Electrochemical device and electric device

Abstract

An electrochemical device is provided, including a positive electrode sheet including a positive electrode active material layer, the electrochemical device having, in a full charged state, an X-ray diffraction pattern of the positive electrode active material layer having a first diffraction peak and a second diffraction peak in a range of 17.8° to 19.2°, and the diffraction angle of the first diffraction peak being smaller than the diffraction angle of the second diffraction peak. The electrochemical device can have an improved energy density and improved cycle performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to an electrochemical device and an electrical device. Background Technology

[0002] To address the severe global energy crisis, environmental pollution, and climate change, lithium-ion batteries are widely used in electric vehicles and energy storage. The positive electrode active material is one of the key materials in lithium-ion batteries. Currently, manganese metal is relatively inexpensive, and spinel-type LiMn2O4 has advantages such as low cost and high initial efficiency. However, in traditional batteries using LiMn2O4 as the positive electrode active material, the negative electrode requires the consumption of active lithium to form a solid electrolyte interphase (SEI) film, preventing some active lithium from returning to the LiMn2O4 positive electrode, ultimately leading to a loss of the LiMn2O4 discharge specific capacity. Furthermore, during cycling, manganese ions dissolve and damage the SEI film, requiring further consumption of lithium ions to repair it. This further loss of lithium ions reduces the structural stability of LiMn2O4, exacerbating manganese ion dissolution, creating a vicious cycle and causing rapid degradation of the lithium-ion battery's cycle life. Summary of the Invention

[0003] In view of this, this application provides an electrochemical device and an electrical device to improve the cycle performance of the electrochemical device.

[0004] In a first aspect, this application provides an electrochemical device including a positive electrode plate. The positive electrode plate includes a positive electrode active material layer. In a fully discharged state, the X-ray diffraction pattern of the positive electrode active material layer exhibits a first diffraction peak and a second diffraction peak in the range of 17.8° to 19.2°, and the diffraction angle of the first diffraction peak is smaller than that of the second diffraction peak. The first diffraction peak near 17.8° is Li. x The characteristic peaks of MnO2 materials, and the second diffraction peak near 19.2° are characteristic peaks of spinel-type lithium manganese oxide. The Li in the positive electrode active material layer... x The presence of MnO2 material can provide active lithium for the formation and repair of SEI film, inhibit the excessive extraction of lithium ions from spinel-type lithium manganese oxide, thereby inhibiting the decrease in structural stability of spinel-type lithium manganese oxide and the excessive dissolution of manganese ions, and improving the cycle performance of electrochemical devices.

[0005] In some embodiments, the peak intensity of the first diffraction peak is I. A The peak intensity of the second diffraction peak is I. B Satisfying: 0.01≤I A / I B ≤0.2. By satisfying 0.01≤I A / I BA value of ≤0.2 enables electrochemical devices to have high capacity while improving cycle performance.

[0006] In some implementations, 0.03 ≤ I A / I B ≤0.12. At this point, it can prevent damage caused by Li. x An excessively high MnO2 content results in an excess of active lithium in the system, reducing the risk of lithium plating and thus improving the safety performance of the electrochemical device.

[0007] In some embodiments, the difference between the diffraction angle of the second diffraction peak and the diffraction angle of the first diffraction peak is less than or equal to 1°.

[0008] In some embodiments, the full width at half maximum (FWHM) of the first diffraction peak is W. A The full width at half maximum (FWHM) of the second diffraction peak is W. B Satisfying: 1≤W A / W B ≤2. At this time, Li x MnO2 materials possess good crystallinity, reducing electrolyte erosion during cycling, inhibiting structural collapse, and thus improving the cycling performance of electrochemical devices. In some embodiments, 1.05 ≤ W A / W B ≤1.56.

[0009] In some embodiments, the positive electrode active material layer comprises a first lithium manganese oxide having a spinel structure.

[0010] In some embodiments, the X-ray diffraction pattern of the positive electrode active material layer has a third diffraction peak in the range of 35° to 37° and a fourth diffraction peak in the range of 43° to 45°. The third diffraction peak corresponds to the characteristic peak of the (311) crystal plane of the first lithium manganese oxide with spinel structure, and the fourth diffraction peak corresponds to the characteristic peak of the (400) crystal plane of the first lithium manganese oxide with spinel structure.

[0011] In some embodiments, the first lithium manganese oxide contains elements M and Mn, wherein the element M includes at least one of Al, Cr, Nb, Mg, Ti, V, Cu, Zr, Mo, La, Zn, Ga, Ru, Ag, Sn, Au, Ce, Pr, Nd, Sm, Gd, Fe, Co, Ni, W, or Y, and the molar ratio of element M to element Mn in the first lithium manganese oxide is (0.0001 to 0.1):1.

[0012] In some embodiments, the first lithium manganese oxide includes Li x1 Mn y1 M z1 O4-t A t Wherein, 0.6≤x1≤1.2, 1.8≤y1≤2, 0≤z1≤0.2, 0≤t≤0.5, M includes at least one of Al, Cr, Nb, Mg, Ti, V, Cu, Zr, Mo, La, Zn, Ga, Ru, Ag, Sn, Au, Ce, Pr, Nd, Sm, Gd, Fe, Co, Ni, W, or Y, and A includes at least one of S, N, F, Cl, or Br. In some embodiments, 0.6≤x1≤1.2, 1.8≤y1≤, 0.0002≤z1≤0.2, 0≤t≤0.5.

[0013] In some embodiments, the positive electrode active material layer further comprises a second lithium manganese oxide, which includes secondary particles formed by the aggregation of layered primary particles. In this case, Li has a layered structure. x MnO2 material particles can efficiently provide active lithium for the formation and repair of SEI films, thereby improving the cycle performance of electrochemical devices.

[0014] In some embodiments, the second lithium manganese oxide comprises Al, Mn, and optionally Q, wherein the Q element comprises at least one of Cr, Nb, Ti, Mg, V, Cu, Zr, Mo, La, Zn, Ga, Ru, Ag, Sn, Au, Ce, Pr, Nd, Sm, Gd, Fe, Co, Ni, W, or Y; the molar ratio of Al to Mn in the second lithium manganese oxide is (0.0001 to 0.1):1; and the molar ratio of Q to Mn in the second lithium manganese oxide is (0 to 0.1):1.

[0015] In some embodiments, the second lithium manganese oxide includes Li x2 Mn y2 Al z2 Q q O2, wherein 0.1≤x2≤1.1, 0.9≤y2≤1, 0≤z2≤0.1, 0≤q≤0.1, and Q includes at least one of Cr, Nb, Ti, Mg, V, Cu, Zr, Mo, La, Zn, Ga, Ru, Ag, Sn, Au, Ce, Pr, Nd, Sm, Gd, Fe, Co, Ni, W, or Y. In some embodiments, 0.1≤x2≤1.1, 0.9≤y2≤1, 0.0001≤z2≤0.1, and 0≤q≤0.1.

[0016] In some embodiments, the electrochemical device further includes a negative electrode plate, the negative electrode plate comprising a negative electrode active material layer; the area of ​​the positive electrode active material layer is S. c The area of ​​the negative electrode active material layer is S aThe molar content of lithium in the positive electrode active material layer with the first test area S1 is n. Lic The molar content of manganese is n Mn The molar content of lithium in the negative electrode active material layer with a second test area of ​​S2 is n. Lia Where, S2 = S1 × S a / S c n Li =n Lic +n Lia Satisfies: 0.54≤n Li / n Mn ≤0.65. n Li / n Mn Within the aforementioned range, it is possible to increase the energy density and cycle performance of electrochemical devices while reducing the risk of lithium plating and improving the safety performance of electrochemical devices.

[0017] In some embodiments, the electrochemical device further includes a negative electrode plate, the negative electrode plate comprising a negative electrode active material layer; the area of ​​the positive electrode active material layer is S. c The area of ​​the negative electrode active material layer is S a Let the test area be S. tc The positive electrode is assembled into a coin cell using lithium metal as the counter electrode. The capacity of the positive electrode is measured at 0.2C within a voltage range of 3V to 4.3V. tc Take the test area as S ta The negative electrode is assembled into a coin cell using lithium metal as the counter electrode. The capacity of the negative electrode is measured at 0.2C within a voltage range of 2V to 0.005V. ta Where, CB = (C ta ×S a / S ta ) / (C tc ×S c / S tc ), satisfying: 0.97≤CB≤1.35.

[0018] In some implementations, 1.01 ≤ CB ≤ 1.2. Within this range, CB can improve the cycle performance of the electrochemical device while reducing the risk of lithium plating, thus enhancing the safety performance of the electrochemical device.

[0019] In some embodiments, the negative electrode active material layer includes a negative electrode active material, which includes at least one of graphite, silicon material, silicon-oxygen material, silicon-carbon composite material, or silicon alloy.

[0020] In a second aspect, this application provides an electrical device comprising any of the aforementioned electrochemical devices. Attached Figure Description

[0021] To better describe and illustrate the technical solutions of this application, reference may be made to one or more of the following drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of this application.

[0022] Figure 1 The XRD diffraction pattern provided in Embodiment 1 of this application;

[0023] Figure 2 This is a partial enlarged view of the XRD diffraction pattern provided in Embodiment 1 of this application;

[0024] Figure 3 The cross-sectional SEM image provided in Embodiment 1 of this application. Detailed Implementation

[0025] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings. Preferred embodiments of this application are shown in the drawings. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0027] This application provides an electrochemical device, including a positive electrode plate, the positive electrode plate including a positive electrode active material layer, the electrochemical device in a fully discharged state, the X-ray diffraction pattern of the positive electrode active material layer has a first diffraction peak and a second diffraction peak in the range of 17.8° to 19.2°, and the diffraction angle of the first diffraction peak is smaller than the diffraction angle of the second diffraction peak.

[0028] Understandably, in this application, the first diffraction peak is close to 17.8°, which is Li x Characteristic peaks of MnO2 materials; the second diffraction peak is close to 19.2°, which is a characteristic peak of spinel-type lithium manganese oxide. Li in the positive electrode active material layer... x The presence of MnO2 material can provide active lithium for the formation and repair of SEI film, inhibit the excessive extraction of lithium ions from spinel-type lithium manganese oxide, thereby inhibiting the decline in structural stability of spinel-type lithium manganese oxide and the dissolution of manganese ions, and improving the cycle performance of electrochemical device.

[0029] In some embodiments, the peak intensity of the first diffraction peak is I. A The peak intensity of the second diffraction peak is I. B Satisfying: 0.01≤I A / I B ≤0.2. By satisfying 0.01≤I A / I B ≤0.2 enables electrochemical devices to achieve high capacity while improving cycle performance. Understandably, in this application, I A / I B The values ​​include, but are not limited to, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.12, 0.14, 0.16, 0.18, and 0.2.

[0030] In some embodiments, 0.03 ≤ I A / I B ≤0.12. At this point, it can prevent damage caused by Li. x An excessively high MnO2 content results in an excess of active lithium in the system, reducing the risk of lithium plating and thus improving the safety performance of the electrochemical device.

[0031] In some embodiments, the difference between the diffraction angle of the second diffraction peak and the diffraction angle of the first diffraction peak is less than or equal to 1°. It is understood that, in this application, the difference between the diffraction angle of the second diffraction peak and the diffraction angle of the first diffraction peak includes, but is not limited to, 0.1°, 0.2°, 0.3°, 0.4°, 0.5°, 0.6°, 0.7°, 0.8°, 0.9°, and 1.0°.

[0032] In some embodiments, the full width at half maximum (FWHM) of the first diffraction peak is W. A The full width at half maximum (FWHM) of the second diffraction peak is W. B Satisfying: 1≤W A / W B ≤2. At this time, Li x MnO2 materials possess excellent crystallinity, reducing electrolyte erosion during cycling, inhibiting structural collapse, and thus improving the cycling performance of electrochemical devices. Understandably, in this application, W... A / W B The values ​​include, but are not limited to, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, and 2.0. In some implementations, 1.05 ≤ W A / W B ≤1.56.

[0033] In some embodiments, the positive electrode active material layer comprises a first lithium manganese oxide having a spinel structure.

[0034] In some embodiments, the X-ray diffraction pattern of the positive electrode active material layer has a third diffraction peak in the range of 35° to 37° and a fourth diffraction peak in the range of 43° to 45°. The third diffraction peak corresponds to the characteristic peak of the (311) crystal plane of the first lithium manganese oxide with spinel structure, and the fourth diffraction peak corresponds to the characteristic peak of the (400) crystal plane of the first lithium manganese oxide with spinel structure.

[0035] In some embodiments, the first lithium manganese oxide contains elements M and Mn. The element M includes at least one of Al, Cr, Nb, Mg, Ti, V, Cu, Zr, Mo, La, Zn, Ga, Ru, Ag, Sn, Au, Ce, Pr, Nd, Sm, Gd, Fe, Co, Ni, W, or Y. The molar ratio of element M to element Mn in the first lithium manganese oxide is (0.0001 to 0.1):1. Understandably, in this application, the molar ratio of M to Mn in the first lithium manganese oxide includes, but is not limited to, 0.0001:1, 0.0002:1, 0.0005:1, 0.001:1, 0.002:1, 0.003:1, 0.005:1, 0.01:1, 0.015:1, 0.02:1, 0.025:1, 0.03:1, 0.05:1, 0.06:1, 0.08:1, 0.09:1, and 0.1:1.

[0036] In some embodiments, the first lithium manganese oxide includes Li x1 Mn y1 M z1 O 4-t A t Wherein, 0.6≤x1≤1.2, 1.8≤y1≤2, 0≤z1≤0.2, 0≤t≤0.5, M includes at least one of Al, Cr, Nb, Mg, Ti, V, Cu, Zr, Mo, La, Zn, Ga, Ru, Ag, Sn, Au, Ce, Pr, Nd, Sm, Gd, Fe, Co, Ni, W, or Y, and A includes at least one of S, N, F, Cl, or Br. In some embodiments, 0.6≤x1≤1.2, 1.8≤y1≤2, 0.0002≤z1≤0.2, 0≤t≤0.5.

[0037] In some embodiments, the positive electrode active material layer further comprises a second lithium manganese oxide, which includes secondary particles formed by the aggregation of layered primary particles. In this case, Li has a layered structure. x MnO2 material particles can efficiently provide active lithium for the formation and repair of SEI films, thereby improving the cycle performance of electrochemical devices.

[0038] In some embodiments, the second lithium manganese oxide comprises Al, Mn and optionally Q, wherein the Q element comprises at least one of Cr, Nb, Ti, Mg, V, Cu, Zr, Mo, La, Zn, Ga, Ru, Ag, Sn, Au, Ce, Pr, Nd, Sm, Gd, Fe, Co, Ni, W or Y; the molar ratio of Al to Mn in the second lithium manganese oxide is (0.0001 to 0.1):1; the molar ratio of Q to Mn in the second lithium manganese oxide is (0 to 0.1):1.

[0039] Understandably, in this application, the molar ratio of Al to Mn in the second lithium manganese oxide includes, but is not limited to, 0.0001∶1, 0.0002∶1, 0.0005∶1, 0.001∶1, 0.002∶1, 0.003∶1, 0.005∶1, 0.01∶1, 0.015∶1, 0.02∶1, 0.04∶1, 0.06∶1, 0.08∶1, and 0.1∶1.

[0040] Understandably, in this application, the molar ratio of Q to Mn in the second lithium manganese oxide includes, but is not limited to, 0.0001∶1, 0.0002∶1, 0.0005∶1, 0.001∶1, 0.002∶1, 0.003∶1, 0.005∶1, 0.01∶1, 0.015∶1, 0.02∶1, 0.04∶1, 0.06∶1, 0.08∶1, and 0.1∶1.

[0041] In some embodiments, the second lithium manganese oxide includes Li x2 Mn y2 Al z2 Q q O2, wherein 0.1≤x2≤1.1, 0.9≤y2≤1, 0≤z2≤0.1, 0≤q≤0.1, and Q includes at least one of Cr, Nb, Ti, Mg, V, Cu, Zr, Mo, La, Zn, Ga, Ru, Ag, Sn, Au, Ce, Pr, Nd, Sm, Gd, Fe, Co, Ni, W, or Y. In some embodiments, 0.1≤x2≤1.1, 0.9≤y2≤1, 0.0001≤z2≤0.1, and 0≤q≤0.1.

[0042] In some embodiments, the electrochemical device further includes a negative electrode plate, the negative electrode plate comprising a negative electrode active material layer; the area of ​​the positive electrode active material layer is S. c The area of ​​the negative electrode active material layer is S a The molar content of lithium in the positive electrode active material layer with a first test area of ​​S1 is n. Lic The molar content of manganese is n MnThe molar content of lithium in the negative electrode active material layer with a second test area of ​​S2 is n. Lia Where, S2 = S1 × S a / S c n Li =n Lic +n Lia Satisfies: 0.54≤n Li / n Mn ≤0.65.

[0043] In this application, n Li / n Mn Within the aforementioned range, it is possible to increase the energy density and cycle performance of electrochemical devices while reducing the risk of lithium plating and improving the safety performance of electrochemical devices.

[0044] In some embodiments, the electrochemical device further includes a negative electrode plate, the negative electrode plate comprising a negative electrode active material layer; the area of ​​the positive electrode active material layer is S. c The area of ​​the negative electrode active material layer is S a Let the test area be S. tc The positive electrode is assembled into a coin cell using lithium metal as the counter electrode. The capacity of the positive electrode is measured at a current of 0.2C within a voltage range of 3V to 4.3V, and is determined to be C. tc Take the test area as S ta The negative electrode is assembled into a coin cell using lithium metal as the counter electrode. The capacity of the negative electrode is measured at a current of 0.2C within a voltage range of 2V to 0.005V. ta Where, CB = (C ta ×S a / S ta ) / (C tc ×S c / S tc The following condition is met: 0.97≤CB≤1.35. It is understood that in this application, the value of CB includes, but is not limited to, 0.97, 1.0, 1.01, 1.05, 1.08, 1.10, 1.12, 1.15, 1.20, 1.25, 1.30, and 1.35.

[0045] In some embodiments, 1.01 ≤ CB ≤ 1.2. In this application, CB being within the above range can improve the cycle performance of the electrochemical device while reducing the risk of lithium plating and enhancing the safety performance of the electrochemical device.

[0046] In some embodiments, the positive electrode active material layer further comprises a conductive agent and a binder. In some embodiments, the binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, or acrylated styrene-butadiene rubber, etc. In some embodiments, the conductive agent includes, but is not limited to: carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from graphite, carbon black, acetylene black, Ketjen black, carbon nanotubes, carbon fibers, graphene, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fibers, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0047] In some embodiments, the positive electrode sheet further includes a positive current collector, which can be a metal foil or a composite current collector. For example, aluminum foil can be used. The composite current collector can be formed by forming a metallic material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer substrate.

[0048] In some embodiments, the negative electrode active material layer includes a negative electrode active material, which includes at least one of graphite, silicon material, silicon-oxygen material, silicon-carbon composite material, or silicon alloy.

[0049] In some embodiments, the negative electrode active material layer further includes a conductive agent and a binder. In some embodiments, the binder includes at least one selected from polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polytetrafluoroethylene, polyhexafluoropropylene, or styrene-butadiene rubber. In some embodiments, the conductive agent includes at least one selected from conductive carbon black, acetylene black, carbon nanotubes, Ketjen black, carbon fiber, or graphene.

[0050] In some embodiments, the negative electrode sheet further includes a negative current collector. The negative current collector may be copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or a combination thereof.

[0051] The electrochemical device of this application also includes an electrolyte, which includes lithium salts and non-aqueous solvents.

[0052] In some embodiments, the lithium salt is selected from one or more of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, and lithium difluoroborate. For example, LiPF6 can be selected as the lithium salt.

[0053] The non-aqueous solvent may be a carbonate compound, a carboxylic acid ester compound, an ether compound, other organic solvents, or a combination thereof.

[0054] The aforementioned carbonate compounds may be chain carbonate compounds, cyclic carbonate compounds, fluorocarbonate compounds, or combinations thereof.

[0055] Examples of the aforementioned chain carbonate compounds are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof. Examples of cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), and combinations thereof. Examples of fluorocarbonate compounds are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, and combinations thereof.

[0056] Examples of the above-mentioned carboxylic acid ester compounds are methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerate lactone, mevalonic acid lactone, caprolactone, and combinations thereof.

[0057] Examples of the above-mentioned ether compounds are dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.

[0058] Examples of other organic solvents mentioned above include dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters and combinations thereof.

[0059] In some embodiments, a separator is provided between the positive and negative electrodes in the electrochemical device to prevent short circuits. The material and shape of the separator used in the embodiments of this application are not particularly limited, and can be any technology disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application. For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer includes at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane can be selected. At least one surface of the substrate layer is provided with a surface treatment layer, which can be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials. The inorganic layer comprises inorganic particles and a binder. The inorganic particles include at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder includes at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The polymer layer contains a polymer, the polymer material of which includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).

[0060] According to some embodiments of this application, the electrochemical device of this application includes, but is not limited to, all types of primary or secondary batteries. In some embodiments, the electrochemical device is a lithium secondary battery. In some embodiments, the lithium secondary battery includes, but is not limited to, lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0061] This application also provides an electrical device, including the above-described electrochemical device.

[0062] In some embodiments, the electrical device includes, but is not limited to: laptop computers, pen input computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, portable cleaners, portable CD players, electronic notebooks, calculators, portable recorders, radios, backup power supplies, electric vehicles, motorcycles, electric bicycles, lighting fixtures, toys, game consoles, clocks, power tools, cameras, large household batteries or lithium-ion capacitors, etc.

[0063] The present application will be further described in detail below with reference to specific embodiments. Unless otherwise specified, the raw materials used in the following embodiments are all commercially available products.

[0064] Example 1

[0065] I. Preparation of positive electrode active materials:

[0066] (1) Mn(OOH) was placed in an alumina crucible and heated to 500℃ at a heating rate of 5℃ / min under air atmosphere and held at a constant temperature for 1h to obtain anhydrous Mn3O4. Anhydrous Mn3O4 and LiOH were weighed according to a Li:Mn molar ratio of 1.05:1, and nano-Al2O3 was added according to an Al:Mn molar ratio of 0.03:1. The mixture was then homogenized using a sand mill to obtain a mixed precursor. The precursor was placed in an alumina crucible and heated at a rate of 2m... 3 Nitrogen gas was introduced at a rate of 1 h, and the temperature was increased to 940℃ at a rate of 5℃ / min and held constant for 10 h. The material was then naturally cooled to room temperature to obtain layered LiMnO2 material.

[0067] (2) Weigh Li2CO3 and MnO2 according to the Li:Mn molar ratio of 0.56:1, add Al2O3 and Nb2O5 according to the Al:Mn molar ratio of 0.05:1 and the Nb:Mn molar ratio of 0.01:1, and mix in a high-speed mixer at a speed of 300 r / min for 20 min to obtain a mixture. Place the mixture in an air furnace and heat it to 790℃ at 5℃ / min, keep it for 24 h, and take it out after natural cooling. After passing it through a 300 mesh sieve, spinel-type lithium manganese oxide is obtained.

[0068] (3) Mix spinel-type lithium manganese oxide and LiMnO2 at a mass ratio of 92:8 and sinter in air at 200°C for 2 hours to obtain positive electrode active material.

[0069] II. Preparation of Lithium-ion Batteries:

[0070] Preparation of the positive electrode sheet: The positive electrode active material, conductive agent Super P, and binder polyvinylidene fluoride were mixed at a mass ratio of 96:24:1.6. N-methylpyrrolidone (NMP) was added, and the mixture was stirred evenly under vacuum to obtain a positive electrode slurry with a solid content of 75 wt%. The positive electrode slurry was uniformly coated onto one surface of a 10 μm thick aluminum foil for the positive electrode current collector. The aluminum foil was dried at 85 °C to obtain a positive electrode sheet with a single-sided coating of positive electrode active material layer with a coating thickness of 110 μm. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode active material layer. After cold pressing, cutting, and slitting, the sheet was dried under vacuum at 85 °C for 4 h to obtain a positive electrode sheet with a size of 74 mm × 867 mm.

[0071] Preparation of the negative electrode sheet: Artificial graphite (negative electrode active material), Super P (conductive agent), sodium carboxymethyl cellulose (CMC) (thickener), and styrene-butadiene rubber (SBR) (binder) were mixed in a mass ratio of 96.4:1.5:0.5:1.6. Deionized water was added, and the mixture was stirred evenly under vacuum to obtain a negative electrode slurry with a solid content of 70 wt%. The negative electrode slurry was uniformly coated onto one surface of a 10 μm thick copper foil current collector. The copper foil was dried at 85 °C to obtain a negative electrode sheet with a single-sided coating of the negative electrode active material layer, with a coating thickness of 79 μm. The above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of the negative electrode active material layer. After cold pressing, cutting, and slitting, the sheet was dried under vacuum at 120 °C for 12 h to obtain a negative electrode sheet with dimensions of 79 mm × 972 mm.

[0072] Electrolyte preparation: In an argon-atmospheric glove box with a water content <10ppm, diethyl carbonate (DEC) and ethylene carbonate (EC) were mixed at a mass ratio of 57.5:30 to obtain a base solvent. Lithium salt LiPF6 was then added to the base solvent, dissolved, and mixed thoroughly to obtain the electrolyte. The mass percentage of LiPF6 in the electrolyte was 125%, with the remainder being the base solvent.

[0073] Preparation of the separator membrane: Polyvinylidene fluoride and aluminum oxide were mixed at a mass ratio of 1:8, added to deionized water, and stirred to obtain a coating slurry with a solid content of 50 wt%. The coating slurry was uniformly coated on one surface of a 5 μm thick PE porous film and dried at 85 °C to obtain a separator membrane with a single-sided coating thickness of 5 μm.

[0074] The positive electrode, separator, and negative electrode prepared above are stacked in sequence, with the separator positioned between the positive and negative electrode sheets and the coating facing the positive electrode sheet. The electrode assembly is then wound up to obtain the electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, degassing, and edge trimming, a lithium-ion battery is obtained.

[0075] Example 2

[0076] Except for step (3), in which the mass ratio of spinel-type lithium manganese oxide to LiMnO2 is adjusted to 95:5 and the thickness of the single-sided positive electrode active material layer is adjusted to 112μm, the other steps are the same as in Example 1.

[0077] Example 3

[0078] Except for step (3), in which the mass ratio of spinel-type lithium manganese oxide to LiMnO2 is adjusted to 90:10, the other steps are the same as in Example 1.

[0079] Example 4

[0080] Except for step (3), in which the mass ratio of spinel-type lithium manganese oxide to LiMnO2 is adjusted to 85:15, the other steps are the same as in Example 1.

[0081] Example 5

[0082] Except for step (3), in which the mass ratio of spinel-type lithium manganese oxide to LiMnO2 is adjusted to 80:20 and the thickness of the single-sided positive electrode active material layer is adjusted to 111 μm, the other steps are the same as in Example 1.

[0083] Example 6

[0084] Except for adjusting the Al:Mn molar ratio to 0.1:1 in step (1) to add nano-Al2O3, the other steps are the same as in Example 1.

[0085] Example 7

[0086] Except for adjusting the Al:Mn molar ratio in step (1) to 0.06:1 to add nano-Al2O3, the other steps are the same as in Example 1.

[0087] Example 8

[0088] Except for adjusting the Al:Mn molar ratio in step (1) to 0.02:1 to add nano-Al2O3, the other steps are the same as in Example 1.

[0089] Example 9

[0090] Except for adjusting the Al:Mn molar ratio to 0.01:1 in step (1) to add nano-Al2O3, the other steps are the same as in Example 1.

[0091] Example 10

[0092] Except for adjusting the Al:Mn molar ratio to 0.0001:1 in step (1) to add nano-Al2O3, the other steps are the same as in Example 1.

[0093] Example 11

[0094] Except for adjusting the thickness of the single-sided negative electrode active material layer to 74 μm, the other steps are the same as in Example 1.

[0095] Example 12

[0096] Except for adjusting the thickness of the single-sided negative electrode active material layer to 82 μm, the other steps are the same as in Example 1.

[0097] Example 13

[0098] Except for adjusting the thickness of the single-sided negative electrode active material layer to 87 μm, the other steps are the same as in Example 1.

[0099] Example 14

[0100] Except for adjusting the thickness of the single-sided negative electrode active material layer to 72 μm, the other steps are the same as in Example 1.

[0101] Example 15

[0102] Except for adjusting the thickness of the single-sided negative electrode active material layer to 95 μm, the other steps are the same as in Example 1.

[0103] Comparative Example 1

[0104] Except for the preparation of the positive electrode active material, which involves weighing Li₂CO₃ and MnO₂ according to a Li:Mn molar ratio of 0.56:1, adding Al₂O₃ and Nb₂O₅ according to an Al:Mn molar ratio of 0.05:1 and a Nb:Mn molar ratio of 0.01:1, and mixing in a high-speed mixer at 300 r / min for 20 min to obtain a mixture, placing the mixture in an air furnace, heating it to 790°C at 5°C / min, maintaining it for 24 h, and then naturally cooling it before removing it and passing it through a 300-mesh sieve to obtain spinel-type lithium manganese oxide. The thickness of the single-sided positive electrode active material layer was adjusted to 118 μm, and the other steps were the same as in Example 1.

[0105] Characterization and efficacy verification experiments

[0106] (1) XRD test

[0107] The lithium-ion battery was fully discharged to 2.8V. The battery was then disassembled, and the positive electrode was removed. The positive electrode was immersed in dimethyl carbonate (DMC) for 30 minutes to remove electrolyte and byproducts from its surface. It was then dried in a fume hood for 4 hours. The positive active material layer was scraped off with a scraper to obtain a powder. This powder was then placed in the sample stage of an XRD instrument (Brook, D8 model) and XRD diffraction patterns were obtained using a scan rate of 2° / min and a scan angle range of 10° to 90°.

[0108] In the XRD diffraction pattern, the peak intensity I of the first diffraction peak near 17.8° was read within the range of 17.8° to 19.2°. A The full width at half maximum (FWHM) of the first diffraction peak is W. A The peak intensity I of the second diffraction peak near 17.8° B The full width at half maximum (FWHM) of the second diffraction peak is W. B I was calculated A / I B and W A / W B value.

[0109] (2) Morphological testing methods

[0110] The fully loaded positive electrode sheet was cleaned and disassembled using DMC, and then dried at 60°C for 2 hours. The positive electrode sheet was then cut along its own thickness direction using an ion polisher to obtain a flat cross-section. The cross-section was tested using a scanning electron microscope (SEM) to determine the particle morphology.

[0111] (3) Al / Mn element content test

[0112] Elemental analysis (EDS) was used to test selected particles on the electrode cross-section to determine the content of elements such as Al and Mn, and the ratio was calculated.

[0113] (4)n Li / n Mn test

[0114] After disassembling the lithium-ion battery to 2.8V, the inside of the battery was rinsed with organic solvent and the solvent was collected. After the electrodes were dried, the area of ​​the positive electrode active material layer was measured as Sc and the area of ​​the negative electrode active material layer was measured as Sa. A positive electrode with an area of ​​S1 was taken, and the positive electrode active material layer was collected. After burning off the binder and conductive agent in the positive electrode active material layer, the mass of the remaining powder was weighed as m1. The mass percentage of lithium element in the powder was measured as x1 and the mass percentage of Mn element as y using inductively coupled atomic emission spectrometry (ICP-AES). The molar content of lithium element in the positive electrode was then determined to be n. Lic =x1×m1 / MLi The molar content of Mn element is n Mn =m1×y / M Mn , of which M Li M is the molar mass of Li. Mn denoted as Mn, where Mn is the molar mass of the element.

[0115] Take a negative electrode sheet with a negative electrode active material layer area of ​​S2, where S2 = S1 × Sa / Sc. Collect the negative electrode active material layer, and after burning off the binder in the negative electrode active material layer, weigh the remaining powder as m2. Measure the mass percentage of lithium in the powder using ICP-AES as x2. Then, the molar content of lithium in the negative electrode sheet is n. Lia = x2×m2 / M Li Then n Li =n Lic +n Lia .

[0116] (5) CB test

[0117] A positive electrode with a test area of ​​Stc is assembled into a coin cell using lithium metal as the counter electrode, and the capacity of the positive electrode is measured as Ctc. Similarly, a negative electrode with a test area of ​​Sta is assembled into a coin cell using lithium metal as the counter electrode, and the capacity of the negative electrode is measured as Cta. Therefore, CB = (Ctc × Sc / Stc) / (Cta × Sa / Sta). The voltage test range for the negative electrode is 2V-0.005V. The voltage test range for the positive electrode is 3V-4.3V. The current for both electrodes is 0.2C, where 1C equals 100mAh / g.

[0118] (6) Discharge capacity test at 25℃ / 0.2C

[0119] At 25°C, the lithium-ion battery was charged to 4.2V at a constant current of 0.5C, then charged to 0.05C at a constant voltage of 4.2V, and then discharged to 2.8V at a constant current of 0.2C. The discharge capacity was recorded as D01.

[0120] The discharge capacity D is calculated using the following formula: D = D01 / m, where the unit is mAh / g and m is the mass of the positive electrode active material.

[0121] (7) Cyclic performance test

[0122] 25℃ 500-cycle capacity retention

[0123] The lithium-ion battery was charged at 25°C with a constant current of 0.5C to 4.2V, then charged with a constant voltage to a current of 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 1C to 2.8V. This constitutes one charge-discharge cycle, and the discharge capacity is recorded as D02. The lithium-ion battery was subjected to 500 cycles following the same procedure, and the discharge capacity of the 500th cycle was measured as D2. The capacity retention rate (%) after 500 cycles at 25°C is calculated as D2 / D02 × 100%.

[0124] 55℃ 200-cycle capacity retention

[0125] The lithium-ion battery was charged at 55℃ with a constant current of 0.5C to 4.2V, then charged with a constant voltage to a current of 0.05C, allowed to stand for 5 minutes, and then discharged at a constant current of 1C to 2.8V. This constitutes one charge-discharge cycle, and the discharge capacity is recorded as D03. The lithium-ion battery was subjected to 200 cycles following the same procedure, and the discharge capacity of the 200th cycle was measured as D3. The capacity retention rate (%) after 200 cycles at 55℃ is calculated as D3 / D03 × 100%.

[0126] (8) Lithium plating test

[0127] The lithium-ion battery was charged at 0°C with a constant current of 0.5C to 4.2V, then charged with a constant voltage to a current of 0.05C, left to stand for 5 minutes, and then discharged with a constant current of 1C to 2.8V. This charge-discharge cycle was repeated 10 times, and the charge was stopped after the 10th full charge cycle. After disassembling the battery, the surface of the negative electrode was analyzed, and the percentage of lithium plating area to the total negative electrode area was measured.

[0128] The XRD diffraction pattern of the positive electrode active material layer of the lithium-ion battery in Example 1 under fully discharged state is as follows: Figures 1-2 As shown, the cross-sectional SEM image is as follows. Figure 3 As shown.

[0129] The characterization and effect verification results of Examples 1-15 and Comparative Example 1 are shown in Table 1.

[0130] Table 1

[0131]

[0132] As shown in Table 1, Examples 1-15, which exhibit first and second diffraction peaks in the X-ray diffraction pattern of the positive electrode active material layer within the range of 17.8°–19.2°, demonstrate significantly improved discharge specific capacity and enhanced cycle performance. This is attributed to the presence of Li in the positive electrode active material layer. x The presence of MnO2 material can provide active lithium for the formation and repair of SEI film, inhibit the excessive extraction of lithium ions from spinel-type lithium manganese oxide, thereby inhibiting the decrease in structural stability of spinel-type lithium manganese oxide and the dissolution of manganese ions.

[0133] The results of Examples 1-5 show that different LiMnO2 contents affect I A / I B The value, and at the same time causing n Li / n Mn Changes affect the discharge capacity, cycle performance, and safety performance of lithium-ion batteries; with the increase of LiMnO2 material content, I A / I B and n Li / n Mn Increased Ic leads to improved specific capacity and better cycle performance. A / I B When the value reaches 0.19, although the cycle performance continues to improve, the discharge capacity no longer increases. At the same time, it will cause the lithium plating area to increase during low-temperature charging of lithium-ion batteries, affecting the safety performance of lithium-ion batteries.

[0134] The results of Examples 6-10 show that changes in the Al content in LiMnO2 materials affect the structural stability of the LiMnO2 materials. Higher Al content results in a more stable structure, a narrower full width at half maximum (FWHM) of the first diffraction peak, and better cycle performance. A / W B Examples 6-9, in the range of 1.05 to 1.56, exhibit superior cycling performance.

[0135] The results of Examples 11-15 show that as the CB value increases, the discharge specific capacity increases, but the cycle performance decreases. When the CB is small, the lithium plating area of ​​the lithium-ion battery increases during low-temperature charging, affecting safety performance. Therefore, lithium-ion batteries with a CB value in the range of 1.01 to 1.2 can have both improved specific capacity and better cycle performance, while also possessing excellent safety performance.

[0136] The embodiments described above are merely illustrative of several implementation methods of this application, intended to facilitate a detailed understanding of the technical solutions of this application by those skilled in the art, but should not be construed as limiting the scope of protection of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these modifications and improvements all fall within the scope of protection of this application.

Claims

1. An electrochemical device comprising a positive electrode, said positive electrode comprising a positive active material layer, characterized in that, When the electrochemical device is in a fully discharged state, the X-ray diffraction pattern of the positive electrode active material layer has a first diffraction peak and a second diffraction peak in the range of 17.8° to 19.2°, and the diffraction angle of the first diffraction peak is smaller than that of the second diffraction peak. The difference between the diffraction angle of the second diffraction peak and the diffraction angle of the first diffraction peak is less than or equal to 1°; The peak intensity of the first diffraction peak is I A The peak intensity of the second diffraction peak is I. B Satisfying: 0.03≤I A / I B ≤0.12; The positive electrode active material layer contains a first lithium manganese oxide having a spinel structure; the positive electrode active material layer also contains a second lithium manganese oxide, the second lithium manganese oxide comprising secondary particles formed by the aggregation of lamellar primary particles.

2. The electrochemical device according to claim 1, characterized in that, The full width at half maximum (FWHM) of the first diffraction peak is W A The full width at half maximum (FWHM) of the second diffraction peak is W. B Satisfying: 1≤W A / W B ≤2.

3. The electrochemical device according to claim 2, characterized in that, 1.05≤W A / IN B ≤1.56。 4. The electrochemical device according to claim 1, characterized in that, At least one of the following conditions must be met: (a) The X-ray diffraction pattern of the positive electrode active material layer has a third diffraction peak in the range of 35° to 37° and a fourth diffraction peak in the range of 43° to 45°; (b) The first lithium manganese oxide contains elements M and Mn, wherein the element M includes at least one of Al, Cr, Nb, Mg, Ti, V, Cu, Zr, Mo, La, Zn, Ga, Ru, Ag, Sn, Au, Ce, Pr, Nd, Sm, Gd, Fe, Co, Ni, W or Y, and the molar ratio of element M to element Mn in the first lithium manganese oxide is (0.0001~0.1):1; (c) The first lithium manganese oxide includes Li x1 Mn y1 M z1 O 4-t A t Wherein, 0.6≤x1≤1.2, 1.8≤y1≤2, 0≤z1≤0.2, 0≤t≤0.5, M includes at least one of Al, Cr, Nb, Mg, Ti, V, Cu, Zr, Mo, La, Zn, Ga, Ru, Ag, Sn, Au, Ce, Pr, Nd, Sm, Gd, Fe, Co, Ni, W or Y, and A includes at least one of S, N, F, Cl or Br.

5. The electrochemical device according to claim 4, characterized in that, The second lithium manganese oxide satisfies at least one of the following conditions: (1) The second lithium manganese oxide contains Al, Mn and optional Q, wherein the Q element contains at least one of Cr, Nb, Ti, Mg, V, Cu, Zr, Mo, La, Zn, Ga, Ru, Ag, Sn, Au, Ce, Pr, Nd, Sm, Gd, Fe, Co, Ni, W or Y; the molar ratio of Al to Mn in the second lithium manganese oxide is (0.0001~0.1):1; the molar ratio of Q to Mn in the second lithium manganese oxide is (0~0.1):1; (2) The second lithium manganese oxide includes Li x2 Mn y2 Al z2 Q q O2, wherein 0.1≤x2≤1.1, 0.9≤y2≤1, 0≤z2≤0.1, 0≤q≤0.1, and Q includes at least one of Cr, Nb, Ti, Mg, V, Cu, Zr, Mo, La, Zn, Ga, Ru, Ag, Sn, Au, Ce, Pr, Nd, Sm, Gd, Fe, Co, Ni, W, or Y.

6. The electrochemical device according to claim 1, characterized in that, The electrochemical device further includes a negative electrode plate, which comprises a negative electrode active material layer; the area of ​​the positive electrode active material layer is S. c The area of ​​the negative electrode active material layer is S a The molar content of lithium in the positive electrode active material layer with the first test area S1 is n. Lic The molar content of manganese is n Mn The molar content of lithium in the negative electrode active material layer with a second test area of ​​S2 is n. Lia Where S2 = S1 × S a / S c n Li =n Lic +n Lia ; satisfies: 0.54≤n Li / n Mn ≤0.

65.

7. The electrochemical device according to claim 1, characterized in that, The electrochemical device further includes a negative electrode plate, which comprises a negative electrode active material layer; the area of ​​the positive electrode active material layer is S. c The area of ​​the negative electrode active material layer is S a Let the test area be S. tc The positive electrode is assembled into a coin cell using lithium metal as the counter electrode. The capacity of the positive electrode is measured at 0.2C within a voltage range of 3V to 4.3V. tc Take the test area as S ta The negative electrode is assembled into a coin cell using lithium metal as the counter electrode. The capacity of the negative electrode is measured at 0.2C within a voltage range of 2V to 0.005V. ta ; Where CB = (C ta ×S a / S ta ) / (C tc ×S c / S tc ), satisfying: 0.97≤CB≤1.

35.

8. The electrochemical device according to claim 7, characterized in that, 1.01≤CB≤1.

2.

9. The electrochemical device according to claim 6 or 7, characterized in that, The negative electrode active material layer includes a negative electrode active material, which includes at least one of graphite, silicon material, silicon-oxygen material, silicon-carbon composite material, or silicon alloy.

10. An electrical appliance, characterized in that, Includes the electrochemical device according to any one of claims 1 to 9.

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