Electrochemical device and electronic device including the same

Abstract

The present invention relates to an electrochemical device, which includes a positive electrode sheet, a negative electrode sheet, and an electrolytic solution. The positive electrode sheet includes a positive electrode active layer, the positive electrode active layer includes a positive electrode active material, the positive electrode active material includes an additive, and when the electrochemical device is charged and discharged and the electrochemical device is in a fully discharged state, the X-ray diffraction pattern of the positive electrode sheet has a characteristic diffraction peak 1 within the range of diffraction angle 2θ of 17.5° to 19.5°. The additive contains a manganese element. With this electrochemical device, the charge and discharge capacity of the positive electrode active material can be significantly increased, and the cycle characteristics and high-temperature storage characteristics of the electrochemical device can be improved.

Description

Technical Field

[0001] The present invention relates to the field of energy storage, and more specifically, to an electrochemical device and an electronic device including the electrochemical device.

Background Art

[0002] Electrochemical devices such as lithium-ion batteries have advantages such as being lightweight and having a high energy density, so their market share has been increasing year by year. With the rapid development of new energy vehicles and the field of energy storage, there is a demand for improving the charge and discharge capacity of cathode active materials such as lithium manganate, as well as improving the cycle characteristics and storage characteristics of electrochemical devices.

Summary of the Invention

[0003] According to a first aspect of the present invention, the present invention provides an electrochemical device, which includes a positive electrode plate, a negative electrode plate, and an electrolytic solution. The positive electrode plate includes a positive electrode active layer, the positive electrode active layer includes a positive electrode active material, the positive electrode active material includes an additive, and when the electrochemical device is charged and discharged and the electrochemical device is in a fully discharged state, the X-ray diffraction pattern of the positive electrode plate has a characteristic diffraction peak 1 within a range where the diffraction angle 2θ is 17.5° to 19.5°. The additive contains manganese element, and relates to an electrochemical device. The additive can supplement the lithium ions consumed by the formation of the CEI film during the first charge of the positive electrode active material, and can provide a diffusion path for the lithium ions, so it is convenient for the insertion and rapid release of lithium ions. In addition, since the additive has a relatively low voltage platform, it is advantageous for the slow re-insertion of lithium ions during the processes of cycling and storage, thereby increasing the charge and discharge capacity of the positive electrode active material and significantly improving the cycle characteristics and high-temperature storage characteristics of the electrochemical device.

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

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

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

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

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

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

[0010] In some embodiments, based on the mass of the positive electrode active material, the mass percentage of the additive in the positive electrode active material is 3% to 20%. By limiting the content of the additive within the above range, the capacity per gram and the initial Coulomb efficiency of the first charge of the electrochemical device can be increased.

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

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

[0013] In some embodiments, the electrolyte contains an electrolyte additive, the electrolyte additive contains at least one of a sulfur-oxygen double bond-containing compound, vinylene carbonate, and fluoroethylene carbonate, and based on the mass of the electrolyte, the mass percentage of the electrolyte additive is 0.001% to 10%. The electrolyte additive can stabilize the original form and structure of the positive electrode active material, form a dense interfacial protective film on the surface of the positive electrode sheet, enhance the stability of the positive electrode material, reduce the interfacial impedance of the positive electrode, and further improve the cycle characteristics of the electrochemical device. In some embodiments, based on the mass of the electrolyte, the mass percentage of the electrolyte additive is 0.01% to 5%.

[0014] In some embodiments, the sulfur-oxygen double bond-containing compound contains at least one of 1,3-propanesultone (PS), 1,3-propenesultone (PES), and divinyl sulfate (DTD).

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

[0016] In some embodiments, the particles of the additive have a layered structure, and there are steps with a width of 1 nm to 1000 nm on its surface. By adding the layered-structure manganese-containing compound additive to the cathode active material, the electrochemical device can replenish the active ions consumed by the formation of the CEI during the first charge, which is advantageous for improving the cycle characteristics and storage characteristics of the electrochemical device. Further, by adding the layered-structure manganese-containing compound additive to the cathode active material, a diffusion path is provided for lithium ions, so that the charge and discharge capacity of the cathode active material can be increased, and the rate characteristics, high-temperature storage characteristics and cycle characteristics of the electrochemical device can be further improved.

[0017] In some embodiments, when the average particle size of the additive is F, F ranges from 5 μm to 40 μm. By controlling the average particle size of the additive to be within the above range, the charge and discharge capacity of the cathode active material can be increased, and the high-temperature storage characteristics and cycle characteristics of the electrochemical device can be improved.

[0018] According to another aspect of the present invention, the present invention relates to an electronic device including the electrochemical device described in any one of the above embodiments.

[0019] In the present invention, by adding a manganese element-containing additive to the cathode active material, when the electrochemical device is in a fully discharged state, the X-ray diffraction pattern of the cathode sheet can have a characteristic diffraction peak 1 within a range where the diffraction angle 2θ is from 17.5° to 19.5°. The added manganese-containing additive can replenish the lithium ions consumed by the formation of the CEI film during the first charge of the cathode active material and can provide a diffusion path for lithium ions, which is convenient for the insertion and rapid release of lithium ions. Further, since the additive has a relatively low voltage platform, it is advantageous for the slow re-insertion of lithium ions during the cycling and storage processes, thereby increasing the capacity of the cathode active material and significantly improving the cycle characteristics and high-temperature storage characteristics of the electrochemical device.

Brief Description of the Drawings

[0020] [Figure 1] Figure 1 is an XRD diagram of the positive electrode plate in the fully discharged state of the electrochemical device of Example 1-1. [Figure 2] Figure 2 is an XRD diagram of the positive electrode plate in the fully discharged state of the electrochemical device of Comparative Example 1-1. [Figure 3] Figures 3(a) and 3(b) are SEM diagrams of the positive electrode active material of Example 1-1 in the fully discharged state.

Mode for Carrying Out the Invention

[0021] Hereinafter, the present invention will be described in detail. The terms used in the specification and the appended claims should not be construed as being limited to the general meaning and the meaning in the dictionary, and it should be understood that the terms should be appropriately defined so as to correspond to the technical aspects of the present application based on the principle that the inventor is allowed to interpret them optimally. Therefore, the embodiments described in the specification and the explanations based on the drawings are merely specific examples for explanation and are not intended to represent all the technical aspects of the present application. It should be understood that various alternative equivalents and modifications can be completed regarding this when submitting the present application.

[0022] In the specific embodiments and claims, a list of items connected by terms such as "one of", "one of", "one kind of", or other similar terms means any one of the listed items. For example, when items A and B are listed, the phrase "one of A and B" means only A or only B. In other examples, when items A, B, and C are listed, the phrase "one of A, B, and C" means only A, only B, or only C. Item A may include one element or a plurality of elements. Item B may include one element or a plurality of elements. Item C may include one element or a plurality of elements.

[0023] In specific embodiments and claims, a list of items connected by the terms "at least one of", "at least one", "at least one kind of", or other similar terms means any combination of the listed items. For example, if item A and item B are listed, the phrase "at least one of A and B" means only A, only B, or A and B. In other examples, if item A, item B, and item C are listed, the phrase "at least one of A, B, and C" means only A, 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 include one element or multiple elements. Item B may include one element or multiple elements. Item C may include one element or multiple elements.

[0024] Also, in this specification, quantities, ratios, and other numerical values may be presented in range form. Such range form is for the purpose of convenience and brevity and should be understood flexibly. The range form not only includes the numerical values clearly specified as range limitations, but also includes each and every numerical value or sub-range included in the said range, which is equivalent to each numerical value or sub-range being clearly specified. I. Electrochemical device

[0025] According to a first aspect of the present invention, the present invention relates to an electrochemical device, which includes a positive electrode sheet, a negative electrode sheet, and an electrolyte. The positive electrode sheet includes a positive electrode active layer, the positive electrode active layer includes a positive electrode active material, the positive electrode active material includes an additive, and when the electrochemical device is charged and discharged and the electrochemical device is in a fully discharged state, the X-ray diffraction (XRD) pattern of the positive electrode sheet has a characteristic diffraction peak 1 within a range where the diffraction angle 2θ is 17.5° to 19.5°. The additive contains a manganese element, and relates to an electrochemical device. The characteristic diffraction peak 1 is a characteristic diffraction peak of the additive. Since the additive can replenish lithium ions consumed by the formation of the cathode-electrolyte interface (CEI) during the first charge of the cathode active material, it is advantageous for improving the cycle characteristics and high-temperature storage characteristics of the electrochemical device. Moreover, since it provides a diffusion path for lithium ions, it is convenient for the insertion and rapid release of lithium ions. In addition, since the additive has a relatively low voltage platform (for example, a platform of 3.9V), it is advantageous for the gentle re-insertion of lithium ions during the cycle and storage processes of the electrochemical device, thereby improving the charge and discharge capacity of the cathode active material.

[0026] In some embodiments, the additive includes a manganese-containing compound having a layered structure. In some embodiments, the manganese-containing compound includes at least one of LiMn2O3, Li2MnO3, and LiMnO2.

[0027] In some embodiments, the positive electrode active material includes lithium manganate. When the electrochemical device is in a fully discharged state, the X-ray diffraction pattern of the positive electrode sheet further has a characteristic diffraction peak 2 within a range where the diffraction angle 2θ is 17.5° to 19.5°. The difference in peak positions between the characteristic diffraction peak 1 and the characteristic diffraction peak 2 satisfies 0.33° ≤ Δθ1 ≤ 0.53°.

[0028] In some embodiments, the positive electrode active material contains lithium iron phosphate. When the electrochemical device is in a fully discharged state, it has a characteristic diffraction peak 3 within the range of diffraction angle 2θ of 19.8° to 21.8°, and the difference in peak positions between the characteristic diffraction peak 3 and the characteristic diffraction peak 1 satisfies 2° ≤ Δθ2 ≤ 3°.

[0029] In some embodiments, based on the mass of the positive electrode active material, the mass percentage of the additive is 3% to 20%. In some embodiments, based on the mass of the positive electrode active material, the mass percentage of the additive is 3%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, or within a range consisting of any two of the above numerical values. If the content of the additive is too low, the capacity per gram of the first charge of the electrochemical device manufactured thereby will decrease. If the content of the additive is too high, the first Coulomb efficiency of the electrochemical device manufactured thereby will decrease. This is mainly because the additive has a relatively high capacity per gram of the first charge, and lithium manganate consumes Li + compensated by the formation of the CEI film during the first charge, but the additive can only re-embed a part of Li during the first discharge. According to research, by limiting the content of the additive within the above range, both the capacity per gram of the first charge and the first Coulomb efficiency of the electrochemical device are significantly improved. In some embodiments, based on the mass of the positive electrode active material, the mass percentage of the additive is 3% to 15%. In this case, the electrochemical device has a relatively high capacity per gram of the first charge and Coulomb efficiency.

[0030] 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, based on the mass of the positive electrode active layer, the mass percentage of the positive electrode active material is 94% to 98%.

[0031] In some embodiments, the electrolyte contains an electrolyte additive, the electrolyte additive contains at least one of a sulfur-oxygen double bond-containing compound, vinylene carbonate (VC), and fluoroethylene carbonate (FEC), and based on the mass of the electrolyte, the mass percentage of the electrolyte additive is 0.001% to 10%. In some embodiments, based on the mass of the electrolyte, the mass percentage of the electrolyte additive is 0.001%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or within a range consisting of any two of the above numerical values. In some embodiments, the sulfur-oxygen double bond-containing compound contains at least one of 1,3-propanesultone (PS), 1,3-propenesultone (PES), and divinyl sulfate (DTD). Different electrolyte additives have different improving effects on the battery system. Among them, VC and FEC are used as CEI film-forming additives and can form a more stable CEI film. Also, VC and FEC can improve the flexibility of the CEI film and reduce the impedance at the interface of the positive electrode. Since the sulfur-oxygen double bond-containing compound can form a protective film at the interfaces of the positive and negative electrodes, it can reduce the side reaction between the positive and negative electrode interfaces and the electrolyte, reduce the transmission impedance inside the battery, and thus is beneficial to the improvement of the normal-temperature cycle characteristics, high-temperature cycle characteristics, and high-temperature storage characteristics of the battery. The electrolyte additive can stabilize the original form and structure of the positive electrode active material and form a dense interfacial film on the surface of the positive electrode sheet, thereby enhancing the stability of the positive electrode material, reducing side reactions, reducing the impedance of the material, and improving the cycle characteristics of the battery. In some embodiments, the mass percentage of the electrolyte additive is 0.01% to 5%. In this case, since the electrolyte additive can form a flexible protective film at the interfaces of the positive and negative electrodes, it can reduce the interfacial impedance and effectively improve the normal-temperature / high-temperature cycle characteristics and high-temperature storage characteristics of the electrochemical device.

[0032] In some embodiments, the positive electrode active layer contains element M, where M includes at least one of Al, Nb, Mg, Ti, Ce, W, Ga, Zr, W, Y, V, Na, Sr, Mo, Cr, Sn, and La. In some embodiments, based on the mass of the positive electrode active layer, the mass percentage of element M is 0.03% to 3.5%. In some embodiments, based on the mass of the positive electrode active layer, 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 within a range consisting of any two of the above numerical values. Element M can contribute to the diffusion of lithium ions, improve the cycle characteristics and high-temperature storage characteristics of the electrochemical device, because it stabilizes the structure of the positive electrode active material, reduces phase change, and suppresses the elution of transition metals. If the content of element M is too high, it will expand the lattice inside the positive electrode active material and destroy the stability of the material structure, thus affecting the cycle characteristics of the electrochemical device. In some embodiments, based on the mass of the positive electrode active layer, the mass percentage of element M is 0.03% to 1.5%. When the mass percentage of element M is within the above range based on the mass of the positive electrode active layer, element M can effectively suppress the elution of metal and enhance the diffusion of lithium ions, so as to improve the cycle characteristics and high-temperature storage characteristics of the electrochemical device.

[0033] In some embodiments, the positive electrode active material contains aluminum element. Based on the mass of the positive electrode active layer, the mass percentage of aluminum element is C%, and the mass percentage of VC in the electrolyte is D%, where C and D satisfy 0.03 ≤ C / D ≤ 0.5. Adding aluminum element can further stabilize the structure of the positive electrode active material. VC can form a stable CEI film on the interface of the positive electrode. By controlling the mass percentages of aluminum element and VC to satisfy the above relational expression, the structure of the positive electrode active material can be further stabilized, so as to improve the high-temperature storage characteristics and cycle characteristics of the electrochemical device.

[0034] In some embodiments, when the average particle size of the additive is F, F ranges from 5 μm to 40 μm, and there are steps with a width of 1 nm to 1000 nm on the surface of the additive particles. As shown in FIGS. 3(a) and 3(b), the relatively large particles are additive particles. The additive has a layered structure, with several layers of steps on the surface, and the width of the steps is 1 nm to 1000 nm. By adding the layered manganese-containing compound to the positive electrode active material, all of the capacity characteristics, rate characteristics, high-temperature storage characteristics, and cycle characteristics of the electrochemical device are significantly improved. This is mainly because the layered manganese-containing compound can replenish the lithium ions consumed by the formation of CEI during the first charge of the electrochemical device, which is advantageous for improving the cycle characteristics and storage characteristics of the electrochemical device. At the same time, it provides a diffusion path for lithium ions, which is convenient for the insertion and rapid release of lithium ions. In addition, since the layered manganese-containing compound has a relatively low voltage platform (for example, a platform of 3.9 V), it is advantageous for the gentle re-insertion of lithium ions during the cycle and storage processes, thereby improving the charge-discharge capacity of the positive electrode active material.

[0035] According to another aspect of the present invention, the present invention relates to an electronic device including the electrochemical device described in any one of the above embodiments. II. Manufacture of Electrochemical Device

[0036] Hereinafter, the manufacturing method of the electrochemical device of the present invention will be described in detail by taking a lithium-ion battery as an example.

[0037] Manufacture of negative electrode: The negative electrode active material, conductive agent, binder, and thickener are dispersed in a solvent system at a certain mass ratio, stirred sufficiently to be uniformly mixed, then coated on the negative electrode current collector, dried, and cold-pressed to obtain a negative electrode sheet.

[0038] As an example, the negative electrode active material may 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 with a spinel structure Li4Ti5O 12 , Li-Al alloy, and metallic lithium. The conductive agent may be one or more of graphite, superconducting carbon, acetylene black, carbon black, ketjen black, carbon dot, carbon nanotube, graphene, and carbon nanofiber. 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).

[0039] For the negative electrode current collector, materials such as a metal foil material or a porous metal plate material can be used. For example, it is a foil material or a porous plate made of a metal such as copper, nickel, titanium, or iron, such as copper foil, or an alloy thereof.

[0040] Manufacture of the positive electrode: Preparation of the additive in the positive electrode active material: a) Place Mn3O4 in a corundum crucible, heat it to 500 °C at a heating rate of 5 °C / min in an air atmosphere, maintain it at a constant temperature for 1 hour to obtain anhydrous Mn3O4. b) Weigh anhydrous Mn3O4 and LiOH at a molar ratio of Li:Mn of 1.05:1, and simultaneously add nano-Al2O3 at an elemental mass ratio of Al:Mn of 0.015:1, and mix them for 8 hours using a mixer to obtain a mixture precursor. c) Place the mixture precursor in a corundum crucible, ventilate nitrogen gas at a rate of 2m 3 / h, heat it to 940 °C at a heating rate of 5 °C / min, maintain it at a constant temperature for 10 hours, and cool it naturally to room temperature to obtain the additive.

[0041] The positive electrode active material (lithium manganate (LiMn2O4), lithium iron phosphate or other positive electrode active materials), the above-mentioned additive, the conductive agent, and the binder are mixed at a certain weight ratio, a solvent is added, and they are uniformly stirred to form a slurry. The slurry is uniformly coated on an aluminum foil which is a positive electrode current collector, and dried under the condition of 90 °C to obtain an initial positive electrode sheet. The initial positive electrode sheet is subjected to processes such as cold pressing and cutting to obtain a positive electrode sheet.

[0042] In some embodiments, the conductive agent improves the conductivity of the positive electrode active layer by providing a conductive path for the positive electrode active material. The conductive agent may include at least one of acetylene black, ketjen black, natural graphite, carbon black, carbon fiber, metal powder and metal fiber (for example, copper, nickel, aluminum or silver), but the examples of the conductive agent are not limited thereto. In some embodiments, the amount of the conductive agent can be appropriately adjusted. Based on 100 parts by weight of the total amount of the positive electrode active material, the conductive agent and the positive electrode binder, the amount of the conductive agent is in the range of 1 part by weight to 30 parts by weight.

[0043] In some embodiments, examples of the solvent include, but are not limited to, N-methylpyrrolidone, acetone or water. In some embodiments, the amount of the solvent can be appropriately adjusted.

[0044] In some embodiments, the binder improves the adhesion characteristics between the positive electrode active material particles and the adhesion characteristics between the positive electrode active material particles and the current collector. Examples of the positive electrode binder include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), ethylene-vinyl acetate copolymer (EVA) and polyvinyl alcohol (PVA), but are not limited thereto. Based on 100 parts by weight of the total amount of the positive electrode active material, the conductive agent and the positive electrode binder, the amount of the positive electrode binder is in the range of 1 part by weight to 30 parts by weight.

[0045] In some embodiments, the current collector has a thickness in the range of 3 μm to 20 μm, but the content of the present 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 alloy), but the content of the present invention is not limited thereto. In some embodiments, in order to strengthen the adhesion of the active material to the surface of the current collector, the surface of the current collector may have fine irregularities (e.g., surface roughness). In some embodiments, the current collector may be used in various forms, and examples thereof include films, sheets, foils, meshes, porous structures, foams, or non-woven fabrics, but the content of the present invention is not limited thereto.

[0046] Separator Embodiments of the present invention have no particular limitation on the separator. The separator includes a polyolefin microporous film and a coating layer (coated on the surface of the polyolefin microporous film). The separator is a single-layer or multi-layer polyolefin microporous film composed of one or more selected from polyethylene (PE), ethylene-propylene copolymer, polypropylene (PP), ethylene-butene copolymer, ethylene-hexene copolymer, and ethylene-methyl methacrylate copolymer. The coating layer contains inorganic ceramic particles. The inorganic ceramic particles are one or more selected from SiO2, Al2O3, CaO, TiO2, ZnO, MgO, ZrO2, and SnO2.

[0047] Electrolyte According to an embodiment of the present invention, the electrolyte contains a non-aqueous organic solvent and a lithium salt. The non-aqueous organic solvent may include a carbonate, a carboxylic acid ester, an ether compound, a sulfone compound, 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, butylene carbonate, bis(2,2,2-trifluoroethyl) carbonate, and the like. 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, 1,4-dioxane, and the like. Examples of sulfone compound solvents include ethyl vinyl sulfone, methyl isopropyl sulfone, isopropyl-sec-butyl sulfone, cyclobutyl sulfone, and the like.

[0048] According to an embodiment of the present invention, the non-aqueous organic solvent in the electrolyte may be a single non-aqueous organic solvent or a mixture of a plurality of non-aqueous organic solvents. When using a mixed solvent, the mixing ratio can be controlled according to the characteristics of the desired electrochemical device.

[0049] According to an embodiment of the present invention, the lithium salt in the electrolyte contains at least one of an organic lithium salt and an inorganic lithium salt, or is selected from them. The lithium salt is 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 perfluorobutanesulfonate (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.), and contains at least one of lithium chloride (LiCl) and lithium fluoride (LiF), or is selected from them.

[0050] Preparation of electrolyte: In a glove box with an argon atmosphere and a water content of <10 ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP), and propyl propionate (PP) are uniformly mixed at a mass ratio of 1:1:1:1:1, and further, LiPF6, a sufficiently dried lithium salt, is dissolved in the above non-aqueous solvent to obtain a base electrolyte. Here, the mass percentage of LiPF6 is 12.5%.

[0051] A separator is interposed between the positive and negative electrodes to play a role of isolation, and the positive electrode, separator, and negative electrode are stacked and wound in this order to obtain a bare cell. The obtained bare cell by winding is placed in an outer package, injected with the electrolyte and packaged, and through processes such as formation, degassing, and trimming, a lithium-ion battery is obtained. III. Electronic device

[0052] The present invention provides an electronic device including the electrochemical device described in the above content.

[0053] According to some embodiments of the present invention, the electronic device includes, but is not limited to, a laptop, a pen-input computer, a mobile computer, an e-book player, a mobile phone, a portable facsimile, a portable copier, a portable printer, a stereo headset, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disk, a transceiver, an electronic notebook, a calculator, a memory card, a portable tape recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, an auxiliary bicycle, a bicycle, a lighting fixture, a toy, a game machine, a clock, a power tool, a flash, a camera, a large household storage battery, etc. IV. Specific Embodiments

[0054] Hereinafter, taking a lithium-ion battery as an example, the present invention will be described in more detail with reference to the embodiments. However, it should be understood that the following embodiments are merely illustrative and the embodiments of the present invention are not limited thereto. Method for Measuring Characteristics

[0055] XRD Measurement Method A lithium-ion battery in a fully discharged state was taken, disassembled to obtain a positive electrode sheet, and XRD measurement was performed on the positive electrode sheet. The positive electrode sheet was placed on the sample stage of an XRD measurement device (model: BRUKER, D8), and an XRD diffraction pattern was obtained at a scanning speed of 2° / min and a scanning angle range of 10° to 90°. The corresponding diffraction peaks were read, and the peak positions and half-value widths were recorded.

[0056] Measurement of Particle Morphology A lithium-ion battery was disassembled to obtain a positive electrode sheet, and using a scanning electron microscope (JSM-6360LV type manufactured by JEOL), an SEM photograph of the positive electrode sheet obtained by disassembling the lithium-ion battery was taken, and the morphology of the particles of the positive electrode active material was observed.

[0057] Measurement of Average Particle Size The lithium-ion battery was disassembled to obtain a positive electrode sheet. Using a scanning electron microscope, an SEM photograph of the positive electrode sheet obtained by disassembling the lithium-ion battery was taken to observe the particles of the positive electrode active material. Then, using image analysis software, 30 particles were randomly selected from the SEM photograph, and the area of each of these particles was calculated. Next, assuming that the particles are spherical, with S1 being the area of the particle, D = 2×(S1 / π) 1 / 2 was used to calculate the particle diameter D (diameter) of each particle. By taking the arithmetic mean of the particle diameters of the 30 obtained particles, the average particle diameter of the said particles was calculated.

[0058] Method for measuring element content The lithium-ion battery was disassembled to obtain a positive electrode sheet. 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 doctor blade, and the positive electrode active layer (for example, 0.4 g of the positive electrode active layer was dissolved using a mixed solvent of 10 ml of aqua regia (a mixture of nitric acid and hydrochloric acid in a 1:1 ratio) and 2 ml of HF).) was dissolved and made up to a constant volume of 100 mL. Then, using an ICP analyzer, the mass percentages of Al, Nb, Mg, Ti, Ce, W, Ga, Zr, W, Y, V, Na, Sr, Mo, Cr, Sn, and La in the solution (based on the mass of the positive electrode active layer) were measured.

[0059] Measurement of lithium-ion battery capacity - Capacity per gram (mAhg) of the first discharge at 25°C and 0.2C -1 ) Four lithium-ion batteries manufactured using the positive electrode materials shown in the examples and comparative examples were taken in each group. Under constant temperature conditions of 25°C, they were charged at a constant current with a current of 0.5C (i.e., the current value that completely discharges the theoretical capacity within 2 hours), charged up to 4.2V, then charged at a constant voltage, and then discharged at a constant current with a current of 0.2C until 2.8V. The first discharge capacity at 0.2C was calculated and taken as the battery capacity.

[0060] Cycle characteristic test of lithium-ion battery Four lithium-ion batteries manufactured using the cathode materials shown in the examples and comparative examples were taken in groups of four, and for each of the four lithium-ion batteries, charging and discharging were repeated according to the following steps to calculate the discharge capacity retention rate of the lithium-ion battery. First, at an environment of 25°C / 45°C, the first charge and discharge were performed respectively. Constant current charging was carried out at a current of 0.5C until charged to 4.2V, then constant voltage charging was carried out, and then constant current discharging was carried out at a current of 1C until discharged to 2.8V, and the discharge capacity of the first cycle was recorded. Then, 1500 / 400 charge and discharge cycles were performed, and the discharge capacity of the 1500 / 400th cycle was recorded. Cycle capacity retention rate at 25°C = (Discharge capacity of the 1500th cycle / Discharge capacity of the first cycle) × 100% Cycle capacity retention rate at 45°C = (Discharge capacity of the 400th cycle / Discharge capacity of the first cycle) × 100%

[0061] High-temperature storage test of lithium-ion battery Four lithium-ion batteries manufactured using the cathode materials shown in the examples and comparative examples were taken in groups of four. At an environment of 60°C, constant current charging was carried out at a current of 0.5C until charged to 4.2V, then constant voltage charging was carried out, and then constant current discharging was carried out at a current of 1C until discharged to 2.8V, and the discharge capacity was recorded as the capacity before storage. Charging was carried out at a constant current of 0.5C until 3.99V, and then constant voltage charging was carried out until the current was less than 0.05C. After the battery was placed in an oven at 60°C and stored for 14 days, constant current discharging was carried out at a discharge current of 1C until discharged to 2.8V, and then constant current and constant voltage charging were carried out at a charging current of 0.5C until the upper limit voltage reached 4.2V, and then constant current discharging was carried out at a discharge current of 1C until discharged to 2.8V, and the discharge capacity was recorded as the capacity after storage. High-temperature storage capacity retention rate at 60°C = Capacity after storage / Capacity before storage × 100% A. Examples 1-1 to 1-8 and Comparative Example 1-2

[0062] Preparation method of Example 1-1: Step (1): a) Place MnOOH in a corundum crucible, heat it to 500 °C at a heating rate of 5 °C / min in an air atmosphere, maintain the temperature for 1 hour to obtain anhydrous Mn3O4. b) Weigh anhydrous Mn3O4 and LiOH at a molar ratio of Li:Mn of 1.05:1, and simultaneously add nano-Cr2O3 at an elemental mass ratio of Cr:Mn of 0.015:1, and mix for 8 hours using a mixer to obtain a mixture precursor. c) Place the mixture precursor in a corundum crucible, 3 vent nitrogen gas at a rate of 2 m / h, heat it to 940 °C at a heating rate of 5 °C / min, maintain the temperature for 10 hours, and naturally cool to room temperature to obtain an additive. Here, the average particle size of the additive is 18.9 μm, and there are steps with a width of 600 nm - 700 nm on the surface of the additive particles (see Figure 3(a) and Figure 3(b)).

[0063] Step (2): Lithium manganate (LiMn2O4) as the cathode active material (the average particle size of lithium manganate is 2.7 μm), the above additive, conductive carbon black (Super P), carbon nanotubes (CNT), and polyvinylidene fluoride (PVDF) are mixed at a weight ratio of 90:5:1.8:1.2:2, add N-methylpyrrolidone (NMP) as a solvent, prepare a slurry with a solid content of 0.75, stir uniformly to obtain a slurry. The slurry is uniformly coated on both sides of an aluminum foil, which is the cathode current collector, and dried at 90 °C to obtain an initial cathode sheet. The initial cathode sheet undergoes processes such as cold pressing and cutting to obtain a cathode sheet.

[0064] Anode: Graphite as the anode active material, conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) are mixed at a weight ratio of 97:1.0:2.0, add N-methylpyrrolidone (NMP) as a solvent, prepare a slurry with a solid content of 0.8, and stir uniformly. The slurry is uniformly coated on a copper foil, which is the anode current collector, and dried at 80 °C to obtain an initial anode sheet. The initial anode sheet undergoes processes such as cold pressing and cutting to obtain an anode sheet.

[0065] Electrolyte: In an argon atmosphere glove box with a water content of less than 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP), and propyl propionate (PP) were uniformly mixed at a mass ratio of 1:1:1:1:1. Further, a sufficiently dried lithium salt LiPF6 was dissolved in the above non-aqueous solvent to obtain a base electrolyte. Here, the mass percentage of LiPF6 was 12.5 wt%.

[0066] Separator: A PE porous polymer film was used as the separator.

[0067] The separator was interposed between the positive and negative electrodes to play a role of isolation. The positive electrode, separator, and negative electrode were stacked and wound in this order, placed in an outer package, and the prepared electrolyte was injected and packaged. Through processes such as formation, degassing, and trimming, a lithium-ion battery was obtained.

[0068] The differences between Examples 1-2 to 1-5 and Example 1-1 are only the differences in the content of the additive (the adjustment of the additive content was carried out based on the fact that the total weight percentage of the additive and lithium manganate was 95%, and the total weight of the additive and lithium manganate accounted for 95% of the weight of the positive electrode active material). The difference between Example 1-6 and Example 1-1 is that lithium iron phosphate was used instead of lithium manganate (the average particle size of lithium iron phosphate was 0.4 μm). The differences between Examples 1-7 and 1-8 and Example 1-6 are only the differences in the content of the additive (the adjustment of the additive content was carried out based on the fact that the total weight percentage of the additive and lithium iron phosphate was 95%, and the total weight of the additive and lithium iron phosphate accounted for 95% of the weight of the positive electrode active material). The positive electrode active material of Comparative Example 1-1 contained only lithium manganate, and the positive electrode active material of Comparative Example 1-2 contained only lithium iron phosphate. Specifically, refer to Table 1 below. Table 1 shows the differences in the configuration and characteristics of the electrochemical devices between Examples 1-1 to 1-8 and Comparative Examples 1-1 and 1-2.

[0069]

Table 1

[0070] From Table 1, Figure 1, and Figure 2, it can be seen that additives are added to the positive electrode active layers of Examples 1-1 to 1-8. When the electrochemical device is in a fully discharged state, the X-ray diffraction (XRD) pattern of the positive electrode sheet has a characteristic diffraction peak 1 within the range of diffraction angle 2θ of 17.5° to 19.5°. For lithium manganese oxide as the positive electrode active material, comparing Examples 1-1 to 1-5 with Comparative Example 1-1, and for lithium iron phosphate as the positive electrode active material, comparing Examples 1-6 to 1-8 with Comparative Example 1-2, the electrochemical characteristics of the examples with additives (capacity per gram of the first discharge under the conditions of 25°C and 0.2C, capacity retention rate after 1500 cycles at 25°C, capacity retention rate after 400 cycles at 45°C, and high-temperature storage capacity retention rate at 60°C) are all significantly improved compared to the comparative examples without the corresponding additives. This is mainly because the additive can replenish the Li consumed by the formation of SEI during the first charge of the positive electrode active material, which is beneficial to the improvement of the cycle characteristics and storage characteristics of the lithium-ion battery. And the additive provides a diffusion path for lithium ions, which is convenient for the insertion and rapid release of lithium ions. Also, since the additive has a relatively low voltage platform, it is beneficial to the gentle re-insertion of lithium ions during the cycle and storage processes, thereby improving the capacity of the positive electrode active material.

[0071] B. Example 1-1 and Examples 2-1 to 2-10 The differences between Examples 2-1 to 2-10 and Example 1-1 were only the differences in the content of Al element in the positive electrode active layer of Examples 2-1 to 2-7 and the difference in the VC content in the used electrolytic solution. Examples 2-2 to 2-7 were different from Example 1-1 in the preparation process when adding aluminum element as an additive. In this step b), anhydrous Mn3O4 and LiOH were weighed at a molar ratio of Li:Mn of 1.05:1, and nano-Al2O3 was added at the required Al:Mn element ratio at the same time, and they were mixed for 8 hours using a mixer to obtain a mixture precursor, and further an additive containing aluminum element was prepared. The specific contents are shown in Table 2. Table 2 below shows the differences in the configuration and characteristics of the electrochemical devices between Example 1-1 and Examples 2-1 to 2-7.

[0072]

Table 2

[0073] From Table 2, it can be seen that by adding aluminum element to the positive electrode active material, the cycle characteristics and high-temperature storage characteristics of the lithium-ion battery can be further improved. For example, compared with Example 1-1 that does not contain aluminum element, in Examples 2-2 to 2-7 where aluminum element is added, the capacity retention rate after 1500 cycles at 25 °C, the capacity retention rate after 400 cycles at 45 °C, and the high-temperature storage capacity retention rate at 65 °C are all significantly improved. This is mainly because the aluminum element improves the stability of the unit cell during the insertion or extraction of lithium ions, stabilizes the crystal structure, and further stabilizes the structure of the positive electrode active material, thus improving the cycle characteristics of the lithium-ion battery. In the research of the present invention, it was discovered that by limiting the content of the element to 0.1% to 3.5%, the lithium-ion battery can be given relatively excellent characteristics. According to the examples of the present invention, when 0.03 ≦ C / D ≦ 0.5 is satisfied, the cycle characteristics and high-temperature storage characteristics of the electrochemical device are more excellent. By adding aluminum element, the structure of the positive electrode active material is further stabilized, VC forms a stable CEI film on the interface of the positive electrode, and by controlling the mass percentage of aluminum element and VC to satisfy the above relational expression, the positive electrode active material can be further stabilized, the interface of the positive electrode can be protected, and the high-temperature storage characteristics and cycle characteristics of the lithium-ion battery can be improved. It should be understood that the aluminum element may be added to the additive, may be added to lithium manganate, or both the additive and lithium manganate contain aluminum element. The aluminum element stabilizes the crystal structure of the material, improves the structural stability of the material during the insertion or extraction of lithium ions, and improves the cycle characteristics of the lithium-ion battery. When the aluminum element is added to the additive, the difference in its preparation process from Example 1-1 is step b), that is, anhydrous Mn3O4 and LiOH are weighed at a molar ratio of Li:Mn of 1.05:1, and nano-Al2O3 is added at the required Al:Mn molar ratio at the same time, and mixed for 8 hours using a mixer to obtain a mixture precursor. When the aluminum element is added to lithium manganate, those skilled in the art can prepare it by the usual technical means in this field

[0074] C. Example 1-1 and Examples 3-1 to 3-8 The differences between Examples 3-1 to 3-8 and Example 1-1 were the types and contents of additives in the electrolytic solution.

[0075] Hereinafter, the preparation of the electrolytic solution will be described using Example 3-1 as an example. In an argon atmosphere glove box with a water content of <10 ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP), and propyl propionate (PP) were uniformly mixed at a mass ratio of 1:1:1:1:1, and further, LiPF6, a lithium salt that had been sufficiently dried, was dissolved in the above non-aqueous solvent to obtain an electrolytic solution. Here, the mass percentage of LiPF6 was 12.5%. 1,3-Propane sultone (PS) was added to the electrolytic solution in an amount of 1.5% (based on the mass of the electrolytic solution).

[0076] The preparation methods of the electrolytic solutions of Examples 3-2 to 3-8 were almost the same as that of Example 3-1, and the differences were only the types and contents of the electrolytic solution additives. For example, Example 3-2 was the same as the steps of Example 3-1 except that vinylene carbonate (VC) was added to the electrolytic solution in an amount of 1.5%.

[0077] Hereinafter, Table 3 shows the differences in the configurations and characteristics of the electrochemical devices of Example 1-1 and Examples 3-1 to 3-8.

Table 3

[0078] From the examples in Table 3, it can be seen that by adding an electrolyte additive, the characteristics 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 - propene sultone (PES), fluoroethylene carbonate (FEC), and vinyl sulfate (DTD) to the electrolyte, both the capacity retention rate after 1500 cycles at 25°C and the high - temperature storage capacity retention rate at 60°C of the electrochemical device were improved. This is mainly because different electrolyte additives bring different improvement effects to the battery system. VC and FEC can form a more stable CEI film as CEI film - forming additives. Furthermore, VC and FEC can improve the flexibility of the CEI film and reduce the impedance at the interface of the positive electrode. Compounds containing sulfur - oxygen double bonds can form a protective film at the interfaces of the positive and negative electrodes, thus reducing the side reaction between the positive and negative electrode interfaces and the electrolyte, and reducing the transmission impedance inside the lithium - ion battery. This is advantageous for improving the normal - temperature cycle characteristics, high - temperature cycle characteristics, and high - temperature storage characteristics of the battery. The electrolyte additive of the present invention stabilizes the original form and structure of the positive - electrode active material and forms a dense interfacial film on the surface of the positive electrode, thereby enhancing the stability of the positive - electrode material, reducing side reactions, reducing the impedance of the material, and improving the cycle characteristics of the lithium - ion battery.

[0079] Throughout the specification, references to "some embodiments", "a part of an embodiment", "one embodiment", "another example", "an example", "a specific example", or "a part of an example" mean that at least one embodiment or example of the present invention includes the specific features, structures, materials, or characteristics described in that embodiment or example. Thus, references such as "in some embodiments", "in an embodiment", "in one embodiment", "in another example", "in one example", "in a specific example", or "an example" described throughout the specification do not necessarily refer to the same embodiment or example in the present invention. Also, the specific features, structures, materials, or characteristics in this specification can be combined in any suitable way in one or more embodiments or examples.

[0080] Exemplary embodiments have been disclosed and described, but those skilled in the art should understand that the above embodiments cannot be construed as limiting the present invention, and that the embodiments can be modified, substituted, and changed without departing from the technical idea, principle, and scope of the present invention.

Claims

1. An electrochemical device, wherein the electrochemical device includes a positive electrode sheet, a negative electrode sheet, and an electrolytic solution, the positive electrode sheet includes a positive electrode active layer, the positive electrode active layer includes a positive electrode active material, the positive electrode active material includes an additive, when the electrochemical device is charged and discharged and the electrochemical device is in a fully discharged state, the X-ray diffraction pattern of the positive electrode sheet has a characteristic diffraction peak 1 within a range where the diffraction angle 2θ is from 17.5° to 19.5°, the additive contains a manganese element, an electrochemical device.

2. The electrochemical device according to claim 1, wherein the positive electrode active material contains lithium manganese oxide.

3. The electrochemical device according to claim 2, wherein when the electrochemical device is in a fully discharged state, the X-ray diffraction pattern of the positive electrode sheet further has a characteristic diffraction peak 2 within a range where the diffraction angle 2θ is from 17.5° to 19.5°.

4. The electrochemical device according to claim 3, wherein the 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 contains lithium iron phosphate.

6. The electrochemical device according to claim 5, wherein when the electrochemical device is in a fully discharged state, the X-ray diffraction pattern of the positive electrode sheet has a characteristic diffraction peak 3 within a range where the diffraction angle 2θ is from 19.8° to 21.8°.

7. The electrochemical device according to claim 6, wherein the 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 based on the mass of the positive electrode active material, the mass percentage of the additive is 3% to 20%, preferably, the mass percentage of the additive is 3% to 15%.

9. the positive electrode active layer contains an 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, and La, Based on the mass of the positive electrode active layer, the mass percentage of the element M is 0.03% to 3.5%, preferably, the mass percentage of the element M is 0.3% to 1.5%, the electrochemical device according to claim 1.

10. the electrolytic solution contains an electrolytic solution additive, the electrolytic solution additive contains at least one of a sulfur-oxygen double bond-containing compound, vinylene carbonate, and fluoroethylene carbonate. Based on the mass of the electrolyte, the mass percentage of the electrolyte additive is 0.001% to 10%, preferably, the mass percentage of the electrolyte additive is 0.01% to 5%, for the electrochemical device according to claim 1.

11. The positive electrode active layer contains aluminum element, 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, for the electrochemical device according to claim 1.

12. The additive is (1) when the average particle size of the additive is F, F is in the range of 5 μm to 40 μm, and (2) there are steps with a width of 1 nm to 1000 nm on the surface of the particles of the additive, for the electrochemical device according to claim 1, satisfying at least one of the above.

13. An electronic device comprising the electrochemical device according to any one of claims 1 - 12.

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