CN114883524A - Electrochemical device and electronic device - Google Patents

Electrochemical device and electronic device Download PDF

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Publication number
CN114883524A
CN114883524A CN202210587475.XA CN202210587475A CN114883524A CN 114883524 A CN114883524 A CN 114883524A CN 202210587475 A CN202210587475 A CN 202210587475A CN 114883524 A CN114883524 A CN 114883524A
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particles
positive electrode
electrochemical device
equal
lithium
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谷风
郎野
刘文元
彭刚
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Ningde Amperex Technology Ltd
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Ningde Amperex Technology Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The present disclosure provides an electrochemical device and an electronic device, wherein the electrochemical device includes: a positive electrode; a negative electrode; a separator disposed between the positive electrode and the negative electrode; the positive electrode comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, the positive electrode active material layer comprises a positive electrode material, the positive electrode material comprises a lithium-containing transition metal oxide, the positive electrode material comprises first particles and second particles, the particle size of the first particles is larger than that of the second particles, the proportion of lithium element in the first particles is x ppm based on the total mass of the first particles, the proportion of lithium element in the second particles is y ppm based on the total mass of the second particles under the condition that the voltage of the electrochemical device is 2.5V, and x/y is more than or equal to 1.001 and less than or equal to 1.2. The stress release of particles with different particle sizes in the anode material is balanced, so that the particles of the anode material are prevented from being broken in the circulation process of an electrochemical device.

Description

Electrochemical device and electronic device
The present application is a divisional application of an invention patent entitled "electrochemical device and electronic device" filed on 30/11/2020, application No. 202011378025.7.
Technical Field
The present application relates to the field of electrochemical technologies, and in particular, to an electrochemical device and an electronic device.
Background
Electrochemical devices (such as lithium ion batteries) are widely applied to various fields, in the process of charging and discharging, lithium ions are repeatedly inserted and extracted between a positive electrode material and a negative electrode material, the crystal volume of the positive electrode material expands and contracts in the process of insertion and extraction, particles of the positive electrode material are broken in the circulation process, the broken positive electrode material increases the consumption of electrolyte, and the safety performance of the circulation process is reduced.
Disclosure of Invention
The application provides an electrochemical device and an electronic device, which can solve the problem that an anode material of the electrochemical device is broken in a circulation process, thereby improving the circulation performance of the electrochemical device and the safety performance in the circulation process.
In some embodiments, the present application provides an electrochemical device comprising: a positive electrode; a negative electrode; a separator disposed between the positive electrode and the negative electrode; the positive electrode comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, the positive electrode active material layer comprises a positive electrode material, the positive electrode material comprises a lithium-containing transition metal oxide, the positive electrode material comprises first particles and second particles, the particle size of the first particles is larger than that of the second particles, the proportion of lithium element in the first particles is x ppm based on the total mass of the first particles, the proportion of lithium element in the second particles is y ppm based on the total mass of the second particles under the condition that the voltage of the electrochemical device is 2.5V, and x/y is more than or equal to 1.001 and less than or equal to 1.2.
In some embodiments, the positive electrode material satisfies at least one of the following conditions (a) to (f):
(a)60000≤x≤65000；
(b)55000≤y≤60000；
(c)500≤x-y≤10000；
(e) specific surface area BET of the first particles 1 Satisfies the following conditions: 0.1m 2 /g≤BET 1 ≤1.5m 2 (ii)/g, specific surface area BET of the second particle 2 Satisfies the following conditions: 0.5m 2 /g≤BET 2 ≤2m 2 /g；
(f) The first particles have a Dv50 of 8 μm to 15 μm and the second particles have a Dv50 of 1 μm to 6 μm.
In some embodiments, the mass ratio R of the first particles to the second particles in the positive electrode material satisfies: r is more than 0 and less than or equal to 10.
In some embodiments, the mass ratio R of the first particles to the second particles in the positive electrode material satisfies: r is more than or equal to 0.6 and less than or equal to 1.5.
In some embodiments, the positive electrode material has particles of at least two different morphologies therein.
In some embodiments, the shape of the cross-section of the first particle comprises: and (4) a circular shape.
In some embodiments, the shape of the cross-section of the second particle comprises: a polygon.
In some embodiments, the porosity of the positive electrode active material layer is 5% to 35%.
In some embodiments, the positive electrode active material layer has a compacted density of 2.0g/cm 3 -4.5g/cm 3 。
In some embodiments, at least one of the first particles or the second particles comprises: li m [Ni a Mn b Co 1-(a+b+c) M c ]O 2 Wherein a is more than or equal to 0.45 and less than or equal to 0.9, b is more than or equal to 0.05 and less than or equal to 0.5, and 0<c is less than or equal to 0.1, a + B + c is less than or equal to 1, M is less than or equal to 1.10 and is more than or equal to 0.97, and M comprises at least one of W, B, Al, Ti, Mg, Cr, Zr or Si
In some embodiments, the electrochemical device further comprises: an electrolytic solution containing at least one of a polynitrile compound or lithium difluorophosphate.
In some embodiments, the polynitrile compound comprises: at least one of succinonitrile, adiponitrile, ethylene glycol bis (propionitrile) ether, 1,3, 6-hexanetricarbonitrile, 1,2, 6-hexanetricarbonitrile, or 1,2, 3-tris (2-cyanoethoxy) propane;
the mass content of the polynitrile compound in the electrolyte is 1-15%.
In some embodiments, the lithium difluorophosphate is present in the electrolyte in an amount of 0.001% to 1% by mass.
In some embodiments of the present application, an electronic device is provided, comprising the electrochemical device of any one of the above.
The stress of particles with different particle diameters in the positive electrode material is balanced by controlling the mass ratio of lithium element in the first particles and the second particles, so that the particles of the positive electrode material are prevented from being broken in the circulation process of the electrochemical device.
Drawings
The above and other features, advantages and aspects of various embodiments of the present disclosure will become more apparent by referring to the following detailed description when taken in conjunction with the accompanying drawings. Throughout the drawings, the same or similar reference numbers refer to the same or similar elements. It should be understood that the drawings are schematic and that elements and elements are not necessarily drawn to scale.
Fig. 1 is a schematic diagram of the composition of an electrochemical device according to an embodiment of the present disclosure.
Detailed Description
Embodiments of the present application will be described in more detail below. This application is capable of implementation in various forms and should not be construed as limited to the embodiments set forth herein but is to be provided for a more thorough and complete understanding of the application.
Positive electrode
During charging and discharging, the extraction and insertion of lithium ions can cause the material to increase or decrease in the c-axis direction of the unit cell, which is macroscopically represented by the volume expansion or contraction of the particles. When the amount of the lithium removed is the same, the stress of the particles with different particle diameters is different, the material is broken due to nonuniform stress release in the circulation process, and the breakage can expose a fresh interface to generate side reaction with electrolyte, so that the circulation performance is reduced. The single crystal anode material with larger primary particles, the anode material with mixed large and small particles or the anode material is prepared into a hollow core-shell structure, however, the single crystal with larger primary particles can increase the lithium ion transmission path, which causes the impedance of the electrochemical device to be increased, the dynamic performance to be reduced, and the cycle performance and the high-temperature performance to be deteriorated; under the condition of the same voltage and the same delithiation amount, the anode material mixed by large and small particles can cause the stress release of particles with different particle diameters to be nonuniform, and the material is cracked; the use of a hollow core-shell structure results in a decrease in the energy density of the material and is easily crushed at the time of rolling of the positive electrode.
The present application solves the above-mentioned problems by using first particles and second particles having a specific lithium element content in combination and adjusting the ratio thereof. The present application, in some embodiments, provides an electrochemical device, as shown in fig. 1, comprising: a positive electrode 10, a negative electrode 20, and a separator 30, the separator 30 being disposed between the positive electrode 10 and the negative electrode 20; the positive electrode 10 comprises a positive electrode current collector 11 and a positive electrode active material layer 12 arranged on the positive electrode current collector 11, the positive electrode active material layer 12 comprises a positive electrode material, the positive electrode material comprises a lithium-containing transition metal oxide, the positive electrode material 12 comprises first particles and second particles, the particle size of the first particles is larger than that of the second particles, the proportion of lithium element in the first particles is x ppm based on the total mass of the first particles, the proportion of lithium element in the second particles is y ppm based on the total mass of the second particles under the condition that the voltage of the electrochemical device is 2.5V, and the requirement that x/y is more than or equal to 1.001 and less than or equal to 1.2 is met.
In some embodiments, the electrochemical device may be a lithium ion battery and the positive electrode material may be, for example, doped or undoped, coated or uncoated lithium nickel cobalt manganese oxide containing other elements. In the present application, the first particle size is larger than the second particle size, and the ratio of the mass of lithium element in the first particles to the mass of lithium element in the second particles to y ppm satisfies 1.001. ltoreq. x/y, this indicates that the mass content of lithium element contained in the first particles having a larger particle diameter is larger than that contained in the second particles having a smaller particle diameter, and therefore, during the process of extracting and intercalating lithium ions from the positive electrode material, more lithium ions are extracted and intercalated from the first particles than from the second particles, however, since the first particle size is larger than the second particle size, and x/y.ltoreq.1.2, that is, the lithium ions extracted and inserted from the first particles are not too different from the lithium ions inserted and extracted from the second particles, and the strains generated by the first particles and the second particles due to the lithium ions extracted and inserted are generally similar, so that the particles of the cathode material are not easy to break in the circulation process of the electrochemical device. The stress of particles with different particle diameters in the positive electrode material is balanced by controlling the mass ratio of lithium element in the first particles and the second particles, so that the particles of the positive electrode material are prevented from being broken in the circulation process of the electrochemical device. In the electrochemical device, the first particles and the second particles in the positive electrode active material layer may be separated in the following manner: adjusting an electrochemical device such as a lithium ion battery to a voltage of 2.5V, disassembling the battery, scraping the anode active material layer powder, burning in a muffle furnace for 6-9 hours at 600 ℃, and sieving by using a 500-mesh sieve to obtain first granules and second granules.
In some embodiments of the present application, 60000 ≦ x ≦ 65000. In some embodiments, when x is greater than 65000, the mass content of lithium element in the first particles is too high, and lithium ions deintercalated and intercalated during cycling of the electrochemical device may be too much, resulting in breakage of the first particles due to excessive stress caused by deintercalation and intercalation of lithium ions, and when x is less than 60000, the mass content of lithium element in the first particles is too low, resulting in low capacity density of the electrochemical device.
55000 ≦ y ≦ 60000 in some embodiments of the present application. In some embodiments, when y is more than 60000, the content by mass of lithium element in the second particles is too high, and lithium ions deintercalated and intercalated during the cycle of the electrochemical device may be too much, resulting in the second particles being fractured due to too much stress caused by the deintercalation and intercalation of lithium ions, and when y is less than 55000, the content by mass of lithium element in the second particles is too low, resulting in the low capacity density of the electrochemical device.
In some embodiments of the present application, 500 ≦ x-y ≦ 10000. In some embodiments, when the difference between x and y is less than 500, the difference between lithium ions extracted and inserted from the first particle and the second particle is small, and since the second particle has a smaller particle size than the first particle, the stress of the second particle is greater than that of the first particle, which may cause the second particle to be easily broken. When the difference between x and y is greater than 10000, lithium ions extracted and inserted from the first particle may be much more than that from the second particle, so that the stress generated by the first particle is much greater than that generated by the second particle, and the first particle is easy to break; in some embodiments, the stress difference between the first particle and the second particle is prevented from being too large by controlling 500. ltoreq. x-y. ltoreq.5000.
In some embodiments of the present application, the specific surface area BET of the first particles 1 Satisfies the following conditions: 0.1m 2 /g≤BET 1 ≤1.5m 2 (ii)/g, specific surface area BET of the second particle 2 Satisfies the following conditions: 0.5m 2 /g≤BET 2 ≤2m 2 (ii) in terms of/g. In some embodiments, controlling the specific surface area of the first particles and the second particles within the above range may balance the overall performance of the electrochemical device.
In some embodiments of the present application, the Dv50 of the first particles is between 8 μm and 15 μm, and the Dv50 of the second particles is between 1 μm and 6 μm; in some embodiments, by limiting the Dv50 of the first particle and the second particle within the above range and limiting the x/y value, it can be ensured that the stress difference between the first particle and the second particle is small in the circulation process, so that the stress of the positive electrode material is uniformly distributed in the circulation process, the problem of particle fracture is not easily caused, and the electrochemical device is ensured to have a good circulation capacity retention rate, and the gas generation in the circulation process is reduced, thereby improving the safety performance.
In some embodiments of the present application, a mass ratio R of the first particles to the second particles in the positive electrode material satisfies: r is more than 0 and less than or equal to 10. When the mass ratio of the first particles to the second particles is greater than 10, the number of the second particles in the positive electrode material is small, and the second particles cannot sufficiently fill gaps between the first particles, which may result in a low compaction density of the positive electrode active material layer, resulting in a decrease in the energy density of the electrochemical device. Also, when the mass ratio of the first particles to the second particles is greater than 10, since the first particles are excessive and the first particle size is greater than the second particle size, the transmission path of lithium ions may be increased to increase the impedance, lowering the dynamic performance of the electrochemical device, resulting in a reduction in cycle performance.
In some embodiments, the mass ratio R of the first particles to the second particles in the positive electrode material satisfies: r is more than or equal to 0.6 and less than or equal to 5. When R is less than 0.6, compared with the condition that R is more than or equal to 0.6 and less than or equal to 5, the safety performance of the cycle process is reduced because the second particles are relatively more and are easy to generate gas by side reaction, and when R is more than 5, compared with the condition that R is more than or equal to 0.6 and less than or equal to 5, the dynamic performance of the electrochemical device is reduced because the mass content of the first particles is more, so that the cycle capacity retention rate is reduced, and therefore, when R is more than or equal to 0.6 and less than or equal to 5, the overall performance of the electrochemical device is better.
In some embodiments, the particles have at least two different morphologies in the positive electrode material; the shape of the cross-section of the first particle includes: a circular shape; the shape of the cross-section of the second particle includes: a polygon. When the cross section of the first particles includes a circle and the cross section of the second particles includes a polygon, the second particles are easily filled in the gaps between the first particles, thereby increasing the compaction density of the positive electrode active material layer, and further increasing the volumetric energy density.
In some embodiments, the molar ratio of the lithium element in the first particles to the transition metal element in the first particles is 1.00 to 1.06, which may cause the electrochemical device to be liable to generate gas when the molar ratio of the lithium element to the transition metal element in the first particles is less than 1, thereby reducing safety during cycling, and which may reduce cycling performance of the electrochemical device when the molar ratio of the lithium element to the transition metal element in the first particles is greater than 1.04.
In some embodiments of the present application, a molar ratio of the lithium element in the second particles to the transition metal element in the second particles is 0.98 to 1.02, and when the molar ratio of the lithium element to the transition metal element in the second particles is within the above range, a cycle capacity retention rate of the electrochemical device is high, gas generation during a cycle is low, and safety performance is good.
In some embodiments of the present application, when the first particles and/or the second particles are used as a cathode material, the ratio of the lithium element content to the transition metal content in the cathode material dissociated in the electrochemical device is reduced due to consumption of lithium ions during formation or cycling of the electrochemical device, such as a lithium ion battery. For example, in some embodiments, the molar ratio of lithium element in the first particles to transition metal element in the first particles in the electrochemical device is 0.95 to 1.01. For example, in some embodiments, the molar ratio of lithium element in the second particles to transition metal element in the second particles in the electrochemical device is 0.95 to 1.00.
In some embodiments of the present application, the positive electrode active material layer has a porosity of 5% to 35%. When the porosity of the positive electrode active material layer is less than 5%, lithium ions inside the positive electrode active material layer are not easily migrated, which may cause an increase in impedance of an electrochemical device and a decrease in kinetic performance, and when the porosity of the positive electrode active material layer is greater than 35%, a decrease in volumetric energy density may be caused.
In some embodiments of the present application, the positive electrode active material layer has a compacted density of 2.0g/cm 3 -4.5g/cm 3 . In some embodiments, when the compacted density of the positive electrode active material layer is less than 2.0g/cm 3 When the volume energy density of the electrochemical device is small, the compacted density of the positive electrode active material layer is more than 4.5g/cm 3 When the positive electrode material particles are broken due to excessive pressure in the rolling process.
In some embodiments of the present application, at least one of the first particles or the second particles comprises: li m [Ni a Mn b Co 1-(a+b+c) M c ]O 2 Wherein a is more than or equal to 0.45 and less than or equal to 0.9, b is more than or equal to 0.05 and less than or equal to 0.5, and 0<c is less than or equal to 0.1, a + B + c is less than or equal to 1, M is less than or equal to 1.10 and is more than or equal to 0.97, and M comprises at least one of W, B, Al, Ti, Mg, Cr, Zr or Si.
In some embodiments, the current collector of the positive electrode may be an Al foil, and of course, other current collectors commonly used in the art may be used. In some embodiments, the thickness of the current collector of the positive electrode may be 3 to 50 μm. In some embodiments, the positive electrode active material layer may be coated only on a partial area of the positive electrode collector. In some embodiments, the thickness of the single-sided positive electrode active material layer may be 30 μm to 150 μm. It should be understood that these are merely exemplary and that other suitable thicknesses may be employed.
Negative electrode
The anode 20 includes an anode current collector 21 and an anode active material layer 22 provided on at least one surface of the anode current collector 21, and the anode active material layer 22 contains an anode active material. The specific kind of the negative electrode active material is not particularly limited and may be selected as desired.
In some embodiments, the negative active material comprises 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, SnO 2 Spinel-structured lithiated TiO 2 -Li 4 Ti 5 O 12 And one or more of Li-Al 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.
In some embodiments, the negative active material layer may include a binder and optionally further include a conductive material.
The binder improves the binding of the negative active material particles to each other and the binding of the negative active material to the current collector. Non-limiting examples of binders include 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, nylon, and the like.
The negative electrode active material layer includes a conductive material, thereby imparting conductivity to the electrode. The conductive material may include any conductive material as long as it does not cause a chemical change. Non-limiting examples of the conductive material include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., such as copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.
The current collector for the negative electrode described 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.
Electrolyte solution
In some embodiments of the present application, the electrochemical device further comprises: an electrolytic solution containing at least one of a polynitrile compound or lithium difluorophosphate. The polynitrile compound can form a stable SEI (solid electrolyte interphase) film with a positive electrode material, thereby improving the cycle performance and safety performance of an electrochemical device. Lithium difluorophosphate can improve the cycle performance and high-temperature storage performance of the electrochemical device.
In some embodiments of the present application, the polynitrile compound comprises: at least one of succinonitrile, adiponitrile, ethylene glycol bis (propionitrile) ether, 1,3, 6-hexanetricarbonitrile, 1,2, 6-hexanetricarbonitrile, or 1,2, 3-tris (2-cyanoethoxy) propane.
In some embodiments of the present application, the polynitrile compound is present in the electrolyte in an amount of 1% to 15% by mass. In some examples, when the mass content of the polynitrile compound in the electrolyte is less than 1%, the improvement effect may not be significant because the content is too low, and when the mass content of the polynitrile compound in the electrolyte is more than 15%, a reduction reaction may occur with the anode active material layer, and the product of the reduction reaction may damage the SEI film of the anode.
In some embodiments, the lithium difluorophosphate is present in the electrolyte in an amount of 0.001% to 1% by mass.
In some embodiments, the electrolyte includes a lithium salt and a non-aqueous solvent.
In some embodiments, the lithium salt is selected from LiPF 6 、LiBF 4 、LiClO 4 、LiB(C 6 H 5 ) 4 、LiCH 3 SO 3 、LiCF 3 SO 3 、LiN(SO 2 CF 3 ) 2 、LiC(SO 2 CF 3 ) 3 、LiSiF 6 One or more of LiBOB or lithium difluoroborate. For example, LiPF is selected as lithium salt 6 Since it can give high ionic conductivity and improve cycle characteristics.
In some embodiments, the non-aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvent, or a combination thereof.
The carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, or a combination thereof.
Examples of the chain carbonate compound are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate, methyl propyl carbonate, Ethyl Methyl Carbonate (EMC), and combinations thereof. Examples of the cyclic carbonate compound are Ethylene Carbonate (EC), Propylene Carbonate (PC), butylene carbonate, vinyl ethylene carbonate, or a combination thereof. Examples of carboxylate compounds are ethyl acetate, n-acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, gamma-butyrolactone, decalactone, valerolactone, mevalonolactone, caprolactone, or combinations thereof.
Examples of the ether compound are dibutyl ether, tetraglyme, diglyme, 1, 2-dimethoxyethane, 1, 2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or a combination thereof.
Examples of other organic solvents are dimethylsulfoxide, 1, 2-dioxolane, sulfolane, methyl sulfolane, 1, 3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or combinations thereof.
Isolation film
In some embodiments, the separator comprises at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the polyethylene includes at least one selected from high density polyethylene, low density polyethylene, or ultra high molecular weight polyethylene. Particularly polyethylene and polypropylene, which have a good effect on preventing short circuits and can improve the stability of the battery through a shutdown effect. In some embodiments, the thickness of the isolation film is in the range of about 5 μm to 50 μm.
In some embodiments, the separator surface may further include a porous layer disposed on at least one surface of the separator, the porous layer including inorganic particles selected from at least one of alumina, silica, magnesia titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate, and a binder. In some embodiments, the pores of the separator film have a diameter in the range of about 0.01 μm to 1 μm. The binder of the porous layer is at least one selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethylcellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene. The porous layer on the surface of the isolating membrane 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.
In some embodiments of the present application, the electrochemical device is of a rolled or stacked type.
Electrochemical device
In some embodiments, the electrochemical device comprises a primary battery or a secondary battery. In some embodiments, the electrochemical device comprises a lithium ion battery, but the application is not so limited.
Electronic device
Embodiments of the present application also provide an electronic device including the electrochemical device described above. The electronic device of the embodiment of the present application is not particularly limited, and may be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, an electronic book player, a cellular phone, a portable facsimile machine, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a handheld cleaner, a portable CD player, a mini-disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power source, an electric motor, an automobile, a motorcycle, a moped, a bicycle, a lighting fixture, a toy, a game machine, a clock, an electric power tool, a flashlight, a camera, a large household battery, and the like.
In order to better illustrate the proposed solution of the present application, the following description is made with reference to examples and comparative examples, and the specific solution is as follows:
preparation of lithium ion battery
1. Preparation of the Positive electrode
In examples 1 to 31, the positive electrode material prepared as described below, the binder, the conductive carbon black, and the conductive carbon nanotube were uniformly mixed in a certain ratio, and an appropriate amount of N-methylpyrrolidone was added thereto and sufficiently stirred to prepare a uniform positive electrode active material slurry. And coating the positive active material slurry on a positive current collector aluminum foil, and drying to obtain a positive active material layer. Then rolling, cutting edge, cutting piece, slitting, cutting piece, welding tab and obtaining the anode.
The preparation process of the cathode material is as follows:
(1) preparing a nickel-cobalt-manganese metal salt solution, a precipitator solution, an ammonia water solution and a dispersant solution;
(2) adding the precipitant solution prepared in the step (1) and an ammonia water solution into a reaction kettle, and adjusting the ammonia concentration and the pH value under a stirring state;
(3) on the basis of the step (2), adding a nickel-cobalt-manganese metal salt solution, a precipitator solution and an ammonia water solution into a reaction kettle at the same time to prepare a nickel-cobalt-manganese hydroxide crystal nucleus; under the stirring state, adjusting the ammonia concentration and the pH value to promote the crystal nucleus growth, so that the primary particles are tightly packed into secondary particles;
(4) stopping the kettle when the particle size value of the reaction slurry reaches 60-80% of the target Dv50, and extracting the supernatant for concentration;
(5) stopping the reaction and aging after the particle size in the reaction slurry reaches a target value to obtain a first particle precursor;
(6) reducing the target Dv50, and repeating the steps (1) to (5) to obtain a precursor of the second particle;
(7) mixing the first particle precursor obtained in the step (5) with lithium hydroxide at a high speed, controlling the molar ratio of Li to M (M ═ Ni + Co + Mn) to be within the range of 1.02-1.06, and performing oxygen introduction calcination by using a high-temperature atmosphere furnace to obtain a positive electrode material with the molar ratio of Li to M being more than 1.02;
(8) mixing the second particle precursor obtained in the step (6) with lithium hydroxide at a high speed, controlling the molar ratio of Li to M (M ═ Ni + Co + Mn) to be within the range of 0.98-1.02, and performing oxygen introduction calcination by using a high-temperature atmosphere furnace to obtain a cathode material with the molar ratio of Li to M being less than 1.02;
(9) and (4) mixing the positive electrode materials obtained in the steps (7) and (8) according to a certain proportion to obtain the positive electrode material mixed with particles with different lithium contents and different sizes.
Comparative example 1
(1) Preparing a nickel-cobalt-manganese sulfate solution, a sodium hydroxide solution, ammonia water and a triethanolamine solution with certain concentrations;
(2) adding the sodium hydroxide solution and the ammonia water solution prepared in the step (1) into a reaction kettle, and simultaneously adding the nickel-cobalt-manganese sulfate solution, the sodium hydroxide solution and the ammonia water solution under a stirring state;
(3) by adjusting the temperature, pH, ammonia concentration and flow rate, the obtained Dv50 is 12 μm, and the specific surface area is 0.5m 2 A ternary positive electrode material precursor per gram of the first particles;
(4) and (4) mixing the first particle ternary cathode material precursor obtained in the step (3) with lithium hydroxide, and controlling the molar ratio of lithium to transition metal to be 1.04. And calcining the lithium-rich ternary cathode material in an oxygen atmosphere to obtain the first particle lithium-rich ternary cathode material.
Comparative example 2
Comparative example 2 is different from comparative example 1 in that a cobalt sulfate solution is used instead of a nickel cobalt manganese sulfate solution, and a positive electrode material prepared is lithium cobaltate instead of nickel cobalt lithium manganate, and the rest is the same.
Example 1
(1) Preparing a nickel-cobalt-manganese sulfate solution, a sodium hydroxide solution, ammonia water and a triethanolamine solution with certain concentrations;
(2) adding the sodium hydroxide solution and the ammonia water solution prepared in the step (1) into a reaction kettle, and simultaneously adding the nickel-cobalt-manganese sulfate solution, the sodium hydroxide solution and the ammonia water solution under a stirring state;
(3) by adjusting the temperature, pH, ammonia concentration and flow rate, a Dv50 of 10 μm and a specific surface area of 0.5m were obtained 2 A precursor of the first particles per gram;
(4) the above steps are repeated to obtain the product with Dv50 of 3 μm and specific surface area of 1m 2 A precursor of a second particle;
(5) mixing the first particle precursor obtained in the above (3) with lithium hydroxide, wherein the molar ratio of lithium to transition metal is controlled within the range of 1.01 to 1.03. Calcining in an oxygen atmosphere to obtain lithium-rich first particles;
(6) mixing the precursor of the second particle having a small particle size obtained in the above (4) with lithium hydroxide, wherein the molar ratio of lithium to transition metal is controlled within the range of 0.99 to 1.01. Calcining in an oxygen atmosphere to obtain second particles;
(7) mixing the first particles in the step (5) with the second particles in the step (6) according to a mass ratio of 5:5 to obtain a ternary cathode material with mixed large and small particles;
(9) preparing the positive electrode material obtained in the step (7) into a positive electrode, wherein the positive electrode compaction density is 3.4g/cm 3 The positive electrode of (1).
Example 2 example 28
Example 2-example 28 differs from example 1 in the data shown in table 1.
Example 29
Example 29 differs from example 1 in that the starting material used was a cobalt sulfate solution instead of a nickel cobalt manganese sulfate solution, and the resulting positive electrode material was lithium cobaltate instead of nickel cobalt manganese lithium manganate, the rest being the same.
Example 30 to example 35
Examples 30 to 35 are different from example 1 in that the specific surface area, the proportion of the positive electrode material in the positive electrode active material layer, the positive electrode active material layer compaction density, or the porosity of the positive electrode active material layer is adjusted, and specifically, see table 2.
2. Preparation of the negative electrode
Fully stirring and mixing artificial graphite, acetylene black, Styrene Butadiene Rubber (SBR) and sodium carboxymethylcellulose (CMC) in a proper amount of deionized water solvent according to a weight ratio of 95:2:2:1 to form uniform cathode active material slurry. And coating the negative active material slurry on a copper foil of a negative current collector, and drying to obtain a negative active material layer. Then rolling, trimming, cutting into pieces, slitting, cutting into pieces, welding lugs to obtain the negative electrode.
3. Preparation of the electrolyte
Example 1-example, comparative example 1-comparative example 2
Under dry argon atmosphere, 1.5% of vinylene carbonate and LiPF are added to a solvent in which Propylene Carbonate (PC), Ethylene Carbonate (EC) and diethyl carbonate (DEC) are mixed in a weight ratio of 1:1:1 6 Mixing uniformly, wherein LiPF 6 Was 1.15mol/L, to obtain a base electrolyte.
Example 36 example 47
Example 36-example 47 differs from example 1 in that a polynitrile compound or lithium difluorophosphate is added, as shown in table 3.
4. Preparation of the separator
A Polyethylene (PE) porous polymer film was used as the separator.
5. Preparation of lithium ion battery
And (3) sequentially stacking the anode, the isolating membrane and the cathode, winding, placing in an outer package, injecting electrolyte, and packaging. The lithium ion battery 6 is obtained through the process flows of formation, degassing, edge cutting and the like, and the performance test method and the result are as follows:
1) retention ratio of 500 cycles
The lithium ion batteries prepared in examples and comparative examples were charged to 4.2V at a rate of 2C at 45 ℃, then charged to 0.05C at a constant voltage, and then discharged to 2.8V at a rate of 10C, the discharge capacity of the first cycle was recorded, the discharge capacity of the 500 th cycle was recorded by repeating 500 times, and then the 500-cycle capacity retention rate was calculated.
The 500-cycle capacity retention rate is the 500 th cycle discharge capacity/the first cycle discharge capacity × 100%.
2)500 cycles cyclic battery expansion ratio
The lithium ion batteries prepared in examples and comparative examples were charged to 4.2V at a rate of 2C at 45C, then charged to 0.05C at a constant voltage, and then discharged to 2.8V at a rate of 10C, and the thickness at this time was recorded as the initial thickness of the battery before cycling, and thus cycled 500 times, and the thickness at this time was recorded as the thickness of the battery at 500 th cycling, and then the swelling ratio (%) of the battery at 500 cycles was calculated.
The 500-cycle cell swelling ratio (cell thickness at 500 th cycle-initial cell thickness before cycle)/initial cell thickness before cycle x 100%.
The parameters and performance test results of each example and comparative example are shown in table 1.
TABLE 1
Figure BDA0003662137710000151
Figure BDA0003662137710000161
Figure BDA0003662137710000171
As can be seen from Table 1, 1.001. ltoreq. x/y. ltoreq.1.2, 60000. ltoreq. x.ltoreq.65000, 55000. ltoreq. y.ltoreq.60000, 500. ltoreq. x-y. ltoreq.5000 in examples 1 to 29, the retention rate of 500-cycle capacity is higher than 89.6% and the expansion rate of 500-cycle battery is less than 10%, which shows good cycle performance and safety performance, while the second particles are not present in comparative examples 1 and 2, the retention rate of 500-cycle capacity is less than or equal to 85% and the expansion rate of battery is more than or equal to 20% in the 45 ℃ cycle of comparative examples 1 and 2, and thus, the schemes adopted in examples 1 to 29 can ensure the cycle performance and safety performance of the lithium ion battery.
From examples 1 to 8, it can be seen that, when the Dv50 of the first particles is within the range of 8 μm to 15 μm defined in examples 1 to 8, the lithium ion battery has a high cycle capacity retention rate and a small battery expansion rate after 500 cycles at a temperature of 45 ℃, and thus, when the Dv50 of the first particles is within the range of 8 μm to 15 μm, the cycle performance and safety performance of the electrochemical device can be ensured.
It can be seen from examples 1 and 9-12 that when the Dv50 of the second particles is within the range of 1 μm to 5 μm defined in examples 1 and 9-12, the battery has a high retention rate of the cycling capacity and a small expansion rate after 500 cycles of cycling at 45 ℃, and thus, the cycling performance and the safety performance of the electrochemical device can be ensured by controlling the Dv50 of the second particles.
It can be seen from example 1, example 13 to example 16 that when the molar ratio of lithium element to transition metal element in the first particles is in the range of 1.00 to 1.02, the retention rate of 500 cycles of the battery increases and then decreases with increasing molar ratio of lithium element to transition metal element in the first particles, and the expansion rate of the battery decreases with 500 cycles of the battery, and the cycle performance and safety performance of the lithium ion battery in the above examples are maintained at high levels.
It can be seen from example 1 and examples 17 to 22 that when the molar ratio of the lithium element to the transition metal element in the second particles is in the range of 0.98 to 1.02, the 500-cycle capacity retention ratio is high and the 500-cycle battery expansion ratio is small.
As can be seen from example 1 and examples 23 to 28, when the mass ratio of the first particles to the second particles is within the range shown in example 1 and 23 to 28, the retention rate of 500-cycle capacity is high, and the battery expansion rate is low at 500-cycle, both having good cycle performance and safety performance.
The BET, the positive electrode active material layer compaction density, and the porosity of the material were adjusted on the basis of example 1 to obtain the properties shown in table 2.
TABLE 2
Figure BDA0003662137710000181
As can be seen from comparison of example 1 and examples 30 to 33, the cycle retention and gassing of the battery can be affected by adjusting the porosity and the compaction density of the positive electrode active material layer, and when the compaction density and the porosity are within the ranges of the above examples, the lithium ion battery has a higher 500-cycle capacity retention rate and a smaller 500-cycle battery expansion rate.
The electrolyte used in examples 34 to 45 was obtained by adding a polynitrile compound or lithium difluorophosphate to the electrolyte used in example 1, the components of the compound added in examples 34 to 45 and the results of the performance test of examples 34 to 45 are shown in table 3, and the contents of the electrolyte in table 3 were calculated based on the weight of the electrolyte.
TABLE 3
Figure BDA0003662137710000182
Figure BDA0003662137710000191
Comparing example 1 and example 34 to example 40, it can be seen that as the content of lithium difluorophosphate in the electrolyte increases, the retention rate of 500-cycle capacity of the lithium ion battery increases, and the expansion rate of 500-cycle battery decreases, and the retention rate of 500-cycle capacity of examples 34 to example 40 is higher than that of example 1, and the expansion rate of 500-cycle battery is lower than that of example 1, and thus it can be seen that adding lithium difluorophosphate in the electrolyte in the content shown in the above examples is beneficial to improving the cycle performance and safety performance of the lithium ion battery.
Comparing example 1 and example 41-example 44, it can be seen that the retention rate of 500 cycles of the cycling capacity of examples 41-example 44 is higher than that of example 1, and the expansion rate of the 500 cycles of cycling battery is lower than that of example 1, so that the addition of the polynitrile compound in the content shown in the above examples to the electrolyte is beneficial to improving the cycling performance and safety performance of the lithium ion battery.
The above description is only a preferred embodiment of the application and is illustrative of the principles of the technology employed. It will be appreciated by those skilled in the art that the scope of the disclosure herein is not limited to the particular combination of features described above, but also encompasses other combinations of features described above or equivalents thereof. For example, the above features and the technical features having similar functions disclosed in the present application are mutually replaced to form the technical solution.

Claims (10)

1. An electrochemical device, comprising:
a positive electrode;
a negative electrode;
a separator disposed between the positive electrode and the negative electrode;
the positive electrode comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, the positive electrode active material layer comprises a positive electrode material, the positive electrode material comprises a lithium-containing transition metal oxide, the positive electrode material comprises first particles and second particles, the particle size of the first particles is larger than that of the second particles, the proportion of lithium element in the first particles is x ppm based on the total mass of the first particles, the proportion of lithium element in the second particles is y ppm based on the total mass of the second particles in a state that the voltage of the electrochemical device is 2.5V, and the condition that 1.001 is larger than or equal to x/y is smaller than or equal to 1.2 is met;
the electrochemical device further includes: an electrolyte comprising at least one of a polynitrile compound or lithium difluorophosphate.
2. The electrochemical device according to claim 1, wherein the positive electrode material satisfies at least one of the following conditions (a) to (g):
(a)60000≤x≤65000；
(b)55000≤y≤60000；
(c)500≤x-y≤10000；
(e) the specific surface area BET of the first particles 1 Satisfies the following conditions: 0.1m 2 /g≤BET 1 ≤1.5m 2 (ii)/g, specific surface area BET of the second particles 2 Satisfies the following conditions: 0.5m 2 /g≤BET 2 ≤2m 2 /g；
(f) The first particles have a Dv50 of 8 μm to 15 μm and the second particles have a Dv50 of 1 μm to 6 μm;
(g)1.01≤x/y≤1.18。
3. the electrochemical device according to claim 1,
the mass ratio R of the first particles to the second particles in the positive electrode material satisfies: r is more than 0 and less than or equal to 10.
4. The electrochemical device according to claim 3,
the mass ratio R of the first particles to the second particles in the positive electrode material satisfies: r is more than or equal to 0.6 and less than or equal to 5.
5. The electrochemical device according to claim 1,
the porosity of the positive electrode active material layer is 5% -35%.
6. The electrochemical device according to claim 1,
the compacted density of the positive electrode active material layer is 2.0g/cm 3 -4.5g/cm 3 。
7. The electrochemical device according to claim 1,
at least one of the first particles or the second particles comprises:
Li m [Ni a Mn b Co 1-(a+b+c) M c ]O 2
wherein a is more than or equal to 0.45 and less than or equal to 0.9, B is more than or equal to 0.05 and less than or equal to 0.5, c is more than 0 and less than or equal to 0.1, a + B + c is less than or equal to 1, M is more than or equal to 0.97 and less than or equal to 1.10, and M comprises at least one of W, B, Al, Ti, Mg, Cr, Zr or Si.
8. The electrochemical device according to claim 1,
the polynitrile compound includes: at least one of succinonitrile, adiponitrile, ethylene glycol bis (propionitrile) ether, 1,3, 6-hexanetricarbonitrile, 1,2, 6-hexanetricarbonitrile, or 1,2, 3-tris (2-cyanoethoxy) propane;
the mass content of the polynitrile compound in the electrolyte is 1-15%, and preferably 1-3%.
9. The electrochemical device according to claim 1,
the mass content of the lithium difluorophosphate in the electrolyte is 0.001% -1%, and preferably 0.01% -1%.
10. An electronic device comprising the electrochemical device according to any one of claims 1 to 9.
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