Electrochemical and electronic devices

Abstract

The present invention provides an electrochemical device and an electronic device, the electrochemical device comprising a positive electrode, a negative electrode and an electrolyte, the electrolyte comprising an organic solvent, a lithium salt and an additive, the organic solvent comprising an acetate compound and a carbonate compound, the carbonate compound comprising ethylene carbonate and propylene carbonate, and the mass fraction A of the acetate compound is 4%-50%, and the mass fraction B of the ethylene carbonate is 5%-20%, relative to the total mass of the electrolyte. The present invention optimizes the content and type of the solvent in the electrolyte and utilizes the interface modification effect of the additive to improve the charging ability of the electrochemical device and reduce the rise in charging temperature during charging.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS The present invention claims priority to a Chinese patent application bearing application number 202111243754.6, filed on October 25, 2021, and entitled "Electrochemical Device and Electronic Device," the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to the technical field of energy storage, in particular to electrochemical and electronic devices. [Background technology]

[0003] Electrochemical devices such as lithium-ion batteries have advantages such as high operating voltage, high energy density, environmental friendliness, stable cycling, and safety, and are therefore widely used in fields such as wearable devices, smartphones, drones, and laptops. With the development of modern information technology and the expansion of applications of electrochemical devices, the requirements for the charging capacity and charging temperature of electrochemical devices are becoming increasingly higher. Therefore, in the field of energy storage technology, improving the charging capacity of electrochemical devices and reducing the rise in charging temperature have become urgent problems that need to be solved. Summary of the Invention

[0004] An object of the present invention is to provide an electrochemical device and an electronic device that reduce the rise in charging temperature.

[0005] According to a first aspect of the present invention, there is provided an electrochemical device comprising a positive electrode, a negative electrode, and an electrolyte solution, wherein the electrolyte solution comprises an organic solvent, a lithium salt, and an additive, the organic solvent comprises an acetate ester compound and a carbonate compound, the carbonate compound comprises ethylene carbonate (EC) and propylene carbonate (PC), and a mass fraction A of the acetate ester compound is 4% to 50% and a mass fraction B of the ethylene carbonate is 5% to 20% relative to the total mass of the electrolyte solution. After extensive investigation, the present inventors have found that by containing the acetate ester compound and the carbonate compound in the above amounts in the organic solvent, the cycle characteristics of the electrochemical device can be improved and an increase in charging temperature can be reduced.

[0006] In some embodiments of the first aspect of the present invention, the acetate ester compound comprises at least one of methyl acetate, ethyl acetate, and propyl acetate.

[0007] In some embodiments of the first aspect of the present invention, the electrolyte solution further comprises a polynitrile compound, the polynitrile compound comprising at least two of succinonitrile, adiponitrile, 1,3,6-hexanetricarbonitrile, 1,2,3-tris(2-cyanoethoxy)propane, ethylene glycol (bispropionitrile) ether, and 1,4-dicyano-2-butene. By selecting the polynitrile compound, the cycle characteristics of the electrochemical device can be further improved and the rise in charging temperature can be further reduced.

[0008] In some embodiments of the first aspect of the present invention, the mass fraction C of the polynitrile compound is 0.1% to 10%.

[0009] In some embodiments of the first aspect of the present invention, the mass fraction C of the polynitrile compound and the mass fraction A of the acetate compound satisfy the relationship 0.1≦C / A≦0.8. By controlling the value of C / A within this range, the cycle characteristics of the electrochemical device can be improved.

[0010] In some embodiments of the first aspect of the present invention, the additive comprises fluoroethylene carbonate (FEC), and a mass fraction D of the fluoroethylene carbonate and a mass fraction E of the propylene carbonate satisfy the relationship 0.2≦D / E≦1.

[0011] In some embodiments of the first aspect of the present invention, the mass fraction E of the propylene carbonate is 5% to 30%, or the mass fraction D of the fluoroethylene carbonate is 0.1% to 15%. By controlling the mass fraction of the fluoroethylene carbonate or the mass fraction of the propylene carbonate within the above ranges, the cycle characteristics of the electrochemical device can be improved.

[0012] In some embodiments of the first aspect of the present invention, the lithium salt is LiPF6, and the mass fraction of the lithium salt is 10% to 20% relative to the total mass of the electrolyte solution.

[0013] In some embodiments of the first aspect of the present invention, the compressed density of the negative electrode active material in the negative electrode is 1.40 g / cm 3 ~1.70g / cm 3 By controlling the compressed density of the negative electrode active material within the above range, the cycle characteristics of the electrochemical device can be further improved and the rise in charging temperature can be further reduced.

[0014] In some embodiments of the first aspect of the present invention, the negative electrode includes pores, and the pores have (a) a pore diameter of 20 μm to 100 μm, (b) a pore depth range of 5 μm to 50 μm, and (c) a pore number per unit area of ​​0.5 / mm 2 ~100 pieces / mm 2 By controlling the pore diameter, pore depth, and number of pores per unit area of ​​the negative electrode pores within the above ranges, the cycle characteristics of the electrochemical device can be further improved and the rise in charging temperature can be further reduced.

[0015] A second aspect of the present invention provides an electronic device comprising an electrochemical device provided by the first aspect of the present invention.

[0016] The electrochemical device and electronic device of the present invention can improve the dynamic characteristics of the electrochemical device, increase the charging capacity, and reduce the rise in charging temperature by optimizing the content and type of solvent in the electrolyte. The addition of an appropriate additive to the electrolyte can further improve the charging capacity and reduce the rise in charging temperature.

[0017] Of course, it is not necessary for the implementation of any one product or method of the present invention to simultaneously achieve all of the above advantages. DETAILED DESCRIPTION OF THE INVENTION

[0018] In order to clarify the purpose, technical solution and advantages of the present invention, the present invention will be described in more detail. Obviously, the described embodiments are only a part of the embodiments of the present invention, but are not all of the embodiments. Based on the embodiments in the present invention, all other embodiments that can be obtained by those skilled in the art without creative work fall within the protection scope of the present invention. It should be noted that, in the present invention, a lithium ion battery is used as an example of an electrochemical device to describe the present invention, but the electrochemical device of the present invention is not limited to a lithium ion battery. Those skilled in the art should understand that the following description is merely an illustrative example and does not limit the scope of protection of the present invention.

[0019] Hereinafter, the embodiments of the present invention will be described in more detail with reference to examples and comparative examples. Various tests and evaluations were carried out according to the following methods. Unless otherwise specified, "parts" and "%" are by mass.

[0020] According to a first aspect of the present invention, there is provided an electrochemical device comprising a positive electrode, a negative electrode, and an electrolyte solution, the electrolyte solution comprising an organic solvent, a lithium salt, and an additive, the organic solvent comprising an acetate ester compound and a carbonate compound, the carbonate compound comprising ethylene carbonate and propylene carbonate, a mass fraction A of the acetate ester compound is 4% to 50% relative to the total mass of the electrolyte solution, for example, the mass fraction A of the acetate ester compound may be 4%, 10%, 12%, 20%, 28%, 36%, 50%, or any range therebetween, and a mass fraction B of the ethylene carbonate is 5% to 20%, for example, the mass fraction B of the ethylene carbonate may be 5%, 8%, 11%, 14%, 17%, 20%, or any range therebetween.

[0021] As a result of the investigation, the inventors found that adjusting the organic solvent to contain an acetate compound and a carbonate compound and controlling the mass fraction of the acetate compound and ethylene carbonate within the above ranges contributes to improving the dissociation rate of the lithium salt and improving the stability of the solid electrolyte interface (SEI) film during the cycling process of the electrochemical device, thereby improving the kinetic characteristics and cycling characteristics of the electrochemical device and reducing the rise in charging temperature.

[0022] In some embodiments of the present invention, the acetate ester compound includes at least one of methyl acetate, ethyl acetate, and propyl acetate. Without being limited to any theory, the inventors have found that the acetate ester compounds all have low viscosity, which is advantageous for improving the transport of lithium ions during charging and reducing transport impedance, thereby reducing the rise in charging temperature of the electrochemical device.

[0023] In some embodiments of the present invention, the electrolyte solution further comprises a polynitrile compound, which comprises at least two of succinonitrile (SN), adiponitrile (AND), 1,3,6-hexanetricarbonitrile (HTCN), 1,2,3-tris(2-cyanoethoxy)propane (TCEP), ethylene glycol (bispropionitrile) ether (DENE), and 1,4-dicyano-2-butene (HEDN). Without being limited to any theory, the inventors have found that selecting a combination of at least two of the polynitrile compounds is advantageous in improving the stability of the SEI film during cycling of the electrochemical device, thereby improving the cycling characteristics of the electrochemical device and reducing the rise in charging temperature.

[0024] In some embodiments of the first aspect of the present invention, the mass fraction C of the polynitrile compound is 0.1% to 10%, for example, the mass fraction C of the polynitrile compound can be 0.1%, 1%, 2%, 4%, 6%, 8%, 10%, or any range therebetween.

[0025] In some embodiments of the first aspect of the present invention, the mass fraction C of the polynitrile compound and the mass fraction A of the acetate ester compound satisfy the relationship 0.1≦C / A≦0.8. For example, the value of C / A can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or any range therebetween. The inventors have found that if the value of C / A is too low, e.g., less than 0.1, the improvement in the cycle characteristics of the electrochemical device and the improvement in the increase in charging temperature are not significant. On the other hand, if the value of C / A is too high, e.g., greater than 0.8, the content of the polynitrile compound is too high or the content of the acetate ester is too low, increasing the viscosity of the electrolyte and increasing polarization during cycling, thereby affecting the increase in charging temperature and the cycle characteristics of the electrochemical device. Controlling the value of C / A within this range is advantageous for further improving the cycle characteristics of the electrochemical device and further reducing the increase in charging temperature.

[0026] In some embodiments of the present invention, the additive includes fluoroethylene carbonate (FEC), the mass fraction of the fluoroethylene carbonate is D, and the mass fraction of the fluoroethylene carbonate, D, and the mass fraction of the propylene carbonate, E, satisfy the relationship 0.2≦D / E≦1. For example, the value of D / E can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, or any range therebetween. Without being bound by any theory, the inventors have found that if the ratio of the mass fraction of FEC to the mass fraction of propylene carbonate is too low, for example, if the D / E ratio is less than 0.2, the viscosity of the solvent is high, resulting in increased internal resistance of the lithium-ion battery, an increased rise in charging temperature, and insufficient protection for the anode, resulting in poor cycling performance; and if the ratio of the mass fraction of FEC to the mass fraction of propylene carbonate is too high, for example, if the D / E ratio is greater than 1, insufficient dissociation of the lithium salt occurs, an increased rise in temperature, and the FEC content is too high, resulting in poor high-temperature stability and poor cycling performance. Controlling the ratio of the mass fraction of fluoroethylene carbonate to the mass fraction of propylene carbonate within the above range is advantageous in improving the cycling performance of the electrochemical device and reducing the increase in charging temperature.

[0027] In some embodiments of the present invention, the mass fraction E of the propylene carbonate is 5% to 30%, or the mass fraction D of the fluoroethylene carbonate is 0.1% to 15%. For example, E can be 5%, 10%, 12%, 14%, 16%, 18%, 20%, 30%, or any range therebetween, and D can be 0.1%, 1%, 3%, 5%, 7%, 9%, 11%, 15%, or any range therebetween.

[0028] In some embodiments of the present invention, the lithium salt is LiPF6, and the mass fraction of the lithium salt is 10% to 20% based on the total mass of the electrolyte. For example, the mass fraction of the lithium salt can be 10%, 12%, 14%, 16%, 18%, 20%, or any range therebetween. Without being limited by any theory, the present inventors have found that controlling the mass fraction of the lithium salt within this range is advantageous in improving the electrical conductivity during cycling of the electrochemical device, thereby improving the cycling characteristics of the electrochemical device.

[0029] In the present invention, the electrolyte solution may further contain other non-aqueous solvents. The other non-aqueous solvents are not particularly limited as long as the objectives of the present invention are achieved. For example, the other non-aqueous solvents may include, but are not limited to, at least one of a carboxylic acid ester compound, an ether compound, and another organic solvent. The carboxylic acid ester compound may include, but is not limited to, at least one of methyl formate, ethyl formate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decalactone, valerolactone, and caprolactone. The ether compound may include, but is 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, and tetrahydrofuran. The other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylmethylamide, trimethyl phosphate, triethyl phosphate, and trioctyl phosphate. The total mass fraction of the other nonaqueous solvents relative to the total mass of the electrolyte solution is 5% to 60%, and may be, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or any range therebetween.

[0030] In the present invention, the electrolyte may further contain other additives. The present invention does not particularly limit the other additives as long as the object of the present invention can be achieved. For example, the other additives may include at least one of lithium tetrafluoroborate (LiBF), vinyl sulfate (DTD), vinylidene carbonate (VC), vinyl sulfite (PS), and lithium bis(oxalato)borate (LiBOB), but are not limited thereto.

[0031] Some embodiments of the present invention include a negative electrode, wherein the compressed density of the negative electrode active material in the negative electrode is 1.40 g / cm 3 ~1.70g / cm 3 For example, the compressed density of the negative electrode active material is 1.40 g / cm 3 , 1.45g / cm 3 , 1.50g / cm 3 , 1.55g / cm 3 , 1.60g / cm 3 , 1.65g / cm 3 , 1.70g / cm 3 Without being limited to any theory, the present inventors believe that if the compressed density of the negative electrode active material is too low, for example, 1.40 g / cm 3 If the density is less than 1.70 g / cm, the contact between the negative electrode materials in the electrochemical device is insufficient, the electronic conduction and ionic conduction are hindered, the charging temperature increases, and the cycle characteristics deteriorate. If the compressed density of the negative electrode active material is too high, for example, 1.70 g / cm 3 The inventors have found that if the compressed density of the negative electrode active material is greater than 100 kJ / cm 2 , the negative electrode is prone to overvoltage, resulting in poor charging performance, a high rise in charging temperature, and poor cycle characteristics. At the same time, there is a risk of material particles being crushed due to the overvoltage. By controlling the compressed density of the negative electrode active material within the above range, the cycle characteristics of the electrochemical device can be improved and the rise in charging temperature can be reduced.

[0032] In some embodiments of the present invention, the negative electrode material in the negative electrode includes at least one of a carbon material, silicon, a silicon-oxygen material, and a silicon-carbon material, and the carbon material includes at least one of natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, and soft carbon.

[0033] In some embodiments of the present invention, the negative electrode includes pores, and the pores have: (a) a pore diameter of 20 μm to 100 μm, for example, the pore diameter may be 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, or any range therebetween; (b) a pore depth range of 5 μm to 50 μm, for example, the pore depth may be 5 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, or any range therebetween; and (c) a pore number per unit area of ​​0.5 / mm 2 ~100 pieces / mm 2 For example, the number of pores per unit area is 0.5 / mm 2 , 1 piece / mm 2 , 10 pieces / mm 2 , 20 pieces / mm 2 , 30 pieces / mm 2 , 40 pieces / mm 2 , 50 pieces / mm 2 , 60 pieces / mm 2 , 70 pieces / mm 2 , 80 pieces / mm 2 , 90 pieces / mm 2 , 100 pieces / mm 2 Without being limited to any theory, the inventors have found that controlling the intensity of the infrared laser to drill holes on the surface of the negative electrode piece and controlling the pore diameter, pore depth, and number of pores per unit area within the above ranges is beneficial to the infiltration of the electrolyte and the transport of lithium ions between the materials, reducing the transport impedance, and thereby improving the cycle characteristics of the electrochemical device and reducing the rise in charging temperature.

[0034] The positive electrode pieces of the present invention are not particularly limited as long as they can achieve the objectives of the present invention. The positive electrode pieces typically include a positive electrode current collector and a positive electrode active material. The positive electrode current collector is not particularly limited and may be any positive electrode current collector known in the art, such as copper foil, aluminum foil, aluminum alloy foil, or a composite current collector. The positive electrode active material is not particularly limited and may be any positive electrode active material known in the art, such as at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, and lithium iron manganese phosphate.

[0035] In the present invention, the thickness of the positive electrode current collector and the thickness of the positive electrode active material are not particularly limited as long as the object of the present invention can be achieved. For example, the thickness of the positive electrode current collector is 8 μm to 12 μm, and the thickness of the positive electrode active material is 30 μm to 120 μm.

[0036] In the present invention, the positive electrode active material layer may further include a conductive agent. The conductive agent is not particularly limited as long as it achieves the objectives of the present invention. For example, the conductive agent may include at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fiber, flake graphite, Ketjen black, graphene, a metal material, and a conductive polymer, but is not limited thereto. The carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The carbon fiber may include, but is not limited to, vapor-grown carbon fiber (VGCF) and / or nanocarbon fiber. The 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, and silver. The conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, and polypyrrole.

[0037] In the present invention, the positive electrode active material layer may further contain a binder. The present invention is not particularly limited to the binder as long as the object of the present invention can be achieved. For example, the binder may include, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, (1,1-difluoroethylene) polymer, polyethylene, polypropylene, styrene-butadiene rubber, acrylated (esterified) styrene-butadiene rubber, epoxy resin, and nylon.

[0038] The positive electrode may also optionally include a conductive layer located between the positive electrode current collector and the positive electrode active material layer. The present invention is not particularly limited to the composition of the conductive layer, and the conductive layer may be a conductive layer commonly used in this technical field. For example, the composition of the conductive layer may include the conductive agent and the binder, but is not limited thereto.

[0039] The negative electrode current collector in the present invention is not particularly limited as long as it can achieve the objectives of the present invention. Materials such as foils or porous plates of metals such as copper, nickel, titanium, or iron, or alloys thereof, for example, metal foils such as copper foil or porous metal plates, may be used. The negative electrode active material layer includes a negative electrode active material, a conductive agent, an adhesive, and a thickener. The adhesive may be at least one of styrene butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), water-based acrylic resin, and carboxymethyl cellulose (CMC), and the thickener may be sodium carboxymethyl cellulose (CMC). In the present invention, the thickness of the negative electrode current collector is not particularly limited as long as it can achieve the objectives of the present invention. For example, the thickness of the negative electrode current collector is 4 μm to 12 μm.

[0040] In the present invention, the negative electrode active material layer may further contain a conductive agent, and the present invention is not particularly limited to the conductive agent as long as the object of the present invention can be achieved.

[0041] In the present invention, the negative electrode active material layer may further contain an adhesive, and the present invention is not particularly limited to the adhesive, as long as the object of the present invention can be achieved.

[0042] The negative electrode may also optionally include a conductive layer located between the negative electrode current collector and the negative electrode active material layer. The present invention does not place any particular limitations on the composition of the conductive layer, and the conductive layer may be any conductive layer commonly used in this technical field.

[0043] The separator of the present invention is not particularly limited as long as it can achieve the objectives of the present invention. The separator may include a substrate layer and a surface treatment layer. The present invention is not particularly limited to the material of the substrate layer. For example, the material of the substrate layer may include, but is not limited to, at least one of polyethylene (PE), polypropylene (PP), polytetrafluoroethylene-based polyolefin (PO), polyester (e.g., polyethylene terephthalate (PET)), cellulose, polyimide (PI), polyamide (PA), spandex, and aramid. The type of the substrate layer may include, but is not limited to, at least one of woven fabric film, nonwoven fabric film (nonwoven fabric), microporous membrane, composite membrane, membrane paper, laminate film, and spun film. It is preferred that the material of the substrate layer is PP. The separator of the present invention may have a porous structure, and the pore size is not particularly limited as long as it can achieve the objectives of the present invention. For example, the pore size may be 0.01 μm to 1 μm. In the present invention, the thickness of the separator is not particularly limited as long as the object of the present invention can be achieved, and the thickness of the separator can be, for example, 5 μm to 500 μm.

[0044] In the present invention, a surface treatment layer may be provided on at least one surface of the substrate layer. The surface treatment layer is not particularly limited in the present invention, and may be a polymer layer, an inorganic layer, or a layer formed by mixing a polymer and an inorganic material. The inorganic layer may include, but is not limited to, inorganic particles and an inorganic layer adhesive. The inorganic particles are not particularly limited in the present invention, and for example, the inorganic particles may include, but are not limited to, at least one of alumina, silica, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium oxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The present invention does not particularly limit the inorganic layer adhesive, and for example, the inorganic layer adhesive can include at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylic ester, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene, but is not limited to these. The polymer layer includes a polymer, and the polymer material can include at least one of polyamide, polyacrylonitrile, acrylic ester polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0045] The electrochemical device of the present invention is not particularly limited and may include any device that undergoes an electrochemical reaction. In some embodiments, the electrochemical device may include, but is not limited to, a lithium ion battery.

[0046] The manufacturing process for an electrochemical device is well known to those skilled in the art and is not particularly limited in the present invention, and may include, for example, but is not limited to, a process of stacking a positive electrode piece, a separator, and a negative electrode piece in this order, and optionally winding and folding them to obtain a wound electrode assembly, placing the electrode assembly in a packaging bag, injecting an electrolyte into the packaging bag and sealing it to obtain an electrochemical device; or a process of stacking a positive electrode, a separator, and a negative electrode in this order, securing the four corners of the entire stack with tape to obtain a stacked electrode assembly, placing the electrode assembly in a packaging bag, injecting an electrolyte into the packaging bag and sealing it to obtain an electrochemical device. Furthermore, an overcurrent protection element, lead plates, etc. may be placed in the packaging bag as needed, which can prevent pressure buildup and overcharge and overdischarge within the electrochemical device.

[0047] A second aspect of the present invention provides an electronic device including an electrochemical device according to any of the above-described embodiments of the present invention. The electrochemical device provided by the present invention has good cycle characteristics and a low charging temperature rise, and therefore the electronic device provided by the present invention has a long life and good performance.

[0048] The electronic device of the present invention is not particularly limited and may be any electronic device known in the prior art, including, but not limited to, display devices, notebook computers, pen-input computers, mobile computers, electronic book players, mobile phones, portable facsimiles, portable copiers, portable printers, stereo headsets, video recorders, LCD televisions, portable vacuum cleaners, portable CD players, minidiscs, walkie-talkies, electronic organizers, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, automobiles, motorcycles, power-assisted bicycles, bicycles, lighting equipment, toys, game consoles, clocks, power tools, flashlights, cameras, large-scale household storage batteries, and lithium-ion capacitors.

[0049] Measurement method and device: Lithium Deposition Test: The battery was charged at 3C at 25°C to 4.45V, then charged at a constant voltage of 0.05C from 4.45V, and then discharged at a constant current of 1.0C to 3.0V. This charge / discharge cycle was repeated 10 times, after which the battery was disassembled and the degree of lithium deposition was observed. Cases where no lithium deposition was found or the lithium deposition area was less than 2% were referred to as "no lithium deposition," cases where the lithium deposition area was between 2% and 20% were referred to as "light lithium deposition," and cases where the lithium deposition area was more than 20% were referred to as "severe lithium deposition."

[0050] Temperature rise test: At a test temperature of 25°C, the lithium-ion battery was charged at a constant current of 0.5C to 4.45V, then further charged at a constant voltage of 0.05C, and allowed to stand for 60 minutes. The lithium-ion battery was then discharged at a constant current of 0.5C to 3V, and allowed to stand for 60 minutes. The lithium-ion battery was then charged at a constant current of 6C to 4.45V, then further charged at a constant voltage of 0.05C. The temperature during this high-current charging was monitored, and the test temperature of 25°C was subtracted to obtain the 6C charging temperature rise.

[0051] High temperature cycle test: The battery was placed in a thermostatic chamber at 45°C, charged at a constant current of 1.5C to 4.45V, charged at a constant voltage of 0.05C from 4.45V, and then discharged at a constant current of 1.0C to 3.0V, constituting one charge-discharge cycle. This charge-discharge cycle was repeated 800 times, and the capacity retention rate was monitored. The 45°C cycle capacity retention rate = (discharge capacity at the 800th cycle / initial discharge capacity) x 100%.

[0052] Electrolyte component content test: The cell was discharged and centrifuged, and the liquid obtained by centrifugation was subjected to GC-MS testing to detect the mass fraction of each component (acetate ester, EC, PC, and additives).

[0053] Compressed density test of negative electrode active material: The compressed density of the negative electrode active material was measured by the following method. Using a negative double-sided pole piece, the area is 1540.25 mm 2The weight and thickness of 20 small wafers were measured, and the compressed density of the negative electrode active material = (weight of small wafer - weight of substrate) / (1540.25 x (thickness of both sides of small wafer - thickness of substrate)) x 1000, and the test average value was taken, which was used as the compressed density of the negative electrode in this example. The weight and thickness of the substrate (copper foil) were obtained by measuring the weight and thickness using an area without active material. The weight of the small wafer and the weight of the substrate were in mg. The thicknesses of both sides of the small wafer and the thickness of the substrate were measured in μm.

[0054] Pore ​​characteristics test on negative electrode pieces: Pore ​​characteristics data (pore diameter, pore depth, number of pores per unit area) on the negative electrode pieces were obtained by scanning tunneling microscope examination.

[0055] Example 1 (1) Preparation of negative electrode pieces: The negative electrode active materials, artificial graphite, styrene butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC), were mixed in a mass ratio of 97.4:1.2:1.4. Deionized water was then added as a solvent to prepare a slurry with a solids content of 70 wt%. The mixture was then uniformly stirred. The slurry was uniformly coated onto one surface of an 8 μm-thick copper foil, dried at 110°C, and cold-rolled to obtain a negative electrode piece with a 150 μm-thick negative electrode active material layer coated on one side. The coating process was then repeated on the other surface of the negative electrode piece, resulting in a negative electrode piece with a double-coated negative electrode active material layer. The negative electrode piece was cut to the required dimensions (74 mm x 867 mm), and a tab was welded. The piece was then stored for future use.

[0056] (2) Preparation of Positive Electrode Pieces: The positive electrode active material, lithium cobalt oxide (LiCoO), the conductive agent, acetylene black, and the adhesive, polyvinylidene fluoride (PVDF), were mixed in a mass ratio of 96:2:2, and N-methylpyrrolidone (NMP) was added as a solvent. The mixture was stirred using a vacuum mixer until homogeneous, yielding a positive electrode slurry with a solids content of 75 wt%. The positive electrode slurry was uniformly applied to a 12 μm-thick aluminum foil positive electrode current collector, dried at 85°C, and cold-rolled to obtain a positive electrode piece with a 100 μm-thick positive electrode active material layer. The application process was then repeated on the other surface of this positive electrode piece, yielding a positive electrode piece coated on both sides with a positive electrode active material layer. The positive electrode piece was cut to a 74 mm x 867 mm size and tabs were welded. The piece was then stored for future use.

[0057] (3) Electrolyte preparation: In an argon-filled glove box with a water content of <10 ppm, ethylene carbonate (EC), propylene carbonate (PC), ethyl acetate (EA), and ethyl propionate (EP) were uniformly mixed, and then thoroughly dried lithium salt LiPF6 was dissolved in the non-aqueous solvent and the additive fluoroethylene carbonate was added to obtain the base electrolyte. The mass fraction of the lithium salt was 10%, and the mass fractions of EC, PC, EA, and FEC were 10%, 15%, 4%, and 7.5%, respectively. The remainder of the electrolyte was ethyl propionate, and the ratio of the mass fraction of fluoroethylene carbonate to the mass fraction of ethylene carbonate was 0.5.

[0058] (4) Separator: A PE porous polymer film was used as the separator.

[0059] (5) Preparation of lithium-ion battery: The positive electrode pieces, separator, and negative electrode pieces were stacked in this order, and a separator film was interposed between the positive electrode pieces and the negative electrode pieces to function as a separator. The stack was then wound up to obtain a bare battery. The bare battery was placed in an exterior foil, and the electrolyte prepared above was injected into the dried battery. The lithium-ion battery was then prepared through processes such as vacuum sealing, standing, chemical conversion, and shaping.

[0060] In Examples 2 to 21, the negative electrode piece preparation process, the positive electrode piece preparation process, the electrolyte preparation process, the separator preparation process, and the lithium ion battery preparation process are all the same as in Example 1, and the changes in the relevant preparation parameters and performance parameters are shown in Table 1.

[0061] Examples 22 to 43 and 46 were the same as Example 3, except that a polynitrile compound was added to the electrolytic solution of Example 3, and the type and content of the polynitrile compound, the total content of the polynitrile compound, and the ratio of the content of the polynitrile compound to the content of the acetate ester compound were adjusted as shown in Table 2.

[0062] Example 44 was the same as Example 2, except that a polynitrile compound was added to the electrolytic solution of Example 2, and the type and content of the polynitrile compound, the total content of the polynitrile compound, and the ratio of the content of the polynitrile compound to the content of the acetate ester compound were adjusted as shown in Table 2.

[0063] Example 45 was the same as Example 10, except that a polynitrile compound was added to the electrolytic solution of Example 10, and the type and content of the polynitrile compound, the total content of the polynitrile compound, and the ratio of the content of the polynitrile compound to the content of the acetate ester compound were adjusted as shown in Table 2.

[0064] In Examples 47 to 55, the compressed density of the negative electrode active material, and the pore diameter, pore depth, and number of pores per unit area of ​​the pores on the negative electrode pieces were adjusted based on the electrolyte solutions of Examples 23 to 31, as shown in Table 3, but were the same as Examples 23 to 31.

[0065] In Comparative Examples 1 to 7, the process for preparing the negative electrode pieces, the process for preparing the positive electrode pieces, the process for preparing the electrolyte, the process for preparing the separator, and the process for preparing the lithium ion battery are all the same as in Example 1, and the related preparation parameters and performance changes are shown in Table 1.

[0066] Tables 1 to 3 show the preparation parameters and performance tests for each of the Examples and Comparative Examples.

[0067] [Table 1] In Table 1, " / " indicates that the corresponding preparation parameter does not exist.

[0068] [Table 2]

[0069] [Table 3]

[0070] From Examples 1 to 10 and Comparative Examples 1 to 3, it can be seen that as the content of ethyl acetate increases, the lithium deposition state and the rise in charging temperature improve; however, when the content of ethyl acetate is high, the cycle characteristics deteriorate; when an acetate ester compound is not included, lithium deposition deteriorates, the cycle characteristics deteriorate, and the rise in charging temperature increases significantly; when the content of acetate ester compound is too low, lithium is severely deposited, the cycle characteristics deteriorate, and the rise in charging temperature increases; and when the content of acetate ester compound is too high, cycling is impossible, gas is generated, and a sudden drop in capacity occurs.

[0071] From Example 3, Examples 11 to 13, Comparative Example 4, and Comparative Example 5, it can be seen that when the EC content is low, the interfacial stability improves due to dissociation of the lithium salt, and the dynamic properties improve, resulting in improved cycle characteristics; when the EC content is too high, the viscosity increases and stability deteriorates; and when the EC content is too low, the cycle characteristics deteriorate and lithium precipitates heavily; and when the EC content is too high, the cycle characteristics deteriorate and lithium precipitates heavily.

[0072] From Example 3, Examples 14 to 21, Comparative Example 6, and Comparative Example 7, it can be seen that when the FEC / PC value is within the range of the present invention, the lithium deposition state and the increase in charging temperature are improved, and when the FEC / PC is too small, the cycle characteristics deteriorate, and when the FEC / PC is too high, lithium is severely deposited. From Examples 2, 3, 10, and 22 to 46, it can be seen that the addition of a polynitrile compound further improves the stability of the SEI film during the cycle process, thereby improving the cycle characteristics.

[0073] From Example 40 and Examples 47 to 49, it can be seen that the lithium deposition state and the rise in charging temperature are improved as the pore diameter of the pores on the negative electrode pieces increases.

[0074] From Examples 48, 50, and 51, it can be seen that when the pore depth range of the pores on the negative electrode piece is within the range of the present invention, the resulting lithium ion battery exhibits slight or no lithium precipitation, a low rise in charging temperature, and a high cycle capacity retention rate, which indicates that the lithium ion battery has good cycle characteristics, the problem of a rise in charging temperature is improved, and lithium precipitation is less likely to occur during cycling.

[0075] From Examples 48, 52, and 53, it can be seen that when the number of pores per unit area on the negative electrode piece is within the range of the present invention, the resulting lithium ion battery exhibits slight or no lithium deposition, a low rise in charging temperature, and a high cycle capacity retention rate, which indicates that the lithium ion battery has good cycle characteristics, the problem of a rise in charging temperature is improved, and lithium deposition is less likely to occur during cycling.

[0076] From Examples 47, 54, and 55, it can be seen that when the compressed density of the negative electrode active material in the negative electrode pieces is within the range of the present invention, the resulting lithium ion battery exhibits slight or no lithium precipitation, a low rise in charging temperature, and a high cycle capacity retention rate, which indicates that the lithium ion battery has good cycle characteristics, the problem of the rise in charging temperature is improved, and lithium precipitation is less likely to occur during cycling.

[0077] The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the scope of protection of the present invention.

Claims

1. An electrochemical device comprising a positive electrode, a negative electrode, and an electrolyte, the electrolyte solution comprises an organic solvent, a lithium salt, and an additive; the organic solvent contains an acetate compound and a carbonate compound, the carbonate compound comprises ethylene carbonate and propylene carbonate; a mass fraction A of the acetate compound is 4% to 50% and a mass fraction B of the ethylene carbonate is 5% to 20% relative to the total mass of the electrolyte solution; the negative electrode includes pores, The pores are (a) the pore size is 20 μm to 100 μm; (b) the pore depth range is 5 μm to 50 μm; and (c) An electrochemical device that satisfies the requirement that the number of pores per unit area is 0.5 / mm 2 to 100 / mm 2 .

2. 10. The electrochemical device of claim 1, wherein the acetate compound comprises at least one of methyl acetate, ethyl acetate, and propyl acetate.

3. The electrolyte solution further contains a polynitrile compound, 2. The electrochemical device of claim 1, wherein the polynitrile compound comprises at least two of succinonitrile, adiponitrile, 1,3,6-hexanetricarbonitrile, 1,2,3-tris(2-cyanoethoxy)propane, ethylene glycol (bispropionitrile) ether, and 1,4-dicyano-2-butene.

4. 4. The electrochemical device according to claim 3, wherein the mass fraction C of the polynitrile compound is 0.1% to 10%.

5. 4. The electrochemical device according to claim 3, wherein the mass fraction C of the polynitrile compound and the mass fraction A of the acetate ester compound satisfy 0.1≦C / A≦0.

8.

6. the additive comprises fluoroethylene carbonate; 2. The electrochemical device according to claim 1, wherein the mass fraction D of the fluoroethylene carbonate and the mass fraction E of the propylene carbonate satisfy the relationship 0.2≦D / E≦1.

7. 7. The electrochemical device according to claim 6, wherein the mass fraction E of the propylene carbonate is 5% to 30%, or the mass fraction D of the fluoroethylene carbonate is 0.1% to 15%.

8. The compressed density of the negative electrode active material in the negative electrode is 1.40 g / cm ３ ~1.70 g / cm ３ 2. The electrochemical device of claim 1 , wherein:

9. An electronic device comprising the electrochemical device according to any one of claims 1 to 8.

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