An electrochemical device and an electronic device including the same

Abstract

The present application relates to an electrochemical device comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte, the negative electrode sheet comprising a negative electrode active layer, the positive electrode sheet comprising a positive electrode active layer, the positive electrode active layer comprising a positive electrode active material, the positive electrode active layer comprising an aluminum element, wherein a content A (mmol) of the aluminum element in the positive electrode active layer and a total area B (mm 2 ) of the negative electrode active layer satisfy: 3≤A / B≤25, the positive electrode active material comprising lithium manganate and a manganese-containing compound.

Description

Technical Field

[0001] This application relates to the field of energy storage, specifically to an electrochemical device and an electronic device comprising the electrochemical device. Background Technology

[0002] Electrochemical devices such as lithium-ion batteries have seen their market share increase year by year due to their advantages such as light weight and high energy density. With the rapid development of new energy vehicles and energy storage, there is a demand for higher charge and discharge capacity in positive electrode active materials such as lithium manganese oxide, as well as for electrochemical devices to have better cycle performance and storage performance. Summary of the Invention

[0003] According to one aspect of this application, this application relates to an electrochemical device comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode includes a negative active layer, the positive electrode includes a positive active layer, the positive active layer includes a positive active material, and the positive active layer includes aluminum, wherein the content A (mmol) of the aluminum in the positive active layer is proportional to the total area B (m²) of the negative active layer. 2 The following conditions must be met: 3 ≤ A / B ≤ 25. The positive electrode active material includes lithium manganese oxide and manganese-containing compounds. Aluminum can stabilize the crystal structure, improve the cell stability during lithium ion insertion or extraction, make the positive electrode active material structure more stable, and improve the cycle performance of the electrochemical device. Manganese-containing compounds have a lower voltage plateau, which can replenish the lithium ions consumed by lithium manganese oxide in the formation of the CEI film during the first charge, provide a diffusion channel for lithium ions, facilitate the insertion and rapid extraction of lithium ions, and facilitate the slow re-insertion of lithium ions during cycling and storage, thereby improving the charge and discharge capacity of the positive electrode active material. When the aluminum content A (mmol) of the positive electrode active layer and the total area B (m²) of the negative electrode active layer are equal, the positive electrode active material can achieve the desired effect. 2 When the above relationship is satisfied, the structure of lithium manganese oxide and manganese-containing compounds can be made more stable, and the synergistic effect of lithium manganese oxide and manganese-containing compounds can be brought into play, significantly improving the cycle performance and high-temperature storage performance of electrochemical devices.

[0004] In some embodiments, the aluminum content A (mmol) in the positive electrode active layer and the total area B (m²) of the negative electrode active layer are... 2 The following condition must be met: 8 ≤ A / B ≤ 23.

[0005] In some embodiments, the manganese-containing compound comprises 3% to 20% by mass, based on the mass of the positive electrode active material.

[0006] In some embodiments, the range of A is 0.005 to 0.04.

[0007] In some embodiments, the range of A is 0.01 to 0.035.

[0008] In some embodiments, the average particle size of the lithium manganese oxide is C μm, and the average particle size of the manganese-containing compound is D μm, satisfying: 1≤D / C≤15.

[0009] In some embodiments, the manganese-containing compound satisfies at least one of the following conditions: (1) the Dv50 of the manganese-containing compound is 5 μm to 40 μm; (2) the surface of the manganese-containing compound has a step with a width of 1 nm to 1000 nm.

[0010] In some embodiments, the tap density of the positive electrode active material is 1.5 g / cm³. 3 Up to 2.5g / cm 3 .

[0011] In some embodiments, the positive electrode active layer further contains at least one of the elements Nb, Mg, Ti, Ce, W, Ga, Zr, W, Y, V, Na, Sr, Mo, Cr, Sn, or La.

[0012] In some embodiments, based on the mass of the positive electrode active layer, the mass percentage M of the elements Nb, Mg, Ti, Ce, W, Ga, Zr, W, Y, V, Na, Sr, Mo, Cr, Sn, or La is from 0.01% to 3.5%.

[0013] In some embodiments, the negative electrode active layer comprises a negative electrode active material, the negative electrode active material comprising graphite, wherein the d(002) of the graphite is...

[0014] In some embodiments, at least one of the following conditions is met: (1) the OI value of the graphite is 4±1; (2) the porosity of the negative electrode active layer is 25±5%; (3) the compaction density of the negative electrode sheet is 1.3 g / cm³. 3 Up to 1.8 g / cm 3 .

[0015] In some embodiments, the compaction density of the positive electrode sheet is 2.2 g / cm³. 3 Up to 2.8 g / cm 3 .

[0016] According to another aspect of this application, this application relates to an electronic device that includes an electrochemical device according to any of the foregoing embodiments.

[0017] In this application, the positive electrode active layer includes aluminum, and the aluminum content A (mmol) in the positive electrode active layer is related to the total area B (m²) of the negative electrode active layer. 2The following conditions must be met: 3 ≤ A / B ≤ 25, and the positive electrode active material includes lithium manganese oxide and manganese-containing compounds. Aluminum can make the structure of the positive electrode active material more stable, while manganese-containing compounds can replenish the lithium ions consumed by the formation of the CEI film during the first charge of lithium manganese oxide, and also provide diffusion channels for lithium ions, thereby improving the charge and discharge capacity of the positive electrode active material. When the aluminum content A (mmol) of the positive electrode active layer and the total area B (m²) of the negative electrode active layer are... 2 When the above relationship is satisfied, the structures of lithium manganese oxide and manganese-containing compounds become more stable, and the synergistic effect of lithium manganese oxide and manganese-containing compounds is utilized, significantly improving the cycle performance and high-temperature storage performance of the electrochemical device. Therefore, the electrochemical device described in this application, as well as the electronic device containing it, can simultaneously possess significantly improved cycle performance and high-temperature storage performance. Attached Figure Description

[0018] Figure 1(a) and Figure 1(b) are SEM images of the positive electrode active material of Example 1-1. Detailed Implementation

[0019] The present application will now be described in detail. It should be understood that the terminology used in the specification and appended claims should not be construed as limited to its general and dictionary meanings, but rather interpreted based on the meanings and concepts corresponding to the technical aspects of the present application, on the basis of the principle that the inventor is permitted to appropriately define the terms for best interpretation. Therefore, the descriptions of the embodiments described in the specification are merely specific examples for illustrative purposes and are not intended to show all technical aspects of the present application, and it should be understood that many alternative equivalents and variations may be made thereto at the time of filing this application.

[0020] In the detailed description and claims, a list of items connected by the terms "one of," "among," "a kind of," or other similar terms may mean any of the listed items. For example, if items A and B are listed, then the phrase "one of A and B" means only A or only B. In another example, if items A, B, and C are listed, then the phrase "one of A, B, and C" means only A; only B; or only C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0021] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0022] Additionally, quantities, ratios, and other numerical values ​​are sometimes presented in range format in this document. It should be understood that such range format is for convenience and brevity and should be interpreted flexibly to include not only the numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0023] I. Electrochemical Device

[0024] According to one aspect of this application, this application relates to an electrochemical device comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode includes a negative active layer, the positive electrode includes a positive active layer, the positive active layer includes a positive active material, and the positive active layer includes aluminum, wherein the content A (mmol) of the aluminum in the positive active layer is proportional to the total area B (m²) of the negative active layer. 2 The following conditions must be met: 3 ≤ A / B ≤ 25. The positive electrode active material includes lithium manganese oxide and manganese-containing compounds. The manganese-containing compounds can supplement lithium manganese oxide, replenishing the lithium ions consumed during the formation of the positive electrode-electrolyte interface (CEI) of the positive electrode active material during the first charge. This is beneficial for improving the cycle performance and high-temperature storage performance of the electrochemical device. It provides a diffusion channel for lithium ions, facilitating their insertion and rapid extraction. Furthermore, it has a lower voltage plateau (e.g., a 3.9V plateau), which facilitates the slow re-insertion of lithium ions during the cycle and storage of the electrochemical device, thereby increasing the charge-discharge capacity of the positive electrode active material and significantly improving the cycle performance and high-temperature storage performance of the electrochemical device. Simultaneously, aluminum can improve the cell stability during lithium ion insertion or extraction, making the crystal structure more stable and improving the structural stability of the positive electrode active material, thus improving the cycle performance of the electrochemical device. However, excessive aluminum content will reduce the amount of lithium insertion / extraction, lowering the reversible capacity. Therefore, the aluminum content A (mmol) in the positive electrode active layer and the total area B (m²) of the negative electrode active layer are limited. 2The following conditions must be met: 3 ≤ A / B ≤ 25; Manganese compounds can replenish the lithium ions consumed by lithium manganese oxide during the first charge to form the CEI film, and can also provide diffusion channels for lithium ions, thereby improving the charge and discharge capacity of the positive electrode active material. When the aluminum content A (mmol) of the positive electrode active layer and the total area B (m²) of the negative electrode active layer are equal, the charge and discharge capacity of the positive electrode active material is improved. 2 When the above relationship is satisfied, the structures of lithium manganese oxide and manganese-containing compounds can be made more stable, and the synergistic effect of lithium manganese oxide and manganese-containing compounds can be exerted, significantly improving the cycle performance and high-temperature storage performance of the electrochemical device. In some embodiments, the content A (mmol) of aluminum element in the positive electrode active layer and the total area B (m²) of the negative electrode active layer are related. 2 If the condition is satisfied that 8≤A / B≤23, then aluminum can more effectively stabilize the structure of lithium manganese oxide and manganese-containing compounds, further improving the cycle performance and high-temperature storage performance of electrochemical devices.

[0025] In some embodiments, A ranges from 0.005 to 0.04 mmol. Aluminum can improve the cell stability during lithium-ion insertion or extraction, making the crystal structure more stable, improving the structural stability of the positive electrode active material, and improving the cycle performance of the electrochemical device. However, when the aluminum content is too low, the improvement effect is limited, and when the aluminum content is too high, it will reduce the amount of lithium insertion / extraction and reduce the reversible capacity. Therefore, the aluminum content in the positive electrode active layer is limited to the range of 0.005 mmol to 0.04 mmol to further improve the cycle performance of the electrochemical device. In some embodiments, A ranges from 0.01 to 0.035 mmol. When the aluminum content is within this range, the positive electrode active material can have a more stable crystal structure, resulting in better cycle performance of the electrochemical device.

[0026] In some embodiments, the mass percentage of the manganese-containing compound is 3% to 20% based on the mass of the positive electrode active material. In some embodiments, the mass percentage of the manganese-containing compound is 3%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, or a range between any two of the foregoing values, based on the mass of the positive electrode active material.

[0027] When the content of manganese-containing compounds is too low, the initial charge specific capacity of the electrochemical device prepared from them decreases; when the content of manganese-containing compounds is too high, the initial coulombic efficiency of the electrochemical device prepared from them decreases. This is mainly because the manganese-containing compounds have a high initial charge specific capacity, which can compensate for the Li+ consumed by lithium manganese oxide in forming the CEI film during the first charge. However, during the first discharge, only a portion of Li can be re-intercalated from the manganese-containing compounds. Through research, limiting the content of manganese-containing compounds within the above-mentioned range significantly improves both the initial charge specific capacity and the initial coulombic efficiency of the electrochemical device.

[0028] In some embodiments, the manganese-containing compound has a layered structure. In some embodiments, the manganese-containing compound includes LiMn2O3, Li2MnO3, or LiNi. 0.5 Mn 0.5 One or more of O2.

[0029] In some embodiments, the lithium manganese oxide has an average particle size of C μm, and the manganese-containing compound has an average particle size of D μm, satisfying: 1 ≤ D / C ≤ 15. In some embodiments, 5 ≤ D / C ≤ 10.

[0030] In some embodiments, the manganese-containing compound satisfies at least one of the following conditions: (1) the Dv50 of the manganese-containing compound is 5 μm to 40 μm; (2) the surface of the manganese-containing compound has steps with a width of 1 nm to 1000 nm. In some embodiments, the compaction density of the positive electrode sheet is 2.2 g / cm³. 3 Up to 2.8 g / cm 3 In some embodiments, the tap density of the positive electrode active material is 1.5 g / cm³. 3 Up to 2.5g / cm 3 .

[0031] See appendix Figure 1(a) and 1(b) The larger particles are manganese-containing compound particles with a layered structure and a surface with stepped surfaces ranging from 1 nm to 1000 nm in width. By incorporating this layered manganese-containing compound into the positive electrode active material, the capacity, rate performance, high-temperature storage, and cycle performance of the electrochemical device are significantly improved. This is mainly because the layered manganese-containing compound replenishes the lithium ions consumed in the formation of CEI during the first charge of the electrochemical device, which is beneficial for improving the cycle and storage performance of the electrochemical device. It also provides diffusion channels for lithium ions, facilitating their insertion and rapid extraction. Furthermore, its low voltage plateau (3.9V) promotes slow re-insertion of lithium ions during cycling and storage, thereby increasing the charge / discharge capacity of the positive electrode active material.

[0032] On the other hand, the matching between manganese compound particles and lithium manganese oxide particles improves compaction density, enhances interparticle contact, increases active ion diffusion channels, improves the cycle performance of the electrochemical device, and improves electrolyte wetting. Smaller average particle size of lithium manganese oxide particles results in a larger specific surface area, leading to more severe manganese dissolution, which damages the cathode structure and deteriorates the cycle performance of the electrochemical device. Smaller manganese compound particle size exposes more active surface area for the same dosage, significantly improving the first-cycle charging capacity. Furthermore, smaller manganese compound particle size results in shorter lithium-ion diffusion channels, which is more conducive to lithium-ion insertion and extraction, thus improving the material's capacity and cycle life. By limiting the D / C ratio within the above range, ideal device performance can be obtained.

[0033] In some embodiments, the positive electrode active layer further comprises at least one of the elements Nb, Mg, Ti, Ce, W, Ga, Zr, W, Y, V, Na, Sr, Mo, Cr, Sn, or La. In some embodiments, based on the mass of the positive electrode active layer, the mass percentage M of the element Nb, Mg, Ti, Ce, W, Ga, Zr, W, Y, V, Na, Sr, Mo, Cr, Sn, or La is from 0.01% to 3.5%. In some embodiments, based on the mass of the positive electrode active material, the mass percentage M is 0.01%, 0.05%, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.4%, 2.6%, 2.8%, 3.0%, 3.2%, 3.4%, 3.5%, or a range between any two of the foregoing values. When the mass percentage M is within the above range, the above elements can stabilize the structure of the positive electrode active material, facilitate the diffusion of lithium ions, reduce material phase transitions, inhibit the dissolution of transition metals, and improve the cycle performance and high-temperature storage performance of the electrochemical device. However, excessive content of the above elements will cause the internal lattice of the positive electrode active material to expand, destroy the stability of the material structure, and affect the cycle performance of the electrochemical device.

[0034] In some embodiments, the negative electrode active layer comprises a negative electrode active material, the negative electrode active material comprising graphite, wherein the d(002) of the graphite is... The graphite that meets this condition has a better degree of graphitization. The better the degree of graphitization, the higher the crystallinity of the graphite, the denser the internal structure, and the higher the initial coulombic efficiency of the graphite. When combined with the aforementioned positive electrode active material with a higher charging capacity, the electrochemical device has a higher discharge capacity.

[0035] In some embodiments, the OI value of the graphite is 4 ± 1. A smaller OI value indicates better isotropy of the graphite, which is more conducive to improving Li+ solid-phase diffusion, thereby reducing the charge transfer resistance of the electrochemical device, improving graphite kinetics, and thus enhancing the cycle performance of the electrochemical device. In some embodiments, the OI value of the graphite is 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, or a range between any two of the aforementioned values.

[0036] The graphite described in this application has higher surface crystallinity and fewer surface defects, which is conducive to lithium ion diffusion. At the same time, the graphite has a single-particle structure and better kinetics. Under the combined effect of these two factors, the charge transfer resistance (Rct) of the negative electrode sheet is significantly reduced.

[0037] In some embodiments, the porosity of the negative electrode active layer is 25±5%. When the porosity of the negative electrode active layer exceeds the above range, more electrolyte will be consumed during the SEI film formation process, thereby reducing the initial coulombic efficiency of the electrochemical device. At the same time, the consumption of electrolyte will affect the cycle performance of the electrochemical device.

[0038] In some embodiments, the compaction density of the negative electrode sheet is 1.3 g / cm³. 3 Up to 1.8 g / cm 3 Within this compaction density range, the particles possess a suitable effective active area, and the particle surface remains undamaged, which is beneficial for improving the initial coulombic efficiency of graphite and increasing the battery's discharge capacity. Simultaneously, a suitable compaction density facilitates better electrolyte wetting, improves kinetics, and thus enhances the cycle performance of the electrochemical device.

[0039] According to another aspect of this application, this application relates to an electronic device that includes an electrochemical device according to any of the foregoing embodiments.

[0040] II. A method for preparing the aforementioned electrochemical device

[0041] The preparation method of the electrochemical device of this application is described in detail below, taking a lithium-ion battery as an example.

[0042] Preparation of negative electrode: The negative electrode active material, conductive agent, binder and thickener are dispersed in a solvent system in a certain mass ratio and thoroughly mixed. The mixture is then coated on the negative electrode current collector, dried and cold-pressed to obtain the negative electrode sheet.

[0043] As an example, the negative electrode active material can be natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, SiO, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, or spinel-structured lithium titanate Li4Ti5O. 12 One or more of Li-Al alloys and metallic lithium; the conductive agent may be one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers; the binder may be one or more of styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), water-based acrylic resin and carboxymethyl cellulose (CMC); the thickener may be carboxymethyl cellulose (CMC).

[0044] The negative electrode current collector can be made of materials such as metal foil or porous metal plate, for example, using metals such as copper, nickel, titanium or iron or their alloys, such as copper foil.

[0045] Preparation of the positive electrode:

[0046] Preparation of manganese-containing compounds in positive electrode active materials:

[0047] a) Place Mn3O4 in a corundum crucible and heat it to 500℃ at a heating rate of 5℃ / min under an air atmosphere and keep it at a constant temperature for 1h to obtain anhydrous Mn3O4.

[0048] b) Weigh anhydrous Mn3O4 and LiOH in a molar ratio of Li:Mn of 1.05:1, mix them using a mixing device for 8 hours, and simultaneously add nano-Al2O3 in a molar ratio of Al:Mn of 0.08:1 to obtain a mixed precursor.

[0049] c The mixture precursor was placed in a corundum crucible and heated to 2m. 3 Nitrogen gas is introduced at a rate of 1 h, and the temperature is increased to 940°C at a rate of 5°C / min and maintained at a constant temperature for 10 h. The mixture is then allowed to cool naturally to room temperature to obtain the manganese-containing compound.

[0050] The positive electrode active material (lithium manganese oxide (LiMn2O4)), the aforementioned manganese-containing compound, conductive agent, and binder are mixed in a certain weight ratio, added to a solvent, and stirred evenly to obtain a slurry. The slurry is uniformly coated onto the positive electrode current collector aluminum foil and dried at 90°C to obtain the initial positive electrode sheet. The initial positive electrode sheet is then subjected to cold pressing, cutting, and other processes to obtain the final positive electrode sheet.

[0051] In some embodiments, the conductive agent improves the conductivity of the positive electrode active layer by providing a conductive path to the active material. The conductive agent may include at least one of the following: acetylene black, Ketjen black, natural graphite, carbon black, carbon fiber, metal powder, or metal fiber (e.g., copper, nickel, aluminum, or silver), but examples of the conductive agent are not limited thereto. In some embodiments, the amount of the conductive agent may be suitably adjusted. Based on the total amount of 100 parts by weight of the positive electrode active material, the conductive agent, and the positive electrode binder, the amount of the conductive agent ranges from 1 part by weight to 30 parts by weight.

[0052] In some embodiments, examples of the solvent include, but are not limited to, N-methylpyrrolidone, acetone, or water. In some embodiments, the amount of solvent may be adjusted appropriately.

[0053] In some embodiments, the binder improves the adhesion between the positive electrode active material particles and between the positive electrode active material particles and the current collector. Examples of the positive electrode binder include, but are not limited to, one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), ethylene-vinyl acetate copolymer (EVA), and polyvinyl alcohol (PVA). Based on the total amount of active material, conductive agent, and positive electrode binder, the amount of the positive electrode binder ranges from 1 part by weight to 30 parts by weight.

[0054] In some embodiments, the current collector has a thickness ranging from 3 μm to 20 μm, but this disclosure is not limited thereto. The current collector is conductive and does not cause adverse chemical changes in the manufactured battery. Examples of the current collector include copper, stainless steel, aluminum, nickel, titanium, or alloys (e.g., copper-nickel alloys), but this disclosure is not limited thereto. In some embodiments, the surface of the current collector may include fine irregularities (e.g., surface roughness) to enhance the adhesion of the current collector surface to the active material. In some embodiments, the current collector may be used in various forms, including films, sheets, foils, meshes, porous structures, foams, or barrier materials, but this disclosure is not limited thereto.

[0055] Separator: The embodiments of this application do not particularly limit the separator, which comprises a polyolefin microporous membrane and a coating (applied to the surface of a polyethylene microporous membrane). The separator is selected from one or more of polyethylene (PE), ethylene-propylene copolymer, polypropylene (PP), ethylene-butene copolymer, ethylene-hexene copolymer, and ethylene-methyl methacrylate copolymer, and is a single-layer or multi-layer polyolefin microporous membrane. The coating comprises inorganic ceramic particles, which are selected from one or more of SiO2, Al2O3, CaO, TiO2, ZnO2, MgO, ZrO2, and SnO2.

[0056] Electrolyte: According to embodiments of this application, the electrolyte comprises a non-aqueous organic solvent and a lithium salt. The non-aqueous organic solvent may comprise carbonates, carboxylic acid esters, ether compounds, sulfone compounds, or other aprotic solvents. Examples of carbonate solvents include dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, butene carbonate, and bis(2,2,2-trifluoroethyl) carbonate. Examples of ether compound solvents include ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, dibutyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, bis(2,2,2-trifluoroethyl) ether, 1,3-dioxane, and 1,4-dioxane. Examples of sulfone compound solvents include ethyl vinyl sulfone, methyl isopropyl sulfone, isopropyl sec-butyl sulfone, and sulfolane.

[0057] According to embodiments of this application, the non-aqueous organic solvent in the electrolyte can be a single non-aqueous organic solvent or a mixture of multiple non-aqueous organic solvents. When a mixed solvent is used, the mixing ratio can be controlled according to the desired performance of the electrochemical device.

[0058] According to embodiments of this application, the lithium salt in the electrolyte includes or is selected from at least one of organic or inorganic lithium salts, and the lithium salt includes or is selected from lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(oxalato)borate (LiB(C2O4)2, LiBOB), lithium difluorooxalato)borate (LiBF2(C2O4), LiDFOB), lithium hexafluoroantimonyrate (LiSbF6), lithium hexafluoroarsenate (LiAsF6), lithium perfluorobutyl sulfonate (LiC4F9SO3), lithium perchlorate (LiClO4), lithium aluminate (LiAlO2), lithium tetrachloroaluminate (LiAlCl4), lithium bis(sulfonyl)imide (LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2), where x and y are natural numbers, lithium chloride (LiCl), and lithium fluoride (LiF), at least one of these.

[0059] Electrolyte preparation: In an argon-atmospheric glove box with a water content <10ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP), and propyl propionate (PP) were mixed uniformly in a mass ratio of 1:1:1:1:1. Then, thoroughly dried lithium salt LiPF6 was dissolved in the above non-aqueous solvent to obtain the basic electrolyte, wherein the mass percentage of LiPF6 was 12.5%.

[0060] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The resulting bare cell is then wound. The wound bare cell is placed in outer packaging, injected with electrolyte, and sealed. After processes such as formation, degassing, and edge trimming, a lithium-ion battery is obtained.

[0061] III. Electronic Devices

[0062] This application provides an electronic device that includes the electrochemical device described above.

[0063] According to some embodiments of this application, the electronic device includes, but is not limited to: laptop computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, and large household batteries, etc.

[0064] IV. Specific Implementation Examples

[0065] The following uses a lithium-ion battery as an example to further describe this application in detail. However, it should be understood that the following embodiments are merely examples, and the embodiments of this application are not limited thereto.

[0066] Performance testing methods

[0067] Test methods for particle morphology and particle size

[0068] Particle morphology: SEM images of the positive electrode sheets obtained from disassembled lithium-ion batteries were taken using a scanning electron microscope (JEOL JSM-6360LV) to observe the particle morphology of the positive electrode active material.

[0069] Measurement of average particle size: SEM images of the positive electrode sheet obtained from the disassembled lithium-ion battery were taken using a scanning electron microscope to observe the positive electrode active material particles. Then, using image analysis software, 30 particles were randomly selected from the SEM images, and the area of ​​each particle was calculated. Next, assuming that the particles are spherical, the particle diameter D was calculated using the following formula: D = 2 × (S1 / π)¹ / ², where S1 is the area of ​​the particle. The particle diameters of the 30 particles were then averaged arithmetically to obtain the average particle size.

[0070] Test method for compacted density

[0071] The positive electrode sheet (double-sided coated) was obtained by disassembling the lithium-ion battery. An area of ​​1540.25 mm² was cut from the region of the positive electrode sheet coated with the positive active layer. 2 The small circular piece was weighed, and its weight m1 and thickness d1 were measured. Simultaneously, a piece with an area of ​​1540.25 mm² was also cut from the blank current collector region of the positive electrode. 2 The small round pieces are weighed, and their weight m0 and thickness d0 are measured. The compacted density is calculated as (m1-m0) / 2 / 1540.25 / ((d1-d0) / 2).

[0072] Element content testing methods

[0073] The positive electrode sheet is obtained by disassembling the lithium-ion battery. The positive electrode sheet is cleaned with DMC. The positive active layer of the cleaned positive electrode sheet is scraped off with a scraper and dissolved in a mixed solvent (for example, 0.4g of positive active layer is dissolved in a mixed solvent of 10mL aqua regia (nitric acid and hydrochloric acid mixed in a 1:1 ratio) and 2mL HF). The volume is adjusted to 100mL. Then, the mass percentage of elements Nb, Mg, Ti, Ce, W, Ga, Zr, W, Y, V, Na, Sr, Mo, Cr, Sn or La in the solution is tested using an ICP (Inductively Coupled Plasma) analyzer.

[0074] Methods for testing interplanar spacing and OI value

[0075] X-ray diffraction analysis was performed on the graphite powder.

[0076] Instrument model: Bruker D8 ADVANCE, target material: Cu Kα, scanning angle: 5-80°.

[0077] Lithium-ion battery capacity testing: Initial charge / discharge capacity (mAh g) at -25°C and 0.2C conditions. -1 )

[0078] Four lithium-ion batteries were prepared using the cathode materials shown in the examples and comparative examples. Under constant temperature conditions of 25°C, they were first charged with a constant current of 0.5C (i.e., the current value at which the theoretical capacity is completely discharged within 2 hours) to 4.2V, and then charged with a constant voltage. Finally, they were discharged with a constant current of 0.2C to 2.8V. The capacity of the first discharge at 0.2C was calculated as the capacity of the battery.

[0079] First-cycle coulombic efficiency = First-cycle discharge capacity / First-cycle charge capacity

[0080] Cycle performance testing of lithium-ion batteries

[0081] Four lithium-ion batteries were prepared using the cathode materials shown in the examples and comparative examples. The four lithium-ion batteries were repeatedly charged and discharged using the following steps, and the discharge capacity retention rate of the batteries was calculated.

[0082] First, the initial charge and discharge cycles were performed at 25°C and 45°C respectively. The system first used a constant current of 0.5C to charge the battery to 4.2V, then used a constant voltage to charge it. Finally, it used a constant current of 1C to discharge the battery to 2.8V, and the discharge capacity of the first cycle was recorded. Then, 1500 and 400 charge and discharge cycles were performed, and the discharge capacity of the 1000 and 500th cycles was recorded.

[0083] 25℃ cycle capacity retention rate = (discharge capacity of the 1500th cycle / discharge capacity of the first cycle) × 100%.

[0084] 45℃ cycle capacity retention rate = (discharge capacity of the 400th cycle / discharge capacity of the first cycle) × 100%.

[0085] High-temperature storage test of lithium-ion batteries

[0086] Four lithium-ion batteries were prepared using the cathode materials shown in the examples and comparative examples. In an environment of 60°C, they were first charged with a constant current of 0.5C until 4.2V, then charged with a constant voltage, and then discharged with a constant current of 1C until 2.8V. The discharge capacity was recorded as the capacity before storage. The batteries were then charged with a constant current of 0.5C until 3.99V, and then charged with a constant voltage until the current dropped below 0.05C. After storing the batteries in a 60°C oven for 14 days, they were discharged with a constant current of 1C until 2.8V. Then, they were charged with constant current and constant voltage at a charging current of 0.5C until the upper limit voltage reached 4.2V, and then discharged with a constant current of 1C until 2.8V. The discharge capacity was recorded as the capacity after storage.

[0087] 60℃ high temperature storage capacity retention rate = (capacity after storage / capacity before storage) × 100%.

[0088] A. Examples 1-1 to 1-5 and Comparative Examples 1 to 2

[0089] Preparation method of Example 1-1:

[0090] positive electrode:

[0091] Step (1) - Preparation of manganese-containing compounds:

[0092] a) Place MnOOH in a corundum crucible and heat it to 500℃ at a heating rate of 5℃ / min under an air atmosphere and keep it at a constant temperature for 1h to obtain anhydrous Mn3O4.

[0093] b) Weigh anhydrous Mn3O4 and LiOH in a Li:Mn molar ratio of 1.05:1. Simultaneously, add nano-Al2O3 with an aluminum molar content of 0.014 mmol and nano-Cr2O3 with a Cr:Mn mass ratio of 0.213:1. Mix the above substances evenly using a sand mill and mix for 8 hours to obtain a mixed precursor.

[0094] c) Place the mixture precursor in an alumina crucible, at a depth of 2m 3 Nitrogen gas was introduced at a rate of 1 h, and the temperature was increased to 940 °C at a rate of 5 °C / min and held at a constant temperature for 10 h. The mixture was then allowed to cool naturally to room temperature to obtain a manganese-containing compound. The manganese-containing compound particles had steps with a width of 600 nm to 700 nm on their surface, and their Dv50 was 19.3 μm.

[0095] Step (2):

[0096] The manganese-containing compound, lithium manganese oxide, conductive carbon black (Super P), carbon nanotubes (CNTs), and polyvinylidene fluoride (PVDF) prepared in step (1) were mixed in a weight ratio of 90:5:1.8:1.2:2. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 0.75%, and the mixture was stirred evenly. The slurry was uniformly coated on both sides of the positive current collector aluminum foil and dried at 90°C to obtain the initial positive electrode sheet. The initial positive electrode sheet was then subjected to cold pressing and cutting processes to obtain the final positive electrode sheet.

[0097] Negative electrode: Graphite negative electrode active material, conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97:1.0:2.0. N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 0.8%, and the mixture is stirred evenly. The slurry is uniformly coated onto the copper foil of the negative electrode current collector and dried at 80°C to obtain the initial negative electrode sheet. The initial negative electrode sheet is then subjected to cold pressing and cutting processes to obtain the final negative electrode sheet.

[0098] Electrolyte: In an argon atmosphere glove box with a water content of <10ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP), and propyl propionate (PP) are mixed evenly in a mass ratio of 1:1:1:1:1. Then, fully dried lithium salt LiPF6 is dissolved in the above non-aqueous solvent to obtain the basic electrolyte, wherein the mass percentage of LiPF6 is 12.5wt%.

[0099] Separating membrane: PE porous polymer film is used as the separating membrane.

[0100] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. They are then wound, placed in an outer packaging, injected with the prepared electrolyte, and sealed. After formation, degassing, and edge trimming processes, a lithium-ion battery is obtained.

[0101] The only difference between Examples 1-2 to 1-5 and Example 1-1 is the content of manganese compound (the adjustment of the manganese compound content is based on a total weight fraction of 95% for manganese compound and lithium manganese oxide); the difference between Examples 1-6 and Example 1-1 is the content of manganese compound and the graphite used in the negative electrode, wherein the graphite in Examples 1-6 is non-high-efficiency graphite (its d(0002) = 3.3710 and OI value = 12.3 are respectively); the difference between Comparative Example 1 and Example 1-1 is that the positive electrode active material in Comparative Example 1 only contains lithium manganese oxide and does not contain manganese compound, and the aluminum content in the positive electrode active layer in Comparative Example 1 is 0.008 mmol. In Table 1, the average particle size of the manganese-containing compound is 18.9 μm, and the average particle size of lithium manganese oxide is 2.7 μm. The aluminum content in the positive electrode active layer of Examples 1-1 to 1-6 differs from that of Comparative Examples 1 and 2. With the increase of the manganese-containing compound content, the aluminum content per unit area of ​​the active layer increases. Please refer to Table 1 below for details, which shows the differences in composition and performance between the lithium-ion batteries of Examples 1-1 to 1-5 and Comparative Examples 1 and 2.

[0102] Table 1:

[0103]

[0104] Note: A is the aluminum content in the positive electrode active layer, in mmol; B is the total area of ​​the negative electrode active layer, in m². 2 .

[0105] As shown in Table 1, compared with Comparative Example 1, which only contains lithium manganese oxide as the positive electrode active material, the lithium-ion batteries of Examples 1-1 to 1-6, which contain lithium manganese oxide and manganese compounds as the positive electrode active material, showed significant improvements in the first discharge specific capacity at 25°C and 0.2C and the capacity retention rate after 1500 cycles at 25°C, while still maintaining a high first-cycle coulombic efficiency. Manganese compounds can replenish the lithium ions consumed by lithium manganese oxide during the initial charging process to form the positive electrode-electrolyte interface (CEI), thus improving the cycle performance and high-temperature storage performance of lithium-ion batteries. They provide diffusion channels for lithium ions, facilitating their insertion and rapid extraction. Furthermore, their relatively low voltage plateau (3.9V) promotes slow re-insertion of lithium ions during cycling and storage, thereby increasing the charge / discharge capacity of the positive electrode active material and significantly improving the cycle performance and high-temperature storage performance of lithium-ion batteries. However, during the initial discharge, only a portion of the Li in manganese compounds can be re-inserted, affecting the coulombic efficiency of the lithium-ion battery. Aluminum can stabilize the crystal structure, improving the cell stability during lithium ion insertion and extraction, making the positive electrode active material structure more stable and improving the cycle performance of the electrochemical device. When the aluminum content A (mmol) in the positive electrode active layer and the total area B (m²) of the negative electrode active layer are... 2 When 3≤A / B≤25, lithium-ion batteries can achieve better cycle performance and high-temperature storage performance.

[0106] B. Examples 1-1 and Examples 2-1 to 2-8

[0107] The only difference between Examples 2-1 to 2-8 and Example 1-1 is the graphite used in the negative electrode of Examples 2-1 to 2-8. Table 2 below shows the differences in the composition and performance of the lithium-ion batteries of Examples 1-1 and Examples 2-1 to 2-8.

[0108] Table 2:

[0109]

[0110] As shown in Table 2, with increasing graphitization temperature, d(002) decreases, and the higher the degree of graphitization, the higher the first-cycle coulombic efficiency and first-cycle discharge capacity of the lithium-ion battery prepared from it. However, excessively high temperatures increase cost while offering limited performance gains. Research indicates that when the d(002) of graphite is... At this stage, graphite exhibits good graphitization, high crystallinity, and a dense internal structure, resulting in high initial coulombic efficiency. When combined with the aforementioned positive electrode active material possessing high charging capacity, it enables lithium-ion batteries to achieve even higher discharge capacity.

[0111] C. Examples 1-1 and 3-1 to 3-4

[0112] The only difference between Examples 3-1 to 3-4 and Example 1-1 is the OI value of the graphite.

[0113] Table 3 below shows the differences in the composition and performance of the lithium-ion batteries in Examples 1-1 and 3-1 to 3-4.

[0114] Table 3:

[0115]

[0116] As can be seen from the examples in Table 3, when the OI value of the graphite is between 3 and 12, the lithium-ion battery prepared from it has better cycle performance. At this time, the graphite has better isotropy, which is conducive to improving the diffusion of Li+ solid phase, thereby reducing the charge transfer resistance of the lithium-ion battery, improving graphite kinetics, and thus improving the cycle performance of the lithium-ion battery.

[0117] D. Examples 1-1 and 4-1 to 4-3

[0118] The difference between Examples 4-1 to 4-3 and Example 1-1 lies only in the ratio (D / C) of the average particle size C (μm) of lithium manganese oxide to the average particle size D (μm) of the manganese-containing compound, and the resulting difference in electrode compaction density. The difference in D / C is primarily achieved by altering the particle size of the raw materials.

[0119] Table 4 below shows the differences in the composition and performance of the lithium-ion batteries in Examples 1-1 and 4-1 to 4-3.

[0120] Table 4:

[0121]

[0122] As shown in Table 4, the average particle size C μm of lithium manganese oxide and the average particle size D μm of manganese-containing compounds satisfy the following condition: 1 ≤ D / C ≤ 15.

[0123] The manganese compound particles and lithium manganese oxide particles are well-matched, resulting in better interparticle contact. This shortens the lithium-ion diffusion channel, facilitating lithium-ion insertion and extraction, increasing the material's capacity, improving the cathode compaction density, and enhancing the cycle performance and high-temperature storage performance of lithium-ion batteries. By limiting the D / C ratio within the aforementioned range, ideal device performance can be achieved.

[0124] E. Examples 1-1 and Examples 5-1 to 5-5

[0125] The only difference between Examples 5-1 to 5-5 and Example 1-1 is the compaction density of the negative electrode sheet. Table 5 below shows the differences in composition and performance of the lithium-ion batteries of Examples 1-1 and Examples 5-1 to 5-5.

[0126] Table 5:

[0127]

[0128] As shown in Table 5, when the compaction density of the negative electrode sheet is 1.3 g / cm³ 3 Up to 1.8 g / cm 3 At this time, the negative electrode active particles have a suitable effective active area and the particle surface is not damaged, which makes the lithium-ion battery have a higher initial coulombic efficiency and improves the discharge capacity of the lithium-ion battery. At the same time, the appropriate compaction density is conducive to better electrolyte wetting, improves the internal dynamics of the battery, and improves the cycle performance of the lithium-ion battery.

[0129] Throughout this specification, references to "some embodiments," "partial embodiments," "one embodiment," "another example," "example," "specific example," or "partial example" mean that at least one embodiment or example in this application includes a specific feature, structure, material, or characteristic described in that embodiment or example. Therefore, descriptions appearing throughout this specification, such as "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in an example," "in a specific example," or "example," do not necessarily refer to the same embodiments or examples in this application. Furthermore, specific features, structures, materials, or characteristics described herein can be combined in any suitable manner in one or more embodiments or examples.

[0130] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. An electrochemical device comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode includes a negative active layer, the positive electrode includes a positive active layer, the positive active layer includes a positive active material, and the positive active layer includes aluminum, wherein the content of the aluminum in the positive active layer is A mmol and the total area of ​​the negative active layer is B m. 2 The following conditions must be met: 3 ≤ A / B ≤ 25, and the positive electrode active material includes lithium manganese oxide and manganese-containing compounds; wherein, The range of A is 0.005 to 0.04, the negative electrode active layer includes a negative electrode active material, the negative electrode active material includes graphite, and the d(002) of the graphite is 3.363 ± 0.004 Å; wherein, the manganese-containing compound includes one or more of LiMn2O3 and Li2MnO3, and the aluminum element is located in the manganese-containing compound; the lithium manganese oxide includes LiMn2O4.

2. The electrochemical device according to claim 1, wherein, The electrochemical device satisfies at least one of the following: (1) The content of aluminum element A mmol in the positive electrode active layer and the total area B m of the negative electrode active layer 2 Satisfies: 8 ≤ A / B ≤ 23; (2) The range of A is 0.01 to 0.

035.

3. The electrochemical device according to claim 1, wherein, The average particle size of the lithium manganese oxide is C μm, and the average particle size of the manganese-containing compound is D μm, where D / C satisfies 1 ≤ D / C ≤ 15.

4. The electrochemical device according to claim 3, wherein, The D / C ratio satisfies 5 ≤ ​​D / C ≤ 10.

5. The electrochemical device according to claim 1, wherein the manganese-containing compound satisfies at least one of the following conditions: (1) The Dv50 of the manganese-containing compound is 5 μm to 40 μm; (2) The surface of the manganese-containing compound has steps with a width of 1 nm to 1000 nm.

6. The electrochemical device according to claim 1, wherein the positive electrode active layer further contains element Cr, wherein the mass percentage M of element Cr is from 0.01% to 3.5% based on the mass of the positive electrode active layer.

7. The electrochemical device according to claim 6, wherein at least one of the following conditions is satisfied: (1) The OI value of the graphite is 4±1; (2) The porosity of the negative electrode active layer is 25±5%; (3) The compaction density of the negative electrode sheet is 1.3 g / cm³. 3 Up to 1.8 g / cm 3 .

8. The electrochemical device according to claim 1, wherein the compaction density of the positive electrode sheet is 2.2 g / cm³. 3 Up to 2.8 g / cm 3 .

9. An electronic device comprising an electrochemical device according to any one of claims 1-8.

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