Electrochemical device and electronic device comprising the same

Abstract

The application relates to an electrochemical device and an electronic device comprising the same. The electrochemical device of the application comprises a positive electrode, a negative electrode, a separator and an electrolyte. The positive electrode comprises a first positive electrode material and a second positive electrode material, the first positive electrode material has better cycle stability and higher initial coulomb efficiency, and the second positive electrode material has higher initial specific charge capacity and lower initial coulomb efficiency, and can compensate for the loss of active lithium caused by the formation of SEI. The electrochemical device provided by the application has the advantages of high energy density, good rate performance and long cycle life.

Description

Technical Field

[0001] This application relates to the field of energy storage, and particularly to an electrochemical device and an electronic device including the same, especially a lithium-ion battery. Background Art

[0002] In recent years, with the continuous expansion of the industrial scale of batteries and the development of related technologies, the energy density of lithium-ion batteries has received increasing attention and challenges. During the first charge-discharge process of a lithium-ion secondary battery, a solid electrolyte interface (SEI) forms on the surface of the negative electrode, resulting in irreversible capacity loss and reducing the energy density of lithium-ion energy storage devices. In lithium-ion energy storage devices using a graphite negative electrode, about 10% of the active lithium source is consumed during the first cycle. When using high specific capacity negative electrode materials such as alloys (silicon, tin, etc.), oxides (silicon oxide, tin oxide), and amorphous carbon negative electrodes, the consumption of the active lithium source will be further aggravated. Therefore, a suitable lithium supplementation method is of great significance for further improving the energy density of lithium-ion energy storage devices. Summary of the Invention

[0003] This application provides an electrochemical device and an electronic device with improved cycle performance and energy density to solve, to some extent, the problems existing in the prior art.

[0004] In one embodiment, this application provides an electrochemical device, which includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive electrode current collector and a positive electrode material layer located on at least one surface of the positive electrode current collector. The positive electrode material layer includes a first positive electrode material represented by formula (I):

[0005] Li 1+x Fe y Mn z M 1-y-z PO 4-t A t Formula (I),

[0006] where, -0.1 < x < 0.1, 0 < y ≤ 1, 0 ≤ z ≤ 1, 0 < y + z ≤ 1, 0 ≤ t < 0.2, M includes at least one of Ti, Zr, V, or Cr, and A includes at least one of S, N, F, Cl, or Br; and

[0007] a second positive electrode material represented by formula (II):

[0008] Li 1+r Mn 1-p X p O 2-s T s Formula (II),

[0009] Where, -0.1 < r < 0.2, 0 ≤ p < 0.2, 0 ≤ s < 0.2, X includes at least one of Fe, Co, Ni, Ti, Zn, Mg, Al, V, Cr or Zr, and T includes at least one of S, N, F, Cl or Br; and

[0010] The positive electrode satisfies formula (1):

[0011] 0.5 ≤ R × P / Q ≤ 16 Formula (1),

[0012] Where, R is the resistance of the positive electrode, with the unit of Ω; P is the tap density of the positive electrode, with the unit of g / cm 3 ; and Q is the single-sided areal density of the positive electrode, with the unit of g / 1540.25mm 2 .

[0013] In some embodiments, the positive electrode satisfies formula (2): 1.5 ≤ R × P / Q ≤ 10 Formula (2).

[0014] In some embodiments, R ≤ 3.5 Ω.

[0015] In some embodiments, 1.6 g / cm 3 < P < 2.6 g / cm 3 .

[0016] In some embodiments, 0.16 g / 1540.25mm 2 < Q < 0.45 g / 1540.25mm 2 .

[0017] In some embodiments, the mass ratio of the first positive electrode material to the second positive electrode material is 5:1 to 99:1.

[0018] In some embodiments, based on the total mass of the positive electrode material layer, the content of the first positive electrode material is 80% to 98%.

[0019] In some embodiments, the X-ray diffraction pattern of the second positive electrode material has a characteristic diffraction peak A in the range of 15° to 16°, and / or has a characteristic diffraction peak B in the range of 18° to 19°. The ratio I A of the intensity I of the characteristic diffraction peak A and the intensity I B of the characteristic diffraction peak B satisfies formula (3): 0 < I A / I B ≤ 0.2 Formula (3). A / I B .

[0020] In some embodiments, in the X-ray diffraction spectrum of the second cathode material after the first charge, both characteristic diffraction peak A and characteristic diffraction peak B are shifted to a lower angle direction, with a shift amplitude of <0.5°.

[0021] In some embodiments, the electrolyte comprises vinylene carbonate, wherein the content of vinylene carbonate is 0.05% to 5% based on the total mass of the electrolyte.

[0022] In another embodiment, this application provides an electronic device that includes the electrochemical device described in the embodiments of this application.

[0023] This application provides a lithium-ion secondary battery containing a positive electrode lithium replenishment material. Firstly, the second positive electrode material used in this application has a low surface free lithium content and excellent processing performance. Furthermore, compared to the first positive electrode material, this material has a higher specific capacity and can release a large amount of lithium ions during the first charge to replenish active lithium. Combining it with the first positive electrode material can effectively improve the battery's energy density and cycle life. Secondly, this application significantly improves the cycle life and energy density of the lithium-ion secondary battery through comprehensive design of the positive electrode's film resistance, compaction density, and areal density. Thirdly, by adding vinylene carbonate additive to the electrolyte, a more uniform and dense SEI film is formed on the negative electrode, suppressing the continuous loss of active lithium and further improving the cycle life of the lithium-ion secondary battery.

[0024] Additional aspects and advantages of this application will be described and shown in part in the following description, or illustrated by practice of the embodiments of this application. Attached Figure Description

[0025] Figure 1 The XRD patterns of the second cathode material in Example 1 before and after the first charge cycle are shown.

[0026] Figure 2 It shows Figure 1 A magnified view of a portion of the image. Detailed Implementation

[0027] The embodiments of this application will be described in detail below. These embodiments should not be construed as limiting the scope of this application.

[0028] Additionally, quantities, ratios, and other numerical values ​​are sometimes presented in range format in this document. It should be understood that such range format is for convenience and brevity and should be interpreted flexibly to include not only the numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0029] In the detailed description and claims, a list of items connected by terms such as "one of", "a", "a kind of" or other similar terms may mean any one of the listed items. For example, if items A and B are listed, the phrase "one of A and B" means only A or only B. In another example, if 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 a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements.

[0030] In the detailed description and claims, a list of items connected by terms such as "at least one of", "at least a", "at least a kind of" or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements.

[0031] I. Electrochemical device

[0032] In some embodiments, the present application provides an electrochemical device, which includes a positive electrode, a negative electrode, and an electrolyte.

[0033] 1. Positive electrode

[0034] In some embodiments, the positive electrode includes a positive electrode current collector and a positive electrode material layer located on at least one surface of the positive electrode current collector, and the positive electrode material layer includes a first positive electrode material represented by formula (I):

[0035] Li 1+x Fe y Mn z M 1-y-z PO 4-t A t Formula (I),

[0036] where -0.1 < x < 0.1, 0 < y ≤ 1, 0 ≤ z ≤ 1, 0 < y + z ≤ 1, 0 ≤ t < 0.2, M includes at least one of Ti, Zr, V or Cr, and A includes at least one of S, N, F, Cl or Br; and

[0037] A second positive electrode material represented by formula (II):

[0038] Li1+r Mn 1-p X p O 2-s T s Formula (II),

[0039] where, -0.1 < r < 0.2, 0 ≤ p < 0.2, 0 ≤ s < 0.2, X includes at least one of Fe, Co, Ni, Ti, Zn, Mg, Al, V, Cr or Zr, and T includes at least one of S, N, F, Cl or Br; and

[0040] the positive electrode satisfies Formula (1):

[0041] 0.5 ≤ R × P / Q ≤ 16 Formula (1),

[0042] where, R is the resistance of the positive electrode, in the unit of Ω; P is the tap density of the positive electrode, in the unit of g / cm 3 ; and Q is the single-sided surface density of the positive electrode, in the unit of g / 1540.25mm 2 .

[0043] In this article, the calculation of R·P / Q only involves numerical calculations. For example, the resistance R of the positive electrode is 0.5 Ω, the tap density P is 2.2 g / cm 3 , the single-sided surface density Q of the positive electrode is 0.3 g / 1540.25mm 2 , then R·P / Q = 3.7.

[0044] The resistance R of the positive electrode is the resistance value measured by the DC two-probe method, where the contact area between the probe and the positive electrode is 49π mm 2 . As an example, the upper and lower sides of the positive electrode are clamped between the two conductive terminals of the electrode resistance tester, and pressure is applied to fix them. The diameter of the conductive terminal is 14 mm, and the applied pressure is 15 MPa to 27 MPa. The electrode resistance tester is the HIOKI BT23562 type internal resistance tester.

[0045] The tap density of the positive electrode can be calculated by the formula P = m / v, where m is the weight of the positive electrode material layer, in the unit of g; v is the volume of the positive electrode material layer, in the unit of cm 3 . Where the volume v of the positive electrode material layer can be the product of the area A r of the positive electrode material layer and the thickness of the positive electrode material layer.

[0046] The single-sided surface density Q of the positive electrode can be calculated by the formula Q = 1540.25m / A r calculated, where m is the weight of the positive electrode material layer, in the unit of g; A r is the area of the positive electrode material layer, in the unit of mm 2 .

[0047] In some embodiments, the positive electrode material layer is located on one surface of the positive electrode current collector. In some embodiments, the positive electrode material layer is located on both surfaces of the positive electrode current collector.

[0048] In some embodiments, the first cathode material includes LiFePO4, LiFe 0.5 Mn 0.5 PO4, Li 0.9 Fe 0.5 Mn 0.45 Ti 0.05 PO4, Li 0.9 Fe 0.5 Mn 0.45 Ti 0.04 Zr 0.01 PO4 or Li 0.95 FePO 3.95 F 0.05 At least one of them. In some embodiments, the second cathode material includes LiMnO2, LiMn 0.9 Ni 0.1 O2, LiMn 0.9 Ni 0.05 Cr 0.05 O2, Li 0.95 MnO 1.95 F 0.05 Or Li 0.95 MnO 1.9 S 0.05 F 0.05 At least one of them.

[0049] In some embodiments, 1.5 ≤ R×P / Q ≤ 10. In some embodiments, the value of R×P / Q is 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 or a range of any two of these values.

[0050] In some embodiments, R ≤ 3.5Ω. In some embodiments, R is a range of 0.2Ω, 0.5Ω, 1Ω, 1.2Ω, 1.5Ω, 1.8Ω, 2.0Ω, 2.2Ω, 2.5Ω, 3.0Ω, 3.2Ω, 3.5Ω, or any combination of these values. When R is within the above range, it is beneficial to improve the cycle performance and rate performance of lithium-ion secondary batteries.

[0051] In some embodiments, 1.6 g / cm 3 <P<2.6g / cm 3 In some embodiments, P is 1.6 g / cm³. 3 1.8g / cm 32.0g / cm 3 2.2g / cm 3 2.4g / cm 3 2.6g / cm 3 Or a range of any two of these values. When P is within the above range, it is beneficial for the migration of electrons and ions in the positive electrode, thereby improving the cycle performance of lithium-ion secondary batteries.

[0052] In some embodiments, 0.16g / 1540.25mm 2 <Q<0.45g / 1540.25mm 2 In some embodiments, Q is 0.16 g / 1540.25 mm. 2 0.18g / 1540.25mm 2 0.2g / 1540.25mm 2 0.25g / 1540.25mm 2 0.28g / 1540.25mm 2 0.30g / 1540.25mm 2 0.34g / 1540.25mm 2 0.36g / 1540.25mm 2 0.38g / 1540.25mm 2 0.40g / 1540.25mm 2 0.42g / 1540.25mm 2 0.45g / 1540.25mm 2 Or a range of any two of these values. When Q is within the above range, the cycle performance and rate performance of lithium-ion secondary batteries can be improved while ensuring charge and discharge capacity.

[0053] In some embodiments, the mass ratio of the first cathode material to the second cathode material is from 5:1 to 99:1. In some embodiments, the mass ratio of the first cathode material to the second cathode material is 5:1, 9:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1, 50:1, 55:1, 60:1, 65:1, 70:1, 75:1, 80:1, 85:1, 90:1, 95:1, 99:1, or any combination of these values. When the mass ratio of the first cathode material to the second cathode material is within the above range, the cathode includes a higher content of the first cathode material, resulting in higher structural stability. This reduces capacity loss and impedance increase caused by structural damage to the cathode material, thereby maintaining the cycle stability and kinetic performance of the lithium-ion battery.

[0054] In some embodiments, the content of the first positive electrode material is 80% to 98% based on the total mass of the positive electrode material layer. In some embodiments, the content of the first positive electrode material is 80%, 82%, 84%, 85%, 88%, 90%, 92%, 94%, 96%, 98%, or any combination of these values, based on the total mass of the positive electrode material layer.

[0055] In some embodiments, the X-ray diffraction spectrum of the second cathode material has a characteristic diffraction peak A in the range of 15° to 16°, and / or a characteristic diffraction peak B in the range of 18° to 19°, wherein the intensity I of the characteristic diffraction peak A is... A and the intensity I of characteristic diffraction peak B B The ratio I A / I B Satisfying equation (3): 0 A / I B ≤0.2 Equation (3).

[0056] In some embodiments, I A / I B The value is 0.1, 0.12, 0.14, 0.16, 0.18, 0.2, or a range of any two of these values.

[0057] In some embodiments, in the X-ray diffraction spectrum of the second cathode material after the first charge, both characteristic diffraction peak A and characteristic diffraction peak B are shifted to a lower angle direction, with a shift amplitude of <0.5°. In some embodiments, the shift amplitude is 0.1°, 0.2°, 0.3°, 0.4°, 0.45°, or any combination of these values.

[0058] In some embodiments, the positive electrode material layer includes a conductive agent. In some embodiments, the conductive agent includes at least one of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0059] In some embodiments, the content of the conductive agent is 0.5% to 20% based on the total mass of the positive electrode material layer. In some embodiments, the content of the conductive agent is 0.5%, 1%, 5%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, or any combination of these values, based on the total mass of the positive electrode material layer.

[0060] ​In some embodiments, the positive electrode material layer includes an adhesive. In some embodiments, the adhesive includes at least one of styrene-butadiene rubber (SBR), aqueous acrylic resin, carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), ethylene-vinyl acetate copolymer (EVA), or polyvinyl alcohol (PVA).

[0061] In some embodiments, the binder content is from 0.1% to 2.5% based on the total mass of the positive electrode material layer. In some embodiments, the binder content is 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.5%, or a range of any two of these values, based on the total mass of the positive electrode material layer.

[0062] In some embodiments, the positive current collector comprises a metal foil or a porous metal plate. In some embodiments, the positive current collector comprises a foil or porous plate of a metal such as aluminum, copper, nickel, titanium, or silver, or alloys thereof. In some embodiments, the positive current collector comprises at least one of copper foil or aluminum foil.

[0063] In some embodiments, the thickness of the positive current collector is from 5 μm to 20 μm. In some embodiments, the thickness of the positive current collector is 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, or a range of any two of these values.

[0064] In some embodiments, the positive electrode can be obtained by mixing a positive electrode active material, a conductive agent, and a binder in a solvent to prepare an active material composition, and then coating the active material composition onto a current collector. In some embodiments, the solvent may include, but is not limited to, N-methylpyrrolidone, etc.

[0065] The cathode of this application fully leverages the synergistic effect between the first and second cathode materials. On one hand, during the first charge cycle, the high specific capacity and low initial efficiency of the second cathode material effectively compensate for the loss of active lithium caused by SEI formation. During the first discharge cycle, sufficient lithium ions are re-intercalated into the first cathode material, effectively improving the battery's energy density. On the other hand, the first cathode material selected in this application has a stable structure, minimal volume change during charge and discharge, and excellent cycle stability. Furthermore, by designing the film resistance, compaction density, and areal density of the cathode, the energy density, rate performance, and cycle life of the lithium-ion secondary battery can be further improved. Therefore, using the cathode of this application enables lithium-ion secondary batteries to achieve high energy density, good rate performance, and long cycle life.

[0066] It is important to note that the film resistance, compaction density, and areal density of the positive electrode are key parameters in the design and fabrication of lithium-ion rechargeable batteries. Excessive film resistance in the positive electrode will deteriorate the cycle performance and rate performance of the lithium-ion rechargeable battery. Conversely, excessively high or low compaction density will also worsen the battery's cycle performance and rate performance. Excessively high areal density in the positive electrode reduces the battery's cycle life and also affects electrolyte penetration, thus impacting the battery's rate performance, particularly reducing the discharge capacity at high rates. Conversely, insufficient areal density in the positive electrode means an increase in the length of the current collector and separator for the same battery capacity, increasing the battery's ohmic internal resistance.

[0067] This application, by comprehensively designing parameters such as film resistance, compaction density, and single-sided areal density of the positive electrode, enables the electrochemical performance of the lithium-ion secondary battery to achieve the expected results when the positive electrode simultaneously includes a first positive electrode material and a second positive electrode material.

[0068] 2. Electrolyte

[0069] In some embodiments, the electrolyte used in the electrochemical device of this application comprises an electrolyte and a solvent for dissolving the electrolyte. In some embodiments, the electrolyte includes an additive comprising vinylene carbonate, wherein the content of vinylene carbonate is 0.05% to 5% based on the total mass of the electrolyte.

[0070] In some embodiments, the content of the vinylene carbonate is 0.05%, 1%, 2%, 3%, 4%, 5%, or a range of any two of these values.

[0071] When the content of additives in the electrolyte is within the range specified in this application, the cycle performance and energy density of lithium-ion secondary batteries can be further improved.

[0072] In some embodiments, the electrolyte may further include other additives, which can be any additive that can be used as a lithium-ion secondary battery. This application does not impose specific limitations, and the additives can be selected according to actual needs. In some embodiments, other additives include at least one of ethylene ethylene carbonate (VEC), succinate (SN), adiponitrile (AND), 1,3-propenesulfonate lactone (PST), sulfonate cyclic quaternary ammonium salts, tris(trimethylsilane) phosphate (TMSP), or tris(trimethylsilane) borate (TMSB).

[0073] In some embodiments, the electrolyte further comprises any non-aqueous solvent that can be used as a solvent for the electrolyte.

[0074] In some embodiments, the non-aqueous solvent includes, but is not limited to, one or more of the following: cyclic carbonates, chain carbonates, cyclic carboxylic esters, chain carboxylic esters, cyclic ethers, chain ethers, phosphorus-containing organic solvents, sulfur-containing organic solvents, and aromatic fluorine-containing solvents.

[0075] In some embodiments, the non-aqueous solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butenyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), or diethyl sulfone (ESE).

[0076] There are no particular limitations on the electrolyte. In some embodiments, in the case of a lithium secondary battery, the electrolyte includes a lithium salt. Examples of electrolytes may include, but are not limited to, lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0077] There are no particular limitations on the content of the electrolyte, as long as it does not impair the effectiveness of this application. In some embodiments, the total molar concentration of lithium in the electrolyte is greater than 0.3 mol / L, greater than 0.4 mol / L, or greater than 0.5 mol / L. In some embodiments, the total molar concentration of lithium in the electrolyte is less than 3 mol / L, less than 2.5 mol / L, or less than 2.0 mol / L. In some embodiments, the total molar concentration of lithium in the electrolyte is within the range of any two of the above values. When the electrolyte concentration is within the above range, the amount of lithium as charged particles will not be too low, and the viscosity can be kept within an appropriate range, thus easily ensuring good conductivity.

[0078] 3. Negative electrode

[0079] In some embodiments, the negative electrode includes a negative electrode current collector and a layer of negative electrode active material located on one or both surfaces of the negative electrode current collector. The negative electrode active material layer contains negative electrode active material. The negative electrode active material layer can be one or more layers, and each layer in a multilayer negative electrode active material layer can contain the same or different negative electrode active materials. The negative electrode active material is any material capable of reversibly inserting and deintercalating metal ions such as lithium ions. In some embodiments, the rechargeable capacity of the negative electrode active material is greater than the discharge capacity of the negative electrode active material to prevent unintentional deposition of lithium metal on the negative electrode during charging.

[0080] Examples of negative electrode current collectors, used to retain the active material of the negative electrode, include, but are not limited to, metallic materials such as aluminum, copper, nickel, stainless steel, and nickel-plated steel. In some embodiments, the negative electrode current collector is copper.

[0081] When the negative electrode current collector is a metallic material, its form may include, but is not limited to, metal foil, metal cylinder, metal strip roll, metal plate, metal film, metal mesh, stamped metal, foamed metal, etc. In some embodiments, the negative electrode current collector is a metal film. In some embodiments, the negative electrode current collector is copper foil. In some embodiments, the negative electrode current collector is rolled copper foil based on rolling or electrolytic copper foil based on electrolysis.

[0082] In some embodiments, the thickness of the negative electrode current collector is greater than 1 μm or greater than 5 μm. In some embodiments, the thickness of the negative electrode current collector is less than 100 μm or less than 50 μm. In some embodiments, the thickness of the negative electrode current collector is within the range of any two of the above values.

[0083] There are no particular restrictions on the negative electrode active material, as long as it can reversibly absorb and release lithium ions. Examples of negative electrode active materials may include, but are not limited to, carbon materials such as natural graphite and artificial graphite; metals such as silicon (Si) and tin (Sn); or oxides of metal elements such as Si and Sn. Negative electrode active materials can be used alone or in combination.

[0084] In some embodiments, the negative electrode active material layer may further include a negative electrode binder. The negative electrode binder can improve the bonding between the negative electrode active material particles and the bonding between the negative electrode active material and the current collector. There are no particular limitations on the type of negative electrode binder, as long as it is a material stable to the electrolyte or the solvent used in electrode manufacturing. In some embodiments, the negative electrode binder includes a resin binder. Examples of resin binders include, but are not limited to, fluoropolymers, polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, etc. When preparing the negative electrode slurry using an aqueous solvent, the negative electrode binder includes, but is not limited to, carboxymethyl cellulose (CMC) or its salts, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salts, polyvinyl alcohol, etc.

[0085] In some embodiments, the negative electrode can be prepared by coating a negative electrode slurry containing a negative electrode active material, a resin binder, etc. onto a negative electrode current collector, drying it, and then calendering it to form a negative electrode active material layer on both sides of the negative electrode current collector, thereby obtaining the negative electrode.

[0086] 4. Separating membrane

[0087] In some embodiments, a separator is typically provided between the positive and negative electrodes to prevent short circuits. In this case, the electrolyte of this application is typically used after penetrating the separator.

[0088] There are no particular limitations on the material and shape of the separator, as long as it does not significantly impair the effectiveness of this application. The separator may be a resin, glass fiber, inorganic material, or other material formed from a material stable to the electrolyte of this application. In some embodiments, the separator includes a porous sheet or non-woven fabric-like material with excellent liquid retention properties. Examples of materials for resin or glass fiber separators may include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, etc. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The above-mentioned separator materials can be used alone or in any combination.

[0089] The separator can also be a material formed by laminating the above-mentioned materials, examples of which include, but are not limited to, a three-layer separator formed by laminating polypropylene, polyethylene, and polypropylene in that order.

[0090] Examples of inorganic materials may include, but are not limited to, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates (e.g., barium sulfate, calcium sulfate, etc.). Inorganic materials may be in, but are not limited to, particulate or fibrous forms.

[0091] The separator can be in the form of a thin film, examples of which include, but are not limited to, nonwoven fabrics, woven fabrics, microporous membranes, etc. In the form of a thin film, the pore size of the separator is 0.01 μm to 1 μm, and the thickness is 5 μm to 50 μm. In addition to the above-mentioned independent thin film separator, the following separator can also be used: a separator formed by using a resin-based adhesive to form a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive electrode and / or negative electrode, for example, a separator formed by using fluororesin as an adhesive to form a porous layer of alumina particles with a particle size of less than 1 μm on both sides of the positive electrode.

[0092] The thickness of the separator is arbitrary. In some embodiments, the thickness of the separator is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the separator is less than 50 μm, less than 40 μm, or less than 30 μm. In some embodiments, the thickness of the separator is within the range of any two of the above values. When the thickness of the separator is within the above range, insulation and mechanical strength can be ensured, and the rate capability and energy density of the electrochemical device can be ensured.

[0093] When using porous materials such as porous sheets or nonwoven fabrics as the separator, the porosity of the separator is arbitrary. In some embodiments, the porosity of the separator is greater than 10%, greater than 15%, or greater than 20%. In some embodiments, the porosity of the separator is less than 60%, less than 50%, or less than 45%. In some embodiments, the porosity of the separator is within the range of any two of the above values. When the porosity of the separator is within the above range, insulation and mechanical strength can be ensured, and membrane resistance can be suppressed, giving the electrochemical device good safety characteristics.

[0094] The average pore size of the separator is also arbitrary. In some embodiments, the average pore size of the separator is less than 0.5 μm or less than 0.2 μm. In some embodiments, the average pore size of the separator is greater than 0.05 μm. In some embodiments, the average pore size of the separator is within the range of any two of the above values. If the average pore size of the separator exceeds the above range, a short circuit is likely to occur. When the average pore size of the separator is within the above range, the electrochemical device has good safety characteristics.

[0095] 5. Electrochemical device

[0096] The electrochemical device of this application includes any device in which an electrochemical reaction occurs, and specific examples include all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery, including lithium metal secondary batteries or lithium-ion secondary batteries.

[0097] This application also provides an electronic device that includes the electrochemical device described in this application.

[0098] The application of the electrochemical device in this application is not particularly limited, and it can be used in any electronic device known in the prior art. In some embodiments, the electrochemical device of this application can be used in, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors, etc.

[0099] The following uses a lithium-ion battery as an example and combines specific embodiments to illustrate the preparation of a lithium-ion battery. Those skilled in the art will understand that the preparation method described in this application is only an example, and any other suitable preparation method is within the scope of this application.

[0100] Example

[0101] The following describes the performance evaluation based on the embodiments and comparative examples of the lithium-ion battery of this application.

[0102] I. Preparation of Lithium-ion Batteries

[0103] Example 1

[0104] 1. Preparation of the negative electrode

[0105] Artificial graphite (anode active material), sodium carboxymethyl cellulose (CMC) thickener, SBR binder, and conductive carbon black were mixed in a mass ratio of 95.7:1.0:1.8:1.5. Deionized water was added as a solvent, and the mixture was stirred in a vacuum mixer to obtain a cathode slurry. The cathode slurry was then uniformly coated onto a copper foil current collector. The mixture was then transferred to an oven for drying at 120°C. After cold pressing, slitting, and welding of tabs, the cathode was obtained.

[0106] 2. Preparation of the positive electrode

[0107] The first cathode material, LiFePO4, the second cathode material, LiMnO2, the binder PVDF, and conductive carbon black were mixed in a mass ratio of 90.4:6.0:2.1:1.5. N-methylpyrrolidone (NMP) was added as a solvent, and the mixture was stirred under vacuum until a homogeneous and transparent system was obtained, yielding a cathode slurry. The cathode slurry was uniformly coated onto a cathode current collector aluminum foil, then transferred to an oven for drying at 120°C. After cold pressing, slitting, and welding of tabs, the cathode was obtained. Based on the total mass of the cathode material layers, the content of the first cathode material, LiFePO4, was 90.4%, and the content of the second cathode material, LiMnO2, was 6.0%.

[0108] 3. Preparation of electrolyte

[0109] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed thoroughly at a volume ratio of 1:1:1 to obtain an organic solvent. LiPF6 was dissolved in the above organic solvent to obtain a basic electrolyte, wherein the concentration of LiPF6 in the basic electrolyte was 1 mol / L. Ethylene carbonate was added to this basic electrolyte and mixed thoroughly to obtain the electrolyte solution, wherein the content of vinylene carbonate was 3% based on the total mass of the electrolyte solution.

[0110] 4. Preparation of the separating membrane

[0111] A porous polyethylene membrane with an alumina coating and a thickness of 9 μm was used as the separator.

[0112] 5. Preparation of lithium-ion batteries

[0113] The obtained positive electrode, separator, and negative electrode are wound in sequence and placed in an outer packaging foil, leaving an injection port. Electrolyte is poured in through the injection port, the battery is sealed, and then processed through formation, capacity testing, and other procedures to produce a lithium-ion battery.

[0114] Examples 2 to 16 :

[0115] The differences between Examples 2 to 16 and Example 1 lie in the type of cathode material, related performance parameters, and the content of additives in the electrolyte, as detailed in Table 1.

[0116] Comparative Example 1 :

[0117] The difference between Comparative Example 1 and Example 1 is that the cathode material in Comparative Example 1 contains only LiFePO4.

[0118] Comparative Example 2 :

[0119] The difference between Comparative Example 2 and Example 1 is that the cathode material in Comparative Example 2 contains only LiMnO2.

[0120] Comparative Examples 3 to 4 :

[0121] The difference between Comparative Examples 3 and 4 and Example 1 lies in the different mass ratios of the first and second cathode materials in the cathode, as detailed in Table 1.

[0122] Comparative examples 5 to 6 :

[0123] The difference between Comparative Examples 5 and 6 and Example 1 lies in the different film resistance, compaction density, and single-sided areal density of the positive electrode, as detailed in Table 1.

[0124] Comparative examples 7 to 8 :

[0125] The difference between Comparative Examples 7 and 8 and Example 1 lies in the different mass percentage content of vinylene carbonate in the electrolyte, as detailed in Table 1.

[0126] II. Testing Methods

[0127] 1. Test method for the film resistance of the positive electrode

[0128] The film resistance of the positive electrode was tested using a HIOKI BT3562 resistance tester. The test method included: clamping the positive electrode between the two conductive terminals of the internal resistance tester and applying pressure to fix it, and testing the resistance R of the positive electrode. The diameter of the conductive terminals was 14 mm, the applied pressure was 15 MPa to 27 MPa, and the sampling time ranged from 5 s to 17 s.

[0129] 2. Test methods for high-temperature cycle performance of lithium-ion secondary batteries

[0130] At 60℃, the lithium-ion secondary battery was charged at a constant current rate of 1C to 4.2V, then charged at a constant voltage rate until the current was less than or equal to 0.05C, and then discharged at a constant current rate of 1C to 2.5V. This constitutes one charge-discharge cycle. The discharge capacity of the lithium-ion secondary battery in the first cycle was recorded. The lithium-ion secondary battery was charged and discharged in the same manner, and the discharge capacity of each cycle was recorded, until the discharge capacity of the lithium-ion secondary battery decreased to 80% of the discharge capacity of the first cycle. The number of charge-discharge cycles at this point was recorded.

[0131] 3. Test methods for the rate performance of lithium-ion secondary batteries

[0132] At 25°C, the lithium-ion secondary battery was charged at a constant current rate of 0.5C to 4.2V, then charged at a constant voltage rate until the current was less than or equal to 0.05C, and then discharged at a constant current rate of 0.5C to 2.5V. The discharge capacity at the 0.5C rate was recorded.

[0133] At 25°C, the lithium-ion secondary battery was charged at a constant current rate of 0.5C to 4.2V, then charged at a constant voltage rate until the current was less than or equal to 0.05C, and then discharged at a constant current rate of 2C to 2.5V. The discharge capacity at the 2C rate was recorded.

[0134] The 2C rate discharge capacity retention rate (%) of a lithium-ion secondary battery = 2C rate discharge capacity / 0.5C rate discharge capacity × 100%.

[0135] 4. Test methods for the energy density of lithium-ion secondary batteries

[0136] At 25°C, the lithium-ion secondary battery was charged at a constant current rate of 0.2C to 4.2V, then charged at a constant voltage rate until the current was less than or equal to 0.05C. After resting for 30 minutes, it was discharged at a constant current rate of 0.2C to 2.5V. The discharge capacity D0 (Ah) and discharge plateau V0 (V) of the lithium-ion secondary battery at the 0.2C rate were recorded. The weight of the lithium-ion battery was weighed and recorded as m0 (kg).

[0137] Calculate the energy density of a lithium-ion secondary battery using the following formula:

[0138] Energy density = D0 * V0 / m0.

[0139] III. Test Results

[0140] Table 1 shows the composition and related performance parameters of the positive electrodes in Comparative Examples 1 to 8 and Examples 1 to 16, as well as the types and contents of additives in the electrolyte. The contents of the first and second positive electrode materials are calculated based on the total mass of the positive electrode material layers, and the content of vinylene carbonate in the electrolyte is calculated based on the total mass of the electrolyte.

[0141] Table 1

[0142]

[0143]

[0144] The " / " indicates that the substance does not exist.

[0145] Table 2 shows the high-temperature cycling performance, rate performance, and energy density of the lithium-ion secondary batteries in Comparative Examples 1 to 8 and Examples 1 to 16.

[0146] Table 2

[0147] Serial Number R·P / Q High temperature cycle number Ratio performance (%) Energy density (Wh / Kg) Comparative Example 1 4.71 1450 98.4 162 Comparative Example 2 7.29 1 81.2 151 Comparative Example 3 4.71 1487 98.3 163 Comparative Example 4 4.71 2212 86.3 159 Comparative Example 5 56.9 1642 93.2 113 Comparative Example 6 0.36 1792 94.4 170 Comparative Example 7 4.71 1128 98.3 171 Comparative Example 8 4.71 2131 96.9 171 Example 1 4.71 2398 97.5 172 Example 2 4.71 2417 97.4 190 Example 3 4.71 2432 97.6 190 Example 4 4.71 2459 97.9 191 Example 5 4.71 2325 97.4 172 Example 6 4.71 2392 97.1 173 Example 7 4.71 2298 97.4 171 Example 8 4.71 2312 97.1 170 Example 9 4.71 2348 97.0 172 Example 10 4.71 2036 98.0 168 Example 11 4.71 2728 96.5 175 Example 12 0.67 2322 97.6 181 Example 13 8.80 2286 97.5 163 Example 14 15.2 2285 97.7 161 Example 15 4.71 2201 97.8 172 Example 16 4.71 2425 97.4 171

[0148] By comparing the above embodiments and contrasts, it can be seen that compared with lithium-ion batteries containing only the first or second cathode material, lithium-ion batteries containing both the first and second cathode materials have significantly improved high-temperature cycle performance and energy density, while the rate performance remains largely unchanged. This demonstrates that using both the first and second cathode materials together produces a synergistic effect. Without being theoretically constrained, the aforementioned synergistic effect may arise from the following reasons: First, the second cathode material used in this application has extremely low surface free lithium content, resulting in a stable slurry with excellent processing performance. Second, the second cathode material used in this application has a high initial charge specific capacity and low initial efficiency, which better compensates for the loss of active lithium caused by SEI formation, allowing more lithium ions to be re-intercalated into the first cathode material lattice during discharge, effectively improving the energy density of the lithium-ion secondary battery. Third, the first cathode material has a stable structure and good cycle performance; by controlling the film resistance R, compaction density P, and areal density Q of the cathode within the scope of this application, the lithium-ion secondary battery can achieve good cycle performance and rate performance.

[0149] Furthermore, the comparison results between Comparative Example 7 and Example 1 show that the vinylene carbonate added to the electrolyte can work synergistically with the positive electrode that simultaneously contains the first positive electrode material and the second positive electrode material. This may be because during the first charge, a large amount of active lithium extracted from the second positive electrode material is embedded in the negative electrode, which further reduces the true potential of the negative electrode, causing continuous reduction of the solvent in the electrolyte and affecting the cycle performance. Using vinylene carbonate additive can induce the formation of a denser and thinner SEI layer, preventing the continuous consumption of the electrolyte.

[0150] Throughout this specification, references to "some embodiments," "partial embodiments," "one embodiment," "another example," "example," "specific example," or "partial example" mean that at least one embodiment or example in this application includes a specific feature, structure, material, or characteristic described in that embodiment or example. Therefore, descriptions appearing throughout this specification, such as "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in an example," "in a specific example," or "example," do not necessarily refer to the same embodiments or examples in this application. Furthermore, specific features, structures, materials, or characteristics described herein can be combined in any suitable manner in one or more embodiments or examples.

[0151] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. An electrochemical device, comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode comprises a positive electrode current collector and a positive electrode material layer on at least one surface of the positive electrode current collector, the positive electrode material layer comprising a first positive electrode material represented by formula (I) : Li 1+x Fe y Mn z M 1-y-z PO 4-t A t Formula (I), wherein -0.1 < x < 0.1, 0 < y ≤ 1, 0 ≤ z ≤ 1, 0 < y + z ≤ 1, 0 ≤ t < 0.2, M comprises at least one of Ti, Zr, V or Cr, and A comprises at least one of S, N, F, Cl or Br; and a second positive electrode material represented by formula (II) : Li 1+r Mn 1-p X p O 2-s T s formula (II), wherein -0.1 < r < 0.2, 0 ≤ p < 0.2, 0 ≤ s < 0.2, X comprises at least one of Fe, Co, Ni, Ti, Zn, Mg, Al, V, Cr or Zr, and T comprises at least one of S, N, F, Cl or Br; and the positive electrode satisfies formula (1) : 0.5 ≤ R × P / Q ≤ 16 formula (1), wherein R is the electrical resistance of the positive electrode in Ω; P is the compacted density of the positive electrode in g / cm 3 ; and Q is the single-sided area density of the positive electrode in g / 15 40.25 mm 2 ; the mass ratio of the first positive electrode material to the second positive electrode material is 5: 1 to 99: 1; and the electrolyte comprises vinylene carbonate, wherein the content of the vinylene carbonate is 0.05% to 5% based on the total mass of the electrolyte. wherein 1.6 g / cm 3 < P < 2.6 g / cm 3 . 2.The electrochemical device according to claim 1, wherein the positive electrode satisfies formula (2) : 1.5 ≤ R × P / Q ≤ 10 formula (2). 3.The electrochemical device according to claim 1, wherein R ≤ 3.5 Ω.

4. The electrochemical device of claim 1, wherein 0.16 g / 15 40.25 mm 2 <0.45 g / 15 40.25 mm 2 . 5.The electrochemical device according to claim 1, wherein the content of the first positive electrode material is 80% to 98% based on the total mass of the positive electrode material layer.

6. The electrochemical device according to claim 1, wherein the X-ray diffraction spectrum of the second cathode material has a characteristic diffraction peak A in the range of 15° to 16°, and / or a characteristic diffraction peak B in the range of 18° to 19°, and the intensity I of the characteristic diffraction peak A is... A and the intensity I of characteristic diffraction peak B B The ratio I A / I B Satisfying equation (3): 0 < I A / I B ≤0.2 Equation (3). 7.The electrochemical device according to claim 6, wherein both the characteristic diffraction peak A and the characteristic diffraction peak B of the second positive electrode material are shifted to a low angle direction after the first cycle of charging, and the shift amplitude is < 0.5°.

8. The electrochemical device according to claim 1, wherein the first positive electrode material comprises LiFePO4, LiFe 0.5 Mn 0.5 PO4, Li 0.9 Fe 0.5 Mn 0.45 Ti 0.05 PO4, Li 0.9 Fe 0.5 Mn 0.45 Ti 0.04 Zr 0.01 PO4 or Li 0.95 FePO 3.95 F 0.05 At least one of the following; and / or the second cathode material includes LiMnO2, LiMn 0.9 Ni 0.1 O2, LiMn 0.9 Ni 0.05 Cr 0.05 O2, Li 0.95 MnO 1.95 F 0.05 Or Li 0.95 MnO 1.9 S 0.05 F 0.05 At least one of them. 9.An electronic device comprising the electrochemical device according to any one of claims 1-8.

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