WO2021189406A1

WO2021189406A1 - Electrochemical device and electronic device

Info

Publication number: WO2021189406A1
Application number: PCT/CN2020/081608
Authority: WO
Inventors: 杜鹏; 谢远森; 董佳丽; 范国凌
Original assignee: 宁德新能源科技有限公司
Priority date: 2020-03-27
Filing date: 2020-03-27
Publication date: 2021-09-30
Also published as: CN115280567A

Abstract

The present application relates to an electrochemical device and an electronic device. Specifically, the present application provides an electrochemical device comprising a positive electrode, a negative electrode, and an electrolyte. The negative electrode comprises a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer comprises a negative electrode active material. The negative electrode active material comprises fragment particles, and the particle fragmentation rate of the negative electrode active material is from 20% to 80%. The electrochemical device of the present application improves cycle performance and safety performance.

Description

Electrochemical device and electronic device

Technical field

This application relates to the field of energy storage, in particular to an electrochemical device and an electronic device.

Background technique

Electrochemical devices (for example, lithium-ion batteries) are widely used due to their environmental friendliness, high working voltage, large specific capacity and long cycle life, and have become a new type of green chemical power source with the most development potential in the world today. Small-sized lithium-ion batteries are generally used as power sources for driving portable electronic communication devices (for example, camcorders, mobile phones, or notebook computers, etc.), especially high-performance portable devices. In recent years, medium-sized and large-sized lithium-ion batteries with high output characteristics have been developed for use in electric vehicles (EV) and large-scale energy storage systems (ESS). As the application field of lithium-ion batteries is expanded from consumer electronics to hybrid and pure power fields, its cycle performance and safety have become key technical issues that need to be solved urgently. Improving the active material in the electrode is one of the research directions to solve the above problems.

In view of this, it is indeed necessary to provide an improved electrochemical device and electronic device.

Summary of the invention

By providing an electrochemical device and an electronic device, this application attempts to solve at least one problem existing in the related field at least to some extent.

According to one aspect of the present application, the present application provides an electrochemical device, which includes a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, so The anode active material layer includes an anode active material, the anode active material includes crushed particles, and a particle crushing rate of the anode active material is 20% to 80%. In some embodiments, the particle crushing rate of the negative active material is 30% to 60%. In some embodiments, the particle crushing rate of the negative active material is 40% to 50%. In some embodiments, the particle crushing rate of the negative active material is 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%. % Or 80%.

According to an embodiment of the present application, the broken particles have cracks or cracks with a width not greater than 4 μm. In some embodiments, the broken particles have cracks or cracks with a width not greater than 3.5 μm. In some embodiments, the broken particles have cracks or cracks with a width not greater than 2.5 μm. In some embodiments, the broken particles have cracks or cracks with a width not greater than 2 μm.

According to an embodiment of the present application, the roughness of the negative active material layer is not more than 6 μm. In some embodiments, the roughness of the negative active material layer is not greater than 5 μm. In some embodiments, the roughness of the negative active material layer is not more than 3 μm. In some embodiments, the roughness of the negative active material layer is not more than 1 μm. In some embodiments, the roughness of the negative active material layer is 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or 6 μm.

According to an embodiment of the present application, the cohesive strength of the negative active material is 5 N/m to 30 N/m. In some embodiments, the cohesive strength of the negative active material is 8N/m to 25N/m. In some embodiments, the cohesive strength of the negative active material is 5N/m, 10N/m, 15N/m, 20N/m, 25N/m, or 30N/m.

According to an embodiment of the present application, the binding force between the negative active material layer and the negative current collector is 5 N/m to 20 N/m. In some embodiments, the binding force between the negative active material layer and the negative current collector is 10 N/m to 15 N/m. In some embodiments, the binding force between the negative active material layer and the negative current collector is 5N/m, 8N/m, 10N/m, 12N/m, 14N/m, 16N/m, 18N. /m or 20N/m.

According to the embodiment of the present application, the half-height width Id of the peak appearing ^{at 1345 cm -1} to 1355 cm ^-1 of the negative electrode active material measured by Raman spectroscopy and ^{the peak appearing at 1595 cm -1} to 1605 cm ^-1 The ratio Id/Ig of the half-height peak width Ig is 0.7 to 1.5. In some embodiments, the Id/Ig of the negative active material measured by Raman spectroscopy is 1.0 to 1.2. In some embodiments, the Id/Ig of the negative active material measured by Raman spectroscopy is 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, or 1.5.

According to the embodiment of the present application, the Id is 200 cm ^-1 to 1100 ^{cm -1} . In some embodiments, Id of 2200cm ^-1 to 1000cm ^-1. In some embodiments, the Id is 2500 cm ^-1 to ^{900 cm -1} . In some embodiments, Id is ^{^{^{200cm -11, 300cm -1, 400cm -1}}} , 500cm -1, 550cm -1, 600cm -1, 700cm -1, 850cm -1, 900cm -1, 1000cm -1, 1100cm - ¹ .

According to an embodiment of the present application, the negative active material includes at least one of a metal element or a non-metal element, and the metal element includes gold, silver, platinum, zirconium, zinc, magnesium, calcium, barium, vanadium, iron, or At least one of aluminum, based on the total weight of the negative active material, the content of the metal element is 20 ppm to 400 ppm; the non-metal element includes at least one of phosphorus, boron, silicon, arsenic or selenium, based on The total weight of the negative active material and the content of the non-metal elements are 50 ppm to 400 ppm.

In some embodiments, the content of the metal element is 50 ppm to 300 ppm based on the total weight of the negative active material. In some embodiments, based on the total weight of the negative active material, the content of the metal element is 100 ppm to 200 ppm. In some embodiments, based on the total weight of the negative active material, the content of the metal element is 20 ppm, 50 ppm, 80 ppm, 100 ppm, 150 ppm, 200 ppm, 250 ppm, 300 ppm, 350 ppm, or 400 ppm.

In some embodiments, the content of the non-metal elements is 100 ppm to 350 ppm based on the total weight of the negative active material. In some embodiments, based on the total weight of the negative active material, the content of the non-metal elements is 50 ppm, 60 ppm, 70 ppm, 80 ppm, 90 ppm, 100 ppm, 110 ppm, 120 ppm, 130 ppm, 140 ppm, 150 ppm, 160 ppm, 170 ppm, 180ppm, 190ppm, 210ppm, 240ppm, 280ppm, 310ppm, 380ppm or 400ppm.

According to an embodiment of the present application, the negative active material has pores, the pore diameter of the pores is not greater than 3 μm, and the inner wall of the pores has the metal element.

According to an embodiment of the present application, the negative electrode active material has pores, the pore diameter of the pores is not greater than 3 μm, and the inner wall of the pores has the non-metallic element.

According to an embodiment of the present application, the hole diameter is not greater than 2.5 μm. In some embodiments, the pore diameter of the pores is not greater than 2 μm. In some embodiments, the pore diameter of the hole is not greater than 1.5 μm. In some embodiments, the pore diameter is 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, or 3 μm.

According to an embodiment of the present application, the anode current collector includes a region where the anode active material layer is not provided, and based on the total area of the anode current collector, the region where the anode active material layer is not provided does not exceed 10%. In some embodiments, based on the total area of the negative electrode current collector, the area where the negative electrode active material layer is not provided does not exceed 8%. In some embodiments, based on the total area of the negative electrode current collector, the area where the negative electrode active material layer is not provided does not exceed 5%. In some embodiments, based on the total area of the negative electrode current collector, the area where the negative electrode active material layer is not provided does not exceed 3%. In some embodiments, based on the total area of the negative electrode current collector, the area where the negative electrode active material layer is not provided is 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8% , 9% or 10%.

According to another aspect of the present application, the present application provides an electronic device, which includes the electrochemical device according to the present application.

The additional aspects and advantages of the present application will be partially described, shown, or explained through the implementation of the embodiments of the present application in the subsequent description.

Description of the drawings

Hereinafter, the drawings necessary to describe the embodiments of the present application or the prior art will be briefly described in order to describe the embodiments of the present application. Obviously, the drawings in the following description are only part of the embodiments in the present application. For those skilled in the art, without creative work, the drawings of other embodiments can still be obtained according to the structures illustrated in these drawings.

Fig. 1 is a scanning electron microscope (SEM) image of a negative active material with crushed particles according to an embodiment of the present application.

Detailed ways

The embodiments of this application will be described in detail below. In the specification of this application, the same or similar components and the components with the same or similar functions are denoted by similar reference numerals. The embodiments related to the drawings described herein are illustrative, diagrammatic, and used to provide a basic understanding of the present application. The embodiments of this application should not be construed as limitations on this application.

In the detailed description and claims, a list of items connected by the term "at least one of" can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (exclude B); B and C (exclude A); or all of A, B, and C. Project A can contain a single element or multiple elements. Project B can contain a single element or multiple elements. Project C can contain a single element or multiple elements.

As used herein, "pore" refers to a pore structure or pore structure in a single negative electrode active material particle.

As used herein, "pores" refer to voids between a plurality of particles of the negative active material.

As used herein, "particle crushing rate" refers to the percentage of the number of crushed particles in the negative active material to the total number of negative active material particles.

In order to improve the energy density, cycle performance, and safety performance of electrochemical devices (for example, lithium ion batteries), improving the active materials of the electrodes is one of the research directions. The upper limit of the theoretical electrochemical capacity of the graphitized negative active material is 372 mAh/g, and it is difficult for the electrochemical capacity of the previously known graphitized negative active material to break through this upper limit. The silicon anode active material has a high electrochemical capacity. With the increase in the content of the doped material in the silicon anode active material, the energy density of the electrochemical device can be significantly improved, but the anode active material will undergo significant volume expansion, which will decrease significantly. The performance of the electrochemical device, in particular, will significantly reduce the capacity retention rate during long cycles.

In order to solve these problems, the present application provides an electrochemical device, which includes a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The active material layer contains a negative active material that contains a certain amount of crushed particles.

negative electrode

In the electrochemical device of the present application, the particle crushing rate of the anode active material is 20% to 80%. In some embodiments, the particle crushing rate of the negative active material is 30% to 60%. In some embodiments, the particle crushing rate of the negative active material is 40% to 50%. In some embodiments, the particle crushing rate of the negative active material is 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%. % Or 80%. The crushed particles can increase the specific surface area of the negative electrode active material and increase the contact points between the negative electrode active material and the electrolyte, thereby improving the cycle performance and energy density of the electrochemical device. The particle crushing rate of the negative electrode active material can be obtained by statistics of the negative electrode active particles in the scanning electron microscope (SEM) image. Specifically, select at least 4 regions (5μm×5μm) in the scanning electron microscope (SEM) image of the negative active material, count the number of broken particles and the total number of negative active material particles in the 4 regions, and calculate the negative electrode by the following formula Particle crushing rate of the active material: particle crushing rate=number of crushed particles/total number of anode active material particles×100%.

According to an embodiment of the present application, the broken particles have cracks or cracks with a width not greater than 4 μm. In some embodiments, the broken particles have cracks or cracks with a width not greater than 3.5 μm. In some embodiments, the broken particles have cracks or cracks with a width not greater than 2.5 μm. In some embodiments, the broken particles have cracks or cracks with a width not greater than 2 μm. Figure 1 shows a scanning electron microscope (SEM) image of a negative active material with broken particles. The particles circled in solid circles are broken particles with cracks, and those circled in dotted circles are broken particles with cracks.

According to an embodiment of the present application, the roughness of the negative active material layer is not more than 6 μm. In some embodiments, the roughness of the negative active material layer is not greater than 5 μm. In some embodiments, the roughness of the negative active material layer is not more than 3 μm. In some embodiments, the roughness of the negative active material layer is not more than 1 μm. In some embodiments, the roughness of the negative active material layer is 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or 6 μm. The negative active material layer is formed by randomly arranging negative active material particles, and its surface roughness depends on the unevenness of the particles with small spacing and minute peaks and valleys on the surface. The roughness of the negative active material layer can be obtained by the following method: within the sampling length, the arithmetic mean of the absolute value of the distance from the point on the particle profile to the reference line is calculated, that is, the profile arithmetic mean deviation Ra. The smaller the Ra, the smaller the roughness of the negative electrode active material layer, and the smoother the negative electrode active material layer.

According to an embodiment of the present application, the cohesive strength of the negative active material is 5 N/m to 30 N/m. In some embodiments, the cohesive strength of the negative active material is 8N/m to 25N/m. In some embodiments, the cohesive strength of the negative active material is 5N/m, 10N/m, 15N/m, 20N/m, 25N/m, or 30N/m. The presence of broken particles invalidates the contact sites of part of the active material and the binder, thereby reducing the cohesive strength of the negative active material. When the cohesive strength of the negative electrode active material is within the above range, the particles of the negative electrode active material have proper adhesion, which can avoid the phenomenon of powder falling during the rolling and winding process, and avoid the formation of the inside of the lithium ion battery. Micro-short-circuit sites avoid potential safety hazards; the negative active material can also expand in volume during the charge and discharge process to avoid incomplete lithium insertion, thereby ensuring the capacity of the electrochemical device. The cohesive strength of the negative electrode active material can be tested with the Instron (model 33652) tester: take the negative electrode sheet (width 30mm, length 100-160mm), use double-sided adhesive paper (model: 3M9448A, width 20mm, length (90-150mm) fix it on the steel plate, stick the adhesive tape on the surface of the negative active material layer, connect one side of the adhesive tape to the paper tape of equal width, adjust the limit block of the tensile machine to a suitable position, and attach the tape Folding and sliding up 40mm, the sliding rate was 50mm/min, and the polymerization strength between the particles in the negative active material layer was tested at 180° (that is, stretched in the opposite direction).

According to an embodiment of the present application, the binding force between the negative active material layer and the negative current collector is 5 N/m to 20 N/m. In some embodiments, the binding force between the negative active material layer and the negative current collector is 10 N/m to 15 N/m. In some embodiments, the binding force between the negative active material layer and the negative current collector is 5N/m, 8N/m, 10N/m, 12N/m, 14N/m, 16N/m, 18N. /m or 20N/m. When the binding force between the negative electrode active material layer and the negative electrode current collector is within the above range, it is possible to avoid film peeling or burrs during the rolling or slitting process, thereby avoiding potential safety hazards and ensuring the battery core The internal resistance is within an acceptable range to ensure the dynamic performance and cycle performance of the electrochemical device. The peeling strength between the negative electrode active material layer and the negative electrode current collector can be achieved by controlling the rolling process in the preparation process of the negative electrode. Specifically, the binding force between the negative electrode active material layer and the negative electrode current collector can be tested using an Instron (model 33652) tester: take the pole piece (width 30mm, length 100-160mm), use double-sided adhesive tape (Model: 3M9448A, width 20mm, length 90-150mm) Fix it on the steel plate, stick the adhesive tape on the surface of the negative active material layer, connect one side of the adhesive tape to the paper tape of equal width, adjust the tension machine Place the limit block to a suitable position, fold the paper tape upwards and slide it 40mm, with a slip rate of 50mm/min, and test the adhesion between the negative electrode active material layer and the negative electrode current collector at 180° (ie, stretching in the opposite direction) Knot force.

According to the embodiment of the present application, the half-height width Id of the peak appearing ^{at 1345 cm -1} to 1355 cm ^-1 of the negative electrode active material measured by Raman spectroscopy and ^{the peak appearing at 1595 cm -1} to 1605 cm ^-1 The ratio Id/Ig of the half-height peak width Ig is 0.7 to 1.5. In some embodiments, the Id/Ig of the negative active material measured by Raman spectroscopy is 1.0 to 1.2. In some embodiments, the Id/Ig of the negative active material measured by Raman spectroscopy is 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, or 1.5. When the Id/Ig of the negative electrode active material is in the above range, the crystal defects and the degree of disorder on the surface of the negative electrode active material are in an appropriate range, which helps to increase the gram capacity of the negative electrode active material.

According to the embodiment of the present application, the Id is 200 cm ^-1 to 1100 ^{cm -1} . In some embodiments, Id of 2200cm ^-1 to 1000cm ^-1. In some embodiments, the Id is 2500 cm ^-1 to ^{900 cm -1} . In some embodiments, Id as ^{^{^{200cm -1, 300cm -1, 400cm -1}}} , 500cm -1, 550cm -1, 600cm -1, 700cm -1, 850cm -1, 900cm -1, 1000cm -1, 1100cm - ¹ .

In some embodiments, the content of the metal element is 50 ppm to 300 ppm based on the total weight of the negative active material. In some embodiments, based on the total weight of the negative active material, the content of the metal element is 100 ppm to 200 ppm. In some embodiments, based on the total weight of the negative active material, the content of the metal element is 20 ppm, 50 ppm, 80 ppm, 100 ppm, 150 ppm, 200 ppm, 250 ppm, 300 ppm, 350 ppm or 400 ppm.

According to an embodiment of the present application, the hole diameter is not greater than 2 μm. In some embodiments, the pore diameter of the hole is not greater than 1 μm. In some embodiments, the pore diameter of the hole is not greater than 0.5 μm. In some embodiments, the pore diameter is 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, or 3 μm. The negative electrode active material with pores has a larger specific surface area, and the inner wall of the pores can effectively adsorb lithium, which helps to increase the electrochemical capacity of the negative electrode active material. When the pore diameter is within the above range, the electrolyte can effectively infiltrate the negative electrode active material to form a solid-liquid interface.

In some embodiments, the negative active material may include, but is not limited to, natural graphite, artificial graphite, mesophase carbon microspheres (referred to as MCMB for short), hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn Alloy, Li-Sn-O alloy, Sn, SnO, SnO ₂ , spinel structure lithiated TiO ₂ -Li ₄ Ti ₅ O ₁₂ or LI-l alloy. Non-limiting examples of carbon materials include crystalline carbon, amorphous carbon, and mixtures thereof. The crystalline carbon may be amorphous or flake-shaped, flake-shaped, spherical or fibrous natural graphite or artificial graphite. Amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbide, calcined coke, and the like.

According to an embodiment of the present application, the negative electrode further includes a conductive layer. In some embodiments, the conductive material of the conductive layer may include any conductive material as long as it does not cause a chemical change. Non-limiting examples of conductive materials include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, carbon nanotubes, graphene, etc.), metal-based materials (e.g., metal Powder, metal fibers, etc., such as copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

According to an embodiment of the present application, the negative electrode further includes a binder, and the binder is selected from at least one of the following: polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, and diacetyl cellulose , Polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, poly Propylene, styrene butadiene rubber, acrylic (ester) styrene butadiene rubber, epoxy resin or nylon, etc.

The negative electrode current collector used in the present application may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, polymer substrates coated with conductive metals, and combinations thereof.

positive electrode

The positive electrode includes a positive electrode current collector and a positive electrode active material provided on the positive electrode current collector. The specific types of positive electrode active materials are not subject to specific restrictions, and can be selected according to requirements.

In some embodiments, the positive electrode active material includes a positive electrode material capable of absorbing and releasing lithium (Li). Examples of positive electrode materials capable of absorbing/releasing lithium (Li) may include lithium cobalt oxide, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, lithium manganate, lithium iron manganese phosphate, lithium vanadium phosphate, lithium vanadyl phosphate, and phosphoric acid. Lithium iron, lithium titanate and lithium-rich manganese-based materials.

Specifically, the chemical formula of lithium cobalt oxide can be as chemical formula 1:

Li _x Co _a M1 _b O _2-c Chemical formula 1

Wherein M1 represents selected from nickel (Ni), manganese (Mn), magnesium (Mg), aluminum (A1), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), Copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), tungsten (W), yttrium (Y), lanthanum (La), zirconium (Zr) and For at least one of silicon (Si), the values of x, a, b, and c are within the following ranges: 0.8≤x≤1.2, 0.8≤a≤1, 0≤b≤0.2, -0.1≤c≤0.2.

The chemical formula of lithium nickel cobalt manganate or lithium nickel cobalt aluminate can be as chemical formula 2:

Li _y Ni _d M2 _e O _2-f Chemical formula 2

Wherein M2 represents selected from cobalt (Co), manganese (Mn), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), At least one of copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), tungsten (W), zirconium (Zr), and silicon (Si), The values of y, d, e, and f are in the following ranges: 0.8≤y≤1.2, 0.3≤d≤0.98, 0.02≤e≤0.7, -0.1≤f≤0.2.

The chemical formula of lithium manganate can be as chemical formula 3:

Li _z Mn _2-g M3 _g O _4-h Chemical formula 3

Wherein M3 represents selected from cobalt (Co), nickel (Ni), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), At least one of copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr) and tungsten (W), with z, g and h values in the following ranges respectively Inner: 0.8≤z≤1.2, 0≤g≤1.0 and -0.2≤h≤0.2.

In some embodiments, the weight of the positive electrode active material layer is 1.5 to 15 times the weight of the negative electrode active material layer. In some embodiments, the weight of the positive active material layer is 3 to 10 times the weight of the negative active material layer. In some embodiments, the weight of the positive active material layer is 5 to 8 times the weight of the negative active material layer. In some embodiments, the weight of the positive active material layer is 1.5 times, 2 times, 3 times, 4 times, 5 times, 6 times, 7 times, 8 times, 9 times the weight of the negative active material layer. , 10 times, 11 times, 12 times, 13 times, 14 times or 15 times.

In some embodiments, the positive active material layer may have a coating on the surface, or may be mixed with another compound having a coating. The coating may include oxides of coating elements, hydroxides of coating elements, oxyhydroxides of coating elements, oxycarbonates of coating elements, and hydroxycarbonates of coating elements ( At least one coating element compound selected from hydroxycarbonate). The compound used for the coating may be amorphous or crystalline. The coating element contained in the coating may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, F, or a mixture thereof. The coating can be applied by any method as long as the method does not adversely affect the performance of the positive electrode active material. For example, the method may include any coating method well-known to those of ordinary skill in the art, such as spraying, dipping, and the like.

In some embodiments, the positive active material layer further includes a binder, and optionally further includes a positive conductive material.

The binder can improve the binding of the positive electrode active material particles to each other, and also improve the binding of the positive electrode active material to the current collector. Non-limiting examples of binders include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl chloride Vinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylic (ester) styrene butadiene rubber, epoxy resin, nylon, etc.

The positive electrode active material layer includes a positive electrode conductive material, thereby imparting conductivity to the electrode. The positive electrode conductive material may include any conductive material as long as it does not cause a chemical change. Non-limiting examples of positive electrode conductive materials include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., Including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (for example, polyphenylene derivatives), and mixtures thereof.

The positive electrode current collector used in the electrochemical device according to the present application may be aluminum (Al), but is not limited thereto.

Electrolyte

The electrolyte that can be used in the embodiments of the present application may be an electrolyte known in the prior art.

The electrolyte that can be used in the electrolyte in the embodiments of the present application includes, but is not limited to: inorganic lithium salts, such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiSO ₃ F, LiN(FSO ₂ ) _2, etc.; Fluorine-containing organic lithium salts, such as LiCF ₃ SO ₃ , LiN(FSO ₂ )(CF ₃ SO ₂ ), LiN(CF ₃ SO ₂ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ , cyclic 1,3- Lithium hexafluoropropane disulfonimide, lithium cyclic 1,2-tetrafluoroethane disulfonimide, LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) _3. LiPF ₄ (CF ₃ ) ₂ , LiPF ₄ (C ₂ F ₅ ) ₂ , LiPF ₄ (CF ₃ SO ₂ ) ₂ , LiPF ₄ (C ₂ F ₅ SO ₂ ) ₂ , LiBF ₂ (CF ₃ ) ₂ , LiBF2(C2F5)2, LiBF ₂ (CF ₃ SO ₂ ) ₂ , LiBF ₂ (C ₂ F ₅ SO ₂ ) ₂ ; Lithium salt containing dicarboxylic acid complex, such as bis(oxalato) lithium borate, difluorooxalic acid Lithium borate, tris(oxalato) lithium phosphate, difluorobis(oxalato) lithium phosphate, tetrafluoro(oxalato) lithium phosphate, etc. In addition, the above-mentioned electrolytes may be used singly, or two or more of them may be used at the same time. In some embodiments, the electrolyte includes a combination of _{LiPF 6} and LiBF _4. In some embodiments, the electrolyte includes a combination of an inorganic lithium salt such as _{LiPF 6} or LiBF ₄ and a fluorine-containing organic lithium salt such as _{LiCF 3} SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , and LiN(C ₂ F ₅ SO ₂ ) ₂ . In some embodiments, the electrolyte includes LiPF ₆ .

In some embodiments, the concentration of the electrolyte is in the range of 0.8-3 mol/L, for example, in the range of 0.8-2.5 mol/L, in the range of 0.8-2 mol/L, in the range of 1-2 mol/L, for example It is 1mol/L, 1.15mol/L, 1.2mol/L, 1.5mol/L, 2mol/L or 2.5mol/L.

Solvents that can be used in the electrolyte of the embodiments of the present application include, but are not limited to: carbonate compounds, ester-based compounds, ether-based compounds, ketone-based compounds, alcohol-based compounds, aprotic solvents, or combinations thereof.

Examples of carbonate compounds include, but are not limited to, linear carbonate compounds, cyclic carbonate compounds, fluorocarbonate compounds, or combinations thereof.

Examples of chain carbonate compounds include, but are not limited to, diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethylene propyl carbonate ( EPC), ethyl methyl carbonate (MEC) and their combinations. Examples of the cyclic carbonate compound are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), and combinations thereof. Examples of the fluorocarbonate compound are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate Fluoroethylene, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2 carbonate -Difluoro-1-methylethylene, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, and combinations thereof.

Examples of ester-based compounds include, but are not limited to, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolide, Valerolactone, mevalonolactone, caprolactone, methyl formate, and combinations thereof.

Examples of ether-based compounds include, but are not limited to, dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane Alkanes, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.

Examples of ketone-based compounds include, but are not limited to, cyclohexanone.

Examples of alcohol-based compounds include, but are not limited to, ethanol and isopropanol.

Examples of aprotic solvents include, but are not limited to, dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl- 2-pyrrolidone, formamide, dimethylformamide, acetonitrile, nitromethane, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters and combinations thereof.

Isolation film

In some embodiments, a separator is provided between the positive electrode and the negative electrode to prevent short circuits. The material and shape of the isolation film that can be used in the embodiments of the present application are not particularly limited, and they can be any technology disclosed in the prior art. In some embodiments, the isolation membrane includes a polymer or an inorganic substance formed of a material that is stable to the electrolyte of the present application, or the like.

For example, the isolation film may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, film or composite film with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be selected. The porous structure can improve the heat resistance, oxidation resistance and electrolyte infiltration performance of the isolation membrane, and enhance the adhesion between the isolation membrane and the pole piece.

A surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic substance layer, or a layer formed by a mixed polymer and an inorganic substance.

The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from alumina, silica, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, One or a combination of yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, One or a combination of polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.

The polymer layer contains a polymer, and the material of the polymer is selected from polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, poly At least one of (vinylidene fluoride-hexafluoropropylene).

Electrochemical device

The present application also provides an electrochemical device, which includes a positive electrode, an electrolyte, and a negative electrode. The positive electrode includes a positive electrode active material layer and a positive electrode current collector. The negative electrode includes a negative electrode active material layer and a negative electrode current collector. The material layer includes the negative active material according to the present application.

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

Electronic device

The application also provides an electronic device, which includes the electrochemical device according to the application.

The use of the electrochemical device of the present application is not particularly limited, and it can be used in any electronic device known in the prior art. In some embodiments, the electrochemical device of the present application can be used in, but not limited to, notebook computers, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, and headsets. Stereo headsets, video recorders, LCD TVs, portable cleaners, portable CD players, mini discs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power assistance Bicycles, bicycles, lighting equipment, toys, game consoles, clocks, power tools, flashlights, cameras, large household storage batteries and lithium-ion capacitors, etc.

The following takes a lithium ion battery as an example and describes the preparation of a lithium ion battery in conjunction with specific examples. Those skilled in the art will understand that the preparation methods described in this application are only examples, and any other suitable preparation methods are described in this application. Within range.

Example

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

1. Preparation of Lithium Ion Battery

1. Preparation of negative electrode active material

Disperse 2 kg of artificial graphite in ethanol to obtain the first solution. Dissolve 0.05 mol of triammonium citrate in 1 mL of isopropanol. After it is completely dissolved, add 1.5 mol of zinc acetate, stir at 1000 rpm for at least 30 minutes, and filter through an aqueous membrane to obtain a zinc oxide sol-gel solution. The same amount of hydrochloric acid as zinc acetate is added to the zinc oxide sol-gel solution to obtain a second solution. 1000 mL of the second solution was added to the first solution, and stirring was continued at 50° C. for 90 minutes to obtain the third solution. Then, the obtained third solution was allowed to stand for 180 minutes, dried at 70° C. for 10 hours to remove the solvent, and then heat-treated at 1000° C. in an argon atmosphere to remove impurities to obtain a negative electrode active material.

The negative electrode active material obtained in this step is prepared into a pole piece, and the negative electrode active material with the desired particle crushing rate can be formed by controlling the rolling pressure and/or the rolling time control. Controlling the content of the second solution in the third solution can also realize the control of the particle crushing rate.

2. Preparation of negative electrode

The negative active material, the binder styrene-butadiene rubber (SBR) and the thickener sodium carboxymethyl cellulose (CMC) prepared above are fully stirred and mixed in an appropriate amount of deionized water at a weight ratio of 97:1:2 to make it A uniform negative electrode slurry is formed, wherein the solid content of the negative electrode slurry is 54 wt%. This slurry was coated on a negative electrode current collector (copper foil), dried at 85°C, and then cold pressed, cut into pieces, and cut, and dried under vacuum conditions at 120°C for 12 hours to obtain a negative electrode.

3. Preparation of positive electrode

Mix lithium cobaltate (LiCoO ₂ ), Super P and polyvinylidene fluoride (PVDF) in an appropriate amount of N-methylpyrrolidone (NMP) solvent at a weight ratio of 97:1.4:1.6 to form a uniform The positive electrode slurry, wherein the solid content of the positive electrode slurry is 72 wt%. The slurry was coated on the positive electrode current collector aluminum foil, dried at 85°C, and then cold-pressed, cut into pieces, and cut, and dried under vacuum at 85°C for 4 hours to obtain a positive electrode.

4. Preparation of electrolyte

In a dry argon atmosphere glove box, mix ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a mass ratio of EC:EMC:DEC=30:50:20 , Then add 3% fluoroethylene carbonate, 1.5% 1,3 propane sultone, dissolve and stir well, add lithium salt LiPF ₆ , and mix well to obtain electrolyte, in which _{the concentration of LiPF 6} is 1 mol/ L.

5. Preparation of isolation membrane

A polyethylene (PE) porous polymer film with a thickness of 7 μm was used as the separator.

6. Preparation of Lithium Ion Battery

Lay the positive electrode, separator film, and negative electrode in order, so that the separator film is located between the positive electrode and the negative electrode for isolation, and then wound, after welding the tabs, place it in the outer packaging foil aluminum plastic film, and inject the above-prepared The electrolyte is vacuum packaged, standing, forming, shaping, capacity testing and other processes to obtain a soft-packed lithium-ion battery.

2. Test method

1. Test method for the cycle capacity retention rate of lithium-ion batteries

In an environment of 25°C, charge the lithium-ion battery at a constant current of 0.7C to a voltage of 4.4V, and then charge at a constant voltage; discharge at a constant current of 1C to a voltage of 3V, this is recorded as a cycle, and the discharge capacity of the first cycle is recorded. Perform 200 cycles, and record the discharge capacity of the 200th cycle. Calculate the cycle capacity retention rate of lithium-ion batteries by the following formula:

Cycle capacity retention ratio=(discharge capacity at the 200th cycle/discharge capacity at the first cycle)×100%.

Five samples were tested for each example or comparative example, and the average value was taken.

2. Test method of thermal shock endurance time of lithium ion battery

The lithium-ion battery is fully charged and placed in a high temperature box at 150°C. The time when the lithium-ion battery starts to show flames is recorded as the thermal shock endurance time. Five samples were tested for each example or comparative example, and the average value was taken.

3. Overcharge test method of lithium ion battery

Under 10V, the lithium-ion battery was overcharged at a current density of 1C, and the surface temperature of the lithium-ion battery was tested. Five samples were tested for each example or comparative example, and the average value was taken.

4. Nail penetration test method for lithium-ion batteries

Place the lithium-ion battery in a thermostat at 25°C and let it stand for 30 minutes to bring the lithium-ion battery to a constant temperature. The lithium ion battery that has reached a constant temperature is charged at a constant current of 0.5C to a voltage of 4.4V, and then charged at a constant voltage of 4.4V to a current of 0.025C. Transfer the fully charged lithium ion battery to the nail piercing tester, keep the test environment at 25°C±2°C, use a steel nail with a diameter of 4mm to pass through the center of the lithium ion battery at a speed of 30mm/s at a constant speed, and keep it for 300 seconds. Test the surface temperature of the lithium ion battery. Five samples were tested for each example or comparative example, and the average value was taken.

5. Impact test method of lithium ion battery

At 25℃, the lithium-ion battery is charged at a constant current of 0.5C to a voltage of 4.3V, and then charged at a constant voltage of 4.3V to a current of 0.05C. The UL1642 test standard is adopted. The weight of the weight is 9.8kg and the diameter is 15.8mm, drop height of 61±2.5cm, impact test on lithium ion battery. Test the surface temperature of the lithium ion battery. Five samples were tested for each example or comparative example, and the average value was taken.

6. Test method of cohesive strength of negative active material

Use the Instron (model 33652) tester to test: take the pole piece (width 30mm, length 100-160mm), and fix it with double-sided adhesive paper (model: 3M9448A, width 20mm, length 90-150mm) On the steel plate, stick the tape on the surface of the negative active material layer, connect one side of the tape to the paper tape of the same width, adjust the limit block of the tension machine to a suitable position, fold the tape upwards and slide 40mm, The slip rate was 50 mm/min, and the polymerization strength between particles inside the negative active material layer at 180° (that is, stretched in the opposite direction) was tested.

7. Test method for the binding force between the negative electrode active material layer and the negative electrode current collector

Use the Instron (model 33652) tester to test: take the pole piece (width 30mm, length 100-160mm), and fix it with double-sided adhesive paper (model: 3M9448A, width 20mm, length 90-150mm) On the steel plate, stick the tape on the surface of the negative active material layer, connect one side of the tape to the paper tape of the same width, adjust the limit block of the tension machine to a suitable position, fold the tape upwards and slide 40mm, The slip rate was 50 mm/min, and the binding force between the negative electrode active material layer and the negative electrode current collector at 180° (that is, stretched in the opposite direction) was tested.

8. Test method for particle crushing rate of negative active material

Select at least 4 regions (5 μm×5 μm) in the scanning electron microscope (SEM) image of the disassembled negative active material to observe the particles of the negative active material. The particles without the binder at the particle interface are broken particles. Count the number of broken particles and the total number of anode active material particles in the 4 regions, and calculate the particle crushing rate of the anode active material by the following formula: particle crushing rate=number of crushed particles/total number of anode active material particles×100%. Five samples were tested for each example or comparative example.

Three, test results

Table 1 shows the impact of the particle crushing rate of the negative active material and Id/Ig on the cycle performance and safety of the lithium ion battery. The width of the cracks or cracks of the crushed particles in Table 1 is not greater than 4 μm.

Table 1

The results show that, compared to the comparative example, when the negative electrode active material contains crushed particles and the particle crushing rate is 20% to 80%, the cycle capacity retention rate of the lithium ion battery is significantly increased, the thermal shock endurance time is significantly extended, and the battery is overcharged. The surface temperature in the test, nail penetration test, and impact test is significantly reduced, that is, the cycle performance and safety of the lithium-ion battery are significantly improved. On this basis, controlling the Id/Ig of the negative electrode active material within the range of 0.7 to 1.5 can further improve the cycle capacity retention rate of lithium-ion batteries, extend the thermal shock endurance time, and reduce the overcharge test, nail penetration test and impact test. The surface temperature in the. On the basis of Id / Ig of 0.7 to 1.5 on the control Id 200cm ^-1 to 1100cm ^-1, it helps to further improve the cycle characteristics and safety of the lithium ion battery.

Table 2 shows the influence of metallic elements, non-metallic elements and pores in the negative active material on the cycle performance and safety of lithium-ion batteries. Except for the parameters listed in Table 2, the other settings of Embodiments 13-40 are consistent with those of Embodiment 3, and the other settings of Embodiment 41 are consistent with those of Embodiment 2.

Table 2

The results show that when the negative electrode active material contains 20 ppm to 400 ppm of metal elements and/or 50 ppm to 400 ppm of non-metal elements, it helps to further improve the cycle performance and safety of the lithium ion battery. When the negative electrode active material has pores and the inner wall of the pores has metal elements and/or non-metal elements, it helps to further improve the cycle performance and safety of the lithium ion battery.

Table 3 shows the influence of the properties of the negative electrode active material on the cycle performance and safety of lithium-ion batteries. Except for the parameters listed in Table 3, Examples 42-54 are consistent with the other settings of Example 3.

table 3

The results show that when the roughness of the negative electrode active material layer is not greater than 6μm, the cohesive strength of the negative electrode active material is in the range of 5N/m to 30N/m, and/or the binding force between the negative electrode active material layer and the negative electrode current collector When it is in the range of 5N/m to 20N/m, it helps to further improve the cycle performance and safety of the lithium ion battery.

Table 4 shows the influence of the proportion of the area of the negative electrode current collector where the negative electrode active material layer is not provided on the cycle performance and safety of the lithium ion battery. Except for the parameters listed in Table 4, the other settings of Examples 55-58 are the same as those of Example 3.

Table 4

The results show that when the area where the negative electrode active material layer is not provided does not exceed 10%, it helps to further improve the cycle performance and safety of the lithium ion battery.

Improving the cycle performance of lithium-ion batteries while ensuring their safety will help expand the application fields of lithium-ion batteries and provide a broad space for their development.

References to "embodiments", "partial examples", "one embodiment", "another example", "examples", "specific examples" or "partial examples" throughout the specification mean that At least one embodiment or example in this application includes the specific feature, structure, material, or characteristic described in the embodiment or example. Therefore, descriptions appearing in various places throughout the specification, such as: "in some embodiments", "in an example", "in one example", "in another example", "in an example "In", "in a specific example" or "exemplified", which are not necessarily quoting the same embodiment or example in this application. In addition, the specific features, structures, materials or characteristics herein can be combined in one or more embodiments or examples in any suitable manner.

Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above-mentioned embodiments should not be construed as limiting the present application, and the embodiments can be changed without departing from the spirit, principle, and scope of the present application , Substitution and modification.

Claims

An electrochemical device comprising a positive electrode, a negative electrode and an electrolyte, wherein the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, the negative electrode active material layer contains a negative electrode active material, and The negative active material includes crushed particles, and the particle crushing rate of the negative active material is 20% to 80%.
The electrochemical device according to claim 1, wherein the crushed particles have cracks or cracks with a width of not more than 4 μm.
The electrochemical device according to claim 1, wherein the roughness of the anode active material layer is not more than 6 μm.
The electrochemical device according to claim 1, wherein the cohesive strength of the anode active material is 5 N/m to 30 N/m.
The electrochemical device according to claim 1, wherein the binding force between the anode active material layer and the anode current collector is 5 N/m to 20 N/m.
The electrochemical device according to claim 1, wherein the Raman spectroscopy obtained by the test half height width of the negative electrode active material occurring Id at 1345cm -1 to 1355cm -1 and a peak at 1595cm -1 to 1605cm - The ratio Id/Ig of the half-height width Ig of the peak appearing at one point is 0.7 to 1.5.
The electrochemical device according to claim 6, wherein Id is 200 cm -1 to 1100 cm -1 .
The electrochemical device according to claim 1, wherein the anode active material contains at least one of a metal element or a non-metal element, and the metal element includes gold, silver, platinum, zirconium, zinc, magnesium, calcium, barium, At least one of vanadium, iron or aluminum, based on the total weight of the negative active material, the content of the metal element is 20 ppm to 400 ppm; the non-metal element includes at least one of phosphorus, boron, silicon, arsenic or selenium One type, based on the total weight of the negative active material, the content of the non-metal elements is 50 ppm to 400 ppm.
8. The electrochemical device according to claim 8, wherein the anode active material has pores having a pore diameter of not more than 3 μm, and the inner wall of the pores has the metal element.
The electrochemical device according to claim 1, wherein the anode current collector includes a region where the anode active material layer is not provided, and based on the total area of the anode current collector, the region where the anode active material layer is not provided Not more than 10%.
An electronic device comprising the electrochemical device according to any one of claims 1-10.