An electrochemical device and an electronic device including the same

Abstract

The application relates to an electrochemical device, which comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, the positive electrode sheet comprises a positive electrode active layer, the positive electrode active layer comprises a positive electrode active material, the positive electrode active material comprises an additive, the electrochemical device is subjected to charging and discharging, wherein when the electrochemical device is in a full discharge state, the positive electrode sheet has a characteristic diffraction peak 1 at a diffraction angle 2theta of 17.5-19.5 degrees in an X-ray diffraction pattern, wherein the additive contains manganese elements, can significantly improve the charging and discharging capacity of the positive electrode active material, and improves the cycle performance and high-temperature storage performance of the electrochemical device.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of energy storage, in particular to an electrochemical device and an electronic device comprising the same. BACKGROUND

[0002] Electrochemical devices such as lithium ion batteries have an increasing market share year by year due to their advantages of light weight, high energy density, etc. With the rapid development of new energy vehicles and energy storage, it is required that the positive active material such as lithium manganate has a higher charge and discharge capacity, and the electrochemical device has a more optimal cycle performance and storage performance. SUMMARY

[0003] According to an aspect of the present application, the present application relates to an electrochemical device, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, the positive electrode sheet comprising a positive active layer, the positive active layer comprising a positive active material, the positive active material comprising an additive, the electrochemical device being subjected to charge and discharge, wherein when the electrochemical device is in a full discharge state, the X-ray diffraction pattern of the positive electrode sheet has a characteristic diffraction peak 1 in the range of diffraction angle 2θ of 17.5° to 19.5°, and the additive contains manganese element. The additive can supplement the lithium ions consumed by the formation of the CEI film of the positive active material during the first charge, and can provide a diffusion channel for lithium ions, facilitating the embedding and rapid extraction of lithium ions, and the additive has a lower voltage platform, which is beneficial to the slow re-embedding of lithium ions during the cycle and storage process, thereby improving the charge and discharge capacity of the positive active material and significantly improving the cycle performance and high-temperature storage performance of the electrochemical device.

[0004] In some embodiments, the positive active material comprises lithium manganate.

[0005] In some embodiments, when the electrochemical device is in a full discharge state, the X-ray diffraction pattern of the positive electrode sheet further has a characteristic diffraction peak 2 in the range of diffraction angle 2θ of 17.5° to 19.5°.

[0006] In some embodiments, the peak position difference of the characteristic diffraction peak 1 and the characteristic diffraction peak 2 satisfies 0.33°≤Δθ1≤0.53°.

[0007] In some embodiments, the positive active material comprises lithium iron phosphate.

[0008] In some embodiments, when the electrochemical device is in a full discharge state, the X-ray diffraction pattern of the positive electrode sheet has a characteristic diffraction peak 3 in the range of diffraction angle 2θ of 19.8° to 21.8°.

[0009] In some embodiments, the peak position difference of the characteristic diffraction peak 3 and the characteristic diffraction peak 1 satisfies 2°≤Δθ2≤3°.

[0010] In some embodiments, the additive accounts for 3% to 20% of the mass of the positive electrode active material, based on the mass of the positive electrode active material, limiting the content of the additive within the above range can improve the initial charge specific capacity and the initial coulombic efficiency of the electrochemical device.

[0011] In some embodiments, the positive electrode active layer contains element M, the element M contains at least one of Al, Nb, Mg, Ti, Ce, W, Ga, Zr, W, Y, V, Na, Sr, Mo, Cr, Sn or La, the mass percentage of the element M is 0.03% to 3.5%, based on the mass of the positive electrode active layer, the element M can inhibit metal dissolution, stabilize the structure of the positive electrode active material, improve the diffusion of lithium ions, and improve the cycle performance and high-temperature storage performance of the electrochemical device.

[0012] In some embodiments, the mass percentage of the element M is 0.3% to 1.5%, based on the mass of the positive electrode active layer.

[0013] In some embodiments, the electrolyte contains an electrolyte additive, the electrolyte additive includes at least one of a sulfur-oxygen double bond compound, vinylene carbonate or fluoroethylene carbonate, the mass percentage of the electrolyte additive is 0.001% to 10%, based on the mass of the electrolyte. The electrolyte additive can stabilize the original morphology and structure of the positive electrode active material, while forming a dense interface protection film on the surface of the positive electrode sheet, improving the stability of the positive electrode material, reducing the positive electrode interface impedance, and further improving the cycle performance of the electrochemical device. In some embodiments, the mass percentage of the electrolyte additive is 0.01% to 5%, based on the mass of the electrolyte.

[0014] In some embodiments, the sulfur-oxygen double bond compound contains at least one of 1,3-propane sulfone lactone (PS), 1,3-propylene sulfone lactone (PES) or vinyl sulfate (DTD).

[0015] In some embodiments, the positive electrode active material contains aluminum element, the mass percentage of the aluminum element is C%, based on the mass of the positive electrode active material, the mass percentage of the vinylene carbonate (VC) in the electrolyte is D%, C / D satisfies 0.03≤C / D≤0.5. Adding aluminum element can further stabilize the structure of the positive electrode active material, and VC can form a stable CEI film on the positive electrode interface. By controlling the mass percentage of the aluminum element and VC to satisfy the above relationship, the structure of the positive electrode active material can be further stabilized, and the high-temperature storage performance and cycle performance of the electrochemical device can be improved.

[0016] In some embodiments, the additive particles have a layered structure, and the surface thereof has steps with a width of 1 nm to 1000 nm. By adding the layered structure manganese-containing compound additive to the positive electrode active material, active ions consumed in the formation of CEI during the first charge of the electrochemical device can be supplemented, which is conducive to improving the cycle and storage performance of the electrochemical device, and at the same time, diffusion channels for lithium ions can be provided, the charge and discharge capacity of the positive electrode active material is improved, and the rate performance, high-temperature storage and cycle performance of the electrochemical device are further improved.

[0017] In some embodiments, the average particle size of the additive is F, and F ranges from 5 μm to 40 μm. When the average particle size of the additive is controlled within the above range, the charge and discharge capacity of the positive electrode active material can be improved, and the high-temperature storage and cycle performance of the electrochemical device is improved.

[0018] According to another aspect of the present application, the present application relates to an electronic device comprising the electrochemical device according to any one of the preceding embodiments.

[0019] In the present application, the additive containing manganese element is added to the positive electrode active material, and the X-ray diffraction pattern of the positive electrode tab of the electrochemical device in the full discharge state has a characteristic diffraction peak 1 in the range of diffraction angle 2θ of 17.5° to 19.5°. The added manganese-containing additive can supplement the lithium ions consumed in the formation of the CEI film of the positive electrode active material during the first charge, and at the same time, diffusion channels for lithium ions can be provided, which facilitates the insertion and rapid extraction of lithium ions, and the additive has a lower voltage platform, which is conducive to the slow reinsertion of lithium ions during the cycle and storage process, thereby improving the capacity of the positive electrode active material and significantly improving the cycle performance and high-temperature storage performance of the electrochemical device. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is the XRD pattern of the positive electrode tab of the electrochemical device of Example 1-1 in the full discharge state.

[0021] Figure 2 is the XRD pattern of the positive electrode tab of the electrochemical device of Comparative Example 1-1 in the full discharge state.

[0022] Fig. 3(a) and Fig. 3(b) are SEM images of the positive electrode active material of Example 1-1 in the full discharge state. DETAILED DESCRIPTION

[0023] Hereinafter, the present application is described in detail. It should be understood that the terms used in the specification and the appended claims should not be construed as limited to general and dictionary meanings, but interpreted in conjunction with the meaning and concepts of the technical aspects of the present application based on the principle that the inventors are allowed to define appropriate terms in order to best explain the application. Therefore, the description set forth in the specification and the appended claims is merely exemplary and explanatory, and it should be understood that the scope of the present application is not limited to the embodiments set forth in the specification and the appended claims. Embodiments shown in the description of the embodiments described in the specification are merely specific examples and are not intended to show all technical aspects of the present application, and it should be understood that various alternative equivalents and modifications can be made thereto at the time of filing the present application.

[0024] In the DETAILED DESCRIPTION and in the claims, a list of items joined by the term "one of," "one," "an," or similar term means any single one of the listed items. For example, if a list of items A and B is provided, the phrase "one of A and B" means only A or, alternatively, only B. In another example, if a list of items A, B, and C is provided, the phrase "one of A, B, and C" means only A, or, only B, or, only C.

[0025] In the DETAILED DESCRIPTION and in the claims, a list of items joined by the term "at least one of," "at least one," "one or more of," or similar term means any combination of the listed items. For example, if a list of items A and B is provided, the phrase "at least one of A and B" means only A, or, alternatively, only B, or, additionally, A and B. In another example, if a list of items A, B, and C is provided, the phrase "at least one of A, B, and C" means only A, or, only B, or, only C, or, additionally, A and B (excluding C), or, additionally, A and C (excluding B), or, additionally, B and C (excluding A), or, additionally, A, B, and C. Item A can include a single element or multiple elements. Item B can include a single element or multiple elements. Item C can include a single element or multiple elements.

[0026] In addition, quantities, ratios, and other numerical values are sometimes presented in a range format. It is to be understood that such range format is used for convenience and brevity and should be construed as having been followed had the numerical values been recited individually, to the same extent as if each numerical value were individually recited herein.

[0027] I. Electrochemical devices

[0028] According to an aspect of the present application, the present application relates to an electrochemical device, comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, 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 material comprising an additive, the electrochemical device being subjected to charge and discharge, wherein, when the electrochemical device is in a full discharge state, the positive electrode sheet has a characteristic diffraction peak 1 in the range of diffraction angle 2θ of 17.5° to 19.5° in an X-ray diffraction (XRD) pattern, wherein the additive contains manganese element. The characteristic diffraction peak 1 is a characteristic diffraction peak of the additive. The additive can supplement lithium ions consumed by the positive electrode active material in forming a positive electrode-electrolyte interface (CEI) during the first charge, which is beneficial to improve the cycle performance and high-temperature storage performance of the electrochemical device, can provide diffusion channels for lithium ions, facilitate the embedding and rapid extraction of lithium ions; and has a lower voltage platform (such as a platform of 3.9V), which is beneficial to the slow re-embedding of lithium ions during the cycle and storage of the electrochemical device, thereby improving the charge and discharge capacity of the positive electrode active material.

[0029] In some embodiments, the additive comprises a manganese-containing compound with a layered structure. In some embodiments, the manganese-containing compound comprises at least one of LiMn2O3, Li2MnO3 or LiMnO2.

[0030] In some embodiments, the positive electrode active material comprises lithium manganate, and when the electrochemical device is in a full discharge state, the positive electrode sheet has a characteristic diffraction peak 2 in the range of diffraction angle 2θ of 17.5° to 19.5° in an X-ray diffraction pattern, and the peak position difference between the characteristic diffraction peak 1 and the characteristic diffraction peak 2 satisfies 0.33°≤Δθ1≤0.53°.

[0031] In some embodiments, the positive electrode active material comprises lithium iron phosphate, and when the electrochemical device is in a full discharge state, the positive electrode sheet has a diffraction peak 3 at a position of diffraction angle 2θ of 19.8° to 21.8°, and the peak position difference between the characteristic diffraction peak 3 and the characteristic diffraction peak 1 satisfies 2°≤Δθ2≤3°.

[0032] In some embodiments, the mass percentage of the additive is 3% to 20% based on the mass of the positive electrode active material. In some embodiments, the mass percentage of the additive is 3%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, or a range between any two of the aforementioned values, based on the mass of the positive electrode active material. When the content of the additive is too low, the first charge gram capacity of the electrochemical device prepared therefrom is reduced, and when the content of the additive is too high, the first coulombic efficiency of the electrochemical device prepared therefrom is reduced, mainly because the additive has a relatively high first charge gram capacity, which can compensate for the Li+ consumed by lithium manganate for forming a CEI film during the first charge, but only part of the Li can be re-embedded in the additive during the first discharge. Through research, the content of the additive is limited within the above range, and both the first charge gram capacity and the first coulombic efficiency of the electrochemical device are significantly improved. In some embodiments, the mass percentage of the additive is 3% to 15% based on the mass of the positive electrode active material, at which the electrochemical device has a relatively high first charge gram capacity and coulombic efficiency.

[0033] In some embodiments, the single-sided coating weight of the positive electrode active layer is 100 mg to 500 mg / 1540.25 mm 2 wherein the mass percentage of the positive electrode active material in the positive electrode active layer is 94% to 98%.

[0034] In some embodiments, the electrolyte comprises an electrolyte additive, which comprises at least one of a sulfur-oxygen double bond compound, vinylene carbonate (VC), or fluoroethylene carbonate (FEC), with a mass percentage of 0.001% to 10% of the electrolyte additive based on the mass of the electrolyte. In some embodiments, the mass percentage of the additive is 0.001%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range between any two of the foregoing values, based on the mass of the electrolyte. In some embodiments, the sulfur-oxygen double bond compound comprises at least one of 1,3-propane sultone (PS), 1,3-propene sultone (PES), or ethylene sulfate (DTD). Different electrolyte additives have different improvement effects on the battery system. Among them, VC and FEC can be used as CEI film-forming additives, and can form a more stable CEI film. VC and FEC can also increase the flexibility of the CEI film and reduce the impedance of the positive electrode interface. The compound containing sulfur-oxygen double bond can form a protective film at the positive and negative electrode interface, reduce the side reaction between the positive and negative electrode interface and the electrolyte, reduce the transmission impedance inside the battery, and is conducive to improving the room temperature and high temperature cycle performance and high temperature storage performance of the battery. The above electrolyte additives stabilize the original morphology and structure of the positive active material, and at the same time make the positive electrode plate surface form a dense interface film, improve the stability of the positive material, reduce the side reaction, thereby reducing the impedance of the material and improving the cycle performance of the battery. In some embodiments, the mass percentage of the electrolyte additive is 0.01% to 5%, at which the electrolyte additive can form a flexible protective film at the positive and negative electrode interface, reduce the interface impedance, and effectively improve the room temperature / high temperature cycle performance and high temperature storage performance of the electrochemical device.

[0035] In some embodiments, the positive electrode active layer comprises an element M, wherein M comprises at least one of Al, Nb, Mg, Ti, Ce, W, Ga, Zr, W, Y, v, Na, Sr, Mo, Cr, Sn, or La. In some embodiments, the mass percentage of element M is 0.03% to 3.5% based on the mass of the positive electrode active layer. In some embodiments, the mass percentage of element M is 0.03%, 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. Element M can stabilize the structure of the positive electrode active material, reduce phase transition, inhibit transition metal dissolution, facilitate diffusion of lithium ions, improve the cycle performance and high-temperature storage performance of the electrochemical device, and excessive content of element M can cause expansion of the internal lattice of the positive electrode active material, destroy the material structure stability, and affect the cycle performance of the electrochemical device. In some embodiments, the mass percentage of element M is 0.03% to 1.5% based on the mass of the positive electrode active layer, and within this content range, element M can effectively inhibit metal dissolution, improve the diffusion of lithium ions, and improve the cycle performance and high-temperature storage performance of the electrochemical device.

[0036] In some embodiments, the positive electrode active material comprises an aluminum element, the mass percentage of the aluminum element is C% based on the mass of the positive electrode active layer, the mass percentage of VC in the electrolyte is D%, and 0.03≤C / D≤0.5 is satisfied. The addition of the aluminum element further stabilizes the structure of the positive electrode active material, and VC can form a stable CEI film at the positive electrode interface. By controlling the mass percentage of the aluminum element and VC to satisfy the above relationship, the structure of the positive electrode active material can be further stabilized, and the high-temperature storage performance and cycle performance of the electrochemical device can be improved.

[0037] In some embodiments, the average particle size of the additive is F, F ranges from 5 μm to 40 μm, and the surface of the additive particles has steps with a width of 1 nm to 1000 nm. See FIG. 1. Figure 3(a) and 3(b)The larger particles are the particles of the additive, which are layered structures with a layer-by-layer step on the surface, wherein the width of the step is 1 nm to 1000 nm. By adding the layered structure 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 structure manganese-containing compound supplements the lithium ions consumed in the formation of CEI when the electrochemical device is first charged, which is beneficial to improve the cycle and storage performance of the electrochemical device, and at the same time, it provides a diffusion channel for lithium ions, facilitates the embedding and rapid extraction of lithium ions, and has a lower voltage platform (such as a 3.9V platform), which is beneficial to the slow re-embedding of lithium ions during the cycle and storage process, thereby improving the charge and discharge capacity of the positive electrode active material.

[0038] According to another aspect of the present application, the present application relates to an electronic device comprising the electrochemical device according to any one of the preceding embodiments.

[0039] II. Preparation of the electrochemical device

[0040] The preparation method of the electrochemical device of the present application is described in detail below taking a lithium ion battery as an example.

[0041] Preparation of the negative electrode: the negative electrode active material, the conductive agent, the binder, and the thickening agent are dispersed in the solvent system in a certain mass ratio, and then fully stirred and mixed uniformly, coated on the negative electrode current collector, and then dried and cold-pressed to obtain the negative electrode sheet.

[0042] As an example, the negative electrode active material can be one or more of natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, lithium titanate Li4Ti5O 12 , Li-Al alloy, and metallic lithium; the conductive agent can be one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; the binder can 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); and the thickening agent can be carboxymethyl cellulose (CMC).

[0043] The negative electrode current collector can use metal foil or porous metal plate materials, for example, foils or porous plates of metals such as copper, nickel, titanium, or iron, or their alloys, such as copper foil.

[0044] Preparation of the positive electrode:

[0045] Preparation of an additive in a positive electrode active material

[0046] a) The Mn304 was placed in a corundum crucible, heated to 500°C at a temperature increase rate of 5°C / min under an air atmosphere, and kept constant for 1 h to obtain anhydrous Mn304.

[0047] b) The anhydrous Mn304 was weighed with LiOH in a molar ratio of Li:Mn of 1.05:1, and nano-Al203 was added in a ratio of Al:Mn element mass ratio of 0.015:1, mixed for 8 h using a mixing device to obtain a mixture precursor.

[0048] c) The mixture precursor was placed in a corundum crucible, nitrogen was passed at a rate of 2 m 3 / h, heated to 940°C at a temperature increase rate of 5°C / min and kept constant for 10 h, and naturally cooled to room temperature to obtain the additive.

[0049] The positive electrode active material (lithium manganate (LiMn2O4), lithium iron phosphate or other positive electrode active material), the above-mentioned additive, the conductive agent, and the binder were mixed in a certain weight ratio, added to a solvent, and stirred uniformly to obtain a slurry. The slurry was uniformly coated on a positive electrode current collector aluminum foil, dried at 90°C to obtain an initial positive electrode sheet. The initial positive electrode sheet was subjected to cold pressing, cutting and other processes to obtain a positive electrode sheet.

[0050] 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 can include at least one of acetylene black, ketjen black, natural graphite, carbon black, carbon fiber, metal powder or metal fiber (such as copper, nickel, aluminum or silver), but examples of the conductive agent are not limited thereto. In some embodiments, the amount of the conductive agent can be appropriately adjusted. The amount of the conductive agent ranges from 1 part by weight to 30 parts by weight based on 100 parts by weight of the total amount of the positive electrode active material, the conductive agent and the positive electrode binder.

[0051] In some embodiments, examples of the solvent include, but are not limited to, N-methyl pyrrolidone, acetone or water. In some embodiments, the amount of the solvent can be appropriately adjusted.

[0052] In some embodiments, the binder improves the adhesion between the positive active material particles and between the positive active material particles and the current collector. Examples of the positive binder include, but are not limited to, the binder can be one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), ethylene-vinyl acetate copolymer (EVA), and polyvinyl alcohol (PVA). The amount of the positive binder ranges from 1 part by weight to 30 parts by weight, based on 100 parts by weight of the total amount of the active material, the conductive agent, and the positive binder.

[0053] In some embodiments, the current collector has a thickness ranging from 3 micrometers to 20 micrometers, but the present disclosure is not limited thereto. The current collector is electrically 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 alloy), but the present disclosure is not limited thereto. In some embodiments, the surface of the current collector can include fine irregularities (e.g., surface roughness) to enhance adhesion of the active material to the surface of the current collector. In some embodiments, the current collector can be used in various forms, examples of which include a film, a sheet, a foil, a mesh, a porous structure, a foam, or a non-turbid material, but the present disclosure is not limited thereto.

[0054] Separator: Embodiments of the present application do not particularly limit the separator, which includes a polyolefin microporous membrane, and a coating layer (coated on the surface of the polyethylene microporous membrane), the separator being selected from a single layer or a multilayer polyolefin microporous membrane composed of one or more of polyethylene (PE), ethylene-propylene copolymer, polypropylene (PP), ethylene-butene copolymer, ethylene-hexene copolymer, ethylene-methyl methacrylate copolymer. The coating layer includes inorganic ceramic particles selected from one or more of SiO2, Al2O3, CaO, TiO2, ZnO2, MgO, ZrO2, and SnO2.

[0055] Electrolyte: According to embodiments of the present application, the electrolyte includes a non-aqueous organic solvent and a lithium salt. The non-aqueous organic solvent can include a carbonate, a carboxylate, an ether compound, a sulfone compound, or other aprotic solvent. Examples of the carbonate solvent include dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, di(2,2,2-trifluoroethyl) carbonate, etc. Examples of the ether compound solvent 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, 1,4-dioxane, etc. Examples of the sulfone compound solvent include ethyl vinyl sulfone, methyl isopropyl sulfone, isopropyl sec-butyl sulfone, cyclobutyl sulfone, etc.

[0056] According to embodiments of the present application, the nonaqueous organic solvent in the electrolyte can use a single nonaqueous organic solvent, or a plurality of nonaqueous organic solvents can be mixed. When mixed solvents are used, the mixing ratio can be controlled according to the desired electrochemical device performance.

[0057] According to embodiments of the present application, the lithium salt in the electrolyte includes or is selected from at least one of an organic lithium salt or an inorganic lithium salt, and the lithium salt includes or is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(oxalato)borate (LiB(C2O4)2, LiBOB), lithium difluoro(oxalato)borate (LiBF2(C2O4), LiDFOB), lithium hexafluoroantimonate (LiSbF6), lithium hexafluoroarsenate (LiAsF6), lithium perfluorobutylsulfonate (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), wherein x and y are natural numbers, lithium chloride (LiCl), lithium fluoride (LiF).

[0058] Preparation of the electrolyte: In an argon atmosphere glove box with water content <10 ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP), and propyl propionate (PP) are mixed uniformly in a mass ratio of 1:1:1:1:1. A fully dried lithium salt LiPF6 is dissolved in the above nonaqueous solvent to obtain a base electrolyte, wherein the mass percentage of LiPF6 is 12.5%

[0059] The positive electrode, the separator, and the negative electrode are stacked in order, with the separator between the positive electrode and the negative electrode to play a separating role, and are wound to obtain a bare battery cell. The bare battery cell obtained by winding is placed in an outer package, electrolyte is injected and packaged, and a lithium ion battery is obtained through processes such as formation, degassing, and edge cutting.

[0060] III. Electronic device

[0061] The present application provides an electronic device comprising the electrochemical device according to the foregoing.

[0062] According to some embodiments of the present application, the electronic device includes, but is not limited to, a notebook computer, a pen input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a head-mounted stereo headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, an illuminating appliance, a toy, a game machine, a timepiece, an electric tool, a flashlight, a camera, a household large storage battery, and the like.

[0063] III. Specific Embodiments

[0064] The present application will be further described in detail below with lithium ion batteries as examples in combination with embodiments. However, it should be understood that the following embodiments are only examples, and the embodiments of the present application are not limited thereto.

[0065] Performance test method

[0066] XRD Test Method

[0067] A full discharge lithium ion battery was disassembled to obtain a positive electrode sheet, and the positive electrode sheet was subjected to XRD test. The positive electrode sheet was placed on a sample stage of an XRD testing instrument (Brucker, D8), a scanning rate of 2° / min was used, and a scanning angle range of 10° to 90° was used to obtain an XRD diffraction pattern. The corresponding diffraction peaks were read, and the peak position and half-peak width were recorded.

[0068] Particle Morphology Test

[0069] A lithium ion battery was disassembled to obtain a positive electrode sheet, and a scanning electron microscope (JSM-6360LV type of JEOL) was used to take SEM photos of the positive electrode sheet obtained by disassembling the lithium ion battery, and the particle morphology of the positive electrode active material was observed.

[0070] Average Particle Size Test

[0071] A lithium ion battery was disassembled to obtain a positive electrode sheet, and a scanning electron microscope was used to take SEM photos of the positive electrode sheet obtained by disassembling the lithium ion battery, and the particles of the positive electrode active material were observed. Then, 30 particles were randomly selected from the SEM photos using image analysis software, the areas of the particles were calculated, and then, assuming that the particles were spherical, the particle diameter D (diameter) of each particle was calculated using the following formula: D = 2 x (S1 / π)1 / 2; where S1 is the area of the particle; and the particle diameters of the 30 particles were arithmetically averaged to obtain the average particle diameter of the particles.

[0072] Element Content Test Method

[0073] The positive electrode sheet was obtained by disassembling the lithium ion battery, and the positive electrode sheet obtained by disassembling the lithium ion battery was washed with DMC. The positive electrode active layer of the washed positive electrode sheet was scraped off with a scraper. The positive electrode active layer was dissolved using a mixed solvent (for example, 0.4 g of the positive electrode active layer was dissolved using 10 ml of aqua regia (nitric acid and hydrochloric acid mixed at a ratio of 1:1) and 2 ml of HF), and the volume was made to 100 ml. Then, the mass percentage of Al, Nb, Mg, Ti, Ce, W, Ga, Zr, W, Y, v, Na, Sr, Mo, Cr, Sn, or La in the solution was tested using an ICP analyzer (based on the mass of the positive electrode active layer).

[0074] Capacity test of lithium ion battery - 25 °C 0.2C first discharge capacity (mAh g -1 )

[0075] Four lithium ion batteries prepared using the positive electrode materials shown in the examples and comparative examples were taken from each group, and the batteries were first charged at a current of 0.5C (i.e., a current value at which the theoretical capacity was completely discharged within 2h) under constant temperature conditions at 25°C, and then charged at a constant voltage after charging to 4.2V. Then, the batteries were discharged at a current of 0.2C to 2.8V, and the 0.2C first discharge capacity was calculated as the capacity of the battery.

[0076] Cycle performance test of lithium ion battery

[0077] Four lithium ion batteries prepared using the positive electrode materials shown in the examples and comparative examples were taken from each group, and the batteries were first charged at a current of 0.5C (i.e., a current value at which the theoretical capacity was completely discharged within 2h) under constant temperature conditions at 25°C, and then charged at a constant voltage after charging to 4.2V. Then, the batteries were discharged at a current of 0.2C to 2.8V, and the 0.2C first discharge capacity was calculated as the capacity of the battery.

[0078] First, the first charge and discharge were performed in an environment of 25 / 45°C, respectively. The batteries were first charged at a current of 0.5C, and then charged at a constant voltage after charging to 4.2V. Then, the batteries were discharged at a current of 1C to 2.8V, and the discharge capacity of the first cycle was recorded. Then, the batteries were subjected to 1500 / 400 cycles of charge and discharge, and the discharge capacity of the 1000th / 500th cycle was recorded.

[0079] 25°C cycle capacity retention rate = (discharge capacity of the 1500th cycle / discharge capacity of the first cycle) x 100%.

[0080] 45°C cycle capacity retention rate = (discharge capacity of the 400th cycle / discharge capacity of the first cycle) x 100%.

[0081] High-temperature storage test of lithium ion battery

[0082] Lithium ion batteries prepared using the positive electrode materials shown in the examples and comparative examples were taken 4 pieces per group, and were first charged at a current of 0.5C in an environment of 60°C, and then charged at a constant voltage after charging to 4.2V, and then discharged at a current of 1C to 2.8V, and the discharge capacity was recorded as the pre-storage capacity; charged at a constant current of 0.5C to 3.99V, and charged at a constant voltage until the current was less than 0.05C, and then the batteries were placed in a 60°C oven for storage for 14D, and then discharged at a constant current of 1C to 2.8V; then charged at a constant current and constant voltage at a charge current of 0.5C until the upper limit voltage was 4.2V, and then discharged at a constant current of 1C to 2.8V, and the discharge capacity was recorded as the post-storage capacity.

[0083] 60°C high-temperature storage capacity retention rate = post-storage capacity / pre-storage capacity x 100%.

[0084] A. Examples 1-1 to 1-8 and Comparative Example 1-2

[0085] Preparation method of Example 1-1:

[0086] Step (1):

[0087] a) The MnOOH was placed in a corundum crucible, heated to 500°C at a heating rate of 5°C / min under an air atmosphere and kept at a constant temperature for 1h to obtain anhydrous Mn3O4.

[0088] b) The anhydrous Mn3O4 was weighed with LiOH according to a molar ratio of Li:Mn of 1.05:1, and nano-Cr2O3 was added according to a Cr:Mn element mass ratio of 0.015:1, mixed using a mixing device for 8h to obtain a mixture precursor.

[0089] c) The mixture precursor was placed in a corundum crucible, nitrogen was passed at a rate of 2m 3 / h, heated to 940°C at a heating rate of 5°C / min and kept at a constant temperature for 10h, and naturally cooled to room temperature to obtain the additive. The average particle size of the additive was 18.9 microns, and the additive particle surface had steps with a width of 600nm to 700nm, which can be seen from FIG. 3(a) and FIG. 3(b).

[0090] Step (2): The positive active material lithium manganate (LiMn2O4) (average particle size of lithium manganate is 2.7 microns), the above-mentioned additive, conductive carbon black (Super P), carbon nanotube (CNT), polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 90:5:1.8:1.2:2, N-methyl pyrrolidone (NMP) is added as a solvent, a slurry with a solid content of 0.75 is prepared, and stirring is performed to obtain a slurry. The slurry is uniformly coated on both sides of the positive current collector aluminum foil, dried at 90°C, and an initial positive electrode sheet is obtained. The initial positive electrode sheet is subjected to cold pressing, cutting and other processes to obtain a positive electrode sheet.

[0091] Negative electrode: The graphite negative active material, conductive carbon black (Super P), polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97:1.0:2.0, N-methyl pyrrolidone (NMP) is added as a solvent, a slurry with a solid content of 0.8 is prepared, and stirring is performed to obtain a slurry. The slurry is uniformly coated on the negative current collector copper foil, dried at 80°C, and an initial negative electrode sheet is obtained. The initial negative electrode sheet is subjected to cold pressing, cutting and other processes to obtain a negative electrode sheet.

[0092] Electrolyte: In an argon atmosphere glove box with water content <10 ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP), propyl propionate (PP) are mixed uniformly in a mass ratio of 1:1:1:1:1, and then a fully dried lithium salt LiPF6 is dissolved in the above-mentioned non-aqueous solvent to obtain a basic electrolyte, wherein the mass percentage of LiPF6 is 12.5wt%

[0093] Separator: PE porous polymer film is used as a separator.

[0094] The positive electrode, the separator, and the negative electrode are stacked in order, with the separator between the positive and negative electrodes to serve as a separator, and are wound and placed in an outer package, injected with the prepared electrolyte and packaged, subjected to formation, degassing, edge cutting and other processes to obtain a lithium ion battery.

[0095] Examples 1-2 to 1-5 differ from Example 1-1 only in the different content of the additive (wherein the content of the additive is adjusted based on the total weight fraction of the additive and lithium manganate being 95%, the total weight of the additive and lithium manganate accounting for 95% of the weight of the positive active material), Example 1-6 differs from Example 1-1 in that lithium iron phosphate is used to replace lithium manganate (wherein the average particle size of the lithium iron phosphate is 0.4 microns), Examples 1-7 and 1-8 differ from Example 1-6 only in the different content of the additive (wherein the content of the additive is adjusted based on the total weight fraction of the additive and lithium iron phosphate being 95%, the total weight of the additive and lithium iron phosphate accounting for 95% of the weight of the positive active material), the positive active material of Comparative Example 1-1 only contains lithium manganate, and the positive active material of Comparative Example 1-2 only contains lithium iron phosphate. Please refer to Table 1 below for the differences in the composition of the electrochemical devices of Examples 1-1 to 1-8 and Comparative Examples 1-1 and 1-2, and the performance.

[0096] Table 1:

[0097]

[0098] Note: Diffraction peak 1 is the characteristic diffraction peak of the X-ray diffraction pattern of the positive electrode sheet at diffraction angle 2θ in the full discharge state. Peak position difference Δθ1 is the peak position difference between diffraction peak 1 and diffraction peak 2, and peak position difference Δθ2 is the peak position difference between diffraction peak 1 and diffraction peak 3, wherein the peak position difference is understood to be the absolute value. Comparative Example 1-1 has no peak of the additive, so the peak position difference Δθ1 in the above table is actually the diffraction peak 2 of the X-ray diffraction pattern of the positive electrode sheet prepared from lithium manganate at diffraction angle 2θ in the full discharge state. Comparative Example 1-2 has no peak of the additive, so the peak position difference Δθ2 in the above table is actually the diffraction peak 3 of the X-ray diffraction pattern of the positive electrode sheet prepared from lithium iron phosphate at diffraction angle 2θ in the full discharge state.

[0099] Reference is made to Table 1 and the accompanying Figure 1 、 Figure 2It can be seen that the positive electrode active layer of embodiments 1-1 to 1-8 contains an additive, and when the electrochemical device is in a full state, the X-ray diffraction (XRD) pattern of the positive electrode tab has a characteristic diffraction peak 1 in the range of diffraction angle 2θ of 17.5° to 19.5°. For lithium manganate positive electrode active material, comparative examples 1-1 to 1-5 and comparative example 1-1, for lithium iron phosphate positive electrode active material, comparative examples 1-6 to 1-8 and comparative example 1-2, it can be seen that compared with the corresponding comparative example without additive, the electrochemical performance (first discharge capacity at 25°C, 0.2C, capacity retention rate after 1500 cycles at 25°C, 400 cycles at 45°C, and high-temperature storage capacity retention rate at 60°C) of the embodiment with additive is significantly improved. This is mainly because the additive can supplement the Li consumed by the formation of SEI of the positive electrode active material during the first charge, which is beneficial to improve the cycle and storage performance of the lithium ion battery, can provide diffusion channels for lithium ions, facilitate the insertion and rapid extraction of lithium ions and have a lower voltage platform, which is beneficial to the slow re-embedding of lithium ions during the cycle and storage process, thereby improving the capacity of the positive electrode active material.

[0100] B. Embodiments 1-1 and 2-1 to 2-10

[0101] The difference between embodiments 2-1 to 2-10 and embodiment 1-1 is only the difference in the content of Al element in the positive electrode active layer of embodiments 2-1 to 2-7 and the difference in the content of VC in the electrolyte used. When aluminum element is added to the additive, the preparation process of embodiments 2-2 to 2-7 is different from that of embodiment 1-1 in step b): anhydrous Mn3O4 and LiOH are weighed according to the molar ratio of Li:Mn of 1.05:1, and nano-Al2O3 is added according to the required Al:Mn element ratio, mixed for 8h using a mixing device, to obtain a mixture precursor, and then an additive containing aluminum element is prepared, and the specific content is shown in Table 2. The difference between the composition of the electrochemical device of embodiments 1-1 and 2-1 to 2-7 and the performance is shown in the following Table 2.

[0102] Table 2:

[0103]

[0104] Note: C is the value of the mass percentage of aluminum element based on the mass of the positive electrode active layer; D is the value of the mass percentage of VC in the electrolyte.

[0105] As can be seen by referring to Table 2, by adding the aluminum element to the positive electrode active material, the cycle performance and high-temperature storage performance of the lithium ion battery can be further improved. For example, the capacity retention rate at 25°C for 1500 cycles, the capacity retention rate at 45°C for 400 cycles, and the high-temperature storage capacity retention rate at 65°C of Examples 2-1 to 2-7, which added the aluminum element, were all significantly improved relative to Example 1-1, which did not contain the aluminum element. This is mainly because the aluminum element can improve the cell stability when lithium ions are inserted or extracted, stabilize the crystal structure, and thus make the positive electrode active material structure more stable, improving the cycle performance of the lithium ion battery. The present application found that by limiting the type and content of the element to 0.1% to 3.5%, the lithium ion battery can have better performance. According to the present application, when 0.2≤A / B≤1.5 or 0.03≤C / D≤0.5, the cycle performance and high-temperature storage performance of the electrochemical device are better. Adding the aluminum element can further stabilize the structure of the positive electrode active material, and VC can form a stable CEI film at the positive electrode interface, and by controlling the mass percentage of the aluminum element and VC to satisfy the above relationship, the positive electrode active material and the positive electrode interface can be further stabilized, and the high-temperature storage performance and cycle performance of the lithium ion battery can be improved. In addition, it should be understood that the aluminum element can be added to the additive, added to the lithium manganate, or both the additive and the lithium manganate contain the aluminum element, to stabilize the crystal structure of the material, improve the material structure stability when lithium ions are inserted or extracted, and improve the cycle performance of the lithium ion battery. When the aluminum element is added to the additive, the difference from Example 1-1 is in step b): anhydrous Mn304 and LiOH are weighed according to a molar ratio of Li:Mn of 1.05:1, and nano-Al203 is added according to the desired molar ratio of Al:Mn, mixed using a mixing device for 8 h to obtain a mixture precursor. When the aluminum element is added to the lithium manganate, it can be prepared by those skilled in the art based on the conventional technical means in the art.

[0106] C. Example 1-1 and Examples 3-1 to 3-8

[0107] Examples 3-1 to 3-8 differ from Example 1-1 only in the type and content of the additive in the electrolyte.

[0108] The electrolyte was prepared as follows using Example 3-1 as an example: in an argon atmosphere glove box with water content < 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP), and propyl propionate (PP) were mixed in a mass ratio of 1:1:1:1:1, and then a fully dried lithium salt LiPF6 was dissolved in the above non-aqueous solvent to obtain an electrolyte, wherein the mass percentage of LiPF6 was 12.5%. 1,3-propane sultone (PS) was added to the electrolyte in an amount of 1.5% (based on the mass of the electrolyte).

[0109] The preparation method of the electrolyte of Examples 3-2 to 38 was basically the same as that of Example 3-1, and the only difference was the type and content of the electrolyte additive, for example, in addition to adding vinylene carbonate (VC) to the electrolyte in an amount of 1.5%, the steps of Example 3-1 were repeated.

[0110] The differences in the composition of the electrochemical devices of Example 1-1 and Examples 3-1 to 3-8 and the performance are shown in Table 3 below.

[0111] Table 3:

[0112]

[0113]

[0114] As can be seen from the examples in Table 3, by adding electrolyte additives, the performance of the electrochemical device can be further improved. For example, by adding at least one of 1,3-propane sultone (PS), vinylene carbonate (VC), 1,3-propylene sultone (PES), fluoroethylene carbonate (FEC), or ethylene sulfate (DTD) to the electrolyte, the high-temperature storage capacity retention rate of the electrochemical device at 25°C for 1500 cycles and at 60°C is improved. This is mainly because different electrolyte additives have different improvement effects on the battery system, among which VC and FEC can be used as CEI film-forming additives to form a more stable CEI film, VC and FEC can also increase the flexibility of the CEI film, reduce the impedance of the positive electrode interface, and compounds containing sulfur-oxygen double bonds can form a protective film at the positive and negative electrode interface, reduce the side reactions between the positive and negative electrode interface and the electrolyte, reduce the transmission impedance inside the lithium ion battery, and help to improve the room temperature and high temperature cycle performance and high temperature storage performance of the battery. The additives described in the present technology stabilize the original morphology and structure of the positive active material, and at the same time form a dense interface film on the positive electrode surface, improve the stability of the positive electrode material, reduce side reactions, thereby reducing the impedance of the material and improving the cycle performance of the lithium ion battery.

[0115] References in the specification to "some embodiments," "particular embodiments," "one embodiment," "another embodiment," "an embodiment," "some aspects," "some alternatives," "one alternative," "certain embodiments," "certain alternatives," "some implementations," "some examples," "one example," "certain examples," or "an example" are not necessarily to the same embodiment or example, and such references mean at least one. Furthermore, the particular features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments or examples. It will be apparent to those skilled in the art that various modifications and variations can be made to the present application without departing from the spirit and scope of the application. Thus, it is intended that the present application cover the modifications and variations of this application provided they come within the scope of the appended claims and their equivalents.

[0116] While the illustrative embodiments have been described and illustrated, it will be understood by those skilled in the art that the above-described embodiments are not the only ways in which the present application can be practiced. Changes can be made to the embodiments in light of the teachings of the present disclosure, and it is understood that well-known elements have not been described in order to not obscure the present application.

Claims

1. An electrochemical device comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte, wherein the positive electrode sheet comprises a positive electrode active layer, the positive electrode active layer comprises a positive electrode active material, and the positive electrode active material comprises an additive, wherein the electrochemical device is charged and discharged, wherein: When the electrochemical device is in a fully charged state, the X-ray diffraction pattern of the positive electrode sheet has a characteristic diffraction peak 1 within a diffraction angle 2θ range of 17.5° to 19.5°, and the additive includes manganese; The positive electrode active layer contains aluminum element, and based on the mass of the positive electrode active layer, the mass percentage of the aluminum element is C (%), the mass percentage of vinylene carbonate in the electrolyte is D%, and C / D satisfies 0.03≤C / D≤0.

5.

2. The electrochemical device according to claim 1, wherein the positive electrode active material comprises lithium manganate.

3. The electrochemical device according to claim 2, wherein when the electrochemical device is in a fully charged state, the X-ray diffraction pattern of the positive electrode plate further has a characteristic diffraction peak 2 within a diffraction angle 2θ range of 17.5° to 19.5°. 4 . The electrochemical device according to claim 3 , wherein a peak position difference Δθ1 between the characteristic diffraction peak 2 and the characteristic diffraction peak 1 satisfies 0.33°≤Δθ1≤0.53°. 5 . The electrochemical device according to claim 1 , wherein the positive electrode active material comprises lithium iron phosphate. 6 . The electrochemical device according to claim 5 , wherein when the electrochemical device is in a fully charged state, the X-ray diffraction pattern of the positive electrode sheet has a characteristic diffraction peak 3 within a diffraction angle 2θ range of 19.8° to 21.8°. 7 . The electrochemical device according to claim 6 , wherein a peak position difference Δθ2 between the characteristic diffraction peak 3 and the characteristic diffraction peak 1 satisfies 2°≤Δθ2≤3°. 8 . The electrochemical device according to claim 1 , wherein the additive has a mass percentage of 3% to 20% based on the mass of the positive electrode active material. 9 . The electrochemical device according to claim 8 , wherein the additive has an amount of 3% to 15% by mass based on the mass of the positive electrode active material.

10. The electrochemical device according to claim 1, wherein the positive electrode active layer comprises an element M, wherein the element M comprises at least one of Al, Nb, Mg, Ti, Ce, W, Ga, Zr, W, Y, V, Na, Sr, Mo, Cr, Sn, or La, and the mass percentage of the element M is 0.03% to 3.5% based on the mass of the positive electrode active layer. 11 . The electrochemical device according to claim 10 , wherein the mass percentage of the element M is 0.3% to 1.5% based on the mass of the positive electrode active layer.

12. The electrochemical device according to claim 1, wherein the electrolyte contains an electrolyte additive, the electrolyte additive comprising at least one of a sulfur-oxygen double bond compound, vinylene carbonate, or fluoroethylene carbonate, and the mass percentage of the electrolyte additive is 0.001% to 10% based on the mass of the electrolyte. 13 . The electrochemical device according to claim 12 , wherein the electrolyte additive has a mass percentage of 0.01% to 5% based on the mass of the electrolyte.

14. The electrochemical device according to claim 1, wherein the additive satisfies at least one of the following: (1) The average particle size of the additive is F, and F ranges from 5 μm to 40 μm; (2) The surface of the additive particle has steps with a width of 1 nm to 1000 nm.

15. An electronic device comprising the electrochemical device according to any one of claims 1 to 14.

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