Electrochemical devices and electronic devices

Abstract

Provided are an electrochemical device and an electronic device. The electrochemical device includes a positive electrode including a current collector (2) and a film layer including a positive electrode active material, the film layer being disposed on at least one surface of the current collector, the positive electrode active material including primary particles and / or secondary particles (1); when the primary particles (1) in the positive electrode active material satisfy 20%≤A≤100% based on a mass percentage content A of the positive electrode active material, the film layer, the positive electrode active material, and the current collector (2) satisfy: D l ≥Dv99‑D c ; when the primary particles (1) in the positive electrode active material satisfy 0≤A’<20% based on a mass percentage content A’ of the positive electrode active material, the film layer, the positive electrode active material, and the current collector satisfy: D1≥1.1Dv99. The electronic device includes the electrochemical device. The electrochemical device can improve the appearance of the electrode sheet and simultaneously have fast charging performance, storage performance, and cycle performance.

Description

[0001] This application is a divisional application of the original invention patent application (application date: February 23, 2021, application number: 2021800018588, invention name: "Electrochemical device and electronic device"). TECHNICAL FIELD

[0002] The present application relates to an electrochemical device and an electronic device. BACKGROUND

[0003] Electrochemical devices, such as lithium ion batteries, are widely used in the fields of intelligent products (including mobile phones, notebooks, cameras, etc.), electric tools, and electric vehicles, etc. due to their high energy density, low maintenance, low self-discharge rate, wide operating temperature range, long cycle life, no memory effect, stable operating voltage, and environmental friendliness, etc. With the rapid development of technology and the diversity of market demand, people have higher requirements for the performance of electrochemical devices, such as fast charging performance.

[0004] However, when improving the fast charging performance of lithium ion batteries, other performances of lithium ion batteries, such as storage performance and cycle performance, are decreased. Therefore, there is an urgent need for a technical solution that improves the fast charging performance of lithium ion batteries without reducing their storage performance and cycle performance. SUMMARY

[0005] In some embodiments, the present application provides an electrochemical device, comprising a positive electrode, the positive electrode comprising a current collector and a film layer comprising a positive electrode active material, the film layer being disposed on at least one surface of the current collector, the positive electrode active material comprising primary particles and / or secondary particles; when the primary particles in the positive electrode active material satisfy 20%≤A≤100% based on the mass percentage content A of the positive electrode active material, the film layer, the positive electrode active material, and the current collector satisfy: D1≥Dv99-D c ; when the primary particles in the positive electrode active material satisfy 0≤A’<20% based on the mass percentage content A’ of the positive electrode active material, the film layer, the positive electrode active material, and the current collector satisfy: D1≥1.1Dv99; wherein D1 is the thickness of the film layer, D c is the thickness of the current collector, and Dv99 is the particle size corresponding to the cumulative volume percentage of the positive electrode active material reaching 99%.

[0006] In some embodiments, the thickness D1 of the film layer and the thickness D c satisfy the relationship: 0.05≤D1 / D c ≤3.75.

[0007] In some embodiments, the thickness D1 of the film layer is 1 μm to 30 μm.

[0008] In some embodiments, the thickness D of the current collector is 4-20 μm. c

[0009] In some embodiments, the particle size Dv99 of the positive active material is 5-48 μm.

[0010] In some embodiments, the compaction density of the diaphragm layer is 2-4.3 g / dm 3 3

[0011] In some embodiments, the current collector comprises a blank area and a covered area; the blank area is an area on the current collector that is not covered by the diaphragm layer, the roughness of the blank area is 500-2000 mm -1 -1 ; the covered area is an area on the current collector that is covered by the diaphragm layer, the roughness of the covered area is 1500-8000 mm -1 -1

[0012] In some embodiments, the electrochemical device further comprises an electrolyte, the electrolyte comprises an ether dinitrile compound, the mass percentage of the ether dinitrile compound in the total mass of the electrolyte is 0.01%-15%.

[0013] In some embodiments, the conductivity of the electrolyte is greater than or equal to 7 mS / cm.

[0014] In some embodiments, the present application further provides an electronic device comprising the electrochemical device as described above.

[0015] The technical solution of the present application has at least the following beneficial effects: the present application takes into account the different structural characteristics of primary particles and secondary particles, and designs the sizes of the positive diaphragm layer, the positive active material and the positive current collector to meet specific relationships, which can maximize the avoidance of risks in the use of fast-charging batteries, and is not easy to be crushed during cold pressing, can improve the appearance of the diaphragm, and has fast-charging performance, storage performance and cycle performance. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a schematic diagram of the positional relationship between the primary particles and the current collector after cold pressing when the positive active material is primary particles;

[0017] Figure 2 is a schematic diagram of the positional relationship between the secondary particles and the current collector after cold pressing when the positive active material is secondary particles;

[0018] ​​​​​​wherein the reference signs are: 1 - positive electrode active material particle, 2 - positive electrode current collector. DETAILED DESCRIPTION

[0019] The exemplary embodiments are described in detail below with reference to the attached drawing figures, but it is to be understood that the exemplary embodiments are not limited to the specific embodiments rendered by way of example in the figures, but are applicable to any manufacturing method having the same structure, the same function and / or the same result. Rather, the exemplary embodiments are intended to describe and deliver the scope of the present application to those skilled in the art.

[0020] (Electrochemical device)

[0021] The electrochemical device of the present application is, for example, a primary battery, a secondary battery, a fuel cell, a solar cell, or a capacitor. The secondary battery is, for example, a lithium secondary battery, which includes but is not limited to a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0022] In some embodiments, the electrochemical device includes a positive electrode, a negative electrode, and a separator.

[0023] [Positive electrode]

[0024] The positive electrode includes a positive electrode current collector and a positive electrode tab layer disposed on at least one surface of the positive electrode current collector, the positive electrode tab layer including a positive electrode active material, the positive electrode active material including primary particles and / or secondary particles.

[0025] In the present application, the term "primary particle" is an active material particle of a single crystal grain, and two or more primary particles can be aggregated to form a secondary particle. In some embodiments, the primary particles can have any of a variety of shapes, including rod-like and rectangular, or a combination thereof. The term "secondary particle" is formed by aggregation of two or more primary particles, and is no longer further aggregated with other particles. The primary particles and the secondary particles have respective independent structural characteristics. In the present application, the primary particles can be obtained by over-sintering relatively small particles, and the secondary particles can be obtained by agglomerating primary particles.

[0026] In some embodiments, the positive electrode active material includes primary particles, the primary particles being 100% by mass content based on the positive electrode active material, and the positive electrode tab layer, the positive electrode active material, and the positive electrode current collector satisfy: D1≥Dv99-D c ; wherein D1 is the thickness of the positive electrode tab layer; D is the thickness of the positive electrode current collector; and Dv99 is the particle diameter corresponding to the cumulative volume percentage of the positive electrode active material reaching 99%.

[0027] As Figure 1As shown, the primary particles are single-crystal positive electrode active material particles 1, which are generally non-spherical. The friction between particles is relatively low, and during the preparation of the positive electrode sheet, they are prone to lateral displacement and relative slippage when subjected to cold pressure rollers, thus compressing the positive electrode current collector 2. In some embodiments, the positive electrode current collector is a metal foil. The metal foil includes, but is not limited to, copper foil and aluminum foil. In some embodiments, the positive electrode current collector is aluminum foil.

[0028] When there are only primary particles in the positive electrode active material, if the sum of the thickness of the positive electrode film layer and the thickness of the positive electrode current collector is less than the particle size Dv99 of the positive electrode active material particles, the particles are very prone to appearance problems such as particle scratches and bumps during coating. The particles are also very prone to being crushed during cold pressing, resulting in poor electrode appearance and easily causing problems such as high-temperature storage gas expansion and accelerated cycling of the manufactured battery cells.

[0029] In some embodiments, the positive electrode active material particles consist only of secondary particles, and the primary particles have a mass percentage content of 0% based on the positive electrode active material. The positive electrode film layer and the positive electrode active material satisfy the following condition: D1 ≥ 1.1Dv99.

[0030] like Figure 2 As shown, the secondary particles are formed by the aggregation of two or more primary particles. The friction between the particles is relatively large, and they are not easy to slip relative to each other when subjected to cold pressure rollers during the preparation of the positive electrode sheet. Therefore, the positive electrode active material particles 1 will not compress the positive electrode current collector 2.

[0031] When only secondary particles exist in the positive electrode active material, due to the special structural characteristics of the secondary particles, when designing the size relationship between the positive electrode film layer and the positive electrode active material particles, the design size is based on 1.1 times the Dv99 of the secondary particles. If the thickness of the positive electrode film layer is less than 1.1 times the particle size Dv99 of the positive electrode active material particles, the particles are very prone to appearance problems such as particle scratches and bumps during coating. The particles are also very prone to being crushed during cold pressing, resulting in poor electrode appearance and easily causing problems such as high-temperature storage gas expansion and accelerated cycling in the manufactured battery cells.

[0032] In some embodiments, the positive electrode active material comprises primary particles and secondary particles, wherein the primary particles comprise at least 20% of the positive electrode active material by mass, and the positive electrode film layer, the positive electrode active material, and the positive electrode current collector satisfy the following relationship: D1 ≥ Dv99 - D cWhen both primary particles and secondary particles exist in the positive electrode active material, if the mass percentage content of the primary particles is greater than or equal to the aforementioned range, the primary particles can be well distributed in the secondary particles, effectively preventing contact between the secondary particles and playing a lubricating role, which is similar to the case where the positive electrode active material only includes primary particles. At this time, if the sum of the thickness of the positive electrode film layer and the thickness of the positive electrode current collector is less than the particle size Dv99 of the positive electrode active material particles, particle scratches, bumps and other appearance problems are extremely likely to occur during coating, and the particles are also extremely likely to be crushed during cold pressing, resulting in poor appearance of the pole piece and easily leading to problems such as high-temperature storage swelling and cycle acceleration of the battery cell produced. In some embodiments, the positive electrode active material includes primary particles and secondary particles, and the mass percentage content of the primary particles based on the positive electrode active material is greater than or equal to 40%.

[0033] In some embodiments, the positive electrode active material includes primary particles and secondary particles, and the mass percentage content of the primary particles based on the positive electrode active material is less than 20%, and the positive electrode film layer, the positive electrode active material, and the positive electrode current collector satisfy D1≥1.1Dv99. When both primary particles and secondary particles exist in the positive electrode active material, if the mass percentage content of the primary particles is less than the aforementioned range, the primary particles cannot sufficiently prevent contact between the secondary particles, and the difficulty of sliding between the secondary particles increases, which is similar to the case where the positive electrode active material only includes secondary particles. At this time, if the thickness of the positive electrode film layer is less than 1.1 times the particle size Dv99 of the positive electrode active material particles, particle scratches, bumps and other appearance problems are extremely likely to occur during coating, and the particles are also extremely likely to be crushed during cold pressing, resulting in poor appearance of the pole piece and easily leading to problems such as high-temperature storage swelling and cycle acceleration of the battery cell produced. In some embodiments, the positive electrode active material includes primary particles and secondary particles, and the mass percentage content of the primary particles based on the positive electrode active material is less than or equal to 10%.

[0034] The fast charging and discharging technology refers to a technology of charging and discharging a battery at more than 1C rate. When the fast charging and discharging technology is used to charge the battery, fast charging of the battery can be achieved without damaging the battery and affecting the service life. However, the fast charging and discharging technology requires the battery to have the function of large-rate charging, and thus the ion polarization of the battery cell needs to be reduced to achieve the function of large-rate charging. The inventors have found that the battery with a thin electrode design can shorten the lithium ion transmission path, thereby reducing the ion polarization of the battery cell. However, in the battery with a thin electrode design, if the size of the main material is not reasonably designed, the particles are easily crushed during cold pressing, which further affects the appearance of the pole piece and the performance of the battery.

[0035] In the electrochemical device of the present application, the different structural features of primary particles and secondary particles are considered simultaneously when designing the positive electrode, and the sizes of the positive electrode film layer, the positive electrode active material and the positive electrode current collector are designed to meet a specific relationship, which can maximize the avoidance of risks during the use of fast-charging batteries, is not easy to be crushed by particles during cold pressing, can improve the appearance of the electrode sheet and enhance the performance of the battery, and can have fast-charging performance, storage performance and cycle performance.

[0036] In some embodiments of the present application, the upper limit of the thickness of the positive electrode film layer corresponding to the positive electrode current collector on one side is 30 μm. In some embodiments, the thickness D1 of the positive electrode film layer is 1 μm to 30 μm. The positive electrode sheet with such a film layer thickness indicates that it has a relatively thin electrode design, which can better shorten the lithium ion transmission path and reduce the ion polarization of the battery cell, and when matched with the positive electrode current collector and the positive electrode active material size of the present application, it can have better fast-charging performance, storage performance and cycle performance.

[0037] In some embodiments, the thickness D c of the positive electrode current collector is 4 μm to 20 μm.

[0038] In some embodiments, the thickness D1 of the positive electrode film layer and the thickness D c of the positive electrode current collector satisfy the relationship: 0.05 ≤ D1 / D c ≤ 3.75. The thickness ratio of the positive electrode film layer and the positive electrode current collector in the above range can reduce the safety risk; if the ratio is too small, the thickness of the positive electrode film layer is relatively small, which may increase the probability of scratches and exposed metal during the production of the electrode sheet; if the ratio is too large, the thickness of the positive electrode film layer is relatively large and the thickness of the positive electrode current collector is relatively small, which may increase the probability of brittle fracture of the inner circle during the cold pressing and winding of the electrode sheet. In some embodiments, the thickness D1 of the positive electrode film layer and the thickness D c of the positive electrode current collector satisfy the relationship: 0.3 ≤ D1 / D c ≤ 3.1.

[0039] The particle size of the positive electrode active material affects the solid-phase diffusion resistance of the positive electrode active material particles in the positive electrode film layer, and further affects the battery performance. In some embodiments, the particle size Dv99 of the positive electrode active material is 5 μm to 48 μm. If the particle size of the positive electrode active material is too large, its solid-phase diffusion resistance will be relatively large, causing relatively large battery charge and discharge polarization, and further affecting the cycle performance. In some embodiments, the particle size Dv99 of the positive electrode active material is 20 μm to 40 μm.

[0040] In some embodiments, the positive electrode film layer has a compaction density of 2 g / dm 3 to 4.3 g / dm 3 .

[0041] In the present application, each parameter of the positive electrode film layer, the positive electrode current collector, and the positive electrode active material can be tested by the following method, or by other known methods in the art, and the test results obtained are within the error range:

[0042] The Dv99 of the positive electrode active material can be tested by a Malvern 3000 laser particle size analyzer, and the average of three tests is the test result.

[0043] The thickness D of the positive electrode current collector c The thickness D of the positive electrode current collector

[0044] The thickness D1 of the positive electrode film layer is the thickness of the film layer on one side of the positive electrode current collector after the positive electrode sheet is cold-pressed. When the positive electrode film layer is arranged on one side surface of the positive electrode current collector, the thickness of the positive electrode film layer = the thickness of the positive electrode sheet - the thickness of the positive electrode current collector; when the positive electrode film layer is arranged on both side surfaces of the positive electrode current collector, the thickness of the positive electrode film layer = (the thickness of the positive electrode sheet - the thickness of the positive electrode current collector) / 2. The thickness of the positive electrode sheet can be tested by using a micrometer, taking five points evenly on the surface of the positive electrode sheet and testing, and the average of the five test values is the test result.

[0045] The compaction density of the positive electrode film layer = the mass of the positive electrode film layer / the area of the positive electrode film layer / the thickness of the positive electrode film layer.

[0046] The positive electrode active material can be selected from various conventional materials known in the art that can be reversibly intercalated and deintercalated with active ions for use in electrochemical devices. In some embodiments, the positive electrode active material includes at least one of lithium cobaltate, lithium manganate, lithium nickel cobalt manganese oxide (NCM), and lithium nickel cobalt aluminum oxide (NCA).

[0047] The positive electrode film layer also includes a positive electrode conductive agent. The positive electrode conductive agent can be selected from conductive agents known in the art that can be used as a positive electrode film layer. In the present application, the positive electrode conductive agent includes, but is not limited to, natural graphite, artificial graphite, conductive carbon black, acetylene black, ketjen black, carbon fibers, polyphenylene derivatives, metal powder, metal fibers, wherein the metal powder and metal fibers are, for example, but not limited to, copper, nickel, aluminum, silver powder or fibers.

[0048] The positive electrode film layer further includes a positive electrode binder. The positive electrode binder can be selected from binders known in the art that can be used as a positive electrode film layer. In the present application, the positive electrode binder is, for example, but not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, nylon.

[0049] The method of preparing the positive electrode sheet can employ a method of preparing a positive electrode sheet known in the art that can be used for an electrochemical device. In some embodiments, in the preparation of the positive electrode slurry, a solvent is generally added, and the positive electrode active material, the positive electrode binder, and the positive electrode conductive agent and the thickening agent, if necessary, are dissolved or dispersed in the solvent to prepare the positive electrode slurry. The solvent is removed by volatilization during drying. The solvent is known in the art that can be used as a solvent for the positive electrode film layer, and the solvent is, for example, but not limited to, N-methylpyrrolidone (NMP). The present application does not have a particular limitation on the mixing ratio of the positive electrode active material, the positive electrode binder, and the positive electrode conductive agent in the positive electrode film layer, and the mixing ratio can be controlled according to the desired performance of the electrochemical device.

[0050] In some embodiments, the positive electrode current collector includes a blank area, which is an area of the positive electrode current collector not covered by the positive electrode film layer, and a covered area, which is an area of the positive electrode current collector covered by the positive electrode film layer.

[0051] If the surface roughness of the blank area is too low, the contact points between the binder and the positive electrode current collector are relatively few, affecting the initial adhesion of the positive electrode sheet, and a certain degree of delamination problem can occur after the sheet is covered. If the surface roughness of the blank area is too high, the positive electrode current collector has relatively more defects, and the mechanical properties can be lost to a certain extent, affecting the brittleness of the sheet. In some embodiments, the roughness of the blank area is 500 mm -1 to 2000 mm -1 , which can have good sheet adhesion and improve brittleness, effectively improving the performance of the battery. In some embodiments, the roughness of the blank area is 700 mm -1 to 1500 mm -1 .

[0052] If the surface roughness of the covered area is too low, the riveting effect of the positive electrode active material and the positive electrode current collector is relatively weak, to a certain extent, affecting the adhesion of the sheet. If the surface roughness of the covered area is too high, the positive electrode current collector is relatively severely damaged during cold pressing, which can cause the particles to be crushed and the positive electrode current collector to be pressed through to a certain extent, thereby causing the risk of loss of electrical performance and P.D. window. In some embodiments, the roughness of the covered area is 1500 mm-1 to 8000 mm -1 , can have better tab adhesion and reduce the risk of particle crushing and current collector crushing, effectively improving battery performance. In some embodiments, the roughness of the covered area is 2000 mm -1 to 5000 mm -1 .

[0053] In the present application, the roughness of the current collector can be controlled by setting open pits on its surface, or other methods known in the art can be used. Those skilled in the art can choose according to the actual situation. In the present application, the roughness of the current collector can be measured by methods known in the art, for example, the roughness of the blank area and the covered area of the positive electrode current collector can be tested by using a Mitutoyo SJ-210 roughness tester. In some embodiments, the test method for the covered area is as follows: the positive electrode tab is soaked in N-methyl pyrrolidone (NMP) solution for 10 min, after taking out, the positive electrode active film layer on the surface of the positive electrode current collector is scraped off using a scraper, then the surface of the positive electrode current collector is rinsed again with clean NMP to make the surface of the positive electrode current collector free of foreign matter, finally the positive electrode current collector is placed in an oven at 85°C for drying, then the roughness value is tested using a Mitutoyo SJ-210 roughness tester, which is the roughness of the covered area.

[0054] [Negative electrode]

[0055] The negative electrode includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material. In some embodiments, the negative electrode current collector is a metal, such as but not limited to a copper foil, a nickel foil, a stainless steel foil, a titanium foil, a foamed nickel, a foamed copper, a polymer substrate coated with a conductive metal, or a combination thereof.

[0056] The negative electrode active material can be any material that can be used as an electrochemical device capable of intercalating and deintercalating active ions or capable of doping and dedoping active ions. In some embodiments, the negative electrode active material includes at least one of a carbon material, a metal alloy, a lithium-containing oxide, and a silicon-containing material. In some embodiments, the carbon material is selected from a graphite material. In some embodiments, the negative electrode active material is surface-coated or uncoated.

[0057] The negative electrode film layer also includes a negative electrode binder. The negative electrode binder is not particularly limited in the present application, and for example, but not limited to, styrene butadiene rubber (abbreviated as SBR). The method of preparing the negative electrode sheet can employ a method of preparing a negative electrode sheet for an electrochemical device known in the art. In some embodiments, in the preparation of the negative electrode slurry, a solvent is generally added, and the negative electrode active material is dissolved or dispersed in the solvent after being added to the negative electrode binder and, if necessary, an electrically conductive material and a thickening agent are added to prepare the negative electrode slurry. The solvent is removed by evaporation during the drying process. The solvent is a solvent known in the art that can be used as a solvent for the negative electrode film layer, and for example, but not limited to, water. The thickening agent is a thickening agent known in the art that can be used as a thickening agent for the negative electrode film layer, and for example, but not limited to, sodium carboxymethyl cellulose (abbreviated as CMC). The present application does not have a particular limitation on the mixing ratio of the negative electrode active material, the negative electrode binder, and the thickening agent in the negative electrode film layer, and the mixing ratio thereof can be controlled according to the desired performance of the electrochemical device.

[0058] [Separator]

[0059] In some embodiments of the present application, a separator is provided between the positive electrode and the negative electrode to prevent short circuiting. The material and shape of the separator used in the electrochemical device of the present application are not particularly limited, and a separator known in the art that can be used for an electrochemical device can be used. In some embodiments, the separator includes at least one of polyethylene (PE), ethylene-propylene copolymer, polypropylene (PP), ethylene-butene copolymer, ethylene-hexene copolymer, and ethylene-methyl methacrylate copolymer. In some embodiments, the separator is a single layer or a multi-layer.

[0060] [Electrolyte]

[0061] The electrochemical device also includes an electrolyte. In the present application, the type of the electrolyte is not particularly limited.

[0062] In some embodiments, the electrolyte includes a lithium salt and an organic solvent. The type of the lithium salt and the organic solvent are not particularly limited, and can be selected according to the actual needs. The lithium salt is, for example, but not limited to, lithium hexafluorophosphate (LiPF6). The organic solvent is, for example, but not limited to, a carbonate, a carboxylate, an ether, a sulfone, or other aprotic solvents. The organic solvent can be used alone or as a mixture, and when used as a mixture, the ratio of the mixture can be controlled according to the desired performance of the electrochemical device.

[0063] In some embodiments, the electrolyte also includes an additive. The type of the additive is also not particularly limited, and can be a negative electrode film-forming additive, a positive electrode film-forming additive, or an additive capable of improving certain performance of the battery, such as an additive for improving the overcharge performance of the battery, an additive for improving the high-temperature performance of the battery, an additive for improving the low-temperature performance of the battery, etc.

[0064] In some embodiments, the additive includes an ether dinitrile compound. The ether dinitrile compound is capable of forming a film on the surface of the cathode, improving the thermal stability of the cathode, and further improving the high-temperature storage performance of the electrochemical device.

[0065] The term "ether dinitrile compound" refers to a compound having an ether bond and two cyano groups. In some embodiments, the ether dinitrile compound includes at least one of ethylene glycol bis(propionitrile) ether, diethylene glycol bis(2-cyanoethyl) ether, triethylene glycol bis(2-cyanoethyl) ether, tetraethylene glycol bis(2-cyanoethyl) ether, ethylene glycol bis(4-cyanobutyl) ether, or 3,3'-oxydipropionitrile.

[0066] In some embodiments, the mass percentage of the ether dinitrile compound is 0.01% to 15% based on the total mass of the electrolyte. If the amount of the ether dinitrile compound added is greater than the above range, it will react more with the electrolyte, which may affect the initial efficiency of the battery cell, and it will form a thicker film on the cathode, which may increase the ion transfer impedance, thereby affecting the ability of the battery cell to fast charge and discharge. If the amount of the ether dinitrile compound added is less than the above range, it may not effectively form a film on the cathode, thereby affecting the exertion of the protective effect of the ether dinitrile compound. In some embodiments, the mass percentage of the ether dinitrile compound is less than or equal to 5% based on the total mass of the electrolyte.

[0067] In the present application, the conductivity of the electrolyte is not specifically limited. In some embodiments, the conductivity of the electrolyte is greater than or equal to 7 ms / cm. When the conductivity of the electrolyte is within the above range, it has a high ion conductivity, which can meet the fast movement of lithium ions in the fast charging and discharging technology. If the conductivity is too small, it may cause the battery to have relatively large polarization, which will affect the charging and discharging performance of the battery to some extent. The present application does not limit the method of controlling the conductivity of the electrolyte, and those skilled in the art can select the method known in the art to adjust the conductivity of the electrolyte according to the actual situation. In the present application, the conductivity of the electrolyte can be controlled by controlling the type and concentration of lithium salt added, the viscosity and dielectric constant of the organic solvent.

[0068] (electrochemical device)

[0069] The electronic device of the present application is any electronic device such as, but not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a head-mounted stereo headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a timepiece, a power tool, a flashlight, a camera, a home-use large storage battery, a lithium ion capacitor. Note that the electrochemical device of the present application is applicable not only to the above-mentioned electronic devices but also to energy storage power stations, sea-borne vehicles, air-borne vehicles. The air-borne vehicles include air-borne vehicles within the atmosphere and air-borne vehicles outside the atmosphere.

[0070] In some embodiments, the electronic device comprises the electrochemical device of the present application.

[0071] The present application is further illustrated by the following examples. It should be understood that these examples are intended to illustrate the present application and are not intended to limit the scope of the present application. In the following specific examples, only the examples in which the battery is a lithium ion battery are shown, but the present application is not limited thereto. In the following examples, the reagents, materials and instruments used are commercially available or synthesized unless otherwise specified.

[0072] Example 1

[0073] Preparation of the positive electrode

[0074] The lithium cobaltate particles having a particle size distribution of about 38 μm were sieved after performing the pulverization process, and the Dv99 of the lithium cobaltate positive electrode active material was measured by a Malvern 3000 laser particle size analyzer to be 38.2 μm.

[0075] The positive electrode active material, polyvinylidene fluoride and conductive carbon black (SP) were mixed in a weight ratio of 97:1.5:1.5 in an appropriate amount of NMP to form a uniform positive electrode slurry, and the slurry was coated on a current collector aluminum foil (thickness D c = 10 μm) to obtain a positive electrode sheet. The compaction density of the positive electrode sheet layer was measured to be 4.15 g / dm 3 .

[0076] The thickness D1 of the positive electrode sheet layer was measured by a micrometer to be 30 μm, and the thickness of the positive electrode sheet was 70 μm. The roughness of the current collector blank area was measured by a Mitutoyo SJ-210 roughness tester to be 800 mm -1 , and the roughness of the covered area was 2300 mm -1 .

[0077] Preparation of the negative electrode

[0078] The graphite, styrene-butadiene rubber, sodium carboxymethyl cellulose are mixed in a proper amount of deionized water in a weight ratio of 97.4:1.2:1.4, and stirred sufficiently to form a uniform negative electrode slurry, which is coated on the current collector copper foil, dried, and cold-pressed to obtain a negative electrode sheet.

[0079] Preparation of the separator

[0080] The PE porous polymer film is used as the separator film.

[0081] Preparation of the electrolyte

[0082] In an argon atmosphere glove box with a water content of less than 10 ppm, the organic solvents ethylene carbonate (abbreviated as EC), propylene carbonate (abbreviated as PC), diethyl carbonate (abbreviated as DEC), ethyl propionate (abbreviated as EP), and propyl propionate (abbreviated as PP) are mixed uniformly in a mass ratio of 1:1:1:1:1, and then a proper amount of dried lithium salt LiPF6 is dissolved in the above organic solvents, and finally 5% of ether dinitrile (3,3'-oxydipropionitrile) by mass of the total electrolyte is added. The conductivity of the electrolyte is tested by a conductivity meter and is 10 mS / cm.

[0083] Preparation of the lithium ion battery

[0084] The positive electrode sheet, the separator film, and the negative electrode sheet are wound in the order of one layer of positive electrode sheet, one layer of separator film, and one layer of negative electrode sheet to form an electrode assembly, which is then packaged, injected with electrolyte, and allowed to stand to obtain an electrode assembly that is fully infiltrated, and then subjected to formation and capacity steps to form a SEI film on the surface of the negative electrode, thereby activating the lithium ion battery, allowing it to be in a charged state, and further obtaining a finished lithium ion battery.

[0085] Examples 2 to 19

[0086] The preparation method is consistent with that of Example 1, except that in Examples 2 to 19, some parameters of the positive electrode active material, the current collector, the positive electrode film layer, and the electrolyte are adjusted, and the specific parameters are shown in Table 1.

[0087] Example 20

[0088] The preparation method is consistent with that of Example 1, except that in Example 20, the mass percentage of ether dinitrile in the electrolyte is 13%, the conductivity of the electrolyte is 12 mS / cm, and the preparation of the positive electrode is as follows:

[0089] The lithium cobaltate particles with small particle size are screened after performing the pulverizing process, and are broken by using the jet mill after sintering, to obtain lithium cobaltate secondary particles with a particle size distribution of about 18 μm; the lithium cobaltate secondary particles with a particle size distribution of about 18 μm and the primary particles are fully mixed according to a mass ratio of 5:5 to obtain the positive electrode active material including the primary particles and the secondary particles. The Dv99 of the positive electrode active material is tested by a Malvern 3000 laser particle size analyzer to be 18 μm.

[0090] The positive electrode active material, polyvinylidene fluoride, and conductive carbon black (SP) are fully stirred and mixed in an appropriate amount of NMP according to a weight ratio of 97:1.5:1.5, so that a uniform positive electrode slurry is formed. The slurry is coated on a current collector aluminum foil (thickness D c = 10 μm), dried, cold-pressed to obtain a positive electrode sheet, and the compaction density of the positive electrode sheet layer is tested to be 3.5 g / dm 3 .

[0091] The thickness D1 of the positive electrode sheet layer is tested by a micrometer to be 20 μm; the thickness of the positive electrode sheet is 50 μm. The roughness of the current collector blank area is tested by a Mitutoyo SJ-210 roughness tester to be 1300 mm -1 , and the roughness of the covered area is 3800 mm -1 .

[0092] Examples 21 to 26

[0093] The preparation method is consistent with that of Example 20, except that some parameters of the positive electrode active material, the current collector, the positive electrode sheet layer, and the electrolyte are adjusted in Examples 21 to 26. The specific parameters are shown in Table 1.

[0094] Example 27

[0095] The preparation method is consistent with that of Example 1, except that the mass percentage content of the ether dinitrile in the electrolyte is 1% in Example 27, the conductivity of the electrolyte is 9.8 mS / cm, and the preparation of the positive electrode:

[0096] The lithium cobaltate particles with small particle size are screened after performing the pulverizing process, and are broken by using the jet mill after sintering, to obtain lithium cobaltate secondary particles with a particle size distribution of about 18 μm; the lithium cobaltate secondary particles with a particle size distribution of about 18 μm and the primary particles are fully mixed according to a mass ratio of 5:5 to obtain the positive electrode active material including the primary particles and the secondary particles. The Dv99 of the positive electrode active material is tested by a Malvern 3000 laser particle size analyzer to be 18 μm.

[0097] The positive electrode active material, polyvinylidene fluoride, and conductive carbon black (SP) are fully stirred and mixed in an appropriate amount of NMP according to a weight ratio of 97:1.5:1.5, so that a uniform positive electrode slurry is formed. The slurry is coated on a current collector aluminum foil (thickness D c = 8 μm), dried, cold-pressed to obtain a positive electrode sheet, and the compaction density of the positive electrode sheet layer is tested to be 4.15 g / dm3

[0098] The thickness D1 of the positive electrode film layer was 23.5 pm by a micrometer test; the thickness of the positive electrode sheet was 55 pm. The roughness of the current collector blank area was 800 mm -1 , and the roughness of the covered area was 5700 mm -1 .

[0099] Examples 28 to 36

[0100] The preparation method was consistent with that of Example 27, except that the parameters of the positive electrode active material, the current collector, the positive electrode film layer, and the electrolyte were adjusted in Examples 28 to 36. The specific parameters are shown in Table 2.

[0101] Comparative Example 1

[0102] The preparation method was consistent with that of Example 1, except that the Dv99 of the positive electrode active material in Comparative Example 1 was 45 pm.

[0103] Comparative Example 2

[0104] The preparation method was consistent with that of Example 20, except that the thickness D1 of the positive electrode film layer was 7.5 pm; the thickness of the positive electrode sheet was 25 pm; and the compacted density of the positive electrode film layer was 4.15 g / dm 3 .

[0105] Comparative Example 3

[0106] The preparation method was consistent with that of Example 24, except that the thickness D1 of the positive electrode film layer was 5 pm; the thickness of the positive electrode sheet was 20 pm; and the compacted density of the positive electrode film layer was 4.15 g / dm 3 . The roughness of the current collector blank area was 900 mm -1 , and the roughness of the covered area was 6300 mm -1 .

[0107] Comparative Example 4

[0108] The preparation method was consistent with that of Example 27, except that the Dv99 of the positive electrode active material in Comparative Example 4 was 25 pm; the thickness D c of the aluminum foil was 12 pm; the thickness D1 of the positive electrode film layer was 24 pm; and the thickness of the positive electrode sheet was 60 pm.

[0109] Comparative Example 5

[0110] The preparation method was consistent with that of Example 26, except that the Dv99 of the positive electrode active material in Comparative Example 5 was 17 pm; the thickness D​c The thickness D1 of the positive electrode film layer was 9 μm; the thickness of the positive electrode film layer was 18 μm; the thickness of the positive electrode sheet was 45 μm; the compacted density of the positive electrode film layer was 3.8 g / dm 3 .

[0111] It should be noted that the primary particles used in Examples 1-36 and Comparative Examples 1-5 can be obtained directly by commercial purchase in addition to being obtained according to the method described in the examples and comparative examples of the present application; the secondary particles used in Examples 1-36 and Comparative Examples 1-5 can be obtained by sintering the primary particles according to the method described in the examples and comparative examples of the present application in addition to being obtained directly by commercial purchase.

[0112] Performance test method of lithium ion battery:

[0113] 85°C storage performance test

[0114] The lithium ion battery was charged at 0.5 C to 4.48 V at 25°C, and then charged at constant voltage to a current of 0.025 C, and the thickness of the lithium ion battery at this time was tested and recorded as d0; then the lithium ion battery was placed in an 85°C oven, and after 6h of storage, the thickness of the lithium ion battery was tested and recorded as d (hot test).

[0115] Thickness expansion rate (%) after 6h of 85°C high temperature storage = (d-d0) / d0x100%.

[0116] (If the thickness expansion rate is greater than 10%, it is not up to standard)

[0117] 45°C cycle performance test

[0118] The lithium ion battery was discharged at 1.0 C to 3.0 V at 45°C, and then charged to 4.48 V at a current of 0.7 C, and then charged at constant voltage to 0.025 C, and then left to stand for 5 minutes. The above process was taken as one cycle, and the fourth discharge capacity was taken as 100%, and the number of cycles when the discharge capacity was 80% was recorded.

[0119] Positive electrode sheet appearance test

[0120] The appearance of the prepared positive electrode sheet was observed, and classified according to the following standards:

[0121] If the appearance is free of scratches, bumps and other abnormal phenomena, it is recorded as excellent;

[0122] If the appearance has less than 1 scratch, and no exposed metal or bumps ≤ 3, it is recorded as good;

[0123] If the appearance has more than 1 scratch or bumps > 3, it is recorded as poor.

[0124]

[0125]

[0126] From the data analysis of Table 1 and Table 2, when the primary particles in the positive electrode active material satisfy the mass percentage content of greater than or equal to 20% and less than or equal to 100% based on the positive electrode active material, the positive electrode film layer Dl, the positive electrode active material Dv99, and the positive electrode current collector Dc satisfy D1≥Dv99-Dc; or when the primary particles in the positive electrode active material satisfy the mass percentage content of greater than or equal to 0% and less than 20% based on the positive electrode active material, the positive electrode film layer, the positive electrode active material, and the positive electrode current collector satisfy D1≥1.1Dv99; at this time, the prepared positive electrode sheet has a good appearance, and the prepared lithium ion battery has good high-temperature storage performance and high-temperature cycle performance.

[0127] From the data comparison of Comparative Example 1 and Example 1, when the positive electrode active material only includes primary particles, if the sum of the thickness of the positive electrode film layer and the thickness of the current collector aluminum foil is less than the particle size Dv99 of the positive electrode active material particles, the particles are extremely prone to appearance problems such as particle scratches and convex points during coating, and the high-temperature storage performance and high-temperature cycle performance of the lithium ion battery are deteriorated.

[0128] From the data comparison of Comparative Example 2 and Example 20, and Comparative Example 3 and Example 24, when the positive electrode active material includes primary particles and secondary particles and the mass percentage of the primary particles is greater than or equal to 20%, if the sum of the thickness of the positive electrode film layer and the thickness of the current collector aluminum foil is less than the particle size Dv99 of the positive electrode active material particles, the particles are extremely prone to appearance problems such as particle scratches and convex points during coating, and the high-temperature storage performance and high-temperature cycle performance of the lithium ion battery are deteriorated.

[0129] From the data comparison of Comparative Example 4 and Example 27, when the positive electrode active material only includes secondary particles, if the thickness of the positive electrode film layer is less than 1.1 times the particle size Dv99 of the positive electrode active material particles, the particles are extremely prone to appearance problems such as particle scratches and convex points during coating, and the high-temperature storage performance and high-temperature cycle performance of the lithium ion battery are deteriorated.

[0130] From the data comparison of Comparative Example 5 and Example 26, when the positive electrode active material includes primary particles and secondary particles and the mass percentage of the primary particles is less than 20%, if the thickness of the positive electrode film layer is less than 1.1 times the particle size Dv99 of the positive electrode active material particles, the particles are extremely prone to appearance problems such as particle scratches and convex points during coating, and the high-temperature storage performance and high-temperature cycle performance of the lithium ion battery are deteriorated.

[0131] The data of comparative examples 7-8 and examples 11-12 can be obtained that the roughness of the blank area of the positive electrode current collector and the roughness of the covered area are too high or too low, which affects the appearance of the electrode sheet and the high-temperature storage performance and high-temperature cycle performance of the lithium ion battery. In example 11, the roughness of the blank area of the current collector is less than 500 mm -1 , the roughness of the covered area is less than 1500 mm -1 , the appearance of the electrode sheet is poor, and the thickness expansion rate after 85℃ high-temperature storage is relatively large, and the cycle number when the discharge capacity is 80% at 45℃ is reduced; in example 12, the roughness of the blank area of the current collector is more than 2000 mm -1 , the roughness of the covered area is more than 8000 mm -1 , the appearance of the electrode sheet is prone to problems such as particle scratches and convex points, and the thickness expansion rate after 85℃ high-temperature storage is relatively large, and the cycle number when the discharge capacity is 80% at 45℃ is reduced.

[0132] The data of comparative example 8 and examples 13-14 can be obtained that the ether dinitrile additive affects the storage and high-temperature cycle performance of the lithium ion battery. In example 13, no ether dinitrile additive is added, and the thickness expansion rate after 85℃ high-temperature storage is relatively large, and the cycle number when the discharge capacity is 80% at 45℃ is reduced; in example 14, an excessive amount of ether dinitrile additive is added, and the thickness expansion rate after 85℃ high-temperature storage is relatively large, and the cycle number when the discharge capacity is 80% at 45℃ is reduced.

[0133] The data of comparative example 10 and example 15 can be obtained that the conductivity of the electrolyte affects the high-temperature cycle performance of the lithium ion battery. In example 15, the conductivity of the electrolyte is less than 7 ms / cm, and the cycle number when the discharge capacity is 80% at 45℃ is reduced.

[0134] The data of comparative example 10 and examples 16-17 can be obtained that the thickness of the positive electrode film layer and the thickness of the positive electrode current collector affect the appearance of the electrode sheet and the high-temperature cycle performance. The data of comparative examples 10, 16, 18 and 19 can be obtained that the compaction density of the positive electrode film layer affects the high-temperature storage and high-temperature cycle performance of the lithium ion battery.

[0135] The data of comparative example 28 and examples 35-36 can be obtained that the particle size Dv99 of the positive electrode active material affects the high-temperature cycle performance of the lithium ion battery, and when the particle size Dv99 of the positive electrode active material is less than 5 μm or more than 48 μm, the cycle number when the discharge capacity is 80% at 45℃ is reduced.

Claims

1. An electrochemical device comprising a positive electrode and an electrolyte, the positive electrode comprising a current collector and a film layer comprising a positive electrode active material, the film layer being disposed on at least one surface of the current collector, the positive electrode active material comprising primary particles and / or secondary particles; The primary particles in the positive electrode active material satisfy 20%≤A≤100% based on the mass percentage content A of the positive electrode active material, and the following is satisfied among the diaphragm layer, the positive electrode active material, and the current collector: D l - (Dv99-D c ) ≥ 0.8 μm; wherein D l D is the thickness of the membrane layer c Dv99 is the particle diameter corresponding to 99% of the cumulative volume percentage of the positive electrode active material The current collector includes a blank area and a cover area, the cover area is an area of a cover diaphragm layer on the current collector, and the roughness of the cover area is 1500 mm -1 to 7200 mm -1 ; the electrolyte comprising an ether dinitrile compound at a mass percentage of 0.01% to 15% based on the total mass of the electrolyte.

2. The electrochemical device of claim 1, wherein, D l - (Dv99- D c ) ≥ 1.8 μm.

3. The electrochemical device of claim 1, wherein, D l - (Dv99- D c ) ≥ 8.7 μm.

4. The electrochemical device according to claim 1, wherein the primary particles in the positive electrode active material satisfy 20% < A < 100% based on the mass percentage content A of the positive electrode active material, wherein, D l - (Dv99- D c ) ≥ 5 μm. 5.The electrochemical device according to claim 1, wherein The membrane layer thickness D l The current collector thickness D c The relationship satisfies: 0.05≤D l / D c ≤3.

75.

6. The electrochemical device of claim 5, wherein, 1.08 < D l / D c ≤ 2.

96. 7.The electrochemical device according to claim 1, wherein The thickness D of the membrane layer l The range is from 1 μm to 30 μm. 8.The electrochemical device according to claim 7, wherein The thickness D of the membrane layer l The range is from 14μm to 30μm. 9.The electrochemical device according to claim 1, wherein The thickness D of the current collector c is from 4 pm to 20 pm. 10.The electrochemical device according to claim 1, wherein the particle size Dv99 of the positive electrode active material is 5 μm to 48 μm. 11.The electrochemical device according to claim 1, wherein The compacted density of the film sheet layer is 2 g / dm 3 up to 4.3 g / dm 3 . 12.The electrochemical device according to claim 1, wherein The blank area is an area on the current collector not covered by the diaphragm layer, and the roughness of the blank area is 500 mm -1 up to 2000 mm -1 .

13. The electrochemical device of claim 1, wherein, the mass percentage of the ether dinitrile compound is 1% to 5%. 14.The electrochemical device according to claim 1, wherein the conductivity of the electrolyte is greater than or equal to 7 mS / cm. 15.An electronic device comprising the electrochemical device according to any one of claims 1 to 14.

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