Electrochemical devices and electronic devices

Abstract

The present application relates to an electrochemical device and an electronic device. Specifically, the present application provides an electrochemical device comprising: a positive electrode, a negative electrode, and an electrolyte. The negative electrode comprises a negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector, wherein the negative electrode current collector comprises tin, and the electrolyte comprises a compound containing a sulfur-oxygen double bond. The electrochemical device of the present application has improved high-temperature cycling performance and overcharge resistance.

Description

[0001] This application is a divisional application of the Chinese invention patent application with the invention name “Electrochemical Device and Electronic Device”, application number 202011101422.X, and application date October 15, 2020. Technical Field

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

[0003] With the development of technology and the increasing demand for mobile devices, people's demand for electrochemical devices (e.g., lithium-ion batteries) under different usage conditions has increased significantly, thereby putting higher requirements on the performance of lithium-ion batteries, including high capacity, long cycle life, high temperature resistance, high rate discharge performance and anti-overcharge performance.

[0004] During the use of lithium-ion batteries, if the charging control circuit malfunctions, the lithium-ion battery is prone to overcharging, causing irreversible reduction reactions of lithium ions in the negative electrode, reducing the charge and discharge cycle efficiency of the lithium-ion battery. When the charging voltage reaches the decomposition voltage of the electrolyte, the electrolyte will decompose at the positive electrode of the lithium-ion battery, generating gas, which will increase the pressure and temperature inside the lithium-ion battery and reduce its stability, thus seriously affecting the high-temperature cycling and expansion performance and safety of the lithium-ion battery, and may even cause the lithium-ion battery to fail completely.

[0005] In view of the above, there is a real need to provide electrochemical devices and electronic devices with improved performance. Summary of the Invention

[0006] The embodiments of the present application provide an electrochemical device and an electronic device with improved high-temperature cycle performance and overcharge resistance to at least some extent solve at least one safety problem existing in the related art.

[0007] In one aspect of the present application, the present application provides an electrochemical device comprising: a positive electrode, a negative electrode and an electrolyte, wherein the negative electrode comprises a negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector, wherein the negative electrode current collector comprises tin, and the electrolyte comprises a compound containing a sulfur-oxygen double bond.

[0008] According to an embodiment of the present application, the negative electrode current collector includes copper.

[0009] According to an embodiment of the present application, the content of tin is a%, based on the weight of the negative electrode current collector, and a is in the range of 0.01 to 0.2.

[0010] According to an embodiment of the present application, the negative electrode current collector further includes silver, and the content of the silver is 0.01% to 0.2% based on the weight of the negative electrode current collector.

[0011] According to an embodiment of the present application, the negative electrode current collector has at least one of the following characteristics:

[0012] 1) Average surface roughness of 0.05 μm to 1.5 μm;

[0013] 2) Tensile strength is 100N / mm 2 above;

[0014] 3) 0.2% endurance is 30N / mm 2 above;

[0015] 4) The thickness is 1 μm to 100 μm.

[0016] According to an embodiment of the present application, the negative electrode mixture layer has at least one of the following characteristics:

[0017] a) a reflectivity Ra at a wavelength of 550 nm of 7% to 15%;

[0018] b) Density da is 1.3 g / cm 3 to 1.9g / cm 3 ;

[0019] c) The weight per unit area La is 4.5 mg / cm 2 Up to 12.5 mg / cm 2 ;

[0020] d) The porosity Pa is 20% to 40%.

[0021] According to an embodiment of the present application, the compound containing a sulfur-oxygen double bond includes at least one of the following compounds: cyclic sulfate, chain sulfate, chain sulfonate, cyclic sulfonate, chain sulfite, or cyclic sulfite.

[0022] According to an embodiment of the present application, the compound containing a sulfur-oxygen double bond includes a compound of formula 1:

[0023]

[0024] in:

[0025] W is selected from

[0026] L is independently selected from a single bond or a methylene group, and two Ls in the same ring structure are not single bonds at the same time;

[0027] m is 1, 2, 3 or 4;

[0028] n is 0, 1 or 2; and

[0029] p is 0, 1, 2, 3, 4, 5 or 6.

[0030] According to an embodiment of the present application, the compound of formula 1 includes at least one of the following:

[0031]

[0032] According to an embodiment of the present application, the content of the compound containing sulfur-oxygen double bonds is b%, based on the weight of the electrolyte, and b is in the range of 0.01 to 10.

[0033] According to an embodiment of the present application, the electrolyte further includes propionate, and the propionate includes a compound of formula 2:

[0034]

[0035] in:

[0036] R 1 Selected from ethyl or halogenated ethyl,

[0037] R 2 is selected from C1-C6 alkyl or C1-C6 haloalkyl; and

[0038] The content of the propionate is in a range of 10% to 60% based on the weight of the electrolyte.

[0039] According to an embodiment of the present application, the content of the compound containing sulfur-oxygen double bonds is b% based on the weight of the electrolyte, b is in the range of 0.01 to 10, and 1≤b / a≤100.

[0040] According to an embodiment of the present application, the reaction area dm of the negative electrode mixture layer is 2 The content of the compound containing sulfur-oxygen double bonds is b%, satisfying the following relationship: 0.5≤d / b≤30.

[0041] In another aspect of the present application, the present application provides an electronic device comprising the electrochemical device according to the present application.

[0042] Additional aspects and advantages of the embodiments of the present application will be described, shown, or explained in part in the following description through implementation of the embodiments of the present application. DETAILED DESCRIPTION

[0043] The embodiments of the present application will be described in detail below. The embodiments of the present application should not be interpreted as limiting the present application.

[0044] Unless expressly stated otherwise, the following terms used herein have the meanings indicated below.

[0045] In the detailed description and claims, a list of items linked by the term "at least one of" can mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A can contain a single element or multiple elements. Item B can contain a single element or multiple elements. Item C can contain a single element or multiple elements. The term "at least one of" has the same meaning as the term "at least one of."

[0046] As used herein, the term "alkyl" is intended to be a straight chain saturated hydrocarbon structure with 1 to 20 carbon atoms. "Alkyl" is also intended to be a branched or cyclic hydrocarbon structure with 3 to 20 carbon atoms. When specifying an alkyl group with a specific carbon number, it is intended to encompass all geometric isomers with that carbon number; therefore, for example, "butyl" means including n-butyl, sec-butyl, isobutyl, tert-butyl and cyclobutyl; "propyl" includes n-propyl, isopropyl and cyclopropyl. Alkyl examples include, but are not limited to methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl, isopentyl, neopentyl, cyclopentyl, methylcyclopentyl, ethylcyclopentyl, n-hexyl, isohexyl, cyclohexyl, n-heptyl, octyl, cyclopropyl, cyclobutyl, norbornyl, etc.

[0047] As used herein, the term "halo" refers to a group in which some or all of the hydrogen atoms are replaced by halogen atoms (eg, fluorine, chlorine, bromine, or iodine).

[0048] During the use of lithium-ion batteries, when the charging control circuit fails, the lithium-ion battery is prone to overcharging and overheating, which will seriously affect the performance of the lithium-ion battery. Physical methods (for example, integrated circuit protection method) and chemical methods (for example, overcharge protection additive method) can usually be used to avoid this problem. Although the integrated circuit method has the advantages of being reliable, fast and widely used, it requires a complex structure (for example, it must have a plastic outer packaging) and is expensive. The overcharge protection additive method can use additives based on polymerization reactions (for example, biphenyl, cyclohexylbenzene, etc.) or additives based on reduction-oxidation reciprocating reactions (for example, lithium halides, metallocenes and their derivatives, benzene derivatives, etc.). However, biphenyl and cyclohexylbenzene will increase the internal resistance of the lithium-ion battery, reducing the performance of the lithium-ion battery. When the lithium-ion battery is under high charging current, lithium halides, metallocenes and their derivatives, and benzene derivatives cannot exert their protective effect, and may also reduce the cycle performance of the lithium-ion battery.

[0049] The present application solves the above-mentioned problems by using a combination of a negative electrode current collector containing tin and an electrolyte containing a compound containing a sulfur-oxygen double bond, significantly improving the high-temperature performance and overcharge resistance of the lithium-ion battery. When the electrochemical device of the present application is in a high-temperature or overcharged state, the generated lithium-containing reduced product is spread out thinly and evenly on the entire surface of the negative electrode, which helps to reduce the irreversible capacity and improve the discharge capacity, thereby improving the high-temperature cycle performance and overcharge resistance of the electrochemical device, allowing the electrochemical device to maintain good performance while not deforming.

[0050] In one embodiment, the present application provides an electrochemical device comprising a positive electrode, a negative electrode, and an electrolyte as described below.

[0051] I. Negative electrode

[0052] The negative electrode includes a negative electrode current collector and a negative electrode mixture layer disposed on one or both surfaces of the negative electrode current collector.

[0053] 1. Negative electrode current collector

[0054] A feature of the electrochemical device of the present application is that the negative electrode current collector contains tin. The presence of tin helps to improve the strength and processability of the negative electrode current collector, inhibits the expansion or contraction of the negative electrode caused by the charge and discharge process of the electrochemical device, and significantly improves the high-temperature cycling performance and overcharge resistance of the electrochemical device.

[0055] In some embodiments, the tin content is a%, based on the weight of the negative electrode current collector, wherein a is in the range of 0.01 to 0.2. In some embodiments, a is in the range of 0.05 to 0.15. In some embodiments, a is in the range of 0.08 to 0.10. In some embodiments, a is 0.01, 0.03, 0.05, 0.08, 0.1, 0.12, 0.15, 0.18, 0.2, or in a range consisting of any two of the foregoing values.

[0056] In some embodiments, the negative electrode current collector further comprises silver. The presence of silver helps to further improve the high temperature cycle performance and overcharge resistance of the electrochemical device.

[0057] In some embodiments, the silver content is 0.01% to 0.2% based on the weight of the negative electrode current collector. In some embodiments, the silver content is 0.05% to 0.15% based on the weight of the negative electrode current collector. In some embodiments, the silver content is 0.08% to 0.10% based on the weight of the negative electrode current collector. In some embodiments, the silver content is 0.01%, 0.03%, 0.05%, 0.08%, 0.1%, 0.12%, 0.15%, 0.18%, 0.2%, or a range consisting of any two of the foregoing values, based on the weight of the negative electrode current collector.

[0058] When the content of tin or silver in the negative electrode current collector is in the range of 0.01% to 0.2%, it helps to inhibit the oxidation of the surface of the negative electrode current collector, so that the negative electrode current collector has good electrical conductivity. At the same time, the negative electrode current collector can be recrystallized during the drying step after coating the negative electrode mixture layer in the process of preparing the negative electrode, further improving the high temperature cycle performance and anti-overcharge performance of the electrochemical device.

[0059] In some embodiments, the negative electrode current collector may be in the form of, but not limited to, metal foil, metal cylinder, metal coil, metal plate, metal film, expanded metal, stamped metal, foamed metal, etc. In some embodiments, the negative electrode current collector is metal foil. In some embodiments, the metal foil is in a mesh shape.

[0060] In some embodiments, the negative electrode current collector includes copper.

[0061] In some embodiments, the negative electrode current collector is a copper foil. As used herein, the term "copper foil" includes copper alloy foil.

[0062] In some embodiments, the negative electrode current collector comprises at least one of tough pitch copper or oxygen-free copper. As used herein, the term "tough pitch copper" includes copper alloy foils based on tough pitch copper, and the term "oxygen-free copper" includes copper alloy foils based on oxygen-free copper.

[0063] In some embodiments, the tough pitch copper complies with the JIS-H3100-C1100 standard. In some embodiments, the oxygen-free copper complies with the JIS-H3100-C1020 standard. Tough pitch copper or oxygen-free copper that complies with the above standards has a composition close to that of pure copper and has good electrical conductivity, making it particularly suitable for use as a negative electrode current collector.

[0064] In some embodiments, the oxygen content of the tough pitch copper (based on copper) is 0.01% to 0.02%. In some embodiments, the oxygen content of the oxygen-free copper (based on copper) is less than 0.001%.

[0065] In some embodiments, the copper foil contains impurities, including at least one of P, Fe, Zr, Mg, S, Ge, or Ti. In some embodiments, the impurity content is 20 ppm or less based on the weight of the copper foil. When the impurity content in the copper foil is within the above range, the copper foil is less susceptible to bending deformation, thereby reducing crystal orientation rotation and avoiding the formation of shear bands, which helps improve the fracture resistance of the negative electrode current collector.

[0066] In some embodiments, the negative electrode current collector has at least one of the following features (1)-(4):

[0067] (1) Average surface roughness

[0068] In some embodiments, the average surface roughness of the negative electrode current collector is 0.05 μm to 1.5 μm. In some embodiments, the average surface roughness of the negative electrode current collector is 0.1 μm to 1.3 μm. In some embodiments, the average surface roughness of the negative electrode current collector is 0.15 μm to 1.0 μm. In some embodiments, the average surface roughness of the negative electrode current collector is 0.2 μm to 0.8 μm. In some embodiments, the average surface roughness of the negative electrode current collector is 0.3 μm to 0.5 μm. In some embodiments, the average surface roughness of the negative electrode current collector is 0.05 μm, 0.1 μm, 0.3 μm, 0.5 μm, 0.8 μm, 1 μm, 1.3 μm, 1.5 μm, or in a range consisting of any two of the above values. When the average surface roughness of the negative electrode collector is within the above range, the interface area between the negative electrode collector and the negative electrode mixture layer increases and the close adhesion between the negative electrode collector and the negative electrode active material is improved, which helps to improve the high temperature cycle performance and overcharge resistance of the electrochemical device.

[0069] The average surface roughness of the negative electrode current collector can be measured by the method described in ISO1302:2002.

[0070] (2) Tensile strength

[0071] As used herein, the term "tensile strength" refers to the ratio of the maximum tensile force required to break a specimen to the cross-sectional area of ​​the specimen.

[0072] In some embodiments, the tensile strength of the negative electrode current collector is 100 N / mm 2 In some embodiments, the tensile strength of the negative electrode current collector is 150N / mm 2 In some embodiments, the tensile strength of the negative electrode current collector is 200N / mm 2 In some embodiments, the tensile strength of the negative electrode current collector is 250N / mm 2 In some embodiments, the tensile strength of the negative electrode current collector is 300N / mm 2 In some embodiments, the tensile strength of the negative electrode current collector is 350N / mm 2 In some embodiments, the tensile strength of the negative electrode current collector is 400N / mm 2 In some embodiments, the tensile strength of the negative electrode current collector is 450N / mm 2 In some embodiments, the tensile strength of the negative electrode current collector is 500N / mm 2 When the tensile strength of the negative electrode current collector is within the above range, cracking of the negative electrode current collector caused by expansion or contraction of the negative electrode mixture layer during charge / discharge of the electrochemical device can be suppressed, thereby improving the high-temperature cycle performance and overcharge resistance of the electrochemical device.

[0073] The tensile strength of the negative electrode current collector can be measured using the same device and method as for measuring elongation (refer to the test method of GB-228-87).

[0074] (3) 0.2% Stamina

[0075] As used herein, the term "0.2% proof strength" refers to the load required to produce a 0.2% plastic deformation (i.e., permanent deformation) of a specimen. In other words, after the load is applied to produce a 0.2% plastic deformation of the specimen, the specimen maintains the 0.2% plastic deformation even after the load is removed.

[0076] In some embodiments, the 0.2% endurance of the negative electrode current collector is 30 N / mm 2 In some embodiments, the 0.2% endurance of the negative electrode current collector is 50N / mm 2 In some embodiments, the 0.2% endurance of the negative electrode current collector is 100 N / mm 2 In some embodiments, the 0.2% endurance of the negative electrode current collector is 150 N / mm 2In some embodiments, the 0.2% endurance of the negative electrode current collector is 200 N / mm 2 In some embodiments, the 0.2% endurance of the negative electrode current collector is 300N / mm 2 When the 0.2% resistance of the negative electrode current collector is within the above range, cracking of the negative electrode current collector caused by expansion or contraction of the negative electrode mixture layer during charge / discharge of the electrochemical device can be suppressed, thereby improving the high-temperature cycle performance and overcharge resistance of the electrochemical device.

[0077] The 0.2% resistance of the negative electrode current collector can be measured using the same device and method as that used to measure the elongation (refer to the test method of GB-228-87).

[0078] (4) Thickness

[0079] In some embodiments, the thickness of the negative electrode current collector is 1 μm to 100 μm. In some embodiments, the thickness of the negative electrode current collector is 3 μm to 80 μm. In some embodiments, the thickness of the negative electrode current collector is 5 μm to 50 μm. In some embodiments, the thickness of the negative electrode current collector is 10 μm to 30 μm. In some embodiments, the thickness of the negative electrode current collector is 15 μm to 20 μm. In some embodiments, the thickness of the negative electrode current collector is 1 μm, 3 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, or within a range consisting of any two of the above values. When the thickness of the negative electrode current collector is within the above range, the negative electrode current collector has high strength and is easy to apply, and the shape of the negative electrode is less likely to be deformed such as curling.

[0080] 2. Negative electrode mixture layer

[0081] The negative electrode mixture layer comprises a negative electrode active material layer, which in turn comprises a negative electrode active material. The negative electrode mixture layer may be one or more layers, and each layer of the multiple layers of negative electrode active material may comprise the same or different negative electrode active materials. The negative electrode active material is any substance capable of reversibly intercalating and deintercalating metal ions such as lithium ions. In some embodiments, the charge capacity of the negative electrode active material is greater than the discharge capacity of the positive electrode active material to prevent unintentional deposition of lithium metal on the negative electrode during charging.

[0082] In some embodiments, the negative electrode mixture layer has at least one of the following characteristics (a)-(d):

[0083] (a) Reflectivity

[0084] The reflectivity of the negative electrode mixture layer reflects the smoothness of the negative electrode mixture surface and the surface compression state of the negative electrode active material in the negative electrode mixture layer. The reflectivity of the negative electrode mixture layer can be controlled by the type of negative electrode active material, the forming conditions of the negative electrode active material layer, and the post-forming post-processing process. It can also be controlled by the rolling pressure, number of rolling passes, heating conditions during rolling, and the material and surface shape of the rolling plate and rollers used during rolling.

[0085] In some embodiments, the reflectivity Ra of the negative electrode mixture layer at a wavelength of 550 nm is 7% to 15%. In some embodiments, the reflectivity Ra of the negative electrode mixture layer at a wavelength of 550 nm is 8% to 14.8%. In some embodiments, the reflectivity Ra of the negative electrode mixture layer at a wavelength of 550 nm is 10% to 12%. In some embodiments, the reflectivity Ra of the negative electrode mixture layer at a wavelength of 550 nm is 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or within a range consisting of any two of the above values. When the reflectivity of the negative electrode mixture layer is within the above range, side reactions on the surface of the negative electrode mixture layer can be suppressed, and the permeability of the electrolyte from the surface of the negative electrode mixture layer to the interior of the negative electrode mixture layer can be improved, thereby improving the fast charging characteristics of the electrochemical device.

[0086] The reflectance of the negative electrode mixture layer can be measured using a spectrocolorimeter (for example, SPECTROPHOTOMETER CM-5 manufactured by Konica Minolta).

[0087] (b) Density

[0088] In some embodiments, the density da of the negative electrode mixture layer is 1.3 g / cm 3 to 1.9g / cm 3 In some embodiments, the density da of the negative electrode mixture layer is 1.35 g / cm 3 to 1.62g / cm 3 In some embodiments, the density da of the negative electrode mixture layer is 1.4 g / cm 3 Up to 1.6g / cm 3 In some embodiments, the density da of the negative electrode mixture layer is 1.3 g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 , 1.9g / cm 3 Or within the range consisting of any two of the above values.

[0089] (c) Weight

[0090] In some embodiments, the weight per unit area of ​​the negative electrode mixture layer La is 4.5 mg / cm 2 Up to 12.5 mg / cm 2 In some embodiments, the weight per unit area of ​​the negative electrode mixture layer La is 6.0 mg / cm 2 Up to 12.0 mg / cm 2 In some embodiments, the weight per unit area of ​​the negative electrode mixture layer La is 4.5 mg / cm 2 , 5mg / cm 2 , 5.5mg / cm 2 , 6mg / cm 2 、6.5mg / cm 2 , 7mg / cm 2 , 7.5mg / cm 2 , 8mg / cm 2 、8.5mg / cm 2 , 9mg / cm 2 , 9.5mg / cm 2 、10mg / cm 2 、10.5mg / cm 2 、11mg / cm 2 、11.5mg / cm 2 , 12mg / cm 2 、12.5mg / cm 2 Or within the range consisting of any two of the above values.

[0091] The weight per unit area of ​​the negative electrode mixture layer in this application is the mass (mg) of the negative electrode mixture layer relative to the area (cm 2 ) ratio. The mass and area of ​​the negative electrode mixture layer are obtained as follows: cut a test piece of appropriate size from the negative electrode and measure its area as S1 and mass as W0. Then, peel the negative electrode current collector from the negative electrode and measure the mass of the negative electrode current collector as W1. The mass of the negative electrode mixture layer is calculated from (W0-W1): weight per unit area = (W0-W1) / S1. If the selected negative electrode has a double-sided mixture layer, the weight per unit area = (W0-W1) / S1 / 2.

[0092] Examples of a method for peeling the negative electrode mixture layer include immersing the negative electrode mixture layer in a solvent capable of dissolving or swelling the negative electrode mixture layer, and wiping the mixture layer with a cloth or the like.

[0093] The weight per unit area of ​​the negative electrode mixture layer can be adjusted using known methods. For example, when the negative electrode mixture layer is formed by coating, the weight can be adjusted by varying the solid content concentration of the coating solution used to form the negative electrode mixture layer, the number of coating passes, the gap between the coating liquid inlet of the coating machine, and the like. The weight per unit area of ​​the negative electrode mixture layer can be increased by increasing the solid content concentration, increasing the number of coating passes, or increasing the gap. The weight per unit area of ​​the negative electrode mixture layer can be decreased by decreasing the solid content concentration, reducing the number of coating passes, or decreasing the gap.

[0094] (d) Porosity

[0095] In some embodiments, the porosity Pa of the negative electrode mixture layer is 20% to 40%. In some embodiments, the porosity Pa of the negative electrode mixture layer is 26.5% to 31.3%. In some embodiments, the porosity Pa of the negative electrode mixture layer is 26% to 31%. In some embodiments, the porosity Pa of the negative electrode mixture layer is 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, or within a range consisting of any two of the foregoing values.

[0096] The porosity of the negative electrode mixture layer can be determined as follows: Use a punching machine to punch the negative electrode into 13mm discs and measure the thickness of the discs with a micrometer. Place a certain number of discs into the sample chamber of the AccuPyc1340 instrument. After purging the sample with helium 30 times, introduce helium according to the program. By measuring the pressure in the sample chamber, the true volume of the sample chamber is calculated using Bohr's law PV = nRT. After the test is completed, count the number of discs and calculate the apparent volume of the sample. The porosity of the sample is calculated using the following formula:

[0097] Porosity = 1 - true volume / apparent volume.

[0098] In some embodiments, the negative electrode mixture layer has both the density and porosity described above. In this case, excessive penetration of the electrolyte from the surface of the negative electrode mixture layer into the interior of the negative electrode mixture layer can be suppressed, thereby improving the diffusion of the electrolyte within the negative electrode mixture layer, increasing the reactivity of the negative electrode mixture layer, and suppressing side reactions in the negative electrode mixture layer, thereby improving the high-temperature performance and overcharge resistance of the electrochemical device.

[0099] The thickness of the negative electrode mixture layer refers to the thickness of the negative electrode mixture layer coated on a single side of the negative electrode current collector. In some embodiments, the thickness of the negative electrode mixture layer is 15 μm or more. In some embodiments, the thickness of the negative electrode mixture layer is 20 μm or more. In some embodiments, the thickness of the negative electrode mixture layer is 30 μm or more. In some embodiments, the thickness of the negative electrode mixture layer is 150 μm or less. In some embodiments, the thickness of the negative electrode mixture layer is 120 μm or less. In some embodiments, the thickness of the negative electrode mixture layer is 100 μm or less. In some embodiments, the thickness of the negative electrode mixture layer is within the range consisting of any two of the above values. When the thickness of the negative electrode mixture layer is within the above range, the electrolyte can penetrate into the vicinity of the negative electrode current collector interface, thereby improving the charge and discharge characteristics of the electrochemical device at high current density; at the same time, the volume ratio of the negative electrode current collector to the negative electrode active material is within an appropriate range, which can ensure the capacity of the electrochemical device.

[0100] The thickness ratio of the negative electrode mixture layer to the negative electrode current collector refers to the thickness of the single-sided negative electrode mixture layer divided by the thickness of the negative electrode current collector, and its value is not particularly limited. In some embodiments, the thickness ratio is 50 or less. In some embodiments, the thickness ratio is 30 or less. In some embodiments, the thickness ratio is 20 or less. In some embodiments, the thickness ratio is 10 or less. In some embodiments, the thickness ratio is 1 or more. In some embodiments, the thickness ratio is within the range consisting of any two of the above values. When the thickness ratio is within the above range, the capacity of the electrochemical device can be ensured, and the heat release of the negative electrode current collector during high current density charging and discharging can be suppressed.

[0101] Negative electrode active material

[0102] In some embodiments, the negative electrode active material includes, but is not limited to, graphite, hard carbon, soft carbon, MCMB and other carbon materials, silicon, SiO x Silicon compounds such as silicon oxide represented by (0<x<2), metallic lithium, metals forming alloys with lithium and their alloys, amorphous compounds mainly composed of oxides such as tin dioxide, and lithium titanate (Li4Ti5O 12 ).

[0103] In some embodiments, the negative electrode active material comprises a carbon material. In some embodiments, the negative electrode active material comprises a carbon material having a graphite structure. In some embodiments, the negative electrode active material is at least one of artificial graphite or natural graphite.

[0104] In some embodiments, metals alloyed with metallic lithium include, but are not limited to, aluminum, silicon, tin, and germanium.

[0105] In some embodiments, the negative electrode active material includes different components, wherein a carbon material having a graphite structure is predominant. In some embodiments, the carbon material having a graphite structure comprises 70.0% or more of the negative electrode mixture layer by weight. In some embodiments, the carbon material having a graphite structure comprises 90.0% or more of the negative electrode mixture layer by weight. In some embodiments, the carbon material having a graphite structure comprises 95.0% or more of the negative electrode mixture layer by weight.

[0106] In some embodiments, the negative electrode active material is a metal or semi-metal represented by silicon that forms an alloy with lithium, and their alloys, which have high charge and discharge capacity.

[0107] In some embodiments, the negative electrode active material includes a mixture of a metal or semimetal that forms an alloy with lithium, represented by silicon, or an alloy thereof, and a carbon material having a graphite structure.

[0108] Adhesives

[0109] In some embodiments, the negative electrode mixture layer further includes a negative electrode binder. The negative electrode binder can improve the bonding between the negative electrode active material particles and the bonding between the negative electrode mixture layer and the negative electrode current collector. The type of negative electrode binder is not particularly limited, as long as it is a material that is stable in the electrolyte or solvent used in electrode manufacturing.

[0110] Examples of negative electrode binders include, but are not limited to, resin polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, aromatic polyamide, cellulose, and nitrocellulose; rubber polymers such as SBR (styrene-butadiene rubber), isoprene rubber, butadiene rubber, fluororubber, NBR (acrylonitrile-butadiene rubber), and styrene-propylene rubber; thermoplastic elastomer polymers such as styrene-butadiene-styrene block copolymers or their hydrogenated products; EPDM (ethylene-propylene-diene terpolymer), styrene-ethylene-butadiene-styrene copolymers, styrene-isobutylene-styrene block copolymers or their hydrogenated products; soft resin polymers such as syndiotactic 1,2 polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, and propylene-α-olefin copolymers; fluorine-based polymers such as polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymers; polymer compositions having ion conductivity for alkali metal ions (especially lithium ions), etc. The above-mentioned negative electrode binders can be used alone or in any combination.

[0111] In some embodiments, the content of the negative electrode binder is greater than 0.1%, greater than 0.5%, or greater than 0.6% based on the weight of the negative electrode mixture layer. In some embodiments, the content of the negative electrode binder is less than 10%, less than 8%, less than 5%, or less than 4% based on the weight of the negative electrode mixture layer. In some embodiments, the content of the negative electrode binder is within a range consisting of any two of the above values. When the content of the negative electrode binder is within the above range, the capacity of the electrochemical device and the strength of the negative electrode can be fully ensured.

[0112] When the negative electrode mixture layer contains a rubbery polymer (e.g., SBR), in some embodiments, the negative electrode binder content is greater than 0.1%, greater than 0.5%, or greater than 0.6% based on the weight of the negative electrode mixture layer. In some embodiments, the negative electrode binder content is less than 5%, less than 3%, or less than 2% based on the weight of the negative electrode mixture layer. In some embodiments, the negative electrode binder content is within a range formed by any two of the above values ​​based on the weight of the negative electrode mixture layer.

[0113] When the negative electrode mixture layer contains a fluorine-based polymer (e.g., polyvinylidene fluoride), in some embodiments, the negative electrode binder content is greater than 1%, greater than 2%, or greater than 3% based on the weight of the negative electrode mixture layer. In some embodiments, the negative electrode binder content is less than 15%, less than 10%, or less than 8% based on the weight of the negative electrode mixture layer. The negative electrode binder content, based on the weight of the negative electrode mixture layer, is within a range consisting of any two of the aforementioned values.

[0114] thickener

[0115] Thickeners are typically used to adjust the viscosity of the negative electrode slurry. The type of thickener is not particularly limited, and examples include, but are not limited to, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and their salts. These thickeners can be used alone or in any combination.

[0116] In some embodiments, the thickener content is greater than 0.1%, greater than 0.5%, or greater than 0.6% based on the weight of the negative electrode mixture layer. In some embodiments, the thickener content is less than 5%, less than 3%, or less than 2% based on the weight of the negative electrode mixture layer. When the thickener content is within the above ranges, the capacity reduction and resistance increase of the electrochemical device can be suppressed, while ensuring good coating properties of the negative electrode slurry.

[0117] solvent

[0118] The type of solvent used to form the negative electrode slurry is not particularly limited, as long as it is a solvent that can dissolve or disperse the negative electrode active material, the negative electrode binder, and the thickener and conductive material used as needed. In some embodiments, the solvent used to form the negative electrode slurry can use any of an aqueous solvent and an organic solvent. Examples of aqueous solvents may include, but are not limited to, water, alcohol, etc. Examples of organic solvents may include, but are not limited to, N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N,N-dimethylaminopropylamine, tetrahydrofuran (THF), toluene, acetone, diethyl ether, hexamethylphosphoramide, dimethyl sulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene, hexane, etc. The above solvents can be used alone or in any combination.

[0119] Preparation of negative electrode

[0120] The negative electrode in the electrochemical device of the present application can be prepared using any known method. For example, a binder, solvent, and, if necessary, a thickener, conductive material, and filler are added to the negative electrode active material to form a slurry. This slurry is then applied to the negative electrode current collector, dried, and pressed to form an electrode. The negative electrode active material can also be roll-formed to form a sheet electrode or compression-molded to form a pellet electrode.

[0121] II. Electrolyte

[0122] The electrolyte used in the electrochemical device of the present application includes an electrolyte and a solvent for dissolving the electrolyte. In some embodiments, the electrolyte used in the electrochemical device of the present application further includes an additive.

[0123] Another main feature of the electrochemical device of the present application is that the electrolyte includes a compound containing a sulfur-oxygen double bond.

[0124] In some embodiments, the compound containing a sulfur-oxygen double bond comprises at least one of the following compounds: cyclic sulfate, chain sulfate, chain sulfonate, cyclic sulfonate, chain sulfite, or cyclic sulfite.

[0125] In some embodiments, the cyclic sulfates include, but are not limited to, one or more of the following: 1,2-ethylene glycol sulfate, 1,2-propylene glycol sulfate, 1,3-propylene glycol sulfate, 1,2-butylene glycol sulfate, 1,3-butylene glycol sulfate, 1,4-butylene glycol sulfate, 1,2-pentanediol sulfate, 1,3-pentanediol sulfate, 1,4-pentanediol sulfate, 1,5-pentanediol sulfate, and the like.

[0126] In some embodiments, the chain sulfate ester includes, but is not limited to, one or more of the following: dimethyl sulfate, ethyl methyl sulfate, and diethyl sulfate.

[0127] In some embodiments, the linear sulfonate includes, but is not limited to, one or more of the following: fluorosulfonates such as methyl fluorosulfonate and ethyl fluorosulfonate, methyl methanesulfonate, ethyl methanesulfonate, butyl dimethanesulfonate, methyl 2-(methylsulfonyloxy)propionate and ethyl 2-(methylsulfonyloxy)propionate, etc.

[0128] In some embodiments, the cyclic sulfonate includes, but is not limited to, one or more of the following: 1,3-propane sultone, 1-fluoro-1,3-propane sultone, 2-fluoro-1,3-propane sultone, 3-fluoro-1,3-propane sultone, 1-methyl-1,3-propane sultone, 2-methyl-1,3-propane sultone, 3-methyl-1,3-propane sultone, 1-propylene-1,3-sultone, 2-propylene-1,3-sultone, 1-fluoro-1-propylene-1,3-sultone, 2-fluoro-1-propylene-1,3-sultone, 3-fluoro-1-propylene-1,3-sultone Ester, 1-fluoro-2-propylene-1,3-sultone, 2-fluoro-2-propylene-1,3-sultone, 3-fluoro-2-propylene-1,3-sultone, 1-methyl-1-propylene-1,3-sultone, 2-methyl-1-propylene-1,3-sultone, 3-methyl-1-propylene-1,3-sultone, 1-methyl-2-propylene-1,3-sultone, 2-methyl-2-propylene-1,3-sultone, 3-methyl-2-propylene-1,3-sultone, 1,4-butane sultone, 1,5-pentane sultone, methylene methanedisulfonate and ethylene methanedisulfonate, etc.

[0129] In some embodiments, the chain sulfite includes, but is not limited to, one or more of the following: dimethyl sulfite, ethyl methyl sulfite, and diethyl sulfite.

[0130] In some embodiments, the cyclic sulfite includes, but is not limited to, one or more of the following: 1,2-ethylene glycol sulfite, 1,2-propylene glycol sulfite, 1,3-propylene glycol sulfite, 1,2-butylene glycol sulfite, 1,3-butylene glycol sulfite, 1,4-butylene glycol sulfite, 1,2-pentanediol sulfite, 1,3-pentanediol sulfite, 1,4-pentanediol sulfite, 1,5-pentanediol sulfite, and the like.

[0131] In some embodiments, the compound containing a sulfur-oxygen double bond comprises a compound of Formula 1:

[0132]

[0133] in:

[0134] W is selected from

[0135] L is each independently selected from a single bond or a methylene group;

[0136] m is 1, 2, 3 or 4;

[0137] n is 0, 1 or 2; and

[0138] p is 0, 1, 2, 3, 4, 5 or 6.

[0139] In some embodiments, the compound of Formula 1 comprises at least one of the following:

[0140]

[0141] In some embodiments, the content of the compound containing a sulfur-oxygen double bond is b%, based on the weight of the electrolyte, and b is in the range of 0.01 to 10. In some embodiments, b is in the range of 0.1 to 8. In some embodiments, b is in the range of 0.5 to 5. In some embodiments, b is in the range of 1 to 3. In some embodiments, b is 0.01, 0.05, 0.1, 0.5, 0.8, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, or in a range consisting of any two of the foregoing values. When the content of the compound containing a sulfur-oxygen double bond in the electrolyte is within the above range, it helps to further improve the high temperature performance and overcharge resistance of the electrochemical device.

[0142] In some embodiments, the content of the compound containing a sulfur-oxygen double bond in the electrolyte is b%, and the content of tin in the negative electrode current collector is a% satisfying the following relationship: 1 ≤ b / a ≤ 100. In some embodiments, 5 ≤ b / a ≤ 80. In some embodiments, 10 ≤ b / a ≤ 50. In some embodiments, 20 ≤ b / a ≤ 30. In some embodiments, b / a is 1, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, or within a range consisting of any two of the foregoing values. When the content of the compound containing a sulfur-oxygen double bond in the electrolyte is b%, and the content of tin in the negative electrode current collector satisfies the above relationship, it helps to further improve the high-temperature performance and overcharge resistance of the electrochemical device.

[0143] In some embodiments, the reaction area dm of the negative electrode mixture layer 2The content of the compound containing sulfur-oxygen double bonds in the electrolyte is b% and satisfies the following relationship: 0.5≤d / b≤30. In some embodiments, 1≤d / b≤25. In some embodiments, 5≤d / b≤20. In some embodiments, 10≤d / b≤15. In some embodiments, d / b is 0.5, 1, 5, 10, 15, 20, 25, 30 or within a range consisting of any two of the above values. When the reaction area dm 2 When the content of the compound containing sulfur-oxygen double bonds in the electrolyte is b% and the above relationship is satisfied, it helps to further improve the high temperature performance and overcharge resistance of the electrochemical device.

[0144] In some embodiments, the reaction area of ​​the negative electrode mixture layer is 0.005 m 2 Up to 300m 2 In some embodiments, the reaction area of ​​the negative electrode mixture layer is 0.01m 2 Up to 250m 2 In some embodiments, the reaction area of ​​the negative electrode mixture layer is 0.05m 2 Up to 200m 2 In some embodiments, the reaction area of ​​the negative electrode mixture layer is 0.1m 2 Up to 150m 2 In some embodiments, the reaction area of ​​the negative electrode mixture layer is 0.5m 2 Up to 100m 2 In some embodiments, the reaction area d of the negative electrode mixture layer is 1m 2 Up to 50m 2 In some embodiments, the reaction area of ​​the negative electrode mixture layer is 5m 2 Up to 30m 2 In some embodiments, the reaction area of ​​the negative electrode mixture layer is 10m 2 Up to 20m 2 In some embodiments, the reaction area of ​​the negative electrode mixture layer is 0.005m 2 , 0.01m 2 , 0.05m 2 , 0.1m 2 , 0.5m 2 , 1m 2 , 5m 2 、10m 2 50m 2 , 100m 2 、150m 2 , 200m 2 , 250m 2 、300m 2 Or within the range consisting of any two of the above values.

[0145] The reaction area of ​​the negative electrode mixture layer can be measured by the following method: using a surface area meter (fully automatic surface area measuring device manufactured by Okura Riken), pre-dry the sample at 350°C for 15 minutes under nitrogen flow, and then use a nitrogen-helium mixed gas with a relative pressure value of nitrogen accurately adjusted to 0.3 relative to atmospheric pressure, and measure it by the nitrogen adsorption BET single-point method using the gas flow method. The specific surface area of ​​the negative electrode mixture layer is tested according to this method. The specific surface area of ​​the negative electrode mixture layer refers to the specific surface area of ​​the entire negative electrode mixture layer containing the negative electrode active material and additives (binders, conductive agents, thickeners and fillers, etc.). Measure the weight of the negative electrode mixture layer, that is, the weight of the entire negative electrode mixture layer containing the negative electrode active material and additives (binders, conductive agents, thickeners and fillers, etc.). Calculate the reaction area of ​​the negative electrode mixture layer by the following formula:

[0146] Reaction area = specific surface area of ​​negative electrode mixture layer × weight of negative electrode mixture layer.

[0147] In some embodiments, the electrolyte further comprises at least one of the following compounds:

[0148] (i) propionate;

[0149] (ii) organic compounds having a cyano group;

[0150] (iii) lithium difluorophosphate;

[0151] (iv) Compounds of formula 3:

[0152]

[0153] Wherein R is substituted or unsubstituted C1-C 10 The substituent is a halogen.

[0154] (i) Propionate

[0155] In some embodiments, the propionate ester comprises a compound of Formula 2:

[0156]

[0157] in:

[0158] R 1 is selected from ethyl or haloethyl, and

[0159] R 2 Selected from C1-C6 alkyl or C1-C6 haloalkyl.

[0160] In certain embodiments, the propionic ester includes, but is not limited to, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, amyl propionate, halogenated methyl propionate, halogenated ethyl propionate, propyl propionate, halogenated butyl propionate and amyl propionate. In certain embodiments, the propionic ester is selected from at least one of methyl propionate, ethyl propionate, propyl propionate, butyl propionate and amyl propionate. In certain embodiments, the halogen group in the halogenated methyl propionate, halogenated ethyl propionate, propyl propionate, halogenated butyl propionate and amyl propionate is selected from one or more of fluoro group (F), chloro group (Cl), bromo group (Br) and iodo group (I). In certain embodiments, the halogen group is a fluoro group (F), which can achieve more excellent effect.

[0161] In some embodiments, the propionate ester comprises 10% to 60% by weight of the electrolyte. In some embodiments, the propionate ester comprises 20% to 50% by weight of the electrolyte. In some embodiments, the propionate ester comprises 30% to 40% by weight of the electrolyte. In some embodiments, the propionate ester comprises 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60% by weight of the electrolyte, or within a range consisting of any two of the foregoing values. When the propionate ester content in the electrolyte is within the above range, it helps further improve the high-temperature performance and overcharge resistance of the electrochemical device.

[0162] (ii) Compounds having a cyano group

[0163] In some embodiments, compounds having a cyano group include, but are not limited to, one or more of the following: succinonitrile, glutaronitrile, adiponitrile, 1,5-dicyanopentane, 1,6-dicyanohexane, tetramethylsuccinonitrile, 2-methylglutaronitrile, 2,4-dimethylglutaronitrile, 2,2,4,4-tetramethylglutaronitrile, 1,4-dicyanopentane, 1,2-dicyanobenzene, 1,3-dicyanobenzene, 1,4-dicyanobenzene, ethylene glycol bis(propionitrile) ether, 3,5-dioxa-heptane dinitrile, 1,4-bis(cyanoethoxy)butane, diethylene glycol bis(2-cyanoethyl) ether, triethylene glycol bis(2-cyanoethyl) ether, tetraethylene glycol bis(2-cyanoethyl) ether, 1,3-bis(2-cyanoethoxy)propane, 1,4-bis(2-cyanoethoxy)butane, 1,5-bis(2-cyanoethoxy)pentane, ethylene glycol bis(4-cyanobutyl) ether, 1,4-dicyano-2-butene, 1,4-Dicyano-2-methyl-2-butene, 1,4-Dicyano-2-ethyl-2-butene, 1,4-Dicyano-2,3-dimethyl-2-butene, 1,4-Dicyano-2,3-diethyl-2-butene, 1,6-Dicyano-3-hexene, 1,6-Dicyano-2-methyl-3-hexene, 1,3,5-pentanetricarboxylic acid nitrile, 1,2,3-propanetricarboxylic acid nitrile, 1,3,6-hexatricarboxylic acid nitrile, 1,2,6-hexatricarboxylic acid nitrile , 1,2,3-tris(2-cyanoethoxy)propane, 1,2,4-tris(2-cyanoethoxy)butane, 1,1,1-tris(cyanoethoxymethylene)ethane, 1,1,1-tris(cyanoethoxymethylene)propane, 3-methyl-1,3,5-tris(cyanoethoxy)pentane, 1,2,7-tris(cyanoethoxy)heptane, 1,2,6-tris(cyanoethoxy)hexane and 1,2,5-tris(cyanoethoxy)pentane.

[0164] The above-mentioned compounds having a cyano group can be used alone or in any combination. If the electrolyte contains two or more compounds having a cyano group, the content of the compound having a cyano group refers to the total content of the two or more compounds having a cyano group. In some embodiments, the content of the compound having a cyano group is 0.1% to 15% based on the weight of the electrolyte. In some embodiments, the content of the compound having a cyano group is 0.5% to 10% based on the weight of the electrolyte. In some embodiments, the content of the compound having a cyano group is 1% to 8% based on the weight of the electrolyte. In some embodiments, the content of the compound having a cyano group is 3% to 5% based on the weight of the electrolyte. In some embodiments, the content of the compound having a cyano group is 0.1%, 0.5%, 1%, 3%, 5%, 8%, 10%, 13%, 15% or within a range consisting of any two of the above values ​​based on the weight of the electrolyte.

[0165] (iii) Lithium difluorophosphate (LiPO2F2)

[0166] In some embodiments, the lithium difluorophosphate is present in an amount of 0.01% to 1.5% by weight of the electrolyte. In some embodiments, the lithium difluorophosphate is present in an amount of 0.05% to 1.2% by weight of the electrolyte. In some embodiments, the lithium difluorophosphate is present in an amount of 0.1% to 1.0% by weight of the electrolyte. In some embodiments, the lithium difluorophosphate is present in an amount of 0.5% to 0.8% by weight of the electrolyte. In some embodiments, the lithium difluorophosphate is present in an amount of 0.01%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.8%, 1%, 1.5%, or a range consisting of any two of the foregoing values, based on the weight of the electrolyte.

[0167] (iv) Compounds of formula 3

[0168] In some embodiments, the compound of formula 3 comprises at least one of the following structural formulas:

[0169]

[0170] In some embodiments, the content of the compound of formula 3 is 0.01% to 5% based on the weight of the electrolyte. In some embodiments, the content of the compound of formula 3 is 0.05% to 3% based on the weight of the electrolyte. In some embodiments, the content of the compound of formula 3 is 0.1% to 2% based on the weight of the electrolyte. In some embodiments, the content of the compound of formula 3 is 0.5% to 1% based on the weight of the electrolyte. In some embodiments, the content of the compound of formula 3 is 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or a range consisting of any two of the foregoing values, based on the weight of the electrolyte.

[0171] solvent

[0172] In some embodiments, the electrolyte further comprises any non-aqueous solvent known in the art that can be used as a solvent for an electrolyte.

[0173] In some embodiments, the non-aqueous solvent includes, but is not limited to, one or more of the following: cyclic carbonates, chain carbonates, cyclic carboxylates, chain carboxylates, cyclic ethers, chain ethers, phosphorus-containing organic solvents, sulfur-containing organic solvents, and aromatic fluorine-containing solvents.

[0174] In some embodiments, examples of the cyclic carbonate may include, but are not limited to, one or more of the following: ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate. In some embodiments, the cyclic carbonate has 3-6 carbon atoms.

[0175] In some embodiments, examples of the chain carbonates may include, but are not limited to, one or more of the following: dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate (DEC), methyl n-propyl carbonate, ethyl n-propyl carbonate, di-n-propyl carbonate, etc. Examples of fluorine-substituted chain carbonates may include, but are not limited to, one or more of the following: bis(fluoromethyl) carbonate, bis(difluoromethyl) carbonate, bis(trifluoromethyl) carbonate, bis(2-fluoroethyl) carbonate, bis(2,2-difluoroethyl) carbonate, bis(2,2,2-trifluoroethyl) carbonate, 2-fluoroethyl methyl carbonate, 2,2-difluoroethyl methyl carbonate, and 2,2,2-trifluoroethyl methyl carbonate.

[0176] In some embodiments, examples of the cyclic carboxylic acid ester may include, but are not limited to, one or more of the following: one or more of γ-butyrolactone and γ-valerolactone. In some embodiments, some hydrogen atoms of the cyclic carboxylic acid ester may be substituted with fluorine.

[0177] In some embodiments, examples of the chain carboxylic acid esters may include, but are not limited to, one or more of the following: methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, sec-butyl acetate, isobutyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, ethyl isobutyrate, methyl valerate, ethyl valerate, methyl pivalate, and ethyl pivalate. In some embodiments, some of the hydrogen atoms of the chain carboxylic acid esters may be substituted with fluorine. In some embodiments, examples of fluorine-substituted chain carboxylic acid esters may include, but are not limited to, methyl trifluoroacetate, ethyl trifluoroacetate, propyl trifluoroacetate, butyl trifluoroacetate, and 2,2,2-trifluoroethyl trifluoroacetate.

[0178] In some embodiments, examples of the cyclic ether may include, but are not limited to, one or more of the following: tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 2-methyl1,3-dioxolane, 4-methyl1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, and dimethoxypropane.

[0179] In some embodiments, examples of the chain ether may include, but are not limited to, one or more of the following: dimethoxymethane, 1,1-dimethoxyethane, 1,2-dimethoxyethane, diethoxymethane, 1,1-diethoxyethane, 1,2-diethoxyethane, ethoxymethoxymethane, 1,1-ethoxymethoxyethane and 1,2-ethoxymethoxyethane, etc.

[0180] In some embodiments, examples of the phosphorus-containing organic solvent may include, but are not limited to, one or more of the following: trimethyl phosphate, triethyl phosphate, dimethyl ethyl phosphate, diethyl methyl phosphate, ethylidene methyl phosphate, ethylidene ethyl phosphate, triphenyl phosphate, trimethyl phosphite, triethyl phosphite, triphenyl phosphite, tris(2,2,2-trifluoroethyl) phosphate, and tris(2,2,3,3,3-pentafluoropropyl) phosphate, etc.

[0181] In some embodiments, examples of the sulfur-containing organic solvent may include, but are not limited to, one or more of the following: sulfolane, 2-methylsulfolane, 3-methylsulfolane, dimethyl sulfone, diethyl sulfone, ethyl methyl sulfone, methylpropyl sulfone, dimethyl sulfoxide, methyl methanesulfonate, ethyl methanesulfonate, methyl ethanesulfonate, ethyl ethanesulfonate, dimethyl sulfate, diethyl sulfate, and dibutyl sulfate. In some embodiments, some of the hydrogen atoms of the sulfur-containing organic solvent may be substituted with fluorine.

[0182] In some embodiments, the aromatic fluorine-containing solvent includes, but is not limited to, one or more of the following: fluorobenzene, difluorobenzene, trifluorobenzene, tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene, and trifluoromethylbenzene.

[0183] In some embodiments, the solvent used in the electrolyte of the present application includes cyclic carbonates, chain carbonates, cyclic carboxylates, chain carboxylates, and combinations thereof. In some embodiments, the solvent used in the electrolyte of the present application includes an organic solvent selected from the group consisting of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, n-propyl acetate, ethyl acetate, and combinations thereof. In some embodiments, the solvent used in the electrolyte of the present application includes ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, γ-butyrolactone, and combinations thereof.

[0184] additive

[0185] In some embodiments, examples of the additive may include, but are not limited to, one or more of the following: fluorocarbonate, ethylene carbonate containing a carbon-carbon double bond, and acid anhydride.

[0186] In some embodiments, the additive is present in an amount of 0.01% to 15%, 0.1% to 10%, or 1% to 5% based on the weight of the electrolyte.

[0187] According to an embodiment of the present application, based on the weight of the electrolyte, the content of the propionate is 1.5 to 30 times, 1.5 to 20 times, 2 to 20 times, or 5 to 20 times that of the additive.

[0188] In some embodiments, the additive comprises one or more fluorocarbonates. During charge / discharge of the lithium-ion battery, the fluorocarbonates can work together with the propionate to form a stable protective film on the surface of the negative electrode, thereby inhibiting decomposition of the electrolyte.

[0189] In some embodiments, the fluorocarbonate has the formula C=O(OR x )(OR y ), where R x and R y Each is selected from an alkyl group or a halogenated alkyl group having 1 to 6 carbon atoms, wherein R x and R y At least one of them is selected from a fluoroalkyl group having 1 to 6 carbon atoms, and R x and R y Optionally, together with the atoms to which it is attached, it forms a 5- to 7-membered ring.

[0190] In some embodiments, examples of the fluorocarbonate may include, but are not limited to, one or more of the following: fluoroethylene carbonate, cis-4,4-difluoroethylene carbonate, trans-4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4-fluoro-4-methylethylene carbonate, 4-fluoro-5-methylethylene carbonate, trifluoromethyl methyl carbonate, trifluoroethyl methyl carbonate, and trifluoroethyl ethyl carbonate, etc.

[0191] In some embodiments, the additive comprises one or more ethylene carbonates containing carbon-carbon double bonds. Examples of the ethylene carbonates containing carbon-carbon double bonds may include, but are not limited to, one or more of the following: vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, 1,2-dimethyl vinylene carbonate, 1,2-diethyl vinylene carbonate, fluorovinylene carbonate, trifluoromethyl vinylene carbonate; vinyl ethylene carbonate, 1-methyl-2-vinylethylene carbonate, 1-ethyl-2-vinylethylene carbonate, 1-n-propyl-2-vinylethylene carbonate, 1-methyl-2-vinylethylene carbonate, 1,1-divinylethylene carbonate, 1,2-divinylethylene carbonate, 1,1-dimethyl-2-methyleneethylene carbonate, and 1,1-diethyl-2-methyleneethylene carbonate. In some embodiments, the ethylene carbonate containing carbon-carbon double bonds includes vinylene carbonate, which is easily available and can achieve better results.

[0192] In some embodiments, the additive is a combination of a fluorocarbonate and ethylene carbonate containing a carbon-carbon double bond. In some embodiments, the additive is a combination of a fluorocarbonate and a compound containing a sulfur-oxygen double bond. In some embodiments, the additive is a combination of a fluorocarbonate and a compound with 2-4 cyano groups. In some embodiments, the additive is a combination of a fluorocarbonate and a cyclic carboxylic acid ester. In some embodiments, the additive is a combination of a fluorocarbonate and cyclic phosphoric acid anhydride. In some embodiments, the additive is a combination of a fluorocarbonate and a carboxylic acid anhydride. In some embodiments, the additive is a combination of a fluorocarbonate and a sulfonic acid anhydride. In some embodiments, the additive is a combination of a fluorocarbonate and a carboxylic acid sulfonic acid anhydride.

[0193] electrolytes

[0194] The electrolyte is not particularly limited, and any substance known as an electrolyte can be used arbitrarily. In the case of a lithium secondary battery, a lithium salt is generally used. Examples of the electrolyte may include, but are not limited to, inorganic lithium salts such as LiPF6, LiBF4, LiClO4, LiAlF4, LiSbF6, and LiWF7; lithium tungstates such as LiWOF5; lithium carboxylates such as HCO2Li, CH3CO2Li, CH2FCO2Li, CHF2CO2Li, CF3CO2Li, CF3CH2CO2Li, CF3CF2CO2Li, CF3CF2CF2CO2Li, CF3CF2CF2CF2CO2Li; lithium salts such as FSO3Li, CH3SO3Li, etc. , CH2FSO3Li, CHF2SO3Li, CF3SO3Li, CF3CF2SO3Li, CF3CF2CF2SO3Li, CF3CF2CF2CF2SO3Li and other lithium sulfonates; LiN(FCO)2, LiN(FCO)(FSO2), LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic 1,2-perfluoroethane bissulfonimide lithium, cyclic 1,3-perfluoropropane bissulfonimide Lithium, LiN (CF3SO2) (C4F9SO2) and other imide lithium salts; LiC (FSO2) 3, LiC (CF3SO2) 3, LiC (C2F5SO2) 3 and other methylated lithium salts; bis (malonate) borate lithium salts, difluoro (malonate) borate lithium salts and other (malonate) borate lithium salts; tri (malonate) phosphate lithium, difluorobis (malonate) phosphate lithium, tetrafluoro (malonate) phosphate lithium salts and other (malonate) phosphate lithium salts; and LiPF4 (CF3) 2, LiPF4 (C2F5) 2, Fluorine-containing organic lithium salts such as LiPF4(CF3SO2)2, LiPF4(C2F5SO2)2, LiBF3CF3, LiBF3C2F5, LiBF3C3F7, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, LiBF2(C2F5SO2)2; lithium oxalatoborate salts such as lithium difluorooxalatoborate and lithium bis(oxalato)borate; lithium oxalato phosphate salts such as lithium tetrafluorooxalato phosphate, lithium difluorobis(oxalato)phosphate and lithium tris(oxalato)phosphate, etc.

[0195] In some embodiments, the electrolyte is selected from LiPF6, LiSbF6, FSO3Li, CF3SO3Li, LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic 1,2-perfluoroethane bissulfonyl imide lithium, cyclic 1,3-perfluoropropane bissulfonyl imide lithium, LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiBF3CF3, LiBF3C2F5, LiPF3(CF3)3, LiPF3(C2F5)3, lithium difluorooxalatoborate, lithium bis(oxalato)borate or lithium difluorobis(oxalato)phosphate, which helps to improve the output power characteristics, high-rate charge and discharge characteristics, high-temperature storage characteristics and cycle characteristics of the electrochemical device.

[0196] There is no particular limitation on the content of the electrolyte, as long as the effect of the present application is not impaired. In some embodiments, the total molar concentration of lithium in the electrolyte is greater than 0.3 mol / L, greater than 0.4 mol / L or greater than 0.5 mol / L. In some embodiments, the total molar concentration of lithium in the electrolyte is less than 3 mol / L, less than 2.5 mol / L or less than 2.0 mol / L. In some embodiments, the total molar concentration of lithium in the electrolyte is within the range consisting of any two of the above values. When the electrolyte concentration is within the above range, there will not be too little lithium as a charged particle, and the viscosity can be kept within an appropriate range, thereby easily ensuring good conductivity.

[0197] When two or more electrolytes are used, the electrolyte includes at least one salt selected from the group consisting of monofluorophosphate, borate, oxalate and fluorosulfonate. In some embodiments, the electrolyte includes a salt selected from the group consisting of monofluorophosphate, oxalate and fluorosulfonate. In some embodiments, the electrolyte includes a lithium salt. In some embodiments, based on the weight of the electrolyte, the content of the salt selected from the group consisting of monofluorophosphate, borate, oxalate and fluorosulfonate is greater than 0.01% or greater than 0.1%. In some embodiments, based on the weight of the electrolyte, the content of the salt selected from the group consisting of monofluorophosphate, borate, oxalate and fluorosulfonate is less than 20% or less than 10%. In some embodiments, the content of the salt selected from the group consisting of monofluorophosphate, borate, oxalate and fluorosulfonate is within the range composed of any two of the above values.

[0198] In some embodiments, the electrolyte comprises one or more substances selected from the group consisting of monofluorophosphates, borates, oxalates, and fluorosulfonates, and one or more salts other than these. Salts other than these include the lithium salts exemplified above, and in some embodiments, include LiPF6, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic 1,2-perfluoroethane bissulfonyl imide lithium, cyclic 1,3-perfluoropropane bissulfonyl imide lithium, LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiBF3CF3, LiBF3C2F5, LiPF3(CF3)3, and LiPF3(C2F5)3. In some embodiments, the salt other than these is LiPF6.

[0199] In some embodiments, the amount of the other salts is greater than 0.01% or greater than 0.1% based on the weight of the electrolyte. In some embodiments, the amount of the other salts is less than 20%, less than 15%, or less than 10% based on the weight of the electrolyte. In some embodiments, the amount of the other salts is within a range consisting of any two of the above values. The above amounts of the other salts help balance the conductivity and viscosity of the electrolyte.

[0200] In addition to the above-mentioned solvents, additives and electrolyte salts, the electrolyte may contain additional additives such as a negative electrode film former, a positive electrode protective agent, and an anti-overcharge agent as needed. As additives, additives generally used in non-aqueous electrolyte secondary batteries can be used, examples of which may include, but are not limited to, vinylene carbonate, succinic anhydride, biphenyl, cyclohexylbenzene, 2,4-difluoroanisole, and the like. These additives may be used alone or in any combination. In addition, the content of these additives in the electrolyte is not particularly limited and can be appropriately set according to the type of the additive, etc. In some embodiments, the content of the additive is less than 5%, in the range of 0.01% to 5%, or in the range of 0.2% to 5%, based on the weight of the electrolyte.

[0201] III. Positive electrode

[0202] The positive electrode includes a positive electrode current collector and a positive electrode mixture layer disposed on one or both surfaces of the positive electrode current collector.

[0203] 1. Positive electrode mixture layer

[0204] The positive electrode mixture layer comprises a positive electrode mixture layer, which contains a positive electrode active material. The positive electrode mixture layer may be one or more layers. Each layer of the multilayer positive electrode active material layer may contain the same or different positive electrode active materials. The positive electrode active material is any substance that can reversibly intercalate and deintercalate metal ions such as lithium ions.

[0205] The type of positive electrode active material is not particularly limited, as long as it can electrochemically absorb and release metal ions (e.g., lithium ions). In some embodiments, the positive electrode active material is a material containing lithium and at least one transition metal. Examples of positive electrode active materials may include, but are not limited to, lithium transition metal composite oxides and lithium-containing transition metal phosphate compounds.

[0206] In some embodiments, the transition metal in the lithium transition metal composite oxide includes V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. In some embodiments, the lithium transition metal composite oxide includes lithium cobalt composite oxides such as LiCoO2, lithium nickel composite oxides such as LiNiO2, lithium manganese composite oxides such as LiMnO2, LiMn2O4, Li2MnO4, etc., LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2、LiNi 0.5 Mn 0.3 Co 0.2 O2 and other lithium nickel manganese cobalt composite oxides, wherein a portion of the transition metal atoms serving as the main body of these lithium transition metal composite oxides are replaced by other elements such as Na, K, B, F, Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Si, Nb, Mo, Sn, W, etc. Examples of lithium transition metal composite oxides may include, but are not limited to, LiNi 0.5 Mn 0.5 O2、LiNi 0.85 Co 0.10 Al 0.05 O2、LiNi 0.33 Co 0.33 Mn 0.33 O2、LiNi 0.45 Co 0.10 Al 0.45 O2、LiMn 1.8 Al 0.2 O4 and LiMn 1.5 Ni 0.5 O4, etc. Examples of combinations of lithium transition metal composite oxides include, but are not limited to, combinations of LiCoO2 and LiMn2O4, wherein a portion of the Mn in LiMn2O4 can be replaced by a transition metal (e.g., LiNi 0.33 Co 0.33 Mn 0.33 O2), part of the Co in LiCoO2 can be replaced by transition metals.

[0207] In some embodiments, the transition metal in the lithium-containing transition metal phosphate compound includes V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. In some embodiments, the lithium-containing transition metal phosphate compound includes iron phosphates such as LiFePO4, Li3Fe2(PO4)3, and LiFeP2O7, and cobalt phosphates such as LiCoPO4, wherein a portion of the transition metal atoms serving as the main body of these lithium transition metal phosphate compounds are replaced by other elements such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, and Si.

[0208] In some embodiments, the positive electrode active material includes lithium phosphate, which can improve the continuous charging characteristics of the electrochemical device. There is no limitation on the use of lithium phosphate. In some embodiments, the positive electrode active material and lithium phosphate are mixed. In some embodiments, the content of lithium phosphate is greater than 0.1%, greater than 0.3%, or greater than 0.5% relative to the weight of the above-mentioned positive electrode active material and lithium phosphate. In some embodiments, the content of lithium phosphate is less than 10%, less than 8%, or less than 5% relative to the weight of the above-mentioned positive electrode active material and lithium phosphate. In some embodiments, the content of lithium phosphate is within the range formed by any two of the above values.

[0209] surface coating

[0210] A substance having a different composition than the positive electrode active material may be attached to the surface of the positive electrode active material. Examples of surface-attached substances include, but are not limited to: oxides such as aluminum oxide, silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate; and carbon.

[0211] These surface attachment substances can be attached to the surface of the positive electrode active material by the following methods: a method in which the surface attachment substance is dissolved or suspended in a solvent and then added to the positive electrode active material and dried; a method in which a surface attachment substance precursor is dissolved or suspended in a solvent, added to the positive electrode active material, and then reacted by heating or the like; and a method in which the surface attachment substance is added to the positive electrode active material precursor and then fired simultaneously. In the case of carbon attachment, a method in which a carbon material (e.g., activated carbon) is mechanically attached can also be used.

[0212] In some embodiments, the surface-adherent substance content is greater than 0.1 ppm, greater than 1 ppm, or greater than 10 ppm based on the weight of the positive electrode mixture layer. In some embodiments, the surface-adherent substance content is less than 10%, less than 5%, or less than 2% based on the weight of the positive electrode mixture layer. In some embodiments, the surface-adherent substance content is within a range formed by any two of the above values ​​based on the weight of the positive electrode mixture layer.

[0213] By attaching a substance to the surface of the positive electrode active material, the oxidation reaction of the electrolyte on the surface of the positive electrode active material can be suppressed, thereby improving the life of the electrochemical device. If the amount of surface-attached substance is too small, this effect will not be fully realized. If the amount of surface-attached substance is too large, it will hinder the entry and exit of lithium ions, sometimes increasing the resistance.

[0214] In the present application, a positive electrode active material in which a substance having a composition different from that of the positive electrode active material is attached to the surface of the positive electrode active material is also referred to as a “positive electrode active material”.

[0215] shape

[0216] In some embodiments, the shape of the positive electrode active material particles includes, but is not limited to, block, polyhedron, sphere, ellipsoid, plate, needle, and column. In some embodiments, the positive electrode active material particles include primary particles, secondary particles, or a combination thereof. In some embodiments, the primary particles may aggregate to form secondary particles.

[0217] Tap density

[0218] In some embodiments, the tap density of the positive electrode active material is greater than 0.5 g / cm 3 , greater than 0.8g / cm 3 or greater than 1.0g / cm 3 . When the tap density of the positive electrode active material is within the above range, the amount of dispersion medium and the required amount of conductive material and positive electrode binder required for the formation of the positive electrode mixture layer can be suppressed, thereby ensuring the filling rate of the positive electrode active material and the capacity of the electrochemical device. By using a composite oxide powder with a high tap density, a high-density positive electrode mixture layer can be formed. The larger the tap density, the better, and there is no particular upper limit. In some embodiments, the tap density of the positive electrode active material is less than 4.0 g / cm 3 , less than 3.7g / cm 3 or less than 3.5g / cm 3 When the tap density of the positive electrode active material has the upper limit as described above, degradation of load characteristics can be suppressed.

[0219] The tap density of the positive electrode active material can be calculated by placing 5 g to 10 g of the positive electrode active material powder in a 10 mL glass graduated cylinder and vibrating the cylinder 200 times with a stroke of 20 mm to obtain the powder packing density (tap density).

[0220] Median particle size (D50)

[0221] When the positive electrode active material particles are primary particles, the median particle size (D50) of the positive electrode active material particles refers to the primary particle size of the positive electrode active material particles. When the primary particles of the positive electrode active material particles aggregate to form secondary particles, the median particle size (D50) of the positive electrode active material particles refers to the secondary particle size of the positive electrode active material particles.

[0222] In some embodiments, the median particle size (D50) of the positive electrode active material particles is greater than 0.3 μm, greater than 0.5 μm, greater than 0.8 μm or greater than 1.0 μm. In some embodiments, the median particle size (D50) of the positive electrode active material particles is less than 30 μm, less than 27 μm, less than 25 μm or less than 22 μm. In some embodiments, the median particle size (D50) of the positive electrode active material particles is within the range formed by any two of the above values. When the median particle size (D50) of the positive electrode active material particles is within the above range, a positive electrode active material with a high tap density can be obtained, which can suppress the degradation of the performance of the electrochemical device. On the other hand, during the preparation process of the positive electrode of the electrochemical device (that is, when the positive electrode active material, conductive material and binder are slurried with a solvent and applied in a thin film), problems such as streaks can be prevented. Here, by mixing two or more positive electrode active materials with different median particle sizes, the filling property during the preparation of the positive electrode can be further improved.

[0223] The median particle size (D50) of the positive electrode active material particles can be measured using a laser diffraction / scattering particle size distribution measuring device: when using LA-920 manufactured by HORIBA as a particle size distribution meter, a 0.1% sodium hexametaphosphate aqueous solution is used as the dispersion medium used in the measurement, and the measurement is performed after 5 minutes of ultrasonic dispersion with the refractive index set to 1.24.

[0224] Average primary particle size

[0225] In the case where the primary particles of the positive electrode active material particles agglomerate to form secondary particles, in some embodiments, the average primary particle size of the positive electrode active material is greater than 0.05 μm, greater than 0.1 μm or greater than 0.5 μm. In some embodiments, the average primary particle size of the positive electrode active material is less than 5 μm, less than 4 μm, less than 3 μm or less than 2 μm. In some embodiments, the average primary particle size of the positive electrode active material is within the range formed by any two of the above values. When the average primary particle size of the positive electrode active material is within the above range, the powder filling property and specific surface area can be ensured, the reduction in battery performance can be suppressed, and appropriate crystallinity can be obtained, thereby ensuring the reversibility of charge and discharge of the electrochemical device.

[0226] The average primary particle size of the positive electrode active material can be obtained by observing the image obtained by a scanning electron microscope (SEM): in an SEM image with a magnification of 10,000 times, for any 50 primary particles, the longest value of the slice obtained by the left and right boundary lines of the primary particles relative to the horizontal straight line is obtained, and the average value is obtained to obtain the average primary particle size.

[0227] Specific surface area (BET)

[0228] In some embodiments, the specific surface area (BET) of the positive electrode active material is greater than 0.1 m 2 / g, greater than 0.2m 2 / g or greater than 0.3m 2 In some embodiments, the specific surface area (BET) of the positive electrode active material is less than 50 m 2 / g, less than 40m 2 / g or less than 30m 2 In some embodiments, the positive electrode active material has a specific surface area (BET) within the range defined by any two of the above values. When the specific surface area (BET) of the positive electrode active material is within the above range, the performance of the electrochemical device can be ensured while also providing good coating properties for the positive electrode active material.

[0229] The specific surface area (BET) of the positive electrode active material can be measured by the following method: using a surface area meter (for example, a fully automatic surface area measuring device manufactured by Okura Riken), pre-drying the sample at 150°C for 30 minutes under nitrogen flow, and then using a nitrogen-helium mixed gas in which the relative pressure value of nitrogen relative to atmospheric pressure is accurately adjusted to 0.3, the nitrogen adsorption BET single-point method using the gas flow method is used for measurement.

[0230] Positive electrode conductive material

[0231] There are no restrictions on the type of positive electrode conductive material; any known conductive material may be used. Examples of positive electrode conductive materials include, but are not limited to, graphites such as natural graphite and artificial graphite; carbon blacks such as acetylene black; carbon materials such as amorphous carbon such as needle coke; carbon nanotubes; and graphene. These positive electrode conductive materials may be used alone or in any combination.

[0232] In some embodiments, the positive electrode conductive material content is greater than 0.01%, greater than 0.1%, or greater than 1% based on the weight of the positive electrode mixture layer. In some embodiments, the positive electrode conductive material content is less than 10%, less than 8%, or less than 5% based on the weight of the positive electrode mixture layer. When the positive electrode conductive material content is within the above ranges, sufficient conductivity and capacity of the electrochemical device can be ensured.

[0233] positive electrode binder

[0234] There is no particular restriction on the type of positive electrode binder used in the manufacture of the positive electrode mixture layer. In the case of a coating method, any material that can be dissolved or dispersed in the liquid medium used in the manufacture of the electrode can be used. Examples of positive electrode binders may include, but are not limited to, one or more of the following: resin polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose; rubber polymers such as styrene-butadiene rubber (SBR), nitrile rubber (NBR), fluororubber, isoprene rubber, polybutadiene rubber, and ethylene-propylene rubber; styrene-butadiene-styrene block copolymers or their hydrogenates, ethylene-propylene-diene terpolymers (EPDM), Thermoplastic elastomer polymers such as styrene-ethylene-butadiene-ethylene copolymers, styrene-isoprene-styrene block copolymers, or their hydrogenated forms; soft resin polymers such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, and propylene-α-olefin copolymers; fluorinated polymers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymers; and polymer compositions with ion conductivity for alkali metal ions (particularly lithium ions). These positive electrode binders may be used alone or in any combination.

[0235] In some embodiments, the positive electrode binder content is greater than 0.1%, greater than 1%, or greater than 1.5% based on the weight of the positive electrode mixture layer. In some embodiments, the positive electrode binder content is less than 10%, less than 5%, less than 4%, or less than 3% based on the weight of the positive electrode mixture layer. When the positive electrode binder content is within the above ranges, the positive electrode can have good conductivity and sufficient mechanical strength, while ensuring the capacity of the electrochemical device.

[0236] solvent

[0237] There is no limitation on the type of solvent used to form the positive electrode slurry, as long as it is a solvent that can dissolve or disperse the positive electrode active material, conductive material, positive electrode binder, and thickener used as needed. Examples of solvents used to form the positive electrode slurry may include any of aqueous solvents and organic solvents. Examples of aqueous media may include, but are not limited to, water and mixed media of alcohol and water. Examples of organic media may include, but are not limited to, aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and tetrahydrofuran (THF); amides such as N-methylpyrrolidone (NMP), dimethylformamide, and dimethylacetamide; aprotic polar solvents such as hexamethylphosphoramide and dimethyl sulfoxide, etc.

[0238] thickener

[0239] Thickeners are generally used to adjust the viscosity of the slurry. When using an aqueous medium, the slurry can be formed using a thickener and a styrene-butadiene rubber (SBR) emulsion. The type of thickener is not particularly limited, and examples thereof include, but are not limited to, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and salts thereof. These thickeners may be used alone or in any combination.

[0240] In some embodiments, the thickener content is greater than 0.1%, greater than 0.2%, or greater than 0.3% based on the weight of the positive electrode mixture layer. In some embodiments, the thickener content is less than 5%, less than 3%, or less than 2% based on the weight of the positive electrode mixture layer. In some embodiments, the thickener content is within a range consisting of any two of the above values ​​based on the weight of the positive electrode mixture layer. When the thickener content is within the above range, the positive electrode slurry can have good coating properties and can suppress the reduction in capacity and increase in resistance of the electrochemical device.

[0241] Content of positive electrode active material

[0242] In some embodiments, the content of the positive electrode active material is greater than 80%, greater than 82%, or greater than 84% based on the weight of the positive electrode mixture layer. In some embodiments, the content of the positive electrode active material is less than 99% or less than 98% based on the weight of the positive electrode mixture layer. In some embodiments, the content of the positive electrode active material is within the range formed by any two of the above arrays based on the weight of the positive electrode mixture layer. When the content of the positive electrode active material is within the above range, the capacitance of the positive electrode active material in the positive electrode mixture layer can be ensured while maintaining the strength of the positive electrode.

[0243] Density of the positive electrode active material layer

[0244] The positive electrode mixture layer obtained by coating and drying can be compacted by a manual press or a roller press to increase the packing density of the positive electrode active material. In some embodiments, the density of the positive electrode mixture layer is greater than 1.5 g / cm 3 , greater than 2g / cm 3 or greater than 2.2g / cm 3 In some embodiments, the density of the positive electrode mixture layer is less than 5 g / cm 3 , less than 4.5g / cm 3 or less than 4g / cm 3 In some embodiments, the density of the positive electrode mixture layer is within the range formed by any two of the above values. When the density of the positive electrode mixture layer is within the above range, the electrochemical device can have good charge and discharge characteristics while suppressing the increase in resistance.

[0245] Thickness of the positive electrode mixture layer

[0246] The thickness of the positive electrode mixture layer refers to the thickness of the positive electrode mixture layer on either side of the positive electrode current collector. In some embodiments, the thickness of the positive electrode mixture layer is greater than 10 μm or greater than 20 μm. In some embodiments, the thickness of the positive electrode mixture layer is less than 500 μm or less than 450 μm.

[0247] Method for producing positive electrode active material

[0248] Positive electrode active materials can be manufactured using common methods for manufacturing inorganic compounds. To produce spherical or ellipsoidal positive electrode active materials, the following manufacturing method can be used: dissolve or crush the transition metal raw material and disperse it in a solvent such as water, adjust the pH while stirring, prepare a spherical precursor, recover it, dry it as needed, add a lithium source such as LiOH, Li2CO3, or LiNO3, and sinter it at high temperature to obtain the positive electrode active material.

[0249] 2. Positive electrode current collector

[0250] The type of positive electrode current collector is not particularly limited and can be any known material suitable for use as a positive electrode current collector. Examples of positive electrode current collectors include, but are not limited to, metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; and carbon materials such as carbon cloth and carbon paper. In some embodiments, the positive electrode current collector is a metal material. In some embodiments, the positive electrode current collector is aluminum.

[0251] There is no particular limitation on the form of the positive electrode current collector. When the positive electrode current collector is a metal material, the form of the positive electrode current collector may include, but is not limited to, metal foil, metal cylinder, metal strip roll, metal plate, metal foil, metal mesh, stamped metal, foamed metal, etc. When the positive electrode current collector is a carbon material, the form of the positive electrode current collector may include, but is not limited to, carbon plate, carbon film, carbon cylinder, etc. In some embodiments, the positive electrode current collector is a metal foil. In some embodiments, the metal foil is mesh-shaped. There is no particular limitation on the thickness of the metal foil. In some embodiments, the thickness of the metal foil is greater than 1 μm, greater than 3 μm, or greater than 5 μm. In some embodiments, the thickness of the metal foil is less than 1 mm, less than 100 μm, or less than 50 μm. In some embodiments, the thickness of the metal foil is within the range formed by any two of the above values.

[0252] In order to reduce the electronic contact resistance between the positive electrode current collector and the positive electrode mixture layer, the surface of the positive electrode current collector may include a conductive additive. Examples of conductive additives include, but are not limited to, carbon and precious metals such as gold, platinum, and silver.

[0253] The thickness ratio of the positive electrode active material layer to the positive electrode current collector refers to the thickness of the positive electrode active material layer on a single side divided by the thickness of the positive electrode current collector, and its value is not particularly limited. In some embodiments, the thickness ratio is less than 50, less than 30, or less than 20. In some embodiments, the thickness ratio is greater than 0.5, greater than 0.8, or greater than 1. In some embodiments, the thickness ratio is within the range formed by any two of the above values. When the thickness ratio is within the above range, the heat release of the positive electrode current collector during high current density charging and discharging can be suppressed, and the capacity of the electrochemical device can be ensured.

[0254] 3. Preparation method of positive electrode

[0255] The positive electrode can be made by forming a positive electrode mixture layer containing a positive electrode active material and a binder on a current collector. The positive electrode using the positive electrode active material can be manufactured by conventional methods, that is, the positive electrode active material and the binder, as well as the conductive material and thickener as needed, are dry-mixed to form a sheet, and the resulting sheet is press-bonded to the positive electrode current collector; or these materials are dissolved or dispersed in a liquid medium to form a slurry, and the slurry is applied to the positive electrode current collector and dried to form a positive electrode mixture layer on the current collector, thereby obtaining the positive electrode.

[0256] IV. Isolation membrane

[0257] To prevent short circuits, a separator is usually provided between the positive electrode and the negative electrode. In this case, the electrolyte of the present application is usually used by permeating the separator.

[0258] There is no particular restriction on the material and shape of the isolation membrane, as long as the effect of the present application is not significantly impaired. The isolation membrane may be a resin, glass fiber, inorganic substance, etc. formed of a material that is stable to the electrolyte of the present application. In some embodiments, the isolation membrane includes a porous sheet or a non-woven fabric-like material with excellent liquid retention. Examples of materials for resin or glass fiber isolation membranes may include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, etc. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The materials of the above-mentioned isolation membranes can be used alone or in any combination.

[0259] The isolation film may also be a material formed by laminating the above materials, and examples thereof include, but are not limited to, a three-layer isolation film formed by laminating polypropylene, polyethylene, and polypropylene in this order.

[0260] Examples of inorganic materials include, but are not limited to, oxides such as aluminum oxide and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates (e.g., barium sulfate, calcium sulfate, etc.) The inorganic material may be in the form of, but is not limited to, particles or fibers.

[0261] The separator may be in the form of a thin film, examples of which include, but are not limited to, nonwoven fabrics, woven fabrics, and microporous films. In the thin film form, the separator has a pore size of 0.01 μm to 1 μm and a thickness of 5 μm to 50 μm. In addition to the above-mentioned independent thin film separators, separators may also be used: separators formed by forming a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive electrode and / or negative electrode using a resin-based binder. For example, a separator formed by forming a porous layer on both sides of the positive electrode using fluororesin as a binder with aluminum oxide particles having a particle size of 90% less than 1 μm.

[0262] The thickness of the separator is arbitrary. In some embodiments, the separator has a thickness greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the separator has a thickness less than 50 μm, less than 40 μm, or less than 30 μm. In some embodiments, the separator has a thickness within a range defined by any two of the above values. When the separator has a thickness within the above range, insulation and mechanical strength can be ensured, and the rate characteristics and energy density of the electrochemical device can be ensured.

[0263] When a porous material such as a porous sheet or non-woven fabric is used as the separator, the porosity of the separator is arbitrary. In some embodiments, the porosity of the separator is greater than 10%, greater than 15%, or greater than 20%. In some embodiments, the porosity of the separator is less than 60%, less than 50%, or less than 45%. In some embodiments, the porosity of the separator is within a range consisting of any two of the above values. When the porosity of the separator is within the above range, insulation and mechanical strength can be ensured, membrane resistance can be suppressed, and the electrochemical device has good safety characteristics.

[0264] The average pore size of the isolation membrane is also arbitrary. In some embodiments, the average pore size of the isolation membrane is less than 0.5 μm or less than 0.2 μm. In some embodiments, the average pore size of the isolation membrane is greater than 0.05 μm. In some embodiments, the average pore size of the isolation membrane is within a range consisting of any two of the above values. If the average pore size of the isolation membrane exceeds the above range, short circuits are likely to occur. When the average pore size of the isolation membrane is within the above range, the electrochemical device has good safety characteristics.

[0265] V. Electrochemical Device Components

[0266] The electrochemical device assembly includes an electrode group, a current collecting structure, an outer casing and a protective element.

[0267] Electrode group

[0268] The electrode group may be any of a laminated structure formed by stacking the positive electrode and the negative electrode with the separator interposed therebetween, or a structure formed by spirally winding the positive electrode and the negative electrode with the separator interposed therebetween. In some embodiments, the ratio of the mass of the electrode group to the internal volume of the battery (electrode group occupancy) is greater than 40% or greater than 50%. In some embodiments, the electrode group occupancy is less than 90% or less than 80%. In some embodiments, the electrode group occupancy is within the range formed by any two of the above values. When the electrode group occupancy is within the above range, the capacity of the electrochemical device can be ensured while suppressing the degradation of characteristics such as repeated charge and discharge performance and high-temperature storage associated with increased internal pressure.

[0269] Current collection structure

[0270] There is no particular limitation on the current collection structure. In some embodiments, the current collection structure is a structure that reduces the resistance of the wiring portion and the joint portion. When the electrode group is the above-mentioned stacked structure, it is suitable to use a structure in which the metal core portions of each electrode layer are bundled and welded to the terminal. When the electrode area of ​​a piece increases, the internal resistance increases, so it is also suitable to provide more than two terminals in the electrode to reduce the resistance. When the electrode group is the above-mentioned winding structure, the internal resistance can be reduced by providing more than two lead structures at the positive electrode and the negative electrode respectively, and bundling them at the terminal.

[0271] External shell

[0272] The material of the outer casing is not particularly limited, as long as it is stable with the electrolyte used. The outer casing can be made of, but is not limited to, nickel-plated steel, stainless steel, aluminum or aluminum alloys, magnesium alloys, or other metals, or a laminate of resin and aluminum foil. In some embodiments, the outer casing is made of aluminum or an aluminum alloy or a laminate.

[0273] The outer casing of the metal type includes, but is not limited to, a packaged sealed structure formed by welding metals to each other by laser welding, resistance welding, and ultrasonic welding; or a riveted structure formed by using the above-mentioned metal type through a resin gasket. The outer casing using the above-mentioned laminated film includes, but is not limited to, a packaged sealed structure formed by thermally bonding resin layers to each other. In order to improve the sealing performance, a resin different from the resin used in the laminated film can also be sandwiched between the above-mentioned resin layers. When the resin layer is thermally bonded to form a sealed structure through the collector terminal, due to the bonding between the metal and the resin, a resin with a polar group or a modified resin into which a polar group is introduced can be used as the sandwiched resin. In addition, the shape of the outer casing is also arbitrary, for example, it can be any of cylindrical, square, laminated, button-shaped, large, etc.

[0274] Protection components

[0275] Protective elements may include positive temperature coefficient (PTC) devices, which increase resistance when abnormal heat generation or excessive current flows, temperature fuses, thermistors, and valves (current cutoff valves) that interrupt current flow in the circuit by rapidly increasing the internal pressure or temperature of the battery during abnormal heat generation. These protective elements may be selected to operate under conditions that do not allow for normal high-current use, and may be designed so that abnormal heat generation or thermal runaway does not occur even without the protective element.

[0276] VI. Application

[0277] The electrochemical device of the present application includes any device that generates an electrochemical reaction, and specific examples thereof include all kinds of primary batteries, secondary batteries, fuel cells, solar cells or capacitors. In particular, the electrochemical device is a lithium secondary battery, including a lithium metal secondary battery or a lithium ion secondary battery.

[0278] The present application further provides an electronic device, which includes the electrochemical device according to the present application.

[0279] The use of the electrochemical device of the present application is not particularly limited, and it can be used in any electronic device known in the prior art. In some embodiments, the electrochemical device of the present application can be used in, but is not limited to, laptop computers, pen-type computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors.

[0280] The preparation of lithium-ion batteries is described below using lithium-ion batteries as an example and in combination with specific embodiments. Those skilled in the art will understand that the preparation method described in this application is only an example, and any other suitable preparation method is within the scope of this application.

[0281] Example

[0282] The following describes the performance evaluation of the lithium-ion battery according to the embodiments and comparative examples of the present application.

[0283] 1. Preparation of lithium-ion batteries

[0284] 1. Preparation of negative electrode

[0285] Artificial graphite, styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed with deionized water in a mass ratio of 96%:2%:2% and stirred evenly to produce a negative electrode slurry. This slurry was then coated onto a 12μm current collector. The slurry was dried, cold-pressed, cut into pieces, and then welded to the tabs to produce the negative electrode.

[0286] 2. Preparation of positive electrode

[0287] Lithium cobalt oxide (LiCoO2), a conductive material (Super-P), and polyvinylidene fluoride (PVDF) were mixed with N-methylpyrrolidone (NMP) in a mass ratio of 95%:2%:3% and stirred evenly to produce a positive electrode slurry. This slurry was then coated onto 12μm aluminum foil, dried, cold-pressed, cut into pieces, and welded to the tabs to produce the positive electrode.

[0288] 3. Preparation of electrolyte

[0289] Under a dry argon atmosphere, EC, PC, and DEC (weight ratio of 1:1:1) were mixed, and LiPF6 was added and mixed thoroughly to form a base electrolyte solution, wherein the LiPF6 concentration was 1.15 mol / L. Electrolytes of different examples and comparative examples were obtained by adding various additives to the base electrolyte solution.

[0290] The abbreviations and names of the components in the electrolyte are shown in the following table:

[0291]

[0292] 4. Preparation of isolation membrane

[0293] A polyethylene (PE) porous polymer film was used as the separator.

[0294] 5. Preparation of lithium-ion batteries

[0295] The resulting positive electrode, separator, and negative electrode are wound in order and placed in an outer packaging foil, leaving a liquid injection port. The electrolyte is poured through the injection port, packaged, and then undergoes formation and capacity testing to produce a lithium-ion battery.

[0296] 2. Test Method

[0297] 1. Test method for high temperature cycle capacity retention of lithium-ion batteries

[0298] At 65°C, the lithium-ion battery is charged to 4.45V at a constant current of 1C, then charged to a current of 0.05C at a constant voltage of 4.45V, and then discharged to 3.0V at a constant current of 1C. This is the first cycle. The lithium-ion battery is cycled 200 times under the above conditions. "1C" is the current value that completely discharges the battery capacity within 1 hour. The high-temperature cycle capacity retention rate of the lithium-ion battery is calculated by the following formula:

[0299] High-temperature cycle capacity retention rate=(discharge capacity after cycle / discharge capacity at first cycle)×100%.

[0300] 2. Test method for thickness expansion rate of lithium-ion batteries during high temperature cycling

[0301] At 65°C, let the lithium-ion battery stand for 30 minutes, then charge it to 4.45V at a constant current rate of 0.5C, then charge it to 0.05C at a constant voltage rate at 4.45V, let it stand for 5 minutes, and measure the thickness of the lithium-ion battery. After 100 cycles under the above conditions, measure the thickness of the lithium-ion battery again. The high-temperature cycle thickness expansion rate of the lithium-ion battery is calculated by the following formula:

[0302] High temperature cycle thickness expansion ratio = [(thickness after cycle - thickness before cycle) / thickness before cycle] × 100%.

[0303] 3. Test method for overcharge deformation rate of lithium-ion batteries

[0304] At 25°C, let the lithium-ion battery rest for 30 minutes, then charge it to 4.45V at a constant current rate of 0.5C. Then, charge it to 0.05C at a constant voltage rate at 4.45V and let it rest for 60 minutes. Measure the thickness T1 of the lithium-ion battery. Then, charge it to 60 minutes at a constant current rate of 0.1C, let it rest for 30 minutes, and repeat this step five times until the lithium-ion battery reaches a state of charge (SOC) of 150%. Measure the thickness T2 of the lithium-ion battery. Calculate the overcharge deformation rate of the lithium-ion battery using the following formula:

[0305] Overcharge deformation rate = [(T2-T1) / T1]×100%.

[0306] 4. Test method for discharge capacity retention rate of lithium-ion batteries

[0307] The lithium-ion battery was discharged at a constant current of 0.5C to 3.0V, allowed to stand for 5 minutes, then charged at a constant current of 0.5C to 4.45V, and charged at a constant voltage to a cutoff current of 0.05C. The battery was allowed to stand for 5 minutes, and then discharged at constant currents of 0.2C and 5C to a cutoff voltage of 3.0V. The discharge capacity at 5C was recorded as D1, and the discharge capacity at 0.2C was recorded as D0. The discharge capacity retention rate of the lithium-ion battery at 5C was calculated based on the discharge capacity at 0.2C using the following formula:

[0308] Discharge capacity retention rate = [(D1-D0) / D0] × 100%

[0309] For each embodiment or comparative example, five samples were tested and the average value was taken.

[0310] 3. Test Results

[0311] Table 1 shows the effects of sulfur-oxygen double bond compounds in the negative electrode current collector and the electrolyte on the high-temperature cycle capacity retention rate, high-temperature cycle expansion rate and overcharge deformation rate of lithium-ion batteries.

[0312] Table 1

[0313]

[0314]

[0315] “ / ” means that the feature is not added or does not exist

[0316] The results show that when the negative electrode current collector of a lithium-ion battery contains tin and the electrolyte includes a compound containing a sulfur-oxygen double bond, tin can inhibit the expansion / contraction of the negative electrode caused by the charge and discharge process, and the compound containing a sulfur-oxygen double bond helps to stabilize the surface structure of the negative electrode, the interface between the negative electrode mixture layer and the negative electrode current collector, and the interface between the negative electrode mixture layer and the electrolyte, thereby significantly improving the high-temperature cycle capacity retention rate of the lithium-ion battery and significantly reducing the high-temperature cycle expansion rate and overcharge deformation rate of the lithium-ion battery.

[0317] When the tin content in the negative electrode current collector is in the range of 0.01% to 0.2%, the improvement of the high-temperature cycle capacity retention rate, high-temperature cycle expansion rate and overcharge deformation rate of the lithium-ion battery is particularly obvious.

[0318] Table 2 shows the effect of the presence of silver in the negative electrode current collector on the high-temperature cycle capacity retention, high-temperature cycle expansion rate, and overcharge deformation rate of lithium-ion batteries. The only difference between Examples 2-1 to 2-9 and Example 1-1 is the parameters listed in Table 2.

[0319] Table 2

[0320]

[0321] The results show that, on the basis of the negative electrode collector of the lithium-ion battery containing tin and the electrolyte including a compound containing a sulfur-oxygen double bond, when the negative electrode collector further contains 0.01% to 0.2% silver, the high-temperature cycle capacity retention rate of the lithium-ion battery can be further improved and the high-temperature cycle expansion rate and overcharge deformation rate of the lithium-ion battery can be further reduced.

[0322] Table 3 shows the effects of negative electrode current collector thickness, tensile strength, and 0.2% yield strength on high-temperature cycle capacity retention, high-temperature cycle expansion, and overcharge deformation of lithium-ion batteries. Examples 3-1 and 3-5 differ from Example 1-1 only in the parameters listed in Table 3.

[0323] Table 3

[0324]

[0325] As shown in Table 3, the negative electrode current collector may have the following characteristics: tensile strength of 100N / mm 2 Above, 0.2% endurance is 30N / mm 2When the negative electrode current collector has a tensile strength, 0.2% endurance and / or thickness within the above ranges, it helps to further improve the high-temperature cycle capacity retention rate of the lithium-ion battery and further reduce the high-temperature cycle expansion rate and overcharge deformation rate of the lithium-ion battery.

[0326] Table 4 shows the effects of the reflectivity (Ra) of different negative electrode active materials and negative electrode mixture layers at a wavelength of 550nm on the high-temperature cycle capacity retention, high-temperature cycle expansion rate, overcharge deformation rate, and discharge capacity retention rate of lithium-ion batteries. Examples 4-1 to 4-6 differ from Example 1-1 only in the parameters listed in Table 4.

[0327] Table 4

[0328]

[0329]

[0330] The results show that using different negative electrode active materials to make the reflectivity Ra of the negative electrode mixture layer at a wavelength of 550nm be 7% to 15% can further improve the high-temperature cycle capacity retention rate of the lithium-ion battery and further reduce the high-temperature cycle expansion rate and overcharge deformation rate of the lithium-ion battery, while significantly improving the discharge capacity retention rate of the lithium-ion battery.

[0331] Table 5 shows the effects of electrolyte composition on the high-temperature cycle capacity retention, high-temperature cycle expansion rate, and overcharge deformation rate of lithium-ion batteries. The only difference between Examples 5-1 to 5-31 and Example 1-1 is the parameters listed in Table 5.

[0332] Table 5

[0333]

[0334]

[0335] “ / ” means that the feature is not added or does not exist

[0336] The results show that, on the basis of the negative electrode current collector of the lithium-ion battery containing tin and the electrolyte including a compound containing a sulfur-oxygen double bond, when the electrolyte further contains propionate, an organic compound with a cyano group, lithium difluorophosphate and / or a compound of formula 3, the high-temperature cycle capacity retention rate of the lithium-ion battery can be further significantly improved and the high-temperature cycle expansion rate and overcharge deformation rate of the lithium-ion battery can be further significantly reduced.

[0337] Table 6 shows the effects of the sulfur-oxygen double bond compound content (b%) in the electrolyte and its relationship to the tin content (a%) in the negative electrode current collector on the high-temperature cycling capacity retention, high-temperature cycling expansion ratio, and overcharge deformation ratio of lithium-ion batteries. Examples 6-1 to 6-7 differ from Example 1-1 only in the parameters listed in Table 6.

[0338] Table 6

[0339]

[0340] The results show that when the content of sulfur-oxygen double bond compounds in the electrolyte is between 0.01% and 10%, it helps to further improve the high-temperature cycle capacity retention rate of lithium-ion batteries and reduce the high-temperature cycle expansion rate and overcharge deformation rate of lithium-ion batteries.

[0341] When b and a further satisfy 1≤b / a≤100, it is particularly beneficial to improve the high-temperature cycle capacity retention rate of the lithium-ion battery and reduce the high-temperature cycle expansion rate and overcharge deformation rate of the lithium-ion battery.

[0342] Table 7 shows the reaction area dm between the content b% of sulfur-oxygen double bond compound in electrolyte and the negative electrode mixture layer 2 The relationship between the high temperature cycle capacity retention rate, high temperature cycle expansion rate and overcharge deformation rate of lithium-ion batteries is shown in Table 7. The only difference between Examples 7-1 to 7-5 and Example 1-1 is the parameters listed in Table 7.

[0343] Table 7

[0344]

[0345] The results show that when the content of sulfur-oxygen double bond compound in electrolyte is b%, the reaction area of ​​negative electrode mixture layer is dm 2 When 0.5≤d / b≤30 is met, it helps to further improve the high-temperature cycle capacity retention rate of the lithium-ion battery and reduce the high-temperature cycle expansion rate and overcharge deformation rate of the lithium-ion battery.

[0346] References throughout this specification to "an embodiment," "part of an embodiment," "one embodiment," "another example," "an example," "a specific example," or "a portion of an example" mean that at least one embodiment or example in this application includes the specific features, structures, materials, or characteristics described in that embodiment or example. Therefore, descriptions appearing throughout this specification, such as, "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in an example," "in a specific example," or "an example," are not necessarily references to the same embodiment or example in this application. In addition, the specific features, structures, materials, or characteristics described herein may be combined in any suitable manner in one or more embodiments or examples.

[0347] Although illustrative embodiments have been shown and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the present application, and that changes, substitutions, and modifications may be made to the embodiments without departing from the spirit, principles, and scope of the present application.

Claims

1. An electrochemical device comprising: A positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode includes a negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector, wherein the negative electrode current collector contains tin, and the electrolyte includes a compound containing a sulfur-oxygen double bond, wherein the weight per unit area La of the negative electrode mixture layer is 4.5 mg / cm 2 Up to 12.5 mg / cm 2 Based on the weight of the electrolyte, the content of the compound containing sulfur-oxygen double bonds is b%, b is in the range of 0.01 to 10, and the reaction area of ​​the negative electrode mixture layer is dm 2 The content b% of the compound containing sulfur-oxygen double bonds satisfies the following relationship: 0.5≤d / b≤30, and the reaction area of ​​the negative electrode mixture layer is equal to the specific surface area of ​​the negative electrode mixture layer multiplied by the weight of the negative electrode mixture layer. 2 . The electrochemical device according to claim 1 , wherein the negative electrode current collector comprises copper. 3 . The electrochemical device according to claim 1 , wherein the content of tin is a %, based on the weight of the negative electrode current collector, and a is in the range of 0.01 to 0.

2. The electrochemical device according to claim 3 , wherein a is in the range of 0.01 to 0.

1. 5 . The electrochemical device according to claim 1 , wherein the negative electrode current collector further comprises silver, and the content of the silver is 0.01% to 0.2% based on the weight of the negative electrode current collector. The electrochemical device according to claim 5 , wherein the content of silver is 0.01% to 0.1%.

7. The electrochemical device according to claim 1, wherein the negative electrode current collector has at least one of the following characteristics: 1) Average surface roughness of 0.05 μm to 1.5 μm; 2) 0.2% endurance is 30N / mm 2 above; 3) The thickness is 1 μm to 100 μm.

8. The electrochemical device according to claim 7, wherein the negative electrode current collector has a 0.2% resistance of 50 N / mm 2 above. 9 . The electrochemical device according to claim 7 , wherein the thickness of the negative electrode current collector is 5 μm to 50 μm.

10. The electrochemical device according to claim 1, wherein the negative electrode mixture layer has at least one of the following characteristics: a) a reflectivity Ra at a wavelength of 550 nm of 7% to 15%; b) Density da is 1.3 g / cm 3 to 1.9g / cm 3 ; c) The porosity Pa is 20% to 40%. 11 . The electrochemical device according to claim 10 , wherein the negative electrode mixture layer has a reflectivity Ra of 7.5% to 15% at a wavelength of 550 nm. 12 . The electrochemical device according to claim 1 , wherein the compound containing a sulfur-oxygen double bond comprises at least one of the following compounds: cyclic sulfate, chain sulfate, chain sulfonate, cyclic sulfonate, chain sulfite, or cyclic sulfite.

13. The electrochemical device according to claim 1, wherein the compound containing a sulfur-oxygen double bond comprises a compound of Formula 1: ; in: W is selected from ; L is each independently selected from a single bond or a methylene group; m is 1, 2, 3 or 4; n is 0, 1 or 2; and p is 0, 1, 2, 3, 4, 5 or 6.

14. The electrochemical device according to claim 13, wherein the compound of Formula 1 comprises at least one of the following: 。 The electrochemical device according to claim 1 , wherein b is in the range of 0.1 to 10.

16. The electrochemical device of claim 1 , wherein the electrolyte further comprises a propionate ester, and the propionate ester comprises a compound of Formula 2: ； in: R 1 Selected from ethyl or halogenated ethyl, R 2 is selected from C1-C6 alkyl or C1-C6 haloalkyl; and The content of the propionate is in a range of 10% to 60% based on the weight of the electrolyte. 17 . The electrochemical device according to claim 16 , wherein the content of the propionate ester is in the range of 20% to 60% based on the weight of the electrolyte.

18. The electrochemical device according to claim 3, wherein the content of the compound containing a sulfur-oxygen double bond is b% based on the weight of the electrolyte, b is in the range of 0.01 to 10, and 1≤b / a≤100. The electrochemical device according to claim 18 , wherein 30≤b / a≤100.

20. The electrochemical device according to claim 1, wherein 0.5≤d / b≤5.

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

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