Electrochemical device and electronic device

Abstract

The application relates to the technical field of batteries, in particular to an electrochemical device, which comprises a positive electrode sheet, the positive electrode sheet comprising a positive electrode current collector, a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, and a protective layer arranged on at least a part of the surface of the positive electrode active material layer, the protective layer comprising an organic compound, and the thickness ratio of the positive electrode active material layer to the protective layer being 10:1 to 200:1. In the electrochemical device provided by the application, an organic protective layer is arranged on the outer surface of the side of the positive electrode sheet exposed to air, so that the positive electrode sheet does not directly contact CO2 in the air and react during the manufacturing process of the electrochemical device, the reaction with CO2 during transportation and operation is avoided, the processing performance is ensured, and the storage performance of the electrochemical device is not affected. The application further provides an electronic device comprising the above electrochemical device.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more specifically to an electrochemical device and an electronic device including the electrochemical device. Background Technology

[0002] With the increasing depletion of fossil fuels and growing pressure from environmental pollution, industries such as 3C and automobiles urgently need a new energy source to power them. Lithium-ion batteries have stood out due to their high energy density, lack of memory effect, and high operating voltage, becoming the preferred solution for new energy products.

[0003] Lithium-ion batteries mainly consist of an electrolyte, a positive electrode, a negative electrode, a separator, and a casing. High-nickel ternary positive electrode active materials for lithium-ion batteries have a theoretical specific capacity and high safety performance, with a potential of approximately 4.3V relative to the lithium electrode, making them a promising candidate for next-generation lithium-ion battery positive electrode active materials. However, high-nickel ternary positive electrode active materials for lithium-ion batteries suffer from surface instability. On the one hand, they easily absorb moisture and carbon dioxide during slurry preparation, causing a sharp rebound in slurry viscosity and hindering proper coating. On the other hand, the high-nickel material in the positive electrode easily absorbs carbon dioxide from the air along with moisture, resulting in a layer of non-electrochemically active bicarbonates, carbonates, and basic carbonates adhering to the surface. Lithium-ion batteries made using these positive electrode materials exhibit severe gas generation during high-temperature storage.

[0004] Therefore, it is necessary to develop cathode active materials with superior performance to further improve the performance of lithium-ion batteries. Summary of the Invention

[0005] The purpose of this application is to overcome the above-mentioned deficiencies of the prior art and provide an electrochemical device that solves the technical problem that the positive electrode active material and positive electrode sheet of the lithium-ion battery are sensitive to air during the processing.

[0006] The purpose of this application is achieved through the following technical solution.

[0007] One aspect of this application provides an electrochemical device comprising a positive electrode, the positive electrode comprising a positive current collector, a positive active material layer disposed on at least one surface of the positive current collector, and a protective layer having a protective layer on at least a portion of the surface of the positive active material layer, the protective layer comprising an organic compound, and the thickness ratio of the positive active material layer to the protective layer being 10:1 to 200:1.

[0008] In this application, the thickness ratio of the positive electrode active material layer to the protective layer is set in the range of 10:1 to 200:1 to obtain ideal results. If the thickness ratio is too large, the energy density of the battery will decrease; if the thickness ratio is too small, the positive electrode sheet will not achieve the purpose of hydrophobicity, causing the positive electrode active material to absorb moisture from the air and deteriorate the storage performance of the electrochemical device.

[0009] In the electrochemical device provided in this application, a protective layer is provided on the outer surface of the positive electrode sheet exposed to air, so that the positive electrode sheet does not come into direct contact with CO2 in the air and react during the manufacturing process of the electrochemical device, thereby avoiding reaction with CO2 during transportation and operation, thus ensuring processing performance and ensuring that the storage performance of the electrochemical device is not affected.

[0010] In some embodiments of this application, the thickness of the protective layer is between 200 nm and 10 μm. Within this thickness range, the protective layer can effectively isolate the positive electrode from air, making the positive electrode more stable in air. If the thickness of the protective layer is less than 200 nm, the thickness is too small, resulting in poor protection of the positive electrode. If the thickness of the protective layer is greater than 10 μm, it will lead to an increase in the impedance of the positive electrode, deteriorating the performance of the electrochemical device.

[0011] In some embodiments of this application, the contact angle of the protective layer with water is 100° to 180°. The larger the contact angle of the protective layer with water, the better the hydrophobicity of the positive electrode, and the less likely the positive electrode is to absorb water and undergo side reactions.

[0012] In some embodiments of this application, the protective layer is an organic compound layer. Further, the organic compound includes at least one of an aromatic compound and a silane compound. The aromatic compound has a phenyl group, which can coordinate with oxygen atoms on the surface of the positive electrode active material. Simultaneously, the benzene ring itself is hydrophobic. The silane compound has a long-chain structure, which is hydrophobic. The silane compound can undergo a hydrolysis reaction with hydroxyl groups (-OH) on the surface of the positive electrode active material, causing one end of the silane compound to adhere to the surface of the positive electrode active material layer, while the other end becomes hydrophobic. In this application, after coating the surface of the positive electrode active material with an aromatic compound or a silane compound, one end of the compound molecule can chemically adsorb onto the surface of the positive electrode active material, while the long chain or benzene ring structure at the other end acts as a hydrophobic group, thus providing a hydrophobic effect.

[0013] In some embodiments of this application, the aromatic compound may include aromatic compounds commonly found in the art. For example, the aromatic compound is selected from at least one of toluene, ethylbenzene, xylene, naphthalene and its derivatives, anthracene and its derivatives, phenanthrene and its derivatives, styrene, phenylacetylene, phenol, p-phenol, nitrobenzene, bromobenzene, phenylboronic acid, benzenesulfonic acid, benzoic acid, benzaldehyde, and 2,6-dimethyl-p-phenol.

[0014] In some embodiments of this application, the silane compound is selected from at least one of alkyl and / or alkoxy-substituted silane compounds and fluorine-substituted silane compounds. For example, the silane compound is selected from at least one of n-octyltrimethoxysilane, n-dodecyltrimethoxysilane, n-hexadecyltrimethoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, tridecafluorooctyltrimethoxysilane, and 1H,1H,2H,2H-heptadecylfluorodecyltrimethoxysilane.

[0015] In some embodiments of this application, the mass fraction of silicon in the positive electrode active material is 0.01% to 5% based on the total mass of the positive electrode active material. By limiting the silicon content, the content of silane compounds in the positive electrode active material can be indirectly limited. If the content of silicon-containing organic compounds is too low, the expected effect cannot be achieved, while if the content of silane compounds is too high, the performance of the electrochemical device will deteriorate.

[0016] In some embodiments of this application, the organic compound in the protective layer is selected from phenol (C6H5OH), phenylboronic acid (C6H7BO2), and trimethylphenol (C9H5OH). 12 O), 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane (C 16 H 19 F 17 O3Si), 1H, 1H, 2H, 2H-heptadecyltrimethoxysilane (C 13 H 13 F 17 O3Si), 1H, 1H, 2H, 2H-perfluorooctyltrimethoxysilane (C 11 H 13 F 13 O3Si) and n-dodecyltrimethoxysilane (C 15 H 34 O3Si), octyltriethoxysilane (C 14 H 32 O3Si), trimethoxysilane (H3C(CH2)) 15 Si(OCH3)3), pentyltriethoxysilane (C 11 H 26 O3Si), hexadecyltrimethoxysilane (H3C(CH2))15 Si(OCH3)3), 3-glycidyl etheroxypropyltriethoxysilane (C 12 H 26 At least one of the following: O5Si), polyvinylidene fluoride, polytetrafluoroethylene, polyethylene glycol or polyvinyl alcohol, and sodium carboxymethyl starch ([C6H7O2(OH)2OCH2COONa]n). Coating the surface of the positive electrode active material layer with the above organic compounds can better improve the stability of the positive electrode sheet. The boiling point of the organic compounds is preferably in the range of 200-300°C. When the boiling point of the organic compounds is within this range, even if high-temperature drying is required during the coating process, the volatilization of the organic compounds is minimized, thereby increasing the amount of organic compounds bonded to the positive electrode sheet and further saving costs.

[0017] In the electrochemical device of this application, the type of positive electrode current collector is not specifically limited and can be selected according to actual needs. For example, the positive electrode current collector can be aluminum foil, nickel foil, or a polymer conductive film; preferably, the positive electrode current collector is aluminum foil.

[0018] In the electrochemical device of this application, the positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder. The positive electrode active material can be a common positive electrode active material in the art. In some embodiments of this application, the positive electrode active material comprises a compound represented by general formula (1):

[0019] Li x Ni y Co z Mn k M q O b-a X a (1)

[0020] Where M represents at least one element selected from boron, magnesium, aluminum, silicon, phosphorus, sulfur, titanium, chromium, iron, cobalt, nickel, copper, zinc, gallium, yttrium, zirconium, molybdenum, silver, tungsten, indium, tin, lead, antimony, and cerium, X represents a halogen, and x, y, z, k, q, a, and b satisfy 0.2 < x ≤ 1.2, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, 0 ≤ k ≤ 1, 0 ≤ q ≤ 1, 0 ≤ a ≤ 1, and 1 ≤ b ≤ 2, respectively.

[0021] Ternary cathode active materials containing nickel, cobalt, and manganese are currently popular and are commonly referred to as NCM cathode active materials. If the nickel content in an NCM cathode active material is too high, the high-nickel material easily absorbs both moisture and carbon dioxide from the air, forming bicarbonate, carbonate, and basic carbonate on its surface. When cathode active materials containing bicarbonate, carbonate, and basic carbonate are used to make cathode plates for lithium-ion batteries, it leads to severe gas generation in the batteries under high-temperature storage conditions. In this application, a protective layer is formed on the surface of the high-nickel cathode active material to prevent contact between the material and carbon dioxide in the air, thereby avoiding the formation of bicarbonate, carbonate, and basic carbonate.

[0022] In some embodiments of this application, the mass fraction of Ni element in the positive electrode active material is greater than or equal to 50% based on the mass of the positive electrode active material. For positive electrode active materials, if the positive electrode active material has a high nickel (Ni) content (e.g., nickel content greater than or equal to 50%), the positive electrode active material is prone to absorbing water. In this case, by providing a protective layer on the surface of the positive electrode active material, the adsorption of moisture on the surface of the positive electrode active material is prevented, thus ensuring the performance of the electrochemical device.

[0023] In some embodiments of this application, the mass ratio of the positive electrode active material, conductive agent, binder, and organic compound is (84-95):(5-10):(3-5):(0.2-3). Within this mass ratio range, the organic compound can fully combine with the positive electrode active material, conductive agent, and binder, thereby achieving optimal protection for the positive electrode sheet.

[0024] The types and amounts of conductive agents and binders used in the positive electrode sheet are not specifically limited and can be selected according to actual needs. In some embodiments of this application, the conductive agent used in the positive electrode sheet is selected from at least one of carbon nanotubes, acetylene black, graphene, Ketjen black, and carbon black, and the binder is selected from at least one of polyvinylidene fluoride (PVDF), carboxymethyl cellulose, and styrene-butadiene rubber.

[0025] In some embodiments of this application, the positive electrode active material is a spherical or near-spherical secondary spherical particle with a particle size of 1 μm to 20 μm, wherein the particle size Dv50 of the secondary spherical particle is 9 μm to 12 μm, and the primary particles on the surface of the secondary spherical particle are hexagonal plate-like particles with a particle size of 1 μm to 1.5 μm. When the positive electrode active material is a ternary active material, the secondary particles of the ternary positive electrode active material are easily broken, and after breaking, they easily absorb moisture from the air, leading to performance degradation of the electrochemical device. In this application, by providing a protective layer on the surface of the positive electrode active material, moisture adsorption on the surface of the positive electrode active material is prevented, thereby avoiding performance degradation of the electrochemical device.

[0026] In some embodiments of this application, the positive electrode active material is a hexagonal single-crystal primary particle with a particle size of 1 μm to 20 μm, wherein the particle size Dv50 of the single-crystal primary particle is 3 μm to 9 μm. For positive electrode active materials, especially ternary materials, the surface of single-crystal primary particles has high activity and is prone to water absorption. In this application, by providing a protective layer on the surface of the positive electrode active material, water adsorption on the surface of the positive electrode active material is prevented, thereby avoiding performance degradation of the electrochemical device.

[0027] In some embodiments of this application, the silicon content of the positive electrode sheet is directly proportional to the BET (Bright Electron Equivalent) of the positive electrode active material; the higher the BET, the higher the silicon content. The BET of the material can be tested before the formation of the organic protective layer, and then the added silicon content can be calculated based on the BET value. By adjusting the relationship between BET and silicon content, the electrochemical device can achieve better performance.

[0028] In the electrochemical device provided by this invention, a protective layer is coated on the outer surface of the positive electrode, reducing the formation of residual lithium on the surface of the positive electrode active material and greatly improving the storage and cycle performance of the electrochemical device. In the preparation of the positive electrode of this application, an organic compound is coated on the surface of the positive electrode. The material on the positive electrode is modified by high-temperature treatment. The material on the positive electrode (positive electrode active material, conductive agent, and binder) is connected to the organic compound through chemical bonds, intermolecular forces, or hydrogen bonds, forming a nano-organic protective layer. This layer protects the entire positive electrode, preventing the positive electrode active material from contacting carbon dioxide in the air and forming bicarbonate, carbonate, and basic carbonate. The resulting electrochemical device exhibits higher storage and cycle performance.

[0029] The electrochemical device of this application includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode is the positive electrode as described above, and the negative electrode includes a negative current collector and a negative active material coated on the negative current collector.

[0030] The negative electrode active material can be selected from commonly used active materials in the field, the separator can be selected from commonly used separators in the field, and the electrolyte can be a commonly used electrolyte in the field, which will not be elaborated here.

[0031] Another aspect of this application provides an electronic device comprising the electrochemical device described above.

[0032] The technical solution provided in this application can achieve the following beneficial effects:

[0033] In the electrochemical device provided by this invention, a protective layer is uniformly coated on the surface of the positive electrode active material, isolating the entire positive electrode sheet from air and significantly reducing the exposed area of ​​the positive electrode sheet in air. The electrochemical device of this application is relatively stable in air, preventing the positive electrode sheet from reacting with CO2 during transport and operation, thus avoiding any impact on subsequent processing performance and battery performance. This ensures the inherent performance of the positive electrode sheet and reduces storage and transport costs. Attached Figure Description

[0034] Figure 1 This is an infrared spectrum of the positive electrode active material in one embodiment of this application;

[0035] Figure 2 This is the Raman spectrum of the positive electrode active material in one embodiment of this application;

[0036] Figure 3 This is a scanning electron microscope image of the structure of the positive electrode in one embodiment of this application;

[0037] Figure 4 The image shows the contact angle between water and the positive electrode plate, as measured by a contact angle tester.

[0038] Figure 5 This shows the silicon content in the protective layer. Detailed Implementation

[0039] To make the technical problem to be solved, the technical solution, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0040] Example 1

[0041] This embodiment provides a lithium-ion battery and its preparation method, the preparation process of which is described below.

[0042] Preparation of lithium-ion batteries

[0043] (1) Preparation of positive electrode sheet

[0044] According to the positive electrode active material (NCM811, LiNi) 0.818 Co 0.12 Mn 0.6 Zr 0.02 A slurry was prepared using a mass ratio of O2:conductive carbon black (Super P):PVDF:conductive carbon nanotubes = 97.5:0.7:1.2:0.6, and the viscosity of the slurry was adjusted to 3000 Pas to 6000 Pas. The mixed slurry was uniformly coated onto aluminum foil, with a single layer thickness of 20 μm, and double-layer coating was performed. After the slurry dried, it was rolled to form a conventional positive electrode sheet. A 1% (w / w) phenylboronic acid (C6H7BO2) organic solution (the remaining 99% solvent was NMP, N-methylpyrrolidone) was prepared. The positive electrode slurry was replaced with the organic solution on the cold-pressed electrode sheet using an extrusion coating machine. The pump speed was adjusted to 8 rpm, the left blade spacing to 50 μm, the right blade spacing to 50 μm, and the conveyor speed to 5 m / min. The thickness of the organic solution on the electrode surface was controlled to be 200 nm (0.2 μm) and uniformly covered. The thickness of the organic protective layer was controlled by adjusting the left and right blade spacing and the pump speed. The ambient humidity during the processing and transport of the positive electrode sheet was adjusted to 45%. In this embodiment, the compacted density of the positive electrode sheet was 3.4 g / cc. The positive electrode sheet was tested using an infrared spectrometer, and the infrared spectrum was visible at 1593.16 cm⁻¹. -1 The strongest peak is at 1220.75 cm⁻¹, and a second strongest peak is at 1220.75 cm⁻¹. Apart from this, the infrared spectrum shows a peak at 3214.56 cm⁻¹. -1 There are peaks, such as Figure 1 As shown, this indicates the presence of C6H7BO2 in the positive electrode.

[0045] The positive electrode was tested using Raman spectroscopy, and the Raman spectrum was at 110 cm⁻¹. -1 125cm -1 1000cm -1 1600cm -1 3100cm -1 The presence of a peak further indicates the presence of C6H7BO2 in the positive electrode plate, such as... Figure 2 As shown. The positive electrode was tested using ion polishing (CP) ion beam profiling, scanning electron microscopy (SEM), and X-ray energy dispersive spectroscopy (EDS). The test results showed that boron was present in the outermost layer of the active layer.

[0046] In this embodiment, the prepared positive electrode sheet includes an aluminum foil, a positive electrode active material layer covering the surface of the aluminum foil, and an organic protective layer covering the surface of the positive electrode active material layer, such as... Figure 3 As shown. The contact angle between water and the positive electrode plate, measured by a contact angle tester, is 107.1°. Figure 4 As shown.

[0047] Specific steps for contact angle testing:

[0048] 1. Ensure the surface of the positive electrode sheet is flat and clean. Cut the positive electrode sheet into 5cm*5cm square pieces and place them flat on the test platform of the contact angle tester.

[0049] 2. Dispense a droplet of approximately 2 μl from the syringe;

[0050] 3. You can see the droplet forming a suspended shape through the lens. Then move the needle downwards until it contacts the sample surface. Note: Do not move it too low to avoid bending the needle.

[0051] 4. Move the needle upwards. Due to the surface tension system, the liquid will remain on the sample surface. Continue moving the needle until it disappears from the lens, usually by about 3mm.

[0052] 5. Adjust the position of the horizontal line and obtain the contact angle between the droplet and the electrode surface through software data analysis.

[0053] (2) Preparation of negative electrode sheet

[0054] Artificial graphite (anode active material), Super P (conductive agent), sodium carboxymethyl cellulose (CMC) (thickener), and styrene-butadiene rubber (SBR) (binder) were mixed in a weight ratio of 96.4:1.5:0.5:1.6. Deionized water was added, and the mixture was stirred in a vacuum mixer to obtain a cathode slurry with a solid content of 54 wt%. The cathode slurry was uniformly coated onto a copper foil (cathode current collector). The copper foil was dried at 85°C, then cold-pressed, cut, and slit, and finally dried under vacuum at 120°C for 12 hours to obtain the cathode sheet.

[0055] (3) Electrolyte preparation

[0056] In a dry argon-atmospheric glove box, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC:PC:DEC = 3:3:4. Additives were then added, dissolved, and thoroughly stirred before adding lithium salt LiPF6. The mixture was then thoroughly mixed to obtain the electrolyte. The concentration of LiPF6 was 1 mol / L. The specific types and amounts of additives used in the electrolyte are shown in Table 1. In Table 1, the additive content is a mass percentage calculated based on the total mass of the electrolyte.

[0057] (4) Preparation of the separating membrane

[0058] A polyethylene (PE) film with a thickness of 7μm was selected as the separator.

[0059] (5) Preparation of lithium-ion batteries

[0060] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. Then, they are wound to obtain a wound assembly. After welding the tabs, the wound assembly is placed in an outer packaging foil aluminum-plastic film. The prepared electrolyte is injected into the dried wound assembly. After vacuum sealing, settling, formation (0.3C constant current charging to 3.0V, then 0.5C constant current charging to 3.6V, and finally 1C constant current charging to 4.25V), shaping, and capacity testing, a soft-pack lithium-ion battery (thickness 3.3mm, width 39mm, length 96mm) is obtained.

[0061] Example 2

[0062] The method for preparing the lithium-ion battery provided in this embodiment is the same as that in Embodiment 1, except that the positive electrode sheet is prepared by the following method.

[0063] A slurry was prepared according to the mass ratio of positive electrode active material (NCM811): conductive carbon black (Super P): PVDF: conductive carbon nanotubes (CNT) = 97.5:0.7:1.2:0.6, and the viscosity of the slurry was adjusted to 3000 Pas-6000 Pas. The mixed slurry was uniformly coated onto aluminum foil, with a single layer thickness of 20 μm, and double-layer coating was performed. After the slurry dried, it was rolled to form a conventional positive electrode sheet. A 5% phenol (C6H5OH) solution (the remaining 99% solvent was NMP) was prepared, and the positive electrode slurry was replaced with an organic solution to coat the cold-pressed electrode sheet on an extrusion coating machine. The pump speed was adjusted to 20 rpm, the left blade spacing to 100 μm, the right blade spacing to 100 μm, and the conveyor speed to 10 m / min. The coating thickness of the organic solution on the electrode surface was controlled to be 1 μm and uniform. The thickness of the organic coating was controlled by adjusting the left and right blade spacing and the pump speed. The ambient humidity during the processing and transportation of the positive electrode sheet was 45%. In this embodiment, the compacted density of the positive electrode sheet was 3.4 g / cc. The positive electrode sheet was tested using an infrared spectrometer, and the infrared spectrum was at 1471.79 cm⁻¹. -1 The strongest peak is found at 1271.03 cm⁻¹. In addition, the infrared spectrum at 1271.03 cm⁻¹ shows... -1 The presence of a secondary strong peak indicates the presence of phenol (C6H5OH) in the positive electrode.

[0064] The positive electrode was tested using Raman spectroscopy, and the Raman spectrum was at 115 cm⁻¹. -1 1100cm -1 1650cm -1 3050cm -1 The presence of a peak further indicates the presence of phenol (C6H5OH) in the positive electrode.

[0065] Example 3

[0066] The method for preparing the lithium-ion battery provided in this embodiment is the same as that in Embodiment 1, except that the method for preparing the positive electrode sheet is as follows.

[0067] The electrode composition is as follows: positive electrode active material (NCM811): conductive carbon black (Super P): PVDF: conductive carbon nanotubes (CNT): hexadecyltrimethoxysilane H3C(CH2). 15 A slurry was prepared using Si(OCH3)3 at a mass ratio of 97.3:0.7:1.2:0.6:0.2, and the viscosity was adjusted to 3000 Pas-6000 Pas. The mixed slurry was uniformly coated onto aluminum foil, with a single layer thickness of 20 μm. Double-layer coating was performed. After drying, the slurry was rolled to form the desired positive electrode sheet. A 5% (w / w) C6H7BO2 solution (the remaining 99% solvent was NMP) was prepared. The positive electrode slurry was replaced with an organic solution on the cold-pressed electrode sheet using an extrusion coating machine. The pump speed was adjusted to 20 rpm, the left and right blade spacing to 100 μm, and the conveyor speed to 10 m / min. The organic solution coating thickness on the electrode surface was controlled to be 4 μm, ensuring uniform coverage. The thickness of the organic coating was controlled by adjusting the left and right blade spacing and the pump speed. The ambient humidity during positive electrode sheet processing and transport was 45%. In this embodiment, the compaction density of the positive electrode is 3.4 g / cc. The positive electrode was tested using an infrared spectrometer, and the infrared spectrum is at 2853.70 cm⁻¹. -1 It has the strongest peak. In addition, the infrared spectrum is at 1331.60 cm⁻¹. -1 The presence of a secondary strong peak indicates the presence of H3C(CH2) in the positive electrode plate. 15 The positive electrode of Si(OCH3)3 and C6H7BO2 was tested using Raman spectroscopy. The Raman spectrum was at 110 cm⁻¹. -1 1000cm -1 1450cm -1 3100cm -1 There are peaks at various points. In the positive electrode sheet of this embodiment, the elemental content was tested using ICP (inductively coupled plasma) technology. Based on the total mass of the positive electrode active material, the mass ratio of silicon in the organosilicon compound was 0.01%. Figure 5 As shown.

[0068] Example 4

[0069] The method for preparing the lithium-ion battery provided in this embodiment is the same as that in Embodiment 1, except that the method for preparing the positive electrode sheet is as follows.

[0070] According to the positive electrode active material (NCM811): conductive carbon black (Super P): PVDF: conductive carbon nanotubes (CNT): 3-glycidyl etheroxypropyltriethoxysilane (C 12 H26 A slurry was prepared using a mass ratio of O5Si = 97.3:0.7:1.2:0.6:0.2. The viscosity of the slurry was adjusted to 3000 Pas to 6000 Pas. The mixed slurry was then uniformly coated onto aluminum foil, with a single layer thickness of 40 μm. Double-layer coating was performed. After drying, the slurry was rolled to form the desired positive electrode sheet. A 5% (w / w) phenol (C6H5OH) solution (the remaining 99% solvent was NMP) was prepared. The positive electrode slurry was replaced with the organic solution on the cold-pressed electrode sheet using an extrusion coating machine. The pump speed was adjusted to 20 rpm, the left blade spacing to 100 μm, the right blade spacing to 100 μm, and the conveyor speed to 10 m / min. The organic solution coating thickness on the electrode surface was controlled to be 1 μm and uniformly covered. The thickness of the organic coating was controlled by adjusting the left and right blade spacing and the pump speed. The ambient humidity during the processing and transport of the positive electrode sheet was 45%. In this embodiment, the compaction density of the positive electrode sheet is 3.4 g / cc. The positive electrode sheet was tested using an infrared spectrometer, and the infrared spectrum is located at 1074.52 cm⁻¹. -1 The strongest peak is observed at 2941.75 cm⁻¹. In addition, the infrared spectrum shows a peak at 2941.75 cm⁻¹. -1 1220.75cm -1 The presence of a secondary strong peak indicates the presence of 3-glycidyl etheroxypropyltriethoxysilane (C) in the positive electrode. 12 H 26 O5Si) and C6H5OH. The positive electrode was tested using Raman spectroscopy, with the Raman spectrum at 110 cm⁻¹. -1 650cm -1 1000cm -1 1600cm -1 2800cm -1 There is a peak at this place.

[0071] Example 5

[0072] The method for preparing the lithium-ion battery provided in this embodiment is the same as that in Embodiment 1, except that the method for preparing the positive electrode sheet is as follows.

[0073] A slurry was prepared according to the mass ratio of positive electrode active material (NCM811): conductive carbon black (Super P): PVDF: conductive carbon nanotubes (CNT) = 97.5:0.7:1.2:0.6. The viscosity of the slurry was adjusted to 3000 Pas to 6000 Pas, and the mixed slurry was uniformly coated onto aluminum foil, with a single layer thickness of 20 μm, resulting in a double-layer coating. After drying, the slurry was rolled to form the desired positive electrode sheet.

[0074] Prepare 1% (w / w) hexadecyltrimethoxysilane (H3C(CH2)) 15In an extrusion coating machine, a Si(OCH3)3 organic solution 1 (with the remaining 99% solvent being NMP) was used to coat the cold-pressed electrode sheet by replacing the positive electrode slurry with the organic solution. The pump speed was adjusted to 8 rpm, the left blade spacing to 50 μm, the right blade spacing to 50 μm, and the conveyor speed to 5 m / min. The organic coating thickness on the electrode surface was controlled to be 400 nm and uniformly covered. The thickness of the organic coating was controlled by adjusting the left and right blade spacing and the pump speed.

[0075] A 5% (w / w) organic solution of phenylboronic acid (C6H7BO2) was prepared (the remaining 99% of the solvent was NMP). Organic solution 2 was then used to coat the aforementioned electrode using an extrusion coating machine. The pump speed was adjusted to 20 rpm, the left blade spacing to 100 μm, the right blade spacing to 100 μm, and the conveyor speed to 10 m / min. The coating thickness of the organic coating 2 was controlled to be 1400 nm and uniform. The coating thickness was controlled by adjusting the left and right blade spacing and the pump speed.

[0076] The ambient humidity during the processing and transportation of the positive electrode sheet was 45%. In this embodiment, the compacted density of the positive electrode sheet was 3.4 g / cc. The positive electrode sheet was tested using an infrared spectrometer, and the infrared spectrum was at 1331.60 cm⁻¹. -1 The strongest peak is located there. In addition, it is at 3078.00cm. -1 A secondary strong peak is observed. This indicates the presence of hexadecyltrimethoxysilane (H3C(CH2)) in the positive electrode. 15 Si(OCH3)3) and C6H7BO2. In this embodiment, the contact angle between water and the positive electrode sheet was measured to be 150° using a contact angle tester.

[0077] Examples 6 to 22

[0078] The lithium-ion batteries of Examples 6 to 22 were prepared according to the preparation process of Example 1.

[0079] The main parameters of Examples 1 to 22 are shown in Table 1.

[0080] Comparative Example 1

[0081] The lithium-ion battery provided in Comparative Example 1 is prepared using the same method as in Example 1, except that the preparation method of the positive electrode sheet is as follows.

[0082] A slurry was prepared according to a mass ratio of positive electrode active material (NCM811): conductive carbon (Super P): PVDF = 98:1:1. The viscosity of the slurry was adjusted to 3000 Pas to 6000 Pas, and the mixed slurry was uniformly coated onto aluminum foil with a single layer thickness of 20 μm, resulting in double-layer coating. After drying, the slurry was rolled to form the desired positive electrode sheet. The ambient humidity during the processing and transportation of the positive electrode sheet was 45%. In Comparative Example 1, the compaction density of the positive electrode sheet was 3.4 g / cc.

[0083] Comparative Examples 2 to 4

[0084] Following the preparation process of Comparative Example 1, lithium-ion batteries of Comparative Examples 2 to 4 were prepared.

[0085] The main parameters of Comparative Examples 1 to 4 are shown in Table 1.

[0086] Performance testing methods for lithium-ion batteries

[0087] Test 1: Lithium-ion battery specific capacity test

[0088] Place the lithium-ion battery in a 25°C constant temperature chamber and let it stand for 5 minutes to allow it to reach a constant temperature. Charge the lithium-ion battery at a constant current of 0.2C to 4.25V, then charge it at a constant voltage of 4.25V to a current of 0.025C, and let it stand for 5 minutes. Next, discharge it at a constant current of 0.2C to a voltage of 2.8V, and let it stand for 3 minutes to obtain the battery's discharge capacity.

[0089] Lithium-ion battery discharge capacity (mAh / g) = First discharge capacity / Mass of positive electrode active material. Test 2: High-temperature storage performance test of lithium-ion batteries.

[0090] The battery was discharged to 3.0V at 0.5C at 25℃, then charged to 4.25V at a constant current of 0.7C, and finally charged at 4.25V at a constant voltage until the current reached 0.05C. The thickness of the battery was measured and recorded using a micrometer and denoted as H. 11 ; Charge at 85℃ and store for 24 hours. After 24 hours, measure and record the battery thickness using a micrometer, denoted as H. 12 .

[0091] Thickness expansion coefficient = (H) 12 -H 11 ) / H 11 *100%

[0092] Test 3: High-Temperature Cycling Test of Lithium-ion Batteries

[0093] The lithium-ion battery was placed in a 45°C constant temperature chamber and left to stand for 30 minutes to allow it to reach a constant temperature. The battery was then discharged at a constant current of 0.2C to 3.0V at 45°C, and left to stand for 3 minutes. Next, it was charged at a constant current of 0.7C to 4.25V, then charged at a constant voltage of 4.25V to a current of 0.025C, and left to stand for 5 minutes. Finally, it was discharged at a constant current of 0.2C to a voltage of 3.0V, and left to stand for 3 minutes. This constitutes one charge-discharge cycle. The capacity retention rate was calculated after 50, 100, 200, 300, and 500 cycles of this charge / discharge cycle.

[0094] Capacity retention rate (%) of a lithium-ion battery after N cycles = Discharge capacity in the Nth cycle / Discharge capacity in the first cycle × 100%

[0095] Test 4: Number of cycles for lithium-ion batteries with a high-temperature cycle expansion rate >10%

[0096] 1) The initial thickness of lithium-ion batteries before cycling was tested using the flat plate contact method;

[0097] 2) Place the lithium-ion battery in a 45℃ constant temperature chamber and let it stand for 30 minutes to allow it to reach a constant temperature. Discharge the battery at a constant current of 0.2C to 3.0V at 45℃, let it stand for 3 minutes; then charge it at a constant current of 0.7C to 4.25V, then charge it at a constant voltage of 4.25V to a current of 0.025C, let it stand for 5 minutes; finally, discharge it at a constant current of 0.2C to a voltage of 3.0V, let it stand for 3 minutes; this completes one charge / discharge cycle. Repeat this charge / discharge cycle > 1000 times.

[0098] 3) The thickness of the battery cell during cycling was tested in situ using the flat plate contact method;

[0099] 4) When the lithium-ion battery cell expansion rate (%) is greater than 10%, record the current number of cycles.

[0100] Comparative Examples 2 to 4

[0101] Following the preparation process of Comparative Example 1, lithium-ion batteries of Comparative Examples 2 to 4 were prepared.

[0102] The main parameters of Comparative Examples 1 to 4 are shown in Table 1.

[0103] The performance parameters of the lithium-ion batteries prepared by the above embodiments and comparative examples are summarized in Table 1 below (2.8 to 4.25V).

[0104]

[0105]

[0106] As shown in Table 1, in the lithium-ion batteries of Examples 1 to 22 of this application, since an organic protective layer is coated on the surface of the positive electrode active material, the entire positive electrode sheet is isolated from the air. Compared with Comparative Examples 1 to 3, the exposed area of ​​the positive electrode sheet in the air can be greatly reduced, thereby making the positive electrode sheet more stable in the air, preventing the positive electrode sheet from reacting with CO2, and ultimately improving the high-temperature cycle performance of the lithium-ion battery.

[0107] Specifically, in Table 1, the lithium-ion batteries in Comparative Examples 1 to 4 showed a capacity retention rate below 90% after 500 cycles, while the lithium-ion batteries using the positive electrode sheets of Examples 1 to 6 of the present invention still maintained a capacity retention rate greater than 90%. In a cycle test at 45°C, the lithium-ion battery in Comparative Example 1 started producing gas in significantly fewer cycles than those in Examples 1 to 22. Furthermore, at a high temperature (85°C), the battery thickness increased by less than 10% after 24 hours, while the thickness increase of the lithium-ion batteries in Comparative Examples 1 to 3 was significantly greater than 10%, far exceeding the thickness growth rate of the lithium-ion batteries using the positive electrode sheets of Examples 1 to 22 of the present invention.

[0108] The thickness ratio of the positive electrode active material layer to the organic protective layer affects battery capacity, cycle life, and high-temperature storage. A larger ratio results in higher battery capacity but poorer cycle life and high-temperature storage performance. To balance overall battery performance, the ratio needs to be controlled to achieve optimal capacity while improving cycle life and high-temperature storage. Comparative Example 4 shows that when the ratio exceeds 200:1, the organic protective layer fails to provide adequate protection, leading to suboptimal cycle and storage performance in the lithium-ion battery. Example 16 shows that when the ratio is less than 10:1, the organic protective layer is too thick, failing to guarantee optimal battery capacity.

[0109] When silane compounds are uniformly distributed in the positive electrode active material layer of the positive electrode sheet, they can alleviate the erosion of the positive electrode material by the electrolyte, reduce the side reactions caused by particle breakage, and improve gas generation during high-temperature cycling. When silane compounds are used as a coating on the surface, they can improve the air stability of the electrode sheet during the production process, reduce water absorption of the electrode sheet, and reduce gas generation of lithium-ion batteries during high-temperature storage.

[0110] Furthermore, as can be seen from Examples 3 and 4, for lithium-ion batteries containing organic compounds both inside and on the surface of the positive electrode sheet, the battery exhibits superior performance in terms of the number of cycles at which gas production begins during cycle testing at 45°C and the thickness increase after 24 hours at high temperature (85°C), provided that other performance parameters are not compromised.

[0111] In summary, this invention reduces the formation of residual lithium on the surface of the positive electrode active material by coating the outer surface of the positive electrode with an organic protective layer, which isolates moisture and carbon dioxide in the air, and greatly improves the storage and cycle performance of the electrochemical device.

Claims

1. An electrochemical device, comprising a positive electrode plate, the positive electrode plate including a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector, at least a part of the surface of the positive electrode active material layer having a protective layer, the protective layer including an organic compound, the ratio of the thickness of the positive electrode active material layer to the thickness of the protective layer being 10:1 to 200:1; The contact angle of the protective layer with water is 100° to 180°; The organic compound is phenylboronic acid; Based on the mass of the positive electrode active material, the mass fraction of Ni element in the positive electrode active material is greater than or equal to 50%; The thickness of the protective layer is 200 nm to 10 μm.

2. The electrochemical device according to claim 1, characterized in that, The positive electrode active material contains a compound represented by the general formula (1): Li x Ni y Co z Mr k M q O b-a X a (1) Wherein, M represents at least one element selected from boron, magnesium, aluminum, silicon, phosphorus, sulfur, titanium, chromium, iron, cobalt, nickel, copper, zinc, gallium, yttrium, zirconium, molybdenum, silver, tungsten, indium, tin, lead, antimony and cerium, X represents a halogen, and x, y, z, k, q, a and b respectively satisfy 0.2 < x ≤ 1.2, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, 0 ≤ k ≤ 1, 0 ≤ q ≤ 1, 0 ≤ a ≤ 1 and 1 ≤ b ≤ 2.

3. The electrochemical device according to claim 1, characterized in that, The positive electrode active material includes at least one of the following characteristics: (1) The positive electrode active material includes secondary particles, the Dv50 of the secondary particles is 9 μm to 15 μm, and there are primary particles on the surface of the secondary particles, and the particle size of the primary particles is 1 μm to 1.5 μm; (2) The positive electrode active material includes single crystal type primary particles, and the Dv50 of the single crystal type primary particles is 3 μm to 9 μm.

4. The electrochemical device according to any one of claims 1 to 3, characterized in that, The organic compound is included in the positive electrode active material layer.

5. An electronic device, comprising the electrochemical device according to any one of claims 1 to 4.

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