-temperature conductivity advantage of FEC is balanced with the high-temperature stability of the other two additives.

[0070] In the embodiments of this application, A / (B+C) can be 0.1, 1, 10, 20, 30, 40, or any value within the above-mentioned range, and this application does not limit it in this regard.

[0071] As a preferred embodiment, the electrochemical device also satisfies: 0.5 ≤ A / (B+C) ≤ 20.

[0072] When the electrochemical device further satisfies 0.5≤A / (B+C)≤20, the synergistic effect of the first additive, the second additive, and the third additive is better, which can improve the battery's high-temperature cycle and high-temperature storage performance, as well as its low-temperature discharge performance.

[0073] In the embodiments of this application, A / (B+C) can be 0.5, 1, 10, 20, or any value within the above-mentioned range, and this application does not limit it in this regard.

[0074] As an optional embodiment, the structural formula of the fluorine-containing unsaturated chain compound includes at least one of the compounds having the following structural formulas:

[0075] Structural Formula 1

[0076] Structural Formula 2 R1 is an alkane group containing 1 to 3 carbon atoms, or a fluorine atom or a hydrogen atom, and R2 and R3 are alkane groups containing 1 to 20 fluorine atoms.

[0077] As a preferred embodiment, the fluorine-containing unsaturated chain compound includes at least one of the following compounds:

[0078] Compound 1

[0079] Compound 2

[0080] Compound 3

[0081] Compound 4

[0082] Compound 5

[0083] Compound 6

[0084] Compound 7

[0085] Compound 8

[0086] Compound 9.

[0087] In this application embodiment, the above-mentioned fluorine-containing unsaturated chain compound is used as a second additive to form a three-dimensional gel network through electrochemical polymerization. Its mechanism of action is mainly manifested in: ① Fluorine atoms promote the formation of LiF inorganic phase and enhance the high-temperature stability of SEI; ② The dynamic cross-linked network has self-healing properties and can automatically fill the SEI cracks generated by high-temperature cycling; ③ Cobalt ions are anchored through the fluorinated layer to block their catalytic decomposition of electrolyte.

[0088] As an optional embodiment, the acrylate compound containing multiple double bonds includes at least one of the following compounds:

[0089] compound a

[0090] Compound b

[0091] Compound C

[0092] compound d

[0093] compound e

[0094] compound f

[0095] compound g

[0096] compound h

[0097] Compound i.

[0098] In this application embodiment, a three-dimensional cross-linked SEI film is constructed through free radical polymerization using the aforementioned multifunctional acrylate compound containing multiple double bonds as a third additive. The mechanism of action is mainly reflected in: ① the ester group (-COOR) forms a stable coordination bond with cobalt ions, chemically anchoring the dissolved cobalt ions; ② the nanoscale cross-linked network physically blocks the migration of cobalt ions, reducing the Co ion exchange rate induced by electron tunneling. 2+ ③ Reduction deposition; the dense structure fixes the electrolyte decomposition products and inhibits the interface damage caused by FEC high-temperature gas production.

[0099] As an optional embodiment, the electrochemical device also satisfies: 0.1 ≤ B / C ≤ 10.

[0100] In this embodiment, the synergistic mechanism of the second and third additives is as follows: A fluorinated unsaturated chain compound forms a gel network through electrochemical polymerization, providing self-healing properties to fill SEI cracks and anchor cobalt ions, thus enhancing high-temperature stability; an acrylate compound containing multiple double bonds constructs a three-dimensional cross-linked network through free radical polymerization, fixing cobalt ions through carbonyl oxidation and utilizing nanopores to physically block their migration. The two synergistically form a "rigid-flexible composite" interface, where the dynamics of the gel network and the rigidity of the cross-linked network complement each other, achieving cobalt ion gradient capture (chemical anchoring synergistic physical barrier) and maintaining interface integrity. When the B / C ratio is between 0.1 and 10, the gel layer thickness and cross-linking density are balanced, optimizing high-temperature cycling stability and -20℃ discharge efficiency. If the B / C ratio is <0.1 (e.g., insufficient B, excessive C): high cross-linking density increases the lithium-ion migration activation energy, deteriorates low-temperature discharge efficiency, and high-temperature interface instability reduces cobalt barrier capacity, significantly worsening cycling performance. If B / C > 10 (e.g., excessive B and insufficient C): weakening of the gel network leads to failure of self-repair, accelerated SEI crack propagation exacerbates oxidation of the cobalt-catalyzed electrolyte, increased high-temperature cycling decay rate, and significant deterioration during high-temperature storage.

[0101] In the embodiments of this application, B / C can be 0.1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or any value within the above-mentioned range, and this application does not limit it in this regard.

[0102] As a preferred embodiment, the electrochemical device also satisfies: 0.2≤B / C≤5.

[0103] When the electrochemical device further satisfies 0.2≤B / C≤5, the synergistic effect of the second and third additives is even better, which can improve the battery's high-temperature cycle and high-temperature storage performance, as well as its low-temperature discharge performance.

[0104] In some embodiments, the electrolyte further includes a lithium salt.

[0105] Lithium salts are existing technology and are not limited in this application. For example, the lithium salt can be at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium difluorophosphate, lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium tetrafluoroborate, and lithium difluorodi(oxalate)borate.

[0106] In some embodiments, the electrolyte further includes a solvent, which includes at least one selected from ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, diphenyl carbonate, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, propyl acetate, ethyl butyrate, propyl propionate, γ-butyrolactone, 1,3-dioxolane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0107] Specifically, the solvents mentioned above are mainly used to dissolve the first additive, the second additive, the third additive, and the lithium salt.

[0108] In some embodiments, the initiator may have a mass percentage content of 0.05% to 0.5% in the electrolyte.

[0109] In some embodiments, the initiator comprises at least one of azo initiators and diacyl peroxide initiators.

[0110] It should be noted that this application does not impose any particular limitation on the preparation method of the electrolyte. Those skilled in the art can prepare the electrolyte using conventional technical means, such as mixing the raw materials evenly according to the specified ratio.

[0111] As an optional embodiment, the positive electrode active material includes a transition metal lithium oxide with the chemical formula Li. （1+x） Ni y Co z M (1-y-z)O2, where -0.1≤x≤1; 0≤y≤1, 0≤z≤1, and 0≤y+z≤1; where M is selected from one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr.

[0112] In this application, there is no particular limitation on the type of positive electrode current collector; it can be any known material suitable for use as a positive electrode current collector. In one embodiment, the positive electrode current collector includes metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum, as well as carbon materials such as carbon cloth and carbon paper. In one embodiment, the positive electrode current collector is a metallic material.

[0113] In some embodiments, the positive electrode active material layer further includes a positive electrode conductive agent, a positive electrode binder, and a solvent.

[0114] In some embodiments, the type of positive conductive agent mentioned in the present application is not limited, and any known conductive agent can be used.

[0115] In some embodiments, the positive electrode conductive agent mentioned in the embodiments of this application includes at least one of carbon materials such as natural graphite, artificial graphite, acetylene black, needle coke, carbon nanotubes, and graphene.

[0116] In one embodiment, there is no limitation on the type of positive electrode binder mentioned in the embodiments of this application, and any known positive electrode binder can be used.

[0117] In some embodiments, the positive electrode binder includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose.

[0118] As an optional embodiment, the negative electrode active layer includes a negative electrode active material, which includes artificial graphite and / or silicon-carbon composite materials.

[0119] In the embodiments of this application, there are no particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application, such as copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collector, etc.

[0120] In some preferred embodiments, the negative current collector comprises copper foil.

[0121] In some embodiments, the negative electrode active layer may further include a negative electrode conductive agent, a negative electrode binder, a thickener, and a solvent.

[0122] The negative electrode conductive agent includes at least one of the following carbon materials: natural graphite, artificial graphite, acetylene black, needle coke, carbon nanotubes, and graphene. The negative electrode binder includes styrene-butadiene latex, and the thickener includes CMC. The solvent includes deionized water.

[0123] In the lithium-ion batteries mentioned in this application, a separator is typically provided between the positive and negative electrodes to prevent short circuits. There are no particular restrictions on the material and shape of the separator, as long as it does not significantly impair the effectiveness of this application.

[0124] In some embodiments, the diaphragm includes a porous sheet-like or non-woven material with excellent liquid retention properties. The diaphragm includes resin or glass fiber diaphragm materials, including but not limited to polyolefins, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, etc.

[0125] In some embodiments, the lithium-ion battery may include an outer packaging that can be used to encapsulate the electrode assembly and electrolyte described above.

[0126] In some implementations, the outer packaging of a lithium-ion battery can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of a lithium-ion battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0127] This application does not impose any particular restrictions on the shape of the lithium-ion battery; it can be cylindrical, square, or any other arbitrary shape.

[0128] On the other hand, one embodiment of this application provides an electrical device including the lithium-ion battery described above.

[0129] For example, the aforementioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0130] To further understand the embodiments of this application, the following description is based on the embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of this application.

[0131] I. Preparation of the positive electrode sheet Example 1 1. Preparation of positive electrode sheet The positive electrode active material lithium cobalt oxide, the positive electrode conductive agent acetylene black (SuperP) and polyvinylidene fluoride (PVDF) binder are mixed evenly at a mass ratio of 97:1.5:1.5, and then evenly dispersed with 1-methyl-2-pyrrolidone (NMP) to form a uniform positive electrode slurry. The mixed slurry is coated on both sides of the aluminum foil current collector, and then baked, rolled, and cut into sheets to obtain the positive electrode sheet.

[0132] 2. Preparation of negative electrode sheet The negative electrode active material, artificial graphite, silicon carbide, negative electrode conductive agent acetylene black (Super P), thickener CMC, and negative electrode binder SBR were mixed evenly at a mass ratio of 84:10:2:1.2:2.8, and then uniformly dispersed with deionized water to form a uniform negative electrode slurry. The mixed slurry was coated on both sides of a copper foil current collector, and then baked, rolled, and cut into sheets to obtain the negative electrode sheet. The specific values ​​of cobalt content in the negative electrode active layer are shown in Table 1.

[0133] 3. Preparation of electrolyte a. Mix ethylene carbonate (EC), propyl propionate (EP), and diethyl carbonate (DEC) in a mass ratio of 30:40:30 to form a mixed solvent. Remove water using a molecular sieve and set aside. Add 1M LiPF6 and mix thoroughly. b. Add 0.1% of the initiator azobisisobutyronitrile and additives (the types and amounts of additives are shown in Table 1) to the liquid obtained in step a to obtain the electrolyte.

[0134] 4. Manufacturing of lithium-ion batteries The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator in the middle of the positive and negative electrodes. After winding and welding the tabs, a bare cell is obtained. The bare cell is placed in an aluminum-plastic film for liquid injection and encapsulation to obtain a lithium-ion battery.

[0135] Examples 2-43 and Comparative Examples 1-22 Examples 2-43 and Comparative Examples 1-22 follow the same basic steps as Example 1, except that the types and contents of additives in the electrolyte and the cobalt content in the negative electrode active layer are different, as detailed in Table 1.

[0136] The method for testing the cobalt content in the negative electrode active layer is as follows: Take 5 mg of the negative electrode active layer from the formed lithium-ion battery, add 3 mL of concentrated sulfuric acid and 3 mL of concentrated nitric acid in sequence, heat to 180°C until the solution is clear and transparent, cool, add water to make up to 50 mL, send the sample for testing, and use an ICP (Inductively Coupled Plasma Emission Spectrometer) to test the cobalt content.

[0137] It should be noted that the positive electrode sheet, separator, and manufacturing process are basically the same in the various embodiments and comparative examples of this application for single-factor comparison. Therefore, the content of cobalt dissolved into the negative electrode active layer after battery fabrication is not significantly different. However, to demonstrate the effect of different X values ​​on the long-term cycle use of the battery, the value of X can be adjusted by directly adding elemental cobalt to the negative electrode slurry. Therefore, the X values ​​in Table 1 are different. This ensures both single-factor comparison experiments and allows for the simulation of batteries with different application scenarios and manufacturing systems using different X values.

[0138] Table 1. Formulas and Relationships

[0139] II. Performance Testing The lithium-ion batteries prepared in the above embodiments and comparative examples were tested as follows.

[0140] 1. Storage performance test at 60℃ The lithium-ion batteries prepared in the above embodiments and comparative examples were charged at 25°C at a rate of 1C to the cutoff voltage, with a cutoff current of 0.025C, and left to stand for 5 minutes. The thickness H1 of the lithium-ion battery was then measured. After that, the batteries were stored at 60°C for 60 days, and the thickness H2 of the lithium-ion battery was measured after the storage period.

[0141] Thickness expansion rate = [(H2-H1) / H1]×100%.

[0142] 2. 45℃ Cyclic Performance Test The lithium-ion batteries prepared in the above embodiments and comparative examples were charged and discharged at 45°C at a rate of 1C / 1C within the charge and discharge cutoff voltage range. The discharge capacity of the first cycle was recorded as C1, and the discharge capacity of the Nth cycle was recorded as C2. The capacity of the Nth cycle was divided by the capacity of the first cycle to obtain the cycle capacity retention rate R2 = C2 / C1. The number of cycles of the lithium-ion battery when the cycle capacity retention rate R2 was 70% was recorded.

[0143] 3. -20℃ Low Temperature Discharge Test The lithium-ion batteries prepared in the above embodiments and comparative examples were subjected to charge-discharge cycles at 25°C for 3 weeks at a rate of 0.2C / 0.2C within the charge-discharge cutoff voltage range. The discharge capacity of the third week was measured as C3. The lithium-ion batteries were then subjected to charge-discharge cycles at -20°C for 3 weeks at a rate of 0.2C / 0.2C within the charge-discharge cutoff voltage range. The discharge capacity of the third week was measured as C4. The low-temperature charging capacity retention rate at -20°C was obtained as R3 = C4 / C3.

[0144] The test results are shown in Table 2.

[0145] Table 2 Test Results

[0146] According to Examples 2, 1 to 7, and 15 to 17, the overall performance of the battery can only be significantly improved when the first additive, the second additive, and the third additive are added simultaneously.

[0147] According to Examples 1 to 6, Comparative Examples 8 and 9, as the content of the first additive increases, the battery's high-temperature cycling and low-temperature discharge improve, but high-temperature storage deteriorates. A content of 1% to 40% of the first additive in the electrolyte is preferred. According to Examples 7 to 11, Comparative Examples 10 and 11, as the content of the second additive increases, the battery's low-temperature discharge slightly deteriorates, but high-temperature cycling and high-temperature storage improve. A content of 0.5% to 5% of the second additive in the electrolyte is preferred. According to Examples 12 to 16, Comparative Examples 12 and 13, as the content of the third additive increases, low-temperature discharge significantly deteriorates, but high-temperature cycling and high-temperature storage improve markedly. A content of 0.5% to 5% of the third additive in the electrolyte is preferred.

[0148] According to Examples 17 to 22 and Comparative Example 14, during the formation stage of the electrochemical device, when the content of cobalt dissolved from the positive electrode active material into the negative electrode active layer exceeds 2000 ppm, even if three additives are used in combination, their interface modification and electrolyte stabilization effects are offset by the negative effects of cobalt, and the continuous deterioration of electrode performance cannot be reversed.

[0149] According to Examples 23 and 24, and Comparative Examples 18 and 19, when 0.1 ≤ B / C ≤ 10, the synergistic effect of electrolyte additives can be effectively utilized, and when 0.2 ≤ B / C ≤ 5, the overall performance of the battery is better. According to Examples 25 and 26, and Comparative Examples 20 and 21, in the silicon-based anode battery system, when 0.1 ≤ A / (B+C) ≤ 40, the synergistic effect of electrolyte additives can be effectively utilized, and when 0.5 ≤ A / (B+C) ≤ 20, the overall performance of the battery is better.

[0150] According to Example 27 and Comparative Example 22, when (A+B+C) / X<0.001, the insufficient content of the three additives will cause systemic failure and cannot effectively suppress the degradation of battery performance by cobalt; and when (A+B+C) / X>0.004, the synergistic effect of electrolyte additives can be better exerted.

[0151] According to Examples 2 and 28 to 43, when the second / third additive is selected from the compounds provided in the examples of this application, the improvement effect is basically the same.

[0152] Although this application has been described with reference to preferred embodiments, those skilled in the art will understand that various changes can be made and equivalents can be substituted for the elements, as long as they do not depart from the scope of this application. Furthermore, many modifications can be made to adapt particular situations or materials to the teachings of this application, as long as they do not depart from the essential scope of this application. Therefore, this application is not intended to be limited to the specific embodiments disclosed as the best mode of carrying out this application as conceived, but rather this application will include all embodiments falling within the scope of the appended claims.

[0153] All scopes disclosed in this application include endpoints, and endpoints can be combined with each other.

[0154] The various embodiments of this application have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. An electrochemical device, characterized in that, The electrochemical device includes a positive electrode, a negative electrode, and an electrolyte. The electrolyte comprises a first additive, a second additive, a third additive, and an initiator. The first additive comprises fluoroethylene carbonate, and the mass percentage of the first additive in the electrolyte is A. The second additive comprises a fluorinated unsaturated chain compound, and the mass percentage of the second additive in the electrolyte is B. The third additive comprises an acrylate compound containing multiple double bonds, and the mass percentage of the third additive in the electrolyte is C. The negative electrode comprises a negative electrode current collector and a negative electrode active layer coated on at least one side of the negative electrode current collector. After the electrochemical device is manufactured, the cobalt content in the negative electrode active layer is X ppm. The electrochemical device satisfies the following relationship: (A+B+C) / X≥0.001 Where 1≤A≤40, 0.5≤B≤5, 0.5≤C≤5, and 0<X≤2000.

2. The electrochemical device according to claim 1, characterized in that, The electrochemical device satisfies: (A+B+C) / X≥0.

004.

3. The electrochemical device according to claim 1, characterized in that, The electrochemical device also satisfies: 0.1≤A / (B+C)≤40.

4. The electrochemical device according to claim 3, characterized in that, The electrochemical device also satisfies: 0.5≤A / (B+C)≤20.

5. The electrochemical device according to claim 1, characterized in that, The fluorine-containing unsaturated chain compound includes at least one compound having the following structural formula: Structural Formula 1 Structural Formula 2 R1 is an alkane group containing 1 to 3 carbon atoms, or a fluorine atom or a hydrogen atom, and R2 and R3 are alkane groups containing 1 to 20 fluorine atoms.

6. The electrochemical device according to claim 5, characterized in that, The fluorine-containing unsaturated chain compound includes at least one of the following compounds: Compound 1 Compound 2 Compound 3 Compound 4 Compound 5 Compound 6 Compound 7 Compound 8 Compound 9.

7. The electrochemical device according to claim 1, characterized in that, The acrylate compounds containing multiple double bonds include at least one of the following compounds: compound a Compound b Compound C compound d compound e compound f compound g compound h Compound i.

8. The electrochemical device according to claim 1, characterized in that, The electrochemical device also satisfies: 0.1≤B / C≤10.

9. The electrochemical device according to claim 8, characterized in that, The electrochemical device also satisfies: 0.2≤B / C≤5.

10. The electrochemical device according to claim 1, characterized in that, The positive electrode active material includes a transition metal lithium oxide, the chemical formula of which is Li. （1+x） Ni y Co z M (1-y-z) O2, wherein -0.1≤x≤1; 0≤y≤1, 0≤z≤1, and 0≤y+z≤1; wherein M is selected from one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr; and / or, the negative electrode active layer comprises a negative electrode active material, wherein the negative electrode active material comprises at least one of graphite and silicon carbide.

11. An electrical appliance, characterized in that, Includes the electrochemical device according to any one of claims 1 to 10.

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