Electrochemical device and electronic device

Abstract

The invention provides an electrochemical device and an electronic device.The electrochemical device comprises a positive pole piece and electrolyte, the electrolyte comprises lithium hexafluorophosphate, the positive pole piece comprises a positive pole material layer, and the positive pole material layer comprises a compound shown in the formula I, r1 is selected from hydrogen atoms, C1-C10 alkyl groups which are not substituted or have end groups substituted by cyano groups, C1-C5 acyl groups, and amino groups which are not substituted or have end groups substituted by methyl groups; based on the mass of the positive electrode material layer, the mass percentage A of the compound in the formula I is 0.5-5%. The electrochemical device provided by the invention has good high-temperature cycle performance and safety performance. # imgabs0 #

Description

Technical Field

[0001] The present application relates to the field of electrochemical technologies, and particularly to an electrochemical device and an electronic device. Background Art

[0002] With the continuous update and development of lithium-ion battery technologies, the application fields of lithium-ion batteries have been continuously expanding, and the accompanying safety issues have received more attention. With the continuous increase in energy density, the thermal stability of lithium-ion batteries has deteriorated, and the failure temperature of the thermal box test has been continuously decreasing and approaching the national standard, bringing additional resistance to the development of lithium-ion batteries. How to improve the safety performance of lithium-ion batteries is a thorny problem in the current lithium battery industry.

[0003] In lithium-ion batteries, lithium hexafluorophosphate, a commonly used lithium salt in electrolytes, is prone to hydrolysis in high-temperature and humid environments, generating hydrofluoric acid. Hydrofluoric acid will damage the surface structure of the positive electrode active material, and it is easy to cause a large amount of heat to be generated by the reaction of the fully charged positive electrode sheet and the electrolyte at high temperatures, increasing the risk of thermal runaway of lithium-ion batteries. Therefore, developing materials that can effectively reduce the HF content in electrolytes is of great significance for improving the safety performance of lithium-ion batteries. Summary of the Invention

[0004] The purpose of the present application is to provide an electrochemical device and an electronic device to improve the high-temperature cycling performance and safety performance of the electrochemical device.

[0005] It should be noted that in the summary of the invention of the present application, a lithium-ion battery is used as an example of the electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to lithium-ion batteries. The specific technical solutions are as follows:

[0006] The first aspect of the present application provides an electrochemical device, which includes a positive electrode sheet and an electrolyte. The electrolyte includes lithium hexafluorophosphate, and the positive electrode sheet includes a positive electrode material layer, and the positive electrode material layer includes a compound of Formula I.

[0007]

[0008] Wherein, R 1 is selected from a hydrogen atom, C1 to C that is unsubstituted or has a cyano group at the end group 10alkyl groups having 1 to 5 carbon atoms, acyl groups having 1 to 5 carbon atoms, unsubstituted or methyl-substituted amino groups. Based on the mass of the positive electrode material layer, the mass percentage content A of the compound of Formula I is 0.5% to 5%. When the positive electrode material layer includes the compound of Formula I and the mass percentage content A of the compound of Formula I is within the scope of this application, the side reaction between the positive electrode sheet and the electrolyte at high temperature can be reduced, the heat generation of the positive electrode sheet can be lowered, the thermal runaway temperature of the electrochemical device can be increased, thereby improving the safety performance of the electrochemical device; on the other hand, the compound of Formula I can increase the conductivity of the positive electrode sheet and the stability of the positive electrode interface, and can increase the stability of the positive electrode structure under high temperature conditions, thereby improving the high temperature cycle performance of the electrochemical device.

[0009] In one embodiment of the present application, based on the mass of the positive electrode material layer, the mass percentage content A of the compound of Formula I is 0.5% to 1%. When the mass percentage content A of the compound of Formula I is within the above range, the safety performance and high temperature cycle performance of the electrochemical device can be further improved.

[0010] In one embodiment of the present application, the porosity B of the positive electrode material layer is 12% to 20%, preferably, the porosity B of the positive electrode sheet is 12% to 15%. When the porosity B of the positive electrode material layer is within the above range, the high temperature cycle performance of the electrochemical device can be further improved.

[0011] In one embodiment of the present application, 1 / 40 ≤ A / B ≤ 1 / 6, preferably, 1 / 30 ≤ A / B ≤ 1 / 12. When the value of A / B is within the above range, the mass percentage content of the compound of Formula I and the porosity of the positive electrode sheet are more matched, the electron transfer rate and ion transfer rate of the positive electrode sheet can be increased, thereby further improving the high temperature cycle performance of the electrochemical device.

[0012] In one embodiment of the present application, the compound of Formula I includes at least one of the following compounds:

[0013]

[0014]

[0015] When the compound of Formula I includes at least one of the above compounds, the safety performance and high temperature cycle performance of the electrochemical device can be further improved.

[0016] In one embodiment of the present application, in the infrared spectrum of the positive electrode sheet, at 1200 ± 10 cm -1 、1450 ± 10 cm -1 、1640 ± 10 cm -1 and 3000 cm -1 to 3500 cm -1Characteristic peaks exist. When the infrared spectrum of the positive electrode sheet has the above-mentioned characteristic peaks, it indicates that the positive electrode sheet contains the compound of formula I, which can improve the safety performance and high-temperature cycling performance of the electrochemical device.

[0017] In one embodiment of the present application, the 1 In the 1H solid nuclear magnetic resonance test spectrum of the positive electrode sheet, characteristic peaks exist at 12 ppm to 13 ppm, 8.035 ppm to 8.435 ppm, 7.51 ppm to 7.71 ppm, and 7.01 ppm to 7.41 ppm. When the 1 1H solid nuclear magnetic resonance test spectrum of the positive electrode sheet has the above-mentioned characteristic peaks, it indicates that the positive electrode sheet contains the compound of formula I-1, which can further improve the safety performance and high-temperature cycling performance of the electrochemical device.

[0018] In one embodiment of the present application, the positive electrode material layer includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder; based on the mass of the positive electrode material layer, the mass percentage of the positive electrode active material is 80% to 99.3%, the mass percentage of the positive electrode conductive agent is 0.1% to 10%, and the mass percentage of the positive electrode binder is 0.1% to 10%. When the mass percentages of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder are within the above ranges, the electrochemical device has good high-temperature cycling performance and safety performance.

[0019] In one embodiment of the present application, based on the mass of the positive electrode material layer, the mass percentage of the positive electrode active material is 90% to 99.1%, the mass percentage of the positive electrode conductive agent is 0.2% to 5%, and the mass percentage of the positive electrode binder is 0.2% to 5%. When the mass percentages of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder are within the above ranges, the high-temperature cycling performance and safety performance of the electrochemical device are further improved.

[0020] In one embodiment of the present application, based on the mass of the electrolyte, the mass percentage of lithium hexafluorophosphate is 9% to 14%. When the mass percentage of lithium hexafluorophosphate is within the above range, it is beneficial to regulate the content of lithium ions in the electrolyte within a suitable range, provide more lithium ions for the electrochemical device, and improve the high-temperature cycling performance of the electrochemical device.

[0021] The second aspect of the present application provides an electronic device, and the electronic device includes the electrochemical device in any of the foregoing embodiments. The electronic device of the present application has good high-temperature cycling performance and safety performance.

[0022] Advantages of the present application:

[0023] The present application provides an electrochemical device and an electronic device. The electrochemical device includes a positive electrode sheet and an electrolyte. The electrolyte includes lithium hexafluorophosphate. The positive electrode sheet includes a positive electrode material layer, and the positive electrode material layer includes a compound of Formula I. Based on the mass of the positive electrode material layer, the mass percentage content A of the compound of Formula I is 0.5% to 5%. When the positive electrode material layer includes the compound of Formula I, by regulating the mass percentage content A of the compound of Formula I within the scope of the present application, the high-temperature cycle performance and safety performance of the electrochemical device can be improved.

[0024] Of course, it is not necessary for any product or method implementing the present application to achieve all of the above advantages simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other embodiments can also be obtained based on these drawings.

[0026] Figure 1 Mass spectrometry diagram of an acetonitrile standard solution of the compound of Formula I-1;

[0027] Figure 2 For the deuterated dimethyl sulfoxide standard solution of the compound of Formula I-1 at 1 mmol / L 1 1H solid nuclear magnetic resonance test spectrum;

[0028] Figure 3 For the deuterated dimethyl sulfoxide standard solution of the compound of Formula I-2 at 1 mmol / L 1 1H solid nuclear magnetic resonance test spectrum;

[0029] Figure 4 For the deuterated dimethyl sulfoxide standard solution of the compound of Formula I-10 at 1 mmol / L 1 1H solid nuclear magnetic resonance test spectrum;

[0030] Figure 5 Infrared spectrum diagram of the compound of Formula I-1;

[0031] Figure 6 Infrared spectrum diagram of the compound of Formula I-2;

[0032] Figure 7 Infrared spectrum diagram of the compound of Formula I-3;

[0033] Figure 8 Infrared spectrum diagram of the compound of Formula I-7;

[0034] Figure 9 Infrared spectrum diagram of the compound of Formula I-10. Detailed implementation manners

[0035] The technical solutions in the present application will be clearly and completely described below in conjunction with the embodiments of the present application and the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0036] It should be noted that in the specific implementation manners of the present application, a lithium-ion battery is used as an example of the electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to the lithium-ion battery.

[0037] In the electrochemical device, lithium hexafluorophosphate (LiPF6), a commonly used lithium salt in the electrolyte, is prone to hydrolysis in a high-temperature or humid environment, generating hydrofluoric acid (HF). The specific hydrolysis process is as follows: (1) LiPF6 → LiF + PF5; (2) PF5 + H2O → POF3 + 2HF; (3) POF3 + H2O → HF + HPO2F2; (4) HPO2F2 + LiF → LiPO2F2 + HF. And HF will damage the surface structure of the positive electrode active material, resulting in the reaction of the fully charged positive electrode sheet and the electrolyte at high temperature, increasing the heat generation of the positive electrode sheet and increasing the risk of thermal runaway of the electrochemical device.

[0038] The first aspect of the present application provides an electrochemical device. The electrochemical device includes a positive electrode sheet and an electrolyte. The electrolyte includes lithium hexafluorophosphate. The positive electrode sheet includes a positive electrode material layer, and the positive electrode material layer includes a compound of Formula I.

[0039]

[0040] wherein, R 1 is selected from a hydrogen atom, a C1 to C alkyl that is unsubstituted or has a cyano group at the end group, an acyl group of C1 to C5, and an amino group that is unsubstituted or substituted with a methyl group. The above substitution can be total substitution or partial substitution. C1 to C 10 and C1 to C5 acyl groups, and an amino group that is unsubstituted or substituted with a methyl group. The above substitutions can be total substitutions or partial substitutions. C1 to C 10The alkyl groups include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl or decyl; the acyl groups with 1 to 5 carbon atoms include formyl, acetyl, propionyl, butyryl or valeryl. Based on the mass of the positive electrode material layer, the mass percentage content A of the compound of Formula I is 0.5% to 5%, preferably, the mass percentage content A of the compound of Formula I is 0.5% to 1%. For example, the mass percentage content A of the compound of Formula I can be 0.5%, 1%, 2%, 3%, 4%, 5% or a range composed of any two of these values. When the positive electrode material layer includes the compound of Formula I and the mass percentage content A of the compound of Formula I is within the scope of this application, the compound of Formula I can react with the decomposition product phosphorus pentafluoride (PF5) of LiPF6 in the electrolyte at high temperature, thereby slowing down the generation of the hydrolysis product HF of PF5, reducing the damage to the surface structure of the positive electrode active material in the fully charged state by HF, reducing the side reaction between the positive electrode sheet and the electrolyte at high temperature, reducing the heat generation of the positive electrode sheet, increasing the thermal runaway temperature of the electrochemical device, and thus improving the safety performance of the electrochemical device; on the other hand, the compound of Formula I can increase the conductivity of the positive electrode sheet and the stability of the positive electrode interface, and can increase the stability of the positive electrode structure under high temperature conditions, thereby improving the high temperature cycling performance of the electrochemical device. When the value of A is too small, for example, less than 0.5%, the capture efficiency of the compound of Formula I for the decomposition product PF5 of LiPF6 is low, the improvement of the thermal stability performance of the electrochemical device is small, and the safety performance and high temperature cycling performance of the electrochemical device are reduced; when the value of A is too large, for example, higher than 5%, the excessive compound of Formula I will affect the conductive network of the positive electrode sheet, resulting in a continuous increase in the impedance of the electrochemical device during the cycling process, thereby reducing the high temperature cycling performance of the electrochemical device. When the positive electrode material layer includes the compound of Formula I, the electrolyte includes lithium hexafluorophosphate, and the mass percentage content A of the compound of Formula I is regulated within the scope of this application, the safety performance and high temperature cycling performance of the electrochemical device can be improved. In this application, "high temperature cycling" can be a cycling test carried out within the temperature range of 45°C to 60°C.

[0041] In this application, the mass percentage content A of the compound of Formula I is regulated by means known to those skilled in the art, as long as the purpose of this application can be achieved. For example, the mass percentage content A of the compound of Formula I can be regulated by regulating the addition amount of the compound of Formula I during the preparation process of the positive electrode sheet. Exemplarily, when the addition amount of the compound of Formula I increases, the mass percentage content A of the compound of Formula I increases; when the addition amount of the compound of Formula I decreases, the mass percentage content A of the compound of Formula I decreases.

[0042] In an embodiment of the present application, the porosity B of the positive electrode material layer is 12% to 20%, preferably, the porosity B of the positive electrode material layer is 12% to 15%. For example, the porosity B of the positive electrode material layer can be 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% or a range composed of any two of these values. When the porosity B of the positive electrode material layer is within the above range, the positive electrode sheet can store more electrolyte, so as to meet the relatively large consumption of electrolyte by the positive electrode sheet under high-temperature cycling, thereby further improving the high-temperature cycling performance of the electrochemical device.

[0043] In the present application, the porosity B of the positive electrode material layer is adjusted by means known to those skilled in the art, as long as the object of the present application can be achieved. For example, the porosity B of the positive electrode material layer can be adjusted by adjusting the thickness of the positive electrode sheet after cold pressing or the compaction density of the positive electrode sheet. Exemplarily, when the thickness of the positive electrode sheet after cold pressing increases, the porosity B of the positive electrode material layer increases; when the thickness of the positive electrode sheet after cold pressing decreases, the porosity B of the positive electrode material layer decreases. When the compaction density of the positive electrode sheet increases, the porosity B of the positive electrode material layer decreases; when the compaction density of the positive electrode sheet decreases, the porosity B of the positive electrode material layer increases.

[0044] In an embodiment of the present application, 1 / 40 ≤ A / B ≤ 1 / 6, preferably, 1 / 30 ≤ A / B ≤ 1 / 12. For example, the value of A / B can be 1 / 40, 1 / 30, 1 / 25, 1 / 20, 1 / 15, 1 / 12, 1 / 10, 1 / 6 or a range composed of any two of these values. When the value of A / B is within the above range, the mass percentage content of the compound of formula I and the porosity of the positive electrode material layer are more matched, which can improve the electron transfer rate and ion transfer rate of the positive electrode sheet, thereby further improving the high-temperature cycling performance of the electrochemical device.

[0045] In the present application, the value of A / B is adjusted by means known to those skilled in the art, as long as the object of the present application can be achieved. For example, the value of A / B can be adjusted by adjusting the respective values of A and B, and the adjustment method is as described above.

[0046] In an embodiment of the present application, the compound of formula I includes at least one of the following compounds:

[0047]

[0048]

[0049] When the compound of Formula I includes at least one of the above compounds, the compound of Formula I can react with phosphorus pentafluoride (PF5), a decomposition product of LiPF6 in the electrolyte, at high temperature, thereby slowing down the generation of HF, the hydrolysis product of PF5, reducing the damage to the surface structure of the positive electrode active material in the fully charged state by HF, reducing the side reaction between the positive electrode sheet and the electrolyte at high temperature, reducing the heat generation of the positive electrode sheet, and further improving the safety performance of the electrochemical device; on the other hand, the compound of Formula I can improve the stability of the positive electrode structure under high temperature conditions, thereby further improving the high temperature cycle performance of the electrochemical device. The compound of Formula I can be prepared by methods known in the art or obtained through commercial channels.

[0050] In one embodiment of the present application, in the infrared spectrum of the positive electrode sheet, there are characteristic peaks at 1200±10 cm -1 , 1450±10 cm -1 , 1640±10 cm -1 and 3000 cm -1 to 3500 cm -1 . The characteristic peak at 1200±10 cm -1 is the stretching vibration peak of C-N, the characteristic peak at 1450±10 cm -1 is the stretching vibration peak of the C═C aromatic ring, the characteristic peak at 1640±10 cm -1 is the stretching vibration peak of C═N, and the characteristic peak at 3000 cm -1 to 3500 cm -1 is the stretching vibration peak of N-H. When the above characteristic peaks exist in the infrared spectrum of the leaching solution of the positive electrode sheet, it indicates that the positive electrode sheet contains the compound of Formula I. As can be seen from Figures 5 to 9 , in the infrared spectra of the compounds of Formula I-1, Formula I-2, Formula I-3, Formula I-7 and Formula I-10, there are characteristic peaks at 1200±10 cm -1 , 1450±10 cm -1 , 1640±10 cm -1 and 3000 cm -1 to 3500 cm -1 . The compound of Formula I can react with phosphorus pentafluoride (PF5), a decomposition product of LiPF6 in the electrolyte, at high temperature, thereby slowing down the generation of HF, the hydrolysis product of PF5, reducing the damage to the surface structure of the positive electrode active material in the fully charged state by HF, reducing the side reaction between the positive electrode sheet and the electrolyte at high temperature, reducing the heat generation of the positive electrode sheet, and improving the safety performance of the electrochemical device; on the other hand, the compound of Formula I can improve the stability of the positive electrode structure under high temperature conditions, thereby improving the high temperature cycle performance of the electrochemical device.

[0051] In one embodiment of the present application, the positive electrode sheet1 In the 1H solid nuclear magnetic resonance test spectrum of H, characteristic peaks exist at 12 ppm to 13 ppm, 8.035 ppm to 8.435 ppm, 7.51 ppm to 7.71 ppm, and 7.01 ppm to 7.41 ppm. Among them, the characteristic peak at 12 ppm to 13 ppm is the first characteristic peak, and the characteristic peak at 7.01 ppm to 7.41 ppm is the second characteristic peak. The peak area C of the first characteristic peak and the peak area D of the second characteristic peak satisfy: C / D = 0.5. Among them, the deuterated dimethyl sulfoxide standard solution of the compound of formula I-1 at 1 mmol / L 1 The 1H solid nuclear magnetic resonance test spectrum is as Figure 2 shown. It can be seen from the figure that the compound of formula I-1 has obvious characteristic peaks at the above four chemical shifts. When the 1 1H solid nuclear magnetic resonance test spectrum of the positive electrode sheet leaching solution has the above characteristic peaks and the value of C / D is 0.5, it indicates that the positive electrode sheet contains the compound of formula I-1. The compound of formula I-1 can react with the decomposition product phosphorus pentafluoride (PF5) of LiPF6 in the electrolyte at high temperature, thereby slowing down the generation of the hydrolysis product HF of PF5, reducing the damage to the surface structure of the positive electrode active material in the fully charged state by HF, further reducing the side reaction between the positive electrode sheet and the electrolyte at high temperature, reducing the heat generation of the positive electrode sheet, and thus further improving the safety performance of the electrochemical device; on the other hand, the compound of formula I-1 can improve the stability of the positive electrode structure under high temperature conditions, thereby further improving the high temperature cycle performance of the electrochemical device.

[0052] In one embodiment of the present application, the positive electrode material layer includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder; based on the mass of the positive electrode material layer, the mass percentage content of the positive electrode active material is 80% to 99.3%, preferably 90% to 99.1%; the mass percentage content of the positive electrode conductive agent is 0.1% to 10%, preferably 0.2% to 5%; the mass percentage content of the positive electrode binder is 0.1% to 10%, preferably 0.2% to 5%. For example, the mass percentage content of the positive electrode active material can be 80%, 85%, 90%, 95%, 99.1%, 99.3% or a range composed of any two of these values; the mass percentage content of the positive electrode conductive agent can be 0.1%, 0.2%, 1%, 3%, 5%, 7%, 10% or a range composed of any two of these values; the mass percentage content of the positive electrode binder can be 0.1%, 0.2%, 1%, 3%, 5%, 7%, 10% or a range composed of any two of these values. When the mass percentage content of the positive electrode active material, the mass percentage content of the positive electrode conductive agent, and the mass percentage content of the positive electrode binder are within the above ranges, the electrochemical device has good high temperature cycle performance and safety performance.

[0053] In the present application, the positive electrode plate includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector. The above-mentioned "positive electrode material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be disposed on one surface of the positive electrode current collector along its own thickness direction, or can be disposed on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of the surface of the positive electrode current collector, or a partial area of the surface of the positive electrode current collector. There is no special limitation in the present application as long as the purpose of the present application can be achieved.

[0054] The present application has no special limitation on the positive electrode current collector as long as the purpose of the present application can be achieved. For example, a metal foil or a composite current collector can be used. For example, the metal foil can include, but is not limited to, aluminum foil; the composite current collector can be obtained by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer substrate.

[0055] The present application has no special limitation on the positive electrode active material as long as the purpose of the present application can be achieved. For example, the positive electrode active material can include, but is not limited to, at least one of lithium cobaltate (LiCoO2), lithium iron phosphate, lithium nickel manganate, lithium nickel cobalt manganate (such as NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminate, lithium-rich manganese-based material, lithium manganate, lithium manganese iron phosphate, lithium titanate, lithium nickel manganese aluminate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, or lithium manganese silicate.

[0056] The present application does not particularly limit the types of the positive electrode conductive agent and the positive electrode binder, as long as the object of the present application can be achieved. For example, the positive electrode conductive agent may include, but is not limited to, at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fiber, flake graphite, graphene, metal material or conductive polymer. The above-mentioned conductive carbon black may include, but is not limited to, at least one of SuperP, acetylene black or Ketjen black. The above-mentioned carbon nanotubes may include, but is not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fiber may include, but is not limited to, vapor-grown carbon fiber (VGCF) and / or nanofiber. The above-mentioned metal material may include, but is not limited to, metal powder and / or metal fiber. Specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole. The positive electrode binder may include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamideimide, polyvinylidene fluoride, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin or nylon.

[0057] The present application does not particularly limit the thickness of the positive electrode current collector and the thickness of the positive electrode material layer, as long as the object of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, and the thickness of the single-sided positive electrode material layer after cold pressing is 30 μm to 150 μm.

[0058] Optionally, the positive electrode sheet may further include a conductive layer, and the conductive layer is located between the positive electrode current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited and may be a commonly used conductive layer in the art. The conductive layer includes a conductive agent and a binder. The present application does not particularly limit the conductive agent and the binder in the conductive layer. For example, it may be at least one of the aforementioned positive electrode conductive agent and the aforementioned positive electrode binder.

[0059] In an embodiment of the present application, based on the mass of the electrolyte, the mass percentage content of lithium hexafluorophosphate is 9% to 14%. For example, the mass percentage content of lithium hexafluorophosphate can be 9%, 10%, 11%, 12%, 13%, 14%, or a range composed of any two of these values. Lithium hexafluorophosphate has good solubility in organic solvents, can provide high ionic conductivity, and the production process is relatively mature. When the electrolyte includes lithium hexafluorophosphate and the mass percentage content of lithium hexafluorophosphate is within the above range, it is beneficial to control the content of lithium ions in the electrolyte within a suitable range, provide more lithium ions for the electrochemical device, and improve the high-temperature cycle performance of the electrochemical device.

[0060] In the present application, the electrolyte may further include a first lithium salt. The present application places no particular limitation on the first lithium salt, as long as the object of the present application can be achieved. For example, the first lithium salt may include, but is not limited to, at least one of LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. The present application places no particular limitation on the mass percentage content of the first lithium salt in the electrolyte, as long as the object of the present application can be achieved.

[0061] In the present application, the electrolyte further includes a non-aqueous solvent. There is no particular limitation on the non-aqueous solvent in the present application, as long as the object of the present application can be achieved. For example, the non-aqueous solvent may include, but is not limited to, at least one of carbonate compounds, carboxylate compounds, ether compounds, or other organic solvents. The above carbonate compounds may include, but are not limited to, at least one of linear carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The above linear carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The above cyclic carbonate compounds may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinylene ethylene carbonate (VEC). The above fluorinated carbonate compounds may include, but are not limited to, at least one of 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethyl ethylene carbonate. The above carboxylate compounds may include, but are 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, decanolide, valerolactone, or caprolactone. The above ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The above other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, methylcyclobutanesulfone, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. There is no particular limitation on the mass percentage content of the non-aqueous solvent in the electrolyte in the present application, as long as the object of the present application can be achieved. For example, based on the mass of the electrolyte, the mass percentage content of the non-aqueous solvent may be 86% to 91%.

[0062] In one embodiment of the present application, the electrolyte may include lithium hexafluorophosphate and a non-aqueous solvent. The mass percentage content of lithium hexafluorophosphate is as described above, and the mass percentage content of the non-aqueous solvent is 86% to 91%. The electrochemical device including the above electrolyte has good high-temperature cycle performance and safety performance.

[0063] In the present application, the electrochemical device further includes a negative electrode plate, which includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The above-mentioned "negative electrode material layer 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 own thickness direction, or can be disposed on both surfaces of the negative electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of the surface of the negative electrode current collector, or a partial area of the surface of the negative electrode current collector. There is no special limitation in the present application, as long as the purpose of the present application can be achieved.

[0064] There is no special limitation on the negative electrode current collector in the present application, as long as the purpose of the present application can be achieved. For example, it can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, lithium-copper composite current collector, carbon-copper composite current collector, nickel-copper composite current collector, or titanium-copper composite current collector, etc.

[0065] In the present application, the negative electrode material layer includes a negative electrode active material. There is no special limitation on the negative electrode active material in the present application, as long as the purpose of the present application can be achieved. For example, the negative electrode active material can include, but is not limited to, at least one of silicon, artificial graphite, natural graphite, mesophase carbon microspheres, hard carbon, or soft carbon.

[0066] In some embodiments of the present application, the negative electrode material layer may further include a negative electrode conductive agent and a negative electrode binder. There is no special limitation on the types of the negative electrode conductive agent and the negative electrode binder in the present application, as long as the purpose of the present application can be achieved. For example, the negative electrode conductive agent can include, but is not limited to, at least one of conductive carbon black, conductive graphite, carbon nanotubes, metal materials, or carbon fibers. The above-mentioned conductive carbon black can include, but is not limited to, at least one of Super P, acetylene black, or Ketjen black. The above-mentioned carbon nanotubes can include, but is not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers can include, but is not limited to, vapor-grown carbon fibers (VGCF) and / or nanofibers. The above-mentioned metal materials can include, but is not limited to, metal powders and / or metal fibers. Specifically, the metal can include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The negative electrode binder can include, but is not limited to, at least one of sodium carboxymethyl cellulose, styrene-butadiene rubber, polyvinylidene fluoride (PVDF), polytetrafluoroethylene, or polyethylene oxide. There is no special limitation on the mass ratio of the negative electrode active material, the negative electrode conductive agent, and the negative electrode binder in the negative electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved. For example, the mass ratio of the negative electrode active material, the negative electrode conductive agent, and the negative electrode binder can be (80 to 99.8):(0.1 to 10):(0.1 to 10). Preferably, the mass ratio of the negative electrode active material, the negative electrode conductive agent, and the negative electrode binder can be (90 to 99.6):(0.2 to 5):(0.2 to 5).

[0067] In some embodiments of the present application, the negative electrode material layer may further include a negative electrode conductive agent, a negative electrode binder, and a thickening agent. The present application does not particularly limit the types of the negative electrode conductive agent, the negative electrode binder, and the thickening agent, as long as the purpose of the present application can be achieved. For example, the negative electrode conductive agent and the negative electrode binder may be at least one of the aforementioned negative electrode conductive agent and the aforementioned negative electrode binder. The thickening agent may include, but is not limited to, at least one of carboxymethyl cellulose, sodium carboxymethyl cellulose, or lithium carboxymethyl cellulose. The present application does not particularly limit the mass ratio of the negative electrode active material, the negative electrode conductive agent, the negative electrode binder, and the thickening agent in the negative electrode material layer, and those skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved.

[0068] The present application does not particularly limit the thickness of the negative electrode current collector and the thickness of the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm, and the thickness of the single-sided negative electrode material layer after cold pressing is 60 μm to 180 μm.

[0069] Optionally, the negative electrode plate may further include a conductive layer, and the conductive layer is located between the negative electrode current collector and the negative electrode material layer. The present application does not particularly limit the composition of the conductive layer, and it may be a commonly used conductive layer in the art. For example, the conductive layer includes a negative electrode conductive agent and a negative electrode binder. The present application does not particularly limit the negative electrode conductive agent and the negative electrode binder in the conductive layer. For example, it may be at least one of the aforementioned negative electrode conductive agent and the aforementioned negative electrode binder.

[0070] In the present application, the electrochemical device further includes a separator. The present application does not particularly limit the separator, as long as the purpose of the present application can be achieved. For example, the material of the separator may include, but is not limited to, at least one of polyolefins (PO) mainly composed of polyethylene (PE) and polypropylene (PP), polyester (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of the separator may include at least one of a woven film, a non-woven film, a microporous film, a composite film, a rolled film, or a spun film.

[0071] In some embodiments of the present application, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric or a composite film having 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 film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used.

[0072] Optionally, a surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer can be a polymer layer, an inorganic layer, or a layer formed by mixing polymers and inorganic substances. In some embodiments of the present application, the inorganic layer includes inorganic particles and a separator binder. There is no particular limitation on the inorganic particles in the present application. For example, the inorganic particles can include at least one of alumina, silica, magnesia, titania, hafnium dioxide, tin dioxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. There is no particular limitation on the separator binder in the present application. For example, the separator binder can include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamideimide, polyvinylidene fluoride, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon. In some embodiments of the present application, the polymer layer includes a polymer, and the materials of the polymer include at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene ether, polyvinylidene fluoride, or poly(vinylidene fluoride - hexafluoropropylene).

[0073] In the present application, there is no particular limitation on the thickness of the separator, as long as the object of the present application can be achieved. For example, the thickness of the separator can be 3 μm to 30 μm.

[0074] In the present application, the electrochemical device further includes a housing for accommodating the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte, as well as other components known in the field of electrochemistry. There is no limitation on the above other components in the present application. There is no particular limitation on the housing in the present application, and it can be a housing well-known in the art, as long as the object of the present application can be achieved. For example, the housing can be a hard shell housing or a flexible housing. The material of the hard shell housing can be metal. There is no limitation on the type of metal in the present application, and a metal hard shell housing known in the art can be used, as long as the object of the present application can be achieved. The flexible housing can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0075] There is no particular limitation on the type of the electrochemical device in the present application, and it can include any device that undergoes an electrochemical reaction. In the present application, the electrochemical device can include, but is not limited to: lithium metal electrochemical devices, lithium-ion electrochemical devices (lithium-ion batteries), lithium polymer electrochemical devices, or lithium-ion polymer electrochemical devices (lithium-ion polymer batteries), etc.

[0076] The preparation process of the electrochemical device of the present application is well-known to those skilled in the art, and there is no special limitation in the present application. For example, the preparation process of the electrochemical device may include, but is not limited to, the following steps: stacking the positive electrode sheet, the separator, and the negative electrode sheet in sequence, and winding, folding, etc. as needed to obtain a wound electrode assembly, placing the electrode assembly into a housing, injecting an electrolyte into the housing and sealing it to obtain an electrochemical device. Alternatively, stack the positive electrode sheet, the separator, and the negative electrode sheet in sequence, and then fix the four corners of the entire laminated structure with tape to obtain a laminated electrode assembly, place the electrode assembly into a housing, inject an electrolyte into the housing and seal it to obtain an electrochemical device. In addition, an overcurrent protection element, a guide plate, etc. can be placed in the housing as needed to prevent the pressure inside the electrochemical device from rising and overcharging and discharging.

[0077] The second aspect of the present application provides an electronic device, which includes the electrochemical device in any of the foregoing embodiments. The electronic device of the present application has good high-temperature cycle performance and safety performance.

[0078] The electronic device of the present application is not particularly limited, and it can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset stereo, a video recorder, a liquid crystal TV, a portable cleaner, a portable CD player, a minidisc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power source, a motor, an automobile, a motorcycle, a moped, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flash, a camera, a large household battery, and a lithium-ion capacitor, etc.

[0079] Examples

[0080] Hereinafter, examples and comparative examples are given to more specifically illustrate the embodiments of the present application. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0081] Testing method and equipment:

[0082] Gas chromatography-mass spectrometry test:

[0083] Prepare a 1 mmol / L acetonitrile solution of the compound of formula I as a standard solution, and use a gas chromatography-mass spectrometer (GC-MS, model Agilent GC 5977B) to measure the spectrum of the standard solution and integrate to obtain the peak area of the compound of formula I. Among them, the mass spectrum of the acetonitrile standard solution of the compound of formula I-1 is as Figure 1 shown.

[0084] After discharging the lithium-ion battery at 0.1C to 3.0V, disassemble it, take out the positive electrode sheet, wash the residual electrolyte of the positive electrode sheet with dimethyl carbonate (DMC), dry it, then immerse the positive electrode sheet into acetonitrile with a volume of V1 mL to obtain the leaching solution of the positive electrode sheet. Use a gas chromatography-mass spectrometry instrument to measure the chromatogram of the leaching solution, integrate to obtain the peak area of the compound of Formula I in the leaching solution. By comparing the peak emergence time and mass spectrometry results of the leaching solution chromatogram with those of the standard solution chromatogram, it can be qualitatively analyzed whether there is a compound of Formula I in the positive electrode sheet. By converting and comparing the peak areas of the compound of Formula I in the leaching solution chromatogram and the standard solution chromatogram, the concentration of the compound of Formula I in the leaching solution can be obtained, and then the mass percentage content of the compound of Formula I can be known.

[0085] Test for the mass percentage content of lithium hexafluorophosphate:

[0086] After discharging the lithium-ion battery at 0.1C to 3.0V, disassemble it to obtain the positive electrode sheet and the negative electrode sheet. Put the positive electrode sheet and the negative electrode sheet into a centrifuge tube for centrifugation to obtain the electrolyte. Take the centrifuged electrolyte and use an ion chromatograph (IC, model Thermo Fisher Aquion) to detect the mass percentage content of lithium hexafluorophosphate.

[0087] For the positive electrode sheet 1 1H solid nuclear magnetic resonance test:

[0088] Prepare a deuterated dimethyl sulfoxide solution of the compound of Formula I at 1 mmol / L as the standard solution, and use a nuclear magnetic resonance spectrometer (model Bruker AVANCE III 400WB) to measure the nuclear magnetic spectrum of the standard solution. Among them, the 1 1H solid nuclear magnetic resonance test spectrum of the deuterated dimethyl sulfoxide standard solution of 1 mmol / L of the compound of Formula I-1 is as Figure 2 shown; the 1 1H solid nuclear magnetic resonance test spectrum of the deuterated dimethyl sulfoxide standard solution of 1 mmol / L of the compound of Formula I-2 is as Figure 3 shown; the 1 1H solid nuclear magnetic resonance test spectrum of the deuterated dimethyl sulfoxide standard solution of 1 mmol / L of the compound of Formula I-10 is as Figure 4 shown.

[0089] Taking the compound of formula I-1 as an example, a deuterated dimethyl sulfoxide solution of the compound of formula I-1 with a concentration of 1 mmol / L was prepared as a standard solution. Using a nuclear magnetic resonance spectrometer (model: Bruker AVANCE III 400WB), the nuclear magnetic resonance spectrum of the standard solution was measured. The characteristic peak at 12 ppm to 13 ppm was the first characteristic peak, and the characteristic peak at 7.01 ppm to 7.41 ppm was the second characteristic peak. The peak areas C of the first characteristic peak and D of the second characteristic peak were obtained by integration.

[0090] The lithium-ion battery was discharged to 3.0 V at 0.1C and then disassembled. The positive electrode plate was taken out, and the residual electrolyte was washed with dimethyl carbonate (DMC) and then dried. The positive electrode plate was immersed in deuterated dimethyl sulfoxide with a volume of V2 mL to obtain the leaching solution of the positive electrode plate. The nuclear magnetic resonance spectrum of the leaching solution was measured using a nuclear magnetic resonance spectrometer. By comparing the peak positions of the characteristic peaks in the nuclear magnetic resonance spectrum of the standard solution and the leaching solution of the positive electrode plate, and calculating whether the area ratio C / D of the peak area C of the first characteristic peak and the peak area D of the second characteristic peak in the nuclear magnetic resonance spectrum satisfies C / D = 0.5, it is possible to qualitatively analyze whether the compound of formula I-1 exists in the positive electrode plate.

[0091] Infrared spectrum test:

[0092] Using an infrared spectrum analyzer (model: Nicolet iS50), the infrared spectrum of the compound of formula I was tested by the potassium bromide (KBr) tablet pressing method. Among them, the infrared spectrum of the compound of formula I-1 is as Figure 5 shown; among them, the infrared spectrum of the compound of formula I-2 is as Figure 6 shown; the infrared spectrum of the compound of formula I-3 is as Figure 7 shown; the infrared spectrum of the compound of formula I-7 is as Figure 8 shown; the infrared spectrum of the compound of formula I-10 is as Figure 9 shown.

[0093] The lithium-ion battery was discharged to 3.0 V at 0.1C and then disassembled. The positive electrode plate was taken out, and the residual electrolyte was washed with dimethyl carbonate (DMC) and then dried. Then the positive electrode plate was immersed in acetonitrile with a volume of V3 mL to obtain the leaching solution of the positive electrode plate. Using an infrared spectrum analyzer (model: Nicolet iS50) and an attenuated total reflection (ATR) infrared accessory, the leaching solution was dropped onto the sample stage of the ATR accessory, and the infrared spectrum of the leaching solution of the positive electrode plate could be measured after the acetonitrile was completely volatilized.

[0094] Porosity test of the positive electrode material layer:

[0095] The gas replacement method is adopted for testing. A mold is used to punch and cut the positive electrode material layer to prepare samples. Those skilled in the art can select molds with common sizes and shapes in the art according to factors such as the size and shape of the test object and the requirements of the test equipment. The true volume V0 of the sample is measured by a true density tester, and the apparent volume V of the sample can be calculated by measuring the area and thickness of the sample. Then, the percentage P of the pore volume of the sample in the total volume is P=(V - V0) / V×100%, and the porosity of the positive electrode material layer can be obtained.

[0096] 45°C cycle capacity retention rate test:

[0097] Under the condition of 45°C, the lithium-ion battery in the example or comparative example is charged at a constant current of 1C to 4.53V, then charged at a constant voltage of 4.53V to 0.02C, and then discharged at a constant current of 0.5C to 3.0V, and cycled 500 times under this condition. The discharge capacity of the first cycle is recorded as the initial discharge capacity C0, the discharge capacity of the 100th cycle is recorded as C1, the discharge capacity of the 300th cycle is recorded as C2, and the discharge capacity of the 500th cycle is recorded as C3. The cycle capacity retention rate (%) of the 100th cycle at 45°C = C1 / C0×100%, the cycle capacity retention rate (%) of the 300th cycle at 45°C = C2 / C0×100%, and the cycle capacity retention rate (%) of the 500th cycle at 45°C = C3 / C0×100%.

[0098] The high-temperature cycle performance of the lithium-ion battery is characterized by the cycle capacity retention rate of the lithium-ion battery at 45°C. The higher the cycle capacity retention rate at 45°C, the better the high-temperature cycle performance of the lithium-ion battery.

[0099] Hot box test:

[0100] (1) The lithium-ion battery in the example or comparative example is charged at a constant current of 0.5C to 4.53V, and then charged at a constant voltage of 4.53V to 0.02C. At this time, the lithium-ion battery is in a fully charged state, and then it is left to stand for 5 minutes.

[0101] (2) Stick a temperature-sensitive wire on the fully charged lithium-ion battery between the two pole tabs, connect the two pole tabs to monitor the voltage, and hang the lithium-ion battery vertically in the box.

[0102] (3) The hot box is heated at a heating rate of 5°C / min to 130°C and maintained for 60 minutes.

[0103] (4) 10 lithium-ion batteries are tested in each group. The evaluation criterion is that the lithium-ion battery does not burn or explode, then it passes. Calculate the passing rate of the hot box test of the lithium-ion battery.

[0104] 130℃ hot box test pass rate (%) = number of lithium-ion batteries that passed the hot box test / 10 × 100%. The 135℃ hot box test pass rate can be obtained by raising the hot box temperature to 135℃. The 140℃ hot box test pass rate can be obtained by raising the hot box temperature to 140℃.

[0105] The hot box test pass rate is used to characterize the safety performance of lithium-ion batteries. The higher the hot box test pass rate, the better the thermal stability and safety performance of the lithium-ion battery.

[0106] Example 1-1

[0107] <Preparation of positive electrode sheet>

[0108] The positive electrode active material lithium cobalt oxide, the positive electrode conductive agent acetylene black, the positive electrode binder polyvinylidene fluoride (PVDF), and the compound of formula I-1 are mixed in a mass ratio of 95:2:2:1, and then the positive electrode solvent N-methylpyrrolidone (NMP) is added to prepare a positive electrode slurry with a solid content of 70wt% and stir evenly. The positive electrode slurry is evenly coated on one surface of an aluminum foil with a thickness of 9μm, and dried at 100°C to obtain a positive electrode sheet coated with a positive electrode material layer on one side. Then repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet coated with a positive electrode material layer on both sides. The positive electrode sheet coated with a positive electrode material layer on both sides is cold pressed, cut into a specification of 82.4mm×1435mm, and welded to the pole ears for standby use. Among them, the thickness of the single-sided positive electrode material layer after cold pressing is 80μm, and the coating weight of the positive electrode material layer is 517.44mg / 1540.25mm 2 The compaction density of the positive electrode material layer is 4.2g / cm 3 , the porosity B of the positive electrode material layer is 13.5%.

[0109] <Preparation of negative electrode sheet>

[0110] The negative electrode active material artificial graphite, the negative electrode conductive agent acetylene black, the negative electrode binder styrene butadiene rubber, and the thickener sodium carboxymethyl cellulose are mixed in a mass ratio of 96:1:1.5:1.5, and then the negative electrode solvent deionized water is added to prepare a negative electrode slurry with a solid content of 70% and stir evenly. The negative electrode slurry is evenly coated on one surface of a copper foil with a thickness of 8μm, and dried at 110°C to obtain a negative electrode sheet coated with a negative electrode material layer on one side. Then repeat the above steps on the other surface of the copper foil to obtain a negative electrode sheet coated with a negative electrode material layer on both sides. The negative electrode sheet coated with a negative electrode material layer on both sides is cold pressed, cut into a specification of 83.7mm×1564mm, and welded to the pole ears for standby use. Among them, the thickness of the single-sided negative electrode material layer after cold pressing is 100.7μm, and the coating weight of the negative electrode material layer is 272.86mg / 1540.25mm 2, the tap density of the negative electrode material layer is 1.76 g / cm 3 .

[0111] <Preparation of Electrolyte>

[0112] In an argon atmosphere glove box with a water content < 10 ppm, ethylene carbonate (EC), methyl ethyl carbonate (MEC), and diethyl carbonate (DEC) were mixed uniformly in a volume ratio of 1:1:1 to obtain a base solvent. LiPF6 was added to the base solvent and stirred evenly to obtain the electrolyte. Among them, based on the total mass of the electrolyte, the mass percentage of LiPF6 was 12.5%, and the mass percentage of the base solvent was 87.5%.

[0113] <Separator>

[0114] A polyethylene separator with a thickness of 5 μm was selected.

[0115] <Preparation of Lithium-Ion Battery>

[0116] The positive electrode sheet, separator, negative electrode sheet, and separator were stacked in sequence, with the separator placed in the middle of the positive electrode sheet and the negative electrode sheet to play a role in isolation, and then wound to obtain an electrode assembly. The electrode assembly was placed in an aluminum-plastic film, dried in a vacuum oven at 80 °C for 16 hours to remove moisture, injected with the above-prepared electrolyte, and then subjected to vacuum packaging, standing, formation (constant current charging at 1C to 4.53V at 85 °C), and hot pressing and shaping to obtain a lithium-ion battery.

[0117] Examples 1-2 to Examples 1-5

[0118] Except that the relevant preparation parameters were adjusted according to Table 1 in <Preparation of Positive Electrode Sheet>, the rest was the same as Example 1-1.

[0119] Examples 1-6 to Examples 1-12

[0120] Except that in <Preparation of Positive Electrode Sheet>, the porosity B of the positive electrode material layer was made as shown in Table 1 by controlling the thickness of the positive electrode sheet after cold pressing and the relevant preparation parameters were adjusted according to Table 1, the rest was the same as Example 1-1.

[0121] Examples 1-13 to Examples 1-17

[0122] Except that in <Preparation of Positive Electrode Sheet>, the types of Compound I were adjusted according to Table 1, the rest was the same as Example 1-1.

[0123] Examples 1-18 to Examples 1-22

[0124] Except that in <Preparation of Positive Electrode Sheet>, the relevant preparation parameters were adjusted according to Table 1, the rest was the same as Example 1-1.

[0125] Examples 1-23 to 1-26

[0126] Except for adjusting the mass percentage of lithium hexafluorophosphate in <Preparation of Electrolyte> according to Table 1, the rest is the same as Example 1-1. Among them, when the mass percentage of lithium hexafluorophosphate changes, the mass percentage of the base solvent changes accordingly, and the volume ratio of each component in the base solvent remains unchanged.

[0127] Comparative Example 1

[0128] Except for not adding the compound of Formula I in <Preparation of Positive Electrode Sheet> and the mass percentage of the positive electrode active material changing accordingly, the rest is the same as Example 1-1.

[0129] Comparative Example 2

[0130] Except for replacing <Preparation of Electrolyte> with the following steps, the rest is the same as Example 1-1.

[0131] In an argon atmosphere glove box with a water content <10 ppm, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed evenly in a volume ratio of 1:1:1 to obtain a base solvent. A first lithium salt, LiN(SO2CF3)2, was added to the base solvent and stirred evenly to obtain an electrolyte. Among them, based on the total mass of the electrolyte, the mass percentage of LiN(SO2CF3)2 was 12.5%, and the mass percentage of the base solvent was 87.5%.

[0132] Comparative Examples 3 to 4

[0133] Except for adjusting the relevant preparation parameters in <Preparation of Positive Electrode Sheet> according to Table 1, the rest is the same as Example 1-1.

[0134] Comparative Example 5

[0135]

[0136] Except for replacing the compound of Formula I with the compound of Formula II in <Preparation of Positive Electrode Sheet>, the rest is the same as Example 1-1.

[0137] The preparation parameters and performance tests of each example and comparative example are shown in Table 1.

[0138]

[0139]

[0140] As can be seen from Examples 1-1 to 1-26 and Comparative Examples 1 to 5, when the positive electrode material layer includes the compound of Formula I, the electrolyte includes lithium hexafluorophosphate, and the mass percentage content A of the compound of Formula I is within the scope of the present application, the cycle capacity retention rates of the obtained lithium-ion batteries after 100 cycles, 300 cycles, and 500 cycles at 45 °C are relatively high, and the passing rates of the hot box tests at 130 °C, 135 °C, and 140 °C are relatively high, indicating that the high-temperature cycle performance and safety performance of the lithium-ion batteries of the present application are improved. The positive electrode material layer in Comparative Example 1 does not contain the compound of Formula I, the electrolyte in Comparative Example 2 does not contain lithium hexafluorophosphate, the mass percentage content A of the compound of Formula I in Comparative Examples 3 to 4 is not within the scope of the present application, and the types of compounds used in the positive electrode material layer in Comparative Example 5 are not within the scope of the present application. The cycle capacity retention rates of the obtained lithium-ion batteries after 100 cycles, 300 cycles, and 500 cycles at 45 °C are relatively low, and / or the passing rates of the hot box tests at 130 °C, 135 °C, and 140 °C are relatively low, indicating that the high-temperature cycle performance and / or safety performance of the lithium-ion batteries in the comparative examples are poor.

[0141] The porosity B of the positive electrode material layer generally affects the high-temperature cycle performance of the lithium-ion battery. As can be seen from Examples 1-1, 1-6 to 1-12, when the value of B is within the scope of the present application, the cycle capacity retention rates of the obtained lithium-ion batteries after 100 cycles, 300 cycles, and 500 cycles at 45 °C are relatively high, and the passing rates of the hot box tests at 130 °C, 135 °C, and 140 °C are relatively high, indicating that the high-temperature cycle performance of the lithium-ion batteries of the present application is improved and they also have good safety performance.

[0142] The value of A / B generally affects the high-temperature cycle performance and safety performance of the lithium-ion battery. As can be seen from Examples 1-1 to 1-12, when the value of A / B is within the scope of the present application, the cycle capacity retention rates of the obtained lithium-ion batteries after 100 cycles, 300 cycles, and 500 cycles at 45 °C are relatively high, and the passing rates of the hot box tests at 130 °C, 135 °C, and 140 °C are relatively high, indicating that the high-temperature cycle performance and safety performance of the lithium-ion batteries of the present application are improved.

[0143] The type of the compound of Formula I generally affects the high-temperature cycle performance and safety performance of the lithium-ion battery. As can be seen from Examples 1-1, 1-13 to 1-17, when the type of the compound of Formula I is within the scope of the present application, the cycle capacity retention rates of the obtained lithium-ion batteries after 100 cycles, 300 cycles, and 500 cycles at 45 °C are relatively high, and the passing rates of the hot box tests at 130 °C, 135 °C, and 140 °C are relatively high, indicating that the high-temperature cycle performance and safety performance of the lithium-ion batteries of the present application are improved.

[0144] The mass percentage content of the positive electrode active material, the mass percentage content of the positive electrode conductive agent, and the mass percentage content of the positive electrode binder usually affect the high-temperature cycling performance and safety performance of lithium-ion batteries. It can be seen from Example 1-1, Example 1-18 to Example 1-22 that when the mass percentage content of the positive electrode active material, the mass percentage content of the positive electrode conductive agent, and the mass percentage content of the positive electrode binder are within the scope of this application, the cycling capacity retention rate of the obtained lithium-ion battery after 100 cycles, 300 cycles, and 500 cycles at 45 °C is relatively high, and the passing rate of the hot box test at 130 °C, 135 °C, and 140 °C is relatively high, indicating that the high-temperature cycling performance and safety performance of the lithium-ion battery of this application are improved.

[0145] The mass percentage content of lithium hexafluorophosphate usually affects the high-temperature cycling performance of lithium-ion batteries. It can be seen from Example 1-1, Example 1-23 to Example 1-26 that when the mass percentage content of lithium hexafluorophosphate is within the scope of this application, the cycling capacity retention rate of the obtained lithium-ion battery after 100 cycles, 300 cycles, and 500 cycles at 45 °C is relatively high, and the passing rate of the hot box test at 130 °C, 135 °C, and 140 °C is relatively high, indicating that the high-temperature cycling performance of the lithium-ion battery of this application is improved, and it also has good safety performance.

[0146] From Figure 3 it can be seen that in the 1 1H solid nuclear magnetic resonance test spectrum of the compound of Formula I-2, characteristic peaks exist at 7.373 ppm to 7.573 ppm, 7.017 ppm to 7.217 ppm, and 2.306 ppm to 2.706 ppm.

[0147] From Figure 4 it can be seen that in the 1 1H solid nuclear magnetic resonance test spectrum of the compound of Formula I-10, characteristic peaks exist at 6.16 ppm to 6.36 ppm, 6.762 ppm to 6.962 ppm, and 7.016 ppm to 7.216 ppm.

[0148] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method or article including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method or article.

[0149] Each embodiment in this specification is described in a related manner. For the same or similar parts among the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments.

[0150] The foregoing are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. An electrochemical device, comprising a positive electrode sheet and an electrolyte, wherein the electrolyte comprises lithium hexafluorophosphate, the positive electrode sheet comprises a positive electrode material layer, and the positive electrode material layer comprises a compound of formula I, in, R 1 selected from hydrogen atoms, C1 to C 10 alkyl, C1 to C5 acyl, unsubstituted or methyl-substituted amino; Based on the mass of the positive electrode material layer, the mass percentage A of the compound of formula I is 0.5% to 5%.

2. The electrochemical device according to claim 1, wherein: Based on the mass of the positive electrode material layer, the mass percentage A of the compound of formula I is 0.5% to 1%.

3. The electrochemical device according to claim 1, wherein The porosity B of the positive electrode material layer is 12% to 20%.

4. The electrochemical device according to claim 3, wherein: The porosity B of the positive electrode material layer is 12% to 15%.

5. The electrochemical device according to claim 3, wherein: 1 / 40≤A / B≤1 / 6.

6. The electrochemical device according to claim 5, wherein: 1 / 30≤A / B≤1 / 12.

7. The electrochemical device according to claim 1, wherein: The compound of formula I includes at least one of the following compounds:

8. The electrochemical device according to claim 1, wherein In the infrared spectrum of the positive electrode, at 1200±10cm -1 、1450±10cm -1 、1640±10cm -1 and 3000cm -1 Up to 3500cm -1 There are characteristic peaks.

9. The electrochemical device according to claim 7, wherein: The positive electrode 1 In the H solid nuclear magnetic resonance test spectrum, characteristic peaks exist at 12ppm to 13ppm, 8.035ppm to 8.435ppm, 7.51ppm to 7.71ppm, and 7.01ppm to 7.41ppm.

10. The electrochemical device according to claim 1, wherein The positive electrode material layer includes a positive electrode active material, a positive electrode conductor and a positive electrode binder; based on the mass of the positive electrode material layer, the mass percentage of the positive electrode active material is 80% to 99.3%, the mass percentage of the positive electrode conductor is 0.1% to 10%, and the mass percentage of the positive electrode binder is 0.1% to 10%.

11. The electrochemical device according to claim 10, wherein: Based on the mass of the positive electrode material layer, the mass percentage of the positive electrode active material is 90% to 99.1%, the mass percentage of the positive electrode conductor is 0.2% to 5%, and the mass percentage of the positive electrode binder is 0.2% to 5%.

12. The electrochemical device according to claim 1, wherein Based on the mass of the electrolyte, the mass percentage of the lithium hexafluorophosphate is 9% to 14%.

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

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