Electrochemical device and electronic device

Abstract

An electrochemical device and an electronic device. The electrochemical device includes a positive electrode including a current collector and a positive electrode active material layer on at least one surface of the current collector and including a first positive electrode active material layer and a second positive electrode active material layer. Wherein the first positive electrode active material layer is located between the current collector and the second positive electrode active material layer, the binding force between the current collector and the first positive electrode active material layer is F1N / m, the cohesive force of the second positive electrode active material layer is F2N / m, and the positive electrode meets the condition that F1 / F2 is larger than or equal to 6. When the positive electrode is applied to the electrochemical device, the safety performance of the electrochemical device can be enhanced, the direct-current internal resistance of the electrochemical device at high pressure and high temperature can be fully inhibited, and the cycle performance of the electrochemical device is improved.

Description

[0001] This application is a divisional application of the Chinese patent application submitted to the China Patent Office on October 8, 2021, with application number 202180013405.7 and invention name “Electrochemical Device and Electronic Device”. Technical Field

[0002] The present application relates to the field of energy storage, and in particular to an electrochemical device and an electronic device. Background Art

[0003] In recent years, people have been demanding higher and higher energy density for electrochemical devices. However, in the pursuit of high energy density, the safety issues it brings are becoming increasingly prominent. For example, when electrochemical devices are abused by squeezing, puncture, overcharging, etc., short circuits are likely to occur inside them, accumulating a large amount of heat, leading to thermal runaway, and then fire, explosion and other problems.

[0004] By changing the configuration of the pole piece in the electrochemical device, the safety of the electrochemical device during use can be improved to a certain extent. For example, in the prior art, by providing a safety coating on the surface of the pole piece, the contact internal resistance can be increased and the risk of thermal runaway can be reduced. However, the provision of a safety coating (e.g., a ceramic layer) will reduce the energy density of the electrochemical device and deteriorate other electrochemical properties. Therefore, how to improve the energy density and electrochemical performance of the electrochemical device while ensuring the safety performance of the electrochemical device has received increasing attention. Summary of the invention

[0005] The present application solves the problems existing in the prior art to some extent by improving the positive electrode configuration of the electrochemical device and the matching between the positive electrode and the electrolyte.

[0006] According to one aspect of the present application, the present application provides an electrochemical device, which includes a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode includes: a current collector; and a positive electrode active material layer, wherein the positive electrode active material layer is located on at least one surface of the current collector and includes a first positive electrode active material layer and a second positive electrode active material layer, wherein the first positive electrode active material layer is located between the current collector and the second positive electrode active material layer; wherein the bonding force between the current collector and the first positive electrode active material layer is F 1 N / m, the cohesive force of the second positive electrode active material layer is F 2 N / m, the positive electrode satisfies: F 1 / F 2 ≥6.

[0007] According to an embodiment of the present application, in the above electrochemical device, F 1 ≥200.

[0008] According to an embodiment of the present application, in the above-mentioned electrochemical device, the first positive electrode active material layer includes a first binder, and the first binder satisfies at least one of the following conditions: (1) the first binder is water-soluble; (2) the first binder has an unsaturated acid functional group; (3) the first binder includes a polyacrylate with a polar functional group; (4) based on the mass of the first positive electrode active material layer, the mass fraction of the first binder is b%, where 2≤b≤20.

[0009] According to an embodiment of the present application, in the above electrochemical device, the first positive electrode active material layer includes a first binder, and based on the mass of the first positive electrode active material layer, the mass fraction of the first binder is b%, wherein F 1 and b satisfies: F 1 ≥200, 2≤b≤20 and F 1 / b≥10.

[0010] According to an embodiment of the present application, in the above-mentioned electrochemical device, the second positive electrode active material layer includes a second binder, and the second binder satisfies at least one of the following conditions: (1) the second binder is non-water-soluble; (2) the second binder includes a fluorine-containing polymer; (3) the second binder includes polyvinylidene fluoride having an α crystal form; (4) based on the mass of the second positive electrode active material layer, the mass fraction of the second binder is a%, where 0.5≤a≤5.

[0011] According to an embodiment of the present application, in the above-mentioned electrochemical device, the second positive electrode active material layer includes a second binder; based on the mass of the second positive electrode active material layer, the mass fraction of the second binder is a%, wherein F 2 The relationship with a satisfies: 5≤F 2 ≤60, 0.5≤a≤5 and F 2 / a≥1.

[0012] According to an embodiment of the present application, in the above electrochemical device, the first positive electrode active material layer includes a water-soluble binder, and the second positive electrode active material layer includes a water-insoluble binder.

[0013] According to an embodiment of the present application, in the above-mentioned electrochemical device, the first positive electrode active material layer includes a first binder, and the mass fraction of the first binder is b% based on the mass of the first positive electrode active material layer; the second positive electrode active material layer includes a second binder, and the mass fraction of the second binder is a% based on the mass of the second positive electrode active material layer; wherein a and b satisfy: 2.5≤a+b≤25; 1≤b / a≤40.

[0014] According to an embodiment of the present application, in the above electrochemical device, the thickness of the first positive electrode active material layer is H 1 μm, the thickness of the positive electrode active material layer is H μm, and the positive electrode satisfies: H 1 / H≤0.1.

[0015] According to an embodiment of the present application, in the above electrochemical device, 0.1≤H 1 ≤5.

[0016] According to an embodiment of the present application, in the above electrochemical device, the electrolyte includes a compound having a cyano group.

[0017] According to an embodiment of the present application, in the above electrochemical device, based on the mass of the electrolyte, the content of the compound having a cyano group is x%, where 0.1≤x≤15.

[0018] According to an embodiment of the present application, in the above electrochemical device, F 1 ≥200, and F 1 / x≥13.33.

[0019] According to an embodiment of the present application, in the above electrochemical device, the compound having a cyano group includes at least one of the following: succinonitrile, glutaronitrile, adiponitrile, 1,5-dicyanopentane, 1,6-dicyanohexane, tetramethylsuccinonitrile, 2-methylglutaronitrile, 2,4-dimethylglutaronitrile, 2,2,4,4-tetramethylglutaronitrile, 1,4-dicyanopentane, 1,2-dicyanobenzene, 1,3-dicyanobenzene, 1,4-dicyanobenzene, ethyl Diol bis(propionitrile) ether, 3,5-dioxa-heptanenitrile, 1,4-bis(cyanoethoxy)butane, diethylene glycol bis(2-cyanoethyl) ether, triethylene glycol bis(2-cyanoethyl) ether, tetraethylene glycol bis(2-cyanoethyl) ether, 1,3-bis(2-cyanoethoxy)propane, 1,4-bis(2-cyanoethoxy)butane, 1,5-bis(2-cyanoethoxy)pentane, ethylene glycol bis(4-cyanobutyl) ether, 1,4-dicyano- 2-Butene, 1,4-dicyano-2-methyl-2-butene, 1,4-dicyano-2-ethyl-2-butene, 1,4-dicyano-2,3-dimethyl-2-butene, 1,4-dicyano-2,3-diethyl-2-butene, 1,6-dicyano-3-hexene, 1,6-dicyano-2-methyl-3-hexene, 1,3,5-pentanetricarbonitrile, 1,2,3-propanetricarbonitrile, 1,3,6-hexanetricarbonitrile, 1,2,6-hexanetricarbonitrile tricarbonitrile, 1,2,3-tris(2-cyanoethoxy)propane, 1,2,4-tris(2-cyanoethoxy)butane, 1,1,1-tris(cyanoethoxymethylene)ethane, 1,1,1-tris(cyanoethoxymethylene)propane, 3-methyl-1,3,5-tris(cyanoethoxy)pentane, 1,2,7-tris(cyanoethoxy)heptane, 1,2,6-tris(cyanoethoxy)hexane or 1,2,5-tris(cyanoethoxy)pentane.

[0020] According to an embodiment of the present application, in the above electrochemical device, the electrolyte includes propylene carbonate.

[0021] According to an embodiment of the present application, in the above electrochemical device, based on the mass of the electrolyte, the content of propylene carbonate is y%, where 2≤y≤25.

[0022] According to an embodiment of the present application, in the above electrochemical device, based on the mass of the electrolyte, the content of propylene carbonate is y%, wherein F 2 / y≥0.5.

[0023] According to an embodiment of the present application, in the above electrochemical device, the electrolyte includes propyl propionate, wherein the content of the propyl propionate is z% based on the mass of the electrolyte, wherein 5≤z≤50.

[0024] According to an embodiment of the present application, in the above-mentioned electrochemical device, the electrolyte includes a compound having a cyano group and propyl propionate, wherein based on the mass of the electrolyte, the content of the compound having a cyano group is x%, and the content of the propyl propionate is z%, wherein 12≤x+z≤65, and 0.5≤z / x≤50.

[0025] According to an embodiment of the present application, in the above-mentioned electrochemical device, the electrolyte includes propylene carbonate and propyl propionate, wherein based on the mass of the electrolyte, the content of propylene carbonate is y%, and the content of propyl propionate is z%, wherein 15≤y+z≤70, and 1≤z / y≤5.

[0026] According to an embodiment of the present application, in the electrochemical device, the electrolyte includes at least one of the following: fluoroethylene carbonate, 1,3-propane sultone, vinyl sulfate, vinylene carbonate, or 1-propylphosphoric acid cyclic anhydride.

[0027] According to one aspect of the present application, the present application provides an electronic device, which includes the electrochemical device described in the above embodiment.

[0028] In at least one aspect, by controlling the bonding force F between the first positive electrode active material layer and the current collector 1 The cohesive force F of the second positive electrode active material layer 2 When the ratio is within an appropriate range, the probability of internal short circuit occurring when the electrochemical device is squeezed, punctured, overcharged or other abuse conditions can be effectively reduced, thereby improving the safety of the electrochemical device; at the same time, it can also effectively improve the cycle performance of the electrochemical device under high pressure and high temperature, and reduce its DC internal resistance under high pressure and high temperature.

[0029] Additional aspects and advantages of the embodiments of the present application will be described, shown, or explained in part in the subsequent description through implementation of the embodiments of the present application. DETAILED DESCRIPTION

[0030] The embodiments of the present application will be described in detail below. The embodiments described here are illustrative and are used to provide a basic understanding of the present application. The embodiments of the present application should not be interpreted as limiting the present application.

[0031] Amounts, ratios and other numerical values ​​are presented herein in a range format. It should be understood that such a range format is used for convenience and brevity, and should be flexibly interpreted to include not only the values ​​explicitly specified as range limits, but also all individual values ​​or sub-ranges encompassed within the range, as if each value and sub-range were explicitly specified.

[0032] In the detailed description and claims, a list of items connected by the term "at least one of" may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements. The term "at least one of" has the same meaning as the term "at least one of."

[0033] I. Positive electrode

[0034] In the present application, the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active material and a binder. In the present application, the positive electrode active material can be any substance that can reversibly embed and extract metal ions such as lithium ions and sodium ions. In some embodiments, the positive electrode current collector can be a positive electrode current collector commonly used in the art, including, but not limited to, aluminum foil or nickel foil.

[0035] In at least one aspect, the present application has found that by coating at least two layers of positive electrode active material layers on at least one surface of the positive electrode current collector and controlling the cohesion and adhesion of the at least two layers of positive electrode active material layers within an appropriate range, the safety performance of the electrochemical device can be enhanced, while also reducing the DC internal resistance of the electrochemical device in a high temperature and high pressure environment and improving its cycle stability.

[0036] Specifically, in some embodiments, the present application provides a positive electrode, which includes a current collector and a positive electrode active material layer, wherein the positive electrode active material layer is located on at least one surface of the current collector and includes a first positive electrode active material layer and a second positive electrode active material layer; wherein the first positive electrode active material layer is located between the current collector and the second positive electrode active material layer; wherein the bonding force between the current collector and the first positive electrode active material layer is F 1 N / m, the cohesive force of the second positive electrode active material layer is F 2 N / m, the positive electrode satisfies: F 1 / F 2 ≥6.

[0037] There are forces between different layers of the electrode sheet of an electrochemical device and within each layer. For example, during the charge and discharge cycle of the electrochemical device, due to the deintercalation of active metal ions (e.g., lithium ions) in the active material particles, the active material particles will expand or rupture, resulting in the existence of interaction forces between the current collector of the electrode sheet, the first active material layer and the second active material layer. 1 / F 2 The value of can reflect the mechanical stability of the positive electrode under the abuse of electrochemical devices such as extrusion, puncture, overcharging, or during the charge and discharge cycle. 1 / F 2 The value of satisfies the relation F 1 / F 2 When the value is ≥6, the stress of the electrode and the current collector is uniform, and the probability of dislocation or short circuit is lower when squeezed or punctured or during the charge and discharge cycle under high temperature and high pressure, thereby effectively improving the safety of the electrochemical device and effectively improving the cycle performance of the electrochemical device under high temperature and high pressure. In addition, unexpectedly, the above-mentioned positive electrode can also reduce the DC internal resistance of the electrochemical device under high temperature and high pressure.

[0038] In some embodiments, F 1 and F 2 Satisfaction: F 1 / F 2 ≥10. In some embodiments, F 1 and F 2 Satisfaction: F 1 / F 2 ≥20. In some embodiments, F 1 and F 2 Satisfaction: F 1 / F 2 ≥30. In some embodiments, F 1 and F 2 Satisfaction: F 1 / F 2 ≥40. In some embodiments, F 1 and F 2 Satisfaction: F 1 / F 2 ≥ 50. When the electrochemical device satisfies the above relationship, the performance can be further improved, especially the safety stability, cycle performance and impedance performance.

[0039] As the bonding force F between the positive electrode current collector and the first positive electrode active material layer increases 1 As the F increases, the probability of delamination between the positive electrode active material layer and the current collector decreases, so when the electrochemical device is subjected to high temperature, high pressure or abuse, the risk of short circuit in the device decreases, and the thermal safety performance increases. 1≥200. In some embodiments, F 1 ≥220. In some embodiments, F 1 250, 300, 350, 400, 450, 500, 600, 700, 800 or within the range consisting of any two of the above values.

[0040] In some embodiments, 5≤F 2 ≤100. In some embodiments, 15≤F 2 ≤80. In some embodiments, F 2 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100 or within the range consisting of any two of the foregoing values.

[0041] The present application has found that at least by selecting the type or content of the binder in the first positive electrode active material layer and / or the second positive electrode active material layer, it is helpful to further achieve F 1 / F 2 ≥6. In some embodiments, the first positive electrode active material layer includes a first binder, and the first binder satisfies at least one of the following conditions:

[0042] (1) The first binder is water-soluble;

[0043] (2) the first binder has an unsaturated acid functional group;

[0044] (3) The first binder includes polyacrylate having polar functional groups;

[0045] (4) Based on the mass of the first positive electrode active material layer, the mass fraction of the first binder is b%, where 2≤b≤20.

[0046] The use of a water-soluble binder in the first positive electrode active material layer can more effectively improve the performance of the electrochemical device. This may be due to hydrogen bonding or other intermolecular forces between the water-soluble binder and polar functional groups such as hydroxyl groups on the surface of the positive electrode current collector (e.g., aluminum foil), thereby increasing the bonding force between the positive electrode active material layer and the current collector, greatly reducing the risk of the active material layer falling off from the current collector, thereby greatly reducing the probability of dislocation or short circuit, effectively improving the safety of the electrochemical device and improving the cycle stability of the electrochemical device under high temperature and high pressure.

[0047] In some embodiments, when the first positive electrode active material layer satisfies F 1 When / b≥10, a positive electrode with better stability can be obtained, thereby further improving the electrochemical performance of the electrochemical device (for example, thermal safety performance, cycle performance and DC internal resistance under high temperature and high pressure). 1and b simultaneously satisfy: F 1 ≥200, 2≤b≤20 and F 1 / b≥10, the stability of the positive electrode can be further improved.

[0048] In some embodiments, the second positive electrode active material layer includes a second binder, and the second binder satisfies at least one of the following conditions:

[0049] (1) The second binder is water-insoluble;

[0050] (2) the second binder comprises a fluorine-containing polymer;

[0051] (3) The second binder includes polyvinylidene fluoride having an α-crystal structure;

[0052] (4) Based on the mass of the second positive electrode active material layer, the mass fraction of the second binder is a%, where 0.5≤a≤5.

[0053] In some embodiments, when the second positive electrode active material layer satisfies F 2 When / a≥1, a positive electrode with better stability can be obtained, thereby further improving the electrochemical performance of the electrochemical device (for example, thermal safety performance, cycle performance and DC internal resistance under high temperature and high pressure). 2 and a simultaneously satisfy: 5≤F 2 ≤60, 0.5≤a≤5 and F 2 / a≥1, the stability of the positive electrode can be further improved.

[0054] In some embodiments, the positive electrode satisfies both F 1 / b≥10 and F 2 / a≥1. Under this configuration, the positive electrode has better stability and the obtained electrochemical device also exhibits better electrochemical performance. In some embodiments, the positive electrode also satisfies, F 1 ≥200,2≤b≤20,F 1 / b≥10,5≤F 2 ≤60, 0.5≤a≤5 and F 2 / a≥1.

[0055] When the first positive electrode active material layer and the second positive electrode active material layer use binders with different solubility, the obtained electrochemical device exhibits more excellent thermal safety performance, cycle performance and impedance characteristics under high temperature and high pressure. In particular, the use of a water-soluble binder in the first positive electrode active material layer and a non-water-soluble binder in the second positive electrode active material layer can significantly improve the electrochemical performance of the electrochemical device.

[0056] Since the binder cannot achieve the deintercalation of metal ions, excessive addition will sacrifice the energy density of the electrochemical device. When the content of the binder is too low, the active material layer cannot be firmly attached to the positive electrode current collector, thereby increasing the risk of defilming. Therefore, by adjusting the content of the first binder and the second binder in the first positive electrode active material layer and the second positive electrode active material layer, respectively, the energy density of the electrochemical device and other electrochemical properties (for example, safety performance, cycle stability and low impedance) can be taken into account. In some embodiments, the mass fractions b% and a% of the first binder and the second binder satisfy 2.5≤a+b≤25 and 1≤b / a≤40. In some embodiments, a and b satisfy: 3≤a+b≤20 and 2≤b / a≤30. In some embodiments, a and b satisfy: 3.5≤a+b≤15 and 5≤b / a≤20. In some embodiments, a and b satisfy: 6≤a+b≤12 and 5≤b / a≤10.

[0057] In some embodiments, a satisfies 0.5≤a≤5. In some embodiments, a satisfies 1≤a≤4. In some embodiments, a is 0.8, 1, 1.2, 1.5, 1.8, 2, 2.5, 3, 3.5, 4, 4.5, 5, or is within a range consisting of any two of the foregoing values.

[0058] In some embodiments, b satisfies 2≤b≤20. In some embodiments, b satisfies 3≤b≤18. In some embodiments, b is 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 18, 20, or is within a range consisting of any two of the foregoing values.

[0059] The cohesion and adhesion tests were carried out as described in detail in the specific examples section of the present application.

[0060] The electrochemical performance of the electrochemical device can be further improved by adjusting the thickness of the first positive electrode active material layer, wherein the thickness mentioned here refers to the thickness of the positive electrode active material layer in a direction perpendicular to the current collector. In some embodiments, the thickness of the first positive electrode active material layer is H 1 μm, the thickness of the positive electrode active material layer is H μm, and the positive electrode satisfies: H 1 / H≤0.1. In some embodiments, the thickness H of the first positive electrode active material layer 1 μm is 0.1≤H 1 In some embodiments, the thickness H of the first positive electrode active material layer is 1 μm is 0.1≤H 1 In particular, when a water-soluble binder is used in the first positive electrode active material layer, controlling the thickness of the first positive electrode active material layer within the above range can further optimize the performance of the electrochemical device.

[0061] The present application does not particularly limit the type of positive electrode active material, as long as it can absorb and release metal ions (e.g., lithium ions, sodium ions) electrochemically. In addition, the positive electrode active materials applicable to the first positive electrode active material layer and the second positive electrode active material layer of the present application can be independently lithium-containing oxides, and can be the same or different. Lithium-containing transition metal oxides can be used as lithium-containing oxides.

[0062] In some embodiments, the positive electrode active material is a material containing lithium and at least one transition metal. Examples of the positive electrode active material may include, but are not limited to, lithium-containing transition metal oxides and lithium-containing transition metal phosphate compounds.

[0063] In some embodiments, the transition metal in the lithium-containing transition metal oxide includes V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. In some embodiments, the lithium-containing transition metal oxide includes LiCoO 2 Lithium cobalt composite oxide, LiNiO 2 Lithium nickel composite oxide, LiMnO 2 、LiMn 2 O 4 , Li 2 MnO 4 Lithium manganese composite oxide, LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O 2 、LiNi 0.5 Mn 0.3 Co 0.2 O 2 Lithium nickel manganese cobalt composite oxides, wherein a portion of the transition metal atoms as the main body of these lithium-containing transition metal oxides are replaced by other elements such as Na, K, B, F, Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Si, Nb, Mo, Sn, W, etc. Examples of lithium-containing transition metal oxides may include, but are not limited to, LiNi 0.5 Mn 0.5 O 2 、LiNi 0.85 Co 0.10 Al 0.05 O 2 、LiNi 0.33 Co 0.33 Mn 0.33 O 2 、LiNi 0.45 Co 0.10 Al 0.45 O 2 、LiMn 1.8 Al 0.2 O4 and LiMn 1.5 Ni 0.5 O 4 Examples of combinations of lithium-containing transition metal oxides include, but are not limited to, LiCoO 2 With LiMn 2 O 4 Combination of LiMn 2 O 4 A portion of the Mn in the 0.33 Co 0.33 Mn 0.33 O 2 ), LiCoO 2 Part of the Co can be replaced by transition metals.

[0064] In some embodiments, the transition metal in the lithium-containing transition metal phosphate compound includes V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. In some embodiments, the lithium-containing transition metal phosphate compound includes LiFePO 4 , Li 3 Fe 2 (PO 4 ) 3 、LiFeP 2 O 7 Iron phosphate, LiCoPO 4 Cobalt phosphates, etc., in which a part of the transition metal atoms serving as the main body of these lithium transition metal phosphate compounds are replaced by other elements such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, Si, etc.

[0065] In some embodiments, the positive electrode active material includes lithium phosphate, which can improve the continuous charging characteristics of the electrochemical device. There is no limitation on the use of lithium phosphate. In some embodiments, the positive electrode active material and lithium phosphate are mixed. In some embodiments, the content of lithium phosphate is greater than 0.1%, greater than 0.3% or greater than 0.5% relative to the mass of the above-mentioned positive electrode active material and lithium phosphate. In some embodiments, the content of lithium phosphate is less than 10%, less than 8% or less than 5% relative to the mass of the above-mentioned positive electrode active material and lithium phosphate. In some embodiments, the content of lithium phosphate is within the range formed by any two of the above-mentioned values.

[0066] A substance having a different composition from that of the positive electrode active material may be attached to the surface of the positive electrode active material. Examples of the surface-attached substance may include, but are not limited to: oxides such as aluminum oxide, silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; and carbon.

[0067] These surface-attached substances can be attached to the surface of the positive electrode active material by the following methods: a method in which the surface-attached substance is dissolved or suspended in a solvent and then added to the positive electrode active material and dried; a method in which a surface-attached substance precursor is dissolved or suspended in a solvent, added to the positive electrode active material, and then reacted by heating or the like; and a method in which the surface-attached substance is added to the positive electrode active material precursor and then fired simultaneously, etc. In the case of carbon attachment, a method in which a carbon material (e.g., activated carbon, etc.) is mechanically attached can also be used.

[0068] In some embodiments, the content of the surface-attached substance is greater than 0.1 ppm, greater than 1 ppm, or greater than 10 ppm based on the mass of the positive electrode active material layer. In some embodiments, the content of the surface-attached substance is less than 10%, less than 5%, or less than 2% based on the mass of the positive electrode active material layer. In some embodiments, the content of the surface-attached substance is within the range of any two of the above values ​​based on the mass of the positive electrode active material layer.

[0069] By attaching substances to the surface of the positive electrode active material, the oxidation reaction of the electrolyte on the surface of the positive electrode active material can be suppressed, and the life of the electrochemical device can be improved. When the amount of surface-attached substances is too small, the effect cannot be fully demonstrated; when the amount of surface-attached substances is too large, it will hinder the entry and exit of lithium ions, and the resistance may sometimes increase.

[0070] In the present application, a positive electrode active material in which a substance having a composition different from that of the positive electrode active material is attached to the surface of the positive electrode active material is also referred to as a “positive electrode active material”.

[0071] In some embodiments, the shape of the positive electrode active material particles includes, but is not limited to, block, polyhedron, sphere, ellipsoid, plate, needle and column, etc. In some embodiments, the positive electrode active material particles include primary particles, secondary particles or a combination thereof. In some embodiments, the primary particles can be agglomerated to form secondary particles.

[0072] In some embodiments, the tap density of the positive electrode active material is greater than 0.5 g / cm 3 , greater than 0.8g / cm 3 Or greater than 1.0g / cm 3. When the tap density of the positive electrode active material is within the above range, the amount of dispersion medium and the required amount of conductive material and positive electrode binder required for the formation of the positive electrode active material layer can be suppressed, thereby ensuring the filling rate of the positive electrode active material and the capacity of the electrochemical device. By using a composite oxide powder with a high tap density, a high-density positive electrode active material layer can be formed. The larger the tap density, the better, and there is no particular upper limit. In some embodiments, the tap density of the positive electrode active material is less than 4.0 g / cm 3 , less than 3.7g / cm 3 or less than 3.5g / cm 3 When the tap density of the positive electrode active material has the upper limit as described above, a decrease in load characteristics can be suppressed.

[0073] The tap density of the positive electrode active material can be calculated by placing 5 g to 10 g of the positive electrode active material powder in a 10 mL glass measuring cylinder and vibrating the cylinder 200 times with a stroke of 20 mm to obtain the powder packing density (tap density).

[0074] When the positive electrode active material particles are primary particles, the median particle size (D50) of the positive electrode active material particles refers to the primary particle size of the positive electrode active material particles. When the primary particles of the positive electrode active material particles aggregate to form secondary particles, the median particle size (D50) of the positive electrode active material particles refers to the secondary particle size of the positive electrode active material particles.

[0075] In some embodiments, the median particle size (D50) of the positive electrode active material particles is greater than 0.3 μm, greater than 0.5 μm, greater than 0.8 μm or greater than 1.0 μm. In some embodiments, the median particle size (D50) of the positive electrode active material particles is less than 30 μm, less than 27 μm, less than 25 μm or less than 22 μm. In some embodiments, the median particle size (D50) of the positive electrode active material particles is within the range composed of any two of the above values. When the median particle size (D50) of the positive electrode active material particles is within the above range, a positive electrode active material with a high tap density can be obtained, which can inhibit the reduction of the performance of the electrochemical device. On the other hand, in the preparation process of the positive electrode of the electrochemical device (that is, when the positive electrode active material, the conductive material and the binder are slurried with a solvent and coated in a thin film), problems such as streaks can be prevented. Here, by mixing two or more positive electrode active materials with different median particle sizes, the filling property during the preparation of the positive electrode can be further improved.

[0076] The median particle size (D50) of the positive electrode active material particles can be measured using a laser diffraction / scattering particle size distribution measuring device: when using LA-920 manufactured by HORIBA as a particle size distribution meter, a 0.1% sodium hexametaphosphate aqueous solution is used as the dispersion medium used in the measurement, and the measurement refractive index is set to 1.24 after 5 minutes of ultrasonic dispersion.

[0077] In at least one aspect, the present application also provides a method for manufacturing the above-mentioned positive electrode, the method comprising:

[0078] Dispersing a first positive electrode active material, a first conductive material, and a first binder in a solvent to prepare a slurry for a first positive electrode active material layer, and dispersing a second positive electrode active material, a second conductive material, and a second binder in a solvent to prepare a slurry for a second positive electrode active material layer;

[0079] The slurry for the first positive active material layer is applied to at least one surface of the positive current collector, and the slurry for the second positive active material layer is applied thereon before or after the first positive active material layer is dried.

[0080] In the above method, if the slurry for the first and second positive electrode active material layers is applied on both surfaces of the positive electrode collector, the thickness and loading amount of the first positive electrode active material layer and the second positive electrode active material layer applied on one side of the positive electrode collector may be the same as or different from the thickness and loading amount applied on the other side of the positive electrode collector.

[0081] II. Electrolyte

[0082] The electrolyte used in the electrochemical device of the present application includes an electrolyte and a solvent for dissolving the electrolyte. In some embodiments, the electrolyte used in the electrochemical device of the present application also includes an additive.

[0083] In some embodiments, the electrolyte described herein includes a compound having a cyano group. The compound having a cyano group can form a stable protective film on the surface of the positive electrode active material, thereby improving the thermal safety, cycle performance and impedance characteristics of the electrochemical device under high temperature and high pressure.

[0084] In some embodiments, the compound having a cyano group includes, but is not limited to, at least one of the following: succinonitrile, glutaronitrile, adiponitrile, 1,5-dicyanopentane, 1,6-dicyanohexane, tetramethylsuccinonitrile, 2-methylglutaronitrile, 2,4-dimethylglutaronitrile, 2,2,4,4-tetramethylglutaronitrile, 1,4-dicyanopentane, 1,2-dicyanobenzene, 1,3-dicyanobenzene, 1,4-dicyanobenzene, ethylene glycol bis(ethylene glycol); 1,4-bis(cyanoethoxy)butane, diethylene glycol di(2-cyanoethyl)ether, triethylene glycol di(2-cyanoethyl)ether, tetraethylene glycol di(2-cyanoethyl)ether, 1,3-bis(2-cyanoethoxy)propane, 1,4-bis(2-cyanoethoxy)butane, 1,5-bis(2-cyanoethoxy)pentane, ethylene glycol di(4-cyanobutyl)ether, 1,4-dicyano-2-butylene glycol di(2-cyanoethyl)ether 1,4-dicyano-2-methyl-2-butene, 1,4-dicyano-2-ethyl-2-butene, 1,4-dicyano-2,3-dimethyl-2-butene, 1,4-dicyano-2,3-diethyl-2-butene, 1,6-dicyano-3-hexene, 1,6-dicyano-2-methyl-3-hexene, 1,3,5-pentanetricarbonitrile, 1,2,3-propanetricarbonitrile, 1,3,6-hexatriconitrile, 1,2,6-hexatriconitrile nitrile, 1,2,3-tris(2-cyanoethoxy)propane, 1,2,4-tris(2-cyanoethoxy)butane, 1,1,1-tris(cyanoethoxymethylene)ethane, 1,1,1-tris(cyanoethoxymethylene)propane, 3-methyl-1,3,5-tris(cyanoethoxy)pentane, 1,2,7-tris(cyanoethoxy)heptane, 1,2,6-tris(cyanoethoxy)hexane or 1,2,5-tris(cyanoethoxy)pentane.

[0085] The above compounds having a cyano group may be used alone or in any combination. When the electrolyte contains two or more compounds having a cyano group, the content of the compound having a cyano group refers to the total content of the two or more compounds having a cyano group.

[0086] The protective effect of the compound having a cyano group is correlated to its dosage. In some embodiments, based on the mass of the electrolyte, the content of the compound having a cyano group is x%, where 0.1≤x≤15. In some embodiments, x is in the range of 0.5≤x≤10, 1≤x≤8 or 3≤x≤5. In some embodiments, x can be, but is not limited to, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15 or in the range consisting of any two of the above values.

[0087] Since the compound with cyano group can form a stable protective film on the surface of the positive electrode active material, it is particularly important for repairing the broken part of the particles. The present application further found that when the bonding force F between the current collector and the first positive electrode active material layer is controlled 1 When the content x% of the compound having a cyano group satisfies the relationship in the following embodiment, it can further compensate for the particle breakage caused by the electrochemical device during the charge and discharge cycle, thereby further improving the thermal safety performance and cycle performance of the electrochemical device under high temperature and high pressure, and reducing its DC internal resistance. In some embodiments, F 1 and x satisfies: F 1 / x≥13.33. In some embodiments, F 1 and x satisfies: F 1 / x≥25. In some embodiments, F 1 and x satisfies: F 1 / x≥33.33. In some embodiments, F 1 and x satisfies: F 1 / x≥50. In some embodiments, F 1 and x satisfies: F 1 / x≥100. In particular, in the above embodiment, control F 1 Above 200 N / m, better electrochemical performance can be achieved.

[0088] In some embodiments, the electrolyte further comprises any non-aqueous solvent known in the prior art that can be used as a solvent for the electrolyte.

[0089] In some embodiments, the non-aqueous solvent includes, but is not limited to, one or more of the following: cyclic carbonates, chain carbonates, cyclic carboxylates, chain carboxylates, cyclic ethers, chain ethers, phosphorus-containing organic solvents, sulfur-containing organic solvents, and aromatic fluorine-containing solvents.

[0090] In some embodiments, examples of the cyclic carbonate may include, but are not limited to, one or more of the following: ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate. In some embodiments, the cyclic carbonate has 3-6 carbon atoms.

[0091] In some embodiments, the electrolyte contains propylene carbonate. By controlling the content of propylene carbonate in the electrolyte, an electrochemical device having excellent thermal safety performance and cycle performance and low DC impedance under high temperature and high pressure can be obtained. In some embodiments, based on the mass of the electrolyte, the content of propylene carbonate is y%, where 2≤y≤25. In some embodiments, y can be, but is not limited to, 6, 7, 8, 10, 12, 14, 18, 20, 22, 25 or within a range consisting of any two of the above values.

[0092] In addition, the present application has found that by controlling the cohesive force F of the second positive electrode active material layer 2 The relationship between the content of propylene carbonate and y% can further optimize the thermal safety performance, cycle performance and DC impedance of the electrochemical device. Under high temperature and high pressure conditions, propylene carbonate easily causes swelling of the positive electrode and may damage the interface between the positive electrode and the electrolyte, causing side reactions. When the cohesive force of the second positive electrode active material layer increases, although the swelling decreases, the side reaction of the electrolyte being oxidized by the positive electrode increases; and when the cohesive force of the second positive electrode active material layer decreases, although the side reaction weakens, it will cause swelling to increase. Therefore, controlling F 2 The certain relationship between F and y can better balance swelling and side reactions, thereby further improving the performance of the electrochemical device. 2 and y satisfies: F 2 / y≥0.5. In some embodiments, F 2 and y satisfies: F 2 / y≥1. In some embodiments, F 2 and y satisfies: F 2 / y≥2. In some embodiments, F 2 and y satisfies: F 2 / y≥5. In some embodiments, F 2 and y satisfies: F 2 / y≥6.

[0093] In some embodiments, the electrolyte includes propyl propionate. By controlling the content of propyl propionate in the electrolyte, the resulting electrochemical device exhibits excellent thermal safety and cycle performance under high temperature and high pressure; in addition, unexpectedly, the low-temperature rate performance of the resulting electrochemical device can also be greatly improved. In some embodiments, based on the mass of the electrolyte, the content of propyl propionate is z%, where 5≤z≤50. In some embodiments, z can be, but is not limited to, 6, 8, 10, 20, 25, 30, 35, 40 or within a range consisting of any two of the above values.

[0094] When the electrolyte includes both the cyano compound and propyl propionate, by controlling the relationship between the contents of the cyano compound and propyl propionate in the electrolyte, an electrochemical device having excellent thermal safety and cycle performance and low DC impedance at high temperature and high pressure can also be obtained. In some embodiments, x and z satisfy: 12≤x+z≤65, and 0.5≤z / x≤50.

[0095] When the electrolyte includes both propylene carbonate and propyl propionate, by controlling the relationship between the contents of propylene carbonate and propyl propionate in the electrolyte, an electrochemical device having excellent thermal safety performance and cycle performance and low temperature rate performance under high temperature and high pressure can also be obtained. In some embodiments, y and z satisfy: 15≤y+z≤70; and 1≤z / y≤5.

[0096] In some embodiments, the electrolyte further comprises at least one of fluoroethylene carbonate, 1,3-propane sultone, vinyl sulfate, vinylene carbonate, and 1-propyl phosphoric acid cyclic anhydride. When a compound having a cyano group, propylene carbonate, propyl propionate, fluoroethylene carbonate, 1,3-propane sultone, vinyl sulfate, vinylene carbonate, and 1-propyl phosphoric acid cyclic anhydride are used in combination, the interface between the electrode and the electrolyte can be further stabilized, thereby improving the thermal safety performance and cycle performance of the electrochemical device under high temperature and high pressure, especially the storage performance at high temperature will be greatly improved.

[0097] In some embodiments, the electrolyte is not particularly limited, and any substance known as an electrolyte may be used arbitrarily. In the case of a lithium secondary battery, a lithium salt is generally used. Examples of the electrolyte may include, but are not limited to, LiPF 6 , LiBF 4 、LiClO 4 、LiAlF 4 、LiSbF 6 ,LiWF 7 Inorganic lithium salts such as LiWOF 5 Lithium tungstate, etc.; HCO 2 Li, CH 3 CO 2 Li, CH 2 FCO 2 Li, CHF 2 CO 2 Li, CF 3 CO 2 Li, CF 3 CH 2 CO 2 Li, CF 3 CF 2 CO 2 Li, CF 3 CF 2 CF 2 CO 2 Li, CF 3 CF 2 CF 2 CF 2 CO 2 Lithium carboxylates such as Li; FSO 3 Li, CH3 SO 3 Li, CH 2 FSO 3 Li, CHF 2 SO 3 Li, CF 3 SO 3 Li, CF 3 CF 2 SO 3 Li, CF 3 CF 2 CF 2 SO 3 Li, CF 3 CF 2 CF 2 CF 2 SO 3 Lithium sulfonate salts such as Li; LiN(FCO) 2 、LiN(FCO)(FSO 2 )、LiN(FSO 2 ) 2 、LiN(FSO 2 )(CF 3 SO 2 )、LiN(CF 3 SO 2 ) 2 、LiN(C 2 F 5 SO 2 ) 2 、Cyclic 1,2-perfluoroethane bissulfonyl imide lithium、Cyclic 1,3-perfluoropropane bissulfonyl imide lithium、LiN(CF 3 SO 2 )(C 4 F 9 SO 2 ) and other lithium imide salts; LiC(FSO 2 ) 3 、LiC(CF 3 SO 2 ) 3 、LiC(C 2 F 5 SO 2 ) 3 Methylated lithium salts; (malonate) borate lithium salts such as bis(malonate) borate and difluoro(malonate) borate lithium salts; (malonate) phosphate lithium salts such as tris(malonate) phosphate, difluorobis(malonate) lithium phosphate, tetrafluoro(malonate) lithium phosphate; and LiPF 4 (CF 3 ) 2 、LiPF4 (C 2 F 5 ) 2 、LiPF 4 (CF 3 SO 2 ) 2 、LiPF 4 (C 2 F 5 SO 2 ) 2 , LiBF 3 CF 3 , LiBF 3 C 2 F 5 , LiBF 3 C 3 F 7 , LiBF 2 (CF 3 ) 2 , LiBF 2 (C 2 F 5 ) 2 , LiBF 2 (CF 3 SO 2 ) 2 , LiBF 2 (C 2 F 5 SO 2 ) 2 Fluorine-containing organic lithium salts; lithium oxalate borate salts such as lithium difluorooxalatoborate and lithium bis(oxalato)borate; lithium oxalate phosphate salts such as lithium tetrafluorooxalato phosphate, lithium difluorobis(oxalato)phosphate, and lithium tris(oxalato)phosphate.

[0098] In some embodiments, the electrolyte is selected from LiPF 6 、LiSbF 6 、FSO 3 Li, CF 3 SO 3 Li、LiN(FSO 2 ) 2 、LiN(FSO 2 )(CF 3 SO 2 )、LiN(CF 3 SO 2 ) 2 、LiN(C 2 F 5 SO 2 ) 2、Cyclic 1,2-perfluoroethane bissulfonyl imide lithium、Cyclic 1,3-perfluoropropane bissulfonyl imide lithium、LiC(FSO 2 ) 3 、LiC(CF 3 SO 2 ) 3 、LiC(C 2 F 5 SO 2 ) 3 , LiBF 3 CF 3 , LiBF 3 C 2 F 5 、LiPF 3 (CF 3 ) 3 、LiPF 3 (C 2 F 5 ) 3 , lithium difluorooxalatoborate, lithium bis(oxalate)borate or lithium difluorobis(oxalato)phosphate, which help to improve the output power characteristics, high-rate charge and discharge characteristics, high-temperature storage characteristics and cycle characteristics of electrochemical devices.

[0099] The present application has no particular restrictions on the content of the electrolyte, as long as it does not impair the effect of the present application. In some embodiments, the total molar concentration of lithium in the electrolyte is above 0.3 mol / L, above 0.4 mol / L, or above 0.5 mol / L. In some embodiments, the total molar concentration of lithium in the electrolyte is below 3.0 mol / L, below 2.5 mol / L, or below 2.0 mol / L. In some embodiments, the total molar concentration of lithium in the electrolyte is within the range consisting of any two of the above values. When the electrolyte concentration is within the above range, there will not be too little lithium as a charged particle, and the viscosity can be kept within an appropriate range, thereby easily ensuring good conductivity.

[0100] When two or more electrolytes are used, the electrolyte includes at least one salt selected from the group consisting of monofluorophosphate, borate, oxalate and fluorosulfonate. In some embodiments, the electrolyte includes a salt selected from the group consisting of monofluorophosphate, oxalate and fluorosulfonate. In some embodiments, the electrolyte includes a lithium salt. In some embodiments, based on the mass of the electrolyte, the content of the salt selected from the group consisting of monofluorophosphate, borate, oxalate and fluorosulfonate is greater than 0.01% or greater than 0.1%. In some embodiments, based on the mass of the electrolyte, the content of the salt selected from the group consisting of monofluorophosphate, borate, oxalate and fluorosulfonate is less than 20% or less than 10%. In some embodiments, the content of the salt selected from the group consisting of monofluorophosphate, borate, oxalate and fluorosulfonate is within the range of any two of the above values.

[0101] In some embodiments, the electrolyte comprises one or more substances selected from the group consisting of monofluorophosphate, borate, oxalate and fluorosulfonate and one or more salts other than these. As salts other than these, the lithium salts exemplified above can be cited, and in some embodiments, LiPF 6 、LiN(FSO 2 )(CF 3 SO 2 )、LiN(CF 3 SO 2 ) 2 、LiN(C 2 F 5 SO 2 ) 2 、Cyclic 1,2-perfluoroethane bissulfonyl imide lithium、Cyclic 1,3-perfluoropropane bissulfonyl imide lithium、LiC(FSO 2 ) 3 、LiC(CF 3 SO 2 ) 3 、LiC(C 2 F 5 SO 2 ) 3 , LiBF 3 CF 3 , LiBF 3 C 2 F 5 、LiPF 3 (CF 3 ) 3 、LiPF 3 (C 2 F 5 ) 3 In some embodiments, the salt other than LiPF 6 .

[0102] In some embodiments, the content of the other salts is greater than 0.01% or greater than 0.1% based on the mass of the electrolyte. In some embodiments, the content of the other salts is less than 20%, less than 15%, or less than 10% based on the mass of the electrolyte. In some embodiments, the content of the other salts is within the range formed by any two of the above values. The other salts having the above content help balance the conductivity and viscosity of the electrolyte.

[0103] III. Negative electrode

[0104] The negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, and the negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer can be one or more layers, and each layer of the multi-layer negative electrode active material can contain the same or different negative electrode active materials. The negative electrode active material is any material that can reversibly embed and deintercalate metal ions such as lithium ions and sodium ions. In some embodiments, the charge capacity of the negative electrode active material is greater than the discharge capacity of the positive electrode active material to prevent lithium metal from being accidentally precipitated on the negative electrode during charging.

[0105] In some embodiments, the negative electrode current collector may be a negative electrode current collector commonly used in the art, including, but not limited to, metal materials such as aluminum, copper, nickel, stainless steel, and nickel-plated steel.

[0106] In the case where the negative electrode current collector is a metal material, the negative electrode current collector may include, but is not limited to, metal foil, metal cylinder, metal strip, metal plate, metal film, metal mesh, stamped metal, foamed metal, etc. In some embodiments, the negative electrode current collector is a metal film. In some embodiments, the negative electrode current collector is a copper foil. In some embodiments, the negative electrode current collector is a rolled copper foil based on a rolling method or an electrolytic copper foil based on an electrolytic method.

[0107] In some embodiments, the thickness of the negative electrode current collector is greater than 1 μm or greater than 5 μm. In some embodiments, the thickness of the negative electrode current collector is less than 100 μm or less than 50 μm. In some embodiments, the thickness of the negative electrode current collector is within the range of any two of the above values.

[0108] There is no particular limitation on the negative electrode active material, as long as it can reversibly absorb and release lithium ions or sodium ions. Examples of negative electrode active materials may include, but are not limited to, carbon materials such as natural graphite and artificial graphite; metals such as silicon (Si) and tin (Sn); or oxides of metal elements such as Si and Sn. Negative electrode active materials may be used alone or in combination.

[0109] The negative electrode active material layer also includes a negative electrode binder. The negative electrode binder can improve the bonding between the negative electrode active material particles and the bonding between the negative electrode active material and the current collector. The type of negative electrode binder is not particularly limited, as long as it is a material that is stable to the solvent used in the electrolyte or electrode manufacturing. In some embodiments, the negative electrode binder includes a resin binder. Examples of resin binders include, but are not limited to, fluororesins, polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, and the like. When an aqueous solvent is used to prepare the negative electrode mixture slurry, the negative electrode binder includes, but is not limited to, carboxymethyl cellulose (CMC) or its salt, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salt, polyvinyl alcohol, and the like.

[0110] IV. Electrochemical Devices

[0111] In at least one aspect, the present application provides an electrochemical device comprising a positive electrode, a negative electrode, an electrolyte, and a separator between the positive electrode and the negative electrode. In some embodiments, the positive electrode comprises the positive electrode described in the above embodiment of the present application. In some embodiments, the electrolyte comprises the electrolyte described in the above embodiment of the present application.

[0112] The present application has no particular restrictions on the material and shape of the isolation membrane, as long as it does not significantly impair the effect of the present application. The isolation membrane may be a resin, glass fiber, inorganic material, etc. formed by a material that is stable to the electrolyte of the present application. In some embodiments, the isolation membrane includes a porous sheet or a non-woven fabric-like material with excellent liquid retention. Examples of materials for resin or glass fiber isolation membranes may include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, polyether sulfone, etc. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The materials of the above isolation membranes can be used alone or in any combination.

[0113] The isolation film may also be a material formed by laminating the above materials, and examples thereof include, but are not limited to, a three-layer isolation film formed by laminating polypropylene, polyethylene, and polypropylene in this order.

[0114] Examples of inorganic materials may include, but are not limited to, oxides such as aluminum oxide and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates (e.g., barium sulfate, calcium sulfate, etc.) The form of the inorganic material may include, but is not limited to, granular or fibrous.

[0115] The separator may be in the form of a thin film, examples of which include, but are not limited to, nonwoven fabrics, woven fabrics, microporous films, etc. In the thin film form, the separator has a pore size of 0.01 μm to 1 μm and a thickness of 5 μm to 50 μm. In addition to the above-mentioned independent thin film separators, the following separators may also be used: a separator formed by forming a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive electrode and / or the negative electrode using a resin-based adhesive, for example, a separator formed by using a fluororesin as an adhesive to form a porous layer on both sides of the positive electrode with aluminum oxide particles having a particle size of 90% less than 1 μm.

[0116] The thickness of the isolation membrane is arbitrary. In some embodiments, the thickness of the isolation membrane is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the isolation membrane is less than 50 μm, less than 40 μm, or less than 30 μm. In some embodiments, the thickness of the isolation membrane is within the range formed by any two of the above values. When the thickness of the isolation membrane is within the above range, the insulation and mechanical strength can be ensured, and the rate characteristics and energy density of the electrochemical device can be ensured.

[0117] When a porous material such as a porous sheet or non-woven fabric is used as an isolation membrane, the porosity of the isolation membrane is arbitrary. In some embodiments, the porosity of the isolation membrane is greater than 10%, greater than 15%, or greater than 20%. In some embodiments, the porosity of the isolation membrane is less than 60%, less than 50%, or less than 45%. In some embodiments, the porosity of the isolation membrane is within the range formed by any two of the above values. When the porosity of the isolation membrane is within the above range, insulation and mechanical strength can be ensured, and membrane resistance can be suppressed, so that the electrochemical device has good safety characteristics.

[0118] The average pore size of the isolation membrane is also arbitrary. In some embodiments, the average pore size of the isolation membrane is less than 0.5 μm or less than 0.2 μm. In some embodiments, the average pore size of the isolation membrane is greater than 0.05 μm. In some embodiments, the average pore size of the isolation membrane is within the range formed by any two of the above values. If the average pore size of the isolation membrane exceeds the above range, short circuit is likely to occur. When the average pore size of the isolation membrane is within the above range, the electrochemical device has good safety characteristics.

[0119] V. Application

[0120] The electrochemical device of the present application includes any device that generates an electrochemical reaction, and its specific examples include all kinds of primary batteries, secondary batteries, fuel cells, solar cells or capacitors. In particular, the electrochemical device is a lithium secondary battery, including a lithium metal secondary battery or a lithium ion secondary battery.

[0121] The present application further provides an electronic device, which includes the electrochemical device according to the present application.

[0122] The use of the electrochemical device of the present application is not particularly limited, and it can be used for any electronic device known in the prior art. In some embodiments, the electrochemical device of the present application can be used for, but not limited to, laptop computers, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.

[0123] The preparation of lithium-ion batteries is described below by taking lithium-ion batteries as an example and combining specific embodiments. Those skilled in the art will understand that the preparation method described in this application is only an example, and any other suitable preparation method is within the scope of this application. Specific embodiments

[0125] (I) Preparation of lithium-ion batteries

[0126] (1) Preparation of negative electrode: Artificial graphite, styrene-butadiene rubber and sodium carboxymethyl cellulose were mixed with deionized water in a mass ratio of 96%:2%:2% and stirred evenly to obtain slurry. The slurry was coated on a 9μm copper foil. After drying and cold pressing, the negative electrode was obtained by cutting and welding the tabs.

[0127] (2) Preparation of positive electrode: lithium iron phosphate, conductive carbon black Super-P and the first binder are mixed with deionized water in a mass ratio of 96.5%:1%:b%, and stirred evenly to prepare the first positive electrode active material layer slurry; lithium cobalt oxide, conductive carbon black Super-P and the second binder are mixed with N-methylpyrrolidone (NMP) in a mass ratio of 97.5%:1%:a%, and stirred evenly to prepare the second positive electrode active material layer slurry. The first positive electrode active material layer slurry is coated on the front and back surfaces of the positive electrode current collector made of aluminum foil with a thickness of 5μm; then the second positive electrode active material layer slurry is coated thereon with a thickness of 50μm, and the total thickness of single-sided coating is 55μm. Then, it is dried, cold pressed, cut into pieces, and the pole ears are welded to obtain the positive electrode.

[0128] (3) Preparation of electrolyte: EC and DEC were mixed in a mass ratio of 1:1 under dry argon atmosphere, and LiPF 6 Mix well to form a basic electrolyte, in which LiPF 6The concentration is 1.15 mol / L. Additives of different contents are added to the basic electrolyte to obtain the electrolytes of the examples and comparative examples described in the present application.

[0129] The abbreviations and names of the components in the electrolyte are shown in the following table:

[0130] Material Name abbreviation Material Name abbreviation Ethylene carbonate EC Propylene carbonate PC Diethyl carbonate DEC Propyl Propionate PP Succinonitrile SN Adiponitrile ADN Ethylene glycol di(2-cyanoethyl) ether EDN 1,3,6-Hexanetrinitrile HTCN 1,2,3-Tris(2-cyanoethoxy)propane TCEP Fluoroethylene carbonate FEC 1,3-Propane sultone PS Vinyl Sulfate DTD Vinylene carbonate VC 1-Propylphosphonic acid cyclic anhydride T3P

[0131] (4) Preparation of isolation membrane: 8 μm polyethylene film was used as the isolation membrane.

[0132] (5) Preparation of lithium-ion batteries: The obtained positive electrode, separator and negative electrode are wound in order and placed in an outer packaging foil, leaving a liquid injection port. The electrolyte is poured from the liquid injection port, packaged, and then the lithium-ion battery is manufactured through the formation and capacity processes.

[0133] (II) Test methods for positive electrodes and lithium-ion batteries

[0134] (1) Cohesion test: Take the pole pieces disassembled from the battery, select the single-sided coated pole pieces (or process the double-sided coated pole pieces into single-sided pole pieces through a scraper), and cut them into test samples with a length of 100 mm and a width of 10 mm. Take a stainless steel plate with a width of 25 mm, stick 3M double-sided tape (width 11 mm), and paste the test sample on the 3M double-sided tape on the stainless steel plate, where the current collector is bonded to the double-sided tape; use a 2000g roller to roll back and forth on the surface of the sample three times (300mm / min). Then paste a 10mm wide and 50μm thick tape (model NITTO.NO5000NS) on the surface of the active material layer, and use a 2000g roller to roll back and forth on its surface three times (300mm / min). Bend the tape 180 degrees, manually peel off the tape and the active material layer by 25 mm, fix the sample on an Instron 336 tensile tester, keep the peeling surface consistent with the force line of the tester (i.e., perform 180° peeling), and continuously peel at 300 mm / min to obtain the cohesion curve. The average value of the stable section is taken as the peeling force F. 0 , then the cohesive force of the tested electrode is: F 2 =F 0 / Width of the sample to be tested, F 2 The unit of measurement is N / m.

[0135] (2) Adhesion test: Take the pole pieces disassembled from the battery, cut them into test strips of 20mm×10cm in size, and adhere them to a clean stainless steel plate with a 20mm wide double-sided tape (model NITTO.NO5000NS). Use a tensile testing machine to perform a 180° peel test, and the tensile speed of the tensile testing machine is 50mm / min. The average value of the peeling force collected when the first positive electrode active material layer is completely peeled off from the positive electrode current collector is the adhesion F between the positive electrode current collector and the first positive electrode active material layer. The adhesion of the pole piece under test is: F 1 = F / width of the sample to be tested, F 1 The unit of measurement is N / m.

[0136] (3) Thermal safety temperature rise test

[0137] At 25°C, the lithium-ion battery was left to stand for 30 minutes and the thickness was measured as T 1 Then, the temperature was raised to 130°C at a rate of 5°C / min and maintained for 30 minutes. The thickness was measured as T 2 The thickness expansion rate of lithium-ion batteries is calculated by the following formula:

[0138] Temperature rise thickness expansion rate = [(T 2 -T 1 ) / T 1 ]×100%.

[0139] (4) DC internal resistance test under high temperature and high pressure

[0140] At 65°C, charge the lithium-ion battery to 4.7V at 1.5C constant current, then charge to 0.05C at 4.7V constant voltage, and leave it for 30 minutes. Discharge at 0.1C for 10 seconds, and record the voltage value as U 1 , discharge at 1C for 360 seconds, record the voltage value as U 2 Repeat the charge and discharge steps 5 times. "1C" is the current value that completely discharges the capacity of the lithium-ion battery within 1 hour.

[0141] DC resistance R=(U 2 -U 1 ) / (1C-0.1C).

[0142] (5) Capacity retention test under high temperature and high pressure

[0143] At 45°C, the lithium-ion battery is charged to 4.7V at a constant current of 1C, then charged to a current of 0.05C at a constant voltage, and then discharged to 3.0V at a constant current of 1C. This is the first cycle, and the discharge capacity C of the first cycle is recorded. 1 According to the above conditions, the lithium-ion battery was charged and discharged 800 times, and the discharge capacity C after 800 cycles was recorded. 800The capacity retention rate after cycling is calculated according to the following formula:

[0144] Capacity retention rate = (C 800 / C 1 )×100%.

[0145] (6) Low temperature rate performance test

[0146] At 25°C, charge at 0.5C constant current to 4.7V, charge at constant voltage to 0.05C cut-off, then discharge at 0.5C constant current to 3.0V cut-off, record the discharge capacity at 25°C as C(25°C). At 25°C, charge at 0.5C constant current to 4.7V, charge at constant voltage to 0.05C cut-off, then place the battery in a -20°C thermostat, let it stand for 2 hours, then discharge at 0.5C constant current to 3.0V cut-off, record the discharge capacity at -20°C as C(-20°C). The capacity retention rate of lithium-ion batteries at low temperatures compared to normal temperature is calculated by the following formula:

[0147] Capacity retention rate = [C (-20°C) / C (25°C)] × 100%.

[0148] (7) High temperature storage performance test

[0149] At 25°C, the lithium-ion battery was left to stand for 30 minutes, then charged to 4.7V at a constant current rate of 0.5C, and then charged to 0.05C at a constant voltage rate of 4.7V. After standing for 5 minutes, the battery thickness was measured as T. 3 The battery thickness was measured at 60°C after 21 days of storage. 4 The high temperature storage thickness expansion rate of lithium-ion batteries is calculated by the following formula:

[0150] High temperature storage thickness expansion rate = [(T 4 -T 3 ) / T 3 ]×100%.

[0151] (III) Test results

[0152] The lithium ion batteries of Examples 1-1 to 1-8 and Comparative Examples 1-1 to 1-4 were prepared according to the above preparation method, and the difference between them was the binder content, the first binder was water-soluble polyacrylate, and the second binder was oil-soluble PVDF. Table 1 shows the bonding force F between the positive electrode current collector and the first positive electrode active material layer 1 The cohesive force F of the second positive electrode active material layer 2 Impact on the thermal safety performance, DC internal resistance and cycle performance of lithium-ion batteries under high temperature and high pressure.

[0153] Table 1

[0154]

[0155] It can be seen from the electrochemical test results in Table 1 that, compared with Comparative Examples 1-1 to 1-4, the positive electrodes in Examples 1-1 to 1-8 of the present application all meet F 1 / F 2 ≥6, and the corresponding electrochemical device has a lower thickness expansion at high temperature, and has a lower DC impedance and a higher capacity retention rate during high temperature and high pressure charging and discharging. In addition, referring to the data of Examples 1-5 to 1-8, it can be seen that as the bonding force F between the positive electrode current collector and the first positive electrode active material layer increases, 1 The increase in the thermal conductivity of the electrochemical device corresponds to a lower risk of internal short circuit and a higher thermal safety performance under high temperature, high pressure or abuse conditions.

[0156] Table 2 shows the effects of the first binder and the second binder on the thermal safety performance, DC internal resistance and cycle performance of lithium-ion batteries under high temperature and high pressure, wherein Examples 2-1 to 2-14 differ from Example 1-1 only in the parameters listed in Table 2.

[0157] Table 2

[0158]

[0159] Comparing the data of Example 2-9 and Example 2-12 in Table 2, it can be seen that when the first positive electrode active material layer uses a water-soluble binder, the electrochemical performance of the corresponding electrochemical device is better. Comparing Example 2-8 with Example 2-11, the same conclusion can be drawn. This may be due to the hydrogen bonding or other intermolecular forces between the water-soluble binder and the polar functional groups such as hydroxyl groups on the surface of the positive electrode current collector aluminum foil, thereby increasing the bonding force. In addition, comparing Examples 2-13 and 2-14 with Example 2-9, it can be seen that when the same binder is used, when the content of the first binder and the second binder satisfies 2.5≤a+b≤25 and 1≤b / a≤40, the structure of the positive electrode is more stable, which can further improve the performance of the electrochemical device. In addition, referring to the data of Examples 1-1 and 2-1 to 2-12, when other binders are used and the content of other binders satisfies 2.5≤a+b≤25 and 1≤b / a≤40, a more stable positive electrode can also be obtained.

[0160] Table 3 shows the F 1 / b and F 2 The influence of / a on the thermal safety performance, DC internal resistance and cycle performance of the electrochemical device under high temperature and high pressure. The difference between Examples 3-1 to 3-6 and Example 1-1 is only the parameters listed in Table 3.

[0161] Table 3

[0162]

[0163] As can be seen from the electrochemical test results in Table 3, when the positive electrode further meets the F 1 / b≥10 and F 2 When / a≥1, the corresponding electrochemical device has lower thickness expansion, lower DC internal resistance and higher capacity retention rate under high temperature and high pressure.

[0164] Table 4 shows the total thickness H of the positive electrode active material layer and the thickness H of the first positive electrode active material layer 1 Effects on thermal safety performance, DC internal resistance and cycle performance of electrochemical devices under high temperature and high pressure. The difference between Examples 4-1 to 4-5 and Example 1-1 is only the parameters listed in Table 4.

[0165] Table 4

[0166]

[0167] As can be seen from the electrochemical test results in Table 4, when the positive electrode further satisfies H 1 When / H≤0.1, the corresponding electrochemical device has lower thickness expansion, lower DC internal resistance and higher capacity retention rate under high temperature and high pressure.

[0168] Table 5 shows the effect of the cyano compound contained in the electrolyte on the thermal safety performance, DC internal resistance and cycle performance of the electrochemical device at high temperature and high pressure. The difference between Examples 5-1 to 5-25 and Example 1-1 is only the parameters listed in Table 5.

[0169] Table 5

[0170]

[0171] As can be seen from the electrochemical test results in Table 5, when a compound having a cyano group is added to the electrolyte, the thermal safety, cycle performance and impedance characteristics of the electrochemical device under high temperature and high pressure can be further improved. 1 and x satisfies F 1 When / x≥13.33, the improvement on the electrochemical performance of the electrochemical device is more prominent.

[0172] Table 6 shows the effect of propylene carbonate in the electrolyte on the thermal safety performance, DC internal resistance and cycle performance of the electrochemical device at high temperature and high pressure. The difference between Examples 6-1 to 6-8 and Example 1-1 is only the parameters listed in Table 6.

[0173] Table 6

[0174]

[0175] As shown in the electrochemical test results in Table 6, when propylene carbonate is added to the electrolyte, especially F 2 and y further satisfy F 2 When / y≥0.5, the corresponding electrochemical device not only exhibits excellent thermal safety and cycle performance under high temperature and high pressure, but also its DC impedance is unexpectedly greatly reduced.

[0176] Table 7 shows the effects of the content of the compound having a cyano group and propyl propionate on the thermal safety performance, DC internal resistance and cycle performance of the electrochemical device at high temperature and high pressure. The difference between Examples 7-1 to 7-16 and Example 1-1 is only the parameters listed in Table 7.

[0177] Table 7

[0178]

[0179] Referring to the electrochemical test results in Table 7, it can be seen that when a cyano compound and propyl propionate are added to the electrolyte at the same time, especially when the contents of the above two in the electrolyte satisfy 12≤x+z≤65 and 0.5≤z / x≤50, the thermal safety performance, cycle performance and impedance characteristics of the electrochemical device under high temperature and high pressure can be further optimized.

[0180] Table 8 shows the effects of the contents of propylene carbonate and propyl propionate on the thermal safety performance, low temperature rate performance and cycle performance of the electrochemical device at high temperature and high pressure. The difference between Examples 8-1 to 8-8 and Example 1-1 is only the parameters listed in Table 8.

[0181] Table 8

[0182]

[0183] Referring to the electrochemical test results in Table 8, it can be seen that compared with Examples 8-7 and 8-8, Examples 1-1 and 8-1 to 8-6 simultaneously added propylene carbonate and propyl propionate to the electrolyte, and the corresponding electrochemical devices exhibited more excellent thermal safety performance, low temperature rate performance and cycle performance under high temperature and high pressure. Compared with Examples 8-4 to 8-6, the contents of propylene carbonate and propyl propionate in Examples 8-1 to 8-3 simultaneously satisfied 15≤y+z≤70 and 1≤z / y≤5, and the electrochemical performance of the corresponding electrochemical devices under high temperature and high pressure was further improved, especially the low temperature rate performance was greatly improved.

[0184] Table 9 shows the effects of solvents and additives in the electrolyte on the thermal safety performance and cycle performance of the electrochemical device at high temperature and high pressure. The difference between Examples 9-1 to 9-17 and Example 1-1 is only the parameters listed in Table 9.

[0185] Table 9

[0186]

[0187] Referring to the electrochemical test results in Table 9, it can be seen that when a cyano compound, propylene carbonate, propyl propionate, fluoroethylene carbonate, 1,3-propane sultone, vinyl sulfate, vinylene carbonate, and 1-propylphosphoric acid cyclic anhydride are used in combination in the electrolyte, the resulting electrochemical device exhibits very excellent thermal safety performance under high temperature and high pressure, storage performance at high temperature, and cycle performance.

[0188] References to "embodiments", "partial embodiments", "one embodiment", "another example", "example", "specific example" or "partial example" throughout the specification mean that at least one embodiment or example in the present application includes the specific features, structures, materials or characteristics described in the embodiment or example. Therefore, descriptions appearing in various places throughout the specification, such as: "in some embodiments", "in an embodiment", "in one embodiment", "in another example", "in an example", "in a specific example" or "example", do not necessarily refer to the same embodiment or example in the present application. In addition, the specific features, structures, materials or characteristics herein may be combined in one or more embodiments or examples in any suitable manner.

[0189] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the present application, and that changes, substitutions and modifications may be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. An electrochemical device comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode include: current collector; as well as A positive electrode active material layer, the positive electrode active material layer is located on at least one surface of the current collector and includes a first positive electrode active material layer and a second positive electrode active material layer, wherein the first positive electrode active material layer is located between the current collector and the second positive electrode active material layer; The bonding force between the current collector and the first positive electrode active material layer is F 1 N / m, the cohesive force of the second positive electrode active material layer is F 2 N / m, the positive electrode satisfies: F 1 / F 2 ≥6; The electrolyte includes a compound having a cyano group, and the compound having a cyano group includes at least one of the following: succinonitrile, glutaronitrile, adiponitrile, 1,5-dicyanopentane, 1,6-dicyanohexane, tetramethylsuccinonitrile, 2-methylglutaronitrile, 2,4-dimethylglutaronitrile, 2,2,4,4-tetramethylglutaronitrile, 1,4-dicyanopentane, 1,2-dicyanobenzene, 1,3-dicyanobenzene, 1,4-dicyanobenzene ... 1,6-dicyanohexane, 1,6-dicyanopentane, 1,6-dicyanohexane, 1,6-dicyanohexane, 1,6-dicyanopentane, 1,6-dicyanohexane, 1,6-dicyanopentane, 1,6-dicyanohexane, 1,6-dicyanopentane, 1,6-dicyanopentane, 1,6-dicyanopentane, 1,6-dicyanopentane, 1,6-dicyanopentane, 1,6-dicyanopentane, 1,6-dicyanopentane, 1,6-dicyanopentane, 1,6-dicyanopentane, 1,6-dicyanopentane, 1,6-dicyanopentane, 1,6-dic Alcohol bis(propionitrile) ether, 3,5-dioxa-heptanenitrile, 1,4-bis(cyanoethoxy)butane, diethylene glycol di(2-cyanoethyl) ether, triethylene glycol di(2-cyanoethyl) ether, tetraethylene glycol di(2-cyanoethyl) ether, 1,3-bis(2-cyanoethoxy)propane, 1,4-bis(2-cyanoethoxy)butane, 1,5-bis(2-cyanoethoxy)pentane, ethylene glycol di(4-cyanobutyl) ether, 1,4-dicyano-2 -Butene, 1,4-dicyano-2-methyl-2-butene, 1,4-dicyano-2-ethyl-2-butene, 1,4-dicyano-2,3-dimethyl-2-butene, 1,4-dicyano-2,3-diethyl-2-butene, 1,6-dicyano-3-hexene, 1,6-dicyano-2-methyl-3-hexene, 1,3,5-pentanetricarbonitrile, 1,2,3-propanetricarbonitrile, 1,3,6-hexatricarbonitrile, 1,2,6-hexatricarbonitrile Carbonitrile, 1,2,3-tris(2-cyanoethoxy)propane, 1,2,4-tris(2-cyanoethoxy)butane, 1,1,1-tris(cyanoethoxymethylene)ethane, 1,1,1-tris(cyanoethoxymethylene)propane, 3-methyl-1,3,5-tris(cyanoethoxy)pentane, 1,2,7-tris(cyanoethoxy)heptane, 1,2,6-tris(cyanoethoxy)hexane or 1,2,5-tris(cyanoethoxy)pentane.

2. The electrochemical device according to claim 1, wherein F 1 ≥200.

3. The electrochemical device according to claim 1, wherein the first positive electrode active material layer includes a first binder, and the first binder satisfies at least one of the following conditions: (1) The first binder is water-soluble; (2) the first binder has an unsaturated acid functional group; (3) The first binder includes polyacrylate having polar functional groups; (4) Based on the mass of the first positive electrode active material layer, the mass fraction of the first binder is b%, where 2≤b≤20.

4. The electrochemical device according to claim 1, wherein the first positive electrode active material layer comprises a first binder, and the mass fraction of the first binder is b% based on the mass of the first positive electrode active material layer, wherein F 1 and b satisfies: F 1 ≥200, 2≤b≤20 and F 1 / b≥10.

5. The electrochemical device according to claim 1, wherein the second positive electrode active material layer includes a second binder, and the second binder satisfies at least one of the following conditions: (1) The second binder is water-insoluble; (2) the second binder comprises a fluorine-containing polymer; (3) The second binder includes polyvinylidene fluoride having an α-crystal structure; (4) Based on the mass of the second positive electrode active material layer, the mass fraction of the second binder is a%, where 0.5≤a≤5.

6. The electrochemical device according to claim 1, wherein the second positive electrode active material layer comprises a second binder; based on the mass of the second positive electrode active material layer, the mass fraction of the second binder is a%, wherein F 2 The relationship with a satisfies: 5≤F 2 ≤60, 0.5≤a≤5 and F 2 / a≥1. 7 . The electrochemical device according to claim 1 , wherein the first positive electrode active material layer includes a water-soluble binder, and the second positive electrode active material layer includes a water-insoluble binder.

8. The electrochemical device according to claim 1, wherein the first positive electrode active material layer comprises a first binder, and the mass fraction of the first binder is b% based on the mass of the first positive electrode active material layer; the second positive electrode active material layer comprises a second binder, and the mass fraction of the second binder is a% based on the mass of the second positive electrode active material layer; wherein a and b satisfy: 2.5≤a+b≤25; 1≤b / a≤40.

9. The electrochemical device according to claim 1, wherein the thickness of the first positive electrode active material layer is H 1 μm, the thickness of the positive electrode active material layer is H μm, and the positive electrode satisfies: H 1 / H≤0.

1.

10. The electrochemical device according to claim 9, wherein 0.1≤H 1 ≤5. 11 . The electrochemical device according to claim 1 , wherein the content of the compound having a cyano group is x % based on the mass of the electrolyte, wherein 0.1≤x≤15.

12. The electrochemical device according to claim 1, wherein the content of the compound having a cyano group is x%, based on the mass of the electrolyte. 1 ≥200, and F 1 / x≥13.

33.

13. The electrochemical device of claim 1, wherein the electrolyte comprises propylene carbonate.

14. The electrochemical device according to claim 13, wherein the content of the propylene carbonate is y% based on the mass of the electrolyte, wherein 2≤y≤25.

15. The electrochemical device according to claim 13, wherein the content of propylene carbonate is y% based on the mass of the electrolyte, wherein F 2 / y≥0.

5.

16. The electrochemical device according to claim 1, wherein the electrolyte comprises propyl propionate, wherein the content of the propyl propionate is z% based on the mass of the electrolyte, wherein 5≤z≤50.

17. The electrochemical device according to claim 1, wherein the electrolyte comprises a compound having a cyano group and propyl propionate, wherein the content of the compound having a cyano group is x%, and the content of the propyl propionate is z%, based on the mass of the electrolyte, wherein 12≤x+z≤65, and 0.5≤z / x≤50.

18. The electrochemical device according to claim 1, wherein the electrolyte comprises propylene carbonate and propyl propionate, wherein based on the mass of the electrolyte, the content of propylene carbonate is y%, the content of propyl propionate is z%, wherein 15≤y+z≤70, and 1≤z / y≤5.

19. The electrochemical device of claim 1, wherein the electrolyte comprises at least one of fluoroethylene carbonate, 1,3-propane sultone, vinyl sulfate, vinylene carbonate, or 1-propylphosphoric acid cyclic anhydride.

20. An electronic device comprising the electrochemical device according to any one of claims 1 to 19.

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