Electrochemical device and electronic device comprising the same

Abstract

The present application relates to electrochemical devices and electronic devices comprising the same. The present application discloses a lithium ion secondary battery comprising 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, wherein the first positive electrode material has better cycle stability and higher initial coulombic efficiency, and the second positive electrode material has higher initial charge specific capacity and lower initial coulombic efficiency, which can compensate for the loss of active lithium caused by the formation of SEI. The lithium ion secondary battery provided by the present application has the advantages of good rate performance and long cycle life.

Description

TECHNICAL FIELD

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

[0002] In recent years, with the continuous expansion of the industrialization scale of batteries and the development of related technologies, the cycle life of lithium ion batteries has attracted more and more attention and challenges. In the first charge-discharge process of lithium ion secondary batteries, a solid electrolyte interface (SEI) is formed on the surface of the negative electrode, causing irreversible capacity loss. In lithium ion energy storage devices using graphite negative electrodes, about 10% of the active lithium source is consumed in the first cycle. When high-capacity negative electrode materials such as alloy-based (silicon, tin, etc.), oxide-based (silicon oxide, tin oxide) and amorphous carbon negative electrodes are used, the consumption of active lithium source will be further intensified. In addition, in the subsequent cycle process, due to the destruction and regeneration of SEI, the active lithium source will be further consumed, causing the cycle life to decay. Therefore, a suitable lithium supplement method is of great significance to further improve the cycle life of lithium ion energy storage devices. SUMMARY

[0003] The present application provides an electrochemical device and an electronic device with improved rate performance and cycle life to solve the problems existing in the prior art to some extent.

[0004] In an embodiment, the present application provides an electrochemical device, which comprises a positive electrode, a negative electrode and an electrolyte. 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):

[0005] Li 1+x Co y Me z M 1-y-z O 2-t A t formula (I),

[0006] wherein -0.1 < x < 0.2, 0.8 < y ≤ 1, 0 ≤ z ≤ 1, 0 < y + z ≤ 1, 0 ≤ t < 0.2, Me and M each independently comprise at least one of Ni, Mn, Al, Mg, Ti, Zr, La or Y, Me and M are not the same, and A comprises 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 Ts Formula (II),

[0009] 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

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

[0011] 2.0 < R x P / Q < 36 Formula (1),

[0012] 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 / 1540.25 mm 2 .

[0013] In some embodiments, the positive electrode satisfies Formula (2): 5.0 < R x P / Q < 32 Formula (2).

[0014] In some embodiments, R < 3 Ω.

[0015] In some embodiments, 4.0 g / cm 3 < P < 4.3 g / cm 3 .

[0016] In some embodiments, 0.16 g / 1540.25 mm 2 < Q < 0.38 g / 1540.25 mm 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, the content of the first positive electrode material is 80% to 98% based on the total mass of the positive electrode material layer.

[0019] In some embodiments, the X-ray diffraction spectrum of the second positive electrode 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°, the ratio of the intensity I A of the characteristic diffraction peak A to the intensity I B of the characteristic diffraction peak B satisfies Formula (3): 0 < I A / I B < 0.2 Formula (3). A B In some embodiments, the X-ray diffraction spectrum of the second positive electrode 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°, the ratio of the intensity I

[0020] ​In some embodiments, the second positive electrode material has both the characteristic diffraction peak A and the characteristic diffraction peak B shifted to a low angle direction after the first charge, and the shift range is <0.5°.

[0021] In some embodiments, the first positive electrode material comprises LiCoO2, LiCo 0.9 Ni 0.1 O2, LiCo 0.9 Ni 0.05 Mn 0.05 O2, or Li 0.95 Co 0.99 Al 0.01 O 1.95 F 0.05 , and / or the second positive electrode material comprises 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 .

[0022] In some embodiments, the electrolyte comprises fluoroethylene carbonate, and the content of the fluoroethylene carbonate is 1% to 15% based on the total mass of the electrolyte.

[0023] In another embodiment, the present application provides an electronic device comprising the electrochemical device according to the embodiments of the present application.

[0024] The present application provides a positive electrode containing a positive electrode lithium supplement material and a lithium ion secondary battery comprising the same. In one aspect, the surface free lithium content of the second positive electrode material used in the present application is low, and the processing performance is excellent. In addition, compared with the first positive electrode material, the specific capacity of the second positive electrode material is relatively high, and a large amount of lithium ions can be released during the first charge to supplement active lithium. The combination of the first positive electrode material with a high specific capacity and a layered structure can effectively improve the cycle life of the battery. In the second aspect, by designing the film resistance, the compaction density and the area density of the positive electrode, the cycle life and the rate performance of the lithium ion secondary battery can be significantly improved. In the third aspect, by adding fluoroethylene carbonate additive in the electrolyte, the negative electrode forms a SEI film rich in LiF component and uniform and dense, which inhibits the continuous loss of active lithium. At the same time, fluoroethylene carbonate is more resistant to high pressure oxidation at the positive electrode side, which can further improve the cycle life of the lithium ion secondary battery.

[0025] Additional aspects and advantages of the application will be described and will become apparent in the following description. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 XRD patterns of the second positive electrode material in Example 1 before and after the first cycle charging are shown.

[0027] Figure 2 A partial enlarged view of Figure 1 DETAILED DESCRIPTION

[0028] Embodiments of the application will be described in detail below. Embodiments of the application should not be construed as limiting the application.

[0029] Additionally, amounts, ratios, and other quantities in this document are sometimes presented in a range format. It is to be understood that the description in range format is merely for convenience and brevity and that one or more individual values within the range can also be considered as the lower or upper limit. All individual values and sub-ranges within the disclosed ranges are considered as disclosed.

[0030] In the DETAILED DESCRIPTION and in the claims, a list of items joined by the term "one of" or "one of each" can mean any single one of the listed items. For example, if the items enumerated are A and B, the phrase "one of A and B" means only A or, as an alternative, only B. In another example, if the items enumerated are A, B, and C, the phrase "one of A, B, and C" means only A; only B; or, only C. Item A can include a single element or multiple elements. Item B can include a single element or multiple elements. Item C can include a single element or multiple elements.

[0031] In the DETAILED DESCRIPTION and in the claims, a list of items joined by the term "at least one of" or "at least one of each" can mean any combination of the listed items. For example, if the items enumerated are A and B, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if the items enumerated are A, B, and C, 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, A, B, and C. Item A can include a single element or multiple elements. Item B can include a single element or multiple elements. Item C can include a single element or multiple elements.

[0032] I. Electrochemical devices

[0033] ​In some embodiments, the present application provides an electrochemical device, comprising a positive electrode, a negative electrode and an electrolyte.

[0034] 1. A positive electrode

[0035] In some embodiments, 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):

[0036] Li 1+x Co y Me z M 1-y-z O 2-t A t Formula (I),

[0037] wherein -0.1 < x < 0.2, 0.8 < y < 1, 0 < z < 1, 0 < y + z < 1, 0 < t < 0.2, Me and M each independently comprise at least one of Ni, Mn, Al, Mg, Ti, Zr, La or Y, Me and M are not the same, and A comprises at least one of S, N, F, Cl or Br; and

[0038] a second positive electrode material represented by formula (II):

[0039] Li 1+r Mn 1-p X p O 2-s T s Formula (II),

[0040] 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

[0041] The positive electrode satisfies formula (1):

[0042] 2.0 < R x P / Q < 36 Formula (1),

[0043] wherein R is the resistance of the positive electrode, unit is Ω; P is the compacted density of the positive electrode, unit is g / cm 3 ; and Q is the single face area density of the positive electrode, unit is g / 1540.25mm 2 .

[0044] In this context, the calculation of R·P / Q only involves the calculation of numerical values, for example, the resistance R of the positive electrode is 1.0 Ω, the compacted density P is 4.2 g / cm 3The single surface density Q of the positive electrode is 0.26 g / 1540.25 mm 2 Thus, R·P / Q = 16.15.

[0045] The resistance R of the positive electrode is the resistance value measured by the direct current two-probe method, wherein the contact area of the probe with the positive electrode is 49π mm 2 . As an example, the upper and lower sides of the positive electrode are clamped between two conductive terminals of an electrode sheet resistance tester, and pressure is applied to fix it. The diameter of the conductive terminal is 14 mm, and the applied pressure is 15 MPa-27 MPa. The electrode sheet resistance tester is a Denchi BT23562 type internal resistance tester.

[0046] The compacted density of the positive electrode can be calculated by the formula P = m / v, wherein m is the weight of the positive electrode material layer, in g; and v is the volume of the positive electrode material layer, in cm 3 . 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.

[0047] The single surface density Q of the positive electrode can be calculated by the formula Q = 1540.25m / A r , wherein m is the weight of the positive electrode material layer, in g; and A r is the area of the positive electrode material layer, in mm 2 .

[0048] 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 two surfaces of the positive electrode current collector.

[0049] In some embodiments, the first positive electrode material includes at least one of LiCoO2, LiCo 0.9 Ni 0.1 O2, LiCo 0.9 Ni 0.05 Mn 0.05 O2, or Li 0.95 Co 0.99 Al 0.01 O 1.95 F 0.05 . In some embodiments, the second positive electrode 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 S0.05 F 0.05 at least one of R, P, and Q.

[0050] In some embodiments, 5.0≤R×P / Q≤32. In some embodiments, R×P / Q has a value of 5.0, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, or a range consisting of any two of these values.

[0051] In some embodiments, R≤3Ω. In some embodiments, R is 0.2Ω, 0.5Ω, 1Ω, 1.2Ω, 1.5Ω, 1.8Ω, 2.0Ω, 2.2Ω, 2.5Ω, 3.0Ω, or a range consisting of any two of these values. When R is within the above range, the cycle performance and rate performance of the lithium ion secondary battery are improved.

[0052] In some embodiments, 4.0g / cm 3 < P < 4.3g / cm 3 In some embodiments, P is 4.0g / cm 3 , 4.1g / cm 3 , 4.2g / cm 3 , 4.3g / cm 3 , or a range consisting of any two of these values. When P is within the above range, the migration of electrons and ions in the positive electrode is facilitated, thereby improving the cycle performance of the lithium ion secondary battery.

[0053] In some embodiments, 0.16g / 15 40.25mm 2 < Q < 0.38g / 15 40.25mm 2 In some embodiments, Q is 0.16g / 15 40.25mm 2 , 0.18g / 15 40.25mm 2 , 0.2g / 15 40.25mm 2 , 0.25g / 15 40.25mm 2 , 0.28g / 15 40.25mm 2 , 0.30g / 15 40.25mm 2 , 0.34g / 15 40.25mm 2 , 0.36g / 15 40.25mm 2 , 0.38g / 15 40.25mm 2 , or a range consisting of any two of these values. When Q is within the above range, the cycle performance and rate performance of the lithium ion secondary battery are improved while ensuring the charge and discharge capacity.

[0054] 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.

[0055] 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.

[0056] 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).

[0057] 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.

[0058] 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.

[0059] ​In some embodiments, the cathode material layer includes a conductive agent. In some embodiments, the conductive agent includes at least one of graphite, super-P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, or carbon nanofibers.

[0060] In some embodiments, the content of the conductive agent is 0.5 to 20% based on the total mass of the cathode material layer. In some embodiments, the content of the conductive agent is 0.5%, 1%, 5%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, or a range consisting of any two of these values, based on the total mass of the cathode material layer.

[0061] In some embodiments, the cathode material layer includes a binder. In some embodiments, the binder includes at least one of styrene butadiene rubber (SBR), water-based acrylic resin, carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), ethylene-vinyl acetate copolymer (EVA), or polyvinyl alcohol (PVA).

[0062] In some embodiments, the content of the binder is 0.1 to 2.5% based on the total mass of the cathode material layer. In some embodiments, the content of the binder is 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.5%, or a range consisting of any two of these values, based on the total mass of the cathode material layer.

[0063] In some embodiments, the cathode current collector includes a metal foil or a porous metal plate. In some embodiments, the cathode current collector includes a foil or a porous plate of a metal such as aluminum, copper, nickel, titanium, or silver, or an alloy thereof. In some embodiments, the cathode current collector includes at least one of a copper foil or an aluminum foil.

[0064] In some embodiments, the thickness of the cathode current collector is 5 μm to 20 μm. In some embodiments, the thickness of the cathode current collector is 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, or a range consisting of any two of these values.

[0065] In some embodiments, the cathode can be obtained by mixing a cathode active material, a conductive agent, and a binder in a solvent to prepare an active material composition, and coating the active material composition on a current collector. In some embodiments, the solvent can include N-methylpyrrolidone, etc., but is not limited thereto.

[0066] The positive electrode provided by the application can fully exert the synergistic effect between the first positive electrode material and the second positive electrode material. On one hand, the second positive electrode material has the characteristics of high first charge specific capacity and low first effect, which can effectively compensate for the active lithium loss caused by the formation of SEI, and there are sufficient lithium ions to be embedded into the first positive electrode material during the first discharge, thereby effectively improving the energy density of the battery. On the other hand, the first positive electrode material selected by the application has high specific capacity, small volume change during charging and discharging, and good cycle stability. In addition, by designing the film resistance, the compaction density and the area density of the positive electrode, the energy density and the rate performance of the lithium ion secondary battery can be further improved. Therefore, by using the positive electrode provided by the application, the lithium ion secondary battery can have high energy density, good rate performance and long cycle life.

[0067] It should be noted that the film resistance, the compaction density and the single-face area density of the positive electrode are key parameters in the design and production of lithium ion secondary batteries. If the film resistance of the positive electrode is too large, the cycle performance and the rate performance of the lithium ion secondary battery will be deteriorated. If the compaction density is too large or too small, the cycle performance and the rate performance of the battery will be deteriorated. If the single-face area density of the positive electrode is too large, the cycle life of the battery will be reduced, and the penetration of the electrolyte will be affected, thereby affecting the rate performance of the battery, especially reducing the discharge capacity of the battery at high rate. If the single-face area density of the positive electrode is too small, the length of the current collector and the separator will be increased under the same battery capacity, thereby increasing the ohmic resistance of the battery.

[0068] In the case where the positive electrode comprises the first positive electrode material and the second positive electrode material, by comprehensively designing the film resistance, the compaction density and the single-face area density of the positive electrode, the electrochemical performance of the lithium ion secondary battery can achieve the expected results.

[0069] 2. Electrolyte

[0070] In some embodiments, the electrolyte used in the electrochemical device of the application comprises an electrolyte and a solvent for dissolving the electrolyte. In some embodiments, the electrolyte comprises an additive, and the additive comprises fluoroethylene carbonate, wherein the content of the fluoroethylene carbonate is 1%-15% based on the total mass of the electrolyte.

[0071] In some embodiments, the content of the fluoroethylene carbonate is 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15% or a range formed by any two of these values.

[0072] In some embodiments, the 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), butylene carbonate (BC), vinylene carbonate (VC), 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).

[0073] In some embodiments, the electrolyte further includes other additives, which can be any additive that can be used for lithium ion secondary batteries. In some embodiments, the other additives can be at least one of vinyl ethylene carbonate (VEC), succinonitrile (SN), adiponitrile (AND), 1,3-propanesultone (PST), sulfonate cyclic quaternary ammonium salt, tris(trimethylsilyl)phosphate (TMSP), or tris(trimethylsilyl)borate (TMSB).

[0074] The electrolyte is not particularly limited. In some embodiments, in the case of a lithium secondary battery, the electrolyte can include a lithium salt. Examples of the electrolyte can include, but are not limited to, lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorobisoxalate borate (LiDFOB), lithium bisoxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0075] In some embodiments, the content of the electrolyte is not particularly limited as long as the effects of the present application are not impaired. In some embodiments, the total molar concentration of lithium in the electrolyte is greater than 0.3 mol / L or more, 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 or less. In some embodiments, the total molar concentration of lithium in the electrolyte is within a range between any two of the above values. When the electrolyte concentration is within the above range, lithium as a charged particle is not too small, and the viscosity can be kept within an appropriate range, thus making it easy to ensure good electrical conductivity.

[0076] The electrolyte described above can be prepared using methods conventional in the art. It can be prepared by uniformly mixing an organic solvent, a lithium electrolyte salt, fluoroethylene carbonate, and other optional additives, with no particular restriction on the order of addition. For example, the lithium electrolyte salt, fluoroethylene carbonate, and other optional additives can be added to an organic solvent and mixed uniformly to obtain the electrolyte. Alternatively, the lithium electrolyte salt can be added to the organic solvent first, followed by the fluoroethylene carbonate and other optional additives, either separately or simultaneously.

[0077] 3. Negative electrode

[0078] 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.

[0079] In some embodiments, the negative electrode active material includes natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, and spinel-structured lithium titanate Li4Ti5O. 12 At least one of Li-Al alloy or metallic lithium. In some embodiments, the negative electrode active material may be used alone or in combination.

[0080] In some embodiments, the negative current collector can be made of materials such as metal foil or porous metal plates, for example, foil or porous plates of metals or alloys thereof such as copper, nickel, titanium or iron, such as copper foil.

[0081] In some embodiments, when the negative electrode current collector is a metallic material, the form of the negative electrode current collector 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 a range between any two of the above-mentioned values.

[0083] In some embodiments, the negative electrode active material layer can further include a negative electrode binder. The negative electrode binder can improve the binding between the negative electrode active material particles and the binding between the negative electrode active material and the current collector. The type of the negative electrode binder is not particularly limited as long as it is a material stable to the electrolyte or a solvent used in the electrode manufacturing. In some embodiments, the negative electrode binder includes at least one of styrene butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), an aqueous acrylic resin, or carboxymethyl cellulose (CMC).

[0084] In some embodiments, the negative electrode active material layer can further include a thickening agent. In some embodiments, the thickening agent includes carboxymethyl cellulose (CMC).

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

[0086] 4. Separation Film

[0087] In some embodiments, a separation film is generally provided between the positive electrode and the negative electrode in order to prevent short circuiting. In this case, the electrolyte of the present application is generally used by permeating into the separation film.

[0088] The material and shape of the separation film are not particularly limited as long as they do not significantly impair the effects of the present application. The separation film can be a resin, a glass fiber, an inorganic substance, etc. formed of a material stable to the electrolyte of the present application. In some embodiments, the separation film includes a porous sheet or a nonwoven fabric-like substance having excellent liquid retention, etc. Examples of the material of the resin or glass fiber separation film can include, but are not limited to, polyolefin, aramid, polytetrafluoroethylene, polyether sulfone, etc. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The above-mentioned materials of the separation film can be used alone or in any combination.

[0089] The separation film can also be a material in which the above-mentioned materials are layered, examples of which include, but are not limited to, a three-layer separation film in which polypropylene, polyethylene, and polypropylene are layered in this order, etc.

[0090] Examples of the inorganic material can include, but are not limited to, oxides such as alumina, silica, and the like, nitrides such as aluminum nitride, silicon nitride, and the like, sulfates (e.g., barium sulfate, calcium sulfate, and the like). The inorganic material can be in the form of, but is not limited to, a particulate or a fiber.

[0091] The separator film can be in the form of a thin film, examples of which include, but are not limited to, a nonwoven fabric, a woven fabric, a microporous film, and the like. In the thin film form, the separator film has a pore size of 0.01 μm to 1 μm and a thickness of 5 μm to 50 μm. In addition to the above-mentioned stand-alone thin film separator, a separator film formed by forming a composite porous layer containing the above-mentioned inorganic material particles on the surface of the positive electrode and / or the negative electrode using a resin-based adhesive can be used, for example, a separator film formed by forming a porous layer of alumina particles having a 90% particle size of less than 1 μm on both sides of the positive electrode using a fluororesin as an adhesive.

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

[0093] When a porous sheet or a nonwoven fabric or the like is used as the separator film, the porosity of the separator film is arbitrary. In some embodiments, the porosity of the separator film is greater than 10%, greater than 15%, or greater than 20%. In some embodiments, the porosity of the separator film is less than 60%, less than 50%, or less than 45%. In some embodiments, the porosity of the separator film is within a range defined by any two of the above-mentioned values. When the porosity of the separator film is within the above-mentioned range, the insulating properties and mechanical strength can be ensured, and the film resistance can be suppressed, allowing the electrochemical device to have good safety characteristics.

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

[0095] In some embodiments, the separator film is a single or multi-layer film of one or more of glass fiber, non-woven fabric, polyethylene (PE), polypropylene (PP), and polyvinylidene fluoride (PVDF).

[0096] 5. Electrochemical device

[0097] The electrochemical device of the present application includes any device in which an electrochemical reaction occurs, and specific examples thereof include primary batteries, secondary batteries, fuel cells, solar cells, or capacitors of all kinds. In particular, the electrochemical device is a lithium secondary battery, including a lithium metal secondary battery or a lithium ion secondary battery.

[0098] The present application also provides an electronic device including the electrochemical device according to the present application.

[0099] The use of the electrochemical device of the present application is not particularly limited, and it can be used in any electronic device known in the art. In some embodiments, the electrochemical device of the present application can be used in, but not limited to, notebook computers, pen-input computers, mobile computers, e-book players, portable telephones, portable facsimile machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, liquid crystal televisions, portable cleaners, portable CD players, mini-disc players, transceivers, electronic organizers, calculators, memory cards, portable audio recorders, radios, backup power supplies, motors, automobiles, motorcycles, power-assisted bicycles, bicycles, lighting appliances, toys, game machines, timepieces, power tools, flashlights, cameras, home-use large storage batteries, and lithium ion capacitors, etc.

[0100] The preparation of lithium ion batteries will be described below with lithium ion batteries as an example and in connection with specific embodiments, and those skilled in the art will understand that the preparation methods described in the present application are only examples, and any other suitable preparation method is within the scope of the present application.

[0101] Embodiments

[0102] The following describes performance evaluation of embodiments and comparative examples of lithium ion batteries according to the present application.

[0103] I. Preparation of lithium ion batteries

[0104] Example 1

[0105] 1. Preparation of positive electrodes

[0106] The first positive electrode material LiCoO2, the second positive electrode material LiMnO2, the binder PVDF and the conductive carbon black are mixed, wherein the weight ratio of LiCoO2, LiMnO2, PVDF and the conductive carbon black is 90.0:7.6:1.3:1.1, a solvent NMP is added, and the positive electrode slurry is obtained by stirring under the action of vacuum stirring until a uniform transparent system is formed. The positive electrode slurry is uniformly coated on the positive electrode current collector aluminum foil, and then transferred to an oven for drying, with a drying temperature of 120°C. After cold pressing and slitting, the positive electrode is obtained. The content of the first positive electrode material LiCoO2 is 90.0% and the content of the second positive electrode material LiMnO2 is 7.6% based on the total mass of the positive electrode material layer.

[0107] 2. Preparation of the negative electrode

[0108] The negative electrode active material artificial graphite, silicon monoxide, the binder polyacrylic acid (PAA) and the conductive carbon black are mixed according to the mass ratio of 85.9:10:2.8:1.3%, and a solvent deionized water is added to obtain the negative electrode slurry under the action of a vacuum stirrer. The negative electrode slurry is uniformly coated on the negative electrode current collector copper foil. It is transferred to an oven for drying, with a drying temperature of 120°C. After cold pressing and slitting, the negative electrode is obtained.

[0109] 3. Preparation of the electrolyte

[0110] Vinyl carbonate (EC), methyl ethyl carbonate (EMC) and diethyl carbonate (DEC) are mixed uniformly according to the volume ratio of 1:1:1 to obtain an organic solvent. LiPF6 is dissolved in the above-mentioned organic solvent to obtain a basic electrolyte, wherein the concentration of LiPF6 in the basic electrolyte is 1 mol / L. Fluoroethylene carbonate is added to the basic electrolyte and mixed uniformly to obtain the electrolyte, wherein the content of fluoroethylene carbonate is 5% based on the total mass of the electrolyte.

[0111] 4. Preparation of the separator

[0112] A polypropylene (PP) film (provided by Celgard Company) with a thickness of 14 μm is used as the separator.

[0113] 5. Preparation of the lithium ion battery

[0114] The positive electrode, the separator and the negative electrode are sequentially stacked and arranged, with the separator between the positive electrode and the negative electrode to play a separating role, and then wound into a bare cell and welded with the tabs. The bare cell is loaded into a shell, injected with electrolyte and sealed, and then subjected to processes such as standing, formation and shaping to obtain a lithium ion secondary battery.

[0115] Examples 2 to 15 :

[0116] Examples 2 to 15 differ from Example 1 in the kind of positive electrode material and the related performance parameters and the content of the additive in the electrolyte, see Table 1.

[0117] Comparative Example 1 :

[0118] Comparative Example 1 differs from Example 1 in that the positive electrode material in Comparative Example 1 contains only LiCoO2.

[0119] Comparative Example 2 :

[0120] Comparative Example 2 differs from Example 1 in that the positive electrode material in Comparative Example 2 contains only LiMnO2.

[0121] Comparative Examples 3 to 4 :

[0122] Comparative Examples 3 to 4 differ from Example 1 in the mass ratio of the first positive electrode material and the second positive electrode material in the positive electrode, see Table 1.

[0123] Comparative Examples 5 to 7 :

[0124] Comparative Examples 5 to 7 differ from Example 1 in the sheet resistance, the compact density and the single-sided area density of the positive electrode, see Table 1.

[0125] Comparative Examples 8 to 9 :

[0126] Comparative Examples 8 to 9 differ from Example 1 in the content of the fluoroethylene carbonate in the electrolyte, see Table 1.

[0127] II. Test Methods

[0128] 1. Test Method for the Sheet Resistance of the Positive Electrode

[0129] The sheet resistance of the positive electrode is tested using a Sugiwa BT3562 resistance tester. The test method comprises clamping the positive electrode between two conductive terminals of the internal resistance tester and applying pressure to fix it, and testing the resistance R of the positive electrode, wherein the diameter of the conductive terminals is 14 mm, the applied pressure is 15 MPa to 27 MPa, and the sampling time ranges from 5 s to 17 s.

[0130] 2. Test Method for the High Temperature Cycle Performance of the Lithium Ion Secondary Battery

[0131] The lithium ion secondary battery was charged at 45°C at a constant current of 1.5C rate to 4.5V, then charged at a constant voltage until the current was less than or equal to 0.05C, and then discharged at a constant current of 1C rate to 3.0V. This was one charge-discharge cycle, and the discharge capacity of the first cycle was recorded. The lithium ion secondary battery was subjected to charge-discharge cycles according to the above method, 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, and the number of charge-discharge cycles was recorded.

[0132] 3. Test method for rate capability of lithium ion secondary battery

[0133] The lithium ion secondary battery was charged at 25°C at a constant current of 0.2C rate to 4.5V, then charged at a constant voltage until the current was less than or equal to 0.05C, and then discharged at a constant current of 0.2C rate to 3.0V. The discharge capacity at 0.2C rate was recorded.

[0134] The lithium ion secondary battery was charged at 25°C at a constant current of 0.2C rate to 4.5V, then charged at a constant voltage until the current was less than or equal to 0.05C, and then discharged at a constant current of 2C rate to 3.0V. The discharge capacity at 2C rate was recorded.

[0135] The lithium ion secondary battery 2C rate discharge capacity retention rate (%) = 2C rate discharge capacity / 0.2C rate discharge capacity x 100%.

[0136] III. Test results

[0137] Table 1 shows the composition and related performance parameters of the positive electrode in Comparative Examples 1 to 9 and Examples 1 to 15, and the type and content of the additive in the electrolyte. The content of the first and second positive electrode materials is calculated based on the total mass of the positive electrode material layer, and the content of the fluoroethylene carbonate in the electrolyte is calculated based on the total mass of the electrolyte.

[0138] Table 1

[0139]

[0140]

[0141] Where " / " indicates the absence of the substance.

[0142] Table 2 shows the high-temperature cycle performance and rate capability of the lithium ion secondary battery in Comparative Examples 1 to 9 and Examples 1 to 15.

[0143] Table 2

[0144]

[0145] By comparing the above examples and comparative examples, it can be seen that, compared with the lithium ion battery in which the positive electrode only contains the first positive electrode material or the second positive electrode material, the lithium ion battery in which the positive electrode contains both the first positive electrode material and the second positive electrode material has significantly improved high-temperature cycle performance, while the rate performance does not change significantly. Therefore, the use of the first positive electrode material and the second positive electrode material together produces a synergistic effect. Without being bound by theory, the above-mentioned synergistic effect may be caused by the following reasons: first, the second positive electrode material used in the present application has a low free lithium content on the surface, and when it is added to the positive electrode, the obtained slurry has good stability and excellent processing performance; second, the second positive electrode material used in the present application has a high first-charge specific capacity and a low initial efficiency, which can better compensate for the loss of active lithium caused by the formation of SEI, and more lithium ions can be embedded into the first positive electrode material lattice during discharge, effectively improving the energy density of the lithium ion secondary battery; and third, the first positive electrode material has good cycle performance and high specific capacity, and by controlling the membrane resistance R, the compaction density P and the single-face area density Q of the positive electrode sheet within the range of the present application, the lithium ion secondary battery can have good cycle performance and rate performance.

[0146] In addition, as can be seen from the comparison results of Comparative Example 7 and Example 1, the fluorinated ethylene carbonate added to the electrolyte and the positive electrode containing both the first positive electrode material and the second positive electrode material can play a synergistic effect, which may be due to the fact that during the first charge, a large amount of active lithium released by the second positive electrode material is embedded into the negative electrode, causing the true potential of the negative electrode to further decrease, resulting in continuous reduction of the solvent in the electrolyte, affecting the cycle performance. The use of fluorinated ethylene carbonate additive can induce the formation of a more compact and light SEI layer, preventing the continuous consumption of the electrolyte. Moreover, fluorinated ethylene carbonate is more resistant to high-pressure oxidation and is more conducive to matching the high-voltage first positive electrode material.

[0147] The reference to "some embodiments", "certain embodiments", "one embodiment", "another embodiment", "an embodiment", "the embodiment", "particular embodiments" or "some aspects" in the present specification, means that at least one embodiment or aspect of the application contains the particular feature, structure, material, or characteristic being described in connection with that reference. Therefore, appearances of such phrases in various places throughout the specification are not necessarily referring to the same embodiment or aspect of the application. Furthermore, the particular features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments or aspects.

[0148] While the illustrative embodiments have been described and illustrated, it will be understood by those skilled in the art that the above-described embodiments are not the only ways in which the present application can be practiced. Changes can be made to the embodiments in light of the teachings of the present disclosure, and it is understood that many variations and modifications can be made within the 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 located on at least one surface of the positive electrode current collector, and the positive electrode material layer comprises a first positive electrode material having a layered structure represented by formula (I): Li 1+x Co y Me z M 1-y-z O 2-t A t Formula (I), in, -0.1 < x < 0.2, 0.8 < y ≤ 1, 0 ≤ z ≤ 1, 0 < y + z ≤ 1, 0 ≤ t < 0.2, Me and M each independently comprise at least one of Ni, Mn, Al, Mg, Ti, Zr, La or Y, and Me and M are different, 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): 2.0 ≤ R × P / Q ≤ 36 Formula (1), Where R is the resistance of the positive electrode, in Ω; P is the compaction density of the positive electrode, in g / cm³. 3 Q is the areal density of the positive electrode, expressed in g / 1540.25 mm². 2 ; Among them, 4.0 g / cm 3 ≤P≤4.3 g / cm 3 .

2. The electrochemical device according to claim 1, wherein the positive electrode satisfies formula (2): 5.0 ≤ R × P / Q ≤ 32 Formula (2).

3. The electrochemical device according to claim 1, wherein R ≤ 3 Ω.

4. The electrochemical device according to claim 1, wherein 0.16 g / 1540.25 mm 2 <Q<0.38 g / 1540.25mm 2 .

5. The electrochemical device according to claim 1, wherein the mass ratio of the first positive electrode material to the second positive electrode material is 5:1 to 99:

1.

6. The electrochemical device according to claim 1, wherein based on the total mass of the positive electrode material layer, the content of the first positive electrode material is 80% to 98%.

7. 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 A / I B ≤0.2 Equation (3).​ 8. The electrochemical device according to claim 7, wherein in the X-ray diffraction spectrum after the first cycle of charging of the second positive electrode material, both the characteristic diffraction peak A and the characteristic diffraction peak B shift towards the low angle direction, and the shift amplitude < 0.5°.

9. The electrochemical device according to claim 1, wherein the first positive electrode material comprises LiCoO2, LiCo 0.9 Ni 0.1 O2, LiCo 0.9 Ni 0.05 Mn 0.05 O2 or Li 0.95 Co 0.99 Al 0.01 O 1.95 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.

10. The electrochemical device according to claim 1, wherein the electrolyte contains fluoroethylene carbonate, and based on the total mass of the electrolyte, the content of fluoroethylene carbonate is 1% to 15%.

11. An electronic device, comprising the electrochemical device according to any one of claims 1-10.

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