CN117059876A

CN117059876A - Electrochemical device and electronic device comprising same

Info

Publication number: CN117059876A
Application number: CN202310989497.3A
Authority: CN
Inventors: 王可飞; 戴振; 王莹莹; 周丰
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2019-12-25
Filing date: 2019-12-25
Publication date: 2023-11-14
Also published as: CN111129594B; CN111129594A

Abstract

The present application relates to an electrochemical device and an electronic device including the same. Specifically, 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 active material layer, wherein the negative electrode active material layer has a contact angle of not more than 60 ° with respect to a nonaqueous solvent as measured by a contact angle measurement method. The electrochemical device of the present application has improved cycle performance.

Description

Electrochemical device and electronic device comprising same

The present application is a divisional application of application having an application date of 2019, 12, 25, application number 201911360667.1 and an application name of "electrochemical device and electronic device including the same".

Technical Field

The present application relates to the field of energy storage, and in particular, to an electrochemical device and an electronic device including the same, and particularly, to a lithium ion battery.

Background

As technology advances and demand for mobile devices increases, demand for electrochemical devices (e.g., lithium ion batteries) increases significantly. Lithium ion batteries having both high energy density and excellent life and cycle characteristics are one of the research directions.

The theoretical capacity of a lithium ion battery may vary with the kind of the anode active material. As the cycle proceeds, the lithium ion battery generally generates a phenomenon in which the charge/discharge capacity is reduced, degrading the performance of the lithium ion battery. In recent years, in the production of lithium ion batteries, an aqueous slurry composition using an aqueous medium as a dispersion medium has been attracting attention in order to reduce environmental load and the like, but the aqueous slurry has a problem that defects such as pinholes and pits are generated in an active material layer due to the presence of bubbles in the slurry composition, thereby affecting the cycle performance of an electrochemical device.

In view of the foregoing, it is desirable to provide an improved electrochemical device having excellent cycle performance and an electronic device including the same.

Disclosure of Invention

Embodiments of the present application solve at least one problem existing in the related art to at least some extent by providing an electrochemical device and an electronic device including the same.

In one aspect of the present application, there is provided an electrochemical device comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode comprises a negative electrode active material layer, wherein the negative electrode active material layer has a contact angle with respect to a nonaqueous solvent of not more than 60 ° as measured by a contact angle measurement method; the porosity of the anode active material layer is 10% to 60%; the electrolyte further contains difluorophosphate and an iron group element including cobalt element, nickel element, or a combination thereof, and the content of the iron group element is not more than 0.05wt% based on the total weight of the electrolyte.

According to some embodiments of the application, the non-aqueous solvent has a droplet diameter on the anode active material layer of no more than 30mm as measured by contact angle measurement.

According to some embodiments of the application, the contact angle measurement method refers to measuring the contact angle of a droplet of 3 microliters of diethyl carbonate on the surface of the negative electrode active material layer within 100 seconds after the droplet is dropped on the surface of the negative electrode active material layer.

According to some embodiments of the application, the anode active material layer comprises a carbon material having at least one of the following characteristics:

(a) Less than 5m ² Specific surface area/g;

(b) Median particle size of 5 μm to 30 μm.

According to some embodiments of the application, the negative electrode active material layer includes at least one of artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, hard carbon, amorphous carbon, silicon-containing material, tin-containing material, alloy material.

According to some embodiments of the application, the anode active material layer further includes at least one metal of molybdenum, iron, and copper, and the content of the at least one metal is not more than 0.05wt% based on the total weight of the anode active material layer.

According to some embodiments of the application, the anode active material layer further comprises an auxiliary agent having at least one of the following features:

(a) An oxidation potential of not less than 4.5V and a reduction potential of not more than 0.5V;

(b) A surface tension of not more than 30mN/m;

(c) Including nonionic surfactants;

(d) The content of the auxiliary agent is not more than 3000ppm based on the total weight of the anode active material layer.

According to some embodiments of the application, the adjuvant comprises a nonionic surfactant comprising at least one of a polyoxyethylene ether, a polyol ester, an amide, or a block polyether.

According to some embodiments of the application, the nonionic surfactant comprises at least one of: polyoxyethylene alkyl alcohol amide, octyl phenol polyoxyethylene ether, nonylphenol polyoxyethylene ether, higher fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ester, polyoxyethylene amine, alkyl alcohol amide, lauryl alcohol polyoxyethylene ether, 12-14 carbon primary alcohol polyoxyethylene ether, 12-14 carbon secondary alcohol polyoxyethylene ether, branched 13 carbon guerbet alcohol polyoxyethylene ether, branched 10 carbon guerbet alcohol polyoxyethylene, linear 10 carbon alcohol polyoxyethylene ether, linear 8 carbon octanol polyoxyethylene ether, linear 8 carbon isooctyl alcohol polyoxyethylene ether, fatty acid monoglyceride, glyceryl monostearate, fatty acid sorbitan, composite silicone polyether complex, polysorbate, polyoxyethylene fatty acid ester, polyoxyethylene fatty alcohol ether, polyoxyethylene polyoxypropylene block copolymer, polyether modified trisiloxane or polyether modified silicone polyether siloxane.

According to some embodiments of the present application, the electrolytic solution contains ethylene carbonate in an amount of X mg in the electrolytic solution with a reaction area Y m of the anode active material layer ² The following relationship is satisfied: X/Y is more than or equal to 10 and less than or equal to 100.

According to some embodiments of the application, the electrolyte further comprises a compound of formula 1:

wherein R is a linear or non-linear alkyl radical having 1 to 5 carbon atoms or-SiR ₂ R ₃ R ₄ Wherein R is ₂ 、R ₃ And R is ₄ Each independently is an alkyl group having 1 to 5 carbon atoms, and

R ₁ is an alkylene group having 2 to 3 carbon atoms and substituted with a substituent selected from the group consisting of: at least one fluorine atom or an alkyl group containing at least one fluorine atom and having 1 to 3 carbon atoms.

According to some embodiments of the application, in formula 1, R is-SiR ₂ R ₃ R ₄ And R is ₁ Is an alkylene group having 2 carbon atoms and substituted with a substituent selected from the group consisting of: at least one fluorine atom or an alkyl group containing at least one fluorine atom and having 1 to 3 carbon atoms.

According to some embodiments of the application, the compound of formula 1 comprises at least one of the compounds represented by formulas 1a to 1 h:

according to some embodiments of the application, the compound of formula 1 is present in an amount of 0.001wt% to 10wt% based on the total weight of the electrolyte.

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

Additional aspects and advantages of embodiments of the application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of embodiments of the application.

Detailed Description

Embodiments of the present application will be described in detail below. The embodiments of the present application should not be construed as limiting the application.

The following terms used herein have the meanings indicated below, unless explicitly indicated otherwise.

In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items a and B are listed, the phrase "at least one of a and B" means only a; only B; or A and B. In another example, if items A, B and C are listed, then 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 A, B and C. Item a may comprise a single element or multiple elements. Item B may comprise a single element or multiple elements. Item C may comprise a single element or multiple elements.

The term "alkyl" is intended to be a straight chain saturated hydrocarbon structure having from 1 to 20 carbon atoms. "alkyl" is also intended to be a branched or cyclic hydrocarbon structure having 3 to 20 carbon atoms. When alkyl groups having a specific carbon number are specified, all geometric isomers having that carbon number are contemplated; thus, for example, reference to "butyl" is intended to include n-butyl, sec-butyl, isobutyl, tert-butyl and cyclobutyl; "propyl" includes n-propyl, isopropyl and cyclopropyl. Examples of alkyl groups 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, and the like.

The term "alkylene" means a divalent saturated hydrocarbon group that may be straight or branched. Unless otherwise defined, the alkylene groups typically contain 2 to 10 carbon atoms and include, for example, -C _2-3 Alkylene and-C _2-6 Alkylene-. Representative alkylene groups include, for example, methylene, ethane-1, 2-diyl ("ethylene"), propane-1, 2-diyl, propane-1, 3-diyl, butane-1, 4-diyl, pentane-1, 5-diyl, and the like.

The theoretical capacity of an electrochemical device (e.g., a lithium ion battery) may vary with the kind of the anode active material. As the cycle proceeds, the electrochemical device generally generates a phenomenon in which the charge/discharge capacity is reduced. This is because the electrode interface of the electrochemical device is changed during charge and/or discharge, so that the electrode active material cannot function.

The application ensures the interface stability of the electrochemical device in the circulation process by using the specific anode material, thereby improving the circulation performance of the electrochemical device. The specific negative electrode material of the present application is realized by controlling the contact angle of the surface of the negative electrode active material layer, and as a control method of the contact angle, the addition of an auxiliary agent to the negative electrode slurry or the provision of an auxiliary agent coating layer on the surface of the negative electrode active material layer can be controlled.

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

I. Negative electrode

The anode includes an anode current collector and anode active material layers disposed on one or both surfaces of the anode current collector.

1. Negative electrode active material layer

The anode active material layer contains an anode active material. The anode active material layer may be one or more layers, and each of the multiple layers of anode active material may contain the same or different anode active material. The negative electrode active material is any material capable of reversibly intercalating and deintercalating metal ions such as lithium ions. In some embodiments, the chargeable capacity of the negative electrode active material is greater than the discharge capacity of the positive electrode active material to prevent the inadvertent precipitation of lithium metal on the negative electrode during charging.

(1) Contact angle

One feature of the electrochemical device of the present application is that the contact angle of the anode active material layer with respect to the nonaqueous solvent is not more than 60 ° as measured by contact angle measurement. In some embodiments, the negative electrode active material layer has a contact angle of no greater than 50 ° with respect to a nonaqueous solvent as determined by contact angle measurement. In some embodiments, the negative electrode active material layer has a contact angle of no greater than 30 ° with respect to a nonaqueous solvent as determined by contact angle measurement. When the anode active material layer has the contact angle as described above with respect to the nonaqueous solvent, the anode active material layer interface has less defects, and has good stability in charge and discharge cycles of the electrochemical device, and can ensure cycle performance of the electrochemical device.

The contact angle of the anode active material layer with respect to the nonaqueous solvent may reflect the surface property of the anode active material layer, which is one of the physicochemical parameters characterizing the anode active material layer. The smaller the contact angle, the smoother the surface of the negative electrode active material layer, and the fewer pinholes or pit defects, which can significantly improve the cycle performance of the electrochemical device. The contact angle of the anode active material layer with respect to the nonaqueous solvent may be affected by various factors, mainly including an auxiliary agent, the porosity of the anode active material layer, and the like.

According to some embodiments of the application, the non-aqueous solvent has a droplet diameter on the anode active material layer of no more than 30mm as measured by contact angle measurement. In some embodiments, the non-aqueous solvent has a droplet diameter on the anode active material layer of no greater than 20mm as determined by contact angle measurement. In some embodiments, the non-aqueous solvent has a droplet diameter on the anode active material layer of no greater than 15mm as determined by contact angle measurement. In some embodiments, the non-aqueous solvent has a droplet diameter on the anode active material layer of no greater than 10mm as determined by contact angle measurement. When the anode active material layer has the above contact angle with respect to the nonaqueous solvent and the nonaqueous solvent has the above droplet diameter at the same time, the cycle performance of the electrochemical device is further improved.

The contact angle of the anode active material layer with respect to the nonaqueous solvent and the diameter of the nonaqueous solvent droplet can be measured by the following method: 3 microliters of diethyl carbonate is dripped on the surface of the negative electrode active material layer, the diameter of a liquid drop is tested by using a JC2000D3E contact angle measuring instrument within 100 seconds, and a 5-point fitting method (namely, firstly taking 2 points on the left plane and the right plane of the liquid drop, determining a liquid-solid interface, and then taking 3 points on the circular arc of the liquid drop) is selected for fitting, so that the contact angle of the negative electrode active material layer relative to a nonaqueous solvent is obtained. Each sample is measured at least 3 times, at least 3 data with the difference less than 5 degrees are selected, and the average value is taken to obtain the contact angle of the negative electrode active material layer relative to the nonaqueous solvent.

The nonaqueous solvent used in the contact angle test can be selected from common electrolyte solvents such as diethyl carbonate, methylethyl carbonate, dimethyl carbonate, methylpropyl carbonate or methyl isopropyl carbonate.

(2) Porosity of the porous material

According to some embodiments of the application, the anode active material layer has a porosity of 10% to 60%. In some embodiments, the porosity of the anode active material layer is 15% to 50%. In some embodiments, the porosity of the anode active material layer is 20% to 40%. In some embodiments, the porosity of the anode active material layer is 25% to 30%. In some embodiments, the porosity of the anode active material layer is 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60% or within a range consisting of any two of the above values.

The porosity of the anode active material layer can be measured by the following method: the test was performed using a true density tester AccuPyc II 1340, with at least 3 measurements per sample, and at least 3 data were averaged. The porosity of the anode active material layer was calculated according to the following formula: porosity= (V1-V2)/v1×100%, where V1 is the apparent volume v1=sample surface area×sample thickness×sample number; v2 is the true volume.

(3) Carbon material

According to some embodiments of the application, the negative electrode active material layer comprises a carbon material.

According to some embodiments of the application, the negative electrode active material layer includes at least one of artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, hard carbon, and amorphous carbon.

According to some embodiments of the application, the carbonaceous material has amorphous carbon on its surface.

According to some embodiments of the application, the shape of the carbonaceous material includes, but is not limited to, fibrous, spherical, granular, and scaly.

According to some embodiments of the application, the carbon material has at least one of the following features:

(a) Less than 5m ² Specific surface area per gram (BET); and

(b) Median particle diameter (D50) of 5 μm to 30 μm.

Specific surface area (BET)

In some embodiments, the carbon material has a thickness of less than 5m ² Specific surface area per gram. In some embodiments, the carbon material has a thickness of less than 3m ² Specific surface area per gram. In some embodiments, the carbon materialHaving a diameter of less than 1m ² Specific surface area per gram. In some embodiments, the carbon material has a thickness of greater than 0.1m ² Specific surface area per gram. In some embodiments, the carbon material has a thickness of less than 0.7m ² Specific surface area per gram. In some embodiments, the carbon material has a thickness of less than 0.5m ² Specific surface area per gram. In some embodiments, the specific surface area of the carbon material is within a range consisting of any two of the values recited above. When the specific surface area of the carbon material is within the above range, precipitation of lithium on the electrode surface can be suppressed, and gas generation caused by reaction of the anode with the electrolyte can be suppressed.

The specific surface area of the anode active material layer can be measured by the following method: the sample was pre-dried at 350℃for 15 minutes using a surface area meter (fully automatic surface area measuring apparatus manufactured by Dagaku Kogyo Co., ltd.) under a nitrogen flow, and then measured by a nitrogen adsorption BET single point method using a nitrogen-helium mixed gas in which the relative pressure value of nitrogen to the atmospheric pressure was accurately adjusted to 0.3.

Median particle diameter (D50)

The median particle diameter (D50) of the carbon material refers to a volume-based average particle diameter obtained by a laser diffraction/scattering method. In some embodiments, the carbon material has a median particle diameter (D50) of 5 μm to 30 μm. In some embodiments, the carbon material has a median particle diameter (D50) of 10 μm to 25 μm. In some embodiments, the carbon material has a median particle diameter (D50) of 15 μm to 20 μm. In some embodiments, the carbon material has a median particle diameter (D50) of 1 μm, 3 μm, 5 μm, 7 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, or in a range of any two values above. When the median particle diameter of the carbon material is within the above range, the irreversible capacity of the electrochemical device is small, and it is easy to uniformly coat the anode.

The median particle diameter (D50) of the carbon material can be determined by the following method: the carbon material was dispersed in a 0.2wt% aqueous solution (10 mL) of polyoxyethylene (20) sorbitan monolaurate, and tested by a laser diffraction/scattering particle size distribution meter (LA-700 manufactured by horiba, ltd.).

X-ray diffraction pattern parameters

According to some embodiments of the application, the interlayer distance of the lattice plane (002 plane) of the carbon material is in the range of 0.335nm to 0.360nm, in the range of 0.335nm to 0.350nm, or in the range of 0.335nm to 0.345nm based on an X-ray diffraction pattern of a vibrometry.

According to some embodiments of the application, the crystallite size (Lc) of the carbon material is greater than 1.0nm or greater than 1.5nm based on an X-ray diffraction pattern of a vibrometry.

Raman spectral parameters

In some embodiments, the carbon material has a raman R value of greater than 0.01, greater than 0.03, or greater than 0.1. In some embodiments, the carbon material has a raman R value of less than 1.5, less than 1.2, less than 1.0, or less than 0.5. In some embodiments, the carbon material has a raman R value within a range consisting of any two of the values recited above.

The carbon material is 1580cm ^-1 The nearby raman half-peak width is not particularly limited. In some embodiments, the carbon material is at 1580cm ^-1 The Raman half-peak width is larger than 10cm ^-1 Or greater than 15cm ^-1 . In some embodiments, the carbon material is at 1580cm ^-1 The Raman half-peak width in the vicinity is less than 100cm ^-1 Less than 80cm ^-1 Less than 60cm ^-1 Or less than 40cm ^-1 . In some embodiments, the carbon material is at 1580cm ^-1 The raman half-peak width in the vicinity is within the range consisting of any two values described above.

The raman R value and the raman half-peak width are indices indicating crystallinity of the surface of the carbon material. The moderate crystallinity can keep the interlayer sites of the carbon material for containing lithium in the charge and discharge process, and the interlayer sites cannot disappear, thereby being beneficial to the chemical stability of the carbon material.

When the raman R value and/or the raman half-width are within the above-described ranges, the carbon material can form an appropriate coating film on the surface of the negative electrode, which contributes to improvement of storage characteristics, cycle characteristics, load characteristics, and the like of the electrochemical device, and can suppress efficiency degradation and gas generation due to reaction of the carbon material with the electrolyte.

The raman R value or raman half-peak width can be determined by argon ion laser raman spectroscopy: the sample was naturally dropped and filled in a measuring cell using a raman spectrometer (manufactured by japan spectroscopy), and the cell was rotated in a plane perpendicular to the laser beam while irradiating the sample surface in the cell with an argon ion laser beam. For the obtained Raman spectrum, the measurement was performed at 1580cm ^-1 Intensity IA of the nearby peak PA and at 1360cm ^-1 The intensity IB of the nearby peak PB was calculated as the intensity ratio R (r=ib/IA).

The measurement conditions of the raman spectroscopy are as follows:

argon ion laser wavelength: 514.5nm

Laser power on sample: 15-25mW

Resolution: 10-20cm ^-1

Measurement range: 1100cm ^-1 -1730cm ^-1

Raman R value, raman half-peak width analysis: background processing

Smoothing processing: simple average, convolution 5 points

Roundness of

The definition of "roundness" is as follows: roundness= (circumference of equivalent circle having the same area as the particle projected shape)/(actual circumference of particle projected shape). When the roundness is 1.0, the spherical ball is a theoretical positive sphere.

In some embodiments, the carbon material has a particle size of 3 μm to 40 μm and a roundness of greater than 0.1, greater than 0.5, greater than 0.8, greater than 0.85, greater than 0.9, or 1.0.

The greater the roundness of the carbon material, the higher the filling property, which helps to suppress the inter-particle resistance for the high current density charge-discharge characteristics, thereby improving the charge-discharge characteristics of the electrochemical device at high current density.

The roundness of the carbon material can be measured using a flow type particle image analyzer (FPIA manufactured by Sysmex corporation): after dispersing 0.2g of the sample in a 0.2wt% aqueous solution (50 mL) of polyoxyethylene (20) sorbitan monolaurate and irradiating with ultrasonic waves at an output of 60W for 1 minute at 28kHz, particles having a particle diameter ranging from 3 μm to 40 μm were measured in a prescribed detection range of 0.6 μm to 400 μm.

The method of improving the roundness is not particularly limited. The spheroidization treatment may be employed so that the shape of voids between carbon material particles is uniform when the electrode is prepared. The spheroidization treatment may be performed by mechanical means such as application of a shearing force or a compressive force, or by mechanical/physical means such as granulation of a plurality of fine particles by application of a binder or by adhesion force of the particles themselves, so that the carbon material particles are made nearly spherical.

Tap density

In some embodiments, the carbon material has a tap density of greater than 0.1g/cm ³ Greater than 0.5g/cm ³ Greater than 0.7g/cm ³ Or greater than 1g/cm ³ . In some embodiments, the carbon material has a tap density of less than 2g/cm ³ Less than 1.8g/cm ³ Or less than 1.6g/cm ³ . In some embodiments, the carbon material has a tap density within a range consisting of any two of the values recited above. When the tap density of the carbon material is within the above range, the capacity of the electrochemical device can be ensured while the increase in resistance between the carbon material particles can be suppressed.

The tap density of the carbon material can be tested by the following method: the sample was passed through a 300 μm sieve and dropped into 20cm ³ After the sample is filled up to the upper end surface of the tank, the tank is vibrated 1000 times with a stroke length of 10mm by a powder density measuring instrument (for example, tap sensor manufactured by Seishin corporation), and the Tap density is calculated from the mass at that time and the mass of the sample.

Orientation ratio

In some embodiments, the orientation ratio of the carbon material is greater than 0.005, greater than 0.01, or greater than 0.015. In some embodiments, the orientation ratio of the carbon material is less than 0.67. In some embodiments, the carbon material has an orientation ratio within a range consisting of any two of the values recited above. When the orientation ratio of the carbon material is within the above range, the electrochemical device can be made to have excellent high-density charge-discharge characteristics.

The orientation ratio of the carbon material can be measured by X-ray diffraction after compression molding the sample: a molding machine having a diameter of 17mm was charged with 0.47g of a sample, and the sample was fed to a molding machine having a diameter of 58.8 MN.m ^-2 The resultant molded body was compressed and fixed with clay, and the molded body was set to the same surface as the surface of the measurement sample holder, whereby X-ray diffraction measurement was performed. The ratio of the (110) diffraction peak intensity/(004) diffraction peak intensity was calculated from the (110) diffraction and (004) diffraction peak intensities of the obtained carbon.

The X-ray diffraction measurement conditions were as follows:

target material: cu (K alpha ray) graphite monochromator

Slit: divergent slit = 0.5 degrees; light receiving slit = 0.15mm; scattering slit = 0.5 degrees

Measurement range and step angle/measurement time ("2θ" indicates diffraction angle):

(110) And (3) surface: 2 theta is 75 degrees or less and 80 degrees or less and 1 degree/60 seconds or less

(004) And (3) surface: 2 theta less than or equal to 52 degrees less than or equal to 57 degrees 1 degree/60 seconds

Length to thickness ratio

In some embodiments, the carbon material has a length to thickness ratio of greater than 1, greater than 2, or greater than 3. In some embodiments, the carbon material has a length to thickness ratio of less than 10, less than 8, or less than 5. In some embodiments, the carbon material has a length to thickness ratio within a range consisting of any two of the values recited above.

When the long-thick ratio of the carbon material is within the above range, more uniform coating can be performed, and thus the electrochemical device can be provided with excellent high-current density charge-discharge characteristics.

(4) Microelements

According to some embodiments of the application, the anode active material layer further includes at least one metal of molybdenum, iron, and copper. These metal elements can react with some organic matters having poor conductivity in the anode active material, thereby facilitating the film formation on the surface of the anode active material.

According to some embodiments of the present application, the above-mentioned metal element is present in the anode active material layer in a minute amount, and an excessive metal element is liable to form a non-conductive by-product and adhere to the surface of the anode. In some embodiments, the at least one metal is present in an amount of no greater than 0.05wt%, based on the total weight of the anode active material layer. In some embodiments, the at least one metal is present in an amount of no greater than 0.03wt%. In some embodiments, the at least one metal is present in an amount of no greater than 0.01wt%.

(5) Auxiliary agent

According to some embodiments of the application, the negative electrode active material layer further includes an auxiliary agent.

According to some embodiments of the application, the adjuvant has at least one of the following features:

(b) A surface tension of not more than 30mN/m;

(c) Including nonionic surfactants;

Oxidation/reduction potential

In some embodiments, the adjuvant has an oxidation potential of no less than 4.5V and a reduction potential of no greater than 0.5V. In some embodiments, the adjuvant has an oxidation potential of no less than 5V and a reduction potential of no greater than 0.3V. The auxiliary agent having the above oxidation/reduction potential has stable electrochemical properties and contributes to improvement of the cycle performance of the electrochemical device.

Surface tension

In some embodiments, the adjuvant has a surface tension of no greater than 30mN/m. In some embodiments, the adjuvant has a surface tension of no greater than 25mN/m. In some embodiments, the adjuvant has a surface tension of no greater than 20mN/m. In some embodiments, the adjuvant has a surface tension of no greater than 15mN/m. In some embodiments, the adjuvant has a surface tension of no greater than 10mN/m. The surface tension of the adjuvant is measured under the condition of 1% solid content of aqueous adjuvant solution. The auxiliary agent having the surface tension as described above allows the anode active material layer to have a good interface, contributing to improvement of the cycle performance of the electrochemical device.

The surface tension of the auxiliary agent can be determined by the following method: and testing the aqueous solution of the auxiliary agent with the solid content of 1% by using a JC2000D3E contact angle measuring instrument, testing each sample at least 3 times, selecting at least 3 data, and taking an average value to obtain the surface tension of the auxiliary agent.

Nonionic surfactant

In some embodiments, the adjuvant comprises a nonionic surfactant, and the nonionic surfactant comprises at least one of a polyoxyethylene ether, a polyol ester, an amide, or a block polyether.

In some embodiments, the nonionic surfactant comprises at least one of: polyoxyethylene alkyl alcohol amide, octyl phenol polyoxyethylene ether, nonylphenol polyoxyethylene ether, higher fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ester, polyoxyethylene amine, alkyl alcohol amide, lauryl alcohol polyoxyethylene ether, 12-14 carbon primary alcohol polyoxyethylene ether, 12-14 carbon secondary alcohol polyoxyethylene ether, branched 13 carbon guerbet alcohol polyoxyethylene ether, branched 10 carbon guerbet alcohol polyoxyethylene, linear 10 carbon alcohol polyoxyethylene ether, linear 8 carbon octanol polyoxyethylene ether, linear 8 carbon isooctyl alcohol polyoxyethylene ether, fatty acid monoglyceride, glyceryl monostearate, fatty acid sorbitan, composite silicone polyether complex, polysorbate, polyoxyethylene fatty acid ester, polyoxyethylene fatty alcohol ether, polyoxyethylene polyoxypropylene block copolymer, polyether modified trisiloxane or polyether modified silicone polyether siloxane.

Content of auxiliary agent

In some embodiments, the adjuvant is present in an amount of no greater than 2500ppm based on the total weight of the anode active material layer. In some embodiments, the adjuvant is present in an amount of no greater than 2000ppm based on the total weight of the negative electrode active material layer. In some embodiments, the adjuvant is present in an amount of no greater than 1500ppm based on the total weight of the negative electrode active material layer. In some embodiments, the auxiliary agent is contained in an amount of not more than 1000ppm based on the total weight of the anode active material layer. In some embodiments, the adjuvant is present in an amount of no greater than 500ppm based on the total weight of the negative electrode active material layer. In some embodiments, the adjuvant is present in an amount of no greater than 200ppm based on the total weight of the negative electrode active material layer. The auxiliary agent having the above content contributes to improvement of the following characteristics of the electrochemical device: output power characteristics, load characteristics, low temperature characteristics, cycle characteristics, high temperature storage characteristics, and the like.

(6) Other components

Material containing silicon and/or tin elements

According to some embodiments of the application, the negative electrode active material layer further includes at least one of a silicon-containing material, a tin-containing material, and an alloy material. According to some embodiments of the application, the anode active material layer further includes at least one of a silicon-containing material and a tin-containing material. In some embodiments, the negative electrode active material layer further includes one or more of a silicon-containing material, a silicon-carbon composite material, a silicon oxygen material, an alloy material, and a lithium-containing metal composite oxide material. In some embodiments, the anode active material layer further comprises other types of anode active materials, for example, one or more materials comprising a metal element capable of forming an alloy with lithium and a metalloid element. In some embodiments, examples of the metallic element and the metalloid element include, but are not limited to, mg, B, al, ga, in, si, ge, sn, pb, bi, cd, ag, zn, hf, zr, Y, pd and Pt. In some embodiments, examples of the metallic element and metalloid element include Si, sn, or a combination thereof. Si and Sn have excellent capability of extracting lithium ions, and can provide high energy density for lithium ion batteries. In some embodiments, other kinds of anode active materials may further include one or more of metal oxides and high molecular compounds. In some embodiments, the metal oxide includes, but is not limited to, iron oxide, ruthenium oxide, and molybdenum oxide. In some embodiments, the polymeric compounds include, but are not limited to, polyacetylenes, polyanilines, and polypyrroles.

Negative electrode conductive material

In some embodiments, the anode active material layer further comprises an anode conductive material, which may include any conductive material as long as it does not cause a chemical change. Non-limiting examples of conductive materials include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

Negative electrode binder

In some embodiments, the anode active material layer further includes an anode binder. The anode binder can improve the bonding of anode active material particles to each other and the bonding of anode active material to the current collector. The type of the negative electrode binder is not particularly limited as long as it is a material stable to the electrolyte or the solvent used in the electrode production.

Examples of the negative electrode binder include, but are not limited to, resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, aromatic polyamide, polyimide, cellulose, and nitrocellulose; rubbery polymers such as Styrene Butadiene Rubber (SBR), isoprene rubber, butadiene rubber, fluororubber, acrylonitrile-butadiene rubber (NBR), and ethylene-propylene rubber; styrene-butadiene-styrene block copolymers or hydrides thereof; thermoplastic elastomer-like polymers such as ethylene-propylene-diene terpolymers (EPDM), styrene-ethylene-butadiene-styrene copolymers, styrene-isoprene-styrene block copolymers, and hydrogenated products thereof; soft resinous 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; and polymer compositions having ion conductivity of alkali metal ions (e.g., lithium ions). The negative electrode binder may be used alone or in any combination.

In some embodiments, the negative electrode binder is present in an amount greater than 0.1wt%, greater than 0.5wt%, or greater than 0.6wt%, based on the total weight of the negative electrode active material layer. In some embodiments, the negative electrode binder is present in an amount of less than 20wt%, less than 15wt%, less than 10wt%, or less than 8wt%, based on the total weight of the negative electrode active material layer. In some embodiments, the negative electrode binder is present in an amount within the range consisting of any two of the values recited above. When the content of the anode binder is in the above range, the capacity of the electrochemical device and the strength of the anode can be sufficiently ensured.

In the case where the anode active material layer contains a rubbery polymer (e.g., SBR), in some embodiments, the anode binder is contained in an amount of more than 0.1wt%, more than 0.5wt%, or more than 0.6wt% based on the total weight of the anode active material layer. In some embodiments, the negative electrode binder is present in an amount of less than 5wt%, less than 3wt%, or less than 2wt%, based on the total weight of the negative electrode active material layer. In some embodiments, the negative electrode binder is present in an amount within the range consisting of any two values described above, based on the total weight of the negative electrode active material layer.

In the case where the anode active material layer contains a fluorine-based polymer (e.g., polyvinylidene fluoride), the anode binder is contained in an amount of more than 1wt%, more than 2wt%, or more than 3wt% based on the total weight of the anode active material layer in some embodiments. In some embodiments, the negative electrode binder is present in an amount of less than 15wt%, less than 10wt%, or less than 8wt%, based on the total weight of the negative electrode active material layer. The content of the anode binder is in the range consisting of any two values described above, based on the total weight of the anode active material layer.

Solvent(s)

The type of solvent used to form the anode slurry is not particularly limited as long as it is a solvent capable of dissolving or dispersing the anode active material, the anode binder, and the thickener and the conductive material, which are used as needed. In some embodiments, the solvent used to form the anode slurry may use any one of an aqueous-based solvent and an organic-based solvent. Examples of aqueous solvents may include, but are not limited to, water, alcohols, and the like. Examples of the organic-based solvent may include, but are not limited to, N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methylethylketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N-dimethylaminopropylamine, tetrahydrofuran (THF), toluene, acetone, diethyl ether, hexamethylphosphoramide, dimethylsulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene, hexane, and the like. The above solvents may be used alone or in any combination.

Thickening agent

The thickener is generally used for adjusting the viscosity of the anode slurry. The kind of the thickener is not particularly limited, and examples thereof may include, but are not limited to, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, salts thereof, and the like. The above thickeners may be used alone or in any combination.

In some embodiments, the thickener is present in an amount of greater than 0.1wt%, greater than 0.5wt%, or greater than 0.6wt%, based on the total weight of the anode active material layer. In some embodiments, the thickener is present in an amount of less than 5wt%, less than 3wt%, or less than 2wt%, based on the total weight of the anode active material layer. When the content of the thickener is not within the above range, it is possible to suppress a decrease in capacity and an increase in resistance of the electrochemical device, while ensuring good coatability of the negative electrode slurry.

Surface coating

In some embodiments, the surface of the anode active material layer may be attached with a material having a composition different from that of the anode active material layer. Examples of the surface-adhering substance of the negative electrode active material layer include, but are not limited to, oxides such as alumina, silica, titania, zirconia, magnesia, calcium oxide, boron oxide, antimony oxide, bismuth oxide, sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, aluminum sulfate, carbonates such as lithium carbonate, calcium carbonate, magnesium carbonate, and the like.

(7) Content of negative electrode active material

In some embodiments, the content of the anode active material is greater than 80wt%, greater than 82wt%, or greater than 84wt%, based on the total weight of the anode active material layer. In some embodiments, the content of the anode active material is less than 99wt% or less than 98wt% based on the total weight of the anode active material layer. In some embodiments, the content of the anode active material is within the range consisting of any two arrays described above, based on the total weight of the anode active material layer.

(8) Thickness of negative electrode active material layer

The thickness of the anode active material layer refers to the thickness of the anode active material layer on either side of the anode current collector. In some embodiments, the thickness of the anode active material layer is greater than 15 μm, greater than 20 μm, or greater than 30 μm. In some embodiments, the thickness of the anode active material layer is less than 300 μm, less than 280 μm, or less than 250 μm. In some embodiments, the thickness of the anode active material layer is in the range consisting of any two values described above.

(9) Density of negative electrode active material

In some embodiments, the density of the anode active material in the anode active material layer is greater than 1g/cm ³ Greater than 1.2g/cm ³ Or greater than 1.3g/cm ³ . In some embodiments, the density of the anode active material in the anode active material layer is less than 2.2g/cm ³ Less than 2.1g/cm ³ Less than 2.0g/cm ³ Or less than 1.9g/cm ³ . In some embodiments, the density of the anode active material in the anode active material layer is in a range consisting of any two values described above.

When the density of the anode active material is within the above range, breakage of the anode active material particles can be prevented, deterioration of high-current density charge-discharge characteristics due to an increase in initial irreversible capacity of the electrochemical device or a decrease in permeability of the electrolyte near the anode current collector/anode active material interface can be suppressed, and decrease in capacity and increase in resistance of the electrochemical device can be suppressed.

2. Negative electrode current collector

As the current collector for holding the anode active material, a known current collector can be arbitrarily used. Examples of the negative electrode current collector include, but are not limited to, metal materials such as aluminum, copper, nickel, stainless steel, nickel-plated steel, and the like. In some embodiments, the negative current collector is copper.

In the case that the negative electrode current collector is a metal material, the negative electrode current collector form may include, but is not limited to, a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, a metal expanded metal, a punched metal, a foamed metal, and the like. In some embodiments, the negative electrode current collector is a metal thin film. In some embodiments, the negative current collector is copper foil. In some embodiments, the negative electrode current collector is a rolled copper foil based on a rolling method or an electrolytic copper foil based on an electrolytic method.

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

The thickness ratio of the anode current collector to the anode active material layer refers to the ratio of the thickness of the anode active material layer on one side before the injection of the electrolyte solution to the thickness of the anode current collector, and the numerical value thereof is not particularly limited. In some embodiments, the thickness ratio of the anode current collector to the anode active material layer is less than 150, less than 20, or less than 10. In some embodiments, the thickness ratio of the anode current collector to the anode active material layer is greater than 0.1, greater than 0.4, or greater than 1. In some embodiments, the thickness ratio of the anode current collector to the anode active material layer is in the range consisting of any two values described above. When the thickness ratio of the anode current collector to the anode active material layer is in the above range, the capacity of the electrochemical device can be ensured, while heat release of the anode current collector at the time of high-current density charge and discharge can be suppressed.

II. Electrolyte solution

The electrolyte used in the electrochemical device of the present application includes an electrolyte and a solvent that dissolves the electrolyte. In some embodiments, the electrolyte used in the electrochemical device of the present application further comprises an additive.

According to some embodiments of the present application, the electrolytic solution contains ethylene carbonate in an amount of X mg in the electrolytic solution with a reaction area Y m of the anode active material layer ² The following relationship is satisfied: X/Y is more than or equal to 10 and less than or equal to 100. In some embodiments, X and Y satisfy the following relationship: 10-10% (X/Y)<100. In some embodiments, X and Y satisfy the following relationship: 20 (X/Y)<70。

According to some embodiments of the application, the compound of formula 1 is present in an amount of 0.001wt% to 10wt% based on the total weight of the electrolyte. In some embodiments, the compound of formula 1 is present in an amount of 0.005wt% to 9wt% based on the total weight of the electrolyte. In some embodiments, the compound of formula 1 is present in an amount of 0.01wt% to 8wt% based on the total weight of the electrolyte. In some embodiments, the compound of formula 1 is present in an amount of 0.05wt% to 7wt% based on the total weight of the electrolyte. In some embodiments, the compound of formula 1 is present in an amount of 0.1wt% to 6wt% based on the total weight of the electrolyte. In some embodiments, the compound of formula 1 is present in an amount of 0.5wt% to 5wt% based on the total weight of the electrolyte. In some embodiments, the compound of formula 1 is present in an amount of 1wt% to 4wt% based on the total weight of the electrolyte. In some embodiments, the compound of formula 1 is present in an amount of 2wt% to 3wt% based on the total weight of the electrolyte.

According to some embodiments of the application, the electrolyte further contains difluorophosphate and an iron group element including cobalt element, nickel element, or a combination thereof, and the content of the iron group element is not more than 0.05wt% based on the total weight of the electrolyte. In some embodiments, the iron group element is present in an amount of no greater than 0.03wt%, based on the total weight of the electrolyte. In some embodiments, the content of the iron group element is not greater than 0.02wt% based on the total weight of the electrolyte. In some embodiments, the iron group element is present in an amount of no greater than 0.01wt%, based on the total weight of the electrolyte. In some embodiments, the content of the iron group element is not greater than 0.005wt% based on the total weight of the electrolyte. In some embodiments, the content of the iron group element is not greater than 0.004wt% based on the total weight of the electrolyte. In some embodiments, the content of the iron group element is not greater than 0.002wt% based on the total weight of the electrolyte.

In some embodiments, the electrolyte further comprises any nonaqueous solvent known in the art that can be used as a solvent for the electrolyte.

In some embodiments, the nonaqueous 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.

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 to 6 carbon atoms.

In some embodiments, examples of the chain carbonate may include, but are not limited to, one or more of the following: and chain carbonates such as dimethyl carbonate, methylethyl carbonate, diethyl carbonate (DEC), methyl n-propyl carbonate, ethyl n-propyl carbonate, and di-n-propyl carbonate. 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-trifluoroethyl) carbonate, 2-fluoroethyl methyl carbonate, 2-difluoroethyl methyl carbonate, 2-trifluoroethyl methyl carbonate and the like.

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

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, ethyl pivalate, and the like. In some embodiments, a portion of the hydrogen atoms of the chain carboxylate may be substituted with fluorine. In some embodiments, examples of fluorine substituted chain carboxylates may include, but are not limited to, methyl trifluoroacetate, ethyl trifluoroacetate, propyl trifluoroacetate, butyl trifluoroacetate, 2-trifluoroethyl trifluoroacetate, and the like.

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-methyl-1, 3-dioxolane, 4-methyl-1, 3-dioxolane, 1, 3-dioxane, 1, 4-dioxane and dimethoxypropane.

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

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, methyl diethyl phosphate, ethylene methyl phosphate, ethylene ethyl phosphate, triphenyl phosphate, trimethyl phosphite, triethyl phosphite, triphenyl phosphite, tris (2, 2-trifluoroethyl) phosphate, tris (2, 3-pentafluoropropyl) phosphate, and the like.

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-methylsulfanyl sulfone, 3-methylsulfanyl sulfone, dimethyl sulfone, diethyl sulfone, ethyl methyl sulfone, methyl propyl sulfone, dimethyl sulfoxide, methyl methanesulfonate, ethyl methanesulfonate, methyl ethanesulfonate, ethyl ethanesulfonate, dimethyl sulfate, diethyl sulfate and dibutyl sulfate. In some embodiments, a portion of the hydrogen atoms of the sulfur-containing organic solvent may be replaced with fluorine.

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.

In some embodiments, the solvents used in the electrolytes of the present application include 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 at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, n-propyl acetate, or ethyl acetate. In some embodiments, the solvent used in the electrolyte of the present application comprises: ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, gamma-butyrolactone, and combinations thereof.

After the chain carboxylic acid ester and/or the cyclic carboxylic acid ester are added to the electrolyte, the chain carboxylic acid ester and/or the cyclic carboxylic acid ester can form a passivation film on the surface of the electrode, thereby improving the capacity retention rate of the electrochemical device after intermittent charge cycles. In some embodiments, the electrolyte contains 1wt% to 60wt% of a chain carboxylate, a cyclic carboxylate, and combinations thereof. In some embodiments, the electrolyte contains ethyl propionate, propyl propionate, gamma-butyrolactone, and combinations thereof in an amount of 1wt% to 60wt%, 10wt% to 50wt%, 20wt% to 50wt%, based on the total weight of the electrolyte. In some embodiments, the electrolyte contains 1wt% to 60wt%, 10wt% to 60wt%, 20wt% to 50wt%, 20wt% to 40wt%, or 30wt% propyl propionate, based on the total weight of the electrolyte.

In some embodiments, examples of the additives may include, but are not limited to, one or more of the following: fluorocarbonates, ethylene carbonates containing carbon-carbon double bonds, compounds containing sulfur-oxygen double bonds and anhydrides.

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 total weight of the electrolyte.

According to an embodiment of the application, the propionate is present in an amount of 1.5 to 30 times, 1.5 to 20 times, 2 to 20 times or 5-20 times the additive, based on the total weight of the electrolyte.

In some embodiments, the additive comprises one or more fluorocarbonates. The fluorocarbonate may act together with the propionate to form a stable protective film on the surface of the negative electrode upon charge/discharge of the lithium ion battery, thereby suppressing the decomposition reaction of the electrolyte.

In some embodiments, the fluorocarbonate has the formula c=o (OR ₁ )(OR ₂ ) Wherein R is ₁ And R is ₂ Each selected from alkyl or haloalkyl having 1 to 6 carbon atoms, wherein R ₁ And R is ₂ At least one of which is selected from fluoroalkyl groups having 1 to 6 carbon atoms, and R ₁ And R is ₂ Optionally together with the atoms to which they are attached form a 5-to 7-membered ring.

In some embodiments, examples of the fluorocarbonates 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, ethyl trifluoroethyl carbonate, and the like.

In some embodiments, the additive comprises one or more ethylene carbonates containing carbon-carbon double bonds. Examples of the carbon-carbon double bond containing ethylene carbonate may include, but are not limited to, one or more of the following: vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, 1, 2-dimethylvinylene carbonate, 1, 2-diethylvinylene carbonate, fluorovinylene carbonate, trifluoromethyl vinylene carbonate; vinyl ethylene carbonate, 1-methyl-2-vinyl ethylene carbonate, 1-ethyl-2-vinyl ethylene carbonate, 1-n-propyl-2-vinyl ethylene carbonate, 1-methyl-2-vinyl ethylene carbonate, 1-divinyl ethylene carbonate, 1, 2-divinyl ethylene carbonate, 1-dimethyl-2-methylene ethylene carbonate, 1-diethyl-2-methylene ethylene carbonate, and the like. In some embodiments, the carbon-carbon double bond containing ethylene carbonate includes vinylene carbonate, which is readily available and may achieve more excellent results.

In some embodiments, the additive comprises one or more sulfur-oxygen double bond containing compounds. Examples of the sulfur-oxygen double bond containing compound may include, but are not limited to, one or more of the following: cyclic sulfate, chain sulfonate, cyclic sulfonate, chain sulfite, cyclic sulfite, and the like.

Examples of the cyclic sulfate may 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-butanediol sulfate, 1, 3-butanediol sulfate, 1, 4-butanediol sulfate, 1, 2-pentanediol sulfate, 1, 3-pentanediol sulfate, 1, 4-pentanediol sulfate, 1, 5-pentanediol sulfate, and the like.

Examples of the chain sulfate may include, but are not limited to, one or more of the following: dimethyl sulfate, methyl ethyl sulfate, diethyl sulfate, and the like.

Examples of such chain sulfonates may include, but are not limited to, one or more of the following: fluorosulfonates such as methyl fluorosulfonate and ethyl fluorosulfonate, methyl methanesulfonate, ethyl methanesulfonate, butyl methanesulfonate, methyl 2- (methylsulfonyloxy) propionate, ethyl 2- (methylsulfonyloxy) propionate, and the like.

Examples of the cyclic sulfonate may include, but are 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-propene-1, 3-propane sultone, 2-propene-1, 3-propane sultone, 1-fluoro-1-propene-1, 3-propane sultone, 2-fluoro-1-propene-1, 3-propane sultone, 3-fluoro-1-propene-1, 3-propane sultone 1-fluoro-2-propene-1, 3-sultone, 2-fluoro-2-propene-1, 3-sultone, 3-fluoro-2-propene-1, 3-sultone, 1-methyl-1-propene-1, 3-sultone, 2-methyl-1-propene-1, 3-sultone, 3-methyl-1-propene-1, 3-sultone, 1-methyl-2-propene-1, 3-sultone, 2-methyl-2-propene-1, 3-sultone, 3-methyl-2-propene-1, 3-sultone, 1, 4-butanesultone, 1, 5-pentanolactone, methylene methane disulfonate, ethylene methane disulfonate, and the like.

Examples of the chain sulfite may include, but are not limited to, one or more of the following: dimethyl sulfite, methyl ethyl sulfite, diethyl sulfite, and the like.

Examples of the cyclic sulfite may include, but are 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.

In some embodiments, the additive comprises one or more anhydrides. Examples of the acid anhydride may include, but are not limited to, one or more of cyclic phosphoric anhydride, carboxylic anhydride, disulfonic anhydride, and carboxylic sulfonic anhydride. Examples of the cyclic phosphoric anhydride may include, but are not limited to, one or more of trimethyl phosphoric anhydride, triethyl phosphoric anhydride, and tripropyl phosphoric anhydride. Examples of the carboxylic anhydride may include, but are not limited to, one or more of succinic anhydride, glutaric anhydride, and maleic anhydride. Examples of the disulfonic anhydride may include, but are not limited to, one or more of ethane disulfonic anhydride and propane disulfonic anhydride. Examples of the carboxylic acid sulfonic anhydride may include, but are not limited to, one or more of sulfobenzoic anhydride, sulfopropionic anhydride, and sulfobutyric anhydride.

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

The electrolyte is not particularly limited, and any known electrolyte may be used. In the case of a lithium secondary battery, a lithium salt is generally used. Examples of electrolytes may include, but are not limited to, liPF ₆ 、LiBF ₄ 、LiClO ₄ 、LiAlF ₄ 、LiSbF ₆ 、LiTaF ₆ 、LiWF ₇ An inorganic lithium salt; liWOF ₅ Lithium tungstate; HCO (hydrogen chloride) ₂ Li、CH ₃ CO ₂ Li、CH ₂ FCO ₂ Li、CHF ₂ CO ₂ Li、CF ₃ CO ₂ Li、CF ₃ CH ₂ CO ₂ Li、CF ₃ CF ₂ CO ₂ Li、CF ₃ CF ₂ CF ₂ CO ₂ Li、CF ₃ CF ₂ CF ₂ CF ₂ CO ₂ Lithium carboxylates such as Li; FSO (FSO) ₃ Li、CH ₃ SO ₃ Li、CH ₂ FSO ₃ Li、CHF ₂ SO ₃ Li、CF ₃ SO ₃ Li、CF ₃ CF ₂ SO ₃ Li、CF ₃ CF ₂ CF ₂ SO ₃ Li、CF ₃ CF ₂ CF ₂ CF ₂ SO ₃ Lithium sulfonate such as Li; liN (FCO) ₂ 、LiN(FCO)(FSO ₂ )、LiN(FSO ₂ ) ₂ 、LiN(FSO ₂ )(CF ₃ SO ₂ )、LiN(CF ₃ SO ₂ ) ₂ 、LiN(C ₂ F ₅ SO ₂ ) ₂ Cyclic 1, 2-perfluoroethane bissulfonylimide lithium, cyclic 1, 3-perfluoropropane bissulfonylimide lithium, liN (CF) ₃ SO ₂ )(C ₄ F ₉ SO ₂ ) Lithium imide salts; liC (FSO) ₂ ) ₃ 、LiC(CF ₃ SO ₂ ) ₃ 、LiC(C ₂ F ₅ SO ₂ ) ₃ Isomethylated lithium salts; lithium (malonate) borates such as lithium bis (malonate) borate and lithium difluoro (malonate) borate; tris (malonate)) Lithium phosphate salts such as lithium phosphate, lithium difluorobis (malonate) phosphate, and lithium tetrafluoro (malonate) phosphate; liPF (liquid crystal display) and LiPF ₄ (CF ₃ ) ₂ 、LiPF ₄ (C ₂ F ₅ ) ₂ 、LiPF ₄ (CF ₃ SO ₂ ) ₂ 、LiPF ₄ (C ₂ F ₅ SO ₂ ) ₂ 、LiBF ₃ CF ₃ 、LiBF ₃ C ₂ F ₅ 、LiBF ₃ C ₃ F ₇ 、LiBF ₂ (CF ₃ ) ₂ 、LiBF ₂ (C ₂ F ₅ ) ₂ 、LiBF ₂ (CF ₃ SO ₂ ) ₂ 、LiBF ₂ (C ₂ F ₅ SO ₂ ) ₂ Fluorine-containing organolithium salts; lithium oxalato borate salts such as lithium difluorooxalato borate and lithium bis (oxalato) borate; lithium oxalate phosphates such as lithium tetrafluorooxalate phosphate, lithium difluorobis (oxalato) phosphate and lithium tris (oxalato) phosphate.

In some embodiments, the electrolyte is selected from LiPF ₆ 、LiSbF ₆ 、LiTaF ₆ 、FSO ₃ Li、CF ₃ SO ₃ Li、LiN(FSO ₂ ) ₂ 、LiN(FSO ₂ )(CF ₃ SO ₂ )、LiN(CF ₃ SO ₂ ) ₂ 、LiN(C ₂ F ₅ SO ₂ ) ₂ Cyclic 1, 2-perfluoroethane bissulfonylimide lithium, cyclic 1, 3-perfluoropropane bissulfonylimide lithium, liC (FSO) ₂ ) ₃ 、LiC(CF ₃ SO ₂ ) ₃ 、LiC(C ₂ F ₅ SO ₂ ) ₃ 、LiBF ₃ CF ₃ 、LiBF ₃ C ₂ F ₅ 、LiPF ₃ (CF ₃ ) ₃ 、LiPF ₃ (C ₂ F ₅ ) ₃ Lithium difluorooxalato borate, lithium bis (oxalato) borate or lithium difluorobis (oxalato) phosphate, which contribute to improvement of output characteristics, high-rate charge-discharge characteristics, high-temperature storage characteristics, cycle characteristics, and the like of electrochemical devices.

The content of the electrolyte is not particularly limited 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 0.3mol/L or greater than 0.4mol/L or greater than 0.5mol/L. In some embodiments, the total molar concentration of lithium in the electrolyte is less than 3.0mol/L, less than 2.5mol/L, or less than 2.0mol/L or less. In some embodiments, the total molar concentration of lithium in the electrolyte is within a range consisting of any two of the values recited above. When the electrolyte concentration is within the above range, lithium as charged particles is not excessively small, and the viscosity can be brought into an appropriate range, so that good conductivity is easily ensured.

In the case where two or more electrolytes are used, the electrolytes include at least one salt selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate. In some embodiments, the electrolyte comprises a salt selected from the group consisting of monofluorophosphate, oxalate, and fluorosulfonate. In some embodiments, the electrolyte comprises a lithium salt. In some embodiments, the salt selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate is present in an amount greater than 0.01wt% or greater than 0.1wt%, based on the total weight of the electrolyte. In some embodiments, the salt selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate is present in an amount of less than 20wt% or less than 10wt%, based on the total weight of the electrolyte. In some embodiments, the salt selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate is present in an amount within the range of any two values recited above.

In some embodiments, the electrolyte comprises one or more materials selected from the group consisting of monofluorophosphate, borate, oxalate, and fluorosulfonate, and one or more salts other than. As other salts, there may be mentioned the lithium salts exemplified hereinabove, in some embodiments LiPF ₆ 、LiN(FSO ₂ )(CF ₃ SO ₂ )、LiN(CF ₃ SO ₂ ) ₂ 、LiN(C ₂ F ₅ SO ₂ ) ₂ Cyclic 1, 2-perfluoroethane bissulfonylimide lithium, cyclic 1, 3-perfluoropropane bissulfonylimide lithium, liC (FSO) ₂ ) ₃ 、LiC(CF ₃ SO ₂ ) ₃ 、LiC(C ₂ F ₅ SO ₂ ) ₃ 、LiBF ₃ CF ₃ 、LiBF ₃ C ₂ F ₅ 、LiPF ₃ (CF ₃ ) ₃ 、LiPF ₃ (C ₂ F ₅ ) ₃ . In some embodiments, the other salt is LiPF ₆ 。

In some embodiments, the other salts are present in an amount greater than 0.01wt% or greater than 0.1wt% based on the total weight of the electrolyte. In some embodiments, the other salts are present in an amount of less than 20wt%, less than 15wt%, or less than 10wt%, based on the total weight of the electrolyte. In some embodiments, the other salts are present in an amount within the range consisting of any two of the values recited above. The other salts with the above content help balance the conductivity and viscosity of the electrolyte.

The electrolyte solution may contain, in addition to the above-mentioned solvent, additive, and electrolyte salt, an additional additive such as a negative electrode film forming agent, positive electrode protecting agent, and overcharge preventing agent, as required. As the additive, an additive generally used in a nonaqueous electrolyte secondary battery may be used, and examples thereof may include, but are not limited to, vinylene carbonate, succinic anhydride, biphenyl, cyclohexylbenzene, 2, 4-difluoroanisole, propane sultone, propylene sultone, and the like. These additives may be used alone or in any combination. The content of these additives in the electrolyte is not particularly limited, and may be appropriately set according to the kind of the additives. In some embodiments, the additive is present in an amount less than 5wt%, in a range of 0.01wt% to 5wt%, or in a range of 0.2wt% to 5wt%, based on the total weight of the electrolyte.

III, positive electrode

The positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on one or both surfaces of the positive electrode current collector.

1. Positive electrode active material layer

The positive electrode active material layer contains a positive electrode active material, and may be one or more layers. Each layer of the multi-layer positive electrode active material may contain the same or different positive electrode active materials. The positive electrode active material is any material capable of reversibly intercalating and deintercalating metal ions such as lithium ions.

The kind of the positive electrode active material is not particularly limited as long as it is capable of electrochemically occluding and releasing metal ions (for example, lithium ions). In some embodiments, the positive electrode active material is a material containing lithium and at least one transition metal. Examples of the positive electrode active material may include, but are not limited to, lithium transition metal composite oxides and lithium-containing transition metal phosphate compounds.

In some embodiments, the transition metal in the lithium transition metal composite oxide includes V, ti, cr, mn, fe, co, ni, cu and the like. In some embodiments, the lithium transition metal composite oxide includes LiCoO ₂ Equal lithium cobalt composite oxide, liNiO ₂ Equal lithium nickel composite oxide, liMnO ₂ 、LiMn ₂ O ₄ 、Li ₂ MnO ₄ Equal lithium manganese composite oxide, liNi _1/3 Mn _1/3 Co _1/3 O ₂ 、LiNi _0.5 Mn _0.3 Co _0.2 O ₂ And lithium nickel manganese cobalt composite oxides in which a part of transition metal atoms which are the main body of these lithium transition metal composite oxides are substituted with 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. Examples of lithium transition metal composite oxides may include, but are not limited to, liNi _0.5 Mn _0.5 O ₂ 、LiNi _0.85 Co _0.10 Al _0.05 O ₂ 、LiNi _0.33 Co _0.33 Mn _0.33 O ₂ 、LiNi _0.45 Co _0.10 Al _0.45 O ₂ 、LiMn _1.8 Al _0.2 O ₄ And LiMn _1.5 Ni _0.5 O ₄ Etc. Examples of combinations of lithium transition metal composite oxides include, but are not limited to, liCoO ₂ With LiMn ₂ O ₄ In which LiMn ₂ O ₄ Part of Mn in (B) may be substituted by transition metal(e.g., liNi _0.33 Co _0.33 Mn _0.33 O ₂ )，LiCoO ₂ A portion of Co in (c) may be replaced with a transition metal.

In some embodiments, the transition metal in the lithium-containing transition metal phosphate compound includes V, ti, cr, mn, fe, co, ni, cu, and the like. In some embodiments, the lithium-containing transition metal phosphate compound comprises LiFePO ₄ 、Li ₃ Fe ₂ (PO ₄ ) ₃ 、LiFeP ₂ O ₇ Isophosphates, liCoPO ₄ Cobalt phosphates in which a part of the transition metal atoms that are the main body of these lithium transition metal phosphate compounds are substituted with other elements such as Al, ti, V, cr, mn, fe, co, li, ni, cu, zn, mg, ga, zr, nb, si.

In some embodiments, lithium phosphate is included in the positive electrode active material, which may improve continuous charging characteristics of the electrochemical device. The use of lithium phosphate is not limited. In some embodiments, the positive electrode active material and lithium phosphate are used in combination. In some embodiments, the content of lithium phosphate is greater than 0.1wt%, greater than 0.3wt%, or greater than 0.5wt%, relative to the total weight of the positive electrode active material and lithium phosphate described above. In some embodiments, the content of lithium phosphate is less than 10wt%, less than 8wt%, or less than 5wt%, relative to the total weight of the positive electrode active material and lithium phosphate. In some embodiments, the lithium phosphate is present in an amount within the range consisting of any two of the values recited above.

Surface coating

A material having a composition different from that of the positive electrode active material may be attached to the surface of the positive electrode active material. Examples of the surface-adhering substance may include, but are not limited to, oxides such as alumina, silica, titania, zirconia, magnesia, calcium oxide, boron oxide, antimony oxide, bismuth oxide, sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, aluminum sulfate, carbonates such as lithium carbonate, calcium carbonate, magnesium carbonate, carbon, and the like.

These surface-attached substances can be attached to the surface of the positive electrode active material by the following method: a method in which the surface-adhering substance is dissolved or suspended in a solvent, and the solution is impregnated into the positive electrode active material and dried; a method in which a surface-attached substance precursor is dissolved or suspended in a solvent, and is added to the positive electrode active material by infiltration, and then reacted by heating or the like; and a method of adding to a positive electrode active material precursor while firing, and the like. In the case of attaching carbon, a method of mechanically attaching a carbon material (for example, activated carbon or the like) may also be used.

In some embodiments, the surface-adherent content is greater than 0.1ppm, greater than 1ppm, or greater than 10ppm, based on the total weight of the positive electrode active material layer. In some embodiments, the surface-adherent content is less than 20%, less than 10%, or less than 10% based on the total weight of the positive electrode active material layer. In some embodiments, the surface-adherent content is within a range consisting of any two of the values described above, based on the total weight of the positive electrode active material layer.

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, and the life of the electrochemical device can be improved. When the amount of the surface-adhering substance is too small, the effect thereof cannot be sufficiently exhibited; if the amount of the surface-adhering substance is too large, the ingress and egress of lithium ions are hindered, and thus the electrical resistance may be increased.

In the present application, a positive electrode active material having a composition different from that of the positive electrode active material attached to the surface of the positive electrode active material is also referred to as a "positive electrode active material".

Shape and shape

In some embodiments, the shape of the positive electrode active material particles includes, but is not limited to, block, polyhedral, spherical, ellipsoidal, plate-like, needle-like, columnar, and the like. 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 agglomerate to form secondary particles.

Tap density

In some embodiments, the positive electrode active material has a tap density of greater than 0.5g/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 amounts of the conductive material and the positive electrode binder required at the time of forming the positive electrode active material layer can be suppressed, whereby the filling rate of the positive electrode active material and the capacity of the electrochemical device can be ensured. By using a composite oxide powder having a high tap density, a high-density positive electrode active material layer can be formed. The larger the tap density is, the more preferable is generally, and there is no particular upper limit. In some embodiments, the positive electrode active material has a tap density of less than 4.0g/cm ³ Less than 3.7g/cm ³ Or less than 3.5g/cm ³ . When the tap density of the positive electrode active material has the upper limit as described above, a decrease in load characteristics can be suppressed.

The tap density of the positive electrode active material can be calculated by: 5g to 10g of positive electrode active material powder was put into a 10mL glass cylinder and vibrated for 200 strokes of 20mm to obtain a powder filling density (tap density).

Median particle diameter (D50)

When the positive electrode active material particles are primary particles, the median particle diameter (D50) of the positive electrode active material particles refers to the positive electrode active material particle primary particle diameter. When primary particles of the positive electrode active material particles are aggregated to form secondary particles, the median particle diameter (D50) of the positive electrode active material particles refers to the positive electrode active material particle secondary particle diameter.

In some embodiments, the median particle diameter (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 diameter (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 diameter (D50) of the positive electrode active material particles is within a range consisting of any two of the values described above. When the median particle diameter (D50) of the positive electrode active material particles is within the above range, a positive electrode active material with high tap density can be obtained, and degradation of the performance of the electrochemical device can be suppressed. On the other hand, in the process of producing the positive electrode of the electrochemical device (that is, when the positive electrode active material, the conductive material, the binder, and the like are applied in a film form by slurrying them with a solvent), the occurrence of the problem of the occurrence of the streaks or the like can be prevented. Here, by mixing two or more positive electrode active materials having different median particle diameters, the filling property at the time of positive electrode preparation can be further improved.

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

Average primary particle diameter

In the case where primary particles of the positive electrode active material particles are aggregated to form secondary particles, in some embodiments, the average primary particle diameter 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 diameter of the positive electrode active material is within a range consisting of any two of the values described above. When the average primary particle diameter of the positive electrode active material is within the above range, the powder filling property and the specific surface area can be ensured, the decrease in battery performance can be suppressed, and appropriate crystallinity can be obtained, whereby the reversibility of charge and discharge of the electrochemical device can be ensured.

The average primary particle diameter of the positive electrode active material can be obtained by observing an image obtained by a Scanning Electron Microscope (SEM): in an SEM image of 10000 times, the longest value of a slice obtained from the left and right boundary lines of primary particles with respect to a horizontal straight line is obtained for any 50 primary particles, and the average value thereof is obtained, thereby obtaining an average primary particle diameter.

Specific surface area (BET)

In some embodiments, the positive electrode active material has a specific surface area (BET) of greater than 0.1m ² /g, greater than 0.2m ² /g or greater than 0.3m ² And/g. In some implementationsIn an embodiment, the positive electrode active material has a specific surface area (BET) of less than 50m ² /g, less than 40m ² /g or less than 30m ² And/g. In some embodiments, the specific surface area (BET) of the positive electrode active material is in the range consisting of any two of the values described above. 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 the positive electrode active material can be provided with good coatability.

The specific surface area (BET) of the positive electrode active material can be measured by the following method: the sample was pre-dried at 150℃for 30 minutes using a surface area meter (for example, a fully automatic surface area measuring apparatus manufactured by Dagaku Kogyo Co., ltd.) under a nitrogen flow, and then measured by a nitrogen adsorption BET single point method using a nitrogen helium mixed gas in which the relative pressure value of nitrogen to the atmospheric pressure was accurately adjusted to 0.3.

Positive electrode conductive material

The kind of the positive electrode conductive material is not limited, and any known conductive material may be used. Examples of the positive electrode conductive material may include graphite such as natural graphite, artificial graphite, and the like; carbon black such as acetylene black; amorphous carbon material such as needle coke; a carbon nanotube; graphene, and the like. The above positive electrode conductive materials may be used alone or in any combination.

In some embodiments, the content of the positive electrode conductive material is greater than 0.01wt%, greater than 0.1wt%, or greater than 1wt%, based on the total weight of the positive electrode active material layer. In some embodiments, the content of the positive electrode conductive material is less than 50wt%, less than 30wt% or less than 15wt%, based on the total weight of the positive electrode active material layer. When the content of the positive electrode conductive material is within the above range, sufficient conductivity and capacity of the electrochemical device can be ensured.

Positive electrode binder

The type of the positive electrode binder used in the production of the positive electrode active material layer is not particularly limited, and in the case of the coating method, the binder may be any material that is soluble or dispersible in a liquid medium used in the production of the electrode. 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; rubbery polymers such as Styrene Butadiene Rubber (SBR), nitrile Butadiene Rubber (NBR), fluororubber, isoprene rubber, butadiene rubber, and ethylene-propylene rubber; thermoplastic elastomer-like polymers such as styrene-butadiene-styrene block copolymers or their hydrogenated products, ethylene-propylene-diene terpolymers (EPDM), styrene-ethylene-butadiene-ethylene copolymers, styrene-isoprene-styrene block copolymers or their hydrogenated products; soft resinous 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 (PVDF), polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymers; and polymer compositions having ion conductivity of alkali metal ions (particularly lithium ions). The above positive electrode binders may be used alone or in any combination.

In some embodiments, the content of the positive electrode binder is greater than 0.1wt%, greater than 1wt%, or greater than 1.5wt%, based on the total weight of the positive electrode active material layer. In some embodiments, the content of the positive electrode binder is less than 80wt%, less than 60wt%, less than 40wt%, or less than 10wt%, based on the total weight of the positive electrode active material layer. When the content of the positive electrode binder is within the above range, the positive electrode can be made to have good conductivity and sufficient mechanical strength, and the capacity of the electrochemical device can be ensured.

Solvent(s)

The type of solvent used to form the positive electrode slurry is not limited as long as it is a solvent capable of dissolving or dispersing the positive electrode active material, the conductive material, the positive electrode binder, and the thickener, if necessary. Examples of the solvent used to form the positive electrode slurry may include any one of an aqueous solvent and an organic solvent. Examples of the aqueous medium may include, but are not limited to, water and a mixed medium of alcohol and water, and the like. Examples of the organic-based medium 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.

Thickening agent

Thickeners are typically used to adjust the viscosity of the slurry. In the case of using an aqueous medium, the sizing may be performed using a thickener and Styrene Butadiene Rubber (SBR) emulsion. The kind of the thickener is not particularly limited, and examples thereof may include, but are not limited to, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, salts thereof, and the like. The above thickeners may be used alone or in any combination.

In some embodiments, the thickener is present in an amount greater than 0.1wt%, greater than 0.2wt%, or greater than 0.3wt%, based on the total weight of the positive electrode active material layer. In some embodiments, the thickener is present in an amount of less than 5wt%, less than 3wt%, or less than 2wt%, based on the total weight of the positive electrode active material layer. In some embodiments, the thickener is present in an amount within the range of any two values described above, based on the total weight of the positive electrode active material layer. When the content of the thickener is within the above range, the positive electrode slurry can be made to have good coatability, while the capacity decrease and the increase in resistance of the electrochemical device can be suppressed.

Content of positive electrode active material

In some embodiments, the content of the positive electrode active material is greater than 80wt%, greater than 82wt%, or greater than 84wt%, based on the total weight of the positive electrode active material layer. In some embodiments, the content of the positive electrode active material is less than 99wt% or less than 98wt% based on the total weight of the positive electrode active material layer. In some embodiments, the content of the positive electrode active material is within the range consisting of any two arrays described above, based on the total weight of the positive electrode active material 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 active material layer can be ensured, while the strength of the positive electrode can be maintained.

Density of positive electrode active material

The positive electrode active material layer obtained by coating and drying may be subjected to a pressing treatment by a manual press, a roll press, or the like in order to increase the packing density of the positive electrode active material. In some embodiments, the positive electrode active material layer has a density of greater than 1.5g/cm ³ More than 2g/cm ³ Or greater than 2.2g/cm ³ . In some embodiments, the positive electrode active material layer has a density of less than 5g/cm ³ Less than 4.5g/cm ³ Or less than 4g/cm ³ . In some embodiments, the density of the positive electrode active material layer is within a range consisting of any two of the values described above. When the density of the positive electrode active material layer is within the above range, the electrochemical device can be provided with good charge-discharge characteristics while suppressing an increase in resistance.

Thickness of positive electrode active material layer

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

Method for producing positive electrode active material

The positive electrode active material can be produced by a method commonly used for producing inorganic compounds. In order to produce a spherical or ellipsoidal positive electrode active material, the following production method may be employed: dissolving or pulverizing transition metal material in solvent such as water, adjusting pH under stirring, preparing spherical precursor, recovering, drying if necessary, and adding LiOH and Li ₂ CO ₃ 、LiNO ₃ And Li source, firing at high temperature,the positive electrode active material was obtained.

2. Positive electrode current collector

The kind of the positive electrode current collector is not particularly limited, and it may be any material known to be suitable for use as a positive electrode current collector. Examples of the positive electrode current collector may include, but are not limited to, metal materials such as aluminum, stainless steel, nickel plating, titanium, tantalum, and the like; 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.

The form of the positive electrode current collector is not particularly limited. 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, a metal foil, a metal cylinder, a metal coil, a metal plate, a metal film, a metal expanded metal, a punched metal, a foamed metal, and the like. 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, a carbon plate, a carbon thin film, a carbon cylinder, and the like. In some embodiments, the positive electrode current collector is a metal thin film. In some embodiments, the metal film is net-shaped. The thickness of the metal thin film is not particularly limited. In some embodiments, the metal film has a thickness of greater than 1 μm, greater than 3 μm, or greater than 5 μm. In some embodiments, the metal film has a thickness of less than 1mm, less than 100 μm, or less than 50 μm. In some embodiments, the thickness of the metal film is within a range consisting of any two of the values recited above.

In order to reduce the electronic contact resistance of the positive electrode current collector and the positive electrode active material layer, the surface of the positive electrode current collector may include a conductive auxiliary agent. Examples of the conductive aid may include, but are not limited to, carbon and noble metals such as gold, platinum, silver, and the like.

The thickness ratio of the positive electrode current collector to the positive electrode active material layer refers to the ratio of the thickness of the positive electrode active material layer on one side before the injection of the electrolyte solution to the thickness of the positive electrode current collector, and the numerical value thereof is not particularly limited. In some embodiments, the thickness ratio of the positive electrode current collector to the positive electrode active material layer is less than 20, less than 15, or less than 10. In some embodiments, the thickness ratio of the positive electrode current collector to the positive electrode active material layer is greater than 0.5, greater than 0.8, or greater than 1. In some embodiments, the thickness ratio of the positive electrode current collector to the positive electrode active material layer is within a range consisting of any two values described above. When the thickness ratio of the positive electrode current collector to the positive electrode active material layer is within the above range, heat release of the positive electrode current collector during charge and discharge at a high current density can be suppressed, and the capacity of the electrochemical device can be ensured.

3. Positive electrode structure and method for producing same

The positive electrode may be manufactured by forming a positive electrode active material layer containing a positive electrode active material and a binder active material on a current collector. The positive electrode using the positive electrode active material can be produced by a conventional method in which the positive electrode active material and the adhesive active material, and if necessary, the conductive material, the thickener, and the like are dry-mixed to form a sheet, and the resulting sheet is pressure-bonded to the positive electrode current collector; or these materials are dissolved or dispersed in a liquid medium to prepare a slurry, and the slurry is applied to a positive electrode current collector and dried to form a positive electrode active material layer on the current collector, whereby a positive electrode can be obtained.

IV, isolation film

In order to prevent short circuit, a separator is generally provided between the positive electrode and the negative electrode. In this case, the electrolyte of the present application is generally used by penetrating into the separator.

The material and shape of the separator are not particularly limited as long as the effect of the present application is not significantly impaired. The separator may be a resin, glass fiber, inorganic substance, or the like formed of a material stable to the electrolyte of the present application. In some embodiments, the separator includes a porous sheet or a substance in a nonwoven fabric-like form, etc., which is excellent in liquid retention. Examples of materials for the resin or fiberglass barrier film may include, but are not limited to, polyolefin, aromatic polyamide, polytetrafluoroethylene, polyethersulfone, glass filter, and the like. In some embodiments, the material of the separator is a glass filter. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The materials of the above-mentioned separator may be used alone or in any combination.

The separator may be a laminate of the above materials, and examples thereof include, but are not limited to, a three-layer separator laminated in this order of polypropylene, polyethylene, and polypropylene.

Examples of the material of the inorganic substance may include, but are not limited to, oxides such as alumina, silica, nitrides such as aluminum nitride, silicon nitride, etc., sulfates (e.g., barium sulfate, calcium sulfate, etc.). The inorganic forms may include, but are not limited to, particulate or fibrous.

The form of the separator may be a film form, examples of which include, but are not limited to, nonwoven fabric, woven fabric, microporous film, and the like. In the form of a thin film, the separator has a pore diameter of 0.01 μm to 1 μm and a thickness of 5 μm to 50 μm. In addition to the above-described independent film-like separator, the following separator may be used: a separator formed by forming a composite porous layer containing the above inorganic particles on the surface of the positive electrode and/or the negative electrode using a resin-based binder, for example, a separator formed by forming porous layers on both surfaces of the positive electrode with 90% of alumina particles having a particle diameter of less than 1 μm using a fluororesin as a binder.

The thickness of the separator is arbitrary. In some embodiments, the thickness of the barrier film is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the separator is less than 50 μm, less than 40 μm, or less than 30 μm. In some embodiments, the thickness of the separator is in the range of any two values recited above. When the thickness of the separator is within the above range, insulation and mechanical strength can be ensured, and rate characteristics and energy density of the electrochemical device can be ensured.

When a porous material such as a porous sheet or a nonwoven fabric is used as the separator, the porosity of the separator is arbitrary. In some embodiments, the separator has a porosity of greater than 20%, greater than 35%, or greater than 45%. In some embodiments, the separator has a porosity of less than 90%, less than 85%, or less than 75%. In some embodiments, the separator has a porosity within a range consisting of any two of the values recited above. When the porosity of the separator is within the above range, insulation and mechanical strength can be ensured, and membrane resistance can be suppressed, resulting in an electrochemical device having good rate characteristics.

The average pore size of the separator is also arbitrary. In some embodiments, the separator has an average pore size of less than 0.5 μm or less than 0.2 μm. In some embodiments, the separator has an average pore size of greater than 0.05 μm. In some embodiments, the separator has an average pore size within a range consisting of any two of the values recited above. If the average pore diameter of the separator exceeds the above range, short-circuiting is liable to occur. When the average pore diameter of the separator is within the above range, the membrane resistance can be suppressed while preventing short-circuiting, so that the electrochemical device has good rate characteristics.

V, electrochemical device assembly

The electrochemical device assembly includes an electrode assembly, a current collecting structure, an exterior case, and a protection member.

Electrode group

The electrode group may be any of a laminated structure in which the positive electrode and the negative electrode are laminated with the separator interposed therebetween, and a structure in which the positive electrode and the negative electrode are spirally wound with the separator interposed therebetween. In some embodiments, the mass of the electrode set is greater than 40% or greater than 50% of the internal volume of the cell (electrode set occupancy). In some embodiments, the electrode group occupancy is less than 90% or less than 80%. In some embodiments, the electrode group occupancy is within a range consisting of any two of the values described above. When the electrode group occupancy is within the above range, the capacity of the electrochemical device can be ensured, and the deterioration of the characteristics such as repeated charge/discharge performance and high-temperature storage accompanied by an increase in internal pressure can be suppressed, and further, the operation of the gas release valve can be prevented.

Current collecting structure

The current collecting structure is not particularly limited. In some embodiments, the current collecting structure is a structure that reduces the resistance of the wiring portion and the bonding portion. When the electrode group has the above-described laminated structure, a structure in which metal core portions of the electrode layers are bundled and welded to the terminal is suitably used. When the electrode area increases, the internal resistance increases, and thus it is also preferable to provide 2 or more terminals in the electrode to reduce the resistance. When the electrode group has the above-described winding structure, the internal resistance can be reduced by providing 2 or more lead structures on the positive electrode and the negative electrode, respectively, and bundling the lead structures on the terminals.

Outer casing

The material of the outer case is not particularly limited as long as it is stable to the electrolyte solution used. The exterior case may be, but is not limited to, a nickel-plated steel plate, a metal such as stainless steel, aluminum or aluminum alloy, magnesium alloy, or a laminate film of a resin and an aluminum foil. In some embodiments, the outer housing is a metal or laminated film of aluminum or aluminum alloy.

The metal-based exterior case includes, but is not limited to, a package sealing structure formed by welding metals to each other by laser welding, resistance welding, ultrasonic welding; or a caulking structure formed by using the metal compound described above via a resin gasket. The exterior case using the above-mentioned laminated film includes, but is not limited to, a package sealing structure formed by thermally bonding resin layers to each other, and the like. In order to improve the sealing property, a resin different from the resin used for the laminated film may be interposed between the resin layers. When the resin layer is thermally bonded to form a sealed structure by the collector terminal, a resin having a polar group or a modified resin into which a polar group is introduced may be used as the resin to be interposed due to the bonding of the metal and the resin. The shape of the outer body is also arbitrary, and may be any of a cylindrical shape, a square shape, a laminated shape, a button shape, a large shape, and the like, for example.

Protection element

As the protective element, a Positive Temperature Coefficient (PTC) in which resistance increases when abnormal heat release or excessive current flows, a thermal fuse, a thermistor, a valve (current cut-off valve) in which current flowing through a circuit is cut off by rapidly increasing the internal pressure or internal temperature of the battery when abnormal heat release occurs, and the like can be used. The protection element can be selected from elements which are not operated in the normal use of high current, and can be designed in such a way that abnormal heat release or thermal runaway does not occur even if the protection element is not present.

VI, application

The electrochemical device of the present application includes any device in which an electrochemical reaction occurs, 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, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

The application further provides an electronic device comprising the electrochemical device according to the application.

The use of the electrochemical device of the present application is not particularly limited, and it may be used in any electronic device known in the art. In some embodiments, the electrochemical device of the present application may be used in, but is not limited to, notebook computers, pen-input computers, mobile computers, electronic book players, cellular phones, portable fax machines, portable copiers, portable printers, headsets, video recorders, liquid crystal televisions, hand-held cleaners, portable CD players, mini compact discs, transceivers, electronic notepads, calculators, memory cards, portable audio recorders, radios, backup power supplies, motors, automobiles, motorcycles, mopeds, bicycles, lighting fixtures, toys, gaming machines, watches, power tools, flashlights, cameras, home-use large storage batteries, lithium-ion capacitors, and the like.

The preparation of lithium ion batteries is described below by way of example in connection with specific examples, and those skilled in the art will appreciate that the preparation methods described in the present application are merely examples, and any other suitable preparation methods are within the scope of the present application.

Examples

The following describes performance evaluation of examples and comparative examples of lithium ion batteries according to the present application.

1. Preparation of lithium ion batteries

1. Preparation of negative electrode

Mixing artificial graphite, styrene-butadiene rubber and sodium carboxymethyl cellulose with deionized water and an auxiliary agent according to the mass ratio of 96-2%, and uniformly stirring to obtain the negative electrode slurry. The negative electrode slurry was coated on a copper foil of 12 μm. Drying, cold pressing, cutting, and welding the tab to obtain the negative electrode. The negative electrode was set to have the corresponding parameters according to the conditions of the following examples and comparative examples.

2. Preparation of the Positive electrode

Lithium cobalt oxide (LiCoO) ₂ ) The conductive material (Super-P) and polyvinylidene fluoride (PVDF) are mixed with N-methyl pyrrolidone (NMP) according to the mass ratio of 95 percent to 2 percent to 3 percent, and the mixture is uniformly stirred to obtain the positive electrode slurry. The positive electrode slurry is coated on aluminum foil with the thickness of 12 mu m, dried, cold-pressed, cut into pieces and welded with tabs to obtain the positive electrode.

3. Preparation of electrolyte

Mixing EC, PC and DEC (weight ratio 1:1:1) under dry argon, adding LiPF ₆ Uniformly mixing to form a basic electrolyte, wherein the LiPF ₆ The concentration of (C) was 1.15mol/L. Different amounts of additives were added to the base electrolyte to give electrolytes of different examples and comparative examples.

4. Preparation of a separator film

A porous polymer film of Polyethylene (PE) was used as a separator.

5. Preparation of lithium ion batteries

The obtained positive electrode, the separator and the negative electrode are wound in order and placed in an outer packaging foil, and a liquid injection port is left. And (3) pouring electrolyte from the liquid pouring port, packaging, and performing the working procedures of formation, capacity and the like to obtain the lithium ion battery.

2. Test method

1. Method for testing contact angle of negative electrode active material layer relative to nonaqueous solvent

3 microliters of diethyl carbonate is dripped on the surface of the negative electrode active material layer, a JC2000D3E contact angle measuring instrument is used for testing within 100 seconds, and a 5-point fitting method (namely, firstly taking 2 points on the left plane and the right plane of the liquid drop, determining a liquid-solid interface, and then taking 3 points on the circular arc of the liquid drop) is selected for fitting, so that the contact angle of the negative electrode active material layer relative to the nonaqueous solvent is obtained. Each sample is measured at least 3 times, at least 3 data with the difference less than 5 degrees are selected, and the average value is taken to obtain the contact angle of the negative electrode active material layer relative to the nonaqueous solvent.

2. Method for testing droplet diameter of nonaqueous solvent

3. Mu.l of diethyl carbonate was added dropwise to the surface of the negative electrode active material layer, and the droplet diameter was measured in 100 seconds using a JC2000D3E contact angle measuring instrument.

3. Method for testing porosity of anode active material layer

The test was performed using a true density tester AccuPyc II 1340, with at least 3 measurements per sample, and at least 3 data were averaged. The porosity of the anode active material layer was calculated according to the following formula:

porosity= (V1-V2)/v1×100%

Where V1 is the apparent volume, v1=sample surface area x sample thickness x number of samples; v2 is the true volume.

4. Specific surface area (BET) testing method

The sample was pre-dried at 350℃for 15 minutes using a surface area meter (fully automatic surface area measuring apparatus manufactured by Dagaku Kogyo Co., ltd.) under a nitrogen flow, and then measured by a nitrogen adsorption BET single point method using a nitrogen-helium mixed gas in which the relative pressure value of nitrogen to the atmospheric pressure was accurately adjusted to 0.3.

5. Method for testing median particle diameter (D50)

The carbon material was dispersed in a 0.2wt% aqueous solution (10 mL) of polyoxyethylene (20) sorbitan monolaurate, and tested by a laser diffraction/scattering particle size distribution meter (LA-700 manufactured by horiba, ltd.).

6. Test method for surface tension of auxiliary agent

And testing the aqueous solution of the auxiliary agent with the solid content of 1% by using a JC2000D3E contact angle measuring instrument, testing each sample at least 3 times, selecting at least 3 data, and taking an average value to obtain the surface tension of the auxiliary agent.

7. Method for testing reaction area of anode active material layer

The specific surface area of the anode active material layer, which means the specific surface area of the entire anode active material layer containing the anode active material and additives (binder, conductive agent, thickener, filler, etc.), was tested according to the above-described "test method for specific surface area (BET)". The weight of the anode active material layer, that is, the total weight of the entire anode active material layer containing the anode active material and additives (binder, conductive agent, thickener, filler, etc.) was measured. The reaction area of the anode active material layer was calculated by the following formula:

reaction area = specific surface area of the anode active material layer x weight of the anode active material layer.

8. Method for testing capacity retention rate of lithium ion battery after circulation

At 45 ℃, the lithium ion battery is charged to 4.45V at a constant current of 1C, then charged to 0.05C at a constant voltage of 4.45V, and then discharged to 3.0V at a constant current of 1C, which is the first cycle. The lithium ion battery was cycled 200 times according to the conditions described above. "1C" refers to a current value at which the capacity of the lithium ion battery is completely discharged within 1 hour.

The capacity retention after cycling of the lithium ion battery was calculated by:

after-cycle capacity retention= (discharge capacity corresponding to cycle number/discharge capacity of first cycle) ×100%.

9. Method for testing cyclic expansion rate of lithium ion battery

The lithium ion battery was allowed to stand at 25℃for 30 minutes, then charged to 4.45V at a constant current of 0.5C, charged to 0.05C at a constant voltage of 4.45V, and allowed to stand for 5 minutes, and the thickness was measured. The cycling test was then performed and the thickness of the cell was measured after 100 cycles. The thickness expansion ratio of the lithium ion battery for 100 cycles was calculated by the following formula:

the cycle thickness expansion ratio= [ (post-cycle thickness-pre-cycle thickness)/pre-cycle thickness ] ×100%.

3. Test results

Table 1 shows the contact angle of the anode active material layer with respect to the nonaqueous solvent, the porosity, and the auxiliary agent used and the cycle performance of the lithium ion battery in each of the examples and comparative examples. Auxiliary 1 used in the examples: 1000ppm trisiloxane surfactant (CAS No.3390-61-2; 28855-11-0).

TABLE 1

	Contact angle	Porosity of the porous material	Capacity retention after cycling	Cyclic thickness expansion ratio
					Comparative example 1	70°	5％	51％	41％
Example 1	60°	5％	60％	32％
					Example 2	40°	5％	65％	23％
Example 3	35°	65％	75％	18％
					Example 4	35°	20％	82％	15％
Example 5	22°	30％	80％	14％
					Example 6	20°	20％	84％	12％
Example 7	25°	60％	78％	16％
					Example 8	5°	50％	81％	13％

The results show that when the contact angle of the anode active material layer with respect to the nonaqueous solvent is not more than 60 °, the capacity retention rate and the cycle thickness expansion rate of the lithium ion battery are significantly improved after the cycle. On the basis that the contact angle of the negative electrode active material layer relative to the nonaqueous solvent is not more than 60 degrees, the negative electrode active material layer has a porosity of 10 to 60 percent, and the capacity retention rate and the cycle thickness expansion rate after the cycle of the lithium ion battery can be further improved.

Table 2 shows the effect of the specific surface area (BET) and median particle diameter (D50) of the carbon material on the cycle performance of the lithium ion battery. The examples in table 2 are based on the modifications of example 4, differing only in the parameters listed in table 2.

TABLE 2

	BET(m ² /g)	D50(μm)	Capacity retention after cycling	Cyclic thickness expansion ratio
					Example 4	20	35	82％	15％
Example 9	3	20	83％	14％
					Example 10	2	20	84％	13％
Example 11	2	15	85％	12.5％
					Example 12	2	10	86％	12％
Example 13	2	5	85％	11％
					Example 14	2	30	83％	13.8％

The results show that when the ratio of carbon materials isSurface area (BET) of less than 5m ² When the/g and/or median particle diameter (D50) is in the range of 5 μm to 30. Mu.m, the capacity retention after cycling and the cycle thickness expansion ratio of the lithium ion battery are further improved.

Table 3 shows the effect of trace metals in the negative electrode active material layer on the cycle performance of the lithium ion battery. The examples in table 3 are modifications based on example 4, differing only in the parameters listed in table 3.

TABLE 3 Table 3

The results show that the capacity retention after cycling and the cycle thickness expansion rate of the lithium ion battery can be further improved when trace metal elements (e.g., iron, molybdenum, or copper) are present in the anode active material layer.

Table 4 shows the effect of the auxiliary on the cycling performance of the lithium ion battery. Examples 21 to 25 in Table 4 differ from example 4 only in the kind of auxiliary agent.

TABLE 4 Table 4

As shown in comparative example 1, when no auxiliary agent was added, the capacity retention rate after cycling and the cycle thickness expansion rate of the lithium ion battery were poor. As shown in examples 4 and 21-25, the addition of the auxiliary agent can significantly improve the capacity retention rate and the cycle thickness expansion rate after cycling of the lithium ion battery. When the oxidation potential of the auxiliary agent is not less than 4.5V and the reduction potential is not more than 0.5V, the capacity retention rate and the cycle thickness expansion rate of the lithium ion battery after the cycle are further improved. The nonionic surfactant (shown in examples 21 to 23) has a lower surface tension (not more than 30 mN/m) than ethanol and acetone (shown in examples 24 and 25), so that the capacity retention rate and the cycle thickness expansion rate after the cycle of the lithium ion battery can be further improved.

Table 5 shows the EC content (X mg) in the electrolyte and the reaction area (Ym ² ) Impact on cycling performance of lithium ion batteries. The examples in table 5 are modifications based on example 4, with the only differences being the parameters listed in table 5.

TABLE 5

	X/Y	Cycle capacity retention rate	Cyclic thickness expansion ratio
				Example 4	5	82％	15％
Example 26	10	85％	10.8％
				Example 27	30	88％	10.2％
Example 28	50	89％	9.5％
				Example 29	70	90％	8.7％
Example 30	100	81％	16％

The results showed that when the content of EC (X mg) in the electrolyte solution was equal to the reaction area (Ym ² ) When the (X/Y) is less than or equal to 10 and less than or equal to 100, the capacity retention rate and the expansion rate of the cycling thickness of the lithium ion battery after cycling are further improved.

Table 6 shows the effect of electrolyte composition on the cycling performance of lithium ion batteries. The examples in Table 6 are modifications based on example 4, differing only in the compounds listed in Table 6 and their content.

TABLE 6

	Compounds of formula (I)	Content (wt%)	Capacity retention after cycling	Cyclic thickness expansionRate of
					Example 4	/	/	82％	15％
Example 31	1a	1	92％	5.3％
					Example 32	1b	1	88％	6.7％
Example 33	1c	1	85％	8.5％
					Example 34	1d	1	84％	9.5％
Example 35	1e	1	83％	10.2％
					Example 36	1f	1	90％	6.1％
Example 37	1g of	1	85％	7.5％
					Example 38	1h	1	87％	8％
Example 39	1a	0.001	83％	12.2％
					Example 40	1a	0.1	90％	5.8％
Example 41	1a	0.5	93％	5.2％
					Example 42	1a	10	84％	18.5％

The results show that on the basis of using the negative electrode of the embodiment of the application, the addition of the compound of the formula 1 to the electrolyte contributes to the formation of an SEI film on the surface of the electrode, improves the interface stability, and contributes to the improvement of the capacity retention rate and the cycle thickness expansion rate of the lithium ion battery after the cycle. When the content of the compound of formula 1 is 0.001wt% to 10wt%, the capacity retention after cycling and the cycle thickness expansion rate of the lithium ion battery are significantly improved.

Table 7 shows the effect of iron group metals in the electrolyte on the cycling performance of the lithium ion battery. The examples in the table are modifications based on example 4, differing only in the kind of iron group metal and the content thereof as listed in table 7.

TABLE 7

The results show that when a trace amount of iron group metals (e.g., cobalt and nickel) are contained in the electrolyte, the capacity retention rate and the cycle thickness expansion rate after cycling of the lithium ion battery are improved on the basis of using the negative electrode of the embodiment of the present application.

Reference throughout this specification to "an embodiment," "a portion of an embodiment," "one embodiment," "another example," "an example," "a particular example," or "a portion of an example" means that at least one embodiment or example of the present application includes the particular feature, structure, material, or characteristic described in the embodiment or example. Thus, descriptions appearing throughout the specification, for example: "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in one example," "in a particular example," or "example," which do not necessarily reference the same embodiments or examples in the application. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

Although illustrative embodiments have been shown and described, it will be understood by those skilled in the art that the foregoing embodiments are not to be construed as limiting the application, and that changes, substitutions and alterations may be made herein without departing from the spirit, principles and scope of the application.

Claims

1. An electrochemical device comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode comprises a negative electrode active material layer, wherein:

the contact angle of the negative electrode active material layer relative to the nonaqueous solvent is not more than 60 degrees as measured by a contact angle measurement method;

the porosity of the anode active material layer is 10% to 60%;

the electrolyte further contains difluorophosphate and an iron group element including cobalt element, nickel element, or a combination thereof, and the content of the iron group element is not more than 0.05wt% based on the total weight of the electrolyte.

2. The electrochemical device according to claim 1, wherein a droplet diameter of the nonaqueous solvent on the anode active material layer is not more than 30mm as measured by a contact angle measurement method.

3. The electrochemical device according to claim 1, wherein the contact angle measurement method is to test a contact angle of a droplet of 3 microliters of diethyl carbonate on the surface of the anode active material layer within 100 seconds after the droplet is dropped on the surface of the anode active material layer.

4. The electrochemical device of claim 1, wherein the anode active material layer further comprises an auxiliary agent having at least one of the following characteristics:

(b) A surface tension of not more than 30mN/m;

(c) Including nonionic surfactants; and

5. The electrochemical device of claim 1, wherein the anode active material layer comprises a carbon material having at least one of the following characteristics:

(a) Less than 5m ² Specific surface area/g;

(b) Median particle size of 5 μm to 30 μm.

6. The electrochemical device according to claim 1, wherein the anode active material layer comprises at least one of artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, hard carbon, amorphous carbon, a silicon-containing material, a tin-containing material, and an alloy material.

7. The electrochemical device according to claim 1, wherein the anode active material layer further comprises at least one metal of molybdenum, iron, and copper, and a content of the at least one metal is not more than 0.05wt% based on a total weight of the anode active material layer.

8. The electrochemical device of claim 1, wherein the adjunct comprises a nonionic surfactant and the nonionic surfactant comprises at least one of a polyoxyethylene ether, a polyol ester, an amide, or a block polyether.

9. The electrochemical device of claim 8, wherein the non-ionic surfactant comprises at least one of: polyoxyethylene alkyl alcohol amide, octyl phenol polyoxyethylene ether, nonylphenol polyoxyethylene ether, higher fatty alcohol polyoxyethylene ether, fatty acid polyoxyethylene ester, polyoxyethylene amine, alkyl alcohol amide, lauryl alcohol polyoxyethylene ether, 12-14 carbon primary alcohol polyoxyethylene ether, 12-14 carbon secondary alcohol polyoxyethylene ether, branched 13 carbon guerbet alcohol polyoxyethylene ether, branched 10 carbon guerbet alcohol polyoxyethylene, linear 10 carbon alcohol polyoxyethylene ether, linear 8 carbon octanol polyoxyethylene ether, linear 8 carbon isooctyl alcohol polyoxyethylene ether, fatty acid monoglyceride, glyceryl monostearate, fatty acid sorbitan, composite silicone polyether complex, polysorbate, polyoxyethylene fatty acid ester, polyoxyethylene fatty alcohol ether, polyoxyethylene polyoxypropylene block copolymer, polyether modified trisiloxane or polyether modified silicone polyether siloxane.

10. The electrochemical device according to claim 1, wherein the electrolytic solution contains ethylene carbonate, and a content of the ethylene carbonate in the electrolytic solution is X mg and a reaction area Y m of the anode active material layer ² The following relationship is satisfied: X/Y is more than or equal to 10 and less than or equal to 100.

11. The electrochemical device of claim 1, wherein the electrolyte further comprises a compound of formula 1:

12. The electrochemical device of claim 11, wherein:

in formula 1, R is-SiR ₂ R ₃ R ₄ And R is ₁ Is an alkylene group having 2 carbon atoms and substituted with a substituent selected from the group consisting of: at least one fluorine atom or an alkyl group containing at least one fluorine atom and having 1 to 3 carbon atoms.

13. The electrochemical device according to claim 11, wherein the compound of formula 1 comprises at least one of compounds represented by formulas 1a to 1 h:

14. The electrochemical device of claim 10, wherein the compound of formula 1 is present in an amount of 0.001wt% to 10wt%, based on the total weight of the electrolyte.

15. An electronic device comprising the electrochemical device according to any one of claims 1-14.