CN115280567A

CN115280567A - Electrochemical device and electronic device

Info

Publication number: CN115280567A
Application number: CN202080098111.4A
Authority: CN
Inventors: 杜鹏; 谢远森; 董佳丽; 范国凌
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2020-03-27
Filing date: 2020-03-27
Publication date: 2022-11-01
Also published as: WO2021189406A1

Abstract

The present application relates to an electrochemical device and an electronic device. Specifically, the present application provides an electrochemical device, which comprises a positive electrode, a negative electrode and an electrolyte, wherein 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 broken particles, and the particle breakage rate of the negative electrode active material is 20% to 80%. The electrochemical device of the present application has improved cycle performance and safety performance.

Description

Electrochemical device and electronic device

Technical Field

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

Background

Electrochemical devices (e.g., lithium ion batteries) are widely used due to their advantages of environmental friendliness, high operating voltage, large specific capacity, and long cycle life, and have become the most promising new green chemical power source in the world today. Small-sized lithium ion batteries are generally used as power sources for driving portable electronic communication devices (e.g., camcorders, mobile phones, or notebook computers, etc.), particularly high-performance portable devices. In recent years, medium-sized and large-sized lithium ion batteries having high output characteristics have been developed for application to Electric Vehicles (EVs) 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, the cycle performance and safety thereof have become key technical problems to be solved urgently. Improvement of the active material in the electrode is one of the research directions to solve the above problems.

In view of the foregoing, there is a need for an improved electrochemical device and electronic device.

Disclosure of Invention

The present application seeks to solve at least one of the problems presented in the related art, at least to some extent, by providing an electrochemical device and an electronic device.

According to one aspect of the present application, there is provided an electrochemical device including 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 includes a negative electrode active material, the negative electrode active material includes crushed particles, and a particle breakage rate of the negative electrode active material is 20% to 80%. In some embodiments, the anode active material has a particle breakage rate of 30% to 60%. In some embodiments, the anode active material has a particle breakage rate of 40% to 50%. In some embodiments, the anode active material has a particle breakage of 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 80%.

According to an embodiment of the application, the broken particles have cracks or fissures having a width not greater than 4 μm. In some embodiments, the fractured particles have cracks or fissures that are not greater than 3.5 μm in width. In some embodiments, the fractured particles have cracks or fissures that are no greater than 2.5 μm wide. In some embodiments, the fractured particles have cracks or fissures that are no greater than 2 μm wide.

According to an embodiment of the present application, the roughness of the anode active material layer is not more than 6 μm. In some embodiments, the roughness of the anode active material layer is not greater than 5 μm. In some embodiments, the roughness of the anode active material layer is not greater than 3 μm. In some embodiments, the roughness of the anode active material layer is not greater 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 anode active material is 5N/m to 30N/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 adhesive force between the anode active material layer and the anode current collector is 5N/m to 20N/m. In some embodiments, the adhesion between the negative electrode active material layer and the negative electrode current collector is 10 to 15N/m. In some embodiments, the adhesion 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 examples of the present application, the negative active material obtained by the raman spectroscopy test was at 1345cm^-1To 1355cm^-1The half height width Id of the peak appeared and the peak width at 1595cm^-1To 1605cm^-1The ratio Id/Ig of the half height width Ig of the peak appearing at (A) is 0.7 to 1.5. In some embodiments, the Id/Ig of the negative active material obtained from raman spectroscopy testingIs 1.0 to 1.2. In some embodiments, the negative active material has an Id/Ig of 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, or 1.5 as measured by raman spectroscopy.

According to the examples of the present application, id is 200cm^-1To 1100cm^-1. In some embodiments, id is 2200cm^-1To 1000cm^-1. In some embodiments, id is 2500cm^-1To 900cm^-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 anode active material includes at least one of a metal element or a non-metal element, the metal element includes at least one of gold, silver, platinum, zirconium, zinc, magnesium, calcium, barium, vanadium, iron, or aluminum, and a content of the metal element is 20ppm to 400ppm based on a total weight of the anode active material; the non-metallic element includes at least one of phosphorus, boron, silicon, arsenic or selenium, and is included in an amount of 50ppm to 400ppm based on the total weight of the anode active material.

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

In some embodiments, the non-metallic element is included in an amount of 100ppm to 350ppm based on the total weight of the anode active material. In some embodiments, the non-metallic element is present in an amount of 50ppm, 60ppm, 70ppm, 80ppm, 90ppm, 100ppm, 110ppm, 120ppm, 130ppm, 140ppm, 150ppm, 160ppm, 170ppm, 180ppm, 190ppm, 210ppm, 240ppm, 280ppm, 310ppm, 380ppm, or 400ppm based on the total weight of the anode active material.

According to an embodiment of the present application, the anode active material has pores having a pore diameter of not more than 3 μm, and inner walls of the pores have the metal element.

According to an embodiment of the present application, the negative active material has pores having a pore diameter of not more than 3 μm, and inner walls of the pores have the non-metallic element.

According to an embodiment of the application, the pores have a pore diameter of not more than 2.5 μm. In some embodiments, the pores have a pore size of no greater than 2 μm. In some embodiments, the pores have a pore size of no greater than 1.5 μm. In some embodiments, the pores have a pore diameter of 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 negative electrode current collector includes a region where the negative electrode active material layer is not disposed, and the region where the negative electrode active material layer is not disposed is not more than 10% based on a total area of the negative electrode current collector. In some embodiments, the region where the negative electrode active material layer is not disposed is not more than 8% based on the total area of the negative electrode current collector. In some embodiments, the region where the negative electrode active material layer is not disposed is not more than 5% based on the total area of the negative electrode current collector. In some embodiments, the region where the anode active material layer is not disposed is not more than 3% based on the total area of the anode current collector. In some embodiments, the region where the negative active material layer is not disposed is 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10% based on the total area of the negative current collector.

According to yet another aspect of the present application, there is provided an electronic device comprising an electrochemical device according to the present application.

Additional aspects and advantages 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.

Drawings

Drawings necessary for describing embodiments of the present application or the prior art will be briefly described below in order to describe the embodiments of the present application. It is to be understood that the drawings in the following description are only some of the embodiments of the present application. It will be apparent to those skilled in the art that other embodiments of the drawings can be obtained from the structures illustrated in these drawings without the need for inventive work.

Fig. 1 is a Scanning Electron Microscope (SEM) image of a negative active material having crushed particles according to an example of the present application.

Detailed Description

Embodiments of the present application will be described in detail below. In the present specification, the same or similar components and components having the same or similar functions are denoted by like reference numerals. The embodiments described herein with respect to the figures are illustrative in nature, are diagrammatic in nature, and are used to provide a basic understanding of the present application. The embodiments of the present application should not be construed as limiting the present application.

In the detailed description and claims, a list of items linked by the term "at least one of can mean any combination of the listed items. For example, if items a and B are listed, the phrase "at least one of a and B" means a only; only B; or A and B. In another example, if items A, B and C are listed, the phrase "A, B and at least one of C" means a only a; or only B; only C; a and B (excluding C); a and C (excluding B); b and C (excluding A); or A, B and all of 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.

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

As used herein, "porosity" refers to the voids between multiple particles of the anode active material.

As used herein, "particle breakage rate" refers to the percentage of the number of broken particles in the anode active material to the total number of anode active material particles.

In order to improve the energy density, cycle performance, and safety performance of an electrochemical device (e.g., a lithium ion battery), it is one of the research and development directions to improve the active material of an electrode. The upper limit of the theoretical electrochemical capacity of the graphitized anode active material is 372mAh/g, which the electrochemical capacity of previously known graphitized anode active materials has hardly broken through. The silicon cathode active material has high electrochemical capacity, the energy density of the electrochemical device can be remarkably improved along with the increase of the content of the doping material in the silicon cathode active material, but the cathode active material can generate obvious volume expansion, the performance of the electrochemical device can be remarkably reduced, and particularly, the capacity retention rate in long-cycle can be remarkably reduced.

In order to solve these problems, the present application provides an electrochemical device comprising a cathode, an anode, and an electrolyte, wherein the anode comprises an anode current collector and an anode active material layer disposed on the anode current collector, the anode active material layer comprising an anode active material, the anode active material comprising an amount of crushed particles.

Negative electrode

In the electrochemical device of the present application, the anode active material has a particle breakage rate of 20% to 80%. In some embodiments, the anode active material has a particle breakage rate of 30% to 60%. In some embodiments, the anode active material has a particle breakage rate of 40% to 50%. In some embodiments, the anode active material has a particle breakage of 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 active material and increase the contact sites of the negative active material and the electrolyte, thereby improving the cycle performance and energy density of the electrochemical device. The particle breakage rate of the anode active material can be obtained by counting the anode active particles in a Scanning Electron Microscope (SEM) image. Specifically, at least 4 regions (5 μm × 5 μm) were selected in a Scanning Electron Microscope (SEM) image of the anode active material, the number of crushed particles and the total number of anode active material particles in the 4 regions were counted, and the particle crushing rate of the anode active material was calculated by the following formula: particle breakage = the number of broken particles/total number of negative electrode active material particles × 100%.

According to an embodiment of the application, the broken particles have cracks or fissures having a width not greater than 4 μm. In some embodiments, the fractured particles have cracks or fissures that are not greater than 3.5 μm in width. In some embodiments, the fractured particles have cracks or fissures having a width of no greater than 2.5 μm. In some embodiments, the fractured particles have cracks or fissures that are no greater than 2 μm wide. Fig. 1 shows a Scanning Electron Microscope (SEM) image of a negative active material having crushed particles, in which particles circled by solid lines are crushed particles having cracks, and particles circled by dotted lines are crushed particles having cracks.

According to an embodiment of the present application, the roughness of the anode active material layer is not more than 6 μm. In some embodiments, the roughness of the anode active material layer is not greater than 5 μm. In some embodiments, the roughness of the anode active material layer is not greater than 3 μm. In some embodiments, the roughness of the anode active material layer is not greater 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 the surface roughness thereof depends on the unevenness of particles having small pitches and minute peaks and valleys on the surface. The roughness of the anode active material layer may be obtained by: the arithmetic mean of the absolute values of the distances from the points on the particle profile to the reference line, i.e. the arithmetic mean deviation Ra of the profile, is calculated over the sampling length. The smaller Ra, the smaller roughness of the anode active material layer, and the smoother the anode active material layer.

According to an embodiment of the present application, the cohesive strength of the anode active material is 5N/m to 30N/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 the broken particles disables a portion of contact sites of the active material with the binder, thereby reducing the cohesive strength of the negative active material. When the cohesive strength of the negative active material is within the above range, the negative active material particles have proper cohesiveness, so that the powder falling phenomenon in the rolling and winding processes can be avoided, and the formation of micro short-circuit sites inside the lithium ion battery can be avoided, thereby avoiding potential safety hazards; and the volume expansion of the negative active material can be generated in the charging and discharging process, so that incomplete lithium intercalation is avoided, and the capacity of the electrochemical device is ensured. The cohesive strength of the negative active material can be tested using an Instron (model number 33652) tester: taking a negative plate (with the width of 30mm and the length of 100-160 mm), fixing the negative plate on a steel plate by using double-sided adhesive tape (the model: 3M9448A, the width of 20mm and the length of 90-150 mm), attaching the adhesive tape to the surface of a negative active material layer, connecting one side of the adhesive tape with a paper tape with the same width, adjusting a limiting block of a tensile machine to a proper position, turning and sliding the paper tape upwards for 40mm at the sliding speed of 50mm/min, and testing the polymerization strength among particles in the negative active material layer at 180 degrees (namely, stretching in the opposite direction).

According to an embodiment of the present application, the adhesion between the negative electrode active material layer and the negative electrode current collector is 5N/m to 20N/m. In some embodiments, the adhesion between the negative electrode active material layer and the negative electrode current collector is 10 to 15N/m. In some embodiments, the adhesion 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 power between the negative active material layer and the negative current collector is in the range, the stripping or burr generation in the rolling or splitting process can be avoided, so that the potential safety hazard can be avoided, the internal resistance of the battery cell can be ensured to be in an acceptable range, and the dynamic performance and the cycle performance of the electrochemical device can be ensured. The peel strength between the negative active material layer and the negative current collector may be achieved by controlling a rolling process in the negative electrode preparing process. Specifically, the adhesion between the anode active material layer and the anode current collector may be tested using an Instron (model number 33652) tester: taking a pole piece (the width is 30mm, the length is 100-160 mm), fixing the pole piece on a steel plate by using double-sided adhesive paper (the model is 3M9448A, the width is 20mm, and the length is 90-150 mm), attaching the adhesive paper on the surface of a negative active material layer, connecting one side of the adhesive paper with a paper tape with the same width, adjusting a limiting block of a tensile machine to a proper position, turning and sliding the paper tape upwards for 40mm, wherein the sliding rate is 50mm/min, and testing the adhesive force between the negative active material layer and a negative current collector under 180 degrees (namely, stretching in the opposite direction).

According to the examples of the present application, the negative active material obtained by the raman spectroscopy test was at 1345cm^-1To 1355cm^-1The half-height peak width Id of the peak appeared at the position is equal to or greater than 1595cm^-1To 1605cm^-1The ratio Id/Ig of the half height width Ig of the peak appearing at (A) is 0.7 to 1.5. In some embodiments, the negative active material has an Id/Ig of 1.0 to 1.2 as measured by raman spectroscopy. In some embodiments, the negative active material has an Id/Ig of 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, or 1.5 as measured by raman spectroscopy. When Id/Ig of the anode active material is in the above range, crystal defects and disorder degree of the anode active material surface are in an appropriate range, contributing to increase of gram capacity of the anode active material.

According to the examples of the present application, id is 200cm^-1To 1100cm^-1. In some embodiments, id is 2200cm^-1To 1000cm^-1. In some embodiments, id is 2500cm^-1To 900cm^-1. In some embodiments, id is 200cm^-1、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 application, the pores have a pore diameter of not more than 2 μm. In some embodiments, the pores have a pore diameter of no greater than 1 μm. In some embodiments, the pores have a pore size of no greater than 0.5 μm. In some embodiments, the pores have a pore diameter of 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, or 3 μm. The negative active material with the holes has a large specific surface area, and the inner walls of the holes can effectively absorb lithium, thereby being beneficial to improving the electrochemical capacity of the negative active material. When the pore diameter of the pores is within the above range, the electrolyte can effectively infiltrate the negative active material to form a solid-liquid interface.

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

In some embodiments, the negative active material may include, but is not limited to, natural graphite, artificial graphite, mesophase micro carbon spheres (abbreviated as MCMB), hard carbon, soft carbon, silicon-carbon composite, li-Sn alloy, li-Sn-O alloy, sn, snO₂Spinel-structured lithiated TiO₂-Li ₄Ti ₅O ₁₂Or an LI-l alloy. Non-limiting examples of carbon materials include crystalline carbon, amorphous carbon, and mixtures thereof. The crystalline carbon may be natural graphite or artificial graphite in an amorphous form or in a form of a flake, a platelet, a sphere or a fiber. The amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbide, calcined coke, or 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 the conductive material 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 powders, 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 anode further comprises a binder selected from at least one of: polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, or the like.

The negative current collector used herein may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, 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 disposed on the positive electrode current collector. The specific kind of the positive electrode active material is not particularly limited and may be selected as desired.

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

Specifically, the chemical formula of lithium cobaltate may be as shown in chemical formula 1:

Li _xCo _aM1 _bO _2-cchemical formula 1

Wherein M1 represents at least one selected from the group consisting of 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 silicon (Si), and x, a, B, and c values are respectively in the following ranges: x is more than or equal to 0.8 and less than or equal to 1.2, a is more than or equal to 0.8 and less than or equal to 1, b is more than or equal to 0 and less than or equal to 0.2, and c is more than or equal to-0.1 and less than or equal to 0.2.

The chemical formula of lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminate can be as shown in chemical formula 2:

Li _yNi _dM2 _eO _2-fchemical formula 2

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

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

Li _zMn _2-gM3 _gO _4-hchemical formula 3

Wherein M3 represents at least one selected from the group consisting of cobalt (Co), nickel (Ni), magnesium (Mg), aluminum (Al), boron (B), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), molybdenum (Mo), tin (Sn), calcium (Ca), strontium (Sr), and tungsten (W), and z, g, and h values are respectively in the following ranges: z is more than or equal to 0.8 and less than or equal to 1.2, g is more than or equal to 0 and less than 1.0, and h is more than or equal to-0.2 and less than or equal to 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 electrode active material layer is 3 to 10 times the weight of the negative electrode active material layer. In some embodiments, the weight of the positive electrode active material layer is 5 to 8 times the weight of the negative electrode active material layer. In some embodiments, the weight of the positive electrode active material layer is 1.5 times, 2 times, 3 times, 4 times, 5 times, 6 times, 7 times, 8 times, 9 times, 10 times, 11 times, 12 times, 13 times, 14 times, or 15 times the weight of the negative electrode active material layer.

In some embodiments, the positive electrode active material layer may have a coating layer on the surface, or may be mixed with another compound having a coating layer. The coating may include at least one coating element compound selected from an oxide of the coating element, a hydroxide of the coating element, an oxyhydroxide of the coating element, an oxycarbonate (oxycarbonate) of the coating element, and an oxycarbonate (hydroxycarbonate) of the coating element. The compounds used for the coating may be amorphous or crystalline. The coating element contained in the coating layer may include Mg, al, co, K, na, ca, si, ti, V, sn, ge, ga, B, as, zr, F, or a mixture thereof. The coating layer may be applied by any method as long as the method does not adversely affect the properties 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 comprises a binder, and optionally further comprises a positive conductive material.

The binder may 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 pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy, nylon, and the like.

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 the positive electrode conductive material 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 (e.g., polyphenylene derivatives), and mixtures thereof.

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

Electrolyte solution

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

Electrolytes that may be used in the electrolytes of embodiments of the present application include, but are not limited to: inorganic lithium salts, e.g. LiClO₄、LiAsF ₆、LiPF ₆、LiBF ₄、LiSbF ₆、LiSO ₃F、LiN(FSO ₂) ₂Etc.; organic lithium salts containing fluorine, e.g. LiCF₃SO ₃、LiN(FSO ₂)(CF ₃SO ₂)、LiN(CF ₃SO ₂) ₂、LiN(C ₂F ₅SO ₂) ₂Cyclic 1,3-hexafluoropropane disulfonimide lithium, cyclic 1,2-tetrafluoroethane disulfonimide lithium, liN (CF)₃SO ₂)(C ₄F ₉SO ₂)、LiC(CF ₃SO ₂) ₃、LiPF ₄(CF ₃) ₂、LiPF ₄(C ₂F ₅) ₂、LiPF ₄(CF ₃SO ₂) ₂、LiPF ₄(C ₂F ₅SO ₂) ₂、LiBF ₂(CF ₃) ₂、LiBF2(C2F5)2、LiBF ₂(CF ₃SO ₂) ₂、LiBF ₂(C ₂F ₅SO ₂) ₂(ii) a The dicarboxylic acid complex-containing lithium salt may, for example, be lithium bis (oxalato) borate, lithium difluorooxalato borate, lithium tris (oxalato) phosphate, lithium difluorobis (oxalato) phosphate, lithium tetrafluoro (oxalato) phosphate, or the like. The electrolyte may be used alone or in combination of two or more. In some embodiments, the electrolyte comprises LiPF₆And LiBF₄Combinations of (a) and (b). In some embodiments, the electrolyte comprises LiPF₆Or LiBF₄An inorganic lithium salt and LiCF₃SO ₃、LiN(CF ₃SO ₂) ₂、LiN(C ₂F ₅SO ₂) ₂And the like, a combination of fluorine-containing organic lithium salts. In some embodiments, the electrolyte comprises LiPF₆。

In some embodiments, the concentration of the electrolyte is in the range of 0.8 to 3mol/L, such as in the range of 0.8 to 2.5mol/L, in the range of 0.8 to 2mol/L, in the range of 1 to 2mol/L, again such as 1mol/L, 1.15mol/L, 1.2mol/L, 1.5mol/L, 2mol/L, or 2.5mol/L.

Solvents that may be used in the electrolytes of embodiments of the present application include, but are not limited to: a carbonate compound, an ester-based compound, an ether-based compound, a ketone-based compound, an alcohol-based compound, an aprotic solvent, or a combination thereof.

Examples of the carbonate compound include, but are not limited to, a chain carbonate compound, a cyclic carbonate compound, a fluoro carbonate compound, or a combination thereof.

Examples of the chain carbonate compound include, but are not limited to, diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl Propyl Carbonate (MPC), ethyl Propyl Carbonate (EPC), methyl Ethyl Carbonate (MEC), and combinations thereof. 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 fluoro carbonate compounds are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 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, t-butyl acetate, methyl propionate, ethyl propionate, γ -butyrolactone, decalactone, 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, 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, dimethylsulfoxide, 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 and negative electrodes to prevent short circuits. The material and shape of the separation film that can be used for the embodiment of the present application are not particularly limited, and may be any of the techniques disclosed in the prior art. In some embodiments, the separator includes a polymer or inorganic substance or the like formed of a material stable to the electrolyte of the present application.

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

At least one surface of the substrate layer is provided with a surface treatment layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.

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

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

Electrochemical device

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

Electronic device

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, head-mounted stereo headphones, video recorders, liquid crystal televisions, hand-held cleaners, portable CDs, mini-discs, transceivers, electronic organizers, calculators, memory cards, portable recorders, radios, backup power sources, motors, automobiles, motorcycles, mopeds, bicycles, lighting fixtures, toys, game consoles, clocks, electric tools, flashlights, cameras, household large-sized 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.

1. Preparation of lithium ion battery

1. Preparation of negative active material

2kg of artificial graphite was dispersed in ethanol to obtain a first solution. Dissolving 0.05mol of ammonium citrate tribasic in 1mL of isopropanol, adding 1.5mol of zinc acetate after complete dissolution, stirring at 1000rpm for at least 30 minutes, and filtering through a water system filter membrane to obtain a zinc oxide sol-gel solution. Hydrochloric acid in the same amount as zinc acetate is added to the zinc oxide sol-gel solution to obtain a second solution. 1000mL of the second solution was added to the first solution and stirring was continued at 50 ℃ for 90 minutes to give a third solution. Then, the resulting third solution was allowed to stand for 180 minutes, dried at 70 ℃ for 10 hours to remove the solvent, and then subjected to heat treatment at 1000 ℃ under an argon atmosphere to remove impurities, to obtain a negative electrode active material.

Preparing the negative active material obtained in the step into a pole piece, and controlling rolling pressure and/or rolling time to form the negative active material with the required particle breakage rate. The control of the amount of the second solution in the third solution also allows the control of the particle breakage rate.

2. Preparation of the negative electrode

The prepared negative electrode active material, styrene Butadiene Rubber (SBR) as a binder and sodium carboxymethyl cellulose (CMC) as a thickening agent are fully stirred and mixed in a proper amount of deionized water according to the weight ratio of 97: 1: 2 to form uniform negative electrode slurry, wherein the solid content of the negative electrode slurry is 54wt%. The slurry is coated on a negative current collector (copper foil), dried at 85 ℃, then subjected to cold pressing, slitting and cutting, and dried for 12 hours at 120 ℃ under a vacuum condition, so as to obtain a negative electrode.

3. Preparation of the Positive electrode

Mixing lithium cobaltate (LiCoO)₂) Super P and polyvinylidene fluoride (PVDF) are fully stirred and mixed in a proper amount of N-methyl pyrrolidone (NMP) solvent according to the weight ratio of 97: 1.4: 1.6 to form uniform anode slurry, wherein the solid content of the anode slurry is 72wt%. Coating the slurry on an aluminum foil of a positive current collector, drying at 85 ℃, then carrying out cold pressing, cutting and slitting, and drying for 4 hours at 85 ℃ under a vacuum condition to obtain the positive electrode.

4. Preparation of the electrolyte

In a dry argon atmosphere glove box, ethylene Carbonate (EC), ethyl Methyl Carbonate (EMC) and diethyl carbonate (DEC) are mixed according to the mass ratio of EC: EMC: DEC = 30: 50: 20, then 3% fluoroethylene carbonate and 1.5% 1,3 propane sultone are added, dissolved and fully stirred, and lithium salt LiPF is added₆Mixing uniformly to obtain electrolyte, wherein LiPF₆The concentration of (2) is 1mol/L.

5. Preparation of the separator

A Polyethylene (PE) porous polymer film having a thickness of 7 μm was used as a separator.

6. Preparation of lithium ion battery

And sequentially stacking the anode, the isolating film and the cathode to enable the isolating film to be positioned between the anode and the cathode to play an isolating role, then winding, welding a tab, placing the tab into an outer packaging foil aluminum plastic film, injecting the prepared electrolyte, and carrying out vacuum packaging, standing, formation, shaping, capacity test and other procedures to obtain the soft package lithium ion battery.

2. Test method

1. Method for testing cycle capacity retention rate of lithium ion battery

Charging the lithium ion battery to a voltage of 4.4V at a constant current of 0.7C in an environment of 25 ℃, and then charging at a constant voltage; the discharge was made at a constant current of 1C to a voltage of 3V, which was recorded as a cycle, and the discharge capacity was recorded for the first cycle. 200 cycles were performed, and the discharge capacity at the 200 th cycle was recorded. The cycle capacity retention of the lithium ion battery was calculated by the following formula:

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

5 samples were tested per example or comparative example and averaged.

2. Method for testing thermal shock bearing time of lithium ion battery

And (3) enabling the lithium ion battery to reach a full charge state, placing the lithium ion battery in a high-temperature box at 150 ℃, and recording the time when the lithium ion battery starts to generate flame as thermal shock bearing time. 5 samples were tested per example or comparative example and averaged.

3. Overcharge test method of lithium ion battery

And (3) overcharging the lithium ion battery at the current density of 1C multiplying power under 10V, and testing the surface temperature of the lithium ion battery. 5 samples were tested per example or comparative example and averaged.

4. Nail penetration testing method for lithium ion battery

And (3) placing the lithium ion battery in a constant temperature box at 25 ℃, and standing for 30 minutes to keep the temperature of the lithium ion battery constant. The lithium ion battery reaching the constant temperature was 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. And transferring the fully charged lithium ion battery to a nail penetration testing machine, keeping the testing environment temperature at 25 +/-2 ℃, using a steel nail with the diameter of 4mm to penetrate through the center of the lithium ion battery at a constant speed of 30mm/s, and keeping for 300 seconds. And testing the surface temperature of the lithium ion battery. 5 samples were tested per example or comparative example and averaged.

5. Impact test method of lithium ion battery

Charging the lithium ion battery at a constant current of 0.5 ℃ to a voltage of 4.3V at 25 ℃, then charging the lithium ion battery at a constant voltage of 4.3V to a current of 0.05C, and adopting a UL1642 test standard, wherein the weight mass is 9.8kg, the diameter is 15.8mm, and the falling height is 61 +/-2.5 cm, and carrying out an impact test on the lithium ion battery. And testing the surface temperature of the lithium ion battery. 5 samples were tested per example or comparative example and averaged.

6. Method for testing cohesive strength of negative electrode active material

The test was carried out using an Instron (model 33652) tester: taking a pole piece (the width is 30mm, the length is 100-160 mm), fixing the pole piece on a steel plate by using double-sided adhesive paper (the model is 3M9448A, the width is 20mm, and the length is 90-150 mm), attaching the adhesive paper on the surface of a negative active material layer, connecting one side of the adhesive paper with a paper tape with the same width, adjusting a limiting block of a tensile machine to a proper position, turning and sliding the paper tape upwards for 40mm at the sliding speed of 50mm/min, and testing the polymerization strength among particles in the negative active material layer at 180 degrees (namely, stretching in the opposite direction).

7. Method for testing binding force between negative active material layer and negative current collector

The test was carried out using an Instron (model 33652) tester: taking a pole piece (the width is 30mm, the length is 100-160 mm), fixing the pole piece on a steel plate by using double-sided adhesive paper (the model is 3M9448A, the width is 20mm, and the length is 90-150 mm), attaching the adhesive paper on the surface of a negative active material layer, connecting one side of the adhesive paper with a paper tape with the same width, adjusting a limiting block of a tensile machine to a proper position, turning and sliding the paper tape upwards for 40mm, wherein the sliding rate is 50mm/min, and testing the adhesive force between the negative active material layer and a negative current collector under 180 degrees (namely, stretching in the opposite direction).

8. Method for testing particle breakage rate of negative electrode active material

At least 4 regions (5 μm × 5 μm) were selected in a Scanning Electron Microscope (SEM) image of the disassembled anode active material, and the anode active material particles were observed, and the particles without the binder at the particle interface were broken particles. The number of crushed particles and the total number of particles of the negative electrode active material in the 4 regions were counted, and the particle crushing rate of the negative electrode active material was calculated by the following formula: particle breakage = the number of broken particles/total number of negative electrode active material particles × 100%. 5 samples were tested per example or comparative example.

3. Test results

Table 1 shows the effect of the particle breakage rate and Id/Ig of the negative electrode active material on the cycle performance and safety of the lithium ion battery, and the width of the crack or fissure of the broken particles in table 1 is not more than 4 μm.

TABLE 1

The results show that, when the negative active material contains crushed particles and the particle breakage rate is 20% to 80%, the cycle capacity retention rate of the lithium ion battery is significantly increased, the thermal shock withstand time is significantly prolonged, and the surface temperature in the overcharge test, the nail penetration test, and the impact test is significantly decreased, that is, the cycle performance and the safety of the lithium ion battery are significantly improved, as compared to the comparative example. On the basis, the Id/Ig of the negative active material is controlled to be in the range of 0.7-1.5, so that the cycle capacity retention rate of the lithium ion battery can be further improved, the thermal shock bearing time is prolonged, and the surface temperature in an overcharge test, a nail penetration test and an impact test is reduced. Controlling Id to be 200cm on the basis that Id/Ig is 0.7 to 1.5^-1To 1100cm^-1The method is favorable for further improving the cycle performance and the safety of the lithium ion battery.

Table 2 shows the effect of metallic elements, non-metallic elements and pores in the negative active material on the cycle performance and safety of the lithium ion battery. Examples 13-40 were consistent with the other settings of example 3 and example 41 was consistent with the other settings of example 2, except for the parameters listed in table 2.

TABLE 2

The results show that when the negative active material contains 20ppm to 400ppm of the metal element and/or 50ppm to 400ppm of the nonmetal element, it contributes to further improvement of cycle performance and safety of the lithium ion battery. When the negative active material has pores and the inner walls of the pores have a metal element and/or a non-metal element, it is helpful to further improve the cycle performance and safety of the lithium ion battery.

Table 3 shows the effect of the properties of the negative active material on the cycle performance and safety of the lithium ion battery. Examples 42-54 were consistent with the other settings of example 3, except for the parameters listed in table 3.

TABLE 3

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

Table 4 shows the effect of the area occupation ratio of the negative electrode current collector where the negative electrode active material layer is not disposed on the cycle performance and safety of the lithium ion battery. Examples 55-58 are consistent with the other settings of example 3, except for the parameters listed in table 4.

TABLE 4

The results show that when the region where the anode active material layer is not provided does not exceed 10%, it contributes to further improvement in cycle performance and safety of the lithium ion battery.

The cycle performance of the lithium ion battery is improved, the safety of the lithium ion battery is guaranteed, the application field of the lithium ion battery is expanded, and a wide space is provided for the development of the lithium ion battery.

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

An electrochemical device comprising a positive electrode, a negative electrode and an electrolyte, wherein the negative electrode comprises a negative electrode current collector and a negative electrode 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 crushed particles, and the particle breakage rate of the negative electrode active material is 20% to 80%.
The electrochemical device of claim 1, wherein the broken particles have cracks or fissures having a width of no greater than 4 μ ι η.
The electrochemical device according to claim 1, wherein a 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 negative active material is 5N/m to 30N/m.
The electrochemical device according to claim 1, wherein the adhesive force between the negative active material layer and the negative current collector is 5 to 20N/m.
The electrochemical device of claim 1, wherein the negative active material is at 1345cm as measured by raman spectroscopy^-1To 1355cm^-1The half height width Id of the peak appeared and the peak width at 1595cm^-1To 1605cm^-1The ratio Id/Ig of the half height width Ig of the peak appearing at (A) is 0.7 to 1.5.
The electrochemical device of claim 6, wherein Id is 200cm^-1To 1100cm^-1。
The electrochemical device according to claim 1, wherein the anode active material includes at least one of a metal element or a non-metal element, the metal element including at least one of gold, silver, platinum, zirconium, zinc, magnesium, calcium, barium, vanadium, iron, or aluminum, the content of the metal element being 20ppm to 400ppm based on the total weight of the anode active material; the non-metallic element includes at least one of phosphorus, boron, silicon, arsenic or selenium, and is included in an amount of 50ppm to 400ppm based on the total weight of the anode active material.
The electrochemical device according to claim 8, wherein the negative electrode active material has pores having a pore diameter of not more than 3 μm, inner walls of the pores having the metal element.
The electrochemical device according to claim 1, wherein the negative electrode current collector includes a region where the negative electrode active material layer is not disposed, and the region where the negative electrode active material layer is not disposed is not more than 10% based on a total area of the negative electrode current collector.
An electronic device comprising the electrochemical device according to any one of claims 1-10.