Positive pole piece as well as electrochemical device and electronic equipment comprising positive pole piece

Abstract

The invention relates to a positive pole piece and an electrochemical device and electronic equipment comprising the same, and belongs to the technical field of electrochemical energy storage. The lithium ion battery comprises a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises a positive electrode active material, a lithium salt, a functional additive and an ionic conductor; the lithium salt comprises at least one of lithium bis (trifluoromethanesulfonyl) imide, lithium bis (oxalato) borate, lithium difluoro (oxalato) borate, lithium difluorosulfonyl imide, lithium tetrafluoroborate, lithium difluorophosphate and lithium trifluoromethanesulfonate. The lithium source can be released from the positive electrode, high-yield mass production compatibility can be achieved, only the pure organic solvent needs to be injected in the liquid injection stage, the system viscosity is reduced, the infiltration time is shortened, and the ion transport uniformity is improved; and in combination with a thermal activation process, lithium salt directional migration and interface in-situ film formation are triggered after winding and packaging, so that higher battery performance indexes are realized.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, and more particularly to positive electrode plates and electrochemical devices and electronic devices containing them. Background Technology

[0002] Currently, lithium-ion batteries generally adopt a mixed slurry coating process of "positive electrode active material + conductive agent + binder", while the lithium source depends entirely on the dissociable lithium salts in the electrolyte (such as LiPF6 and LiFSI).

[0003] Existing technologies include the incorporation of sacrificial lithium replenishing agents into the cathode slurry to release Li during the initial charge. + These materials compensate for the irreversible capacity of the negative electrode, but they generally suffer from problems such as high-temperature instability, easy oxidation, hydrolysis after coating, or partial failure during drying, resulting in large fluctuations in actual lithium replenishment efficiency and poor batch consistency. Furthermore, these solutions still require traditional salt electrolytes, failing to solve the core bottlenecks of high viscosity, slow liquid injection, and uneven lithium distribution at the interface. Summary of the Invention

[0004] The purpose of this application is to overcome the shortcomings of the prior art and provide a positive electrode and an electrochemical device and electronic device comprising the same. The positive electrode provided by this application can reduce system viscosity, shorten wetting time, improve ion transport uniformity, and comprehensively improve battery performance.

[0005] To achieve the above objectives, the technical solution adopted in this application is as follows: The first aspect of this application provides a positive electrode sheet, including a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer includes a positive active substance, a lithium salt, a functional additive and an ion conductor. The lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium dioxarate borate, lithium difluorooxarate borate, lithium difluorosulfonylimide, lithium tetrafluoroborate, lithium difluorophosphate, and lithium trifluoromethanesulfonate.

[0006] As an embodiment of this application, the positive electrode active material includes at least one of lithium nickel cobalt manganese oxide, lithium iron phosphate, and lithium manganese nickel cobalt oxide.

[0007] As an embodiment of this application, the functional additive includes at least one of lithium sulfide, lithium difluorophosphate, and fluoroethylene carbonate.

[0008] As an embodiment of this application, the ionic conductor comprises polyethylene oxide and lithium lanthanum zirconium oxide.

[0009] As an embodiment of this application, the Dv50 particle size of the lithium lanthanum zirconium oxide is 50-200 nm.

[0010] As an embodiment of this application, in the positive electrode active material layer, the mass percentage content of polyethylene oxide is w1, the mass percentage content of lithium lanthanum zirconium oxide is w2, and 0.2 ≤ w1 / w2 ≤ 3.

[0011] As an embodiment of this application, in the positive electrode active material layer, the mass percentage content of polyethylene oxide is w1, the mass percentage content of lithium lanthanum zirconium oxide is w2, and 0.5 ≤ w1 / w2 ≤ 1.7.

[0012] As an embodiment of this application, the total mass percentage of ionic conductors in the positive electrode active material layer is 2-8%.

[0013] As an embodiment of this application, the mass percentage of the positive electrode active material in the positive electrode active material layer is 60-85%.

[0014] As an embodiment of this application, the mass percentage of lithium salt in the positive electrode active material layer is 5-20%.

[0015] As an embodiment of this application, the mass percentage of functional additives in the positive electrode active material layer is 1-10%.

[0016] As an embodiment of this application, the positive electrode active material layer further includes a conductive agent, wherein the conductive agent has a mass percentage content of 0.5-3% in the positive electrode active material layer.

[0017] As an embodiment of this application, the positive electrode active material layer further includes a binder, wherein the binder has a mass percentage content of 1-3% in the positive electrode active material layer.

[0018] As an embodiment of this application, the conductive agent includes at least one of conductive carbon black, carbon nanotubes, and carbon fibers.

[0019] As an embodiment of this application, the other adhesives include polyvinylidene fluoride.

[0020] As an embodiment of this application, the method for preparing the positive electrode sheet described in this application includes the following steps: S1. The positive electrode active material, lithium salt, functional additives and ionic conductor are premixed by ball milling, and then the solvent, conductive agent and binder are added in sequence and ball milling is continued until uniform. The positive electrode active slurry is obtained by grinding and degassing. S2. The positive electrode active slurry is coated onto the positive electrode current collector, and then dried, shaped and compacted to obtain the positive electrode sheet.

[0021] As an embodiment of this application, the viscosity of the positive electrode active slurry at 25 °C is 18000-20000 cP.

[0022] A second aspect of this application provides an electrochemical device comprising a positive electrode as described above.

[0023] As an embodiment of this application, the electrochemical device further includes an electrolyte comprising a carbonate solvent and an ether solvent, wherein the carbonate solvent comprises 20-95% by mass and the ether solvent comprises 5-80% by mass. As an embodiment of this application, the carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, diphenyl carbonate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. As an embodiment of this application, the ether solvent includes at least one of diethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,4-dioxane, ethylene glycol diethyl ether, 1,2-dimethoxyethane, and 2-methyltetrahydrofuran.

[0024] A third aspect of this application provides an electronic device, including the electrochemical device described above.

[0025] Compared with the prior art, the beneficial effects of this application are as follows: The positive electrode sheet provided in this application uses a specific lithium salt that can be guaranteed to be completely stable in conventional electrode manufacturing processes, avoiding the process sensitivity issues of traditional routes and achieving high-yield mass production compatibility. It eliminates the need to add lithium salts or additives to the electrolyte, reducing the injection viscosity and shortening the wetting time, making it suitable for high-speed winding production lines. It allows the lithium source to be released directly from the positive electrode, naturally close to the electronic conductivity network, making it easier to control the directional migration path compared to the salt-loaded separator solution. It can generate a CEI film in situ, significantly reducing the increase in cycle impedance under high voltage, which is significantly better than traditional salt-containing electrolyte systems. When used in a production line, this positive electrode sheet requires no modification to existing coating machines, drying ovens, or cold presses; only hot rolling and parameter adjustments are needed, resulting in low implementation costs and suitability for rapid deployment in battery factories. Detailed Implementation

[0026] To better illustrate the purpose, technical solution, and advantages of this application, the following detailed description will be provided in conjunction with specific embodiments. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods; and unless otherwise specified, the materials and reagents used are commercially available.

[0027] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0028] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0029] Unless otherwise specified, all components, raw materials, or instruments used in the embodiments and comparative examples of this application are commercially available, and the components and raw materials used in each parallel experiment are the same.

[0030] In the following description, all figures disclosed herein are approximate values, regardless of whether the terms "about" or "approximately" are used in conjunction. They may vary by 1%, 2%, 5%, or sometimes 10% to 20%. Whenever a range of values ​​with a lower limit RL and an upper limit RU is disclosed, any values ​​falling within that range are specifically disclosed. Specifically, the following values ​​within this range are specifically disclosed: R = RL + k * (RU - RL), where k is a variable with a 1% increment from 1% to 100%, i.e., k is 1%, 2%, 3%, 4%, 5%, ..., 50%, 51%, 52%, ..., 95%, 96%, 97%, 98%, 99%, or 100%. Furthermore, any range of values ​​defined by the two R values ​​as defined above are also specifically disclosed.

[0031] General definition The term "positive electrode active material" refers to the core functional material in the positive electrode of a lithium-ion battery that can reversibly insert and extract lithium ions and realize the interconversion of electrical energy and chemical energy. It is the main source of battery capacity and voltage.

[0032] The term "functional additive" refers to auxiliary materials added in a low proportion (usually ≤5%, and ≤10% in some scenarios) to lithium battery systems to specifically optimize one or more performance shortcomings of the battery, and does not constitute the main functional phase of the system.

[0033] The term "ionic conductor" refers to a conductor that exhibits high ionic conductivity at a given temperature (typically ≥10°C at room temperature). -4 Materials capable of rapid directional transport of charge carriers such as lithium ions (S / cm) possess ion conductivity derived from ion vacancies, conduction channels, or coordination effects of polymer segments within their crystalline / amorphous structures, and exhibit extremely low electronic conductivity (typically ≤10). -10 S / cm, belonging to ion insulation).

[0034] The term "anionic internal covalent bond crystal structure" refers to the structure of lithium salt crystals where the cation (Li) is internally covalently bonded. +The interaction between the ion and the anion is an ionic bond, while the atoms inside the anion group are connected by strong covalent bonds to form a stable and rigid composite crystal configuration.

[0035] The term "Dv50 particle size" refers to the particle size value that corresponds to 50% of the cumulative volume in the particle size distribution of powder materials. It is also known as the median particle size or volume average particle size.

[0036] I. Positive electrode sheet This application provides a positive electrode sheet, including a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, wherein the positive active material layer includes a positive active substance, a lithium salt, a functional additive, and an ion conductor. The lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide (C2F6NO4S2Li, LiTFSI), lithium dioxalatoborate (C4BLiO8, LiBOB), lithium difluorooxalatoborate (C2F2BLiO4, LiDFOB), lithium difluorosulfonylimide, lithium tetrafluoroborate, lithium difluorophosphate, and lithium trifluoromethanesulfonate.

[0037] The aforementioned lithium salts all possess a strong covalent crystal structure and a high thermal decomposition temperature, enabling a vapor pressure <10 ohms within a drying range of 80-105℃. -5 Pa, and with almost no mass loss, no color change, and no gas release (TGA-MS verification), the lithium content deviation before and after drying is <0.5% as determined by ICP-OES, which can ensure stability and process compatibility during processing; at the same time, during the operation of the positive electrode, the above lithium salt will not decompose to produce oxygen that supports combustion and will not explode, thus avoiding safety risks.

[0038] In some embodiments, the positive electrode active material includes at least one of lithium nickel cobalt manganese oxide (such as NCM811), lithium iron phosphate (LFP), and lithium manganese nickel cobalt oxide (such as LMR-NMC).

[0039] In some embodiments, the functional additive includes at least one of lithium sulfide (Li2S), lithium difluorophosphate (LiPO2F2), and fluoroethylene carbonate (FEC).

[0040] In some embodiments, the ion conductor comprises polyethylene oxide (PEO) and lithium lanthanum zirconium oxide (LLZO).

[0041] The lithium salts selected in the positive electrode active material layer provided in this application all have anionic internal covalent bond crystal structures, which have high thermochemical stability, low volatility and non-reducing properties. Within the NMP / aqueous process window (≤120 ℃), the combination of the above lithium salts with functional additives can ensure zero loss, zero side reactions and zero structural damage in standard electrode manufacturing processes such as stirring, coating, vacuum drying (80-105 ℃), and rolling, maintaining the high stability of the positive electrode active layer. At the same time, no combustion-supporting substances are generated during use, which greatly reduces safety risks.

[0042] Meanwhile, by adding lithium salt to the positive electrode active material layer, this application enables the prepared positive electrode layer itself to become the main or even the sole lithium source carrier of the battery. This allows for the injection of only organic solvent as the electrolyte during the electrolyte filling stage, reducing system viscosity, shortening wetting time, and improving ion transport uniformity. The added functional additives assist film formation and suppress gas generation, while the ion conductors help lithium salt migrate and diffuse in the solid phase. Combined with the thermal activation process, this facilitates the triggering of directional lithium salt migration and in-situ interfacial film formation after winding and packaging.

[0043] Furthermore, the ionic conductor used in this application can soften and form a binder network during the hot rolling stage of battery preparation, and transform into a temperature-induced partial melting of lithium salt (such as the melting point of LiTFSI is 240 ℃, but it can be reduced to ≈90 ℃ in PEO to form a eutectic system). With the help of concentration gradient and potential field, a three-stage migration of "solid → liquid → interface embedding" is achieved, thereby suppressing dendrite formation.

[0044] The positive electrode sheet provided in this application can be used in electrochemical devices such as batteries. After encapsulation, it undergoes hot rolling at 0.5-3 MPa and 70-90 °C, followed by a formation activation step at 45-75 °C. This allows for the controllable release of lithium salt from the inside of the positive electrode towards the separator or negative electrode, completing interface pre-lithiation and SEI / CEI construction. This avoids the process sensitivity issues of traditional routes and achieves high compatibility. Furthermore, it significantly reduces the annual electrolyte injection time and immersion time, making it suitable for high-speed production lines. It also significantly improves the increase in cycle impedance while maintaining good cycle performance, which is superior to traditional salt-containing electrolyte systems and has high application value.

[0045] In some embodiments, the lithium lanthanum zirconium oxide (LLZO) may be Li7La3Zr2O. 12 Li 6.4 La3Zr 1.4 Ta 0.6 O 12 Li 7-x Al x La3Zr2O 12 Or doped and modified LLZO series such as niobium-doped LLZO (Li 6.5 La3Zr1.5 Nb 0.5 O 12 ), Yttrium-doped LLZO (Li 7-x Y x La 3-x Zr2O 12 )wait.

[0046] In some embodiments, the Dv50 particle size of the lithium lanthanum zirconium oxide is 50-200 nm, for example, it can be a range of 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm or any two of these values.

[0047] In some embodiments, the mass percentage of polyethylene oxide in the positive electrode active material layer is w1, the mass percentage of lithium lanthanum zirconium oxide is w2, and 0.2 ≤ w1 / w2 ≤ 3. For example, it can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.67, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, or any two of these values.

[0048] In some embodiments, the positive electrode active material layer contains polyethylene oxide by mass percentage w1 and lithium lanthanum zirconium oxide by mass percentage w2, and 0.5 ≤ w1 / w2 ≤ 1.7.

[0049] In some embodiments, the total mass percentage of ionic conductors in the positive electrode active material layer is 2-8%, for example, it can be 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8% or any two of these values.

[0050] In some embodiments, the mass percentage of the positive electrode active material in the positive electrode active material layer is 60-85%, for example, it can be 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 80.5%, 81%, 82%, 83%, 84%, 85%, or any two of these values.

[0051] In some embodiments, the mass percentage of lithium salt in the positive electrode active material layer is 5-20%, for example, it can be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, 19%, 19.5%, 20%, or a range of any two of these values.

[0052] In some embodiments, the mass percentage of functional additives in the positive electrode active material layer is 1-10%, for example, it can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, or any two of these values.

[0053] In some embodiments, the positive electrode active material layer further includes a conductive agent, and the mass percentage of the conductive agent in the positive electrode active material layer is 0.5-3%, for example, it can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3% or any two of these values.

[0054] In some embodiments, the positive electrode active material layer further includes a binder, wherein the mass percentage of the binder in the positive electrode active material layer is 1-3%, for example, it can be 1%, 1.5%, 2%, 2.5%, 3% or any two of these values.

[0055] In some embodiments, the conductive agent includes at least one of conductive carbon black, carbon nanotubes, and carbon fibers.

[0056] In some embodiments, the other binder includes polyvinylidene fluoride.

[0057] In some of these embodiments, the type of positive current collector is not particularly limited, and it may be any material known to be suitable for use as a positive current collector.

[0058] In some embodiments, the positive current collector includes metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum, as well as carbon materials such as carbon cloth and carbon paper.

[0059] There are no particular restrictions on the form of the positive electrode current collector. When the positive electrode current collector is a metallic material, it can be in the form of metal foil, metal cylinder, metal strip, metal plate, metal foil, metal mesh, stamped metal, foamed metal, etc. When the positive electrode current collector is a carbon material, it can be in the form of carbon plate, carbon film, carbon cylinder, etc.

[0060] II. Preparation method of positive electrode sheet This application provides a method for preparing the positive electrode sheet, comprising the following steps: S1. The positive electrode active material, lithium salt, functional additives and ionic conductor are premixed by ball milling, and then the solvent, conductive agent and binder are added in sequence and ball milling is continued until uniform. The positive electrode active slurry is obtained by grinding and degassing. S2. The positive electrode active slurry is coated onto the positive electrode current collector, and then dried, shaped and compacted to obtain the positive electrode sheet.

[0061] In some embodiments, the viscosity of the positive electrode active slurry at 25 °C is 18,000-20,000 cP.

[0062] III. Electrochemical Device This application provides an electrochemical device including a positive electrode as described above. In some embodiments, the electrochemical device further includes a negative electrode, a separator, and an electrolyte.

[0063] The electrochemical device of this application includes any device in which an electrochemical reaction occurs, and specific examples include all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0064] negative electrode The electrochemical device of this application includes a negative electrode, wherein the negative electrode includes a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector.

[0065] In some of these embodiments, the type of positive current collector is not particularly limited, and it may be any material known to be suitable for use as a positive current collector.

[0066] In some embodiments, the negative electrode current collector is a metal foil or a composite current collector. In this application, there are no particular limitations on the negative electrode current collector, as long as it can achieve the purpose of this application; for example, it can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector, etc.

[0067] In some embodiments, the negative electrode active layer includes a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent.

[0068] diaphragm The separator separates the negative and positive electrodes and provides a pathway for lithium-ion migration. The use of the separator is not particularly limited, as long as it is a separator commonly used in lithium-ion secondary batteries. In particular, separators with low resistance to electrolyte ion movement and excellent electrolyte permeability are preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes formed from polyolefin-based polymers (e.g., ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, ethylene / methacrylate copolymers, etc.) or laminated structures with two or more layers. Alternatively, nonwoven fabrics formed from conventional porous nonwoven fabrics (e.g., glass fibers with high melting points, polyethylene terephthalate fibers, etc.) can be used. Furthermore, coated separators containing ceramic components or polymer materials to ensure heat resistance or mechanical strength can be used, and can optionally be used as single-layer or multi-layer structures.

[0069] Generally, a diaphragm includes a substrate and a coating applied to the surface of the substrate.

[0070] electrolyte The electrolyte used in this application consists only of organic solvents and does not contain any dissociable lithium salts.

[0071] In some embodiments, the electrochemical device further includes an electrolyte comprising a carbonate solvent and an ether solvent, wherein the carbonate solvent comprises 20-95% by mass and the ether solvent comprises 5-80% by mass.

[0072] In some embodiments, the carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, diphenyl carbonate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. In some embodiments, the ether solvent includes at least one selected from diethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,4-dioxane, ethylene glycol diethyl ether, 1,2-dimethoxyethane, and 2-methyltetrahydrofuran.

[0073] Using a pure solvent as the electrolyte significantly reduces viscosity and allows for a synergistic mechanism with the positive electrode active material, preventing uneven ion flux caused by solute competitive migration and facilitating the release of Li from the positive electrode. + It becomes the dominant ion source.

[0074] IV. Electronic Equipment This application provides an electronic device, including the electrochemical device described above.

[0075] The electronic device described in this application is not particularly limited and may be any electronic device known in the prior art.

[0076] The application of the electrochemical device in this application is not particularly limited, and it can be used in any electronic device known in the prior art. According to some embodiments of this application, the electronic device includes, but is not limited to, mobile phones, smartphones, laptops, tablets, wearable devices, smartwatches, smart bracelets, smart glasses, power banks, televisions, game consoles, game controllers, digital cameras, smart speakers, headphones, keyboards, mice, monitors, drones, audio equipment, home appliances, toys, power tools, automobiles, motorcycles, electric bicycles, bicycles, robots, robot dogs, industrial robots, android robots, etc.

[0077] The following uses a lithium-ion battery as an example and combines specific embodiments to illustrate the preparation of a lithium-ion battery. Those skilled in the art will understand that the preparation method described in this application is only an example, and any other suitable preparation method is within the scope of this application.

[0078] In the following examples and comparative examples, the battery disassembly and pretreatment methods are as follows: the battery is frozen at -20 ℃ for 12 hours, then dissected at room temperature, and the electrode sheets are dried in a vacuum drying oven for 12 hours to remove residual electrolyte; In the following examples and comparative examples, the test method for the particle size of lithium lanthanum zirconium oxide Dv50 is as follows: using a laser particle size analyzer, LLZO powder is dispersed in anhydrous ethanol to form a suspension, the scattered light signal is collected by a detector and fitted by an algorithm to obtain the Dv50 particle size; In the following examples and comparative examples, the test methods for the mass percentage of positive electrode active material, lithium salt, functional additives, and ion conductor components in the positive electrode active material layer are as follows: The mass of the active material is determined by a combined verification method of standard ashing-ICP-OES + pyrolysis-TGA + XPS, calculated from the Co / Ni / Mn molar ratio. The lithium salt content is obtained by ICP correction after deducting the lithium source additives, with an error ≤ ±0.5%. The proportion of PEO in the fast ion conductor component is determined by the infrared characteristic peak normalization integration method, with an error range of ±0.3%. The LLZO content is calculated by ICP-La / Zr / Li total conversion. The inductively coupled plasma instrument used is a PerkinElmer 5110 model, and the samples are tested repeatedly more than three times. In the following examples and comparative examples, the method for testing the vapor pressure of lithium salt in the drying section at 80-120 °C is as follows: the lithium salt is placed in a Knudsen cell with tiny openings, and the vapor pressure is calculated by measuring the rate at which gas molecules escape from the openings under vacuum at 80-120 °C. In the following examples and comparative examples, the method for testing the thermal decomposition temperature of lithium salts is as follows: under an inert atmosphere, the lithium salt is linearly heated, and the change in sample mass with temperature is monitored in real time. The starting temperature at which the sample shows significant mass loss is the thermal decomposition temperature.

[0079] The sources of raw materials and parameters used in the following examples and comparative examples are shown in Table 1 below.

[0080] Table 1 Example 1 This application discloses a method for preparing a lithium-ion battery, comprising the following steps: (I) Preparation of the positive electrode S1. Slurry preparation steps: The positive electrode active material NCM811 (80.5 g), lithium salt LiTFSI (6.0 g), functional additive Li2S (2.5 g), ion conductor PEO (3.0 g), and LLZO with a Dv50 particle size of 100 nm (3.0 g) are pre-mixed by ball milling at 200 rpm for 30 min using an agate jar and zirconia balls. Add NMP (110 g, moisture <10 ppm) and stir for 60 minutes until homogeneous; continue to add the conductive agent Super P (3.0 g) and other binder PVDF (2.0 g) to the mixed slurry, and continue stirring for 30 minutes. Then transfer to a three-roll mill for grinding (pressure settings: 20 bar → 18 bar → 15 bar for 3 passes), vacuum degas for 30 minutes, and pass through a 100-mesh sieve to obtain the positive electrode active slurry with a solid content of 84.0%. S2. The slurry is coated onto an 8 μm thick aluminum foil using a slot extrusion coating machine (CT-7000) at a coating speed of 3.0 m / min (compatible with high-speed winding), with a wet thickness of 120 μm (dry thickness of 65 μm). The following drying conditions were used: NMP pre-drying at 75 °C for 2 minutes; main drying at 110 °C for 4 minutes; cooling and setting at 50 °C for 2 minutes. The material was processed using a constant pressure cold press at 18 MPa for 30 s, resulting in a compacted density of 3.65 g / cm³. 3 ; (II) Preparation of the negative electrode sheet: (iii) Separator: PE separator with a thickness of 7 μm.

[0081] (iv) Preparation of electrolyte: At room temperature, in a glove box filled with argon (H2O<1ppm, O2<1ppm), EMC and TTE are mixed evenly at a mass ratio of 4:1 to obtain electrolyte. The viscosity of the electrolyte (25 °C) measured by Ubbelohde viscometer method is 0.31 mPa·s.

[0082] (V): Assembly of lithium-ion batteries: The prepared positive electrode, separator and negative electrode are stacked in sequence, with the separator in the middle of the positive and negative electrode. After winding, hot pressing and shaping, Hi-pot test, and tab welding, bare cells are obtained. The bare cells are packaged in an outer aluminum-plastic film and baked in an oven at 100±5 ℃ for 48h. The electrolyte prepared above (injection coefficient of 4.0g / Ah) is injected into the dried battery. After standing, hot pressing, formation and capacity testing, lithium-ion batteries are obtained.

[0083] The hot pressing parameters are: temperature 85 ℃, pressure 2.0 MPa, and time 10 min. The formation parameters are: 0.05 C charged to 3.0 V; Charge to 3.8V at 0.1C; Discharge from 0.1 C to 3.0 V; Standardized to: 0.5 C to 4.3 V, constant voltage until current decays to 0.05 C.

[0084] Example 2-10 The only difference between Examples 2-10 and Example 1 is that the positive electrode active material layer in the prepared positive electrode sheet uses different component selections, specifically: Example 2: Lithium salt LiTFSI was replaced with an equal mass of LiBOB; Example 3: Lithium salt LiTFSI was replaced with an equal mass of LiDFOB; Example 4: The functional additive Li2S was replaced with an equal mass of LiPO2F2; Example 5: The functional additive Li2S was replaced with an equal mass of FEC; Example 6 replaces PEO in the ionic conductor with an equal mass of P (BVIM-TFSI); In Examples 7-10, the nano LLZO in the ionic conductors was replaced with nano LLZO of the same series with Dv50 particle sizes of 20 nm, 50 nm, 200 nm and 500 nm, respectively.

[0085] The comparison between Examples 2-10 and Example 1 is shown in Table 2 below.

[0086] Table 2 Examples 11-21 The only difference between Examples 11-21 and Example 1 is that the positive electrode active material layer in the prepared positive electrode sheet uses different component mass percentage ratios (keeping the amount of conductive agent and binder unchanged), as shown in Table 3 below.

[0087] Table 3 Comparative Examples 1-5 The specific differences between Comparative Examples 1-5 and Example 1 are as follows: In Comparative Example 1, no lithium salt was added to the positive electrode active material layer, while LiPF6 was added to the electrolyte to make its concentration 1 M. In Comparative Example 2, an equal amount of LiClO4 was used to replace the lithium salt LiTFSI in the positive electrode active material layer; Thermal roll pressing activation was not performed during the preparation of Comparative Example 3 battery; The positive electrode active material layer prepared in Comparative Example 4 did not contain the functional additive Li2S; The positive electrode active material layer prepared in Comparative Example 5 does not contain ionic conductor PEO or nano LLZO.

[0088] Example of effect To investigate the performance of the positive electrode and lithium-ion battery provided in this application, the following tests were conducted: (1) Cycling performance: Cycling performance was tested using the Xinwei BTS4000 test system. 500 cycles were performed at a 0.5C rate with limited voltage, and the ambient temperature was 25±2℃. The first charge capacity (Qc1) and discharge capacity (Qd1) were recorded and the first efficiency was calculated.

[0089] (2) In-plane SOC of electrode: The SOC distribution in the electrode was determined by sampling in 9 regions and comparing it with the Li content of ICP-OES. ΔSOC is the maximum SOC deviation value.

[0090] (3) Interface impedance: The interface impedance was tested using a Solartron 1260 EIS system with a frequency range of 10 mHz to 100 kHz and an AC amplitude of 5 mV at 25±1℃. The SEI film resistance value was analyzed using ZView software combined with the Randle model.

[0091] (4) Lithium dendrite suppression: Refer to (1) 200 cycles, test the length of lithium dendrites, observe by Cryo-FIB cross-section cutting + SEM, and calculate the average of 5 regions for each sample.

[0092] The test results are shown in Table 4 below.

[0093] Table 4 As shown in Table 4: The positive electrode sheet provided in this application significantly improves the cycle performance and cycle capacity stability of the battery. It can suppress dendrite growth, achieving an initial efficiency of over 91.6%, a capacity retention rate of over 81.2% after 500 cycles, and a dendrite length of less than 5.5 μm after 200 cycles. Furthermore, it exhibits excellent interface performance, with an in-plane ΔSOC below 4.6%, and a minimum of less than 2.5%. After 50 cycles, the interface impedance is 11.8 Ω·cm. 2 the following.

[0094] In contrast, Comparative Example 1 used a traditional lithium salt addition method, resulting in a significant decrease in stability, a significant decrease in cycle capacity retention, a significant increase in interfacial impedance, and lithium dendrites penetrating the separator. Comparative Example 2 used LiClO4 to replace the lithium salt specified in this application. However, because LiClO4 released combustion-supporting gases during cycling, the battery caught fire and failed. Comparative Example 3 did not implement hot rolling activation, resulting in rapid overall performance degradation, a significant increase in interfacial impedance, and lithium dendrites penetrating the separator after cycling. Comparative Example 4 did not add any functional additives to the positive electrode active material layer, which mainly caused a significant increase in interfacial impedance, a decrease in cycle capacity retention, and obvious lithium dendrite precipitation, resulting in poor performance. Comparative Example 5 did not add ionic conductor PEO and nano-LLZO to the positive electrode active material layer, resulting in a significant decrease in cycle capacity retention, a significant increase in interfacial impedance, lithium dendrites penetrating the separator, and a significant deterioration in lithium plating suppression performance.

[0095] In summary, this application provides a positive electrode sheet that uses a specific lithium salt in the positive electrode active material layer, ensuring complete stability in conventional electrode manufacturing processes. This avoids the process sensitivity issues of traditional lithium salt oxidation, decarboxylation, and hydrolysis, achieving high-yield mass production compatibility. Since the positive electrode can be used as a lithium source, there is no need to add lithium salt or additives to the electrolyte, significantly reducing costs and shortening the wetting time to ≤25 s, making it suitable for high-speed winding lines. The lithium source is released from the positive electrode, naturally close to the electronic conductive network, making it easier to control the directional migration path compared to the membrane salt loading scheme. The degree of lithium insertion / extraction is highly consistent in different regions, increasing performance gains. It can generate a high-LiF, BO / PO rich CEI film in situ, significantly reducing the increase in cycling impedance under high voltage and improving electrochemical performance, which is significantly superior to traditional salt-containing electrolyte systems.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A positive electrode plate, characterized in that, It includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer includes a positive electrode active substance, a lithium salt, a functional additive, and an ion conductor. The lithium salt includes at least one of lithium bis(trifluoromethanesulfonyl)imide, lithium dioxarate borate, lithium difluorooxarate borate, lithium difluorosulfonylimide, lithium tetrafluoroborate, lithium difluorophosphate, and lithium trifluoromethanesulfonate.

2. The positive electrode sheet as described in claim 1, characterized in that, The functional additives include at least one of lithium sulfide, lithium difluorophosphate, and fluoroethylene carbonate.

3. The positive electrode sheet as described in claim 1, characterized in that, The ionic conductor comprises polyethylene oxide and lithium lanthanum zirconium oxide.

4. The positive electrode sheet as described in claim 3, characterized in that, The Dv50 particle size of the lithium lanthanum zirconium oxide is 50-200 nm.

5. The positive electrode sheet as described in any one of claims 3-4, characterized in that, In the positive electrode active material layer, the mass percentage of polyethylene oxide is w1, the mass percentage of lithium lanthanum zirconium oxide is w2, and 0.2 ≤ w1 / w2 ≤ 3.

6. The positive electrode sheet as described in claim 1, wherein the total mass percentage of ionic conductors in the positive electrode active material layer is 2-8%.

7. The positive electrode sheet as described in claim 1, characterized in that, The mass percentage of the positive electrode active material in the positive electrode active material layer is 60-85%; And / or, the lithium salt content in the positive electrode active material layer is 5-20% by mass; And / or, the mass percentage of functional additives in the positive electrode active material layer is 1-10%.

8. The positive electrode sheet as described in claim 1, characterized in that, The positive electrode active material layer further includes a conductive agent, wherein the conductive agent has a mass percentage content of 0.5-3% in the positive electrode active material layer; And / or, the positive electrode active material layer further includes a binder, wherein the binder has a mass percentage content of 1-3% in the positive electrode active material layer.

9. An electrochemical device, characterized in that, Includes the positive electrode sheet as described in any one of claims 1-8.

10. The electrochemical device according to claim 9, characterized in that, The electrochemical device further includes an electrolyte comprising carbonate solvents and ether solvents, wherein the carbonate solvents constitute 20-95% by mass and the ether solvents constitute 5-80% by mass.

11. The electrochemical device according to claim 10, characterized in that, The carbonate solvents include at least one of ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, diphenyl carbonate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. And / or, the ether solvent includes at least one of diethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,4-dioxane, ethylene glycol diethyl ether, 1,2-dimethoxyethane, and 2-methyltetrahydrofuran.

12. An electronic device, characterized in that, Includes the electrochemical device as described in any one of claims 9-11.

Images