Electrochemical device and electronic device including the same

Abstract

The present invention provides an electrochemical device and an electronic device including the same. The lithium ion secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode includes a first positive electrode material and a second positive electrode material, where the first positive electrode material has good cycle stability and high initial coulombic efficiency, and the second positive electrode material has high initial charge specific capacity and low initial coulombic efficiency, which can compensate for the loss of active lithium due to the formation of SEI. The lithium ion secondary battery has the advantages of good rate characteristics and long cycle life.

Description

[Technical Field]

[0001] The present invention relates to the field of energy storage, and in particular to electrochemical devices and electronic devices containing same, especially lithium-ion batteries. [Background technology]

[0002] In recent years, with the expansion of the battery industrial scale and the development of related technologies, the cycle life of lithium-ion batteries has received increasing attention and challenges. In lithium-ion secondary batteries, a solid electrolyte interface (SEI) forms on the surface of the negative electrode during the initial charge / discharge process, resulting in irreversible capacity loss. In lithium-ion energy storage devices using graphite as the negative electrode, approximately 10% of the active lithium source is consumed during the first cycle. This consumption is even greater when using negative electrode materials with high specific capacity, such as alloys (e.g., silicon and tin), oxides (e.g., silicon oxide and tin oxide), and amorphous carbon. Furthermore, during subsequent cycles, the destruction and regeneration of the SEI further consumes the active lithium source, thereby reducing the cycle life. Therefore, it is important to provide an appropriate method for replenishing lithium to further improve the cycle life of lithium-ion energy storage devices. Summary of the Invention

[0003] The present invention provides electrochemical and electronic devices with improved rate capabilities and cycle life to overcome some of the problems present in the prior art.

[0004] In one embodiment, the present invention provides 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, the positive electrode material layer comprising a first positive electrode material and a second positive electrode material; The first positive electrode material is represented by formula (I): Li 1+x Co y Me z M 1-y-z O2-t A t Formula (I) where -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 contain at least one of Ni, Mn, Al, Mg, Ti, Zr, La, and Y, and Me and M are different, and A contains at least one of S, N, F, Cl, and Br, The second positive electrode material is represented by formula (II), Li 1+r Mn 1-p X p O 2-s T s Formula (II) where -0.1 < r < 0.2, 0 ≤ p < 0.2, 0 ≤ s < 0.2, X contains at least one of Fe, Co, Ni, Ti, Zn, Mg, Al, V, Cr, and Zr, and T contains at least one of S, N, F, Cl, and 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, with the unit of Ω, P is the compression density of the positive electrode, with the unit of g / cm 3 and Q is the areal density of one side of the positive electrode, with the unit of g / 1540.25mm 2 is.

[0005] In some embodiments, the positive electrode satisfies formula (2). 5.0 ≤ R × P / Q ≤ 32 Formula (2)

[0006] In some embodiments, R satisfies R ≤ 3Ω.

[0007] In some embodiments, P is 4.0g / cm 3 ≤ P ≤ 4.3g / cm 3 satisfies.

[0008] In some embodiments, Q is 0.16g / 1540.25mm 2 < Q < 0.38g / 1540.25mm 2 satisfies.

[0009] In some embodiments, the weight ratio of the first positive electrode material to the second positive electrode material is between 5:1 and 99:1.

[0010] In some embodiments, the content of the first positive electrode material is 80% to 98% of the total mass of the positive electrode material layer.

[0011] 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°, and the intensity I of the characteristic diffraction peak A A and the intensity of characteristic diffraction peak B I B The ratio value I A / I B satisfies equation (3). 0 A / I B ≦0.2 Equation (3)

[0012] In some embodiments, in the X-ray diffraction spectrum of the second positive electrode material after charging in the first cycle, both characteristic diffraction peak A and characteristic diffraction peak B are shifted to lower angles, and the shift width satisfies a shift width of <0.5°.

[0013] In some embodiments, the first cathode material is LiCoO, LiCo 0.9 Ni 0.1 O2, LiCo 0.9 Ni 0.05 Mn 0.05 O2 and Li 0.95 Co 0.99 Al 0.01 O 1.95 F 0.05 and / or the second positive electrode material comprises at least one of 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 and Li 0.95 MnO​1.9 S 0.05 F 0.05 The above-mentioned configuration includes at least one of the following:

[0014] In some embodiments, the electrolyte comprises fluoroethylene carbonate, where the content of fluoroethylene carbonate is 1% to 15% based on the total weight of the electrolyte.

[0015] In another embodiment, the present invention provides an electronic device comprising an electrochemical device according to any embodiment of the present invention.

[0016] The present invention provides a positive electrode containing a positive electrode lithium supplement material and a lithium-ion secondary battery containing the same. First, the second positive electrode material used in the present invention has a low surface free lithium content and excellent processability. Furthermore, the specific capacity of this second positive electrode material is relatively high compared to the first positive electrode material, allowing it to release a large amount of lithium ions during the first charge, thereby compensating for the loss of active lithium. Combining this second positive electrode material with the first positive electrode material having a layered structure and high specific capacity effectively improves the cycle life of the battery. Second, the present invention significantly improves the cycle life and rate performance of lithium-ion secondary batteries by engineering the sheet resistance, compaction density, and areal density of the positive electrode. Third, adding fluoroethylene carbonate as an additive to the electrolyte forms a uniform and dense SEI film containing a large amount of LiF component on the negative electrode, thereby suppressing the continuous loss of active lithium. At the same time, fluoroethylene carbonate has stronger resistance to high-pressure oxidation on the positive electrode side, which can further improve the cycle life of the lithium ion secondary battery.

[0017] Additional aspects and advantages of embodiments of the invention are set forth in part in the description that follows, and in part are illustrated by the description, or may be learned through the practice of embodiments of the invention. [Brief explanation of the drawings]

[0018] [Figure 1]FIG. 1 shows the XRD spectra of the second positive electrode material in Example 1 before and after charging in the first cycle. [Figure 2] FIG. 2 shows an enlarged view of a portion of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0019] Examples of the present invention are described in detail below, but should not be construed as limiting the present invention.

[0020] It should be noted that quantities, ratios, and other numerical values ​​may be presented in range format herein. It should be understood that such range format is used for convenience and brevity. It should also be understood that the range format should be read flexibly to encompass not only the numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or subranges contained within the ranges where each numerical value and subrange is explicitly specified.

[0021] In specific embodiments and in the claims, a list of items connected by the terms "one of," "one of," "one of," or other similar terms means any of the listed items. For example, if item A and item B are listed, the phrase "one of A and B" means only A or only B. In other examples, if item A, item B, and item 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.

[0022] In specific embodiments and claims, a list of items connected by terms such as "at least one of", "at least one", "at least one kind of", or other similar terms means any combination of the listed items. For example, if 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 other examples, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A, only B, only C, A and B (excluding C), A and C (excluding B), B and C (excluding A), or all of A, B, and C. Item A may include 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.

[0023] I. Electrochemical device In some embodiments, the present invention provides an electrochemical device including a positive electrode, a negative electrode, and an electrolyte.

[0024] 1. Positive electrode 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 and a second positive electrode material. The first positive electrode material is represented by formula (I). Li 1+x Co y Me z M 1-y-z O 2-t A t Formula (I) Here, -0.1 < x < 0., 0.8 < y ≤ 1, 0 ≤ z ≤ 1, 0 < y + z ≤ 1, 0 ≤ t < 0.2, Me and M each independently include at least one kind of Ni, Mn, Al, Mg, Ti, Zr, La, and Y, and Me and M are different, and A includes at least one kind of S, N, F, Cl, and Br. The second positive electrode material is represented by formula (II). [[ID=第34]]Li 1+r Mn1-p X p O 2-s T s Formula (II) where -0.1 < r < 0.2, 0 ≤ p < 0.2, 0 ≤ s < 0.2, X contains at least one of Fe, Co, Ni, Ti, Zn, Mg, Al, V, Cr, and Zr, and T contains at least one of S, N, F, Cl, and 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, with the unit of Ω, P is the compression density of the positive electrode, with the unit of g / cm 3 and Q is the areal density of one side of the positive electrode, with the unit of g / 1540.25mm 2 .

[0025] In this specification, the calculation of R·P / Q is only related to the calculation of numerical values. For example, if the resistance R of the positive electrode is 1.0 Ω, the compression density P is 4.2 g / cm 3 , and the areal density Q of one side of the positive electrode is 0.26 g / 1540.25mm 2 , then R·P / Q = 16.15.

[0026] 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 sandwiched between the two conductive terminals of the electrode resistance meter and fixed by applying pressure. The diameter of the conductive terminal is 14 mm, and the applied pressure is 15 Mpa to 27 MPa. The electrode resistance meter is a Hioki BT23562 type battery tester.

[0027] The compression density of the positive electrode can be calculated by the formula P = m / v. In this formula, m is the weight of the positive electrode material layer, with the unit of g, and v is the volume of the positive electrode material layer, with the unit of cm 3 . Here, the volume v of the positive electrode material layer may be the product of the area A r of the positive electrode material layer and the thickness of the positive electrode material layer.

[0028] The areal density Q of one side of the positive electrode is given by the formula Q = 1540.25m / Ar In this formula, 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 is.

[0029] 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.

[0030] In some embodiments, the first cathode material is LiCoO, LiCo 0.9 Ni 0.1 O2, LiCo 0.9 Ni 0.05 Mn 0.05 O2 and Li 0.95 Co 0.99 Al 0.01 O 1.95 F 0.05 In some embodiments, the second positive electrode material includes at least one of 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 and Li 0.95 MnO 1.9 S 0.05 F 0.05 It includes at least one of the following:

[0031] In some embodiments, R, P, and Q satisfy the relationship 5.0≦R×P / Q≦32. In some embodiments, the value of R×P / Q is 5.0, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, or 32, or a range consisting of any two of these values.

[0032] In some embodiments, R satisfies R≦3Ω. In some embodiments, R is 0.2Ω, 0.5Ω, 1Ω, 1.2Ω, 1.5Ω, 1.8Ω, 2.0Ω, 2.2Ω, 2.5Ω, or 3.0Ω, or is within a range consisting of any two of these values. R within the above range is advantageous for improving the cycle characteristics and rate characteristics of the lithium-ion secondary battery.

[0033] In some examples, P is 4.0 g / cm 3 <P<4.3g / cm 3 In some embodiments, P is 4.0 g / cm 3 , 4.1g / cm 3 , 4.2g / cm 3 , or 4.3 g / cm 3 or within a range consisting of any two of these values. When P is within the above range, it contributes to the movement of electrons and ions in the positive electrode, thereby improving the cycle characteristics of the lithium ion secondary battery.

[0034] In some embodiments, Q is 0.16 g / 1540.25 mm 2 <Q<0.38g / 1540.25mm 2 In some embodiments, Q satisfies 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 , or 0.38g / 1540.25mm 2 or within a range consisting of any two of these values. When Q is within the above range, the cycle characteristics and rate characteristics of the lithium ion secondary battery can be improved while ensuring the charge / discharge capacity.

[0035] In some embodiments, the mass ratio of the first positive electrode material to the second positive electrode material is 5:1 to 99:1. In some embodiments, the mass ratio of the first positive electrode material to the second positive electrode 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, or 99:1, or any range consisting of any two of these values. When the mass ratio of the first positive electrode material to the second positive electrode material is within the above range, the content of the first positive electrode material in the positive electrode is higher, resulting in higher structural stability of the positive electrode, which can reduce capacity loss and impedance increase due to structural destruction of the positive electrode material, thereby maintaining the cycling stability and kinetic performance of the lithium-ion battery.

[0036] In some embodiments, the content of the first positive electrode material is 80% to 98% of the total mass of the positive electrode layer, or 80%, 82%, 84%, 85%, 88%, 90%, 92%, 94%, 96%, or 98%, or any range consisting of any two of these values, of the total mass of the positive electrode layer.

[0037] 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°, and the intensity I of the characteristic diffraction peak A A and the intensity of characteristic diffraction peak B I B The ratio value I A / I B satisfies equation (3). 0 A / I B ≦0.2 Equation (3)

[0038] In some embodiments, I A / I B ​The value of is 0.1, 0.12, 0.14, 0.16, 0.18, or 0.2, or is within a range consisting of any two of these values.

[0039] In some embodiments, the second positive electrode material has an X-ray diffraction spectrum after charging in the first cycle, in which both characteristic diffraction peak A and characteristic diffraction peak B are shifted to a lower angle, and the shift width is less than 0.5°, 0.1°, 0.2°, 0.3°, 0.4°, or 0.45°, or within a range consisting of any two of these values.

[0040] In some embodiments, the positive electrode layer includes a conductive agent, which in some embodiments includes at least one of graphite, superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0041] In some embodiments, the conductive agent is present in an amount of 0.5 to 20% by weight of the positive electrode layer, or 0.5%, 1%, 5%, 8%, 10%, 12%, 14%, 16%, 18%, or 20% by weight of the positive electrode layer, or any range consisting of any two of these values.

[0042] In some embodiments, the positive electrode material layer includes a binder, which in some embodiments 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), and polyvinyl alcohol (PVA).

[0043] In some embodiments, the binder content is 0.1 to 2.5% by weight of the total weight of the positive electrode layer, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or 2.5%, or any range consisting of any two of these values, based on the total weight of the positive electrode layer.

[0044] In some embodiments, the positive electrode current collector comprises a metal foil or a porous metal plate. In some embodiments, the positive electrode current collector comprises 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 positive electrode current collector comprises at least one of copper foil and aluminum foil.

[0045] In some embodiments, the thickness of the positive electrode current collector is 5 μm to 20 μm, hi some embodiments, the thickness of the positive electrode current collector is 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, or 20 μm, or any range consisting of any two of these values.

[0046] 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 on a current collector. In some embodiments, the solvent can include, but is not limited to, N-methylpyrrolidone.

[0047] The positive electrode provided by the present invention can fully utilize the synergistic effect between the first and second positive electrode materials. Meanwhile, during the first charge cycle, the high initial charge specific capacity and low initial coulombic efficiency of the second positive electrode material effectively compensate for the loss of active lithium due to the formation of an SEI. This allows sufficient lithium ions to be inserted back into the first positive electrode material during the first discharge, effectively improving the battery's energy density. Meanwhile, the high specific capacity and small volume change during charge and discharge of the first positive electrode material used in the present invention result in good cycle stability. Furthermore, by engineering the sheet resistance, compaction density, and areal density of the positive electrode, the energy density and rate performance of lithium-ion secondary batteries can be further improved. Therefore, using the positive electrode provided by the present invention, lithium-ion secondary batteries can achieve high energy density, good rate performance, and long cycle life.

[0048] The sheet resistance, packing density, and single-sided areal density of the positive electrode are important parameters in the design and manufacture of lithium-ion secondary batteries. If the sheet resistance of the positive electrode is too high, the cycle and rate characteristics of the lithium-ion secondary battery will deteriorate. On the other hand, if the packing density is too high or too low, the cycle and rate characteristics of the battery will also deteriorate. If the single-sided areal density of the positive electrode is too high, it will reduce the cycle life of the battery, affect the electrolyte impregnation, and further affect the rate characteristics of the battery, particularly reducing the battery's discharge capacity at high rates. If the single-sided areal density of the positive electrode is too low, the length of the current collector and separator will increase for the same battery capacity, increasing the battery's ohmic internal resistance.

[0049] In the present invention, when the positive electrode contains both a first positive electrode material and a second positive electrode material, parameters such as the sheet resistance, compaction density, and single-sided areal density of the positive electrode are comprehensively designed to achieve desired electrochemical properties of the lithium-ion secondary battery.

[0050] 2. Electrolyte In some embodiments, the electrolytic solution used in the electrochemical device of the present invention includes an electrolyte and a solvent for dissolving the electrolyte. In some embodiments, the electrolytic solution includes an additive, and the additive includes fluoroethylene carbonate, where the content of the fluoroethylene carbonate is 1% to 15% based on the total mass of the electrolytic solution.

[0051] In some embodiments, the fluoroethylene carbonate content is 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%, or any range consisting of any two of these values.

[0052] In some embodiments, the solvent comprises 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), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE).

[0053] In some embodiments, the electrolyte solution further includes other additives that can be optionally used as additives 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-propene sultone (PST), sulfonate ester cyclic quaternary ammonium salt, tris(trimethylsilyl)phosphate (TMSP), and tris(trimethylsilyl)borate (TMSB).

[0054] The electrolyte is not particularly limited. In some embodiments, in the case of a lithium-ion secondary battery, the electrolyte can include a lithium salt. Illustrative examples of the electrolyte include, but are not limited to, lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium hexafluoroarsenate (LiAsF), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate (LiPOF), lithium difluorobis(oxalato)phosphate (LiDFOP), and lithium tetrafluoro(oxalato)phosphate (LiTFOP).

[0055] In some embodiments, the content of the electrolyte is not particularly limited as long as it does not impair the effects of the present invention. 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 a range consisting of any two of the above values. When the electrolyte concentration is within the above range, the amount of lithium, which is a charged particle, is not too small, and the viscosity can be adjusted to an appropriate range, making it easy to ensure good conductivity.

[0056] The electrolyte solution can be prepared according to common methods in the art. The electrolyte solution can be obtained by uniformly mixing an organic solvent, an electrolyte lithium salt, fluoroethylene carbonate, and other optional additives. The order of addition of each material is not particularly limited. For example, the electrolyte lithium salt, fluoroethylene carbonate, and other optional additives can be added to an organic solvent and uniformly mixed to obtain the electrolyte solution. After the electrolyte lithium salt is added to the organic solvent, the fluoroethylene carbonate and other optional additives can be added to the organic solvent separately or simultaneously.

[0057] 3.Negative electrode In some embodiments, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on one or two surfaces of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material. The negative electrode active material layer may be a single layer or a multilayer, and each layer in the multilayer negative electrode active material may include the same or different negative electrode active materials. The negative electrode active material is any material that can reversibly absorb and release metal ions, such as lithium ions. In some embodiments, the chargeable 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.

[0058] In some embodiments, the negative electrode active material is natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, or spinel-structured lithium titanate Li4Ti5O 12 , Li-Al alloys, and lithium metal. In some embodiments, the negative electrode active materials may be used alone or in combination.

[0059] In some embodiments, the negative electrode current collector may be a metal foil or a porous metal plate, such as a foil or a porous metal plate made of a metal such as copper, nickel, titanium, or iron, or an alloy thereof, and for example, a copper foil may be used.

[0060] In some embodiments, when the negative electrode current collector is a metal material, the form of the negative electrode current collector may include, but is not limited to, a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, a metal mesh sheet, a punched metal, a metal foam, etc. In some embodiments, the negative electrode current collector is a metal thin film. In some embodiments, the negative electrode current collector is a copper foil. In some embodiments, the negative electrode current collector is a rolled copper foil obtained by a rolling method or an electrolytic copper foil obtained by an electrolytic method.

[0061] 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 consisting of any two of the above values.

[0062] In some embodiments, the negative electrode active material layer further includes a negative electrode binder. The negative electrode binder can improve the bonding between particles of the negative electrode active material and the bonding between the negative electrode active material and the current collector. The type of negative electrode binder is not particularly limited, and it may be a material that is stable with respect to the electrolyte or the solvent used during electrode fabrication. In some embodiments, the negative electrode binder includes at least one of styrene butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), water-based acrylic resin, and carboxymethyl cellulose (CMC).

[0063] In some embodiments, the negative electrode active material layer may further include a thickener, hi some embodiments, the thickener includes carboxymethyl cellulose (CMC).

[0064] In some embodiments, the negative electrode can be prepared by the following method: A negative electrode mixture slurry containing a negative electrode active material, a resin binder, etc. is applied onto a negative electrode current collector, dried, and then pressed to form a negative electrode active material layer on both sides of the negative electrode current collector, thereby obtaining a negative electrode.

[0065] 4. Separator In some embodiments, a separator is typically provided between the positive electrode and the negative electrode to prevent short circuits, and in this case, the electrolyte solution of the present invention is typically used by impregnating the separator.

[0066] The material and shape of the separator are not particularly limited as long as they do not significantly impair the effects of the present invention. The separator may be a resin, glass fiber, inorganic material, or the like, made of a material stable to the electrolyte solution of the present invention. In some embodiments, the separator includes a porous sheet or nonwoven fabric-like material with excellent liquid retention. Examples of materials for the resin or glass fiber separator include, but are not limited to, polyolefin, aromatic polyamide, polytetrafluoroethylene, polyethersulfone, and the like. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The above separator materials may be used alone or in any combination.

[0067] The separator may be a material formed by laminating the above materials, and examples thereof include, but are not limited to, a three-layer separator formed by laminating polypropylene, polyethylene, and polypropylene in this order.

[0068] Examples of inorganic materials may include, but are not limited to, oxides such as aluminum oxide and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, sulfates (e.g., barium sulfate, calcium sulfate, etc.), etc. The form of the inorganic material may include, but is not limited to, particulate or fibrous.

[0069] The separator may be in the form of a thin film, examples of which include, but are not limited to, nonwoven fabric, woven fabric, microporous film, etc. In the thin film form, the separator 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 independent thin film separator, a separator in which a composite porous layer containing the above-mentioned inorganic particles is formed on the surface of the positive electrode and / or negative electrode using a resin binder can also be used, such as a separator in which a porous layer of aluminum oxide particles with a 90% particle size of less than 1 μm is formed on both sides of the positive electrode using a fluororesin as a binder.

[0070] The separator may have any thickness. In some embodiments, the separator has a thickness greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the separator has a thickness less than 50 μm, less than 40 μm, or less than 30 μm. In some embodiments, the separator has a thickness within a range consisting of any two of the above values. When the separator has a thickness within the above range, the rate characteristics and energy density of the electrochemical device can be ensured while ensuring insulation and mechanical strength.

[0071] When a porous material such as a porous sheet or nonwoven fabric is used 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 a range consisting of any two of the above values. When the porosity of the separator is within the above range, sheet resistance can be reduced while ensuring insulation and mechanical strength, thereby providing good safety to the electrochemical device.

[0072] 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 a range consisting of any two of the above values. If the average pore size of the separator exceeds the above range, short circuits are likely to occur. If the average pore size of the separator is within the above range, the electrochemical device will have good safety.

[0073] In some embodiments, the separator is a single-layer or multi-layer film of one or more of glass fiber, nonwoven fabric, polyethylene (PE), polypropylene (PP), and polyvinylidene fluoride (PVDF).

[0074] 5. Electrochemical Device The electrochemical device of the present invention includes any device in which an electrochemical reaction occurs, and specific examples thereof include all types of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery, including a lithium metal secondary battery or a lithium ion secondary battery.

[0075] The present invention further provides an electronic device comprising an electrochemical device according to the present invention.

[0076] The application of the electrochemical device of the present invention 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 the present invention is used in, but is not limited to, notebook computers, pen-input personal computers, mobile personal computers, electronic book players, mobile phones, mobile fax machines, mobile copiers, mobile printers, headphone stereos, video movie players, LCD televisions, handheld vacuum cleaners, portable CD players, minidiscs, walkie-talkies, electronic organizers, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, automobiles, motorcycles, mopeds, bicycles, lighting equipment, toys, game machines, watches, power tools, flash devices, cameras, large-scale household storage batteries, and lithium-ion capacitors.

[0077] Hereinafter, the preparation of a lithium ion battery will be described with reference to specific examples, taking a lithium ion battery as an example. Those skilled in the art should understand that the preparation method described in the present invention is merely exemplary, and any other suitable preparation method is also within the scope of the present invention.

[0078] Example The characteristics of the lithium ion battery according to the present invention will be evaluated below with respect to examples and comparative examples.

[0079] 1. Preparation of lithium-ion batteries Example 1 1. Preparation of the Positive Electrode LiCoO2 as the first positive electrode material and LiMnO as the second positive electrode material 2、PVDF binder and conductive carbon black were mixed in a mass ratio of 90.0:7.6:1.3:1.1, NMP solvent was added, and the mixture was stirred under vacuum until the mixture was uniform and transparent to obtain a positive electrode slurry. The positive electrode slurry was uniformly applied to an aluminum foil positive electrode current collector and then transferred to an oven for drying at 120°C. After cold pressing and slicing, a positive electrode was obtained. Here, the LiCoO2 content of the first positive electrode material was 90.0% and the LiMnO2 content of the second positive electrode material was 7.6% relative to the total mass of the positive electrode material layer.

[0080] 2. Preparation of the Negative Electrode The negative electrode materials, artificial graphite, silicon monoxide, polyacrylic acid (PAA) as a binder, and conductive carbon black were mixed in a mass ratio of 85.9:10:2.8:1.3, deionized water as a solvent was added, and the mixture was mixed using a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry was then uniformly applied to copper foil as a negative electrode current collector. The mixture was then transferred to an oven and dried at a drying temperature of 120°C. After cold pressing and slicing, the negative electrode was obtained.

[0081] 3. Electrolyte Preparation Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were uniformly mixed in a volume ratio of 1:1:1 to obtain an organic solvent. LiPF6 was dissolved in the organic solvent to obtain a base electrolyte solution, where the concentration of LiPF6 in the base electrolyte solution was 1 mol / L. Fluoroethylene carbonate was added to the base electrolyte solution and mixed uniformly to obtain an electrolyte solution. The content of fluoroethylene carbonate was 5% of the total mass of the electrolyte solution.

[0082] 4. Separator Preparation A 14 μm thick polypropylene (PP) thin film (manufactured by Celgard) was used as the separator.

[0083] 5. Preparation of Lithium-ion Batteries The positive electrode, separator, and negative electrode were stacked in this order, with a separator between them to isolate them, and then the stack was rolled up to form a bare cell. The bare cell was then placed in a housing, injected with electrolyte, and sealed. The cell was then left to stand, formed, and shaped to obtain a lithium-ion secondary battery.

[0084] Examples 2 to 15 The differences between Examples 2 to 15 and Example 1 are the type of positive electrode material, related characteristic parameters, and the content of additives in the electrolyte solution, and the details are shown in Table 1.

[0085] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the positive electrode material in Comparative Example 1 contains only LiCoO2.

[0086] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the positive electrode material in Comparative Example 2 contains only LiMnO2.

[0087] Comparative Examples 3 and 4 The difference between Comparative Examples 3 and 4 and Example 1 is that the mass ratio of the first positive electrode material to the second positive electrode material in the positive electrode is different, and details are shown in Table 1.

[0088] Comparative Examples 5 to 7 The differences between Comparative Examples 5 to 7 and Example 1 are the sheet resistance, compression density, and surface density of one side of the positive electrode.

[0089] Comparative Examples 8-9 The difference between Comparative Examples 8 and 9 and Example 1 is the content of fluoroethylene carbonate in the electrolyte solution.

[0090] 2.Measurement method 1.Method for measuring the sheet resistance of the positive electrode The sheet resistance of the positive electrode was measured using a HIOKI BT3562 battery tester. The measurement method involves clamping the positive electrode between the two conductive terminals of the battery tester, applying pressure to fix it, and measuring the resistance R of the positive electrode. Here, 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.

[0091] 2.Method for measuring high-temperature cycle characteristics of lithium-ion secondary batteries At 45°C, the lithium-ion secondary battery was charged at a constant current of 1.5 C up to 4.5 V, then charged at a constant voltage until the current fell to 0.05 C or less, and then discharged at a constant current of 1 C down to 3.0 V. This operation constituted one charge-discharge cycle, and the discharge capacity of the lithium-ion secondary battery was recorded for the first cycle. 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.

[0092] 3.Method for measuring rate characteristics of lithium-ion secondary batteries At 25°C, the lithium-ion secondary battery was charged at a constant current of 0.2 C up to 4.5 V, then charged at a constant voltage until the current fell to 0.05 C or less, and then discharged at a constant current of 0.2 C down to 3.0 V, and the discharge capacity at a rate of 0.2 C was recorded.

[0093] At 25°C, the lithium-ion secondary battery was charged at a constant current of 0.2C up to 4.5V, then charged at a constant voltage until the current fell to 0.05C or less, and then discharged at a constant current of 2C down to 3.0V, and the discharge capacity at a rate of 2C was recorded.

[0094] Discharge capacity retention rate (%) of lithium-ion secondary battery at a rate of 2C = discharge capacity at a rate of 2C / discharge capacity at a rate of 0.2C × 100%.

[0095] 3. Measurement results Table 1 shows the positive electrode compositions, related characteristic parameters, and the types and contents of additives in the electrolyte in Comparative Examples 1 to 9 and Examples 1 to 15. Here, the contents of the first positive electrode material and the second positive electrode material are calculated based on the total mass of the positive electrode material layer, and the content of fluoroethylene carbonate in the electrolyte is calculated based on the total mass of the electrolyte.

[0096] [Table 1]

[0097] Table 2 shows the high-temperature cycle characteristics and rate characteristics of the lithium ion secondary batteries in Comparative Examples 1 to 9 and Examples 1 to 15.

[0098] [Table 2]

[0099] As can be seen from the comparison between the above examples and comparative examples, compared to lithium-ion batteries whose cathodes contain only the first or second cathode material, lithium-ion batteries whose cathodes contain both the first and second cathode materials exhibit significantly improved high-temperature cycle performance without significantly changing their rate characteristics. This indicates that the combined use of the first and second cathode materials produces a synergistic effect. Without being limited by any theory, the above synergistic effect may be due to the following reasons. First, the second cathode material used in the present invention has a low content of free lithium on the surface, which means that the slurry obtained by adding the second cathode material to the cathode has good stability and excellent processability. Second, the second cathode material used in the present invention has a high initial charge specific capacity and a low initial coulombic efficiency, which better compensates for the loss of active lithium due to the formation of an SEI. This allows more lithium ions to be inserted back into the crystal lattice of the first cathode material during discharge, effectively improving the energy density of lithium-ion secondary batteries. Third, since the first positive electrode material has good cycle characteristics and a high specific capacity, by controlling the sheet resistance R, compaction density P, and single-side areal density Q of the positive electrode piece within the ranges of the present invention, it is possible to provide a lithium-ion secondary battery with good cycle characteristics and rate characteristics.

[0100] Furthermore, as can be seen from the comparison between Comparative Example 7 and Example 1, the addition of fluoroethylene carbonate to the electrolyte exhibits a synergistic effect with a positive electrode containing both a first positive electrode material and a second positive electrode material. This is because, during the first charge, a large amount of active lithium released from the second positive electrode material is inserted into the negative electrode, further reducing the real potential of the negative electrode and causing the solvent in the electrolyte to be continuously reduced, affecting cycle performance. The use of fluoroethylene carbonate as an additive induces the formation of a denser and thinner SEI layer, preventing the continuous consumption of the electrolyte. Furthermore, fluoroethylene carbonate has stronger resistance to high-pressure oxidation, making it advantageous for incorporation into a high-voltage first positive electrode material.

[0101] Throughout the specification, references to "some embodiments," "some of the embodiments," "one embodiment," "another example," "an example," "a specific example," or "some of the examples" mean that at least one embodiment or example of the present invention includes the particular feature, structure, material, or characteristic described in that embodiment or example. Thus, the appearances of, for example, "some embodiments," "in an embodiment," "in one embodiment," "in another example," "in one example," "in a particular example," or "an example" throughout the specification do not necessarily refer to the same embodiment or example of the present invention. Furthermore, particular features, structures, materials, or characteristics herein may be combined in any suitable manner in one or more embodiments or examples.

[0102] Although exemplary embodiments have been described and illustrated, those skilled in the art should understand that the above-described embodiments are not to be construed as limiting the present invention, and that changes, substitutions, and modifications to the embodiments are possible without departing from the spirit, principle, and scope of the present invention.

Claims

1. An electrochemical device including 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 including a first positive electrode material and a second positive electrode material; The first positive electrode material is represented by formula (I): Li １＋ｘ Co ｙ Me ｚ M １－ｙ－ｚ O ２－ｔ A ｔ Formula (I) 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 contain at least one of Ni, Mn, Al, Mg, Ti, Zr, La, and Y, and Me and M are different from each other; A contains at least one of S, N, F, Cl, and Br; The second positive electrode material is 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 includes at least one of Fe, Co, Ni, Ti, Zn, Mg, Al, V, Cr, and Zr, and T includes at least one of S, N, F, Cl, and Br; the positive electrode satisfies 12≦R×P / Q≦36, where R is the resistance of the positive electrode in Ω, and P is the compressed density of the positive electrode in g / cm ３ and Q is the surface density of one surface of the positive electrode, expressed in g / 1540.25 mm ２ and the P satisfies 4.0 g / cm 3 ≦P≦4.3 g / cm 3 ; The electrochemical device, wherein the electrolyte contains fluoroethylene carbonate, and the content of the fluoroethylene carbonate is 1% to 15% based on the total mass of the electrolyte.

2. The electrochemical device according to claim 1 , wherein the positive electrode satisfies 12≦R×P / Q≦32.

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

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

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

1.

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

7. The X-ray diffraction spectrum of the second positive electrode material is and / or has a characteristic diffraction peak A within the range of 15° to 16°; It has a characteristic diffraction peak B in the range of 18° to 19°, Intensity I of characteristic diffraction peak A Ａ and the intensity I of the characteristic diffraction peak B Ｂ The ratio value I Ａ / I Ｂ satisfies equation (3). 0<I Ａ / I Ｂ ≦0.2 Formula (3), The electrochemical device of claim 1 .

8. 8. The electrochemical device according to claim 7, wherein in an X-ray diffraction spectrum of the second positive electrode material after charging in the first cycle, both characteristic diffraction peak A and characteristic diffraction peak B are shifted to lower angles, and the shift width satisfies a shift width of <0.5°.

9. The first positive electrode material is LiCoO ２ , LiCo ０．９ Ni ０．１ O ２ , LiCo ０．９ Ni ０．０５ Mn ０．０５ O ２ and Li ０．９５ Co ０．９９ Al ０．０１ O １．９５ F ０．０５ and / or The second positive electrode material is LiMnO ２ , LiMn ０．９ Ni ０．１ O ２ , LiMn ０．９ Ni ０．０５ Cr ０．０５ O ２ , Li ０．９５ MnO １．９５ F ０．０５ and Li ０．９５ MnO １．９ S ０．０５ F ０．０５ including at least one of The electrochemical device of claim 1 .

10. An electronic device comprising the electrochemical device according to any one of claims 1 to 9.

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