CN111129498A

CN111129498A - Electrochemical device and electronic device comprising same

Info

Publication number: CN111129498A
Application number: CN201911360672.2A
Authority: CN
Inventors: 王可飞; 张青文; 戴振; 王莹莹
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2019-12-25
Filing date: 2019-12-25
Publication date: 2020-05-08

Abstract

The present application relates to an electrochemical device and an electronic device including the same. Specifically, the present application provides an electrochemical device including a positive electrode, a negative electrode, and an electrolytic solution, wherein the negative electrode has a negative electrode mixture layer on a negative electrode current collector, the negative electrode mixture layer contains a carbon material as a negative electrode active material, and a polymer compound having Si — C and Si — O bonds is included on a surface of the negative electrode mixture layer or at least a part of a surface of the carbon material. The electrochemical device of the present application has improved cycle performance and storage performance.

Description

Electrochemical device and electronic device comprising same

Technical Field

The present disclosure relates to the field of energy storage, and more particularly to an electrochemical device and an electronic device, especially a lithium ion battery, including the electrochemical device.

Background

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

The theoretical capacity of the lithium ion battery may vary depending on the kind of the negative active material. As the cycle progresses, the lithium ion battery generally generates a phenomenon in which the charge/discharge capacity is reduced, deteriorating 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 more and more attention in order to reduce environmental load and the like, but the presence of air bubbles in the slurry composition causes defects such as a plurality of pinholes, pits and the like in the active material layer, thereby affecting the cycle and high-temperature storage performance of the electrochemical device.

In view of the above, there is a need for an improved electrochemical device having high power characteristics and high safety performance and an electronic device including the same.

Disclosure of Invention

Embodiments of the present application address at least one of the problems 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 electrolytic solution, wherein the negative electrode has a negative electrode mixture layer on a negative electrode current collector, the negative electrode mixture layer contains a carbon material as a negative electrode active material, and a polymer compound having Si — C and Si — O bonds is included on a surface of the negative electrode mixture layer or at least a part of a surface of the carbon material.

According to some embodiments of the application, the high molecular compound having Si-C and Si-O bonds has at least one of the following characteristics:

(a) comprising a polyether siloxane;

(b) the oxidation potential is not less than 4.5V, and the reduction potential is not more than 0.5V;

(c) an aqueous solution containing 0.1% by weight of the polymer compound having Si-C and Si-O bonds has a surface tension of not more than 30 mN/m.

According to some embodiments of the present application, the content of the polymer compound having Si — C and Si — O bonds is 3000ppm or less based on the total weight of the negative electrode mixture layer.

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

(a) less than 5m²Specific surface area per gram;

(b) a median particle diameter of 5 μm to 30 μm;

(c) the surface has amorphous carbon.

According to some embodiments of the application, the negative electrode mixture layer has at least one of the following features:

(a) the thickness is not more than 200 μm;

(b) has a porosity of 10% to 60%;

(c) when balls having a diameter of 15mm and a weight of 12 g were dropped on the negative electrode mixture layer, the minimum height of the balls having cracks in the negative electrode mixture layer was 50cm or more.

According to some embodiments of the application, the electrolyte comprises at least one of the following compounds:

(a) propionate esters;

(b) an organic compound having a cyano group;

(c) lithium difluorophosphate; and

(d) a compound of formula 1:

wherein:

w is selected from

L is selected from a single bond or methylene;

m is an integer of 1 to 4;

n is an integer of 0 to 2; and is

p is an integer of 0 to 6.

According to some embodiments of the present application, the electrolyte includes the compound of formula 1, and the compound of formula 1 is selected from at least one of:

m is an integer of 1 to 4;

n is an integer of 0 to 2; and is

p is an integer of 0 to 6.

According to some embodiments of the present application, the electrolyte includes the propionate, and the propionate has formula 2:

wherein:

R¹is selected from the group consisting of ethyl or haloethyl,

R²is selected from C₁-C₆Alkyl or C₁-C₆A haloalkyl group; and is

The propionate content is 10 wt% to 65 wt% based on the weight of the electrolyte.

According to some embodiments of the present application, the propionate is selected from at least one of methyl propionate, ethyl propionate, propyl propionate, butyl propionate, or pentyl propionate.

According to some embodiments of the application, the organic compound having a cyano group is selected from at least one of: succinonitrile, glutaronitrile, adiponitrile, 1, 5-dicyanopentane, 1, 6-dicyanohexane, tetramethylsuccinonitrile, 2-methylglutaronitrile, 2, 4-dimethylglutaronitrile, 2,4, 4-tetramethylglutaronitrile, 1, 4-dicyanopentane, 1, 2-dicyanobenzene, 1, 3-dicyanobenzene, 1, 4-dicyanobenzene, ethylene glycol bis (propionitrile) ether, 3, 5-dioxa-pimelonitrile, 1, 4-bis (cyanoethoxy) butane, diethylene glycol bis (2-cyanoethyl) ether, triethylene glycol bis (2-cyanoethyl) ether, tetraethylene glycol bis (2-cyanoethyl) ether, 1, 3-bis (2-cyanoethoxy) propane, 1, 4-bis (2-cyanoethoxy) butane, 1, 5-bis (2-cyanoethoxy) pentane, ethylene glycol di (4-cyanobutyl) ether, 1, 4-dicyano-2-butene, 1, 4-dicyano-2-methyl-2-butene, 1, 4-dicyano-2-ethyl-2-butene, 1, 4-dicyano-2, 3-dimethyl-2-butene, 1, 4-dicyano-2, 3-diethyl-2-butene, 1, 6-dicyano-3-hexene, 1, 6-dicyano-2-methyl-3-hexene, 1,3, 5-pentanetrimethylnitrile, 1,2, 3-propanetricitrile, 1,3, 6-hexanetricarbonitrile, 1,2, 3-tris (2-cyanoethoxy) propane, 1,2, 4-tris (2-cyanoethoxy) butane, 1,1, 1-tris (cyanoethoxymethylene) ethane, 1,1, 1-tris (cyanoethoxymethylene) propane, 3-methyl-1, 3, 5-tris (cyanoethoxy) pentane, 1,2, 7-tris (cyanoethoxy) heptane, 1,2, 6-tris (cyanoethoxy) hexane and 1,2, 5-tris (cyanoethoxy) pentane; and the content of the organic compound having a cyano group is 0.1 to 15 wt% based on the total weight of the electrolyte.

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

Additional aspects and advantages of embodiments of the present 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 present 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 present 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 linked by the term "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 a only; only B; or A and B. In another example, if items A, B and C are listed, the phrase "at least one of A, B and C" means a only; 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. At least one of the terms has the same meaning as at least one of the terms.

As used herein, the term "alkyl" is intended to be a straight chain saturated hydrocarbon structure having from 1 to 20 carbon atoms. "alkyl" is also contemplated to be a branched or cyclic hydrocarbon structure having from 3 to 20 carbon atoms. When an alkyl group having a particular carbon number is specified, all geometric isomers having that carbon number are intended to be encompassed; thus, for example, "butyl" is meant 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.

As used herein, the term "halo" refers to substitution by a stabilizing atom belonging to group 17 of the periodic table of elements (e.g., fluorine, chlorine, bromine, or iodine).

The theoretical capacity of an electrochemical device (e.g., a lithium ion battery) may vary depending on the kind of the negative electrode active material. As the cycle progresses, the electrochemical device generally generates a phenomenon in which the charge/discharge capacity is reduced. This is because the electrochemical device undergoes a change in the electrode interface during charging and/or discharging, resulting in failure of the electrode active material to perform its function.

The interface stability of the electrochemical device in the circulation process is ensured by using the combination of the specific cathode material and the specific electrolyte, so that the circulation and high-temperature storage performance of the electrochemical device are improved.

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

1. Negative electrode mixture layer

The negative electrode mixture layer contains a negative electrode active material layer, and the negative electrode active material layer contains a negative electrode active material. The negative electrode mixture layer may be one or more layers, and each of the plurality of layers of negative electrode active materials may contain the same or different negative electrode active materials. 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 unintentional precipitation of lithium metal on the negative electrode during charging.

(1) Polymer compound having Si-C and Si-O bonds

One main feature of the electrochemical device of the present application is that the negative electrode mixture layer contains a carbon material as a negative electrode active material, and a polymer compound having Si — C and Si — O bonds is included on the surface of the negative electrode mixture layer or at least a part of the surface of the carbon material.

The polymer compound having Si — C and Si — O bonds provided on at least a part of the surface of the negative electrode mixture layer or the surface of the negative electrode active material (carbon material) can effectively improve the interface stability of the negative electrode mixture layer, and thus can effectively improve the cycle performance and storage performance of the electrochemical device.

The bonding state of the elements in the negative electrode mixture layer can be detected by X-ray photoelectron spectroscopy (XPS): in XPS, in a device which was energy-calibrated so that the peak of the 4f orbital of a gold atom (Au4f) was at 84.0eV, the respective peaks of the 2p orbitals of silicon (Si2p1/2Si-O and Si2p3/2Si-O) bonded with oxygen were observed at 104.0eV (Si2p1/2Si-O) and 103.4eV (Si2p3/2 Si-O); meanwhile, respective peaks of the 2p orbitals of silicon bonded to carbon (Si2p1/2Si-C and Si2p3/2Si-C) were observed in regions lower than the 2p orbitals of silicon bonded to oxygen (Si2p1/2Si-O and Si2p3/2Si-O), respectively.

(a) comprising a polyether siloxane;

(c) an aqueous solution containing 0.1% by weight of the polymer compound having Si-C and Si-O bonds has a surface tension of not more than 30 mN/m. In some embodiments, the polymeric compound having Si-C and Si-O bonds comprises a polyether siloxane.

Polyether siloxanes

In some embodiments, the polymeric compound having Si-C and Si-O bonds comprises a polyether siloxane. In some embodiments, the polyether siloxane comprises at least one of a complex silicone polyether complex, a polyether modified trisiloxane, or a polyether modified silicone polyether siloxane.

Examples of polyether siloxanes include, but are not limited to, trisiloxane surfactants (CAS No. 3390-61-2; 28855-11-0), silicone surfactants (Sylgard 309), dihydroxy polydimethylsiloxanes ((PMX-0156)), or methyl silicone oil polydimethylsiloxanes (CAS No. 63148-62-9).

The polyether siloxanes described above can be used alone or in any combination. When the polymer compound having Si-C and Si-O bonds contains two or more polyether siloxanes, the content of polyether siloxanes refers to the total content of two or more polyether siloxanes. In some embodiments, the polyether siloxane is present in an amount of 3000ppm or less, 2000ppm or less, 1000ppm or less, 500ppm or less, 300ppm or less, or 200ppm or less, based on the total weight of the negative electrode mixture layer. When the content of the polyether siloxane is within the above range, it is advantageous to improve the following properties of the electrochemical device: output characteristics, load characteristics, low-temperature characteristics, cycle characteristics, high-temperature storage characteristics, and the like.

Oxidation/reduction potential

In some embodiments, the oxidation potential of the high molecular compound having Si — C and Si — O bonds is not less than 4.5V, and the reduction potential is not more than 0.5V. In some embodiments, the oxidation potential of the high molecular compound having Si — C and Si — O bonds is not less than 5V, and the reduction potential is not more than 0.3V. The high molecular compound having Si-C and Si-O bonds having the above oxidation/reduction potential is stable in electrochemical properties, and contributes to improvement of cycle and high-temperature storage properties of an electrochemical device.

Surface tension

In some embodiments, an aqueous solution containing 0.1 wt% of the polymer compound having Si-C and Si-O bonds has a surface tension of not more than 30 mN/m. In some embodiments, an aqueous solution containing 0.1 wt% of the polymer compound having Si-C and Si-O bonds has a surface tension of not more than 25 mN/m. In some embodiments, an aqueous solution containing 0.1 wt% of the polymer compound having Si-C and Si-O bonds has a surface tension of not more than 20 mN/m. In some embodiments, an aqueous solution containing 0.1 wt% of the polymer compound having Si-C and Si-O bonds has a surface tension of not more than 15 mN/m. In some embodiments, an aqueous solution containing 0.1 wt% of the polymer compound having Si-C and Si-O bonds has a surface tension of not more than 10 mN/m. The polymer compound having Si-C and Si-O bonds with the surface tension as described above allows the negative electrode mixture layer to have a good interface, contributing to improvement of cycle and high-temperature storage performance of the electrochemical device.

The surface tension of the polymer compound having Si-C and Si-O bonds can be measured by the following method: the test is carried out on the water solution of the high molecular compound with the Si-C and Si-O bonds and the solid content of 1% by using a JC2000D3E type contact angle measuring instrument, each sample is tested at least 3 times, at least 3 data are selected, and the average value is taken to obtain the surface tension of the high molecular compound with the Si-C and Si-O bonds.

According to some embodiments of the present application, the content of the polymer compound having Si — C and Si — O bonds is 3000ppm or less based on the total weight of the negative electrode mixture layer. In some embodiments, the content of the polymer compound having Si — C and Si — O bonds is 2500ppm or less based on the total weight of the negative electrode mixture layer. In some embodiments, the content of the polymer compound having Si — C and Si — O bonds is 2000ppm or less based on the total weight of the negative electrode mixture layer. In some embodiments, the content of the polymer compound having Si — C and Si — O bonds is 1500ppm or less based on the total weight of the negative electrode mixture layer. In some embodiments, the content of the polymer compound having Si — C and Si — O bonds is 1000ppm or less based on the total weight of the negative electrode mixture layer. In some embodiments, the content of the polymer compound having Si — C and Si — O bonds is 500ppm or less based on the total weight of the negative electrode mixture layer.

(2) Carbon material

According to some embodiments of the present application, the carbon material comprises at least one of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, hard carbon and amorphous carbon.

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

(a) less than 5m²Specific surface area per gram (BET);

(b) a median particle diameter (D50) of 5 to 30 μm;

(c) the surface has amorphous carbon.

Specific surface area (BET)

In some embodiments, the carbon material has less than 5m²Specific surface area in g. In some embodiments, the carbon material has less than 3m²Specific surface area in g. In some embodiments, the carbon material has less than 1m²Specific surface area in g. In some embodiments, the carbon material has greater than 0.1m²Specific surface area in g. In some embodiments, the carbon material has less than 0.7m²Specific surface area in g. In some embodiments, the carbon material has less than 0.5m²Specific surface area in g. In some embodiments, the carbon material has a specific surface area within a range consisting of any two of the above values. 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 due to reaction of the negative electrode with the electrolyte can be suppressed.

The specific surface area (BET) of the carbon material can be determined by the following method: the sample was preliminarily dried at 350 ℃ for 15 minutes under a nitrogen flow using a surface area meter (full-automatic surface area measuring apparatus manufactured by large-scale research), and then measured by a nitrogen adsorption BET single-point method using a gas flow method using a nitrogen-helium mixed gas in which the relative pressure value of nitrogen with respect to the atmospheric pressure was accurately adjusted to 0.3.

Median diameter (D50)

The median particle diameter (D50) of the carbon material is a volume-based average particle diameter obtained by a laser diffraction/scattering method. In some embodiments, the carbon material has a median particle size (D50) of 5 μ ι η to 30 μ ι η. In some embodiments, the carbon material has a median particle size (D50) of 10 μm to 25 μm. In some embodiments, the carbon material has a median particle size (D50) of 15 μ ι η to 20 μ ι η. In some embodiments, the carbon material has a median particle diameter (D50) of 1 μ ι η,3 μ ι η,5 μ ι η,7 μ ι η, 10 μ ι η, 15 μ ι η, 20 μ ι η, 25 μ ι η, 30 μ ι η, or a range of any two values thereof. 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 negative electrode.

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

X-ray diffraction pattern parameters

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

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

The carbon material is 1580cm^-1The near Raman half-peak width is not particularly limitedAnd (5) preparing. In some embodiments, the carbon material is at 1580cm^-1Near Raman half-peak width of more than 10cm^-1Or more than 15cm^-1. In some embodiments, the carbon material is at 1580cm^-1Near Raman half-peak width of less than 100cm^-1Less than 80cm^-1Less than 60cm^-1Or less than 40cm^-1. In some embodiments, the carbon material is at 1580cm^-1The near raman half-peak width is within a range consisting of any two of the above values.

The raman R value and the raman half-value width are indices indicating the crystallinity of the carbon material surface. The appropriate crystallinity can keep the interlayer sites of the carbon material for accommodating lithium during the charge and discharge processes, and the interlayer sites do not disappear, thereby being beneficial to the chemical stability of the carbon material. When the raman R value and/or the raman half-peak width are within the above ranges, the carbon material can form an appropriate coating 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 reduction in efficiency and gas generation due to the reaction between the carbon material and the electrolyte.

The raman R value or raman half-peak width can be determined by argon ion laser raman spectroscopy: the measurement was performed by using a raman spectrometer (manufactured by japan spectroscopy corporation) to fill the measurement cell with a sample by naturally dropping the sample, and irradiating the surface of the sample in the cell with an argon ion laser while rotating the cell in a plane perpendicular to the laser. The Raman spectrum obtained was measured at 1580cm^-1The intensity IA of the nearby peak PA is 1360cm^-1The intensity IB of the nearby peak PB is calculated as the intensity ratio R (R ═ IB/IA).

The measurement conditions of the raman spectroscopy were as follows:

argon ion laser wavelength: 514.5nm

Laser power on the 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 degree

The "roundness" is defined as follows: roundness (the perimeter of an equivalent circle having the same area as the projected shape of the particle)/(the actual perimeter of the projected shape of the particle). When the roundness is 1.0, the spherical ball is theoretically perfect.

In some embodiments, the carbon material has a particle size of 3 μm to 40 μm and a circularity 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 circularity of the carbon material, the higher the filling property for high current density charge-discharge characteristics, which contributes to suppressing the resistance between particles, thereby improving the charge-discharge characteristics of the electrochemical device at high current density.

The circularity of the carbon material can be measured using a flow type particle image analyzer (FPIA manufactured by Sysmex): a0.2 g sample was dispersed in a 0.2 wt% aqueous solution (50mL) of polyoxyethylene (20) sorbitan monolaurate, irradiated with ultrasonic waves of 28kHz at an output of 60W for 1 minute, and measured for particles having a particle diameter in the range of 3 μm to 40 μm while designating a detection range of 0.6 μm to 400 μm.

The method for improving the circularity is not particularly limited. Spheroidization can be used to make the void shapes between carbon material particles uniform when preparing electrodes. The spheroidization treatment may be performed by a mechanical means such as applying a shearing force or a compression force, or may be performed by a mechanical/physical means such as applying a binder or granulating a plurality of fine particles by an adhesive force of the particles themselves, thereby making the carbon material particles approach a regular spherical shape.

Tap density

In some embodiments, the carbon material has a tap density greater than 0.1g/cm³More than 0.5g/cm³More than 0.7g/cm³Or more than 1g/cm³. In some embodiments, the carbon material has a tap density of less than 2g/cm³Less than 1.8g/cm³Or less than 1.6g/cm³. In some embodiments, the carbon material has a tap density within a range consisting of any two of the above values.When the tap density of the carbon material is within the above range, the capacity of the electrochemical device can be secured, and the increase in the electrical resistance between the carbon material particles can be suppressed.

The tap density of a carbon material can be tested by the following method: the sample was passed through a sieve having a mesh opening of 300 μm and dropped into a 20cm cell³Until the sample is filled up to the upper end face of the tank, the Tap density of the tank (2) is calculated from the mass at the time and the mass of the sample by performing 1000 times of vibration with a stroke length of 10mm using a powder density measuring instrument (for example, Tap densifier manufactured by Seishin corporation).

Orientation ratio

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

Length to thickness ratio

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

When the length-to-thickness ratio of the carbon material is within the above range, more uniform coating can be performed, and thus the electrochemical device can have excellent high current density charge and discharge characteristics.

(3) Contact angle

According to some embodiments of the present application, the negative electrode mixture layer has a contact angle of not more than 60 ° with respect to a non-aqueous solvent as measured by a contact angle measuring method. In some embodiments, the negative electrode mixture layer has a contact angle of not more than 50 ° with respect to a non-aqueous solvent as measured by a contact angle measuring method. In some embodiments, the negative electrode mixture layer has a contact angle of not more than 30 ° with respect to a non-aqueous solvent as measured by a contact angle measuring method. When the negative electrode mixture layer has the contact angle with respect to the nonaqueous solvent as described above, the negative electrode mixture layer has fewer defects at the interface, has good stability in charge and discharge cycles of the electrochemical device, and can ensure cycle and high-temperature storage performance of the electrochemical device.

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

According to some embodiments of the present application, a droplet diameter of the non-aqueous solvent on the negative electrode mixture layer is not more than 30mm as measured by contact angle measurement. In some embodiments, the non-aqueous solvent has a droplet diameter on the negative electrode mixture layer of no greater than 20mm as measured by contact angle measurement. In some embodiments, the non-aqueous solvent has a droplet diameter on the negative electrode mixture layer of no greater than 15mm as measured by contact angle measurement. In some embodiments, the non-aqueous solvent has a droplet diameter on the negative electrode mixture layer of no greater than 10mm as measured by contact angle measurement. When the negative electrode mixture layer has the above contact angle with respect to the nonaqueous solvent and the nonaqueous solvent has the above droplet diameter, the cycle and high-temperature storage performance of the electrochemical device are further improved.

The contact angle of the negative electrode mixture layer with respect to the nonaqueous solvent and the diameter of the nonaqueous solvent droplet can be measured by the following methods: 3 microliter of diethyl carbonate is dripped on the surface of the negative electrode mixture layer, the diameter of the liquid drop is tested by using a JC2000D3E type contact angle measuring instrument within 100 seconds, and a 5-point fitting method (namely, 2 points on the left plane and the right plane of the liquid drop are taken firstly, a liquid-solid interface is determined, and then 3 points are taken on the circular arc of the liquid drop) is adopted for fitting to obtain the contact angle of the negative electrode mixture layer relative to the non-aqueous solvent. And measuring each sample at least 3 times, selecting at least 3 data with the difference value smaller than 5 degrees, and averaging to obtain the contact angle of the negative electrode mixture layer relative to the non-aqueous solvent. The non-aqueous solvent used in the contact angle test may be selected from common electrolyte solvents such as diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, methyl propyl carbonate or methyl isopropyl carbonate.

(4) Porosity of the material

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

The porosity of the negative electrode mixture layer may be measured by the following method: the test was performed using a true density tester, AccuPyc II1340, with at least 3 measurements per sample, and at least 3 data were taken and averaged. The porosity of the negative electrode mixture layer was calculated according to the following formula: porosity (V1-V2)/V1 × 100%, where V1 is the apparent volume and V1 is the sample surface area × sample thickness × number of samples; v2 is the true volume.

(5) Thickness of

The thickness of the negative electrode mixture layer refers to the thickness of the negative electrode mixture layer on either side of the negative electrode current collector. In some embodiments, the negative electrode mixture layer has a thickness of not greater than 200 μm. In some embodiments, the negative electrode mixture layer has a thickness of not greater than 150 μm. In some embodiments, the negative electrode mixture layer has a thickness of not greater than 100 μm. In some embodiments, the negative electrode mixture layer has a thickness of not greater than 50 μm. In some embodiments, the thickness of the negative electrode mixture layer is not less than 15 μm. In some embodiments, the thickness of the negative electrode mixture layer is not less than 20 μm. In some embodiments, the thickness of the negative electrode mixture layer is not less than 30 μm. In some embodiments, the thickness of the negative electrode mixture layer is within a range of any two of the above values.

(6) Ball-crush test of negative electrode mixture layer

According to some embodiments of the present application, when balls having a diameter of 15mm and a weight of 12 g are dropped onto the negative electrode mixture layer, the minimum height of the balls causing cracks in the negative electrode mixture layer is 50cm or more. In some embodiments, when a ball having a diameter of 15mm and a weight of 12 g is dropped on the negative electrode mix layer, the minimum height of the ball causing cracking of the negative electrode mix layer is 150cm or less.

The minimum height of the negative electrode mixture layer crack-producing ball is related to the interface of the mixture layer. When the minimum height is 50cm or more, the interface of the negative electrode mixture layer does not crack in an undesired direction at the time of cutting.

The minimum height of the balls for cracking the negative electrode mixture layer is related to the thickness and porosity of the negative electrode mixture layer, while the balance between the Machine Direction (MD) and the Transverse Direction (TD) is obtained. The larger the thickness of the negative electrode mixture layer is, the larger the minimum height of the ball that cracks the negative electrode mixture layer is, but the excessively thick negative electrode mixture layer lowers the energy density of the electrochemical device. The smaller the porosity of the negative electrode mixture layer, the larger the minimum height of the sphere that causes cracking of the negative electrode mixture layer, but too low a porosity may degrade the electrochemical performance (e.g., rate capability) of the electrochemical device.

(7) Other Components

Trace elements

According to some embodiments of the present application, the negative electrode mix layer further includes at least one metal of molybdenum, iron, and copper. The metal elements can react with some organic matters with poor electric conductivity in the negative active material, thereby being beneficial to forming a film on the surface of the negative active material.

According to some embodiments of the present application, the metal element is present in a trace amount in the negative electrode mixture layer, and an excessive amount of the metal element easily forms a nonconductive by-product and adheres to the surface of the negative electrode. In some embodiments, the at least one metal is present in an amount of no greater than 0.05 wt%, based on the total weight of the negative electrode mixture layer. In some embodiments, the at least one metal is present in an amount no greater than 0.03 wt%. In some embodiments, the at least one metal is present in an amount no greater than 0.01 wt%.

Material containing silicon and/or tin element

According to some embodiments of the present application, the negative electrode mixture layer further comprises at least one of a silicon-containing material, a tin-containing material, an alloy material. According to some embodiments of the present application, the negative electrode mixture layer further includes at least one of a silicon-containing material and a tin-containing material. In some embodiments, the negative electrode mixture layer further comprises 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 negative electrode mix layer further comprises other kinds of negative electrode 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 and metalloid elements 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 metal element and metalloid element include Si, Sn, or a combination thereof. Si and Sn have excellent ability to deintercalate lithium ions, and can provide a high energy density for a lithium ion battery. In some embodiments, the other kind of anode active material may further include one or more of a metal oxide and a polymer compound. 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, polyacetylene, polyaniline, and polypyrrole.

Negative electrode conductive material

In some embodiments, the negative electrode mixture layer further comprises a negative electrode conductive material, which may include any conductive material as long as it does not cause a chemical change. Non-limiting examples of the conductive material 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 negative electrode mixture layer further comprises a negative electrode binder. The negative electrode binder may improve the binding of the negative electrode active material particles to each other and the binding of the negative electrode active material to the current collector. The kind of the negative electrode binder is not particularly limited as long as it is a material that is stable to the electrolyte solution or the solvent used in the production of the electrode.

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 cellulose nitrate, rubbery polymers such as styrene-butadiene rubber (SBR), isoprene rubber, butadiene rubber, fluororubber, acrylonitrile-butadiene rubber (NBR), ethylene-propylene rubber, thermoplastic elastomer-based polymers such as styrene-butadiene-styrene block copolymer or a hydrogenated product thereof, soft resin-based polymers such as ethylene-propylene-diene terpolymer (EPDM), styrene-ethylene-butadiene-styrene copolymer, styrene-isoprene-styrene block copolymer or a hydrogenated product thereof, syndiotactic-1, 2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymer, and propylene- α -olefin copolymer, fluorine-based polymers such as polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, and polytetrafluoroethylene-ethylene copolymer, and polymer compositions having ion conductivity of alkali metal ions (for example, lithium ions).

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

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

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

Solvent(s)

The kind of the solvent used for forming the anode slurry is not particularly limited as long as it can dissolve or disperse the anode active material, the anode binder, and the thickener and the conductive material used as needed. In some embodiments, the solvent used to form the anode slurry may use any one of an aqueous solvent and an organic solvent. Examples of the aqueous solvent may include, but are not limited to, water, alcohol, and the like. Examples of the organic solvent may include, but are not limited to, N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, 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 thereof.

Thickening agent

The thickener is generally used for adjusting the viscosity of the negative electrode 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, and salts thereof, and the like. The thickeners may be used alone or in any combination thereof.

In some embodiments, the thickener is present in an amount greater than 0.1 wt%, greater than 0.5 wt%, or greater than 0.6 wt%, based on the total weight of the negative electrode mixture layer. In some embodiments, the thickener is present in an amount less than 5 wt%, less than 3 wt%, or less than 2 wt%, based on the total weight of the negative electrode mixture layer. When the content of the thickener is not within the above range, the negative electrode slurry can be ensured to have good coatability while suppressing a decrease in capacity and an increase in resistance of the electrochemical device.

(8) Surface coating

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

(9) Content of negative electrode active material

In some embodiments, the negative active material is present in an amount greater than 80 wt%, greater than 82 wt%, or greater than 84 wt%, based on the total weight of the negative electrode mixture layer. In some embodiments, the negative active material is present in an amount of less than 99 wt% or less than 98 wt%, based on the total weight of the negative electrode mixture layer. In some embodiments, the content of the negative electrode active material is within a range consisting of any two of the above-described arrays, based on the total weight of the negative electrode mixture layer.

(10) Density of negative electrode active material

In some embodiments, the density of the negative electrode active material in the negative electrode mixture layer is greater than 1g/cm³Greater than 1.2g/cm³Or more than 1.3g/cm³. In some embodiments, the density of the negative electrode active material in the negative electrode mixture layer is less than 2.2g/cm³Less than 2.1g/cm³Less than 2.0g/cm³Or less than 1.9g/cm³. In some embodiments, the negative electrode active material in the negative electrode mixture layerThe density is within a range consisting of any two of the above values.

When the density of the negative electrode active material is within the above range, the negative electrode active material particles can be prevented from being broken, deterioration of high current density charge-discharge characteristics due to increase of initial irreversible capacity of the electrochemical device or decrease of permeability of the electrolyte in the vicinity of the negative electrode current collector/negative electrode active material interface can be suppressed, and decrease of capacity and increase of resistance of the electrochemical device can be suppressed.

2. Negative current collector

As the current collector for holding the negative electrode active material, a known current collector may be used arbitrarily. 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 where the negative electrode current collector is a metal material, the form of the negative 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 lath, a stamped 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 a copper foil. In some embodiments, the negative electrode current collector is a rolled copper foil based on a rolling process or an electrolytic copper foil based on an electrolytic process.

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

The thickness ratio of the negative electrode current collector to the negative electrode mixture layer is a ratio of the thickness of the single-sided negative electrode mixture layer before the electrolyte is injected to the thickness of the negative electrode current collector, and the numerical value is not particularly limited. In some embodiments, the ratio of the thickness of the negative electrode current collector to the negative electrode mixture layer is less than 150, less than 20, or less than 10. In some embodiments, the ratio of the thickness of the negative electrode current collector to the negative electrode mixture layer is greater than 0.1, greater than 0.4, or greater than 1. In some embodiments, the ratio of the thickness of the negative electrode current collector to the negative electrode mixture layer is within a range consisting of any two of the above values. When the thickness ratio of the negative electrode current collector to the negative electrode mixture layer is within the above range, the heat release of the negative electrode current collector during high current density charge and discharge can be suppressed while the capacity of the electrochemical device is ensured.

II. Electrolyte solution

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

(a) propionate esters;

(b) an organic compound having a cyano group;

(c) lithium difluorophosphate; and

(d) a compound of formula 1:

wherein:

w is selected from

L is selected from a single bond or methylene;

m is an integer of 1 to 4;

n is an integer of 0 to 2; and is

p is an integer of 0 to 6.

(a) Propionic acid ester

According to some embodiments of the present application, the propionate is of formula 2:

wherein:

R¹is selected from the group consisting of ethyl or haloethyl,

R²is selected from C₁-C₆Alkyl or C₁-C₆A haloalkyl group.

In some embodiments, the propionic acid esters include, but are not limited to, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, pentyl propionate, methyl halopropionate, ethyl halopropionate, propyl halopropionate, butyl halopropionate, and pentyl halopropionate. In some embodiments, the propionate is selected from at least one of methyl propionate, ethyl propionate, propyl propionate, butyl propionate, and pentyl propionate. In some embodiments, the halogen group of the methyl, ethyl, propyl, butyl and pentyl halopropionates is selected from one or more of a fluorine group (-F), a chlorine group (-Cl), a bromine group (-Br) and an iodine group (-I). In some embodiments, the halogen group is a fluorine group (-F), which may achieve more excellent effects.

In some embodiments, the propionate is present in an amount of 10 wt% to 65 wt%, based on the total weight of the electrolyte. In some embodiments, the propionate is present in an amount of 15 wt% to 60 wt%, based on the total weight of the electrolyte. In some embodiments, the propionate is present in an amount of 30 wt% to 50 wt%, based on the total weight of the electrolyte. In some embodiments, the propionate is present in an amount of 30 wt% to 40 wt%, based on the total weight of the electrolyte. The use of the propionate having the above content can achieve more excellent effects.

(b) Compound having cyano group

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

The above-mentioned compounds having a cyano group may be used alone or in any combination. When the electrolyte contains two or more compounds having a cyano group, the content of the compounds having a cyano group means the total content of the two or more compounds having a cyano group. In some embodiments, the compound having a cyano group is contained in an amount of 0.1 to 15 wt% based on the total weight of the electrolyte. In some embodiments, the compound having a cyano group is contained in an amount of 0.5 to 10 wt% based on the total weight of the electrolyte. In some embodiments, the content of the compound having a cyano group is 1 to 8 wt% based on the total weight of the electrolyte. In some embodiments, the content of the compound having a cyano group is 3 to 5 wt% based on the total weight of the electrolyte.

₂ ₂(c) Lithium difluorophosphate (LiPOF)

In some embodiments, the lithium difluorophosphate is present in an amount of 0.01 to 15 wt%, based on the total weight of the electrolyte. In some embodiments, the lithium difluorophosphate is present in an amount of 0.05 wt% to 12 wt%, based on the total weight of the electrolyte. In some embodiments, the lithium difluorophosphate is present in an amount of 0.1 to 10 wt%, based on the total weight of the electrolyte. In some embodiments, the lithium difluorophosphate is present in an amount of 0.5 wt% to 8 wt%, based on the total weight of the electrolyte. In some embodiments, the lithium difluorophosphate is present in an amount of 1 to 5 wt%, based on the total weight of the electrolyte. In some embodiments, the lithium difluorophosphate is present in an amount of 2 wt% to 4 wt%, based on the total weight of the electrolyte.

(d) Compounds of formula 1

m is an integer of 1 to 4;

n is an integer of 0 to 2; and is

p is an integer of 0 to 6.

Solvent(s)

In some embodiments, the electrolyte further comprises any non-aqueous solvent known in the art that can act as a solvent for the electrolyte.

In some embodiments, the non-aqueous solvent includes, but is not limited to, one or more of the following: cyclic carbonate, chain carbonate, cyclic carboxylate, chain carboxylate, cyclic ether, chain ether, phosphorus-containing organic solvent, sulfur-containing organic solvent, and aromatic fluorine-containing solvent.

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 carbonates can 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 chain carbonates substituted with fluorine may include, but are not limited to, one or more of the following: bis (fluoromethyl) carbonate, bis (difluoromethyl) carbonate, bis (trifluoromethyl) carbonate, bis (2-fluoroethyl) carbonate, bis (2, 2-difluoroethyl) carbonate, bis (2,2, 2-trifluoroethyl) carbonate, 2-fluoroethyl methyl carbonate, 2, 2-difluoroethyl methyl carbonate, and 2,2, 2-trifluoroethyl methyl carbonate, and the like.

In some embodiments, examples of the cyclic carboxylic acid ester may include, but are not limited to, one or more of the following: one or more of 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 ester may include, but are not limited to, one or more of the following: methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, sec-butyl acetate, isobutyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, isopropyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, ethyl isobutyrate, methyl valerate, ethyl valerate, methyl pivalate, and ethyl pivalate, and the like. In some embodiments, a part of hydrogen atoms of the chain carboxylic acid ester may be substituted with fluorine. In some embodiments, examples of the fluorine-substituted chain carboxylic acid ester may include, but are not limited to, methyl trifluoroacetate, ethyl trifluoroacetate, propyl trifluoroacetate, butyl trifluoroacetate, 2,2, 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 phosphate, tris (2,2, 2-trifluoroethyl) phosphate, tris (2,2,3, 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-methylsulfolane, 3-methylsulfolane, dimethylsulfone, diethylsulfone, ethylmethylsulfone, methylpropylsulfone, dimethylsulfoxide, 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 substituted 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 solvent used in the electrolyte of the present application includes cyclic carbonates, chain carbonates, cyclic carboxylates, chain carboxylates, and combinations thereof. In some embodiments, the solvent used in the electrolyte of the present application comprises an organic solvent selected from the group consisting of: ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, n-propyl acetate, ethyl acetate, and combinations thereof. In some embodiments, the solvent used in the electrolyte of the present application comprises: ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl propionate, propyl propionate, gamma-butyrolactone, and combinations thereof.

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

Additive agent

In some embodiments, examples of the additive may include, but are not limited to, one or more of the following: fluoro carbonate, ethylene carbonate containing carbon-carbon double bond, compound containing sulfur-oxygen double bond and acid anhydride.

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

According to an embodiment of the present application, the propionate is contained 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 fluoro carbonates. The fluoro carbonate may cooperate with the propionate to form a stable protective film on the surface of the negative electrode at the time of charge/discharge of the lithium ion battery, thereby inhibiting the decomposition reaction of the electrolyte.

In some embodiments, the fluoro carbonate has the formula C ═ O (OR)₁)(OR₂) Wherein R is₁And R₂Each selected from alkyl or haloalkyl groups having 1 to 6 carbon atoms, wherein R is₁And R₂At least one of which is selected from fluoroalkyl groups having 1-6 carbon atoms, and R₁And R₂Optionally together with the atoms to which they are attached form a 5-to 7-membered ring.

In some embodiments, examples of the fluoro-carbonates 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, trifluoroethylmethyl carbonate, and 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 ethylene carbonate containing a carbon-carbon double bond may include, but are not limited to, one or more of the following: vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, 1, 2-dimethyl vinylene carbonate, 1, 2-diethyl vinylene carbonate, fluoroethylene carbonate and 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 ethylene carbonate containing a carbon-carbon double bond includes vinylene carbonate, which is easily available and can achieve more excellent effects.

In some embodiments, the additive comprises one or more compounds containing a sulfur-oxygen double bond. Examples of the compound containing a thiooxy double bond may include, but are not limited to, one or more of the following: cyclic sulfuric acid esters, chain sulfonic acid esters, cyclic sulfonic acid esters, chain sulfurous acid esters, cyclic sulfurous acid esters, and the like.

Examples of the cyclic sulfate may include, but are not limited to, one or more of the following: 1, 2-ethanediol sulfate, 1, 2-propanediol sulfate, 1, 3-propanediol 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, and 1, 5-pentanediol sulfate, etc.

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

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

Examples of the cyclic sulfonate ester 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-sultone, 2-propene-1, 3-sultone, 1-fluoro-1-propene-1, 3-sultone, 2-fluoro-1-propene-1, 3-sultone, 3-fluoro-1-propene-1, 3-sultone, 1, 3-propane sultone, 2-fluoro-1, 3-sultone, 2-propane-1, 3-sultone, 2-fluoro-propane-1, 3-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-pentanesulfonactone, methylene methanedisulfonate, ethylene methanedisulfonate, and the like.

Examples of the chain sulfite may include, but are not limited to, one or more of the following: dimethyl sulfite, ethyl methyl 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-ethanediol sulfite, 1, 2-propanediol sulfite, 1, 3-propanediol sulfite, 1, 2-butanediol sulfite, 1, 3-butanediol sulfite, 1, 4-butanediol sulfite, 1, 2-pentanediol sulfite, 1, 3-pentanediol sulfite, 1, 4-pentanediol sulfite, and 1, 5-pentanediol sulfite, etc.

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 trimethylphosphoric cyclic anhydride, triethylphosphoric cyclic anhydride and tripropylphosphoric cyclic anhydride. Examples of the carboxylic acid anhydride may include, but are not limited to, one or more of succinic anhydride, glutaric anhydride, and maleic anhydride. Examples of the disulfonic anhydride can include, but are not limited to, one or more of ethane disulfonic anhydride and propane disulfonic anhydride. Examples of the carboxylic 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 fluoro carbonate and ethylene carbonate containing a carbon-carbon double bond. In some embodiments, the additive is a combination of a fluoro carbonate and a compound containing a thiooxy double bond. In some embodiments, the additive is a combination of a fluoro carbonate and a compound having 2-4 cyano groups. In some embodiments, the additive is a combination of a fluoro carbonate and a cyclic carboxylic acid ester. In some embodiments, the additive is a combination of a fluoro carbonate and a cyclic phosphoric anhydride. In some embodiments, the additive is a combination of a fluorocarbonate and a carboxylic acid anhydride. In some embodiments, the additive is a combination of a fluoro carbonate and a sulfonic anhydride. In some embodiments, the additive is a combination of a fluorocarbonate and a carboxylic acid sulfonic anhydride.

Electrolyte

The electrolyte is not particularly limited, and any known electrolyte can be used. In the case of a lithium secondary battery, a lithium salt is generally used. Examples of the electrolyte may include, but are not limited to, LiPF₆、LiBF₄、LiClO₄、LiAlF₄、LiSbF₆、LiTaF₆、LiWF₇Inorganic lithium salts; LiWOF₅Lithium tungstate species; HCO₂Li、CH₃CO₂Li、CH₂FCO₂Li、CHF₂CO₂Li、CF₃CO₂Li、CF₃CH₂CO₂Li、CF₃CF₂CO₂Li、CF₃CF₂CF₂CO₂Li、CF₃CF₂CF₂CF₂CO₂Lithium carboxylates such as Li; FSO₃Li、CH₃SO₃Li、CH₂FSO₃Li、CHF₂SO₃Li、CF₃SO₃Li、CF₃CF₂SO₃Li、CF₃CF₂CF₂SO₃Li、CF₃CF₂CF₂CF₂SO₃Lithium sulfonates such as Li; LiN (FCO)₂、LiN(FCO)(FSO₂)、LiN(FSO₂)₂、LiN(FSO₂)(CF₃SO₂)、LiN(CF₃SO₂)₂、LiN(C₂F₅SO₂)₂Cyclic 1, 2-perfluoroethane bis-sulfonyl imide lithium, cyclic 1, 3-perfluoropropane bis-sulfonyl imide lithium, LiN (CF)₃SO₂)(C₄F₉SO₂) Lithium imide salts; LiC (FSO)₂)₃、LiC(CF₃SO₂)₃、LiC(C₂F₅SO₂)₃Lithium methide salts; lithium (malonate) borate salts such as lithium bis (malonate) borate salt and lithium difluoro (malonate) borate salt; lithium (malonate) phosphates such as lithium tris (malonate) phosphate, lithium difluorobis (malonate) phosphate, and lithium tetrafluoro (malonate) phosphate; and LiPF₄(CF₃)₂、LiPF₄(C₂F₅)₂、LiPF₄(CF₃SO₂)₂、LiPF₄(C₂F₅SO₂)₂、LiBF₃CF₃、LiBF₃C₂F₅、LiBF₃C₃F₇、LiBF₂(CF₃)₂、LiBF₂(C₂F₅)₂、LiBF₂(CF₃SO₂)₂、LiBF₂(C₂F₅SO₂)₂Fluorine-containing organic lithium salts; lithium oxalato borate salts such as lithium difluorooxalato borate and lithium bis (oxalato) borate; lithium oxalato phosphate salts such as lithium tetrafluorooxalato phosphate, lithium difluorobis (oxalato) phosphate, and lithium tris (oxalato) phosphate.

In some embodiments of the present invention, the,the electrolyte is selected from LiPF₆、LiSbF₆、LiTaF₆、FSO₃Li、CF₃SO₃Li、LiN(FSO₂)₂、LiN(FSO₂)(CF₃SO₂)、LiN(CF₃SO₂)₂、LiN(C₂F₅SO₂)₂Cyclic 1, 2-perfluoroethane bissulfonylimide lithium, cyclic 1, 3-perfluoropropane bissulfonylimide lithium, and LiC (FSO)₂)₃、LiC(CF₃SO₂)₃、LiC(C₂F₅SO₂)₃、LiBF₃CF₃、LiBF₃C₂F₅、LiPF₃(CF₃)₃、LiPF₃(C₂F₅)₃Lithium difluorooxalato borate, lithium bis (oxalato) borate, or lithium difluorobis (oxalato) phosphate, which contribute to improvement in output characteristics, high-rate charge-discharge characteristics, high-temperature storage characteristics, cycle characteristics, and the like of an electrochemical device.

The content of the electrolyte is not particularly limited as long as the effects of the present application are not impaired. In some embodiments, the total molar concentration of lithium in the electrolyte is greater than 0.3mol/L or greater, greater than 0.4mol/L, or greater than 0.5 mol/L. In some embodiments, the total molar concentration of lithium in the electrolyte is less than 3mol/L, less than 2.5mol/L, or less than 2.0 mol/L. In some embodiments, the total molar concentration of lithium in the electrolyte is within a range consisting of any two of the above values. When the electrolyte concentration is within the above range, lithium as charged particles is not excessively small, and the viscosity can be made to be in an appropriate range, so that good conductivity is easily ensured.

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

In some embodiments, the electrolyte comprises one or more substances selected from the group consisting of monofluorophosphates, borates, oxalates, and fluorosulfonates, and one or more salts in addition thereto. As other salts, there may be mentioned the lithium salts exemplified hereinabove, and LiPF in some examples₆、LiN(FSO₂)(CF₃SO₂)、LiN(CF₃SO₂)₂、LiN(C₂F₅SO₂)₂Cyclic 1, 2-perfluoroethane bissulfonylimide lithium, cyclic 1, 3-perfluoropropane bissulfonylimide lithium, and LiC (FSO)₂)₃、LiC(CF₃SO₂)₃、LiC(C₂F₅SO₂)₃、LiBF₃CF₃、LiBF₃C₂F₅、LiPF₃(CF₃)₃、LiPF₃(C₂F₅)₃. In some embodiments, the additional salt is LiPF₆。

In some embodiments, the amount of the additional salt is greater than 0.01 wt% or greater than 0.1 wt% based on the total weight of the electrolyte. In some embodiments, the amount of the additional salt is less than 20 wt%, less than 15 wt%, or less than 10 wt% based on the total weight of the electrolyte. In some embodiments, the amount of other salts is within a range consisting of any two of the above values. The other salts having the above contents help to balance the conductivity and viscosity of the electrolyte.

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

III, positive electrode

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

1. Positive electrode mixture layer

The positive electrode mixture layer contains a positive electrode active material layer containing a positive electrode active material. The positive electrode active material layer may be one or more layers. Each of the multiple layers of the positive electrode active material may contain the same or different positive electrode active material. 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 can electrochemically occlude and release metal ions (for example, lithium ions). In some embodiments, the positive active material is a material containing lithium and at least one transition metal. Examples of the positive active material may include, but are not limited to, lithium transition metal composite oxides and lithium 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 comprises LiCoO₂Lithium cobalt composite oxide, LiNiO, etc₂Lithium nickel composite oxide and LiMnO₂、LiMn₂O₄、Li₂MnO₄The lithium manganese composite oxide,LiNi_1/3Mn_1/3Co_1/3O₂、LiNi_0.5Mn_0.3Co_0.2O₂And lithium nickel manganese cobalt composite oxides in which a part of transition metal atoms that are the main components of these lithium transition metal composite oxides is replaced with another element 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, and the like. Examples of the lithium transition metal composite oxide may include, but are not limited to, LiNi_0.5Mn_0.5O₂、LiNi_0.85Co_0.10Al_0.05O₂、LiNi_0.33Co_0.33Mn_0.33O₂、LiNi_0.45Co_0.10Al_0.45O₂、LiMn_1.8Al_0.2O₄And LiMn_1.5Ni_0.5O₄And the like. Examples of the combination of lithium transition metal composite oxides include, but are not limited to, LiCoO₂With LiMn₂O₄In which LiMn is₂O₄A part of Mn in (A) may be substituted with a transition metal (e.g., LiNi)_0.33Co_0.33Mn_0.33O₂)，LiCoO₂A part of Co in (a) may be substituted 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 LiFePO₄、Li₃Fe₂(PO₄)₃、LiFeP₂O₇Iso-phosphates, LiCoPO₄And cobalt phosphates in which a part of the transition metal atoms as the main component of the lithium transition metal phosphate compound is replaced with another element such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, or Si.

In some embodiments, lithium phosphate is included in the positive 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 mixture. In some embodiments, the lithium phosphate is present in an amount greater than 0.1 wt%, greater than 0.3 wt%, or greater than 0.5 wt% relative to the total weight of the positive electrode active material and the lithium phosphate. In some embodiments, the lithium phosphate is present in an amount less than 10 wt%, less than 8 wt%, or less than 5 wt% relative to the total weight of the positive electrode active material and the lithium phosphate. In some embodiments, the lithium phosphate is present in an amount within the range of any two of the above recited values.

Surface coating

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

These surface-adhering substances can be adhered to the surface of the positive electrode active material by the following method: a method of dissolving or suspending a surface adhesion substance in a solvent, infiltrating the surface adhesion substance into the positive electrode active material, and drying the positive electrode active material; a method in which a precursor of a surface-adhering substance is dissolved or suspended in a solvent, and the solution is added to the positive electrode active material after being impregnated with the precursor, and then the precursor is 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 carbon attachment, a method of mechanically attaching a carbon material (for example, activated carbon or the like) may also be used.

In some embodiments, the surface attachment species is present in an amount greater than 0.1ppm, greater than 1ppm, or greater than 10ppm based on the total weight of the positive electrode mixture layer. In some embodiments, the surface attachment species is present in an amount of less than 20%, less than 10%, or less than 10% based on the total weight of the positive electrode mixture layer. In some embodiments, the amount of the surface attachment substance is within a range consisting of any two of the above values, based on the total weight of the positive electrode mixture layer.

By adhering 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 cannot be sufficiently exhibited; when the amount of the surface-adhering substance is too large, the entry and exit of lithium ions are inhibited, and the electric resistance may increase.

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

Shape of

In some embodiments, the shape of the positive electrode active material particles includes, but is not limited to, a block shape, a polyhedral shape, a spherical shape, an elliptical spherical shape, a plate shape, a needle shape, a columnar shape, and the like. In some embodiments, the positive 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 tap density of the positive electrode active material is greater than 0.5g/cm³More than 0.8g/cm³Or more than 1.0g/cm³. When the tap density of the positive electrode active material is within the above range, the amount of the dispersion medium and the required amounts of the conductive material and the positive electrode binder required for forming the positive electrode mixture layer can be suppressed, and thereby the filling ratio of the positive electrode active material and the capacity of the electrochemical device can be ensured. By using the composite oxide powder having a high tap density, a high-density positive electrode mixture layer can be formed. The higher the tap density is, the more preferable the tap density is, and there is no particular upper limit. In some embodiments, the tap density of the positive electrode active material is less than 4.0g/cm³Less than 3.7g/cm³Or less than 3.5g/cm³. When the tap density of the positive electrode active material has the above-described upper limit, the reduction in load characteristics can be suppressed.

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

Median 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 primary particle diameter of the positive electrode active material particles. When the primary particles of the positive electrode active material particles aggregate to form secondary particles, the median particle 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 above values. When the median diameter (D50) of the positive electrode active material particles is within the above range, a positive electrode active material having a high tap density can be obtained, and a decrease in the performance of the electrochemical device can be suppressed. On the other hand, in the process of manufacturing a positive electrode for an electrochemical device (that is, when a positive electrode active material, a conductive material, a binder, and the like are slurried in a solvent and applied in a thin film), problems such as occurrence of streaks 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 producing the positive electrode can be further improved.

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

Average primary particle diameter

In the case where the primary particles of the positive electrode active material particles are aggregated to form the 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 size of the positive electrode active material is within a range consisting of any two of the above values. When the average primary particle diameter of the positive electrode active material is within the above range, the reversibility of charge and discharge of the electrochemical device can be ensured by ensuring powder-filling property and specific surface area, suppressing a decrease in battery performance, and obtaining appropriate crystallinity.

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 the SEM image having the magnification of 10000 times, the longest value of a slice obtained from the left and right boundary lines of the primary particles with respect to the horizontal straight line is obtained for any 50 primary particles, and the average primary particle diameter is obtained by obtaining the average value thereof.

Specific surface area (BET)

In some embodiments, the specific surface area (BET) of the positive electrode active material is greater than 0.1m²A ratio of the water to the water of more than 0.2m²A/g or more than 0.3m²(ii) in terms of/g. In some embodiments, the specific surface area (BET) of the positive electrode active material is less than 50m²A ratio of/g to less than 40m²A/g or less than 30m²(ii) in terms of/g. In some embodiments, the specific surface area (BET) of the positive electrode active material is within a range consisting of any two of the above values. When the specific surface area (BET) of the positive electrode active material is within the above range, the performance of the electrochemical device can be ensured while 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 measurement was performed by a nitrogen adsorption BET single point method using a gas flow method using a nitrogen helium mixed gas in which a sample was pre-dried at 150 ℃ for 30 minutes under a nitrogen gas flow using a surface area meter (for example, a full-automatic surface area measuring apparatus manufactured by large-scale research), and then a relative pressure value of nitrogen gas with respect to 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, but are not limited to, graphite such as natural graphite, artificial graphite, and the like; carbon black such as acetylene black; carbon materials such as amorphous carbon such as needle coke; a carbon nanotube; graphene, and the like. The above-mentioned positive electrode conductive materials may be used alone or in any combination.

In some embodiments, the positive electrode conductive material is present in an amount greater than 0.01 wt%, greater than 0.1 wt%, or greater than 1 wt%, based on the total weight of the positive electrode mixture layer. In some embodiments, the content of the positive electrode conductive material is less than 50 wt%, less than 30 wt% or less, or less than 15 wt%, based on the total weight of the positive electrode mixture 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 secured.

Positive electrode binder

The type of the positive electrode binder used for producing the positive electrode mixture layer is not particularly limited, and in the case of the coating method, it is only required to be a material that can be dissolved or dispersed in a liquid medium used for producing the electrode, examples of the positive electrode binder include, but are not limited to, one or more of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose nitrate and other resin-based polymers, Styrene Butadiene Rubber (SBR), Nitrile Butadiene Rubber (NBR), fluororubber, isoprene rubber, polybutadiene rubber, ethylene-propylene rubber and other rubbery polymers, styrene-butadiene-styrene block copolymers or hydrides thereof, ethylene-propylene-diene terpolymers (EPDM), styrene-ethylene-butadiene-ethylene copolymers, styrene-isoprene-styrene block copolymers or hydrides thereof and other thermoplastic elastomeric polymers, syndiotactic-1, 2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, propylene- α -olefin copolymers and other soft resin-based polymers, polyvinylidene fluoride (PVDF), polytetrafluoroethylene fluoride, polytetrafluoroethylene ion-based polymer compositions and other ionic metal-based binders, and particularly lithium ion conductive polymers.

In some embodiments, the positive electrode binder is present in an amount greater than 0.1 wt%, greater than 1 wt%, or greater than 1.5 wt%, based on the total weight of the positive electrode mixture layer. In some embodiments, the positive electrode binder is present in an amount of less than 80 wt%, less than 60 wt%, less than 40 wt%, or less than 10 wt%, based on the total weight of the positive electrode mixture layer. When the content of the positive electrode binder is within the above range, it is possible to provide the positive electrode with good electrical conductivity and sufficient mechanical strength, and to secure the capacity of the electrochemical device.

Solvent(s)

The type of solvent used for forming the positive electrode slurry is not limited as long as it can dissolve or disperse the positive electrode active material, the conductive material, the positive electrode binder, and the thickener used as needed. Examples of the solvent used for forming 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 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; and aprotic polar solvents such as hexamethylphosphoramide and dimethylsulfoxide.

Thickening agent

Thickeners are commonly used to adjust the viscosity of the slurry. In the case of using an aqueous medium, slurrying may be performed using a thickener and a 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, and 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 0.1 wt%, greater than 0.2 wt%, or greater than 0.3 wt%, based on the total weight of the positive electrode mixture layer. In some embodiments, the thickener is present in an amount less than 5 wt%, less than 3 wt%, or less than 2 wt%, based on the total weight of the positive electrode mixture layer. In some embodiments, the thickener is present in an amount within a range consisting of any two of the above values, based on the total weight of the positive electrode mixture layer. When the content of the thickener is within the above range, the positive electrode slurry can have good coatability, and the decrease in capacity and the increase in resistance of the electrochemical device can be suppressed.

Content of positive electrode active material

In some embodiments, the positive electrode active material is present in an amount greater than 80 wt%, greater than 82 wt%, or greater than 84 wt%, based on the total weight of the positive electrode mixture layer. In some embodiments, the content of the positive electrode active material is less than 99 wt% or less than 98 wt% based on the total weight of the positive electrode mixture layer. In some embodiments, the positive electrode active material is present in an amount within a range consisting of any two of the above-described groups, based on the total weight of the positive electrode mixture layer. When the content of the positive electrode active material is within the above range, the positive electrode can maintain the strength while ensuring the capacity of the positive electrode active material in the positive electrode mixture layer.

Density of positive electrode active material

The positive electrode mixture layer obtained by coating and drying may be subjected to a compacting treatment by a hand 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 mixture layer has a density greater than 1.5g/cm³More than 2g/cm³Or more than 2.2g/cm³. In some embodiments, the positive electrode mixture layer has a density of less than 5g/cm³Less than 4.5g/cm³Or less than 4g/cm³. In some embodiments, the density of the positive electrode mixture layer is within a range consisting of any two of the above values. When the density of the positive electrode mixture layer is within the above range, the electrochemical device can have good charge and discharge characteristics while suppressing an increase in resistance.

Thickness of positive electrode mixture layer

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

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 can be used: dissolving or pulverizing transition metal raw material, dispersing in solvent such as water, adjusting pH under stirring to obtain spherical precursor, recovering, drying, and adding LiOH and Li₂CO₃、LiNO₃And firing the Li source at a high temperature to obtain the positive electrode active material.

2. Positive 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, etc.; carbon cloth, carbon paper, and the like. In some embodiments, the positive current collector is a metallic material. In some embodiments, the positive current collector is aluminum.

The form of the positive electrode current collector is not particularly limited. When the positive electrode collector is a metal material, the form of the positive electrode 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 lath, a stamped metal, a foamed metal, and the like. When the positive electrode collector is a carbon material, the form of the positive electrode 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 current collector is a metal thin film. In some embodiments, the metal film is a mesh. The thickness of the metal thin film is not particularly limited. In some embodiments, the metal thin film has a thickness greater than 1 μm, greater than 3 μm, or greater than 5 μm. In some embodiments, the metal thin 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 above values.

In order to reduce the electron contact resistance of the positive electrode current collector and the positive electrode mixture layer, the surface of the positive electrode current collector may include a conductive assistant. 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 mixture layer is a ratio of the thickness of the positive electrode mixture layer on one surface before the electrolyte is injected to the thickness of the positive electrode current collector, and the numerical value is not particularly limited. In some embodiments, the ratio of the thickness of the positive electrode current collector to the positive electrode mixture 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 mixture layer is greater than 0.5, greater than 0.8, or greater than 1. In some embodiments, the ratio of the thickness of the positive electrode current collector to the positive electrode mixture layer is within a range consisting of any two of the above values. When the thickness ratio of the positive electrode current collector to the positive electrode mixture layer is within the above range, heat generation of the positive electrode current collector during high current density charge and discharge can be suppressed, and the capacity of the electrochemical device can be ensured.

3. Positive electrode composition and method for producing the same

The positive electrode can be produced by forming a positive electrode mixture layer containing a positive electrode active material and a binder active material on a current collector. The production of a positive electrode using a positive electrode active material can be carried out by a conventional method in which a positive electrode active material and a binder active material, and if necessary, a conductive material, a thickener, and the like are dry-mixed to be made into a sheet-like form, and the obtained sheet-like form is pressure-bonded to a positive electrode current collector; alternatively, 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 mixture layer on the current collector, thereby obtaining a positive electrode.

IV, isolating film

In order to prevent short-circuiting, 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 the separator.

The material and shape of the separator are not particularly limited as long as the effects of the present application are 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 having excellent liquid retention properties, a nonwoven fabric-like material, or the like. Examples of materials for the resin or glass fiber separator film may include, but are not limited to, polyolefins, aramids, polytetrafluoroethylene, polyethersulfone, glass filters, and the like. In some embodiments, the material of the separation membrane 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 also be a material in which the above materials are laminated, and examples thereof include, but are not limited to, a three-layer separator in which polypropylene, polyethylene, polypropylene are laminated in this order, and the like.

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, and sulfates (e.g., barium sulfate, calcium sulfate, and the like). Forms of inorganic matter may include, but are not limited to, particulate or fibrous.

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

The thickness of the separator is arbitrary. In some embodiments, the thickness of the separator is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the isolation film is less than 50 μm, less than 40 μm, or less than 30 μm. In some embodiments, the thickness of the barrier film is within a range consisting of any two of the above values. When the thickness of the separator is within the above range, the insulating property and the mechanical strength can be secured, and the rate characteristic and the energy density of the electrochemical device can be secured.

When a porous material such as a porous sheet or 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 porosity of the separator is less than 90%, less than 85%, or less than 75%. In some embodiments, the porosity of the separator is within a range consisting of any two of the above values. When the porosity of the separator is within the above range, insulation and mechanical strength can be ensured, and membrane resistance can be suppressed, so that the electrochemical device has good rate characteristics.

The average pore diameter of the separator is also arbitrary. In some embodiments, the mean pore size of the separator is less than 0.5 μm or less than 0.2 μm. In some embodiments, the separator membrane has an average pore size greater than 0.05 μm. In some embodiments, the mean pore size of the separator is within a range consisting of any two of the above values. If the average pore diameter of the separator exceeds the above range, short circuits are likely to occur. When the average pore diameter of the separation membrane 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 group, a current collecting structure, an outer case, and a protective member.

Electrode group

The electrode group may have 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 electrode group has a mass occupying ratio (electrode group occupying ratio) of more than 40% or more than 50% in the battery internal volume. In some embodiments, the electrode set occupancy is less than 90% or less than 80%. In some embodiments, the electrode set occupancy is within a range consisting of any two of the above values. When the electrode group occupancy is within the above range, the capacity of the electrochemical device can be secured, and the deterioration of the characteristics such as repeated charge/discharge performance and high-temperature storage due to the increase in internal pressure can be suppressed, and 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 the metal core portions of the respective electrode layers are bundled and welded to the terminals is suitably used. Since the internal resistance increases when the area of one electrode is increased, 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 wound structure, 2 or more lead structures are provided for the positive electrode and the negative electrode, respectively, and the terminals are bundled together, whereby the internal resistance can be reduced.

External casing

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

The metal-based outer case includes, but is not limited to, a hermetically sealed structure formed by welding metals to each other by laser welding, resistance welding, or ultrasonic welding; or a caulking structure formed by using the metal through a resin spacer. The outer case using the laminated film includes, but is not limited to, a sealed structure formed by thermally bonding resin layers to each other. In order to improve the sealing property, a resin different from the resin used for the laminate film may be interposed between the resin layers. When the resin layer is thermally adhered to the current collecting terminal to form a sealed structure, a resin having a polar group or a modified resin into which a polar group has been introduced may be used as the resin to be interposed, because of the bonding between the metal and the resin. The shape of the outer package is also arbitrary, and may be any of a cylindrical shape, a square shape, a laminated shape, a button shape, a large size, and the like.

Protective element

The protection element may be a Positive Temperature Coefficient (PTC) element whose resistance increases when abnormal heat radiation or an excessive current flows, a temperature fuse, a thermistor, a valve (current cutoff valve) that cuts off a current flowing through a circuit by rapidly increasing the internal pressure or internal temperature of the battery when abnormal heat radiation occurs, or the like. The protective element may be selected from elements that do not operate under normal use of high current, and may be designed so that abnormal heat release or thermal runaway does not occur even if the protective element is not present.

VI, application

The electrochemical device of the present application includes any device in which electrochemical reactions occur, 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 present application further provides an electronic device comprising an electrochemical device according to the present application.

The use of the electrochemical device of the present application is not particularly limited, and it can be used for any electronic device known in the art. In some embodiments, the electrochemical device of the present application can be used in, but is not limited to, notebook computers, pen-input computers, mobile computers, electronic book players, cellular phones, portable facsimile machines, portable copiers, portable printers, headphones, video recorders, liquid crystal televisions, portable cleaners, portable CDs, mini-discs, transceivers, electronic organizers, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, mopeds, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large batteries, lithium ion capacitors, and the like.

Taking a lithium ion battery as an example and describing the preparation of the lithium ion battery with reference to specific examples, those skilled in the art will understand that the preparation method described in the present application is only an example, and any other suitable preparation method is within the scope of the present application.

Examples

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

Preparation of lithium ion battery

1. Preparation of the negative electrode

Mixing the artificial graphite, the styrene-butadiene rubber and the sodium carboxymethylcellulose with deionized water according to the mass ratio of 96% to 2%, adding a high molecular compound with Si-C and Si-O bonds, and uniformly stirring to obtain the cathode slurry. The negative electrode slurry was coated on a copper foil of 12 μm. Drying, cold pressing, cutting into pieces, and welding tabs to obtain the cathode.

The polymer compounds having Si-C and Si-O bonds used in the following examples are as follows:

2. preparation of the Positive electrode

Mixing lithium cobaltate (LiCoO)₂) And mixing the conductive material (Super-P) and polyvinylidene fluoride (PVDF) with N-methyl pyrrolidone (NMP) according to the mass ratio of 95% to 2% to 3%, and uniformly stirring to obtain the anode slurry. And coating the anode slurry on an aluminum foil with the thickness of 12 mu m, drying, cold pressing, cutting into pieces, and welding a tab to obtain the anode.

3. Preparation of the electrolyte

Mixing EC, PC and DEC (weight ratio 1: 1: 1) under dry argon atmosphere, adding LiPF₆Mixing uniformly to form a basic electrolyte, wherein LiPF₆The concentration of (2) is 1.15 mol/L. The electrolytes of different examples and comparative examples were obtained by adding additives of different contents to the base electrolyte. The abbreviations and names of the components in the electrolyte are shown in the following table:

name of Material	Abbreviations	Name of Material	Abbreviations
				Ethylene carbonate	EC	Propylene carbonate	PC
Carbonic acid methyl ethyl ester	EMC	Propionic acid ethyl ester	EP
				Propylpropionate	PP	Gamma-butyrolactone	GBL
Succinonitrile and its use	SN	Adiponitrile	ADN
				Ethylene glycol di (2-cyanoethyl) ether	EDN	1,3, 6-Hexanetricarbonitrile	HTCN
1,2, 3-tris (2-cyanoethoxy) propane	TCEP	Lithium difluorophosphate	LiPO₂F₂

4. Preparation of the separator

Polyethylene (PE) porous polymer films were used as separators.

5. Preparation of lithium ion battery

The obtained positive electrode, separator and negative electrode were wound in order and placed in an outer packaging foil, leaving a liquid inlet. And (4) pouring electrolyte from the electrolyte injection port, packaging, and performing formation, capacity and other processes to obtain the lithium ion battery.

Second, testing method

1. 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 a current of 0.05V 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 above conditions. "1C" is a current value at which the battery capacity is completely discharged within 1 hour.

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

capacity retention after cycling ═ 100% (discharge capacity after cycling/discharge capacity at first cycle).

5. Method for testing direct current impedance (DCR) of lithium ion battery

Charging the lithium ion battery to 4.45V at a constant current of 1.5C and then to 0.05C at a constant voltage of 4.45V at 25 ℃; and standing for 30 minutes. Then discharged at 0.1C for 10 seconds (dot every 0.1 second, corresponding voltage value U1 is recorded), and discharged at 1C for 360 seconds (dot every 0.1 second, corresponding voltage value U2 is recorded). The charging and discharging steps were repeated 5 times. "1C" is a current value at which the battery capacity is completely discharged within 1 hour.

The DCR of the lithium ion battery is calculated according to the following formula:

DCR＝(U2-U1)/(1C-0.1C)。

the DCR described herein is a value at 50% state of charge (SOC).

Third, test results

Table 1 shows the effect of the high molecular compound having Si-C and Si-O bonds on the capacity retention rate and Direct Current Resistance (DCR) after cycling of the lithium ion battery.

TABLE 1

	Compound (I)	Content (ppm)	Capacity retention after cycling	DCR(mΩ)
					Comparative example 1	/	/	55％	77
Example 1	Compound 1	500	77.9％	62
					Example 2	Compound 1	300	78.2％	61
Example 3	Compound 1	1000	85.4％	54
					Example 4	Compound 1	3000	78.3％	59
Example 5	Compound 1	5000	67.2％	68
					Example 6	Compound 2	500	78％	61
Example 7	Compound 3	500	77.5％	63
					Example 8	Compound 4	500	76.4％	63
Example 9	Compound 5	500	75.7％	65
					Example 10	Compound 5	3000	78.4％	57

The result shows that the addition of the high molecular compound with Si-C and Si-O bonds in the negative electrode mixture layer can improve the interface stability of the negative electrode mixture layer, thereby remarkably improving the capacity retention rate of the lithium ion battery after circulation and reducing the Direct Current Resistance (DCR) of the lithium ion battery.

Table 2 shows the effect of surface tension of the high molecular compound having Si-C and Si-O bonds on the capacity retention ratio and Direct Current Resistance (DCR) after cycling of the lithium ion battery.

TABLE 2

The results show that the surface tension of the high molecular compounds with Si-C and Si-O bonds can reflect the influence of the compounds on the cycle and storage performance of the lithium ion battery. When the surface tension of an aqueous solution containing 0.1 wt% of a high molecular compound having Si-C and Si-O bonds is not more than 30mN/m, the capacity retention rate of the lithium ion battery after cycling is remarkably improved, and the Direct Current Resistance (DCR) is remarkably reduced.

Table 3 shows the effect of the carbon material in the negative electrode mixture layer on the capacity retention rate and Direct Current Resistance (DCR) after cycling of the lithium ion battery. The other settings of the example were the same as in example 1 except for the parameters listed in table 3.

TABLE 3

As shown in table 3, the carbon material in the negative electrode mixture layer had the following characteristics: the specific surface area is less than 5m²(ii)/g; the median particle diameter is 5 to 30 μm; and/or the surface has amorphous carbon. When the carbon material in the negative electrode mixture layer has the above characteristics, the capacity retention rate after cycling and the Direct Current Resistance (DCR) of the lithium ion battery can be further improved.

Table 4 shows the effect of the characteristics of the negative electrode mixture layer on the capacity retention rate and Direct Current Resistance (DCR) after cycling of the lithium ion battery. The other settings of the example were the same as in example 1 except for the parameters listed in table 4.

TABLE 4

As shown in table 4, the negative electrode mixture layer had the following characteristics: the thickness is not more than 200 μm; has a porosity of 10% to 60%; and/or a pounding height (i.e., a minimum height of a ball that cracks the negative electrode mixture layer when a ball having a diameter of 15mm and a weight of 12 g is dropped on the negative electrode mixture layer) of 50cm or more. When the negative electrode mixture layer has the above characteristics, the capacity retention rate after cycling and the Direct Current Resistance (DCR) of the lithium ion battery can be further improved.

Table 5 shows the effect of electrolyte composition on capacity retention and Direct Current Resistance (DCR) after cycling of a lithium ion battery. The other settings of the example were the same as in example 1 except for the parameters listed in table 5.

TABLE 5

The results show that when the electrolyte solution contains propionate, an organic compound having a cyano group, lithium difluorophosphate and/or a compound of formula 1 in addition to the use of the negative electrode mix layer of the present application, the interfacial stability of the negative electrode mix layer is further improved, thereby allowing the capacity retention rate after cycling and the Direct Current Resistance (DCR) of the lithium ion battery to be significantly improved.

Reference throughout this specification to "an embodiment," "some embodiments," "one embodiment," "another example," "an example," "a specific example," or "some examples" means that at least one embodiment or example in this application includes a particular feature, structure, material, or characteristic described in the embodiment or example. Thus, throughout the specification, descriptions appear, for example: "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in one example," "in a particular example," or "by example," which do not necessarily refer to the same embodiment or example in this 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 illustrated and described, it will be appreciated by those skilled in the art that the above embodiments are not to be construed as limiting the application and that changes, substitutions and alterations can be made to the embodiments 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 solution is added to the electrolyte solution,

wherein the negative electrode has a negative electrode mixture layer on a negative electrode current collector, the negative electrode mixture layer contains a carbon material as a negative electrode active material, and a polymer compound having Si-C and Si-O bonds is included on a surface of the negative electrode mixture layer or at least a part of a surface of the carbon material.

2. The electrochemical device according to claim 1, wherein the polymer compound having Si-C and Si-O bonds has at least one of the following characteristics:

(a) comprising a polyether siloxane;

3. The electrochemical device according to claim 1, wherein the content of the polymer compound having Si-C and Si-O bonds is 3000ppm or less based on the total weight of the negative electrode mixture layer.

4. The electrochemical device of claim 1, wherein the carbon material has at least one of the following characteristics:

(a) less than 5m²Specific surface area per gram;

(b) a median particle diameter of 5 μm to 30 μm;

(c) the surface has amorphous carbon.

5. The electrochemical device of claim 1, wherein the negative electrode mixture layer has at least one of the following characteristics:

(a) the thickness is not more than 200 μm;

(b) has a porosity of 10% to 60%;

6. The electrochemical device of claim 1, wherein the electrolyte comprises at least one of the following compounds:

(a) propionate esters;

(b) an organic compound having a cyano group;

(c) lithium difluorophosphate; and

(d) a compound of formula 1:

wherein:

w is selected from

L is selected from a single bond or methylene;

m is an integer of 1 to 4;

n is an integer of 0 to 2; and is

p is an integer of 0 to 6.

7. The electrochemical device according to claim 6, wherein the electrolyte comprises the compound of formula 1, and the compound of formula 1 is selected from at least one of:

m is an integer of 1 to 4;

n is an integer of 0 to 2; and is

p is an integer of 0 to 6.

8. The electrochemical device of claim 6, wherein the electrolyte comprises the propionate, and the propionate has formula 2:

wherein:

R¹is selected from the group consisting of ethyl or haloethyl,

R²is selected from C₁-C₆Alkyl or C₁-C₆A haloalkyl group; and is

The propionate content is 10 wt% to 65 wt% based on the weight of the electrolyte,

wherein the propionate is preferably at least one of methyl propionate, ethyl propionate, propyl propionate, butyl propionate or pentyl propionate.

9. The electrochemical device according to claim 6, wherein the organic compound having a cyano group is selected from at least one of: succinonitrile, glutaronitrile, adiponitrile, 1, 5-dicyanopentane, 1, 6-dicyanohexane, tetramethylsuccinonitrile, 2-methylglutaronitrile, 2, 4-dimethylglutaronitrile, 2,4, 4-tetramethylglutaronitrile, 1, 4-dicyanopentane, 1, 2-dicyanobenzene, 1, 3-dicyanobenzene, 1, 4-dicyanobenzene, ethylene glycol bis (propionitrile) ether, 3, 5-dioxa-pimelonitrile, 1, 4-bis (cyanoethoxy) butane, diethylene glycol bis (2-cyanoethyl) ether, triethylene glycol bis (2-cyanoethyl) ether, tetraethylene glycol bis (2-cyanoethyl) ether, 1, 3-bis (2-cyanoethoxy) propane, 1, 4-bis (2-cyanoethoxy) butane, 1, 5-bis (2-cyanoethoxy) pentane, ethylene glycol di (4-cyanobutyl) ether, 1, 4-dicyano-2-butene, 1, 4-dicyano-2-methyl-2-butene, 1, 4-dicyano-2-ethyl-2-butene, 1, 4-dicyano-2, 3-dimethyl-2-butene, 1, 4-dicyano-2, 3-diethyl-2-butene, 1, 6-dicyano-3-hexene, 1, 6-dicyano-2-methyl-3-hexene, 1,3, 5-pentanetrimethylnitrile, 1,2, 3-propanetricitrile, 1,3, 6-hexanetricarbonitrile, 1,2, 3-tris (2-cyanoethoxy) propane, 1,2, 4-tris (2-cyanoethoxy) butane, 1,1, 1-tris (cyanoethoxymethylene) ethane, 1,1, 1-tris (cyanoethoxymethylene) propane, 3-methyl-1, 3, 5-tris (cyanoethoxy) pentane, 1,2, 7-tris (cyanoethoxy) heptane, 1,2, 6-tris (cyanoethoxy) hexane and 1,2, 5-tris (cyanoethoxy) pentane; and the content of the organic compound having a cyano group is 0.1 to 15 wt% based on the total weight of the electrolyte.

10. An electronic device comprising the electrochemical device of any one of claims 1-9.