Electrolyte, electrochemical device, and electronic device

Abstract

This application provides an electrolyte, an electrochemical device, and an electronic device. The electrolyte includes a compound shown in formula (I) and a compound II, wherein compound II includes a compound shown in formula (II-1) or a compound shown in formula (II-2). Based on the mass of the electrolyte, the mass percentage of the compound shown in formula (I) is X, and the mass percentage of compound II is Y, where 0.01% ≤ X ≤ 5%, and 0.01 ≤ X / Y ≤ 6. By selecting the compound shown in formula (I) and compound II, and adjusting the mass percentage of the compound shown in formula (I) and the value of X / Y within the above ranges, it is beneficial to improve the low-temperature performance and overall impedance of the electrochemical device.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to an electrolyte, an electrochemical device, and an electronic device. Background Technology

[0002] Electrochemical devices, such as lithium-ion batteries, have advantages such as high energy density, high open-circuit voltage, low self-discharge rate, long cycle life, and good safety. They are now widely used as power sources in electronic products such as cameras, mobile phones, drones, laptops, and smartwatches.

[0003] As the application scope of lithium-ion batteries continues to expand, the market is placing higher demands on them, such as requiring good performance at low temperatures. Since the electrolyte is a crucial component of lithium-ion batteries, developing a suitable electrolyte to improve their low-temperature performance has become a pressing technical problem for those skilled in the art. Summary of the Invention

[0004] The purpose of this application is to provide an electrolyte, an electrochemical device, and an electronic device to improve the low-temperature performance of the electrochemical device. The specific technical solution is as follows:

[0005] A first aspect of this application provides an electrolyte comprising a compound of formula (I) and a compound II, wherein compound II comprises either the compound of formula (II-1) or the compound of formula (II-2):

[0006]

[0007] Among them, R 11 and R 12 Each group is independently selected from F, unsubstituted or Ra-substituted C1 to C6 alkyl groups, unsubstituted or Ra-substituted C2 to C6 alkenyl groups, unsubstituted or Ra-substituted phenyl groups, and unsubstituted or Ra-substituted Si1 to Si4 silyl groups, wherein Ra in each group is independently selected from F and C1 to C4 alkyl groups.

[0008]

[0009] Among them, R 21 and R 22 Each alkyl group is independently selected from H, F or C1 to C4, and n3 is 1, 2, 3 or 4;

[0010]

[0011] Wherein, D and E are each independently selected from C1 to C8 alkylene groups or C1 to C8 fluoroalkylene groups;

[0012] Based on the mass of the electrolyte, the mass percentage of the compound shown in formula (I) is X, the mass percentage of compound II is Y, 0.01% ≤ X ≤ 5%, and 0.01 ≤ X / Y ≤ 6. By selecting the compound shown in formula (I) and compound II, and adjusting the mass percentage of the compound shown in formula (I) and the value of X / Y within the above ranges, it is beneficial to improve the low-temperature performance, overall impedance, high-temperature cycling performance, and high-temperature storage performance of the electrochemical device.

[0013] In some embodiments of this application, 0.01 ≤ X / Y ≤ 3. Adjusting the value of X / Y within the above range is beneficial to improving the low-temperature performance, overall impedance, high-temperature cycling performance, and high-temperature storage performance of the electrochemical device.

[0014] In some embodiments of this application, 0.01% ≤ Y ≤ 5%. Adjusting the value of Y within the above range is beneficial to improving the low-temperature performance, overall impedance, high-temperature cycling performance, and high-temperature storage performance of the electrochemical device.

[0015] In some embodiments of this application, the compound represented by formula (I) includes at least one of the following compounds:

[0016]

[0017] By selecting the compound shown in formula (I) above, it is more beneficial for the compound shown in formula (I) and compound II to synergistically regulate the composition of the solid electrolyte interphase (SEI) membrane, improve the ionic conductivity and stability of the SEI membrane, and improve the low-temperature performance, overall impedance, high-temperature cycling performance and high-temperature storage performance of the electrochemical device.

[0018] In some embodiments of this application, the compound represented by formula (II-1) includes at least one selected from 1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, 1,2-butanesulfonate lactone, 1,3-butanesulfonate lactone, 2,4-butanesulfonate lactone, or 1,3-pentanesulfonate lactone; the compound represented by formula (II-2) includes at least one selected from methyl methanedisulfonate or ethylene methanedisulfonate. By selecting the compounds represented by formula (II-1) and (II-2) above, it is more advantageous for the compounds represented by formula (I) and compound II to synergistically regulate the composition of the SEI membrane, improve the ionic conductivity and stability of the SEI membrane, and improve the low-temperature performance, overall impedance, high-temperature cycling performance, and high-temperature storage performance of the electrochemical device.

[0019] In some embodiments of this application, the electrolyte further includes a polynitrile compound, said polynitrile compound comprising at least one of the following compounds:

[0020]

[0021] Based on the mass of the electrolyte, the mass percentage of the polynitrile compound is D, where 0.2% ≤ D ≤ 10% and 0.05 ≤ (X + Y) / D ≤ 15. By selecting the above-mentioned polynitrile compound and controlling its mass percentage within the above range, it is beneficial to form a synergistic effect with the electrolyte system containing the compound shown in formula (I) and compound II, thereby improving the ionic conductivity and stability of the SEI membrane, reducing the impedance of the SEI membrane and the positive electrode electrolyte interface membrane (CEI membrane), and improving the low-temperature performance, overall impedance, high-temperature cycling performance, and high-temperature storage performance of the electrochemical device.

[0022] In some embodiments of this application, the electrolyte further includes an acid anhydride compound, the structure of which is shown in formula (VI):

[0023]

[0024] R1 to R8 are each independently selected from H, F, Cl, unsubstituted or F-substituted C1 to C4 chain alkyl, C3 to C5 cyclic alkyl, C2 to C4 alkenyl, C2 to C4 alkynyl, C1 to C4 alkoxy, C6 to C 10 Aryl, amino, aldehyde, acetyl, cyano, hydroxyl, or sulfonic acid groups;

[0025] Based on the mass of the electrolyte, the mass percentage of the anhydride compound is M, where 0.01% ≤ M ≤ 5%. By selecting the above-mentioned anhydride compound and controlling its mass percentage within the above range, it is beneficial to form a synergistic effect with the electrolyte system containing the compound shown in formula (I) and compound II, thereby improving the ionic conductivity and stability of the SEI membrane, reducing the impedance of the SEI membrane, and improving the low-temperature performance, overall impedance, high-temperature storage performance, and high-temperature cycling performance of the electrochemical device.

[0026] In some embodiments of this application, the acid anhydride compound includes at least one of the following compounds:

[0027]

[0028] By selecting the above-mentioned anhydride compounds, it is beneficial to form a synergistic effect with the electrolyte system containing the compound shown in formula (I) and compound II, thereby improving the ionic conductivity and stability of the SEI membrane, reducing the impedance of the SEI membrane, and improving the low-temperature performance, overall impedance, high-temperature storage performance and high-temperature cycling performance of the electrochemical device.

[0029] In some embodiments of this application, it also includes the compound shown in formula (VII);

[0030]

[0031] Among them, R71 R 72 R 73 and R 74 Each is independently selected from H, F, C1 to C 10 Fluoroalkyl, C1 to C 10 Fluoroalkoxy or C1 to C 10 fluoroalkoxyalkyl, and R 71 R 72 R 73 and R 74 Not both H;

[0032] Based on the mass of the electrolyte, the mass percentage of the compound shown in formula (VII) is C, where 0.5% ≤ C ≤ 16%. By selecting the compound shown in formula (VII) and controlling its mass percentage within the above range, it is beneficial to form a synergistic effect with the electrolyte system containing the compound shown in formula (I) and compound II, thereby improving the ionic conductivity, stability, and flexibility of the SEI membrane, reducing the impedance of the SEI membrane, and improving the low-temperature performance, overall impedance, high-temperature storage performance, and high-temperature cycling performance of the electrochemical device.

[0033] In some embodiments of this application, the compound represented by formula (VII) includes at least one of the following compounds:

[0034]

[0035] By selecting the compound shown in formula (VII), it is beneficial to form a synergistic effect with the electrolyte system containing the compound shown in formula (I) and compound II, thereby improving the ionic conductivity, stability and flexibility of the SEI membrane, reducing the impedance of the SEI membrane, and improving the low-temperature performance, overall impedance, high-temperature storage performance and high-temperature cycling performance of the electrochemical device.

[0036] In some embodiments of this application, the electrolyte satisfies at least one of the following characteristics:

[0037] (1) 0.05% ≤ X ≤ 3%;

[0038] (2) 0.5% ≤ Y ≤ 4%;

[0039] (3) The mass percentage of polynitrile compounds is D, 0.5%≤D≤5%, 0.1≤(X+Y) / D≤5;

[0040] (4) The mass percentage of the acid anhydride compound is M, 0.1% ≤ M ≤ 2%;

[0041] (5) The mass percentage of the compound shown in formula (VII) is C, where 1% ≤ C ≤ 10%.

[0042] An electrolyte that meets at least one of the above characteristics is beneficial for improving the low-temperature performance, overall impedance, high-temperature storage performance, and high-temperature cycling performance of electrochemical devices.

[0043] A second aspect of this application provides an electrochemical device comprising the electrolyte found in any of the foregoing embodiments. Thus, the electrochemical device provided by this application exhibits excellent low-temperature performance, high-temperature storage performance, and high-temperature cycling performance, as well as low overall impedance.

[0044] A third aspect of this application provides an electronic device that includes the electrochemical device in any of the foregoing embodiments. Therefore, the electronic device provided by this application has good performance in use.

[0045] The beneficial effects of this application are:

[0046] This application provides an electrolyte, an electrochemical device, and an electronic device. The electrolyte includes a compound shown in formula (I) and a compound II. Compound II includes a compound shown in formula (II-1) or a compound shown in formula (II-2). Based on the mass of the electrolyte, the mass percentage of the compound shown in formula (I) is X, and the mass percentage of compound II is Y, where 0.01% ≤ X ≤ 5% and 0.01% ≤ X / Y ≤ 6. The compound shown in formula (I) and compound II can regulate the inorganic components in the solid electrolyte interphase (SEI) membrane, increase the content of Li2S and Li2SO3 in the SEI membrane, improve the electron blocking property, facilitate the electron side reaction at the interface between the electrolyte and the SEI membrane, reduce the overall thickness of the SEI membrane, and give the formed inorganic components better ionic conductivity, which is beneficial for lithium ion transport at the interface. This helps to improve the ion transport problem caused by low temperature, thereby improving the low-temperature performance of the electrochemical device and reducing the overall impedance of the electrochemical device.

[0047] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Detailed Implementation

[0048] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0049] It should be noted that, in the specific embodiments of this application, a lithium-ion battery is used as an example of a secondary battery to explain this application; however, the secondary battery in this application is not limited to lithium-ion batteries. The specific technical solution is as follows:

[0050] A first aspect of this application provides an electrolyte comprising a compound of formula (I) and a compound II, wherein compound II comprises either the compound of formula (II-1) or the compound of formula (II-2):

[0051]

[0052] Among them, R 11 and R 12 Each group is independently selected from F, unsubstituted or Ra-substituted C1 to C6 alkyl groups, unsubstituted or Ra-substituted C2 to C6 alkenyl groups, unsubstituted or Ra-substituted phenyl groups, and unsubstituted or Ra-substituted Si1 to Si4 silyl groups, wherein Ra in each group is independently selected from F and C1 to C4 alkyl groups.

[0053]

[0054] Among them, R 21 and R 22 Each alkyl group is independently selected from H, F or C1 to C4, and n3 is 1, 2, 3 or 4;

[0055]

[0056] Wherein, D and E are each independently selected from C1 to C8 alkylene groups or C1 to C8 fluoroalkylene groups;

[0057] Based on the mass of the electrolyte, the mass percentage of the compound shown in formula (I) is X, and the mass percentage of compound II is Y, where 0.01 ≤ X ≤ 5% and 0.01 ≤ X / Y ≤ 6; further, 0.05% ≤ X ≤ 3%; further, 0.01 ≤ X / Y ≤ 3. For example, the mass percentage of the compound shown in formula (I) can be 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or any value within the range of any two of the above values, and the value of X / Y can be 0.01, 0.05, 0.1, 0.5, 1, 2, 3, 4, 5, 6, or any value within the range of any two of the above values.

[0058] Compounds (I) and (II) can regulate the inorganic components in the SEI film, increasing the content of Li₂S and Li₂SO₃, improving electron blocking, facilitating electron side reactions at the interface between the electrolyte and the SEI film, reducing the overall thickness of the SEI film, and giving the formed inorganic components better ionic conductivity. This is beneficial for lithium ion transport at the interface, thus improving the ion transport problem caused by low temperature, thereby improving the low-temperature performance of the electrochemical device and reducing the overall impedance of the electrochemical device. When the mass percentage content of the compound shown in formula (I) and the X / Y value are not within the above ranges, the content of Li₂S and Li₂SO₃ in the SEI film cannot be increased to improve the ionic conductivity of the SEI film, thereby improving the low-temperature performance and overall impedance of the electrochemical device. In addition, Li₂S and Li₂SO₃ in the SEI film also help improve the stability of the SEI film, thereby improving the high-temperature cycling performance and high-temperature storage performance of the electrochemical device. By selecting compounds shown in formula (I) and compound II, and adjusting the mass percentage content of the compound shown in formula (I) and the X / Y value within the above range, it is beneficial to improve the low-temperature performance, overall impedance, high-temperature cycling performance, and high-temperature storage performance of the electrochemical device. In this application, improving the overall impedance of the electrochemical device means reducing the overall impedance of the electrochemical device. "Low temperature" refers to a temperature less than or equal to 20°C, and "high temperature" refers to a temperature greater than or equal to 40°C.

[0059] In some embodiments of this application, 0.01% ≤ Y ≤ 5%; further, 0.5% ≤ Y ≤ 4%. For example, the mass percentage of compound II can be 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or any value within the range of any two of the above values. By controlling the mass percentage of compound II within the above range, it is more beneficial for the compound shown in formula (I) and compound II to synergistically regulate the composition of the SEI membrane, improve the ionic conductivity and stability of the SEI membrane, and improve the low-temperature performance, overall impedance, high-temperature cycling performance, and high-temperature storage performance of the electrochemical device.

[0060] For example, the compound shown in formula (I) includes at least one of the following compounds:

[0061]

[0062] By selecting the compound shown in formula (I) above, it is more beneficial for the compound shown in formula (I) and compound II to synergistically regulate the composition of the SEI membrane, improve the ionic conductivity and stability of the SEI membrane, and improve the low-temperature performance, overall impedance, high-temperature cycling performance and high-temperature storage performance of the electrochemical device.

[0063] In some embodiments of this application, the compound represented by formula (II-1) includes at least one of 1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, 1,2-butanesulfonate lactone, 1,3-butanesulfonate lactone, 2,4-butanesulfonate lactone, or 1,3-pentanesulfonate lactone; the compound represented by formula (II-2) includes at least one of methylene disulfonate or ethylene disulfonate. By selecting the compounds represented by formula (II-1) and (II-2) above, it is more advantageous for the compounds represented by formula (I) and compound II to synergistically regulate the composition of the SEI membrane, improve the ionic conductivity and stability of the SEI membrane, and improve the low-temperature performance, overall impedance, high-temperature cycling performance, and high-temperature storage performance of the electrochemical device.

[0064] In some embodiments of this application, the electrolyte further includes a polynitrile compound, which includes at least one of the following compounds:

[0065]

[0066] Based on the mass of the electrolyte, the mass percentage of the polynitrile compound is D, where 0.2% ≤ D ≤ 10%, and 0.05 ≤ (X+Y) / D ≤ 15; further, 0.5% ≤ D ≤ 5%, and 0.1 ≤ (X+Y) / D ≤ 5. For example, the mass percentage of the polynitrile compound can be 0.2%, 0.5%, 1%, 3%, 5%, 7%, 9%, 10%, or any value within the range of any two of the above values, and the value of (X+Y) / D can be 0.05, 0.1, 0.5, 1, 3, 5, 7, 9, 10, 13, 15, or any value within the range of any two of the above values. The cyano group in the polynitrile compound readily forms a complex with the positive electrode active material and adsorbs onto the positive electrode surface, inhibiting the dissolution of metal elements in the positive electrode active material, such as transition metal elements, reducing side reactions between the electrolyte and the positive electrode active material, lowering the impedance of the CEI film, and further improving the low-temperature performance and overall impedance of the electrochemical device. By selecting the aforementioned polynitrile compounds and controlling their mass percentage content within the above range, it is beneficial to form a synergistic effect with the electrolyte system containing the compound shown in formula (I) and compound II, thereby improving the ionic conductivity and stability of the SEI membrane, reducing the impedance of the SEI and CEI membranes, and improving the low-temperature performance, overall impedance, high-temperature cycling performance, and high-temperature storage performance of the electrochemical device. In this application, "positive electrode" also refers to the positive electrode sheet.

[0067] In some embodiments of this application, the electrolyte further includes an acid anhydride compound, the structure of which is shown in formula (VI):

[0068]

[0069] R1 to R8 are each independently selected from H, F, Cl, unsubstituted or F-substituted C1 to C4 chain alkyl, C3 to C5 cyclic alkyl, C2 to C4 alkenyl, C2 to C4 alkynyl, C1 to C4 alkoxy, C6 to C 10 Aryl, amino, aldehyde, acetyl, cyano, hydroxyl, or sulfonic acid groups.

[0070] For example, the acid anhydride compound includes at least one of the following compounds:

[0071]

[0072]

[0073] Based on the mass of the electrolyte, the mass percentage of the anhydride compound is M, where 0.01% ≤ M ≤ 5%; further, 0.1% ≤ M ≤ 2%. For example, the mass percentage of the anhydride compound can be 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or any value within the range of any two of the above values. The C=O in the anhydride compound can stabilize the SEI membrane and improve the high-temperature storage performance and high-temperature cycling performance of the electrochemical device. By selecting the above-mentioned anhydride compound and controlling its mass percentage within the above range, it is beneficial to form a synergistic effect with the electrolyte system containing the compound shown in formula (I) and compound II, thereby improving the ionic conductivity and stability of the SEI membrane, reducing the impedance of the SEI membrane, and improving the low-temperature performance, overall impedance, high-temperature storage performance, and high-temperature cycling performance of the electrochemical device.

[0074] In some embodiments of this application, it also includes the compound shown in formula (VII);

[0075]

[0076] Among them, R 71 R 72 R 73 and R 74 Each is independently selected from H, F, C1 to C 10 Fluoroalkyl, C1 to C 10 Fluoroalkoxy or C1 to C 10 fluoroalkoxyalkyl, and R 71 R 72 R 73 and R 74 They are not both H.

[0077] For example, the compound shown in formula (VII) includes at least one of the following compounds:

[0078]

[0079] Based on the mass of the electrolyte, the mass percentage of the compound shown in formula (VII) is C, where 0.5% ≤ C ≤ 16%; further, 1% ≤ C ≤ 10%. For example, the mass percentage of the compound shown in formula (VII) can be 0.5%, 1%, 3%, 5%, 7%, 9%, 10%, 13%, 15%, 16%, or any value within the range of any two of the above values. The introduction of the compound shown in formula (VII) can react with the lithium salt in the electrolyte to form a protective film containing LiF and alkyllithium on the surface of the SEI membrane, reducing the occurrence of side reactions on the SEI membrane surface, while improving the flexibility of the SEI membrane and improving the low-temperature performance and cycle performance of the electrochemical device. By selecting the compound shown in formula (Ⅶ) and controlling its mass percentage within the above range, it is beneficial to form a synergistic effect with the electrolyte system containing the compound shown in formula (I) and compound II, thereby improving the ionic conductivity, stability and flexibility of the SEI membrane, reducing the impedance of the SEI membrane, and improving the low-temperature performance, overall impedance, high-temperature storage performance and high-temperature cycling performance of the electrochemical device.

[0080] In some embodiments of this application, the electrolyte further includes an organic solvent, which includes carbonate compounds and / or carboxylic acid ester compounds. This application does not particularly limit the types of carbonate compounds and carboxylic acid ester compounds; carbonate compounds and carboxylic acid ester compounds known in the art can be used. Exemplarily, carbonate compounds may include, but are not limited to, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, and carbonates. The electrolyte contains at least one of the following: 1,1-difluoroethylene ester, 1,1,2-trifluoroethylene ester carbonate, 1,1,2,2-tetrafluoroethylene ester carbonate, 1-fluoro-2-methylethylene ester carbonate, 1-fluoro-1-methylethylene ester carbonate, 1,2-difluoro-1-methylethylene ester carbonate, 1,1,2-trifluoro-2-methylethylene ester carbonate, or trifluoromethylethylene ester carbonate; the carboxylic acid ester compound may include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valerate, mevalonate lactone, or caprolactone. This application does not impose any particular limitation on the content of the organic solvent in the electrolyte, as long as the purpose of this application is achieved. For example, based on the mass of the electrolyte, the mass percentage of the organic solvent may be 60% to 88%.

[0081] In some embodiments of this application, the electrolyte further includes a lithium salt. This application does not particularly limit the type of lithium salt; lithium salts known in the art can be used. Exemplarily, the lithium salt may include, but is not limited to, at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium bis(oxalato)borate, or lithium difluorooxalato)borate. This application does not particularly limit the content of the lithium salt in the electrolyte, as long as the purpose of this application is achieved. For example, based on the mass of the electrolyte, the mass percentage of the lithium salt is 10% to 20%.

[0082] A second aspect of this application provides an electrochemical device comprising the electrolyte found in any of the foregoing embodiments. Thus, the electrochemical device provided by this application exhibits excellent low-temperature performance, high-temperature storage performance, and high-temperature cycling performance, as well as low overall impedance.

[0083] In this application, the electrochemical device further includes a positive electrode sheet, which comprises a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The phrase "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its thickness direction, or on two surfaces of the positive current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of ​​the positive current collector or only a portion thereof; this application does not have any particular limitation, as long as the purpose of this application is achieved.

[0084] This application does not impose any particular restrictions on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, it may include aluminum foil, aluminum alloy foil, or composite current collector (such as aluminum-carbon composite current collector).

[0085] The positive electrode material layer includes a positive electrode active material. This application does not impose any particular limitation on the positive electrode active material, as long as it can achieve the purpose of this application. For example, the positive electrode active material may include, but is not limited to, lithium nickel cobalt manganese oxide (such as the common NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate.

[0086] The positive electrode material layer also includes a conductive agent and a binder. This application does not particularly limit the types of conductive agents and binders, as long as they can achieve the purpose of this application. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, Ketjen black, graphene, metallic materials, or conductive polymers. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The aforementioned metallic materials may include, but are not limited to, metal powders and / or metal fibers; specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The aforementioned conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. The binder may include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber, or polyvinylidene fluoride. This application does not impose any particular restrictions on the mass ratio of positive electrode active material, conductive agent, and binder in the positive electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0087] This application does not impose any particular limitation on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector is 6 μm to 12 μm, and the thickness of the positive electrode material layer is 30 μm to 120 μm. The application also does not impose any particular limitation on the thickness of the positive electrode sheet, as long as the purpose of this application can be achieved; for example, the thickness of the positive electrode sheet is 50 μm to 250 μm.

[0088] Optionally, the positive electrode may further include a conductive layer located between the positive current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited and can be any conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer; for example, it can be at least one of the aforementioned conductive agents and binders.

[0089] In this application, the electrochemical device further includes a negative electrode sheet, which comprises a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the positive electrode current collector. The phrase "the negative electrode material layer is disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or on two surfaces of the negative electrode current collector along its thickness direction. It should be noted that the term "surface" here can refer to the entire surface of the negative electrode current collector or a portion of the surface of the positive electrode current collector; this application does not impose any particular limitation, as long as the purpose of this application is achieved.

[0090] This application does not impose any particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collectors (such as carbon copper composite current collectors, nickel copper composite current collectors, titanium copper composite current collectors, etc.).

[0091] The negative electrode material layer includes a negative electrode active material. This application does not impose any particular limitation on the negative electrode active material, as long as it can achieve the purpose of this application. For example, the negative electrode active material may include, but is not limited to, natural graphite, artificial graphite, mesophase micro carbon spheres, hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and spinel-structured lithiated TiO2-Li4Ti5O. 12 Or at least one of Li-Al alloys.

[0092] The negative electrode material layer also includes a conductive agent and a binder. This application does not particularly limit the types of conductive agents and binders, as long as they achieve the purpose of this application. For example, it can be at least one of the aforementioned conductive agents and binders. This application does not particularly limit the mass ratio of the negative electrode active material, conductive agent, and binder in the negative electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application is achieved. The negative electrode material layer may also include a thickener. This application does not particularly limit the content and type of thickener; conventional types and contents known in the art can be used, as long as the purpose of this application is achieved.

[0093] This application does not impose any particular limitation on the thickness of the negative electrode material layer, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode material layer can be from 30 μm to 120 μm. This application does not impose any particular limitation on the thickness of the negative electrode current collector, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode current collector can be from 4 μm to 12 μm. This application does not impose any particular limitation on the thickness of the negative electrode sheet, as long as it achieves the purpose of this application. For example, the thickness of the negative electrode sheet can be from 50 μm to 250 μm.

[0094] Optionally, the negative electrode sheet may further include a conductive layer located between the negative electrode current collector and the negative electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer, which can be a conductive layer commonly used in the art. For example, the conductive layer may include a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer; for example, it can be at least one of the aforementioned conductive agents and binders.

[0095] In this application, the electrochemical device also includes a separator membrane to separate the positive and negative electrode plates, prevent short circuits within the electrochemical device, allow electrolyte ions to pass freely, and not affect the electrochemical charging and discharging process. This application does not impose any particular limitation on the separator membrane, as long as it achieves the purpose of this application. For example, the material of the separator membrane may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) primarily composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid; the type of separator membrane may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0096] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials.

[0097] For example, the inorganic layer comprises inorganic particles and a binder. The inorganic particles are not particularly limited and may include, for example, at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder is not particularly limited and may be, for example, at least one of the binders described above. The polymer layer contains a polymer, the polymer material of which includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0098] The preparation process of the electrochemical device described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, it may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain the electrochemical device; or stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain the electrochemical device. Furthermore, overcurrent protection elements, conductive plates, etc., may be placed in the packaging bag as needed to prevent pressure rise and overcharging / discharging inside the electrochemical device. The packaging bag is any packaging bag known in the art, and this application does not limit its use.

[0099] A third aspect of this application provides an electronic device that includes the electrochemical device in any of the foregoing embodiments. Thus, the electronic device provided by this application has good performance. This application does not particularly limit the type of electronic device; it can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0100] Example

[0101] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below.

[0102] Test methods and equipment:

[0103] 80℃ Storage Thickness Expansion Rate Test:

[0104] The lithium-ion battery was discharged at 25°C with a constant current of 0.5C to 3.0V, then charged at a constant current of 0.5C to 4.5V, and finally charged at a constant voltage of 0.05C at 4.5V. The thickness of the lithium-ion battery was measured and recorded using a micrometer and denoted as H. 11 Place the battery in an 80℃ oven and maintain a constant voltage of 4.5V for 7 hours. After 7 hours, measure and record the thickness of the lithium-ion battery using a micrometer, denoted as H. 12 .

[0105] Thickness expansion rate at 80℃ storage = (H 12 -H 11 ) / H 11 ×100%.

[0106] 45℃ high temperature cycling test:

[0107] The lithium-ion battery was placed in a 45°C constant temperature chamber and left to stand for 30 minutes to allow it to reach a constant temperature. The battery was then charged at a constant current of 0.2C to 4.5V at 45°C, followed by constant voltage charging to 0.05C at 4.5V. After standing for 5 minutes, it was discharged at a constant current of 0.2C to 3.0V and left to stand for 5 minutes. The initial discharge capacity C0 and initial thickness H0 of the lithium-ion battery were then measured. Then charge at a constant current of 1.3C to 4.15V, then charge at a constant voltage of 4.15V to a current of 1C; then charge at a constant current of 1C to 4.25V, then charge at a constant voltage of 4.25V to a current of 0.8C; then charge at a constant current of 0.8C to 4.5V, then charge at a constant voltage of 4.5V to a current of 0.05C; let stand for 5 minutes; then discharge at a constant current of 1C to 3.0V, and let stand for 5 minutes. This is one charge-discharge cycle. After charging / discharging in this way, test the discharge capacity C' and final thickness H' of the lithium-ion battery after 400 cycles.

[0108] Capacity retention rate after 400 cycles at 45℃ = C' / C0 × 100%.

[0109] Thickness expansion rate after 400 cycles at 45℃ = (H'-H0) / H0×100%.

[0110] -10℃ low temperature cycling test:

[0111] Place the lithium-ion battery in a -10℃ constant temperature chamber and let it stand for 30 minutes to allow it to reach a constant temperature. Then, charge the battery at a constant current of 0.2C to 4.5V at -10℃, followed by constant voltage charging to 0.05C at 4.5V. Let it stand for 5 minutes, then discharge it at a constant current of 0.2C to 3.0V, and let it stand for 5 minutes. Test the initial capacity C. 11 Then, charge at a constant current of 0.5C to 4.2V, then charge at a constant voltage of 4.2V to a current of 0.3C; then charge at a constant current of 0.3C to 4.25V, then charge at a constant voltage of 4.5V to a current of 0.05C; let stand for 5 minutes; then discharge at a constant current of 0.2C to 3.0V, and let stand for 5 minutes; this completes one charge / discharge cycle. Repeat this charge / discharge cycle to test the discharge capacity C of the lithium-ion battery after 200 cycles. 12 Calculate the capacity retention rate of a lithium-ion battery after 200 cycles.

[0112] Capacity retention rate after 200 cycles at -10℃ = C12 / C 11 ×100%.

[0113] DC resistance (DCR) test at 25°C:

[0114] The lithium-ion battery was placed in a 25°C constant temperature chamber for 1 hour to achieve a constant temperature. It was then charged at a constant current of 0.5C to 4.2V, then at 0.3C to 4.5V, and finally charged at a constant voltage of 4.5V until the current reached 0.02C. The battery was then allowed to rest for 30 minutes. Next, it was discharged at a constant current of 0.1C to 3.4V and allowed to rest for 30 minutes. This capacity was used as a baseline. At 25°C, the battery was charged at a constant current of 0.5C to 4.2V, then at 0.3C to 4.5V, and finally charged at a constant voltage of 4.5V until the current reached 0.02C. The battery was allowed to rest for 30 minutes. It was then discharged at a constant current of 0.1C for 60 minutes (capacity calculated based on the theoretical capacity of the lithium-ion battery), and the voltage at this point was recorded as V1. Finally, it was discharged at a constant current of 1C for 1 second (capacity calculated based on the theoretical capacity of the lithium-ion battery), and the voltage at this point was recorded as V2. The DC impedance corresponding to the lithium-ion battery at 20% SOC was calculated. 20% SOC DCR = (V1-V2) / 1C. Where SOC refers to the state of charge of a lithium-ion battery.

[0115] -10℃ discharge capacity ratio test:

[0116] The lithium-ion battery was placed in a 25°C constant temperature chamber for 1 hour to achieve a constant temperature. It was then charged at a constant current of 0.5C to 4.2V, followed by a constant current of 0.3C to 4.5V, and then charged at a constant voltage of 4.5V until the current reached 0.02C. The battery was then allowed to rest for 30 minutes. Finally, it was discharged at a constant current of 0.2C to 3.4V and allowed to rest for 30 minutes. This capacity (D0) was used as the baseline. Alternatively, the lithium-ion battery was charged at a constant current of 0.5C to 4.2V at 25°C, followed by a constant current of 0.3C to 4.5V, and then charged at a constant voltage of 4.5V until the current reached 0.02C. The battery was then allowed to rest for 30 minutes. The temperature in the constant temperature chamber was adjusted to -10°C, and the lithium-ion battery was placed in the -10°C chamber for 1 hour to achieve a constant temperature. It was then discharged at a constant current of 0.2C to 3.4V, and the capacity at this point was recorded as D1. The discharge capacity ratio at -10°C = D1 / D0 × 100%.

[0117] Example 1-1

[0118] <Preparation of the positive electrode>

[0119] The prepared positive electrode active material lithium cobalt oxide, conductive agent acetylene black, and binder polyvinylidene fluoride were mixed at a mass ratio of 96:2:2. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum until it became homogeneous and transparent, obtaining a positive electrode slurry with a solid content of 70 wt%. The positive electrode slurry was uniformly coated onto one surface of a 12 μm thick aluminum foil for positive electrode current collectors. The aluminum foil was dried at 120°C for 1 hour to obtain a positive electrode sheet with a single-sided coating of a 100 μm thick positive electrode material layer. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of the positive electrode material layer. After cold pressing, cutting, and slitting, the sheet was dried under vacuum at 120°C for 1 hour to obtain a positive electrode sheet with dimensions of 74 mm × 867 mm.

[0120] <Preparation of Negative Electrode Sheets>

[0121] Artificial graphite (negative electrode active material), acetylene black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (thickener) were mixed in a mass ratio of 95:2:2:1. Deionized water was added, and the mixture was stirred under vacuum to obtain a negative electrode slurry with a solid content of 75 wt%. The negative electrode slurry was uniformly coated onto one surface of a 12 μm thick copper foil current collector. The copper foil was dried at 120 °C to obtain a negative electrode sheet with a single-sided coating of negative electrode material layer with a coating thickness of 130 μm. The above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of negative electrode material layer. After cold pressing, cutting, and slitting, the sheet was dried under vacuum at 120 °C for 1 hour to obtain a negative electrode sheet with a size of 74 mm × 867 mm.

[0122] <Preparation of Electrolyte>

[0123] In an argon-atmospheric glove box with a water content of <10 ppm, ethylene carbonate, diethyl carbonate, and propyl propionate were mixed in a mass ratio of 3:4:3. Lithium hexafluorophosphate (LiPF6), compound I-1 (as shown in formula (I), and compound II 1,3-propanesulfonate lactone) were then added to the organic solvent to obtain the electrolyte. Based on the mass of the electrolyte, the mass percentage of LiPF6 was 12%, the mass percentage of the compound shown in formula (I) was 0.05%, the mass percentage of compound II was 5%, and the remainder was organic solvent.

[0124] <Isolation membrane>

[0125] A porous polyethylene film with a thickness of 7μm (supplied by Celgard) is used.

[0126] <Preparation of Lithium-ion Batteries>

[0127] The positive electrode, separator, and negative electrode prepared above are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then wound to obtain the electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, degassing, and edge trimming, a lithium-ion battery is obtained. The upper limit of the formation voltage is 4.15V, the formation temperature is 70℃, and the formation settling time is 2 hours.

[0128] Examples 1-2 to Examples 1-14

[0129] Except for the types and mass percentages of compounds (I) and II as shown in Table 1, the mass percentage of lithium salt remains unchanged, and the mass percentage of organic solvent changes accordingly, everything else is the same as in Examples 1-1.

[0130] Examples 2-1 to 2-9

[0131] Except for the addition of polynitrile compounds as shown in Table 2 in the <Preparation of Electrolyte>, and the adjustment of the mass percentage and type of polynitrile compounds, the mass percentage of compounds shown in formula (I) and compound II as shown in Table 2, the mass percentage of organic solvents is changed accordingly, and the mass percentage of lithium salt remains unchanged, the rest is the same as in Examples 1-4.

[0132] Examples 3-1 to 3-9

[0133] Except for the addition of an acid anhydride compound as shown in Table 3 in the <Preparation of Electrolyte>, and the adjustment of its mass percentage and type as shown in Table 3, the mass percentage of organic solvent is changed accordingly, and the mass percentage of compound (I), compound II and lithium salt remain unchanged, the rest is the same as in Examples 1-4.

[0134] Examples 4-1 to 4-12

[0135] Except for the addition of the compound shown in formula (VII) in <Preparation of Electrolyte> as shown in Table 4, and the adjustment of its mass percentage and type as shown in Table 4, the mass percentage of organic solvent is changed accordingly, and the mass percentage of compound (I), compound II and lithium salt remain unchanged, the rest is the same as in Examples 1-4.

[0136] Examples 5-1 to 5-4

[0137] Except that in the <Preparation of Electrolyte>, at least two of the polynitrile compound, acid anhydride compound and compound of formula (VII) are added as shown in Table 5, and their mass percentages are adjusted as shown in Table 5, the mass percentage of organic solvent is changed accordingly, and the mass percentage of lithium salt remains unchanged, the rest is the same as in Examples 1-4.

[0138] Comparative Examples 1-1 to 1-4

[0139] Except for the types and mass percentages of compounds (I) and II as shown in Table 1, the mass percentage of organic solvents is changed accordingly, and the mass percentage of lithium salts remains unchanged, the rest is the same as in Examples 1-1.

[0140] The relevant preparation parameters and performance tests for each embodiment and comparative example are shown in Tables 1 to 5.

[0141] Table 1

[0142]

[0143]

[0144] Note: " / " in Table 1 indicates that the corresponding substance or parameter does not exist.

[0145] As can be seen from Examples 1-1 to 1-14 and Comparative Examples 1-1 to 1-4, all embodiments of this application use the electrolyte provided in this application. The types of compounds shown in formula (I) and compound II, and the values ​​of X and X / Y are within the range of this application. The electrolytes in Comparative Examples 1-1 to 1-4 do not contain compounds shown in formula (I) and / or compound II, or the values ​​of X and X / Y are not within the range of this application. The lithium-ion batteries in the embodiments of this application have higher capacity retention after 400 cycles at 45°C, higher discharge capacity ratio at -10°C, higher capacity retention after 200 cycles at -10°C, and lower thickness expansion rate after 400 cycles at 45°C, 20% SOC DCR, and lower storage thickness expansion rate at 80°C. That is, the lithium-ion batteries in the embodiments of this application have better low-temperature performance, high-temperature cycling performance, and high-temperature storage performance, as well as lower impedance. Therefore, the lithium-ion batteries obtained by using the electrolyte provided in this application have better low-temperature performance, high-temperature cycling performance, and high-temperature storage performance, as well as lower impedance.

[0146] The mass percentage Y of compound II typically affects the performance of lithium-ion batteries, such as low-temperature performance, high-temperature cycling performance, high-temperature storage performance, and impedance. As can be seen from Examples 1-1 to 1-14, when the mass percentage Y of compound II is within the range specified in this application, the resulting lithium-ion batteries exhibit high capacity retention after 400 cycles at 45°C, high discharge capacity ratio at -10°C, high capacity retention after 200 cycles at -10°C, and low thickness expansion rate after 400 cycles at 45°C, 20% SOC DCR, and low thickness expansion rate during storage at 80°C. In other words, the lithium-ion batteries possess excellent low-temperature performance, high-temperature cycling performance, and high-temperature storage performance, as well as low impedance.

[0147] Table 2

[0148]

[0149]

[0150] Note: " / " in Table 2 indicates that the corresponding substance or parameter does not exist.

[0151] As can be seen from Examples 1-4 and Examples 2-1 to 2-9, the introduction of polynitrile compounds into the electrolyte can further improve the capacity retention rate and discharge capacity ratio of lithium-ion batteries after 400 cycles at 45°C and -10°C, reduce the thickness expansion rate after 400 cycles at 45°C and the storage thickness expansion rate at 80°C, and at the same time, the 20% SOC DCR is low and the capacity retention rate after 200 cycles at -10°C is high. That is, the introduction of polynitrile compounds can further improve the low-temperature performance, high-temperature cycling performance and high-temperature storage performance of lithium-ion batteries, and lithium-ion batteries have low impedance.

[0152] The mass percentage D and type of polynitrile compounds typically affect the performance of lithium-ion batteries, such as low-temperature performance, high-temperature cycle performance, high-temperature storage performance, and impedance. As can be seen from Examples 2-1 to 2-9, when the mass percentage D and type of polynitrile compounds are within the range of this application, the resulting lithium-ion batteries exhibit high capacity retention after 400 cycles at 45°C, high discharge capacity ratio at -10°C, high capacity retention after 200 cycles at -10°C, and low thickness expansion rate after 400 cycles at 45°C, 20% SOC DCR, and low thickness expansion rate during storage at 80°C. In other words, the lithium-ion batteries exhibit good low-temperature performance, high-temperature cycle performance, high-temperature storage performance, and low impedance. As can be seen from Examples 1-4 and Examples 2-1 to 2-5, when the mass percentage content of the polynitrile compound reaches 10% (Examples 2-5), compared with Examples 1-4, the capacity retention rate of the lithium-ion battery after 200 cycles at -10°C is slightly lower, and the 20% SOC DCR is slightly higher. However, the capacity retention rate after 200 cycles at -10°C is still relatively high, and the 20% SOC DCR is still relatively low. Moreover, the capacity retention rate after 400 cycles at 45°C and the discharge capacity ratio at -10°C are higher than those in Examples 1-4, and the thickness expansion rate after 400 cycles at 45°C and the storage thickness expansion rate at 80°C are lower than those in Examples 1-4. This indicates that when the mass percentage content D of the polynitrile compound is within the scope of this application, it can improve the low-temperature performance, high-temperature cycle performance, high-temperature storage performance, and impedance of the lithium-ion battery.

[0153] The relationship between the mass percentage D of the polynitrile compound, the mass percentage X of the compound shown in formula (I), and the mass percentage Y of compound II typically affects the performance of lithium-ion batteries, such as low-temperature performance, high-temperature cycling performance, high-temperature storage performance, and impedance. As can be seen from Examples 2-1 to 2-9, when the relationship (X+Y) / D between the mass percentage D of the polynitrile compound, the mass percentage X of the compound shown in formula (I), and the mass percentage Y of compound II is within the scope of this application, the resulting lithium-ion battery exhibits high capacity retention after 400 cycles at 45°C, high discharge capacity ratio at -10°C, high capacity retention after 200 cycles at -10°C, and low thickness expansion rate after 400 cycles at 45°C, 20% SOC DCR, and low storage thickness expansion rate at 80°C. In other words, the lithium-ion battery possesses good low-temperature performance, high-temperature cycling performance, and high-temperature storage performance, as well as low impedance.

[0154] Table 3

[0155]

[0156] Note: " / " in Table 3 indicates that the corresponding substance or parameter does not exist.

[0157] As can be seen from Examples 1-4 and Examples 3-1 to 3-9, the introduction of anhydride compounds into the electrolyte can further improve the capacity retention rate and discharge capacity ratio of lithium-ion batteries after 400 cycles at 45°C and -10°C, reduce the thickness expansion rate after 400 cycles at 45°C and the storage thickness expansion rate at 80°C, and at the same time, the 20% SOC DCR is low and the capacity retention rate after 200 cycles at -10°C is high. That is, the introduction of anhydride compounds can further improve the low-temperature performance, high-temperature cycling performance and high-temperature storage performance of lithium-ion batteries, and lithium-ion batteries have low impedance.

[0158] The mass percentage M and type of anhydride compounds typically affect the performance of lithium-ion batteries, such as low-temperature performance, high-temperature cycle performance, high-temperature storage performance, and impedance. As can be seen from Examples 3-1 to 3-9, when the mass percentage M and type of anhydride compounds are within the range of this application, the resulting lithium-ion batteries exhibit high capacity retention after 400 cycles at 45°C, high discharge capacity ratio at -10°C, high capacity retention after 200 cycles at -10°C, and low thickness expansion rate after 400 cycles at 45°C, 20% SOC DCR, and low thickness expansion rate during storage at 80°C. In other words, the lithium-ion batteries exhibit good low-temperature performance, high-temperature cycle performance, high-temperature storage performance, and low impedance. As can be seen from Examples 1-4 and Examples 3-1 to 3-6, when the mass percentage content of the anhydride compound reaches 5% (Examples 3-6), compared with Examples 1-4, the capacity retention rate of the lithium-ion battery after 200 cycles at -10°C is slightly lower, and the 20% SOC DCR is slightly higher. However, the capacity retention rate after 200 cycles at -10°C is still relatively high, and the 20% SOC DCR is still relatively low. Moreover, the capacity retention rate after 400 cycles at 45°C and the discharge capacity ratio at -10°C are higher than those in Examples 1-4, and the thickness expansion rate after 400 cycles at 45°C and the storage thickness expansion rate at 80°C are lower than those in Examples 1-4. This indicates that when the mass percentage content M of the anhydride compound is within the range of this application, it can improve the low-temperature performance, high-temperature cycle performance, high-temperature storage performance, and impedance of the lithium-ion battery.

[0159] Table 4

[0160]

[0161] Note: " / " in Table 4 indicates that the corresponding substance or parameter does not exist.

[0162] As can be seen from Examples 1-4 and Examples 4-1 to 4-12, the introduction of the compound shown in Formula (VII) into the electrolyte can further improve the capacity retention rate and discharge capacity ratio at -10°C after 400 cycles at 45°C of lithium-ion batteries, reduce the thickness expansion rate after 400 cycles at 45°C, and also show low 20% SOC DCR and low thickness expansion rate at 80°C storage, and high capacity retention rate after 200 cycles at -10°C. In other words, the introduction of the compound shown in Formula (VII) can further improve the low-temperature performance and high-temperature cycling performance of lithium-ion batteries, and lithium-ion batteries have good high-temperature storage performance and low impedance.

[0163] The mass percentage C and type of the compound shown in formula (VII) typically affect the performance of lithium-ion batteries, such as low-temperature performance, high-temperature cycling performance, high-temperature storage performance, and impedance. As can be seen from Examples 4-1 to 4-12, when the mass percentage C and type of the compound shown in formula (VII) are within the scope of this application, the resulting lithium-ion battery exhibits high capacity retention after 400 cycles at 45°C, high discharge capacity ratio at -10°C, high capacity retention after 200 cycles at -10°C, and low thickness expansion rate after 400 cycles at 45°C, 20% SOC DCR, and low storage thickness expansion rate at 80°C. In other words, the lithium-ion battery possesses good low-temperature performance, high-temperature cycling performance, and high-temperature storage performance, as well as low impedance. As can be seen from Examples 1-4 and Examples 4-1 to 4-7, when the mass percentage content of the compound shown in formula (VII) reaches 16% (Examples 4-7), compared with Examples 1-4, the capacity retention rate of the lithium-ion battery after 200 cycles at -10°C is slightly reduced, while the 20% SOC DCR and the thickness expansion rate at 80°C are slightly increased. However, the capacity retention rate after 200 cycles at -10°C is still relatively high, and the 20% SOC DCR and the thickness expansion rate at 80°C are still relatively low. Moreover, the capacity retention rate after 400 cycles at 45°C and the discharge capacity ratio at -10°C are higher than those in Examples 1-4, and the thickness expansion rate after 400 cycles at 45°C is lower than that in Examples 1-4. This indicates that when the mass percentage content C of the compound shown in formula (VII) is within the scope of this application, it can improve the low-temperature performance, high-temperature cycle performance, high-temperature storage performance, and impedance of the lithium-ion battery.

[0164] Table 5

[0165]

[0166] Note: " / " in Table 5 indicates that the corresponding substance or parameter does not exist.

[0167] As can be seen from Examples 1-4 and Examples 5-1 to 5-4, when the electrolyte includes at least two of the following compounds in addition to the compounds shown in Formula (I) and Formula (II): an anhydride compound, the compound shown in Formula (VII), and a polynitrile compound, the capacity retention rate after 400 cycles at 45°C, the discharge capacity ratio at -10°C, and the capacity retention rate after 200 cycles at -10°C can be further improved, while the thickness expansion rate after 400 cycles at 45°C, the 20% SOC DCR, and the storage thickness expansion rate at 80°C can be reduced. In other words, the introduction of at least two of the following compounds can further improve the low-temperature performance, high-temperature cycling performance, high-temperature storage performance, and impedance of lithium-ion batteries.

[0168] As can be seen from Examples 5-1 to 5-4, the compounds shown in Formula (I) and Compound II have good compatibility and superposition with the acid anhydride compound, the compound shown in Formula (VII), and the polynitrile compound. The lithium-ion battery obtained by using them in combination has a high capacity retention rate after 400 cycles at 45°C, a discharge capacity ratio at -10°C, a capacity retention rate after 200 cycles at -10°C, and a low thickness expansion rate after 400 cycles at 45°C, a 20% SOC DCR, and a storage thickness expansion rate at 80°C. In other words, the lithium-ion battery has good low-temperature performance, high-temperature cycling performance, and high-temperature storage performance, as well as low impedance.

[0169] It should be noted that, in this document, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0170] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0171] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application are included within the scope of protection of this application.

Claims

1. An electrolyte comprising a compound of formula (I) and a compound II, said compound II comprising a compound of formula (II-1) or a compound of formula (II-2): ； in, R 11 and R 12 Each group is independently selected from F, unsubstituted or Ra-substituted C1 to C6 alkyl groups, unsubstituted or Ra-substituted C2 to C6 alkenyl groups, unsubstituted or Ra-substituted phenyl groups, and unsubstituted or Ra-substituted Si1 to Si4 silyl groups, wherein Ra in each group is independently selected from F and C1 to C4 alkyl groups. ； Among them, R 21 and R 22 Each alkyl group is independently selected from H, F or C1 to C4, and n3 is 1, 2, 3 or 4; ； Wherein, D and E are each independently selected from C1 to C8 alkylene groups or C1 to C8 fluoroalkylene groups; The electrolyte also includes a polynitrile compound, and based on the mass of the electrolyte, the mass percentage of the polynitrile compound is D, the mass percentage of the compound shown in formula (I) is X, the mass percentage of compound II is Y, 0.01%≤X≤5%, 0.01%≤Y≤5%, 0.2%≤D≤10%, 0.01≤X / Y≤6, and 1.2≤(X+Y) / D≤2.

1.

2. The electrolyte according to claim 1, wherein, 0.01≤X / Y≤3.

3. The electrolyte according to claim 1, wherein, The compound represented by formula (I) includes at least one of the following compounds: 。 4. The electrolyte according to claim 1, wherein, The compound represented by formula (II-1) includes at least one of 1,3-propanesulfonate lactone, 1,4-butanesulfonate lactone, 1,2-butanesulfonate lactone, 1,3-butanesulfonate lactone, 2,4-butanesulfonate lactone or 1,3-pentanesulfonate lactone. The compound represented by formula (II-2) includes at least one of methylene methane disulfonate or ethylene methane disulfonate.

5. The electrolyte according to claim 1, wherein the polynitrile compound comprises at least one of the following compounds: 。 6. The electrolyte according to claim 1, further comprising an acid anhydride compound, the structure of which is shown in formula (VI): ； in, R1 to R8 are each independently selected from H, F, Cl, unsubstituted or F-substituted C1 to C4 chain alkyl, C3 to C5 cyclic alkyl, C2 to C4 alkenyl, C2 to C4 alkynyl, C1 to C4 alkoxy, C6 to C 10 Aryl, amino, aldehyde, acetyl, cyano, hydroxyl, or sulfonic acid groups; Based on the mass of the electrolyte, the mass percentage of the anhydride compound is M, where 0.01% ≤ M ≤ 5%.

7. The electrolyte according to claim 6, wherein, The acid anhydride compound includes at least one of the following compounds: 。 8. The electrolyte according to claim 1, further comprising the compound shown in formula (VII); ； in, R 71 R 72 R 73 and R 74 Each is independently selected from H, F, C1 to C 10 Fluoroalkyl, C1 to C 10 Fluoroalkoxy or C1 to C 10 fluoroalkoxyalkyl, and R 71 R 72 R 73 and R 74 Not both H; Based on the mass of the electrolyte, the mass percentage of the compound shown in formula (VII) is C, where 0.5% ≤ C ≤ 16%.

9. The electrolyte according to claim 8, wherein, The compound represented by formula (VII) includes at least one of the following compounds: 。 10. The electrolyte according to any one of claims 1 to 9, wherein it satisfies at least one of the following characteristics: （1）0.05%≤X≤3%； （2）0.5%≤Y≤4%； (3) The mass percentage of polynitrile compounds is D, 0.5%≤D≤5%.

11. The electrolyte according to claim 6 or 7, wherein the mass percentage of the acid anhydride compound is M, 0.1% ≤ M ≤ 2%.

12. The electrolyte according to claim 8 or 9, wherein the mass percentage of the compound shown in formula (VII) is C, 1% ≤ C ≤ 10%.

13. An electrochemical device comprising the electrolyte according to any one of claims 1 to 12.

14. An electronic device comprising the electrochemical device of claim 13.

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