Electrochemical device and electronic device including the same

Abstract

The present invention relates to an electrochemical device and an electronic device including the same. The electrochemical device of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolyte. Here, the positive electrode includes a first positive electrode material and a second positive electrode material. The first positive electrode material has good cycle stability and high initial coulombic efficiency, and the second positive electrode material has a high initial charge specific capacity and a low initial coulombic efficiency, and can replenish the loss of active lithium due to the formation of SEI. The electrochemical device provided by the present invention has the advantages of high energy density, 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 energy density of lithium-ion batteries has been attracting increasing attention and facing challenges. During the initial charge / discharge process of lithium-ion secondary batteries, a solid electrolyte interface (SEI) forms on the surface of the negative electrode, resulting in irreversible capacity loss and a decrease in the energy density of the lithium-ion energy storage device. In lithium-ion energy storage devices using graphite as the negative electrode, the first cycle consumes approximately 10% of the active lithium source. When negative electrode materials with high specific capacity are used, such as alloys (e.g., silicon, tin), oxides (e.g., silicon oxide, tin oxide), and amorphous carbon, the consumption of the active lithium source becomes even more severe. Therefore, to further improve the energy density of lithium-ion energy storage devices, a suitable lithium replenishment method is important. Summary of the Invention

[0003] The present invention provides electrochemical and electronic devices that improve cycleability and energy density to overcome, in part, the problems in the prior art.

[0004] In one embodiment, the present invention provides 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 disposed on at least one surface of the positive electrode current collector. The positive electrode material layer includes a first positive electrode material represented by Formula (I) and a second positive electrode material represented by Formula (II). [ka]

[0005] Here, x, y, z, and t satisfy -0.1 < x < 0.1, 0 < y ≤ 1, 0 ≤ z ≤ 1, 0 < y + z ≤ 1, 0 ≤ t < 0.2, M contains at least one of Ti, Zr, V, and Cr, and A contains at least one of S, N, F, Cl, and Br.

Chemical formula

[0006] Here, r, p, and s satisfy -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.

[0007] The above positive electrode satisfies formula (1).

Number

[0008] Here, R is the resistance of the above positive electrode, with the unit of Ω, P is the compaction density of the above positive electrode, with the unit of g / cm 3 and Q is the areal density of one side of the above positive electrode, with the unit of g / 1540.25mm 2 is.

[0009] In some embodiments, the above positive electrode satisfies formula (2).

Number

[0010] In some embodiments, R satisfies R ≤ 3.5 Ω.

[0011] In some embodiments, P satisfies 1.6 g / cm 3 < P < 2.6 g / cm 3 is satisfied.

[0012] In some embodiments, Q is 0.16 g / 1540.25 mm 2 <Q<0.45g / 1540.25mm 2 Meet the following.

[0013] In some embodiments, the mass ratio of the first positive electrode material to the second positive electrode material is 5:1 to 99:1.

[0014] In some embodiments, the mass content of the first positive electrode material is 80% to 98% based on the total mass of the positive electrode material layer.

[0015] In some embodiments, the X-ray diffraction spectrum of the second positive electrode material is and / or has a characteristic diffraction peak A in 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 of the characteristic diffraction peak B I B Relative to I A / I B satisfies equation (3).

number

[0016] In some embodiments, in the X-ray diffraction spectrum of the second positive electrode material after the first charging cycle, the characteristic diffraction peak A and the characteristic diffraction peak B are both shifted to a lower angle, and the shift width satisfies the shift width <0.5°.

[0017] In some embodiments, the electrolyte solution includes vinylene carbonate, and the mass content of the vinylene carbonate is 0.05% to 5% based on the total mass of the electrolyte solution.

[0018] In another embodiment, the present invention provides an electronic device comprising an electrochemical device according to any embodiment of the present invention.

[0019] The present invention provides a lithium-ion secondary battery containing a positive electrode lithium replenishment material. First, the second positive electrode material used in the present invention has a low content of free lithium on the surface, resulting in excellent processability. Furthermore, the second positive electrode material has a higher specific capacity than the first positive electrode material, allowing it to release more lithium ions and replenish active lithium during the initial charge. Combining the second positive electrode material with the first positive electrode material effectively improves the energy density and cycle life of the battery. Second, the present invention significantly improves the cycle life and energy density of lithium-ion secondary batteries by comprehensively designing the sheet resistance, compaction density, and areal density of the positive electrode. Third, adding vinylene carbonate as an additive to the electrolyte forms a more uniform and dense SEI film on the negative electrode, suppressing the continuous loss of active lithium and further improving the cycle life of lithium-ion secondary batteries.

[0020] Other aspects and advantages of the present invention are set forth in part in the description that follows, and are illustrated in part by way of example, or may be learned through the practice of embodiments of the present invention. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 shows the XRD spectra of the second positive electrode material in Example 1 before and after the first cycle of charging. [Figure 2] FIG. 2 shows an enlarged view of a portion of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0022] The following examples of the present invention will be described in detail, but the examples should not be construed as limiting the present invention.

[0023] It should be noted that quantities, ratios, and other numerical values ​​may be expressed in range format herein. It should be understood that such range formats are used for convenience and brevity. The range formats should be understood flexibly to include not only the numerical values ​​explicitly specified as range limits, but also to include each and every numerical value or subrange contained within the range, as if each numerical value or subrange were explicitly specified.

[0024] In the detailed description and claims, a list of items connected by the terms "one of," "one of," "one of," or other similar terms can mean any of the listed items. For example, if items A and B are listed, the short phrase "one of A and B" means only A or only B. In another example, if items A, B, and C are listed, the short 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.

[0025] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms can refer to 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 A only, B only, or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means A only, B only, C only, 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.

[0026] I. Electrochemical device In some embodiments, the present invention provides an electrochemical device including a positive electrode, a negative electrode, and an electrolytic solution.

[0027] 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 represented by formula (I) and a second positive electrode material represented by formula (II).

Chemical formula

[0028] Here, x, y, z, and t satisfy -0.1 < x < 0.1, 0 < y ≤ 1, 0 ≤ z ≤ 1, 0 < y + z ≤ 1, 0 ≤ t < 0.2, M includes at least one of Ti, Zr, V, and Cr, and A includes at least one of S, N, F, Cl, and Br.

Chemical formula

[0029] Here, r, p, and s satisfy -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.

[0030] The positive electrode satisfies formula (1).

Mathematical formula

[0031] Here, 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 of.

[0032] In this specification, the calculation of R·P / Q only relates to the calculation of numerical values. For example, when the resistance R of the positive electrode is 0.5 Ω and the compressed density P is 2.2 g / cm 3 The surface density Q of one side of the positive electrode is 0.3 g / 1540.25 mm 2 If , then R·P / Q=3.7.

[0033] 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 49πmm 2 As an example, the top and bottom of the positive electrode are sandwiched between two conductive terminals of a pole piece resistance tester 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 positive electrode resistance tester is a Hioki BT3562 internal resistance tester.

[0034] The compressed density of the positive electrode can be calculated by the formula P=m / v, where m is the weight of the positive electrode material layer in g, and v is the volume of the positive electrode material layer in cm. 3 Here, the volume v of the positive electrode layer is expressed as the area A of the positive electrode layer. r and the thickness of the positive electrode material layer.

[0035] The surface density Q of one side of the positive electrode is calculated using the formula Q = 1540.25 m / A r In the 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.

[0036] In some embodiments, the positive electrode material layer is located on one surface of the positive electrode current collector, or on both surfaces of the positive electrode current collector.

[0037] In some embodiments, the first cathode material is LiFePO4, LiFe 0.5 Mn 0.5 PO4, Li 0.9 Fe 0.5 Mn 0.45 Ti0.05 PO4, Li 0.9 Fe 0.5 Mn 0.45 Ti 0.04 Zr 0.01 PO4 and Li 0.95 FePO 3.95 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.

[0038] In some embodiments, R, P, and Q satisfy the relationship 1.5≦R×P / Q≦10. In some embodiments, the value of R×P / Q is 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, or 16, or a range consisting of any two of these values.

[0039] In some embodiments, R satisfies R≦3.5Ω. In some embodiments, R is 0.2Ω, 0.5Ω, 1Ω, 1.2Ω, 1.5Ω, 1.8Ω, 2.0Ω, 2.2Ω, 2.5Ω, 3.0Ω, 3.2Ω, or 3.5Ω, or is in a range consisting of any two of these values. When R is in the above range, it is advantageous for improving the cycle characteristics and rate characteristics of the lithium ion secondary battery.

[0040] In some embodiments, P is 1.6 g / cm 3 <P<2.6g / cm 3 In some embodiments, P is 1.6 g / cm 3 , 1.8g / cm 3 , 2.0g / cm 3 , 2.2g / cm 3, 2.4g / cm 3 , or 2.6 g / cm 3 or in a range consisting of any two of these values. When P is in 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.

[0041] In some embodiments, Q is 0.16 g / 1540.25 mm 2 <Q<0.45g / 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 , 0.38g / 1540.25mm 2 , 0.40g / 1540.25mm 2 , 0.42g / 1540.25mm 2 , or 0.45g / 1540.25mm 2 or a range consisting of any two of these values. When Q is in the above range, the charge / discharge capacity can be ensured, and the cycle characteristics and rate characteristics of the lithium ion secondary battery can be improved.

[0042] 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 a 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 high, 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 dynamic performance of the lithium-ion battery.

[0043] In some embodiments, the mass 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 a range consisting of any two of these values, relative to the total mass of the positive electrode layer.

[0044] 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 the characteristic diffraction peak B I B Relative to I A / I B satisfies equation (3).

number

[0045] In some embodiments, I A / I BThe value of is 0.1, 0.12, 0.14, 0.16, 0.18, or 0.2, or in a range consisting of any two of these values.

[0046] In some embodiments, in the X-ray diffraction spectrum of the second positive electrode material after the first charge cycle, 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°. In some embodiments, the shift width is 0.1°, 0.2°, 0.3°, 0.4°, or 0.45°, or within a range consisting of any two of these values.

[0047] In some embodiments, the positive electrode material layer includes a conductive agent, which includes at least one of graphite, superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0048] In some embodiments, the mass content of the conductive agent is 0.5 to 20% relative to the total mass of the positive electrode layer, or 0.5%, 1%, 5%, 8%, 10%, 12%, 14%, 16%, 18%, or 20%, or a range consisting of any two of these values, relative to the total mass of the positive electrode layer.

[0049] In some embodiments, the positive electrode layer includes a binder, which 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).

[0050] In some embodiments, the weight content of the binder is 0.1 to 2.5% relative to the total weight of the positive electrode layer, or 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or 2.5%, or a range consisting of any two of these values, relative to the total weight of the positive electrode layer.

[0051] 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 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.

[0052] In some embodiments, the thickness of the positive electrode current collector is 5 μm to 20 μm, or 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, or 20 μm, or a range consisting of any two of these values.

[0053] In some embodiments, the positive electrode is 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 may include, but is not limited to, N-methylpyrrolidone.

[0054] The positive electrode of the present invention can fully utilize the synergistic effect between the first positive electrode material and the second positive electrode material. During the first charge cycle, the high initial charge specific capacity and low initial efficiency of the second positive electrode material effectively compensate for the loss of active lithium due to the formation of an SEI. During the first discharge cycle, sufficient lithium ions are absorbed back into the first positive electrode material, effectively improving the energy density of the battery. The first positive electrode material employed in the present invention has a stable structure, undergoes minimal volumetric change during charge and discharge, and exhibits excellent cycle stability. Furthermore, by designing the sheet resistance, compressed density, and areal density of the positive electrode, the energy density, rate performance, and cycle life of the lithium-ion secondary battery can be further improved. Therefore, the positive electrode of the present invention can provide a lithium-ion secondary battery with high energy density, favorable rate performance, and long cycle life.

[0055] The sheet resistance, packing density, and surface 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 deteriorate. If the packing density is too high or too low, the cycle and rate characteristics of the battery deteriorate. If the surface density of the positive electrode is too high, the cycle life of the battery decreases, the electrolyte penetration also decreases, and the rate characteristics of the battery decrease, especially the high-rate discharge capacity of the battery. If the surface density of the positive electrode is too low, the length of the current collector and separator increases for the same battery capacity, increasing the ohmic internal resistance of the battery.

[0056] When a positive electrode simultaneously contains a first positive electrode material and a second positive electrode material, the present invention comprehensively designs parameters such as the sheet resistance, compaction density, and single-sided areal density of the positive electrode to achieve desired electrochemical performance of the lithium-ion secondary battery.

[0057] 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 vinylene carbonate, and the mass content of the vinylene carbonate is 0.05% to 5% based on the total mass of the electrolytic solution.

[0058] In some embodiments, the vinylene carbonate content is 0.05%, 1%, 2%, 3%, 4%, or 5%, or a range consisting of any two of these values.

[0059] When the content of the additive in the electrolyte solution is within the range of the present invention, the cycle characteristics and energy density of the lithium ion secondary battery can be further improved.

[0060] In some embodiments, the electrolyte solution may further contain, as needed, any other additives used as additives for lithium-ion secondary batteries, including, but not limited to, 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).

[0061] In some embodiments, the electrolyte further comprises any non-aqueous solvent that can be used as a solvent for the electrolyte.

[0062] In some embodiments, the non-aqueous solvent includes, but is not limited to, one or more of cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, chain carboxylic acid esters, cyclic ethers, chain ethers, phosphorus-containing organic solvents, sulfur-containing organic solvents, and aromatic fluorine-containing solvents.

[0063] In some embodiments, the non-aqueous 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), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS), and diethyl sulfone (ESE).

[0064] The electrolyte is not particularly limited. In some embodiments, in the case of a lithium secondary battery, the electrolyte includes a lithium salt. Examples of the electrolyte may 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).

[0065] 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 concentration of the electrolyte 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 easier to ensure good conductivity.

[0066] 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 both 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 multiple layers, and each layer of the multiple layers 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.

[0067] Examples of the negative electrode current collector that holds the negative electrode active material include, but are not limited to, metal materials such as aluminum, copper, nickel, stainless steel, nickel-plated steel, etc. In some embodiments, the negative electrode current collector is copper.

[0068] 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 strip roll, a metal plate, a metal film, a metal lath, a stamped metal, a metal foam, etc. In some embodiments, the negative electrode current collector is a metal 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.

[0069] 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 in a range consisting of any two of the above values.

[0070] The negative electrode active material is not particularly limited as long as it can reversibly absorb and release lithium ions. Examples of the negative electrode active material include, but are not limited to, carbon materials such as natural graphite and artificial graphite, metals such as silicon (Si) and tin (Sn), and oxides of metal elements such as Si and Sn. The negative electrode active materials can be used alone or in combination.

[0071] In some embodiments, the negative electrode active material layer may further include a negative electrode binder. The negative electrode binder can improve the bonding between the negative electrode active material particles and the bonding between the negative electrode active material and the current collector. The type of negative electrode binder is not particularly limited, as long as it is a material that is stable against the electrolyte and the solvent used in manufacturing the electrode. In some embodiments, the negative electrode binder includes a resin binder. Examples of resin binders may include, but are not limited to, fluororesin, polyacrylonitrile (PAN), polyimide resin, acrylic acid-based resin, polyolefin resin, etc. When an aqueous solvent is used to prepare the negative electrode mixture slurry, the negative electrode binder includes, but is not limited to, carboxymethyl cellulose (CMC) or a salt thereof, styrene butadiene rubber (SBR), polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol, etc.

[0072] In some embodiments, the negative electrodes can be prepared by applying a negative electrode mixture slurry containing the negative electrode active material, a resin binder, etc., to a negative electrode current collector, drying the mixture, and then rolling the mixture to form a negative electrode active material layer on both sides of the negative electrode current collector.

[0073] 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 of the present invention is typically used by permeating the separator.

[0074] 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 made of a material stable to the electrolyte solution of the present invention, such as a resin, glass fiber, or inorganic material. 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 separator materials can be used alone or in any combination.

[0075] 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.

[0076] Examples of inorganic materials may include, but are not limited to, oxides such as alumina and silica, nitrides such as aluminum nitride and silicon nitride, and sulfates (e.g., barium sulfate, calcium sulfate, etc.) The form of the inorganic material may include, but is not limited to, particulate or fibrous.

[0077] The separator may be in the form of a film, examples of which include, but are not limited to, a nonwoven fabric, a woven fabric, a microporous film, etc. In the 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 independent film-like separator, a separator formed by forming a composite porous layer containing inorganic particles on the surface of the positive electrode and / or negative electrode using a resin-based binder can also be used, for example, a separator formed by forming a porous layer on both sides of the positive electrode using alumina particles with a 90% particle size of less than 1 μm using a fluororesin as a binder.

[0078] 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, insulation and mechanical strength are ensured, and the rate characteristics and energy density of the electrochemical device are ensured.

[0079] 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, insulation properties and mechanical strength are ensured, and sheet resistance is suppressed, resulting in good safety characteristics of the electrochemical device.

[0080] 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 more likely to occur. When the average pore size of the separator is within the above range, the electrochemical device has good safety characteristics.

[0081] 5. Electrochemical equipment The electrochemical device of the present invention includes any device in which an electrochemical reaction occurs, and 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.

[0082] The present invention further provides an electronic device comprising an electrochemical device according to the present invention.

[0083] 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 can be used in, but is not limited to, laptop computers, pen-input computers, mobile computers, electronic book players, mobile phones, portable facsimiles, portable copiers, portable printers, stereo headsets, video recorders, LCD televisions, portable vacuum cleaners, portable CD players, mini CDs, walkie-talkies, electronic notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, automobiles, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, strobes, cameras, large-scale household storage batteries, and lithium-ion capacitors.

[0084] The following describes the preparation of a lithium ion battery with reference to specific examples, taking a lithium ion battery as an example. Those skilled in the art should understand that the preparation methods described in the present invention are merely exemplary, and any other suitable preparation methods are within the scope of the present invention.

[0085] Example In the following, examples and comparative examples of the lithium ion battery according to the present invention will be described and performance evaluation will be carried out. 1. Preparation of lithium-ion batteries Example 1 1. Preparation of the negative electrode Artificial graphite as the negative electrode active material, sodium carboxymethyl cellulose (CMC) as a thickener, SBR (SBR) as a binder, and conductive carbon black were mixed in a mass ratio of 95.7:1.0:1.8:1.5, deionized water was added, and the mixture was used in a vacuum blender 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. The mixture was then cold pressed, cut, and tabs were welded to obtain a negative electrode.

[0086] 2. Preparation of the positive electrode The first positive electrode material, LiFePO4, the second positive electrode material, LiMnO2, the binder, PVDF, and conductive carbon black were mixed in a mass ratio of 90.4:6.0:2.1:1.5. N-methylpyrrolidone (NMP) was added as a solvent and the mixture was stirred in a vacuum blender until a uniform, transparent mixture was obtained. The positive electrode slurry was then uniformly applied to an aluminum foil positive electrode current collector, which was then transferred to an oven and dried at 120°C. The cathode was then cold-pressed, cut, and tab-welded to obtain a positive electrode. The mass content of the first positive electrode material, LiFePO4, and the second positive electrode material, LiMnO2, was 90.4% and 6.0%, respectively, of the total mass of the positive electrode layer.

[0087] 3. Preparation of electrolyte 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 basic electrolyte solution, where the concentration of LiPF6 in the basic electrolyte solution was 1 mol / L. Vinylene carbonate was added to the basic electrolyte solution and mixed uniformly to obtain an electrolyte solution. The mass content of vinylene carbonate was 3% relative to the total mass of the electrolyte solution.

[0088] 4. Preparation of separator A polyethylene porous membrane with an alumina coating was used as the separator, and its thickness was 9 μm.

[0089] 5. Preparation of Lithium-ion Battery The resulting positive electrode, separator, and negative electrode were wound in this order and placed in an outer foil package, with a filling hole left open. Electrolyte was poured through the filling hole, and the package was then packaged. A lithium-ion battery was then manufactured through processes such as formation and capacity grading.

[0090] Examples 2 to 16: The differences between Examples 2 to 16 and Example 1 lie in the type of positive electrode material, related performance parameters, and the content of additives in the electrolyte solution, details of which are shown in Table 1.

[0091] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that the positive electrode material in Comparative Example 1 contains only LiFePO4.

[0092] 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.

[0093] Comparative Examples 3-4: Comparative Examples 3 and 4 differ from Example 1 in 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.

[0094] Comparative Examples 5-6: The differences between Comparative Examples 5 and 6 and Example 1 lie in the sheet resistance, compression density, and surface density of the positive electrode.

[0095] Comparative Examples 7-8: The difference between Comparative Examples 7 and 8 and Example 1 is that the mass percentage of vinylene carbonate in the electrolyte solution is different, and the details are shown in Table 1.

[0096] 2.Measurement method 1. Measurement method for positive electrode sheet resistance The sheet resistance of the positive electrode was measured using a Hiki BT3562 resistance tester. The measurement method involved clamping the positive electrode between two conductive terminals of the internal resistance tester, applying pressure to fix it, and measuring the resistance R of the positive electrode, where 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.

[0097] 2. Measurement method for high-temperature cycle characteristics of lithium-ion secondary batteries At 60°C, the lithium-ion secondary battery was charged at a constant current of 1C up to 4.2V, then charged at a constant voltage until the current fell to 0.05C or less, and then discharged at a constant current of 1C down to 2.5V. This constituted one charge-discharge cycle, and the discharge capacity of the lithium-ion secondary battery for the first cycle was recorded.

[0098] According to the above method, the lithium ion secondary battery was subjected to charge / discharge cycles, 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 at this point was recorded.

[0099] 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 0.5C up to 4.2V, then charged at a constant voltage until the current dropped to 0.05C or less, and then discharged at a constant current of 0.5C down to 2.5V, and the discharge capacity at a rate of 0.5C was recorded.

[0100] At 25°C, the lithium-ion secondary battery was charged at a constant current of 0.5C up to 4.2V, then charged at a constant voltage until the current dropped to 0.05C or less, and then discharged at a constant current of 2C down to 2.5V, and the discharge capacity at a rate of 2C was recorded.

[0101] 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 0.5C × 100%.

[0102] 4. Measurement method for energy density of lithium-ion secondary batteries At 25°C, the lithium-ion secondary battery was charged at a constant current of 0.2 C to 4.2 V, then charged at a constant voltage until the current dropped to 0.05 C or less. After leaving the battery to stand for 30 minutes, it was discharged at a constant current of 0.2 C to 2.5 V. The discharge capacity D0 (Ah) and discharge platform V0 (V) of the lithium-ion secondary battery at a rate of 0.2 C were recorded. The weight of the lithium-ion battery was measured and recorded as m0 (kg).

[0103] The energy density of the lithium-ion secondary battery was calculated according to the following formula:

number

[0104] 3. Measurement results Table 1 shows the positive electrode compositions, related performance parameters, and the types and contents of additives in the electrolytes of Comparative Examples 1 to 8 and Examples 1 to 16. 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 vinylene carbonate in the electrolyte is calculated based on the total mass of the electrolyte.

[0105] [Table 1]

[0106] Table 2 shows the high-temperature cycle characteristics, rate characteristics, and energy densities of the lithium ion secondary batteries of Comparative Examples 1 to 8 and Examples 1 to 16.

[0107] [Table 2]

[0108] 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 and energy density, without significantly changing their rate characteristics. As can be seen, the combined use of the first and second cathode materials produces a synergistic effect. Without being bound by theory, this synergistic effect may be due to several reasons. First, the second cathode material employed in the present invention has an extremely low free lithium content on the surface. When this second cathode material is added to a cathode, the resulting slurry exhibits good stability and excellent processability. Second, the second cathode material employed in the present invention has a high initial charge specific capacity and a low initial charge efficiency, which better compensates for the loss of active lithium due to the formation of SEI. During discharge, more lithium ions are absorbed back into the lattice of the first cathode material, effectively improving the energy density of the lithium-ion secondary battery. And thirdly, since the first positive electrode material has a stable structure and excellent cycle characteristics, by controlling the sheet resistance R, pressed density P, and single-side areal density Q of the positive electrode within the ranges of the present invention, it is possible to provide a lithium ion secondary battery with good cycle characteristics and rate characteristics.

[0109] Furthermore, as can be seen from a comparison between Comparative Example 7 and Example 1, the addition of vinylene carbonate to the electrolyte exhibits a synergistic effect with a positive electrode containing both the first and second positive electrode materials. This is for the following reasons: During the first charge, a large amount of active lithium released from the second positive electrode material is absorbed 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 vinylene carbonate as an additive induces the formation of a denser and thinner SEI layer, preventing continuous consumption of the electrolyte.

[0110] 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 phrases such as "in 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.

[0111] While 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 modifications, substitutions, and alterations to the embodiments are possible without departing from the spirit, principle, and scope of the present invention.

Claims

1. An electrochemical device comprising a positive electrode, a negative electrode, and an electrolyte, the positive electrode includes a positive electrode current collector and a positive electrode material layer located on at least one surface of the positive electrode current collector, the positive electrode material layer includes a first positive electrode material represented by formula (I) and a second positive electrode material represented by formula (II), 【number】 wherein x, y, z, and t satisfy −0.1<x<0.1, 0<y≦1, 0≦z≦1, 0<y+z≦1, 0≦t<0.2, M includes at least one of Ti, Zr, V, and Cr, and A includes at least one of S, N, F, Cl, and Br; 【number】 wherein r, p, and s satisfy −0.1<r<0.2, 0≦p<0.2, and 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 ratio of the mass of the first positive electrode material to the mass of the second positive electrode material is 5:1 to 99:1; The positive electrode satisfies formula (1), [Equation 1] where R is the resistance of the positive electrode, expressed in Ω, and P is the compressed density of the positive electrode, expressed 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 electrolyte solution contains vinylene carbonate; The electrochemical device, wherein the mass content of the vinylene carbonate is 0.05% to 5% relative to the total mass of the electrolyte.

2. The positive electrode satisfies formula (2): [Equation 2] The electrochemical device of claim 1 .

3. The electrochemical device according to claim 1 , wherein R satisfies R≦3.5Ω.

4. The P is 1.6 g / cm ３ <P<2.6g / cm ３ The electrochemical device according to claim 1 , wherein

5. The Q is 0.16 g / 1540.25 mm ２ <Q<0.45g / 1540.25mm ２ The electrochemical device according to claim 1 , wherein

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

7. The first positive electrode material is LiFePO ４ , LiFe ０．５ Mn ０．５ P.O. ４ , Li ０．９ Fe ０．５ Mn ０．４５ Ti ０．０５ P.O. ４ , Li ０．９ Fe ０．５ Mn ０．４５ Ti ０．０４ Zr ０．０１ P.O. ４ , and Li ０．９５ FePO ３．９５ 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 .

8. An electronic device comprising the electrochemical device according to any one of claims 1 to 7.

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